Thèses sur le sujet « Microwave pyrolysi »
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1
Al, Sayegh Hassan. « Microwave pyrolysis of forestry waste ». Thesis, University of Nottingham, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.576151.
Texte intégralRésumé :
This thesis reports a fundamental study of the unassisted pyrolysis of wood using microwave energy for the production of bio-oils. The majority of previous work on the microwave pyrolysis of woody biomass to produce bio-oils has been performed in domestic type multimode cavity based microwaves ovens and has concluded that attaining temperatures required for pyrolysis (500°C) is not possible due to the microwave transparent nature of the material. To overcome this, many researchers have resorted to adding microwave susceptible doping agents to stimulate heating of the wood through conductive heat transfer. Although this method generates overall process effects, it does not realise the unique heating characteristics that microwave energy may offer, such as volumetric and highly selective heating. An in-depth study of the effect of temperature on the dielectric properties concluded that at room temperature, wood is a relatively good microwave absorber with a loss tangent (tan δ) of 0.20 at 2.142 GHz compared to water which has a tan δ of 0.15 under the same conditions. However, as temperature is increased, wood starts to become microwave transparent as the inherent moisture (the microwave significant material from a microwave heating point of view) evaporates causing a decrease in tan 15. Dielectric property results indicated that wood can be classified as a microwave transparent cellular matrix of cellulose, hemicellulose and lignin containing a microwave absorbing phase (water). Selective heating of the bound water before evaporation may be used to heat the remaining bulk to pyrolysis temperatures of circa. 500°C It has been demonstrated that the rate of heating has a marked effect on the microwave susceptibility of the wood above 300°C. As heating rate increases, wood remains microwave responsive up to pyrolysis temperatures of 500°C. At a heating rate of 2°C/min, tan δ was measured at 0.03 at 2.142 GHz, whilst at a heating rate of 15°C/min, tan δ increased more than six fold to 0.19 under the same conditions. A TMo1n applicator was designed and fabricated for the pyrolysis of wood, based directly upon the dielectric properties of the wood feed. This, coupled with automatic tuning to minimise reflected power and increase energy efficiency, ensured a high bulk power density of ~108 W/m3 with 1kW of microwave power compared to a domestic microwave oven which would only generate ~104 W/m3 in the wood under the same conditions. Such a high power density leads to a high heating rate which is required to overcome the decrease in tan 0 shown at lower heating rates in the earlier work. As opposed to the majority of literature, this work has categorically shown that the unassisted microwave pyrolysis of wood to produce bio-oil is technically feasible. This could lead to the full utilisation of the benefits of microwave heating and the unique heating gradients generated that may be beneficial for this process. To test the benefits microwave heating may offer, a matrix of batch pyrolysis tests was carried out to determine the effect of power density, particle size, moisture content and residence time on the yield of bio-oil, char and gas produced from pine and spruce samples. An increase in bulk power density from 1.7x107 to 7.5x107 W/m3 increased bio-oil yield from 29% to 55%. A further increase in power density had no effect on the yield of bio-oil. This body of work showed that the dimensions and geometry of the sample are important factors affecting the yields of products produced. Even though microwave energy heats volumetrically, sample cooling is still constrained to conventional heat loss models (conduction, convection and radiation). Results showed that minimising heat loss and maximising bulk power density can lead to higher bio-oil yields. It was demonstrated that as residence time increased (using a constant power of 1kW), the yield of bio-oil also increased from 13% at 90 seconds to 39% at 180 seconds. These results are the opposite to those observed from conventionally heated pyrolysis experiments as the longer residence promotes cracking of the bio-oil into incondensable gases, causing a decrease in bio-oil yield. This may lead to a potential benefit in utilising microwave heating in this process as expensive rapid quenchers need not be designed. From the particle size range tested, an optimum particle size of 25 mm was found to maximise bio-oil yield. This is much greater than the optimum particle size in conventionally heated pyrolysis (<1mm) and has major implications for the economics of scale up as projected comminution energy requirements are drastically reduced from around 800 kWhr/tonne to 50kWhr/tonne.
2
Abdul, Halim Siti. « Biomass pyrolysis using microwave technology ». Thesis, University of Sheffield, 2016. http://etheses.whiterose.ac.uk/17555/.
Texte intégralRésumé :
A series of biomass wastes from Malaysia known as Malaysian wood pellets, and rubberwood were employed in the present work. Using these materials as the feedstock, two different heating techniques; external heating by means of conventional slow pyrolysis (SP) and volumetric heating by means of microwave pyrolysis (MP) were carried out. Two distinct temperatures; 500°C and 800°C were used. The main objective was to characterise both the microwave-pyrolysed products and slow pyrolysed products including the influence of temperature so as to compare and contrast in terms of yield, and composition of the char, oil and high-value fuel gas (H2) or syngas (H2+CO). Whilst there is an increasing interest in comparing microwave pyrolysis with conventional pyrolysis, much of the research work done in the past focussed on using domestic microwave ovens with power control features where indirect temperature measurements were carried out at different power and time settings. In the present research, the control feature for both heating techniques is similar, where the user can conveniently set the desired pyrolysis temperature and therefore, this would allow for a more direct and reliable comparison of products obtained from conventional pyrolysis and microwave pyrolysis. The research found that the use of the microwave oven system to conduct pyrolysis boosted the production of oil but reduced the total gas yield. The char proportion also reduced when microwave heating method was applied. This research also revealed that the configuration of the microwave oven with mode stirrer and bottom-fed waveguide that produces a cyclic controlled output power of 1000 W at any set temperature has yielded different results when compared to previous studies and so provides a new understanding for the microwave pyrolysis community. The results demonstrated that the microwave-pyrolysed chars were slightly more porous than slow-pyrolysed chars at 500°C. However, at a higher temperature of 800°C, lower surface area was obtained from microwave pyrolysis which can be attributed to significant damage to the char structure as the consequence of high power supplied into the cavity and high temperature used. SEM microphotographs revealed that microwave pyrolysis at 500°C led to the formation of char with clearly defined pore structure. In the case of gaseous product, both heating approaches were found to produce a comparable level of H2+CO content except those produced by MP at higher temperature (800°C). Regarding bio-oil quality, the microwave-pyrolysed oil was found to present compounds with higher aliphatic content and contain less polycyclic aromatic hydrocarbon (PAH) content, which is an added quality value as PAH is toxic to the environment. As demonstrated in the present work, employing a microwave oven to conduct pyrolysis process leads to a great time saving where the woody samples required only 8-10 minutes and 15-16 minutes to reach 500 and 800ºC respectively. On the other hand, the electric furnace used to conduct conventional pyrolysis process demonstrated a slower performance where the time required to reach 500 and 800ºC were about 49 and 72 minutes respectively. This again emphasizes that microwave oven is powerful to speed up the pyrolysis process due to the nature of rapid heating within the internal body of the sample. Additionally, from the viewpoint of energy consumption, microwave oven used approximately 62% less energy than the electric furnace to conduct pyrolysis process and therefore leads to greater energy saving. In the present work, COMSOL Multiphysics software has successfully demonstrated solutions of the numerical coupled electromagnetic and heat transfer equations. The results extracted from the simulation using specified cavity geometry, dielectric properties and thermal properties were seen to agree reasonably well with the experimental data in terms of the temperature profile and heating behaviour of the biomass. The location of hot spots and cold spots from the simulation also agreed with that observed from the experiment. The simulation work has proved that the inhomogeneity of temperature of the biomass is reflected by the local occurrence of hot spots and cold spots. These are influenced by the standing waves of different electric field concentration formed at different areas inside the cavity, and this phenomenon is very common for biomass treatment in a microwave environment. The effect of different positions of the waveguide is remarkable where the bottom-fed microwave energy oven was shown to have a poor electric field distribution. However, when simulation was done on combining the effect of having the microwave energy fed from the bottom and the presence of the mode stirrer, the electric field was greatly improved with the heating distribution of the biomass resembling that obtained from the side-fed microwaves energy oven (usually refers to a common home microwave oven). The effect of having a mode stirrer rotating inside the microwave oven is also pronounced where the mode stirrer acts to stir the electric field strength within the cavity so that a more uniform heating within the biomass can be achieved. The simulation work also demonstrated that the amount of microwave power absorbed in the biomass materials varies according to the changes in loading height of the biomass, and sample positioning inside a microwave oven also contributes to the electric field distortion and heating behaviour of the biomass. Interestingly from the simulation, for a specified microwave cavity, an optimum bed size of biomass was found at 50mm height where maximum microwaves energy absorption takes place. In this sense, more microwaves energy can be converted into heat thereby ultimately helping the biomass to reach the desired pyrolysis temperature in shorter time. The COMSOL modelling on microwave heating therefore has shown to be simple and practical for use as a framework in predicting temperature profile of the biomass and intensity of the electric field.
3
Ludlow-Palafox, Carlos. « Microwave induced pyrolysis of plastic wastes ». Thesis, University of Cambridge, 2002. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.620655.
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Adam, Mohamed A. B. « Understanding microwave pyrolysis of biomass materials ». Thesis, University of Nottingham, 2017. http://eprints.nottingham.ac.uk/41301/.
Texte intégralRésumé :
Global challenges related to energy security, resource sustainability and the environmental impacts of burning fossil fuels have led to an increasing need for switching to the use of clean and sustainable resources. Bio-oil produced through pyrolysis has been suggested as one of the sustainable alternatives to fossil resources for power generation as well as chemicals and biofuels production. Pyrolysis is a thermochemical process during which the biomass feedstock is heated in an inert atmosphere to produce gas, liquid (bio-oil) and solid (char) products. Microwave heating has been considered a promising technique for providing the energy required for biomass pyrolysis due to its volumetric and selective heating nature which allows for rapid heating in a cold environment. This helps to preserve the product quality by limiting secondary reactions. The aim of this research was to study the interactions between biomass materials and microwave energy during pyrolysis, and to develop a reliable and scalable microwave pyrolysis process. The dielectric properties of selected biomass materials were studied and found to vary significantly with temperature due to the physical and structural changes happening during pyrolysis. The loss factor of the biomass materials was found to reach a minimum value in the range between 300 oC and 400 oC followed by a sharp increase caused by the char formation. A microwave fluidised bed process was introduced as an attempt to overcome the challenges facing the scaling-up of microwave pyrolysis. The concept of microwave pyrolysis in a fluidised bed process was examined for the first time in this thesis. A systematic approach was followed for the process design taking into account the pyrolysis reaction requirements, the microwave-material interactions and the fluidisation behaviour of the biomass particles. The steps of the process design involved studying the fluidisation behaviour of selected biomass materials, theoretical analysis of the heat transfer in the fluidised bed, and electromagnetic simulations to support the cavity design. The developed process was built, and batch pyrolysis experiments were carried out to assess the yield and quality of the product as well as the energy requirement. Around 60 % to 70 % solid pyrolysed was achieved with 3.5 kJ·g-1 to 4.2 kJ·g-1 energy input. The developed microwave fluidised bed process has shown an ability to overcome many of the challenges associated with microwave pyrolysis of biomass including improvement in heating uniformity and ability to control the solid deposition in the process, placing it as a viable candidate for scaling-up. However, it was found to have some weaknesses including its limitations with regards to the size and shape of the biomass feed. Microwave pyrolysis of biomass submerged in a hydrocarbon liquid was introduced for the first time in this thesis as a potential alternative to overcome some of the limitations of the gas-based fluidised bed process. Batch pyrolysis experiments of wood blocks submerged in different hydrocarbon liquids showed that up 50 % solid pyrolysis could be achieved with only 1.9 kJ·g-1 energy input. It was found that the overall degree of pyrolysis obtained in the liquid system is lower than that obtained from the fluidised bed system. This was attributed to the large temperature gradient between the centre of the biomass particle/block and its surface in the liquid system leaving a considerable fraction of the outer layer of the block unpyrolysed. It was shown that the proposed liquid system was able to overcome many of the limitations of the gas-based systems.
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Lam, Su Shiung. « Microwave-induced pyrolysis of waste automotive oil ». Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610406.
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Wauts, Johann André. « Catalytic microwave pyrolysis to produce upgraded bio-oil ». Diss., University of Pretoria, 2017. http://hdl.handle.net/2263/61344.
Texte intégralRésumé :
To assess the performance and future possibilities of catalytic microwave pyrolysis, laboratory-scale experiments were conducted on a widely available biomass feedstock, Eucalyptus grandis. Non-catalysed microwave pyrolysis was conducted under varying conditions to determine important factors of the microwave pyrolysis process and to conduct a basic performance evaluation. Future possibilities of microwave pyrolysis were determined by comparison to available technologies. Calcined Mg-Al LDH clay (layered double oxide or LDO) was used as catalyst to improve the quality of the pyrolysis process and its products. The heating and reaction mechanisms for microwave pyrolysis show that it offers distinct advantages over conventional pyrolysis. The main advantages are rapid and efficient volumetric heating, as well as acceptable yields at lower temperatures (much lower than those required by conventional pyrolysis), which can possibly lead to significant energy savings.
Comparing the performance of a modified domestic microwave to an off-the-shelf microwave unit (Roto Synth) proved that cheap and comparative microwave research is possible. The yields from the domestic microwave products compared very closely to those of the Roto Synth unit, each having yields for char, oil and gas of 47.9%, 33.2%, 18.9% and of 46.8%, 32.7%, 20.55% respectively. The cost of the modified domestic setup was ~1% of that of the off-the-shelf unit. The use of a quartz reactor and slight adjustments to the stepper motor driver and thermocouple are recommended for future use.
The pyrolysis process was found to be very dependent on power and power density. Higher powers increase the liquid and gas yields and a critical power density was identified between 800W and 1000W. The effects of power density were interesting and led to conclusions regarding the penetration depth of microwaves which could possibly play a significant role in the scale-up of microwave pyrolysis technology.
Microwave pyrolysis undeniably has several advantages over conventional pyrolysis. However, for it to become competitive, microwave fast pyrolysis technologies need to be developed through the use of mixed bed reactors that can achieve fast heating rates. Possible candidates include rotating cone and fluidised bed reactors. Hybrid technology also provides unique advantages and has huge potential. Comparison of pyrolysis technologies is difficult without good data on continuous microwave pyrolysis reactors, and therefore the development of such reactors is recommended for future research.
Catalysis of microwave pyrolysis with LDO proved effective. The catalyst promoted the formation of volatiles (gas and liquid), even when present in small ratios. It also promoted the formation of esters and even anhydrides and small fractions of hydrocarbons at high catalyst ratios. The catalyst activity led to increased water yields. This indicated that it removes oxygen from the pyrolysis products, thereby improving their quality. The catalyst was believed to be limited by the low temperatures used in this investigation and higher temperatures might increase the release of CO2 and should be investigated. Significant reduction in the total acid number (TAN) and an improved dry-basis heating value were also achieved by the addition of the catalyst. The water content increased from 50% to 70%, the TAN reduced from 174 mg KOH/(g oil) to 72 mg KOH/(g oil), and the calorific value increased from 19.1 MJ/kg to 21.5 MJ/kg.Dissertation (MEng)--University of Pretoria, 2017.
Chemical Engineering
MEng
Unrestricted
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Russell, Alan Donald. « Microwave-assisted pyrolysis of HDPE using an activated carbon bed ». Thesis, University of Cambridge, 2013. https://www.repository.cam.ac.uk/handle/1810/244641.
Texte intégralRésumé :
Plastics play an enormous role in modern manufacturing, but the extraction and refining of raw materials, followed by the synthesis of plastics themselves, represents an enormous energy investment into a product that is all too often simply “thrown away” into a landfill after a single use. Microwave-assisted pyrolysis is a recycling technique that allows the recovery of chemical value from plastic waste by breaking down polymers into useful smaller hydrocarbons using microwave heat in the absence of oxygen. This dissertation examines the use of a catalytic activated carbon bed in this procedure, using high density polyethylene (HDPE) as a model plastic. Initial tests with the batch input of HDPE produced a condensed pyrolysis oil comprising 35.5–45.3% aromatics, with the remainder primarily short-chain aliphatics. This oil was approximately three times lighter than that produced in the absence of catalyst, with a narrower range of molecular masses that matched those of the liquid transport fuels petrol and diesel (C5–C21). The non-condensable gases that resulted were short-chain aliphatics that could be used as feedstock for the creation of new chemicals (such as virgin HDPE), or fuels such as natural gas and LPG. The development of apparatus capable of adding sample in a continuous fashion enabled the processing of larger quantities of HDPE, and resulted in condensed products with a significantly higher aromatic content (>80% at 450°C), and which encompassed a somewhat narrower range of molecular masses compared with those produced in the batch mode; this was due to differences in kinetics and residence time that resulted from the different modes of sample introduction. As a result of processing larger quantities of HDPE it became apparent that the activated carbon deactivated over time, with a bed able to process around 3.5 times its mass in HDPE at 450°C before any significant changes in output products occurred. The decomposition of HDPE proceeds via thermal scission and radical-mediated mechanisms; high energy surface active sites facilitate the transfer of hydrogen and radicals, and this enhances overall cracking and lowers the activation energy for the formation of aromatics. Analysis of material deposited on the surface of the activated carbon confirmed that deactivation occurred through coking, with both cracking and deactivation thought to be enhanced by the formation of microwave-induced microplasmas. Overall, the microwave-assisted pyrolysis of HDPE using activated carbon produces a much narrower range of more valuable products compared with non-catalytic processing. While the process is not likely to be economic in its current form owing to the relatively rapid deactivation of the activated carbon, future configurations incorporating online reactivation may be able to economically provide a second use cycle for these materials, avoiding expending energy to extract and process increasingly scarce new raw material from the surface of the earth.
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Ogunkeyede, Akinyemi Olufemi. « Conventional and microwave pyrolysis remediation of crude oil contaminated soil ». Thesis, University of Nottingham, 2016. http://eprints.nottingham.ac.uk/35190/.
Texte intégralRésumé :
The Nigerian economy has relied heavily on crude oil production since independence in 1960. As a consequence, it has seen an influx of multinational petroleum companies with oil exploration and associated activities having significant environmental impacts, particularly oil leakage and spillage into soil and the overall degradation of the ecosystem in the Niger Delta area. This study aims to find a viable solution to the remediation of polluted soil by comparing two thermal remediation techniques, namely microwave pyrolysis and traditional pyrolysis, which has been investigated using a Gray-King retort. The polluted soil was first examined to ascertain the distribution of the soil organic carbon (SOC) with 78% found to be solvent extractable in dichloromethane/methanol, while 95 % was thermally labile and removed under hydropyrolysis (HyPy) conditions at 550 °C. The remaining 5 % of the SOC was composed of a recalcitrant residue being defined as the black or stable polyaromatic carbon fraction. The solvent extractable organic matter (EOM) was then further separated into the maltene (free phase) and asphaltene (bound phase) fractions together for comparison with a sample of Nigerian crude oil provided by the Shell Petroleum Development Company (SPDC), Nigeria. The Nigerian crude oil is a light crude oil with the percentage of maltene (95.2 %) was far higher than the asphaltene (4.8 %). A closer margin was observed in the percentage between the maltene (88.3 %) and asphaltene (11.7 %) in the soil EOM due to biodegradation. The biomarker profile of the EOM was compared with that of a Nigerian crude oil to confirm that the EOM contains the crude oil in the soil. Their biomarker profiles revealed that the source inputs were terrigenous from deltaic settings, of Late Upper Cretaceous age and deposited under oxic conditions. Oleanane (a pentacyclic triterpene, abundant in oils from the Niger Delta) was present in both the crude oil and EOM and the hopane and the sterane distributions (m/z 191 and m/z 217 respectively) were similar in every respect, which indicates that the probable source of the pollutant crude oil in the soil is similar in composition to the Nigerian crude oil. Accordingly, the polluted soil was treated with microwave pyrolysis and Gray-King pyrolysis to remove the crude oil pollutant. The maximum average recovered products from the thermal remediation process with Gray-King pyrolysis is 99.4 % TOC and maximum crude oil pollutant removed by Gray-King pyrolysis was 85.3 % TOC with maximum oil recovery of 70 % TOC from all the different treatment conditions, while the shortest treatment time condition gave the lowest gas yield of 10.2 % TOC. This implies that 100 % removal with respect to EOM and 89 % removal with respect to HyPy as discussed above. Furthermore, the polluted soil was also treated with microwave pyrolysis with maximum pollutant removal of 77 % TOC, which is 98.7 % removal with respect to EOM and 81 % with respect to HyPy. In conclusion, Gray-King pyrolysis removed more of the soil organic carbon than microwave pyrolysis, but the latter does have advantages regarding operability and greater output within a short treatment time.
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Shi, Kaiqi. « Microwave-enhanced pyrolysis of biomass coupled with catalytic reforming for hydrogen production ». Thesis, University of Nottingham, 2015. http://eprints.nottingham.ac.uk/30406/.
Texte intégralRésumé :
Pyrolysis of biomass is a promising and sustainable approach to produce value-added chemicals and biofuels. In order to achieve a high yield of hydrogen-rich syngas from pyrolysis of biomass, the microwave-enhanced pyrolysis of biomass coupled with catalytic reforming was studied systematically in this research. Firstly, microwave-enhanced pyrolysis of biomass was carried out and compared with conventional pyrolysis under the same processing conditions. Characterisations of biomass, pyrolytic char, bio-oil and biogas were conducted to investigate the differences between microwave-enhanced and conventional pyrolysis. It was found that certain types of carbon nano materials were formed on the surface of microwave pyrolytic chars. More biogas was produced via microwave heating, in which the highest H2 content reached 48.2vol.% during the course of microwave-enhanced pyrolysis of bamboo at 800°C. Most of the syngas contents produced from microwave-enhanced pyrolysis of biomass were above 80vol.% at 800°C. Generally, biomass could be converted into biofuel efficiently with microwave-enhanced process. Secondly, in order to increase hydrogen production, microwave-enhanced pyrolysis coupled with catalytic reforming (MPCCR) at 600°C was studied. In catalyst screening, Ni and Fe were applied as active compounds loaded onto different supports such as molecular sieves (13X), Al2O3 and natural minerals. In addition, activated carbon was employed as a reforming agent. It was found that Ni-13X catalyst resulted in a low yield of bio-oil and high yield of biogas around 75wt.%, which was the highest among all the catalysts investigated. It was also observed that activated carbon played a significant role in increasing biogas product and reducing bio-oil yield to less than 1wt.% in both conventional and microwave-enhanced pyrolysis coupled with reforming. MPCCR with Ni-13X and activated carbon enhanced cracking reactions of bio-oil, and subsequently lowed bio-oil yields and narrowed products distribution simultaneously. The maximum H2 content reached 55vol.% by MPCCR of bamboo using activated carbon as the reforming agent. Compared with conventional reforming, there was a sharp increase of H2 yield via microwave-enhanced reforming, resulting in a hydrogen-rich syngas with a high ratio of H2 to CO. Therefore, it is concluded that microwave irradiation enhances the reforming process. Finally, in this study, a novel method for catalyst-free synthesis of multi-walled carbon nanotubes (MWCNTs) from biomass was developed. MWCNTs with a diameter of 50 nm and a wall thickness around 5 nm have been successfully prepared via microwave-enhanced pyrolysis of gumwood at 500 °C. The mechanism for the growth of such carbon nanotubes (CNTs) was proposed as follows: volatiles were released from the biomass and left behind char particles; these char particles then acted as substrates, mineral matter in char particles (originating from biomass) acted as the catalyst, and the volatiles released act as the carbon source gas; the volatiles then underwent thermal and/or catalytic cracking on the surface of char to form amorphous carbon nanospheres; the carbon nanospheres subsequently self-assembled to form multi-walled CNTs under the effects of microwave irradiation. In summary, microwave-enhanced pyrolysis of biomass has the potential to produce high yield of hydrogen-rich syngas not only at high temperatures but also at low temperatures when it is coupled with catalytic reforming processes. It has also been demonstrated that microwave-enhanced pyrolysis of biomass could be used to produce MWCNTs at low temperatures. It can therefore be concluded that microwave-enhanced pyrolysis of biomass is an effective and efficient approach for the conversion of biomass into value-added products under mild conditions.
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Goodman, Steven. « The microwave induced pyrolysis of problematic plastics enabling recovery and component reuse ». Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/23937.
Texte intégralRésumé :
Recent trends toward the effective utilisation of petroleum derived materials to increase the sustainability of their use (both for economic and environmental reasons), has resulted in an increased interest in the development of recycling methods for plastics including Acrylonitrile- co-Butadiene-co Styrene and Poly Vinylchloride. The recycling of these waste plastics that include mixed monomer compositions and halogens poses a great problem, with their decomposition making them hard to recycle due to loss of their material properties or through the production of problematic compounds e.g. HCl, PCBs, PCDD, and PCDF etc. This work has investigated the microwave induced decompositions of these plastics and explored the potential of a carbon (a microwave absorber) assisted microwave decomposition process. This culminated in the examination of the carbon assisted microwave decomposition of ABS and the potential of a one and two step process for the de-hydrochlorination, then pyrolysis of PVC, which is an untried and novel approach for PVC recycling. . The influence of microwave power, exposure time, along with the effect of the proportion of carbon, was investigated for its influence upon the yields of gases, oils, chars and product components. The proportions of gases, oils and chars were quantified in terms of their product distribution and subsequently analysed for their properties/composition by TGA, FT-IR, GCMS, Py-GCMS and bomb calorimetry. From their analyses product distributions in the oils and gases were derived and decomposition mechanisms evaluated. From these investigations it was found that the microwave decomposition process of both plastics was possible and demonstrated great versatility, with oil yields for ABS of between 2wt.% to 70wt.% and gas yields of 28wt.% to 77wt.% achieved in processing times as little as 3 minutes. From this it was also possible to identify that high quantities of monomer were also able to be recovered, significantly greater than that of a thermal process (39.5%TiC as to 34.5%TiC respectively for styrene monomer). For PVC, it was identified by initial investigations that the de-hydrochlorination of PVC was possible, confirming results of Ito et al., (2006) and Moriwaki et al., (2006). However, the discovery of amplitude dependent heating was of significant interest, not previously identified in any microwave decomposition process. It was also recognized that pyrolysis was not possible after de-hydrochlorination of PVC occurred as a result of the reduction in the materials ability to absorb microwaves (lesser dielectric constant), due to chlorine was removal. Hence it was necessary to investigate the use carbon additive to enable achieving sufficient temperatures to induce the pyrolysis of the remaining polyene structure. The identification of key parameters and ensuing relationships with microwave power, heating rate and temperatures was identified herein, giving the first detailed account of the relationship between specific polymer types and microwaves during a pyrolysis process.
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Binti, Mohd Noor Afiqah. « Conventional and microwave pyrolysis of empty fruit bunch and rice husk pellets ». Thesis, University of Sheffield, 2017. http://etheses.whiterose.ac.uk/17948/.
Texte intégralRésumé :
In recent years, microwave pyrolysis has been the focus of intense research due to the claim that it produced better quality products at a lower power input compared to the electrical furnace pyrolysis system. This study aimed to investigate the influence of both pyrolysis methods on yield and product composition obtained from Malaysian biomass, i.e.: empty fruit bunch and rice husk pellets. They represent lignocellulosic biomass procured as by-products of the milling process. In the first part of the thesis, an initial characterisation of biomass was conducted to determine the chemical composition. It was found that the biomass in this study has moisture and volatiles content at around 5.4 wt.% and 70 wt.%, respectively which makes them ideal for the pyrolysis process. 200g of biomass was loaded into a 15.8kW fixed bed pyrolysis reactor once the reactor had reached the set temperature. Typically, 40g of biomass was pyrolysed in a specially designed 1000W multi mode microwave oven, where microwaves were fed into the oven cavity through a bottom feed waveguide. It was found that microwave pyrolysis gave a higher bio oil and char yield than conventional pyrolysis at a similar reaction temperature. Up to 8.40% increase in bio oil yield was observed when rice husk pellets were pyrolysed under microwave radiation at 800ºC. GC-MS analysis revealed a greater content of mono-aromatics compounds obtained from microwave pyrolysis oils with negligible Polycyclic Aromatic Hydrocarbons (PAH) than conventional pyrolysis oils. Similarly, greater cracking of heavier hydrocarbons at high temperature resulted in up to 44% increase in phenol formation from microwave pyrolysis oils. A maximum surface area of 410m2/g was also recorded during microwave pyrolysis of rice husk pellets at 500ºC, where this value reduces with an increase in pyrolysis temperature. Moreover, microwave pyrolysis resulted in up to 29% increase in syngas (H2+CO) evolution and about 42% lower greenhouse gases (CH4+CO2) than conventional pyrolysis. These differences can be attributed to internal heat generation during microwave processing in contrast to conduction from the surface inwards during conventional heating. Energy yield analysis suggested that microwave pyrolysis can be optimised for the production of high quality char and bio oil. Meanwhile, conventional pyrolysis can be optimised to enhance syngas production. The second part of this thesis looks into the effect of waveguide position and biomass bed height on the electric field and its corresponding temperature distribution. Numerical modelling has shown that higher temperature rise can be generated in a larger load due to greater microwave power deposited. Moreover, an increase in relative permittivity was observed as biomass was converted into char during pyrolysis. This showed that microwave pyrolysis of biomass can be a self-sustaining process, without any addition of microwave absorber. It was concluded that viable industrial application of microwave pyrolysis is very promising.
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Antreou, Evangelia. « Improved microwave-assisted pyrolysis of HDPE using catalysts and a fluidised-bed reactor ». Thesis, University of Cambridge, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.648805.
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Li, Pik Kei 1978. « High pressure and microwave assisted generation and pyrolysis-GCMS analysis of glycated proteins ». Thesis, McGill University, 2002. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=79033.
Texte intégralRésumé :
The extent of denaturation and glycation of lysozyme and BSA with the application of high hydrostatic pressure (HHP) at 400 MPa at 30°C from 8 to 48 hours and focused microwave irradiation at 50°C under varying microwave power and from 10 to 60 minutes was investigated in the presence and absence of D-glucose. The HHP treatment caused 10 to 20% denaturation of lysozyme whereas microwave irradiation caused 20 to 40% denaturation, with more destruction to the lysozyme in the presence of glucose compared to the control. The extent of glycation was also higher with the high pressure samples, causing 60% glycation upon 8 hours of high pressure exposure, but decreasing to around 40% thereafter. Microwave irradiation brought about 40% glycation to the lysozyme samples upon 20 min of irradiation. BSA, on the other hand, was more susceptible to damage by high energy exposures. BSA samples were denatured to a greater extent compared to lysozyme, up to 80% upon the prolonged exposures, but in all treatments, glucose seemed to act as a protectant contrary to the case of lysozyme. The extent of glycation detected was also minimal, ranging from 8 to 20%.The feasibility of analyzing glycated proteins using pyrolysis-GC/MS was also investigated. Taking advantage of the formation of a diagnostic marker---2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one---upon pyrolysis of glycated proteins, the intensity of this peak was used to correlate the extent of glycation. The intensity of this peak in the pyrograms of glycated lysozymes was found to increase linearly with increasing incubation times and subsequently with the sugar loads of the glycated lysozyme. In addition, using the pyrograms as unique fingerprints, the extent of structural changes between modified and unmodified proteins were also assessed.
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Šimek, Radim. « Energetické využití čistírenských kalů a produktů mikrovlnné pyrolýzy ». Master's thesis, Vysoké učení technické v Brně. Fakulta stavební, 2019. http://www.nusl.cz/ntk/nusl-392031.
Texte intégralRésumé :
The diploma thesis is focused on the energy utilization of sewage sludge before and after microwave pyrolysis process. The first part of the thesis deals with sludge management, treatment of sludge and its subsequent use or disposal. In the second part of the thesis prepared and modified samples of sludge from WWTP 1 and WWTP 2 are subjected to microwave pyrolysis process. Subsequently, samples are taken for analyzes to determine the total organic carbon, the specific surface area, the heavy metal content and the calorific values. The resulting data was processed in Microsoft Office Excel and presented at work. At the end of the thesis two case studies are then proposed for a specific design of the conceptual location of microwave pyrolysis for the sludge drying process and the drying process of the sewage sludge in the direct combustion boiler room.
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Ramanayaka, Aruna N. « Magnetotransport in Two Dimensional Electron Systems Under Microwave Excitation and in Highly Oriented Pyrolytic Graphite ». Digital Archive @ GSU, 2012. http://digitalarchive.gsu.edu/phy_astr_diss/54.
Texte intégralRésumé :
This thesis consists of two parts. The first part considers the effect of microwave radiation on magnetotransport in high quality GaAs/AlGaAs heterostructure two dimensional electron systems. The effect of microwave (MW) radiation on electron temperature was studied by investigating the amplitude of the Shubnikov de Haas (SdH) oscillations in a regime where the cyclotron frequency $\omega_{c}$ and the MW angular frequency $\omega$ satisfy $2\omega \leq \omega_{c} \leq 3.5\omega$. The results indicate negligible electron heating under modest MW photoexcitation, in agreement with theoretical predictions. Next, the effect of the polarization direction of the linearly polarized MWs on the MW induced magnetoresistance oscillation amplitude was investigated. The results demonstrate the first indications of polarization dependence of MW induced magnetoresistance oscillations. In the second part, experiments on the magnetotransport of three dimensional highly oriented pyrolytic graphite (HOPG) reveal a non-zero Berry phase for HOPG. Furthermore, a novel phase relation between oscillatory magneto- and Hall- resistances was discovered from the studies of the HOPG specimen.
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O'Mahoney, T. Karl P. « An investigation of perfluorocarbons and bromofluorosilanes : pyrolysis, GC-ECD, GC-MS, FTIR and microwave spectroscopic studies and analysis ». Thesis, University of Bristol, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.259467.
Texte intégral
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Jackson, Edward A. « Total Synthesis of a [5,5] Nanotube End-cap ». Thesis, Boston College, 2008. http://hdl.handle.net/2345/1357.
Texte intégralRésumé :
Thesis advisor: Lawrence T. ScottCarbon nanotubes are theorized to possess many extraordinary properties. To a certain extent, these properties have been demonstrated using the products of current nanotube growth technologies; however, the specific characteristics of distinct nanotube topographies remain untapped on the industrial scale. Carbon vaporization and “flame” methods produce mixtures of various nanotube chiralities and diameters. Although progress has been made, separation techniques are limited. Currently, organic synthesis and subsequent elongation of a select hydrocarbon template is the only approach that promises significant access to specific nanotube topographies without the need for separation
Thesis (PhD) — Boston College, 2008
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Chemistry
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Merlak, Marek Radoslaw. « Design and Characterization of Microwave Assisted Plasma Spray Deposition System : Application to Eu Doped Y2O3 Nano-Particle Coatings ». Scholar Commons, 2010. https://scholarcommons.usf.edu/etd/1711.
Texte intégralRésumé :
This thesis presents a Microwave Plasma Assisted Spray Deposition (MPASD) system design, characterization, and application to produce nano-sized particle coatings of metal oxides. A commercially available rectangular waveguide microwave power delivery system is utilized to initiate and sustain the plasma discharge within the customized plasma applicator where micron-sized droplets of a metal ion solution are heated to evaporate the solvent and thermally process the resulting nano-sized particles. The investigation of optimum conditions for oxygen, argon, and air plasma ignition in the MPASD system was presented. Measured electron temperature of the plasma was between 6000K and 40000K for the plasma conditions used in the MPASD process. Successful deposition of Y2O3:Eu nano-particles using the MPASD system was achieved. MPASD process allows control of the particle's properties, shown through XRD and photoluminescence studies of the Y2O3:Eu coatings. The MPASD process settings effect on particles activated doping concentration and, as a result, its photoluminescence was shown.
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Wangensteen, Ted. « Growth And Characterization Of Functional Nanoparticulate Films By A Microwave Plasma-Assisted Spray Deposition Process ». Scholar Commons, 2012. http://scholarcommons.usf.edu/etd/4417.
Texte intégralRésumé :
Nanoparticle and nanoparticulate films have been grown by a unique approach combining a microwave and nebulized droplets where the concentration and thus the resulting particle size can be controlled. The goal of such a scalable approach was to achieve it with the least number of steps, and without using expensive high purity chemicals or the precautions necessary to work with such chemicals. This approach was developed as a result of first using a laser unsuccessfully to achieve the desired films and particles. Some problems with the laser approach for growing desired films were solved by substituting the higher energy microwave for the laser. Additionally, several materials were first attempted to be grown with the laser and the microwave, and what was learned as result of failures was implemented to successfully demonstrate the technique.
The microwave system was characterized by using direct temperature measurements and models. Where possible, the temperature of deposition was determined using thermocouples. In the region of the waveguide, the elemental spectral lines were measured, and the temperature was calculated from measured spectral peaks. From the determined temperature, a diffusion calculation modeled the rate of heat transfer to the nebulized droplets. The result of the diffusion calculations explained the reason for the failure of the laser technique, and success for the microwave technique for simple chemistries.
The microwave assisted spray pyrolysis (MPAS) technique was used to grow ZnO nanoparticles of varying size. The properties of the different size particles was measured by optical spectroscopy and magnetic measurements and was correlated to the defects created.
The MPAS technique was used to grow films of Ca3Co4O9 containing varying sizes of nanoparticulates. The resistivity, Seebeck coefficient, and the power factor (PF) measured in the temperature range of 300-700 K for films grown by MPAS process with varying concentrations of calcium and cobalt chlorides are presented. Films with larger nanoparticles showed a trend toward higher PFs than those with smaller nanoparticles. Films with PFs as high as 220 μW/mK 2 were observed in films containing larger nanoparticles.
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Tarat, Afshin. « Nanocrystalline ZnO obtained from pyrolytic decomposition of layered basic zinc acetate : introducing a novel rapid microwave-assisted hydrothermal technique ». Thesis, Swansea University, 2014. https://cronfa.swan.ac.uk/Record/cronfa42303.
Texte intégralRésumé :
Zinc oxide (ZnO) crystal with a direct wide band gap (3.37 eV) and large excition binding energy (60 meV) is one of the most potential semiconductors in numerous application fields such as room-temperature UV-Iaser, light-emitting- diode (LED), photocatalyst, gas sensor, solar cell, piezoelectric device, etc. In past decades, different methods have been investigated to produce a variety of different shapes of nano and submicron ZnO nanostructures. Among them, the ZnO nanobelts (NBs) with a rectangular cross section have unique optoelectronic properties due to its unusual shape and structure. It is well demonstrated by recent success in field-effect transistor, nanoresonator, and spintronics applications of the ZnO NBs. Two-dimensional (2D) nanostructures such as nanosheets (NSs) and thin films have also great potential for unique purposes where a large uniform coverage at nanoscale is essential. One of the conventional methods for synthesis of the ZnO nanostructures is vapour transport and condensation process at high temperature, in some cases up to 1400°C. Such an extreme condition for vaporization of precursor could induce many oxygen defects on surface of the ZnO nanobelts. These specific defects hinder progress to the applications of ZnO in optoelectronic and lasing devices. In this respect, mild processing is strongly demanded for the synthesis of the ZnO nanoparticles. In terms of low energy consumption and simplicity, soft- solution process based on hydrothermal reactions at low temperature (under 100°C) is a green chemical procedure. However, there are only few reports on the synthesis of the ZnO NBs and NSs due to their unusual growth habit against typical growth rate of the ZnO crystal. Here we are reporting a developed simple, low cost and high yield hydrothermal technique to synthesis layered basic zinc acetate (LBZA) NBs and also a novel rapid microwave-assisted hydrothermal technique to grow LBZA NSs only in 2 minutes. Growth procedures are followed by pyrolytic decomposition to produce nanocrystalline NBs and NSs. SEM and AFM results revealed that the morphology and quantity of the nanobelts and nanosheets are strongly temperature and pH dependent. In addition, results showed that as-grown LBZA nanostructures could be easily transformed to corresponding ZnO nanostructures through pyrolytic decomposition without.
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Tolonen, Erik. « Evaporation Characteristics of a Liquid Bio-Fuel from Chicken Litter ». Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/26060.
Texte intégralRésumé :
Alternative fuels are becoming more important as fossil fuels become more expensive. This thesis describes the production and properties of a bio-oil produced from waste biomass, in this case chicken litter. A higher quality fuel was produced through thermal and chemical upgrading of the raw bio-oil; this fuel is similar in some respects to fossil fuels, as it has a high hydrocarbon content and energy density comparable to gasoline.
Combustion of liquid fuels commonly occurs in clouds of droplets, and studying the evaporation of single liquid drops provides information on the evaporation characteristics of the fuel as a whole. Droplet evaporation tests on the chicken litter fuel were carried out using the suspended droplet/moving furnace technique. For some tests, a fine wire thermocouple was used as the droplet suspension in order to measure the distillation characteristics of the fuel. An existing computational model based on continuous ther- modynamics was used to model the evaporation of the fuel. The modelled composition of the fuel was based on an existing pyrolysis field ionization mass spectrometry (Py-FIMS) analysis and used five major groups of compounds. The properties for these groups re- quired for the model were determined using several prediction methods and the values then used in a numerical model.
Model predictions of droplet temperatures calculated for the fuel showed good agree- ment with the measured temperatures, indicating that the modelled composition gave an accurate picture of the fuel. Droplet evaporation histories also agreed well with mea- surements, but were not capable of reproducing the observed disruption of the droplet produced by internal boiling at higher temperatures, nor the formation of a solid residue at the end of evaporation. Further enhancements to the model should allow the prediction of residue formation.Model predictions of droplet temperatures calculated for the fuel showed good agree- ment with the measured temperatures, indicating that the modelled composition gave an accurate picture of the fuel. Droplet evaporation histories also agreed well with mea- surements, but were not capable of reproducing the observed disruption of the droplet produced by internal boiling at higher temperatures, nor the formation of a solid residue at the end of evaporation. Further enhancements to the model should allow the prediction of residue formation.
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RAMBO, CARLOS R. « Obtenção de sílica e carbeto de silício a partir da exposição da palha de arroz a microondas e a campos eletromagnéticos na faixa de r.f ». reponame:Repositório Institucional do IPEN, 1997. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10676.
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Made available in DSpace on 2014-10-09T12:42:56Z (GMT). No. of bitstreams: 0Made available in DSpace on 2014-10-09T14:07:27Z (GMT). No. of bitstreams: 1 06117.pdf: 4530638 bytes, checksum: 5ac55fe8275fe0771c6b87d47945e7ef (MD5)
Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
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Borges, Fernanda Cabral. « Estudo do processamento termoquímico de biomassas com micro-ondas : pirólise rápida de biomassas residuais e microalgas ». reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2014. http://hdl.handle.net/10183/100151.
Texte intégralRésumé :
Alguns conceitos de biorrefinarias estão baseados em processos termoquímicos, sendo a pirólise rápida um dos mais promissores desses processos. Os produtos da pirólise rápida são: o bio-óleo, gases combustíveis e carvão, sendo a distribuição típica de 50:30:20 em base mássica. O bio-óleo é o principal produto, e pode ser diretamente usado como combustível, ou pós-processados para a obtenção de químicos de maior valor agregado. O aquecimento com micro-ondas, amplamente empregado na química verde, começa a ser estudado como uma alternativa de aquecimento. Entretanto os rendimentos alcançados em bio-óleo são inferiores aos obtidos pela pirólise rápida convencional, devido essencialmente às suas baixas taxas de aquecimento. Para resolver esse problema esta tese está propondo a utilização de absorvedores de micro-ondas para auxiliar no processo de aquecimento, e também permitir a alimentação semi-contínua e contínua de biomassa ao processo. O uso de leito fluidizado e catalisadores pode ser integrado a esse conceito. As condições de pirólise-rápida são alcançadas devido ao aumento da taxa de aquecimento da biomassa, que passa a ser aquecida de forma híbrida pelo mecanismo de condução de calor através das partículas de absorvedores de micro-ondas aquecidos, e diretamente através do aquecimento dielétrico por micro-ondas. O aumento das taxas de aquecimento resulta em maiores velocidades de reação, possibilitando um aumento de rendimento em bio-óleo. Esse conceito foi testado experimentalmente em uma unidade em escala de bancada para o processamento de biomassas residuais e microalgas, usando carbeto de silício (SiC) como absorvedor de micro-ondas. Foram verificadas elevadas taxas de aquecimento, sendo a biomassa aquecida e os voláteis removidos do reator quase instantaneamente. Foram obtidos 65% e 64% em rendimentos de bio-óleo para a serragem de madeira e farelo de sabugo de milho, respectivamente. O mesmo sistema foi utilizado para testar a pirólise rápida catalítica. Microalgas foram processadas com e sem a presença de HZSM-5. Rendimentos de 57% e 59% em bio-óleo foram alcançados para Chlorella sp. e Nannochloropsis, respectivamente. Verificaram-se maiores rendimentos comparados com a literatura. Esses resultados indicam que o conceito de pirólise rápida com aquecimento por micro-ondas é tecnicamente viável, necessitando de estudos complementares para evidenciar a sua viabilidade econômica.Some concepts of biorefineries are based on thermochemical processes and fast pyrolysis is one of the most promising of these processes. The fast pyrolysis products are biooil, fuel gas and char, with typical distribution of 50:30:20 in weight basis. The bio-oil is the main product, and it can be directly used as fuel, or post-processed in order to obtain higher value added chemicals. The microwave heating, widely used in green chemistry, begins to be studied as an alternative heating. However the yields achieved in bio-oil are lower than those obtained by the conventional fast pyrolysis, mainly due to its low heating rates. To solve this problem this thesis is proposing the use of microwave absorbers to improve the heating process, and that also allow semi-continuous and continuous feeding of biomass to the process. The use of fluidized bed and catalysts can be integrated into this concept. The fast pyrolysis conditions are achieved due to increased heating rate of biomass, which becomes heated in a hybrid way by heat conduction mechanism from heated microwave absorbers, and directly through the dielectric heating from microwaves. The increase in heating rates results in higher reaction rates, allowing higher yields of bio-oil. This concept has been experimentally tested in a bench scale unit for processing waste biomass and microalgae using silicon carbide (SiC) as a microwave absorber. High heating rates were observed, the heated biomass and the volatiles were removed from the reactor almost instantaneously. A maximum bio-oil yield of 65% and 64% was obtained for wood sawdust and corn stover, respectively. The same system was used to test the catalytic fast pyrolysis. Microalgae were processed with and without the presence of HZSM-5. Yields of 57% and 59% of bio-oil were achieved for Chlorella sp. and Nannochloropsis, respectively. Higher yields of bio-oil were observed compared to the literature. These results suggest that the concept of fast microwave-assisted pyrolysis is technically feasible, requiring further studies to demonstrate its economic viability.
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Meindl, Jiří. « Stanovení organických sloučenin ve vzorcích biouhlu získaných mikrovlnou torefakcí biomasy ». Master's thesis, Vysoké učení technické v Brně. Fakulta chemická, 2019. http://www.nusl.cz/ntk/nusl-401893.
Texte intégralRésumé :
The thesis is focused on a determination of polycyclic aromatic hydrocarbons (PAHs) contained in dried pelletized sewage sludge and pelletized biochar. Biochars were made in mild conditions by microwave torrefaction of prepared sewage sludge. There were analyzed and quantified the 34 of standardized PAHs compounds in two series. The first serie, also called “Sada 1”, has been aimed at comparison of extraction methods for the chosen sample of sewage sludge and the sample of biochar. In serie “Sada 1”, there were compared efficiencies of chosen type of solvent or solvent mixture by comparison of yields for 34 standardized analytes in a sample of biochar and a sample of sewage sludge. There were compared also to total yields of PAHs and to number of quantified compounds in analyzed samples. The most reliable extraction method has been used for the next analyses of samples in the second serie called “Sada 2”. In Sada 2, there were compared different samples of the same type (e.g. biochar, sludge). The origin of sewage sludge (small or big sewage treatment plant expressed as PE) and used additives (cellulose, chaff, hay) as modificators for torrefaction process were variables for different type of sample. The results of analysis were identification of the most suitable sewage sludge and additive to be used as modificator for microwave torrefaction process. The main goal of correctly chosen sludge and additive was to minimize production of PAH’s during torrefaction and in samples of biochar.
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Krishnamoorthi, Ramesh, et Zhang Shinzhao. « Recycling of Glass Fiber Composites ». Thesis, Högskolan i Borås, Institutionen Ingenjörshögskolan, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:hb:diva-16494.
Texte intégralRésumé :
Composites are the materials which can be used for a wide variety of applications andproducts such as sports equipment, aerospace and marine because of light and stiffnessproperties. Composites are often made from thermoset resin with glass fibers.In this study, two ways of recycling composites were evaluated, which are microwavepyrolysed composites (MGC) and mechanical composites (GC). These glass fibers weregoing to be compounded with Polypropylene (PP) or Maleic Anhydride ModifiedPolypropylene (MAPP) and then injection moulded the sample by Micro-compounder.In order to get better adhesion to the polymer, a coating was added. The Neoxil 5682-polypropylene water emulsion was evaluated.The samples were characterized by Tensile Testing, Thermogravimetric Analysis (TGA),Different Scanning Calorimetry (DSC), and Dynamic Mechanical Analysis (DMA) to find aoptimum combination of recycled glass fiber reinforced polymer.Microwave pyrolysis is a new research area. The glass fiber, polymer oil and gas can beobtained by heating the composite with microwaves to in an inert atmosphere. The polymeroil can be distillated and then evaluated with GC-MS; in order to obtain the chemicalcompositions.Keywords: Composites, grinded and microwave pyrolyse composites (MGC), grindedcomposites (GC), Polypropylene (PP), Maleic Anhydride Modified Polypropylene (MAPP),Micro-compounder, Tensile Testing, Thermogravimetric Analysis (TGA), Different ScanningCalorimetry (DSC), and Dynamic Mechanical Analysis (DMA), Microwave pyrolysis,polymer oil, distillation, GCMS Analysis.Program: MSc in Resource Recovery - Sustainable Engineering
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UNDRI, ANDREA. « Waste polymeric materials valorization through microwave assisted pyrolysis ». Doctoral thesis, 2014. http://hdl.handle.net/2158/852894.
Texte intégralRésumé :
Microwave assisted pyrolysis (MAP) was exploited to convert several classes of waste polymers into a solid, a liquid, and a gas product with promising application as energy, power, and chemical sources. The polymeric material tested were: tires, high density poly(ethylene) (HDPE), poly(propylene) (PP), poly(styrene) (PS), multilayer packaging beverage (WMP), wood pellets (WP), poly(lactic acid) (PLA), and corn-derived plastic bags (CDP).
Pyrolysis experiments were carried out in a batch laboratory scale reactor, using a microwave (MW) oven operating at 2.45 GHz, an energy output up to 6KW, and for some pyrolysis a fractionating system, directly connected to the pyrolysis oven. The presence of a fractionating system minimized the influence of different MW powers enhancing the residence time and usually improving the quality of the liquid product.
MAP of tire might be run without the addition of a MW absorber. The liquid obtained showed a reduced density (from 0.92 to 0.88 g/cm3), and viscosity (from 3.92 to 1.25 cPs) when working with the fractionating system. Furthermore aromatic and olefinic compounds were formed in high amount. Different tire affected the MAP results: Tires containing a large amount of aromatics (styrene copolymers) were pyrolyzed faster than tire containing large amount of natural rubber. X-ray diffraction of solid from MAP of tire showed two different crystalline forms of ZnS, spharelite or wurtzite were present due to the different amount of waste tires employed. Their presence of these compounds suggested that tires were heated to a temperature higher than the usually accounted.
MAP of polyolefins, HDPE, PP, and PS was performed using different MW absorbers (tire, carbon, or Fe) and MW power, obtaining a high quality liquid fraction with tailoring properties. From HDPE a mixture of linear alkanes, the corresponding 1-alkenes, and a very low amount of aromatics was obtained. On the contrary liquids from MAP of PP contained a mixture of methyl branched alkanes and alkenes, some aromatics and dienes. From MAP of PS a clear and low viscosity liquids were always collected together with low amount of gas (3.0 wt %) and solid (0.9 wt %). Using a MW power of 3 KW the styrene in the liquid was increased up to 65.98 %.
MAP of WMP might by run with or without a MW absorber, and five products were always collected: char, gas, unscratched Al, and two liquid fractions. The organic phase liquid contained large amount of hydrocarbons, useful as fuel or the source of chemicals. The other phase contained large amount of water and oxygenated organic compounds, such as acetic acid, 2-hydroxypropan-2-one and levoglucosan.
MAP of WP might be run without a MW absorber but the pyrolysis could not be completed. WP were converted into a char which preserved their former shape and a two phase liquid. These latter phases were characterized using an innovative chromatographic methodology.
MAP of PLA was performed using different MW absorbers (tire, carbon, or Fe) and MW power, obtaining a liquid rich in lactide (the cyclic dimer of lactic acid) and other oxygenated hydrocarbons. The collected lactide was enantiopure and it was collected, separate, and purified directly from the liquid. Up to 9 wt% of initial PLA was recovered as L-lactide.
MAP CDP was performed using different MW absorbers (carbon or Fe) and MW power, obtaining a three phase liquid and large amount of gas accordingly to the pyrolysis conditions. The liquid after spinning separate in three phases, upper, medium, and lower. Medium fractions were mainly composed of water (70 wt%), acids, alcohols, and anydrosugars and their pyrolysis products. Upper and lower fractions showed close properties and composition except that the lower fraction was a wax. Indeed the lower fraction was composed of oligomers and the upper phase was composed of the pyrolyzed form of these oligomers. The upper fractions contained large amount of aromatic acid and phthalates and their derivatives.
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Huang, Yu-Fong, et 黃于峯. « Microwave-Induced Pyrolysis of Biomass Waste ». Thesis, 2010. http://ndltd.ncl.edu.tw/handle/79517717579063757490.
Texte intégralRésumé :
博士臺灣大學
環境工程學研究所
98
This study utilized the microwave irradiation of single (focused) mode to induce the pyrolysis of biomass waste. Thus products with high heating values or economic worth can be obtained. In this study, rice straw was chosen to be the primary researching target. Some other common biomass waste was also researched for the purpose of results comparison. The increase of microwave power helped to promote the heating rate and maximal temperature of pyrolysis, so higher mass reduction ratio of feedstock can be achieved. Thus by applying higher microwave power, it is expectable that the irradiation time of microwave can be shortened. Besides, particle size of feedstock affected the reaction performance as well. This might imply that the smaller feedstock had the higher bulk density and the more contact area between particles. Therefore, the heat transfer inside the feedstock was enhanced, and the entire pyrolysis reaction turned to be more rapid. By the results of specific surface area analysis and zeta potential analysis, it is expectable that the solid product (char) can be applied in the cation adsorption in the water and wastewater treatment. The result of copper adsorption experiment shows that, even under the acidic condition (pH 5), the adsorption removal rate of copper can be over 90%. The primary components of gas product (fuel gas) were hydrogen, carbon dioxide, carbon monoxide, and methane. The hydrogen content (50.67 vol.%) of the gas product was higher than of traditional pyrolysis (25 vol.%). Thus the technology of microwave-induced pyrolysis shall have the high potential to produce hydrogen-rich fuel gas. According to the result of quantitative analysis of gas product, stoichiometric analysis was also executed to conclude to a nearly balanced chemical equation. There were mainly three categories of compounds in the liquid product (tar): (1) long-chained aliphatic compounds; (2) polar compounds (e.g., phenol and its derivatives); (3) low-ringed polycyclic aromatic hydrocarbons (PAHs). The liquid product shall be low poisonous due to the low content of PAHs and their low ring numbers. The gravimetric percentages of gas, solid, and liquid product were 54.31 wt.%, 28.07 wt.%, and 17.62 wt.%, respectively. Over half of rice straw sample can be converted into gas product. This result is also better than the traditional manner of pyrolysis. This study also researched relevant characteristics of rice straw, rice husks, corn leaves, coffee hulls, bamboo leaves, sugarcane bagasse, sugarcane peel, hemicellulose, cellulose, and lignin by means of thermal analysis-mass spectrometry (TA-MS) experiments. The result showed that the primary production of gas product occurred during the highest mass-loss rate of biomass waste. However, there was also an obvious production of hydrogen at higher temperatures (667-749 °C). From the semi-quantitative analysis of hydrogen content, both rice husks and bamboo leaves had lower hydrogen production, and coffee hulls had the most. The pyrolysis of biomass waste was assumed to be pseudo first-order reaction, and the Arrhenius equation was applied to the analysis of chemical kinetics. The activation energy and frequency factor of biomass waste differed a lot from each other, and showed an inverse proportion. This might be due to the difference among the contents of biomass waste. Besides, the reaction rate constants of biomass waste did not differ much, which was about one order at the most. This might be the reason why there was an inverse relationship between the frequency factor and the effective collision probability. The gas product of microwave-induced pyrolysis of rice straw can be effectively generated under microwave power of 300 W, and the maximal reaction temperature can be reached in 10 minutes. Under this condition, the total heating value of the gas product was about 29.34 % of input energy needed. This percentage can be increased to about 57 % when adding heating values of the solid and liquid product. Therefore, in the microwave-induced pyrolysis, there was about 43 % of input energy that might be used for microwaves generation or extra energy consumption due to reflectional microwave power. The technology feasibility of microwave-induced pyrolysis was assessed by SWOT analysis. The result shows that inner factors of technology maturity, performance, quality and quantity of products, and outer factors such as government policy, economy and energy, are most important for the feasibility. The promotion of microwave-induced pyrolysis should start with enhancement of technology productivity and performance to raise its competitiveness, and try to expand suitable market to increase its visibility and market proportion. According to the international and domestic energy situation and policy direction so far, the demand of renewable energy shall keep increasing. However, there are so many technologies relevant to renewable energy. It is believed that to maximize advantages and to minimize disadvantages of microwave-induced pyrolysis are best policies to make it more favorable.
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Pan, Meng-Wei, et 潘孟暐. « Microwave-Enhanced Pyrolysis ofWaste Printed Circuit Board ». Thesis, 2016. http://ndltd.ncl.edu.tw/handle/40845732899575044768.
Texte intégralRésumé :
碩士國立臺灣大學
環境工程學研究所
104
The concentration of gold in waste printed circuit board （WPCB） used in this study can be up to 20 ppmw, whereas it is only 0.5 ppmw in the gold ore. Moreover, it also contains other precious metals such as silver, platinum, and palladium. Therefore, as one of the most important branches of the waste electrical and electronic equipment （WEEE） stream, if WPCBs can be recycled properly, the city will be an abundant vein of various metals. Besides, urban mining not only achieves materials recycling but also diminishes environmental impact from ore mining. The aim of this study is to provide a simple, high efficiency, and low environment impact technique to recover the metals in WPCBs. By microwave-enhanced pyrolysis （MEP）, the inner layers of WPCBs separated, and thus metal recovery efficiency was enhanced. The maximum weight loss in thermogravimetric analysis （TGA） occurred at 350 °C, which was also achieved by MEP at 300W. Afterwards, the pyrolyzed WPCB was treated by a three-step hydrometallurgical process to recover metals separately. The first two steps are sulfuric acid leaching to dissolve copper and tin. The final stage is the leaching of gold, palladium, and silver by using thiourea and ferric ion.
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BARTOLI, MATTIA. « Microwave pyrolysis of polymeric materials : lignocellulosic biomasses as case of study ». Doctoral thesis, 2017. http://hdl.handle.net/2158/1071381.
Texte intégralRésumé :
This research project was focused on the use of microwaves (MWs) as an alternative energy source, microwave (MW), for pyrolytic treatments of waste polymeric materials. Particularly it was focused on processing waste biomasses using a multimode microwave oven in a batch process using different reaction conditions and correlating the products obtained with the biomass tested and the conditions adopted.
The liquid fraction, also known as bio-oil, has been obtained with very interesting yields (from 20 to 40 %) and showed very promising performances (i.e. low viscosity and limited water content). A large set of analysis was run to characterize the very complex nature of bio-oil: gas chromatographic analysis (GC-MS, GC-FID; spectroscopic analysis (UV-Vis, FT-IR ATR); NMR (1H-NMR); rheological and proximate analysis.
Solids, also known as biochar, have been characterized by FT-IR ATR, ultimate and proximate analysis to assess its possible uses and proving to be suitable as a solid fuel for carbon sequestration processes. Furthermore the samples did not contain any extractable materials.
-cellulose was studied in order to evaluate the behaviour of the main component of lignocellulosic biomasses during microwave assisted pyrolysis (MAP). With the same aim MAP of Kraft lignin at different pressure was tested to correlate the residual pressure on the yield of aromatics compounds generated from the most abundant aromatic containing polymer.
Finally MAP of common wastes coming from different lignocellulosic sources such as Arundo donax, Oliva europea, Vitis vinifera, and different poplar clones, were tested under different pyrolysis conditions in order to evidence their behaviour during MAP experiments.
Various degradation mechanisms of cellulose and Kraft lignin were deeply investigated and some reaction pathways proposed. The interaction between microwave absorbers and feedstocks was also object of this study.
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Merckel, R. D. (Ryan David). « Fast and microwave-induced pyrolysis bio-oil from Eucalyptus grandis : possibilities for upgrading ». Diss., 2015. http://hdl.handle.net/2263/43913.
Texte intégralRésumé :
The hardwood Eucalyptus grandis has been shown to be an important commodity for forestry-related industries as it has significantly faster specific growth rates per annum when compared with other types of tree species. It has therefore been suggested that residues from E. grandis may be a useful source of biomass for use in the production of biofuels for the transportation industry. Notably, E. grandis plantations within the Southern Hemisphere have some of the fastest growth rates worldwide. Due to the inherent nature of biomasses, such as lignocellulosic types having a significant amount of oxygen present, upgrading of biofuels produced from E. grandis is necessary. Several approaches were therefore evaluated to upgrade pyrolysis oils produced from E. grandis so as to increase their calorific values by decreasing oxygen content and subsequently increasing the hydrogen ratio. The hydrogen-to-carbon (H/C) and oxygen-to-carbon (O/C) ratios may be used successfully to evaluate the performances of catalyst-based upgrading techniques for either in situ or ex situ pyrolysis. In this regard the van Krevelen diagram, in which biofuels can be compared for their suitability as transportation fuels, along with their respective calorific values, is useful.
The pyro-gas chromatography/mass spectroscopy (GC/MS) equipment is useful for the rapid and accurate evaluation of different catalysts for fast pyrolysis applications, and it was used here to evaluate the performances of the catalysts bentonite and ZSM-5 zeolite for upgrading pyrolysis oil produced from E. grandis biomass. A van Krevelen diagram was used to evaluate the performance of these catalysts, in conjunction with calorific values, based on the higher heating values
v
for the pyrolysis oils. Further studies were completed for microwave pyrolysis as it is a less harsh form of pyrolysis based on energy-transfer mechanisms. Mass balances were done and demonstrated good repeatability, with more stable pyrolysis oils being produced. This stability may be attributed to similarities between microwave pyrolysis and hydrothermal liquefaction as microwave pyrolysis induces conditions comparable to those of hydrothermal liquefaction within the wood cells, and both methods produce a stable product called bio-crude. Furthermore, it was found that these pyrolysis oils could be distilled so as to remove some of the water content and improve the higher heating value (HHV) from 13.80 to 23.30 MJ/kg. However, this was not as high as the theoretical yield of 26.70 MJ/kg, and better performance was obtained for fast pyrolysis catalysed with ZSM-5 zeolite at 300 °C, which achieved an HHV of 34.54 MJ/kg. It is recommended that ZSM-5 zeolite catalysis be used in microwave-assisted vacuum pyrolysis to determine whether a similar improvement may be realised. Microwave-assisted pyrolysis should also be investigated as a possible technology for inducing conditions similar to hydrothermal liquefaction processes within the cells that make up the biomass.Dissertation (MEng)--University of Pretoria, 2015.
Chemical Engineering
Unrestricted
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(5929736), Alicia O. Hernandez-Castillo. « BROADBAND MICROWAVE SPECTROSCOPY OF LIGNIN, BIOFUELS AND THEIR PYROLYSIS INTERMEDIATES ». Thesis, 2019.
Trouver le texte intégralRésumé :
The chemical complexity of hydrocarbon fuels and the fast-expanding list of potential plantderived biofuels pose a challenge to the scientific community seeking to provide a molecular understanding of their combustion. More refined spectroscopic tools and methodologies must be developed to selectively detect and characterize the widening array of fuel components and combustion reactive intermediates. The direct relationship between molecular structure and rotational frequencies makes rotational spectroscopy highly structural specific; therefore, it offers a powerful means of characterizing pyrolysis ntermediates. This thesis describes experimental work using broadband microwave spectroscopy to address a number of challenging problems in the spectroscopy of gas complex mixtures.
Usually, the observed rotational spectra contain contributions from many distinct species, creating a complicated spectrum with interleaved transitions that make spectral assignment challenging. To assist with the process, a protocol called “strong-field coherence breaking” (SFCB) has been developed. It exploits multi-resonance effects that accompany sweeping the microwave radiation under strong-field conditions to output a set of transitions that can confidently be assigned to a single component in a mixture, thereby reducing the spectral assignment time.
The broadband chirped pulse Fourier transform microwave (CP-FTMW) spectra of guaiacol, syringol, 4-methyl guaiacol, 4-vinyl guaiacol were recorded under jet- cooled conditions over the 2-18 GHz frequency range. Using data from the 13C isotopomers the r0 structure of guaiacol was determined by means of a Kraitchman analysis. The tunneling due to OH hindered rotation was observed in syringol and the V2 barrier was deduced to be 50% greater than phenol’s barrier. This is due to the intramolecular H-bonding between the hydroxy and the methoxy groups. The internal rotation barrier for the methyl group for 4-methyl guaiacol was also determined. Moreover, the spectral assignment of the two conformers of 4-vinyl guaiacol was sped-up by using SFCB. The main structural insight from these lignin-related molecules was that polar substituents dictate the magnitude and type of structural shift that occurs relative to that of the unsubstituted aromatic ring.
In the next part of my work, the pyrolysis of 2-methoxy furan was carried out over the 300-1600 K temperature range, with microwave detection in the 2-18 GHz frequency range, using hightemperature flash pyrolysis micro-reactor coupled with a supersonic expansion. The SFCB technique was used to analyze and speed up the line assignment. The 2-furanyloxy radical, a primary, resonance-stabilized radical formed by loss of a methyl group in the pyrolysis of 2-methoxy furan, was detected and its molecular parameters were determined.
Finally, a unique setup that combines the high-resolution spectroscopic data provided by chirped pulse Fourier transform microwave (CP-FTMW) spectroscopy with photoionization mass spectra from a vacuum ultraviolet (VUV) time-of-flight mass spectrometer (TOF-MS) was used to find optimal conditions to detect reactive intermediates and make full assignments for the microwave spectra of phenoxy radical and o-hydroxy phenoxy radical over the 2-18 GHz range. Phenoxy radical was generated through the pyrolysis of anisole and allyl phenyl ether. Using a combination of data from 13C isotopomers and fully deuterated phenoxy radical, in combination with high level ab initio calculations, a near-complete r0 structure for the radical was obtained. The structural data point to the radical being a primarily carbon-centered rather than oxygencentered radical. Using guaiacol as precursor, we studied the spectroscopy of the o-hydroxy phenoxy radical, whose structural data is compared with that of phenoxy to understand the role played by the hydroxyl group in modifying the resonance stabilization of the radical.
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Zeng, Jun-Yan, et 曾俊諺. « Characteristics Of Bio-sludge Pyrolysis With The Microwave Heating Technique ». Thesis, 2015. http://ndltd.ncl.edu.tw/handle/vtj365.
Texte intégralRésumé :
碩士輔英科技大學
環境工程與科學系碩士班
103
Biological processes areamongthe most extensively used methods for wastewater treatment. The biosludge produced during process is frequently buried, cremated, or applied in agricultural activities. In order to achieve the objective of waste resource recycling, in the present study, the biosludge formed during the wastewater treatment was subjected to microwavepyrolysis as an alternative to conventional treatments. The solid, liquid, and gas products under variouspyrolysistemperatures were collected, and the impacts of variables such as pyrolysistemperature and time on the pyrolysis products were investigated. The major elements in the pyrolysis residues were analyzed by Elemental Analysis (EA). The volatile organiccompounds (VOCs) in the gaseous products were examined by Gas Chromatography/Mass Spectrometry (GC-MS). The organic compound composition of the pyrolysis oil was also determined by GC/MS. For the solid residue, the specific surface area (m2/g) and particle size distribution were assessed. The results indicated that the optimal pyrolysis oil production reached 20.27% at 600℃ for the petrochemicals industry and 23.78% at 500℃ for the industrial zone. The heat value obtained following the sludge pyrolysis oil analysis was found to be 9600~11000 (kcal/kg). The specific surfaceareas of the solid residues from the biosludge pyrolysis for the petrochemicals industry and industrial zone fell in the range of 4.39~49.54 m2/g. In the organic composition analysis of pyrolysis oil, it was found that the sludge from the petrochemicals industry was composed of mostly monocyclic benzene or bicyclic naphthalene products. In addition to benzene or naphthalene, ethylene and propane were identified as the major components in the sludge pyrolysis oil from the industrial zone. In the gaseous products from the pyrolysis at 700℃ of sludge from the petrochemicals industry, benzene, toluene, ethylbenzene, m,p-xylene, styrene, and o-xylene were discovered to be the most abundant. The kinetic results of the sludge microwavepyrolysissuggested that, for the sludge from the petrochemicals industry, the averageactivationenergy was 28.87 kJ/mol, the frequency factor was 1.80 (1/sec), and the reaction order was 0.62.For the sludge from the industrial zone, the averageactivationenergy was 24.51 kJ/mol, the average frequency factor was 2.21 (1/sec), and the reaction order was 0.66.
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Chi-Cheng, Lu, et 盧麒丞. « Transforming agricultural wastes into usable energy using microwave–induced pyrolysis ». Thesis, 2010. http://ndltd.ncl.edu.tw/handle/56102199144175597639.
Texte intégralRésumé :
碩士明志科技大學
生化工程研究所
98
As energy runs out and people realized the importance of environmental protection, more and more clean, harmless and infinite renewable alternative energies so called renewable energy are discovered and applied to daily life. These alternative energies include solar, wind, geothermal, water, and the biomass energy which will be discussed specifically in this study. In general, wastes from plants are composed by cellulose, hemicellulose, lignin and small amount of organic components, which all have different pyrolysis or retrodegration rates, reactions and paths. Furthermore, the major source for biomass wastes is from forestry and agriculture. The microwave process,which characteristic of rapid increasing in temperature of microwave to make biomass go through pyrolysis and collects the products and analysis. In this research, agricultural wastes decrease obviously in volume as microwave power increases from 300W to 500W, especially sugarcane bagasse decrease in weight, 79.11 wt% at 300W and 88.71 wt% when microwave power increases to 500W, which proofed microwave does have great efficiency in decreasing waste volume. Regarding to the solid phase products (Char), gaseous phase products (Fuel gas), and liquid phase products (Tar) are analysis, the average heating value of Char of agricultural waste is above 4000 cal/g, which is valuable for further study. For the agricultural waste, the H2 and CO concentrations from fuel gas are 15~30 vol% and 40~56 vol%, which is helpful in producing syngas, which indicates this system has great potential in producing fuel gas. Lastly, the liquid phase product has two main compounds: (1) polar compound, (2) low ring PAHs. Besides, the differences of composition of biomass wastes, the change of gaseous products from microwave pyrolysis needs further study. In addition, when contained cellulose increases from 28.70% to 51.24%, the production of CH4 also increases from 15.98 ml/g to 48.08 ml/g; in addition, when contained hemicellulose increase from 23.75% to 31.37%, the production of H2 increases from 56.45 ml/g to 105.49 ml/g. As a result, microwave pyrolysis can be a new choice of technology in environmental protection and energy fields.
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Schumann, James. « Bio-oil generation from microwave assisted pyrolysis of stockpiled biosolids ». Thesis, 2017. https://researchonline.jcu.edu.au/63005/1/JCU_63005_schumann_2017_thesis.pdf.
Texte intégralRésumé :
This project employed microwave assisted pyrolysis (MWAP) to recover resources from stockpiled biosolids from Victoria, Australia. Biosolids are the stabilised sludge that results from sewage wastewater treatment. The presence of contaminants, unpleasant odours and poor public acceptance make biosolids disposal challenging. Over three million tonnes of biosolids are currently stockpiled in Victoria, having no identified end use.
MWAP applies a microwave electromagnetic field to biosolids in a low-oxygen environment, which heats the material, thermally decomposing the organic matter into volatile bio-oils and incondensable gases, leaving behind a biochar. This work focused on assessing the feasibility of generating bio-oil from MWAP of the Victorian biosolids, with a particular focus on analysing the composition of the bio-oil and identifying ways to enhance the process value. A comparative study was also done using local biosolids.
MWAP was carried out using a single-mode microwave pyrolysis unit with a nitrogen-gas purge, enabling condensers to trap the resultant bio-oil. Biosolids mixed with a microwave susceptor that absorbed the microwave energy and re-emitted it as heat (activated carbon) were pyrolyzed in sets of experiments where the oil composition and yield were evaluated. As bio-oil produced from MWAP can contain hundreds of organic compounds, a method was developed to analyse the yield of selected compounds with Gas Chromatography Mass Spectrometry and Gas Spectrometry Flame Ionization Detection. To improve the separation of the bio-oil in the chromatography column, samples were first derivatized using N,O-Bis(trimethylsilyl)trifluoroacetamide (BSTFA).
The bio-oil derived from stockpiled biosolids contained a range of compounds, with the largest groups being phenols and carboxylic acids, and had a calorific value similar to that of bio-diesel. Bio-oil yield was low due to the degradation of the biosolids from the extended periods of stockpiling. The MWAP also consumed a large amount of energy per unit mass of biosolids pyrolysed.
Under some conditions the MWAP was cost competitive against land application, which costs an average $300/dry tonne. MWAP of stockpiled biosolids cost as little as $218/dry tonne, though >90% of the savings were due to mass reduction and not bio-oil in this case. Larger scale tests are needed to determine whether the costs and technical complexity of the process could be managed. Unidentified components of the bio-oil that were not quantified may improve the economics.
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FAN, SHU YA, et 范淑雅. « Transforming bio-waste into adsorbents by a microwave–induced pyrolysis method ». Thesis, 2017. http://ndltd.ncl.edu.tw/handle/84033973375723013816.
Texte intégralRésumé :
碩士明志科技大學
環境與安全衛生工程系環境工程碩士班
105
This study utilized the microwave–induced pyrolysis to pyrolyze different bio-waste into bio-adsorbents. Because of the varied characteristics of original bio-waste, the bio-adsorbents showed quite different physical and chemical properties. A series of adsorption experiments were conducted to evaluate the feasibility of the bio-adsorbent applied to contaminant removal and material recovery. The technology of this research has the advantages of low cost, novelty and recycling, etc., and can achieve the purpose of recycling of waste resources. By the analysis of N2-adsorption-desorption, all the produced bio-adsorbents displayed the properties of type Ⅳ isotherm and slit-shaped opening. The pore structure of bio-adsorbent is mostly related to the lignin and cellulose content in the starting waste. The measurements of CO2 adsorption on the bio-adsorbents were carried out by thermogravimetric analyzer (TGA). Among all the produced bio-adsorbents, the bio-adsorbent derived from the waste corn showed the best adsorption performance of 58.65 mg CO2/g bio-adsorbent, which value is competent to the commercial activated carbon published in previous literatures. The results indicated that the methods to produce bio-adsorbents was feasible and could be further explored. In addition, this study also carried out the waste iodide stream recovery by comparing three bio-adsorbents prepared by microwave–induced pyrolysis with a commercially available activated carbon. The results showed that the iodide adsorption yield better performance in acidic condition than alkaline. Furthermore, a coating of silver ion on bio-adsorbents could enhance the iodide recovery. In the experiment, the silver ion impregnated bio-adsorbent derived from waste peanut shells had the best iodide adsorption of 555.98 μmole iodide/g silver-impregnated-bio-adsorbent. The results show that it is feasible to adsorb iodide from water by silver-coated bio-adsorbent. The results may be helpful for the iodide recovery from waste stream in the optoelectronic industry
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Chou, Szu-Ling, et 周思伶. « Precious Metals Recovery from Waste Printed Circuit Board Using Microwave Pyrolysis ». Thesis, 2017. http://ndltd.ncl.edu.tw/handle/qwab29.
Texte intégralRésumé :
碩士國立臺灣大學
環境工程學研究所
105
In recent years, a rapid increase in mobile phone market led to growing demand of precious metals such as gold and palladium. Printed circuit boards of mobile phones are made of up to 50 different elements such as gold, silver, platinum, palladium, and other precious metals. Although recycling precious metals from waste printed circuit boards (WPCBs) is promising, inappropriate handing may cause pollution to air, water, and soil. Current trends in recycling WPCBs including mechanical process, pyrometallurgy and hydrometallurgy; however, they have problems about recovery rate, energy consumption and environment pollution. Therefore, the hydrometallurgy combined with thermal pyrolysis to recover precious metals of WPCBs has attracted such attentions. The aim of this study is to find out a technique for metals recovery from WPCBs, which has high efficiency, low energy consumption, and low environmental pollution. The main component of the printed circuit board is glass fiber, which is composed of carbon material. Carbon is a good microwave absorber, and its heating rate can reach 9.98 to 21℃per seconds under microwave irradiation. Thus, microwaves can enhance the pyrolysis of WPCBs. Microwave-enhanced pyrolysis (MEP) was used as a pretreatment to separate the inner layers of WPCBs, and to enhance metal recovery efficiency. Meanwhile, thermogravimetric analysis (TGA) was used to determine the maximum weight loss of WPCBs, as a reference for controlling the power of microwave-enhanced pyrolysis. According to the experiment, the maximum weight loss of WPBCs occurred at 400℃, which was achieved by MEP at 350 W to complete pyrolysis in 40 minutes. Sulfuric acid and Thiosulfate were used to leach the pyrolysis WPCBs for copper and gold recovery. The best recovery from copper is using 2 M sulfate with hydrogen peroxide up to 95% or more. The high recovery rates of gold are using by 0.1 M thiosulphate, 0.015 M CuSO4 and 0.2 M NH3. At the extraction part, extraction gold from thiosulphate is not sufficiently effective. Finally, the leachate of gold was reduced by oxidant as H2O2. The combination of microwave pyrolysis and hydrometallurgical can reduce energy consumption and decrease environmental pollution. This study is an environmentally friendly technique for the recover precious metals from WPCBs. Key Words: Microwave-Enhanced Pyrolysis; Precious Metal Recovery; Waste Printed Circuit Boards
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ZHOU, ZHI-WEI, et 周志維. « Microwave pyrolysis of sludge for potential use as fuel and adsorbent ». Thesis, 2019. http://ndltd.ncl.edu.tw/handle/j983t5.
Texte intégralRésumé :
碩士輔英科技大學
環境工程與科學系碩士班
107
In this study, microwave heating was used to investigate the pyrolysis characteristics of biosludge, which the effects of different activators, pyrolysis temperature, and activator dose and immersion time were also considered. The adsorption efficiency of residual solids to organic dyes and inorganic metals was investigated, and it was evaluated whether the residual solids were suitable as an adsorbent. In addition, the chemical composition of liquid oil and the content of PAHs in oil were determined to evaluate the feasibility of liquid oil as an alternative fuel. Compared to the pyrolysis of the raw sludge, the KOH addition sludge resulted in a decrease in liquid oil yield and a decrease in heat value to about half of the raw sludge. If H3PO4 was added, the liquid oil production after pyrolysis was lower than that of KOH sludge. Compared with the raw sludge pyrolysis, the KOH addition increased the specific surface area of the solid residue to 311.51 m2/g (at 600 °C, sludge： KOH = 1：0.5; w/w). High KOH dose increased adsorption efficiency of the sludge-derived adsorbent to metal ions and methylene blue. The maximum adsorption capacity of metal ions (Qm) was in the order Ni(II) (3.701 mmol/g) > Zn(II) (3.121mmol/g) > Cd(II) (2.471 mmol/g) > Pb (II) (1.378 mmol/g). The maximum adsorption capacity of methylene blue was 0.947 mmol/g.
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Wang, Sheng-Yuan, et 王勝遠. « Recovery of Indium from Waste Liquid Crystal Display by Microwave-induced Pyrolysis ». Thesis, 2017. http://ndltd.ncl.edu.tw/handle/aydgjy.
Texte intégralRésumé :
碩士國立臺灣大學
環境工程學研究所
105
Indium is a kind of rare metal because of its scarcity in the earth’s crust and difficulty in refining. The major application of indium is indium tin oxide (ITO), a transparent current-conductive material playing a critical role in the liquid crystal display (LCD) function. With the mass production of LCD screens, indium resource was estimated to be exhausted by 2025. Therefore, the recovery of indium from waste LCD is important and urgent. The indium recovery process in this study incorporates the microwave-induced pyrolysis in the hydrometallurgy to enhance the recovery efficiency of indium from waste LCD and get high purity and concentration of indium aqueous solution. The process include four steps: microwave-induced pyrolysis, leaching, extraction, and stripping. First, the microwave-induced pyrolysis process can remove the organics and make the separation between the layers of LCD panel to enhance the leaching rate in the following process. According to the thermal gravimetric analysis (TGA) results, the maximum decay rate of waste LCD occurred at 361.2 °C. Consequently, The microwave-induced pyrolysis process was carried out at the microwave power of 150 W for the processing time of 50 min. Secondly, in the leaching process, indium can be dissolved in the acid solution. 98.27 wt.% of the indium was leached out in 0.5M sulfuric acid with 1:10 solid/liquid ratio, 2 hr, 90 ℃ and stirring at 360 rpm. The purity and concentration of indium are 40.07 % and 25.97 ppm. Thirdly, di(2-ethylhexly)phosphoric acid (D2EHPA) can extract indium from the sulfuric acid solution to separate indium from the other metals and enrich the indium concentration. In the extraction process, the best condition for indium was 20 % (v/v) D2EHPA dissolved in the kerosene at organic-to-aqueous phase ratio (O/A) of 1:10. The purity, concentration and recovery rate of indium are 86.17 %, 228.23 ppm and 81.7 wt.%. Finally, indium in the loaded organic phase can be stripped by hydrochloric acid to separate and enrich indium again. In the stripping process, 68.99 wt.% of the indium was recovered in 6 M hydrochloric acid at O/A of 10:1. The purity and concentration of indium in the final production are 99.98 % and 1892.38 ppm. In this study, the final product (hydrochloric acid solution) containing high purity and high concentration of indium is beneficial to electrolytic refining or replacement to get indium metal. The result indicates that the recovery process of indium from waste LCD by microwave-induced pyrolysis is a promising technique.
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CHEN, KUO-YUEU, et 陳國源. « Recovery of Waste Polarizing Film Using Microwave-Induced Pyrolysis To Resources and Energy ». Thesis, 2018. http://ndltd.ncl.edu.tw/handle/gw43sc.
Texte intégralRésumé :
碩士明志科技大學
環境與安全衛生工程系環境工程碩士班
106
Due to mounting demand of liquid crystal displays (LCD), polarizing films, the main material of LCD, have been manufactured at an ever-accelerating pace in Taiwan. It brings on that the problem of treatment for waste polarizing film, cutting edge materials, defective products and recycled materials. The current treatment method for waste polarizing films is incineration in Taiwan. However, the iodide contained in polarizing films will generate the purple color iodine flue and draw lots of protest from the residents and public medias. Subsequently, most of the waste polarizing films were rejected from all incinerator plants in Taiwan. The study try to covert the waste polarizing films to energy and resources using microwave induced pyrolysis. The optimal carrier gas is nitrogen with a flow rate of 50 ml / min, and reaction time of 10 min. The higher power yields higher heating rate. As the reaction time lasting, the solid products are reduced and converted into the gas phase. On the other hands, majority of the iodine was distributed into the liquid and the least in the solid phase. When the power is higher than 300 W, the iodine distributed into liquid phase over 85% of overall quantity. As the reaction time increasing, the iodine concentration enriched in the liquid products of which weight decreasing. Most of the solid, liquid, and gas-phase products could be recycling and recovery to resources and energy. The solid phase has specific surface area of 580.2 m2 /g which was potential to be activated carbon for adsorption. The liquid phase consisted mainly of phenol and benzencarboxylic acid, accounting for 24.2% and 36.2% of overall liquid weight, respectively. Surprisingly, the gas phase using microwave-induced pyrolysis barely produced CO2 and syngas accounted for 85% of gas products. Four scenarios of the waste polarizing films treatment on the issues of the carbon reduction and economic evaluation were: landfill, incineration, alternative fuels, and utilization of microwave pyrolysis as a pre-treatment resource assessment. The results show that microwave-induced pyrolysis used as the pre-treatment produced liquid and gas-phase compounds which could be used as fuel to generate electricity. This scenario could reduce carbon emissions by 30,647 tons of CO2 per year. Also, it can produce 57,870,000 kWh of power, and pyrolyzed solid products can be developed as activated carbon material to solve the current landfill capacity oversaturated problems and prolong the landfill life in Taiwan.
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Dos, Santos Antunes Elsa Marisa. « Investigations on biochar production from biosolids via microwave assisted pyrolysis and its potential applications ». Thesis, 2017. https://researchonline.jcu.edu.au/53048/1/53048-dos-santos-antunes-2017-thesis.pdf.
Texte intégralRésumé :
Biosolids are the treated solid fraction produced in a municipal wastewater treatment plant. Biosolids production has been increasing every year mainly because of: 1) population increase, 2) more access to a sewage network, in particular in developing countries, and 3) more restrictive environmental regulations. Land application is typically used to manage biosolids, but contaminant leaching from biosolids to soil and groundwater has restricted this approach. Currently in Europe, biosolids are mainly incinerated, but in Australia there are no incineration plants, so a new environmental and sustainable solution for biosolids management has to be established in the near future. These new approaches must be focused on biosolids recycling and by-products valorisation, mitigating environmental impact and resource depletion.
This research studied microwave assisted pyrolysis (MWAP) as a methodology for biosolids treatment and investigated the potential applications of the final biochar. This study investigated the dielectric properties of biosolids and the impact of MWAP conditions on biosolids processing and biochar properties. The dielectric properties of compacted biosolids with varying moisture content were measured at different microwave frequencies using a network analyser. Results showed that as the moisture content increased in biosolids, the dielectric constant and dielectric loss factor both increased. Dry biosolids were almost transparent to microwaves, indicating that the ability to absorb microwave energy is very low. To overcome this problem, an addition of a microwave susceptor (activated carbon) was employed for the biosolids pyrolysis experiments.
As single-mode microwave cavities have just one "hot spot", it is fundamental to place the biosolids sample in this area to maximize coupling between microwaves and the sample. Numerical simulations were carried out to assess the impact of biosolids load and moisture content on microwave field intensity and distribution. These simulations were done by using Inventor Professional 2015 software (AutoDesk Co., USA) and XFdtd software, version 7.5.1.3.r43518 (Remcom Co., USA) to solve the Maxwell's electromagnetic equations for the pre-defined materials and microwave feed ports conditions in XFdtd. Results showed that distribution and intensity of the microwave field were significantly affected by moisture content. As the moisture increases the intensity and distribution of microwave field decreased due to the adsorption of electromagnetic energy by the sample because water is a good microwave absorber. As the sample load increased, the electromagnetic field decreased, and its distribution was clearly affected due to field perturbation.
Pyrolysis conditions affect product yield and distribution, and the properties of the final by-products. Of all the conditions, temperature is the pyrolysis process variable with the greater impact on by-products properties. In this study, pyrolysis temperature impacted on biochar yield, surface area and resultant functional groups present on the biochar. Biochar yield decreased while surface area increased at higher pyrolysis temperatures. The heavy metals of biosolids accumulated in the final biochar and the percentage of heavy metals increased as the biochar yield decreased. Microwave susceptors affected the heating rate and consequently the pyrolysis energy consumption, biochar yield and properties. Activated carbon was the best option for biosolids MWAP due to the lower energy consumption, and the biochar had the highest stability and surface area, which are fundamental requirements for biochar soil application.
The biosolids biochar was successfully used for phosphorus and silver recovery from synthetic and real solutions. The phosphorus removal capacity by biochar was affected by the calcium content in biochar, contact time between biochar and phosphorus solution, pH and initial concentration of phosphorus of the aqueous solution. As the calcium content increased in biosolids, the phosphorus removal capacity increased due to more available calcium cations to complex with phosphate species. The phosphorus removal capacity of biochar (11.5% of Ca) was maximised at pH 4, corresponding to 147 mg-P/g of biochar. The main mechanism of phosphorus removal was precipitation, and the experimental data was well described by a pseudo second-order kinetic model and the isotherms followed the Langmuir model. Brushite (calcium hydrogen phosphate dehydrate: CaHPO₄·2H₂O) was the main precipitation product resultant from the combination of calcium cations with phosphate species.
Silver is an emerging pollutant in wastewater treatment plants due to the wide use of this element as an anti-bacterial in final products. This element represents a serious threat to life even when present in very small amounts. This study showed that silver removal by biochar is a spontaneous process of physical adsorption. Silver removal capacity increased with initial silver concentration and temperature of the silver aqueous solution. Experimental data fitted was well described by the pseudo second-order kinetic model and intra-particle diffusion model. The final composite (Ag-biochar) after silver adsorption can be further used for methylene blue degradation and adsorption.
The results of this study demonstrated that MWAP is an environmentally sustainable approach to deal with the anticipated increases in biosolids production. The final biochar can be used as adsorbent for contaminant removal, water pollution mitigation and resource recovery, thereby avoiding future natural resource depletion.
41
Chang, Jyun-Yuan, et 張峻愿. « Effects of various pretreatment on the gaseous products of corn leaf using microwave-induced pyrolysis ». Thesis, 2015. http://ndltd.ncl.edu.tw/handle/3cqbhx.
Texte intégralRésumé :
碩士明志科技大學
環境與安全衛生工程系環境工程碩士班
103
As the use of the fossil fuels raises seriously environmental concerns, much attention has been paid to the research of the environmental symbiosis in recent years. People attempt to develop clean, safe and renewable energy to meet the increasing demand for the energy consuming. Among the various choice of alternative energy, biomass energy, along with the idea of the recycling, is a promising kind. Taiwan is a country founded on farming and the agricultural waste, most of which are organic like cellulose, hemicellulose, and lignin, is a useful resource for biomass reuse. However, the difference on the waste processing may affect the efficiency of the microwave induced pyrolysis. The study applied the microwave induced pyrolysis method on corn leaves, by altering the size of corn leaves and the catalyst (Al2O3) and combining with various pretreatments, observing the gaseous phase product generated by the microwave induced pyrolysis method. The laboratory conditions are controlled and the result suggests that the temperature difference can reach up to 107 degree Celsius among five sizes fractured corn leaves. The varied violently and the most differece reached yield of CO and H2 in the gaseous phase changes 11.4 % and 4.2 %. The most yield of liquid phase was up to 15 % , while the bigger size waste generates the more CO and the smaller one generates more H2. The result also suggests that adding 10 and 50 mesh Al2O3 to waste can reach a higher temperature curve than the system without catalyst. Meanwhile, the highest temperature will increase 17 degree Celsius in the condition of catalyst addition. The yield of CO and H2 increased 9.26 % and 3.5 %, while the yield of CO2 and CH4 changed less than 1%. In the catalyst addition condition both size of the catalyst have the effect of catalyzing the liquid phase product, but the effect of 10 mesh one is more significant. The affecting factor might be the specific surface area of the catalyst. The variety of pretreatment can also differ the results. The orthophosphoric acid soaking pretreatment results in the increasing of the liquid phase product but not effecting the amount of gaseous phase product. The stream explosion pretreatment retarded the gassing peak time of gas production because of catalyzing the transformation of the liquid phase product into the gaseous phase product, moreover, as adding the Al2O3, the reaction also improves the generation of CO and H2 in a smaller amount.
42
Lan, Chen-Laun, et 藍宸鑾. « Study on recycling of waste printed circuit board by microwave pyrolysis and its potential pollution ». Thesis, 2019. http://ndltd.ncl.edu.tw/handle/tkr99x.
Texte intégralRésumé :
碩士輔英科技大學
環境工程與科學系碩士班
107
The studied PCB is FR-4 material. PCB was planed, crushed and sorted to obtain the non-metallic part of PCB. The pyrolysis onto non-metallic part of PCB was carried out in a microwave pyrolysis furnace. The effects of distinct particle size, NaOH addition, NaOH dose, residence time and temperature on pyrolysis characteristics were investigated. After pyrolysis, the solid residues and liquid oils were analyzed to evaluate their potential use as adsorbents and alternative fuels, respectively. The experimental results indicated that the solid product decreased and the gas product increased, with increasing in pyrolysis temperature. For raw PCB pyrolysis, the lowest solid residue yield and the highest liquid oil yield can be found at pyrolysis temperature of 600 °C. For the pyrolysis with PCB added NaOH, which resulted in a reduction in liquid oil production and also increases the bromine content of the solid residues. In other words, almost no Br was released to the liquid oil and gas under pyrolysis with NaOH addition. Compared to the pyrolysis of the raw PCB, the NaOH addition improved pore development, increasing the solid residue specific surface area and total pore volume to 16.69 m2/g and 0.034 cm3/g, respectively. For pyrolysis of the raw PCB, the chemical composition of liquid oil indicates that the carbon number of the compound species was in the range of C6-C12, with phenol, 4-isopropylphenol, 4-phenylphenol and 3-bromophenol, 4-bromo-2,6-xylidine as the main species. After NaOH addition, the brominated compounds such 3-bromophenol, 4-bromo-2,6-xylidine could not be detected in pyrolysis liquid oil. Keywords: Pyrolysis, Printed circuit board, Brominated epoxy
43
Dias, Sandra Raquel da Silva. « Production of activated carbons by microwave pyrolysis of industrial wastes for the removal of pharmaceuticals from water ». Master's thesis, 2018. http://hdl.handle.net/10773/24698.
Texte intégralRésumé :
The presence of pharmaceuticals in water bodies, being biologically active compounds, have raised concerns due to the adverse effects in non-target organisms. With the conventional treatments, applied in the wastewater treatment plants (WWTPs), being inefficient for the removal of these contaminants, WWTPs are pointed out as the main source of pharmaceuticals into the environment. The use of adsorption, as an advanced treatment for the removal of pharmaceuticals from water, in particular by using activated carbons (ACs), has shown to be an easy-handling and cost-efficient process, without sub-products formation.
Since the production of ACs can be an expensive process, due to the high energy requirements and the use of expensive precursors, the alternative microwave (MW) pyrolysis of paper mill primary sludge (PS) can be a promising solution, contributing simultaneously for industrial waste valorisation. In the scope of this work, ACs were produced by MW pyrolysis of PS impregnated in KOH (activating agent) for 10 min at 800 W, washed with hydrochloric acid and sieved to obtain the fraction of particles with a size up to 180 μm. Different ACs were obtained by changing activating agent:precursor ratios, namely 0.5:1, 1:1 and 1.5:1. The produced ACs were physico-chemically characterised. In order to assess the performance of the produced ACs, batch adsorption experiments were performed with ultra-pure water to determine the adsorption percentages of the anti-epileptic carbamazepine (CBZ). The effect of AC dosage and the effect of contact time were also tested.
The obtained results have shown that, overall, the ACs produced with an activating agent:precursor ratio of 0.5:1 presented specific surface areas (SBET) between 773 and 1190 m2/g and high percentages of CBZ removed from ultra-pure water solutions, above 80 %, for AC dosages of 0.1 g/L and a contact time of 24 h. The lab-made ACs have shown a more developed porous structure than the reference commercial AC and comparable SBET. Nevertheless, under the same experimental conditions, different production batches resulted in ACs with different properties and performances, highlighting that further research work is required to optimise its production process, making it repeatable.Sendo os fármacos compostos biologicamente ativos, a sua presença nos recursos hídricos tem gerado preocupações devido aos efeitos adversos em organismos não-alvo. Sendo os tratamentos convencionais, aplicados nas estações de tratamento de águas residuais (ETARs), ineficientes para a remoção destes contaminantes, as ETARs são apontadas como a principal fonte de fármacos no meio ambiente. O processo de adsorção, enquanto tratamento avançado para a remoção de fármacos da água, em particular com o uso de carvões ativados (CAs), tem-se mostrado um processo de fácil aplicação e eficiente, sem formação de subprodutos. Como a produção de CAs pode ser um processo dispendioso, devido aos requisitos energéticos e ao uso de precursores de elevado custo, a alternativa pirólise em micro-ondas (MO) de lama primária (LP) da indústria papeleira pode ser uma solução promissora, contribuindo simultaneamente para a valorização de resíduos industriais. Neste trabalho, os CAs foram produzidos por pirólise em MO de LP impregnada com KOH (agente ativante) durante 10 min a 800 W, lavados com ácido clorídrico e crivados para obtenção da fração de partículas com dimensão inferior ou igual a 180 μm. Obtiveram-se diferentes CAs alterando as razões de agente ativante:precursor, nomeadamente 0.5:1, 1:1 e 1.5:1. Os CAs produzidos foram física e quimicamente caraterizados. No sentido de avaliar o desempenho dos CAs produzidos, realizaram-se testes de adsorção em descontínuo com água ultra-pura para determinar a percentagem de adsorção do anti-epilético carbamazepina (CBZ). O efeito da concentração de CA e o efeito do tempo de contacto também foram testados. Os resultados obtidos demonstraram que, de um modo geral, os CAs produzidos numa razão de 0.5:1 de agente ativante:precursor apresentaram áreas superficiais específicas (SBET) entre 773 e 1190 m2/g e elevadas percentagens de remoção de CBZ de soluções de água ultra-pura, acima de 80 %, para concentrações de CA de 0.1 g/L e tempos de contacto de 24 h. Os CAs produzidos em laboratório demonstraram ter uma estrutura porosa mais desenvolvida do que o CA comercial de referência e SBET comparáveis. Todavia, para as mesmas condições experimentais, diferentes lotes de produção originaram CAs com propriedades e desempenhos diferentes, denotando que mais trabalho de investigação deve ser investido de modo a otimizar o seu processo de produção, tornando-o repetível.
Mestrado em Estudos Ambientais
44
Skolo, Kholiswa Patricia. « Controlled wet-chemical dissolution of simulated high-temperature reactor coated fuel particles ». Diss., 2012. http://hdl.handle.net/2263/29908.
Texte intégralRésumé :
High-temperature reactors make use of tri-structural coated fuel particles as basic fuel components. These TRISO particles consist of fissionable uranium dioxide fuel kernels, about 0.5 mm in diameter, with each kernel individually encased in four distinct coating layers, starting with a porous carbon buffer, then an inner pyrolytic carbon (IPyC) layer, followed by a layer of ceramic silicon carbide (SiC) and finally an outer pyrolytic carbon layer (OPyC). Collectively, the coating layers provide the primary barrier that prevents release of fission products generated during burn up in the UO2 fuel kernel. It is crucial to understand how the fission products contained within the fuel interact with the coating layers and how they are distributed within the fuel. The first step commonly performed to obtain the information on distribution is removal of the coating layers. The purpose of this study was to investigate the possible use of wet chemical etching techniques with the aim of removing the coating layers of ZrO2 coated fuel particles in a controlled way and to establish experimental parameters for controlled dissolution of irradiated fuel particles. Stepwise dissolution of coated fuel particle coating layers, containing zirconia kernels has been investigated by chemical etching experiments with acidic solutions of different mixtures. The heating methods used include heating by conventional methods, hot plates and a muffle furnace, a reflux-heating system and microwave-assisted digestion. The etching mixtures were prepared from a number of oxidizing acids and other dehydrating agents. The capability of each reagent to etch the layer completely and in a controlled manner was examined. On etching the first layer, the OPyC, the reflux heating method gave the best results in removing the layer, its advantage being that the reaction can be carried out at temperatures of about 130 ºC for a long time without the loss of the acid. The experimental results demonstrated that a mixture composed of equal amounts of concentrated nitric and sulfuric acid mixed with chromium trioxide dissolves the OPyC layer completely. The most favourable experimental conditions for removal of OPyC from a single coated fuel particle were identified and found to depend on the etching solution composition and etching temperature. Light microscopy yielded first-hand information on the surface features of the samples. It allowed fast comparison of etched and untreated sample features. The outer surface of particles prior to chemical etching of the outer pyrolytic carbon layer appeared black in colour with an even surface compared to the etched surfaces which appeared to have an uneven metallic grey, shiny texture. The scanning electron microscope (SEM) examination of the chemically treated outer carbon layer samples gave information on the microstructure and it demonstrated that the outer pyrolytic carbon layer could be readily removed using a solution of HNO3/H2SO4/CrO3, leaving the exposed SiC layer. Complete removal of the layer was confirmed by energy dispersive X-ray spectroscopic (EDS) analysis of the particle surface. For etching the second layer, the silicon carbide layer, microwave-assisted chemical etching was the only heating technique found to be useful. However, experimental results demonstrated that this method has limited ability to digest the sample completely. Also common chemical etchants were found to be ineffective for dissolving this layer. Only fluoride containing substances showed the potential to etch the layer. The results show that a mixture consisting of equal amounts of concentrated hydrofluoric and nitric acid under microwave heating at 200 ºC yielded partial removal of the coating and localized attack of the underlying coating layers. The SEM analyses at different intervals of etching showed: partial removal of the layer, attack of the underlying layers and, in some instances, that attack started at grain boundaries and progressed to the intra-granular features. The SEM results provide evidence that etching of the silicon carbide layer is strongly influenced by its microstructure. From these findings, it is concluded that etching of the silicon carbide under the investigated experimental conditions yields undesirable results and that it does not provide complete removal of the layer. This method has the potential to etch the layer to some extent but has limitations. CopyrightDissertation (MSc)--University of Pretoria, 2013.
Chemical Engineering
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