Dissertations / Theses on the topic 'Liquid Fuel Production'

Since the oil crisis of 1973 considerable interest has been shown in the production of liquid fuels from alternative sources. In particular processes utilizing coal as the feedstock have received considerable interest. These processes can be divided into direct and indirect liquefaction and pyrolysis. This thesis describes the modelling of indirect coal liquefaction processes for the purpose of performing technical and economic assessment of the production of liquid fuels from coal and lignite, using a variety of gasification and synthesis gas liquefaction technologies. The technologies were modeled on a 'step model' basis where a step is defined as a combination of individual unit operations which together perform a significant function on the process streams, such as a methanol synthesis step or a gasification and physical gas cleaning step. Sample results of the modelling, covering a wide range of gasifiers, liquid synthesis processes and products are presented in this thesis. Due to the large number of combinations of gasifier, liquid synthesis processes, products and economic sensitivity cases, a complete set of results is impractical to present in a single publication. The main results show that methanol is the cheapest fuel to produce from coal followed by fuel alcohol, diesel from the Shell Middle Distillate Synthesis process,gasoline from Mobil Methanol to Gasoline (MTG) process, diesel from the Mobil Methanol Olefins Gasoline Diesel (MOGD) process and finally gasoline from the same process. Some variation in production costs of all the products was shown depending on type of gasifier chosen and feedstock.

In the effort to introduce fuel cell technology in the field of decentralized and mobile power generators, a hydrocarbon reformer to syngas seems to be the way for the market uptake. In this thesis, a potential technology is developed and investigated, in order to convert commercial liquid fuel (diesel, kerosene and biodiesel) to syngas. The fundamental concept is to oxidise the fuel in a oxygen depleted environment, obtaining hydrogen and carbon monoxide as main products of the reaction. In order to extend the flammability limit of hydrocarbon/air mixtures, the rich combustion experiments have been carried out in a two-layer porous medium combustor, which stabilises a flame at the matrix interface and recirculates the enthalpy of the hot products in order to enhance the reaction rates at ultra-rich equivalence ratio. This thesis demonstrates the feasibility of the concept, by exploring characteristic parameters for a compact, reliable and cost effective device. Specifically, a range of equivalence ratios, thermal loads and porous materials have been examined. n-heptane was successfully reformed up to an equivalence ratio of 3, reaching a conversion efficiency (based on the lower heating value of H2 and CO over the fuel input) up to 75% for a packed bed of alumina beads. Thermal loads from P=2 to 12 kW at phi=2.0 demonstrated that heat losses can be reduced to 10%.Similarly, diesel, kerosene and bio-diesel were reformed to syngas in a Zirconia foam burner with conversion efficiency over 60%. The effect of different burners, thermal loads and equivalence ratios have also been assessed for these commercial fuels, leading to equivalent conclusions. A preliminary attempt to reduce the content of CO and hydrocarbons in the reformate has been also performed using commercial steam reforming and water-gas shift reaction catalysts, obtaining encouraging results. Finally, soot emission has been assessed, demonstrating particle formation for all the fuels above phi=2.0, with biodiesel showingthe lowest soot formation tendency among all the fuels tested.

The purpose of this study is to analyse the development of South Africa's liquid fuels industry from 1930s to the present and the various ways in which the state has extended subsidies and other measures of support to liquid fuels producers. The nature and extent of government support to the South African liquid fuels industry has remained hidden for many years, due to the veil of secrecy surrounding the industry prior to the country's transition to democracy. The study expands past analyses to identify and estimate the magnitude of subsidies to liquid fuels production in South Africa in the present. Using the historical institutional approach, the study then places these measures of support in the South African political economy environment so as to understand the institutional barriers to their reform. In doing so, the study sheds light on the drivers informing the endurance of the liquid fuels subsidy regime and state support to the liquid fuels industry following the transition to democracy.

Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2019
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 50-54).
This work is a first order assessment of the technical feasibility and characteristics of technologies to produce fuel onboard aircraft carriers, which is of interested to the United States Navy. They are interested because the logistical burden and supply chain required for delivering fuel at sea is dangerous, expensive, and subject to changes in markets price for liquid fuels. This work is a first order assessment of the technical feasibility and characteristics of technologies to produce fuel onboard aircraft carriers. The plant is evaluated for three technology pathways: Alkaline electrolysis and the reverse water gas shift (AE+RWGS), solid oxide electrolysis and RWGS (SOEC+RWGS), and co-electrolysis of steam and CO₂. They are evaluated within two scenarios: a small infrequently operating plant leveraging excess nuclear power (Scenario A) and a large frequently operating plant with dedicated nuclear capacity.
In addition, a parameter sweep of fuel production capacity and capacity factor is conducted to assess impacts on fuel production costs. In Scenario A, the energy requirements ranged from 152-22OMWe and fuel production cost ranged from 1.91-4.49$/L. In Scenario B, the energy requirements ranged in 1380-2066MWe and fuel production costs ranged from 3.25-4.23$/L. In both scenarios, AE+RWGS was the most cost effective and co-electrolysis was the most energy efficient. The fuel produced reduced lifecycle CO₂ equivalent emissions by 85.3-90.2%. The plant volume and weight were 50-67% and 432% of a current aircraft carrier design at large scales. The results of the parameter sweep indicate that generally a larger more frequently operating plant is more cost effective, but dedicated nuclear capacity requirements diminishes this benefit.
The overall results indicate that a fuel production plant on an aircraft carrier is technically feasible and has the potential to be cost effective, though research into cost, weight, and volume reduction are still necessary.
by Liam Jacob Frank Comidy.
S.M.
S.M. Massachusetts Institute of Technology, Department of Aeronautics and Astronautics

The research described in this dissertation was motivated by the global demand for energy that is not dependent on coal, oil, natural gas and other non-renewable fossil fuels. The technology used in this project is related to the use of biomass to produce a viable alternative to conventional sources of fuel. A bench scale biomass to liquid (BTL) facility was built and tested. This produced results confirming the feasibility of the BTL process. The findings of the pilot study outlined in this dissertation justified the conclusion that the next step will be to expand the capacity and productivity of the BTL pilot plant to an industrial scale. Biomass comes from a variety of renewable sources that are readily available. In this case, the material used in the fixed bed biomass gasification facility to generate wood gas was agricultural and forestry waste, such as straw and wood chips. The gasifier had the capacity to produce up to 10 cubic metres/hr of gas with a carbon monoxide and hydrogen content of between 20–40% by volume, when it was operated at ambient pressure and with air as the oxidizer. The gas, produced at a temperature above 700º C, was cooled in a quench/water scrubber in order to remove most of the mechanical impurities (tars and water-soluble inorganic particles), condensed and dried with corn cobs before being compressed in cylinders at over 100 bar (g) for use in the Fischer-Tropsch Synthesis (FTS). The syngas was subjected further to a series of refining processes which included removal of sulphur and oxygen. The sulphur removal technology chosen entailed applying modified activated carbon to adsorb H2S with the help of hydrolysis in order to convert organic sulphur impurities into H2S which reduced the sulphur content of the gas to less than 5 ppbv. Supported cobalt catalyst (100 grams), were loaded into a single-tube fixed bed FT reactor with an inner diameter of 50 mm. The reactor was fitted with a heating jacket through which, heated oil ran to cool the reactor during a normal reaction occurring at < 250 ºC, while nitrogen was used in the heating jacket during reduction, which occurred at temperatures up ~ 350 ºC. The FTS reaction was carried out at different pressures and temperatures. Liquid and wax products were produced from the facility. The properties of the liquid and solid hydrocarbons produced were found to be the same as FT products from other feed stocks, such as natural gas and coal.

Against the backdrop of rising fuel prices and increasing demand for transport fuels, coupled with government’s imperative to reduce high unemployment levels by developing the agricultural sector to support a bio-fuels sector, it was considered necessary to conduct research to determine the factors that would influence the success of bio-ethanol production for use in liquid transport fuels. The literature review highlighted five key factors that were developed into research questions to establish whether these factors are relevant to the South African context and which are considered more important. The research was conducted using a combination of face-to-face interviews and telephonic interviews to gather opinions from 16 subject matter experts in the field of bio-fuels. A questionnaire was used to drill down into each of the factors individually, to determine the importance of that factor as it relates to bio-ethanol production. The findings reveal that the absence of clear and sound government policy poses the biggest hindrance to the establishment of the industry. Furthermore, that agricultural development is a major factor for the success of bio-ethanol production as the industry is dependant on the availability of competitive feed stocks in order to be sustainable. Finally, that job creation is the motivating factor for the establishment of the industry since it addresses a government imperative to reduce unemployment levels in South Africa.
Dissertation (MBA)--University of Pretoria, 2007.
Gordon Institute of Business Science (GIBS)
unrestricted

One of the impacts of climate change is the emergence of food, energy and water shortages which can be circumvented through intensified technologies in agriculture, energy and chemical/biological processes. Furthermore, depleting fossil fuel reserves requires the establishment of alternative sustainable energy resources. Biomass based energy and chemicals technology is an important component of sustainable development which can be integrated with food and water generation. However, due to distributed nature of biomass, biomass based energy technology needs to be distributed generation which would benefit from low temperature and pressure operation. Syngas produced from gasification of waste/biomass can be. converted to power or liquid fuel after cleaning. Although process intensification (PI) is still in its infancy, potentially, it is highly suitable for the distributed production of power and liquid fuels. The objective of this study is to develop a syngas-to-liquid fuel conversion process suitable for distributed production using principles of PI through the intensification of Fischer Tropsch Synthesis (FTS). The first approach was by using structured catalysts in monolithic forms for FTS. The second approach was to couple the structured catalyst with non thermal plasma by using dielectric barrier discharge (DBD) in hybrid FTS reactors. A hybrid reactor was designed and fabricated to test this novel catalytic system. Co and Co/Cu catalysts were prepared and characterised using scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction and transmission electron microscopy. The reactor was used in the FTS using H, and CO under various processing conditions (temperature, pressure, Hz/CO molar ratio, gas flowrate and plasma power) and the products were analysed using gas chromatography. It is shown that Co/Cu catalyst in plasma assisted FTS was feasible, converting up to 38% of CO at 90W, 1 bar, Hz/CO= 2, 25ml/min and 25°C. This conversion was obtained at 230°C and 6 bar in conventional FTS. This research showed that DBD in FTS enables running the reaction at room temperature and atmospheric pressure avoiding the risks and costs associated with high pressure processes. It was also shown that plasma affected the activity of the catalysts, preventing it from agglomeration.

This dissertation includes two process modeling studies -- (1) predictive modeling of large-scale integrated refinery reaction and fractionation systems from plant data – hydrocracking process; and (2) integrated process modeling and product design of biodiesel manufacturing. \r\n1. Predictive Modeling of Large-Scale Integrated Refinery Reaction and Fractionation Systems from Plant Data -- Hydrocracking Processes: This work represents a workflow to develop, validate and apply a predictive model for rating and optimization of large-scale integrated refinery reaction and fractionation systems from plant data. We demonstrate the workflow with two commercial processes -- medium-pressure hydrocracking unit with a feed capacity of 1 million ton per year and high-pressure hydrocracking unit with a feed capacity of 2 million ton per year in the Asia Pacific. This work represents the detailed procedure for data acquisition to ensure accurate mass balances, and for implementing the workflow using Excel spreadsheets and a commercial software tool, Aspen HYSYS from Aspen Technology, Inc. The workflow includes special tools to facilitate an accurate transition from lumped kinetic components used in reactor modeling to the boiling point based pseudo-components required in the rigorous tray-by-tray distillation simulation. Two to three months of plant data are used to validate models' predictability. The resulting models accurately predict unit performance, product yields, and fuel properties from the corresponding operating conditions.\r\n2. Integrated Process Modeling and Product Design of Biodiesel Manufacturing: This work represents first a comprehensive review of published literature pertaining to developing an integrated process modeling and product design of biodiesel manufacturing, and identifies those deficient areas for further development. It also represents new modeling tools and a methodology for the integrated process modeling and product design of an entire biodiesel manufacturing train. We demonstrate the methodology by simulating an integrated process to predict reactor and \r\nseparator performance, stream conditions, and product qualities with different feedstocks. The results show that the methodology is effective not only for the rating and optimization of an existing biodiesel manufacturing, and but also for the design of a new process to produce biodiesel with specified fuel properties.
Ph. D.

This study focuses on upgrading biomass derived syngas for the synthesis of liquid fuels using Fischer-Tropsch synthesis (FTS). The process includes novel gasification of biomass via a tri-reforming process which involves a synergetic combination of CO2 reforming, steam reforming, and partial oxidation of methane. Typical biomass-derived syngas H2:CO is 1:1 and contains tars that deactivate FT catalyst. This innovation allows for cost-effective one-step production of syngas in the required H2:CO of 2:1 with reduction of tars for use in the FTS. To maximize the performance of the tri-reforming catalyst, an attempt to control oxygen mobility, thermal stability, dispersion of metal, resistance to coke formation, and strength of metal interaction with support is investigated by varying catalyst synthesis parameters. These synthesis variables include Ce and Zr mixed oxide support ratios, amount Mg and Ni loading, and the preparation of the catalyst. Reaction conditions were also varied to determine the influences reaction temperature, gas composition, and GHSV have on the catalyst performance. Testing under controlled reaction conditions and the use of several catalyst characterization techniques (BET, XRD, TPR, XAFS, SEM-EDS, XPS) were employed to better explain the effects of the synthesis parameters. Applications of the resulting data were used to design proof of concept solar powered BTL plant. This paper highlights the performance of the tri-reforming catalyst under various reaction conditions and explains results using catalyst characterization.

This work begins with an introduction to catalysis focusing on heterogeneous systems and surface science phenomena. A study on the partial oxidation reaction of n-butane to maleic anhydride (MA) is presented in the first part. MA supplies are barely adequate for market requirements due to continued strong demand. Only slight improvement in catalytic performance would be welcome in the industrial community. The vanadium phosphorus oxide (VPO) catalyst was used in this work. The reaction is highly exothermic and the need to properly support the catalyst, not only for good dispersion but adequate heat dissipation is of crucial importance. For this, alpha-SiC commercial powders were used in synthesizing the catalyst due to its high thermal conductivity. Up to 25% MA yields were obtained and the reaction temperature was lowered by up to 28% using SiC/VPO mixed catalysts. The second part of this work is focused on the Fischer-Tropsch synthesis (FTS) process using cobalt silica supported catalysts. The main objective is the production of synthetic ultra high purity jet fuel (JP5). This is a very timely topic given the energy issues our world is facing. Almost all aspects of the FTS process have been extensively studied, however the effects of calcination temperature and silica support structure on the catalyst performance are lacking in literature. The catalysts were prepared using various silica supports. The catalysts had different drying and calcination temperatures. It was found that lower support surface area and calcination temperature catalysts exhibited higher activity due to lower support cobalt phase interaction. Co/silica catalysts calcined at 573K showed the highest CO conversion and the lowest CH4 selectivity. Catalysts prepared with 300m²/g support surface area exhibited 79.5% C5+ selectivity due to higher reducibility and less metal support interaction. The properties and performance of various prepared catalysts in both VPO and Co/silica systems are characterized by FTIR, XRD, BET, GC and XPS techniques. Theoretical FTS deactivation by sintering calculations and SiC/VPO particle temperature gradient calculations are presented as well. Finally, conclusions and future work on improving the yield and selectivity and scaling up the bench top setups are also presented.

The path towards mitigation of anthropogenic greenhouse gas emissions lies in the transition from conventional to sustainable energy resources. The Hydrogen Economy, a cyclic economy based on hydrogen as a fuel, is suggested as a tool in the necessary energy transition. Photocatalysis makes use of sunlight to promote thermodynamically non-favoured reactions such as water splitting, allowing for sustainable hydrogen production. Harvesting thermal energy along with photonic energy is an interesting concept to decrease the activation energy of water splitting (i.e. ΔG = + 237.2 kJ∙mol−1). This work aims to confront this hypothesis in a gas phase photo-thermal reactor designed specifically for this study. The photocatalyst chosen is graphitic carbon nitride (g-C3N4), an organic semiconductor possessing a narrow band gap (i.e. 2.7 eV) as well as a band structure which theoretically permits water splitting. The photocatalytic performance of Pt/g-C3N4 for hydrogen evolution was tuned by altering its synthetic temperature. Electron paramagnetic resonance was used to gain insight on the evolution of the photocatalyst activity with synthesis temperature. Then, gold nanoparticles were deposited on g-C3N4 surface. Localized surface plasmon resonance properties of gold nanoparticles are reported in the literature to be influenced by temperature. Therefore Au/g-C3N4 appeared as a promising candidate for photo-thermal water splitting. X-ray spectroscopy unveiled interesting observations on the gold oxidation state. Moreover, under specific reduction conditions, gold nanoparticles with a wide variety of shapes characterized by sharp edges were formed. Finally, the development of the photo-thermal reactor is presented. The design process and the implementation of this innovative reactor are discussed. The reactor was successfully utilized to probe photoreactions. Then, the highly energy-demanding photocatalytic water splitting was proven not to be activated by temperature in the photo-thermal apparatus.

Compte tenu du récent taux alarmant d'épuisement des réserves de combustibles fossiles et de l'augmentation drastique des niveaux de CO2 dans l'atmosphère qui a conduit au réchauffement de la planète et à des changements climatiques sévères, l'exploitation de toutes sortes d'énergies renouvelables a été la Parmi les principales priorités de la recherche Champs à travers le monde. L'une des nombreuses voies de ce genre est la réduction du CO2 aux combustibles utilisant des énergies renouvelables, plus communément appelées cellules photoélectro-catalytiques (PEC). Des essais expérimentaux sur la réduction du CO2 ont été réalisés sur différents types de catalyseurs dans les deux cellules (Conçu par un laboratoire) afin de comprendre la sélectivité, la productivité et les produits de réaction obtenus. Des essais expérimentaux ont été réalisés sur différents types de catalyseurs à la fois dans les cellules en phase gazeuse et en phase liquide pour comprendre la sélectivité, la productivité et les produits de réaction obtenus. Pour les études sur la réduction EC du CO2 en phase gazeuse, une série d'électrodes (à base de nanoparticules (NPs) de Cu, Fe, Pt et CuFe déposées sur des nanotubes de carbone ou de noir de carbone puis placées à l'interface entre une membrane Nafion et Une électrode à couche de diffusion de gaz). Les résultats démontrent le type divers de produits formés et leurs productivités. Dans des conditions sans électrolyte, la formation de produits ≥C1 tels que l'éthanol, l'acétone et l'isopropanol a été observée la plus élevée étant pour Fe et suivie de près par Pt. Pour améliorer Combustibles nets, un ensemble différent d'électrodes a été préparé sur la base de revêtements MOF de type imidazolate de type zéolitique substitué (SIM-1) (Fe-CNT, Pt-CNT et CuFe-CNT basés sur MOF) Et Pt-MOF a montré des carburants améliorés. En se reportant aux études sur la réduction EC du CO2 dans une cellule en phase liquide, un ensemble similaire d'électrodes a été prepare (NP - Cu, Fe, Pt, Ru, Co déposées sur des nanotubes de carbone ou du noir de carbone ont). Pour les conditions de phase liquide, en termes de produits C nets, les électrodes catalytiques à base de Pt sont en tête de la catégorie, suivies de près par Ru et Cu, tandis que Fe a obtenu la position la plus basse. Le mécanisme réactionnel sous-jacent probable a également été fourni. Afin d'améliorer encore les performances, on a synthétisé des NP de metal (Ru, Fe, Pt et Cu) de différentes tailles en utilisant différentes techniques de synthèse: (i) l'itinéraire d'imprégnation (ImR) pour obtenir des NP dans la plage de tailles de 10 à 50 nm; (Ii) Approche organométallique (OM) pour synthétiser des NPs uniformes et ultrafines dans la plage de tailles de 1-5 nm. Fe ont été synthétisés par une nouvelle voie de synthèse et des conditions pour atteindre des NP de 1 à 3 nm. (Iii) Approche de haut en bas de Nanowire pour obtenir des NP de cuivre ultrafin dans la plage de taille de 2-3,8 nm. Les améliorations apportées à la productivité du carburant se sont révélées être de 5 à 30 fois plus élevées pour les petites NP sur les NP plus importantes et, en outre, une charge réduite de 10 à 1-2% en poids. Un autre ensemble d'électrodes à base de nano-mousses (Cu NF et Fe NF sur Feuille de Cu, Feuille de Foie, Al Foil, Inconel foil et Al grid / mesh) préparés par électrodéposition ont également été étudiés afin d'améliorer encore la conversion de CO2 / carburant. Après, l'optimisation du dépôt et de la tension à l'aide de la voltamétrie cyclique, les carburants se sont améliorés de 2 à 10 fois par rapport aux combustibles nets les plus élevés obtenus à l'aide d'électrodes CNT dopées à base de NP
In view of the recent alarming rate of depletion of fossil fuel reserves and the drastic rise in the CO2 levels in the atmosphere leading to global warming and severe climate changes, tapping into all kinds of renewable energy sources has been among the top priorities in the research fields across the globe. One of the many such pathways is CO2 reduction to fuels using renewable energies, more commonly referred as photo-electro-catalytic (PEC) cells. Experimental tests were carried out on various types of catalysts in both the gas and liquid phase cells (lab-designed) to understand the different selectivity, productivity and the reaction products obtained. For the studies on the EC reduction of CO2 in gas phase cell, a series of electrodes (based on Cu, Fe, Pt and Cu/Fe metal nanoparticles – NPs - deposited on carbon nanotubes – CNTs - or carbon black and then placed at the interface between a Nafion membrane and a gas-diffusion-layer) were prepared. Under gas phase, the formation of ≥C1 products (such as ethanol, acetone and isopropanol) were observed, the highest being for Fe and closely followed by Pt, evidencing that also non-noble metals can be used as efficient catalysts under these conditions. To enhance the net fuels, a different set of electrodes were also prepared based on substituted Zeolitic Imidazolate (SIM-1) type MOF coatings (MOF-based Fe-CNTs, Pt-CNTs and Cu/Fe-CNTs) and Pt-MOF showed improved fuels. Moving to the studies on the EC reduction of CO2 in liquid phase cell, a similar set of electrodes were prepared (metal NPs of Cu, Fe, Pt, Ru and Co deposited on CNTs or carbon black). For liquid phase conditions, in terms of net C-products, catalytic electrodes based on Pt topped the class, closely followed by Ru and Cu, while Fe got the lowest position. The probable underlying reaction mechanism was also provided. In order to improve further the performances, varied sized metal NPs (Ru, Fe, Pt and Cu) have been synthesized using different techniques: (i) impregnation (ImR) route to achieve NPs in the size range of 10-50 nm; (ii) organometallic (OM) approach to synthesize uniform and ultrafine NPs in the size range of 1-5 nm (i.e., Fe NPs were synthesized through a novel synthesis route to attain 1-3 nm NPs); (iii) Nanowire (NW) top-down approach to obtain ultrafine copper metal NPs in the size range of 2-3.8 nm. The enhancements in the fuel productivity were found to be 5-30 times higher for the smaller metal NPs over the larger metal NPs and moreover, with reduced metal loading from 10 to 1-2 wt %. A different set of electrodes based on nano-foams (Cu NF and Fe NF on Cu foil, Fe foil, Al foil, Inconel foil and Al grid/mesh) prepared via electro-deposition were also investigated, to further improve CO2 to fuels conversion. After, optimization of deposition and voltage using cyclic voltammetry, the fuels improved by 2-10 times over the highest net fuels achieved using metal NPs doped CNT electrodes

The use of pyrolysis as a waste disposal method for waste plastics has been well established. However, the market value of the recycled plastic products and separate upgrading of the pyrolysis product liquid are some of the challenges facing the process. Therefore, the use of pyrolysis-catalysis of waste plastic in a two-stage pyrolysis-catalysis reactor system could bring a balance between sustainability and market value of the products generated. Hence, this work investigated the influence of different types of zeolite catalysts on the pyrolysis-catalytic upgrading of waste plastics for quality liquid fuels and valuable chemical production. Initially, two zeolite Y and ZSM-5 catalysts, in the form of pellets, were used for pyrolysis-catalysis of WEEE. Zeolite catalyst with a lower Si-Al ratio (Y zeolite) produced a higher conversion of the styrene to other aromatic products, particularly benzene and toluene. Thereafter, the influence of six zeolite catalysts with different surface areas and Si: Al ratios was investigated on the catalytic pyrolysis of waste high-density polyethylene (HDPE). Overall, the results suggest that the catalyst properties influenced the conversion of HDPE to more valuable products such as fuel-range hydrocarbons and chemicals. Similarly, pyrolysis of real-world mixed plastics, simulated mixed plastic (SMP), and virgin plastics were investigated in the presence of HZSM-5 catalyst. In addition, a sample of spent FCC catalyst was also tested for the pyrolysis of the plastic samples. Finally, the influence of spent FCC, fresh zeolite Y and ZSM-5 catalysts was investigated under different bed temperatures from 400 – 600 °C. This final work confirmed that the choice of a bed tempetrure of 500 °C, for most of this research was appropriately justified. Overall, the product oils gave fuel properties similar to gasoline, the aromatic content of the oil make them suitable as chemical feedstocks, the gas products with very high-calorific values can be used as fuel gas.

Thesis: S.M., Massachusetts Institute of Technology, Department of Aeronautics and Astronautics, 2014.
Cataloged from PDF version of thesis.
Includes bibliographical references (pages 55-63).
The thesis is divided into two parts - 1) assessing the energy return on investment for alternative jet fuels, and 2) quantifying the tradeoffs associated with the aviation and non-aviation use of agricultural residues. We quantify energy return on energy investment (EROI) as one metric for the sustainability of alternative jet fuel production. Lifecycle energy requirements are calculated and subsequently used for calculating three EROI variants. EROI₁ is defined as the ratio of the lower heating value (LHV) of the liquid fuel produced, to lifecycle (direct and indirect) process fossil fuel energy inputs and fossil feedstock losses during conversion. EROI₂ is defined as the ratio of fuel LHV to total fossil fuel energy input, inclusive of the fossil energy embedded in the fuel. EROI₃ is defined as the ratio of fuel LHV to the sum of renewable and non-renewable process fuel energy required and feedstock energy losses during conversion. We also define an approximation for EROI₁ using lifecycle CO₂ emissions. This approach agrees to within 20% of the actual EROI₁ and can be used as an alternative when necessary. Feedstock-to-fuel pathways considered include jet fuel from conventional crude oil; jet fuel production from Fischer-Tropsch (FT) processes using natural gas, coal and/or switchgrass; HEFA (hydroprocessed esters and fatty acids) jet fuel from soybean, palm, rapeseed and jatropha; and advanced fermentation jet (AF-J) fuel from sugarcane, corn grain and switchgrass. We find that ERO₁ 1 for conventional jet fuel from conventional crude oil ranges between 4.9-14.0. Among the alternative fuel pathways considered, FT-J fuel from switchgrass has the highest baseline EROI₁ of 9.8, followed by AF-J fuel from sugarcane at 6.7. Jet fuel from oily feedstocks has an EROI₁ between 1.6 (rapeseed) and 2.9 (palm). EROI₂ differs from EROI₁ only in the case of fossil-based jet fuels. Conventional jet from crude oil has a baseline EROI₂ of 0.9, and FT-J fuel from NG and coal have values of 0.6 and 0.5, respectively. EROI 3 values are on average 36% less than EROI₁ for HEFA pathways. EROI₃ for AF-J and FT-J fuels considered is 50% less than EROI₁ on average. All alternative fuels considered have a lower baseline EROI₃ than conventional jet fuel. Using corn stover, an abundant agricultural residue, as a feedstock for liquid fuel or power production has the potential to offset anthropogenic climate impacts associated with conventional utilities and transportation fuels. We quantify the environmental and economic opportunity costs associated with the usage of corn stover for different applications, of which we consider combined heat and power, ethanol, Fischer-Tropsch (FT) middle distillate (MD) fuels, and advanced fermentation (AF) MD. Societal costs comprise of the monetized attributional lifecycle greenhouse gas (GHG) footprint and supply costs valued at the shadow price of resources. The sum of supply costs and monetized GHG footprint then provides the societal cost of production and use of corn stover for a certain application. The societal costs of conventional commodities, assumed to be displaced by renewable alternatives, are also calculated. We calculate the net societal cost or benefit of different corn stover usages by taking the difference in societal costs between corn stover derived fuels and their conventional counterparts, and normalize the results on a feedstock mass basis. Uncertainty associated with the analysis is captured using Monte-Carlo simulation. We find that corn stover derived electricity and fuels reduce GHG emissions compared to conventional fuels by 21-92%. The mean reduction is 89% for electricity in a CHP plant, displacing the U.S. grid-average, 70% for corn stover ethanol displacing U.S. gasoline and 85% and 55% for FT MD and AF MD displacing conventional U.S. MD, respectively. Using corn stover for power and CHP generation yields a net mean societal benefit of $48.79/t and $131.23/t of corn stover, respectively, while FT MD production presents a mean societal benefit of $27.70/t of corn stover. Ethanol and AF MD production from corn stover result in a mean societal cost of $24.86/t and $121.81/t of corn stover use, respectively, driven by higher supply costs than their conventional fuel counterparts. Finally, we note that for ethanol production, the societal cost of CO₂ that would need to be assumed to achieve a 50% likelihood of net zero societal cost of corn stover usage amounts to approximately -$100/tCO₂, and for AF MD production to ~$600/tCO₂.
by Parthsarathi Trivedi.
S.M.

The current societal needs for fuels and chemical commodities strongly depend on fossil resources. This dependence can lead to economic instabilities, political problems and insecurity of supplies. Moreover, global warming, which is associated with the massive use of fossil resources, is a dramatic “collateral damage” that endangers the future of the planet. Biomass is the main renewable source available today that can, produce various liquid, gaseous and solid products. Due to their lignocellulosic origin are considered CO2 neutral and thus can generate CO2 credits. Biomass processing can meet to the challenge of reducing of fossil resources by producing a liquid feedstock that can lessen the “fossil dependence” and /or meet the increased demand via a rapidly emerging thermochemical technology: pyrolysis. The ultimate goal of this process is to produce liquid with improved properties that could directly be used as liquid fuel, fuel additive and/or feedstock in modern oil refineries and petrochemical complexes. However, the liquids derived from biomass thermal processing are problematic with respect to their handling and end use applications. Thus, alternative routes of advanced liquid feedstock production are needed. Heterogeneous catalysis has long served the oil refining and petrochemical industries to produce a wide range of fuels and products. The combination of biomass pyrolysis and heterogeneous catalysis (by bringing in contact the produced vapours/liquids with suitable catalysts) is a very promising route. In this dissertation, the exploitation of biomass to produce of liquid feedstock via pyrolysis over a multifunctional catalyst and in a steam atmosphere is investigated.  Steam pyrolysis in a fixed bed reactor demonstrated that steam can be considered a reactive agent even at lower temperatures affecting the yields and the composition of all the products. The devolatilisation accelerates and the amount of final volatile matter in the char. Fast pyrolysis in the presence of steam results in improved and controlled thermal decomposition of the biomass; higher liquid yields and slightly deoxygenated liquid products are also obtained. Steam pyrolysis over a bi-metallic Ni-V catalyst can produce liquids of improved quality (lower O content) and also provide routes for selective deoxygenation. However, a decrease in liquid yield was observed. The combination of metal and acid catalysts (Ni-V/HZSM5) shows enhanced deoxygenation activity and increased H preservation in the produced liquid. The final O content in the liquid was 12.83wt% at a zeolite (HZSM5) loading of~75wt%; however, the yield of the obtained liquid was substantially decreased. Moreover, increased coke formation on the catalyst was observed at highest zeolite rate. The increased catalyst space time (τ) results in a lower liquid yield with reduced oxygen (7.79 wt% at τ =2h) and increased aromatic content. The coke deposited per unit mass of catalyst is lower for longer catalyst space times, while the char yield seems to be unaffected. The evaluation of the stability of the hybrid catalyst showed no significant structural defects and activity loss when the catalyst was regenerated at a low temperature (550οC).
Det nuvarande samhällets behov av bränslen och kemiska produkter är starkt knutet till fossila resurser. Detta beroende kan leda till ekonomisk instabilititet, politiska svårigheter och osäker leveranssäkerhet. Dessutom riskeras allvarliga skador i framtiden på grund av global uppvärmning, vilket är relaterat till det ökande och massiva användandet av fossila bränslen.   Biomassa är en förnybar resurs som är tillgänglig idag, möjlig att utnyttja för produktion av diverse flytande, gasformiga och fasta produkter. Dessa produkter, beroende på biogeniskt ursprung, betraktas som koldioxidneutrala och kan därför generera koldioxidkrediter. Processande av biomassa kan möta utmaningen av minskad fossilbränsleanvändning, genom produktion av flytande råvara som kan reducera beroendet och/eller möta ökad efterfrågan, via en snabbt expanderande termokemisk teknik - pyrolys.    Det slutgiltiga målet med en sådan process är att producera en flytande produkt med förbättrade egenskaper som direkt skulle kunna användas som flytande bränslen, bränsleadditiv och/eller som råmaterial i moderna oljeraffinaderier och petrokemiska komplex. Vätskor som utvinns från termiska processer är problematiska med avseende på hantering och slutanvändningen i olika applikationer, därmed behövs olika spår för produktion av avancerade flytande råvaror. Heterogena katalysen har länge tjänat raffinaderi- och petrokemisk industri, som producerar ett brett utbud av bränslen och produkter, lämpliga för säker användning. Kombinationen av biomassapyrolys och heterogen katalys  (genom att bringa pyrolysångorna i kontakt med en lämplig katalysator) är ett väldigt lovande spår. I denna avhandling undersöks användningen av biomassa för produktion av flytande råvara, via pyrolys över en flerfunktionel katalysator i ångatmosfär. Ångpyrolys i en fastbäddsreaktor visade att ånga kan betraktas som ett reaktivt medium,  även vid låga temperaturer, som påverkar utbyten och sammansättning av alla produkter. Avgasningen sker snabbare och den slutliga flykthalten i kolresterna blir lägren vid användning av ånga. Snabbpyrolys i ångatmosfär resulterar i förbättrad och mer kontrollerad termisk nedbrytning av biomassa, vilket ger ett högre vätskeutbyte och en något deoxygenerad flytande produkten. ångpyrolys i kombination med bimetalliska NiV-katalysatorer, ger upphov till en flytande råvara med förbättrad kvalitet och selektiv deoxygenering. Dock med ett minskande utbyte som följd. Kombinationen av metall och en sur katalysator (Ni-V/HZSM5) visade förstärkt deoxygenering med bibehållen vätehalt i den flytande produkten. Den slutliga syrehalten i vätskan var 12.83 vikt% vid en zeolithalt (HZSM5) på 75 vikt%, dock med ett kraftigt minskande vätskeutbyte. Dessutom noterades ökad koksbildning på katalysatormaterialet med den högsta zeolithalten. Ökad rymd-tid  för katalysatorn (τ) ger ett lägre vätskeutbyte med reducerad syrehalt (7.79 vikt% vid τ=2h) och ökad aromathalt. Koksbildning på ytan, per massenhet katalysatormaterial, minskade vid längre rymd-tider medan utbytet av kolrester förblev opåverkat.  Undersökningen av stabiliteten hos hybridkatalysatorn visade inga strukturella defekter och ingen signifikant minskad aktivitet efter regenerering vid låg temperatur (550οC).
Οι σύγχρονες ανάγκες της κοινωνίας για παραγωγή υγρών καυσίμων και χημικών προϊόντων εξαρτώνται από τους ορυκτούς πόρους. Αυτή η εξάρτηση μπορεί να οδηγήσει σε οικονομικά προβλήματα, πολιτκή αστάθεια, όπως επίσης και αβεβαιότητα στις προμήθειες της ενεργειακής εφοδιαστικής αλυσίδας. Επιπροσθέτως, μια δραματική «παράπλευρη απώλεια» η οποία θέτει σε κίνδυνο το μέλλον του πλανήτη είναι η υπερθέρμανσή του, η οποία έχει συσχετισθεί με την εκτεταμένη χρήση ορυκτών πόρων. Σήμερα, η βιομάζα είναι η μόνη ανανεώσιμη πηγή από την οποία μπορούν να παραχθούν υγρά, αέρια και στερεά προϊόντα, που λόγω της λιγνοκυταρρινικής τους προελεύσεως, η συνεισφορά τους στις εκομπές CO2 θεώρειται μηδενική. Η θερμοχημική επεξεργασία της βιομάζας συνεισφέρει στον περιορισμό της χρήσης ορυκτών πόρων, με την παραγωγή υγρών προϊόντων, τα οποία μπορούν να μειώσουν την εξάρτηση ή /και την αυξημένη ζήτηση μέσω μιας ταχέως αναπτυσόμενης τεχνολογίας, της πυρόλυσης. Στόχος της διεργασίας είναι η παραγωγή υγρών προϊόντων με ιδιότητες, που επιτρέπουν την απευθείας χρήση τους ως υγρά καύσιμα ή ως πρώτη ύλη, για την παραγώγη χημικών προϊόντων σε συγχρονες μονάδες διύλισης πετρελαίου και σε πετροχημικά συγκτροτήματα. Εν τούτοις, τα υγρά προϊόντα της θερμικής διάσπασης (πυρόλυση) είναι προβληματικά στη διαχείρηση και στις τελικές τους εφαρμογές, λόγω της σύστασής τους. Ως εκ τούτου, απαιτούνται νέες τεχνικές για παραγωγή προηγμένων υγρών προοϊόντων. Η ετερογενής κατάλυση έχει επιτυχώς εφαρμοσθεί στην πετρελαϊκή και χημική βιομηχανία, παράγοντας ένα μεγάλο εύρος προϊόντων. Ο συνδυασμός της με την πυρόλυση (φέρνοντας σε επαφη τα υγρά/ατμούς με κατάλληλο καταλύτη) αποτελεί μια πολλά υποσχόμενη ενναλακτική. Στην παρούσα διατριβή μελετάται η αξιοποίηση βιομάζας για παραγωγή υγρών προϊόντων μέσω καταλυτικής πυρόλυσης, με χρήση πολυλειτουρικού καταλύτη (multi-functional catalyst) υπό την παρουσία ατμού. Η χρήση ατμου κατά τη διαρκειά πυρόλυσης βιομαζας σε αντιδραστήρα σταθερής κλίνης, μεταβάλει τη σύσταση των επιμέρους προϊόντων. Η παρουσία ατμού έχει ως αποτέλεσμα την ταχύτερη αποπτητικοποίηση του υλικού, ενώ παράλληλα η περιεκτικότητα του υπολειπόμενου εξανθρακώματος σε πτητικά είναι μικρότερη. Τα πειραματικά αποτελέσματα ταχείας πυρόλυσης σε αντιδραστήρα ρευστοστερεάς κλίνης δείχνουν ό,τι η χρήση ατμού βελτιώνει την θερμική διάσπαση της βιομαζας, αυξάνοντας την απόδοση σε υγρά προϊοντά, ενώ παράλληλα βοηθάει στην αποξυγόνωσή τους. Ο συνδυασμός της πυρόλυσης υπό την παρουσία ατμού και διμεταλλικού καταλύτη νικελίου–βαναδίου μπορεί να  βελτιώσει την ποιότητα των παραγόμενων υγρών (αποξυγόνωση) με παραλλήλη μείωση της απόδοσής τους, ενώ μπορεί να  παράγει προϊόντα εκλεκτικής αποξυγόνωσης. Συνδυασμός μεταλλικών και ζεολιθικών καταλυτών (Ni-V/HZSM5) εμφανίζει βελτιωμένη δραστικότητα στις αντιδράσεις αποξυγόνωσης, με παράλληλη συγκράτηση υδρογόνου (Η) στα υγρά προϊόντα. Η τελική περιεκτικότητα των υγρών προϊόντων σε οξυγόνου (Ο) μετά από 90 min αντίδρασης είναι 12.83 wt%, με περιεκτικότητα ζεόλιθου (ΗZSΜ5) ~75 wt% στον καταλύτη. Ωστόσο, η αυξηση της περεικτικότητας σε ζεόλιθο έχει ως αποτέλεσμα την αύξηση των επικαθήσεων άνθρακα επάνω στον κατάλυτη, καθώς και την σημαντική μειώση της απόδοσης των υγρών προϊόντων (24.35wt% επι ξηρής βιομάζας).  Η αύξηση του χώρου χρόνου του καταλύτη (τ) έχει ως αποτέλεσμα: τη μείωση των υγρών προϊόντων, τη μείωση του περιεχόμενου Ο στα υγρά προϊόντα (7.79 wt% at τ =2h), την αύξηση των αρωματικών υδρογονανθράκων και τη μείωση του επικαθήμενου κωκ ανά μονάδα μάζας καταλύτη. Η απόδοση του εξανθρακώματος παρέμεινε πρακτικά αμετάβλητη. Η αναγέννηση του υβριδικού καταλύτη σε χαμηλές θερμοκρασιές (550οC) δεν επέφερε σημαντικές δομικές αλλαγές και απώλεια δραστικότητας.

QC 20140306

The transportation sector in New Zealand accounts for the highest CO2 emission. Replacing the fossil fuels with liquid biofuels derived from woody biomass as a carbon neutral resource can decrease the CO2 emission and secure future liquid fuel supply. The Fischer-Tropsch (FT) liquid fuel production using syngas from gasification is a promising technology for commercialisation in the next 5 to 10 years in New Zealand. However, in order to achieve the maximum benefits by using the woody biomass for liquid fuel production, the plant design and operation need to be optimised. The objectives of this study were: (1). Develop an integrated system model for production of FT liquid fuels from woody biomass; 2) Finding an optimum plant configuration by using energy and exergy analyses; 3) Performing techno-economic analysis on the plant. The integrated system models for conversion of woody biomass to FT liquid fuels (BTL) were developed based on two different scenarios. Scenario I included biomass pretreatment (chipping and drying), biomass gasification in a dual fluidised bed (DFB) gasifier with steam as the gasification agent, producer gas cleaning and gas conditioning, and FT liquid fuel synthesis. Scenario II included biomass pretreatment (chipping, drying and grinding), biomass densification through fast pyrolysis, entrained flow gasification of bio-slurry, gas cleaning and gas conditioning, and FT liquid fuel synthesis. For Scenario I, it was assumed that woody biomass chips were transported from the biomass field to the processing plant where the chips were dried and then fed to the DFB gasifier. For Scenario II, the wood chips were firstly converted to bio-slurry by fast pyrolysis reactors in the biomass field, and then the bio-slurry was transported to the main process plant. The scale of the fast pyrolysis plant was fixed at 20 MWth thus when the main process plant had greater capacity, more than one such pyrolysis systems were operated simultaneously in different biomass fields. The unit operations of each scenario were modelled in a UniSim simulation environment by using a combination of built-in and user-defined unit operations. In the modelling, energy and mass balances in each operation unit were considered. In addition, chemical reactions in pyrolysis, gasification and FT reactors were also modelled using quasi-equilibrium and kinetic approaches. The system models were solved, and the results were compared with reported data. Finally, the system models were applied for a 100 MWth (based on the lower heating value of biomass feed) plant to analyse energy efficiency, exergy efficiency and economic returns. Parametrical analysis was also performed to investigate the effects of feedstock and operational conditions on the system performance. As part of the energy analysis, the pinch analysis was performed to optimise the heat recovery of the system and steam generation. The simulation results show that the energy efficiency of the BTL plant based on Scenario I varies from 55 % to 61.5 % while it is 53 % for the BTL plant based on Scenario II. For improving the energy efficiency, the exhaust heat should be entirely used for biomass drying and steam generation, and the FT off gas should be used for electricity generation. Also, the steam-methane reforming reactor should be chosen over the high-temperature shift converter for the gas conditioning method in Scenario I in order to achieve higher energy efficiency. The model simulation results also indicate that the exergy efficiency of the BTL plant based on Scenario I varies between 38 % and 48 % while it is 33 % for the BTL plant based on Scenario II. Power generation is identified as the largest source of exergy loss in the system. It is proposed to maximise the liquid fuel yields and minimise the power generation capacity for improving the exergy efficiency of the system. Also, the number of process steps should be minimised in a plant configuration. The developed system models were also applied for techno-economic analysis on the BTL plant based on the two scenarios. A sensitivity analysis was conducted to investigate the effect of various parameters on production cost and total capital investment of the BTL plant based on each scenario. These parameters included plant scale, feed biomass moisture content, unit operations’ conditions, and transportation distance between the biomass field and the BTL plant. From the feasibility analysis, it was found that the capital investment required for the BTL plant based on Scenario I was $NZ187 million which was considerably less than that of $NZ 248.5 million required for the BTL plant based on Scenario II. The production costs of FT liquid fuels produced from the Scenario I BTL plant were at $NZ 1.34/litre for diesel and $NZ 1.27/litre for gasoline. These costs were lower than the costs of corresponding products produced from the Scenario II BTL plant ($NZ 1.95/litre for diesel and $NZ1.85/litre for gasoline). The key factor for the higher production costs in the Scenario II BTL plant is the additional cost for biomass pyrolysis to produce bio-slurry that cannot be compensated by the cost of biomass transportation. At the scale of 100 MWth, the Scenario I BTL plant is competitive for commercialisation considering the actual market prices of petroleum-derived diesel and gasoline at $NZ 1.3/litre and $NZ 1.23/litre, respectively. However, the extra costs of production of bio-slurry may be paid by the cost of biomass transportation at large scale of plant (>150 MWth) when more biomass needs to be transported over a long distance. It should be emphasised that at the time of the study in October 2013, the BTL plant was economically feasible. Unfortunately, the plant is not feasible currently as the price of crude oil has been declined significantly to $US 62.5/barrel from $US 105.5/barrel in October 2013. Therefore, the FT liquid fuel production has to compete against the conventional liquid fuels unless some subsidies are provided by the government.

Doutoramento em Engenharia Química
For the past decades it has been a worldwide concern to reduce the emission of harmful gases released during the combustion of fossil fuels. This goal has been addressed through the reduction of sulfur-containing compounds, and the replacement of fossil fuels by biofuels, such as bioethanol, produced in large scale from biomass. For this purpose, a new class of solvents, the Ionic Liquids (ILs), has been applied, aiming at developing new processes and replacing common organic solvents in the current processes. ILs can be composed by a large number of different combinations of cations and anions, which confer unique but desired properties to ILs. The ability of fine-tuning the properties of ILs to meet the requirements of a specific application range by mixing different cations and anions arises as the most relevant aspect for rendering ILs so attractive to researchers. Nonetheless, due to the huge number of possible combinations between the ions it is required the use of cheap predictive approaches for anticipating how they will act in a given situation. Molecular dynamics (MD) simulation is a statistical mechanics computational approach, based on Newton’s equations of motion, which can be used to study macroscopic systems at the atomic level, through the prediction of their properties, and other structural information. In the case of ILs, MD simulations have been extensively applied. The slow dynamics associated to ILs constitutes a challenge for their correct description that requires improvements and developments of existent force fields, as well as larger computational efforts (longer times of simulation). The present document reports studies based on MD simulations devoted to disclose the mechanisms of interaction established by ILs in systems representative of fuel and biofuels streams, and at biomass pre-treatment process. Hence, MD simulations were used to evaluate different systems composed of ILs and thiophene, benzene, water, ethanol and also glucose molecules. For the latter molecules, it was carried out a study aiming to ascertain the performance of a recently proposed force field (GROMOS 56ACARBO) to reproduce the dynamic behavior of such molecules in aqueous solution. The results here reported reveal that the interactions established by ILs are dependent on the individual characteristics of each IL. Generally, the polar character of ILs is deterministic in their propensity to interact with the other molecules. Although it is unquestionable the advantage of using MD simulations, it is necessary to recognize the need for improvements and developments of force fields, not only for a successful description of ILs, but also for other relevant compounds such as the carbohydrates.
Nas últimas décadas a redução de emissões de gases poluentes resultantes da combustão de combustíveis fósseis tem sido uma preocupação mundial. Para tal, a redução de compostos à base de enxofre e a sua substituição por biocombustíveis (como o bioetanol, produzido em elevadas quantidades a partir de sacarose, amido ou compostos lenhocelulósicos) tem sido estudada e aplicada. Visando este propósito, uma nova classe de solventes denominada de líquidos iónicos (LIs) têm sido estudada visando o desenvolvimento de novos processos de separação para a substituição dos solventes orgânicos atualmente utilizados. Os LIs podem ser constituídos por diferentes combinações de catiões e aniões, conferindo propriedades únicas a estes solventes. A capacidade de ajustar estas propriedades para um determinado fim ou aplicação é um dos aspetos mais relevantes dos LIs. Dado o número elevado de combinações possíveis para os iões constituintes dos LIs, é necessário recorrer a abordagens preditivas que permitam avaliar, a priori, o potencial dos LIs para uma dada aplicação. Uma abordagem possível consiste em técnicas de simulação de dinâmica molecular, baseadas em mecânica estatística e nas leis de movimento de Netwon, que permitem a reprodução e caracterização de sistemas macroscópicos, pela previsão de propriedades e organização estrutural dos átomos nos sistemas em questão. No caso dos LIs, a aplicação da dinâmica molecular tem sido amplamente usada, com um desafio adicional dada a dinâmica (lenta) característica dos LIs, o que requer melhorias nos campos de força atualmente usados, como também um acrescido esforço computacional. Esta tese aborda diferentes estudos realizados em sistemas representativos de linhas de produção dos combustíveis e biocombustíveis, onde são estudados os mecanismos de interação estabelecidos pelos LIs, através de simulações de dinâmica molecular. Desta forma, sistemas compostos por LIs e tiofeno, benzeno, água, etanol, e moléculas de glucose, serão caracterizados e avaliados. No caso das moléculas de glucose, será também estudado um campo de força recentemente publicado, de forma a avaliar a sua capacidade para reproduzir o comportamento dinâmico do sistema em solução aquosa. Os resultados obtidos mostram que as interações estabelecidas pelos LIs estão relacionadas com as características individuais de cada LI. Em geral, a polaridade dos LIs estudados é determinante nas interações estabelecidas. Embora seja inquestionável as vantagens de usar simulação de dinâmica molecular nestes sistemas, é preciso reconhecer a necessidade de melhorias nos campos de força atuais, não só para uma correta descrição dos sistemas contendo LIs, mas também para os hidratos de carbono.

The production of synthetic fuels (synfuels) in coal–to–liquids (CTL) facilities has contributed to global warming due to the huge CO2 emissions of the process. This corresponds to inefficient carbon conversion, a problem growing in importance particularly given the limited lifespan of coal reserves. These simultaneous challenges of environmental sustainability and energy security associated with CTL facilities have been defined in earlier studies. To reduce the environmental impact and improve the carbon conversion of existing CTL facilities, this paper proposes the concept of a nuclear–assisted CTL plant where a hybrid sulphur (HyS) plant powered by 10 modules of the high temperature nuclear reactor (HTR) splits water to produce hydrogen (nuclear hydrogen) and oxygen, which are in turn utilised in the CTL plant. A synthesis gas (syngas) plant mass–analysis model described in this paper demonstrates that the water–gas shift (WGS) and combustion reactions occurring in hypothetical gasifiers contribute 67% and 33% to the CO2 emissions, respectively. The nuclear–assisted CTL plant concept that we have developed is entirely based on the elimination of the WGS reaction, and the consequent benefits are investigated. In this kind of plant, the nuclear hydrogen is mixed with the outlet stream of the Rectisol unit and the oxygen forms part of the feed to the gasifier. The significant potential benefits include a 75% reduction in CO2 emissions, a 40% reduction in the coal requirement for the gasification plant and a 50% reduction in installed syngas plant costs, all to achieve the same syngas output. In addition, we have developed a financial model for use as a strategic decision analysis (SDA) tool that compares the relative syngas manufacturing costs for conventional and nuclear–assisted syngas plants. Our model predicts that syngas manufactured in the nuclear–assisted CTL plant would cost 21% more than that produced in the conventional CTL plant when the average cost of producing nuclear hydrogen is US$3/kg H2. The model also evaluates the cost of CO2 avoided as $58/t CO2. Sensitivity analyses performed on the costing model reveal, however, that the cost of CO2 avoided is zero at a hydrogen production cost of US$2/kg H2 or at a delivered coal cost of US$128/t coal. The economic advantages of the nuclear–assisted plant are lost above the threshold cost of $100/t CO2. However, the cost of CO2 avoided in our model works out to below this threshold for the range of critical assumptions considered in the sensitivity analyses. Consequently, this paper demonstrates the practicality, feasibility and economic attractiveness of the nuclear–assisted CTL plant.
Thesis (M.Ing. (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2011.

Fast pyrolysis of biomass is a significant technology for producing pyrolysis liquids [also known as bio-oil], which contain a number of chemicals. The pyrolysis liquid can be used as a fuel, can be produced solely as a source of chemicals or can have some of the chemicals extracted and the residue used as a fuel. There were two primary objectives of this work. The first was to determine the fast pyrolysis conditions required to maximise the pyrolysis liquid yield from a number of biomass feedstocks. The second objective was to selectively increase the yield of certain chemicals in the pyrolysis liquid by pre-treatment of the feedstock prior to pyrolysis. For a particular biomass feedstock the pyrolysis liquid yield is affected by the reactor process parameters. It has been found that, providing the other process parameters are restricted to the values shown below, reactor temperature is the controlling parameter. The maximum pyrolysis liquid yield and the temperature at which it occurs has been found by a series of pyrolysis experiments over the temperature range 400-600°C. high heating rates > 1000°C/s; pyrolysis vapour residence times <2 seconds; pyrolysis vapour temperatures >400 but <500°C; rapid quenching of the product vapours. Pre-treatment techniques have been devised to modify the chemical composition and/or structure of the biomass in such a way as to influence the chemical composition of the pyrolysis liquid product. The pre-treatments were divided into two groups, those that remove material from the biomass and those which add material to the biomass. Component removal techniques have selectively increased the yield of levoglucosan from 2.45 to 18.58 mf wt.% [dry feedstock basis]. Additive techniques have selectively increased the yield of hydroxyacetaldehyde from 7.26 to 11.63 mf w.% [dry feedstock basis]. Techno-economic assessment has been carried out on an integrated levoglucosan production process [incorporating pre-treatment, pyrolysis and chemical extraction stages] to assess which method of chemical production is the more cost effective. It has been found that it is better to pre-treat the biomass in order to increase the yield of specific chemicals in the pyrolysis liquid and hence improve subsequent chemicals extraction.

Three species of white-rot fungi, Phlebia radiata, Phanerochaete chrysosporium, and Trametes versicolor, were monitored for laccase and lignin peroxidase production in a defined medium. P. radiata was selected for fed-batch reactor experiments due to its early laccase production, which was determined to be growth-associated. A second peak in laccase activity was observed after several days of nutrient deprivation and was attributed to autolysis of the culture. The effect of protease activity on the accumulation of extracellular laccase activity differed during primary and secondary metabolism, as observed under various conditions of nitrogen and glucose availability. A mixed culture of P. radiata and P. chrysosporium was grown on ammonium lignosulfonate, a by-product of the pulp and paper industry, as sole source of carbon and nitrogen. Under these conditions, laccase production appeared to exceed laccase production by P. radiata in defined culture medium.

The RBF strategy has successfully produced fungal mycelial biomass and EPS in a very strictly regulated manner at high productivity rates compared to batch fermentation. The problematic lag phase and seed culture preparation were reduced in length; harvesting volume doubled, yield of product increased, and medium consumption was reduced in an RBF relative to batch. 80% broth replacement volume and transition phase were optimised. Dispersed mycelial filaments with ovoid-shaped pellets are the typical morphological characteristics associated with EPS production. N-limiting medium in an unbaffled 2.5-L bioreactor stimulated EPS formation during RBF compared to in baffled condition. The current study has managed to alter the molecule's hydrophobicity thus making it water-soluble as proved by compositional analysis and spectroscopy. The sulphated derivative of native glucan was identified as (1, 3)-(Sb(B-D-glucan. Sulphation was an effective approach to improve antibacterial, antifungal, antiproliferative and immunomodulatory (NO stimulation) activity of the sulphated (1,3)-(Sb(B-D-glucan or GS. GS maybe safe in in vitro trials due to its demonstrated lack of toxicity towards a normal human prostate cell line (PN2TA). GS also showed antimicrobial-antifungal-immunomodulatory activities derived from a single compound. Fungal cells tended to grow well in the porous structure of PUF cubes and the RBF using immobilised fungal cells was an efficient method for production of (Sb(B-glucan with a high yield. This study could be beneficial for other medicinal mushroom fermentation.

Ethanol has been blended with petrol in Malawi for over thirty years. However the strategic decisions for energy security regarding liquid fuels conspicuously omit ethanol. Fossil fuels continue to occupy first place in spite of the acknowledged fact that fossils reserves are getting exhausted and unsustainable. The goal of the research was to develop a strategic framework for sustainably promoting ethanol production so as to make it a significant part of the liquid fuels portfolio and reduce fossil fuel dependence in Malawi. The purpose of the research was to find possible pathways for increasing the production of and use of ethanol. Five pathways for increased ethanol production and use emerged from the interviews. An analysis of the interview findings identified three pathways for increased ethanol production. These were increasing feedstock for ethanol production, increasing sugarcane yields and increasing land under sugarcane. The analysis of the interviews identified two pathways for increasing ethanol use, one was government incentives and the other was the reduction of the ethanol price. Three interventions by government for achieving an optimal liquid fuel portfolio were identified as the introduction of ethanol driven vehicles, importation of flexi-fuel vehicles and the inclusion of ethanol tanks in the strategic fuel storage plan. There has been no research which explored strategically increasing ethanol in the liquid fuels portfolio in the Malawi context, as such this represents a significant contribution to knowledge. Specifically seventeen sustainability criteria for ethanol production and use were ranked and six were found to be most relevant. The positive economic contribution criterion was seen as the most relevant by the respondents in contrast to the European Union, Brazil, America and elsewhere where green house gas (GHG) mitigation is number one. The land use change (LUC) or indirect land use change criterion had mixed responses signifying that it is not well known. Both the goal and purpose of the research were achieved. A strategic framework was developed and pathways identified.

Biomass has become an increasingly important renewable source of energy forenhanced energy security and reduced CO[subscript]2 emissions. Gasification is at the core of many biomass utilisation technologies for such purposes as the generation of electricity and the production of hydrogen, liquid fuels and chemicals. However, gasification faces a number of technical challenges to become a commercially feasible renewable energy technology. The most important one is the presence of tar in the gasification product gas. The ultimate purpose of this thesis was to investigate the catalytic reforming of tar using cheap catalysts as an effective means of tar destruction.In this thesis, natural ilmenite ore and novel char-supported catalysts were studied as catalysts for the steam reforming of biomass tar derived from the pyrolysis of mallee biomass in situ in two-stage fluidised-bed/fixed-bed quartz reactors. In addition to the quantification of tar conversion, the residual tar samples were also characterised with UV-fluorescence spectroscopy. Both fresh and spent catalysts were characterised with X-ray diffraction spectroscopy, FT-Raman spectroscopy and thermogravimetric analysis.The results indicate that ilmenite has activity for the reforming of tar due to its highly dispersed iron-containing species. Both the externally added steam and low concentration oxygen affect the tar reforming on ilmenite significantly. The properties of biomass affect the chemical composition of its volatiles and therefore their reforming with the ilmenite catalyst. Compared with sintering, coke deposited on ilmenite is the predominant factor for its deactivation.During the steam reforming process, the char-supported iron/nickel catalysts exhibit very high activity for the reforming of tar. In addition, NO[subscript]x precursors could be decomposed effectively on the char-supported iron catalyst during the steam reforming process. The hydrolysis of HCN and the decomposition of NH[subscript]3 on the catalyst are the key reactions for the catalytic destruction of NO[subscript]x precursors.The kinetic compensation effects demonstrate that the reaction pathways on the char-supported catalysts are similar but different from those on ilmenite. The proprieties of catalyst support could play important roles for the activities of the catalysts and the reaction pathways on the catalysts. The char support as part of the char-supported catalysts can undergo significant structural changes during the catalytic reforming of biomass volatiles.

The last decade has seen a rise in the demand for energy from growing economies such as Brazil, China, India, and South Africa. Recent trends suggest a shift in focus towards the development of sustainable energy processes that are environmentally friendly. This has led to an increased interest in carbon containing waste materials such as plastic, rubber and biomass that can be converted to synthetic liquid fuels (Doss, T. (2012) Low severity Fischer-Tropsch synthesis for the production of synthetic hydrocarbon fuels. Aston University). Studies have shown that these waste materials can be converted into synthetic liquid fuels by a two-step process: gasification/pyrolysis of waste material to synthesis gas (a mixture of CO + H2) and further conversion of the syngas generated to synthetic liquid hydrocarbons fuels by the Fischer-Tropsch synthesis (FTS) (Tijmensen, M.J., Faaji, A.P., Hamelinck, C.N. and van Hardeveld, M.R. (2002) Exploration of the possibilities for production of Fischer Tropsch liquids and power via biomass gasification. Biomass and Bioenergy 23:129–152). Waste or biomass can be used as feedstock material for Fischer-Tropsch synthesis in producing clean liquid hydrocarbon fuels (Hamelinck, C.N., Faaij, A.P.C., den Uil, H. and Boerrigter, H. (2004) Production of FT Transportation Fuels from Biomass; Technical Options, Process Analysis and Optimisation, and Development Potential. Energy. 29(11): 1743-1771.). Fischer-Tropsch synthesis produces ultra-clean fuels such as the low-sulfur diesel with a high cetane number (Dry, M.E. (1990) The Fischer-Tropsch Process - Commercial Aspects. Catalysis Today 6(3):183-206.). Previous FTS studies have consistently established optimum operating conditions suitable to the Coal-To-Liquid (CTL) and Gas-To-Liquid(GTL) processes. However, this has not been the case for Biomass-to-Liquid (BTL) processes mostly because of the undefined feed syngas composition generated from pyrolysis or gasification of waste materials. Therefore there is a need to investigate these effects of syngas composition (H2/CO molar ratio) particularly at low H2/CO molar ratios of 1:1 to 1.5:1 and low-pressure and this was the motivation behind this work. The motivation behind low-pressure Fischer-Tropsch synthesis studies was the need to evaluate the feasibility of implementing simple and easy to operate Fischer-Tropsch synthesis processes which could be applied to resources that were previously thought to be stranded and uneconomical (waste, etc.) without the need of complex process control and safety requirements. A maximum average CO conversion of 58% was achieved for Low Temperature Fischer-Tropsch (LTFT) studies conducted at low reactor pressures (8 bars and 15bars) over Fe30K2Cu3.75SiO2 iron-based catalyst while a maximum average CO conversion of 6% was achieved for Low Temperature Fischer-Tropsch (LTFT) studies over Co/Ru/TiO2 cobalt-based catalyst at low reactor pressure of 10bars. The iron-based catalyst was highly selective towards heavy molecular weight hydrocarbons at these operating conditions.
MT2016

A Dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, South Africa, in fulfillment for the degree of Master of Science Johannesburg, 20th of September 2017
Energy is an important utility to human kind. Since the beginning of human civilization, human beings have become acquainted with travelling and transportation of goods. The use of conventional energy fuels for automobile engines is no longer sustainable due to finite crude oil reserves available in the world, of which many are facing the crisis of being depleted. The use of conventional fuels is a major contributor to environmental concerns such as global warming. Therefore there is an urgent need to explore alternative sources of fuel energy that are sustainable and environmentally friendly. The production of biofuels has been receiving increased academic and industrial attention as practical alternative fuel sources that can partially or completely replace conventional fuels. A study of the production of biogasoline from waste cooking oil as an alternative and re-usable source of liquid fuel was conducted in this project. This work focused on the variety of parameters that would deliver the optimum conversion and yield of biogasoline. The waste cooking oil was converted through catalytic hydrocracking in the presence of an acid activated Ni-Mo/Al2C>3 catalyst and constant hydrogen gas pressure of 0.5 kPa. A number of Ni-Mo/A^Oa catalysts were synthesized with varying Ni-loadings from 5-25 wt. % and calcination temperatures from 300 °C to 700 °C. The catalysts were characterised using ICP-OES, TGA, BET, SEM, FT-IR and Raman spectroscopy. Catalyst characterisation results revealed that the catalyst with 5 wt. % Ni possessed the greatest thermal strength, with the maximum BET surface area of 61.61 m /g and high dispersion of the active species in the catalyst. The optimal calcination temperature range for this catalyst was found from 500 °C to 600 °C. The effects of reaction temperature, reaction time, catalyst: oil ratio, catalyst calcination temperature and Ni-loading (wt. %) were investigated. The highest percentage of produced biogasoline was 59.50 wt. % at a reaction temperature of 250 °C, catalyst: oil ratio of 1:75, reaction time of 1 hr with a catalyst loaded with 5 wt. % Ni and calcinated at 300 °C. The use of stainless steel reactors that can handle higher reaction temperatures and pressure is recommended for future studies that will allow more severe cracking of the raw material into lighter hydrocarbons. The Ni-Mo/AhCT catalyst can also be modified with boron or fluorine to enhance its catalytic activity.
MT 2018

To mitigate the emissions from the widely studied and even applied coal to FT liquid (FTL) fuels systems, two kinds of promising renewable energy, biomass and solar energy, have been proposed and assessed as a partial or total substitute for coal feed. The concept of a solar hybridized FTL fuels production system has the potential to obtain higher productivity with lower greenhouse gas emissions, when compared with a conventional system. However, less attention has been paid to the comprehensive system analysis of this topic. Hence, the aim of the present thesis is to achieve the annual performance of the solar hybridized solid fuels to FTL fuels processes with novel configurations. A novel solar hybridized dual fluidized bed (SDFB) gasification process for FTL fuels production is proposed and investigated in the present thesis for cases with high reactivity solid fuels as the feedstock. The concept offers sensible thermal storage of the bed material and a process that delivers a constant production rate and quality of syngas despite solar variability. As a reference scenario for this concept, the proposed solar hybridized coal-to-liquids (SCTL) process is simulated for the case with lignite as the feedstock using a pseudo-dynamic model that assumes steady state operation at each time step for a one-year, hourly integrated solar insolation time series. For a solar multiple of 3 and bed material storage capacity of 16 h, the calculated annual solar share is 21.8%, assuming that the char conversion in the steam gasification process is 100%. However, the solar share is also found to be strongly dependent on the char conversion in the steam gasification process, so that the solar share is calculated to decrease to zero as the conversion is decreased to 57%. New configurations of the solar hybridized solid fuels (biomass and/or coal) to FTL fuels process are proposed and assessed, which are characterized with a novel SDFB gasifier with char separation, the incorporation of carbon capture and sequestration (CCS) and/or the use of FT reactor tail-gas recycle. Montana lignite and spruce wood have been chosen as the studied coal and biomass, respectively. Assessed using the pseudo-dynamic model, the annual solar share of the SCTL system can be increased from 12.2% to 20.3% by the addition of the char separation, for a char gasification conversion of 80%. To achieve well-to-wheel greenhouse gas emissions for FT liquid fuels parity with diesel derived from mineral crude oil, a biomass fraction of 58% is required for the studied non-solar coal and biomass-to-liquids system with a dual fluidized bed (DFB) gasifier. This biomass fraction can be reduced to 30% by the addition of carbon capture and sequestration and further reduced to 17% by the integration of solar energy with a solar multiple of 2.64 and a bed material storage capacity of 16 h. This reduction of the biomass fraction is very important given that biomass is typically more expensive than coal. As the biomass fraction is increased from 0% to 100%, the specific FT liquids output is decreased from 59.6% to 48.3% due to the increasing light hydrocarbons content. These two outputs (for biomass fractions of 0% and 100%, respectively) can both be increased to 71.5% and 70.9%, respectively, by integrating a tail-gas recycling configuration. Co-gasification of biomass with coal has the potential to further reduce the GHG emission from the SCTL systems, as discussed above. The application of biomass is usually limited by some properties (e.g., high moisture, low heating value and so on), which can be improved by torrefaction, as proved by previous work. Previous work also found that torrefaction can impact the bio-char gasification reactivity. In the present thesis, to better understand the influence of torrefaction on the bio-char gasification reactivity, further investigations were carried out on the char physicochemical characteristics that can influence the gasification reactivity, i.e., the char specific surface area, the char carbonaceous structure and the catalytic effect of inorganic matter in the char. The present experimental investigation showed that the influence of the torrefaction on the char gasification reactivity depended strongly on the biomass species and char preparation conditions. For a pyrolysis temperature of 800 ºC, the gasification reactivity of the chars from both the torrefied grape marc and the torrefied macroalgae were found to be lower than that of the chars from their corresponding raw fuels. This is mainly due to a lower specific surface area and a lower content of alkali metals (sodium and/or potassium) in the chars produced from both the torrefied grape marc and the torrefied macroalgae than for those chars produced from their corresponding raw fuels. However, the opposite influence of torrefaction was found for the macroalgae char when the pyrolysis temperature was increased to 1000 ºC. This is mainly due to a higher sodium concentration and a more amorphous carbonaceous structure for the torrefied macroalgae char than for the raw macroalgae char. In the present thesis, the process modelling results can be used for further economic analysis of the proposed novel configurations of solar hybridized coal and/or biomass to FTL fuels system via an SDFB gasifier. In addition, according to the experimental results of this study, the investigation of the influence of torrefaction on the bio-char characteristics can help to better understand the influence of torrefaction on the bio-char gasification reactivity.
Thesis (Ph.D.) (Research by Publication) -- University of Adelaide, School of Chemical Engineering, 2017

Thermochemical water splitting cycles have been conceptualized and researched for over half a century, yet to this day none are commercially viable. The heavily studied Sulfur-Iodine cycle has been stalled in the early development stage due to a difficult HI-H₂O separation step and material compatibility issues. In an effort to avoid the azeotropic HI-H₂O mixture, an imidazolium-based ionic liquid was used as a reaction medium instead of water. Ionic liquids were selected based on their high solubility for SO₂, I₂, and tunable miscibility with water. The initial low temperature step of the Sulfur-Iodine cycle was successfully carried out in ionic liquid reaction medium. Kinetics of the reaction were investigated by I₂ colorimetry. The reaction also evolved H₂S gas, which led to the conceptual idea of a new Sulfur-Sulfur thermochemical cycle, shown below:
4I₂(l)+4SO₂(l)+8H₂O(l)↔4H₂SO₄(l)+ 8HI(l)
8HI(l)+H₂SO₄(l)↔ H₂S(g)+4H₂O(l)+4I₂(l)
3H₂SO₄(g)↔ 3H₂O(g)+3SO₂(g)+1½O₂(g)
H₂S(g)+2H₂O(g)↔ SO₂(g)+3H₂(g)
The critical step in the Sulfur-Sulfur cycle is the steam reformation of H₂S. This highly endothermic step is shown to successfully occur at temperatures in excess of 800˚C in the presence of a molybdenum catalyst. A parametric study varying the H₂O:H₂S ratio, temperature, and residence time in a simple tubular quartz reactor was carried out and Arrhenius parameters were estimated. All reactive steps of the Sulfur-Sulfur cycle have been either demonstrated previously or demonstrated in this work. A theoretical heat-to-hydrogen thermal efficiency is estimated to be 55% at a hot temperature of 1100 K and 59% at 2000 K. As a highly efficient, all-fluid based thermochemical cycle, the Sulfur-Sulfur cycle has great potential for feasible process implementation for the transformation of high quality heat to chemical energy.
Graduation date: 2012

A research report submitted in partial fulfilment requiremenrs of degree Master of Science tothe School of Chemical and Metallurgical Engineering, Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, South Africa, January 2018
South Africa’s energy sector is vital to the development of its economy. Instability in the form of disruption in supply affects production costs, investments, and social and economic growth. Domestic sources are no longer able to meet the country’s demands. South Africa must find a local alternative fuel source in order to reclaim stability and encourage social and economic development. Biomass is one of the most abundant renewable energy sources, and has great potential as a fuel source. Currently biomass contributes 12% of the world’s energy supply, while in some developing countries it is responsible for up to 50% of the energy supply. South Africa is the highest maize producer on the African continent. Many studies carried out indicated that maize, and its residue contain valuable materials, and has the highest lower heating value in comparison to other agricultural crops. This indicates that maize can be a potential biomass for renewable energy generation in South Africa. A means for energy conversion for biomass, is the process of gasification. Gasification results in gaseous products H2, CO and CO2. Since the process of biomass gasification involves a series of complex chemical reactions involving a number of parameters, which include flow, heat transfer and mass transfer, it is very difficult to study the process of gasification by relying on experimentation only. Numerical simulation was used to provide further insight on this process, and accelerate development and application of maize gasification in a cost effective and efficient manner. The objective of this study was therefore, to verify and evaluate the feasibility of maize gasification and liquid fuels production in South Africa from an economic and energy perspective. The simulation model was developed in Aspen Plus® based on two thermodynamic models specified as Soave – Redlich – Kwong and the Peng Robinson equation of state. All binary parameters required for this simulation were available in Aspen Plus®. The gasification unit was modelled based on a modified Gibbs free energy minimization model. Gasification of maize and downstream processing in the form of Fischer-Tropsch (FT) synthesis and gas to liquids (GTL) processing for liquid fuels production was modelled in Aspen Plus®. Sensitivity analyses were carried out on the process variables: equivalence ratio (ER), steam to biomass ratio (SBR), temperature and pressure, to obtain the optimum gasification conditions. The optimum reactor conditions, which maximized syngas volume and quality was found to be an ER of 0.22 and SBR of 0.2 at a temperature of 611ºC. An increase in pressure was found to have a negative effect; therefore atmospheric conditions of 101.325 kPa were chosen, in order to maximize CO and H2 molar volumes. Based on these conditions the produced syngas consisted of 35% H2, 16% CO, 24% CO2 and 3%CH4. The results obtained from gasification, based on a modified Gibbs free energy model, show a closer agreement with experimental data, than other simulations based on the assumption that equilibrium is reached and no tar is formed. However, these results were still idealistic as it under predicted the formation of CO and CH4. Although tar was accounted for as 5.5% of the total product from the gasifier (Barman et al., 2012), it may have been an insufficient estimation resulting in the discrepancy in CO and CH4. The feasibility of maize as a feed for gasification was examined based on quality of syngas produced in relation to the requirements for FT synthesis. A H2/CO ratio of 2.20 was found, which is within range of 2.1 – 2.56 found to support greater conversions of CO with deactivation of the FT catalyst (Lillebo et al., 2017). The syngas produced from maize was found to have a higher H2/CO ratio than conventional fossil fuel feeds; implying that maize can result in a syngas feed which is both renewable and richer in CO and H2 molar volumes. Liquid fuels generation was modelled based on experimental production distributions obtained from literature for FT synthesis and hydrocracking. The liquid fuel production for 1000 kg/hr maize feed, was found to be 152 kg/hr LPG, 517 kg/hr petrol and 155 kg/hr diesel. The simulation of liquid fuels production via the Fischer-Tropsch synthesis and hydrocracking process showed fair agreement with literature. Where significant deviations were found, they could be reasonably explained and supported. This simulation was found to be a suitable means to predict liquid fuels production from maize gasification and downstream processing. The feasibility of liquid fuels production from maize in South Africa was examined based on the country’s resource capacity to support additional maize generation. It was found that based on 450 000 hectares of underutilized land found in the Homelands, an additional 1.216 billion litre/annum of synthetic fuels in the form of diesel and petrol could be produced. This has the potential to supplement South African liquid fuels demand by 6% using a renewable fuel source. This fuel generation from maize will not impact food security due to the use of underutilized arable land for maize cultivation, or impact water supply as maize does not require irrigation. In addition, fuel generation in this manner supports the Biofuels Industry Strategy (2007) by targeting the use of underutilized land, ensuring minimal impact on food security, and exceeds its primary objective of achieving a 2% blending rate from renewable sources. The economic feasibility of liquid fuels derived from maize was determined based on current economic conditions in 2016. Based on these conditions of 49 $/bbl Brent Crude, 40 $/MT coal and 6.5 $/mmBTU of natural gas at a R/$ exchange rate of R14.06 per U.S. dollar, it was found that coal, natural gas and oil processing are more economically viable feeds for fuel generation relative to maize. However, based on projected market conditions for South Africa, the R/$ exchange rate is expected to weaken further, the coal supply is expected to diminish and supply of natural gas is expected to be a continued issue for South Africa. Based on this, maize should be considered as a feed for fuel generation to reduce the dependency on non-renewable fossil fuel sources. The energy feasibility of liquid fuels produced from maize was only evaluated from a thermal energy perspective. It was found that maize gasification and FT processing requires 0.91 kg steam/kg feed. This 0.91kg of steam accounts for the raw material feed, distillation and heating required for every 1kg of maize processed. It was found that 2.56 kg steam/kg feed was generated from the reactor units. This was assumed to be in the form of 10 bar steam, as in this form it can be sent to steam turbines for electricity generation to assist with overall energy efficiency for this process. In addition, the amount of CO2 (kg/kg feed) produced, was examined for maize processing in comparison to fossil fuel feeds: natural gas and coal. The CO2 production from liquid fuels processing based on a maize feed, was found to be the highest at 0.66 kg/kg feed. However, a coal feed has higher ash and fix carbon content indicating greater solid waste generation in the gasifer. While dry reforming of natural gas is a net consumer of CO2, but had significantly higher steam requirements in order to achieve the same H2/CO ratio as maize. This indicates that although maize results in more CO2/kg feed, it is 88% more energy efficient than dry methane reforming. Additional experimental work on FT processing using syngas derived from maize is recommended. This will assist in further verification of liquid fuels quantity, quality and process energy requirements.
XL2018