Dissertations / Theses on the topic 'Desorption kinetic'

Potentially toxic elements (PTEs) can be absorbed and accumulated in vegetables organ and tissues, and this is an important channel through which PTEs can enter into the food chain. Soil management may interfere in the behavior of PTEs in the system. So, the study of the dynamics of elements in the soil is fundamental to a better understanding of factors that influence soil-plant transfer. In the state of Pernambuco, Brazil, the production of vegetables is mainly concentrated in small or medium organic and conventional farms located in the Agreste and Sao Francisco regions. Our aims in this research were: i) to determine the contents of PTEs in soil and in vegetables produced under conventional and organic systems in garden soils of Pernambuco; ii) to investigate the forms of the PTEs and their uptake by the vegetables based on different soil-plant transfer factors; iii) to use the calculated transfer factors to assess the human risk exposure; iv) to assess the effect of aging and organic matter (OM) on copper (Cu) desorption in garden soils; v) to determine if manure application to soils increases water soluble Cu concentrations; and vi) to verify the efficiency of machine learning techniques in the classification of vegetables produced under organic and conventional systems. Acid and complexing solutions were employed to extract total contents of PTEs in plants and to extract pseudototal, reactive and bioavailable fractions of the PTEs in soils. Soil-plant transfer factors and human risk assessment were calculated based on the determined levels of PTEs. Kinetic assays were developed using rates of organic composts added to Cu-spiked soils to model the Cu desorption. Water extractable Cu and dissolved organic carbon (DOC) were extracted from soils amended with dairy manure, and the Cu-DOC interactions were studied using spectroscopic techniques. Lettuce (Lactuca sativa) leaves had the highest capacity to accumulate PTEs; conventional system promoted higher PTEs values in soils and plants than the organic production; regardless of the scenario, children and adults in contact to vegetables cropped in organic system have a lower health risk than individuals exposed to lettuce leaves conventionally produced. The addition of OM promoted greater Cu desorption, while aging lead to a reduction in the Cu release. The Fouriertransform infrared spectroscopy spectra showed increase in the presence of aliphatic and carboxylic groups in the extracts from the manure-amended soils. Carboxylic acid functional groups on the DOC formed strong bonds with Cu, which can promote Cu transport as dissolved Cu-organic complexes in the soil profile. The Support Vector Machine had an accuracy over 90% to classify the vegetables in the two groups (organic and conventional); and this high assertiveness rate highlights the potential of using elemental quantification and algorithms as support techniques in the process of authenticity and inspection of organic products.
Elementos potencialmente toxicos (EPTs) podem estar biodisponiveis para serem absorvidos e acumulados nos tecidos e orgaos vegetais, sendo esta uma importante rota de entrada de EPTs na cadeia alimentar. O manejo do solo pode interferir no comportamento dos EPTs no sistema. Desta forma, o estudo da dinamica desses elementos no solo e fundamental para melhor entendimento dos fatores que influenciam a transferencia solo-planta. No estado de Pernambuco, a producao de hortalicas se concentra em intensos cultivos organicos e convencionais localizados em pequenas ou medias propriedades, principalmente na regiao Agreste e Sao Francisco. Nossos objetivos neste trabalho foram: i) determinar os teores de EPTs no solo e nas hortalicas produzidas em sistemas convencionais e organicos em hortas de Pernambuco; ii) investigar as formas de EPTs e sua absorcao pelas hortalicas com base em diferentes fatores de transferencia solo-planta; iii) usar os fatores de transferencia calculados para investigar o risco de exposicao aos humanos; iv) estudar o efeito do tempo e da materia organica (MO) na dessorcao de cobre (Cu) em solos de horta; v) determinar se a aplicacao de esterco aumenta a concentracao de Cu soluvel em agua; e vi) verificar a eficiencia de tecnicas machine learning na classificacao de hortalicas produzidas em sistemas organicos e convencionais. Solucoes acidas e complexantes foram utilizadas para extrair os teores totais de EPTs nas plantas e os teores pseudototal, reativo e biodisponivel dos EPTs no solo. Fatores de transferencia solo-planta e avaliacao de risco humano foram calculados com base nos teores de EPTs. Estudos de cinetica foram desenvolvidos apos adicao de composto organico em solos contaminados com Cu para modelar a dessorcao de Cu. Cu soluvel em agua e carbono organico dissolvido (COD) foram extraidos de solos adubados com esterco, a interacao Cu-COD foi estudada usando tecnicas espectroscopicas. Folhas de alface (Lactuca sativa) apresentaram a maior capacidade de acumular EPTS; o sistema convencional promoveu maiores tores de EPTs nos solos e plantas do que o sistema organico; independentemente do cenario, criancas e adultos em contato com vegetais produzidos em sistema organico tem um menor risco do que os individuos que consomem folhas de alface convencionalmente produzidas. A adicao de MO promoveu maior dessorcao de Cu, enquanto o aumento no tempo de contato reduziu a liberacao de Cu. Os graficos da espectroscopia de infravermelho com transformada de Fourier mostraram um aumento na presenca de grupos funcionais alifaticos e carboxilicos nos extratos de solos adubados com esterco. Esses grupos funcionais no COD formam ligacoes fortes com Cu, o que promove o transporte do elemento na forma de complexos organicos dissolvidos no perfil do solo. O modelo Support Vector Machine apresentou acuracia superior a 90% na classificacao das hortalicas em dois grupos (organicas e convencionais); e a alta taxa de assertividade mostra o potencial do uso de quantificacao elementar e algoritmos como tecnicas auxiliares no processo de autenticidade de inspecao de produtos organicos.

Trends show that the fraction of the world's population with electronic devices using modern integrated circuits is increasing at a rapid rate. To meet consumer demands: less expensive, faster, and smaller electronics; while still making a profit, manufacturers must shrink transistor dimensions while increasing the number of transistors per integrated circuit; a trend predicted by Gorden E. Moore more than 44 years prior. As CMOS transistors scale down in size, new techniques such as atomic-layer deposition (ALD) are used to grow features one atomic layer at a time. ALD and other manufacturing processes are requiring increasingly stringent purities of process gases and liquids in order to minimize circuit killing defects which reduces yield and drives up manufacturing cost. Circuit killing defects caused by impurity incursions into UHP gas distribution system can come from a variety of sources and one of the impurity transport mechanisms investigated was back diffusion; the transport of impurities against convective flow. Once impurity incursions transpire, entire production lines are shut down and purging with UHP gas is initiated; a process that can take months thus resulting in tens of millions of dollars in lost revenue and substantial environment, safety, and health (ESH) impacts associated with high purge gas consumption. A combination of experimental investigation and process simulation was used to analyze the effect of various operational parameters on impurity back diffusion into UHP gas distribution systems. Advanced and highly sensitive analytical equipment, such as the Tiger Optics MTO 1000 H2O cavity ring-down spectrometer (CRDS), was used in experiments to measure real time back diffusing moisture concentrations exiting an electro-polished stainless-steel (EPSS) UHP distribution pipe. Design and operating parameters; main and lateral flow rates, system pressure, restrictive flow orifice (RFO) aperture size, and lateral length were changed to impact the extent of back diffusing impurities from a venting lateral. The process model developed in this work was validated by comparing its predictions with data from the experiment test bed. The process model includes convection, molecular diffusion in the bulk, surface diffusion, boundary layer transport, and all modes of dispersion; applicable in both laminar and turbulent flow regimes. Fluid dynamic properties were directly measured or were obtained by solving Navier-Stokes and continuity equations. Surface diffusion as well as convection and dispersion in the bulk fluid played a strong role in the transport of moisture from vents and lateral branches into the main line. In this analysis, a dimensionless number (Peclet Number) was derived and applied as the key indicator of the relative significance of various transport mechanisms in moisture back-diffusion. Guidelines and critical values of Peclet number were identified for assuring the operating conditions meet the purity requirements at the point of use while minimizing UHP gas usage. These guidelines allowed the determination of lateral lengths, lateral diameters, flow rates, and restrictive flow device configurations to minimize contamination and UHP gas consumption. Once a distribution system is contaminated, a significant amount of purge time is required to recover the system background due to the strong interactions between moisture molecules and the inner surfaces of the components in a gas distribution system. Because of the very high cost of UHP gases and factory downtime, it is critical for high-volume semiconductor manufacturers to reduce purge gas usage as well as purge time during the dry-down process. The removal of moisture contamination in UHP gas distribution systems was approached by using a novel technique dubbed pressure cyclic purge (PCP). EPSS piping was contaminated with moisture, from a controlled source, and then purged using a conventional purge technique or a PCP technique. Moisture removal rates and overall moisture removal was determined by measuring gas phase moisture concentration in real time via a CRDS moisture analyzer. When compared to conventional purge, PCP reduced the time required and purge gas needed to clean the UHP gas distribution systems. However, results indicate that indiscriminately initiating PCP can have less than ideal or even detrimental results. An investigation of purge techniques on the removal of gas phase, chemisorbed, and physisorbed moisture, coupled with the model predictions, led to the testing of hybrid PCP. The hybrid PCP approach proved to be the most adaptable purge technique and was used in next phase of testing and modeling. Experiments and modeling progressed to include testing the effectiveness of hybrid PCP in systems with laterals; more specifically, laterals that are "dead volumes" and results show that hybrid PCP becomes more purge time and purge gas efficient in systems with increasing number and size of dead volumes. The process model was used as a dry-down optimization tool requiring inputs of; geometry and size, temperature, starting contamination level, pressure swing limits of inline equipment, target cleanliness, and optimization goals; such as, minimizing pure time, minimizing purge gas usage, or minimizing total dry-down cost.

The first part of this thesis deals with hydrogen storage materials, in view of their applications as promising energy carriers. One of the main open problems with these materials is: how can their decomposition temperature be lowered, when hydrogen is wanted to be released, so as to improve the energy efficiency of the process. A possible answer is given by joint decomposition of two or more hydrides, if very stable mixed compounds are formed (‘hydride destabilization’). Aiming at this result, the new hydride composite 2LiBH4-Mg2FeH6 was considered, it was synthesized, and its thermodynamic and kinetic properties were investigated. In the second part of this thesis work lithium oxide materials, of relevant interest for applications to batteries, were investigated. The chemical lithiation reaction of niobium oxide was considered, as equivalent to the electrochemical process of lithium insertion on discharging a Nb2O5 cathode vs. a metal Li anode. Thus, the Li2Nb2O5 compound was synthesized by reaction of monoclinic a-Nb2O5 with n-butyllithium.This material was investigated by neutron powder diffraction (D2B equipment at ILL, France) and its structure was Rietveld refined in space group P2 to wRp=0.045, locating the Li atoms inserted in the a-Nb2O5 framework.

Hydrogen embrittlement is a problem that offers challenges both to technology and to the theory of metallurgy. In the presence of a hydrogen rich environment, applications such as rolling bearings display a significant decrease in alloy strength and accelerated failure due to rolling contact fatigue. In spite of these problems being well recognised, there is little understanding as to which mechanisms are present in hydrogen induced bearing failure. The objective of this thesis are twofold. First, a novel alloy combining the excellent hardness of bearing steels, and resistance to hydrogen embrittlement, is proposed. Second, a new technique to identify the nature of hydrogen embrittlement in bearing steels is suggested. The new alloy was a successful result of computer aided alloy design; thermodynamic and kinetic modelling were employed to design a composition and heat treatment combining (1) fine cementite providing a strong and ductile microstructure, and (2) nano-sized vanadium carbide precipitates acting as hydrogen traps. A novel technique is proposed to visualise the migration of hydrogen to indentation-induced cracks. The observations employing this technique strongly suggest that hydrogen enhanced localised plasticity prevails in bearing steels. While proposing a hydrogen tolerant bearing steel grade, and a new technique to visualize hydrogen damage, this thesis is expected to aid in increasing the reliability of bearings operating in hydrogen rich environments.

In France all of the nuclear power plant facilities in service today are pressurized water reactors (PWR). Some parts of the PWR in contact with the primary circuit medium, such as the steam generator tubes (fabricated in nickel base alloy A600) and some reactor core internal components (fabricated in stainless steel 316L), can fall victim to environmental degradation phenomena such as stress corrosion cracking (SCC). In the late 1950's, H. Coriou observed experimentally and predicted this type of cracking in alloys traditionally renowned for their SCC resistance (A600). Just some 20 to 30 years later his predictions became a reality. Since then, numerous studies have focused on the description and comprehension of the SCC phenomenon in primary water under reactor operating conditions. In view of reactor lifetime extension, it has become both critical and strategic to be capable of simulating SCC phenomenon in order to optimize construction materials, operating conditions, etc. and to understand the critical parameters in order to limit the damage done by SCC. This study focuses on the role hydrogen plays in SCC phenomenon and in particular H-material interactions. Hydrogen, from primary medium in the form of dissolved H gas or H from the water, can be absorbed by the alloy during the oxidation process taking place under reactor operating conditions. Once absorbed, hydrogen may be transported across the material, diffusing in the interstitial sites of the crystallographic structure and interacting with local defects, such as dislocations, precipitates, vacancies, etc. The presence of these [local defect] sites can slow the hydrogen transport and may provoke local H accumulation in the alloy. This accumulation could modify the local mechanical properties of the material and favor premature rupture. It is therefore essential to identify the nature of these H-material interactions, specifically the rate of H diffusion and hydrogen trapping kinetics at these defects. Concerning these H-trap site interactions, literature presents very few complete sets of kinetic data; it is therefore necessary to study and characterize these interactions in-depth. This work is composed of two interdependent parts: (i) the development of a calculation code capable to manage these H-material interactions and (ii) to extract the kinetic constants for trapping and detrapping from experimental results in order to fuel the simulation code and create a solid database. Due to the complexity of industrial materials (A600 and SS316L), \enquote{model materials} were elaborated using a series of thermomechanical treatments allowing for the study of simplified systems and the deconvolution of the different possible trapped and interstitial hydrogen contributions. These \enquote{model} specimens were charged with deuterium (an isotopic hydrogen tracer) by cathodic polarization. After charging, specimens were subjected to thermal desorption mass spectroscopy (TDS) analysis where the deuterium desorption flux is monitored during a temperature ramp or at an isotherm. Interstitial diffusion and kinetic trapping and detrapping constants were extracted from experimental TDS spectra using a numerical fitting routine based upon the numerical resolution of the McNabb and Foster equations. This study allowed for the determination of the hydrogen diffusion coefficient in two alloys, Ni base alloy 600 and stainless steel 316L, and the kinetic trapping and detrapping constants at two trap site types, chromium carbides and dislocations. These constants will be used to construct a kinetic database which will serve as input parameters for a numerical model for the prediction and simulation of SCC in PWRs

Les piles à combustible, alimentée par de l’hydrogène, représentent une solution prometteuse pour limiter la pollution. L’une des alternatives économiques envisagées à court et moyen terme est de produire l’hydrogène à partir d’un carburant tel que le méthane ou le bio-éthanol. Cette transformation a pour objectif d’obtenir un mélange de gaz riche en hydrogène avec une très faible teneur en CO, ce dernier étant un poison pour les piles de type PEM. La réaction de Water-Gas Shift (WGS) est une étape clé du procédé ; elle convertit CO en CO2 par réaction avec l’eau et fournit une quantité d’hydrogène supplémentaire. Des catalyseurs métalliques (Pt, Pd, Ru, Rh, Au, Cu) supportés sur des oxydes (CeO2, TiO2, ZrO2, Fe2O3, CeO2/Al2O3) ont été comparés dans des conditions de WGS identiques en présence de CO2 et H2. Une étude cinétique a été réalisée sur les catalyseurs Pt/CeO2, Au/CeO2, Pt/TiO2 et Au/TiO2. Les énergies d’activation apparentes et les ordres de réaction ont été déterminés à partir d’un modèle de type loi de puissance. Un mécanisme réactionnel avec deux sites a été proposé pour décrire les différentes activités des 4 catalyseurs. Des expériences de désorption programmée en température ont été réalisées pour déterminer les paramètres cinétiques sur le support
The Fuel Cells are promising solution to reduce the air pollution. One of the cost-efficient alternatives is to produce hydrogen from another fuel such as methane or bio-ethanol. A hydrogen fuel processor consists in generating a hydrogen-rich mixture and reducing the carbon monoxide content, as PEM fuel cells are very low CO tolerance. One of these units is the water-gas shift reactor, which converts CO into CO2 by the reaction with water and provides additional hydrogen. Catalysts based on a metal (Pt, Pd, Ru, Rh, Au, Cu) supported on an oxide (CeO2, TiO2, ZrO2, Fe2O3, CeO2/Al2O3) were compared for the WGS reaction in the same conditions and in the presence of CO2 and H2. A kinetic study was conducted on catalysts Pt/CeO2, Au/CeO2, Pt/TiO2 and Au/TiO2. A power law rate model was used to determine apparent activation energies and reaction orders. A dual-site reaction mechanism was proposed to explain the different activities between the four catalysts. The sorption parameters of H2O and CO2 on the supports was quantitatively determined from temperature-programmed desorption experiments

Unique physical properties such as small effective mass, high electron drift velocities, high electron mobility and small band gap energy make InN a candidate for applications in high-speed microelectronic and optoelectronic devices. The aim of this research is to understand the surface properties, desorption kinetics and thermal stability of InN epilayers that affect the growth processes and determine film quality as well as device performance and life time. We have investigated the structural properties, the surface desorption kinetics, and the thermal stability using Auger electron spectroscopy (AES), x-ray diffraction (XRD), Raman spectroscopy, atomic force microscopy (AFM), high resolution electron energy loss spectroscopy (HREELS), and temperature programmed desorption (TPD). Investigations on high pressure chemical vapor deposition (HPCVD)-grown InN samples revealed the presence of tilted crystallites, which were attributed to high group V/III flux ratio and lattice mismatch. A study of the thermal stability of HPCVD-grown InN epilayers revealed that the activation energy for nitrogen desorption was 1.6±0.2 eV, independent of the group V/III flux ratio. Initial investigations on the ternary alloy In0.96Ga0.04N showed single-phase, N-polar epilayers using XRD and HREELS, while a thermal desorption study revealed an activation energy for nitrogen desorption of 1.14 ± 0.06 eV. HREELS investigations of atomic layer epitaxy (ALE)-grown InN revealed vibrational modes assigned to N-N vibrations. The atomic hydrogen cleaned InN surface also exhibited modes assigned to surface N-H without showing In-H species, which indicated N-polar InN. Complete desorption of hydrogen from the InN surface was best described by the first-order desorption kinetics with an activation energy of 0.88 ± 0.06 eV and pre-exponential factor of (1.5 ± 0.5) ×105 s-1. Overall, we have used a number of techniques to characterize the structure, surface bonding configuration, thermal stability and hydrogen desorption kinetics of InN and In0.96Ga0.04N epilayers grown by HPCVD and ALE. High group V/III precursors ratio and lattice mismatch have a crucial influence on the film orientation. The effects of hydrogen on the decomposition add to the wide variation in the activation energy of nitrogen desorption. Presence of surface defects lowers the activation energy for hydrogen desorption from the surface.

Since the advent of diesel fuel use, insufficient storage and inadequate transport and disposal practices have resulted in widespread contamination of the subsurface environment. Beginning in the 1970?s, the United States EPA has established a number of regulations controlling current and future storage, transport, and disposal efforts and address the need to remediate existing contaminated sites. However, regulations provide only the desired goal, not a roadmap of how to accomplish remediation. It falls then, to individuals in research and industry, to devise techniques effective in reducing / eliminating contamination levels at sites of concern. Existing remediation techniques of pump and treat and air sparing / soil vapor extraction are effective, but often take many years to accomplish remediation to regulatory levels. Thermal treatments such as steam stripping and electrical heating of soils, are much less time consuming, but much more costly endeavors. Low temperature thermal desorption (at temperatures less than 80 degrees C) holds promise by incorporating the benefits of higher temperatures, such as the increase in vapor pressure and the decrease in viscosity, without the extreme cost usually associated with thermal treatments. In order to test this hypothesis, a research testing program focused on batch testing in the laboratory setting was developed to assess the viability of increased temperatures on the desorption efficiency of benzene on various soils. Testing consisted of three soils, a poorly graded Ottowa sand, kaolinite, and a natural silty sand soil from the Lockbourne Air Force Base experimental testing site. The contaminant of concern is benzene, a carcinogenic and mutagenic compound that is one of the four major components of BTEX, a constituent of most diesel fuels. Benzene was chosen because of its presence at the LAFB testing site at contamination levels 164 times groundwater regulation limit of 5 ppb. Laboratory testing was conducted at initial benzene solution concentrations of 10, 100 and 1000 mg/L. Four temperatures; 20, 40, 60, and 80 degrees C, were used in the batch testing program. Results from testing support the theory that increased temperatures result in higher desorption efficiency. For lower concentrations of 10 and 100 ppm, temperatures as low as 40 degrees C correlated to increases in desorption levels from 40 percent (at 20 degrees C) to over 80 percent for the kaolinite and natural soil. Sand also experienced a doubling in desorption efficiency (from roughly 30 percent to roughly 70 percent) at the 60 degrees C temperature and 10 and 100 ppm concentrations. The 1000 ppm testing concentration resulted in more modest, but still increasing removal efficiencies at increased temperatures. Remediation at moderately increased temperatures appears to be a promising technique, but further research needs to be performed on soils that have experienced long term exposure to contamination to assess whether or not increased desorption efficiency trends are maintained.

In natural systems, the solution concentration and hence, potential bioavailability of trace metals is primarily controlled by adsorption-desorption reactions at the mineral-water interface. While many studies have been conducted to understand the adsorption of trace metals to soil minerals, less is known about long-term adsorption/desorption processes. In this study, we examined the influence of mixing and sorption period on the desorption of lead from goethite. Lead sorption was rapid and essentially complete in 1 h, with no change in the quantity of lead adsorbed over the 6 month sorption period. Desorption of lead was slower than the adsorption reaction and was best modeled by two first order equations. At all sorption densities, the desorption of lead followed the order Short-term (24 h) > Long-term non-stirred (6 months) > Long-term stirred (6 months). However, statistical analysis indicated that these differences were not statistically significant. Furthermore, the desorption rate coefficients were very similar for all the experiments indicating that there was no significant residence time effect in this study. However, a sample from a previous study that was allowed to age 5 years and then analyzed by the desorption procedure did have statistically significant differences between the long-term (5 years) and the short-term (5 months). These results suggest that longer adsorption periods, perhaps a number of years, may be necessary to determine if residence time effects are an artifact of the experimental conditions or truly the length of the adsorption period.
Master of Science

In organic-rich sediments with a thin oxidised surface layer, sediment resuspension by physical or biological processes may contribute to the manganese flux by exposing Mn(II)-laden anoxic sediment to the water column. The adsorbed Mn(II) can then be desorbed to the water column or sequestered by the solid phase upon oxidation to insoluble Mn(IV) oxides. Ultimately, the flux of Mn(II) to the water column depends on the relative rates of Mn(II) desorption and Mn(II) oxidation at the surface of sediment particles. First-order rate constants for adsorption, desorption and oxidation of Mn(II) in natural anoxic sediment were determined experimentally by monitoring dissolved manganese concentrations in sediment incubations. Adsorption and desorption reactions were initiated by mixing anoxic sediment and bottom water from the Lower St. Lawrence Estuary in closed reactors under anoxic conditions. Once sorption reactions reached a steady state, oxidation was initiated by introducing ambient air into the reactors. The kinetics of Mn(II) adsorption, desorption, and oxidation were fitted to first-order rate laws and the following first-order rate constants were obtained: kads' = 7.0±3.4 h-1, kdes' = 12.7±3.3 h-1, kox' = 0.020±0.006 h-1 . According to our results, desorption occurs more rapidly than oxidation and allows dissolved manganese to be released upon exposure of reducing sediment to oxygenated bottom seawater.
Dans un sédiment riche en matière organique et ayant un horizon oxydé mince, la mise en suspension de sédiments par des processus physiques ou biologiques pourrait contribuer au flux sortant de manganèse en exposant des sédiments anoxiques à la colonne d'eau. Le Mn(II) adsorbé aux particules sédimentaires peut être désorbé dans la colonne d'eau ou séquestré suite à son oxydation et à la formation d'oxydes de Mn(IV) insolubles. Le flux de Mn(II) vers la colonne d'eau dépend ultimement de la vitesse relative des réactions de désorption et d'oxydation à la surface de ces particules. Afin de déterminer si la mise suspension de sédiments réduits contribue au flux sortant de manganèse, nous avons déterminé les constantes de vitesse de premier ordre pour les réactions d'adsorption, de désorption et d'oxydation du Mn(II) en suivant l'évolution des concentrations de manganèse dissout dans des suspensions de sédiments naturels. Les réactions d'adsorption et de désorption ont été initiées en mélangeant des sédiments anoxiques et de l'eau de fond provenant de l'estuaire maritime du Saint-Laurent dans des réacteurs fermés en absence d'oxygène. Lorsque les réactions de sorption ont atteint un état stationnaire, l'oxydation fut initiée en introduisant de l'air ambiant dans les réacteurs. Les cinétiques d'adsorption, de désorption et d'oxydation du Mn(II) ont été représentées par des cinétiques d'ordre 1 et les constantes de vitesse suivantes ont été obtenues : kads' = 7.0±3.4 h-1, kdes' =12.7±3.3 h-1, kox' = 0.020±0.006 h-1. Selon nos résultats, la désorption du Mn(II) est plus rapide que son oxydation et contribuerait par conséquent au flux sortant de manganèse lors de la mise en suspension de sédiments réduits.

The formal solution to the diffusion equation for transient adsorption in a semiinfinite medium with a strongly concentration dependent diffusivity, originally derived by Fujita ( 3 ), has been extended to desorption. Profiles for adsorption and desorption are compared and simplified asymptotic expressions which are useful when the diffusivity ratio is large are derived. The effect of a strongly concentration dependent diffusivity on adsorption and desorption kinetics is briefly considered.

Adsorption kinetics and adsorption-desorption of atrazine on organoclay composites prepared with the surfactant 6-piperazin-1-yl-N,N'-bis-(1,1,3,3-tetramethyl-butyl)-(1,3,5)triazine-2,4-diamine and Houston Black clay were studied using the indirect batch equilibration procedure. The organoclay composites sorbed significantly more atrazine than the Houston Black clay. Adsorption equilibrium was reached after 72 h for the organoclay composites. Atrazine adsorption isotherms were described by linear partitioning. The Koc values ranged from 605 to 5271 L kg-1 for the organoclay composites compared to a value of 41 L kg-1 for the Houston Black clay. The organoclay composite containing 20% surfactant on a total weight basis provided the most efficient adsorption of atrazine, although organoclay composites containing much lower amounts of surfactant also adsorbed significant amounts of atrazine. An average of 11% of sorbed atrazine was released during desorption. Characterization of desorption products showed only atrazine molecules being released from the organoclay composites.

Many agricultural fields that have received long-term applications of P often contain levels of P exceeding those required for optimal crop production. Knowledge of the effect of the P remaining in the soil (residual effect) is of great importance for fertilization management. In order to characterize P forms in soils, a wide variety of methods have been proposed. The use of dialysis membrane tubes filled with hydrous ferric oxide (DMT-HFO) has recently been reported as an effective way to characterize P desorption over a long-term in laboratoty studies. However, there is little information on the relationship between kinetics of P release using this new method and plant P uptake. This method consist of a procedure of shaking a sample for a long period of time there by exploiting the whole volume of the soil which is in contrast to the actual plant mode of uptake. This method has also practical limitations in employing it for a routine soil analysis, as it is very expensive and time consuming. The objectives of this study were (i) to study the changes in labile, non-labile and residual P using successive P desorption by DMT-HFO followed by a subsequent fractionation method (combined method) (ii) to assess how the information gained from P desorption kinetic data relates to plant growth at green house and field trials (iii) to investigate the effect of varying shaking time on DMT-HFO extractable P and (iv) to propose a short cut approach to the combined method. The release kinetics of the plots from long term fertilizer trials at the University of Pretoria and Ermelo were studied. P desorption kinetics were described relatively well by a two-component first-order model (R2 = 0.947, 0.918,&0.993 for NPK, MNK,&MNPK treatments respectively). The relative contributions of both the labile pool (SPA) and the less labile pool (SPB) to the total P extracted increased with increased P supply levels. Significant correlations were observed between the rate coefficients and maize grain yield for both soil types. The correlation between the cumulative P extracted and maize yield (r = 0.997**) however was highly significant for Ermelo soils. This method was also used to determine the changes in the different P pools and to relate these P fractions with maize yield. Highly significant correlations were observed between maize grain yield and the different P fractions including total P. In both soil types the contribution of both the labile and non-labile inorganic P fractions in replenishing the solution Pi was significant where as the contributions from the organic fractions were limited. The C/HCl-Pi is the fraction that decreased most in both cases as well. Investigation was carried out to evaluate the effect of varying shaking periods on the extractable DMT-HFO-Pi for UP soils of varying P levels. Four shaking options were applied. Significant difference was observed for the treatment of high P application. Shaking option 2 seemed relatively better than the others since it showed the strongest correlation. Thus for soils with high releasing kinetics and high total P content, provided that the P release from the soil is a rate limiting step, reducing the length of shaking time could shorten the duration one needs to complete the experiment with out influencing the predicting capacity of the methodology. The other objective of this thesis was also to present a short cut method alternative to the combined fractionation method. Comparison of the sum of DMT-HFO-Pi, NaHCO3-Pi, NaOH-Pi, D/HCl-Pi and C/HCl-Pi extracted by a conventional step-by-step method with the sum of DMT-HFO-Pi and a single C/HCl-Pi extraction as a short cut approach for all extraction periods resulted in strong and significant correlations. The C/HCl-Pi fraction extracted by both methods was correlated with maize grain yield and it was found to be highly significant. This study revealed that this short cut approach could be a simplified and economically viable option to study the P dynamics of soils especially for soils where the P pool acting as a source in replenishing the labile portion of P is already identified. The method employed here therefore could act as an analytical tool to approximate successive cropping experiments carried out under green house or field condition. However, data from a wider range of soils is needed to evaluate the universality of this method. More work is also required in relating desorption indices of this method with yield parameters especially at field level.
Thesis (PhD)--University of Pretoria, 2009.
Plant Production and Soil Science
PhD
unrestricted

The formal solution to the diffusion equation for transient adsorption in a semiinfinite medium with a strongly concentration dependent diffusivity, originally derived by Fujita ( 3 ), has been extended to desorption. Profiles for adsorption and desorption are compared and simplified asymptotic expressions which are useful when the diffusivity ratio is large are derived. The effect of a strongly concentration dependent diffusivity on adsorption and desorption kinetics is briefly considered.

Trace metal concentrations in soil solution, and hence trace metal bioavailability and toxicity, are primarily controlled by sorption/desorption reactions at the mineral-water interface. While numerous studies have been conducted to understand the initial adsorption of these metals to soil minerals, less in known about long-term adsorption/ desorption processes. The objective of this study was to examine the influence of residence time and organic acids on the desorption of Pb2+and Cd2+ from goethite. Adsorption experiments were conducted at pH 6.0. Lead adsorption was nearly completed after 4 hours, with very little additional sorption during a 20-week period. In contrast cadmium showed a continuous slight increase in the amount of adsorption over the 20-week period. Desorption experiments were conducted at pH 4.5 and similar to previous studies examining trace metal desorption from oxide surfaces, the desorption kinetics for Pb2+and Cd2+ were slow compared to the sorption reaction. None of the experiments were completely reversible after an eight-hour desorption period. For all experiments except long-term Pb2+ desorption, the quantity of metal desorbed from goethite followed the order salicylate >NaNO3 > oxalate. Based on differences in cation affinity for the iron oxide surface one would expect a greater quantity of Cd2+ to be removed compared to Pb2+, for each of the extracting solutions. However at a pH of 4.5 we did not find a statistically significant trend. We observed a difference between the amount of metal removed for short and long-term experiments in five of six experiments, but these differences were only significant for Pb2+ experiments in the presence of salicylate. Two first order rate equations best fit the kinetics of trace metals desorption, with R2 values greater than 0.910 in all cases. Although our results show a decrease in rate coefficients (expect k1 for oxalate) with increased residence time, statistical analysis indicates that these results were only significant for Pb2+ experiments in the presence of salicylate. However raw and transformed data both suggest that desorption values are diverging as a function of aging time. Similar to other researchers we believe that Pb2+ and Cd2+ are sequestered by the goethite surface with an increase in residence time. These results suggest that residence time effects observed by many researchers are much less prevalent at low pH values. Therefore a reduction in soil pH created by natural anthropogenic processes may reduce the ability of soils to naturally sequester metals over time.
Master of Science

Magnesium is considered as one of the more promising candidates for hydrogen storage, primarily because of its abundance and the high hydrogen capacity of MgH2, magnesium dihydride (7.6 wt%). Unfortunately, practical applications of MgH2 are limited by poor hydrogen sorption kinetics and high thermodynamic stability, resulting in slow charging and the need for high temperatures to release the hydrogen. Methods to improve the sorption kinetics of MgH2, through ball-milling, alloying and introducing small amounts of additives are currently under investigation. The aim of this work was to investigate the effect of different transition metal oxides, as well as other catalysts, on the hydrogen sorption kinetics, hydrogen release temperature and cycling stability of MgH2. The rate of MgH2 absorption is determined by the physisorption and dissociation of molecular hydrogen, diffusion through the hydride layer and then nucleation of the hydride. Whereas desorption is determined by nucleation of metal phase, diffusion of atomic hydrogen through the metal and hydride, and recombination to form molecular hydrogen at the surface before dissociation of the molecule form the surface. The addition of small amounts of additives (< 10 mol%) to MgH2 during milling have been shown to have a significant effect on the kinetics of absorption and desorption of hydrogen. In addition, the effect of oxygen as a component of these additives has been extensively studied. Although a surface layer of MgO is known to slow the diffusion of hydrogen into metal, niobium oxide, Nb2O5, is one of the best additives for kinetic improvement of MgH2. It has been suggested that higher valance oxides have a greater effect on the kinetics; also recent studies have indicated that the formation of magnesium-niobium ternary oxide compound may be responsible for the enhancement, however the exact mechanism by which Nb2O5 enhances the kinetics is still unclear. Various transition metal oxides have proved to be effective additives for hydrogen absorption/desorption of Mg-based hydrides e.g., Nb2O5 and TiO2. In this work organometallic additives based on transition metal oxides (Ti and V) and halides have been chosen, some of which are liquid at room temperature. These additives were chosen to extend the oxide valency to higher values, provide a comparison between liquid and solid oxide additives, and compare a non-oxide transition metal additive (Ti-based chloride). Nb2O5 was used as the benchmark for comparisons. A range of different amounts of transition metal (Ti and V) oxides and other additives, both liquid and solid, were ball milled with pre-milled MgH2 under different gas environments and the hydrogen sorption behaviour of the ball milled composite samples was investigated using a TPD/TDS Sieverts apparatus. A key difference from previous work in this area was the use of organo-metallic compounds, some of which were liquid at room temperature. Samples were characterized using X-Ray Diffraction, and, where feasible, Scanning Electron Microscopy and Raman Spectroscopy before and after recording the hydrogen sorption behaviour. A Sievert apparatus was improved, then modified to include TPD and TDS capability to determine the hydrogen uptake and release and to perform all these measurements in one consistent environment. With the aim of understanding what effect the ball milling gas environment might have on the MgH2 sorption kinetics, two different gases, Ar and H2, were used. MgH2, with and without additives (C60, TTIP (Titanium TetraIsoPropoxide) and Nb2O5) were milled under the two different gases. In most cases the milling gas had little to no effect on desorption kinetics, but a noticeable effect in the absorption uptake was observed - by up to 2 wt% - depending on the gas used. To understand the role of an organo-metallic oxide liquid additive on MgH2 sorption kinetics, a systematic survey was performed by milling up to 2 mol% of TTIP with MgH2 and the results compared to composite samples with Nb2O5 as the additive. TTIP was found to be equally as effective as Nb2O5 with superior hydrogen capacity, and, just as for Nb2O5, only a small amount of additive, 0.5 mol% of TTIP was found to be sufficient for kinetics enhancement. Interestingly, 0.5 mol% TTIP hand-mixed with the pre-milled MgH2 was also found to be effective for desorption, but not for the absorption kinetics. To further investigate the effect of organo-metallic liquid oxides, particularly transition metal oxides, on the enhancement of the sorption kinetics of MgH2, a range of liquid oxides (Ti-based and V-based oxides) were milled with MgH2 and compared to powder oxides. Ti-based oxides were found to have superior desorption enhancement, with the liquids performing better than the powders. The V-based oxides (all liquids) showed faster absorption and higher uptake when compared to Ti-based oxides. The Ti-chloride based organo-metallic additive was investigated to compare a non-oxide transition metal additive to the oxide additives. It was found that a small amount of 1 mol% of additive milled for short time (1 h) had the best desorption of all the additives investigated in this work - but with quite poor absorption. Overall, this project established that the use of transition metal oxides as additives has a great impact on improving the sorption kinetics of MgH2. The TTIP additive produced results at least as good as the benchmark additive Nb2O5, but with the significant advantage of being able to be mixed with MgH2 without ball-milling. The Ti and V based oxides additives were also shown to be effective, Ti-based achieving better desorption enhancement, whereas V-based oxide samples had faster absorption and higher uptake. It was also determined the ball milling gas environment can have a significant effect on the sorption kinetics, but the effect depended on the additive. The difference in the effect of additives on desorption and absorption cycles confirms the need to study combinations of additives for optimal overall benefit.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environment and Sc
Science, Environment, Engineering and Technology
Full Text

Au cœur des réacteurs à eau pressurisée, les pastilles de combustible sont isolées du circuit primaire par des gaines en alliages de zirconium. En conditions nominales de fonctionnement, l’interaction entre ces gaines et le milieu primaire entraîne la formation d’un oxyde et l’absorption d’hydrogène par l’alliage. La désorption de l’hydrogène lors du transport de combustible usé et le relâchement du tritium issu de la réaction de fission au sein des pastilles de combustible en réacteur sont des problématiques importantes pour la sûreté. Il est impératif d’estimer la quantité de tritium susceptible d’être relâchée des assemblages dans le milieu primaire ainsi que les quantités d’hydrogène désorbé sous vide ou gaz neutre pendant le transport. Au-delà de cet aspect quantitatif, comprendre le mécanisme de perméation de l’hydrogène et de ses isotopes dans les gaines en alliage de zirconium est nécessaire si l’on veut maîtriser les rejets et émissions de ces produits et in fine la sûreté. Le processus de perméation du tritium à travers une gaine oxydée peut se décomposer en 9 étapes : 1. Adsorption de tritium à la surface de l’oxyde formé sur la face interne ;2. Passage des sites de surface aux sites de subsurface en tant qu’espèce absorbée ;3. Diffusion de tritium dans l’oxyde jusqu’à l’interface oxyde/métal ;4. Intégration de tritium dans le métal ;5. Diffusion de tritium dans le métal ;6. Intégration de tritium dans l’oxyde ;7. Diffusion de tritium dans l’oxyde jusqu’à la subsurface ;8. Passage des sites de subsurface aux sites de surface en tant qu’espèce adsorbée ;9. Recombinaison et désorption.Les objectifs de l’étude sont de déterminer l’étape cinétiquement limitante du processus de perméation de l’hydrogène dans les alliages Zircaloy-4 et M5Framatome, de quantifier les constantes cinétiques associées et de développer un modèle numérique pouvant prédire les flux de désorption de l’hydrogène. De par la complexité du processus de perméation du tritium à travers une gaine de combustible oxydé, un système simplifié sans couche d’oxyde a initialement été étudié. Le processus de désorption de l’hydrogène a été investigué par thermodésorption en rampe de température ainsi qu’en isotherme, et modélisé par éléments finis avec le code Cast3M. Les constantes cinétiques ont été évaluées et optimisées en couplant le modèle Cast3M et l’outil d’optimisation de la plateforme URANIE. Le flux de désorption s’est avéré être proportionnel au carré de la concentration en hydrogène avec une constante de désorption dont l’énergie d’activation est égale à 290 ± 10 kJ/mol. Pour le M5Framatome, les conclusions et résultats sont quasi-identiques au cas précédent, à ceci près que la désorption de l’hydrogène piégé par les précipités riches en niobium lors de la fabrication semble être assujettie à leur dissolution. Le développement d’un banc de perméation de deutérium gazeux fonctionnant entre 623 et 773 K a permis de mettre en évidence que la cinétique du processus de perméation est également limitée par l’étape de recombinaison de surface pour le Zircaloy-4. Ces essais de perméation ont révélé le rôle important de l’état de surface, puisque l’application par le dispositif d’une contrainte et d’une déformation induit une augmentation du flux de désorption. Des essais d’oxydation ont ensuite été effectués sous diverses atmosphères. Lors d’essai de désorption en rampe de température, la dissolution de l’oxyde dans le métal semble piloter la cinétique de désorption de l’hydrogène. Le développement de modèles numériques et analytiques a permis de démontrer dans le cas d’une dissolution négligeable de la zircone, une cinétique de désorption contrôlée par un régime mixte de diffusion de l’hydrogène dans l’oxyde et de recombinaison surfacique et de quantifier la constante de désorption et le coefficient de diffusion dans la zircone.A partir des résultats de la thèse, une estimation de la quantité de tritium relâché sous vide a pu être établie
At the heart of Pressurized Water Reactors, the uranium oxide fuel leads isolated from the primary circuit by zirconium alloys cladding. Under normal operating conditions, the interaction between these claddings and the primary water results in the formation of an oxide scale and the hydrogen absorption in the alloy. During operation in a reactor and during the transport of used nuclear fuels, the desorption of this hydrogen and the tritium resulting from the ternary fission from the fuel rods is a safety concern. It is imperative to estimate the amount of tritium prone to be released from the fuel assemblies into the primary water and the quantities of hydrogen desorbed under vacuum or neutral gas for the transport issue. Beyond this quantitative aspect, understanding the permeation mechanism of hydrogen and its isotopes in zirconium alloy claddings is necessary if we want to control releases and more generally safety. The tritium permeation through the oxidized fuel cladding can be decomposed into 9 steps: 1. Tritium adsorption on the oxide formed on the inner face; 2. Passing from surface sites to subsurface sites as absorbed species; 3. Tritium diffusion through the oxide towards the oxide/metal interface; 4. Integration into the metal; 5.Tritium diffusion through the metal; 6. Integration into the oxide lattice; 7. Tritium diffusion through the oxide towards the subsurface; 8. Passing from subsurface sites to surface sites as adsorbed species; 9. Recombination and desorption.This study is aimed at identifying, among these 9 steps, the kinetically limiting step of the hydrogen permeation process in Zircaloy-4 and M5Framatome alloys, quantifying the associated kinetic constants and developing a numerical model that can predict hydrogen desorption fluxes. Due to the complexity of the tritium permeation process through an oxidized fuel cladding, a simplified system without an oxide layer was initially studied. A study on the hydrogen desorption process was carried out by thermodesorption in temperature ramp and in isotherm, in order to model by finite elements with the Cast3M tool the desorption kinetics and to quantify the associated kinetic constant by coupling with the URANIE optimization tool. The desorption flux was found to be proportional to the square of the hydrogen concentration with a desorption constant whose activation energy is equal to 290 ± 10 kJ/mol. A similar study on M5Framatome revealed during a temperature ramp that hydrogen desorption from niobium-rich precipitates appears to be controlled by their dissolution. The development of a deuterium permeation device operating between 623 and 773 K has demonstrated that the rate-limiting step of the hydrogen permeation is the surface recombination for Zircaloy-4. These permeation experiments have highlighted the important role of surface state, because the application by the device of stress and strain induces a desorption flux increase. Oxidation tests were then carried out under various atmospheres. During a temperature ramp desorption experiment, the oxide dissolution into the metal appears to control the kinetics of hydrogen desorption. The development of numerical and analytical models made it possible to demonstrate in the case of a negligible zirconia dissolution, a desorption kinetics limited by a mixed regime of hydrogen diffusion through the oxide and surface recombination and to quantify the desorption constant and diffusion coefficient in zirconia. From the thesis results, an estimate of the tritium released quantity under vacuum was established

Le premier objectif dans cette thèse est d'étudier le phénomène de diffusion radiale dans un polymère élastomérique (EVA) de forme sphérique en tenant compte du changement de dimension : gonflement durant l'étape d'absorption et rétrécissement durant l'étape de désorption, modélisation et expérimentation. Le second objectif concerne l'étude des différents paramètres qui influent sur les cinétiques de transfert et les profils de concentration dans différents cas. Plusieurs variables sans dimensions sont considérées : l'expansion volumique, l'expansion linéaire, la diffusivité, le coefficient de transfert convectif et le rayon de la sphère

The objective of this thesis was to investigate the impact of pH on the adsorption equilibria, adsorption kinetics, desorption equilibria and desorption kinetics. A study was conducted by using 2-nitrophenol (2NP) and phenol as organic pollutants and F-400 and WV-B carbons as adsorbents. The batch adsorption isotherms study showed that at pHs less than pK$\rm\sb{a}$ (undissociated form of compounds), 2NP and phenol adsorption was markedly higher than at pHs greater than pK$\rm\sb{a}$ (dissociated form of compounds). Both carbons were similarly impacted by pH in the adsorption process and they had almost the same adsorption capacity in adsorbing phenol while F-400 showed more adsorption capacity in adsorbing 2NP. Adsorption-desorption experiments showed that the adsorption of 2NP by F-400 carbon is fully reversible. The presence of 1% NaCl solution did not affect the extent of reversibility. Accordingly, experiments showed both carbons were similarly impacted by pH in the desorption process. For both compounds, the extent of desorption was much greater for the pHs greater than the pK$\rm\sb{a},$ i.e. when the adsorbate is in its dissociated form. Much greater desorption at high pHs suggests that in an electrochemical regeneration process there is a higher probability of regeneration through enhanced desorption at the cathode, because it has a high localized pH. The initial adsorption and desorption rates were significantly affected by pH. Adsorprion kinetics of 2NP onto both carbons were described by the homogeneous surface diffusion model and it was not necessary to utilize separate terms for slow and rapid adsorption mechanisms. Also, it was found that the surface diffusion coefficient, D$\rm\sb{s},$ within the HSSD model was essentially the same at all pHs. (Abstract shortened by UMI.)

Les enzymes lipolytiques sont solubles en phase aqueuse mais hydrolysent des substrats insolubles. Leurs activités lipolytiques dépendent donc fortement de l’organisation des substrats lipidiques présents sous forme de structures interfaciales telles que des émulsions, des micelles, des liposomes, ou des bicouches lipidiques. Les propriétés cinétiques et la spécificité de substrat de ces enzymes résultent de l’étape initiale d’adsorption à l’interface lipide-eau et des interactions entre le substrat et le site actif. Dans le cadre de ce travail de thèse, la technique des films monomoléculaires a été utilisée pour étudier en détail les étapes séquentielles d’adsorption, de catalyse et d’inhibition de l’enzyme à l’interface lipide-eau. Dans une première partie, nous avons réalisé la caractérisation physico-chimique de la lipase gastrique de chien (DGL), avec l’étude :  de son adsorption sur un film non substrat de dilauroylphosphatidylcholine ; ‚ de l’hydrolyse interfaciale de la 1,2-dicaprine dans des films mixtes en présence d’Orlistat. Concernant l’étape de catalyse, nous avons étudié l’effet du propeptide sur la spécificité de substrat et l’activité interfaciale de la phospholipase A2 sécrétée de groupe X de souris. Enfin, dans une troisième partie, nous avons comparé les propriétés interfaciales de la lipase YLLIP2 de la levure Yarrowia lipolytica qui serait un bon candidat pour l’enzymothérapie de substitution chez les patients atteints d’insuffisance pancréatique exocrine (IPE), la lipase pancréatique humaine et la DGL. Nos résultats ont confirmé le rôle d’YLLIP2 en tant qu’excellent « substitut » non seulement de la HPL en cas d’IPE, mais aussi de la DGL
Lipolytic enzymes are water-soluble whereas their substrates are insoluble in water. Their lipolytic activities depend strongly on the organization of the lipid substrates present in interfacial structures such as oil-in-water emulsions, micelles, liposomes, and membrane bilayers. The kinetic properties and substrate specificity of these enzymes result from both their adsorption at the lipid-water interface, and the interactions occurring between the substrate and the active site. In this thesis work, the monomolecular film technique was used to study in details the sequential steps of adsorption, catalysis and inhibition of model enzymes at the lipid-water interface. In a first part, we performed the physico-chemical characterization of the dog gastric lipase (DGL), by studying:  its adsorption onto a dilauroylphosphatidylcholine non-substrate film; ‚ its interfacial hydrolysis of 1,2-dicaprin in mixed films with various amounts of Orlistat. Regarding the catalysis step, we studied the effect of the propeptide on the substrate specificity and interfacial activity of the murine group X secreted phospholipase A2. A model of this enzyme with its propeptide was built from the available 3D structure of the corresponding mature human enzyme. Finally, in the third part, we compared the interfacial kinetic properties of YLLIP2 lipase of the yeast Yarrowia lipolytica which has been identified as a good candidate for enzyme replacement therapy for patients with exocrine pancreatic insufficiency (EPI), human pancreatic lipase and DGL. Our results confirmed the role of YLLIP2 as an excellent "substitute" not only for HPL in case of PEI, but also for the DGL at acidic pH values

Thermochemical heat storage (TCS) is a thermal energy storage (TES) technology used to store thermal energy for later use. TCS can provide heating or cooling services from intermittently available thermal energy, often low grade waste heat. The system studied here stores and releases the energy in the form of chemical energy by utilizing reversible chemical reactions. TCS has potential to reduce greenhouse gas emissions, increase infrastructure system efficiency, lower society-wide energy system costs and by that contribute to sustainable development. This thesis is part of a joint TCS research project named Neutrons for Heat Storage (NHS), involving three research institutes. The project is funded by Nordforsk and KTH Royal Institute of Technology. KTH´s objective in the NHS project is to design, build and operate a bench-scale TCS system using strontium chloride (SrCl2) and ammonia (NH3) as a solid-gas reaction system for low-temperature heat storage (40-80 ℃). Here, absorption of NH3 into SrCl2⋅NH3 (monoammine) to form SrCl2⋅8NH3 (octaammine) is used for heat release, and desorption (of NH3 from SrCl2⋅8NH3 to form SrCl2⋅NH3) for heat storage. Prior to this thesis project, this TCS system, as well as its reactor+heat exchanger (R-HEX) units, were numerically designed at KTH, and the R-HEX units were manufactured. This system is now being built at the laboratory of Applied Thermodynamics and Refrigeration division at the Department of Energy Technology, KTH. The initial system is comprised of a shared storage tank, expansion valve, ammonia meter and an R-HEX (absorption path); and an R-HEX, ammonia meter, gas cooler, compressor, condenser, and the storage tank (desorption path), to accommodate absorption, desorption, and NH3 storage. This thesis was originally planned to include commissioning, operation and experimental data acquisition, and performance evaluation of this system. However, due to various delays and shortcomings discovered at the beginning of the project, its objectives were then redefined to review the system and its components and propose necessary design adaptations of the initially designed (and partially built) system. This thesis project was partly a joint project, where Harish Seetharaman performed various tasks in the overarching NHS project as part of his own thesis project, performed alongside the work described in this report. For various information and results, referring to Harish´s report therefore will be necessary. A literature review of the research into SrCl2-NH3 systems was conducted, with emphasis on performance evaluation, kinetics, and reaction paths. TES performance evaluation is discussed concerning the TCS key performance indicators, with the 2018 IEA's Annex 30 as a guideline and 2013 IRENA´s E17 technology brief as a comparative reference. Much progress and refinement has been made in the 5-year span between the publications of these documents, but some adaptations and interpretations still need to be made to the Annex 30 approach for a good approach to a TCS system of similar nature as the one studied in this report. Review of the latest research on the kinetics and reaction path of the SrCl2-NH3 reaction pair revealed that the 100-year-old single-line-and-path reaction expression is an oversimplification of the actual chemistry. The reaction path seems to be dependent on the kinetics of the reaction, and varies with heating rate, temperature, and pressure. Various literature was found and compared, which show that the reaction enthalpies and entropies are not settled science. This demonstrates the necessity for further research into the SrCl2-NH3 reaction pair before application-scale product design and commercialization can take place. A comprehensive equipment and system review was conducted, whereby multiple issues were found and addressed, that if gone unnoticed, would have caused difficult setbacks for the project.  Consequently, the previous purchased ammonia flow meters and ammonia compressor, were exchanged for new and better suiting equipment. The original ammonia flow meters were undersized due to miscalculations of converting flow units of NLPH (Normal Liters Per Hour) to the project units of g/s, while wrongly using the density of compressed ammonia to convert to g/s, instead of it at the defined normal conditions. Furthermore, these flow meters were of the wrong type, as they had no digital output for data acquisition. The original compressor was also severely undersized, only capable of evacuating 7-14% of the expected maximum desorption flow. This was due to a similar miscalculation during conversion of NLMP (Normal Liters Per Minute) to g/s, as well as an unrequested compressor stroke reduction. New solutions and additional equipment were then required to accommodate the operational limitations discovered in the final chosen equipment and system configuration. These include limiting the compressor inlet pressure to a maximum of 1.1 bar(a); avoiding risk of NH3 condensation at them inlets of the new mass flow meters and compressor; and maintaining the flow meter and compressor inlet temperatures below 40 °C. The pressure limitations required considerable design adaptations. Firstly, an ammonia by-pass is introduced to keep feeding ammonia into the compressor during low desorption flows. The inlet pressure limitation necessitated active pressure management in the form of pressure reduction valves, which were thus introduced. Secondly, the condensation regulation and temperature management required a new approach, as the cooling and condensation temperatures in the original design were too low, causing risks of far too low temperature and pressure in the desorption path, as well as counter-acting simultaneous heating and cooling between the condenser and the storage tank heating sleeve. As a solution, a shunt pump is proposed, where constant cooling water temperature provides condensation on a tight temperature range using an infinite cold wall approach. Along with reviewing the equipment and the system design, new procedures concerning investigating and confirming homogeneous heat transfer properties of the reactors are proposed. Furthermore, improvements are suggested concerning the commissioning of the experimental rig, that include equipment testing with N2-gas and stepwise changes in temperature in sequential cycles to gain a good understanding of the likely behaviors of the system before it is run at the extremes of the operating range. In conclusion, a new and improved process flow diagram, showing all these adaptations, additions, and changes from the original diagram is presented herein as the final key contribution to the overarching NHS-project. This is complemented with an instruction manual, to allow the next researchers a smooth continuation, in terms of the system build, and later commissioning and operation. Finally, some suitable next steps in the project are suggested. These include a conceptualization of descriptive functions for the performance and behavior of the specific system and reactors. These functions are proposed with temperature and pressure as independent variables, as these are two main variables influencing the kinetics of the reaction in the given system. As no experimental data exists yet, the form of the proposed functions is generic. Furthermore, a suggestion is made for a future adaptation for achieving the phase change from NH3(g) to NH3(l) (which is the storage form of ammonia in the system) by deep cooling at the desorption pressure, resulting in only a liquid pump being required to raise the pressure of the NH3(l) in the storage tank.
Termokemisk energilagring (TCS) är en teknik inom termisk energilagring (TES) som används för att lagra termisk energi för senare bruk. TCS kan tillhandahålla värme och kyla från periodvis tillgänglig termisk energi, ofta lågtemperatur spillvärme. Systemet lagrar energin som kemisk energi genom att använda reversibla kemiska reaktioner och massaseparation av reaktions-produkterna. TCS har potential att minska utsläppet av växthusgaser, öka effektiviteten av system i vår infrastruktur, minska energikostnader i samhället och därmed bidra till hållbar utveckling. Detta exjobbsprojekt är en del av ett gemensamt TCS-forskningsprojekt som heter Neutrons for Heat Storage (NHS), där tre forskningsinstitut deltar. Projektet är finansierat av Nordforsk och Kungliga Tekniska Högskolan. KTH:s mål med NHS-projektet är att projektera, bygga, samt driva ett TCSsystem i bänkskala med strontiumklorid (SrCl2) och ammoniak (NH3) som ett fast-gasreaktionssystem för lågtemperaturvärmelagring (40-80 ℃). Här används absorption av NH3 till SrCl2⋅NH3 (monoammin) för att bilda SrCl2⋅8NH3 (oktaammin) för värmeurladdning och desorption (av NH3 från SrCl2⋅NH3 till SrCl2⋅NH3) för värmelagring. Innan detta exjobbsprojekt började hade detta TCS-system, samt systemets reaktor+värmeväxlare (R-HEX) enheter varit numeriskt projekterad vid KTH, och R-HEX-enheterna hade redan tillverkats. Detta system byggs nu på laboratoriet för Avdelningen för tillämpad termodynamik och kylning vid Institutionen för Energiteknik, KTH. Det initiala systemet består av en gemensam lagringstank, expansionsventil, ammoniakmätare, och en R-HEX (systemets absorptionssida) och en R-HEX, ammoniakmätare, gaskylare, kompressor, en kondensor, och en gemensamma lagringstanken (desorptionssidan), for att rymma absorption, desorption (samtidigt) och NH3-lagring. Exjobbsprojektet var ursprungligen planerat att inkludera driftsättning, drift och experimentdatainsamling samt utvärdering av systemet. På grund av olika förseningar och brister som upptäcktes i projektet, omdefinierades projektets mål och består nu av att granska systemet och, samt att föreslå nödvändiga designanpassningar av det ursprungligen konstruerade systemet och dess komponenter. Projektet var delvis ett gemensamt arbete, där Harish Seetharaman utförde olika uppgifter i det övergripande NHS projektet som en del av sitt eget exjobbssprojekt. För olika uppgifter och resultat kommer det därför att vara nödvändigt att hänvisa till Harishs rapport. Litteraturstudié av forskningen kring SrCl2-NH3 system genomfördes, med betoning på prestandautvärdering, kinetik och reaktionsvägar. Prestandautvärdering av TES system diskuteras angående TCS-nyckelindikatorer, med 2018 års IEA:s Annex 30 som riktlinje och IRENA:s E17 Teknologi-sammandrag från 2013 som en referens. Många framsteg och förbättringar har gjorts under femårsperioden mellan dessa publikationer, men vissa anpassningar och tolkningar måste fortfarande härledas till metoderna i Annex 30 för att få ett bra förhållningssätt till ett TCS-system av liknande karaktär som det som studeras i detta projekt. Granskning av den senaste forskningen avseende reaktionskinetik och reaktionsvägar för SrCl2-NH3 reaktionsparet visade att det hundraåriga enkellinje-och-reaktionsväg-formuleringen är en förenkling av den faktiska kemin. Reaktionsvägen verkar beroende av reaktionens kinetik och varierar med uppvärmnings-takten, temperaturen och även trycket. Olika litteratur jämfördes som visar att reaktionsentalpierna och entropierna inte är fastställd vetenskap. Detta visar behovet av ytterligare forskning avseende SrCl2-NH3 innan produktdesign och kommersialisering i applikations-skala kan utföras. En omfattande granskning av systemet och dess komponenter genomfördes, där flera problem hittades och åtgärdades. Om dessa problem hade gått obemärkt förbi skulle det ha orsakat svåra bakslag för projektet. Följaktligen byttes de tidigare köpta ammoniakflödesmätarna ut till nya och en ammoniakkompressor byttes ut mot en ny, för tillämpningen bättre anpassad. De ursprungliga ammoniak-flödesmätarna var underdimensionerade pga. felberäkningar i omvandling av flödesenheter för NLPH (normal liter per timme) till projektenheterna g/s. Samtidigt var densiteten av komprimerad ammoniak felaktigt använt för omvandling till g/s, istället för densiteten vid de definierade normala förhållandena; 1 bar (a) och 20 ° C. Dessutom var dessa flödesmätare av fel typ, eftersom de inte hade någon digital utgång för datainsamling. Den ursprungliga kompressorn var också kraftigt underdimensionerad, endast kapabel att evakuera 7-14% av det förväntade maximala desorptionsflödet. Detta berodde på en liknande felberäkning vid konvertering av NLPM (normal liter per minute) till g/s, samt en oönskad kompressorslagsminskning. Nya lösningar och ytterligare utrustning krävdes för att tillgodose de operativa begränsningar som upptäcktes i den slutgiltigt valda utrustningen och systemutformningen. Dessa inkluderar: begränsa kompressorns inloppstryck till maximalt 1,1 bar(a); undvika risk för NH3 kondens i de nya massflödesmätarna och kompressorn; samt bibehålla flödesmätarens och kompressorns inloppstemperaturer under 40 °C. Tryckbegränsningarna krävde omfattande projekteringsanpassningar. För det första införs en ammoniak-by-pass för att fortsätta mata ammoniak till kompressorn under låga desorptionsflöden. Inloppstrycksbegränsningen nödvändiggjorde aktiv tryckhantering i form av tryckreduceringsventiler. För det andra krävde kondensregleringen och temperaturhanteringen en ny strategi, eftersom kyl- och kondenseringstemperaturerna i den ursprungliga utformningen var för låga. Detta orsakade risker för alldeles för låg temperatur och tryck på desorptionssidan, samt samtidigt motverkande uppvärmning och kylning av kondensorn och förvaringstankens värmehylsa. Som en lösning föreslås en shunt där konstant kylvattentemperatur ger kondens i ett tätt temperaturintervall med en oändlig kallväggsinriktning. Tillsammans med granskning av utrustningen och systemutformningen föreslås nya tillvägagångssätt för undersökning och bekräftelse av reaktorers förmodade homogena värmeöverförings-egenskaper. Dessutom föreslås förbättringar av idrifttagningen av den experimentella riggen, som inkluderar utrustningstestning med N2-gas och stegvisa temperaturförändringar i sekventiella körningar för att få en god förståelse för systemets troliga beteenden innan det körs i ytterligheterna av systemts arbetsområde. Sammanfattningsvis presenteras ett nytt och förbättrat processflödesdiagram, som visar alla utförda anpassningar, tillägg och ändringar från det ursprungliga diagrammet, som är avhandlingsprojektets huvudbidrag till det övergripande NHS-projektet. Detta kompletteras med en bruksanvisning för att smidigt fasa in kommande forskare avseende systemets konstruktion, driftsättning, och drift. Slutligen föreslås några lämpliga kommande steg i projektet. Dessa inkluderar en konceptualisering av beskrivande funktioner för prestanda och beteende av det specifika systemet och reaktorer. Dessa funktioner föreslås med temperatur och tryck som oberoende variabler, eftersom dessa är två huvudvariabler som påverkar reaktionens kinetik. Eftersom inga experimentella data ännu finns, är formen för de föreslagna funktionerna generisk. Vidare ges förslag om framtida anpassning för att uppnå fasändringen från NH3(g) till NH3(v) (som är lagringsformen för NH3 i systemet) genom djup nedkylning vid desorptionstrycket, vilket resulterar i att endast en vätskepump krävs för att höja trycket för NH3(v) i lagringstanken.

Manganese oxide catalysts supported on Al2O3, ZrO2, TiO2 and SiO2 supports were used to study the effect of support on ozone decomposition kinetics. X-ray diffraction (XRD), in-situ laser Raman spectroscopy, temperature programmed oxygen desorption, surface area measurements, extended and near edge x-ray absorption fine structure (EXAFS and NEXAFS) showed that the manganese oxide was highly dispersed on the surface of the supports. EXAFS spectra suggest that the manganese active centers on all of the surfaces were surrounded by five oxygen atoms. These metal centers were of a mononuclear type for the Al2O3 supported catalyst and multinuclear for the other supports. NEXAFS spectra for the catalysts showed a chemical shift to lower energy and an intensity change in the L-edge features which followed the trend Al2O3 > ZrO2 > TiO2 > SiO2. The trends provided insights into the positive role of available empty electronic states required in the reduction step of a redox reaction. The catalysts were tested for their ozone decomposition reactivity and reaction rates had a fractional order dependency (n < 1) with ozone partial pressure. The apparent activation energies for the reaction was low (3-15 kJ/mol). The support influenced the desorption step (a reduction step) and this effect manifested itself in the pre-exponential factor of the rate constant for desorption. Trends for this pre-exponential factor correlated with trends in NEXAFS features and reflected the ease of electron donation from the adsorbed species to the active center.
Ph. D.

Thesis (Ph.D.); Submitted to the University of California, Berkeley, Berkeley, California (US); 15 Dec 2004.
Published through the Information Bridge: DOE Scientific and Technical Information. "LBNL--56814" Westerberg, Staffan Per Gustav. USDOE Director. Office of Science. Office of Basic Energy Sciences (US) 12/15/2004. Report is also available in paper and microfiche from NTIS.

Room-temperature chemisorption of hexacyclic aromatic hydrocarbons on the 2x1, sputtered, oxidized and H-terminated Si(100) surfaces, as well as those upon post treatments of hydrogenation, oxidization and electron irradiation have been investigated by using thermal desorption spectrometry (TDS), Auger electron spectroscopy (AES) and low energy electron diffraction (LEED). This work focuses on the effects of the functional groups (phenyl, methyl, vinyl, heteroatom, and H atom) in the chemisorbed aromatic hydrocarbons (benzene, toluene, xylene isomers, styrene and pyridine) on organic functionalization of the Si(100) surface, particularly on such surface processes as cycloaddition, dative adsorption, hydrogen abstraction, desorption, dissociation, diffusion, and condensation polymerization. Unlike the earlier notion that hydrogen evolution in the hydrocarbon/Si(100) systems is the result of hydrocarbon dissociation (into smaller hydrocarbon fragments and H atoms) on the surface, condensation polymerization of the adsorbed aromatic hydrocarbons is proposed in the present work, in order to explain the higher-temperature hydrogen evolution feature in the toluene/Si(100) system. This hypothesis is supported by our TDS results for other hydrocarbon adsorbates, especially in the pyridine/Si(100) system where electron-induced condensation polymerization has been observed at room temperature. The improved techniques in the TDS experiments developed in the present work have enabled us to observe condensation polymerization and the effect of H on the surface processes (via surface reconstruction) on Si(100) for the first time. New analysis methods have also been developed to determine the adsorption coverage from the AES data, and this work has not only improved the accuracy of the elemental-coverage evaluation, but also provided a means to estimate the rate and the order of chemisorption. By using the density functional theory with the Gaussian 98 program, the adsorption geometries and the corresponding adsorption energies of various adsorption phases have been calculated. These computational results have provided useful insights into the chemisorption structures on the Si(100) surface. The present work also presents the development of three kinetics models for hydrogen evolution in the aforementioned aromatic-hydrocarbon systems on Si(100). Based on a modified collision theory with consideration of diffusion, these theoretical models have proven to be quite successful in simulating the observed TDS profiles and in estimating the kinetic parameters for the analysis of condensation polymerization in 2-dimensional diffusion systems. The present work illustrates that TDS experiments can be used effectively with quantum computation and theoretical kinetics modelling to elucidate the intricate nature of organosilicon surface chemistry.

Notre objectif était d'étudier la rétention d'herbicides de la famille des phenylurées sur des adsorbants minéraux et dans le sol. Les molécules retenues sont le chloroxuron, le chlortoluron, le metobromuron, l'isoproturon et le difenoxuron. Les adsorbants utilises sont la celite, le florisil, l'alumine, le carbonate et le sulfate de calcium. Les sols étudiés sont un sol limoneux-argileux et un sol limoneux-sableux. Nous poursuivons le double but analytique et environnemental d'améliorer les étapes de purification par chromatographie d'adsorption d'extraits en vue de l'analyse de résidus, et de prévoir leur dispersion dans le sol, leur diffusion en direction des nappes et leur exposition à la dégradation microbienne. La méthode suivie passe essentiellement par le tracé de cinétiques et d'isothermes d'adsorption-désorption, et de courbes de mobilité en présence d'eau ; les variations de concentrations des urées dans la phase liquide ont été mesurées par HPLC-UV. Les isothermes ont été modélisées dans les formalismes de Freundlich, Langmuir et Temkin. Les influences sur la mobilité des urées dans des colonnes de sol, de la concentration saline de la phase aqueuse (cacl#2) et de formulants tensio-actifs (polyphénols ethoxyles) ont été évaluées par la même méthodologie. Ces études ont été complétées par l'examen de spectres IR pour caractériser les groupes structuraux de ces molécules engagés dans leur liaison avec les adsorbants. Nous mettons en évidence le rôle privilégié des groupes phenoxy dans l'adsorption sur le florisil ; des effets hydrophobes dus à la substitution des noyaux aromatiques par le chlore pourraient être à l'origine de la rétention du chloroxuron et du chlortoluron sur tous les adsorbants, et la combinaison d'effets stériques dus à la taille du brome, d'effets électroniques et dipolaires dus au groupe methoxy sur la fonction urée pourraient intervenir dans la faible rétention du metobromuron sur tous les adsorbants. Enfin parmi les formulants étudiés, seul le soprophor FL à une concentration supérieure à 0,05 g/l a un effet accélérateur marqué sur la mobilité de l'isoproturon en colonnes de sol.

La pyrolyse est l’étape primaire de toutes les transformations thermochimiques des solides organiques et, par conséquent, la caractérisation fine des produits de pyrolyse et la compréhension des mécanismes mis en jeu sont indispensables. Dans ce contexte, cette thèse vise à étudier la pyrolyse du PET en utilisant différents appareils analytiques. Dans une première partie, des expériences de pyrolyse lente (5 °C/min) ont été réalisées dans un réacteur tubulaire pour quatre températures finales allant de 410 °C à 480 °C. Contrairement à d’autres études issues de la littérature, les produits légers mais aussi les produits lourds ont été identifiés. Les gaz non condensables ont été analysés en ligne à l’aide d’un micro-Chromatographe en Phase Gazeuse (µ-GC), ce qui a permis d’établir les profils temporels des gaz. Les composés carbonylés ont été piégés, dérivatisés et analysés par Chromatographie Liquide Haute Performance (HPLC). Les condensats ont été caractérisés par Spectroscopie Infrarouge à Transformée de Fourier (IRTF) et par Spectrométrie de Masse à Résonance Cyclotronique Ionique (FT-ICR MS) en utilisant une Ionisation par Electronébuliseur (ESI). Certaines molécules de ces condensats ont été quantifiées par Chromatographie Gazeuse/ Spectrométrie de Masse et Détection par Ionisation de Flamme (GC/MS-FID). La caractérisation du résidu solide a été réalisée par FT-ICR MS couplé avec une Ionisation Désorption Laser (LDI). Dans une seconde partie, la cinétique de formation des composés volatiles au cours de la pyrolyse de PET a été étudiée en couplant la Thermogravimétrie avec des méthodes d’ionisation douces (SPI : Single Photo Ionisation ; REMPI : Resonance Enhanced Multiple Photon Ionization ; APCI : Atmospheric Pressure Chemical Ionization). La combinaison de ces différentes techniques a permis de caractériser de façon détaillée les produits et par conséquent d’identifier les voies réactionnelles de la dégradation de PET, qui sont majoritairement des voies moléculaires
Pyrolysis is the primary step in all thermochemical transformations of solids and therefore the detailed characterization of the pyrolysis products and the understanding of the involved mechanisms are mandatory. In this context, this PhD thesis aims to study the slow pyrolysis of PET using different analytical devices. In the first part, slow pyrolysis experiments (5 °C/min) were carried out in a tubular reactor for four final temperatures ranging from 410 °C to 480 °C. Unlike other studies from the literature, light products as well as heavy products were identified. The non-condensable gas was analyzed online using Gas micro-Chromatography (μ-GC), which allows acquiring the gas temporal profiles. The carbonyl compounds were trapped, derivatized and analyzed by High Performance - Liquid Chromatography (HPLC). The waxy products were characterized by Fourier Transform Infrared Spectroscopy (FTIR) and by Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS) using an Electrospray Ionization (ESI). Some waxy molecules were quantified by Gas Chromatography / Mass Spectrometry and Flame Ionization Detection (GC/MS-FID). The characterization of the solid residue was performed by FT-ICR MS coupled with Laser Desorption ionization (LDI). In the second part, the formation kinetics of volatile compounds during PET pyrolysis was studied using a Thermogravimetric Analyzer coupled with mild ionization methods (SPI: Single Photon Ionization; REMPI: Resonance Enhanced Multiple Photon Ionization; APCI: Atmospheric Pressure Chemical Ionization). The combination of these different techniques allowed a detailed characterization of the products and consequently the identification of reaction pathways of PET degradation, which are mostly molecular pathways