Dissertations / Theses on the topic 'Cellulosic fuels'

Thesis (M. S.)--Chemical Engineering, Georgia Institute of Technology, 2010.
Committee Chair: Banerjee Sujit; Committee Member: Deng Yulin; Committee Member: Haynes Danny. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (M. S.)--Mechanical Engineering, Georgia Institute of Technology, 2008.
Committee Chair: Dr. Sam Shelton; Committee Co-Chair: Dr. John Muzzy; Committee Member: Dr. Sheldon Jeter. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Commercial activated carbon and newly polymer-derived carbon were utilized to selectively remove the model fermentation inhibitor, furfural, from water solution during bio-ethanol production. Morphology, pore structure and surface chemistry of the sorbents were characterized. The oxygen groups on the carbon surface were believed to have contributed to the decrease on the selectivity of activated carbon between furfural and sugars (Sugars are the valuable source of bio-ethanol production and should not be separated from solution). Oxidization of activated carbon by nitric acid generated more information which supports the above assumption. Different adsorption isotherm models and kinetic models were studied to fit commercial activated carbon and polymer-derived carbon individually. Bacterial cell growth, sugar consumption, and ethanol yield during the fermentation were investigated after inhibitors were selectively removed from the broth. The fermentation time was reduced from one week to one day after inhibitor removal. Different methods of sorbent regeneration were investigated, including thermal regeneration, pH adjustment and organic solvent stripping. Low ethanol-containing water solution appears to be the most cost-effective way to regenerate the spent sorbent in the industrial application. A sorption/desorption cycle was designed and the sorbents were regenerated in a fixed-bed column system using ethanol-containing liquid from fermentation. The results were stable after running 20 times of sorption/desorption cycle.

Made available in DSpace on 2014-10-09T12:55:37Z (GMT). No. of bitstreams: 0
Made available in DSpace on 2014-10-09T14:05:55Z (GMT). No. of bitstreams: 0
Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

The major objective of this thesis was to investigate and improve a direct microbial fermentation process, using the thermophilic anaerobic bacteria Clostridium thermocellum and Clostridium thermohvdrosulfuricum for the production of fuel ethanol in economically significant concentrations, from cellulose and hemicellulose contained in renewable biomass. Two model substrates representative of readily available lignocellulosic materials were selected for this study. These were wheat straw, which is the largest single biomass resource available in Australia, and waste paper, which is a major component of municipal solid wastes. At the onset of the research, proximate analyses of the composition of the two substrates were carried out to assess the potential yield of ethanol. Based on the total carbohydrate (hexose as well as pentose sugars) content of the materials, a theoretical potential yield of ethanol over 500 litres per dry tonne of biomass was estimated for both substrates. The feasibility of effecting biomass conversion to ethanol by direct fermentation of the substrates was then examined. Fermentation characteristics of 9 strains of the potent cellulolytic anaerobe, C. thermocelIum and 5 strains of the saccharolytic ethanoloaen. C. thermohvdrosulfuricum. were investigated on a range of sugars. Cellulose hydrolysis and fermentation by C. thermocellum strains were also studied with alpha-cellulose and the two model substrates. Variations in growth characteristics, extent and rates of substrate utilization, as well as in the stoichiometry of product formation were noted, not only between the two species, but also among the different strains. A stable coculture comprising the most potent strains of the two species could be established, and this culture efficiently fermented crystalline and native cellulosic substrates to produce ethanol at substantially higher yields than could be achieved with cultures of C. thermocellum alone. At 1% (w/v) concentration of wheat straw and newspaper, ethanol yield amounting to 70% of theoretical was obtained with the coculture, compared to 25% of theoretical yield exhibited bv C. thermocellum. The metabolic basis for the enhanced fermentation effectiveness of the coculture system has been discussed. The feasibility of attaining higher ethanol concentrations in the fermentations was investigated next by employing increased substrate concentrations in batch as well as fed-batch mode of operation. The bioconversion efficiency was observed to systematically decrease with increased substrate concentration, and a limiting ethanol concentration for the cocultures appeared to be around 10-12g/l. At the highest substrate loadings used, the yield of ethanol was only 25% of theoretical. Lignaceous components of biomass and inhibition of bacterial growth by products of fermentation, as well as the physical nature of the substrates were determined to be the major factors limiting the effectiveness of the fermentation. The above observations led to further studies involving a comparative evaluation of range of substrate delignification treatments and a systematic program of strain improvement with respect to increased ethanol tolerance and end product selectivity. A selective solvent extraction procedure using an alkaline ethanol solvent yielded the best delignification performance of all the alternatives examined. Up to 70% lignin removal with a loss of less than 10% of the available carbohydrates was obtained with this method. Coculture fermentation of wheatstraw and newspaper pretreated by this procedure showed a four-fold increase in the maximum volumetric degradation rate as well as nearly 100% increase in the overall extent of substrate utilization, compared to untreated material. Studies aimed at improving the fermentation efficacy were undertaken on both species of organisms. Improved ethanol tolerance was achieved through progressive adaptation of parent strains to higher ethanol concentrations in the growth medium. The strains isolated in this work however tended to have a significantly higher yield of the acid products concomitant with their enhanced ethanol productivity. A separate program of mutation and selective isolation of low acid producing cultures eventually resulted in strains which in coculture, fed batch fermentations were able to produce ethanol at concentrations of up to 30g/l at a net ethanol yield exceeding 60% of theoretical, when grown on pretreated wheat straw and newspaper. A relatively reduced yield of ethanol however, was noted on real biomass compared to similar fermentations using pure substrates. This coincided with increased production of acetate with the crude substrates. An analysis of fermentation kinetics for the various experiments revealed that the ethanol/acetate ratio for deregulated strains of C. thermocellum and C. thermohvdrosulfuricum was strongly dependent on the specific growth rate the organisms achieve during fermentation, which, in turn is determined by the substrate hydrolysis and/or consumption rates. The implications of this to future process improvement studies has been briefly discussed.

La demande d'énergie au cours des dernières années a augmenté et un grand pourcentage de l'énergie est dérivée des combustibles fossiles, mais l'utilisation de ces carburants a généré des émissions de CO2 et de la pollution environnementale. Pour ce problème, on a mené des recherches sur l'utilisation des énergies alternatives à partir de biomasse lignocellulosique pour produire des carburants qui réduisent les émissions de CO2. Le Canada est un pays avec une abondance de résidus lignocellulosiques qui sont une source pour la production de différents produits chimiques. La première partie de l’étude se concentre sur l’étude cinétique de la production du lévulinate de méthyle et de l’acide lévulinique à partir de la cellulose avec un catalyseur homogène (H2SO4). La deuxième partie porte sur la conversion de la cellulose en lévulinates (molécule plateforme) en utilisant un catalyseur homogène (H2SO4) et un catalyseur solide (Al2(SO4)3). La troisième partie se consacre sur l’étude de l’hydrolyse du lévulinate de méthyle en acide lévulinique en utilisant des catalyseurs à base de cuivre. Des techniques d’analyse tels que le SEM, XRD, TPX ont été utilisés pour étudier les catalyseurs supportés et comprendre leur effet sur la réaction. La quatrième partie du projet porte sur l’étude des résultats obtenus des différentes réactions réalisées pour la production du 2-butanol à partir de la biomasse lignocellulosique en passant par la production du lévulinate de méthyle et de l’acide lévulinique qui sont des molécules plateforme et potentiellement substitutes au biodiesel. Par la suite, l’acide lévulinique est décarboxylé en 2-butanone et le dernier est réduit en 2-butanol en utilisant des catalyseurs bifonctionnels (tels que le Ru / C et le Pt / C) en conditions douces. L’ensemble de ces travaux contribuent à la compréhension des réactions du nouveau procédé de production du butanol
In the last years, the energy demand has increased and a large pourcentage of this energy is obtained from fossil fuels, but the use of these fuels has generated CO2 emissions and environmental pollution. For this reason, this research was focused on the use of alternative energies from lignocellulosic biomass to produce renewal fuels decreasing CO2 gas emissions. Canada is a country with high quantities of lignocellulosic biomass which can represent a cheap source for the high value added molecules and fuels production. The first part of the study focuses on the kinetic study of the production of methyl levulinate and levulinic acid from cellulose with a homogeneous catalyst (H2SO4). The second part study the conversion of cellulose to levulinates (platform molecule) using a homogeneous catalyst and a heterogeneous catalyst (Al2(SO4)3). The third part is devoted to study the hydrolysis of methyl levulinate to levulinic acid using copper-based catalysts. Analytical techniques such as SEM, XRD, TPX were used to study the supported catalysts and understand their effect on the reaction. The fourth part of the project relates to the study of the production of 2-butanol from lignocellulosic biomass through the production of methyl levulinate and levulinic acid which are platform molecules and potentially substitutes for biodiesel. Thereafter, the levulinic acid is decarboxylated to 2-butanone and the latter is reduced to 2-butanol using bifunctional catalysts (such as Ru/C and Pt/C) under mild conditions. All of this work contributes to understanding the reactions of the new butanol production process

Energy production from fossil fuels results in significant carbon dioxide emission, which is a key contributor to global warming and the problems related to climate change. Biomass is recognized as an important part of any strategy to address the environmental issues related to fossil fuels usage for sustainable development. The carbohydrates in lignocellulosic biomass mainly exist as cellulose and hemicellulose. These materials must be broken down through hydrolysis for the production of desired biomass extracts (e.g. sugar products), which can then be converted into ethanol. Developing efficient hydrolysis processes is essential to producing biomass extracts of desired properties. Due to its unique physical and chemical properties, hot compressed water (HCW) may be utilized as both solvent and reactant simultaneously in various applications including hydrolysis. So far, there has been a lack of fundamental understanding of biomass and cellulose hydrolysis in HCW. The present study aims to characterize the formation of glucose oligomers in the primary liquid products, and to bring some new insights into the reaction mechanisms of cellulose hydrolysis in HCW.The specific objectives of this research include the development of a new sampling and analytical method to characterise the glucose oligomers in the liquid products, to investigate the formation of precipitate from fresh liquid products, to understand the primary reactions on the surface of reacting cellulose particle during hydrolysis in HCW at various temperatures, to study the significant differences in hydrolysis behavior of amorphous and crystalline portions within microcrystalline cellulose, to investigate the evolution of primary liquid products with conversion, and to study the effect of ball milling on the hydrolysis of microcrystalline cellulose in HCW. To accomplish these objectives, a semicontinuous reactor system was developed and set up to carry out the experiments of the hydrolysis of various cellulose samples in HCW. The liquid samples were characterised by a number of analytical instruments, including the introduction of a new technique to analyse the glucose oligomers in the liquid sample.First of all, this study shows the presence of a wide range of glucose oligomers with the degree of polymerizations (DPs) up to 30 and their derivatives in the fresh liquid products, which is produced from cellulose hydrolysis in HCW using a semicontinuous reactor system at 280 °C and 20 MPa, by a high performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD). None of those oligomers can be detected by a high performance liquid chromatography with evaporative light scattering detector (HPLC-ELSD) that however can detect glucose oligomers with DPs up to 6 after the liquid solutions are concentrated by 25 times via vacuum evaporation at 40 °C, during which a large amount of precipitate was formed. While quantitative analysis of the glucose oligomers with DPs > 5 cannot be done due to the lack of standards, that of the glucose oligomers from glucose (DP = 1) to cellopentaose (DP = 5) using both HPAEC-PAD and HPLC-ELSD are in good agreement, suggesting that these low- DP glucose oligomers do not contribute to the precipitate formation.Secondly, the study of a set of purposely-designed precipitation experiments indicates that the precipitation starts as the fresh liquid sample is collected and is fast during the initial 8 hours, levels off as the precipitation time increases further and completes after 120 hours (5 days). Based on a new approach developed for the quantification of glucose oligomers retention during the precipitation process, it is found that the contribution of glucose oligomers to precipitate formation increases with DP. The higher the DP is, the lower the solubility of the glucose oligomer is. The glucose oligomers from glucose to cellopentaose and their derivatives (DPs = 1- 5) contribute little to the precipitate formation, which explains why HPLC-ELSD can correctly analyze these glucose oligomers in the concentrated solutions prepared by vacuum evaporation. The glucose oligomers and their derivatives with DPs > 5, which are soluble in HCW but become supersaturated in the solutions under ambient conditions, are responsible for precipitate formation. Most (but not all) of the glucose oligomers and their derivatives with DPs > 16 contribute to the precipitate formation as tiny peaks of these glucose oligomers are still shown in the chromatograms, suggesting that these glucose oligomers have very low (but non-zero) solubilities in ambient water. The retentions of glucose oligomers and their derivatives increase substantially with the DP decreasing from 16 to 6, indicating that less of these lower-DP oligomers contribute to the precipitate formation. To avoid the effect of precipitation on oligomer analysis, the fresh liquid products must be analyzed immediately after sample collection.Thirdly, this study reports the experimental results on the primary liquid products from the hydrolysis of microcrystalline cellulose in HCW at 10 MPa and 230-270 °C using a semicontinuous reactor system under optimised reaction conditions. The primary liquid products contain glucose oligomers and their derivatives with a wide range of degrees of polymerization (DPs) from 1 to a maximal DP, which increases with temperature from 23 at 230 °C, to 25 at 250 °C then to 28 at 270 °C. Temperature also has a significant influence on the distribution of glucose oligomers in the primary liquid products. The results suggest that the hydrolysis reactions proceed on the surface of reacting cellulose particles via the cleavage of the accessible glycosidic bonds within the structure of microcrystalline cellulose in a manner with randomness. Thermal cleavage of glycosidic bonds seems also to occur on the accessible surface of the reacting cellulose particles in a similar manner. The randomness of these reactions seems to be temperature dependent and is likely related to the change in the accessibility of glycosidic bonds as results of the cleavage of hydrogen bonds in the structure of microcrystalline cellulose. The hydrolysis reactions seem also to be accompanied by other parallel reactions (e.g. cross-linking reactions), which may affect the primary liquid products as well, particularly at high temperatures. The post hydrolysis of primary liquid products has a high glucose yield of ~80% on a carbon basis, suggesting that combining HCW and enzymatic hydrolysis may be a promising technology for sugar recovery from lignocellulosic feedstocks.Fourthly, this study finds that the reactivity of microcrystalline cellulose exhibits a considerable reduction in the initial stage during hydrolysis in HCW, due to the presence of amorphous structure in microcrystalline cellulose. Further analysis of the liquid products obtained at various temperatures suggests that amorphous portion within microcrystalline cellulose contains some short glucose chain segments hinged with crystalline cellulose via weak bonds (e.g. hydrogen bonds). These short chain segments are reactive components responsible for the formation of C4-C13 in the primary liquid products during hydrolysis in HCW at temperatures as low as 100 °C. The minimal temperature for breaking the glycosidic bonds in those short chain segments to form glucose monomer from amorphous portion within microcrystalline cellulose is ~150 °C. However, the minimal temperature at which glucose monomer starts to be produced from the crystalline portion within microcrystalline cellulose is around 180 °C, apparently due to the limited accessibility of the glycosidic bonds in the crystalline portion to HCW as results of the strong intra- and inter-molecule hydrogen bonding networks. The differences of chain length and hydrogen bonding pattern between amorphous and crystalline cellulose also greatly affects the distribution of glucose oligomers in their liquid products during hydrolysis in HCW. Generally, amorphous cellulose produces more glucose mono- and oligomers at the same hydrolysis temperature, but the selectivity ratios of glucose oligomers in the primary liquid products from amorphous and crystalline portions do not show a monotonic trend with DP, at least partly resulting from the presence of shorter glucose chain segments in amorphous portion within the microcrystalline cellulose.Fifthly, this study demonstrates the dynamic evolution of the specific reactivity and primary liquid products with conversion during the hydrolysis of both amorphous and crystalline cellulose in HCW. The results suggest the dynamic changes in cellulose structure occur during conversion, and strongly depend on reaction temperature. Results from a set of purposely-designed two-step experiments further confirm at least two mechanisms which may be responsible for such structural changes. One is the selective consumption of the reactive components within the intrinsically heterogeneous cellulose at early conversions. This mechanism dominates during the hydrolysis of at low temperatures, e.g. 180-200 °C for amorphous cellulose and 230 °C for microcrystalline cellulose. The other is the combined effects of various parallel reactions during hydrolysis in HCW, including cleavage of hydrogen bonds, degradation reactions and cross-linking reactions. Enhanced hydrogen bond cleavage increases the production of glucose oligomers. However, parallel degradation reactions and cross-linking reactions decrease the selectivities of glucose oligomers. The effect of cross-linking increases significantly with temperature and becomes dominant at high temperature, leading to a structural condensation hence a reduction in the specific reactivity of cellulose and the selectivities of glucose oligomers in the primary liquid products.Sixthly, this study investigates the effect of ball milling as a pretreatment method on microcrystalline cellulose hydrolysis in HCW. Ball milling leads to a considerable reduction in cellulose particle size and crystallinity therefore a significant increase in the specific reactivity during hydrolysis in HCW. It is found that crystallinity is the dominant factor in determining the hydrolysis reactivity of cellulose in HCW while particle size only plays a minor role. Ball milling also significantly influences the distribution of glucose oligomers in the primary liquid products of hydrolysis. Ball milling increases the selectivities of glucose oligomers at low conversions. At high conversions, the reduction in chain length plays an important role in glucose oligomer formation since cellulose samples become more crystalline. An extensive ball milling completely converts the crystalline cellulose into amorphous cellulose, leading to a significant increase in the formation of high-DP glucose oligomers. It seems that ball milling is a good strategy for improving cellulose hydrolysis reactivity in HCW.Overall, the present research has provided valuable information for the fundamental understanding of the mechanisms of cellulose hydrolysis in HCW. The development of a sampling and analytical method makes it possible to characterise the glucose oligomers in the liquid products and understand the formation of precipitate in the liquid products. The primary liquid products of cellulose hydrolysis in HCW, which were firstly reported in this field, are of great importance to elucidate the primary hydrolysis reactions of cellulose hydrolysis in HCW. The structural differences between amorphous and crystalline cellulose, as well as the evolution of structural changes with conversion during hydrolysis in HCW were also revealed. This study further estimated the effect of ball milling on the improvement in the performance of cellulose hydrolysis in HCW.

The current energy crisis is exponentially growing and widening the chasm between demand and supply. Biofuels such as ethanol not only provide greener alternatives to fossil fuels but have been shown to reduce emissions from vehicles, improving air etc. Biofuel production from sources such as cellulose is believed to be more sustainable due to its low cost, vast availability in nature and sources such as industrial plant waste can be put to good use. However, due to the absence of a low-cost technology to overcome its recalcitrance, a concept called Consolidated Bioprocessing (CBP) has been put forward which proposes to integrate the production of saccharolytic enzymes, hydrolysis of the carbohydrate components to sugar molecules, and the fermentation of hexose and pentose sugars to biofuels into a single process. The present study involves development of cellulolytic E. coli strains towards cellodextrin assimilation by employing an energy-saving strategy in cellulose metabolism through the phosphorolytic cleavage of cellodextrin mixture produced as cellulosic degradation products.

Lors de la production industrielle du biocarburant éthyl tert-butyl éther (ETBE), cet éther forme un azéotrope contenant 20 % d'éthanol. Comparé à la distillation ternaire utilisée pour la purification de l'ETBE, le procédé membranaire de pervaporation pourrait offrir une alternative intéressante et d'importantes économies d'énergie. Des membranes cellulosiques ont principalement été décrites pour cette application. En particulier, la sélectivité de l'acétate de cellulose (CA) était extrêmement élevée mais son flux trop faible. Dans cette thèse, différentes stratégies de greffage ont été explorées pour améliorer ses propriétés membranaires. La première a mis en œuvre la chimie "click" pour le greffage d'oligomères polylactide, conduisant à des membranes bio-sourcés originales pour cette application. Le greffage de liquides ioniques (LIs) a ensuite été étudié, initialement par chimie "click" (échec dû à des réactions secondaires) puis par une autre stratégie en 2 étapes impliquant une simple substitution nucléophile. Une seconde série de matériaux cellulosiques a été obtenue avec des LIs contenant un même anion bromure et différents cations (imidazolium, pyridinium ou ammonium) de polarité croissante. Une troisième série de nouveaux matériaux membranaires a ensuite été développée en échangeant l'anion bromure par différents anions Tf2N-, BF4-, and AcO-. Les propriétés membranaires de tous les matériaux greffés ont finalement été évaluées sur la base du modèle de sorption-diffusion, révélant que la sorption et la pervaporation étaient conjointement améliorées par les différentes stratégies de greffage développées
During the industrial production of ethyl tert-butyl ether (ETBE) biofuel, this ether forms an azeotropic mixture containing 20 wt% of ethanol. Compared to the ternary distillation currently used for ETBE purification, the pervaporation membrane process could offer an interesting alternative and important energy savings. Cellulosic membranes have been mainly reported for this application. In particular, the selectivity of cellulose acetate (CA) was outstanding but its flux was too low. In this work, different grafting strategies were developed for improving the CA membrane properties for ETBE purification. The first strategy used "click" chemistry to graft CA with polylactide oligomers leading to original bio-based membranes for the targeted application. The grafting of ionic liquids onto CA was then investigated first by "click" chemistry (unsuccessful due to side reactions) and then by another two-step strategy implying simple nucleophilic substitution. A second series of cellulosic materials was obtained by grafting different ionic liquids containing the same bromide anion and different cations (imidazolium, pyridinium or ammonium) with increasing polar feature. A third series of new membrane materials was finally developed by exchanging the bromide anion with different anions Tf2N-, BF4-, and AcO-. The membrane properties of all grafted CA membranes were finally assessed on the basis of the sorption-diffusion model, which revealed that both sorption and pervaporation properties were improved by the different grafting strategies

Lignocellulosic bioethanol is currently being explored as a substitution to fossil fuels. Many lignocellulosic materials are being examined but the importance is to find those with attractive agro-energy features. Producing lignocellulosic ethanol is challenging because lignocellulosic biomass is resistant to chemical and biological degradation. To reduce biomass recalcitrance, a pretreatment stage is required. Pretreatment is considered to be the most intensive operating/operating cost component of cellulosic ethanol production. Therefore, research is heavily focused on understanding the effect of pretreatment technologies on the fundamental characteristics of lignocellulosic biomass. The first study in the thesis investigates Buddleja davidii as a potential biomass source for bioethanol production. The work focuses on the determination of ash, extractives, lignin, hemicellulose, and cellulose content in this plant, as well as detailed elucidation of the chemical structures of both lignin and cellulose by NMR spectroscopy. The study showed that B. davidii has several unique agro-energy features as well as some undesired characteristics. The second study presents research on the ethanol organosolv pretreatment (EOP) of B. davidii and its ability to produce enzymatically hydrolysable substrates. It was concluded that the removal of hemicellulose, delignification, reduction in the degree of polymerization (DP) of cellulose, and the conversion of crystalline cellulose dimorphs (Iα/Iβ) to the easily degradable para-crystalline and amorphous celluloses were the characteristics accounted for efficient enzymatic deconstruction of B. davidii after EOP. The third study provides a detailed elucidation of the chemical structure of ethanol organosolv lignin (EOL) of B. davidii by NMR spectroscopy. Such research was needed to understand the pretreatment mechanism in the context of delignification and alteration of the lignin structure. Future applications of the resulted EOL will be valuable for industrially viable bioethanol production process. EOP mainly cleaved β-O-4' interlinkages via homolysis, decreased the DP of lignin, and increased the degree of condensation of lignin. EOL had low oxygen content, molecular weight, and aliphatic OH as well as high phenolic OH, which are qualities that make it suitable for different co-product applications. The last study provides information on the anatomical characteristics of pretreated B. davidii biomass after EOP. The importance of this research was to further understand the alterations that occur to the cellular structure of the biomass which can then be correlated with its enzymatic digestibility. The results concluded that the physical distribution of lignin within the biomass matrix and the partial removal of middle lamella lignin were key factors influencing enzymatic hydrolysis.

Secondary generation biofuels such as cellulosic biofuels rely on large portions of cellulosic bioresources, which may include forests, perennial grasses, wood and agricultural residues. Switchgrass is one promising feedstock for biofuel production. In the present study, thesis work focused on the chemical and structural profiles and hydrothermal pretreatment of switchgrass. Four populations of switchgrass were investigated for their chemical properties among populations and morphological portions, including the compositions of lignin and carbohydrates, extractives content, higher heating value (HHV), and syringyl:guaiacyl (S:G) ratio. The results demonstrate similar chemical profiles and lignin structure among the four populations of switchgrass. Morphological fractions of switchgrass including leaves, internodes, and nodes differ significantly in chemical profiles and S:G ratios of lignin. The structure of isolated cellulose from switchgrass SW9 is similar between leaves and internodes. The structure of isolated lignin from leaves and internodes of switchgrass SW9 differs in S:G ratio and molecular weight. Hydrothermal pretreatment of leaves and internodes indicates that a similar chemical composition and chemical structure for pretreated leaves and internodes. The degree of polymerization (DP) for cellulose of the pretreated internodes is 23.4% greater than that of the pretreated leaves. The accessibility of pretreated leaves measured by Simons' Staining technique is greater than that of pretreated internodes. Pretreated leaves have a 32.5-33.8% greater cellulose-to-glucose conversion yield than do pretreated internodes.

The prediction of the behaviour and spread of bushfires has always been fraught with a large number of unknowns,not the least of which has been the seemingly capricious nature of fire itself. Operational bushfire prediction systems, developed as they are using empirical methods, aim to predict the long-term mean spread of a bushfire based on its steady-state behaviour....

O principal objetivo deste trabalho é o desenvolvimento de uma nova geração de materiais sustentáveis para células de combustível alcalinas de eletrólito solido (SAFC) e tecnologias de hidrogénio. A tecnologia SAFC oferece vantagens a dois níveis: i) o eletrólito polimérico solido é menos sensível a envenenamento por CO2, e especialmente ii) a cinética das reações de elétrodo é melhorada no meio básico criado na célula, que pode não requerer o uso de catalisadores à base da escassa platina. Estas vantagens implicam desafios. O transporte de OH- é inerentemente mais lento que o de H+, e, portanto, polímeros altamente condutores são necessários. O meio alcalino ameaça a integridade tanto da membrana polimérica como do catalisador, então materiais quimicamente estáveis são necessários. Esta tese explora o potencial da celulose bacteriana (BC) como suporte de polieletrólitos catiónicos/quaternários, formando membranas nanocompósitas com excelentes propriedades mecânicas e estáveis em ambientes alcalinos. A comparação de membranas de BC pura e com tratamento ácido ou básico não revela uma deterioração evidente da membrana com tratamento alcalino em termos de degradação térmica, condutividade iónica, propriedades viscoelásticas e até desempenho da célula de combustível. Este último é severamente limitado pela baixa condutividade da BC (<1 ms.cm-1 a 98% de humidade relativa (RH)), produzindo menos de 1 mW.cm-2. Sintetizaram-se membranas nanocompósitas de BC com três polieletrólitos diferentes funcionalizados com grupos NH4+: Poli[2(acrililoxi)etil]trimetilamonio (PAETA), poli(3-acrilamidopropil)- trimetilamonio (PAPTA) e poli(vinilbenzil)trimetilamonio (PVBTA). Membranas à base de PAETA não são estáveis em condições alcalinas, mas nanocompósitos de PAPTA e PVBTA mantêm as excelentes características viscoelásticas da BC, com módulos de armazenamento superiores a 1 GPa e permanecendo estáveis até cerca de 200 °C. O comportamento de absorção de água correlaciona-se com a condutividade iónica, que aumenta com o aumento de RH e de temperatura, atingindo a 94 °C e 98% RH 72.8 mS.cm-1 para BC:PAPTA e 12.4 mS.cm-1 para BC:PVBTA. Testes de célula de combustível de BC:PAPTA atingiram 10 mW.cm-2 a 55 mA.cm-2, um desempenho determinado por polarização dos elétrodos. O estudo dos eletrólitos é complementado pelo estudo de uma serie de perovesquites e fases Ruddlesden-Popper para aplicação enquanto catalisadores para a redução de oxigénio (ORR) e de peroxido de hidrogénio (HPRR) em meio alcalino. Testes de estabilidade em ambiente alcalino (pH>14) indicam que Sr, Ni, Cu e Co nas perovesquites e nas fases Ruddlesden-Popper tendem a dissolver, em conformidade com diagramas de Pourbaix calculados. A superfície dos elétrodos sem catiões metálicos, que por sua vez se acumulam no eletrólito, é provável que resulte em efeitos difíceis de prever nas propriedades electrocatalíticas da amostra. De acordo com os diagramas de Pourbaix, materiais à base de Mn devem ser capazes de resistir a ambientes alcalinos. A perovesquite La0.7Sr0.3MnO3 apresenta a melhor atividade electrocatalítica, e emerge de entre as composições testadas como a única alterativa estável para a catálise de ORR em meio fortemente alcalino. Uma tentativa é feita no sentido de correlacionar composição, estabilidade química e comportamento eletroquímico dos materiais, baseado em modelos molecular-orbitais conhecidos. Isto, contudo, deve ser analisado com cuidado devido a incertezas associadas à composição da superfície e como isso muda com o forte meio alcalino.
The development of a new generation of sustainable materials for solid alkaline fuel cells (SAFC) and hydrogen technologies is the major driver of this work. SAFC technology offers advantages at two levels: i) the base solid polymer electrolyte is less sensitive to CO2 poisoning, and especially ii) the kinetics of the electrode reactions is improved in the basic environment created inside the cell, which may avoid the use of scarce platinum catalysts. These advantages entail challenges. The OH- transport is inherently slower than of H+, and thus highly conductive polymers are necessary. The strong alkaline medium threatens the integrity of both the polymer membrane and the catalyst, so chemically stable materials are necessary. This thesis explores the potential of bacterial cellulose (BC) as support to cationic/quaternary polyelectrolytes, forming nanocomposite membranes with excellent mechanical properties and stable in alkaline environments. Comparison of pristine BC membranes and submitted to acidic or basic treatments reveals no noticeable degradation of the alkaline-treated membrane in terms of thermal degradation, ionic conductivity, visco-elastic properties and even fuel cell performance. The latter is severely limited by the low conductivity of BC (<1 mS.cm1 under 98% relative humidity (RH)), delivering less than 1 mW.cm-2. Nanocomposite membranes of BC with three different polyelectrolytes functionalized with NH4+ groups: Poly[2-(acryloyloxy)ethyl]trimethylammonium (PAETA), Poly(3-acrylamidopropyl)trimethylammonium (PAPTA), and Poly(Vinylbenzyl)trimethylammonium (PVBTA) were synthesized. PAETA-based membranes are not stable in alkaline conditions, but both PAPTA and PVBTA nanocomposites maintain the excellent visco-elastic characteristics of BC, with storage modules in excess of 1 GPa, remaining stable up to about 200 °C. The water adsorption behaviour correlates with the ionic conductivity, both increasing with increasing RH and temperature, reaching, at 94°C and 98% RH a maxima of 72.8 mS.cm-1 for BC:PAPTA and 12.4 mS.cm-1 for BC:PVBTA. Fuel cell tests of BC:PAPTA delivered 10 mW.cm-2 at 55 mA.cm-2, a performance determined by electrode polarization. The electrolyte study is complemented by the study of a range of transition metal perovskite and Ruddlesden-Popper phases for application as catalysts for the oxygen reduction (ORR) and hydrogen peroxide reduction (HPRR) in alkaline media. Stability tests in alkaline environments (pH>14) indicate that Sr, Ni, Cu and Co in perovskite and Ruddlesden-Popper phases tend to dissolve, in agreement with calculated Pourbaix diagrams. An electrode surface depleted of metallic cations, which accumulate on the electrolyte, is likely to have unpredictable effects on the electrocatalytic properties of the system. According to the Pourbaix diagrams, Mn-based materials should be able to withstand the alkaline environments. The perovskite La0.7Sr0.3MnO3 displays the best electrocatalytic activity and emerges from the tested compositions as the only stable alternative to catalyse the ORR in strong alkaline medium. An attempt is made to correlate the composition, chemical stability and electrochemical behaviour of these materials based on known molecular-orbital models. This, however, must be taken with caution in face of the unknowns associated with the surface composition and how it is changed by the strong alkaline medium.
Programa Doutoral em Ciência e Engenharia de Materiais

碩士
雲林科技大學
化學工程與材料工程研究所
98
This study deals with preparation of novel proton conducting membranes using 10 to 20 wt% 2-Acrylamido- 2-methyl-1-propanesulfonic acid (AMPS) as a grafting agents onto bacterial cellulose (BC) through photoinduced UV-grafted polymerization, these membranes name in AMPS10-g-BC, AMPS15-g-BC, AMPS20-g-BC, respectively. 　These membranes have been characterized by FTIR, SEM, EDS and TGA to find successful grafting of AMPS on BC, surface morphology and thermal stability, respectively. Physical properties of these membranes have been assessed in terms of proton conductivity, IEC, and water uptake. The influence of AMPS concentration on physical properties of BC has been discussed in detail. Optimum proton conductivity and IEC value are observed for AMPS20-g-BC, i.e. 2.89×10-2S/cm and 1.79mmol/g. 　In order to find suitability of these membranes in fuel cells, self-diffusion coefficients have been calculated. When methanol concentration increased, self-diffusion coefficient of AMPS-g-BC decreased, and the lower self-diffusion coefficient caused the lower methanol uptake in AMPS-g-BC. The results of solvent uptake indicate that AMPS-g-BC membranes show high selectivity towards water than methanol. 　These membranes have been subjected to H2/O2 single cell test experiments. MEA has been fabricated using AMPS-g-BC and commercialized Pt/C catalyst and gas diffusion layer. The performance of AMPS-g-BC membranes have improved use of higher AMPS concentration , and also with increase in operation temperature(30℃ to 50℃). Optimum results of 348mA/cm2 (current density at 0.2V) and 97 mW/cm2 (power density) have been observed for AMPS20-g-BC membrane. Even though, the results were reasonable good, these is a scope for improvement in thermal and mechanical stability of MEA due to high water uptake (over 200wt %).

Indiana University-Purdue University Indianapolis (IUPUI)
The prevalent applications of energy storage devices have incited wide-spread efforts on production of thin, flexible, and light-weight lithium-ion batteries. In this work, lithium-ion batteries using novel flexible paper-based current collectors have been developed. The paper-based current collectors were fabricated from carbon nanotube (CNT)-coated wood microfibers (CNT-microfiber paper). This thesis presents the fabrication of the CNT-microfiber paper using wood microfibers, coating electrode materials, design and assemblies of battery, testing methodologies, and experimental results and analyses. Wood microfibers were coated with carbon nanotubes and poly(3,4-ethylenedioxythiophene) (PEDOT) through an electrostatic layer-by-layer nanoassembely process and formed into a sheet, CNT-microfiber paper. The CNT loading of the fabricated paper was measured 10.1 μg/cm2 subsequently considered. Electrode material solutions were spray-coated on the CNT-microfiber paper to produce electrodes for the half and full-cell devices. The CNT current collector consists of a network structure of cellulose microfibers at the micro-scale, with micro-pores filled with the applied conductive electrode materials reducing the overall internal resistance for the cell. A bending test revealed that the paper-based electrodes, compared to metal ones, incurred fewer damages after 20 bends at an angle of 300o. The surface fractures on the paper-based electrodes were shallow and contained than metallic-based electrodes. The micro-pores in CNT-microfiber paper structure provides better adherence to the active material layer to the substrate and inhibits detachment while bending. Half-cells and full-cells using lithium cobalt oxide (LCO), lithium titanium oxide (LTO), and lithium magnesium oxide (LMO) were fabricated and tested. Coin cell assembly and liquid electrolyte was used. The capacities of half-cells were measured 150 mAh/g with LCO, 158 mAh/g with LTO, and 130 mAh/g with LMO. The capacity of the LTO/LCO full-cell also was measured 126 mAh/g at C/5 rate. The columbic efficiency of the LTO/LCO full-cell was measured 84% for the first charging cycle that increased to 96% after second cycle. The self-discharge test of the full-cell after charging to 2.7 V at C/5 current rate is showed a stable 2 V after 90 hours. The capacities of the developed batteries at lower currents are comparable to the metallic electrode-based devices, however, the capacities were observed to drop at higher currents. This makes the developed paper-based batteries more suitable for low current applications, such as, RFID tags, flexible electronics, bioassays, and displays. The capacities of the batteries at higher current can be improved by enhancing the conductivity of the fibers, which is identified as the future work. Furthermore, fabrication of an all solid state battery using solid electrolyte is also identified as the future work of this project.