Nesta tese, a ressonância magnética nuclear do estado sólido (SSNMR) foi utilizada para estudar a composição química e estrutura dos componentes da parede celular de plantas. Visando contribuir no desenvolvimento de estratégias de despolimerização da biomassa, SSNMR foi inicialmente utilizada para estudar efeitos dos pré-tratamentos químicos e físicos, e da ação de enzimas sobre algumas biomassas. Os resultados mostraram que, em baixas concentrações, tratamentos ácidos são altamente efetivos na remoção das frações de hemicelulose, com pouco efeito nas frações de lignina e celulose. Já tratamentos alcalinos promovem eficiente deslignificação da biomassa, sendo que a mínima concentração da solução alcalina necessária para obter a máxima deslignificação depende do tipo de biomassa e da temperatura do tratamento. Os estudos por SSNMR foram correlacionados com estudos por outras técnicas, contribuindo para um entendimento mais profundo sobre o efeito dos pré-tratamentos e da hidrolise enzimática em diferentes biomassas. Outra parte da tese aborda a determinação da cristalinidade de celulose nativa (não extraída) de biomassa de bagaço de cana-de-açúcar. Utilizando a técnica de polarização cruzada em múltiplas etapas (Multi-CP) e um procedimento de subtração espectral, foi possível isolar os sinais de RMN da celulose nativa e a partir daí avaliar o índice de cristalinidade (CI). Esse método foi utilizado para avaliar o CI da celulose nativa de bagaço de cana-de-açúcar submetido à pré-tratamentos com H2SO4 e NaOH e os resultados não mostraram variações significativas do CI da celulose nas concentrações utilizadas, apesar do aumento da eficiência da hidrólise. Assim, ao contrário de muitos trabalhos encontrados na literatura, não parece que a cristalinidade da celulose seja um fator primordial no aumento de eficiência da hidrólise enzimática. Na parte final da tese, as interações intermoleculares entre os dois principais polissacarídeos da biomassa: celulose e xilano foram investigadas utilizando uma variedade de técnicas avançadas de RMN bidimensional. Neste trabalho, a arquitetura molecular de hastes de plantas de Arabidopsis Thaliana, sem nunca serem seca foi estudada. Utilizando a técnica refocused J-INADEQUATE (Increadible Natural Abundance Double Quantum Transfer Experiment via J coupling) observamos dois conjuntos de deslocamentos químicos distintos para o xilano, sendo um deles coincidente com aquele observado em solução. Em seguida, utilizamos experimentos SSNMR com o intuito de investigar se algum desses domínios de xilano estaria vinculado com a celulose. Experimentos CP-PDSD (Proton Driven Spin Diffusion detected via 13C through Cross-Polarization) demonstram a existência de proximidade espacial entre o novo domínio do xilano e o domínio da celulose. A comparação de resultados entre as amostras de padrão e o seu mutante deficiente em celulose (irx3) indicaram que o xilano com novo deslocamento químico é fortemente dependente da presença de celulose. A análise da mobilidade molecular pela técnica Dipolar Chemical Shift Correlation (DIPSHIFT), mostrou que as moléculas do novo domínio do xilano são altamente rígidas - uma característica partilhada com a celulose. Combinados, esses dados fornecem evidências de uma arquitetura molecular específica entre os dois polissacarídeos majoritários da parede celular. / Solid-state nuclear magnetic resonance (SSNMR) was used to study the chemical composition and structure of plant cell wall components. Aiming the development of depolymerization strategies, SSNMR was initially used to study the effects of chemical and physical pre-treatments, as well as the enzymatic action on the structure and composition of biomasses. The results showed that, at low concentrations, pre-treatments with acids are highly effective for removal of hemicellulose without significant effect on lignin and cellulose. In turn, the alkaline pre-treatment promotes efficient delignification of the biomass. The minimum concentration of the alkaline solution required to achieve the maximum delignification depends on the type of biomass and treatment temperature. SSNMR studies were correlated with studies using other techniques, contributing to an in-depth understanding of the effect of pre-treatments and enzymatic hydrolysis in different biomasses. Another part of the thesis discusses is the determination of native cellulose crystallinity (not extracted) of sugarcane bagasse biomasses. Using the cross-polarization technique in multiple blocks (Multi-CP) and a spectral subtraction approach, it was possible to isolate the NMR signals of the native cellulose and to evaluate the crystallinity index (CI). This method was used to accessof the CI of cellulose in sugarcane bagasse samples pre-treated with H2SO4 and NaOH. The results did not show significant variations of the cellulose CI, at the concentration used here, despite the increase in the hydrolysis efficiency. Thus, in contrast to some studies in the literature, it does not appear that the crystallinity of cellulose is a primary limiting factor concerning the enzymatic hydrolysis efficiency in biomasses. In the final part of this thesis, the intermolecular interactions between the two main polysaccharides of the plant cell wall, cellulose and xylan, were investigated using advanced two-dimensional NMR techniques. The molecular architecture of 13C labelled never-dried Arabidopsis Thaliana stems was studied. Using refocused J-INADEQUATE (Increadible Natural Abundance Double Quantum Transfer Experiment via J coupling) we observed two distinct chemical shifts in xylan, one of which coincides with that observed in solution. Next, we used SSNMR experiments toinvestigate the interaction between the novel xylan and cellulose domains. CP-PDSD (Proton Driven Spin Diffusion detected via 13C through Cross-Polarization) experiments demonstrated spatial proximity between the new xylan and cellulose domains. The same approach was used to study cellulose deficient (irx3) mutants and the comparison between the results indicate that the new xylan domain is cellulose-dependent. Dipolar Chemical Shift Correlation (DIPSHIFT) experiments were performed to analyse the molecular mobility of these polysaccharides showing that the novel xylan is highly rigid - a characteristic which is shared with cellulose. Combined, these data provide evidence for a specific molecular architecture between the two most common polysaccharides in plant cell walls.

Na atualidade, a geração de eletricidade e a produção de etanol de segunda geração a partir de materiais lignocelulósicos se apresentam como uma alternativa de desenvolvimento tecnológico no setor sucroenergético. Não obstante, a introdução de novos processos produtivos representa um verdadeiro desafio devido à complexidade e diversidade das rotas tecnológicas alternativas que podem ser avaliadas. Além disso, existem fatores econômicos e ambientais, que devem ser considerados durante o desenvolvimento e consolidação destas novas configurações. Nesse sentido, o presente trabalho tem como objetivo desenvolver uma metodologia para realizar a hierarquização exergética e exergo-ambiental de processos para obtenção de etanol e eletricidade a partir da cana-de-açúcar em distintas configurações de biorrefinarias. Para este fim, dados técnicos de operação foram adotados nas rotas tecnológicas envolvidas, bem como os aspectos ambientais da utilização destes sistemas. Os modelos propostos avaliaram as rotas Convencional (Caso 1), Bioquímica (Caso 2) e Termoquímica (Caso 3), utilizando programas de simulação e ferramentas matemáticas para simular estes processos. Ainda, a integração dos processos e diferentes usos para o bagaço excedente foram estudados, junto com diversos métodos de pré-tratamento visando à otimização e hierarquização destas rotas. O resultado final indicou configurações ótimas que permitiram a hierarquização em termos do índice exergético de renovabilidade dos processos de produção das rotas analisadas. Desse modo a rota convencional otimizada apresentou a máxima eficiência exergética dos processos e, por tanto, o menor custo exergético unitário médio das plataformas avaliadas. Ao passo que a rota bioquímica foi o sistema que promoveu um incremento de 28,58 % e 82,87 % na produção de etanol, quando comparado com o Caso 1 e o Caso 3, respectivamente. Além disso, a rota termoquímica apresentou a configuração com a maior taxa de geração de eletricidade excedente (214,98 kWh/TC). Em relação aos resultados do impacto ambiental das rotas tecnológicas, encontrou-se que a configuração mais sustentável foi a plataforma bioquímica, apresentando as menores taxas de emissões globais de CO2 (131,45 gCO2/MJ produtos). / Currently, electricity generation and second-generation bioethanol production from lignocellulosic materials represent technological alternatives in the sugar-energy sector. Nevertheless, the introduction of new production processes represents a real challenge due to the complexity and diversity of the technological routes that can be evaluated. In addition, there are economic and environmental factors that must be considered during the development and consolidation of these new configurations. Accordingly, this project aims to develop a methodology to perform the exergy and exergo-environmental analysis, evaluation and ranking of processes in order to obtain ethanol and electricity from sugarcane in different biorefinery configurations. Hence, operating technical data of each technological route were adopted as well as the environmental aspects of using these systems. The proposed models assessed the Conventional (Case 1), Biochemical (Case 2) and Thermochemical (Case 3) routes using simulation programs and mathematical tools to simulate the ethanol production and electricity generation. Furthermore, the process integration and different uses for the excess bagasse were studied with various pretreatment methods aiming the optimizing and ranking of routes. The results indicated optimal settings that allowed the ranking in terms of the environmental exergy indicator \"renewability\" of the production processes for analyzed routes. In this way, the optimized conventional route presented the maximum exergy efficiency of the processes, therefore the lowest exergetic cost average of the evaluated platforms. While the biochemical route was the system that promoted an increase of 28.58 % and 82.87% in the ethanol production, when compared to Case 1 and Case 3, respectively. In addition, the thermochemical route presented the configuration with the highest power generation rate exceeding (214.98 kWh/TC). Concerning, the environmental impact results, it was found that the most sustainable configuration was the biochemical platform, which presented the lowest overall CO2 emissions rates (131.45 gCO2/MJ products).

Nessa pesquisa avaliou-se a produção fermentativa de hidrogênio e ácidos orgânicos a partir do bagaço de cana-de-açúcar (BCA) usado como substrato em reatores em batelada. Três condições de pré-tratamento (hidrotérmico, autoclave e hidrotérmico mais autoclave) do BCA e condição in natura foram avaliadas a fim de favorecer a produção de hidrogênio. Verificou-se produção molar de hidrogênio de 3,79 mmol/L, 3,47 mmol/L, 1,67 mmol/L e 1,01 mmol/L para BCA autoclavado, BCA in natura, BCA pré-tratado em sistema hidrotérmico e BCA pré-tratado em sistema hidrotérmico seguido de autoclave, respectivamente. A partir desses valores, optou-se por usar o BCA autoclavado como substrato para otimização da produção de hidrogênio e ácidos orgânicos a partir de metodologias de delineamento do composto central e superfície de resposta. Foram monitorados 10 reatores em batelada (R1 a R10), em triplicatas, com diferentes concentrações de substrato (0,8 a 9,2 g/L) e pH (de 4,6 a 7,4). A maior produção de hidrogênio (24,1 mmol/L) e 6,4 g/L de ácidos orgânicos foram obtidos em R4 (8,0 g BCA/L e pH 7,0). Os açúcares glicose, arabinose, xilose, manose e galactose foram observados ao longo do tempo de operação em todos os reatores, sendo arabinose observado em maior concentração nas condições dos reatores R3 (8,0 g BCA/L e pH 5,0) e R8 (5,0 g BCA/L e pH 7,4), respectivamente, 1.415,3 e 1.372,5 mg/L. A produção de hidrogênio foi concomitante à formação de ácidos orgânicos, principalmente butírico (de 14,6 a 33,8% em R1 e R6, respectivamente) e succínico (de 19,5 a 26,4% em R3 e R9, respectivamente). Os dois fatores analisados, concentração de substrato e pH, exerceram efeitos significativos na produção de hidrogênio, ácido butírico e succínico. A partir dos resultados obtidos com o planejamento fatorial, foi possível verificar que o valor máximo de produção de hidrogênio estimado pelo modelo foi de 23,10 mmol/L, para 7,0 g BCA/L e pH 7,2. O valor obtido no experimento de otimização (Rotm) foi de 19,84 mmol/L, com grau de precisão do modelo de 85,9% para produção de hidrogênio a partir de BCA autoclavado. Sequenciamento massivo via plataforma Illumina (Miseq) foi realizado para a identificação de bactérias do reator do ponto central, (R9, 5,0 g BCA/L e pH 6,0), do reator otimizado (Rotm, 7,0 g BCA/L e pH 7,2), de amostras do BCA autoclavado e inóculo. No inóculo foram identificadas principalmente bactérias semelhantes a Clostridium bifermentans (62,69% de abundância relativa), Bacillus coagulans (31,67%) e Enterobacter aerogenes (2,72%). No BCA foram identificadas bactérias semelhantes a C. bifermentans (31,91%), C. cellobioparum (32,29%), C. cellulolyticum (5,69%), C. sartagoforme (14,63%) e Paenibacillus spp. (11,67%). Estas bactérias não foram favorecidas sob as condições impostas em R9 (5,0 g BCA/L e pH 6,0) e Rotm (7,0 g BCA/L e pH 7,2), uma vez que a abundância relativa das bactérias nas amostras dos reatores foram completamente diferentes. Em R9, bactérias semelhantes a Lactobacillus paracasei e Escherichia hermannii foram as principais identificas com 37,50 e 34,32% de abundância relativa, respectivamente. Em Rotm, as principais bactérias identificadas foram semelhantes a Bacteroides sp. e Enterobacter aerogenes, com 37,35 e 27,72% de abundância relativa, respectivamente. Assim, as populações bacterianas, bem como a produção de metabólitos, foram alteradas em função das condições impostas; ou seja, concentração de BCA, pH em reatores em batelada com BCA autoclavado como substrato. / This study evaluated the hydrogen and organic acids fermentative productions from sugarcane bagasse (SCB) as substrate in batch reactors. Three pre-treatment conditions (hydrothermal, autoclave and hydrothermal plus autoclave) of BCA and the in natura condition were evaluated in order to favor the hydrogen production. Hydrogen molar productions of 3.79 mmol/L, 3.47 mmol/L, 1.67 mmol/L and 1.01 mmol/L was found for SCB pretreated in autoclave, BCA in natura, SCB pretreated in hydrothermal system and SCB pretreated in hydrothermal system followed by autoclaving, respectively. From these values, it was decided to use autoclaved BCA as a substrate for optimization of hydrogen and organic acids productions from the design methodologies of the central compound and response surface. Ten batch reactors (R1 to R10) were monitored in triplicates with different substrate concentrations (0.8 to 9.2 g/L) and pH (4.6 to 7.4). The highest production of hydrogen (24.06 mmol/L) and 6.42 g/L of organic acids were obtained in R4 (8.0 g BCA/L and pH 7.0). Glucose, arabinose, xylose, mannose and galactose were produced and consumed throughout the operating time of all reactors, and arabinose was observed at higher concentration, 1,415.26 and 1,372.45 mg/L in R3 (8.0 g BCA/L and pH 5.0) and R8 (5.0 g BCA/L and pH 7.4), respectively. The production of hydrogen was concomitant to the formation of organic acids, mainly butyric (from 14.6 to 33.8% in R1 and R6, respectively) and succinic (from 19.5 to 26.4% in R3 and R9, respectively). The two factors analyzed, substrate concentration and pH, had significant effects on the production of hydrogen, butyric acid and succinic acid. From the results obtained with the factorial design, it was possible to verify that the maximum value of hydrogen production estimated by the model was 23.10 mmol/L, to 7.0 g BCA L and pH 7.2. The value obtained in the optimization experiment (Rotm) was 19.84 mmol/L, with an accuracy of 85.9% for hydrogen production from autoclaved BCA. Sequencing by the Illumina platform (Miseq) was performed for the identification of bacteria from the central point reactor (R9, 5.0 g BCA/L and pH 6.0), optimized reactor (Rotm, 7.0 g BCA/L and pH 7.2), autoclaved BCA and inoculum samples. In the inoculum were identified mainly bacteria similar to Clostridium bifermentans (62,69% of relative abundance), Bacillus coagulans (31,67%) and Enterobacter aerogenes (2,72%). Bacteria similar to C. bifermentans (31.91%), C. cellobioparum (32.29%), C. cellulolyticum (5.69%), C. sartagoforme (14.63%) and Paenibacillus spp. (11.67%). These bacteria were not favored under the conditions imposed on R9 (5.0 g BCA/L and pH 6.0) and Rotm (7.0 g BCA/L and pH 7.2), since the relative abundance of the bacteria in the reactor samples were completely different. In R9, bacteria similar to Lactobacillus paracasei and Escherichia hermannii were the main identified with 37.50 and 34.32% of relative abundance, respectively. In Rotm, the main bacteria identified were similar to Bacteroides sp. and Enterobacter aerogenes, with 37.35 and 27.72% relative abundance, respectively. Thus, bacterial populations, as well as the production of metabolites, were altered as a function of the imposed conditions; ie, BCA concentration, pH in batch reactors with autoclaved BCA as substrate.

Cette thèse s’articule autour de la valorisation de la biomasse lignocellulosique pour la production d’un polymère biosourcé, le poly(acide lactique) PLA. Lors d’une première étude, deux prétraitements de la biomasse lignocellulosique ont été réalisés pour libérer les sucres fermentescibles. Puis plusieurs stratégies de fermentations ont été mises en place et un criblage microorganisme / biomasse a été réalisé en vue de sélectionner la meilleure stratégie de fermentation et le meilleur couple biomasse / microorganisme pour la production d’acide lactique. Les bactéries lactiques, Lactobacillus casei et Lactobacillus delbrueckii et le son de blé ont été retenus pour produire l’acide lactique lors d’une fermentation en milieu liquide sur l’hydrolysat produit par une hydrolyse à l’acide dilué du son de blé. Lors d’une seconde étude, la stratégie choisie a été optimisée et a subi un « scale-up » afin d’augmenter la concentration en acide lactique. Les fermentations en milieu liquide ont été effectuées au sein d’un bioréacteur afin de contrôler les paramètres de croissance bactérienne et de production d’acide lactique (pH, pO2, agitation, production d’acide lactique). Puis une purification de l’acide lactique a été menée par chromatographie échangeuse d’ions. Cette technique a été réalisée en deux étapes clés utilisant successivement une colonne cationique forte et une colonne anionique faible. L’acide lactique purifié a été polymérisé par ouverture de cycle (ROP). Durant toutes ces recherches, la chimie verte a été mise au premier plan d’une part par le sujet de l’étude (valorisation de la biomasse végétale) mais aussi d’autre part par le choix des méthodes employées (pas de solvants, peu de produits chimiques, méthodes propres, économiques et renouvelables). / This thesis is articulated around the lignocellulosic biomass valorization to develop a fully sustainable, green and cheap route of PLA production. During a first study, two pretreatments have been realized on the lignocellulosic biomass in order to release the fermentable sugars. Several fermentations strategies have been considered and a screening of the couples microorganisms / biomasses has been performed in order to select the best strategy and the best couple microorganism / biomass for lactic acid production. The lactic acid bacteria, Lactobacillus casei and Lactobacillus delbrueckii and wheat bran have been selected to produce lactic acid via a liquid state fermentation on the acid hydrolysate obtained thanks to a diluted acid pretreatment on the wheat bran. During a second study, the chosen strategy has been optimized and scaled-up in order to increase the lactic acid concentration. Liquid state fermentations have been made in a bioreactor in order to control parameter needed for the optimal growth and consequently the optimal lactic acid production (pH, pO2, agitation, acid lactic production). Then, the lactic acid purification has been performed by ion exchange chromatography. This technic was made in two key steps using a strong cationic column and a weak anionic column successively. Finally, the purified lactic acid was then polymerized by ring opening polymerization (ROP). During all the researches, the green chemistry has been placed in the first plan in one hand by the choice of the topic of the study (biomass valorization) and in a second hand by the choice of each employed method (no solvent; few chemical products; sustainable, cheap and green methods).

Une technologie prometteuse pour répondre à la demande croissante en énergie renouvelable est la gazéification de biomasse lignocellulosique pour la production de biocarburants de deuxième génération. Ce procédé nécessite une alimentation en biomasse sous forme de poudre. Les problèmes de convoyage et de manipulation liés à la faible coulabilité de la biomasse broyée sont un verrou pour l’industrialisation des procédés BtL. La torréfaction comme procédé de prétraitement, en plus d'augmenter densité énergétique de la biomasse, peut influencer également les propriétés des particules obtenues après broyage, et en conséquence, l’écoulement des poudres. L'évaluation de l'écoulement des poudres de biomasse sous différentes conditions de consolidation est essentielle pour concevoir des technologies de manipulation et de convoyage efficaces.L'objectif de ce travail est d'évaluer l'effet des conditions de torréfaction et de broyage sur l’écoulement de poudres de biomasse. Une première partie consiste en une étude expérimentale dans laquelle la coulabilité d'échantillons torréfiés sous différentes intensités a été évaluée à l'aide d'un appareil de cisaillement annulaire. La coulabilité est corrélée à l'intensité de la torréfaction (mesurée par la perte de masse globale) pour deux essences différentes. La forme des particules semble être le paramètre qui influence de manière prédominante la coulabilité des poudres à l'état consolidé. La caractérisation de la coulabilité à l’état non consolidée a été effectuée à l'aide d'un tambour rotatif par l’analyse des avalanches des poudres. Des corrélations entre les caractéristiques des particules et la coulabilité sont ainsi établies. La modélisation de l'écoulement de la biomasse à l'aide de la Méthode des Éléments Discrets (DEM) constitue une deuxième partie de cette recherche. La taille submillimétrique des particules de biomasse, ainsi que leur faible densité, leur forme allongée et leur comportement cohésif sont des défis pour l’implémentation d’un modèle de réaliste d’écoulement particulaire en DEM. Un modèle DEM des particules de biomasse est mis en œuvre à l'aide d'une représentation simplifiée (assemblement de sphères) à gros grains de la forme des particules, ainsi que d'un modèle de force cohésif. Une procédure systématique de calibration des paramètres DEM permet d'obtenir un ensemble de paramètres ajustés. L'évolution expérimentale des contraintes de cisaillement d’une poudre dans un état consolidé peut alors être reproduite de façon réaliste. De même, le comportement d’avalanche des poudres dans un tambour tournant est également bien reproduit par les simulations, de façon qualitative et quantitative. Ces résultats mettent en évidence le potentiel des simulations DEM pour étudier l'effet des caractéristiques des particules, qui sont influencées par la torréfaction et les conditions de broyage, sur le comportement d'écoulement de la biomasse en poudre. / Gasification of lignocellulosic biomass for production of second-generation biofuels is a promising technology to meet renewable energy needs. However, feeding and handling problems related to the poor flowability of milled biomass considerably hinder the industrial implementation of Biomass-to-Liquid processes. Torrefaction as pretreatment step, in addition to improving energy density of biomass, also affects the properties of the milled particles (namely size and shape) that significantly influence flow behavior. The evaluation of biomass flow characteristics under different flow conditions is essential to design efficient and trouble-free handling solutions.The aim of this work is to assess the effect of the torrefaction and grinding conditions on the biomass flow behavior. A first part consists of an experimental study in which the flow properties of samples torrefied under different intensities were obtained using a ring shear tester. Flowability is correlated to the intensity of torrefaction, as measured by the global mass loss, for two different wood species. Particle shape seems to be the predominant parameter influencing flowability of powders in a consolidated state. Characterization of non-consolidated flowability through avalanching analysis using an in-house rotating drum was also conducted. Correlations between particle characteristics and flow behavior are thus established.The modelling of biomass flow using the Discrete Element Method (DEM) constitutes a second major part of this research. Challenging aspects of biomass particle modeling are their submillimetric size, low density, elongated shape and cohesive behavior. A material DEM model is implemented using a simplified (multisphere) upscaled representation of particle shape, along with a cohesive contact model. A systematic calibration procedure results in an optimal set of DEM parameters. The experimental shear stress evolution and yield locus can then be realistically reproduced. The avalanching behavior of the powders is also well captured by simulations, both qualitatively and quantitatively. These results highlight the potential of DEM simulations to investigate the effect of particle characteristics, which are driven by torrefaction and grinding conditions, on the flow behavior of powdered biomass.

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No description available.

<p dir="ltr">Feedstock variability represents a challenge in the adoption of lignocellulosic biomass for biofuels and biochemicals production, due to the differences in critical chemical and physical properties like lignin content, and water absorption respectively. Thus, difficult continuous manufacturing processes in biorefineries, hinder the transition from liquid feedstocks to renewable materials that consisting of solid particles. Modeling of flow properties based on rheological measurements of treated biomass is a quantitative metric for identifying if different feedstocks form pumpable slurries. Additionally, the correlation of yield stress to physical and chemical properties gives a measure that accounts for the variability in the processing design. This research models rheological properties and relates these to compositional data from different non-pretreated fractions of corn stover biomass slurries. Slurries were formed with solids concentrations of 300 g/L in a 6 hours fed-batch process using the commercial enzymes Celluclast 1.5L or Ctec-2 at 1FPU/g or 3 FPU/g of dry solids, basis to enable the liquefaction (i.e., slurry-forming) mechanism. We found that insoluble lignin content of the different fractions was related to water absorption in pellets and free water on slurries and that free water was a good indicator of the potential for a material to form slurry. Higher flowability (lower yield stress) was found at higher content of lignin, particularly for materials containing 26% lignin where yield stress was reduced to 254Pa when compared with mixtures of 14% lignin that presented yield stresses of around 4000 Pa. We show that rheology modeling linked to compositional characteristics for biomass slurries can be used to predict material flow behavior in a biorefinery to optimize and achieve high solids loadings that enhance the production of ethanol for biofuels. This insight and the ability to form high concentration slurries before pretreatment holds the potential to develop new processing strategies that could help to foster a more efficient and sustainable bio-based industry. </p>

Lignocellulosic biomass is composed of cellulose, hemicellulose, lignin and extraneous compounds (waxes, fats, gums, starches, alkaloids, resins, tannins, essential oils, silica, carbonates, oxalates, etc). The sugars within the complex carbohydrates (cellulose and hemicellulose) can be accessed for cellulosic bioethanol production through ethanologenic microorganisms. However, the composite nature of lignocellulosic biomass, particularly the lignin portion, presents resistance and recalcitrance to biological and chemical degradation during enzymatic hydrolysis/saccharification and the subsequent fermentation process. This leads to a very low conversion rate, which makes the process uneconomically feasible. Thus, biomass structure requires initial breakdown of the lignocellulosic matrix. In this study, two types of biomass pretreatment were applied on barley straw grind: radio-frequency (RF)-based dielectric heating technique using alkaline (NaOH) solution as a catalyst and steam explosion pretreatment at low severity factor. The pretreatment was applied on barley straw which was ground in hammer mill with a screen size of 1.6 mm, so as to enhance its accessibility and digestibility by enzymatic reaction during hydrolysis. Three levels of temperature (70, 80, and 90oC), five levels of ratio of biomass to 1% NaOH solution (1:4, 1:5, 1:6, 1:7, & 1:8), 1 h soaking time, and 20 min residence time were used for the radio frequency pretreatment. The following process and material variables were used for the steam explosion pretreatment: temperature (140-180oC), retention time (5-10 min), and 8-50% moisture content (w.b). The effect of both pretreatments was assessed through chemical composition analysis and densification of the pretreated and non-pretreated biomass samples. Results of this investigation show that lignocellulosic biomass absorbed more NaOH than water, because of the hydrophobic nature of lignin, which acts as an external crosslink binder on the biomass matrix and shields the hydrophilic structural carbohydrates (cellulose and hemicellulose). It was observed in the RF pretreatment that the use of NaOH solution and the ratio of biomass to NaOH solution played a major role, while temperature played a lesser role in the breakdown of the lignified matrix, as well as in the production of pellets with good physical quality. The heat provided by the RF is required to assist the alkaline solution in the deconstruction and disaggregation of lignocellulosic biomass matrix. The disruption and deconstruction of the lignified matrix is also associated with the dipole interaction, flip flop rotation, and friction generated between the electromagnetic charges from the RF and the ions and molecules from the NaOH solution and the biomass. The preserved cellulose from the raw sample (non-treated) was higher than that from the RF alkaline pretreated samples because of the initial degradation of the sugars during the pretreatment process. The same observation applies to hemicellulose. This implies that there is a trade-off between the breakdown of the biomass matrix/creating pores in the lignin and enhancing the accessibility and digestibility of the cellulose and hemicellulose. The use of dilute NaOH solution in biomass pretreatment showed that the higher the NaOH concentration, the lower was the acid insoluble lignin and the higher was the solubilized lignin moieties. The ratio of 1:6 at the four temperatures studied was determined to be the optimal. Based on the obtained data, it is predicted that this pretreatment will decrease the required amount and cost of enzymes by up to 64% compared to using non-treated biomass. However, the use of NaOH led to an increase in the ash content of biomass. The ash content increased with the decreasing ratio of biomass to NaOH solution. This problem of increased ash content can be addressed by washing the pretreated samples. RF assisted-alkaline pretreatment technique represents an easy to set-up and potentially affordable route for the bio-fuel industry, but this requires further energy analysis and economic validation, so as to investigate the significant high energy consumption during the RF-assisted alkaline pretreatment heating process. Data showed that in the steam explosion (SE) pretreatment, considerable thermal degradation of the energy potentials (cellulose and hemicellulose) with increasing acid soluble and insoluble lignin content occurred. The high degradation of the hemicellulose can be accounted for by its amorphous nature which is easily disrupted by external influences unlike the well-arranged crystalline cellulose. It is predicted that this pretreatment will decrease the required amount and cost of enzymes by up to 33% compared to using non-treated biomass.The carbon content of the solid SE product increased at higher temperature and longer residence time, while the hydrogen and oxygen content decreased. The RF alkaline and SE treatment combinations that resulted to optimum yield of cellulose and hemicellulose were selected and then enzymatically digested with a combined mixture of cellulase and β-glucosidase enzymes at 50oC for 96 h on a shaking incubator at 250 rev/min. The glucose in the hydrolyzed samples was subsequently quantified. The results obtained confirmed the effectiveness of the pretreatment processes. The average available percentage glucose yield that was released during the enzymatic hydrolysis for bioethanol production ranged from 78-96% for RF-alkaline pretreated and 30-50% for the SE pretreated barley straw depending on the treatment combination. While the non-treated sample has available average percentage glucose yield of just below 12%. The effects of both pretreatment methods (RF and SE) were further evaluated by pelletizing the pretreated and non-pretreated barley straw samples in a single pelleting unit. The physical characteristics (pellet density, tensile strength, durability rating, and dimensional stability) of the pellets were determined. The lower was the biomass:NaOH solution ratio, the better was the quality of the produced pellets. Washing of the RF-alkaline pretreated samples resulted in pellets with low quality. A biomass:NaOH solution ratio of 1:8 at the three levels of temperature (70, 80, and 90oC) studied are the RF optimum pretreatment conditions. The higher heating value (HHV) and the physical characteristics of the produced pellets increased with increasing temperature and residence time. The steam exploded samples pretreated at higher temperatures (180ºC) and retention time of 10 min resulted into pellets with good physical qualities. Fourier transform infrared-photoacoustic spectroscopy (FTIR-PAS) was further applied on the RF alkaline and SE samples in light of the need for rapid and easy quantification of biomass chemical components (cellulose, hemicellulose, and lignin). The results obtained show that the FTIR-PAS spectra can be rapidly used for the analysis and identification of the chemical composition of biofuel feedstock. Predictive models were developed for each of the biomass components in estimating their respective percentage chemical compositions.

Ce travail porte sur l'étude des voies réactionnelles accompagnant la liquéfaction desconstituants de la biomasse lignocellulosique dans un milieu aqueux proche du pointcritique. La stratégie expérimentale consiste à étudier la réaction en unité pilote decomposés lignocellulosiques modèles et à développer une approche analytiquemultitechnique originale afin de caractériser les structures et les masses moléculairesdes produits. Les résultats obtenus montrent que les schémas réactionnels sontcomplexes faisant intervenir de nombreuses voies de fragmentation et de condensationcompétitives. L'étude cinétique à différents temps de séjour montre que la fractionglucidique de la biomasse lignocellulosique a une réactivité très différente de sa fractionligneuse. / This work deals with the study of the reaction pathway during the lignocellulosicconstituent liquefaction by water near its critical point. Experimental method consists ininvestigation of lignocellulosic model compounds conversion in pilot plant combined withdevelopment of a new multitechnique analytical approach in order to characterizeproduct chemical structures and molecular weights. Results show that reaction pathwaysare very complex consisting to several fragmentation and condensation competitivereactions. The kinetic study with different reaction times reveals an important differenceof comportment for the glucidic fraction than the lignin fraction of biomass.