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Optimisation du prétraitement par explosion à la vapeur des coproduits de l’industrie du bois d’okoumé : vers une production d’éthanol cellulosique

Abstract : The objective of this work is to study the valorization of co-products from the Gabonese okoumé wood industry in a biorefinery context. The production of cellulosic bioethanol and lignin based on a pre-treatment process that can be transposed to an industrial scale was studied. Our work, carried out on a laboratory scale, focused on (1) optimization of pre-treatment by steam explosion (SE), (2) extraction of lignin from exploded wood by percolation with ethanol as solvent, (3) characterization of biopolymers (cellulose and lignin) and study of the impact of pre-treatment parameters on their chemical structure, and (3) conversion of pre-treated wood to ethanol by enzymatic hydrolysis and fermentation. We were first interested in optimizing the different parameters of the SE process (particle size, preimpregnation, SE residence time and temperature) concerning the glucose, xylose and lignin contents of the exploded wood. The impact of the process on the production of sugar degradation products (furfural and HMF) potentially inhibiting enzymes and microorganisms was also studied. It was found that particle size is an important parameter to consider in process improvement, as fine particles lead to significant degradation of cellulose during pre-treatment. The influence of the concentration of acid, used to impregnate the biomass prior to SE, as well as process parameters (residence time and temperature) on the hydrolysis of biopolymers (lignin and hemicelluloses) was then studied. Conditions for optimizing cellulose contents (> 59%) in the pre-treated material were selected. In order to better understand the impact of pre-treatment on the lignin extracted from exploded wood and to anticipate future SE lignin utilizations, spectroscopic (HSQC and 31P NMR) and chromatographic (SEC) analyses were carried out. A decrease in β-O-4 content is observed with the increase in the severity of the treatment of SE with an almost total degradation of the β-O-4 units under conditions of highest severity (T = 210°C, t = 2.5 min and H2SO4 = 0.5%). Recondensation of lignin through radical coupling processes was also observed. The celluloses of the different solid fractions recovered after EV treatment were also characterized by SEC, DRX to study the impact of the treatment and to identify the key parameters in the improvement of the efficiency of cellulose to glucose conversion. An increase in crystallinity with increasing severity was observed with a significant drop in cellulose DP for acid impregnated SE. The enzymatic digestibility of cellulosic residues after SE and lignin extraction by T. Reesei was studied. The main parameters positively affecting the enzymic reactivity are the removal of part of the non-cellulosic polymers and the drop of cellulose DP. At high SE severity, a decrease in reactivity was attributed to the formation of pseudolignins. The optimal conditions for SE before enzymatic hydrolysis are as follows: T = 210°C, t = 5 min and H2SO4 = 0.25%. Good fermentability of the hydrolysates by Saccharomyces Cerevisiae was obtained. From 100 Kg of okoumé sapwood, it is possible to produce 11.9 Kg of ethanol.
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Submitted on : Monday, October 12, 2020 - 4:24:38 PM
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Sebastien Ngwa Obame. Optimisation du prétraitement par explosion à la vapeur des coproduits de l’industrie du bois d’okoumé : vers une production d’éthanol cellulosique. Matériaux. Université de Lorraine, 2020. Français. ⟨NNT : 2020LORR0088⟩. ⟨tel-02964724⟩

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