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Compréhansion des mécanismes de destructuration de la matière cellulosique après prétraitement et de son aptitude à libérer un substrat carbone fermentescible dans un bioprocédé

Abstract : Lignocellulosic biomass consists of several agriculture and industrial by-products that can be used as raw material for several bioprocesses to obtain range of products. Among lignocellulosic sources, the pulp & paper industry is appropriated for modern bio-refining thank to pulp with low lignin content and free of inhibitory compounds. Besides, sugarcane bagasse is a very promising feedstock because of its simple chemical composition and its abundancy especially in tropical countries. In the bioconversion of lignocellulose, enzymatic hydrolysis is a crucial step that allows the transformation of cellulosic and hemicellulosic fibers into fermentable carbon sources. The lack of knowledge about physical limitations and hydrolysis mechanisms, especially at high dry matter content, stands as the main barrier which forbids the scale-up of bio-refinery processes. Thus, the efficient and sustainable use of lignocellulosic resources is currently a major challenge and need to be investigated. In this context, this PhD focused on the enzymatic hydrolysis of lignocellulose by both physical and biochemical approaches. The strategy consisted in carrying out and in analyzing the hydrolysis reactions under different operating conditions with semi-dilute suspensions. Then, obtained results were used to develop a hydrolysis strategy for concentrated suspensions. Different methodologies, in- and ex-situ analyses, were implemented and provided complementary results. From physical approach, analyses consisted in rheological behavior of suspensions as well as the morpho-granulometry of particles. The study was carried out on a reference substrate, Whatman paper, and on two industrial substrates, paper pulp and sugarcane bagasse. The strategy aimed to investigate different stakes: (i) evolution of rheological behaviors and the morphological properties of suspensions, (ii) hydrolysis mechanisms during the degradation of substrates, (iii) impact of substrate composition and structure on solubilization and hydrolysis kinetics, (iv) quantification of the contribution of single enzyme and enzyme mixture activities by multi-scale physical approaches and (v) control and optimization of feeding parameters for fed-batch process in order to access to concentrated suspension. Chapters 1 and 2 of this document are devoted to a research bibliographic and presentation of materials and methods. The third chapter presents obtained results and discussion in three sections. The first one is a study of the properties of different enzymes and substrates, in particular, the determination of semi-dilute and concentrated regime. Subsequently the enzymatic hydrolysis at semi-dilute regime is presented to highlight the hydrolysis mechanisms (fragmentation, solubilization, solvation and agglomerate separation) in relationship with enzyme mixtures and dosages. Finally, results in concentrated regime are discussed in the final section.
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Tuan Le. Compréhansion des mécanismes de destructuration de la matière cellulosique après prétraitement et de son aptitude à libérer un substrat carbone fermentescible dans un bioprocédé. Agricultural sciences. Université Paul Sabatier - Toulouse III, 2017. English. ⟨NNT : 2017TOU30133⟩. ⟨tel-01820661⟩

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