Biomass is considered as the only source of renewable carbon for the production of energy and chemicals. After a first generation of biofuels produced from vegetable oils (biodiesel) or from sugar culture (bioethanol) in the early 2000s, nowadays lignocellulose, coming from nonedible agricultural resources, is the center of research’ attention. Biorefineries were designed to transform and valorize lignocellulose into fuels and chemicals. To improve both economic viability and carbon balance of biorefineries, the use of the entire lignocellulose, including cellulose but also hemicellulose (20−40 wt %) and lignin (15−35 wt %), is essential. In this context, hemicellulose valorization is a key-point of the viability of biorefineries. Hemicelluloses are non-crystalline polysaccharides present in lignocellulose in significant amount, from 20 to 40 wt.%. Their valorization into high added value sugars or platform chemicals is a major stake for biorefineries. For example, polyols (xylitol, arabitol, galactitol), furans (furfural, hydroxymethylfurfural) can be produced from ex-hemicelluloses sugars. However, depolymerization of hemicelluloses by catalytic processes was underinvestigated in the past decades. Here, we present recent results on catalytic hydrolysis of hemicelluloses using robust mixed oxide acid catalysts in batch and in continuous mode. The hydrolysis of xylan with various molecular weights was performed in batch and continuous modes over TiO2-based acid catalysts. Reactions in batch mode were used to screen catalysts, study their recyclability and build a simple kinetic model in which the formation of humins (non identified carbon compounds) was elucidated. Reactions in continuous mode in a fixed bed reactor were used to investigate the catalyst deactivation and regeneration and to study the reaction at short contact times. A robust kinetic model was fed with data from both batch and continuous modes. A first result is that in batch mode, humins are formed in majority from hemicelluloses and in minority from furfural, whereas the pathway “xylose to humins” is negligible (Figure). These results will be helpful to design innovative processes for hemicelluloses valorization in an integrated biorefinery framework.

Catalytic processes for hemicelluloses valorisation in batch and continuous modes

256th National Meeting (2018)

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