Cellulose and xylan, the two most abundant polysaccharides in hardwoods, are widely utilized in the manufacture of bio-based materials and chemicals. Prior to their utilization, these polysaccharides need to be isolated from the wood cell walls, preferably following green chemistry principles as well as biorefinery concepts. Within this context, hydrothermal treatment of biomass is a green method to extract the xylan and to produce a high-purity cellulosic pulp, provided an appropriate delignification process is also performed. Hydrothermal treatments are typically conducted on wood prior to Kraft pulping for the production of dissolving pulps, but they may also be conducted on paper-grade pulps for the separation of the xylan and cellulose fractions.<br/>In this study, we have investigated the effects of hydrothermal treatments of birch wood before pulping (pre-hydrolysis) and after pulping (post-hydrolysis) on the properties and structure of the pulp as well as on the recovery of xylan-based compounds. The results show that increasing the intensity of pre- and post-hydrolysis increases the purity of the cellulosic pulp. For a similar level of pulp purity, decreasing pre-hydrolysis intensity while increasing post-hydrolysis intensity results in a cellulose fraction with higher yield but lower degree of polymerization. On the other hand, the yield of xylan-based compounds in the aqueous hydrolysates is similar for pure pre-hydrolysis and post-hydrolysis treatments. Pre-hydrolysis in a batch reactor allows the recovery of considerable amounts of xylose, xylo-oligosaccharides, and acetic acid, while post-hydrolysis in a flow-through reactor allows the recovery of high-purity polymeric xylan with low degree of substitution. The crystalline structure of cellulose in the pulps and the accessibility of hydroxyl groups is currently being investigated. The utilization of selected cellulosic pulps and xylan-based compounds in high value-added applications is discussed.

Water pre- and post-hydrolysis of birch wood to produce high-purity cellulose and xylan-based compounds for material and chemical applications

253rd National Meeting (2017)

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