Lignocellulosic Biorefineries : Extraction and Valorization of Hemicelluloses

Today, the paper industry represents the most important chemical transformation of wood. Worldwide, the paper industry generates some 135 million tonnes of cellulose fibers annually, with purities ranging from 80% to 97%, using so-called chemical processes. These pulps are mainly produced from wood. Most cellulose fibers are obtained using the kraft process, an alkaline treatment applied to wood chips at high temperature (160°C on average). As the amount of cellulose in wood is only around 40%, even greater quantities of by-products are obtained. Today, these by-products are concentrated and burned, enabling the plants to be self-sufficient or even surplus in energy.

As hemicelluloses are degraded during the kraft process, one way of adding value to them would be to extract them upstream of the kraft process, using an autohydrolysis or acid hydrolysis process. The sugars obtained can be used to produce a multitude of products and materials, such as alcohols by fermentation, green surfactants (for the production of soaps, shampoos, detergents, cosmetics) and bioplastics.

The aims of this article are to compare the extraction of hemicelluloses from hardwood and softwood by autohydrolysis, to study the effect of autohydrolysis process parameters on the quantities of sugars extracted, and to give two examples of valorization of the hemicelluloses thus extracted: one for alcohol production and the second for surfactant production. The characterization and valorization of extracted oligosaccharides are discussed in a final section.