The Paper Pulp Industry: From the Production of Cellulose Fibers to Second Generation Integrated Biorefinery

The paper pulp industry can be considered as the biggest actor in wood chemistry, the processes developped in its mills having been working as biorefineries for over 100 years. This chapter first presents the three main components of wood, namely cellulose, hemicelluloses and lignin, before detailing the two industrial processes used today to produce cellulosic fibers: the acidic bisulfite and the alkaline kraft processes. The chemical reactions taking place during these processes are explained in order to understand how delignification occurs, what impact they have on the extracted lignin, and what is the fate of polysaccharides. The reasons why the kraft process is today the dominating one are explained. The current evolution of some of the kraft mills into more complete integrated biorefineries is presented: kraft lignin could be extracted from the cooking liquor and solubilisation of hemicelluloses in an autohydrolysis step ahead of the kraft cook could give access to oligo- and mono-saccharides (mannose, galactose, glucose, xylose, arabinose). These saccharides could then be used to produce alcohols by fermentation, green surfactants or prebiotics. Adding an autohydrolysis step would also advantageously enable to replace the kraft process by a simple caustic soda cooking which would yield sulfur-free products.