HEMICELLULOSE EXTRACTION FROM SOFTWOOD CHIPS FOR BIOETHANOL PRODUCTION IN A CELLULOSIC FIBRE PRODUCTION MILL

摘要

Wood (composed of cellulose, lignin and hemicelluloses) is the main raw material used to producepaper cellulosic fibers used for the production of paper and board. Worldwide, the production of cellulosic fibers isabout 150 million tons, using about 310 millions tons of wood. The main process used to produce cellulosic fibers isan alkaline process called the Kraft process. These mills look very much like biorefineries : the cellulose is isolatedalmost pure in the kraft process, and then valorised principally as paper, the hemicelluloses and the lignin aredegraded and solubilised during the process, and form a very complex mixture, called “black liquor” that would bedifficult to be valorised chemically. They are thus burnt in a recovery boiler, which covers very largely the energeticneeds of the mill (in many cases, these mills are net electricity producers). The aim of this work is to define anextraction process of the hemicelluloses from softwood, prior to its transformation into cellulosic paper pulp by theprocess described above. The hemicellulose fraction (mainly composed of sugar in C6 for softwood species) that areextracted are relatively pure (contrary to the case where they are solubilised in the black liquor), and the cellulosefraction continues to be obtained as fibers. The lignin is thus left alone in the effluent of the kraft process andcontinues to be valorised thermically for the energetic needs of the mill. The hemicelluloses extracted and hydrolysedin hexoses are then fermented into bio-ethanol and could replace first generation bioethanol produced today fromfood raw material. Wood contains an average of 25 to 30% of hemicelluloses, which represents a huge potential.In this study, softwood chips were submitted to various hydrolysis treatments. Temperature, time and pH were variedso as to optimise the sugars extraction. The pre-hydrolysis liquors of the softwood chips were analysed for their sugarcontent, and submitted to fermentation tests for bio-ethanol production. The process developed in this study wouldrepresent an elegant way of producing second generation bioethanol in parallel to cellulosic fibers in an existing pulpmill.