Separation of hemicellulose and cellulose from wood pulp by means of ionic liquid/cosolvent systems

Pulp of high cellulose content, also known as dissolving pulp, is needed for many purposes, including the production of cellulosic fibers and films. Paper-grade pulp, which is rich in hemicellulose, could be a cheap source but must be refined. Hitherto, hemicellulose extraction procedures suffered from a loss of cellulose and the non-recoverability of unaltered hemicelluloses. Herein, an environmentally benign fractionation concept is presented, using mixtures of a cosolvent (water, ethanol, or acetone) and the cellulose dissolving ionic liquid 1-ethyl-3-methylimidazolium acetate (EMIM OAc). This cosolvent addition was monitored using Kamlet-Taft parameters, and appropriate stirring conditions (3 h at 60 °C) were maintained. This allowed the fractionation of a paper-grade kraft pulp into a separated cellulose and a regenerated hemicellulose fraction. Both of these exhibited high levels of purity, without any yield losses or depolymerization. Thus, this process represents an ecologically and economically efficient alternative in producing dissolving pulp of highest purity.