Comparison of pulp species in IONCELL-P: selective hemicellulose extraction method with ionic liquids

Abstract

Abstract In our recent studies, it was demonstrated that the IONCELL-P process selectively dissolves hemicelluloses from bleached birch kraft pulp in a mixture of 1-ethyl-3-methylimidazolium acetate ([emim][OAc]) and water as a solvent system. The IONCELL-P method refines paper-grade pulp to dissolving pulp with <5% hemicelluloses and allows isolation of polymeric xylan without yield losses or polymer degradation. This paper is a comparative study where paper-grade pine, birch, and eucalyptus pulps are subjected to the IONCELL-P process with two [emim]-based ionic liquids (ILs), i.e. [emim]acetate and [emim]dimethylphosphate. Also, the effect of an endoglucanase pretreatment was investigated to check whether 1) the pulp viscosity could be adjusted for the following process steps before the hemicellulose extraction and 2) the decreasing pulp viscosity would open the fiber structure and thus enhance the extraction. Under optimum conditions, the birch xylan content could be reduced from 25.4% down to 1.3% and for eucalyptus from 16.6% to 2.4%. Pine pulp xylan and glucomannan were decreased from 8.1% and 7.1% to 0.9% and 2.2%, respectively. The residual hemicellulose contents of the pine pulp could be further decreased with a hemicellulase pretreatment. The selectivity of the dissolution towards hemicelluloses was better for hardwoods. Adjusting the pulp viscosity by endoglucanase prior to the IONCELL-P process reduced the selectivity as short-chain cellulose molecules were extracted along with the hemicelluloses.