Annariikka Roselli

Novel concepts of dissolving pulp production

Herein, we report about existing and novel dissolving pulp processes providing the basis for an advanced biorefinery. The SO2–ethanol–water (SEW) process has the potential to replace the acid sulphite process for the production of rayon-grade pulps owing to a higher flexibility in the selection of the raw material source, substantially lower cooking times, and the near absence of sugar degradation products. Special attention is paid to developments that target toward the selective and quantitative fractionation of paper-grade pulps into hemicelluloses and cellulose of highest purity. This target has been accomplished by the IONCELL process where the entire hemicellulose fraction is selectively dissolved in an ionic liquid in which the H-bond basicity and acidity are adequately adjusted by the addition of a co-solvent. At the same time, pure hemicellulose can be recovered by further addition of the co-solvent, which then acts as a non-solvent. The residual pure cellulose fraction may then enter a Lyocell process for the production of regenerated cellulose products.

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.

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

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.

Cellulose fractionation with IONCELL-P

IONCELL-P is a solvent fractionation process, which can separate pulps almost quantitatively into pure cellulose and hemicellulose fractions using IL-water mixtures. In this work the role of the molecular weight of cellulose on its solubility in ionic liquid-water mixtures is studied. The aim of this study was to understand and identify the determining factors of this IONCELL-P fractionation. Cotton linters (CL) served as model cellulose substrate and was degraded by ozone treatment to adjust the molecular weight to that of hemicelluloses and low molar mass cellulose in commercial pulps. The ozone treated CLs were subjected to the IONCELL-P process using 1-ethyl-3-methylimidazolium acetate ([emim][OAc]) and water mixtures with a water content between 13.5 and 19wt%. Based on the molar mass distributions of dissolved and undissolved cellulose the effect of the molecular weight of cellulose in IL-water mixture appears to be a key factor in the fractionation process.

Understanding the role of water in the interaction of ionic liquids with wood polymers

Hemicellulose lean pulps are a raw material source for numerous high value products. We have previously presented the IONCELL-P(ulp) process, a hemicellulose extraction method, based on a binary mixture of ionic liquid and water. The IONCELL-P process does not suffer from yield losses or polymer degradation and retains the Cellulose I crystalline form. In this paper, a selection of cellulose dissolving ionic liquids is tested, in order to compare their applicability in the process. We demonstrate that the extraction selectivity towards low molar mass polymers is related to the anions ability to accept hydrogen bonds (Kamlet-Taft β-value), if divided by the water molar fraction of the solvent system. Pulp consistency, solvent system viscosity and pH are investigated in order to identify the factors affecting the extraction efficiency. The results show that all the tested ionic liquid-water mixtures were able to dissolve hemicelluloses, but there were differences in their efficiency, selectivity and the ability to process high pulp consistencies.