Using ionic liquid (EmimAc)-water mixture in selective removal of hemicelluloses from a paper-grade bleached hardwood kr
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ORIGINAL RESEARCH
Using ionic liquid (EmimAc)-water mixture in selective removal of hemicelluloses from a paper-grade bleached hardwood kraft pulp Bo Yang . Xiaoyu Qin . Huichao Hu . Chao Duan . Zhibin He . Yonghao Ni
Received: 26 June 2020 / Accepted: 29 August 2020 Ó Springer Nature B.V. 2020
Abstract In this paper hemicellulose was separated by using 1-ethyl-3-methylimidazolium acetate (EmimAc, an ionic liquid) -water mixtures from a paper grade market bleached hardwood kraft pulp to produce dissolving pulp. Pure EmimAc dissolves pulp fibers completely in 30 min at ambient temperatures. By adding water (as an antisolvent to EmimAc system) the cellulose dissolution decreases and by optimizing the conditions, hemicellulose is largely removed while cellulose remains as the solid residue (dissolving pulp). At optimal conditions: molar ratio of water to
EmimAc of 2, 60 °C, an alpha-cellulose content of 92.2%, with a high yield (78 wt%) was obtained. The viscosity of the solvent mixture decreases by increasing water to EmimAc molar ratio, which improves the mobility of ions, thus, facilitating their penetration into pores and lumens of the fibers during the dissolution process. Cellulose purity increases and purified cellulose yield decreases with the increases in temperature and water content (up to 2 wt%) in the mixture. This study implies that the optimal EmimAc/ water mixture is an effective system to separate hemicellulose from hemicellulose/cellulose matrix.
Bo Yang and Xiaoyu Qin have contributed equally, therefore are co-first authors.
Keywords Dissolving pulp Cellulose Ionic liquid (IL) EmimAc Hemicellulose removal Fiber swelling Cellulose crystallinity
B. Yang C. Duan Z. He Y. Ni (&) Department of Chemical Engineering, University of New Brunswick, Fredericton, NB E3B5A3, Canada e-mail: [email protected] X. Qin C. Duan (&) College of Bioresources Chemical and Materials Engineering, Shaanxi Provincial Key Laboratory of Papermaking Technology and Specialty Paper Development, Shaanxi University of Science and Technology, Xi’an 710021, China e-mail: [email protected] H. Hu (&) College of Material Engineering, Fujian Agriculture and Forestry University, No. 15 Shangxiadian Road, Cangshan District, Fuzhou City 350002, Fujian Province, People’s Republic of China e-mail: [email protected]
Introduction The processing and dissolution of cellulosic materials using ionic liquids (ILs) have received much interest in the research community, especially, ILs with a low melting point temperature (lower than 100 °C), or socalled room temperature ionic liquids (RTILs). Among the RTILs, the dialkyl imidazolium-based ILs, e.g., AmimCl, BmimCl and EmimAc, have received extensive attention (Zhang et al. 2017). Zhang et al. (2005), by using AmimCl as cellulose
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Cellulose
fiber solvent, prepared a 30 wt% cellulose solution, with a degree of polymerization (DP) of 650. The mechanism of cellulose dissolution using ILs is as follows: (1) the strong H-bondin
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