Synergistic action of EmimAc and aqueous NaOH for selective dissolution of hemicellulose for cellulose purification

Abstract

Aqueous EmimAc has been proved as a novel solvent for the selective separation of hemicellulose from chemical pulp. In this work, aqueous NaOH (NaOH-a) has been incorporated into the EmimAc solution to improve the hemicellulose separation. The interaction between NaOH-a and EmimAc has been investigated. In contrast to EmimAc/H2O system, EmimAc/NaOH-a shows better separation of hemicellulose from chemical pulp. In this case, introduction of NaOH with concentration 3–5% has negligible effect on crystal structure and DP of cellulose. Moreover, a dilute NaOH (3–5%) introduction can reduce the viscosity of the pulp-EmimAc/NaOH-a system, which is beneficial for the subsequent separation process. In addition, concentrated NaOH-a (7–10%) will lead to a substantial cellulose dissolution and therefore significant viscosity increase. The further study indicates that addition of NaOH to the aqueous EmimAc can weaken the acidity of hydrogen bond (α) and increase the net basicity (β − α), which are beneficial for the hemicellulose separation.