Deep eutectic solvent recycling to prepare high purity dissolving pulp

In this work, a novel acid-based deep eutectic solvent (DES) recycling process was developed for the pretreatment of eucalyptus wood chips in the preparation of high purity dissolving pulp. It was found that a large amount of lignin and xylan in the eucalyptus wood material were extracted in the recycling treatment with lactic acid/choline chloride. The dissolved lignin and xylan in DES were recovered by precipitation in water, and the DES solvent was regenerated by removing the water through evaporation. The residual lignin and xylan in the DES pre-treated wood chips were more readily removed in the subsequent kraft cooking and bleaching processes, yielding a high-purity dissolving pulp (DES-KP). Compared with the conventional prehydrolysis kraft based dissolving pulp (PHK), the DES-KP had a higher α-cellulose (94.02% vs. 89.81%) and a markedly higher Fock reactivity (98.94% vs. 60.97%). In addition, the DES pretreatment was also combined with oxygen-alkali cooking and ECF bleaching process, to prepare a dissolving pulp (DES-BP) with a high pulping yield (44.40%). The DES-KP pulping process was advantageous compared with the conventional PHK process in terms of the biorefinery concept, as the total utilization rate of the biomass of the eucalyptus wood chips reached 69.74%. Therefore, the DES pretreatment is a promising process for efficient biomass utilization in dissolving pulp production.