Switchable carbamate coagulants to improve recycling ionic liquid from biomass solutions

Abstract

A reversible amine-carbamate approach has been developed to reduce the use of antisolvents such as water in the coagulation of biopolymers from ionic liquid (IL) solution and thus improve the economy of IL recycle. Cellulose and chitin were recovered from 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc]) solution by introducing the miscible amines triethanolamine (TEA), ethylenediamine (EDA), or butylamine (BA) and bubbling CO2 at 40 °C and atmospheric pressure through the solutions to form carbamate salts in situ which resulted in biopolymer coagulation. BA gave the best results because of its low boiling point and low viscosity, which benefited both biopolymer recovery and IL recycle. Cellulose films and fibers could be formed by extrusion of an MCC/[C2mim]‐[OAc] solution into a coagulating bath comprised of a 1:1 M mixture of [C2mim][OAc] and butylammonium butylcarbamate (BA-carbamate). The cellulose, IL, amine, and CO2 were easily separated, although the cellulose recovered required some water washings to remove traces of IL. Up to 96.4% of the [C2mim][OAc] could be recovered, 76.2% from the coagulation bath and 20.2% from the water washings. The recycled IL was suitable for another cycle of cellulose dissolution and extrusion and 84.6% of the IL used for the second cycle was recovered. Although further work is needed, not the least of which will be reducing the amount of water needed for washing steps, some promising features of this process point the way for new directions for more economically viable IL recycling processes in biomass treatment with ILs.

Keywords

• Carbamate
• Ionic liquid
• Recovery
• Switchable
• Coagulation
• Biopolymers