Dissolution of lignocellulosic biopolymers in ethanolamine-based protic ionic liquids

Abstract

This work evaluates the potential use of 2-hydroxy ethylammonium-based protic ionic liquids (PILs) for dissolving the major lignocellulosic biopolymers such as cellulose, xylose and lignin. Three PILs, 2-hydroxy ethylammonium formate (2-HEAF), 2-hydroxy ethylammonium acetate (2-HEAA) and 2-hydroxy ethylammonium propionate 2-HEAPr, were synthesized and characterized (viscosity, density and conductivity). A small amount of biopolymer was added to the PILs; the biopolymers’ dissolution curves were determined from 30 °C up to 100 °C on these solvents using a hot stage coupled to an optical microscope. The results show that while xylose and lignin could be dissolved by the PILs, cellulose could not, and also that 2-HEAF—which presented the higher ionicity—was the most appropriate PIL among those tested to dissolve these biopolymers (xylose and lignin). They also show that lignin dissolution is faster when an anion with a short alkyl carbon chain is used and that higher heating rates require a somewhat higher temperature to achieve full dissolution.