Dissolution of lignocellulosic biopolymers in ethanolamine-based protic ionic liquids

Abstract

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.