Lignin extraction from black liquor using acetate based ionic liquids: Extraction kinetics and product characterization

Abstract

One ionic liquid, 1-ethyl-3-methylimidazolium acetate [Emim][Ac] and four acetate-protic ionic liquids (PILs), ethanolammonium acetate [Eth][Ac], diethylenammonium acetate [DiEt][Ac], propylammonium acetate [Prop][Ac], and pyrrolidinium acetate [Pyrr][Ac], were employed to extract lignin from Kraft black liquor (BL). Under atmospheric pressure and at 368 K, the total lignin extracted was 75.3 ± 3.4% (wt%) when using [Eth][Ac] in a 20:1 (w/w) [Eth][Ac]:BL ratio and a reaction time of 270 min. Fourier transform infrared (FTIR) spectroscopy and proton nuclear magnetic resonance (1H NMR) were employed to characterize the extracted lignin. Gel permeation chromatography revealed that molecular weights of 2283±67 g mol−1 and 1892±122 g mol−1 were measured for the lignin extracted using [Eth][Ac] and [Prop][Ac], respectively. The kinetics of lignin extraction were examined for a 270 min. reaction time period at three different temperatures. The lowest activation energy (Ea = 6.5 kJ·mol−1) was affiliated with [Prop][Ac]. The PIL with the maximum total lignin extracted, [Eth][Ac], was regenerated using vacuum distillation, and the lignin extraction ability of the regenerated solvent was found to be equivalent to the fresh solvent.