A comparison of the solvent liquefaction of lignin in ethanol and 1,4-butanediol

Abstract

This study compares the depolymerization of soda lignin via solvent liquefaction in ethanol and 1,4-butanediol (BD). The commercial soda lignin was fractionated based on solubility in ethyl acetate and methanol providing three fractions (F1 – soluble in ethyl acetate and methanol, F2 - insoluble in ethyl acetate and soluble methanol, F3 – insoluble in either) which varied mostly based on their molecular weight ranges with the average molecular weight following the order F1 <F2 <F3. The whole lignin and its factions were subjected to solvent liquefaction in ethanol and BD at 300 °C, to test the use of a high boiling solvent (BD) to reduce the required reaction pressure. Use of neat BD resulted in a bio-oil similar to that produced via pyrolysis of lignin, and which had a higher average molecular weight and fewer remaining methoxy groups than those produced in ethanol. This may be attributable to differences in lignin solubility in the two solvents. The addition of formic acid was also examined in each solvent. Use of formic acid in combination with BD promoted crosslinking resulting in bio-oil with higher molecular weight. The use of lignin bio-oils from each solvent were compared as feedstocks for the production of bio-pitch, finding that those produced in BD provided a coking value closer to that required for many applications.