Esterification of organosolv lignin under supercritical conditions

Abstract

An organosolv lignin, extracted in organic acid media, named Biolignin™, was acetylated with acetic anhydride in supercritical carbon dioxide (scCO2). The effect of moisture and specific surface of lignin sample, temperature (50, 80, 100, 150 °C), reaction time and the use of a catalyst have been studied using analytical techniques such as FT-IR, quantitative 31P NMR and Differential Scanning Calorimetry (DSC). The reaction appeared to be more efficient when a dried organosolv lignin was used (97% Dry Matter) and with a specific surface of 0.645 m2/g. The highest degree of substitution of acetylated samples was obtained after 1 h of reaction at a temperature of 100 °C (180 bar) and in the presence of pyridine as a catalyst. When compared with conventionally acetylated lignin (using a solvent medium), it appeared that supercritical conditions allowed a higher yield of acetylation and a decrease of the glass transition temperature of the lignin.