Esterification of organosolv lignin under supercritical conditions

An organosolv lignin, extracted in organic acid media, named Biolignin (TM), was acetylated with acetic anhydride in supercritical carbon dioxide (scCO(2)). The effect of moisture and specific surface of lignin sample, temperature (50, 80, 100, 150 degrees C), reaction time and the use of a catalyst have been studied using analytical techniques such as FT-IR, quantitative P-31 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 m(2)/g. The highest degree of substitution of acetylated samples was obtained after 1 h of reaction at a temperature of 100 degrees 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. (C) 2014 Elsevier B.V. All rights reserved.