Reactive extraction of lignin from wood using supercritical ammonia-water mixtures

Abstract

Supercritical Fluid (SCF) extraction was used to selectively remove lignin from yellow poplar wood ( Liriodendron tulipifera L). The process may serve as an alternative to conventional delignification techniques practiced by the pulp and paper industry. Extraction experiments were performed by flowing supercritical ammonia-water mixtures through a fixed bed of poplar wood. Extraction of cellulose, hemicellulose, and lignin was determined as a function of time (0–3 h), solvent composition (0–20 wt % water), temperature (160–200 °C), and pressure (136–272 atm). The percentage of water in the solvent and temperature were found to be the most important variables in determining extraction efficiency. A simple model involving these variables was developed. The most effective extraction was obtained using 20 wt % water in ammonia at 272 atm and 200 °C, at these conditions about 70% of the lignin, 50% of hemicellulose, and 15% of the cellulose initially present in the wood were extracted in one hour.