Noncatalytic Gasification of Lignin in Supercritical Water

Abstract

This article reports the first results for gasification of lignin in supercritical water in the complete absence of metal catalysis, by using quartz reactors. It also reports the first systematic study of the effects of temperature, lignin loading, water density, and reaction time on the production of H2, CH4, CO, and CO2 from lignin in supercritical water. CH4 and CO2 are always the major products. CO is formed, and its yield decreases with time. The yield of H2 generally increases with time. With other variables fixed, the yields of H2, CH4, and CO2 increase with temperature but exhibit minima as lignin loading and water density increase. The CO yield decreases with increasing lignin loading, water density, and temperature. Manipulating lignin loading provides an efficient means to control the CH4/H2 molar ratio. The highest H2 yield was 7.1 mmol/g, obtained at 725 °C and 60 min. Supercritical water gasification at 5.0 wt % lignin loading and 600 °C provided the highest total gas yield (90 wt %).