Noncatalytic Gasification of Lignin in Supercritical Water

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 H 2, CH 4, CO, and CO 2 from lignin in supercritical water. CH 4 and CO 2 are always the major products. CO is formed, and its yield decreases with time. The yield of H 2 generally increases with time. With other variables fixed, the yields of H 2, CH 4, and CO 2 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 CH 4 /H 2 molar ratio. The highest H 2 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 %).