Transformation of lignin under uniform heating. I. Gasification in a flow of water vapor and supercritical water

Abstract

The paper presents the research results on the lignin gasification in a flow of water vapor and supercritical water (SCW) at uniform heating (1.5 K/min) of the tubular reactor to 928 K. It was revealed that the highest yield of thiols and H2S occurs at T < 613 K; at that, the amount of sulfur in the thiols is by ≈ 3.5 times greater than in the H2S. The temperature dependence of the CO2 yield has a minimum within the range of 703–748 K that results from the superposition of two following processes: exhaustion of O-containing groups in lignin, and acceleration of the steam reforming and water gas shift reactions with increasing temperature. The latter is indicated by a sharp increase in the yield of H2 at T > 748 K. The maximum yield of phenols is observed at 658–703 K. It is shown that in consequence of SCW gasification of lignin, a carbonized microporous residue is formed. According to X-ray diffraction analysis, burkeite, Na6(CO3)(SO4)2 is the major mineral component of the lignin SCW conversion residue.