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

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 approximate to 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 H-2 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, Na-6(CO3)(SO4)(2) is the major mineral component of the lignin SCW conversion residue.