Decomposition Characteristics For China Fir Lignin At Different Hydrothermal Conditions

Nowadays, more and more atterntions are paied to the development and utilization of biomass resources, for the crises of ever-shrinking of the fossil fuel reserves and environmental pollution.The hydrothermal conversion of biomass technology is a promising one with the excellent characteristics of environmental protection and high-efficiency.And abundant phenolic compounds can be obtained by the hydrothermal conversion of lignin, which is an important chemicals. In the present work, decomposition characteristics of enzymatic / mild acid hydrolysis lignin(EMAL) and alkali lignin were explored at different hydrothermal conditions. It is expected to lay the theoretical foundation for the conversion of lignin into high value-added chemicals and high quality liquid fuel.In this study, effect of reaction temperature and retention time of two kinds of lignin on the hydrothermal depolymerization were explored by means of GC/MS, GC-FID, LC-HRMS, elemental analysis and FTIR.The results revealed that EMAL possessed lower high heating value(HHV) and larger molecular weight than alkali lignin. The reaction liquid product(LP) yields of EMAL and alkali lignin increased first and then decreased with the rising of the temperature from 250 ℃-350 ℃, and peaked at 325 ℃. The rate of conversion of energy conversion rate of carbon showed the same trend. At this time, the liquid products were up 40.38%, and 63.57%, respectively. The molecular weight distribution of LP in alkali lignin was lower than that in EMAL. In the process of lignin hydrothermal decomposion, the reactions of decarbonylation, demethylation and dealkylation occurred. When the temperature was up to 350℃, the lignin was condensed, even carbonized.The LP yields of these two kinds of lignin achieved maximum at 30 min, after retention time of 0~60 min. At the retention time of 60 min, the total yields of mainly monophenols for alkali lignin and EMAL are respectively 91.37, and 43.27 mg样g-1. Deoxidation took place in the solid residue(SR) after hydrothermal conversion reaction, and this improved the energy density of SR. There was still the signal of lignin structure in SR, when reaction lasted 60 min. So it was not exact coke at that time.In addition, hydrothermal depolymerization characteristics of lignin at co-catalystic conditions of formic acid/formate and Ru/C were studied in this work. The results showed that the alkali lignin performed a better degradation under the catalyzation of formic acid and Ru/C. Furthermore, there was a higher yields of monophenols when formic acid were added to 0.8 mol样L-1 at 350℃. L1, L2 and L3 for three different fractions of alkali lignin. With the highest HHV,lagest molecular weight, and highest hydroxyl content, L1 made the largest contribution to yields of LP and monophenols, and the yields of main monophenols could reached112.71 mg· g-1.at this time, guaiacol and 4- methy-guaiacol were dominant, and achieved 35.38 and 35.52 mg· g-1, respectively. Proper isolation of lignin before hydrothermal conversion was benefit for the liquefaction reaction.