Influence of alkali and alkaline earth metals on the hydrothermal liquefaction of lignocellulosic model compounds

The alkali and alkaline earth metals (AAEMs) in biomass have a certain influence on its thermochemical conversion process. In order to study the influence of water-soluble AAEMs on hydrothermal liquefaction (HTL) to produce bio-oil, the metal chlorides of K, Na, Ca and Mg were used as additives, and glucose, xylan and lignin were typical lignocellulosic biomass to conduct HTL experiments. The results showed that AAEMs increased the yield of bio-oil from glucose and xylan by 42.1% and 23.8%, respectively, and the catalytic effect of alkaline earth metals was stronger. However, the addition of mixed metal chloride reduced the bio-oil yield and energy recovery of lignin. AAEMs provided more H+ and OH− active radicals in the aqueous phase, which intensified the esterification reaction and decarbonylation reaction, and promoted the diversification of substances. Meanwhile, AAEMs improved the Higher heating value and energy recovery rate of bio-oil, and Mg promoted the reduction reaction, the calorific value of bio-oil was increased by 7.4, 1.5 and 2.5%, respectively.