Alkaline pretreatment and hydrothermal liquefaction of cypress for high yield bio-oil production

• Alkaline pretreatment could markedly enhance bio-oil yield.
• Alkaline pretreatment could inhibit re-polymerization reactions.
• Resulting solid/liquid mixture was divided into six lumps.

The aim of this study is to investigate the feasibility and reaction mechanism of hydrothermal liquefaction of cypress via alkaline pretreatment to increase the bio-oil yield. The solid/liquid products were divided into ethanol insoluble organics, ethanol soluble organics, diethyl ether insoluble oil, diethyl ether soluble oil, acid soluble solid residue, and acid insoluble solid residue. The results showed that alkaline pretreatment could markedly enhance the bio-oil yield from 27.5% to 48.4% at 300 °C and was more helpful for suppression the re-polymerization reactions to form acid insoluble solid residue as compare to the un-pretreated cypress liquefaction runs. The optimum temperature of pretreated cypress liquefaction in hot-compressed water for ethanol soluble organics and diethyl ether soluble oil was raised from 280 to 300 °C. Alkaline pretreatment enhanced the decomposition temperature of cellulose and led to an increase in the crystal structure in cypress.