Co-generation of liquid biofuels from lignocellulose by integrated biochemical and hydrothermal liquefaction process

Abstract Different thermal stability of three major components is a challenge to efficiently liquefy lignocellulosic biomass into bio-oil because the degradation products from holocellulose can react with lignin, resulting in repolymerization reactions. In this work, a biorefinery approach of co-generation of bioethanol and bio-oil from rice straw that integrated separate hydrolysis and fermentation (SHF) and hydrothermal liquefaction (HTL) processes was proposed. SHF of dilute sulfuric acid pretreated rice straw gave a bioethanol concentration of 8.3 g/L with approximately 68% of theoretical yield. The maximum bio-oil yield 31.36 wt% via HTL of solid fermentation residues using bioethanol wastewater as the solvent was obtained under optimum conditions. Mass balance showed that 9.7 wt% bioethanol and 15.0 wt% bio-oil were produced corresponding to 56% energy recovery. Separate conversion of cellulose and lignin could be one promising way to enhance the overall energy recovery from lignocellulose to liquid biofuels.