Synergistic photo-thermal catalytic liquefaction strategy of α-cellulose at low temperature in methanol for efficient biocrude production

In this study, we integrated photocatalysis with biomass thermal liquefaction technology to address the problems of limited yield and unstable quality of biocrude in conventional processes. Specifically, this photo-thermal synergistic system enables the efficient conversion of α-cellulose by fabricating a suspension through the homogeneous dispersion of cellulose and bismuth oxychloride photocatalyst in methanol solvent, followed by conducting the thermal liquefaction reaction under continuous light irradiation. Experiments were performed by selecting different process variables, including the reaction temperature (240-280 °C), holding time (10-50min), and the α-cellulose/methanol ratio (CMR, 5-15 wt%). Single-factor experimental results demonstrated that photocatalysis, functioning as an external energy input, was observed to facilitate reaction progression under relatively mild conditions. Furthermore, according to biocrude yield prediction model constructed based on the Box-Behnken design (BBD) response surface methodology, a maximum biocrude yield of 54.44 wt% was achieved at the optimized conditions of 270 °C, 15 min, and CMR of 5 wt%. Compared with the yield of 27.52 wt% obtained under dark condition without catalyst, this yield increased by 97.8%. In addition, conventional hydrothermal liquefaction (HTL) typically requires temperatures of 300-350 °C to achieve optimal biocrude yield and quality, while photo-thermal synergistic system enables high-yield biocrude production at significantly reduced temperatures of 260-280 °C. Product analysis revealed that the biocrude sample obtained under the photothermal synergistic system exhibited a relatively higher proportion of light fractions (e.g., C7 glycosidic compounds). This compositional shift contributes to improved fuel properties of the biocrude, rendering it better suited for energy-oriented applications.