Enhancing biofuel production in hydrothermal liquefaction of cassava rhizome through alkaline catalyst application and water-soluble product recirculation

Hydrothermal liquefaction (HTL) possesses an outstanding biomass thermal conversion technology for producing biocrude oil (BO). Here, cassava rhizome (CR) was converted into BO via catalytic HTL using 1.0–10.0 wt% of K₂CO₃ and Na₂CO₃ with water-soluble product (WSP) recirculation at 275 °C for 15 min. The catalysts and WSP recirculation could enhance the BO fuel properties. The dominant BO yield of 38.00 and 34.80 wt% and HHV of 25.42 and 25.92 Mj/kg were derived using 4.0 wt% of K₂CO₃ and Na₂CO₃, respectively. Chemical compositions of the BO were principally phenols and hydrocarbons, which can be further upgraded and fractionated into alternative biofuels. On the other hand, the mass yield and HHV of the hydrochar (HC) co-product were reduced by the alkaline catalysts, while being maintained by WSP recirculation. The HC fuel characterization elucidated that the HC can be used as an alternative to coal. Furthermore, WSP characterization determined that organic acids were the major composition of the WSP. Thus, WSP recirculation can enhance CR decomposition according to the proposed reaction mechanism. These results indicate that the alkaline application and WSP recirculation constitute a dominant method for enhancing biofuel production via HTL.