Renewable diesel blends production from hydrothermal liquefaction of food waste: A novel approach coupling fractional distillation and emulsification

Hydrothermal liquefaction (HTL) is a promising approach for producing biocrude oil from wet biowaste, but the suboptimal properties of HTL biocrude hinder its direct utilization as transportation fuel. This study presents an innovative approach by integrating fractional distillation and emulsification to upgrade HTL biocrude derived from food waste into renewable diesel blends. Fractional distillation is effective in removing metals, heavy fractions, and impurities, thus improving the physicochemical properties of the biocrude. Subsequent emulsification of distillates (10-30 wt%) with diesel, using Atlox 4912 as the surfactant, ensures a homogeneous mixture. The solubility of biocrude in diesel increased from 34.80 wt% to 100 wt% after distillation. Compared to direct HTL biocrude emulsification, distillate emulsion exhibited a 17.22% and 20.89% reduction in oxygen and nitrogen content, respectively, as well as significant improvements in terms of higher heating value, carbon and energy recoveries, and reduction of metal elements. The resulting emulsion demonstrated comparable viscosity, molecular weight, and boiling point distributions to the commercial diesel. Moreover, the oxidation and thermal stability tests revealed superior performance of distillate emulsion, with no observable sedimentation during the storage period. In contrast, direct biocrude emulsion experienced 14.37 wt% of phase separation. The mechanism of emulsion aging was then investigated, providing the basis for obtaining emulsions with preferable yield and quality. The comparative evaluation in this study showed that the integrated approach of fractional distillation and emulsification enhances the feasibility and quality of producing renewable diesel blends from HTL biocrude.