Diesel blends produced via emulsification of hydrothermal liquefaction biocrude from food waste

Abstract

Hydrothermal liquefaction (HTL) is a promising method for producing biocrude oil from wet biowaste. However, the complex composition of the HTL biocrude has several undesirable qualities, including high viscosity, total acid number (TAN), oxygen and nitrogen heteroatom content, and lesser higher heating value (HHV) in comparison to petroleum fuels. This study investigated the production of diesel blends and their fuel quality by emulsification of HTL biocrude with the aid of a block copolymer surfactant through centrifugation and ultrasonification. Four emulsion treatment variables were considered: biocrude fraction, surfactant fraction, retention time, and RPM (rotations per minute) for centrifuge or temperature for ultrasonic. Emulsification produced fuel blends with better HHV, viscosity, and TAN in comparison to HTL biocrude oil, and high solubility levels were achieved with surfactant addition and increased retention time. Maximum biocrude solubilities of 65.43 and 75.67 wt% were obtained for centrifugation and ultrasonification, respectively. Meanwhile, the highest HHV of centrifuge and ultrasonic emulsions was 45.39 and 45.73 MJ/kg, respectively. Emulsification led to viscosities as low as 5.91 and 6.06 mm2/s for centrifuge and ultrasonic samples, respectively. The TAN of emulsions were much lower than the biocrude: 14.18–41.31 and 16.22–50.31 mg KOH/g for centrifugation and ultrasonification, respectively. Thermogravimetric analysis, elemental analysis, combustion characteristics, and thermal properties gave further insight into the fuel quality of the emulsions and any deviations from the predicted HHV, viscosity, and TAN fuel properties, as well as comparison to ASTM specifications for biodiesel blends. The results show that emulsification of HTL biocrude could be an efficient and economical pathway for producing renewable diesel blends.