Multi-stage pretreatment of hydrothermal liquefaction biocrude oil as a precursor for sustainable aviation fuel production

Abstract

A major challenge for upgrading hydrothermal liquefaction biocrude into sustainable aviation fuel is the presence of inorganic material. Unlike commercial crude oil or biofuel from energy crops, excessive amounts of contaminants such as salt, water, and ash in biocrude oil from hydrothermal liquefaction can cause catalyst deactivation during hydroprocessing, decreased distillation efficiency, and equipment fouling from alkali deposits. Therefore, efficient removal of these impurities in HTL biocrude oil is essential. This work investigated a novel 3-stage pretreatment process, removing water, salt, and ash without chemicals, to produce a HTL biocrude oil precursor suitable for hydroprocessing. The influence of water to oil (W:O) ratio, temperature, and time on desalting efficiency was determined. After pretreatment, 81% of salt was removed, reducing total salt content to <0.1%. Improvements in elemental composition and physicochemical fuel properties were observed in biocrude oils from two feedstocks, with up to 39.8% decrease in oxygen content, 55% decrease in sulfur content, 22.2% decrease in nitrogen content, 9.86% increase in higher heating value, 73.4% decrease in total acid number, 99.9% decrease in viscosity, and 17.0% decrease in density. Compared with a single-step distillation as pretreatment, 3-stage pretreatment resulted in increased salt and heteroatom removal, improved heating value, and lower acidity. The precursor quality was viable for subsequential hydrotreating and other downstream refinery processes.