Automotive sustainable diesel blendstock production through biocrude obtained from hydrothermal liquefaction of municipal solid waste

Abstract

Hydrothermal liquefaction (HTL) bio-crude is known as a potential alternative to conventional fossil fuels in the existing infrastructure. Although HTL has enormous potential as a process for renewable fuel production, developing economically viable HTL-based value-chains has encountered extensive challenges owing to the contaminants and the complex matrix it possesses. Therefore, devising efficient downstream processing and blending strategies is of high importance. This study evaluates different bio-crude refining scenarios; namely 1) pre-stabilization using partial hydrotreating, 2) fractionation through vacuum distillation and 3) the integration of the former processes, in producing a compliant HTL-derived road diesel blendstock. The combination of the distillation fractions is optimized through a multi-objective optimization method minimizing the deviation from the road diesel standard specifications. The optimized blend fuels are combusted in an optical accessible compression-ignited chamber (OACIC) to assess the exhaust emissions. Partial hydrotreating successfully improves the distillation recovery from 22.7 wt% (raw bio-crude) to 55.6 wt% along with a significant improvement in the physicochemical properties. The hydrotreated bio-crude distillate mixture is an adequate diesel blendstock that complies with the standard specification by at least 5 wt% contribution to the finished fuel. The results also show that with a slight improvement in the desulphurization of bio-crude, the bio-blendstock share can increase up to 10 wt%. With the comparable GHG emission profile to the reference diesel, the hydrotreated bio-crude distillate mixture heralds a promising green blendstock that can significantly contribute to meeting the current road transport diesel fuel demand.