Potential yields and emission reductions of biojet fuels produced via hydrotreatment of biocrudes produced through direct thermochemical liquefaction

Abstract

BackgroundThe hydrotreatment of oleochemical/lipid feedstocks is currently the only technology that provides significant volumes (millions of litres per year) of “conventional” biojet/sustainable aviation fuels (SAF). However, if biojet fuels are to be produced in sustainably sourced volumes (billions of litres per year) at a price comparable with fossil jet fuel, biomass-derived “advanced” biojet fuels will be needed. Three direct thermochemical liquefaction technologies, fast pyrolysis, catalytic fast pyrolysis and hydrothermal liquefaction were assessed for their potential to produce “biocrudes” which were subsequently upgraded to drop-in biofuels by either dedicated hydrotreatment or co-processed hydrotreatment.ResultsA significant biojet fraction (between 20.8 and 36.6% of total upgraded fuel volume) was produced by all of the processes. When the fractions were assessed against general ASTM D7566 specifications they showed significant compliance, despite a lack of optimization in any of the process steps. When the life cycle analysis GHGenius model was used to assess the carbon intensity of the various products, significant emission reductions (up to 74%) could be achieved.ConclusionsIt was apparent that the production of biojet fuels based on direct thermochemical liquefaction of biocrudes, followed by hydrotreating, has considerable potential.

Potential for the Integrated Production of Biojet Fuel in Swedish Plant Infrastructures

“…HTL involves the thermal decomposition of biomass particles in a water slurry into a biocrude. The biocrude contains a complex mixture of organic compounds and has an oxygen content of 5-15 wt% [34]. HTL is an emerging process that is operated under high pressure (70-350 bar) and moderate temperatures (250-450 • C) in the presence of added alkali components that serve as a buffer and catalyst [35].…”

“…The required upgrading to drop-in fuel quality differs between the biofuel intermediates depending on their characteristics (Table 1) but typically includes: (i) oxygen removal, (ii) cracking of large molecules, and (iii) fractionation into different products. There is industrial experience regarding upgrading FT crude (from fossil fuels) to fuel quality, while the upgrading of fast pyrolysis oil and HTL crude is limited to the laboratory and pilot scale [34], and is probably the least developed for lignin oil.…”

“…Cracking of large molecules (with or without hydrogen) can be applied to increase the yield of petrol, jet fuel, and diesel. Furthermore, hydrocracking may be necessary in order to reduce the aromatic content, which is high in HTL biocrude (~60%) and pyrolysis oil (~40%) [34], and is likely to be even higher in lignin oil. The permissible aromatic content in fuel is considerably lower for diesel (<8 vol%), jet fuel (8-25 vol% after blending), and petrol (<35 vol%) [50].…”

“…The distributions presented in Table 4 reflect configurations that benefit jet fuel over petrol and diesel. The biojet fraction in the fuel mix is highest for the upgrading of ethanol at about 70% [45], up to 50% for FT crude, and 20-30% for both HTL crude and fast pyrolysis oil (this could possibly be increased by hydrocracking of the heavy fuel oil) [34]. For comparison, the jet fuel fraction at existing crude oil refineries is typically around 10% [4].…”

“…Characteristics of the biomass conversion technologies and biofuel intermediates, and the key upgrading requirements for producing biojet fuel[4,26,31,34,39,43,45].…”