Techno-economic and life cycle analysis of biofuel production via hydrothermal liquefaction of microalgae in a methanol-water system and catalytic hydrotreatment using hydrochar as a catalyst support

The hydrochar, a by-product of hydrothermal liquefaction (HTL) of algal biomass, was utilized through two methods; combustion and activation, for its usage as a source of heat and a catalyst support for hydrodeoxygenation (HDO) process in the production of algal biofuels. In this study, techno-economic analysis (TEA) and life cycle assessment (LCA) of algal biofuels production in a two-stage process (HTL and HDO) were investigated. Aspen plus simulation and SimaPro software were used to analyze process economics and greenhouse gas (GHG) emissions. Microalgae at 200 dry metric tonnes day-1 was the basis for its conversion to biocrude oil through HTL in the methanol-water system followed by catalytic upgrading to produce biofuels. According to HTL experimental results, maximum biocrude oil yield of 57.8 wt% was obtained using microalgaesolvent mass ratio and methanol-water mass ratio of 1:5 and 3:1, respectively. Produced biocrude oil contained 14.5 wt% of oxygen and HHV of 33.4 MJ kgbiocrude oil - 1 which required upgrading to be utilized as a transportation fuel. HDO was employed to enhance the quality of biocrude oil with decrease in oxygen content (3.1 wt%) and increase in HHV (42 MJ kgbiofuel - 1 ). The minimum fuel selling price (MFSP) for using method #2 (activation) was 2.2 $ L-1 to breakeven the cost of operation, which was about 10% lower than that from method #1 (combustion). The GHG emissions performance was estimated at -1.13 gCO2-eq MJ-1 indicating the significant GHG emissions reduction compared to petroleum-based fuels production.