ALGLIQOL: A two stage integrated process towards synthesis of renewable transportation fuel via catalytic hydrothermal liquefaction of lipid enriched microalgae biomass and distillation

Abstract

Present study demonstrates a two-stage integrated process for production of hydrocarbon oil designated as ALGLIQOL, with potential to be utilized as liquid transportation fuel. Stage-I involves in-situ catalytic hydrothermal liquefaction (HTL) of microalgae biomass to produce biocrude oil and stage-II involves distillation of biocrude to hydrocarbon oil. A strategic attempt has been implemented to develop stage-I, where improvement not only in the biocrude oil yield but also in its quality was achieved in three sequential steps. Step 1: statistical optimization of HTL process parameters i.e. retention time, biomass loading, and temperature; step 2: in-situ catalytic HTL under optimized process parameters, exploiting combinatorial effect of homogenous and heterogenous catalyst, Pd/Al2O3 and formic acid, respectively and step 3: catalytic HTL using lipid enriched biomass as feedstock. The maximum biocrude oil yield was 28.67 wt%, at optimal temperature 300.9 °C, retention time 71 min, biomass loading 8.86% w/v, Pd/Al2O3 loading 10 % w/w, formic acid loading 7.73% w/v and intracellular lipid percentage 20% w/w. The improvement in quality of biocrude oil was marked with improved hydrocarbon fraction and concomitant reduction in oxygenates and nitrogenates fractions. Systematically improved physical parameters of biocrude oil such as kinematic viscosity, density and TAN, were found to be comparable with the ASTM and EN specifications of the diesel fuel and biodiesel. Calorific value of the final product ALGLIQOL was estimated to be 41 MJ kg−1 with density 822 kg m−3, kinematic viscosity 1.61cSt and TAN 0.663 mg KOH g−1. GC–MS analysis of ALGLIQOL indicates a hydrocarbon fraction of 81.25%, with abundance of aromatics, alkene and alkane. Significant similarity in physiochemical properties of ALGLIQOL and gasoline or diesel fuel, indicates its suitability as transportation fuel.