Hydrothermal Decarboxylation of Corn Distillers Oil for Fuel-Grade Hydrocarbons

Catalytic hydrothermal conversion of non-edible corn distillers oil (CDO), a low-value by-product of the ethanol industries, into high value fuel-grade hydrocarbons was investigated in near-supercritical water. The decarboxylation experiments were conducted using activated carbon in a 300 mL batch stirred tank reactor at reaction temperatures of 300–400 °C with pressure ranges from 2200–2500 psi (≈15–17 MPa), water/CDO (v/v) ratios of 2:1 to 5:1, and reaction times of 0.5 to 4 h at constant stirring speed (800 rpm). For the first time, complete removal of the −COO− group from CDO was achieved at 400 °C with 4 h of reaction time and a water/CDO (v/v) ratio of 4:1. The liquid products obtained were a mixture of saturated hydrocarbons, mainly C₈–C₁₆ (selectivity 49.7 %) and heptadecane (48.9 %) which have similar specific gravity, higher heating value (HHV), cloud points, and pour points to those of commercial fuels. 65 % liquid yield was obtained under optimal reaction conditions. The reaction mechanism was found to follow pseudo-first-order kinetics with an activation energy 66.1±3 kJ mol⁻¹, which is much lower than similar reported literature values for the decarboxylation process.