Title: Optimization of process parameters in the upgrading of Scenedesmus obliquus oil to high-quality liquid-phase biofuel by nickel-impregnated biochar catalyst

Abstract

This work investigated the optimization of process parameters in the upgrading of the oil extracted from Scenedesmus obliquus microalgae using a novel nickel-impregnated biochar catalyst. The effects of temperature, dodecane-to-oil mass ratio and pressure on the upgraded liquid-phase biofuel yield were evaluated and optimized using central composite design of the response surface methodology (RSM). The model equation generated from RSM show that dodecane-to-oil mass ratio and pressure, as well as the quadratic effects of all the three factors, were significant model terms in predicting the yield of upgraded liquid-phase biofuel. Maximum liquid biofuel yield was attained at 246.89 °C, 3.72 (w/w) dodecane-to-oil mass ratio and 3.84 MPa hydrogen pressure in 6 h processing time. Validation runs resulted in an upgraded biofuel yield of 69%, which is in close agreement with predicted values generated by RSM. The upgraded biofuel comprised of 100% green liquid hydrocarbons containing 94% alkanes and 6% alkenes. Its main fuel properties, such as heating value (43.78 MJ kg-1), elemental composition, density, and viscosity exceeded those of the fatty acid methyl ester standard and were found comparable to those of petroleum diesel. More importantly, ultimate analysis as confirmed by Fourier transform infrared and gas chromatography – mass spectroscopy analyses showed significantly low oxygen and nitrogen content and absence of sulfur in the upgraded biofuel.