Optimizing the conditions for hydrothermal liquefaction of barley straw for bio-crude oil production using response surface methodology

Abstract

The present paper examines the conversion of barley straw to bio-crude oil (BO) via hydrothermal liquefaction. Response surface methodology based on central composite design was utilized to optimize the conditions of four independent variables including reaction temperature (factor X₁, 260-340°C), reaction time (factor X₂, 5-25min), catalyst dosage (factor X₃, 2-18%) and biomass/water ratio (factor X₄, 9-21%) for BO yield. It was found that reaction temperature, catalyst dosage and biomass/water ratio had more remarkable influence than reaction time on BO yield by analysis of variance. The predicted BO yield by the second order polynomial model was in good agreement with experimental results. A maximum BO yield of 38.72wt% was obtained at 304.8°C, 15.5min, 11.7% potassium carbonate as catalyst and 18% biomass (based on water). GC/MS analysis revealed that the major BO components were phenols and their derivatives, acids, aromatic hydrocarbon, ketones, N-contained compounds and alcohols, which makes it a promising material in the applications of either bio-fuel or as a phenol substitute in bio-phenolic resins.

Keywords: Barley straw; Bio-crude oil; Central composite design; Hydrothermal liquefaction; Response surface methodology.