Catalytic hydrothermal liquefaction of castor residue to bio-oil: Effect of alkali catalysts and optimization study

Abstract Castor (Ricinus communis) is an evergreen, self- pollinating, perennial shrub that grows easily upto 10 m height. India ranks first in the world for the production of castor seed. Per ton of castor plant generates more than 50 % of residue in the form of its leaves and stems. Catalytic hydrothermal liquefaction of castor residue was performed at 260−300 °C for 60 min in the presence of alkali catalysts (KOH and K2CO3). The factorial design of experiments was used to understand the effect of process parameters (temperature and catalysts) on total bio-oil yield and conversion. ANOVA was used to analyze the main and interaction effects, while p-values were used to rank the process variables on product yield. It was observed that the use of catalyst enhances the total bio-oil yield and the maximum total bio-oil yield of ca. 21.20 wt. % was found at 300 °C in the presence of 0.5 M K2CO3. The experimental values are in good agreement with predicted values, indicating the accuracy of model for optimization of catalytic HTL of castor residue. Phenols and its derivatives, aromatics, N-contained compounds, acids were observed in bio-oil using GC–MS. An increase in the carbon and decrease in oxygen content leads to enhance the heating value of the product.