Preparation of biodiesel from waste cooking oil by two-step catalyzed process

Two-step catalyzed process was adopted to prepare biodiesel from waste cooking oil(WCO).Free fatty acid of WCO was esterified with methanol catalyzed by ferric sulfate in the first step,and then triglyceride(TG) of WCO was transesterified with methanol catalyzed by potassium hydroxide.Results showed that ferric sulfate had strong activity to catalyze the estersification,and could be recovered for the further utilization.The optimal parameters of esterification obtained by orthonormal experiment were as follows: 2 % of ferric sulfate,10∶1 of mole ratio of methanol to FFA,4 h of reaction time,and 95℃ of reaction temperature.Under this condition,the esterification rate of free fatty acid was 97.22%.Transesterification was performed at 1 % of potassium hydroxide,65℃ of reaction temperature,1 h of reaction time,and 6∶1 of mole ratio of methanol to TG.The product with 97.02% of biodiesel was obtained after two-step catalyzed process analyzed by gas chromatography.This new process had many advantages compared with the old ones,such as no acidic wastewater,high efficiency,low cost equipment,and the recovery of catalyst.