Simulation of water effect on biodiesel production using waste cooking oil via ester-transesterification in a reactive distillation column

Abstract

This research investigated the effect of water content in waste cooking oil (WCO) on the performance of a reactive distillation column for biodiesel production via ester-transesterification. A mixture of triolein and oleic acid was used as a WCO model compound. Amberlyst-15 was used to catalyze esterification while CaO was used for transesterification. From Langmuir-Hinshelwood-Hougen-Watson (LHHW) kinetic model taking into account water absorption for esterification of oleic acid (FFA), biodiesel yield was decreased with increasing of water content in WCO feedstocks. On the other hand, the initial rate of transesterification was increased with increase of amount of water in WCO feedstocks in the range of 0-5%wt. However, when biodiesel yield reached the maximum value of 30-40%, saponification as a side reaction became significant and the emulsion phase of feedstocks was present, resulting in significant decrease in biodiesel yield. Therefore, the water contaminated in feedstocks should be avoided because of the presence of saponification even when using heterogeneous CaO catalyst for biodiesel production. Interestingly, hybridized reactive distillation can handle the feedstocks with the presence of water in the range of 0-8%wt commonly found in most WCO sources. It was found that the water was vaporized to the top of the column and did not flow down to the transesterification section. The hybridized reactive distillation can produce 97% biodiesel yield with 96.5% biodiesel purity according to EN14214 standard with the use of total stages of 26, reflux ratio of 0.1 and reboiler duty of 50-128 kW for the WCO feed of 1 kmol/h