Continuous Transesterification Reaction of Residual Frying Oil with Pressurized Ethanol Using KF/Clay as Catalyst

The efficiency of a heterogeneous potassium fluoride (KF)/clay catalyst in continuous ester production from residual frying oil using pressurized ethanol is evaluated. Reactions without catalysts are conducted to determine the effect of the catalyst on ester yield. To verify the performance of the catalyst, the reactions are conducted for 3 h with determination of the ester yield every 30 min and characterization of the catalyst after each reaction. The influence of the temperature, catalyst mass used in the catalytic bed, and the residence time are evaluated. KF/clay is found to be efficient in ester synthesis and provides better results compared with non-catalytic reactions and the formation of esters is favored on increasing the temperature. The ester yields remain stable over time at 275 and 300 degrees C but at 225 and 250 degrees C the yields decrease by 48.42% and 38.40%, respectively. This may be due to the lower diffusion coefficient at these temperatures, implying that the reaction occurs preferentially at the catalyst surface. There is an increase in yield with an increase in the catalyst mass up to 2 g. The catalyst maintains its morphological characteristics after the reaction and the average mass loss in each reaction is Practical Applications: Transesterification at high temperature under pressurized conditions has great potential in biodiesel production, due to the efficiency in obtaining esters in short reaction times. In addition, the use of inexpensive and easily obtained clay-based catalysts contributes to higher yields and allows milder operating conditions. These factors make it possible to obtain biodiesel using a low-cost raw material (residual frying oil), under pressurized conditions, which will be of interest worldwide due to the various benefits linked to its use.