Esterification of free fatty acids using ammonium ferric sulphate-calcium silicate as a heterogeneous catalyst

Abstract

In view of the fast depletion of fossil fuels, biodiesel seems to be a possible new alternative to counter the fuel crisis. In order to avoid excessive exploitation of agricultural land for the production of food crop feedstock, the main focus has been on the usage of waste cooking oils meant for disposal to be used in biodiesel production. However, the high free fatty acid (FFA) content in waste oils has been an issue and it is envisaged that heterogeneous acid catalysts can be utilised as they would have a higher tolerance of FFAs and water. In this study, we report the synthesis and the utilisation of an inexpensive heterogeneous acid catalyst, namely ammonium ferric sulphate-calcium silicate (AFS-CS) synthesised via the impregnation method in 2:1 mass ratio in biodiesel production. The reaction conditions for esterification of lauric acid (LA) was optimised by using both standard and statistical analysis method which gave maximum methyl esters conversion of 100% within 2 h reaction time, 4 wt% of AFS-CS catalyst amount and 15:1 molar ratio of methanol to LA at 65 °C. Palm fatty acid distillate (PFAD) was esterified by using the same optimised conditions, which gave 72.6% of methyl esters conversion.