Glycerolysis of high free fatty acid oil by heterogeneous catalyst for biodiesel production

Abstract

The most widely used commercial biodiesel production technique, alkali-catalysed transesterification, requires only moderate temperatures and pressures to achieve a more than 98% conversion yield. Unfortunately, oil feedstock's high free fatty acid (FFA) content limits the technology's usefulness. A heterogeneous base catalysed glycerolysis process was investigated in this study to lower the FFA and meet these requirements. The response surface methodology (RSM) based on I-optimal design was used to model and optimize a CaO catalysed glycerolysis reaction under the influence of five reaction variables: temperature (60–180 °C), residence time (30–120 min), FFA concentration (6–50%), catalyst amount (0.4–0.6 wt (g/g)), and Glycerol to Oil ratio (G/O) (1–1.5). The data were fitted in a quadratic model, and R2 of 0.986 was observed, signifying that the model well defined the experimental data. The model was validated by running four replicates of the experiment, and a residual standard error of 2.7% was obtained, indicating the model would accurately predict future observations. The 48.584% FFA in oil was reduced to 0.98% under optimal conditions of 170 °C, 39.9 min of residence time, 0.591 wt g catalyst concentration, and 1.026 g/g glycerol/oil (G/O) ratio. CaO catalysed glycerolysis has significantly reduced FFA to less than 3% in less than an hour in biodiesel feedstock for biodiesel production.