Acid catalysts including Amberlyst 15 and sulfuric acid were used for heterogeneous and homogeneous catalyst reactions respectively, to reduce high free fatty acid (FFA) in sludge palm oil (SPO) using an esterification process. The goal of this research was to reduce high FFA content in SPO to less than 1 wt.% FFA so that it can be employed as a raw material in a transesterification process to produce biodiesel. Amberlyst 15 is an eco-friendly catalyst with many benefits, such as being reusable and generating non-toxic waste after reactions, compared to homogeneous catalysts, although the reaction time of the homogeneous catalyst was faster than the heterogeneous catalytic reaction. Therefore, esterification reactions with a heterogeneous and homogeneous catalytic reaction were carried out to examine conversion of FFA. The heterogeneous catalytic reaction decreased the FFA content from 89.16 wt.% to 1.26 wt.% under the recommended conditions of 44.7 wt.% methanol, 38.6 wt.% Amberlyst 15 catalyst loading, and 360 min reaction time. For homogeneous catalytic reaction, the FFA content of 1.03 wt.% was achieved under the recommended conditions of 58.4 wt.% methanol, 16.8 wt.% sulfuric acid, and 79.7 min reaction time. Furthermore, the results of the reusability research demonstrate that the heterogeneous catalyst may be reused for at least nine cycles. This research showed the promising potential of using SPO non-edible oil for biodiesel production by employing an eco-friendly heterogeneous catalyst for cost-effective environmental remediation.

In this study, Amberlyst-15 as heterogeneous catalyst was used for the reduction of free fatty acid (FFA) from the palm oil mill effluent (POME) for biodiesel production with acid-catalyzed esterification process. The objective of this study was to decrease a high FFA in POME to less than 2 wt.% FFA, for used as a raw material to produce biodiesel in the second-step transesterification process. Amberlyst-15 as an eco-friendly catalyst with non-toxic wastes after reactions, when compared to homogeneous catalysts such as sulfuric acid. Therefore, an esterification reaction with a heterogeneous acid catalyst was carried out to examine the FFA conversions. The conditions of two parameters of Amberlyst-15 catalyst (10–40 wt.%), and 1–8 h reaction time were varied, whereas the methanol to oil molar ratio and the speed of the stirrer were fixed at 5:1 and 300 rpm, respectively. As a result, the FFA sharply decreased from 89.16 wt.% to 1.75 wt.% under the conditions of 40 wt.% of Amberlyst-15, 5 h reaction time, 5:1 molar ratio methanol to oil, speed of the 300 rpm stirrer. The Amberlyst-15 had the potential to reduce high FFA in POME using the esterification reaction.