Treatment of free fatty acid in sludge palm oil via glycerolysis for biodiesel feedstock

The depletion of fossil fuels has prompted the nation to transition toward sustainable and renewable energy sources. Biodiesel, which is typically produced from fats derived from vegetable oils, is one of the promising alternatives due to its notable attributes. However, the use of these oils as biodiesel feedstock has resulted in high production costs and raised concerns regarding food security. Sludge palm oil (SPO), which is primarily collected from palm oil mill effluent (POME), has the potential to replace vegetable oils as biodiesel feedstock. Nevertheless, the high free fatty acid (FFA) content in SPO is undesirable, as it causes soap formation, resulting in low biodiesel yield. Therefore, in this study, SPO was treated using the glycerolysis method to reduce the FFA content to below 3% prior to biodiesel production. SPO collected from POME was characterized both physically (FFA, moisture content, and saponification value) and chemically (functional groups, fatty acid composition, and chemical composition) to assess its feasibility as a biodiesel feedstock. A comparison between SPO and crude palm oil (CPO) was conducted, and the results indicated that both possessed similar qualities, although SPO required pretreatment. Glycerolysis was then carried out to treat SPO by adding glycerol in the presence of zinc oxide as a catalyst to reduce the FFA content (59%) through the formation of glycerides and water. The effects of reaction temperature (170°C, 190°C, and 220°C), catalyst loading (0.25 wt%, 0.50 wt%, and 1.0 wt%), and SPO to glycerol molar ratio (1:1, 1:1.5, and 1:2) on FFA reduction were investigated to determine the optimum conditions. The lowest FFA value achieved was 0.46%, corresponding to a 99.4% FFA reduction efficiency, at 220°C, 1.0 wt% catalyst loading, and a 1:2 SPO to glycerol molar ratio. The treated SPO with the lowest FFA content was subsequently used for biodiesel production via transesterification. Ethanol was employed as the alcohol, with potassium hydroxide serving as the catalyst. The produced biodiesel was analyzed using Fourier-transform infrared spectroscopy (FTIR) and gas chromatography–mass spectrometry (GC–MS) to confirm biodiesel formation. The formation of palmitic acid ethyl ester as the major composition in produced biodiesel indicated the successful conversion of SPO into biodiesel, signifying the effectiveness of glycerolysis as treatment method to reduce the FFA content in SPO.