Preparation of solid acid catalysts from waste biomass and their application for microwave-assisted biodiesel production from waste palm oil

Abstract

Waste utilization is essential and challenging. Utilization of wastes gives environmental, economic, and social benefits. In this study, inexpensive, sulfonated solid acid catalysts were successfully prepared from palm empty fruit bunch (PEFB), coconut meal residue (CMR), and coconut coir husk (CH) waste by a simple protocol. It was found that prepared PEFB–BCS–SO₃H, CMR–BCS–SO₃H, and CH–BCS–SO₃H catalysts have 4.79, 3.75, and 2.80 mmol g^-1 acid density and 739.0, 89.77, and 61.49 m² g^-1 surface areas, respectively. Further, the presence of active functional groups on the surface of the catalysts was confirmed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. Thermal stability of the catalysts was found below 150°C. Results show that biodiesel yield increases with increasing reaction time and methanol loading, when using microwave heating for biodiesel production from waste palm oil (WPO) and prepared catalysts. A maximum biodiesel yield of 95.5% was obtained by PEFB–BCS–SO₃H in 60 minutes using 20:1 methanol:oil (molar ratio) at 70°C. CMR–BCS–SO₃H and CH–BCS–SO₃H obtained 88.7 and 88.5% biodiesel yields in 60 minutes, using 20:1 and 16:1 methanol:oil (molar ratio), at 70 and 110°C, respectively. Even though, the activity of the catalysts decreased during reuse, these are still of interest as the waste biomass of PEFB, CMR, and CH can be used for catalyst preparation and microwave-assisted biodiesel production from WPO.