Enhanced conversion of used palm cooking oil to biodiesel by a green and recyclable palm kernel shell ash-derived catalyst: Process optimization by response surface methodology

Abstract

Palm kernel shell ash (PKSA) and used palm cooking oil (UPCO) are both waste materials that still have economic value with proper utilization. Thus, the aim of this research was to convert UPCO into biodiesel using a green and recyclable catalyst made from abundant PKSA, employing the response surface methodology with a central composite design (RSM-CCD) approach. Here, the PKSA-derived heterogeneous catalyst (PKSADHC) was synthesized using the solid-state method and characterized using XRD, FTIR, and SEM. The GC-MS instrument was used to characterize the biodiesel produced. Optimized conditions achieved were: catalyst amount of 6 wt%, methanol:UPCO of 15:1, reaction temperature of 50 °C for 90 min, and an excellent biodiesel yield of 99.01%. All tested parameters significantly influence the yield of biodiesel. The produced biodiesel meets the physicochemical properties required by EN 14214 and ASTM D6751 standards. The spent catalyst can be used for up to six cycles with a biodiesel yield above 80%. Therefore, the use of PKSA as a catalyst precursor for UPCO transesterification contributes to a reduction of around 47.24% of PKSA waste compared to the total UPCO waste produced annually, as well as enabling a reduction in biodiesel production costs on a large scale.

Keywords

• PKSA
• Used palm cooking oil
• Biodiesel
• RSM