Optimization of Biodiesel Synthesis from Refined Bleached Deodorized Palm Oil Using Limestone CaO Catalyst Supported Chemically Activated Palm Oil Mill Fly Ash

Since the stability of CaO catalysts for biodiesel production is restricted, support materials are required to enhance their activity. This study examines an optimization of palm oil mill fly ash-supported limestone‐derived CaO for the production of biodiesel from refined, bleached, and deodorized palm oil (RBDPO). The utilization of natural materials such as limestone and FA provides a cost-effective alternative for catalyst production. The optimization consisted of varying two main parameters: the CaO-FA ratio (1:1, 2:1, 3:1) and the methanol molar ratio relative to RBDPO (8:1-14:1). The findings reveal considerable performance variation across conditions. The highest yield of pure CaO reached 81.34% at a molar ratio of 10:1, and the performance of CaO-FA catalysts was better or equivalent to pure CaO for different compositions. The CaO-FA (3:1) catalyst was found to be the best, yielding 88.52% biodiesel at a 14:1 methanol–oil ratio. GC-MS results confirmed high FAME conversion, with methyl palmitate (91.02% yield) as the dominant product, whereas SEM analysis revealed higher SiO₂ content and improved surface structure in FA-doped samples. Nonetheless, biodiesel produced under these operating conditions had total and free glycerol levels above the standard value set by the Indonesian National Standard (SNI). In general, FA-catalyzed CaO provides a stable catalyst for biodiesel production, and the optimization results indicate that the most favorable composition and operating conditions were obtained to produce high-quality biodiesel.