Comparative catalytic performance of mesoporous and microporous NaP zeolites synthesized from natural kaolin via hydrothermal and sonochemical methods for castor oil transesterification

The transition toward renewable energy has positioned biodiesel as a critical component in reducing fossil fuel dependence. In Indonesia, biodiesel is currently blended at 40 %, with government targets set to achieve 100 % pure biodiesel (B100). Castor oil ( Ricinus communis ) offers a sustainable, non-edible feedstock that supports energy diversification without compromising food security, while also promoting agricultural and rural economic development. However, achieving high-efficiency conversion of castor oil to biodiesel requires robust heterogeneous catalysts. Natural kaolin-based zeolite catalysts offer a promising low-cost alternative for biodiesel production, yet suffer from limitations such as low surface area, limited porosity, and uncontrolled crystallinity, which hinder their catalytic efficiency. This study presents a comparative analysis of mesoporous and microporous NaP zeolites synthesized from natural kaolin via ultrasonic-assisted and conventional hydrothermal methods. The synthesized zeolites were characterized using XRD, XRF, nitrogen adsorption–desorption (BET–BJH), and GC–MS to investigate structural, textural, and catalytic properties. The study systematically evaluates the influence of synthesis parameters—specifically stirring duration and SiO₂/Al₂O₃ molar ratio—on the resulting framework crystallinity, and surface area. NaP zeolites synthesized via CTAB-assisted sonochemical methods exhibited improved mesoporosity and higher surface areas compared to conventional hydrothermal products, facilitating better diffusion of bulky castor oil molecules during transesterification. Catalytic performance tests revealed that the optimized mesoporous NaP zeolite significantly enhanced biodiesel yield, as confirmed by GC–MS analysis of methyl ester (99.8 %) composition. These findings demonstrate that tailored synthesis of NaP zeolite can effectively overcome the limitations of raw kaolin and provide a scalable pathway for developing efficient solid-base catalysts for biodiesel production from non-edible oils. • Natural kaolin was transformed into NaP zeolite via hydrothermal and sonochemical routes. • Mesoporous NaP zeolite improved castor oil diffusion and transesterification efficiency. • Optimized NaP zeolite achieved up to 99.8 % methyl ester yield by GC–MS analysis.