MODELING AND OPTIMIZING THE CATALYTIC TRANSESTERIFICATION PARAMETERS IN BIODIESEL PRODUCTION FROM WATERMELON SEED OIL, USING RESPONSE SURFACE METHODOLOGY (RSM) APPROACH

Abstract

The increasing global demand for sustainable energy sources has intensified research into alternative feedstocks and catalysts for biodiesel production. This study investigated the optimization of biodiesel production from watermelon (Citrullus lanatus) seed oil using a novel biogenic catalyst derived from coconut husk ash (CHA) through response surface methodology (RSM). The watermelon seed oil was extracted and characterized, while the coconut husk ash catalyst was synthesized, characterized, and applied in the transesterification process. A central composite design (CCD) under RSM was employed to evaluate the interactive effects of five key process variables: catalyst concentration (0.5-2.0 wt%), methanol-to-oil molar ratio (6:1-14:1), reaction time (1-5 hours), temperature (30-70°C), and agitation speed (100-500 rpm) on biodiesel yield. The quadratic model demonstrated high statistical significance with an R² value of 0.9933, adjusted R² of 0.9812, and adequate precision of 41.0811. The optimal conditions were determined as: catalyst concentration of 1.36 wt%, methanol-to-oil ratio of 9.49:1, reaction time of 3.01 hours, temperature of 50.97°C, and agitation speed of 239.44 rpm, achieving a predicted biodiesel yield of 77.79% with a desirability of 1.0. Analysis of variance (ANOVA) revealed that methanol-to-oil ratio, reaction time, temperature, and agitation speed significantly influenced biodiesel yield (p < 0.05). The produced biodiesel exhibited favorable fuel properties including kinematic viscosity of 9.372 mm²/s at 40°C, flash point of 164°C, cetane number of 50.97, and calorific value of 44.565 MJ/kg. Characterization via FTIR and GC-MS confirmed the successful conversion of triglycerides to fatty acid methyl esters (FAMEs) with dominant peaks corresponding to methyl palmitate, methyl oleate, and methyl linoleate. This study demonstrates the viability of watermelon seed oil as a non-edible feedstock and coconut husk ash as a cost-effective, environmentally friendly heterogeneous catalyst for sustainable biodiesel production.