Acid-catalyzed esterification of castor (Ricinus communis) oil: optimization through a central composite design approach

The present investigation emphasizes the dynamic modeling and optimization of acid esterification of non-edible castor (Ricinus communis) oil towards reduction of free fatty acid (FFA) content considering four process parameters, namely reaction time (0–4 h), reaction temperature (40–80°C), catalyst concentration (0.25–3.25 w/w) and molar ratio of methanol to oil (1:1–20:1) by the response surface methodology 24 full factorial central composite design approach. A quadratic model was developed to evaluate considerable interactive effects on FFA. Reaction temperature exhibited the most significant effect among all of the process variables. Optimal conditions during which the FFA was reduced from 4.04 to 1.08% were: 1% w/w concentrated H2SO4, 15:1 molar ratio of methanol to oil, reaction temperature 50°C and reaction time 2.09 h. Experimental verification of the predicted condition ensured an actual FFA of 1.14%. The small error (0.0634) between the predicted and actual FFA values ascertained the validity and accuracy of the model in representing the experimental data and predicting conversion at any condition within the studied range. Hence, this pre-treatment under optimized conditions could overcome the major constraint of high FFA, thereby rendering suitability for base transesterification.