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

Abstract

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.

Keywords:

• dynamic modeling
• optimization
• central composite design
• castor oil
• free fatty acid

Acknowledgements

The authors are grateful to Mr Anoar Ali Khan, Mr Avinash V. Palodkar, Mr Pradip Das and all other technical personnel from the Department of Chemical Engineering, National Institute of Technology, Durgapur for their immense support in the execution of this work.

Disclosure statement

No potential conflict of interest was reported by the authors.