Epoxidation of melon seed (Citrullus colocynthis L) oil: A kinetic and thermodynamic approach for industrial applications

Abstract

Unsaturated melon seed oil had its epoxidation process studied at varied temperatures (30OC -70OC) within a three hours reaction time, for possible oxirane formation because of its industrial significance. Oil was extracted from melon seeds and characterized for its physicochemical properties using standard methods. The specific gravity (30OC), iodine value, acid value, saponification value, peroxide value and percentage oil content were found as 0.931, 118.69 gI2/100g, 5.08 mg KOH/g, 165.7 mg KOH/g, 4.75 meq/kg and 60% respectively. Physicochemical characteristic of the oil reveals it is semi-drying oil which is rich in high molecular weight fatty acids, with good stability against rancidity. The epoxidation process which was monitored by its oxirane content is seen to proceed faster at the highest studied temperature of 70OC, giving the highest oxirane content of 5.87%. Optimization of the epoxidation process showed that optimum epoxidation of melon seed oil can be achieved at 70OC within one hour; as compared to other temperatures studied. Process kinetics evaluated in terms of its oxirane yield showed that the epoxidation process followed pseudo-zero order kinetics with respect to oxirane formation. Their rate constants were found to be 0.032 hr-1, 0.041 hr-1, 0.059 hr-1 and 0.24 hr-1 for the epoxidation process at 30OC, 50OC, 60OC and 70OC respectively; which shows that the epoxidation rate increases with increasing temperature. Thermodynamic parameters such as activation energy (Ea), activation enthalpy (∆H≠), activation entropy (∆S≠) and Gibb’s free energy (ΔG≠) were determined to be 133.11 kJmol-1, 18.22 kJmol-1, -0.21 kJmol-1 K-1 and 87.95 kJmol-1 respectively. The observed thermodynamic properties indicated strong temperature dependence of the epoxidation reaction rate, endothermicity and non-spontaneity of the process. The findings of this study will guide in maximizing oxirane yield and save cost significantly in the production of epoxidized melon seed oil employed for large scale industrial applications.