Studies on the kinetics of epoxidation of soybean oil using synthetic cationic exchange resin

Abstract

Epoxides of all kinds of plant oils are well known commercially since they can undergo many important reactions. Epoxidation of long chain olefins, and unsaturated fatty acid derivatives such as soybean oil and other plant oils have been carried out on an industrial scale. Nowadays, one of the most important epoxidized vegetable oils is the epoxidized soybean oil (ESO). Fatty epoxides are used directly as plasticizers that are compatible with polyvinyl chloride (PVC) and as stabilizers for PVC resins to improve flexibility, elasticity, and toughness. It also imparts stability of polymer towards heat and UV radiation. As the demands of energy increase and fossil fuel reserves are limited, there has been a growing interest in the utilization of renewable resources as an alternative to petroleum based polymers. Consequently, much attention has been focused on the development of polymeric materials from vegetable oils as a sustainable resource.

Therefore, there is a necessity of a comprehensive method of epoxidation, which is easy, simple and  cost effective, if epoxidised vegetable oils are to be employed in industrial applications as such. In this study an attempt was made to ascertain an unfailing experimental procedure, which is economically viable for the enpoxidation of vegetable oils for industrial uses. The kinetics of epoxidation of soybean oil (SBO) by peroxyacetic acid (PAA) in the presence of synthetic cationic exchange resin (sulfonated tannin- phenol-formaldehyde resin) as catalyst were investigated at 45 oC, 50 oC,  60 oC and 70 oC by determining oxirane ring content using a titrimetric method. Epoxidation with higher conversion of unsaturated carbon and lower oxirane cleavage could be attained by the in situ technique. The rate constant for epoxidation of SBO was found to be of the order of 10-6 mol-1s-1 and activation energy of epoxidation of 33.62 kJmol-1. The enthalpy, entropy and free energy activation were 22.29 kJmol-1, -273.53 Jmol-1K-1 and -68.79 kJmol-1, respectively. The kinetic and thermodynamic parameters of epoxidation obtained from this study indicate that an increase in the process temperature would increase the rate of epoxide formation.