Comparative kinetic analysis of TiO2 and Zeolite ZSM-5 catalysts in the in situ epoxidation of palm kernel oil

In situ epoxidation is a well-established technique for chemically modifying plant-based oils to produce epoxide compounds, which serve as important intermediates in the synthesis of various industrial chemicals. However, homogeneous catalysts in epoxidation face major drawbacks such as high waste generation, difficult separation, nonrecyclability, and high costs. Therefore, heterogeneous solid catalysts are needed to overcome these issues and enable a more sustainable process. This research investigates the catalytic efficiency of TiO₂ and zeolite ZSM-5 in the in situ epoxidation of palm kernel oil (PKO) under different operating conditions. The reaction was conducted in a semibatch, one-pot system using formic acid as the oxygen donor and hydrogen peroxide as the oxidant, with trials at 45 °C, 55 °C, and 65 °C. Reaction time was not fixed but determined by the point at which a decrease in experimental oxirane oxygen content ([OOC]ₑₓₚ) was first detected. Both catalysts were tested at a loading of 5 g to evaluate their effectiveness in enhancing oxirane content (RCO%). Zeolite ZSM-5 showed superior performance, achieving 46% double-bond conversion to epoxide and stabilising epoxide rings within just two minutes at 55 °C. Kinetic analysis using the Langmuir–Hinshelwood model confirmed that the process was not influenced by external mass transfer resistance at an agitation speed of 850 rpm. The surface reaction, particularly performic acid formation, was identified as the rate-determining step. At 55 °C, the surface reaction rate constant was 14.68 L/g catalyst, and the activation energy across the tested temperature range was 147.23 kJ/mol. Overall, ZSM-5 proved to be an effective catalyst for the green epoxidation of PKO, with kinetics well described by the Langmuir– Hinshelwood mechanism.