Hybrid in/ex situ hydrolysis producing dihydroxystearic acid from epoxidized neem oil: synthesis & kinetic studies

Depletion of oil reserve along with its volatility in terms of price and availability arise researchers concern on renewable resource for epoxidized material. Vegetable oils are commonly chosen as the alternative to petroleum resources. In this study, non edible oil, neem oil are chosen to be epoxidized by optimum level of process parameter obtained by Taguchi method. The optimum level of each process parameter involved, with its percentage contribution toward the epoxidation of neem oil is determined by S/N ratio and ANOVA analysis respectively by the Taguchi method. The results show most optimum levels for each process parameter are formic acid/neem oil molar ratio: 1:1, hydrogen peroxide/neem oil molar ratio: 4:1, catalyst loading: 1g, reaction temperature: 70 0C, and agitation speed: 300 rpm. Meanwhile, ANOVA states that catalyst loading was the most significant factor that affected the epoxidized neem oil (30.66%), followed by formic acid/neem oil molar ratio (A) at (29.77%) due to its role as an oxygen carrier compared to hydrogen peroxide, which acts as an oxygen donor and the third one is stirring speed (E) at (20.95%). The highest relative conversion to oxirane of 51.50% was achieved under optimized conditions. Both neem oil and its epoxide form are analysed by FTIR, where the formation of an oxirane ring is shown at a wavenumber of 1240 cm-1. This work focuses on the production of dihydroxystearic acid (DHSA) through both in situ and ex situ hydrolysis, following the epoxidation of neem oil. The epoxidised intermediate was obtained using performic acid generated in situ, and hydrolysis conditions were systematically optimised using the Taguchi approach. Signal-to-noise (S/N) ratio analysis indicated the optimum parameters for achieving the highest hydroxyl value (129.4 mg KOH/g), namely: a water-to-neem oil molar ratio of 2:1, a water addition period of 90 minutes, and a reaction termination time of 120 minutes. Analysis of variance (ANOVA) further demonstrated that the parameters influenced the process in the order: reaction stop time > water addition duration > water/neem oil ratio. To support experimental findings, a kinetic model was constructed in MATLAB using the fourth-order Runge–Kutta algorithm in combination with simulated annealing for optimisation, enabling accurate representation of the system. Overall, the study demonstrates how neem oil can be converted into a high-value product, offering a sustainable alternative to petroleum-derived feedstocks and advancing understanding of the reaction kinetics critical are beneficial when it is supported more by kinetic intrepretation.