Kinetic and thermodynamic study of saponification of Neem oil (Azadirachta indica) with Sodium Hydroxide using Goat milk as a bioactive additive

Abstract

The growing demand for natural therapeutic personal care products has intensified interest in plant-based oils and dairy additives in soap manufacturing. This study investigates the kinetics and thermodynamics of soap production using neem oil (Azadirachta indica) and sodium hydroxide with goat milk as a functional additive at elevated temperatures (303 K, 313 K, and 323 K). The saponification reaction was monitored by measuring the residual oil concentration at time intervals (10-60 seconds). Kinetic analysis revealed that the reaction follows first-order kinetics across all temperatures, with correlation coefficients (R²) of 0.995, 0.997, and 0.956 at 303 K, 313 K, and 323 K, respectively. Rate constants (k) ranged from 0.012 s⁻¹ to 0.014 s⁻¹. The activation energy (Eₐ) was determined to be 6.41 kJ·mol⁻¹ using the Arrhenius equation. Thermodynamic parameters showed positive enthalpy of activation ( ) ranging from 3.89 to 3.72 kJ·mol⁻¹, indicating an endothermic process. The negative entropy of activation ( =-261 J·mol⁻¹·K⁻¹) suggests a more ordered transition state. Gibbs free energy of activation () increased with temperature from 82.94 to 88.16 kJ·mol⁻¹, indicating reduced reaction spontaneity at higher temperatures. These findings demonstrate that goat milk serves as an effective reaction facilitator by lowering the activation energy barrier compared to conventional saponification processes, while the temperature-dependent kinetic behavior provides valuable insights for optimizing industrial soap production.