Kinetics of ultrasound-assisted esterification of maleic acid and butanol using heterogeneous catalyst

The present research investigates the kinetics of ultrasound-assisted synthesis of dibutyl maleate using a heterogeneous catalyst (Amberlyst-15) in solvent-free system. Reaction parameters were optimized based on conversion by varying the various parameters such as n-butanol to maleic acid mole ratio, temperature, molecular sieves, catalyst loading, power, and duty cycle. Optimization of parameters resulted in 56.2% yield at 343 K, alcohol to acid mole ratio as 4:1, catalyst loading of 4%, molecular sieves of 4% with an ultrasound power input of 100 W with 60% duty cycle and 22 kHz frequency. In the presence of ultrasound, the reaction time reduced to 120 min in comparison with 240 min of the conventional process. The experimental kinetic data were correlated using Pseudo-Homogeneous model as well as heterogeneous models like Eley-Rideal model and Langmuir-Hinshelwood-Hougen-Watson (LHHW) model based on single as well as dual-site mechanisms. LHHW (reactants and products) model was found to be the best fit. The results proved that the reaction follows second-order kinetics. The activation energy of the reaction was calculated as 14.64 kJ/mol.