Dibutyl maleate is a perfumery ester used as an intermediate in the production of paints, adhesives, and copolymers. Esterification of maleic acid and butanol was studied in presence of acidic cation exchange resin as a catalyst. The objective of this work was to test the suitability and efficacy of heterogeneous catalysts such as Indion 225H and Amberlyst-15 in the synthesis of dibutyl maleate. Various parameters deciding the conversion of reaction such as mole ratio, catalyst loading, molecular sieves, speed of agitation and effect of temperature were optimized for the maximum rate and conversion. The activation energy was calculated as 71.5 kcal/mol. Diffusivity value D AB (maleic acid in n-butanol) at 80 • C was calculated as 5.08 × 10 −10 m 2 /s and effective diffusivity (D e-A) was calculated as 5.08 × 10 −11 m 2 /s. Solid-liquid mass transfer coefficient (k sl-A) was calculated as 6.77 × 10 −6 m/s for the particle size of Amberlyst-15 as 0.5 mm.
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.
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