Synthesis of Methyl Sorbate Catalyzed by Deep Eutectic Solvent Based on Choline Chloride: Kinetics and Optimization

The synthesis process and kinetics of the ester-ification of methanol with sorbic acid catalyzed by deep eutectic solvents (DESs) were explored in this study. A series of green DESs composed of choline chloride (ChCl) and p-toluene sulfonic acid monohydrate (PTSA) were successfully prepared. Design and optimization of the process were conducted using the response surface methodology with Box-Behnen design. The influences of the value of z (z is the molar ratio of PTSA to ChCl), catalyst loading, methanol/sorbic acid molar ratio, and temperature on the conversion of sorbic acid were evaluated. Using ChCl-1.38PTSA as a catalyst, the kinetic data and chemical equilibrium compositions of the esterification were measured at a temperature range of 340.15-355.15 K. The UNIFAC model was utilized to estimate the equilibrium constants, and the thermodynamic data (Delta rH0, Delta rS0, Delta rG0) of the esterification reaction were calculated as well. The pseudohomogeneous model based on activity was then adopted to describe the reaction kinetics and the model fitted well with the experimental data. The activation energy of the forward and reverse reaction were calculated. In addition, the activity of ChCl-1.38PTSA declined not obviously after five cycles, suggesting that ChCl-1.38PTSA has good stability and recyclability.