(583i) Esterification Kinetics of Citric Acid With n-Butanol and Isoamyl Alcohol

Citrates are used as plasticizers for certain applications where phthalates have been banned. Esterification of citric acid is generally carried out in batch reactors using homogeneous acids as catalysts. Reaction temperature is maintained below 150 C to avoid decomposition of the acid and self-esterification. The minimum molar ratio of alcohol to acid is determined by the solubility of the acid. In the open literature there are few reports on citric acid esterification, and even fewer reporting chemical kinetics.  In this regard this work present the experimental evaluation of a kinetic model for the esterification of citric acid and n-butanol and isoamyl alcohol using Amberlyst 70 as catalyst.   

Initially, the solubility of citric acid in the alcohols was measured at different temperatures. As a result, it was found that the solubility reaches 24.5% w/w and 17.6% w/w at 50 °C (maximum temperature tested) for the system acid / n-butanol and acid / isoamyl alcohol, respectively. A Box-Behnken experimental design was developed to evaluate the kinetic models of reaction, varying reaction temperature (80 to 120 °C), acid:alcohol feed ratio (1:6 to 1:15) and catalyst loading (0.5 to 1.5% w/w).  Experiments were carried out in a 100 mL jacketed stirred SS reactor. Temperature was maintained by a thermal oil circulating bath. The reactor counts with a thermowell for temperature measurement and a sampling nozzle. Reaction time was 6 hours and samples were characterized by acid value and HPLC. Regression of experimental data was performed in MatLab^TM  and a pseudo-homogeneous model agreed reasonably well with experimental kinetics.