Investigation of the esterification reaction for the ethyl acetate production in the presence of various catalysts using pervaporation membrane reactor

Pervaporation membrane reactors are the systems in which the separation and reaction are carried out together in order to increase conversions by removing one or more of the products formed in the equilibrium reactions. In this study esterification reaction of acetic acid and ethanol producing ethyl acetate and water was investigated using two different batch pervaporation membrane reactors made of stainless steel. One of the batch reactors was with recycle, the other was without recycle. In the reactor without recycle most of the experiments were for the removal of the ester but some experiments for water removal were also performed. The experiments were carried out at 50, 60 and 70°C. The ratios of ethanol concentration to acetic acid concentration (M) were chosen as 1 and 1.5. Amberlyst 15, sulfuric acid and Nafion Sac-13 were used as catalysts. Polydimethylsiloxane (PDMS) prepared in our labs was used as membrane material, permselective to ethyl acetate formed by reaction. In this way, conversions were increased by continuous removal of ethyl acetate from the reaction media. Experiments based on water removal were carried out by using polyvinylalcohol (PVA) prepared in our labs and Nafion 117 membranes. The ratio of the membrane area/feed mixture volume was 0.1325 cm-1.Reactions were carried out in batch reactors both with and without membrane under the same conditions. Thus, the effect of membrane on the conversions was determined. The fluxes determined by using PDMS membrane were acceptably high (3000-4500 g/m2h). At the end of 350 minutes of reaction time, conversions were found to increase approximately 9-10%. The effects of the catalyst, temperature and the reactant ratio on the conversions were investigated. Since an increase in temperature enhances both the permeability of the membrane and the reaction rate, the conversions and fluxes increased with the temperature. Since the excess use of a reactant shifts the reaction towards products, increase in the reactant ratio M, increases the conversions. The efficiency of the catalysts used were in the following order: sulfuric acid> Amberlyst 15> Nafion Sac-13. Additionally PVA and Nafion 117 membranes were used for the removal of the water. However it was not possible to enhance the conversions using the PVA membrane because the fluxes were quite low (?100 g/m2h).The experiments using the recycle reactor to remove water from the reaction were carried out in the University of Oviedo in Spain. The membrane used in this system was a PVA based commercial Pervap 2216 membrane of Sulzer. The temperature was 70°C. Sulfuric acid was used as catalyst. The ratios of ethanol to acetic acid (M) were chosen as 8 and 10. The ratio of membrane area/feed mixture volume used was in the range of 0.99-1.37 cm-1. The effect of the ratio of membrane area to feed volume on the conversions was investigated using different values of feed volumes, and the conversions were found to increase by increasing this ratio.A theoretical model for the pervaporation membrane reactor experiments for the ester removal using PDMS membrane with sulfuric acid as catalyst, based on homogenous catalyst kinetics was proposed thus allowing the prediction of the conversion variation with the pervaporation time. The results of the model prediction and experiments are in good agreement.Key words: Pervaporation membrane reactor, esterification, ethyl acetate, membrane, catalyst