KINETIC STUDY OF CATALYTIC HYDROLYSIS REACTION OF * METHYL ACETATE TO ACETIC ACID AND METHANOL M. EHTESHAMI1, N. RAHIMI1, A. A. EFTEKHARI2 AND M. J. NASR1**
National Petrochemical Co., Petrochemical Research & Technology Co. No. 12. Sarv.Alley, Shirazi-south, Mollasadra, 14358, Tehran, I. R. of Iran Email: firstname.lastname@example.org 2 Faculty of Chemical and Petroleum Engineering, Sharif University of Technology, Azadi St. Tehran, I. R. of Iran Abstract– The reaction kinetics and chemical equilibrium of the reversible catalytic hydrolysis reaction of a methyl acetate to acetic acid and methanol using a strongly acidic ion exchange resincatalyst named Amberlyst 15 were studied. To investigate the different behavior of Amberlyst 15 in the adsorption of reactants and product species, the equilibrium behavior of binary non-reactive liquid mixtures, consisting of one reactant and one product were studied experimentally. The Langmuir model was used to describe the equilibrium condition, quantitatively. Then the employed model wascompared with the more complicated thermodynamic models to describe the equilibrium between the catalytic polymer resin and the liquid phase. The results indicated a good agreement. The effects of temperature, catalyst weight, and feed molar ratios on reaction kinetics were investigated. Results revealed that the reaction rate was strongly temperature dependent. The chemical equilibrium compositionswere measured in a wide range of temperatures and feed molar ratios. Finally, pseudo homogeneous and LHHW (Langmuir Hinshelwood Hougen Watson) models were developed to calculate the rate of the reaction. Optimization of the model's parameters indicated that the use of activity instead of mole fraction, and also the use of LHHW rather than a pseudo homogeneous model resulted in much smaller residualerrors. Also the equilibrium compositions obtained from the equation of rates were in good agreement with the experimental results. Keywords– Methyl acetate, kinetics, amberlyst 15, hydrolysis, rate of reaction
1. INTRODUCTION Hydrolysis of methyl acetate (MeOAc) to acetic acid and methanol is one of the major reactions since a great deal of methyl acetate is produced as by-product during thesynthesis of polyvinyl alcohol (PVA) and pure terephthalic acid (PTA). It is estimated that 1.5-1.7 tons of MeOAc is produced per ton of PVA [1, 2]. Methyl acetate can be hydrolyzed into value-added products of methanol and acetic acid which can be recycled on site into the mentioned processes. As well as the industrial application, this system is of major importance as an experimental modelreaction for reactive distillation research . Acetic acid (HOAc) and methanol (MeOH) can be made by the liquid-phase reaction of methyl acetate (MeOAc) and water. The MeOAc hydrolysis reaction is reversible and the reaction equilibrium constant, K, is relatively small. Therefore, H+ ion is employed as the catalyst in order to increase the reaction rate . Strong acids such as sulfuric acid andhydrochloric acid can be used to produce an H+ ion and catalyze the reaction . The reaction is
Received by the editors January 3, 2006; final revised form September 18, 2006. Corresponding author
M. Ehteshami / et al.
H CH 3COOCH 3 + H 2O ←⎯⎯ CH 3OH + CH 3COOH →
Strong acids cause corrosion in the whole process and it is costly to separate and purify the finalproduct . In order to eliminate the mentioned disadvantages, a strongly cation-exchange resin containing a sulfonic acid (SO3H) is usually used as an acid catalyst for hydrolysis. Conventional sulfonic-acid-type resin is prepared by sulfonation of the styrene (St) -divinylbenzene (DVB) copolymer, where the polystyrene chains were cross-linked with DVB  as illustrated in Fig. 1.