Modelling of Deactivation of Pd-Au Catalyst in Vinyl Acetate Synthesis from Oxidation of Ethylene and Acetic Acid in the Gaseous Phase Kazem Motahari, 1 Garry Rempel, 2 * Saba Lashkarara, 3 * Keyhan Ghaseminezhad, 4 Amin Borumandnejad 1 and Babak Hatami 1 1. Department of Chemical Engineering, Arak University, Arak, Iran 2. Department of Chemical Engineering, University of Waterloo, Waterloo, ON, N2L 3G1, Canada 3. Department of Electrical Engineering, University of Louisiana at Lafayette, Lafayette, LA, USA 4. Department of Mining and Metallurgical Engineering, Amirkabir University of Technology, Tehran, Iran Vinyl acetate monomer (VAM) is produced from oxidation of ethylene and acetic acid on a Pd-Au/SiO 2 catalyst in the gaseous phase. A progressive loss in activity occurs during the lifetime of a commercial Pd-Au/SiO 2 VAM synthesis catalyst; thus, the efficiency of the reaction decreases and the process is no longer operational and economically feasible. In this study, the effective parameters on Pd-Au/SiO 2 catalyst deactivation were investigated using a fixed-bed reactor pilot, and a model was proposed to predict the reduction in catalyst activity. The proposed model's output was compared with experimental data and an acceptable agreement was observed. The error was < 10 %. Keywords: vinyl acetate monomer, Pd–Au/SiO 2 catalyst, fixed-bed reactor, deactivation model INTRODUCTION V inyl acetate monomer (VAM) is a raw material used in the production of polyvinyl acetate, polyvinyl alcohol, and polyvinyl butyral, which are widely used in different industries for producing materials such as glue, pigments, resins, textiles, and paper. There are several different methods for VAM synthesis, among which the main and most important method is the oxidation of ethylene and acetic acid. This method is performed in both liquid and gaseous phases. 80 % of the vinyl acetate production in the world is carried out through oxidation of ethylene and acetic acid on a Pd-Au catalyst in the gaseous phase. [1,2] The main reaction is: C 2 H 4 þ CH 3 COOH þ 1 2 O 2 ! C 2 H 3 OOC 2 H 3 þ H 2 O ð1Þ and side reactions include: C 2 H 4 þ 3O 2 ! 2CO 2 þ 2H 2 O ð2Þ C 2 H 4 ! 2H 2 þ 2C ð3Þ CH 3 COOH ! 2H 2 þ CO 2 þ C ð4Þ C 2 H 4 þ 2O 2 ! 2CO þ 2H 2 O ð5Þ CH 3 COOC 2 H 5 ! 3H 2 þ CO 2 þ 3C ð6Þ CH 3 COOH þ C 2 H 4 ! CH 3 COOC 2 H 5 ð7Þ 2CH 3 COOH þ 2C 2 H 4 þ 3O 2 ! 2CH 3 COOCH 3 þ 2H 2 O þ 2CO 2 ð8Þ 2CH 3 COOH þ 2C 2 H 4 þ 3O 2 ! 2CH ¼ CH  CHO þ 4H 2 O þ CO 2 ð9Þ 4CH 3 COOH þ 2C 2 H 4 þ O 2 ! 2C 6 H 10 O 4 þ 2H 2 O ð10Þ In this process, the side reactions lead to deactivation of the catalyst. In addition, the presence of impurities such as fluorine, chlorine, iodine, formic acid, acetaldehyde, and other compounds in the feed cause catalyst poisoning. As a result of catalyst sintering, the activity decreases, and thus the amount of product is reduced. In this situation, the operating system increases the temperature to increase conversion, but this leads to catalyst deactivation. Due to the importance of vinyl acetate in the industry from an economic point of view, several studies have been performed to investigate the reactions and operation conditions, most of which focused on the catalyst structure, its behaviour during the reaction, and exhaustion rate of the Pd-Au catalyst. In spite of this, very few studies have been published on deactivation of VAM catalysts so far [3–7] and there are few algorithms available in the literature for modelling Pd-Au catalyst behaviour. According to a previous study, [8] two different mechanisms are suggested for the synthesis of VAM in a gaseous phase. Nakamura et al. [9,10] and Moiseev et al. [11] proposed that the mechanism for the VAM synthesis from ethylene, acetic acid, and oxygen on the Pd-Au catalyst in the gaseous phase is that ethylene and acetic acid are adsorbed on the active catalyst surface, an active intermediate is developed on the surface, and then VAM is produced. In fact, this is the Langmuir-Hinshelwood adsorption mechanism. On the other hand, Samanos et al. [12] and Zaidi [13] believe that firstly, ethylene is adsorbed on the catalyst active surface and develops an active *Author to whom correspondence may be addressed. E-mail address: grempel@uwaterloo.ca (G.L.Rempel) and saba.lashkarara@gmail.com (S. Lashkarara) Can. J. Chem. Eng. 94:506–511, 2016 © 2015 Canadian Society for Chemical Engineering DOI 10.1002/cjce.22400 Published online in Wiley Online Library (wileyonlinelibrary.com). 506 THE CANADIAN JOURNAL OF CHEMICAL ENGINEERING VOLUME 94, MARCH 2016