Applied Catalysis A: General 489 (2015) 262–271 Contents lists available at ScienceDirect Applied Catalysis A: General jou rn al hom epage: www.elsevier.com/locate/apcata Catalytic activity evaluation of industrial Pd/C catalyst via gray-box dynamic modeling and simulation of hydropurification reactor Abbas Azarpour a , Sharifah R. Wan Alwi a,∗ , Gholamreza Zahedi b , Mazyar Madooli c , Graeme J. Millar d a Process Systems Engineering Center (PROSPECT), Faculty of Chemical Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia b Chemical & Biological Engineering Department, Missouri University of Science & Technology, 1870 Miner Circle, Rolla, MO 65409, USA c PTA/PET Process Engineering Office, Shahid Tondgooyan Petrochemical Company, Petrochemical Economic Special Zone, 667 Mahshahr, Khoozestan, Iran d Science and Engineering Faculty, Queensland University of Technology, Brisbane 4000, QLD, Australia a r t i c l e i n f o Article history: Received 12 May 2014 Received in revised form 18 October 2014 Accepted 25 October 2014 Available online 4 November 2014 Keywords: Gray-box Dynamic modeling 4-Carboxybenzaldehyde Catalyst Artificial neural network Deactivation a b s t r a c t In this paper, dynamic modeling and simulation of the hydropurification reactor in a purified terephthalic acid production plant has been investigated by gray-box technique to evaluate the catalytic activity of palladium supported on carbon (0.5 wt.% Pd/C) catalyst. The reaction kinetics and catalyst deactivation trend have been modeled by employing artificial neural network (ANN). The network output has been incorporated with the reactor first principle model (FPM). The simulation results reveal that the gray- box model (FPM and ANN) is about 32 percent more accurate than FPM. The model demonstrates that the catalyst is deactivated after eleven months. Moreover, the catalyst lifetime decreases about two and half months in case of 7 percent increase of reactor feed flowrate. It is predicted that 10 percent enhancement of hydrogen flowrate promotes catalyst lifetime at the amount of one month. Additionally, the enhancement of 4-carboxybenzaldehyde concentration in the reactor feed improves CO and benzoic acid synthesis. CO is a poison to the catalyst, and benzoic acid might affect the product quality. The model can be applied into actual working plants to analyze the Pd/C catalyst efficient functioning and the catalytic reactor performance. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Catalytic hydrotreating (HDT) is one of the elemental pro- cesses in the refinery and petrochemical industries which is employed to improve the quality of products through catalytic conversion or reduction of low polluting compounds such as sulphur and aromatics [1]. The HDT reactions like hydrodeas- phaltenization, hydrodesulfurization, hydrodemetallization, and hydrodenitrogenation are processed in three phase fixed-bed cat- alytic reactors (FBCRs) [2]. Catalyst deactivation, the catalytic activity and selectivity loss over time, is a significant concern in the practice of industrial cat- alytic processes. Industrial disadvantages of deactivation are the production time loss and waste of investment. Catalyst deactiva- tion is undoubtedly one of the most considerable issues in the accomplishment of HDT processes. The rate of deactivation ∗ Corresponding author. Tel.: +60 7 5535533; fax: +60 7 5588166. E-mail addresses: shasha@cheme.utm.my, sr wanalwi@yahoo.com (S.R. Wan Alwi). depends on the feed properties, especially the impurities low con- centration [3]. Purified terephthalic acid (PTA) is the key raw material to man- ufacture polyethylene terephthalate (PET). PET is broadly utilized in the production of synthetic fibers, beverage bottles, frozen food trays, toiletries, cosmetics, household and pharmaceutical prod- ucts, molding resins, X-ray and other photographic films, magnetic tape, electrical insulation, printing sheets, and food packaging film [4]. In the current technology of PTA production, the oxidation of para-xylene (PX) to crude terephthalic acid (CTA) is catalyzed by metals (Co 2+ , Mn 2+ ) and bromide (Br 1- ) in acetic acid (AA) as solvent. Purification of CTA requires at least one chemical step in addition to the physical processes such as crystallization and wash- ing. One of the major impurities is 4-carboxybenzaldehyde (4-CBA). It is converted to para-toluic acid (pta) by catalytic hydrogenation in an aqueous solution carried out in a trickle-bed reactor (TBR). Artificial neural network (ANN) models can be very efficient to simulate the processes which are very complicated and highly nonlinear, improperly known, and taking much time to be ana- lyzed with different empirical models. They are very flexible and engage less model mismatched [5]. ANN can be applied into the http://dx.doi.org/10.1016/j.apcata.2014.10.048 0926-860X/© 2014 Elsevier B.V. All rights reserved.