Al-MCM-41 catalyzed decomposition of polypropylene and hybrid genetic algorithm for kinetics analysis B. Saha, P. Chowdhury, A.K. Ghoshal * Department of Chemical Engineering, Indian Institute of Technology Guwahati, Guwahati 39, Assam, India 1. Introduction Catalytic pyrolysis of waste plastics has become a subject of growing interest. It not only reduces the process temperature but also produces selective and desired range of products. A large number of studies have been reported in the literatures to find the catalysts textural properties, catalytic activity, and pyrolysis product distribution. The zeolite based catalysts reduce decom- position temperature, decrease activation energy, and produce more gaseous/lighter products including the light olefins and aromatic fractions. But mesoporous catalysts accelerate the degradation process with production of low proportion of aromatics and a higher content of olefin and paraffin species. Several authors reported promising results on the catalytic pyrolysis of polypropylene over catalysts such as ZSM-5 [1–5], ZSM-12 [3], DeLaZSM-5 [4], BEA [5], MOR [5], HZSM-5 [6–9], PZSM-5 [6,9], HMOR [8], HUSY [8], US-Y [1,4,10], Beta [11], FCC [1,10], pillared clay [1], and two mesoporous catalysts SAHA [8] and MCM-41 [7,8,12]. Marcilla et al. [7] concluded that the mesoporous catalysts, with a greater pore size and higher acidity with high aluminium content (MCM-41b) was the most active for the pyrolysis of PP. According to Lin and Yen [8], MCM-41 with large mesopores and SAHA with weaker acid sites resulted in a highly olefinic product and gave a wide carbon number distribu- tion during pyrolysis of PP. Though MCM-41 possesses large surface area, the utilization of MCM-41 in catalysis is now restricted by its relative low acidity and low hydrothermal stability, in comparison with those of microporous zeolites. But incorporation of aluminium in the framework of MCM-41 creates Bro ¨ nsted acid sites solving the problem of the low acidity that present these materials [7]. Therefore, recently a few studies using mesoporous catalyst such as Al-MCM-41 have been conducted showing excellent perfor- mance in catalytic pyrolysis of plastics. Garcı ´a et al. [13] showed that polyolefin cracking over ordered mesoporous Al-MCM-41 proceeds by a random scission mechanism due to its large pore size and mild acidity, yielding hydrocarbons within the gasoline and gas oil fractions. Aguado et al. [14] have reported that the Applied Catalysis B: Environmental 83 (2008) 265–276 ARTICLE INFO Article history: Received 31 December 2006 Received in revised form 20 February 2008 Accepted 22 February 2008 Available online 29 February 2008 Keywords: Al-MCM-41 catalyst Hybrid genetic algorithm Kinetics parameters Polypropylene Reusability ABSTRACT Mesoporous catalysts (Al-MCM-41) are synthesized by sol–gel and hydrothermal methods to study their effects on the catalytic decomposition of polypropylene (PP) sample. The catalysts are characterized by X- ray diffraction (XRD) analysis and nitrogen adsorption study. Since sol–gel Al-MCM-41 catalyst shows better catalytic activity, further experimental studies were conducted to find its reusability and its activity at five different heating rates. The constant pattern behaviour of the TG curves for different catalyst percentages possibly suggests existence of similar reaction mechanism where large polymer fragments are cracked on the external surface of the catalyst and then enters into the mesopores for further cracking. Thus, presence of catalyst surfaces not only converts the polymer into comparatively smaller fractions, but also makes the decomposition of PP energy effective. Kinetics parameters are estimated based on 15 different decomposition models and the multi-heating rate experimental data both for catalytic and noncatalytic decomposition of PP using hybrid genetic algorithm (HGA). Suitability of the model is tested using corrected Akaike’s Information Criteria (AIC c ). Results show that Nucleation and Growth model better predicted the experimental TGA data. However, nth order model also shows good AIC c score and well predicted the experimental TGA data. Thus, though apparently it seems that Nucleation and Growth model controls the decomposition of PP sample, further investigation in detail including infrared or mass spectroscopy, morphology study using SEM or TEM during such decomposition is very much essential to conclude upon the actual reaction mechanism that controls decomposition of PP sample. ß 2008 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +91 361 2582251; fax: +91 361 2582291. E-mail address: aloke@iitg.ernet.in (A.K. Ghoshal). Contents lists available at ScienceDirect Applied Catalysis B: Environmental journal homepage: www.elsevier.com/locate/apcatb 0926-3373/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.apcatb.2008.02.021