Thermochimica Acta 460 (2007) 77–84 Model-free kinetics analysis of decomposition of polypropylene over Al-MCM-41 B. Saha, A.K. Ghoshal ∗ Department of Chemical Engineering, Indian Institute of Technology Guwahati, Guwahati 39, Assam, India Received 29 January 2007; received in revised form 8 May 2007; accepted 21 May 2007 Available online 24 May 2007 Abstract Both thermal and catalytic decomposition of PP sample is studied to understand the effect of catalyst (Al-MCM-41) on the decomposition behaviour. Mesoporous catalyst (Al-MCM-41) is synthesized by sol–gel methods and characterized by X-ray diffraction (XRD) analysis and nitrogen adsorption study. The optimum catalyst composition is found to be around 18.5 wt%, where the reduction in maximum decomposition temperature is around 103 ◦ C. The nonlinear Vyazovkin model-free technique is applied to evaluate the quantitative information on variation of E α with α for PP sample under both catalytic and noncatalytic nonisothermal conditions. The constant pattern behaviour of the TG curves and the similar trend on variation of E α with α for both catalytic and noncatalytic decomposition of PP indicates similar mechanism involved during decomposition. The only effect of catalyst is observed in the form of reduction of the temperature and the activation energy. The literature reported data on such variation are compared with the results of the present study. Results show that Al- MCM-41 is superior to the ZSM-5 catalyst in terms of catalyst loading due to the existence of larger external macropore and mesopore surface in it. © 2007 Elsevier B.V. All rights reserved. Keywords: Activation energy; Al-MCM-41; Catalytic decomposition; Model-free analysis; Polypropylene 1. Introduction Catalytic pyrolysis of waste plastics is a subject of grow- ing interest on the perspective of solid waste management since they are an alternative source of energy or chemical raw materi- als. Zeolite based catalysts reduce decomposition 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 con- tent 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]. According to Marcilla et al. [7], mesoporous catalysts ∗ Corresponding author. Tel.: +91 361 2582251; fax: +91 361 2582291. E-mail address: aloke@iitg.ernet.in (A.K. Ghoshal). (MCM-41b) with a greater pore size and higher acidity with high aluminium content was the most active one for the pyrolysis of PP. Highly olefinic product with a wide carbon number distribu- tion during MCM-41 and SAHA catalyzed pyrolysis of PP were found by Lin and Yen [8]. Recently, mesoporous catalysts (Al-MCM-41) synthesized either by sol–gel or by hydrothermal method have been used for decomposition of HDPE and LDPE to analyze the decomposi- tion products [13–15]. However, much less articles are referred to the effect of MCM-41 on PP [7]. The pyrolysis kinetics study is important to know the decom- position mechanism, rate of reaction, reaction parameters and to predict the products distribution. This in turn helps in proper selection of reactor, optimization of the reactor design and oper- ating conditions. Model-free analysis technique is advantageous over model-fitting analysis when the real kinetics mechanism is unknown. This becomes extremely important during cat- alytic decomposition since reaction mechanism may change drastically with type and concentration of catalyst. Recently, Vyazovkin model-free kinetics technique has extensively been applied for many complex reaction processes to obtain reliable 0040-6031/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.tca.2007.05.016