S. Menargues

Effect of the use of the zeolite Hβ in the catalytic pyrolysis of a commercial ethylene-vinyl acetate copolymer in N2 and air atmospheres

Abstract In this work, the effect of a Hβ zeolite catalyst in the pyrolysis of a commercial ethylene-vinyl acetate (EVA) copolymer (EVA BASF LUPOLEN U-3510-K) is studied, using a thermobalance with N2 and air atmospheres, at several heating rates. A qualitative analysis of the TG curves allows to conclude that in the pyrolysis in N2 atmosphere, the temperature for the first step of the reaction is almost not modified by the catalyst (624, 637 and 676 K at 5, 20 and 35 K min−1, respectively), but the temperature for the second step is lower in the catalytic than in the thermal process (i.e. 751 K for the thermal process vs 715 K for the catalysed process with 3.2% (w/w) of catalyst, at 10 K min−1). A kind of ‘saturating effect’ of the catalyst concentration is observed so that catalyst/polymer ratios higher than a given value do not produce further decrease of the temperature. On the other hand, the temperatures for the different reaction steps in the decomposition in air atmosphere are not affected by the catalyst presence but the thermogram in air is more complicated than in N2. In this way, the first step initiates at lower temperatures, and occurs in a wider temperature interval and with a higher weight loss than in the case of an N2 atmosphere. Thus, other compounds than acetic acid must evolve in this step. A second marked step occurs at higher temperatures, but lower than under N2. Furthermore, and contrarily to the case of N2, two additional steps at higher temperatures take place, and significant weight losses can be observed up to 853 K. Thus a more complicated reaction mechanism is apparent in presence of O2. A pseudo-kinetic model has been suggested for the catalytic pyrolysis in the two atmospheres studied, and the simultaneous fit of the TG curves obtained for each case has been performed in order to obtain the corresponding kinetic parameters which permit the prediction of TG curves for different catalyst contents and heating rates.