MS study of the gases evolved in the pyrolysis of ethylene-vinyl acetate copolymers comparison between thermal and catalytic processes

摘要

In this work, a fixed bed reactor connected to a mass spectrometer (MS) has been used to carry out a qualitative study of the evolution of the gases evolved in the pyrolysis of two commercial ethylene-vinyl acetate (EVA) copolymers (with 13 and 27.5% of vinyl acetate, respectively). The catalyst used was MCM-41 prepared by a two-step sol-gel method, in acid medium, at room temperature. Pure copolymer samples and mixtures of copolymer with around 10% of MCM-41 catalyst were pyrolysed in an He atmosphere at a heating rate of 10 K/min. Once the less volatile compounds condensed, the gas evolved was analysed by MS. The study of the total ion current (TIC) curves as well as the evolution with time of the ions selected as representative of several compounds or groups of compounds confirm the existence of the two reaction steps suggested in the bibliography for the second stage of EVA pyrolysis: cracking of the polyethylene domains and cracking of the polyene domains, both domain types resulting from the first decomposition stage. On the other hand, the analysis and comparison of the evolution of the intensity of current corresponding to the selected mass ions in the thermal and catalytic processes show that the gas evolved always contains a higher amount of olefines than alkanes and that more conversion to gaseous products is obtained in the presence of the catalyst.