TG/FT-IR analysis of HZSM5 and HUSY deactivation during the catalytic pyrolysis of polyethylene

The TG/FT-IR technique has been employed to study the evolution of the gases evolved during the thermal and catalytic decomposition of low density (LDPE) and high density polyethylene (HDPE). This technique allows to obtain the FT-IR spectra of the gases evolved in situ, as they are generated. The evolution of the gases obtained during the progressive deactivation of the catalysts employed (HZSM5 and HUSY) has also been studied. In the thermal processes the relative intensity of bands related to CH2 respect to those related to CH3 is greater, and the presence of aromatics and olefins is nearly negligible, independently on the branching degree of the polymer. Nevertheless, in the catalytic processes, the composition of the gases evolved depends on the zeolite and the polymer structure. The relative intensity of the bands related to the CH3 group increases at the expense of those related to CH2 indicating, as expected, the reduction in the average molecular weight of the gases evolved during the catalytic process. Higher amounts of alkenes and aromatic compounds were detected with HZSM5 than with HUSY. When the coked catalyst is used in successive cycles, the gases obtained become progressively more similar to those generated in the thermal process, and the same happens with the temperature at which decomposition takes place, thus enabling a nice illustration of the catalyst deactivation through the evolution of the FT-IR spectra.