Characterization of vacuum gas oil-low density polyethylene blends by thermogravimetric analysis

The study of the catalytic pyrolysis of mixtures of fuel and polymers is interesting in order to explore the possibility of using commercial fluid catalytic cracking (FCC) units or similar processes for recycling plastic wastes. In this work, different samples of vacuum gas oil (VGO), polyethylene (PE) and vacuum gas oil-polyethylene blends (VGO-PE) have been studied by thermogravimetric analysis. Vacuum gas oil-polyethylene blends with 1, 2.5, 5, 7.5 and 10% w/w of PE were prepared by continuously stirring for 120 min, at 60 rpm at 120 °C, and afterwards, the effect of different catalysts (HZSM-5, HUSY, HBeta zeolites, FCC catalysts and Al-MCM-41) on the decomposition of these mixtures was studied. Moreover, the deposition of coke over each catalyst was studied by thermogravimetric analysis in an oxidant atmosphere. The catalytic pyrolysis behaviour of the VGO-PE mixtures indicates a two-step process, the degradation of the VGO and the PE fraction being almost independent. The degradation or evaporation of the VGO fraction is only slightly affected by the presence of the catalyst, whereas the PE fraction showed similar behaviour as that already described in the literature for the pure polymer. The results show that the HBeta zeolite is the most active catalyst for the decomposition of the mixtures, and that the ZSM-5 zeolite is the catalyst with the lowest amount of coke formation. These results are in very good agreement with the structural characteristics of the different catalysts studied, i.e., with their pore size and acidity.