Study of the decomposition of Vacuum Gas Oils-Low Density Polyethylene blends: evolution of the liquids

Abstract

In this work, dynamic pyrolysis runs of different samples of vacuum gas oil (VGO), polyethylene (PE) and a vacuum gas oil-polyethylene blend with a 10% of PE (VGO-PE) have been performed in a vertical reactor in order to study the products obtained in the thermal and the catalytic pyrolysis using an equilibrium FCC catalyst. Different than the most works studying the composition of the products evolved in the pyrolysis process, which analyzes the overall gaseous or liquid product collected through the complete degradation of polymer, in this case, different samples along the process have been collected, and the evolution with the temperature (or the time) of the composition of the liquids evolved has been studied by GC/MS. The results obtained permit to better know the nature of the processes involved in each step of decomposition and to analyze the possibility of recycling plastics by mixing them with the vacuum gas oil in the refineries. The results obtained indicate that, in the thermal pyrolysis, the sample of VGO was not degraded, but a process similar to a fractionated distillation occurs, and the composition of the condensed product obtained at the exit of the reactor is very similar to that corresponding to the original VGO, where alkanes with more than 20 carbon atoms (CLO) were the main compounds of the liquids obtained. The composition of the liquids observed in the thermal pyrolysis of the VGO, PE blend seems to be a mixture of the corresponding to pure VGO and PE. However, the presence of the catalyst changes the selectivity, and for the three cases studied, the major compounds are in the range of the gasolines.