Pyrolysis of mixed plastic fractions – Development of predictive models for yield and oil quality

Abstract

Pyrolysis of plastic mixtures has shown to form complex mixtures of oil, which is difficult to predict. Interaction effects between plastics have shown to affect both the oil composition and the yield distribution of oil, char, and gas. This work aims to generate models for the prediction of oil and char yield, acid number, and viscosity based on the feed composition. Besides the oil composition based on the reactor feed was mapped. Pyrolysis was performed in a batch reactor with a mixture of PP, PE, EVA, PET, PS and PA, where the content of PET, PS and PA were varied from 0% to 15%. The developed models showed a decrease in oil yield of 10% when 15% PS was interchanged with PET. Char content, acid number, and viscosity were shown to increase with the content of PET and lowered with the content of PS. PA caused an increase in char yield and viscosity, while it did not affect the acid number. The models R2-values varied from 0.87 to 0.96, showing that most of the variation in the responses can be explained by the differences in feed composition. The oil composition was found to mainly consist of hydrocarbons (C10 +), naphta and aromatics with only a small precense of alcohol and acid. The content of aromatic hydrocarbons is increased by the presence of PS, due to formation of styrene and toluene while the acid content increases with the PET content.