Design and simulation of a process to convert different types of plastic wastes into liquid fuel

Abstract

Plastic consumption and production have increased drastically over the years, causing enormous quantities of waste. Insufficient administration has led to serious issues for human wellbeing and the environment. Plastic waste can be converted into liquid fuel by pyrolysis, which produces a fuel with similar characteristics to common fuel. This approach can solve the existence of enormous amounts of plastic waste and reduce the dependency on oil. Thus, in this dissertation I study, design and simulate a process of conversion of different types of plastics wastes into liquid fuel trough the thermal and catalytic pyrolysis of different plastic wastes (HDPE, LDPE, PP, and PS). The simulation is performed in ASPEN HYSYSv1. It was found that in thermal pyrolysis, the cracking temperatures registered were in HDPE (500 – 680oC), LDPE (350 – 450oC), PP (200 – 275oC) and PS (300- 390oC) respectively. The carbon number distribution of the plastics was mostly in range of C5-C12 and C13-C20. The liquid fuel resulting from distillation column of HDPE and LDPE oil has excellent yields of gasoline above 80%. On the other hand, the distillation of PP oil produced high yields of kerosene (57.19%) and gasoline (36.16%), and PS oil distillation produced a high content of diesel (91.34%). Two different type of catalysts, Ni/Al2O3 and activated carbon were applied in the pyrolytic reactions. It was observed that the Ni/Al2O3 has high activity and produces greater amount of oil compared to activated carbon. At 295oC in PS pyrolysis Ni/Al2O3 registered a conversion of 85.43%, whereas in the presence of activated carbon the conversion rate was 79.75%. As compared with thermal pyrolysis, catalytic pyrolysis was the best pyrolysis process for HDPE and LDPE plastics. A low performance was observed in the catalytic pyrolysis of PP plastic due to elevated yields of residue produced. In conclusion, the study shows that the thermal pyrolysis is a suitable method for PP and PS plastics and the catalytic pyrolysis is a great option for HDPE and LDPE respectively.