Catalytic pyrolysis of plastic waste to produce diesel-like fuel.

Abstract

Over the years, plastic generation and usage have increased due to plastics' favourable properties for domestic and industrial purposes. Plastics are cheap to manufacture, durable, flexible, resistant to moulding and rust, amongst other properties. The diverse application of plastics in the different sectors has led to increased plastic waste and management challenges. Plastic waste management options such as recycling, incineration, and landfilling have been used; however, there are drawbacks to these options. Plastics are petroleum-based, and a lot of energy is embedded in them. Several waste to energy technologies have been researched and adopted to deal with plastic waste. Among these technologies are gasification, plasma process, pyrolysis, and incineration. Pyrolysis has emerged as the most desirable process since it significantly reduces the volume of waste, produces various high-energy products, and requires lower decomposition temperature. The process is desirable because of its flexibility. Pyrolysis parameters are manipulated to optimise the desired product yield. The process parameters include but are not limited to temperature, heating rate, residence time, particle size, and catalyst. Different types of plastics and biomass can be thermally devolatilised using the process. In the current study, catalytic devolatisation of polypropylene plastic waste through the pyrolysis process was studied. Key factors affecting the final product, i.e. temperature, feed composition, heating rate and catalysts, were reviewed. The effects of temperature and silica-alumina catalyst on the product yield and quality were investigated. A central composite design was employed for the experimental design. It was observed that increasing the catalyst at lower temperatures impacted on the liquid and solid fraction yield, the liquid fraction yield increased while the solid fraction yield decreased. The use of silica-alumina significantly decreased the process temperature. At 427 °C and 33.9% silica- lumina, an optimum liquid fraction yield of 89.95 wt.% was obtained. It was noted the liquid fraction hydrocarbons in the gasoline range. Shorter hydrocarbons (C3-C18) were predominant in the liquid oil.