Thermal Cracking plus Catalytic Upgrading

The problems in catalytic cracking of MWP by direct contact with the catalyst can be overcome by two-step processing. This method involves an initial thermal cracking of waste plastics to produce low-quality hydrocarbons (vapors or liquid) that are treated afterwards in a catalytic reactor to obtain high-quality liquid fuels. 

A full-scale pyrolysis-catalytic process in which the catalytic cracking zone is directly connected to the pyrolysis zone was developed in Japan (Fuji Process) [19]. In this process, after separation of PVC and impurities by wet techniques, waste plastics are thermally pretreated at 300°C for dechlorination and then introduced into the pyrolysis reactor and thermally cracked at 400°C. Subsequently, degradation products are fed directly to the fixed-bed reactor using a ZSM-5 catalyst. 

The main problem is the sensitivity of the zeolite catalyst towards impurities coming from the waste. 

A lluidized-bed pyrolysis reactor is the most suitable for thermal cracking of MWP to obtain liquid/waxy product. Key features of the lluidized-bed pyrolysis include [3, 20]  

The liquid product obtained from thermal cracking can be either catalytically cracked/ hydrocracked or co-processed with a refinery feed. Since the catalytic cracking of oil derived from MWP is more or less problematic, any cracking catalyst can be applied to oil derived from pyrolysis of plastics. But the yield and the quality of gasohne obtained from cracking step vary with the type of catalyst and the properties of the pyrolytic oil derivated from waste plastics. 

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