Study On The Catalytic Pyrolysis Characteistics And Kinetics Of Mixed Waste Plastics Based On Spent FCC Calalysts

With the rapid development of Chinese economy,the use of plastic products continues to grow.According to statistics,the production of plastic products in 2022 is nearly 80 million tons,becoming the world’s largest "plastic kingdom".At the same time,a large number of waste plastics have been produced,and the problem of waste plastics treatment has become the focus of global attention.The resource utilization of waste plastics has become an inevitable choice.It is an effective way to realize the resource utilization by catalytic pyrolysis to convert it into high-quality liquid fuel.However,since the catalyst cannot be separated from the carbon residue and can only be used once,the development of low-cost catalysts has been a hot topic of research in the industry.In this paper,the waste catalyst(spent FCC catalyst)produced in the process of petroleum processing is used for the pyrolysis of mixed waste plastics.Taking polypropylene,polyethylene and polystyrene as the research objects,the pyrolysis characteristics and kinetics of single plastics,binary mixed plastics,ternary mixed plastics and mixed waste plastics were carried out in turn.The pyrolysis characteristics of mixed waste plastics were studied.The synergistic mechanism between different kinds of plastics in the catalytic pyrolysis process of mixed waste plastics was analyzed.The kinetics of pyrolysis of mixed waste plastics based on spent FCC catalysts was explored.The kinetic parameters of pyrolysis were calculated by the combination of model-free method(FWO method,KAS method and Starink method)and model fitting method(Malek method and Coats-Redfern method),which provided a theoretical basis for the application of spent FCC catalyst in the field of waste plastic pyrolysis.The main research of this paper is as follows:(1)The pyrolysis characteristics and kinetics of plastics based on spent FCC catalyst were studied.According to the test results of thermogravimetric analyzer(TG-DTG curve),the effect of spent FCC catalyst on the catalytic pyrolysis characteristics of different types of plastics was investigated,and the catalytic pyrolysis process of plastics was analyzed.Various kinetic models were used to solve the parameters of the TG-DTG curve data and to determine the best model of pyrolysis mechanism function.Compared with plastic pyrolysis,catalytic pyrolysis will change the pyrolysis characteristics and kinetic parameters of plastics,and is beneficial to reduce the energy consumption of plastic pyrolysis.(2)The synergistic mechanism and the influence of process conditions on the pyrolysis process of mixed plastics were investigated.There is a positive synergistic effect in the pyrolysis of mixed plastics.Compared with the pyrolysis of single plastic,the mixed plastic pyrolysis is beneficial to reduce the cracking energy consumption.With the increase of heating rate,the pyrolysis temperature of plastics has obvious hysteresis,and the maximum weight loss rate also increases with the increase of heating rate.(3)An intelligent experimental platform for continuous pyrolysis of mixed waste plastics with a processing capacity of 10kg/h was developed.The experimental platform includes core devices such as mixed waste plastic crushing,continuous feeding,graded thermal cracking,automatic separation of oil and gas condensation,and tail gas treatment.The experimental platform realizes the removal and separation of most chlorine elements in the continuous catalytic pyrolysis process of mixed waste plastics,and realizes the staged collection of pyrolysis oil at different temperatures by controlling the condensation temperature,so as to improve the product quality of pyrolysis oil.(4)The pyrolysis process of mixed waste plastics in a staged pyrolysis reactor at different speeds was simulated.The movement and heat transfer of waste plastic particles in the reactor at different speeds were analyzed,and the optimum process conditions of the reactor were explored.On the premise of ensuring sufficient pyrolysis to improve the production efficiency,theoretical guidance for the design and operation of the reactor was provided.In summary,this study realizes the synergistic high-value reuse of spent FCC catalysts and mixed waste plastics,and provides theoretical guidance for the application of spent FCC catalysts in the field of pyrolysis of waste plastics,which is of great significance for promoting the construction of ecological civilization and building a beautiful China.