| In 2021,the national production of plastic products were about 8×107tons,an increase of 5.9%year on year,but the recycling rate of waste plastics was low.A large number of waste plastics had a serious negative impact on the ecological environment.Compared with the traditional plastic recovery technology,the use of catalytic cracking method to recover and utilize high value-added pyrolysis oil from waste plastics is an environmentally friendly and sustainable development technology.In this paper,the characteristics and kinetics of polystyrene pyrolysis and catalytic cracking were studied.Three different kinetic models were used to explore the kinetics of polystyrene pyrolysis.The effects of reaction temperature,reaction pressure and catalyst types on liquid yield and product composition were investigated in atmospheric reactor,autoclave and fixed fluidized bed.The kinetic calculation results showed that the DAEM model had strong applicability to the pyrolysis process of polystyrene,and the activation energy increased with the increase of conversion rate.The average apparent activation energy was 130.00 k J/mol,and the frequency factor was 4.42×109min-1.The liquid yields were high in the atmospheric reactor,which can reach 95%when the temperature rose to 410℃.The liquid products were mainly composed of styrene monomer and diphenylbutene.The reaction temperature required for the autoclave reactor was higher,and the reaction pressure had a great influence on the liquid yield.The steam atmosphere was better than the nitrogen atmosphere,and the content of benzene homologues such as toluene and ethylbenzene in the liquid product was high.The reaction was rapid in fixed fluidized bed,and the liquid yields were about 90%.The liquid products of cracking and alkaline Al2O3catalytic cracking were mainly composed of styrene monomer.The benzene homologue content in the liquid products of acidic FCC catalyst was higher.Alkaline Al2O3catalyst can improve the selectivity of styrene monomer in the product,and the styrene can be used as raw material for polystyrene production to achieve the purpose of recycling.The acidic FCC catalyst can improve the selectivity of the reaction to benzene homologues,and the generated benzene homologues can be used as a harmonic component to improve the octane number of gasoline.In order to recycle more styrene monomer for recycling polystyrene,alkaline catalyst such as Al2O3should be selected,and atmospheric reactor or fixed fluidized bed reactor should be used.In order to obtain more benzene homologues as a blending component for improving gasoline octane number,acidic catalysts should be selected and autoclave reactor should be used. |
