Basic Research On The Application Of Natural Mineral-based Catalysts To Degrade Polyethylene Plastics To Produce Alkenes

With the continuous development of social science and technology,plastic products have penetrated into all areas of society due to their performance advantages and cheap costs.However,improper treatment on the issue of plastic recycling and disposal has brought serious pollution to the environment.Although the landfill method has low investment and convenient operation,it will use a large amount of land,affect the permeability of the soil,and prevent plants from photosynthesis.Although the incineration method can achieve the reduction goal and recover part of the energy,the entire process releases a lot of harmful substances.Therefore,the recycling of waste plastics has become one of the key issues of environmental protection.This paper explores and studies catalysts for thermal cracking of plastics into organic gases such as methane,ethylene,and ethane.A natural mineral supported catalyst is prepared by the precipitation method.Ni and Cr supported montmorillonite catalysts were synthesized,and the effects of natural metals supported by different metals on the degradation of plastics were analyzed.XRD,SEM-EDX and IR were used to characterize the physicochemical properties of the catalyst.The best catalytic performance was obtained by studying the reaction temperature and metal content.Research indicates:(1)A Ni-supported mullite catalyst was prepared by a precipitation method.Catalytic pyrolysis experiments were performed on HDPE in a homemade fixed-bed reactor.The pyrolysis of Fe,Co,and Ni on the same plastic was compared,and the catalytic effect was found to be Ni> Co> Fe.Pyrolysis experiments found that the higher the Ni loading,the higher the methane selectivity.Under the optimal experimental conditions,the argon flow rate is 0.4 L / h,the reaction temperature is 500℃,the ratio of nickel nitrate hexahydrate to mullite is 6: 4,and the mixing ratio of Ni-mullite / HDPE is 1: 2.The rate was 15 wt.%,And the methane selectivity was 92.98%.(2)Ni and Cr supported montmorillonite catalysts were prepared by precipitation method,and catalytic pyrolysis experiments were performed on LDPE.The optimal conditions for the catalyst reaction are: when the supported amount is 15 wt.% Ni,the temperature is 450℃,and the mixing mass ratio is 1: 2,the methane selectivity and gas yield are high.Carbon nanotubes with fewer defects in the residue.Cr showed an inhibitory effect on pyrolysis.The pyrolysis of montmorillonite blended LDPE and blended LLDPE was compared.The LDPE methane selectivity was higher at low temperatures and the LLDPE methane selectivity was higher at high temperatures.(3)Through fixed bed microreactors,the pyrolysis of Ni mullite,Ni montmorillonite and Ni basalt catalysts prepared by impregnation method and precipitation method in ethylene gas flow at a fixed flow rate was studied.The results show that these catalysts have a high catalytic conversion effect on ethylene gas.The effects of different temperatures and different loadings of Ni O on the catalytic reaction were studied.It was found that mullite and basalt can give methane a maximum selectivity of about 98%.The catalytic effect of the three minerals as a carrier is ranked as follows: basalt> mullite> montmorillonite.