Microwave Pyrolysis And Catalytic Conversion Of Low Density Polyethylene

The increasing demand for plastics due to the wide application of plastics eventually leads to the accumulation of a large amount of plastic waste,which is still a worrying problem,because the efforts of traditional waste plastic remediation technology are limited,insufficient and environmental problems.The increase in the production of plastic synthetic raw materials has had a dual impact on our ecosystem.Especially since the outbreak of COVID-19,the growth of medical and packaging waste plastics has intensified.It leads to the rapid depletion of non renewable oil resources and the generation of waste.Using waste plastics for product upgrading may achieve the purpose of circular economy.In addition,recently,it has been recognized that biochar is a multifunctional medium for catalytic application.Therefore,the catalytic ability of biochar and the mechanical practice of various ways have been preliminarily studied.Using lignin biochar supported metal to modify the catalyst to catalyze waste plastics is a dual utilization strategy.In this paper,different cracking conditions of LDPE plastics were studied,and the catalytic upgrading of LDPE cracking oil was studied with self-made catalyst.The catalyst and reaction conditions were screened and optimized.The results are as follows:(1)The yield of LDPE cracking will change with different conditions.The yield first increases and then decreases,and two times of cracking will occur when it reaches500 ℃.Compared with no catalyst,the quality of oil with catalyst is significantly improved,the carbon chain is shortened and the freezing point is reduced.Lignin carbon catalyst and phosphorylated lignin catalyst have certain effects.Alkaline catalyst Mg O and acidic catalyst HZSM have different effects and can be used according to different components.In situ catalysis and ectopic catalysis have an effect on the pyrolysis composition of LDPE,and the gas production rate of ectopic catalysis is higher.The catalyst temperature will affect the yield.The higher the temperature is,the higher the gas yield is.(2)After lignin biomass and Ni are fully mixed,biochar catalysts loaded with different metals are prepared by cracking in a tubular furnace at 500 ℃.Metal loaded biochar is different from pure biochar and biochar mixed metals.There are significant differences in the performance of the catalysts.The lignin supported metal nickel biochar was characterized by XRD,XPS and TEM.The nickel compound supported in the biochar is a mixture of Ni(OH)2 and Fe.These characterization results can reflect the pore structure,physical crystal phase and surface activity of biochar,but its catalytic activity can be reflected in specific pyrolysis experiments.(3)Biochar catalyst has certain effect as a catalyst with weak acidic function.Fe catalyst with weak hydrogenation dehydrogenation function can not destroy plastic oil molecules at low temperature.Supported metal catalysts with hydrogen dehydrogenation function,such as Ni,have a certain effect.The increase of cracking capacity of the catalyst can easily increase the amount of aromatics through cyclization reaction.Metal functional groups and acid functional groups can produce a large number of aromatics through dehydrogenation cyclization.Strong hydrogenation can hydrogenate the coke precursor and produce more useful liquid products,that is,by quenching free radicals to prevent additional cracking that may lead to the formation of excess gas,so as to generate oil.Strong metal functional groups also help to reduce the formation of olefins and increase the number of branched products,so as to isomerize olefins on related acidic supports.At higher temperatures,depolymerization is not affected by catalyst activity,and conversion and oil production are not affected by the presence of catalyst,although the type of catalyst used may affect the quality of oil.The pyrolytic plastic oil was upgraded by loading Ni and Fe on biochar,and the plastic oil catalyzed by iron and nickel on lignin biochar had different effects.High aromatic hydrocarbons(80.88%)could be obtained by loading Fe,and high alkane content(90.48%)could be obtained by loading nickel.The feasibility of lignin supported nickel was verified.Pure lignin carbon and pure metal nickel could not be used for catalytic upgrading,which proved that the synergistic effect of the synthesized catalyst upgraded the raw materials.The prepared catalyst can be recycled for 3 times.After optimizing the reactor conditions,the value is 250 ℃,the initial pressure is 2MPa,and the catalyst addition ratio is 10%.In this paper,a low-cost,high activity and environment-friendly lignin supported metal biochar catalyst is used to prepare high selective plastic oil,and the catalyst prepared from biomass is used to catalyze biomass pyrolysis,which provides a reference for the resource utilization of biomass and the recycling of waste plastics and biomass.