| With the development of science and technology,the extensive popularization of agricultural film has provided great development advantages for agricultural production,but the waste PVC film used has caused serious pollution to soil and environment.Plastic waste can be recycled by pyrolysis,which can replace fossil raw materials to prepare chemicals and high calorific value gases.It has great environmental significance.The main component of plastic film is polyvinyl chloride,the chlorine precipitation in these waste plastics containing chlorine will cause a series of problems.At present,pyrolysis studies on polyvinyl chloride mainly focus on catalytic dechlorination,co-pyrolysis with other biomasses,and less systematic analysis of catalytic preparation of hydrocarbons and chlorine distribution.In this paper,polyvinyl chloride was selected as the research object,which was modified with calcium hydroxide.The catalytic pyrolysis technology was used to catalytically convert polyvinyl chloride into hydrocarbon.With the help of pyrolysis furnace reactor,the composition of hydrocarbons and the effect of calcium hydroxide on chlorine distribution in the product during the thermochemical conversion of PVC were studied.The main findings are as follows:1.The catalytic pyrolysis of PVC is closely related to the pore structure and acid content of the catalyst.In this paper,the molecular sieves with different pore structures and HZSM-5(Si/Al=25,50,80,150 and 200)catalysts with different Si/Al ratios were analyzed by means of BET,XRD,TPD,SEM and other analytical methods.According to the experimental results and characterization analysis,ZSM-5 zeolite catalyst has a special structure,and its framework consists of two vertical cross-channel systems.The pyrolysis performance of ZSM-5 zeolite is better than that of other zeolites.With the increase of Si/Al ratio,the catalyst has good crystallinity and the morphology distribution is more regular.HZSM-5/200 shows better catalytic performance.Bifunctional catalysts were prepared by ion exchange method with Co,Ni and Ce metal supported on HZSM-5 zeolite catalyst.The results show that the modified catalyst will increase the total carbon yield of the product during pyrolysis,mainly the yield of the gas product is obviously improved.2.In this paper,the experimental study on the preparation of hydrocarbons by thermal catalytic conversion of polyvinyl chloride was carried out.The effects of Ca(OH)2 loading,residence time and reaction temperature on the distribution of pyrolysis products were investigated.The optimal conditions for the preparation of hydrocarbons were optimized and the deactivation mechanism of the catalysts was studied.The optimum conditions are as follows:using a Ca(OH)2 loading of 10%PVC raw material at about 650℃,using HZSM-5(Si/Al=200)as a catalyst,the residence time in bed is 3.3 seconds and the nitrogen rate was 60 ml/min.Under these conditions,the coke yield was 41.28%,and the aromatic hydrocarbon compound carbon yield was 14.67%,which mainly included 8.85%benzene,3.86%toluene,and 1.96%naphthalene.The carbon yield of the gas is 28.71%.The selectivity of C3H8 and C4H10 is 77.3%and 16.46%,respectively.The yield of aromatic compound decreases to 2.03%after repeated use of the catalyst five times,and the gas yield increases to 31.2%.The main factor affecting the stability is the change of catalyst structure and acid site loss during the reaction process in the catalytic process.3.In this paper,the pyrolysis products were analyzed by GC-MS,XPS,ICP and elemental analysis,and the mechanism of chlorine migration during the pyrolysis of polyvinyl chloride was studied.The results show that chlorine can be immobilized in solid carbon in the form of inorganic CaCl2 by adding calcium hydroxide to pvc. |
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