The Study On The Pyrolysis Characteristics And Pyrolysis Kinetics Of PVC

Polyvinyl chloride(PVC)material was the second largest general-purpose plastic in the world.It had the characteristics of light weight,long life,high strength,abrasion resistance,and chemical corrosion resistance.At the same time,it had the advantages of good flame retardancy and insulation.It was used widely in industry,agriculture,construction,electronic appliances,automobiles,and power communications.A large amount of plastic waste not only caused serious environmental pollution,but also caused a waste of resources.How to reduce quickly the amount of resources into harmless treatment,which was a major problem at present.The traditional treatment methods included landfill and incineration,but they caused serious environmental problems.Waste plastic was converted directly into usable energy,which was converted into gas,fuel,etc through pyrolysis.Pyrolysis was a clean and promising chemical recycling technology.However,when PVC wass pyrolyzed a large amount of harmful substances such as HCl and benzene derivatives and polycyclic aromatic hydrocarbons(PAHS)produced.This paper studied the pyrolysis characteristics of PVC in different atmospheres and adding different catalysts.The experimental test included Ultimate analysis,thermogravimetric analysis(TG),pyrolysis-gas chromatography-mass spectrometry(Py-GC-MS),and thermogravimetric analysis-Mass spectrometry(TG-MS),scanning electron microscopy(SEM),gas chromatography-mass spectrometry(GC-MS)gas chromatography(GC),Fourier transform infrared spectroscopy(FI-IR),X-ray powder diffraction analyzer(XRD).These tests characterized the effects of various catalysts on the composition and morphological structure changes of the gas,liquid,and solid phase products during the pyrolysis of PVC.The research content is as follows:(1)0%,20%,and 50%K2CO3 was added to PVC and were pyrolyzed in SX3-4-10A muffle furnace in N2 or CO2.We studied the mechanism of pyrolysis in different gas atmospheres.The results showed that the influence of K2CO3 on PVC pyrolysis was manifested in the capture of HCl.As the mass fraction of K2CO3 in N2,with the increase of K2CO3 mass fraction,the HCl content decreased from 17.89%to 10.91%.CO2 was an effective carbon scavenger,which changed the course of its thermal decomposition reaction and inhibited the formation of aromatic compounds during the thermal decomposition process.The content of benzene reduced from 12.09%to 9.96%.In general,K2CO3 captures the HCl produced by the pyrolysis of PVC and CO2 inhibited the formation of benzene derivatives and polycyclic aromatic hydrocarbons(PAHS).(2)The effects of two types of transition metal oxides on the pyrolysis characteristics of PVC are studied.The experimental results showed that:The first type of transition metal oxide promoted the cross-linking reaction between molecules by forming a stable physical bond bridge structure to reduce the generation of aromatic hydrocarbons,which was the reduction coupling mechanism.The second type of transition metal oxide formed a cross-linked structure by complexing HCl to form Lewis acid,which was the Lewis acid mechanism.The first type of transition metal oxide had a good effect in order:V2O5>MoO3>TiO2.The second type of transition metal oxide had a good effect in order:CuO>Fe2O3>ZnO>MnO2.Therefore adding transition metal oxides during the pyrolysis of PVC reduce effectively the generation of harmful substances.(3)The pyrolysis characteristics of six typical PVC building materials(selected from PVC powder,PVC particles,PVC pipes,PVC sheets,PVC wallpapers,and PVC cables)were studied,and the pyrolysis kinetics of six PVC building materials were studied.The experimental results showed that additives reduced the release of HCl.The main gas components of pyrolysis were CO,CH4,H2,CO2.The concentration of CO2 produced by PVC board was the highest,with a mass fraction of 21.16%.The concentration of CH4 produced by PVC pipes was the highest,with a mass fraction of 10.18%.The concentration of CO produced by PVC wallpaper was the highest,with a mass fraction of 2.03%.Zinc stearate absorbed quickly HCl and replaced effectively the unstable chlorine atoms on the PVC chain with carboxylate.ZnCl2 was an efficient catalyst for the removal of HCl from PVC.Additives had obvious effects on gas products,liquid products,and solid carbon residue three-phase products,indicating that the additives further crack more volatiles and tar precursors into small molecules The activation energy of the first stage of pyrolysis of PVC building materials was less than.the activation energy of the second stage,indicating that pyrolysis of Cl needs to absorb less energy from the surrounding environment.But aromatization or crosslinking to generate benzene and benzene derivatives needed more energy.