Study On Pyrolysis Characteristics And Kinetics Of Poly (Vinyl Chloride) And Other Plastics Wastes

Pyrolysis technology on waste plastics, especially chlorine-containing plasticsdisposal shows prospects and is of much beneficial to both environment and resource.The research on pyrolysis characteristics of chlorine-containing plastic is essential forthe industrialization of its disposal and recycling. The pyrolysis characteristics andkinetics of four typical thermoplastic samples, poly(vinyl chloride)(PVC),polypropylene (PP), low density polyethylene (LDPE) and high density polyethylene(HDPE), were studied.The pyrolysis characteristics of PVC, PP, LDPE and HDPE were studied bythermogravimetric (TG) analysis respectively. Based on the TG data at differentheating rates, the kinetics parameters, especially the activation energy (E), werecalculated using the Friedman method. The mechanism functions of PVCdecomposition were judged by the Malek method. There were two stages in PVCpyrolysis. The first stage was mainly dechlorination, and the second stage was thecleavage of olefin chains releasing aromatic hydrocarbons. The residue was about10%. The process of PP and PE decomposition was simple, which was in a narrowtemperature range. The residue mount of PP and PE was quite little (<1%). Duringpyrolysis, the reactions of PVC include dehydrochlorination and cyclization of olefinchains. The random breakage of the PP/PE molecular chain occurs when heated, withC9-30alkane fractions generated.Kinds of metal oxides were mixed with PVC during pyrolysis for chlorineabsorption. The pyrolysis process were studied by TG analysis and fixed bedpyrolytic experiments. The gas production was detected by oxygen bomb combustion–ion selective electrode (ISE) method and Fourier transform infrared (FTIR)spectroscopy. Among, zinc oxide (ZnO) showed the best effect on the chlorineabsorption during the PVC pyrolysis.The thermal degradation of PVC in air ambience was investigated by the TGanalysis. The experiments were carried out at different heating rate of5,10,20and40oC/min, respectively. The kinetic parameter, the activation energy (E), was calculatedbased on the Friedman method. The pyrolysis process of PVC in air could be dividedinto two main stages:200-380oC and400-600oC, which obtained by TGA at the heating rate of5oC/min. And the second stage could be further subdivided into twoparts by465oC. It can be concluded that the oxygen in air affected the second stagemore obviously than that of the first one, in comparison with inert atmosphere. Theactivation energy of the second stage was still larger than the first stage. The residuewas little (almost zero).Pine wood and Dunaliella tertiolecta, as the samples of biomass, were mixedwith plastics and the pyrolysis of their blends were analyzed. The kinetics was alsostudied by the Friedman method. The difference between the experimental andtheoretical weight losses (ΔW) was calculated. The PVC-wood blend residuesincreased by10%, LDPE-wood blend residues decreased by1%, HDPE-wood blendresidues decreased by4%, and PP-wood residues remained unchanged. Thedehydrochlorination reaction of PVC and the degradation of hemicellulose andcellulose in wood were found to have synergistic effects during co-pyrolysis. The HClfrom PVC may act as a Lewis acid which shows an acid-catalyzed dehydrationmechanism of cellulose. LDPE, HDPE, and PP interacted with wood in co-pyrolysis.The activation energies of plastics, wood, and their blends were from92.8kJ/mol to359.5kJ/mol. The average activation energies of PVC–wood blend in the two stageswere180.2and254.5kJ/mol, respectively, whereas those of LDPE-wood blend were164.5and229.6kJ/mol, those of HDPE-wood blend were213.2and234.3kJ/mol,and those of PP-wood blend were198.4and263.6kJ/mol. The co-pyrolysis ofplastics and algae were different with the wood, and the variations of residue wereopposite to plastic and wood blends, except PP with no significant change.The investigation on pyrolysis characteristics and kinetics analysis of chlorinecontaining plastics wastes provided a reference to municipal solid waste disposal andresource recycling. And the study provided the basic data support for industrializationof pyrolysis technology.