Co-pyrolysis Behavior Of Pre-dechlorination Treated PVC Residue And Pingshuo Coal

Pyrolysis is an important way to realize the efficient transformation and utilization of carbonaceous materials such as coal and waste plastics.It is well known that halogenated plastics are difficult to be treated harmlessly and recycled.In order to explore an efficient and clean utilization way for the plastic,this article takes polyvinyl chloride（PVC）as the research object.PVC is preheated firstly to remove most of the chlorine,and then PVC pyrolysis residue and coal are co-pyrolyzed on the fixed bed reactor to investigate their reaction behavior and interaction mechanism.It is expected that the high hydrogen content of waste plastics can be used to the hydrogenation upgrade of low-rank coal,meanwhile,the harmlessness treatment and high-efficiency utilization of them can also be realized.Firstly,the pyrolysis law of PVC alone and the dechlorination behavior of PVC at different pyrolysis temperatures were studied in an atmospheric fixed-bed reactor.The results show that with the increase of pyrolysis temperature,the yield of PVC pyrolysis gas and tar increases,and the yield of residue decreases.The residue is in a massive form,and its particles and chlorine content decrease with temperature increase.The chlorine content in the PVC residue at 350 ^oC is only 0.72 wt.%.The pyrolysis characteristics of Pingshuo coal in fixed bed reactor are studied,and the highest tar yield is found at 550 ^oC condition.Based on the above research,the co-pyrolysis reaction behavior and synergistic effect of Pingshuo coal and PVC pretreatment products（DPVC）were further investigated,and the influence of DPVC additive amount on co-pyrolysis was analyzed.The actual weight loss of the mixed samples on the thermogravimetric analyzer is higher than that calculated in theory,which indicates that the co-pyrolysis has synergistic effect of promoting decomposition.The co-pyrolysis kinetics analysis with FWO method shows that the addition of DPVC decreases the activation energy and pressor factor of the reaction.Among them,the experimental value of the tar yield obtained from the pyrolysis of 15%DPVC in coal is 3.35 wt.%higher than the theoretical calculation value.While the water and gas show the obvious negative synergistic effect.Each gas component shows negative synergistic effect,and CH₄ shows the strongest negative synergistic effect.There are many oxygen-containing compounds in the co-pyrolysis char,and their I_D/I_Gvalue is lower than char pyrolysis alone,indicating that there is also a synergistic effect in the formation process of co-pyrolysis char.The analysis of tar showed that co-pyrolysis process promotes the lightening of tar.The light tar content of 10%DPVC in coal pyrolysis is the highest,which is 56 wt.%,and 5 wt.%higher than the theoretical value.The GC/MS results showed that with the increase of DPVC content,the content of benzene and polycyclic aromatic hydrocarbons increase,and the content of phenols and linear aliphatic hydrocarbons decrease.The content of naphthalenes in the co-pyrolysis tar is higher than that of the two pyrolysis alone.The results of NMR showed that the content of aromatic hydrogen and aromatic carbon ratio in tar increase with the addition of DPVC,and the length of side chain extend.This work also explored the migration of chlorine during the co-pyrolysis process.It was found that chlorine mainly remains in char,followed by tar,and is very low in pyrolysis water and gas.The chlorine balance calculation of pyrolysis process verifies the reliability of the experimental data.