Study on the Co-Pyrolysis Interactions and Chlorine Migration Behaviors of Polyvinyl Chloride and Hami Coal

Co-pyrolysis of waste plastics and low-rank coal is an effective way to realize resource recycling, while the chlorides released during the co-pyrolysis process would corrode the equipment and affect the product quality. Therefore, the synergistic effect and chlorine migration behavior during the co-pyrolysis process of Hami (HM) coal and polyvinyl chloride (PVC) were studied through in situ pyrolysis time of flight mass spectrometry (Py-TOF-MS). Meanwhile, the influence of additives in waste PVC plastics on co-pyrolysis was also studied. Co-pyrolysis of PVC polymer (PVC-PO)/PVC pipes (PVC-P) and HM coal exhibits a positive synergistic effect on the generation of char and water, which increase about 2.6%-7.8% and 0.8%-2.4%, respectively, and the synergistic effect is strengthened with the increase of the proportion of PVC-PO/P. The increasing contents on C1-C4 and H2 indicated that the reactions between small molecular fragments and condensation reactions between aromatic rings are strengthened. The analysis of Py-TOF-MS suggested that co-pyrolysis promotes the cyclization, aromatization and rearrangement reactions between volatiles and accelerates the generation of MAHs and PAHs. However, the addition of HM coal inhibits the breaking of β C-C bonds on long-chain hydrocarbons from PVC-PO/P and further inhibits the generation of polyene fragments (which are the origins of aromatic compounds). Moreover, the phenolic antioxidants in PVC-P increase the yield of co-pyrolysis water by 2.4%-2.8%, which is higher than that of HM/PO (0.8%-1.9%). The fillers (CaCO3) in PVC-P accelerate the catalytic cracking of heavy tar and lead to more than 2.15% of the chlorine is fixed in co-pyrolysis char. Co-pyrolysis inhibits the release of HCl and results in a migration of chlorine from the gas phase to the solid/liquid phase, and most of the chlorine is present in the form of inorganic chlorine in the products. From the perspective of co-pyrolysis synergistic effect and chlorine migration, 7:3 is a suitable ratio for co-pyrolysis, which provides guidance for the targeted regulation of chlorine.