Study on preparation of aromatic-rich oil by thermal dechlorination and fast pyrolysis of PVC

Thermal dechlorination and fast pyrolysis experiments of PVC were carried out. Characterizations such as TG, FTIR and 13C NMR were applied to analyze the thermal degradation characteristics and chemical structure evolution characteristics of de-HCl PVC during the dechlorination process. The thermal dechlorination results show that the degree of dechlorination and aromatization of de-HCl PVC is deepened with the increasing dechlorination temperature. The dechlorination efficiency is as high as 99.86% at 320 ℃. Meanwhile, the de-HCl PVC with a chlorine content of 0.22% and the optimal H/Ceff value for aromatics production can be obtained. The de-HCl PVC gradually evolves from a long chain structure with C-C bonds as the skeleton to a long olefin chain structure with partial aromatization during the dechlorination process. The fast pyrolysis results show that the oil generated by the de-HCl PVC (320 °C) pyrolysis has a high aromatic content of 97.32%−99.93%. In addition, there are no chlorine-containing compounds in the oil from de-HCl PVC (320 °C) pyrolysis, while the PVC pyrolysis oil contains chlorinated aromatics with high content of 1.91%−4.02%. During the fast pyrolysis process, the monocyclic aromatic hydrocarbons (MAHs) are mainly formed from the cyclization of polyene fragments released by random fragmentation of de-HCl PVC (320 ℃). Further, the polycondensation reaction is promoted to realize the conversion of MAHs to polycyclic aromatic hydrocarbons (PAHs) under the action of high temperature. The by-products of pyrolysis gas with high HHV and carbon-rich char both can be further utilized. Overall, thermal dechlorination and fast pyrolysis can realize harmless treatment and high-value utilization of PVC.