The study of nickel effect on the hydrothermal dechlorination of PVC

The nickel might have involved in the hydrothermal (HT) treatment of poly(vinyl chloride) (PVC) containing wastes because of the corrosion of Ni-containing reactors, which was caused by the HCI generated in this process. This work has been conducted to investigate if the nickel has a positive effect on the HT dechlorination of PVC, which was usually neglected in previous research. The HT dechlorination of two kinds of PVC was performed in subcritical nickel-containing water with various Ni2+ concentrations under several HT operating conditions in order to investigate the effect of the nickel on the dechlorination efficiency (DE). The FTIR, C-13 NMR and SEM techniques were utilized to characterize the hydro chars and the ICP-OES was used to measure the nickel content in the separated liquid (SL) to explore the possibility of reuse the nickel-containing water. The chlorine in the SLs was measured by potentiometric titration to solve the DE. The results show that the Ni2+ could significantly accelerate the HT dechlorination of PVC at a relative mild condition. The DE was about 76% at a HT temperature of 220 degrees C for 30 min in 0.1 M Ni2+-containing water, 6 times higher than that without Ni2+. The HT temperature has a dominant effect on the DE which reached up to 87% at a HT temperature of 260 degrees C. At higher HT temperature, the acceleration of Ni2+ was not obvious because of the aggravation of the corrosion and also the higher heat and mass transfer. Besides, the DE could not reach 100% at some circumstances because of the cyclization and cross-linking, which would be also weakened under higher temperature. According to the FTIR and C-13 NMR spectrum, both elimination and substitution happened during the HT dechlorination with Ni2+. The Ni2+ could promote the evolution of the pores in PVCs and strengthen the substitution of Cl with OH, which was responsible for the acceleration of dechlorination at mild Ni2+containing system. The ICP-OES result verified that the Ni2+ worked as catalyst and the Ni2+-containing water could be reused. This result was beneficial for both the treatment of the nickel-containing wastewater and also the HT treatment of organic wastes. (C) 2017 Elsevier Ltd. All rights reserved.