Dechlorination of polyvinyl chloride electric wires by hydrothermal treatment using K_2CO_3 in subcritical water

摘要

Polyvinyl chloride (PVC) waste generation has significantly increased in recent years and their disposal is considered a major environmental concern. Removal techniques of chlorine from PVC waste are being studied to minimize a negative environmental impact. In this work, the use of K_2CO_3 as an alkaline additive to improve the dechlorination efficiency (DE) in the hydrothermal degradation of PVC wires was studied. Different experiments were carried out varying both temperature (175, 200, 225, 235 and 250 ℃) and K_2CO_3 concentration (0.025, 0.050 and 0.125 M), using a solid/liquid ratio of 1:5 in order to determine the evolution of the dechlorination efficiency with time. About 4.66, 21.1, 24.4, 45.7 and 92.6 wt% of chlorine in PVC wire was removed during hydrothermal dechlorination (HTD) with an additive/chlorine ratio of 1:25 (K_2CO_3 solution of 0.050 M) at 175, 200, 225, 235 and 250 ℃, respectively. Optimal additive/chlorine ratio decreased to 1:50 (K_2CO_3 solution of 0.025 M) at 250 ℃, obtaining a dechlorination degree of 99.1% after 4h without the need of metallic catalysts. Concerning the solid phase behavior during dechlorination, a linear correlation between the DE reached and the weight loss of PVC was found.