Abstract
To remove chlorine from chlorinated wastes efficiently, the hydrothermal treatment (HT) of PVC was investigated with a lower alkaline dosage in this work. Some typical operating conditions were investigated to find out the most important factor affecting the dechlorination efficiency (DE). The FTIR technique was employed to detect the functional groups in PVC and hydrochars generated to reveal the possible pathways for chlorine removal. The results show that the HT temperature was a key parameter to control the dechlorination reaction rate. At a HT temperature of 240 °C, about 94.3% of chlorine could be removed from the PVC with 1% NaOH. The usage of NaOH was helpful for chlorine removal, while a higher dosage might also hinder this process because of the surface poisoning and coverage of free sites. To some extent, the DE was increased with the residence time. At a residence time of 30 min, the DE reached a maximum of 76.74%. A longer residence time could promote the generation of pores in hydrochar which is responsible for the reduction in DE because of the re-absorption of water-soluble chlorine. According to the FTIR results, the peak intensities of both C=CH and C=C stretching vibrations in hydrochar were increased, while the peak at around 3300 cm−1 representing the –OH group was not obvious, indicating that the dehydrochlorination (elimination reaction) was a main route for chlorine removal under these conditions studied in this work.
Highlights
(vinyl chloride) is one of the most widely applied chlorinated plastics, and it has been utilized in many areas such as packaging, wrappings, bottles and containers because of its low price and good performance [1]
At a hydrothermal treatment (HT) temperature of 240 ◦ C, about 94.3% of chlorine could be removed from PVC with
The usage of NaOH was helpful for chlorine removal from PVC, while a higher dosage might hinder this process because of the surface poisoning and coverage of free sites
Summary
(vinyl chloride) is one of the most widely applied chlorinated plastics, and it has been utilized in many areas such as packaging, wrappings, bottles and containers because of its low price and good performance [1]. Large amounts of PVC-containing wastes are being generated and needed to be disposed of. For PVC-containing wastes, several methods have been proposed for recycling. Thermal recycling (pyrolysis, gasification, hydrogenation, etc.) and incineration have been the main technologies widely applied. PVC is rather resistant to incineration because of its high chlorine content (56.8%). As for the thermal degradation, it suffers from toxic emissions and generate a lot of hydrochloric acid (HCl), which can cause corrosion in the furnace and lead to the release of trace amounts of further harmful gases such as
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