An alkali-enhanced subcritical water treatment strategy of short-chain chlorinated paraffins: Dechlorination and hydrocarbons recovery

Fu-Rong Xiu; Qingyun Bai; Yingying Qi; Xinyue Lei; Ruiqi Yang; Siyi Wang; Yixiao Wang; Jiali Wang; Longsheng Zhan; Haipeng Zhou; Wenting Shao

doi:10.1016/j.scitotenv.2023.166574

An alkali-enhanced subcritical water treatment strategy of short-chain chlorinated paraffins: Dechlorination and hydrocarbons recovery

Sci Total Environ. 2023 Dec 15:904:166574. doi: 10.1016/j.scitotenv.2023.166574. Epub 2023 Aug 28.

Authors

Affiliations

¹ College of Geology and Environment, Xi'an University of Science and Technology, Xi' an 710054, People's Republic of China.
² College of Geology and Environment, Xi'an University of Science and Technology, Xi' an 710054, People's Republic of China. Electronic address: qiyingying@xust.edu.cn.

PMID: 37647949
DOI: 10.1016/j.scitotenv.2023.166574

Abstract

As persistent organic pollutants, short-chain chlorinated paraffins (SCCPs) have attracted wide attention in the field of environmental health risk and hazardous waste management. Efficient dechlorination of high content of SCCPs in plastic waste is the committed step for its detoxification and safety treatment. In this study, a high-efficiency and low-temperature process for dechlorination and hydrocarbons recovery from typical SCCPs (52#SCCPs) by subcritical water (SubCW) with alkali enhancer was developed. The introduction of alkali enhancer in the SubCW process had significantly enhanced effect on the dechlorination of 52#SCCPs, and the order of the enhanced effect of alkali enhancer for the dechlorination was NaOH > Na₂CO₃ > NaHCO₃ > NH₃·H₂O > KOH. The dechlorination behaviors of 52#SCCPs in the NaOH-enhanced SubCW process were studied systematically under different conditions including temperature, residence time, alkali concentration, and volume ratio. The results showed that high-efficiency dechlorination (100 %) of 52#SCCPs could be achieved by the NaOH-enhanced SubCW process at low temperature for a short time (250 °C, 5 min). All of the chlorine released from the molecular chain of 52#SCCPs was transferred to the aqueous phase in the form of inorganic chlorine. The continuous HCl elimination reaction was the primary dechlorination mechanism for 52#SCCPs in the NaOH-enhanced SubCW process. After the dechlorination of 52#SCCPs, high value-added hydrocarbons such as 2,4-hexadiyne (31.74 %) could be obtained. The alkali-enhanced SubCW process proposed in this study is believed to be an environmentally friendly and high-efficiency method for dechlorination/detoxification and resource recovery of SCCPs.

Keywords: Alkali additives; Chlorinated paraffin; Dechlorination; Subcritical water.