Use of methanol and oxygen in promoting the destruction of deca-chlorobiphenyl in supercritical water |
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Authors: | Zhen Fang Hassane Assaaoudi Amr Sobhy Ian S Butler Janusz A Kozinski |
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Affiliation: | a Biomass Group, Xishuangbanna Tropical Botanical Garden, Chinese Academy of Sciences, 88 Xuefulu, Kunming, Yunnan 650223, China b Department of Chemistry, McGill University, 3610 University Street, Wong Building, Montreal, QC, Canada H3A 2B2 c McGill Metals Processing Centre, McGill University, 3610 University Street, Wong Building, Montreal, QC, Canada H3A 2B2 d Department of Chemical Engineering, College of Engineering, 3B48 Engineering Building, University of Saskatchewan, 57 Campus Drive, Saskatoon, SK, Canada S7N 5A9 e Energy and Environmental Research Laboratory, McGill University, 3610 University Street, Wong Building, Montreal, QC, Canada H3A 2B2 |
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Abstract: | The destruction of the well-known PCB, deca-chlorobiphenyl (10-CB), by oxidation and methanolysis in supercritical water (SCW), has been studied in a micro-reactor hydrothermal diamond-anvil cell (DAC, 50 nL) and in larger batch reactors (6 mL). The DAC was coupled to optical and infrared microscopes. In the DAC experiments, 10-CB proved to be stable under pyrolytic conditions, whereas in water, it was hydrolyzed and actually dissolved at temperatures above 475 °C. When partial oxygen was added to the 10-CB/water system, the solubility of 10-CB increased slightly as compared to the pure water experiments, and 10-CB was further decomposed by oxidation. The addition of methanol resulted in further decomposition by methanolysis, as confirmed by FT-IR spectroscopy, and lowered the dissolution temperature to 419 °C. Both oxygen and methanol (25 vol.%) were then used to destroy 10-CB in batch reactors, in which the supercritical water experiments permitted a detailed study of the reaction products of the 10-CB destruction. In the absence of methanol, more than 12 intermediate products were detected by GC-MS, and 99.2% of the 10-CB was destroyed in the presence of 225% excess oxygen at 450 °C within 20 min. When methanol was used in the absence of any excess oxygen, a destruction rate of 100% was achieved at 450 °C within 10 min and only three intermediate products were detected. The enhanced destruction of 10-CB in the presence of methanol is attributed to the homogenous reaction conditions employed and the generation of free radicals. |
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Keywords: | SCWO DAC PCBs Hydrolysis Methanolysis |
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