Zhen Fang, S. Xu, R. Smith
Mar 1, 2005
Citations
1
Influential Citations
35
Citations
Journal
Journal of Supercritical Fluids
Abstract
Abstract Decomposition of deca-chlorobiphenyl (10-CB) during pyrolysis and oxidation in supercritical water (SCW) was studied in a hydrothermal diamond anvil cell (HDAC) and batch reactors. HDAC was coupled with optical and infrared microscopes. Phase behavior was observed in situ in the HDAC. The 10-CB was stable under pyrolytic conditions, whereas in water it reacted and dissolved at temperatures above 475 °C and at high pressures. When 93% excess O 2 was added to the 10-CB and water mixture, dissolution of 10-CB occurred at 450 °C and high pressures. The dissolution conditions determined from the HDAC measurements were used in large-scale batch experiments allowing for detailed study of 10-CB reaction products and corrosion of SS 316 reactor under oxidizing conditions. Experiments were performed with and without Na 2 CO 3 , which was used as a neutralizing agent. It was found that 99.2% 10-CB was destroyed at 225% excess O 2 , 450 °C, 31.8 MPa in 1200-s reaction time. However, severe corrosion of the reactors was detected when no Na 2 CO 3 was used. In the presence of Na 2 CO 3 , the 10-CB destruction rate increased to 99.7% at 93% excess O 2 and little corrosion was observed (when 160% excess O 2 was used, 10-CB was completely destroyed). The following reaction pathway of 10-CB oxidation in supercritical water was elucidated: (i) hydrolysis and initial oxidation of 10-CB to low-chlorinated PCBs, benzene and benzofuran; (ii) dissolution and oxidation of decomposed products; and (iii) homogeneous oxidation of dissolved low-chlorinated benzene, phenol, acetic acid and formic acid, which were transformed to HCl and CO 2 . HCl either reacted with the reactor walls forming corrosion products or with the neutralizing agent to form salts that precipitated from the solution.