Study on Catalytic Wet Air Oxidation of Ferrocyanide or 2,4-Dichlorophenol Solutions

Autor: Bing-Nan Lee, 李炳楠
Rok vydání: 2001
Druh dokumentu: 學位論文 ; thesis
Popis: 89
The objectives of this research were to obtain the optimum operating conditions for a catalytic wet air process and to investigate their reaction kinetics. Either the ferrouscyanide (Fe(CN)64－) or the 2,4-dichlorophenol (2,4-DCP) solution was treated by the catalytic wet air oxidation (CWAO) process using three metal ions (Cu2+, Ce3+, and Mn2+) as catalysts or with the Mn/Ce composite oxide catalysts, respectively. In addition, the biodegradability of the effluent derived from the CWAO (2,4-DCP) process was studied. Results show that the effect of addition of the Cu2+ ion on the wet air oxidation (WAO) of Fe(CN)64－ solution is significant because the Cu2+ ion plays in a role of catalyst, which may lower the activation energy (Ea) during the first-stage of the CWAO process. However, either the Ce3+ or Mn2+ ion did an adverse effect on the Fe(CN)64－ removal, even they had a worse removal than that did by the WAO run without any catalyst addition. The Ea value of the first-stage in the WAO of the Fe(CN)64－ solution process was calculated to be 40.5 KJ mol－1. On the other hand, the Ea values of the CWAO process with an addition of the Cu2+, Ce3+, or Mn2+ ion, were reduced to 14.1, 16.0, and 20.4 KJ mol－1, respectively. Obviously, the values of Ea can be reduced to promote the pollutants removal by an addition of suitable catalysts into the WAO process. It was observed that 2,4-DCP is difficult to be decomposed in the thermal pyrolysis process, but the conversion of 2,4-DCP is significant in the WAO process. With an application of the Mn/Ce composite oxide catalyst in the CWAO process to treat the 2,4-DCP solutions resulted in a better removal than that did by the WAO process. The higher the reaction temperature was applied, the higher 2,4-DCP removal was obtained. Also, the catalyst in a higher Mn/Ce molar ratio would increase the removal of 2,4-DCP during the CWAO runs, while the catalyst in a Mn/Ce molar of 7:3 showed the best 2,4-DCP removal of 96.5%. It is suggested that the reaction temperature of the CWAO process could be controlled 40 K lower than that required in the WAO run to reach an equivalent 2,4-DCP removal efficiency. The Ea value of the WAO of 2,4-DCP process performed in a semi-batch type reactor were 13.6 and 23.7 KJ mol－1, respectively, for the first-stage and the second-stage reactions. However, the Ea values of the both reaction stages in the CWAO of 2,4-DCP run were reduced to 9.1 and 5.7 KJ mol－1, respectively. If the CWAO of 2,4-DCP was performed in an up-flowing fixed -bed reactor, a second-order formula was found. Also, the activation energy and the frequency constant of the CWAO of 2,4-DCP run were calculated to be 11.9 KJ mol－1 and 0.96 sec－1. In the Microtox® toxicity tests, the TUa,15 values of the effluent from the CWAO run were below 8.26, when the CWAO process was operated at 433 K and at a space velocity of less than 11.0 hr－1, and the Mn/Ce (7:3) composite oxide as a catalyst. On the other hand, the toxicity of the 2,4-DCP could be reduced greatly by being treated in the CWAO process over the Mn/Ce (7:3) composite oxide catalyst. It is possible to treat the 2,4-DCP solution in a concentration less than 500 mg L－1 to meet the discharging regulation standards using a CWAO run, and followed by an activated sludge unit in which the retention time of the wastewater could be sorter than twelve hours.
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