Research On The Degrdation Characteristics And Mechanism Of Pentachlorophenol In Solutions By Ultrasonic-Air System

The sonolysis of pentachlorophenol(PCP) in aqueous solutions in ultrasonic(US)-Air system were investigated. HPLC was applied to the quantitative analysis of PCP.The influence of air stripping on PCP was studied and the initial potential of hydrogen(pH), temperature, reactant concentration,air flow,as well as reaction time,besides,it focused on the impact of pH. The impacts of adding different materials,like mental ions: Fe2+, Cu2+, Al3+, Zn2+, Mg2+, metal oxide: Fe3O4, CuO,MnO2, TiO2, oxidizing agent: H2O2, K2S2O8, KIO3, NaClO, KMnO4, carbon tetrachloride(CCl4), and sodium salts:NaCl, Na2CO3, NaHCO3, on US-Air system were discussed. Emphasis was given to the degradation mechanism of US-Air system to PCP, qualitative analysis of intermediates using IC、FTIR and GC-MS, and the results a degradation route of PCP in US-Air system.The results showed that: temperature, air flow, weak acid and alkaline solutions had small effects on air-blowing off. PH value was decreased with the sonolysis. The optimal removal efficiency was obtained when the pH was 5 while the air flow was 25ml/min, a lower temperature or concentration of PCP was conducive to the degradation of PCP.Enhancement research for US-Air system showed that, a degradation enhancement occurred when metal ions were added respectively to the US-air system except Mg2+. The acceerative intensity was Fe2+>Cu2+>Al3+>Zn2+>CK>Mg2+in sequence. It showed a strongest acceleration when the concentration of Fe2+ was50μM. Metal oxide was unsuitable for intensifying US-Air system.The acceerative intensity by oxidizing agent were in order of H2O2>K2S2O8>KIO3>NaClO. Cause a slightly promoting to US-Air system in addition of NaClO, both positive and negative influence on the degradation of PCP were found by adding KIO3,neither were suitable for intensifying US-Air system. Although KMnO4 had a efficient degradation effect on PCP,no acceleration was found by adding KMnO4,KMnO4 is not recommended. CCl4 was a good prodegradant for US-Air system, since a high removal rate of 95.48% was obtained when 1mM CCl4 was added. NaCl had no effect on US-Air system, Na2CO3 and NaHCO3 showed an inhibiting effect in acid condition,while they act as promote role in strong alkaline solutions,Na2CO3 was better than NaHCO3. The degradation of PCP in US-Air and its intensifying systemswas accorded with pseudo-first-order reaction kinetics, the reaction rate of constants in each intensifying systems was CCl4 >Fe2+>H2O2> K2S2O8 in sequence.Chose Fe2+ for further study, it indicated that adding air was evidently promoted the generation of hydrogen peroxide,because of the reaction between Fe2+ and hydrogen peroxide,a sharp decrease of hydrogen peroxide was found when adding Fe2+. The degradation of PCP in US-Air system was mainly based on free radical oxidation, and hydrogen peroxide oxidation played a subsidiary role. Chlorine was in form of Cl- or chloride after the degradation of PCP. Through analysis of IC、FTIR、GC-MS,it suggest that there might be two possible degradation pathway of PCP in US-Air system:(1)tetrachlorohydroquinone�'chloranil�'ring-opening�'carboxylic acids with low molecular et al �' CO2 and water;( 2) PCP �' tetrachlorophenol �'dechlorination one by one �' single chlorophenol, phenol, chlorbenzene and methylbenzene et al�'benzoquinone or quinones material�'ring-opening�'carboxylic acids with low molecular or carboxylic ester�'CO2 and water.