Preparation And Characterization Of Iron-containing Microfibrous Zeolite Membrane Catalyst For Catalytic Wet Peroxide Oxidation Of Phenolic Wastewater

With the development of industry,water pollution became more and more serious.The increasing concentration and type of organic pollutants in wastewater treatment have posed severe threat on human's subsistence.The harm of phenolic wastewater has been a strong concern.Currently,there are kinds of techniques for the treatment of phenolic wastewater,such as physical,chemical and biological.Catalytic wet peroxide oxidation(CWPO)has attracted more and more attention due to the strong oxidizing ability,mild reaction condition,simple operation and low cost.Heterogeneous catalysts can overcome the problems such as secondary pollution and metal contamination that traditional Fenton reagent may cause.Therefore,how to prepare a stable and effective catalyst has good performances in CWPO of phenol have been recognized as a meaningful research topic.In this paper,the fabrication and characterization of Fe2O3/MCM-41 zeolite and microfibrous composite zeolite membrane Fe-ZSM-5/PSSF were investigated.Catalytic wet peroxide oxidation of phenol over Fe2O3/MCM-41 zeolite and FeZSM-5/PSSF zeolite membrane in the fixed bed reactor were systematically studied.Firstly,Fe2O3/MCM-41 catalysts were tested for catalystic wet peroxide oxidation of phenol wastewater in a fixed bed reactor.Fe2O3/MCM-41 zeolites were prepared by incipient wetness impregnation and characterized by using X-ray diffraction(XRD),N2 adsorptiondesorption and X-ray photoelectron spectra(XPS),respectively.Secondly,the effect of temperature of reaction,catalyst bed height and feed flow rate on phenol mineralization,hydrogen peroxide and total organic carbon(TOC)conversions were studied to determine the optimum condition.Moreover,Fe leaching concentration was detected and the catalyst was used four times for the CWPO of phenolic solution to study the stability of the Fe2O3/MCM-41 catalyst.Finally,the evolution of intermediates was monitored to investigate the probable reaction mechanism of phenol oxidation over Fe2O3/MCM-41 catalyst in the fixed bed reactor.The experimental results showed that extra-framework Fe presented in the form of Fe2O3 in Fe2O3/MCM-41 zeolite.Conversion of phenol increased with the increasing temperature,increasing bed height and decreasing feed flow rate.Similar trend can also be observed for the removal of H2O2 and TOC.The conversion of phenol reached 100% and removal of H2O2 and TOC reached 91% and 72.5%,respectively.Few Fe(0.01 mg/L)was detected under optimum condition(namely,feed flow rate of 2.0 m L/min,temperature of 80 °C,catalyst bed height of 4 cm).The catalyst was used four times for the CWPO of phenolic solution and almost complete phenol removal(>98%)was achieved after used four times in 28 h.H2O2 conversion was slightly decreased from 92.5% to 84.7%.TOC conversion decreased from 72.5% to 59.9%.The iron leaching concentration was under 1 mg/L after used four times in 28 h.The probable multistep reaction route in CWPO of phenol by Fe2O3/MCM-41 catalyst in a fixed bed reactor is based on hydroxyl radical reacting with phenol and then converting it to p-benzoquinone,catechol and hydroquinone etc.These aromatic intermediates imply a reactive pathway where byproducts may result from phenol hydroxylation and then oxidate to low-molecular weight acids such as acetic acid,maleic and oxalic acid.Ultimately,these carboxylic acids are decomposed to carbon dioxide and water.Meanwhile,microfibrous composite zeolite membrane Fe-ZMS-5/PSSF was tested for catalystic wet peroxide oxidation of phenol wastewater in a fixed bed reactor.Fe-ZMS-5/PSSF was synthesized by using hydrothermal method and characterized by XRD,N2 adsorptiondesorption,XPS,SEM,FT-IR and TPR,respectively.The effect of ratio of Si to Fe,temperature of reaction,catalyst bed height and feed flow rate on phenol mineralization,hydrogen peroxide and TOC conversions were investigated.Fe leaching concentration was explored and the catalyst was used three times for the CWPO of phenolic solution to study the stability of the Fe-ZMS-5/PSSF.At the same time,compared with the catalytic effect of Fe2O3/ZSM-5/PSSF.The experimental results showed that the Fe was existed in the form of framework.The conversion of phenol reached 100%,removal of H2O2 and TOC reached 98.5% and 54.5% and Fe leaching concentration was about 0.5 mg/L at the optimum condition(namely,Si/Fe = 120,feed flow rate of 2.0 m L/min,temperature of 80 °C,catalyst bed height of 4 cm).At the reaction temperature of 80°C,catalyst bed height of 2 cm,feed flow rate of 2.0 mL/min,Fe2O3/ZSM-5/PSSF(incipient wetness impregnation)and Fe-ZSM-5/PSSF(hydrothermal method)had similar performance in CWPO of phenolic wastewater,while Fe-ZSM-5/PSSF exhibited higher H2O2 and TOC conversions.After 21 h successive runs,phenol conversion still preserved 98%,H2O2 conversion decreased from 98.5% to 96.3%,TOC conversion decreased from 53.8% to 50.4% and Fe leaching concentration still preserved low level(under 0.5 mg/L).