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Preparation And Characterization Of Fe-ZSM-5for The Wet Catalytic Oxidation Of Phenolic Wastewater

Posted on:2014-08-24Degree:MasterType:Thesis
Country:ChinaCandidate:T FuFull Text:PDF
GTID:2251330401958849Subject:Chemical Engineering
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With the development of society and economy, environmental problems have becomeincreasingly conspicious. Water pollution is a global, serious environmental problem.Phenolic wasterwater has received widely attention because of multiple sources and severehazard. Sorts of phenolic wastewater treatment methods have been developed, of whichcatalytic wet peroxide oxidation has become increasingly popular due to the mild reactioncondition, simple equipment and low energy consumption. However, the traditional catalyticwet peroxide oxidation method, represented by Fenton reagent method, has been eliminatedbecause of large H2O2consumption and secondary pollution. Thus, developing an effectiveand stable catalyst, which has good performances in degradating phenols to CO2and H2O2,without secondary pollution, is a meaningful research project. In this paper, the researchprogress on the phenolic wastewater treathment was reviewed. The preparation,characterization,catalytic performance of Fe-ZSM-5zeolite as well as intrinsic reactionkinetics of phenol over Fe-ZSM-5zeolite were systematically studied; The preparation,characterization,catalytic performance of Fe2O3/ZSM-5were studied; The preparation ofFe-ZSM-5membrane was also explored.Firstly, Fe-ZSM-5zeolite was synthesized by using hydrothermal method. Theproperties of Fe-ZSM-5zeolite were characterized via SEM, XRD, FT-IR, H2-TPR andUV-vis. The effects of reaction temperature, catalyst dosage, initial solution pH value, stirringrate and reaction time on the conversion of phenol were investigated. The variation of TOCconversion, selectivity to CO2as well as concentration of aromatic intermediate products withreaction time was explored. The reaction stability of the catalyst was also discussed. Besides,intrinsic reaction kinetics of catalytic wet peroxide oxidation over the prepared Fe-ZSM-5zeolite was analyzed at last. The experimental results showed that most of the Fe was existedin the form of framework, and a certain amount of octahedral Fe3+clusters as well as littleFe2O3was existed in the form of extra-framework in the Fe-ZSM-5zeolite. The conversion of phenol increased with the increasing reaction temperature, catalyst dosage, stirring rate andreaction time, and then all of them were were leveled off with the extension of reacton time.The conversion of phenol increased at the beginning with the increasing initial solution pHvalue, and reached the maximum when the pH value came to4, then decreased. The phenolconversion reached94%at the reaction temperature of70℃, catalyst dosage of2.5g/L, initialsolution pH value of4, strring rate of400rpm, and reaction time of180min. The TOCconversion decreased while the selectivity to CO2increased at the begining, and then both ofthem were leveled off with the extension of reacton time. The concentration of the aromaticintermediate products were firstly increased and then decreased, and finally completelyeliminated over time. The selectivity to CO2came to93.5%and the leached Fe accounted for7.5%of total Fe in Fe-ZSM-5after240min. The reaction was first order catalytic reaction,and the reaction activated energy Ea=27.509kJ/mol under the experimental conditions.Secondly, the Fe2O3/ZSM-5zeolite was synthesized by using ion exchange method andcharacterized by SEM, XRD. The variation of TOC conversion, selectivity to CO2as well asconcentration of aromatic intermediate products with reaction time was explored. Thereaction stability of the catalyst was also discussed at last. The results showed that onlyextra-framework Fe presented in the form of Fe2O3in Fe2O3/ZSM-5zeolite. Fe-ZSM-5andFe2O3/ZSM-5zeolites had the similar performance in catalytic wet peroxide oxidation ofphenolic wastewater. The phenol conversion over Fe2O3/ZSM-5zeolite was higher than thatover Fe-ZSM-5zeolite, while the Fe-ZSM-5zeolite exhibited higer selectivity to CO2. Thecomparision research between Fe-ZSM-5and Fe2O3/ZSM-5zeolites showed that bothframework and extra-framework Fe could catalyze the oxidation reaction of phenol. However,the extra-framework Fe was more active, while the framework Fe could catalyze to oxidizephenol more completely to CO2,and it was more stable than extra-framework Fe.Lastly, the Fe-ZSM-5menbrane covered on Sintered Mental Fibers (SMF) wassynthesized by secondary growth with TEOS as silicon source and TPAOH as structuredirecting agent. The effects of the pretreatment temperature of support, the concentration of seed liquid, the crystallization temperature on the properties of Fe-ZSM-5membrane wereinvestigated. The experimental results showed that higher pretreatment temperature had morefavorable effect on the loading of crystals, however, the extravavagant pretreatmenttemperature would cause crack of fibers; It was beneficial to form the dense membrane withthe increasing concentration of seed liquid, but when the concentration exceeded2wt%, thefiber pores were blocked; The increasing crystallization temperature could improve thecrystallinity and uniformity of the crystals, however, the extravagant crystallizationtemperature would cause dissolution-recrystallization reaction. It was feasible to preparecontinuous and dense Fe-ZSM-5membrane on the surface of SMF when the pretreatmenttemperature of support was650℃,the concentration of seed liquid was between1wt%2wt%, and crystallization temperature was170℃.
Keywords/Search Tags:Catalytic wet peroxide oxidation, Phenol, Zeolite, Batch stirred tank, Intrinsicreaction kinetics
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