Catalytic Wet Peroxide Oxidation Of Phenolic Wastewater Over Microfibrous Zeolite Membrane Catalysts

The expansion of modern industrial engineering has been rapidly promoting the development of social economy and tremendously met the material and cultural requirements of human beings.However,the accompanying pollutants of the industrial development are increasing seriously,e.g.,air pollution,water pollution and waste residue pollution have been drawn highly attention by all walks of life.Among them,phenolic wastewater as a kind of typical pollutant is widely existed in the industrial manufactory processes with high toxic and degradation resistant characteristics.Therefore,the efficient treatment of phenolic wastewater is the key factor for us to realize the sustainable development of human society and thus keep harmony with nature.Technologies used for phenolic wastewater treatment include physical separation,biodegradation and chemical oxidation methods.As a chemical oxidation,catalytic wet peroxide oxidation?CWPO?is highly favored by researchers because it can be used for degradation a wide range of phenolic concentrations under mild reaction conditions with high efficiency by using environment-friendly hydrogen peroxide?H₂O₂?as the oxidant.Most of literatures reporting CWPO of phenolic wastewater were studied in the batch reactor based on the Fenton or Fenton-like paticle catalysts,e.g.,Fe and Cu as the active component.However,the high mass transfer resistant has resulted in the low catalytic activity of traditional particle catalysts.And traditional batch reactor has long retention time which resulted in the production of toxic intermediates,decreasing of the catalyst stability and requirement further separation of catalysts from solution.Therefore,developing a series of catalysts with higher contacting efficiency and higher catalytic activity is a meaningful work.In addition,designing a new set-up used for CWPO of phenolic wastewater based on these catalysts is also a promising project.In this paper,a series of zeolite catalysts were prepared,characterized and used for CWPO of phenol model wastewater in the fixed bed reactor and batch reactor.The kinetics study of CWPO of phenol wastewater in the fixed bed reactor and membrane batch reactor was also studied.Firstly,efficient CWPO of phenol wastewater over Fe-ZSM-5 zeolite catalyst was carried out in a fixed bed reactor.The catalysts were prepared by incipient wetness impregnation method with 9.4wt%Fe active component loaded in the ZSM-5 support.Results showed that Fe-ZSM-5 zeolite catalysts achieved the highest catalytic activity?phenol conversion=99.2%,TOC conversion=77.7%?under the best reaction conditions without Fe leaching detected in the solution.The catalysts showed a high stability with low Fe leaching concentration?about 1.0 mg/L?and kept high phenol conversion?95.0%?after used for three times.Secondly,mono-component Fe-ZSM-5,Cu-ZSM-5 zeolite membrane catalysts and bimetallic FeCu-ZSM-5 zeolite membrane catalyst were developed and systematically characterized by XRD,N₂ adsorption-desorption isotherms,SEM,EDS,H₂-TPR,XPS and FT-IR etc.,and then successfully used for CWPO of phenol wastewater in the fixed bed reactor.CWPO of phenol wastewater showed that the activity of Cu species was higher than Fe species in the fixed bed reactor,resulting in phenol conversions of 100%and 95%,respectively,under the same reaction conditions.On the contrary,the stability of Fe species is higher than Cu species in the reaction,resulting in metallic leaching concentrations of 7 mg/L and 200 mg/L,respectively,under the same reaction conditions.For the bimetallic catalysts,the introducing of Cu species can not only increase the activity of the catalysts but also inhibit the leaching of Fe species thus increase the stability of the catalysts.The Fe-ZSM-5 zeolite membrane catalysts showed very high stability?phenol conversion higher than 95%?after continuously run for 40 hours.The partial deactivation of the Fe-ZSM-5 membrane resulted from the loss and transformation of Fe activity component,structure changes of ZSM-5support,and the blockage of micropores by the coke formation.Thirdly,structured copper-containing MFI type?Cu-MFI?zeolite membrane were developed by a secondary hydrothermal synthesis method and used for CWPO of phenol wastewater in a new-designed batch reactor.The thickness of the Cu-MFI membrane?1-7?m?was adjustable by changing synthesis time and temperature.Both framework and non-framework?CuO?Cu species were confirmed by characterizations.The Cu-MFI zeolite membrane catalysts showed outstanding catalytic activity and stability in the batch reactor,phenol was completely transformed into low-molecular-weight acids with negligible Cu leaching concentration?1mg/L?.A new-designed impeller used for hold the membrane in the batch reactor can be easily separated from the solution which can not only terminate the reaction immediately,but also save the operation time and cost.Finally,reaction kinetics of CWPO of phenol over Fe-ZSM-5 catalysts in the fixed bed reactor was explored by referring the method used for gas-solid catalytic reaction.Power-rate Law kinetic model and Arrhenius equation can be used for the calculation of activation energy.Results indicated that the reaction order of CWPO of phenol wastewater was increased with the temperature and the reaction activation energy was E_a=178.66kJ/mol.Meanwhile,intrinsic reaction kinetics of CWPO of phenol wastewater over Fe-ZSM-5 zeolite particle catalyst and Fe-ZSM-5 zeolite membrane catalyst in the batch reactor were studied.Active energies of the reaction over Fe-ZSM-5 particle catalyst and membrane catalyst were calculated by Power-rate Law kinetic model and Arrhenius equation and the results were E_a=86.69 kJ/mol and E_a=91.74 kJ/mol,respectively.These results confirmed that the CWPO of phenol over membrane catalysts was close to intrinsic reaction and the liquid-solid catalytic reaction was enhanced by the removal of external and inner diffusion of fluid in the solid catalysts.