Study On The Application Of Copper-based Catalyst In Catalytic Wet Air Oxidation To Degrade Coking Wastewater

It is difficult to treat coking wastewater with high phenol value,high COD and high ammonia nitrogen.However,traditional technology cannot achieve its degradation.Catalytic wet air oxidation has the advantages of fast oxidation efficiency,wide scope of application range and no solid waste,and has become the current research hotspot.The key to the effective realization of CWAO is developing the catalyst with good performance.However,there are many problems in CWAO catalyst,foe example,increased cost due to the use of noble metal catalyst.Because of carbon deposition and loss of active components,the catalyst life is shortened.In this paper,CuMgLa/Al2O3 composite oxide catalyst with high catalytic activity,good stability and low cost was developed by coprecipitation method,which was used in coking wastewater.The specific research contents are as follows:Firstly,phenol was used as model compound.After screening the active components and the supports,the selected CuO/Al2O3 is used for phenol degradation.The results showed that CuO/Al2O3 can remove more than 99%of phenol within 60 minutes,showing the good catalytic activity.But after reaction,the loss of the active group was as high as 85.4 mg/L,and carbon deposition occurred on the catalyst surface.In this paper,in order to improve the catalytic activity and reduce the loss of active group and carbon deposition,different alkali metals,alkaline earth metals and rare earth metals are selected by doping.It was found that the phenol removal rate was close to 100%and the loss of copper ion was reduced to 25.1 mg/L within 40 minutes by doping La and Mg.It showed that the doping of La and Mg can improve the activity of the catalyst and avoid the loss of important active component Cu effectively.The catalysts were further analyzed by XRD,BET,XPS,TEM,NH3-TPD and TG.The results showed that the catalyst has a specific surface area of 240.75 m2/g,a pore volume of 0.4789 cm3/g,and a good crystal structure.The co-doping of La and Mg results in the increase of the dispersion of Cu on the surface of the catalyst,which improved the catalytic activity of the catalyst,and the doping of La improved the stability of the catalyst greatly and reduced the loss of 30.2%copper ion and 10%carbon deposition of the catalyst.Then,the catalyst CuMgLa/Al2O3 was used to study the degradation of phenol wastewater.It was found that when the initial concentration of phenol was 2000 mg/L,the catalyst concentration was 0.2 g/L,the reaction temperature was 180?,the partial pressure of oxygen was 1.2 MPa,and the stirring speed was 500 rpm,the phenol conversion rate was 100%and the COD removal rate was close to 90%within 40 minutes.When the initial concentration of quinoline and the concentration of catalyst are 1000 mg/L and 0.2 g/L respectively,the COD removal rate of quinoline wastewater is up to 90.7%after 60 min reaction at 240?.In addition,the intermediate products of phenol degradation were determined by liquid chromatography-mass spectrometry.The degradation mechanism of phenol was as follows:under the action of hydroxyl group and the action of hydroxyl group,the ortho and para positions of phenol were electrophilically substituted to form O/p-hydroquinone,and then with oxygen quinones are formed by gas reaction.Then,the hydroxyl group continued to attack the conjugated structure of benzene ring,making it break to form small carboxylic acids such as maleic acid and propionic acid,and finally oxidized to H2O and CO2.By studying the reaction kinetics of phenol degradation by CWAO,the second-order kinetic model of the degradation process was obtained.The intermediate products of quinoline degradation including 8-hydroxyquinoline,5,8-hydroxy quinoline,2,3-pyridinedicarbaldehyde,and nicotinic acid were determined by LC-MS,and the possible degradation mechanism was inferred.With the ratio of phenol to quinoline in coking wastewater as 4:1,the simulated mixed wastewater was prepared and CWAO degradation experiment was studied.The results showed that the COD removal rate of the mixed wastewater can reach 93.3%under the best condition of quinoline.Finally,the coking wastewater produced in the production process of a coking plant in Taiyuan is selected as the treatment object.In 180 min,about 80%of COD and 40%of NH3-N can be removed.