Study On Discharge And Catalysis During The Process Of Microwave-assisted Wet Air Oxidation

Advanced oxidation technology is a common method to treat refractory organic compounds in water.However,the long hydraulic retention time of conventional advanced oxidation technology makes the process of oxidation unable to concentrate rapid heat release,which affects the recovery and utilization of energy in the oxidation process of organic compounds.Therefore,it is of great practical significance to find a fast and efficient advanced oxidation technology.As a new type of water treatment technology,microwave advanced oxidation technology has natural advantages of high efficiency and rapidity,but it is restricted by the energy dissipation of water in practical application.This paper proposed a new advanced microwave oxidation technology-Microwave-assisted wet oxidation technology(MAWO).This technology combines the advantages of microwave and traditional wet oxidation technology,and high dielectric constant catalysts can efficiently absorb microwave energy to form directional convergence of "High energy sites",which can trigger"Micro-area discharge" and induce the generation of reactive oxygen radicals to achieve efficient in-situ catalytic degradation of organic compounds in the multi-phase environment of high temperature and high pressure.Compared with conventional wet oxidation technology,it can improve the reaction rate,and at the same time,it can reduce the energy dissipation caused by water absorption and evaporation and improve the economy of the process due to the efficient directional absorption of catalysts.In this paper,the discharge and catalytic effect in the process of microwave-assisted wet oxidation are mainly studied,and then the mechanism and influencing factors are analyzed,which aims to find the best treatment process of organic wastewater through experimental research,and provide new ideas for the industrial application of microwave in the field of water treatment.Firstly,the weak discharge effect in microwave-assisted wet oxidation process was studied.Metal materials which have stable discharge process were used as discharge medium,plasma spectral effect and free radical spectral characteristics of discharge in gas and liquid phases were analyzed to explore their mechanism.It can be found that microwave power,pressure,ambient atmosphere,particle size and discharge time can all affect the emission spectra of discharge plasma in gas phase.In addition,the discharge in liquid phase can produce active free radicals such as OH radicals,and the increase of external pressure will increase the gas density in bubbles,resulting in the reduction of free radicals and even the annihilation of the discharge process;the increase of power will make more energetic electrons collide with water molecules,resulting in more active free radicals;and the solution pH and conductivity also have some influence on the peak value of ·OH emission spectrum.Subsequently,the feasibility of microwave-assisted wet air oxidation process was studied.P-nitrophenol was chosen as the simulated pollutant and hydrogen peroxide as the auxiliary oxidant.The results show that this technology has a good catalytic degradation effect on organic pollutants,and high pressure,high power,high concentration of catalysts and oxidants can effectively enhance the degradation efficiency of p-nitrophenol,which is manifested in the following aspects:high pressure can increase boiling point,reduce evaporation energy loss and increase dissolved oxygen concentration;high power can increase hot spot temperature and accelerate the coupling between catalyst and solution;high concentration of catalyst and oxidant can increase the production of hydroxyl radicals per unit time,thus increasing the reaction rate from the oxidant level.Finally,a high-pressure microwave reactor was developed to comprehensively analyze the catalytic degradation effect of microwave-assisted wet oxidation process,and dimethyl phthalate(DMP)was selected as a simulated pollutant.The effects of catalyst types,reaction temperature,microwave power,concentration of catalyst and oxidant were studied.Then,product analysis was carried out and the reaction pathway was deduced as follows:OH oxidized DMP to phthalic acid by attacking the side chains of DMP,then oxidized to small molecular acids,and finally to carbon dioxide and water.The kinetic analysis showed that the increase of reaction temperature can effectively increase the reaction rate constant,while microwave can significantly reduce the activation energy of the reaction system.Energy efficiency analysis showed that the energy consumption of the process is relatively high,and energy consumption can be reduced by setting up heat exchangers and optimizing the process flow.In addition,this technology has also achieved good results in the treatment of actual industrial coal coking wastewater,and the COD content can be reduced from 4161.8 mg/L to 1710.5 mg/L after 5min.Therefore,this technology has a promising application prospect in the field of chemical industry and water resources protection.