Study On The Efficiency And Mechanism Of Micro-nano Bubbles Catalytic Oxidation For VOCs Degradation

At present,volatile organic compounds(VOCs)have become one of the most concerned atmospheric pollutants.Also,the integrated technology of micro-nano bubbles and ozone has presented great potential for VOCs purification.Because of their unique physical,chemical and biological characteristics,micro-nano bubbles have exceeded people’s understanding of traditional bubbles.At the same time,micro-nano bubbles have the advantages of simple generating equipment,mild reaction conditions,no secondary pollution and wide application,and they have been widely used in several directions of environmental engineering.However,many properties such as basic physical properties,overall size effect,interface effect,biological effect and other potential characteristics of micro-nano bubbles needed to be further understood.In this paper,the physical properties of micro-nano bubbles,the VOCs degradation efficiency of the integrated technology of micro-nano bubbles and ozone of,as well as the efficiency and mechanism of catalysts for ozone micro-nano bubbles catalytic oxidation degradation of VOCs were systematically studied.The main contents and conclusions are as follows:(1)Study on the physical properties of micro-nano bubbles.The micro-nano bubbles are firstly prepared by gas dispersion shearing mode and high pressure dissolved gas releasing mode,and then the performance and influencing factors were contrastively investigated.It is found that the dissolved oxygen content of micro-nano bubbles water prepared by gas dispersion shearing mode is higher,but the bubbles concentration is lower than that bubbles concentration prepared by high pressure dissolved gas releasing mode.The higher the preparation temperature,the lower the dissolved oxygen content,but it has little effect on the bubbles concentration.This indicates that there is no direct correlation between the dissolved oxygen content and the concentration of nano bubbles.Also,the bubbles concentration increases with the shear times.For the storage performance evaluation,batch samples are tested.The results show that the lower the storage temperature,the higher the dissolved oxygen content,and the smaller the empty volume reserved for packaging,the higher the dissolved oxygen content.The dissolved oxygen content decreases rapidly at the early stage of storage,and then changes little with the extension of storage time.The Nanoparticle tracking analysis(NTA)shows that the nano bubbles concentration is basically maintained at the same level or even increased,and the particle size distribution is maintained in the range of 50 to 500 nm,mainly in the range of 100 to200 nm.(2)The evaluation of VOCs oxidation degradation efficiency by micro-nano bubbles combined with ozone.For the low water-soluble VOCs,the oxidative degradation plays an important role,and the absorption of water is less.For the high water-soluble VOCs,the absorption of water plays an important role,and the oxidative degradation is less.Toluene is chosen as the target VOC.It is found that the higher the ozone concentration is,the higher the degradation rate of toluene is.The volume loading almost shows a linear relationship with the increase of ozone concentration.The toluene degradation loading is higher in the method of high pressure dissolved gas releasing mode.The toluene degradation loading is higher at low temperature.The volume load is almost less affected by p H value.The volume load is used as the evaluation method of oxidation reaction.It is found that there is a critical gas intake or critical residence time.When the gas intake is less than the critical gas intake or the reaction time is longer than the critical residence time,the volume load almost does not change.Compared with the traditional aeration method,the volume load of the integrated technology increases from 0.27 mg/(L·min)to 0.42 mg/(L·min).For the industrial ozone concentration,it is verified that the volume load almost increases proportionally with ozone concentration increase.These can provide theoretical guidance and calculation basis for the practical engineering applications..(3)The evaluation of VOCs catalytic oxidation degradation efficiency by micro-nano bubbles combined with ozone.The VOCs catalytic oxidation degradation efficiency of 3kinds of homogeneous catalyst and 1 kind of heterogeneous catalyst have been evaluated by the integrated technology.The results show that the addition of catalysts could increase the volume load of toluene.Mn(Ⅱ)catalyst presented the highest volume load of toluene.The utilization of ozone is not less than 95% in the in the catalytic systems.The oxidation mineralization rate of toluene in the homogeneous catalytic system is higher than that in the heterogeneous catalytic system.TOC all accumulated gradually in the water for the four catalytic systems.The TOC amount in the Mn(Ⅱ)catalytic system is the maximum,and the TOC amount in the Cu(Ⅱ)catalytic system is the minimum.(4)The degradation products and degradation mechanism of catalytic systems.It can be seen from GC-MS results,the types of degradation products in liquid phase and gas phase of the four catalytic systems are similar with different contents.Further analysis of Mn(Ⅱ)shows that the main degradation products of end gas are Benzaldehyde,phenol,Cresol,and a small number of degradation products are benzoic acid,epoxybutyl,foreic acid,ethyl benzene and so on.The main degradation products of water are alkanes,alkenes,carboxylic acids,esters,ketones,aldehydes,alcohol,etc.between C2 and C30.These have been indicated that the complicated chain breaking,addition and ring opening reactions occurred in the water due to recycling.Finally,according to the analysis of the degradation products,the reaction route has been reasonably speculated.