Study On Removal Of Gas-phase Benzene By Ozone Oxidation Cooperated With Mn²⁺

The benzene waste gas,a carcinogenic substance,greatly hurts people in the production and living,which is representative of benzene series matter and an important component of volatile organic pollutants.At present,national and local governments have introduced the VOCs emission charges and VOCs emission industry standards have been promulgated,the efficient governance of VOCs is imminent.In this thesis the research of the cooperative ozone oxidation of benzene with metal ions was carried out.Based on the previous experimental study and reference to the relevant literature,and the test of economic and operational considerations,Mn²⁺ was selected as the liquid phase components.Mn²⁺ combined with ozone oxidation of benzene was carried out in the self-made bubbling reactor,the results are as following:In various metal ions Mn²⁺ was be selected as active material promoting the ozone oxidation;Ozone oxidation alone removing benzene experiment was carried out,benzene removal efficiency increased with the increase of ozone concentration before they are slowing,as high as 50% or so.It shows that under the condition of normal temperature ozone decomposition is slow and the oxidation efficiency for organic gases is not high.The efficiency of Mn²⁺ alone removing benzene can be up to 56%,but as time go away,Mn²⁺ is consumed and benzene is reduced;In the experiment of Mn²⁺ combined ozone oxidation removal of gas phase benzene,the efficiency of benzene removal increased significantly,and the maximum of benzene removal efficiency reached 99.69%.The influence of single factor experiment was carried out to study the effect that benzene concentration,ozone concentration,pH,inlet flow rate,the concentration of Mn²⁺ produce on the efficiency of collaborative ozone oxidation of benzene with Mn²⁺.The results showed that in the reaction system including the concentration of benzene choose 100-200 mg/m3,reaction time is 9s,ozone concentration is 8.5mg/L,ion concentration is 1 mmol/L,pH is 3,the best benzene removal efficiency is 99.69%.P-B experiments was carried out to test the effect of various factors on the benzene removal efficiency.Take the corresponding factor level value,12 groups of tests designed by Design Expert software were carried out.According to the result of the experiment,effects of various factors and the importance was evaluated with benzene removal efficiency as an index.The results showed that the relative significant influence of five factors order is ozone concentration > ion concentration > pH > reaction time > benzene concentration,and the three factors including ozone concentration,ion concentration and pH was preliminarily selected as the factors influencing benzene removal efficiency significantly.Response surface experiments were carried out to make ANOVA statistical analysis on the experimental data by the BBD experimental design in the Design Expert software,and then build the model and arrived at the factors fitting regression equation Y=+97.00+1.25*A-2.84*B-3.88*C+1.56*A*B+3.60*A*C-4.34*B*C-1.91*A2-4.67*B2-4.32*C2.Test of significance results show that the variance of the regression equation of the two order model Pr>F <0.05 showed that the model is remarkable,and Pr <0.01 go for more significant.The lack of fit is not significant,which showed response surface method fitting effect is good;Error statistical analysis showed that the test has high reliability,precision and accuracy.Optimization models are consistent with the experimental results: the ozone concentration is 8.45mg/L,the concentration of Mn²⁺ was 1mmol/L,the initial pH value of 3,test get the highest 98.84% benzene removal efficiency.There are 0.85% difference with the single factor test which has the optimum benzene removal efficiency of 99.69%,1.49% higher than the best target prediction value of 97.35%.At the same time,comparing the result of repeated experiment which is 96.87% with the predicted values,the relative error was 0.48%.Under the best condition,tert-butyl alcohol was added and the benzene removal efficiency decreased by 20% 30%,which indicated that ·OH had a certain effect on benzene removal.In order to understand the mechanism of Mn²⁺ to promote the removal of benzene by ozone oxidation,the experimental mechanism was studied.The results showed that Mn²⁺ combined with ozone oxidation removal of benzene can be summarized in three aspects: first,the direct oxidation of ozone;Second,the oxidation of ·OH by ozone decomposition;Third,Mn²⁺ is converted into a high price of manganese to remove benzene,and it is thought that the interaction between the three aspects also promotes the removal of benzene;Kinetic studies show that the process of Mn²⁺ combined with ozone oxidation to remove benzene conforms to the first order reaction kinetics,the kinetic equation is-dC '/dt=[?Ko₃+ KOH*R?* Co₃+ KMn²⁺* CMn²⁺]* C' =K*C'.