Study On Decomposition Of Gaseous Mixed VOCs By Silent Discharge With Bipolar Pulse

Volatile organic compounds(VOCs) is another air pollutant besides SO₂,NO_x and atmospheric particles.Most VOCs are toxic,a lot of which are chemical carcinogens.So the pollution control of VOCs is receiving more and more attention.Recently,non-thermal plasma technology is regarded as a more promising new technology in VOCs control all over the world.In normal temperature and pressure,different kinds of VOCs at various concentrations can be decomposed by this technology in a short time.In plasma chemistry reaction,plasma is the significant way to reduce the energy cost and improve the decomposition rate.In this study,the improvement of decomposing VOCs in air is investigated by silent discharge of plasma technologies.On the elementary theory of non-thermal plasma,a set of equipment for experiment has been set up.In this equipment,the experiment was carried out to study the effect of the decomposition of benzene and m-xylene.First,we study the influences of different power supplies on silent discharge characteristics,and analysis that both industrial frequency AC power and bipolar pulse high voltage power has effect on energy input and VOCs decomposition.Then we further discuss pulse repetition frequency and pulse electric capacitors.On this basis,using bipolar pulse high voltage power,we study the influence of experimental parameters to the VOCs decomposition,such as gas flow rate, gas concentration,size of the reactor,discharge gap and discharge length.Meanwhile, synergistic effect of transition metal catalysts under silent discharge is simply investigated to the VOCs decomposition.The results are summarized:(1) It is proved that the silent discharge system is an effective way to decompose mixed gaseous VOCs.VOCs decomposition depends on bond energy of organic molecules and energy of active species.It appears that benzene is decomposed less easily than m-xylene. Different molecules interact when mixed gases are decomposed.Compared with single-composition gas,benzene in mixed gases is affected by m-xylene,maximum decomposition rate of which decreases from 85.4%to 75.2%of single component.However, benzene has little effect on m-xylene,decomposition characteristics of which remains basically unchanged.(2) Bipolar pulse high voltage power is more helpful to energy input than industrial frequency AC power.The increased discharge gap is beneficial to increase peak voltage and energy density.When high voltage electrode is identical,the larger power density is,the better VOCs decomposition effect is.Longer discharge length can prolong reaction time result to higher decompositon rate.Meanwhile,the control of gas concentration can achieve a balance between the decomposition rate and energy efficiency.Reasonable pulse electric capacitor can input more effective energy to the reactor.In the experimental system,2 nF of pulse electric capacitor is ideal matching with reactor.(3) Both VOCs decompositon and energy efficiency improves high when transition metal catalysts make synergistic effect under silent discharge.7%Mn/γ-Al₂O₃ is the best catalyst in our study.Meanwhile,catalysts have better catalytic effect in the outlet of the reactor than the inlet.