Electric Swing Adsorption Coupled With Electrothermal Catalytic Oxidation To Remove Indoor Low-concentration Formaldehyde

As one of the main pollutants in indoor air,formaldehyde has the characteristics of long release period,low concentration and a wide range of sources,which poses a serious threat to people’s health.Adsorption and catalytic oxidation are the two most widely studied methods for formaldehyde removal.However,the adsorption method has some problems,such as limited adsorption capacity,high energy consumption,difficult regeneration,large volume of regeneration equipment and so on.However,the catalytic oxidation method has some problems,such as high catalytic cost of precious metals and low catalytic efficiency of transition metal oxides at room temperature.In order to effectively remove and thoroughly degrade indoor low concentration formaldehyde,a method of electric swing adsorption coupled with electrothermal catalytic oxidation process is proposed in this thesis.Firstly,indoor low-concentration formaldehyde was enriched by electric swing adsorption,and then it was completely degraded by electrothermal catalysis,the main results are as follows:(1)In this thesis,by using activated carbon fiber felt(ACF)as the precursor of conductive adsorbent,nitrogen-doped activated carbon fiber felts(ACF-U,ACF-D and ACF-M)were prepared by physical impregnation and high temperature pyrolysis approach with urea,dicyandiamine,and melamine used as nitrogen sources.The low-concentration formaldehyde electric swing adsorption performance of ACF,ACF-U,ACF-D and ACF-M was investigated.The results show that ACF with a developed pore structure exhibits excellent electrothermal performance.Nitrogen-doping can not only improve the thermal stability of the ACF,but also affect the pore structure and surface chemistry of the ACF strongly.ACF-M and ACF-D have a slightly higher BET specific surface area than the original ACF,but the pore volume of 0.8-1.1 nm which benefit to formaldehyde adsorption is increased significantly.Moreover,most of the nitrogen species on the surface of ACF after nitrogen doping are pyridinic nitrogen and pyrrolic nitrogen,which are beneficial to the chemical adsorption of formaldehyde.Compared with the original ACF,the nitrogen-doped samples showed better formaldehyde adsorption performance in the low-concentration formaldehyde(2 ppm,500 m L/min)dynamic adsorption test.Among nitrogen-doped ACFs,ACF-M displayed the highest formaldehyde adsorption capacity of 4.75 mg/g,and the penetration time reaches up to 20 h.ACF-M can be regenerated conveniently through direct electric heating.ACF-M exhibits good cyclicity also with the retention rate of formaldehyde adsorption capacity of 88.11% after 6 cycles.(2)Using beech charcoal rod as carrier and reducing agent and KMnO4 as oxidant,birnessite type Mn O2 was supported on the inner-wall of beech charcoal vessel by in-situ redox reaction thus resulted carbon-based supported Mn O2 monolithic catalyst.The results showed that the flower-like Mn O2 assembled from nano-sheets grew on the surface of open cellular carbon wall.The load of Mn O2 increased with the increase of KMnO4 concentration.The loading amount of Mn O2 has a great influence on the performance of electrocatalytic oxidation of formaldehyde: when the concentration of formaldehyde is 50 ppm,the flow rate is 60 ml,and the bias voltage is 3 V,the catalytic efficiency of Mn O2/CB-1,Mn O2/CB-5 and Mn O2/CB-10 with a length of 4.5 cm is 65%,90% and 99.2%,respectively.Mn O2/CB-10 also shows excellent stability,which can be coupled with the first part of the substation adsorption device to achieve efficient removal and degradation of indoor low concentration formaldehyde(2 ppm,500 m L/min).