Study On Preparation Of Flexible Porous Carbon Cloth And Its Gas Adsorption And Separation Performance

Methane,the main component of coalbed methane（CBM）,is an efficient and clean energy source,which is also the source of coal mine gas disasters.Methane is also one of the main greenhouse gases that cause climate warming.The effective separation of methane in CBM can not only optimize energy structure of our country and reduce coal mine safety accidents,but also contribute to the realization of the“dual carbon”goal.In this study,the flexible porous carbon cloth was prepared by physical activation and chemical activation by using common viscose fiber fabric as precursor.The surface chemical properties and porosity structure of the porous carbon cloth were adjusted by controlling the activation conditions,and the optimized activation process was explored to prepare the flexible porous carbon material with excellent performance.The main research contents are as follows:（1）Flexible porous carbon cloth was prepared by a simple one-step carbonization and activation process using viscose fiber fabric as carbon source,and CO₂as active agent under a controlled temperature range of 700-900℃.It shows that CO₂physical activation is an effective way to prepare flexible porous carbon cloth.The as-obtained porous carbon cloth not only retains a part of its own nitrogen atoms,but also produces a large number of micropores,forming a graphite-like microcrystalline structure.The optimum conditions for CO₂activation are 800℃、1 h.The P-FCC-800 possesses the highest ultra-micropore volume of 0.29 cm³/g and nitrogen content of 5.88 wt%,as well as the highest CO₂adsorption capacity of 3.13 mmol/g.According to the ideal adsorption solution theory（IAST）,the selectivity of P-FCC-800 for binary mixture gas CO₂/CH₄（30/70、40/60、50/50）were calculated to be 3.29,2.74,2.35,respectively,which should attribute to the synergistic effect between excellent ultra-microporosity structure and desirable nitrogen content.（2）The K-FCC-x-y series flexible porous carbon cloth was prepared by using viscose fiber fabric as carbon source,KOH as activating agent,through adjusting the KOH concentration and activation temperature.KOH activation method is an efficient way to prepare flexible porous carbon cloth.The carbon cloths after KOH activation still have mechanical flexibility.The optimal conditions for activating viscose fiber fabrics are:KOH soaking concentration of 240 g/l,activation at 700℃for 1 h.The as-obtained porous carbon cloth has the best adsorption and separation ability,and is more economical.It can be seen that the separation selectivity is not the result of single factor,but the synergistic effect between micropore volume,ultra-micropore volume and nitrogen content.Although K-FCC-240-700 is not the best performing in pore structure and nitrogen content,selectivity for CO₂/CH₄binary mixed gas with different mixing proportions of 30/70,40/60,50/50,was calculated to be 3.73,3.13,2.67,respectively.It is the most selective among all carbon cloths in the same series The CO₂adsorption capacity（3.877 mmol/g）of K-FCC-240-700 is much higher than N₂（0.468mmol/g）.According to Henry’s Law and the ideal adsorption solution theory（IAST）,the selectivity of K-FCC-240-700 for binary mixture gas CO₂/N₂was 21.2 and 19.1,respectively,at 1 bar and 25°C.（3）In this study,two common activating agents CO₂and KOH were selected to prepare porous carbon cloth,and the effects of the two activators on the chemical composition,porosity structure and gas adsorption and separation of carbon cloth were comprehensively compared.By comparing the excellent samples,it can find that the porous carbon cloth prepared by KOH activation has better porosity structure than that prepared by physical activation of CO₂.Compared with P-FCC-800,K-FCC-240-700has 45.6%and 24.5%increase in micropore volume and ultra-micropore volume,respectively.The KOH activation has a great influence on the nitrogen content of carbon cloth,the nitrogen content of K-FCC-240-700 decreases by 25.7%compared with P-FCC-800.However,the CO₂adsorption capacity of K-FCC-240-700 increases by 24%,indicating that the CO₂adsorption capacity of porous carbon cloth is greatly affected by the pore structure,under ambient conditions.According to Henry’s Law,the CO₂/CH₄selectivity is calculated at initial pressure,which for K-FCC-240-700increases by 53.2%than that for P-FCC-800.According to IAST calculation,the selectivity of CO₂/CH₄binary mixture gas at 1 bar,improved by 13.4%、14.2%and13.6%at 30/70、40/60 and 50/50 proportion ratios,respectively.The larger specific surface area and total pore volume of K-FCC-240-700 improves the methanol adsorption performance by 18.4%.