Preparation Of High Efficient Coconut Activated Carbon And Adsorption Separation Performance Of CH₄ And N₂

The enrichment and utilization of coal mine methane is a vital subject,which can recycle resources,reduce greenhouse gas emissions and ensure the safety of mine.It plays an important role in the national economy and security of person.The existing adsorbents have the low CH₄ adsorbed capacity and the low CH₄/N₂ selectivity.Therefore,our research work will focus on as follows:Granular activated carbon?GAC?with the high specific surface area is prepared through carbonization of raw coconut shell and KOH activation under optimum conditions,and then the selectivity of CH₄/N₂ is improved with CO2 activation.The CH₄ adsorption capacity on GAC reaches 1.46 mol/kg?T = 303 K,P = 100 kPa?,the equilibrium separation factor is 3.24?T = 303 K,P = 100 kPa?,the competitive adsorption selectivity reaches 4.32?T = 303 K,PCH₄=PN₂=25 kPa?.GAC has not only a high CH₄ adsorption capacity,but also maintains a perfect CH₄/N₂ selectivity.It has a better separation performance of CH₄/N₂ than that of the other commercial activated carbon.The adsorption equilibrium isotherms of CH₄ and N₂ on GAC are measured at 273?363 K up to 1000 kPa using a magnetic suspension balance.Experimental data are fit with Langmuir model,Sips model,Toth model and Multisite Langmuir?MSL?model,and the model parameters,including isosteric heat are obtained.The diluted breakthrough curve experiment are done,and the diffusivities of CH₄ and N₂ on GAC are estimated using the isothermal bidisperse pore model.It's found that the micropore resisitances dominate the whole resisitances on GAC.The adsorption and desorption experiments in fixed-bed are carried out to study the dynamic adsorption separation of CH₄/N₂,in order to explore the separation mechanism of CH₄/N₂ using GAC packed bed.The experimental data of the CH₄/N₂ breakthrough curves verify the accuracy of the adsorption equilibrium data measured by the magnetic suspension balance,and the competitive adsorption equilibrium data also can be predicted by the MSL model well.The effects of specific surface area,micropore size distribution and precursors of activated carbon on CH₄/N₂ separation are investigated in details.It's found that the CH₄ adsorption capacity increases with the increase of the specific surface area until the specific surface area reasearchs 1200 m2/g under this experimental condition.There's a high competitive adsorption selectivity of CH₄/N₂ when activated carbon with 0.6?0.65 nm microporous pore size distribution,that is a narrow microporous pore size distribution.Coconut shell-derived activated carbon has a better CH₄/N₂ adsorption separation performance,while Wood based activated carbon has a poor performance for the CH₄/N₂ adsorption separation.Coal-based activated carbon has a poor CH₄ adsorption capacity due to the lower specific surface area,but these materials have the advantages of high bulk density and regular shape.