Study On Adsorption Separation Process Of CH₄/N₂ With Monolith/granular Activated Carbon

It is very important to recover and utilize methane from coal-bed gas,related to energy structure,coal mine's safety and environment protection of our country.The separation of CH4/N2 is the key step.Adsorption technology is one of the most prospect for CH4/N2 seperation due to its flexsible operation,simple equipments and low power consumption.In this paper,both monolith activated carbon and granular activated carbon are investigated as adsorbents to separate the mixture of CH4 and N2.Experiments are conducted including adsorption equilibrium isotherms,breakthrough curves,and VPSA process.Different adsorption equilibrium models are used to fit experimental data.The adsorption equilibrium isotherms of CH4 and N2 are measured using ASAP2020 gas adsorption analyzer.Both monolith activated carbon and granular activated carbon are tested.The adsorption equilibrium data measured at diffenrent temperature are fitted with Sips,Toth,MSL(Multisite Langmuir),DSL(Dualsite Langmuir)and Virial models,respectively,and the key model parameters are obtained by the nonlinear regression method.The predicted results of models are consistent with experimental data.Breakthrough curve experiments are conducted on monolith activated carbon and granular activated carbon,using the apparatus designed and manufactured by myself.The breakthrough experiments contain single adsorption and two components competitive adsorption tests.The effects of different operation conditions on the separation performance of CH4 and N2 are studied by changing feed concentration,bed pressure and so on.Equilibrium-based separation of methane and nitrogen is verified.According to adsorption equilibrium,breakthrough curves and pressure drop for two kinds of activated carbons,it is found that monolith activated carbon has a low pressure drop,but low adsorption capacity and loading density.That will affect commercialization in the future for monolith activated carbon.Furthermore,both the granular activated carbon and monolith activated carbon are chosen to carry out experiments of vacuum pressure swing adsorption(VPSA)process with single bed.The different factors are found to affect the separation performance of VPSA,including feed concentration,bed pressure,feed flow,residence time and so on.The results demonstrate that VPSA process could be used to purify the feed gas,which contain about 30%CH4,to the CH4 product with purity between 72%and 83%and the CH4 recovery is 56%to 87%.