Research On Competitive Adsorption Dynamics And Vpsa Process For Ch4/N2 Separation With Zeolite ZSM-5

Capture and utilization of low concentration methane can provide significant energy, mining safety and environmental benefits. As a high-silica hydrophobic material, zeolite ZSM-5 was used for the adsorption and recovery of low concentration coal-bed methane. Theoretical and experimental studies were conducted on adsorption equilibrium, adsorption kinetics and cyclic vacuum pressure swing adsorption (VPSA).Single and binary competitive adsorption equilibrium data of CH4/N2 on zeolite ZSM-5 were measured with gravimetric method by the magnetic suspension balance and with fixed-bed breakthrough experiments by analysis of the elution profiles.Both of the experimental datas matched well with each other. The multi-site Langmuir model was used to fit the experimental data. And the multi-site Langmuir model fitted from single adsorption experimental data could be used to predict binary competitive adsorption equilibrium.Microporous diffusion coefficients were calculated based on the experimental data of diluted breakthrough curves and simulated results of an isothermal mathematical bi-disperse model without momentum loss. Micropore resistance was found as the rate limiting step for both CH4 and N2 adsorption on zeolite ZSM-5. Competitive breakthrough curves of CH4 and N2 on zeolite ZSM-5 were well predicted by non-isothermal fixed bed adsorption numerical models.Effects of CH4 concentration in feed, feed flow rate, feed time and purge/feed flow rate ratio on separation performances of the four-step VPSA process with a ZSM-5 packed single column were investigated. It was found that CH4 purity can be concentrated from 20% to 31%-41% with recovery of 93%～98%.Zeolite ZSM-5 was modifided by impregnation with different ions as K+,Sr2+，Mg2+， Cu2+, Ce3+. Effects of types of ions, concentration of ion solutions, and activation methods of adsorbents on the CH4/N2 adsorption and separation performances on ZSM-5 were studied. The adsorption capacity of CH4 and N2 on ZSM-5 decreased after ion-exchange process, while the selectivity between CH4 and N2 can be improved.