Nitrogen rejection from low quality natural gas by pressure swing adsorption experiments and simulation using dynamic adsorption isotherms

In order to remove N₂ from low quality natural gas, a mathematical model has been established by Aspen adsorption, using the CH₄-selective sorbent silicalite-1 pellets. The dynamic adsorption isotherm was first simulated by breakthrough simulation of a CH₄/N₂ mixture at different adsorption pressures and feed flow rates based on breakthrough experiments. The resulting simulated CH₄ dynamic adsorption amounts were very close to the experimental data at three different adsorption pressures (100, 200, and 300 kPa). Moreover, a single-bed, three-step pressure swing adsorption (PSA) experiment was performed, and the results were in good agreement with the simulated data, further corroborating the accuracy of the gas dynamic adsorption isotherm obtained by the simulation method. Finally, based on the simulated dynamic adsorption isotherm of CH₄ and N₂, a four-bed, eight-step PSA process has been designed, which enriched 75% (vol) CH₄ and 80% (vol) CH₄ to 95% (vol) and 99% (vol), and provided 99% (vol) recovery.