A New Composite Sorbent for Methane-Nitrogen Separation by Adsorption

Abstract

Composite sorbents were prepared by depositing molybdenum dioxide on Super A activated carbon. The adsorption isotherms of CH₄ and N₂ were measured. The adsorption capacities and BET surface areas of these adsorbents decreased with an increase in the amount of MoO₂; however, the equilibrium selectivity ratio (CH₄/N₂) increased significantly. Therefore, an optimum quantity of MoO₂ should be used to produce a sorbent with high adsorption capacity and selectivity ratio (CH₄/N₂). An adsorbent containing 18.2 wt% MoO₂ was found to be optimum which showed a CH₄/N₂ selectivity ratio of 4.25. The selectivity ratio decreased with pressure, and leveled off to about 3 at 12 atm. The separation of a CH₄/N₂ (50/50) mixture by pressure swing adsorption (PSA) was studied by using an equilibrium model. A new PSA cycle is described by which pipeline quality methane (>90% CH₄ purity) could be produced using the composite sorbent at a recovery of 73% and a throughput of 200 L STP/h/kg.