Pressure drop changes in a fixed bed of synthetic zeolite NaA and natural clinoptilolite from Ai-Dag field (Azerbaijan) are studied as functions of the incoming gas flow rate. Conditions for attaining the maximum adsorbent capacity during adsorptive separation of a CH4/CO/CO2/N-2 gas mixture are created in the zeolite fixed bed if the pressure drop is maintained in a certain range. A system of equations describing the relationships of the pressure drop during gas-phase adsorption in a clinoptilolite fixed bed and the incoming gas flow rate that ensure the most complete utilization of the adsorbent capacity is proposed.