A modular and compact adsorbent bed structure is disclosed for use in an adsorption-based gas separation plant. The conventional adsorbent bed in a gas separation plant is replaced with a plurality of modular adsorbent bed units connected to make the adsorbent bed structure. Modular adsorbent bed units of this invention provide higher capacity of product per unit volume of adsorbent material (i.e., increased adsorbent utilization) as compared to that obtained from conventional adsorbent beds. The modular design requires lower fabrication costs; is easier to transport; has less maintenance and repair requirements; and is easier to load with adsorbent material.