TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Gas Separation System: The adsorbent modules comprise pressure swing gas (PSA) adsorbent modules, the first module including a second feed gas inlet, and the second gas adsorbent module including a countercurrent blowdown gas outlet coupled to the second feed gas inlet for providing the first gas adsorption module with blowdown gas. The second gas adsorbent module includes a light reflux gas exit for providing pressurized light reflux gas, an expander in communication with the light reflux gas exit for facilitating pressure letdown of the pressurized light reflux gas, and a reflux gas inlet for receiving the light reflux gas from the expander after the pressure letdown. The first gas adsorbent module includes a compressor for providing the feed gas mixture, and a vacuum pump coupled to the compressor and the countercurrent blowdown gas outlet for effecting vacuum regeneration of the second gas adsorbent module. The first gas adsorbent module further includes a heat exchanger coupled between the vacuum pump and the countercurrent blowdown outlet for effecting purging of the first gas adsorbent module. The second gas adsorbent module includes a heavy reflux gas outlet for providing heavy reflux gas, a reflux compressor in communication with the heavy reflux gas outlet for compressing the heavy reflux gas, and a heavy reflux gas inlet for receiving the pressurized heavy reflux gas from the reflux compressor. The second gas adsorbent module includes a light product gas outlet coupled to the first feed gas inlet for enhancing heavy product recovery. The first gas adsorbent module includes a light reflux gas exit for providing pressurized light reflux gas, an expander in communication with the light reflux gas exit for facilitating pressure letdown of the pressurized light reflux gas, and a reflux gas inlet for receiving the light reflux gas from the expander after the pressure letdown. One of the adsorbent modules comprises a dehumidifier. The rotary PSA module includes a stator incorporating function compartments, and a rotor coupled to the stator to cyclically expose each flow path receiving adsorbent material to multiple discrete pressure levels for maintaining uniformity of gas flow through the function compartments.