TECHNOLOGY FOCUS - CHEMICAL ENGINEERING - Preferred Process: The removal of impurities includes chilling the compressed gas to 0.1-10degreesC to remove water and volatile organic compounds (VOCs) and filtering to remove particulate matter. It further includes passing the feed gas through a first membrane to remove carbon dioxide, passing the feed gas through a second membrane to remove oxygen and pressure swing adsorption (PSA) for removing water vapor and VOCs and nitrogen. Alternatively, the removal of impurities includes passing the feed gas through a first membrane for removing carbon dioxide, passing the feed gas through a second membrane for removing oxygen, passing the feed gas through a double cascade membrane for removing nitrogen, and PSA for removing water vapor, VOCs and residual carbon dioxide. Hydrogen sulfide (H2S) removal is conducted by reaction with a hydrated iron oxide in solid form, reaction with an oxidizing redox couple in solid form, scrubbing with a solution of a ferric complex with subsequent regeneration in a separate column with air, and polishing the stream in a downstream membrane, selective absorber process or PSA drier. The feed gas is compressed to 0.3-1.5 MPa. Removing water is carried out by chilling the gas to 0.1-10degreesC to condense the water, selective water vapor permeation across a membrane, and/or using a PSA unit. Removing VOCs comprises chilling the gas to 0.1-10degreesC under pressure of 0.3-1.5 MPa to condense the water and entrain some VOCs, a PSA drier (107), a granular activated carbon (GAC) non-regenerated absorber, and/or a centrifugal separator. Removing particulate material is done by depth filter effect of a porous solid H2S removal system, a scrubber, and/or a low humidity stream at a filter. Removing carbon dioxide is done by using a selective permeable membrane, a reversible absorber unit, a PSA with selective adsorption, and/or a centrifugal separator. Removing nitrogen is carried out by a nitrogen gas selectively permeable membrane, a PSA with selective adsorption, and/or a centrifugal separator. Removing oxygen is carried out by a reversible absorber unit, a wet reduction and subsequent stream drying, a PSA with selective adsorption, a centrifugal separator, and/or dry reduction. Preferred Conditions: Each of the processes leaves the feed gas at 0.3-1.5 MPa.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Materials: The gas to be absorbed is oxygen and the reversible absorber is a cobalt, iron or manganese complex. Alternatively, the gas to be absorbed is carbon dioxide and the reversible absorber is a weak base.    TECHNOLOGY FOCUS - MECHANICAL ENGINEERING - Preferred Components: The chiller is a rifled tube and shell heat exchanger. It has a tangential feed into a smooth bored tube to induce a helical flow to aid the coalescence of larger particles. The chiller further comprises a vortex-inducing tangential flow device, incorporated into each heat exchange bore. The shell is chilled by a refrigerant. A sensor maintains the refrigerant at the same pressure as the gas flow. The reversible absorber unit operates by recirculation between two hollow-fiber gas/liquid contactors under a partial pressure gradient between the feed gas stream and an exhaust. The exhaust is a partial vacuum.