NOVELTY - A gas is separated from a gaseous mixture by introducing a gaseous mixture to the hollow fiber membrane module and through the individual fiber lumens, and absorbing gas from the gaseous mixture by the absorbent solution to reduce the concentration of the at least one gas within the gaseous mixture to a reduced level. The absorption occurs for a predetermined period of time without regeneration or replacement of the absorbent solution.    USE - The method is for separating gas (e.g. carbon dioxide) from gaseous mixture e.g. atmospheric air. It is useful in fuel cell or battery.    ADVANTAGE - The invention can be effectively operated over extended periods and may be regenerated in an efficient manner. It utilizes an absorbent solution that advantageously absorbs the desired component or components from the gaseous mixture for an extended period of time. The absorbent solution is regenerated on a periodic bases, e.g. using a sweep gas that is passed through the hollow fibers.    DETAILED DESCRIPTION - Separation of a gas from a gaseous mixture comprises: providing a hollow fiber membrane module containing hollow fibers that define individual fiber lumens, where the hollow fiber membrane module defines a region between the hollow fibers; providing an absorbent solution in the region defined within the hollow fiber membrane module; introducing a gaseous mixture to the hollow fiber membrane module and through the individual fiber lumens; and absorbing gas from the gaseous mixture by the absorbent solution so as to reduce the concentration of the at least one gas within the gaseous mixture to a reduced level, where the absorption occurs for a predetermined period of time without regeneration or replacement of the absorbent solution.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic diagram of a system for gas separation in the invention.    Hollow fiber membranes (104)    Outer housing (106)    First end (110)    Second end (112)    Pressure gauge (116)    Valves (122)    Gas chromatograph (128)