NOVELTY - Ionic liquid (30) comprising an anion constituted of optionally substituted pyrrolide, optionally substituted pyrazolide, optionally substituted indolide, optionally substituted phospholide or optionally substituted imidazolide, is claimed.    USE - The ionic liquid is useful for separating an acidic gas from a mixture of gases. The ionic liquid is useful in a gas separation device and a combustion device (all claimed).    ADVANTAGE - The ionic liquid is suitable for industrial removal of carbon dioxide and other acidic gases, and the removal of carbon dioxide from combustion exhaust, or from air, reduces the greenhouse effect on global warming.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) a method of separating an acidic gas from a mixture of gases, comprising: either (a) providing sufficient contact between the mixture of gases and the ionic liquid to allow at least a portion of the acidic gas to be absorbed by the ionic liquid to provide a purified gas, and (b) collecting or diverting for use the purified gas and/or the acidic gas; or providing sufficient contact between the mixture of gases and an ionic liquid to allow at least a portion of the acidic gas to be absorbed by the ionic liquid, and recovering the acidic gas from the ionic liquid by applying at least one of heat or reduced pressure to the ionic liquid;    (2) a method of cooling an enclosed volume comprising compressing and expanding a gas in the presence of the ionic liquid;    (3) a method of separating an acidic gas from a combustion exhaust, comprising: providing an exhaust from combustion of a carbon-based fuel, where the exhaust comprises the acidic gas; and providing sufficient contact between the exhaust and the ionic liquid to allow at least a portion of the acidic gas to be absorbed by the ionic liquid;    (4) a gas separation device comprising: a flow component (10) configured to provide a flow of a mixture of gases (15), where the mixture of gases comprises an acidic gas; a separation component (20), in fluid communication with the flow component, configured to allow the flow of the mixture of gases to pass through the separation component from the flow component; and the ionic liquid, coupled to the separation component, where the device is configured to provide sufficient contact between the mixture of gases and the ionic liquid to remove at least a portion of the acidic gas from the mixture of gases; and    (5) a combustion device comprising: a combustion vessel configured to contain a combustion reaction; an exhaust component, in fluid communication with the combustion vessel, which is configured to allow exhaust from the combustion reaction to escape from the combustion vessel, where the exhaust comprises an acidic gas; and the ionic liquid, coupled to the exhaust component, where the device is configured to provide sufficient contact between the exhaust and the ionic liquid to remove at least a portion of the acidic gas from the exhaust.    DESCRIPTION OF DRAWING(S) - The figure shows the schematic representation of a gas separation device.    Flow component (10)    Gases (15)    Separation component (20)    Ionic liquid. (30)