Helium-containing natural gas is processed with three gas separation stages to produce a natural gas product and a Helium-containing gas that may be injected into the reservoir from which the Helium-containing natural gas is obtained. A permeate from the first gas separation membrane stage is compressed and fed to the second gas membrane stage. The permeate from the second gas separation membrane stage is recovered as the Helium-containing gas that may be injected into the reservoir. The non-permeate from the second gas separation membrane stage is fed to the third gas separation membrane stage. The non-permeate from the first gas separation stage is a natural gas product. A permeate from the third gas separation membrane stage is combined with a non-permeate from the first gas separation membrane stage before it is compressed and fed to the second gas separation membrane stage. A non-permeate from the third gas separation membrane stage is fed to the first gas separation membrane stage along with the Helium-containing natural gas.

A multi-stage membrane system is provided to separate helium from a gas stream such as a natural gas stream. There are at least two permeate streams from a first membrane module. One of the permeate streams is compressed and sent to a second membrane module while one of the permeate streams bypasses the compressor. There are control means provided to determine the flow for these two permeate streams based on factors including the compressor capacity, the concentration of the target component in the combined permeate streams and the capacity of the second membrane module.

The present invention relates to a process for obtaining pure helium using a first membrane separation stage a second membrane separation stage and a third membrane separation stage. The first membrane separation stage is supplied with a first helium-containing feed mixture, the second membrane separation stage with a second helium-containing feed mixture and the third membrane separation stage with a third helium-containing feed mixture a first permeate and a first retentate are formed in the first membrane separation stage, a second permeate and a second retentate in the second membrane separation stage and a third permeate and a third retentate in the third membrane separation stage. The first feed mixture is formed using at least part of a helium-containing starting mixture. The second feed mixture is formed using at least part of the first permeate. The third feed mixture is formed using at least part of the second permeate. The third permeate is at least partly processed by pressure swing adsorption to obtain pure helium and a residual mixture at least some of the residual mixture is used in the formation of the second or third feed mixture.

A method for separating a synthesis gas containing carbon monoxide and hydrogen including compressing a flow of synthesis gas received from a source of synthesis gas in a compressor, purifying the compressed synthesis gas in a purification unit to purify it of water and/or carbon dioxide, cooling the compressed and purified flow of synthesis gas, separating the cooled flow of synthesis gas by washing and/or distillation at a cryogenic temperature and optionally by adsorption in a separating unit, and producing at least the following three gases in the separating unit: a carbon monoxide-enriched gas, a hydrogen-enriched gas, a residual gas containing carbon monoxide and hydrogen that is less pure with respect to carbon monoxide than the carbon monoxide-enriched gas and less pure with respect to hydrogen than the hydrogen-enriched gas.

An adsorption process for xenon recovery from a cryogenic liquid or gas stream is described wherein a bed of adsorbent is contacted with the aforementioned xenon containing liquid or gas stream and adsorbs the xenon selectively from this fluid stream. The adsorption bed is operated to at least near full breakthrough with xenon to enable a deep rejection of other stream components, prior to regeneration using the temperature swing method. Operating the adsorption bed to near full breakthrough with xenon, prior to regeneration, enables production of a high purity product from the adsorption bed and further enables oxygen to be used safely as a purge gas, even in cases where hydrocarbons are co-present in the feed stream.

Process for the combined production of a mixture of hydrogen and nitrogen, and of carbon monoxide by cryogenic distillation and cryogenic scrubbing, wherein a methane-rich liquid is introduced at a first intermediate level of a scrubbing column as first scrubbing liquid and at least one nitrogen-rich liquid is introduced at a level higher than the first level of the scrubbing column as second scrubbing liquid and a mixture of hydrogen and nitrogen is drawn off as overhead gas from the scrubbing column.

A method of obtaining helium from a process gas. The process gas is at a pressure less than 15 bar to a first membrane separation stage having a first membrane more readily permeable for helium than for at least one other component in the process gas. A first retentate stream is fed to a second membrane separation stage having a second membrane more readily permeable for helium than for at least one other component in the process gas. Helium is separated from a first helium-containing permeate stream using a pressure swing adsorption to obtain a helium-containing product stream. A second helium-containing permeate stream is recycled to the first membrane separation stage. A purge gas from the pressure swing adsorption is also recycled to the first membrane separation stage.

A method of obtaining helium from a helium-containing feed gas. Helium-containing feed gas is fed to a prepurifying unit that uses a pressure swing adsorption process to remove undesirable components from the helium-containing feed gas and obtain a prepurified feed gas. The prepurified feed gas is fed to a membrane unit connected downstream of the prepurifying unit and that has at least one membrane more readily permeable to helium than to at least one further component present in the prepurified feed gas. A pressurized low-helium retentate stream that has not passed through the membrane is fed to the prepurifying unit. The pressurized low-helium retentate is used to displace helium-rich gas from an adsorber that is to be regenerated into an already regenerated adsorber.

Recovering helium from a gaseous stream includes contacting an acid gas removal membrane with a gaseous stream to yield a permeate stream and a residual stream, removing a majority of the acid gas from the residual stream to yield a first acid gas stream and a helium depleted clean gas stream, removing a majority of the acid gas from the permeate stream to yield a second acid gas stream and a helium rich stream, and removing helium from the helium rich stream to yield a helium product stream and a helium depleted stream. A helium removal system for removing helium from a gaseous stream including hydrocarbon gas, acid gas, and helium includes a first processing zone including a first acid gas removal unit, a second processing zone including a second acid gas removal unit, a third processing zone, and a helium purification unit.

A gas separation membrane includes a gas separation layer that contains the polyimide compound having the structural portion represented by Formula (1). A gas separation module includes the gas separation membrane, a gas separator includes the gas separation module, and a gas separation method is performed using the gas separation membrane.

##STR00001## A.sup.1 and A.sup.2 represent a linking site, a hydrogen atom, a halogen atom, a carboxy group, a carbamoyl group, an acyl group, an acyloxy group, a sulfo group, a sulfamoyl group, an alkylsulfinyl group, an arylsulfinyl group, an alkylsulfonyloxy group, an alkoxycarbonyl group, a non-fluorinated alkyl group, or an aryl group. Here, at least one of A.sup.1 or A.sup.2 represents a linking site.