Abstract: Disclosed herein are membrane-based gas separation methods and systems. The methods and systems may, in particular, be used for separating a feed stream comprising methane and carbon dioxide (such as for example a biogas feed stream) in order to provide a methane product stream (such as for example a biomethane stream).

Abstract: Disclosed herein are methods and systems for producing a liquefied methane product from a methane- and carbon dioxide-containing feed stream, in which a plurality of membrane stages comprising gas separation membranes that are more permeable to carbon dioxide than methane are used to remove carbon dioxide from the feed and form a retentate stream that is enriched in methane, said retentate stream being then cooled and liquefied to provide the liquefied methane product. In particular, the disclosed methods and systems may be used for producing liquefied biomethane from a biogas feed.

Abstract: A method for separating a raw feed gas stream utilizes a compressor, a chiller, a membrane drying stage, and a plurality of membrane separation stages. The raw feed gas stream may comprise biogas. In one example, the raw feed gas stream is supplied to the chiller where it is cooled to a target operating temperature to separate out condensed water. The gas stream is then supplied to a membrane drying stage to separate out water vapor. An off-gas from one of the membrane module stages may be recycled as a low pressure sweep gas on the low pressure side of the membrane drying stage to increase the driving force for water permeation within the membrane drying stage. The gas stream is then supplied to the plurality of membrane separation stages where it is upgraded into a high purity methane stream.

Abstract: A method for separating a raw feed gas stream using a plurality of membrane module stages. The raw feed gas stream may be from a biogas process. Off-gas from another unit process in the system, such as a temperature swing adsorption unit or liquefaction unit, may be used as a low pressure sweep gas on the low pressure side of at least one of the membrane module stages. In one example, the sweep gas is used in a first membrane module stage. In another example, a stripping membrane module stage is provided and the sweep gas is used in the stripping membrane module stage. Optionally, portions of the off-gas could be directed to other streams in the system for the purpose of balancing compressor power requirements.