Method for purifying a natural gas stream

A process for purifying a natural gas feed gas stream comprising methane and hydrocarbons containing at least two carbon atoms, comprising the following steps:

• Step a):
• cooling the feed gas stream in a heat exchanger;
• Step b):
• introducing the stream resulting from step a) into a first phase separator vessel in order to produce a liquid stream depleted in methane and enriched in hydrocarbons containing more than two carbon atoms and a gas stream;
• Step c):
• separating the gas stream resulting from step b) in a membrane permeation unit from which at least one methane-enriched gaseous permeate stream and one partially condensed residue stream enriched in hydrocarbons containing at least two carbon atoms exit;
• Step d):
• introducing the residue stream resulting from step c) into a second phase separator vessel in order to produce at least two phases including a liquid stream and a gas stream;
• Step e):
• introducing at least one portion of the liquid stream resulting from step d) into a Joule-Thomson expansion means;
• Step f):
• heating at least one portion of the expanded stream resulting from step e) by introduction into the heat exchanger used in step a) counter-current to the feed stream.