Membrane separation system and method for operating membrane separation system

A method for operating a membrane separation system including a membrane separation unit, a decompression unit, a first condensation unit, and a second condensation unit,

• the first condensation unit being disposed between the membrane separation unit and the decompression unit,
• the membrane separation unit having a pervaporation membrane, and a feed space and a permeation space separated from each other by the pervaporation membrane,
• the method comprising:
• separating a feed liquid containing a volatile organic compound and a gas into a permeated fluid and a non-permeated fluid with the pervaporation membrane of the membrane separation unit;
• condensing, with the first condensation unit, the organic compound contained in the permeated fluid discharged from the membrane separation unit;
• and
• condensing, with the second condensation unit, the organic compound contained in the permeated fluid discharged from the decompression unit, wherein
• the separating includes decompressing, with the decompression unit, an inside of the permeation space of the membrane separation unit.