Method for separating a mixture of carbon monoxide, methane, hydrogen and optionally nitrogen by cryogenic distillation

A method for separating a mixture comprising carbon monoxide, hydrogen, nitrogen and methane, the method comprising the steps of:

• introducing the mixture to a first separation means;
• introducing at least one liquid fraction from the bottom of the first separation means to a stripping column;
• introducing at least one liquid fraction from the stripping column to a CO/CH4 separation column in order to produce a liquid stream enriched in methane and a carbon monoxide enriched gas stream, wherein the carbon monoxide enriched gas stream comprises carbon monoxide and nitrogen;
• introducing the carbon monoxide enriched gas stream to a denitrogenation column, the denitrogenation column configured to produce a carbon monoxide rich liquid stream and a nitrogen rich gas stream;
• providing refrigeration for the method, at least partially, by a carbon monoxide cycle, said carbon monoxide cycle at least partially providing the condensation at the top of the denitrogenation column, wherein a first portion of the carbon monoxide of the carbon monoxide cycle is compressed in a first cycle compressor to a medium pressure, cooled in an exchange line, and then sent to the bottom of the denitrogenation column to be separated therein;
• and
• compressing a second portion of the carbon monoxide to a high pressure to produce a high pressure (HP) carbon monoxide,
• wherein a first fraction of the HP carbon monoxide is used as product,
• wherein a second fraction of the HP carbon monoxide is used for at least partially providing at least a source of heat transfer selected from the group consisting of reboiling at the bottom of the stripping column, reboiling at the bottom of the CO/CH4 separation column, and combinations thereof,
• wherein the medium pressure is at a pressure between about 3.5 bar and about 5 bar, inclusive,
• wherein the high pressure is at a pressure between about 25 bar and about 45 bar, inclusive.