Method and apparatus for separating a synthesis gas by cryogenic distillation

A process for separating a mixture containing carbon monoxide, hydrogen and carbon dioxide produced by washing with methanol in an acid gas removal unit, the process comprising the steps of:

• i. cooling the mixture in a heat exchanger;
• ii. withdrawing at least a portion of the cooled mixture from the heat exchanger at an intermediate temperature of the heat exchanger between a cold end and a warm end of the heat exchanger;
• iii. contacting the at least part of the cooled mixture by a flow of liquid methanol at a temperature below −40° C. to produce methanol enriched with carbon dioxide and a carbon dioxide depleted gas with respect to the cooled mixture;
• iv. cooling the carbon dioxide depleted gas in the heat exchanger and sending the carbon dioxide depleted gas to a separation unit to produce a carbon monoxide enriched flow with respect to the carbon dioxide depleted gas and a hydrogen enriched flow with respect to the carbon dioxide depleted gas, wherein the separation unit is selected from the group consisting of methane washing, carbon monoxide washing, nitrogen washing, distillation, partial condensation, and combinations thereof, and
• v. heating a stream in the heat exchanger by exchanging heat with the mixture and/or the carbon dioxide depleted gas or heating the stream in another heat exchanger, wherein the stream is selected from the group consisting of the carbon monoxide enriched stream with respect to the carbon dioxide depleted gas, the hydrogen-enriched stream with respect to the carbon dioxide depleted gas, and combinations thereof.