Process for producing carbon monoxide-containing streams

A process for separating synthesis gas into a hydrogen-rich gas stream and a carbon monoxide-rich gas stream in a membrane separation unit comprising at least three membrane separation stages, the process comprising:

• a. providing synthesis gas and pretreating the synthesis gas for at least partial removal of one or more secondary component(s) present in the synthesis gas, to obtain a pretreated synthesis gas;
• b. feeding a feed stream comprising the pretreated synthesis gas and a recyclate stream to a first separation stage to obtain a first retentate and a first permeate, wherein carbon monoxide is enriched in the first retentate and hydrogen is enriched in the first permeate;
• c. feeding the first retentate to a second separation stage to obtain a second retentate and a second permeate, wherein the second retentate is withdrawn as a carbon monoxide-rich gas stream and consists of carbon monoxide to an extent of 85% by volume or more, and wherein the second permeate is recycled upstream of the first separation stage;
• and
• d. feeding the first permeate to a third separation stage to obtain a third retentate and a third permeate, wherein the third permeate is withdrawn as a hydrogen-rich gas stream and consists of hydrogen to an extent of 70% by volume or more, and wherein the third retentate is recycled upstream of the first separation stage,
• wherein the second permeate and the third retentate are combined to form the single recyclate stream and a pressure of the recyclate stream is increased with the aid of a compressor before the recyclate stream is combined with the pretreated synthesis gas upstream of the first separation stage to give the feed stream in b), wherein a ratio of the pretreated synthesis gas to the recyclate stream in the feed stream is in a range of 4:1 to 1:1.5, based on a respective standard volume flow rate of the pretreated synthesis gas and the recyclate stream,
• wherein a ratio of hydrogen to carbon monoxide in the synthesis gas is in a range from 70:30 to 30:70, based on a respective proportion by volume of hydrogen and carbon monoxide in the synthesis gas, and
• wherein the second separation stage or the third separation stage has the highest capacity of the at least three membrane separation stages, and
• wherein the synthesis gas has a CO/CH4 ratio of more than 10 mol/mol.