Patent ID: 7871457

Claim:
A method of producing a carbon dioxide product from a synthesis gas stream formed within a hydrogen plant having a synthesis gas reactor, a water-gas shift reactor located downstream of the synthesis gas reactor to form the synthesis gas stream and a hydrogen pressure swing adsorption unit to produce a hydrogen product from hydrogen contained in the synthesis gas stream, said method comprising: recovering carbon dioxide from at least part of the synthesis gas stream, between the water-gas shift reactor and the hydrogen pressure swing adsorption unit, by separating the carbon dioxide from the at least part of the synthesis gas stream in a vacuum pressure swing adsorption process such that a hydrogen-rich gas stream and a crude carbon dioxide stream having a concentration of the carbon dioxide of between about 70 volume percent and about 98 volume percent are produced and purifying the crude carbon dioxide stream by introducing the crude carbon dioxide stream as a sole feed to a sub-ambient temperature distillation process thereby to produce the carbon dioxide product as a vapor; the sub-ambient temperature distillation process being conducted by compressing and drying the crude carbon dioxide stream, cooling the crude carbon dioxide stream to the sub-ambient temperature, stripping the crude carbon dioxide stream within a stripping column to produce a liquid carbon dioxide containing column bottoms and a tower overhead, expanding a liquid stream, composed of the liquid carbon dioxide containing column bottoms, at least at one pressure to produce refrigeration, vaporizing the liquid stream to produce at least one carbon dioxide product stream as the carbon dioxide product and such that the refrigeration produced by expanding the liquid stream is imparted to the sub-ambient temperature distillation process; forming a hydrogen synthesis gas feed stream, at least in part, from the hydrogen-rich gas stream and introducing the hydrogen synthesis gas feed stream into the hydrogen pressure swing adsorption unit, thereby to produce the hydrogen product.