Cryogenic Separation of Synthesis Gas

Abstract

A process and apparatus for separating a feed containing hydrogen, carbon monoxide, methane, and optionally nitrogen to form a product gas having a desired H 2 :CO molar ratio and optionally a hydrogen product gas and a carbon monoxide product gas. The feed is partially condensed to form a hydrogen-enriched vapor fraction and a carbon monoxide-enriched liquid fraction. The hydrogen-enriched vapor fraction and carbon monoxide-enriched liquid fraction are combined in a regulated manner to form an admixture, which is cryogenically separated to form the product mixture having the desired H 2 :CO molar ratio.

1 . A process for separating a feed comprising hydrogen, carbon monoxide, methane, and optionally nitrogen, comprising:
 partially condensing the feed to provide a hydrogen-enriched vapor fraction and a carbon monoxide-enriched liquid fraction;   combining at least a portion of the carbon monoxide-enriched liquid fraction with a regulated portion of the hydrogen-enriched vapor fraction to form a two-phase admixture having a vapor fraction and a liquid fraction; and   cryogenically separating at least a portion of the two-phase admixture in a first fractionator to form a first product gas and a hydrogen-depleted liquid fraction, wherein the first product gas has a H 2 :CO molar ratio between 0.5:1 and 2.5:1;   wherein at least one of the liquid fraction of the two-phase admixture and the at least a portion of the carbon monoxide-enriched liquid fraction are partially vaporized.   
     
     
         2 . The process of  claim 1  wherein the step of cryogenically separating at least a portion of the two-phase admixture comprises:
 separating the at least a portion of the two-phase admixture in the first fractionator to form a methane-depleted vapor fraction and the hydrogen-depleted liquid fraction;   partially condensing the methane-depleted vapor fraction to form the first product gas and a condensate; and   introducing at least a portion of the condensate into the first fractionator as reflux.   
     
     
         3 . The process of  claim 1  wherein the first product gas is withdrawn from the first fractionator at a pressure of 15 to 40 MPa. 
     
     
         4 . The process of  claim 1  wherein the first product gas H 2 :CO molar ratio is between 0.9:1 and 1.5:1. 
     
     
         5 . The process of  claim 1  further comprising:
 scrubbing a second portion of the hydrogen-enriched vapor fraction, or a vapor portion from phase separation thereof, with a liquid methane wash stream to provide a hydrogen product gas and a carbon monoxide-loaded methane liquid.   
     
     
         6 . The process of  claim 1  further comprising:
 stripping hydrogen from a second portion of the carbon monoxide-enriched liquid fraction and at least a portion of the hydrogen-depleted liquid fraction in a second fractionator to form a second hydrogen-enriched vapor fraction and a hydrogen-freed liquid fraction; and   separating an intermediate feed comprising carbon monoxide and methane in a carbon monoxide/methane fractionator to form a carbon monoxide product gas and a methane-enriched liquid fraction, wherein the intermediate feed is formed from at least a portion of the hydrogen-freed liquid fraction.   
     
     
         7 . The process of  claim 6  further comprising:
 condensing a CO-containing vapor feed to provide a CO-containing condensate; and   introducing at least a portion of the CO-containing condensate into the first fractionator as reflux.   
     
     
         8 . The process of  claim 6  further comprising:
 condensing a CO-containing vapor feed to provide a CO-containing condensate; and   introducing a first portion of the CO-containing condensate into the carbon monoxide/methane fractionator as reflux and introducing a second portion of the CO-containing condensate into the first fractionator as reflux.   
     
     
         9 . The process of  claim 1  further comprising:
 stripping hydrogen from a second portion of the carbon monoxide-enriched liquid fraction and at least a portion of the hydrogen-depleted liquid fraction in a second fractionator to form a second hydrogen-enriched vapor fraction and a hydrogen-freed liquid fraction;   separating an intermediate feed comprising carbon monoxide and methane in a carbon monoxide/methane fractionator to form a carbon monoxide product gas, a methane-enriched liquid fraction, and a second methane-enriched liquid fraction wherein the intermediate feed is formed from at least a portion of the hydrogen-freed liquid fraction; and   vaporizing the second methane-enriched liquid fraction by indirect heat exchange with the feed to partially condense the feed.   
     
     
         10 . The process of  claim 1  further comprising:
 stripping hydrogen from a second portion of the carbon monoxide-enriched liquid fraction and at least a portion of the hydrogen-depleted liquid fraction in a second fractionator to form a second hydrogen-enriched vapor fraction and a hydrogen-freed liquid fraction;   separating at least a portion of the hydrogen-freed liquid fraction in a third fractionator to form a nitrogen-enriched vapor fraction and a nitrogen-depleted liquid fraction;   forming an intermediate feed from at least a portion of the nitrogen-depleted liquid fraction; and   separating the intermediate feed in a carbon monoxide/methane fractionator to form a carbon monoxide product gas and a methane-enriched liquid fraction.   
     
     
         11 . The process of  claim 1  further comprising:
 stripping hydrogen from a second portion of the carbon monoxide-enriched liquid fraction and at least a portion of the hydrogen-depleted liquid fraction in a second fractionator to form a second hydrogen-enriched vapor fraction and a hydrogen-freed liquid fraction;   separating at least a portion of the hydrogen-freed liquid fraction in a third fractionator to form a nitrogen-enriched vapor fraction and a nitrogen-depleted liquid fraction;   dividing the nitrogen-depleted liquid fraction into a first nitrogen-depleted stream and a second nitrogen-depleted stream;   partially vaporizing the first nitrogen-depleted stream to form a partially vaporized nitrogen-depleted stream; and   separating the partially vaporized nitrogen-depleted stream and the second nitrogen-depleted stream in a carbon monoxide/methane fractionator to form a carbon monoxide product gas and a methane-enriched liquid fraction.   
     
     
         12 . The process of  claim 6  further comprising:
 forming at least a portion of the liquid methane wash stream from a portion of the methane-enriched liquid fraction.   
     
     
         13 . An apparatus for separating a feed comprising hydrogen, carbon monoxide, methane, and optionally nitrogen, comprising:
 a first heat exchanger for partially condensing the feed to form a partially condensed feed;   a phase separator for separating the partially condensed feed into a hydrogen-enriched vapor fraction and a carbon monoxide-enriched liquid fraction;   a means for feeding the partially condensed feed to the phase separator from the first heat exchanger;   a means for combining a portion or all of the carbon monoxide-enriched liquid fraction with a regulated portion of the hydrogen-enriched vapor fraction to form a two-phase admixture,   a means for feeding at least one of the portion or all of the carbon monoxide-enriched liquid fraction and at least a portion of the two-phase admixture to the first heat exchanger;   the first fractionator for cryogenically separating the at least a portion of the two-phase admixture to form a first product gas and a hydrogen-depleted liquid fraction; and   a means for feeding the at least a portion of the two-phase admixture to the first fractionator.   
     
     
         14 . The apparatus of  claim 13  further comprising:
 a methane wash column for scrubbing a second portion of the hydrogen-enriched vapor fraction, or a vapor portion from phase separation thereof, with a liquid methane wash stream to provide a hydrogen product gas and a carbon monoxide-loaded methane liquid; and   a means for feeding the second portion of the hydrogen-enriched vapor fraction, or a vapor portion from phase separation thereof, to the methane wash column from the phase separator.   
     
     
         15 . The apparatus of  claim 14  further comprising:
 a second fractionator for stripping hydrogen from a second portion of the carbon monoxide-enriched liquid fraction and at least a portion of the hydrogen-depleted liquid fraction to form a second hydrogen-enriched vapor fraction and a hydrogen-freed liquid fraction;   a means for feeding the second portion of the carbon monoxide-enriched liquid fraction to the second fractionator from the phase separator;   a means for feeding the at least a portion of the hydrogen-depleted liquid fraction to the second fractionator from the first fractionator;   a carbon monoxide/methane fractionator for separating an intermediate feed ( 36 ,  36 ′) to form a carbon monoxide product gas and a methane-enriched liquid fraction; and   a means for feeding at least a portion of the hydrogen-freed liquid fraction to the carbon monoxide/methane fractionator from the second fractionator.   
     
     
         16 . The apparatus of  claim 14  further comprising:
 a second fractionator for stripping hydrogen from a second portion of the carbon monoxide-enriched liquid fraction and at least a portion of the hydrogen-depleted liquid fraction to form a second hydrogen-enriched vapor fraction and a hydrogen-freed liquid fraction;   a means for feeding the second portion of the carbon monoxide-enriched liquid fraction to the second fractionator from the phase separator;   a means for feeding the at least a portion of the hydrogen-depleted liquid fraction to the second fractionator from the first fractionator;   a third fractionator for separating at least a portion of the hydrogen-freed liquid fraction to form a nitrogen-enriched vapor fraction and a nitrogen depleted liquid fraction;   a means for feeding the hydrogen-freed liquid fraction to the third fractionator from the second fractionator;   a carbon monoxide/methane fractionator for separating at least a portion of the nitrogen-depleted liquid fraction to form a carbon monoxide product gas and a methane-enriched liquid fraction; and   a means for feeding the at least a portion of the nitrogen-depleted liquid fraction to the carbon monoxide/methane fractionator from the third fractionator.   
     
     
         17 . The apparatus of  claim 15  further comprising:
 a means for feeding a portion of the methane-enriched liquid fraction to the methane wash column from the carbon monoxide/methane fractionator.