Process For Recovering Hydrogen And Carbon Dioxide

Abstract

The present invention provides a process for recovering hydrogen and carbon dioxide from a process stream utilizing a carbon dioxide separation unit and two membrane separation units. The present invention further provides a process within a hydrogen generation plant to increase recovery of hydrogen and capture equal to or greater than 80% of the carbon dioxide in the syngas stream. By using the process of the present invention, especially in terms of a hydrogen generation plant, it is possible to increase recovery of hydrogen and capture of the carbon dioxide in the syngas stream by balancing the recycle of the hydrogen rich permeate from the hydrogen membrane separation unit to the process unit and/or the water gas shift as capacity allows when a carbon dioxide separation unit, a carbon dioxide membrane separation unit and a hydrogen membrane separation unit are utilized.

1 . A process for producing hydrogen and capturing carbon dioxide from a hydrocarbon containing feed stream ( 16 ) in a hydrogen generation plant, the process comprising the steps of:
 a) reforming the hydrocarbon containing feed stream ( 16 ) in a steam methane reformer unit ( 19 ) to obtain a syngas stream ( 20 );   b) subjecting the syngas stream ( 20 ) to a shift reaction in a water gas shift reactor ( 21 ) to obtain a feed gas ( 15 );   c) subjecting the feed gas ( 15 ) to hydrogen purification in a process unit ( 0 ) to obtain a hydrogen product stream ( 23 ) and a hydrogen depleted process stream ( 1 );   d) withdrawing the hydrogen product stream ( 23 ) and using a portion of this hydrogen product stream ( 23 ) as a fuel for the steam methane reformer unit ( 19 ) or as a fuel for steam generation;   e) optionally compressing at least a portion of the process stream ( 1 ) in a first compressor ( 2 );   f) cooling the optionally compressed portion of the process stream ( 1 ) in a heat exchanger ( 3 ) to a temperature equal to or less than −10° C.;   g) separating and purifying the cooled process stream ( 1 ) in a carbon dioxide separation unit ( 4 ) to produce a carbon dioxide rich liquid stream ( 6 ) and a carbon dioxide lean non-condensable stream ( 5 );   h) withdrawing the carbon dioxide rich liquid stream ( 6 ) as a carbon dioxide product for further use;   i) withdrawing the carbon dioxide lean non-condensable stream ( 5 ) from the carbon dioxide separation unit ( 4 ) and passing the carbon dioxide lean non-condensable stream ( 5 ) through a hydrogen selective membrane separation unit ( 7 ) to form a hydrogen rich permeate stream ( 8 ) with the remaining components in the carbon dioxide lean non-condensable stream ( 5 ) forming a hydrogen lean residue stream ( 9 );   j) passing the hydrogen lean residue stream ( 9 ) through a carbon dioxide selective membrane separation unit ( 10 ) to form a carbon dioxide enriched permeate stream ( 11 ) with the remaining components in the hydrogen lean residue stream ( 9 ) forming a carbon dioxide depleted residue stream ( 12 );   k) optionally compressing the hydrogen rich permeate stream ( 8 ) in a second compressor ( 13 ) and recycling the hydrogen rich permeate stream ( 8 ) for use as a supplemental feed stream in the water gas shift reactor ( 21 ), the process unit ( 0 ) or in both the water gas shift reactor ( 21 ) and the process unit ( 0 );   l) recycling the carbon dioxide enriched permeate stream ( 11 ) to the process stream ( 1 ) prior to the compressor ( 2 ) or within the compressor ( 2 ) between stages of compression or optionally compressing the carbon dioxide enriched permeate stream ( 11 ) and recycling the carbon dioxide enriched permeate stream ( 11 ) to be used in the carbon dioxide separation unit ( 4 ) and recycling the carbon dioxide depleted residue stream ( 12 ) to be used as a supplemental feed stream for the pre-reformer ( 17 ) or the steam methane reformer ( 19 ) or as both a fuel and a feed stream in the present process or in other processes.   
     
     
         2 . The process of  claim 1 , wherein the overall capture rate of carbon dioxide from the hydrogen production process is equal to or greater than 80%. 
     
     
         3 . The process of  claim 1 , wherein the overall capture rate of carbon dioxide from the hydrogen production process is equal to or greater than 90%. 
     
     
         4 . The process of  claim 1 , wherein the overall capture rate of carbon dioxide from the hydrogen production process is equal to or greater than 99%. 
     
     
         5 . The process of  claim 2 , wherein prior to step a), the hydrocarbon containing feed stream ( 16 ) is pre-reformed in at least one pre-reformer ( 17 ) to form a pre-reformed gas stream ( 18 ) that is then reformed in the steam methane reformer unit ( 19 ). 
     
     
         6 . The process of  claim 2 , wherein the process unit ( 0 ) is a pressure swing adsorption unit and the process stream ( 1 ) is a tail gas from the pressure swing adsorption unit. 
     
     
         7 . The process of  claim 6 , wherein the hydrogen rich permeate stream ( 8 ) is recycled to be used as a supplemental feed stream in the water gas shift reactor ( 21 ). 
     
     
         8 . The process of  claim 6 , wherein the hydrogen rich permeate stream ( 8 ) is recycled to be used as a supplemental feed stream in the process unit ( 0 ). 
     
     
         9 . The process of  claim 6 , wherein the hydrogen rich permeate stream ( 8 ) is split into a first hydrogen rich permeate fraction ( 8 . 1 ) to be used as a supplemental feed stream to be added to the syngas stream ( 20 ) prior to being introduced into the water gas shift reactor ( 21 ) and a second hydrogen rich permeate fraction ( 8 . 2 ) to be used as a supplemental feed stream to be added to the feed gas ( 15 ) prior to being introduced into the pressure swing adsorption unit ( 0 ) with the proportion of each fraction depending upon the percentage of production in the steam methane reformer ( 19 ). 
     
     
         10 . The process of  claim 9 , wherein the first hydrogen rich permeate fraction ( 8 . 1 ) is optionally heated prior to being added to the syngas stream ( 20 ). 
     
     
         11 . The process of  claim 10 , wherein the first hydrogen rich permeate fraction ( 8 . 1 ) is heated utilizing a heat exchanger ( 30 ). 
     
     
         12 . The process of  claim 11 , wherein steam ( 29 ) is also injected into the first hydrogen rich permeate fraction ( 8 . 1 ) prior to the fraction ( 8 . 1 ) being added to the syngas stream ( 20 ). 
     
     
         13 . The process of  claim 12 , wherein the proportion of the fraction forming the first hydrogen rich permeate fraction ( 8 . 1 ) is greater than the fraction forming the second hydrogen rich permeate fraction ( 8 . 2 ) when the load for the steam methane reformer is relatively low. 
     
     
         14 . The process of  claim 13 , wherein the quantity of the fraction forming the first hydrogen rich permeate fraction ( 8 . 1 ) is determined by the load of the steam methane reformer unit ( 19 ) and the maximum capacity of the water gas shift reactor ( 21 ) with the remaining fraction of the hydrogen rich permeate stream ( 8 ) being directed to the pressure swing adsorption unit ( 0 ) once this determination is made. 
     
     
         15 . The process of  claim 14 , wherein the separation and purification of the cooled process stream in the carbon dioxide separation unit ( 4 ) is carried out by single or multi-step partial liquefaction, compression and distillation or any combination of single or multi-step partial liquefaction, compression and distillation. 
     
     
         16 . The process of  claim 15 , wherein the hydrogen selective membrane separation unit ( 7 ) includes one or more hydrogen selective membranes, each membrane having a permeate side ( 7 . 1 ) and a residue side ( 7 . 2 ) and allowing for the passing of hydrogen to the permeate side ( 7 . 1 ) of the membrane to form the hydrogen rich permeate stream ( 8 ) with the remaining components in the carbon dioxide lean non-condensable stream ( 5 ) forming the hydrogen lean residue stream ( 9 ) on the residue side ( 7 . 2 ) of the membrane. 
     
     
         17 . The process of  claim 16 , wherein the process stream ( 1 ) is compressed to a pressure above 35 bar, the compression occurring either 1) completely in the compressor ( 2 ) prior to step f), 2) completely in a second compressor that is part of the carbon dioxide separation unit ( 4 ) with the compression occurring just prior to the separation and purification of step g), or 3) partially in the compressor ( 2 ) prior to step  0  and then the remaining compression in the second compressor that is a part of the carbon dioxide separation unit ( 4 ) in order to reach a pressure level that is equal to or greater than 35 bar. 
     
     
         18 . The process of  claim 16 , wherein in step g) the process stream ( 1 ) is cooled to a temperature equal to or less than −30° C. 
     
     
         19 . The process of  claim 16 , wherein the carbon dioxide lean non-condensable stream ( 5 ) from the carbon dioxide separation unit ( 4 ) is heated to a temperature from 50° C. to 150° C. before being fed to the hydrogen selective membrane separation unit ( 7 ). 
     
     
         20 . The process of  claim 16 , wherein the carbon dioxide selective membrane separation unit ( 10 ) includes one or more carbon dioxide selective membranes, each membrane having a permeate side ( 10 . 1 ) and a residue side ( 10 . 2 ) and allowing for the passing of carbon dioxide to the permeate side ( 10 . 1 ) of the membrane to form a carbon dioxide enriched permeate stream ( 11 ) with the remaining components in the hydrogen lean residue stream ( 9 ) forming a carbon dioxide depleted residue stream ( 12 ) on the residue side ( 10 . 2 ) of the membrane. 
     
     
         21 . The process of  claim 20 , wherein the one or more hydrogen selective membranes are polymeric membranes selected from one or more polyamides, polyaramides, polybenzimidazoles, polybenzimidazole blends with polyimides, polyamides/imides and the one or more carbon dioxide selective membranes are polymeric membranes selected from selected from one or more polyimides, polyetherimides polysulfone, polyethersulfones, polyarylsulfone, polycarbonate, tetrabromo-bisphenol A polycarbonate, tetrachloro-bisphenol A polycarbonate, polydimethylsiloxane, natural rubber, cellulose actetate, cellulose triacetate, ethyl cellulose, PDD-TFE and polytriazole. 
     
     
         22 . The process of  claim 21 , wherein the one or more hydrogen selective membranes and the one or more carbon dioxide selective membranes are each membranes of the fiber type. 
     
     
         23 . The process of  claim 21 , wherein the one or more hydrogen selective membranes are different in type from the one or more carbon dioxide selective membranes. 
     
     
         24 . The process of  claim 14 , wherein the carbon dioxide rich liquid stream ( 6 ) that is withdrawn is vaporized to produce a carbon dioxide rich gas stream. 
     
     
         25 . The process of  claim 14 , wherein the pre-reforming is performed with the supply of heat. 
     
     
         26 . The process of  claim 14 , wherein the pre-reforming is performed in two or more adiabatic steps with heat supply between the two or more steps. 
     
     
         27 . The process of  claim 1 , wherein prior to compression in step f), the process stream is passed through a filter. 
     
     
         28 . The process of  claim 1 , wherein the hydrogen rich permeate stream ( 8 ) is subjected to a shift reaction in an optional second water gas shift reactor ( 32 ) prior to being recycled to the water gas shift reactor ( 21 ), the process unit ( 0 ) or both the water gas shift unit ( 21 ) and the process unit ( 0 ). 
     
     
         29 . The process of  claim 28 , wherein the water gas shift reactor ( 32 ) is a low temperature water gas shift reactor. 
     
     
         30 . The process of  claim 1 , wherein the carbon dioxide lean non-condensable stream ( 5 ) is subjected to a shift reaction in an optional third water gas shift reactor ( 33 ) prior to being passed thorough the hydrogen and carbon dioxide membrane separation units ( 7 ,  10 ). 
     
     
         31 . The process of  claim 30 , wherein the water gas shift reactor ( 33 ) is a low temperature water gas shift reactor.