Process For The Production Of Hydrogen And Carbon Dioxide

Abstract

The present invention provides a method to more efficiently recover hydrogen and carbon dioxide as well as a design for carbon dioxide capture from syngas that allows for the simultaneous production of medium to high amounts of hydrogen and the capture of at least 90% of the carbon dioxide in the syngas as a part of the production of hydrogen in a hydrogen generation plant. Through the use of a combination of hydrogen selective membranes and carbon dioxide selective membranes together with a carbon dioxide separation unit it is possible to increase recovery of hydrogen and carbon dioxide and improved process efficiency of the hydrogen generation plant.

1 . A process for recovering hydrogen and carbon dioxide from a process stream ( 1 ) of a process unit ( 0 ), the process stream ( 1 ) containing at least carbon dioxide, hydrogen and methane, and the process comprising the steps of:
 a) optionally compressing the process stream ( 1 ) in a first compressor ( 2 );   b) adjusting the temperature of the process stream ( 1 ) in a heat exchanger ( 3 ) to a temperature from 20° C. to 150° C.;   c) passing the temperature adjusted process stream ( 1 ) through a first hydrogen selective membrane separation unit ( 4 ) to form a first hydrogen rich permeate stream ( 5 ) with the remaining components in the process stream ( 1 ) forming a first hydrogen lean residue stream ( 6 );   d) optionally compressing the first hydrogen rich permeate stream ( 5 ) in a second compressor ( 17 ) and then recycling the first hydrogen rich permeate stream ( 5 ) for use as a supplemental feed stream for the process unit ( 0 ) or in other processes;   e) cooling the first hydrogen lean residue stream ( 6 ) in a heat exchanger ( 7 ) to a temperature equal to or less than −10° C.;   f) separating and purifying the cooled first hydrocarbon lean residue stream ( 6 ) in a carbon dioxide separation unit ( 8 ) to produce a carbon dioxide rich liquid stream ( 9 ) and a carbon dioxide lean non-condensable stream ( 10 );   g) withdrawing the carbon dioxide rich liquid stream ( 9 ) as carbon dioxide product for further use;   h) withdrawing the carbon dioxide lean non-condensable stream ( 10 ) from the carbon dioxide separation unit ( 8 ) and passing the carbon dioxide lean non-condensable stream ( 10 ) through a second hydrogen selective membrane separation unit ( 11 ) to form a second hydrogen rich permeate stream ( 12 ) with the remaining components in the carbon dioxide lean non-condensable stream ( 10 ) forming a hydrogen lean residue stream ( 13 );   i) passing the second hydrogen lean residue stream ( 13 ) through a carbon dioxide selective membrane separation unit ( 14 ) to form a carbon dioxide enriched permeate stream ( 15 ) with the remaining components in the second hydrogen lean residue stream ( 13 ) forming a carbon dioxide depleted residue stream ( 16 ); and   j) optionally compressing the second hydrogen rich permeate stream ( 12 ) in a third compressor ( 28 ) and recycling the hydrogen rich permeate stream ( 12 ) for use as a supplemental feed stream in the process unit ( 0 ) or in other processes; recycling the carbon dioxide enriched permeate stream ( 15 ) 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 ( 15 ) and recycling the carbon dioxide enriched permeate stream ( 15 ) to the carbon dioxide separation unit ( 8 ); and recycling the carbon dioxide depleted residue stream ( 16 ) to be used as a fuel, as a feed stream or as both a fuel and a feed stream in other processes.   
     
     
         2 . The process of  claim 1 , 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. 
     
     
         3 . The process of  claim 2 , wherein the carbon dioxide depleted residue stream ( 16 ) is used to regenerate any dryers that may be used within the process to remove moisture. 
     
     
         4 . The process of  claim 2 , wherein the separation and purification of the cooled process stream in the carbon dioxide separation unit ( 8 ) 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. 
     
     
         5 . The process of  claim 4 , wherein the first hydrogen selective membrane separation unit ( 4 ) that includes one or more hydrogen selective membranes, each membrane of the first hydrogen selective membrane separation unit ( 4 ) having a permeate side ( 4 . 1 ) and a residue side ( 4 . 2 ) and allowing for the passing of hydrogen to the permeate side ( 4 . 1 ) of the membrane to form the first hydrogen rich permeate stream ( 5 ) with the remaining components in the process stream ( 1 ) forming the first hydrogen lean residue stream ( 6 ) on the residue side ( 4 . 2 ) of the membrane; the second hydrogen selective membrane separation unit ( 11 ) that includes one or more hydrogen selective membranes, each membrane having a permeate side ( 11 . 1 ) and a residue side ( 11 . 2 ) and allowing for the passing of hydrogen to the permeate side ( 11 . 1 ) of the membrane to form the second hydrogen rich permeate stream ( 12 ) with the remaining components in the carbon dioxide lean non-condensable stream ( 10 ) forming the second hydrogen lean residue stream ( 13 ) on the residue side ( 11 . 2 ) of the membrane. 
     
     
         6 . The process of  claim 5 , wherein the carbon dioxide selective membrane separation unit ( 14 ) includes one or more carbon dioxide selective membranes, each membrane having a permeate side ( 14 . 1 ) and a residue side ( 14 . 2 ) and allowing for the passing of carbon dioxide to the permeate side ( 14 . 1 ) of the membrane to form a carbon dioxide enriched permeate stream ( 15 ) with the remaining components in the second hydrogen lean residue stream ( 13 ) forming a carbon dioxide depleted residue stream ( 16 ) on the residue side ( 14 . 2 ) of the membrane. 
     
     
         7 . The process of  claim 6 , wherein the one or more hydrogen selective membranes of the first hydrogen selective membrane separation unit ( 4 ) and the second hydrogen selective membrane separation unit ( 11 ) are each polymeric membranes and are each independently 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. 
     
     
         8 . The process of  claim 7 , wherein the one or more hydrogen selective membranes and the one or more carbon dioxide selective membranes are both either fabricated into hollow fibers or fabricated into flat sheets. 
     
     
         9 . The process of  claim 7 , wherein the one or more hydrogen selective membranes are different in form from the one or more carbon dioxide selective membranes 
     
     
         10 . The process of  claim 7 , wherein the one or more hydrogen selective membranes and the one or more carbon dioxide selective membranes are each made of the same polymers. 
     
     
         11 . The process of  claim 7 , wherein the one or more hydrogen selective membranes and the one or more carbon dioxide selective membranes are each made of different polymers. 
     
     
         12 . The process of  claim 2 , wherein the process stream ( 1 ) is compressed to a pressure above 35 bar, the compression occurring either 1) in the compressor ( 2 ), 2) in a compressor that is part of the carbon dioxide separation unit ( 8 ), the compression occurring just prior to the separation and purification of step f), or 3) partially in the compressor ( 2 ) and then the remaining compression in the compressor that is a part of the carbon dioxide separation unit ( 8 ) to reach a pressure level of 35 bar or greater. 
     
     
         13 . The process of  claim 4 , wherein in step e) the first hydrogen lean residue stream ( 6 ) is cooled to a temperature equal to or less than −30° C. 
     
     
         14 . The process of  claim 1 , wherein the carbon dioxide rich liquid stream ( 9 ) that is withdrawn is vaporized to produce a carbon dioxide rich gas stream. 
     
     
         15 . The process of  claim 12 , wherein the carbon dioxide lean non-condensable stream ( 10 ) from the carbon dioxide separation unit ( 8 ) is heated to a temperature from 50° C. to 150° C. before being fed to the second hydrogen selective membrane separation unit ( 11 ). 
     
     
         16 . The process of  claim 1 , wherein the second hydrogen lean residue stream ( 13 ) is cooled to a temperature from −60° C. to 50° C. before being fed to the carbon dioxide selective membrane separation unit ( 14 ). 
     
     
         17 . The process of  claim 1 , wherein at least 50% of the carbon dioxide in the process stream ( 1 ) is recovered. 
     
     
         18 . A process for producing hydrogen and capturing carbon dioxide from a hydrocarbon containing feed stream ( 20 ) in a hydrogen generation plant, the process comprising the steps of:
 a) optionally pre-reforming the hydrocarbon containing feed stream ( 20 ) in at least one pre-reformer ( 21 ) to form a pre-reformed gas stream ( 22 );   b) reforming the pre-reformed gas stream ( 22 ) in a stream methane reformer unit ( 23 ) to obtain a syngas stream ( 24 );   c) subjecting the syngas stream ( 24 ) to a shift reaction in a water gas shift reactor ( 25 ) to obtain a feed gas ( 19 );   d) subjecting the feed gas ( 19 ) to hydrogen purification in a process unit ( 0 ) to obtain a hydrogen product stream ( 27 ) and a process stream ( 1 );   e) withdrawing the hydrogen product stream ( 27 ) and using a portion of this hydrogen product stream ( 27 ) as a fuel for the steam methane reformer unit ( 23 );   f) optionally compressing the process stream ( 1 ) in a first compressor ( 2 );   g) adjusting the temperature of the process stream ( 1 ) in a heat exchanger ( 3 ) to a temperature from 20° C. to 150° C.;   h) passing the temperature adjusted process stream ( 1 ) through a first hydrogen selective membrane separation unit ( 4 ) to form a first hydrogen rich permeate stream ( 5 ) with the remaining components in the process stream ( 1 ) forming a first hydrogen lean residue stream ( 6 );   i) optionally compressing the first hydrogen rich permeate stream ( 5 ) in a second compressor ( 17 ) and then recycling the first hydrogen rich permeate stream ( 5 ) for use as a supplemental feed stream for the process unit ( 0 ) or in other processes;   j) cooling the first hydrocarbon lean residue stream ( 6 ) in a heat exchanger ( 7 ) to a temperature equal to or less than −10° C.;   k) separating and purifying the cooled first hydrocarbon lean residue stream ( 6 ) in a carbon dioxide separation unit ( 8 ) to produce a carbon dioxide rich liquid stream ( 9 ) and a carbon dioxide lean non-condensable stream ( 10 );   l) withdrawing the carbon dioxide rich liquid stream ( 9 ) as carbon dioxide product for further use;   m) withdrawing the carbon dioxide lean non-condensable stream ( 10 ) from the carbon dioxide separation unit ( 8 ) and passing the carbon dioxide lean non-condensable stream ( 10 ) through a second hydrogen selective membrane separation unit ( 11 ) to form a second hydrogen rich permeate stream ( 12 ) with the remaining components in the carbon dioxide lean non-condensable stream ( 10 ) forming a hydrogen lean residue stream ( 13 );   n) passing the hydrogen lean residue stream ( 13 ) through a carbon dioxide selective membrane separation unit ( 14 ) to form a carbon dioxide enriched permeate stream ( 15 ) with the remaining components in the hydrogen lean residue stream ( 13 ) forming a carbon dioxide depleted residue stream ( 16 ); and   o) optionally compressing the second hydrogen rich permeate stream ( 12 ) in a third compressor ( 28 ) and recycling the second hydrogen rich permeate stream ( 12 ) for use as a supplemental feed stream in the steam methane reformer ( 23 ), the water gas shift reactor ( 25 ) or the process unit ( 0 ) or as a fuel for the steam methane reformer ( 23 ), recycling the carbon dioxide enriched permeate stream ( 15 ) 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 ( 15 ) and recycling the carbon dioxide enriched permeate stream ( 15 ) to be used in the carbon dioxide separation unit ( 8 ) and recycling the carbon dioxide depleted residue stream ( 16 ) to be used as a fuel for the steam methane reformer ( 23 ), as a supplemental feed stream for the pre-reformer ( 21 ) or the steam methane reformer ( 23 ) or as both a fuel and a feed stream in the present process or in other processes.   
     
     
         19 . The process of  claim 18 , wherein the carbon dioxide depleted residue stream ( 12 ) is passed through a turbo expander ( 22 ) to recover compressed gas energy prior to being used as a fuel for the steam methane reformer ( 19 ), 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. 
     
     
         20 . The process of  claim 18 , wherein the overall capture rate of carbon dioxide from the hydrogen production process is equal to or greater than 90%. 
     
     
         21 . The process of  claim 18 , wherein the overall capture rate of carbon dioxide from the hydrogen production process is equal to or greater than 99%. 
     
     
         22 . The process of  claim 18 , wherein the overall capture rate of carbon dioxide from the hydrogen production process approaches or achieves 100%. 
     
     
         23 . The process of  claim 20 , 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. 
     
     
         24 . The process of  claim 20 , wherein the separation and purification of the cooled process stream in the carbon dioxide separation unit ( 8 ) 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. 
     
     
         25 . The process of  claim 24 , wherein the first hydrogen selective membrane separation unit ( 4 ) that includes one or more hydrogen selective membranes, each membrane of the first hydrogen selective membrane separation unit ( 4 ) having a permeate side ( 4 . 1 ) and a residue side ( 4 . 2 ) and allowing for the passing of hydrogen to the permeate side ( 4 . 1 ) of the membrane to form the first hydrogen rich permeate stream ( 5 ) with the remaining components in the process stream ( 1 ) forming the first hydrogen lean residue stream ( 6 ) on the residue side ( 4 . 2 ) of the membrane and the second hydrogen selective membrane separation unit ( 11 ) that includes one or more hydrogen selective membranes, each membrane having a permeate side ( 11 . 1 ) and a residue side ( 11 . 2 ) and allowing for the passing of hydrogen to the permeate side ( 11 . 1 ) of the membrane to form the second hydrogen rich permeate stream ( 12 ) with the remaining components in the carbon dioxide lean non-condensable stream ( 10 ) forming the second hydrogen lean residue stream ( 13 ) on the residue side ( 11 . 2 ) of the membrane. 
     
     
         26 . The process of  claim 25 , wherein the carbon dioxide selective membrane separation unit ( 14 ) includes one or more carbon dioxide selective membranes, each membrane having a permeate side ( 14 . 1 ) and a residue side ( 14 . 2 ) and allowing for the passing of carbon dioxide to the permeate side ( 14 . 1 ) of the membrane to form a carbon dioxide enriched permeate stream ( 15 ) with the remaining components in the hydrogen lean residue stream ( 13 ) forming a carbon dioxide depleted residue stream ( 16 ) on the residue side ( 14 . 2 ) of the membrane. 
     
     
         27 . The process of  claim 26 , of the first hydrogen selective membrane separation unit ( 4 ) and the second hydrogen selective membrane separation unit ( 11 ) are each polymeric membranes and are each independently 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. 
     
     
         28 . The process of  claim 27  wherein the one or more hydrogen selective membranes and the one or more carbon dioxide selective membranes are each membranes of the fiber type. 
     
     
         29 . The process of  claim 27 , wherein the one or more hydrogen selective membranes are different in type from the one or more carbon dioxide selective membranes. 
     
     
         30 . The process of  claim 23 , wherein the process stream ( 1 ) is compressed to a pressure above 35 bar, the compression occurring either 1) in the compressor ( 2 ), in a compressor that is part of the carbon dioxide separation unit ( 8 ), the compression occurring just prior to the separation and purification of step f), or 3) partially in the compressor ( 2 ) and then the remaining compression in the compressor that is a part of the carbon dioxide separation unit ( 8 ) to reach a pressure level that is equal to or greater than 35 bar. 
     
     
         31 . The process of  claim 24 , wherein in step e) the process stream ( 1 ) is cooled to a temperature equal to or less than −30° C. 
     
     
         32 . The process of  claim 23 , wherein the carbon dioxide rich liquid stream ( 9 ) that is withdrawn is vaporized to produce a carbon dioxide rich gas stream. 
     
     
         33 . The process of  claim 30 , wherein the carbon dioxide lean non-condensable stream ( 10 ) from the carbon dioxide separation unit ( 8 ) is heated to a temperature from 50° C. to 150° C. before being fed to the second hydrogen selective membrane separation unit ( 11 ). 
     
     
         34 . The process of  claim 33 , wherein the heat brought to the carbon dioxide lean non-condensable stream ( 10 ) is taken from the process stream ( 1 ) after the step of compression. 
     
     
         35 . The process of  claim 23 , wherein the second hydrogen lean residue stream ( 13 ) is cooled to a temperature from −60° C. to 50° C. before being fed to the carbon dioxide selective membrane separation unit ( 14 ). 
     
     
         36 . The process of  claim 35 , wherein the carbon dioxide selective membranes are cold membranes that operate between −55° C. and 30° C. 
     
     
         37 . The process of  claim 18 , wherein the pre-reforming is performed in two or more adiabatic steps with heat supply between the two or more steps.