Process For The Production Of Hydrogen And Carbon Dioxide

Abstract

This present invention provides a method to more efficiently recover hydrogen and carbon dioxide, preferably at least 50%, even more preferably at least 75%, and most preferably at least 90% of the carbon dioxide. The present invention further provides the design for capture of at least 80%, carbon dioxide from syngas that allows for the simultaneous production of medium to high amounts of hydrogen in the syngas as a part of the production of hydrogen in a hydrogen generation plant. 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 units 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 two hydrogen membrane separation units are utilized.

1 . 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) reforming the hydrocarbon containing feed stream ( 20 ) in a stream methane reformer unit ( 23 ) to obtain a syngas stream ( 24 );   b) subjecting the syngas stream ( 24 ) to a shift reaction in a water gas shift reactor ( 25 ) to obtain a feed gas ( 19 );   c) subjecting the feed gas ( 19 ) to hydrogen purification in a process unit ( 0 ) to obtain a hydrogen product stream ( 27 ) and a hydrogen depleted process stream ( 1 );   d) 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 ) 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) adjusting the temperature of the optionally compressed portion of the process stream ( 1 ) in a heat exchanger ( 3 ) to a temperature from 20° C. to 150° C.;   g) 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 );   h) 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 in the water gas shift reactor ( 25 ), the process unit ( 0 ) or in both the water gas shift reactor ( 25 ) and the process unit ( 0 );   i) cooling the first hydrocarbon lean residue stream ( 6 ) in a heat exchanger ( 7 ) to a temperature equal to or less than −10° C.;   j) 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 );   k) withdrawing the carbon dioxide rich liquid stream ( 9 ) as carbon dioxide product for further use;   l) 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 second hydrogen lean residue stream ( 13 );   m) 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   n) 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 water gas shift reactor ( 25 ), the process unit ( 0 ) or both the water gas shift reactor ( 25 ) and the process unit ( 0 ), 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.   
     
     
         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 ( 20 ) is pre-reformed in at least one pre-reformer to form a pre-reformed gas stream that is then reformed in the steam methane reformer. 
     
     
         6 . 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. 
     
     
         7 . The process of  claim 6 , wherein the first hydrogen rich permeate stream ( 5 ) is recycled to be used as a supplemental feed stream in the water gas shift reactor ( 25 ). 
     
     
         8 . The process of  claim 6 , wherein the first hydrogen rich permeate stream ( 5 ) is recycled to be used as a supplemental feed stream in the process unit ( 0 ). 
     
     
         9 . The process of  claim 6 , wherein the first hydrogen rich permeate stream ( 5 ) is split into a primary fraction of the first hydrogen rich permeate stream ( 5 . 1 ) to be used as a supplemental feed stream to be added to the syngas stream ( 24 ) prior to being introduced into the water gas shift reactor ( 25 ) and a secondary fraction of the first hydrogen rich permeate stream ( 5 . 2 ) to be used as a supplemental feed stream to be added to the feed gas ( 19 ) 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 primary fraction of the first hydrogen rich permeate stream ( 5 . 1 ) is optionally heated prior to being added to the syngas stream ( 24 ). 
     
     
         11 . The process of  claim 10 , wherein the primary fraction of the first hydrogen rich permeate stream ( 5 . 1 ) is heated utilizing a heat exchanger ( 36 ). 
     
     
         12 . The process of  claim 11 , wherein the primary fraction of the first hydrogen rich permeate stream ( 5 . 1 ) is heated using steam. 
     
     
         13 . The process of  claim 12 , wherein the proportion of the fraction forming the primary fraction of the first hydrogen rich permeate stream ( 5 . 1 ) is greater than the secondary fraction of the first hydrogen rich permeate stream ( 5 . 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 primary fraction of the first hydrogen rich permeate stream ( 5 . 1 ) is determined by the load of the steam methane reformer unit ( 23 ) and the maximum capacity of the water gas shift reactor ( 25 ) with the remaining fraction of the hydrogen rich permeate stream ( 5 ) 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 ( 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. 
     
     
         16 . The process of  claim 15 , wherein the first hydrogen selective membrane separation unit ( 4 ) includes one or more hydrogen selective membranes, each membrane 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 hydrogen rich permeate stream ( 5 ) with the remaining components in the process stream ( 1 ) forming the hydrogen lean residue stream ( 6 ) on the residue side ( 4 . 2 ) of the membrane. 
     
     
         17 . The process of  claim 16 , wherein the second hydrogen selective membrane separation unit ( 11 ) 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 hydrogen rich permeate stream ( 12 ) with the remaining components in the carbon dioxide lean non-condensable stream ( 10 ) forming the hydrogen lean residue stream ( 13 ) on the residue side ( 11 . 2 ) of the membrane. 
     
     
         18 . The process of  claim 17 , 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 ). 
     
     
         19 . The process of  claim 16 , 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. 
     
     
         20 . The process of  claim 19 , 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. 
     
     
         21 . The process of  claim 20  wherein the one or more hydrogen selective membranes and the one or more carbon dioxide selective membranes are each membranes of the fiber type. 
     
     
         22 . The process of  claim 20 , wherein the one or more hydrogen selective membranes are different in type from the one or more carbon dioxide selective membranes. 
     
     
         23 . The process of  claim 13 , wherein the carbon dioxide rich liquid stream ( 9 ) that is withdrawn is vaporized to produce a carbon dioxide rich gas stream. 
     
     
         24 . The process of  claim 13 , wherein the pre-reforming is performed with the supply of heat. 
     
     
         25 . The process of  claim 13 , wherein the pre-reforming is performed in two or more adiabatic steps with heat supply between the two or more steps. 
     
     
         26 . The process of  claim 1 , wherein prior to the compression in step f), the process stream is passed through a filter. 
     
     
         27 . The process of  claim 1 , wherein one or both of the following occur: the first hydrogen rich permeate stream ( 5 ) is subjected to a shift reaction in an optional second water gas shift reactor ( 38 ) prior to being recycled to the water gas shift reactor ( 25 ), the process unit ( 0 ) or in both the water gas shift reactor ( 25 ) and the second hydrogen rich permeate stream ( 12 ) is subjected to a shift reaction in an optional third water gas shift reactor ( 39 ) prior to being recycled to the water gas shift reactor ( 25 ), the process unit ( 0 ) or both the water gas shift unit ( 25 ) and the process unit ( 0 ). 
     
     
         28 . The process of  claim 27 , wherein each water gas shift reactor ( 38 ,  39 ) is a low temperature water gas shift reactor. 
     
     
         29 . The process of  claim 1 , wherein the process stream ( 1 ) and/or the carbon dioxide lean non-condensable stream ( 10 ) are subjected to a shift reaction in an optional fourth water gas shift reactor ( 40 ) prior to being passed thorough the first hydrogen membrane separation unit ( 4 ) or the second hydrogen membrane separation and carbon dioxide membrane separation units ( 11 ,  14 ). 
     
     
         30 . The process of  claim 29 , wherein the each water gas shift reactor is a low temperature water gas shift reactor.