Hydrogen production

Abstract

The invention relates to a process for generating hydrogen. In this process an aqueous liquid is exposed to carbon dioxide and a current is passed through the aqueous liquid so as to generate hydrogen.

1 . A process for generating hydrogen, said process comprising the steps of:
 a) exposing an aqueous liquid to carbon dioxide at a pressure of about 2 to about 100 atmospheres; and   b) passing a current through the aqueous liquid so as to generate hydrogen.   
     
     
         2 . The process of  claim 1  wherein step b) is conducted at a pressure of about 2 to about 100 atmospheres. 
     
     
         3 . The process of  claim 1  wherein step a) comprises either passing a gas containing carbon dioxide through the aqueous liquid or exposing the surface of the aqueous liquid to a gas containing carbon dioxide or both. 
     
     
         4 . The process of  claim 3  wherein the gas is released to the atmosphere following step a) whereby the process is a process for reduction of emissions of carbon dioxide into the atmosphere. 
     
     
         5 . The process of  claim 4  wherein the gas in step a) is a waste gas from an industrial process. 
     
     
         6 . The process of  claim 1  wherein step a) comprises exposing the aqueous liquid to a gas containing carbon dioxide, said carbon dioxide having a partial pressure in said gas of at least about 0.01 atmospheres. 
     
     
         7 . The process of  claim 6  wherein the gas comprises at least about 95% carbon dioxide on a volume basis. 
     
     
         8 . The process of  claim 1  wherein the aqueous liquid comprises an electrolyte which is not derived from the carbon dioxide. 
     
     
         9 . The process of  claim 1  wherein the aqueous liquid has no electrolyte other than an electrolyte derived from splitting of water by the carbon dioxide. 
     
     
         10 . The process of  claim 1  wherein the aqueous liquid is at a temperature of less than about 15° C. 
     
     
         11 . The process of  claim 1  wherein the current is applied under a voltage of about 0.1 to about 50V. 
     
     
         12 . The process of  claim 11  wherein the voltage is less than about 1.3V. 
     
     
         13 . The process of  claim 1  wherein step b) is conducted at a voltage of about 0.4 to about 4V, whereby the process produces oxygen at the anode. 
     
     
         14 . The process of  claim 13  additionally comprising using the oxygen in Oxyfuel combustion. 
     
     
         15 . The process of  claim 1  wherein the current is less than about 20 amps. 
     
     
         16 . The process of  claim 1  wherein step b) comprises applying a voltage between a cathode and an anode, wherein the cathode is at least partially immersed in the aqueous liquid and the anode is in electrical communication with the aqueous liquid. 
     
     
         17 . The process of  claim 1  wherein hydrogen evolved in said process is at least partially purified by passing through a gas separation membrane. 
     
     
         18 . The process of  claim 1  additionally comprising:
 c) reacting the hydrogen with carbon dioxide so as to produce methane and water. 
 
     
     
         19 . The process of  claim 1  wherein the carbon dioxide is derived from the combustion of a fossil fuel. 
     
     
         20 . The process of  claim 1  wherein the process is conducted in an electrolyser comprising a proton exchange membrane or a polymer electrolyte membrane (PEM). 
     
     
         21 . A method of producing methane and water comprising:
 a) exposing an aqueous liquid to carbon dioxide at a pressure of about 2 to about 100 atmospheres; and   b) passing a current through the aqueous liquid so as to generate hydrogen; and   c) reacting the hydrogen with carbon dioxide so as to produce methane and water.   
     
     
         22 . A method for increasing the rate of hydrogen production in electrolysis of an aqueous solution, said method comprising exposing the aqueous solution to carbon dioxide prior to and/or during said electrolysis at a pressure of about 2 to about 100 atmospheres. 
     
     
         23 . The method of  claim 22  wherein the carbon dioxide is, or is derived from, and industrial waste gas.