Novel process for removal of nitrogen from natural gas

Abstract

A method for removing nitrogen from natural gas includes contacting substantially dry natural gas that contains unwanted nitrogen with lithium metal. The nitrogen reacts with lithium to form lithium nitride, which is recovered for further processing, and pipeline quality natural gas. The natural gas may optionally contain other chemical species that may be reduced by lithium, such as carbon dioxide, hydrogen sulfide, and small amounts of water. These lithium reducible species may be removed from the natural gas concurrently with the removal of nitrogen. The lithium nitride is subjected to an electrochemical process to regenerate lithium metal. In an alternative embodiment, lithium nitride is reacted with sulfur to form lithium sulfide and nitrogen. The lithium sulfide is subjected to an electrochemical process to regenerate lithium metal and sulfur. The electrochemical processes are advantageously performed in an electrolytic cell containing a lithium ion selective membrane separator.

What is claimed is: 
     
         1 . An electrochemical cell for the electrochemical decomposition of lithium nitride comprising:
 an anolyte compartment configured with an anode and capable of housing a quantity of anolyte, the anolyte comprising lithium nitride;   a catholyte compartment configured with a cathode and capable of housing a quantity of catholyte, the catholyte comprising a lithium ion conductive liquid;   a lithium ion selective separator that divides the anolyte compartment and the catholyte compartment; and   a source of electric potential, wherein
 the anode and the cathode are electrically connected to the source of electric potential, and 
 the source of electric potential reduces the lithium metal ions in the catholyte compartment to form elemental lithium metal. 
   
     
     
         2 . The electrochemical cell of  claim 1 , wherein the separator is microporous polymer separator or a microporous ceramic separator. 
     
     
         3 . The electrochemical cell of  claim 1 , wherein the separator is a LiSICON membrane. 
     
     
         4 . The electrochemical cell of  claim 1 , wherein there is little or no gap between the cathode and lithium ion selective separator. 
     
     
         5 . The electrochemical cell of  claim 1 , wherein the cathode comprises a cathode material selected from the group consisting of nickel, copper, titanium, stainless steel, and carbonaceous materials. 
     
     
         6 . The electrochemical cell according to  claim 1 , wherein the anode comprises an anode material selected from the group consisting of stainless steel, carbon steel, nickel-cobalt-ferrous, platinum, lead dioxide, and carbonaceous materials. 
     
     
         7 . The electrochemical cell of  claim 1 , wherein the wherein the lithium nitride is dissolved in a low melting molten salt or an ionic liquid. 
     
     
         8 . The electrochemical cell of  claim 7 , wherein the low melting molten salt is selected from the group consisting of a lithium halo-aluminate, eutectic of lithium halide and an non-lithium alkali metal halide, and a molten lithium bis(fluorosulfonyl) imide. 
     
     
         9 . The electrochemical cell of  claim 7 , wherein the ionic liquid selected from the group consisting of N-methyl-N-alkylpyrrolidinium, bis(fluoromethanesulfonyl)amide and 1-alkyl-3-methylimidazolium tetrafluoroborate. 
     
     
         10 . The electrochemical cell of  claim 1 , wherein the lithium ion conductive liquid comprises a lithium metal salt dissolved in a polar solvent or an ionic liquid solvent. 
     
     
         11 . The electrochemical cell of  claim 10 , wherein the lithium metal salt is selected from the group consisting of lithium chloride, lithium bromide, lithium iodide, lithium perchlorate and lithium hexafluorophosphate. 
     
     
         12 . The electrochemical cell of  claim 10 , wherein the ionic liquid solvent is N-butyl-N-methylpyrrolidinium bis(fluoromethanesulfonyl)imide (Pyr 14 FSI) containing dissolved LiFSI. 
     
     
         13 . The electrochemical cell of  claim 1 , wherein the cell is operated at a temperature below the melting temperature of the lithium. 
     
     
         14 . The electrochemical cell of  claim 1  wherein the anolyte further comprises one or more of lithium polysulfide, lithium carbonate, and lithium hydroxide. 
     
     
         15 . An electrochemical cell for the electrochemical decomposition of lithium polysulfide comprising:
 an anolyte compartment configured with an anode and capable of housing a quantity of anolyte, the anolyte comprising lithium polysulfide ;   a catholyte compartment configured with a cathode and capable of housing a quantity of catholyte, the catholyte comprising a lithium ion conductive liquid;   a lithium ion selective separator that divides the anolyte compartment and the catholyte compartment; and   a source of electric potential, wherein
 the anode and the cathode are electrically connected to a source of electric potential, and 
 the source of electric potential oxidizes the lithium sulfide in the anolyte compartment to form elemental sulfur and reduces lithium ions in the catholyte compartment to produce lithium metal. 
   
     
     
         16 . The electrochemical cell of  claim 15 , wherein the separator is microporous polymer separator or a microporous ceramic separator. 
     
     
         17 . The electrochemical cell of  claim 15 , wherein the separator is a LiSICON membrane. 
     
     
         18 . The electrochemical cell of  claim 15 , wherein there is little or no gap between the cathode and lithium ion selective separator. 
     
     
         19 . The electrochemical cell of  claim 15 , wherein the cathode comprises a cathode material selected from the group consisting of nickel, copper, titanium, stainless steel, and carbonaceous materials. 
     
     
         20 . The electrochemical cell according to  claim 15 , wherein the anode comprises an anode material selected from the group consisting of stainless steel, nickel, iron, iron alloys, and nickel alloys. 
     
     
         21 . The electrochemical cell of  claim 15 , wherein the lithium polysulfide is dissolved in an organic solvent selected from dimethyl ether or tetraglyme. 
     
     
         22 . The electrochemical cell of  claim 15  wherein the lithium ion conductive liquid comprises a lithium metal salt dissolved in a polar solvent or an ionic liquid solvent. 
     
     
         23 . The electrochemical cell of  claim 22 , wherein the polar solvent is selected from the group consisting of tetraglyme, diglyme, dimethyl carbonate, dimethoxy ether, propylene carbonate, ethylene carbonate, diethyl carbonate, and combinations thereof. 
     
     
         24 . The electrochemical cell of  claim 15 , wherein the lithium metal salt is selected from the group consisting of lithium chloride, lithium bromide, lithium iodide, lithium perchlorate, and lithium hexafluorophosphate. 
     
     
         25 . A method for removing nitrogen from natural gas comprising:
 providing substantially dry natural gas, wherein the natural gas contains nitrogen;   contacting the natural gas with lithium metal to cause the nitrogen to react with lithium to form lithium nitride;   recovering the lithium nitride;   disposing the lithium nitride in an electrolytic cell, comprising an anode and a cathode electrically connected to a source of electric potential; and   applying an electric potential to the electrolytic cell to oxidize the lithium nitride at the anode to produce nitrogen, and to reduce lithium ions at the cathode to regenerate lithium metal.   
     
     
         26 . The method of  claim 25 , wherein the electrolytic cell comprises of a lithium ion selective separator that divides the electrolytic cell between an anolyte compartment containing an anode, and a catholyte compartment containing a cathode. 
     
     
         27 . The method of  claim 25 , wherein the lithium nitride is dissolved in a non-aqueous solvent disposed in the electrolytic cell. 
     
     
         28 . The method of  claim 27 , wherein the non-aqueous solvent is a low melting molten salt, selected from the group consisting of a lithium halo-aluminate, eutectic of lithium halide and an non-lithium alkali metal halide, and a molten lithium bis(fluorosulfonyl) imide. 
     
     
         29 . The method of  claim 27 , wherein the non-aqueous solvent is a room temperature ionic liquid selected from the group consisting of N-methyl-N-alkylpyrrolidinium, bis(fluoromethanesulfonyl)amide and 1-alkyl-3-methylimidazolium tetrafluoroborate. 
     
     
         30 . The method of  claim 26 , wherein the separator is a microporous polymer separator. 
     
     
         31 . The method of  claim 26 , wherein the separator is a microporous ceramic separator. 
     
     
         32 . The method of  claim 26 , wherein the separator is a LiSICON membrane. 
     
     
         33 . The method of  claim 26 , wherein there is little or no gap between the cathode and lithium ion selective separator. 
     
     
         34 . The method of  claim 25 , wherein the cathode comprises a cathode material selected from the group consisting of nickel, copper, titanium, stainless steel, and carbonaceous materials. 
     
     
         35 . The method of  claim 25 , wherein the anode is porous. 
     
     
         36 . The process according to  claim 25 , wherein the anode comprises an anode material selected from the group consisting of stainless steel, carbon steel, nickel-cobalt-ferrous, platinum, lead dioxide, and carbonaceous materials. 
     
     
         37 . The method of  claim 25 , wherein the natural gas further comprises one or more lithium reducible species selected from the group consisting of carbon dioxide, hydrogen sulfide, water and mixtures thereof.