Anodes for the Electrolytic Production of Nitrogen Trifluoride and Fluorine

Abstract

A process and an anode for the production of nitrogen trifluoride or fluorine where the anode in the electrolytic cell is made primarily from parallel ordered anisotropic carbon, including needle coke and/or mesocarbon microbeads. The parallel ordered anisotropic carbon anodes minimize the production of CF 4 and improve the purity of the nitrogen trifluoride or fluorine gas produced. Additionally, the anodes may be molded, instead of extruded or machined, providing for improved dimensional and mechanical integrity of the anode.

What is claimed is: 
     
         1 . A process of producing nitrogen trifluoride or fluorine comprising:
 performing electrolysis of an electrolyte by using an electrolytic anode comprising primarily parallel ordered anisotropic carbon to obtain nitrogen trifluoride or fluorine.   
     
     
         2 . The process according to  claim 1 , wherein the parallel ordered anisotropic carbon comprises needle coke. 
     
     
         3 . The process according to  claim 2 , wherein the anode comprises:
 at least 60% needle coke; and   optionally, 0 to 40% of a binding agent.   
     
     
         4 . The process according to  claim 3 , wherein the anode comprises the binding agent and the binding agent is pitch. 
     
     
         5 . The process according to  claim 2 , wherein the anode comprises the binding agent, and the needle coke and binding agent are isostatically pressed into a form. 
     
     
         6 . The process according to  claim 2 , wherein the anode comprises the binding agent, and the needle coke and binding agent have an average particle size of less than 25 microns. 
     
     
         7 . The process according to  claim 2 , wherein the needle coke is not graphitized. 
     
     
         8 . The process according to  claim 1 , wherein the parallel ordered anisotropic carbon comprises mesocarbon microbeads. 
     
     
         9 . The process according to  claim 8 , wherein the mesocarbon microbeads are isostatically pressed mesocarbon microbeads. 
     
     
         10 . The process according to  claim 8 , wherein the mesocarbon microbeads have an average particle size of about 1-5 microns. 
     
     
         11 . The process according to  claim 8 , wherein the mesocarbon microbeads are not graphitized. 
     
     
         12 . The process according to  claim 1 , wherein the parallel ordered anisotropic carbon comprises mesophase carbon, and the anode comprises:
 at least 40% mesophase carbon; and   optionally, up to 10% of a stabilizing aid.   
     
     
         13 . The process according to  claim 1 , wherein the anode has a density of 1.7 g/cm 3  or higher. 
     
     
         14 . The process according to  claim 1 , wherein the anode consists of molded and self-sintered mesocarbon microbeads and optionally a sintering aid. 
     
     
         15 . The process according to  claim 1 , wherein the anode has an active area up to about 70,000 cm 2 . 
     
     
         16 . The process according to  claim 1 , wherein the process produces less than 100 ppm of CF 4  in pure nitrogen trifluoride or fluorine. 
     
     
         17 . The process according to  claim 1 , wherein the process produces less than 25 ppm of CF 4  in pure nitrogen trifluoride or fluorine. 
     
     
         18 . The process according to  claim 1 , wherein the process produces nitrogen trifluoride or fluorine with a selectivity of 70% or greater. 
     
     
         19 . The process according to  claim 1 , wherein the process produces nitrogen trifluoride or fluorine with a selectivity of 80% or greater. 
     
     
         20 . The process according to  claim 1 , wherein nitrogen trifluoride is produced and the electrolyte is a ternary electrolyte composition comprising HF, NH 4 F, and KF. 
     
     
         21 . The process according to  claim 20 , wherein the ternary electrolyte composition comprises 35-45 wt % HF, 15-25 wt % NH 4 F, and 40-45 wt % KF. 
     
     
         22 . The process according to  claim 1 , wherein fluorine is produced and the electrolyte is a binary electrolyte composition comprising HF and KF. 
     
     
         23 . The process according to  claim 1 , wherein nitrogen trifluoride is produced and the electrolyte is electrolyzed at a temperature of about 120-140° C. 
     
     
         24 . The process according to  claim 1 , wherein fluorine is produced and the electrolyte is electrolyzed at a temperature of about 80-90° C. 
     
     
         25 . The process according to  claim 1 , wherein the process is operated at a current density of about 70-250 mA/cm 2 . 
     
     
         26 . The process according to  claim 1 , wherein nitrogen trifluoride is produced and the process is operated at a current density of about 100-250 mA/cm 2 . 
     
     
         27 . The process according to  claim 1 , wherein fluorine is produced and the process is operated at a current density of about 120-250 mA/cm 2 . 
     
     
         28 . An electrolytic cell for producing nitrogen trifluoride or fluorine comprising:
 an anode comprising parallel ordered anisotropic carbon;   a cathode; and   an electrolyte composition comprising HF, optionally KF, and optionally NH 4 F,   wherein the electrolytic cell is operated to produce nitrogen trifluoride or fluorine.   
     
     
         29 . The electrolytic cell according to  claim 28 , wherein the anode consists of self-sintered isostatically pressed mesocarbon microbeads and optionally a sintering aid. 
     
     
         30 . The electrolytic cell according to  claim 28 , wherein the anode consists of needle coke and pitch binder. 
     
     
         31 . The electrolytic cell according to  claim 30  in which the pitch binder and the needle coke are first blended and then ground prior to pressing. 
     
     
         32 . The electrolytic cell according to  claim 28 , where the anode exhibits retained wettability without the addition of a wetting agent.