Process for removing tar-forming high molecular weight hydrocarbons from gas mixture

Abstract

Method for production of iron carbide while removing tar-forming hydrocarbons from effluent gas mixtures from Chemical Vapor Deposition or Chemical Vapor Infiltration processes. Method includes passing effluent gas mixture containing hydrogen, methane, and high molecular weight hydrocarbons through a bed that contains iron pellets at elevated temperature, thereby decomposing tar-forming high molecular weight hydrocarbons in the effluent gas mixture and forming iron carbide. The process can be used to clean up effluent streams and/or for carbon sequestration. Apparatus including a de-tarring vessel ( 5 ) having a packed bed ( 7, 8, 9 ) of iron or iron oxide pellets ( 1 ) resting over a perforated distributor plate ( 2 ) and having an exhaust port ( 12 ), the de-tarring vessel being operatively linked via an exhaust port ( 6 ) to a CVI or CVD reactor vessel.

1 . A process for the production of iron carbide which comprises the step of passing a CVD/CVI effluent gas mixture containing hydrogen, methane, and high molecular weight hydrocarbons through a bed that contains iron pellets at an elevated temperature in order to convert a portion of the iron in said pellets into iron carbide while removing tar-forming high molecular weight hydrocarbons from said gas mixture.  
     
     
         2 . The process of  claim 1 , wherein said iron pellets comprise iron oxide or metallic iron.  
     
     
         3 . The process of  claim 2 , wherein the diameters of said iron pellets range from 1 to 10 centimeters.  
     
     
         4 . The process of  claim 3 , wherein the diameters of said iron pellets range from 1 to 4 centimeters.  
     
     
         5 . The process of  claim 1 , wherein said gas mixture contains 25 or less weight-% hydrogen, 50 or less weight-% methane, and 3 to 30 weight-% tar-forming high molecular weight hydrocarbons.  
     
     
         6 . The process of  claim 5 , wherein the ratio of hydrogen gas to carbon in said gas mixture ranges from 2:1 through 5:1.  
     
     
         7 . The process of  claim 1 , wherein said elevated temperature is in the range 400° C. through 1100° C.  
     
     
         8 . The process of  claim 7 , wherein said elevated temperature is approximately 600° C.  
     
     
         9 . The process of  claim 1 , wherein said gas mixture is an effluent from a Chemical Vapor Deposition process or from a Chemical Vapor Infiltration process.  
     
     
         10 . The process of  claim 9 , wherein said Chemical Vapor Deposition (CVD) process or Chemical Vapor Infiltration (CVI) process deposits carbon in a fibrous matrix.  
     
     
         11 . The process of  claim 10 , wherein said fibrous matrix comprises pitch and/or polyacrylonitrile derived carbon fibers.  
     
     
         12 . The process of  claim 11 , wherein the carbonized fibrous matrix is a carbon-carbon composite configured as an aircraft brake disc.