Methods for treating an offgas containing carbon oxides
A method of treating an offgas includes purifying the offgas to remove particulate matter, water, undesirable gaseous components and inert gases to produce a dried carbon oxide gas feedstock, and converting at least a portion of carbon oxides in the dried carbon oxide gas feedstock into solid carbon. In other embodiments, a method includes passing a dried carbon oxide gas feedstock through a multi-stage catalytic converter. A first stage is configured to catalyze methane-reforming reactions to convert methane into carbon dioxide, carbon monoxide and hydrogen with residual methane. A second stage is configured to catalyze the Bosch reaction and convert carbon oxides and hydrogen to solid carbon and water.
1. A method of treating an offgas, the method comprising:
reacting at least one carbon oxide gas in an offgas from a first unit operation comprising an aluminum smelter or a steel smelter with a reducing gas to form water and at least one of carbon monoxide and carbon dioxide, wherein the offgas comprises the at least one carbon oxide gas, water vapor, and particulate matter;
removing at least a portion of particulate matter from the offgas to produce an intermediate stream;
condensing water vapor from the intermediate stream to produce a dried carbon oxide feedstock gas;
mixing at least one reducing gas with the dried carbon oxide feedstock gas to form a reaction gas mixture;
converting at least a portion of the carbon oxide gas in the reaction gas mixture into solid carbon while forming a gas stream containing water vapor;
processing at least a portion of the solid carbon in a second unit operation to form a recycle feedstock comprising the at least a portion of the solid carbon; and
recycling the recycle feedstock to the first unit operation.
2. The method of claim 1 , further comprising separating and concentrating the at least one carbon oxide gas of the dried carbon oxide feedstock gas to produce a concentrated carbon oxide feedstock.
3. The method of claim 1 , further comprising removing at least a portion of non-carbon oxide gases from the intermediate stream.
4. The method of claim 3 , wherein removing at least a portion of non-carbon oxide gases from the intermediate stream comprises producing the dried carbon oxide-containing gas feedstock to consist essentially of carbon oxides.
5. The method of claim 1 , wherein converting at least a portion of the carbon oxide gas in the reaction gas mixture into solid carbon comprises contacting the reaction gas mixture with a catalyst at a temperature above about 400° C.
6. The method of claim 1 , wherein converting at least a portion of carbon oxide gas in the reaction gas mixture into solid carbon comprises forming carbon nanotubes.
7. The method of claim 1 , wherein converting at least a portion of the carbon oxide gas in the reaction gas mixture into solid carbon comprises forming essentially pure carbon comprising at least one material selected from the group consisting of graphite, graphene, carbon black, soot, fibrous carbon, buckminsterfullerenes, carbon nanotubes, carbon platelets, amorphous carbon and nanodiamond.
8. The method of claim 1 , wherein converting at least a portion of the carbon oxide gas in the reaction gas mixture into solid carbon comprises reacting at least one material selected from the group consisting of carbon monoxide and carbon dioxide with a reducing gas to form solid carbon and water, the reducing gas comprising at least one material selected from the group consisting of hydrogen, alkanes, and alcohols.
9. The method of claim 1 , wherein removing at least a portion of the particulate matter from the offgas to produce an intermediate stream comprises removing substantially all particulate matter from the offgas.
10. The method of claim 1 , further comprising reacting oxygen in the offgas with the reducing gas to form water and at least one material selected from the group consisting of carbon monoxide and carbon dioxide.
11. The method of claim 10 , wherein reacting oxygen in the offgas with the reducing gas comprises reacting oxygen in the offgas with at least one material selected from the group consisting of an alkane, an alcohol, or another hydrocarbon.
12. The method of claim 10 , further comprising recycling at least a portion of the solid carbon to a unit operation configured to produce the offgas.
13. The method of claim 12 , wherein recycling at least a portion of the solid carbon to a unit operation configured to produce the offgas comprises recycling the solid carbon to an aluminum smelter or a steel smelter to form at least one material selected from the group consisting of metal matrix composites, electrodes for electric arc furnaces, and carbon raisers.
14. The method of claim 1 , wherein condensing water vapor from the intermediate stream to produce a dried carbon oxide gas feedstock comprises forming the dried carbon oxide gas feedstock to have a dew point of less than about 10° C.