Novel Schemes for CO2 Utilization Using Methane Bi-Reforming and Carbon Formation Reactions

Production of synthesis gas (CO and H₂) can be derived from methane via CO₂ (dry) or steam reforming. Typical applications of the reformate product gas are the production of methanol, or synthetic fuels via Fischer-Tropsch synthesis. Since a 2:1 ratio of H₂ to CO is optimal for these processes; and since CO₂ is a pollutant, the two reforming pathways can ideally run in concert (bi-reforming). The net result is utilization of an undesirable gas (CO₂), a favorable H₂/CO ratio, and coke suppression due to the presence of steam. Therefore, process schemes are explored, which utilize CO₂ for the conversion of CH₄ to synthesis gas and finally the production of methanol or Fischer-Tropsch liquids.  The carbon footprint of CH₄ steam reforming (owed to the CO₂ produced during combustion of CH₄ for generation of the heat required for the endothermic reforming reactions) can be partially offset by employing bi-reforming and/or reverse water gas shift schemes. However, offsetting sequestered CO₂ streams (e.g., from coal power plants) requires additional reactions.           

The objective of this work is to valorize carbon dioxide by producing liquid fuels and solid carbon. The concept explored is an indirect chemical recycling of CO₂ as a valuable carbon source. The overall objective is to explore sustainable carbon cycles of fuel production and consumption by focusing on concentrated CO₂ conversion, instead of storage.  Carbon formation can be recovered utilizing CO₂ via the Boudouard and/or CO hydrogenation reactions.  In streams deficient in H₂, but rich in CO and CO₂, the forward-Boudouard reaction is sought with purpose: the carbon sequestered safely as an inert solid. On an industrial scale, the Boudouard reaction can be staged; the first stage for bulk conversion to filamentous carbon using Fe/Fe₂O₃ (for sequestration) and CO₂, and a second stage (at a now greatly reduced through-put) tailored for structured carbon formation using Fe-Mo/MoO₂ (a valuable product). Therefore, CO₂ can be utilized in a number processes involving bi-reforming and carbon formation reaction. This presentation will analyze CO₂ utilization process flowsheets (such as this of Figure 1) and experimental results on the carbon formation conversion on Fe-based catalysts.

 

Figure 1: Coupling of DMR SMR, RWGS, C formation and FTS for CO₂-neutral liquid fuels production.