What is syngas?
Syngas is a valuable chemical that is used to produce a host of different chemicals and fuels including methanol, heavy alcohols (e.g., ethanol), acetyls, formaldehyde, methyl tertiary-butyl ether (MTBE), and Fischer-Tropsch liquid fuels (Figure 5). For some synthesis processes, a low H2:CO ratio syngas is preferred.
Traditionally, syngas is produced by steam methane reforming (SMR) with natural gas (mostly methane) as one of the feedstocks. SMR offers an H2/CO molar ratio ranging from 3 to 5 (3–5 times as much hydrogen as carbon monoxide). However, such a ratio is too high for downstream processing to various Fischer-Tropsch chemicals mentioned that typically require an H2/CO molar ratio between 1 and 3.
Steam and Dry Methane Reforming Processes
Syngas produced by SMR must be separated through an expensive gas separation process and then recombined in the desired ratio. To avoid this high cost, dry methane reforming (DMR) presents an attractive alternative because it produces syngas with an intrinsic H2/CO ratio of 1-3 in a single-step process. DMR also consumes CO2, a greenhouse gas. Currently, DMR reaction is performed using the thermal-catalytic DMR process, which is performed in a high-temperature bed filled with proprietary catalysts. Although thermal-catalytic DMR offers a suitable H2/CO ratio, the catalysts are known to suffer from deactivation by carbon deposition, or “coke” formation to deactivate the catalyst and block the feedstream flow. Therefore, high-temperature, high-pressure steam, which is expensive to generate, must be added to the thermal-catalytic DMR reactor to prevent excessive coking. As a result, the operating cost of thermal-catalytic DMR still remains high.
DOE Project Spotlight
In a DOE SBIR Program “Plasma Catalysis for CO2 utilization” (Award Number DE-SC0019664), ACT is developing plasma-assisted methane reforming (PAMR) and catalyst decoking technology. This technology has several advantages:
- It can produce syngas at much lower temperatures (20–550 °C), which is considered too low for the thermal-catalytic DMR (800–900 °C) as shown in Figure 6a.
- Ability to be rapidly turned on and off to make use of inexpensive electricity (the primary operating expense) when available.
- Studies show it to reduce or even eliminate problems with coking which is the most troubling problem for traditional DMR (Figure 6b,c). This can further reduce or eliminate the need for steam addition, directly reducing the production cost of the syngas.
Pearlman, H. et al. Plasma-Assisted Dry Methane Reforming for Syngas Production. in Spring Technical Meeting Eastern States Section of the Combustion Institute (2018).
Xiao, Y. et al. Efficient plasma-assisted methane reforming and catalyst decoking. In 49th IEEE International Conference on Plasma Science (2022).
Uddi, M. et al. Efficient plasma-assisted dry methane reforming, Invited talk in 23rd International Conference on Solid State Ionics (2022).
Ranganathan, R. v, Talukdar, S. & Uddi, M. Optical Diagnostics of Plasma Assisted Chemical Looping Reactions. IEEE Transactions on Plasma Science 50, 899–910 (2022).
Ranganathan, R. v. et al. Plasma-catalysis chemical looping CH4 reforming with water splitting using ceria supported Ni based La-perovskite nano-catalyst. Journal of CO2 Utilization 32, 11–20 (2019).