Efficient Conversion of Carbon Dioxide into Methane using 3rd Generation Ionic Liquids

This work directly addresses a technology of interest listed in Section 9, sub-section H1.01 In-Situ Resource Utilization, specifically "Highly efficient reactors for carbon monoxide/carbon dioxide (CO/CO2) conversion into methane (CH4)." The proposal will investigate combining recent work that demonstrates outstanding CO2 sorption by third generation ionic liquids (ILs) without an increase in viscosity (even in the presence of water) with adaptations of recently developed methodology for electrochemically reducing and polymerizing CO2 in an aqueous IL to polyethylene. The intention is to demonstrate that this methodology is an excellent candidate for creating a highly efficient reactor for carbon dioxide conversion to methane. Unlike conventional electrolytes, ILs generally have very low vapor pressures. This will make it possible for them to be used in the much lower pressure Martian atmosphere without the problem of evaporation. Our goal is to build on the results achieved by other research groups by using our own knowledge and years of experience working with ILs, including electrochemistry, to efficiently reduce CO2. We will prepare the task-specific 3rd generation ILs and then measure their electrochemical properties; i.e., conductivity, electrochemical window, etc. These are currently unknown but are important in order to ascertain whether these ILs are suitable for this application. Anticipating this will be the case, we will then test various electrodes, including TiO2 and silver cathodes, to determine which gives the most selective reduction of CO2 to methane. The efficiency of the process (including power requirements) will be quantified and compared to the Sebatier and Fischer-Tropsch processes.

The proposed electrochemical reduction of CO2 using 3rd generation ionic liquids will provide a means to produce methane from atmospheric CO2 in low pressure and temperature environments such as those found on Mars. The product selectivity and efficiency is thought to be governed by the mass diffusion profile in the electrochemical cell. Consequently, methane quality and conversion rates can be optimized to space applications by the proposed characterization of electrode interfaces. The low volatility, low vapor pressure and anticipated viscosity when loaded with CO2 makes 3rd generation ionic liquids an excellent choice for investigation of applications in both space and terrestrial environments. Since one of NASA's main goals is to produce methane propellant from the CO2 found in the Martian atmosphere, we also propose to determine the effects of small quantities of Martian dust. Any practical space hardware operating on Mars will be designed to capture CO2 directly from the Martian atmosphere. There will no doubt be some sort of filter mechanism in line, but some contaminants are likely to get into the IL. Our group has considerable experience working with meteorites. We will use powder from well characterized Martian meteorites to provide the dust contamination.

Supercritical CO2 (scCO2) extraction is a highly efficient but costly industrial process. It is anticipated that increasing the CO2 in the bulk phase ionic liquid (IL) electrolyte will not lead to large increases in the bulk phase viscosity which is a critical issue in previous studies with IL/CO2 equilibriums. If so, the low viscosity of the saturated IL media will make them excellent candidates for improving supercritical fluid extraction efficiencies and reducing capital costs; scCO2 and ILs are environmentally friendly alternatives to replace traditional solvents. The IL could be integrated into both upstream and downstream syngas production in gas-to-liquid type plants. Application in the water gas shift reactor layout could provide a low temperature route for electrochemically controlling the CO:H2 ratio and impurity of the feed stream into the Fischer-Tropsch reactor which is critical to the operating costs. Downstream processing and recycling could be enhanced as well by replacing or working in tandem with methyldiethanol amine units for increased waste gas absorption and carbon recycle efficiency. The same downstream recycle system could easily be scaled down and adapted for lower capacity carbon sequestering. This has the potential to work in tandem with scCO2 technology to improve syngas production while also reducing costs and improving efficiency for scCO2 separation units.

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