A New Process for Renewable Methane Production Utilizing Carbon Dioxide Captured from Air
Large scale integration of renewable wind and solar energy into the electrical grid is challenged due to volatility of power supply. Hence, there is need for a technology allowing storing excess electricity produced by these fluctuating sources of renewable energy. Power-to-Gas (P2G) process is a perspective approach to renewable energy storage in chemical media. The first step of P2G process is hydrogen generation through electrolysis of water using renewable electrical energy. Considering safety issues regarding hydrogen transportation and storage, it is reasonable to use it on site for methane production via catalytic Sabatier reaction: CO2 + 4H2 = CH4 + 2H2O.
Generated methane, also referred to as synthetic or substitute natural gas (SNG), is a promising energy carrier which can be used as fuel for numerous industrial applications. Renewable methane production by Sabatier process (2) requires a sustainable source of carbon dioxide, e.g. ambient air, which contains ~ 400 ppm CO2. Carbon dioxide can be concentrated from ambient air via direct air capture (DAC) process. Incorporation of the DAC unit with into P2G system offers an opportunity to use anthropogenic carbon dioxide as a valuable feedstock for the production of renewable fuel.
The main goal of our research was to design the Direct Air Capture/Methanation (DACM) process, which would effectively combine CO2 capture from ambient air and methane production from captured CO2 by Sabatier reaction over commercial nickel catalyst. The composite material K2CO3/Al2O3, which is a promising solid absorbent for direct CO2 capture from ambient air, has been synthesized and studied in temperature swing adsorption cycles. It has been shown that the increase in the outer heater temperature from 200 to 325°C during the thermal regeneration step affects the utilization extent of the composite sorbent in the cycle with total CO2 uptake rising from 1.9 to 4.4 wt. %. Further heater temperature increase up to 400°C has not resulted in any significant change in the total CO2 uptake by the material. The process combing thermal regeneration of the composite sorbent in hydrogen atmosphere at T = 325oC and CO2 methanation reaction over commercial nickel catalyst NKM-2V at T = 425oC was studied using the catalytic reactor connected to the outlet of the adsorber with the composite sorbent during the thermal regeneration step in H2 flow. It has been demonstrated that it is possible to transform CO2 into methane with conversion >99 %.