Hydrate-based Carbon Capture via Pressure Swing in a Packed Bed of Ice

The formation of mixed gas hydrates for pre- or post-combustion capture of carbon dioxide is considered a promising alternative to conventional carbon capture technologies. Yet, to keep up with conventional technologies or even reduce the cost of capture associated with them, a hydrate-based technology must have (1) a short induction time, (2) fast formation kinetics, and (3) moderate process conditions. To date, these requirements can only be met by adding promoters to the system, which comes at its own cost and disadvantages. Here, we show that the requirements can also be met without promoters by forming mixed gas hydrates in a packed bed of ice stabilized by fumed silica. While the high specific surface area of the packed bed warrants short induction times and fast kinetics, low temperatures ensure both moderate formation pressures and a high CO2 selectivity. The favorable properties can be maintained and even improved upon over many capture/regeneration cycles when operated at temperatures lower than 253 K, as this ensures a continuous formation of pores in the ice. We demonstrate the advantages of this route for carbon capture on a bench scale through batch, semi-batch, and continuous experiments. In semi-batch operation at 233 K and 40 bar, the mole fraction of CO2 in a synthetic flue gas is reduced from 15 mol% to 2.5 mol%. At the same thermodynamic conditions, a split fraction of 70% and a specific energy consumption below 3.0 GJ/tCO2 are achieved in continuous operation. The inherent advantages and simplicity of this process, a specific energy consumption comparable with the state of the art even though entirely based on the bench-scale experiment, as well as environmental harmlessness, emphasize the potential of this hydrate-based process to meet the demands of the industry at a minimal cost of capture.