Solid materials containing amines are being studied as part of potential CO2 sequestration programmes designed to reduce the impact of the greenhouse gas.
Although these adsorbent materials do a good job of trapping the carbon dioxide, commonly used techniques for separating the CO2from the amine materials − thereby regenerating them for reuse − seem unlikely to be suitable for high-volume industrial applications.
Now, researchers have demonstrated a relatively simple regeneration technique that could use the waste steam generated by many facilities that burn fossil fuels. This steam-stripping technique could produce concentrated carbon dioxide ready for sequestration in the ocean or deep-earth locations − while readying the amine materials for further use.
’We have demonstrated an approach to developing a practical adsorption process for capturing carbon dioxide and then releasing it in a form suitable for sequestration,’ said Christopher Jones, a professor in the School of Chemical and Biomolecular Engineering at the Georgia Institute of Technology.
The work was supported by New York-based Global Thermostat, a company that is developing and commercialising technology for the direct capture of carbon dioxide from the air.
Amine sorbents are often regenerated through a process that involves a change in temperature to supply the energy required to break the amine-carbon-dioxide chemical bonds.
For convenience, researchers commonly remove the CO2 by heating the amine material in the presence of a flowing gas, such as nitrogen or helium. That removes the carbon dioxide, but mixes it with the flowing gas − regenerating the material, but leaving the CO2 mixed with nitrogen or helium.
Another approach is to heat the material in a carbon-dioxide stream, but that is less efficient and can lead to fouling of the amine.
Jones and his team from Georgia Tech, SRI and Global Thermostat took a different approach, heating sorbent amines in steam at a temperature of approximately 105°C, causing the carbon dioxide to separate from the material. The steam can then be compressed, condensing the water and leaving a concentrated flow of carbon dioxide suitable for sequestration or other use − such as a nutrient for algae growth.
Because most coal-burning facilities generate steam, some of that might be bled off to achieve the separation and regeneration without a significant energy penalty. ’In many facilities, steam at this temperature would have no other application, so using it for this purpose would not have a significant cost to the plant,’ Jones noted.
’Steam stripping is widely used in other separation processes, but has never been reported for use with supported amine materials, perhaps due to concerns about sorbent stability,’ Jones said.
Though much remains to be done before solid amine materials can be used in large-scale applications, Jones believes his study demonstrates that such materials could be developed with properties tailored for the steam-regeneration process.
’We believe there is potential for development of materials that will be stable for long-term use during regeneration using this technique,’ he said.