Field of the Invention
The embodiments described herein relate to ionic liquids, such as ionic liquids used for separating or absorbing acidic gases.
Description of the Related Art
Ionic liquids are increasingly being used for a number of applications, such as for separation or purification of gases, or for other applications that involve the absorption of one or more gases. Of particular interest is the separation of acidic gases, such as oxides of carbon, nitrogen, or sulfur. These gases are common impurities in many gas mixtures, and are common air pollutants. For example, carbon capture and sequestration, the removal of carbon dioxide from combustion exhaust, or from air, to reduce the greenhouse effect on global warming, is of particular interest.
The atmospheric concentration of CO2 has increased unabated since the dawn of the industrial revolution, due primarily to CO2 emissions from the combustion of fossil fuels, and this growing carbon burden may have significant implications for the global climate. While the development of a carbon-neutral infrastructure may be a long-term solution to this problem, the increasing world demand for energy and the ready availability of fossil fuels-in particular coal-make it highly likely that fossil fuel combustion will continue to be a substantial fraction of the energy portfolio for the foreseeable future. In this environment, alternative approaches to managing CO2 emissions become desirable.
For coal-fired power plants and other point source emitters, post-combustion carbon capture may be the most straightforward and promising route to limiting CO2 release, but practical carbon capture may depend on the discovery of energy-efficient means of separating CO2 from the other gaseous components of a flue gas. For example a typical 500 MW coal-fired power plant produces about 22 kmol s−1 of flue gas containing ˜15% CO2 in N2, O2, H2O and other trace gases at near ambient temperature and pressure. Separating CO2 from this stream may consume more than 30% of the power of the plant using presently available amine absorption technologies, far above the theoretical minimum work of separation.
Many ionic liquids may be unsuitable for industrial removal of carbon dioxide and other acidic gases because they may become highly viscous when the acidic gas is absorbed, or because they may not be suitable for absorption of the gas and the subsequent removal of the gas to store the gas and/or to recycle the ionic liquid. Therefore, there is a need for additional ionic liquids which may improve one or more of these properties.