Spheroid-Encapsulated Ionic Liquids for Gas Separation
An innovative approach has been developed allowing the use of high viscosity for gas separations. The method involves the encapsulation of ionic liquids (ILs) into polymer spheroids, taking advantage of the gas-absorbing properties and cost-effectiveness of ILs, while circumventing known IL viscosity issues. Significantly, the process permits optimization or ‘tuning’ of the IL-containing spheroids for specific gas separation applications. This technology is available for licensing and/or further collaborative research with the U.S. Department of Energy’s National Energy Technology Laboratory.Description
Combustion of fossil fuels produces carbon dioxide (CO2), a greenhouse gas contributing to global climate change. As the demand for energy continues to increase, atmospheric levels of CO2 will continue to rise. There is thus a growing demand to mitigate CO2 emissions, particularly from industrial sources. Currently, CO2 capture with aqueous amines dominates industrial processes. Although effective, amines are corrosive and require significant energy for regeneration. Indeed, amine scrubbing of flue gas consumes an estimated 30% of the power generated by coal-fired power plants. Thus, there exists a significant need for technologies that are highly efficient at CO2 capture/separation and do so with low cost and energy penalties.
A class of compounds known as ionic liquids (ILs) represents a highly promising CO2 capture/separation technology. Ionic liquids are molten salts, typically containing an organic cation and either an organic or inorganic anion. Significantly, ILs readily absorb CO2, with low affinity for other gases such as CH4, H2 and N2. In addition to their selectiveness for CO2, ILs possess a number of other desirable properties that make them ideal candidates for CO2 capture. ILs are non-volatile and thermally stable. They are inexpensive and more energy efficient than competing technologies, requiring little energy for regeneration. Ionic liquids do have one negative feature, however. Upon binding CO2, many ILs undergo a drastic increase in viscosity. This high viscosity severely limits the use of ILs in liquid absorbers (i.e., scrubbers) and is thus a major obstacle to industrial application of ILs. Modification of ILs is therefore necessary before these agents can be widely accepted as a CO2 capture/separation technology.
NETL researchers have designed a means of overcoming the high viscosity problems associated with ILs. Methods have been developed to fabricate novel porous, core-shell type polymer spheroids in which ILs are subsequently encapsulated. The 1 to 3 mm diameter spheroids possess a high surface area to volume ratio, ideal for gas absorption. The spheroids also offer the advantage of a large internal payload, allowing 70-80 wt.% of IL to be ‘loaded’, resulting in maximal CO2 capture capacity. Encapsulation in polymer spheroids permits the use of ILs not previously compatible with traditional gas-liquid contactors, as the CO2-dependent viscosity increase is now localized to the spheroidal interior. The design of the spheroids allows close packing, enabling a high density of spheroids in any capture vessel, again maximizing CO2 absorption. Significantly, the spheroids can easily be ‘tuned’ for specific applications by modifying or varying the component polymers, ILs, or spheroidal architecture.Benefits
• Takes full advantage of the high CO2 loading capacity and low regeneration energy requirements of ILs while circumventing the viscosity issues of ILs
• Substantially lower costs than conventional CO2 absorption/separation methods
• Encapsulation minimizes the leakage of ILs into pressure vessels or the environment
• Cost-effective approach as component materials are readily available and IL/polymer spheroids could be fabricated into modules enabling retrofit on existing infrastructure
• Spheroids can be ‘tuned’ for optimal performance and specific usesApplications and Industries
• Reversible absorption of gas mixtures such as air (air capture), exhaust gas from coal power plants (post-combustion capture), integrated combined cycle fuel gas (pre-combustion capture) and crude natural gas (natural gas sweetening)
• Gas storage membranes for liquid separation
• Spheroid-encapsulated catalysts can be used in catalyst beds
• Sorbent for liquidsTechnology Status
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