(29b) Carbon Dioxide Separation with Supported Ionic Liquid Membranes

Supported liquid membranes are a class of materials that allow the researcher to utilize the wealth of knowledge available on liquid properties as a direct guide in the development of a capture technology. These membranes also have the advantage of liquid phase diffusivities higher than those observed in polymeric membranes which grant proportionally greater permeabilities. The primary shortcoming of the supported liquid membranes demonstrated in past research has been the lack of stability caused by volatilization of the transport liquid. Ionic liquids, which possess high carbon dioxide solubility relative to light gases such as hydrogen, are an excellent candidate for this type of membrane since they have negligible vapor pressure and are not susceptible to evaporation.

A study has been conducted evaluating the use of several ionic liquids, including 1-hexyl-3-methyl-imidazolium bis(trifuoromethylsulfonyl)imide, 1-butyl-3-methyl-imidazolium nitrate, and 1-ethyl-3-methyl-imidazolium sulfate in supported ionic liquid membranes for the capture of carbon dioxide from streams containing hydrogen. In a joint project, researchers at the University of Notre Dame lent expertise in ionic liquid synthesis and characterization, and researchers at the National Energy Technology Laboratory incorporated candidate ionic liquids into supports and evaluated the resulting materials for membrane performance. Initial results have been very promising with carbon dioxide permeabilities as high as 950 barrers and significant improvements in carbon dioxide/hydrogen selectivity over conventional polymers at 37C and at elevated temperatures. Results include a comparison of the performance of several ionic liquids and a number of supports as well as a discussion of innovative fabrication techniques currently under development.