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Project
Ionic Liquids for Carbon Dioxide Separation on Membranes
Reducing carbon dioxide (CO2) emissions is not only ecologists dream. Re-use of this gas can be beneficial for many industries where it is an important substrate. Since in the majority of the cases CO2 leaves the industrial site mixed with other gases, it has to be purified before it is captured.
One promising method involves the use of membranes incorporating ionic liquids (ILs) that readily absorb CO2. Although several well-performing ILs have been tested for this application, the search for an industrially relevant one is still ongoing. More importantly, the structure-performance relationship of the ILs as well as the dissolution mechanism of CO2 in ILs is not yet fully understood.
ThisPhD thesis focused on the design and synthesis of ILs for the separation of CO2 from N2 or CH4 on Supported Ionic Liquid Membranes (SILMs) and IL-polymer blend membranes, as well as on establishing the structure-performance relation-ship of the novel compounds in CO2 separation.
A study of a series of tri(ethylene glycol)-functionalized ILs based on different cationic cores showed that cations influence CO2 separation toa similar extent as anions. Gas separation selectivities of these monocationic compounds were on average two times lower than those of their dicationic analogues, due to the lower permeances of N2 and CH4 through the IL layer and
more interaction sites for CO2 in the latter.
Similarly to the tri(ethylene glycol), the nitrile group was repeatedly reported to be very efficient in improving CO2 separations. Therefore, both moieties were combined into the pyrrolidinium and imidazolium ILs and used to prepare membranes. These ILs exhibited ca. 2.3 times higher CO2/N2 and CO2/CH4 gas separation selectivities than analogous ILs functionalized only with a glycol chain. In-situ FTIR-ATR spectroscopy was used tostudy the solubility of CO2,
IL swelling and the interactions of CO2with the nitrile group. The difunctionalized ILs were found to interact stronger withCO2 than the glycol-functionalized ILs.
The widespread use of such highly functionalized ILs is restricted by the elaborate synthesis and the difficulties in purification, which lead to low yields. To overcome these problems and to propose a new approach to CO2 separation, metal-containing ILs were designed and evaluated for membrane performance. The compounds were composed of complex cations and bis(trifluoromethylsulfonyl)imide anions. In each cation, six imidazole ligands functionalized with a nitrile or an oligo(ethylene oxide) group were coordinated to a d-block central metal ion. Crystal structures of the nitrile-containing ILs were obtained. In order to explore the potential of
the direct CO2-metal chemical binding, analogous ILs but with four or five ligands were examined for gas separation performance and showed selectivities similar to the hexacoordinate ILs. The membranes prepared from blends of these ILs and polymers, provided moderate selectivities.</></></></></>
One promising method involves the use of membranes incorporating ionic liquids (ILs) that readily absorb CO2. Although several well-performing ILs have been tested for this application, the search for an industrially relevant one is still ongoing. More importantly, the structure-performance relationship of the ILs as well as the dissolution mechanism of CO2 in ILs is not yet fully understood.
ThisPhD thesis focused on the design and synthesis of ILs for the separation of CO2 from N2 or CH4 on Supported Ionic Liquid Membranes (SILMs) and IL-polymer blend membranes, as well as on establishing the structure-performance relation-ship of the novel compounds in CO2 separation.
A study of a series of tri(ethylene glycol)-functionalized ILs based on different cationic cores showed that cations influence CO2 separation toa similar extent as anions. Gas separation selectivities of these monocationic compounds were on average two times lower than those of their dicationic analogues, due to the lower permeances of N2 and CH4 through the IL layer and
more interaction sites for CO2 in the latter.
Similarly to the tri(ethylene glycol), the nitrile group was repeatedly reported to be very efficient in improving CO2 separations. Therefore, both moieties were combined into the pyrrolidinium and imidazolium ILs and used to prepare membranes. These ILs exhibited ca. 2.3 times higher CO2/N2 and CO2/CH4 gas separation selectivities than analogous ILs functionalized only with a glycol chain. In-situ FTIR-ATR spectroscopy was used tostudy the solubility of CO2,
IL swelling and the interactions of CO2with the nitrile group. The difunctionalized ILs were found to interact stronger withCO2 than the glycol-functionalized ILs.
The widespread use of such highly functionalized ILs is restricted by the elaborate synthesis and the difficulties in purification, which lead to low yields. To overcome these problems and to propose a new approach to CO2 separation, metal-containing ILs were designed and evaluated for membrane performance. The compounds were composed of complex cations and bis(trifluoromethylsulfonyl)imide anions. In each cation, six imidazole ligands functionalized with a nitrile or an oligo(ethylene oxide) group were coordinated to a d-block central metal ion. Crystal structures of the nitrile-containing ILs were obtained. In order to explore the potential of
the direct CO2-metal chemical binding, analogous ILs but with four or five ligands were examined for gas separation performance and showed selectivities similar to the hexacoordinate ILs. The membranes prepared from blends of these ILs and polymers, provided moderate selectivities.</></></></></>
Date:1 Oct 2010 → 31 Oct 2014
Keywords:Carbon dioxide capture, Ionic liquids
Disciplines:Condensed matter physics and nanophysics, Analytical chemistry, Pharmaceutical analysis and quality assurance, Inorganic chemistry, Organic chemistry, Physical chemistry
Project type:PhD project