The Research Of Solution-diffusion Of Supported Ionic Liquid Membranes Absorbed CO₂

CO2as the main component of greenhouse gas which caused the greenhouse effect and global warming, is threatening the survival of humanity. The total CO2emissions of our country had surpassed the sum of the European Union and the United States in2013. Capture, storage and utilization of CO2have become important technical means which were used for dealing with global warming and resource shortage.Supported ionic liquid membranes (SILMs) increases gas absorbability and stability of liquid membrane because it possesses the advantages of both high CO2absorption quantity and negligible vapor pressure of ionic liquid and high specific surface area of supporting porous membrane, which has well foreground for industrial application. The CO2permeability and solubility in SILMs were studied in our research, moreover the ionic liquids (IL) and SILMs were characterized and analyzed. The highlights as follows:1. The ILs weight loaded unified as gram per unit membrane area and thickness. We found that five ILs loaded in0.1μm hydrophobic Polyvinylidene fluoride (PVDF) membranes were all a little more than those in0.22μm membranes. Compared with hydrophobic PVDF membrane, the hydrophilic membrane with the same pore size loaded more ILs. In contrast to the hydrophilic membrane, hydrophobic PVDF became transparent after loading five ILs.2. With operating pressure increasing from0.05to0.2MPa, CO2permeability had a slightly improvement for each SILMs. For the same anion, for example [Tf2N] and [PF6]-, the permeability of CO2in SILMs both hydrophilic and hydrophobic PVDF membrane with0.22μm and0.1μm pore size all increased non-significantly with increasing lengths of the alkyl side chain of the cation. In addition, CO2permeability in SILM-[Cgmim][PF6] was higher than the others by one order of magnitude. Besides, CO2permeability in hydrophilic SILMs was all higher than that of hydrophobic SILMs and the difference in pore size (0.1/0.22μm) of PVDF membranes had little effects on CO2permeability.3. All the CO2soluble constants KH in SILMs were far lower than those in the pure ILs by two orders of magnitude, indicating CO2solubility had a great improvement when the same IL loaded in the sub-micrometer’s membrane pores. With operating pressure increasing from0.05to0.2MPa, CO2solubility had a slightly improvement for each SILMs. For the same anion, for example [Tf2N]-and [PF6]", the solubility of CO2in SILMs both hydrophilic and hydrophobic PVDF membrane with0.22μm and0.1μm pore size all increased slightly with the increasing lengths of the alkyl side chain of the cation. Henry constant KH of SILM-[C8mim][PF6] was the minimum of all SILMs, which was consistent with the CO2solubility in [C8mim][PF6] IL was maximum among five ILs. Furthermore, the result showed that the Henry constant KH in hydrophilic SILMs were all higher than that in hydropobic SILMs which indicating CO2solubility in hydropobic SILMs was much higher. Nonetheless, solubility of CO2have little difference in different pore size (0.1/0.22μm).4. The characteristic peaks of ILs and corresponding SILMs which had only a small amount of offset or peak height variation from Raman spectrum and surface enhanced Raman spectrum were obtained.The results also indicated that the Raman spectra of the [C4mim]+cation in three ionic liquids were surprisingly alike, which contribute to the small influence of different anion. Meanwhile, two rotational isomers anti-anti conformer and gauche-anti conformer coexisted in the [C4mim]+cation under the condition of room temperature and normal pressure. The Ag sol surface enhanced Raman spectroscopy of supported ionic liquid hydrophobic membranes and the ordinary Raman spectroscopy of supported ionic liquid hydrophilic membranes were remarkably similar with that of ionic liquid correspondingly. This obviously indicates the advantage and feasibility of the surface enhanced Raman spectra in analyzing the structure characterization of supported ionic liquid membrane.