The Research Of Solution-diffusion Of Supported Functional Ionic Liquid Membranes Absorbing CO₂

With the increasing discharge of CO2, the greenhouse effect is more serious. How to capture CO2 has become the focus of the scholars. The methods of CO2 capture includes physical and chemical absorption, low-temperature condensation, adsorbtion and membrane absorption. Among them, the supported ionic liquid membrane (SILM) has the advantages of low volatile, high stability, high solubility of CO2 and high selectivity. Therefore, the technology has a wide application prospect. Now several scholars have studied the supported traditional ionic liquid membrane for gas absorption, but little paied attention to the functional ionic liquid. The solubility, diffusivity and permeability of CO2 in supported functional ionic liquid membrane were studied in our research and the paper also included the data fitting of the diffusivity and solubility of CO2 in SILMs of the relevant model and experimental data. According to the experimental results, the obtained conclusions are as follows:(1) We found that eight ILs loaded in 0.22μm hydrophobic PVDF membranes were all a little more than those in 0.22μm PES membranes. In contrast to the hydrophobic PES membrane, hydrophobic PVDF became transparent after loading ILs.(2) With operating pressure increasing from 0.05 to 0.2 MPa, CO2 solubility had a slightly improvement for each SILMs. And because TETA contains more N atoms than DETA, the CO2 solubility in the SILM-TETA is better than SILM-DETA. As for different anion, the longer carbon chain is, the higher CO2 solubility is. The reson is that the length of carbon chain can effect the reaction of CO2 and N atom.(3) With the viscosity of ionic liquid increasing, the diffusivity of CO2 in SILMs decreases. Increasing of carbon chain and the substituent in cation could enhance van der Waals force and than improve the viscosity. So the diffusivity of CO2 in SILMs is reduced, such as:TETA>DETA, DEA>TEA>MEA. In addition, the more complex for carbon chain of the anions, the higher the viscosity is and the lower diffusivity is;(4) With the increasing of the pressure, the permeability of CO2 in SILMs increases. And the two important influencing factors of permeability is solubility and diffusivity. As for same cation and different anion, because of the similar solubility, the change rule of permeability is as same as diffusivity. In cases of different cation, due to the dual effects of solubility and diffusivity, the comparison of permeability is:TETA> DETA, DEA>TEA>MEA;(5) As for the different membrane materials, the solubility of CO2 in PVDF-SILMs was lower than those of PES-SILMs. However, the regularity of diffusivity is not obvious, this is because that the diffusivity of CO2 in SILMs is determined by the physical property of the ionic liquid and the gas, not the membrane material. What’s more, the comparison of the permeability of CO2 in SILMs is PES> PVDF.