Preparation of Supported Ionic Liquid Membranes Using a Supercritical Fluid Deposition Method and Study of the Capillary Phase Transition of Ionic Liquids in Supercritical CO₂

Abstract

Supported ionic liquid membranes (SILMs) based on [EMIM]­[Ac] and γ-Al2O3 membranes were prepared using a supercritical fluid deposition (SCFD) method at 12 MPa and 50 °C. The influences of the preparation time, ionic liquid loading, and ethanol content on the performance of SILMs were studied. The CO2/N2 selectivity of the as-prepared SILMs reached the ideal selectivity of [EMIM]­[Ac]. When the ionic liquid (IL) was dissolved in a mixture of supercritical CO2 (scCO2) and ethanol, the IL easily diffused into the small pores in supports. Moreover, the dissolved IL could transition to the liquid phase in the small pores because of the capillary phase transition, leading to the selective filling of the meso- and micropores in the supports. The surface tension of the liquid phase and the ratio of the IL concentration to the saturation IL concentration were found to be the key factors influencing the capillary phase transition of the IL.

Beyond Solution-Based Protocols: MOF Membrane Synthesis in Supercritical Environments for an Elegant Sustainability Performance Balance

“…As an alternative to conventional solvents, SCFs have been widely used in a range of industrial and laboratory processes . It is noticed, however, that to date, SCFs have not been utilized as platform for MOF membrane synthesis, although they hold great promise for the sustainable production because of the following unique properties: (1) near-zero surface tension, low viscosity, and high diffusivity, which facilitate fast diffusion of reagents in nanoscale intercrystalline defects and easy defect patching through further crystal growth in SCF environments, and (2) controllable phase transition and variable solubility. Since simply altering the operating temperature and pressure in the vicinity of critical points enables facile transition of fluids between supercritical and gaseous states, after the completion of membrane preparation in SCF environments, phase segregation between gaseous fluids and solid solute occurs spontaneously upon evacuation of the reaction chamber so that both SCFs and unreacted reagents can be easily recovered and reutilized, thereby making it possible to realize zero pollutant discharge.…”

Nanoconfinement Ionic Liquid Membranes for Efficient Flow Catalytic CO2 Cycloaddition

“…The pore size modification on the surface of the α-Al 2 O 3 ceramic tube was carried out by a sol–gel method, as previously reported, − and the four steps of the preparation process included cutting the tube, glazing the surfaces of both ends (installing sealing O-rings), synthesizing the sol–gel, thermal coating, and calcined membrane. The commercially available α-Al 2 O 3 ceramic base membrane was cut into a total length of 50 mm, soaked in 50 mL of absolute ethanol for 24 h, washed repeatedly with ethanol and water, and dried at 100 °C for 12 h for use.…”

“…Ionic liquids (ILs) are hybridized with membrane processes to form ionic liquid membranes with structural and physicochemical properties that differ from bulk ILs, for instance, local structure (ionic orientation and layer structure), dynamics (diffusion coefficient, viscosity, dielectric relaxation, and ionic conductivity), thermal properties (phase transition and thermal stability), optical properties, and even chemical reactivity. Therefore, specific applications are achieved by designing functionalized ILs with gas absorption, separation, and catalytic properties to bind to nanoporous membranes. − IL nanocomposite membranes are classified into two broad categories, i.e., matrix nanocomposite membrane and thin IL nanocomposite membrane. − In the former, membranes are cast from a premixed nanomaterial/polymer solution, whereas for the latter, ILs are covalently grafted onto supports or physical confinement into porous matrices. There are several preparation strategies including phase inversion, interfacial polymerization, electro-spinning and cross-linking, self-assembly, chemical grafting and layer-by-layer assembly, and long-distance and dynamic low-temperature plasma flow approach .…”

Integrated Hierarchical Inorganic Support Ionic Liquid Membrane for Scalable Utilization of CO2

“…The pore size control of the surface of the hollow α-Al 2 O 3 ceramic tube was carried out by a sol–gel method. − The preparation process includes four steps: cutting the tube, sealing both ends, preparing the sol, and modifying the membrane layer. First of all, commercially purchased α-Al 2 O 3 ceramic base films were cut into lengths of 50 mm, soaked in 50 mL of absolute ethanol for 24 h, washed repeatedly with ethanol and water, and dried at 100 °C for 12 h for use.…”