Effect of temperature on separation performance in ionic liquid/Ag nanocomposite membranes for olefin/paraffin mixtures

Cation-Anion Interactions, Stability, and IR Spectra of Dicationic Amino Acid-Based Ionic Liquids Probed Using Density Functional Theory

In this work, we have theoretically studied the dicationic ionic liquids (DILs) constructed from geminal methylimidazolium dication with varying amino acid anions and spacers using density functional theory. Amino acid-based DILs form via strong C-H···O hydrogen bonds. These hydrogen bonds have a significant role in stabilizing the DILs. The higher cation-anion interaction energy in the order of covalent bond energy and liquid density of DILs imply higher thermal stability than their mono analogues. The C-H stretching frequencies are above 3100 cm^-1 in all complexes and form a signature for DILs. Interestingly, aliphatic and aromatic amino acid anions show similar molecular properties. Overall, the DILs formed from amino acids exhibit high stability and large surface tension and are chemically non-toxic; hence, they can replace inorganic DILs.

Long-Term Stable 1-butyl-3-methylimidazolium Hexafluorophosphate/Ag Metal Composite Membranes for Facilitated Olefin Transport

For the preparation of long-term stable ionic liquid/Ag nanoparticles composites, we compared the separation performance of 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM+BF4-)/Ag, and 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM+PF6-)/Ag composite membranes with time. Separation performance showed that the BMIM+PF6-/Ag metal composite membrane was more stable than the BMIM+BF4-/Ag metal composite membrane for more than 160 h. These differences in long-term stability in BMIM+PF6-/Ag and BMIM+BF4-/Ag metal composite membranes was attributable to the phase separation between ionic liquid and nanoparticles. In particular, the phase separation between ionic liquid and silver nanoparticles was not observed with time in hydrophobic ionic liquid BMIM+PF6-, confirmed by X-ray photoelectron spectroscopy.

Preparation and Characterization of PEBAX-5513/AgBF4/BMIMBF4 Membranes for Olefin/Paraffin Separation

In this study, we investigated a poly(ether-block-amide)-5513 (PEBAX-5513)/AgBF4/1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) composite membrane, which is expected to have a high stabilizing effect on the Ag+ ions functioning as olefin carriers in the amide group. Poly(ethylene oxide) (PEO) only consists of ether regions, whereas the PEBAX-5513 copolymer contains both ether and amide regions. However, given the brittle nature of the amide, the penetration of BMIMBF4 remains challenging. The nanoparticles did not stabilize after their formation in the long-term test, thereby resulting in a poor performance compared to previous experiments using PEO as the polymer (selectivity 3; permeance 12.3 GPU). The properties of the functional groups in the polymers were assessed using Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis, which confirmed that the properties endowed during the production of the film using the ionic liquid can impact the performance.