Sub-ambient Operation Research Articles

Performance optimization of imidazole containing copolyimide/functionalized ZIF-8 mixed matrix membrane for gas separations

The combination of functionalized metal organic frameworks with a polymer with structural similarity is a feasible route to enhance binary phase adhesion of hybrid membranes. Herein, we incorporate amine-modified ZIF-8 with a new type of much permeable imidazole-containing copolyimide (6FBD), which contains the bulky 2,4,6-trimethyl-1,3-diaminobenzene groups, to produce compatible MMMs with optimized gas separation performance. The addition of bulky groups in polymer matrix significantly increases the membrane permeability and the presence of imidazole groups in both polymers and ZIFs ensures the good compatibility. By contrast with ZIF-8 analogs, amine-modified ZIF-8 demonstrates much enhanced interfacial adhesion, ascribed to its hydrogen bonding created between amine groups and polymer matrix. This is manifested as an increase in glass transition temperature, an improvement in thermal stability and increased gas selectivity. Systematic studies of gas separation performance at various temperatures from −20 °C to 60 °C reveal that the hydrogen bonding-induced interfacial force enhancement is more favorable towards CO2/CH4 and H2/CH4 separations especially under sub-ambient temperatures. The CO2/CH4 ideal selectivity of 6FBD/30%ZIF-8-NH2 membrane increases from 16.6 at 60 °C to 119 at −20 °C, which are increased by more than 6 times, while 6FBD/30%ZIF-8 membrane shows only around 2.5 times enhancement. This finding indicates tailoring hybrid membrane interfacial structure by creating hydrogen bonds offers more benefits when applied at sub-ambient operation conditions.

CO2/N2 separation performance of Pebax/MIL-101 and Pebax /NH2-MIL-101 mixed matrix membranes and intensification via sub-ambient operation

Membrane-cryogenic hybrid process has been considered as a potential alternative for standalone CO2 separation. In hybrid process, CO2 from flue gas could be initially concentrated via membrane, and then high concentration CO2 stream is cryogenic-separated via phase change in low energy consumption. However, the sub-ambient separation performance and mechanism of membrane has been less investigated. In this work, Pebax 1657/MIL-101 and Pebax 1657/NH2-MIL-101 mixed matrix membranes have been fabricated and tested at sub-ambient condition. SEM, FITR and XRD results indicated that –NH2 has been successfully grafted to MIL101. Experimental results indicated that operating Pebax/MIL-101 and Pebax/NH2-MIL-101 at sub-ambient temperature (−20 °C) could enhance CO2 selectivity to 89.4 and 95.6, which increased by 96.5% and 145.1% compared with that at ambient condition. It indicated that Pebax 1657/NH2-MIL-101 has the potential to be used as sub-ambient membrane in membrane-cryogenic hybrid CO2 capture processes.

Glass Transition of Elastomers Using Thermal Analysis Techniques

Abstract The paper defines the glass transition temperature (Tg) of elastomers using various thermal analysis techniques (differential scanning calorimetry, DSC; derivative DSC; thermomechanical analysis, TMA; dynamic mechanical analysis, DMA; dielectric analysis, DEA; thermal stimulated current, TSC) and compares Tg values of eight elastomers by the first four techniques. Comparison of Tg by two TMA methods (expansion and penetration) is also included. Necessary information regarding both the specific technique and the sample used to compare published data is mentioned. Their inclusion, along with the Tg data, is emphasized. Correlation of Tg, as determined by thermal methods with that determined by an industrial low-temperature test method (ASTM D 1053-89a) is discussed. The factors that are unique to elastomer Tg determination, such as subambient operation, as compared to other polymers, are pointed out.

Techniques for improving the performance of the Perkin—Elmer scanning calorimeter

The Perkin—Elmer DSC-lB differential scanning calorimeter is now a relatively standard laboratory instrument. Although reasonably well designed, it is possible to improve the operation significantly with a few simple modifications. The most major of these is thermostating the cell compartment. Using a dry nitrogen atmosphere outside as well as inside the thermostated cell greatly reduces noise and decreases drift. Sub-ambient operation under these conditions becomes relatively simple. The baseline drift becomes very reproducible—a significant aid in heat capacity measurement. Simple electronic modifications in the control potentiometers also bring about significant improvements. Directions with drawings and sample runs contrasting operation are given for the optimization of this instrument.