Permeability, Solubility, Diffusivity, and PALS Data of Cross-linkable 6FDA-based Copolyimides

Abstract

The intrinsic gas transport properties of thermally treated cross-linkable 6FDA-based copolyimide membranes have been studied. Grafting various sizes of cyclodextrin (CD) to the copolyimide matrix and then thermally decomposing CD at elevated temperatures are an effective method to micromanipulate microvoids and free volume as well as gas sorption and permeation. The pressure-dependent solubility and permeability coefficients were found to follow the dual-mode sorption model and partial immobilization model, respectively. Solubility and permeability coefficients of CH 4 , CO 2 , C 3 H 6 , and C 3 H 8 were conducted at 35 °C for different upstream pressures. The Langmuir saturation constant, C H ′ , increases with an increase in annealing temperature. On the other hand, Henry's solubility coefficient k D and Langmuir affinity constant b do not change noticeably. The CH 4 permeability decreases with pressure, while some membranes exhibit serious plasticization with an increase in CO 2 , C 3 H 6 and C 3 H 8 pressures. The diffusivity coefficient of the Henry mode (D D ) and Langmuir mode (D H ) were calculated from the permeability and solubility data and their ratio, F, is higher for membranes thermally treated at 425 °C than those treated at 200 °C. Data from positron annihilation lifetime spectroscopy (PALS) confirm that free-volume and the number of micropores increases while the radius of pore sizes decreases during the high temperature annealing process. All CD grafted membranes thermally treated at 425 °C have almost equal or lower solubility selectivity than the original membrane for CO 2 / CH 4 and C 3 H 6 /C 3 H 8 separations but the former has much higher diffusion selectivity than the latter. As a result, diffusion selectivity plays a more important role than solubility in determining the permselectivity of the CD grafted membranes thermally treated at 425 °C.

Altering sorption and diffusion coefficients of gases in 6FDA‐based membrane via addition of functionalized Ti‐based fillers

“…[13] Meanwhile, lower sorption isotherm of CH 4 than CO 2 indicated that weaker polymer interactions and lower condensability are found between the CH 4 gas molecule and the membrane. [43] From Figure 3, membranes M1 and M2 showed higher CO 2 sorption compared to M0 demonstrated that the membrane capacity for CO 2 sorption increased after incorporating MIL-125 (Ti) and NH 2 -MIL-125 (Ti) fillers into 6FDAdurene polymer. This results also show that extra gas sorption side and good affinity between fillers and CO 2 gas are found in the membranes.…”

Thin supported MOF based mixed matrix membranes of Pebax® 1657 for biogas upgrade

“…A similar reduction of permeation flux resulting from compression has been reported for N 2 and CH 4 in rubbery polymers such as PDMS and poly(octylmethylsiloxane) (POMS). 45,46 Besides, as seen in Fig. S6 from the ESI †, both CO 2 and CH 4 permeances follow an exponential tendency as a function of feed pressure as described by Stern et al 47 (Equation S1), with beta (the constant characteristic of the penetrant-membrane system at the testing temperature, 35 °C in this case) values positive for CO 2 (0.11 bar -1 ) and negative for CH 4 (-0.18 bar -1 ).…”

In situ regulation of micro-pore to design high performance polyimide membranes for pervaporation dehydration of isopropanol

“…A fast-fast coincident PALS spectrometer in our laboratory with a system channel width of 50.53 ps per channel was employed. A detailed description of the PALS experimental process and theory can be found elsewhere [39][40][41][42]. The source was sandwiched between two stacks of membrane samples of around 0.5 mm thick which were previously cut into the square shape with a dimension of 1 Â 1 cm 2 .…”