Hierarchical ZIF-8 composite membranes: Enhancing gas separation performance by exploiting molecular dynamics in hierarchical hybrid materials

Abstract

Hierarchical ZIF-8 Mixed matrix membranes Gas separation PolyimideMixed matrix membranes (MMM) incorporating metal-organic framework (MOF) fillers have gained increasing attention in addressing environmental and sustainability challenges. Hierarchical materials combining pore sizes of different length scales are expected to facilitate molecular diffusion and mass transfer for the optimization of catalysis and separation processes. Herein, a novel preparation method for hierarchical ZIF-8 (H-ZIF-8) particles is presented for the synthesis of polyimide (PI)-based MMMs with good compatibility between filler and polymer. Gas permeability measurements of polyimide-Matrimid®/H-ZIF-8 MMMs showed 4-fold improvements in permeability of both CO 2 and CH4 coupled with a marked increase in selectivity and plasticization resistance for MMM with 30 wt% H-ZIF-8 loading. Gas nanspon analysis in these MMMs revealed that the enhanced gas separation performance of the MMMs can be related to the imidazolate modification of the PI structure and the hierarchical structure of H-ZIF-8, as confirmed by N 2 , Ar, mercury porosimeuy, SEM, TEM analysis. CO 2 permeability for all MMMs increases with increasing CO2 concentration and by decreasing temperarure. The proof of concept, as demonstrated in this study, could be extended for the preparation of other hierarchical ZIFs and related MMMs.

RSM Modeling and Optimization of CO2 Separation from High CO2 Feed Concentration over Functionalized Membrane

“…This might have been related to the lower solubility of gas molecules with increasing temperature. The adverse impact of temperature on sorption enthalpy would have affected the transport and sorption behavior of gases over the membrane [ 26 ]. From the obtained results, a maximum CO 2 permeability of 609.1 Barrer was achieved at a feed pressure of 3.5 bar and a temperature of 40 °C.…”

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

“…The highest coefficient of Henry's law (K D ) observed on M0 primarily due to the overall sorption governed by Henry' solubility law sorption. [40] It can be seen that all dual-mode parameters (K D , C 0 H , and b) decreased after the inclusion of MIL-125 (Ti) and NH 2 -MIL-125 (Ti) fillers into the polymer matrix. The reduction of the coefficient of Henry's law (K D ) shows that the addition of MIL-125 (Ti) and NH 2 -MIL-125 (Ti) fillers has reduced the interaction between the CH 4 gas molecule and the membrane due to nonpolar character of CH 4 , and therefore, less CH 4 gas molecule were dissolved in the membrane.…”

“…The CO 2 sorption of M1, and M2 showed significantly higher than that of M0 owing to the high adsorption of filler caused by the increased filler's surface area. [40] Referring to Figure 3, it can be observed that the sorption isotherms obtained from M0, M1, and M2 are concave to the vertical axis at low pressure and tends to approach straight line at higher pressure. This results show that CO 2 sorption is dominated by Langmuir mode (C H ) when the pressure is low, F I G U R E 2 CO 2 plasticization pressure of membranes meanwhile the CO 2 sorption is followed Henry mode (C D ) at high pressure.…”

“…[9] Also, the strong quadrupolar interaction of CO 2 with electron donor groups in polymer matrix (durenediamine moieties) and filler's framework ( NH 2 ) lead to improved CO 2 sorption. [40] Table 4 displays the estimated parameters of the dualmode model for CO 2 sorption over M0, M1, and M2 membranes. All the parameters were obtained by using a data regression via Minitab software.…”

“…The higher solubility coefficient is significantly influenced by the increase in the coefficient of Langmuir sorption capacity (C 0 H , Table 4) [59] that related to the addition of fillers which enhanced the excess free volume of the polymer, thus improved the gas sorption. [40] The increment of CO 2 permeability of the M2 membrane is directly correlated to the higher diffusivity and solubility coefficient after the addition of filler. [54,60,61] The diffusivity coefficient influenced by a few factors including fractional free volume of the membrane, kinetic diameter and shape of the gas, fillers pore size and polymer-filler interface, [61] while solubility coefficient correlated with the condensability and the critical temperature of the gas.…”