Formation of Macrovoid-Free PMDA-MDA Polyimide Membranes Using a Gelation/Non-Solvent-Induced Phase Separation Method for Organic Solvent Nanofiltration

Abstract

For the first time, we demonstrated that the gelation/nonsolvent induced phase separation (Gel-NIPs) method could be applied to fabricate macrovoid-free flat-sheet nanofiltration membranes based on organo-insoluble polyimide (pyromellitic dianhydride–4,4′-diaminodiphenylmethane; PMDA-MDA). Specifically, the PMDA-MDA polyamic acid (PAA)/N-methyl pyrrolidone (NMP) dope was cast on a polyester-based nonwoven, gelatinized in a fridge, and immersed in water. Gelation greatly inhibited the growth of macrovoids and resulted in an asymmetric membrane with high permeability but low rejection. After adding 4 wt % TiO2 sol into the dope, the gelation process was accelerated, and the PMDA-MDA/TiO2 membrane had a dense skin layer with a macrovoid-free cross-sectional structure. Its permeability and rejection to Rose Bengal (RB, M w = 1017 Da) were 8.3–9.2 L·m–2·h–1·bar–1 and 89.5–95.7%, respectively, in solvents including DMF, THF, and DMSO. The separation performance was stable at a feed pressure of 25 bar, indicating a great potential for organic solvent nanofiltration (OSN).

Green lignin‐based polyester nanofiltration membranes with ethanol and chlorine resistance

“…Several organic dyes and inorganic salts were used to determine the rejection of the composite membranes 30 . The rejection ratio ( R ) was computed by the following equation: where C P and C f are the concentrations of permeate and feed, respectively 31…”

State-of-the-Art Organic- and Inorganic-Based Hollow Fiber Membranes in Liquid and Gas Applications: Looking Back and Beyond

“…For instance, poly(4,4′-oxydiphenylene pyromellitimide) (PMDA-ODA) polyimide membranes were synthesized by spinning PMDA-ODA polyamic acid (PAA) into hollow fibers, followed by chemical imidization [ 261 ]. In addition, a gelation/NIPS method was employed in synthesizing pyromellitic dianhydride-4,4′-diaminodiphenylmethane (PMDA-MDA) PAA/TiO 2 mixed matrix membranes to reduce the formation of macrovoids in the membranes [ 262 ]. The gelation of PAA substantially increased the permeability of the membrane, while the addition of TiO 2 in the dope enhanced the rejection of Rose Bengal (RB) in tetrahydrofuran (THF), dimethylsulfoxide (DMSO), and dimethylformamide (DMF) due to the densification of the skin layer.…”

Designing organic solvent separation membranes: polymers, porous structures, 2D materials, and their combinations

“…The membranes are then cross-linked using diamines and conditioned with pore preserving agents, such as hexanediamine (HDA) and polyethylene glycols (PEGs), respectively. 93,[98][99][100][101][102] The processing conditions of phase-inversion, such as casting film thickness and evaporation time, can impact the membrane structure and thus OSN performance, 92,93,103 For example, increasing the evaporation time decreased porosity without changing the pore size, thereby decreasing the permeance, while increasing the film thickness decreased the permeance; polymers with high molecular weight (> 35 kDa) were preferred to obtain defect-free membranes; 99 the introduction of a co-solvent in the dope solution with optimal solubility parameter tightened nanostructures due to delayed demixing; 93,98 and increasing relative humidity created more open structures and decreased the solute rejection. 93,98 Specifically, PMDA-ODA was fabricated into membranes, and the effect of the coagulation and imidization conditions on the structure/property relationship was thoroughly investigated.…”

“…93,98 Specifically, PMDA-ODA was fabricated into membranes, and the effect of the coagulation and imidization conditions on the structure/property relationship was thoroughly investigated. 101,102 Delayed solvent/anti-solvent demixing was essential to preclude the macrovoid formation, and thermal imidization resulted in mechanically stronger and tougher membranes than chemical imidization.…”

“…COFs have low density, high crystallinity, large surface area, and good control over pore size and properties by fine-tuning the type of monomers, chemical reaction, and method of preparation. 2,101,[204][205][206] COFs are classified either based on the type of functionalities they contain or by the method of preparation. On the basis of functionality, COFs are classified in 6 types: (a) imine-based, 207,208 (b) boron-based, 209 (c) keto-enamine based, 72,210 (d) triazine-based, 211 (e) urea-based, 212 and (f) C-C bonded.…”