Performance of Solvent-Pretreated Polyimide Nanofiltration Membranes for Separation of Dissolved Dyes from Toluene

Abstract

The major problem reported for commercially available membranes is their limited chemical stability in organic solvents. This article reports the influence of organic solvents with different polarity (methanol, acetone, acetic acid, toluene, and n-hexane) on the filtration performance of STARMEM membranes. These membranes are specified to be compatible with the solvents used. The pure toluene flux of these membranes and the rejection of azo dyes (Sudan Black and Rhodanile Blue) were measured before and after a week of exposure to one of the above-mentioned solvents. The results show that the structure of the membrane changed after pretreatment with polar solvents (methanol, acetone, acetic acid) and that the membrane performance shifts toward lower rejections with higher solvent flux. Nonpolar solvents do not change the polyimide membrane performances significantly. Contact angle measurements on new and solvent-treated membranes show that organic solvents change the hydrophobicity of polymeric membrane surfaces, leading to different toluene permeabilities before and after solvent treatment. Swelling measurements confirm the theory that a reorganization of the membrane material takes place, which leads to differences in porosity and changes in rejection. The study also shows that pretreatment of polyimide membranes with polar solvents increases the recovery of the membrane system when the solute size is large enough.

Evaluation of reverse osmosis and nanofiltration membranes performance in the permeation of organic solvents

“…All membranes were immersed for 24 h with pure solvents of decreasing polarities (ethanol, isopropanol and n-hexane). Darvishmanesh et al [11] used nanofiltration and reverse osmosis commercial membranes (made of polyamide (PA), polyethersulfone (PES) and sulfonated polyethersulfone) and pretreatment in ethanol for at least 24 h. Darvishmanesh et al [12] used immersion treatments in various organic solvents for one week before permeation in nanofiltration membranes produced with PA. Van der Bruggen et al [13] also reported on their work with NF membranes, treatments of 24 h by immersion in ethanol and nhexane. All the authors noted improvements in the permeate flux after the pretreatment.…”

Recent Advances in Polymeric Solvent‐Resistant Nanofiltration Membranes

“…24,125,128,129 When polymers swell, the reorganization of the molecular structure of the membrane affects the solvent flux. 138,142 Extensive swelling can decrease the selectivity and even cause the peeling of the top layer. Many reports have indicated that the solvent permeability was proportional to the swelling/viscosity.…”

Crosslinking of polyimide atomic-layer-deposited on polyethersulfone membranes for synergistically enhanced performances

“…There are strong intra-and intermolecular interactions, for example, hydrogen bonds, among PI segments. Consequently, membranes derived from PI materials generally possess small pore sizes or even dense nonporous structures and thus find applications typically in the fields such as gas separation, pervaporation and nanofiltration [3][4][5][6][7]. Moreover, high temperature up to 300-400 1C is frequently required for an imidization process to enhance the thermal stability and solvent resistance of PI membranes [3].…”

“…Furthermore, massive consumption of PI or its precursors as well as other organic solvents will be involved, which are considerably expensive and not environmentally benign. Considering higher cost of PI than many other membrane materials, like polyvinyldifluoride and polysulfone, which reduces its popularity in large-scale applications, [5][6][7][8]13] it is of great significance to fabricate composite membranes combining low quantity of PI precursors with costefficient macroporous substrate membranes of high compatibility. In this case, the pore sizes of the PI composite membranes can be flexibly tuned in a broad range and ultimately to extend their practical applications [3,[14][15][16].…”