Binaphthalene-based polymer membranes with enhanced performance for solvent-resistant nanofiltration

Abstract

To improve the performance of the currently available solvent-resistant nanofiltration (SRNF) membranes, a new, unique approach was developed. In this approach, the concept of PIMs is combined with the fabrication of thin film composite membranes by interfacial polymerization (IFP) ànd the possibility to tune the molecular structure of the monomers at wish. This allows to obtain a thin active layer with a high free volume and good permeance for solvents while realizing a high solute retention. The influence of the dihedral angle of the binaphthalene-based di(acid chloride) and the influence of the number and position of the amine functionalities of the amine monomer on the membrane performance is studied. By combining a binaphthalene-based di(acid chloride) with various amine monomers containing 2.5-4 amine functions via IFP on a crosslinked PI (Matrimid) support, the permeance of acetonitrile (ACN) could be increased by a factor of 20 in comparison to standard TFC-membranes consisting of TMC and MPD, at a 99% retention of Rose Bengal (RB, 1017 g/mol). The highest permeance in combination with the best retention were obtained when using the methyl-linked binaphthalene di(acid chloride), which has the smallest dihedral angle.

The significant role of enantiomeric excess of the monomer in binaphthalene-based polymer membranes

“…The selected amine monomers are shown in Fig. 1, with a the amine monomer with the highest number of amine functionalities and the lowest reactivity in the used set-up [14]. As shown in previous work, not only the number and position of the amine functionalities matter, but also their reactivity during IP is key.…”

“…A methyl-linked binaphthalene di(acid chloride) was specifically chosen (Fig. 1), since previous findings showed that a smaller dihedral angle, obtained by using a short linker, gives better results for SRNF [14]. Most importantly, since binaphthalenes are chiral, the enantiomeric excess of the monomer can be varied and its influence on the structure and thus the membrane performance can be studied.…”

Interfacially Polymerized Thin‐Film Composite Membranes for Organic Solvent Nanofiltration

“…As a result, a higher selectivity, improved chemical, and thermal stability could be achieved. The most commonly used polymer is PI, including P84 [ 16,20,22,23,46,49–55 ] and matrimid [ 56–61 ] PI. After covalent crosslinking by diamines (e.g., 1,6‐diaminohexane) in an alcoholic solvent (isopropanol (IPA) or methanol), the resultant cross‐linked PI‐based TFC membrane could be tolerant to a wide range of mild organic solvents as well as a harsh polar aprotic solvent (DMF).…”

“…Additional precautions are necessary to prevent degradation of the free amines when applying the IP reaction; for instance, Ar gas is required to purge into the aqueous solution and the IP set‐up also has to be continuously provided with inert gas. [ 59 ] To achieve a higher solvent permeability but maintain the selectivity of a TFC membrane, amines with non‐planer structure could be used as an additive to enhance the free volume in the selective layer. [ 90 ] Additionally, heterocyclic compounds and aliphatic amines could also be potentially used as the aqueous monomers in the IP reaction due to their chemical stability, lower toxicity, and water solubility.…”

“…further prepared a series of binaphthalene‐based polymer membranes using bridged binaphthalene‐based acid chloride monomers and rigid amine monomers. [ 59 ] The amount of amine functions per monomer unit and the length of the alkyl linker in the binaphthalene‐di(acid chloride) could be separately adjusted. The macromolecular structure and free volume of the active layer could be finely tuned.…”