No abstract

A new form of interfacial polymerization to synthesize thin-film composite membranes realizes a more sustainable membrane preparation and improved nanofiltration performance. By introducing an ionic liquid (IL) as the organic reaction phase, the extremely different physicochemical properties to those of commonly used organic solvents influenced the top-layer formation in several beneficial ways. In addition to the elimination of hazardous solvents in the preparation, the m-phenylenediamine (MPD) concentration could be reduced 20-fold, and the use of surfactants and catalysts became redundant. Together with the more complete recycling of the organic phase in the water/IL system, these factors resulted in a 50 % decrease in the mass intensity of the top-layer formation. Moreover, a much thinner top layer with a high ethanol permeance of 0.61 L m(-2)  h(-1)  bar(-1) [99 % Rose Bengal (RB, 1017 Da) retention; 1 bar=0.1 MPa] was formed without the use of any additives. This EtOH permeance is 555 and 161 % higher than that for the conventional interfacial polymerization (without and with additives, respectively). In reverse osmosis, high NaCl retentions of 97 % could be obtained. Finally, the remarkable decrease in the membrane surface roughness indicates the potential for reduced fouling with this new type of membrane.

No abstract

A simple method for the preparation of highly permeable solvent-resistant nanofiltration (SRNF) membranes was developed. By applying a solvent treatment to cross-linked polyimide ultrafiltration membranes, polymer chain flexibility increased and the matrix rearranged into a more dense structure, creating highly selective SRNF membranes with exceedingly high ethanol permeance. This densification was driven by the ability of the membrane to lower its free energy while in the solvated state via the establishment of extra favorable interactions, like hydrogen bonds and π interactions. Moreover, further reaction of only partly reacted cross-linker molecules was completed during the treatment, thus enhancing the cross-linking degree. The extent of densification depended on the type of solvent, the immersion time and the initial cross-linking degree of the membrane, all influencing the degree of solvation and chain rearrangement. By altering the synthesis conditions, a membrane with equal selectivity to Duramem 300 but showing a 400% higher ethanol permeance was obtained. This demonstrates the high potential of the technique to be applied as novel method for the preparation of SRNF membranes with exceptionally high solvent permeance.

No abstract