Abstract
A frontier to be conquered in the field of membrane technology is related to the very limited scientific base for the rational and task-specific design of membranes. This is especially true for nanofiltration membranes with properties that are based on several solute-membrane interaction mechanisms. “Thinking in terms of Structure-Activity-Relationships” (T-SAR) is a methodology which applies a systematic analysis of a chemical entity based on its structural formula. However, the analysis become more complex with increasing size of the molecules considered. In this study, T-SAR was combined with classical membrane characterization methods, resulting in a new methodology which allowed us not only to explain membrane characteristics, but also provides evidence for the importance of the chemical structure for separation performance. We demonstrate an application of the combined approach and its potential to discover stereochemistry, molecular interaction potentials, and reactivity of two FilmTec nanofiltration membranes (NF-90 and NF-270). Based on these results, it was possible to predict both properties and performance in the recovery of hydrophobic ionic liquids from aqueous solution.
Highlights
Ionic liquids are compounds that consist exclusively of ions and have melting points below 100 °C [1].They are regarded as a promising substance class; because they are potential substituents for volatile solvents as well as allowing the design of new processes
Nanofiltration seems to be a versatile method for this task, because nanofiltration membranes can be selected properly according to the required purpose: either to retain the ionic liquid or to allow it to pass through the membrane [4]
The following key questions were propounded for this study: (1) Considering that the interactions between the chemical structures of the ionic liquid and the membrane are responsible for the separation, is the terms of Structure-ActivityRelationships” (T-SAR) methodology able to provide a better picture of a nanofiltration membrane?
Summary
Ionic liquids are compounds that consist exclusively of ions and have melting points below 100 °C [1] They are regarded as a promising substance class; because they are potential substituents for volatile solvents as well as allowing the design of new processes. The chemical structure should ideally be stated in its corresponding three-dimensional formula, which is the graphical representation of the molecular structure, showing how the atoms are arranged From this structure it is necessary to systematically identify several aspects related to the stereochemistry, the molecular interaction potentials and the reactivity of the desired compound; these three parameters constitute the cornerstones of the T-SAR analysis. The stereochemistry describes the shape of the molecule on the one hand and its flexibility on the other It describes directionality and spatial organization of molecular interaction potentials, which are identified by using a color code (Figure 1).
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