Ligand Effects on the Surface Composition of Rh‐Containing Ionic Liquid Solutions Used in Hydroformylation Catalysis

Abstract

The molecular design of nanoporous membranes with desired morphology and selectivity has attracted significant interest over the past few decades. A major problem in their applications is the trade‐off between sieving property and permeability. Here, we report the discovery of elongation‐induced nano‐pore evolution during the external stretching of a novel polyamide‐imide nanofiltration hollow fiber membrane in a dry‐jet wet‐spinning process that simultaneously leads to a decreased pore size but increased pure water permeability. The molecular weight cutoff, pore size, and pore size distribution were finely tuned using this approach. AFM and polarized FTIR verified the nano‐pore morphological evolution and an enhanced molecular orientation in the surface skin layer. The resultant nanofiltration membranes exhibit highly effective fractionation of the monovalent and divalent ions of NaCl/Na2SO4 binary salt solutions. More than 99.5% glutathione can be rejected by the nanofiltration membranes at neutral pH, offering the feasibility of recovering this tripeptide. © 2009 American Institute of Chemical Engineers AIChE J, 2010

Surface Science and Model Catalysis with Ionic Liquid‐Modified Materials

“…The formed Rh-tppts complex proved to exhibit signifi cant surface activity in the ionic liquid [C 2 C 1 Im][C 2 H 5 OSO 3 ], as compared to an analogous tppts-free system, where for the same Rh-precursor even Rh-depletion from the surface was found. [ 57 ] With these data we provide spectroscopic evidence for results from molecular dynamics studies by Sieffert and Wipff who claimed signifi cant interface (surface) activity of Rh-tppts complexes in organic/ionic liquid (vacuum/IL) multiphase systems. [87][88] [ 45 ] XPS allows not only deriving information on chemical composition and orientational effects, but also gives insight to interionic interactions.…”

“…Indeed, when adding Rh(acac)(CO) 2 to a saturated solution of tppts in [C 2 C 1 Im][C 2 H 5 OSO 3 ], a maximum concentration of 5.1 mol% Rh in the IL is achieved (see corresponding Rh 3d spectra in Figure 6 b), as compared to 0.19 mol% in the same ionic liquid without the tppts ligand. [ 57 ] This induced increase of the Rh concentration is a strong indication for the in-situ transformation of the Rh-complex in the polar ionic liquid solution by the coordination of the tppts ligand. Furthermore, it could be experimentally demonstrated for the fi rst time that the nature of the applied ligand infl uences the preferred position of the catalyst complex in either the bulk phase or at the interface of a multiphase catalytic system.…”

“…In the following, it will be shown for an industrially relevant example that ligands have a pronounced effect not only on the surface activity of the catalyst but also on its bulk solubility. [ 57 ] The aim of these investigations was to study the effect of an ionic phosphine ligand (tppts; tris(3-sodium sulfonatophenyl) phosphine) on the surface composition of a catalytically relevant ionic catalyst solution. For this purpose the chemical surface composition of Rh-containing ionic liquid solutions with and without tppts ligands were investigated by ARXPS.…”

“…Recent work by several groups [30][31][32][33][34][35][36][37][38][39][40][41][42][43] including those of the authors [44][45][46][47][48][49][50][51][52][53][54][55][56][57] shows that a rigorous surface science approach can indeed be applied to IL surfaces and interfaces. There are mainly two aspects, which make such studies possible: First, the vapor pressure of many aprotic ILs is suffi ciently low so that their surfaces can be straightforwardly studied under ultrahigh vacuum (UHV) conditions.…”

“…The obvious challenge here is to understand the physical and chemical properties to an extent which allows for selective tuning of the IL The graphical sketch at the top shows the proposed arrangement of the formed complex at the surface; adapted with permission. [57] …”