Solid supported ionic liquid-phase

Just very recently, Petronas, the Malayan petrochemical company, disclosed at the EUCHEM Molten Salt and Ionic Liquids Conference 2012 in Celtic manor, Wales, the commercial operation of a supported IL phase material for mercury removal from natural gas and other gaseous refinery streams in its plants [1]. The author of this keynote lecture. Dr. Martin Atkins, announced the operation of adsorber/absorber units (note that macroscopicaUy the solid supported ionic liquid phase, SILP, material leads to an adsorption process while microscopically the IL phase absorbs the mercury compound) with a content of 60 tons of SILP material. To the best of our knowledge this marks the first publication on a commercial SILP application on a refinery scale. 

Solid-Supported Ionic Liquid Phase Hydroformylation... 

The term Supported Ionic Liquid Phase (SILP) catalysis has recently been introduced into the literature to describe the heterogenisation of a homogeneous catalyst system by confining an ionic liquid solution of catalytically active complexes on a solid support [68], In comparison to the conventional liquid-liquid biphasic catalysis in organic-ionic liquid mixtures, the concept of SILP-catalysis offers very efficient use of the ionic liquid. Figure 7.10 exemplifies the concept for the Rh-catalysed hydroformylation. 

A rather new concept for biphasic reactions with ionic liquids is the supported ionic liquid phase (SILP) concept [115]. The SILP catalyst consists of a dissolved homogeneous catalyst in ionic liquid, which covers a highly porous support material (Fig. 41.13). Based on the surface area of the solid support and the amount of the ionic liquid medium, an average ionic liquid layer thickness of between 2 and 10 A can be estimated. This means that the mass transfer limitations in the fluid/ionic liquid system are greatly reduced. Furthermore, the amount of ionic liquid required in these systems is very small, and the reaction can be carried in classical fixed-bed reactors. 

An area in which functionalised ionic liquids are already playing an important role in catalysis is heterogenisation on solid supports. The general concept involves the immobilisation of imidazolium and other cationic fragments onto solid supports using appropriate functional groups attached to the cation. An ionic catalyst then resides within the ionic matrix and several examples of such supported ionic liquid phase catalysts are provided in the subsequent chapters of this book. The concept is illustrated in Figure... 

C jimlfPFe] Pd(OAc)2 Pd(PPh3)4 Et3N k2co3 100-150 °C. Supported ionic liquid phase catalysis (SILP) with silica as solid phase catalyst relatively stable for at least 5 runs product decanted and solid phase washed with hexane less than 0.24% catalyst loss. [87]... 

Another method used for recycling TSOSs consists in using the so-called supported ionic liquid phase (SILP) [44-49], The general principle is using an OS with a trialkoxysilane moiety that can be grafted covalently to a particle of silica. The particle, now coated with onium salt, has a special affinity for other onium salts, especially ILs. ILs can therefore get immobilized on a solid particle and subsequently be used for immobilizing other reagents (transition metal complexes, proline, etc.). This method has recently been reviewed and employs mostly non-functional ILs, so it won t be explained in more detail [44-49] (Fig. 17). 

The concept of immobilized ionic liquids entrapped, for instance, on the surface and pores of various porous solid materials (supported ionic liquid phase, SILP) is rapidly become an attractive alternative. In addition, the SILPs can also answer other important issues, such as the difficult procedures for product purification or IL recycling, some toxicity concerns and the problems for application in fixed-bed reactors, which should be addressed for future industrial scale-up. This new class of advanced materials shares the properties of true ILs and the advantages of a solid support, in some cases with an enhanced performance for the solid material. Nevertheless, a central question for the further development of this class of materials is to understand how much the microenvironment provided by the functional surfaces is similar or not to that imparted by ILs. Recent studies carried out using the fluorescence of pyrene to evaluate the polarities of a series of SILPs based on polymeric polystyrene networks reveal an increase in polarity of polymers, whereas the polymer functional surfaces essentially maintain the same polarity as the bulk ILs. However, this is surely not a simple task, in particular if we consider that the basic knowledge of pure ILs is still in its infancy, and we are just starting to understand the fundamentals of pure ILs when used as solvents. 

If the transport limitation is significant, the catalysis occurs predominantly near the surface of the ionic liquid, and the [Rh(CO)2l2] dissolved in the bulk is not fully utilized. One attempt to address these issues was to use a supported ionic liquid phase (SILP) catalyst, as reported by Riisager et al. [Ill], In this system, the ionic liquid (l-butyl-3-methylimidazolium iodide) was supported as a thin film on solid silica (the thin film offers little mass-transport resistance) and used in a fixed-bed continuous reactor with gas-phase methanol. Rates were achieved that were comparable to those in Eastman s bubble column carbonylation reactor with gas-phase reactants [109], but using a much smaller amount of ionic liquid. 

Structured supported ionic liquid-phase (SSILP) catalysis is a new concept that combines the advantages of ionic liquids (ILs) as solvents for homogeneous catalysts with the benefits of structured solid catalysts. In an attempt to prepare a homogeneous IL film on a microstructured support, SMFs were coated by a layer of carbon nanofibers as described above. An IL thin film was then immobilized on the CNF/SMF support. The high interfacial area of the IL film enabled the efficient use of a transition metal catalyst for the selective gas-phase hydrogenation of acetylenic compounds [267,268]. 

Supported liquid-phase catalysis,in which the catalyst is dissolved in a small volume of solvent, adsorbed on, usually, a hydrophilic solid, seeks to resolve issues associated with substrate solubility in multi-phase catalysis and performance/catalyst leaching in supported catalysis reports on the hydroformylation of long-chain alkenes under both supported aqueous phase and supported ionic liquid-phase regimes have been reported. 

In Section 5.3 it was demonstrated with many examples that ionic hquids are indeed a very attractive class of solvents for catalysis in liquid-liquid biphasic operation (for some selected reviews see Refs. [16-20]). In this section, we wfll focus on a different way to apply ionic liquids in catalysis, namely the use of an ionic liquid catalyst phase supported on a solid carrier, a technology that has become known as supported ionic liquid phase (SILP) catalysis. In comparison to the conventional liquid-liquid biphasic catalysis in ionic liquid-organic liquid mixtures, the concept of SILP-catalysis combines well-defined catalyst complexes, nonvolatile ionic liquids, and porous solid supports in a manner that offers a very efficient use of the ionic liquid catalyst phase, since it is dispersed as a thin film on the surface of the high-area support. Recently, the initial applications using such supported ionic liquid catalysts have been briefly summarized [21]. In contrast to this report, where the applications were distinguished by the choice of support material, the compilation here will divide the applications using the supported ionic liquid catalysts into sections according to the nature of the interaction between the ionic liquid catalyst phase and the support. 

Figure 4.1 Major types of supported ionic liquids multilayer ionic liquid film (supported ionic liquid phase SILP) type A, coated heterogeneous catalyst (solid catalyst with ionic liquid layer SCILL) type B, covalently bound monolayer (supported ionic liquid SIL) type C.

If supported ILs are used for catalysis (supported ionic liquid phase, SILP solid catalyst with ionic liquid layer, SCILL), the layer thickness (Sj ) is small, mostly only a few layers or even only a monolayer, that is, 1 run. For a conservative estimation of the characteristic time of diffusion, we assume a value of 10 run, which is in the order of magnitude of the diameter of a mesopore. The characteristic... 

The properties of ILs can also be modified by supporting them on different sohd substrates (e.g., graphite, mica, silica, oxidized silicon, etc.), a concept known as supported ionic liquid phases (SILP) and introduced in the early 2000s by the groups of Mehnert [73], Fehrmann and Wasserscheid [74]. Research done in this area has shown that the SILP strategy can lead to drastically different behavior of the supported ILs, mainly due to the interactions between the anions and/or cations of the I Ls and the solid matrix. For example, Bovio et al. showed that, by supporting the IL l-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIMKNTfj]) on a solid matrix (e.g., amorphous silica, oxidized Si(llO), and mica), hquid-solid phase transitions are induced when thin films of IL rearrange to a sohd-like phase [75]. 

Haumann, M., Schonweiz, A., Breitzke, H., Buntkowsky, G., Werner, S. and Szesni, N., Solid-state NMR investigations of supported ionic liquid phase water-gas shift catalysts Ionic liquid film distribution vs. catalyst performance, Chem. Eng. Technol. 35,1421-1426 (2012). 

A heterogeneous catalytic system was prepared upon grafting a cationic dihydroimidazolium-tagged silane on solid Si02. The resulting supported ionic liquid phase (SILP) has been used to immobilize [y-l,2-H2SiV2Wio04o] and was employed in a mixture of acetonitrile/t-butyl alcohol at 20°C for the oxidation of different substrates terminal olefins (66-82% yield), non-hindered internal olefins (> 70% yield) in 24 h, and sulfides (81-95% yield) in 4—lOh. ... 

Another highly efficient protocol for the hydroformylation consists in the combination of an ionic liquid with a solid support material (Figure 6.1). This process denominated supported ionic liquid phase (SILP) catalysis is a concept that combines the advantages of ionic liquids with those of heterogeneous support materials and allows the use of fixed-bed reactors for continuous reactions. 

Highly polar organocatalysts such as amino acids and peptides are almost insoluble in conventional organic solvents, but they are soluble in ionic liquids. Because of these physical properties, asymmetric syntheses in ionic liquids under biphasic condition have been reported [124], Recently, combinations of solid catalysts and ionic liquids have been studied intensively. The supported ionic liquid phase catalyst is a new generation of the supported liquid-phase catalyst [125]. The supported ionic liquid phase catalyst 232 is readily prepared by adsorption of (S)-proline 13... 

Supporting ionic liquids in the pores of solid materials offers the advantage of high surface areas between the reactant phase and that containing the supported liquid catalyst. This approach is particularly useful for reactants with less than desired solubility in the bulk liquid phase. Another incentive for using such catalysts is that they can be used in continuous processes with fixed-bed reactors (26S). The use of an ionic liquid in the supported phase in addition to an active catalyst can help to improve product selectivity, with the benefit being similar to what was shown for biphasic systems. However, care has to be taken to avoid leaching the supported liquids, particularly when the reactants are concentrated in a liquid phase. 

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