SILP Catalyst Development

On the base of a Rh-price of about 20,000 /kg and a ligand price of about 1000 /kg it becomes quite obvious that the loss of the ionic liquid would only be a minor part of the overall cost arising from the case of complete SILP-catalyst deactivation. It should be noted that a deactivated SILP catalyst may still offer some options for regeneration (e.g. extraction with scC02 to remove heavies). However, these options are not yet developed and their efficiency is unclear at this point. 

A summary of the research activities of the last four years reveals three different important trends (a) The design of new ionic ligands for excellent catalyst immobilisation in ionic liquids and high regioselectivity (b) the successful application of cheap, halogen-free ionic liquids in the biphasic Rh-catalysed hydroformylation (c) the successful development of unusual multiphasic reaction concepts for Rh-catalysed hydroformylation, namely catalysis in ionic liquid/supercritical C02 and SILP-catalysts. 

Wasserscheid P, Joni J, Haumann M (2009) Development of a supported ionic hquid phase (SILP) catalyst for slurry-phase Friedel-Crafts alkylations of cumene. Adv Syn Catal 351 423 31... 

Silica gels have been used in recent years as supports for the immobihzation of ILs in order to improve their applicability and reusabiHty in industrially important catalytic processes. In particular, there have also been numerous studies in which silica gels are used as inorganic supports for the development of recyclable and efficient catalytic systems based on supported ILs, namely, supported ionic hquid phase (SILP) catalysts [57-59], supported ionic liquid catalysts (SILCs) [60-62], and solid catalysts with ionic liquid layers (SCILL) [63]. 

The goal of the IL screening is a time- and cost-efficient development of SILP catalyst systems. The reaction that takes place in the system can be described by equilibrium thermodynamics. For a given reaction (Eq. (9.11)), the equihbrium constant K can be expressed in terms of the previously derived activity... 

In a subsequent series of experiments at Stid-Chemie AG, deeper insight into the catalytic performance could be achieved [68]. As a final result, a comparison of a state-of-the-art heterogeneous Cu/ZnO/AljOj LTS catalyst and the optimized SILP WGS catalyst developed in this thesis was carried out Results from the performance of these two catalysts at different GHSVs and temperatures are depicted in Figure 16.14. 

The first example of SILP-catalysis was the fixation of an acidic chloroaluminate ionic liquid on an inorganic support. The acidic anions of the ionic liquid, [AI2CI7] and [AI3CI10], react with free OH-groups of the surface to create an anionic solid surface with the ionic liquid cations attached [72]. The catalyst obtained was applied in the Friedel-Crafts acylation of aromatic compounds. Later, the immobilisation of acidic ionic liquids by covalent bonding of the ionic liquid cation to the surface was developed and applied again in Friedel-Crafts chemistry [73]. 

The few examples where SILP catalysis has been tested so far showed highly encouraging results. It is very likely that other applications where ionic catalyst solutions were tested in liquid-liquid biphasic reactions could be reinvestigated under SILP conditions. If very high catalyst stability over time can be realised or simple catalyst regeneration protocols can be developed than SILP catalysis can be expected to make its way into industrial processes. 

In summary, the Kobayashi solution to the development of a SILP for catalytic applications in liquid biphasic conditions implies the adoption of a more robust anchoring technique of the catalytically active species to the solid support and of a IL/solvent pair as far as possible in terms of mutual solubility, namely water and [dbim][SbF6]. The role of the IL impregnated on the solid support is that of creating a hydrophobic environment on the surface of the silica material where the catalyst, ionically bound to the organic spacer, exerts its role promoting the desired reaction. Since the catalyst is easily separated from water, the system could be easily optimised for recycle. 

Another example of successful SILP gas-phase reaction is the rhodium-catalyzed carbonylation of methanol [37]. The technical importance of this reaction is indicated by the Monsanto process, the dominant industrial process for the production of acetic acid (and methyl acetate), carried out on a large scale as a homogeneous liquid-phase reaction [38]. Using [Rh(CO)2l2] anions as the catalyticaUy active species, Riisager and coworkers have developed a new silica SILP Monsanto-type catalyst system [39] 21, in which the active rhodium catalyst complex is part of the IL itself. The SILP system was prepared by a one-step impregnation of the silica support using a methanoUc solution of the IL [BMIM]I and the dimeric precursor species [Rh(CO)2l]2, as depicted in Scheme 15.5. 

Apart from acidic catalysis, ionic liquids have been intensively tested in the last two decades for the immobilisation of homogeneously dissolved transition metal catalysts. Successful catalyst immobilisation techniques are essential for industrial homogeneous catalysis to solve the problem of catalyst/product separation and to recover and recycle the often very expensive dissolved transition metal complexes. Different immobilisation concepts applying ionic liquids have been developed, including the use of organic-ionic liquid multiphase reaction systems and the use of SILP catalysis. These concepts will be described in the following sections. 

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