SILP catalyst

Figure 7.11. Set-up for the continuous, Rh-catalysed propene hydroformylation using an impregnated SILP-catalyst...

TABLE 7.5. Continuous, Rh-catalysed hydroformylation of propene using impregnated SILP-catalysts with different ligands - results at 300 min time on stream... 

The ionic liquid investment could be further reduced if future research enables the application of ammonium based alkylsulfate or arylsulfonate ionic liquids. For these systems bulk prices around 15 /kg are expected. Ammonium based alkylsulfate or arylsulfonate ionic liquids usually show melting points slightly above room temperature but clearly below the operating temperature of the hydroformylation reaction. Therefore these systems may be less suitable for the liquid-liquid biphasic process in which the ionic liquid may be involved in process steps at ambient temperature (e.g. phase separation or liquid storage). In contrast, for the SILP catalyst a room temperature ionic liquid is not necessarily required as long as the film becomes a liquid under the reaction conditions. Assuming an ammonium based SILP catalyst, the capital investment for the ionic liquid for the industrial SILP catalyst would add up to 105,000 . 

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. 

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. 

Fig. 41.13 Supported ionic liquid phase (SILP) catalyst. The ionic liquid phase containing a rhodium complex is immobilized on the surface of a silica gel support material.

To our knowledge, there is to date only one report concerning asymmetric hydrogenation using a SILP catalyst [117]. Methyl acetoacetate was hydrogenated using Ru-BINAP dissolved in [BMIM][PF6] and immobilized on the poly(diallyl-dimethy-lammonium chloride) support (Fig. 41.14). 

Fig. 42.7 Ionic liquid and its support used for making SILP catalyst [63].

Fig.1 Schematic presentation of supported ionic Liquid Phase (SILP) catalyst...

The use of catalytic SILP materials has been reviewed recently [10] covering Friedel-Crafts reactions [33-37], hydroformylations (Rh-catalyzed) [38], hydrogenation (Rh-catalyzed) [39,40], Heck reactions (Pd-catalyzed) [41], and hydroaminations (Rh-, Pd-, and Zn-catalyzed) [42]. Since then, the SILP concept has been extended to additional catalytic reactions and alternative support materials. In this paper we will present results from continuous, fixed-bed carbonylation and hydroformylation reactions using rhodium-based SILP catalysts as reaction examples demonstrating the advantages of the SILP technology for bulk chemical production. 

All the preliminary measurements of the Rh-3/5/Si02 (denoted as Rh-3-SILP) catalyst discussed so far were initially studied at 100 °C and 10 bar syngas pressure (H2 CO 1 1) over a period of up to 36 h. This time on stream was further extended to 180 hours to test the long-term stabihty of the Rh-3-SILP dehydroxylated catalyst system (Fig. 3). 

Fig. 3 Long-term stability of Rh-3-SILP catalyst in continuous gas-phase hydroformyla-tion of propene. (Reaction conditions T = 100 °C, ptotai = 10 bar with pH2 = Pco =4.1 bar andppropene = 1.8 bar, M hodium = 3-53 X 10 mol, r = 0.38 s) [31]...

To verify the homogeneous nature of Rh-3-SILP catalysts, as previously suggested based on IR and NMR spectroscopic studies, [30] kinetic experiments have also been conducted with the catalyst. Here, a continuous fixed-bed reactor setup equipped with online gas-chromatography, described elsewhere in detail, [31] was applied. The general rate law for the hydroformylation of propene was assumed ... 

Fig. 5 Activity of Rh-3-SILP catalyst at different syngas compositions (pH2 Pco ratios) and temperatures (Reaction conditions T = 100°C, ptotai = 10bar) [32]...

The SILP catalyst system was applied for water-free gas-phase carbonylation of methanol at two different gas space velocities, using a continuous... 

Interestingly, the dimeric Cr(salen) catalyst 64 supported on silica showed enhanced activity for ARO of 1,2-epoxyhexane and cyclohexene oxide in the presence of ionic liquids particularly with [BMIM][PF6] (64-IL) [86] (Table 6). A significant increase in the product selectivity was also observed with silica supported ionic liquid (64-SILP) for ARO of 1,2-epoxyhexane and cyclohexene oxide (ee, of 87% and 75% respectively) as eompared to silica supported catalyst minus the ionie liquid (Table 6, entries 5,6). However, after repeated recycling, the silica support material deteriorates due to the abrasive forees in the stirred reactor. As a result, silica material was non-recoverable, but the expensive dimeric Cr(salen) catalyst 64 and the ionic liquid was recovered quantitatively by Soxhlet extraction with acetone. SILP-catalyst system was also used in a eontinuous-flow reactor. 

The catalyst/substrate ratio is 1.5 mol% for the supported ionic liquid phase (SILP) catalyst, 3 mol% for the impregnated catalyst and 2 mol% for the homogeneous reaction aRuns 1 -4 are consecutive experiments with the same catalyst in a stirred batch reactor. bDimeric Cr (salen) catalyst impregnated on silica cHomogeneous reaction at 0-2 OC optimized for product selectivity dHomogeneous reaction at room temperature optimized for product selectivity... 

Figure 38. Schematic representation of the surface cross section of a SILP catalyst in a...

Higher alkenes too, liquid at room temperature, can be hydroformylated over a fixed bed SILP catalyst. In this case the carrier gas is scCO . which is soluble in ILs but does not dissolve ionic compounds. For example, 1-octene, CO and H2 are mixed in SCCO2 and flowed through a tubular reactor containing the catalytic system 37 (Figure 40) dissolved in [omim][Tf2N] which, in turn, is supported on silica gel. 

The L-proline-catalyzed direct asymmetric aldol reachons between acetone and aldehydes in a SILP have also been investigated (Scheme 7.29) [83]. The major advantages of SILP catalyst systems are that the amount of expensive iorhc liquid used as the reaction medium can be reduced, the catalyst can be recovered by simple filhation, and it can be used in homogeneous form. The results obtained... 

Hydroformylation and Carbonylation Reactions Promoted by SILP Catalysts... 

Butene has been also successfully hydroformylated under these conditions using the SILP catalyst, which exhibited a higher activity and selectivity with respect to propene. 

SILP catalysts are versatile materials that can be also used under standard batch conditions. Thus, allyl alcohol was hydroformylated with a SILP Rh/ PPhs system, affording 80-90% of linear aldehydes with nii up to 31 (Scheme... 

Another SILP catalyst used under batch conditions employed mesoporous MCM-41 as the solid support. The catalyst was derived from [Rh(CO)2(acac)] and TPPTS (1 5 mol ratio) in the desired IL. The excellent catalytic performance of this SILP catalyst in the hydroformylation of C6-C12 linear alkenes (TOF up to 500 h ) was determined by the large surface area and uniform mesopore structure of MCM-41 and was almost independent of the type of IL used [bmim][BF4], [bmim][PF6] and 1,1,3,3-tetramethylguanidinium lactate. 

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