(32d) Microemulsion Systems As Smart Solvent Systems for Homogeneous Catalysis: Rhodium-Catalyzed Hydroformylation of Long-Chain Alkenes in Aqueous Media

As a part of the Collaborative Research Center InPROMPT (TRR 63) we investigate the application of microemulsion systems as smart solvent systems for homogeneous catalysis. More than 60 scientific from different universities and institutions work together in this scientific network. The long-term goal of our research is to optimize these systems in order to exploit their characteristics in multiphase chemical reaction processes. Based on the kind of catalysis, they allow for the reuse of dissolved catalysts or even for a better solubilisation of hydrophobic reactants. Examples for the application of microemulsion systems in catalysis are reactions with homogeneous catalyst complexes (e.g. rhodium-catalyzed hydroformylation ^[1]), with supported catalysts (e.g. Heck coupling reaction on sol-gel supported palladium catalysts ^[2]), or even with enzymes. One critical aspect from an economic perspective is the quantitative recycling of the catalyst complex dissolved in the multiphase system. Therefore, it is important to know the concentration of the catalyst complex in each of the single phases.

Kinetics of the rhodium-catalyzed hydroformylation of 1-dodecene in microemulsion systems have been thoroughly investigated. Furthermore, the different parameters/factors were analyzed that may have an influence on the distribution of catalyst complexes in microemulsions, e.g. temperature, type of ligand, structure of surfactant, and chain length of surfactant. Finally, the derived information was used for the design of a continuous process for the hydroformylation of long-chain alkenes in microemulsions ^[3].

Experimental Results

Standard experiments were carried out by using a microemulsion system consisting of water (catalyst solution), 1-dodecene, non-ionic surfactant and a sodium sulfate amount of 1 wt%. We studied the phase behaviour of the resulting microemulsion systems with optical methods. The hydroformylation of 1-dodecene was investigated in semi-batch experiments, at temperatures of 80 to 110 °C and at syngas pressures of 3 to 40 bar. The rhodium catalyst carries a bidentate, hydrophilic ligand, SulfoXantPhos. The microemulsion used for the reaction is formulated from 1-dodecene, water and the technical grade non-ionic surfactant Marlipal 24/70. Syngas is used in a ratio of 1:1 and is dispersed in the solution by a gas dispersion stirrer. Conversion and selectivity are determined by GC analysis and online measurement of syngas consumption. We investigated the influence of several parameters on the reaction, e.g. temperature, pressure, surfactant, catalyst concentration, and ligand to metal ratio. In these experiments TOFs of >1000 h^-1and selectivities of 98:2 to the linear aldehyde could be achieved. With the gained knowledge from the separation experiments, the catalyst could be successfully recycled for at least four times and rhodium loss was found to be below 1 ppm.

References

[1] T. Hamerla, A. Rost, Y. Kasaka, R. Schomäcker; ChemCatChem 5 (2013) 1854.

[2] I. Volovych, Y. Kasaka, M. Schwarze, Z. Nairoukh, J. Blum, M. Fanun, D. Avnir, R. Schomäcker; J. Mol. Catal. A Chem. 393 (2014) 210.

[3] T. Pogrzeba, D. Müller, T. Hamerla, E. Esche, N. Paul, G. Wozny, R. Schomäcker; Ind. Eng. Chem. Res. 54 (2015) 11953.