Development of a Continuous Process for the Rhodium-Catalyzed Hydroformylation of Long Chain Olefins in Aqueous Liquid-Liquid Two-Phase Systems

In this contribution a novel low pressure process design for the Rhodium-catalyzed hydroformylation of long chain olefins in an aqueous multiphase system will be presented. The concept of two-phase catalysis is already a well established process for the Rhodium-catalyzed hydroformylation of short chain olefins, which allows easy separation and recycling of the expensive catalyst after the reaction. The hydrophilic metal-ligand complex is immobilized in the water phase and is insoluble in the organic phase (olefin and aldehyde). Generally the solubility of long-chain olefins is too low in the aqueous phase to react with the catalyst. In order to improve the solubilization, surfactant is added to formulate a multiphase system. The multiphase system acts as a tunable solvent, through which the interfacial area is increased during the reaction. The phase separation behaviour can be manipulated through temperature changes, thus allowing for an easy separation of the metal-ligand complex from the organic phase after the reaction. Based on that combination of reaction and phase separation for catalyst recycling a novel process concept for the hydroformylation of long chain olefins is developed, and the main challenges for a transfer to a continuous process are shown on the example of a mini-plant.

The reaction conditions for the hydroformylation of 1-dodecene (model substrate of a long-chain olefin) with a Rhodium-ligand-catalyst system are at temperatures of 80 to 110 °C and at pressures of 20 to 40 bar. The conditions are comparable to the hydroformylation of propene in the Ruhrchemie-Rhône-Poulence-process, but much lower in comparison to the established industrial cobalt catalyzed process for the hydroformylation of long chain olefins. In the hydroformylation reaction the bidentate ligand SulphoXantPhos is used to improve the selectivity to linear aldehydes. The linear aldehyde is the favored product because of its biodegradability and its further use as plasticizer or for the production of surfactants. Different aqueous multiphase systems, formulated by ternary mixtures of 1-dodecene, water and technical grade non-ionic surfactants like nonylphenol ethoxylates or alkyl ethoxylates, are investigated as tunable solvents. Also the influence of different process parameters such as the type and the amount of surfactant, metal/ligand ratio, temperature, pressure and water-to-oil ratio is discussed. The partition coefficients of the different compounds in the single phases of the multiphase systems are evaluated to describe the system adequately. Also the active catalyst species was identified. Under optimized reaction conditions turn over frequencies (TOF) of >300h^-1 and selectivities of 98:2 to the linear product can be achieved. During the recycling experiments the loss of rhodium catalyst through the organic phase can be held under 1ppm. 

In order to reduce development time and to gain experimental data and experience on the feasibility of the novel continuous process, a fully automated mini-plant, operated with the process control system Simatic PCS7^© from Siemens, was built at Berlin Institute of Technology (Technische Universität Berlin) in parallel to the lab scale experiments. The mini-plant includes a reaction section and a catalyst separation section, where a separation of both liquid phases takes place in a temperate decanter. The aqueous phase is recycled to the reaction section to win back the expensive Rhodium catalyst and therefore to establish a cost efficient process. Furthermore the mini-plant allows the investigation of the influence of recycled streams on the performance of the catalyst and on process stability in general.

This work is part of the Collaborative Research Centre "Integrated Chemical Processes in Liquid Multiphase Systems" coordinated by the Technische Universität Berlin. Financial support by the Deutsche Forschungsgemeinschaft (DFG) is gratefully acknowledged (TRR 63).