Enabling Hydroformylation in Micro-Emulsion Systems: Long-Term Performance of a Continuously Operated Mini-Plant

In the Collaborative Research Center SFB/TR 63 InPROMPT, novel process concepts for substitutable base chemicals in multiphase systems are being developed. Hereby, next generation liquid-liquid processes based on innovative solvent concepts are currently under research. One of these concepts is concerned with the hydroformylation of long-chained alkenes in micro emulsions. Hydroformylation has been established as a standard process for the production of short-chained aldehydes from alkenes. Its application to higher alkenes (longer than C₁₂) in a biphasic system with a rhodium catalyst, on the other hand, has not yet been established. To speed-up and aid in the process development within the collaborative research center, a mini-plant has been built at Berlin University of Technology (Technische Universität Berlin, TU Berlin).

The investigated process concept aims at reaching two goals: on the one hand, two normally immiscible liquids are to be mixed, while on the other hand a near to perfect separation of reactants is to be achieved. A promising approach lies in the application of a non-ionic surfactant. By creating a micro-emulsion, the surfactant enables the water soluble rhodium-ligand-catalyst required for the reaction to be brought into contact with the alkene [1]. The reaction is started by injecting syngas (H₂&CO) into the system. After the reaction, the miscibility gap between the hydrophilic catalyst solution and hydrophobic alkene/aldehyde mixture is exploited in order to recycle the valuable rhodium catalyst and separate the almost pure organic product phase. To test the viability of this concept, a long-term test-run in the mini-plant at TU Berlin has been performed.

Figure 1: Process concept for the hydroformylation of long-chained aldehydes in micro-emulsions [2].

The mini-plant was operated continuously for 100 hours supported by an operating team of 14 people in four shifts. The applied substances were 1-dodecene (educt), the non-ionic surfactant Marlipal 24/70 (CAS: 68439-50-9), a water soluble rhodium-based catalyst (CAS: 14874-82-9), and the water soluble ligand Sulfoxantphos (sulfonated form of Xantphos, CAS: 161265-03-8). The desired product is n-tridecanal. The crucial aspects of the concept, with regards to technical and economic feasibility, are the reaction as well as the separation step. The operating conditions for both steps were determined in previous analyses [2 - 4].

During mini-plant operation different reactor residence times, such as 45 and 120 minutes, were tested. In both cases the reactor was operated at 40 bar and 95°C. Batch experiments at similar reaction conditions showed a yield of 2,54% in 30 minutes and 4% in 60 minutes. These results equal those during the start-up of the mini-plant. During continuous operation, an average yield of 1-dodecene to n-tridecanal of about 20% was achieved for a reactor residence time of 45 minutes. In the latter case, where lower feed and recycle streams were applied to increase the reactor residence time to 120 minutes, a yield of about 31% was reached.

The second step of the process is the separation of the catalyst from the product. Here, the phase separation behavior of H₂O-oil-nonionic surfactant systems is exploited [5, 6]. Due to kinetic reasons, the three phase state is desired for the continuous process [2, 3]. Here, a separation into a catalyst-rich, a surfactant rich, and a product rich phase takes place. The lower two phases, catalyst and surfactant, are recycled. The main challenge during plant operation is the shift of the feasible operating points over time due to increasing product concentration inside the system. For the decanter, this means that the temperature needs to be regulated depending on the concentration of product inside the system. During plant operation, a concentration of up to 77 wt.-% of 1-dodecene in the oil and 11 wt.-% in the water phase could successfully be realized in the correct temperature region. Compared to test-tube results, where roughly 90 wt.-% of 1-dodecene remains in the oil phase, this performance is highly satisfactory.

Next to these successful results regarding the reaction and separation step, the long-term operation revealed noteworthy effects. Among these is fractioning of the surfactant during the phase separation step. Thus, another undesired shift of the optimal operating point in the decanter is carried out. As counter measures, surfactant rectification as well as continuous surfactant feeding during plant operation are taken into consideration for consecutive plant runs.

In this contribution selected results from the test run are presented, whereby merits and opportunities for the chemical industry as well as open challenges regarding the process concept are discussed.

Acknowledgment

This work is part of the Collaborative Research Center "Integrated Chemical Processes in Liquid Multiphase Systems" coordinated by the Technische Universität Berlin. Financial support by the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG) is gratefully acknowledged (TRR 63). Furthermore, the authors gratefully acknowledge the support of the company Umicore for sponsoring the rhodium catalyst “Acetylacetonatodicarbonylrhodium(I) (CAS: 14874-82-9)” used in the described experiments.

References

 

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[2]           Müller, D.; Esche, E.; Müller, M.; Wozny, G. (2012) Development of a Short-Cut Model for Three-phase Liquid Separation Dynamics for a Hydroformylation Mini-Plant, Presentation at the AIChE 2012, Pittsburgh, USA.

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