Optimal Reactor Design for the Hydroformylation of Higher Olefins in a Multiphase System

Hydroformylation of alkenes is one of the most important homogeneously catalyzed processes in the chemical industries. The Ruhrchemie-Rhône-Poulenc process used for short chain alkenes cannot be applied for long chain alkenes due to their limited solubility in the aqueous phase. Hence, several innovative solvent concepts which allow catalyst separation were developed for long chain alkenes. Biphasic ionic liquid systems [1, 2] are one of these promising concepts, however, a model based analysis and an optimal reactor design for such systems is still missing. In this work, a model for the Rh-catalyzed hydroformylation of linear long chain alkenes in a biphasic ionic liquid system from literature [2] is extended and an optimal reactor design is proposed. The reaction takes place in the ionic liquid phase. The organic liquid phase supplies the alkene and extracts the aldehyde while the gas phase supplies hydrogen and carbon monoxide. In order to develop an optimal reactor, our recently proposed reactor design methodology [3] based on elementary process functions [4] is applied. By tracking a fluid element on its way through the process the fluxes into the element are adjusted dynamically to optimize a certain objective such as the selectivity. This results in a dynamic optimization problem constrained by the balance equations, reaction kinetics, thermodynamics, and initial and final conditions. The dynamic optimization problem is solved using collocation on finite elements and state-of-the-art NLP solvers such as CONOPT and IPOPT. Instead of choosing a reactor design a priori and optimizing the free parameters of the chosen reactor set-up, an optimal reactor design is developed based on the best route in state space. In a three step approach [3] possible control variables are identified, optimal profiles are calculated and an optimal reactor design, which approximates these profiles best, is proposed. Figure 1 illustrates an improvement in selectivity by 26% along with a significantly reduced residence time for the optimized process compared to the published data [2]. References: [1] Brasse, C. C.; Englert, U.; Salzer, A.; Waffenschmidt, H.; Wasserscheid, P.: Ionic Phosphine Ligands with Cobaltocenium Backbone: Novel Ligands for the Highly Selective, Biphasic, Rhodium-Catalyzed Hydroformylation of 1-Octene in Ionic Liquids. Organometallics, 3818-3823 (19), 2000. [2] Sharma, A.; Julcour Lebigue, C.; Deshpande, R. M.; Kelkar, A. A.; Henri Delmas, H.: Hydroformylation of 1-Octene Using [Bmim][PF6]−Decane Biphasic Media and Rhodium Complex Catalyst: Thermodynamic Properties and Kinetic Study. Ind. Eng. Chem. Res., in press. [3] Peschel, A.; Freund, H.; Sundmacher, K.: Methodology for the Design of Optimal Chemical Reactors Based on the Concept of Elementary Process Functions. Ind. Eng. Chem. Res., in press. [4] Freund, H. and Sundmacher, K.: Towards a Methodology for the Systematic Analysis and Design of Efficient Chemical Processes – Part 1: From Unit Operations to Elementary Process Functions. Chem. Eng. Process., 2051–2060 (47), 2008