Surface-Active Ionic Liquids as Epoxidation Catalysts: Reaction Control via Stimuli-Responsive Phase Change

• Applicants: Dr. Mirza Cokoja; Professor Dr.-Ing. Andreas Jess
• Subject Area: Technical Chemistry ; Chemical and Thermal Process Engineering
• Term: since 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 326649877

This project deals with the development of stimuli-responsive surface-active ionic liquids (SAIL) and their application in the biphasic epoxidation of hydrophobic olefins in water, using hydrogen peroxide as oxidant. The primary goal of the project is to synthesize tailor-made SAILs which quantitatively change their macroscopic micelle structure in aqueous solution and hence, their phase behavior upon application of external stimuli, such as temperature. In our previous project, we have shown that catalytically active SAILs can easily be separated from the hydrophobic product via decantation, whereas on the other hand, they are separable from water only via distillation. While the latter is no issue in batch reactions, in a continuous reactor distillation, i.e. separation is principally possible, but may be detrimental for a continuous reaction and eventually for an applicability, since distillation of water is highly energy consuming. Therefore, a switchable phase change should lead to a scenario, in which the SAIL forms micelles in order to start the epoxidation, while at the end of the reaction, the stimulus (e.g. change of temperature) “switches off” the micelle structure, which in turn leads to formation of a third phase of the SAIL. The pure SAIL can then be used again and can be recycled into the reactor, respectively. Based on this concept, in our cooperation project we will study the influence of systematic variations of different substituents at the imidazolium cation on the temperature range of the SAILs’ melting points, as well as on the temperature-dependent solubilization and micelle formation in aqueous media. The substituents control the strength of intermolecular cation-cation/cation-anion interactions, and the hydrophobicity/hydrophilicity of the SAILs. The most promising SAILs will be further screened for their catalytic activity in the epoxidation of cyclooctene as case model in a batch reactor, before their testing in a continuous flow reaction. From the kinetic and thermodynamic data, a reactor model will be calculated for the sake of transfer to a technical scale. The investigations of external stimuli for switchable phase transfer of SAILs will be concluded by studying light as stimulus. For this, cations of catalytically active SAILs will be functionalized by chromophoric substituents, which induce a structural change of the SAIL, affecting formation or collapse of micelles in solution.

• DFG Programme: Research Grants