Combined impact of pH, catalyst, and strongly non-ideal solvent mixtures (SNISMs) towards boosting acid-catalyzed reactions

• Applicants: Professor Dr.-Ing. Jakob Albert; Privatdozent Dr.-Ing. Christoph Held
• Subject Area: Technical Chemistry ; Chemical and Thermal Process Engineering
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 525252957

The interplay between reaction medium and catalyst tremendously dictates the efficiency of processes involving chemical syntheses. Homogenous catalysis requires monophasic conditions and thus, a high substrate solubility, fast kinetics, high yield, and outstanding recyclability of solvent and catalyst. Chemical reactions under elimination of water require a reaction medium that keeps thermodynamic water activity as low as possible in order to overcome yield limitations caused by thermodynamic equilibrium, while the thermodynamic reactant activity and thermodynamic catalyst activity (e.g., proton’s activity) must be as high as possible. The use of single solvents usually allows tuning only one of these properties, e.g. decreasing water activity in water-elimination reactions might be possible only at cost of decreased kinetics by negative impact on the activity of reactant or catalyst. Thus, in this project we suggest exploring strongly non-ideal solvent mixtures (SNISMs) that show pronounced negative deviations from Raoult’s law and their usefulness in reactions under elimination of water. SNISMs can be more or less hydrophilic, depending on their constituents. So far, the influence of SNISMs on the phase behavior in reaction mixtures as well as yield and kinetics of the reaction is not well known. The multifacetted influence of SNISMs on phase behaviour and reaction efficiency on top of other parameters (temperature, pressure, pH) cannot be investigated by experiments only. Thus, a predictive tool is required to gain insight into the mechanism of strongly acidic catalysts like heteropolyacids (HPAs) and to predictively tailor HPA-SNISM dream teams. These will allow catalyzing reactions under water elimination at comparably low temperatures and a tuneable separation and recycling of the catalyst. The new idea of this project is to link thermodynamic properties of the HPA-catalyst (physical interactions) and the dissociation equilibria (especially of the catalyst) with the reaction efficiency as function of the reaction media (SNISM constituents and concentrations). The dissociation equilibria and the HPA interactions will be predicted by electrolyte thermodynamic models, validated by IR characterization. We postulate that kinetic curves will fall together if the reaction velocity is related to the thermodynamic activity of the catalyst. To sum up, we aim at tailoring SNISMs for liquid-phase reactions, revealing the influence of water and of HPA-catalyst on the phase behaviour of the SNISMs and the influence of SNISMs and of HPA-catalysts on reaction thermodynamics and kinetics, and to validate predictive electrolyte models using the gathered data to finally develop predictive kinetic models. Further, we aim at establishing recyclability concepts for SNISMs and HPA-catalysts and to improve TONs, TOFs, and spacetime yield. We will validate our findings by applying the gained knowledge to another reaction system under water elimination.

• DFG Programme: Research Grants