Molecular Design of Thermomorphic Solvents for the Hydroformylation of Dodecene

Molecular design of thermomorphic solvents for the hydroformylation of dodecene

Kevin McBride¹, Kai Sundmacher^1,2

¹Max Planck Institute for Dynamics of Complex Technical Systems, Magdeburg/DE

²Process Systems Engineering, University of Magdeburg, Magdeburg/DE

The use of thermomorphic multi-component solvent (TMS) systems is an innovative concept to incorporate homogeneous reactions with efficient catalyst separation via a temperature induced phase split. In the rhodium catalyzed hydroformylation of long chain olefins, the TMS is a promising prospect due to the requirement that the expensive catalyst complex be recycled quantitatively. Thus, the key characteristic of the TMS is its temperature sensitivity, meaning that the phase behavior of these solvents can be tuned using temperature as the control variable. We keep the temperature high during the reaction, forming one phase, and then, with a reduction in temperature, form two liquid phases where the catalyst is selectively removed from the other components. Sought after properties are a relatively wide miscibility gap and low distribution of the catalyst. In this regard, selection of the solvent is a critical aspect of the successful implementation of such a reaction.

Current methods used to select candidate solvents for TMS do not contain molecular information. The most current approach uses Hansen parameters and temperature limitations; however, they do not contain information about the liquid-liquid phase behavior. Hence, the design space of the existing methods is limited. In addition, the effect that the product has on the miscibility gap is not considered in the preliminary evaluation. The effect of the TMS process-wide has also not been investigated.

In this work, we take both of these considerations into account. Using other models such as modified UNIFAC or COSMO-RS, which contain information about the solvents at the molecular level, solvent screening is conducted. Using a geometric analysis of the liquid-liquid equilibrium at various temperatures, candidate solvents are identified. Upon further inspection for feasibility, reactivity of the solvents, and influence of the product on the miscibility gap, screened candidates are inserted into an optimizer that finds the minimum cost of the selected process flowsheet. Here, we use the hydroformylation of dodecene as an example reaction with the goal of finding the optimal polar solvent for the TMS with decane as the non-polar component.

By using this procedure, we show that a rigorous TMS screening method combined with process-wide optimization, allows us to consider the overall effects of the TMS on cost during the initial process design.