Computer Aided Design of Green Thermomorphic Solvent Systems for Homogeneous Catalyst Recovery
Introduction
The use of TMS has been shown to be a simple yet effective separation strategy in the recovery of homogeneous catalysts. Recently, a computational framework for a priori TMS design that incorporated predictions of catalyst solubility was developed (McBride and Sundmacher, 2015a) and experimentally validated (McBride et al., 2016) based on the quantum-chemical method COSMO-RS (Klamt, 1995). This design strategy was exemplified on the hydroformylation of 1-dodecene using the rhodium-Biphephos (Rh- BPP) homogeneous transition metal catalyst. Several potential TMS systems were identified and promising candidate systems were experimentally validated. Three of the considered TMS were very successful in recovering the catalyst and facilitating the reaction. Generally, the best performing TMS designs found consisted of mixtures using dimethylformamide (DMF) and alkanes in the range of C8 – C14 as the polar and nonpolar component solvents, respectively.
However, a TMS consisting of DMF and decane has already been used in long-chain olefin hydroformylation research for several years. Since catalyst leaching remains economically high using this TMS (McBride and Sundmacher, 2015b), an alternative recycling strategy using a series of counter-current extraction stages using additional DMF was investigated. An evaluation of this separation strategy as part of an overall process optimization predicted that improved recovery of the catalyst at more economical conditions is possible than previously (McBride et al, 2017). Nevertheless, due to its developmental toxicity, DMF is a solvent that should be substituted with a safer, more benign alternative. Continued use of this solvent is also in direct opposition to the idea of green and sustainable chemistry. Therefore a new computational strategy has been developed to find replacement solvents for DMF that are considered green and that would be suitable for recovering the catalyst as part of a multi-stage extraction.
Section snippets
Screening Method
This new method is based on the previous TMS design strategy first presented by McBride and Sundmacher (2015a), but with two major differences. Since it is known that an extraction process can be used to recover leached catalyst lost after the first decantation step (McBride et al., 2017), a solvent with lower catalyst recovery performance than DMF can be used. This allows one to explore a larger solvent search space than in the previous framework, increasing the potential to find a green
Screening Results
First, those solvents that are contained within the COSMObase (ver. 1301, COSMOlogic GmbH) are considered. The only physical property constraint used in this example is a restriction on molecular weight (< 200 g/mol), which leaves 6261 candidates. After screening the molecules using the criteria outlined in Section 2.1 and 2.2 and evaluating the phase equilibrium behavior of each resulting ternary system as outlined in Section 2.3, only three molecules remain. These are listed in Table 2 on the
Conclusions
This work presents a new framework for green solvent selection in TMS design used in replacing DMF as the currently used solvent in a TMS for catalyst recovery. The method was applied to the hydroformylation of 1-decene using the homogeneous rhodium-Biphephos catalyst. By considering the EHS criteria, catalyst ligand solubility, and LLE behaviors, several green solvents were identified. The LLE and reaction performance in two of these TMS designs were then experimentally validated. It was shown
Acknowledgement
This work was conducted in part in cooperation with the Collaborative Research Centre “Integrated Chemical Processes in Liquid Multiphase Systems”. The financial support from the German Research Foundation (DFG) under the grant SFB/TRR 63 is gratefully acknowledged.
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