Resource-Efficient Solvent Utilization: Understanding the Dependencies of Solvent-Swap Efficiencies

Abstract

The use of solvents during manufacturing significantly impacts the environmental footprint of fine chemicals and pharmaceutical products. Selecting appropriate solvents requires careful consideration of how solvent combinations behave during solvent-swap and recovery processes. This is essential for developing environmentally friendly and efficient manufacturing practices in these industries. Based on our recent work on separation feasibility indicators (SFI) for solvent-swap processes, we investigate the influence of the type and characteristics of the applied solvent-swap procedure, as well as the thermodynamic characteristics of solvent mixtures on the solvent-swap efficiency. For this purpose, we distinguish between basic types of solvent–solvent mixtures based on their thermodynamic behavior. Our analysis reveals the key process-specific parameters influencing the solvent-swap efficiency and demonstrates that the type of the solvent-swap procedure employed (batch or semi-batch) has a considerable quantitative effect on the SFIs, while the overall qualitative ranking of solvent–solvent pairs remains largely unaffected. Consequently, a reliable quantitative assessment of solvent-swap efficiency cannot be conducted without accounting for the specific characteristics of the chosen procedure. Additionally, we demonstrate the importance of considering the real thermodynamic behavior of solvent mixtures, and we show that assuming ideal behavior can lead to large errors in the predicted solvent-swap efficiency and can thus result in the (pre-)selection of inadequate solvents with a low or even bad solvent-swap performance. Finally, this analysis allows us to establish some criteria and rules of thumb for a more adequate selection of solvents and solvent pairs based on their solvent-swap characteristics.