Organic solvent nanofiltration: a potential alternative to distillation for solvent recovery from crystallisation mother liquors

Increasing demand for more sustainable processing has led to a renewed interest in the area of solvent recovery within the pharmaceutical industry. Distillation has been the conventional unit operation of choice, and though generating high purity solvent, distillation can be energy-intensive and a low energy alternative is desirable. A potential method has been identified in emerging separation technique organic solvent nanofiltration (OSN). The work presented here investigates the feasibility of using OSN as an alternative to distillation for solvent recovery. Results demonstrate that OSN is capable of recovering organic solvent with a purity suitable for re-use in subsequent active pharmaceutical ingredient (API) crystallisation. Energy-efficiency calculations for this case study demonstrate that OSN uses 25 times less energy per L of recovered solvent when compared to distillation. However, the efficiency of membrane based solvent recovery is restricted by solubility of the compounds within the waste stream which resulted in recovery of less solvent for OSN. Equivalent recovery volumes can be obtained by using a combined approach of OSN and distillation with the energy consumption remaining 9 times lower than when distillation is used alone.