(755e) Extraction and Phase Separation of Api’s in Low Interfacial Tension Mixtures

Authors: 
Imbrogno, J., Massachusetts Institute of Technology
Rogers, L., Massachusetts Institute of Technology
Thomas, D., Massachusetts Institute of Technology
Jensen, K. F., Massachusetts Institute of Technology
Membranes are widely used in the biotechnology, food, petroleum, and water treatment industries, to name a few. Currently, they have not seen widespread use is in the pharmaceutical industry. This is due to the often harsh or chemically incompatible nature of many of the solvents used when producing pharmaceuticals. Additionally, nearly all pharmaceuticals are still produced using batch or semi-batch unit operations. However, the relatively new movement towards continuous production of pharmaceuticals presents an exciting opportunity for membrane based applications. Although many industries, such as petroleum refining and food production, have been using continuous processing for decades, the approach is relatively new to the pharmaceutical industry. Chemically inert membranes, such as polytetrafluoroethylene (PTFE), can be used for phase separation, purification, and extraction during or after synthesis of a pharmaceutical by utilizing membrane wettability. The organic phase will selectively wet the PTFE surface and permeate through, while the aqueous phase will be retained. This is a powerful tool during synthesis because it allows for continuous purification or extraction, instead of using semi-batch unit operations. Fully continuous production of a pharmaceutical allows for smaller scale and dead volumes, increased heat and mass transfer, faster process control, safer operation, and allows for the exploration of reactions that are too dangerous or difficult to perform in batch.

In this work, we utilize a unique membrane module with integrated pressure control that decouples the separation from downstream disturbances. This unique module removes the need for the user to individually control the pressure of the aqueous and permeate sides of the membrane. The pressure is controlled using a thin perfluoroalkoxy (PFA) polymer diaphragm that acts to modulate the pressure between the aqueous and organic sides of the membrane. The upper and lower bounds for operating this system while achieving complete separation correspond to the capillary and permeation pressure, respectively. The capillary pressure must be greater than the diaphragm pressure and the diaphragm pressure must be greater than the permeation pressure. These pressures can be controlled by varying the pore size and type of membrane and the thickness of the diaphragm.

This system has been successfully applied to the final synthesis steps of the production of several pharmaceuticals, including lidocaine and diazepam. These complex mixtures contained several organic solvents as well as aqueous salt solutions. The goal was to extract the active pharmaceutical ingredients (API’s) into the organic phase; hexanes for lidocaine and ethyl acetate for diazepam. In general, this type of separation would not be possible using a membrane, since the interfacial tension is too low, leading to breakthrough of the aqueous phase into the organic phase. We present a method to modulate the interfacial tension so that complete separation of the two phases is achieved. In addition to completely separating the two phases, 100% of the API’s were extracted into their respective organic phases. This was not previously possible and is a step towards the reliable extraction and phase separation of API’s in a fully continuous operation.