Technology for liquid-liquid extraction process development

In recent years, laboratory scale equipment for flow chemistry has become both commercially available and widely used in industry and academia. There has been particular focus on reactor design, in-line analytics and performing multistage synthesis. One of the challenges that has arisen as a consequence of introducing active mixing of multiple phases and multiple reaction steps is the need to remove impurities from reaction streams and efficiently separate multiple phases from one another. The devices currently available for performing liquid-liquid separation steps at laboratory scale have limitations in performance, control and scalability. This thesis presents a new laboratory scale separation device that utilises nonwoven coalescing filters to separate challenging emulsion systems, adapt to changing system inputs and integrate with current flow technology.
A literature review of flow chemistry and its benefits, liquid-liquid system characteristics, laboratory scale separation equipment and nonwoven coalescing filters has been conducted.
In order to characterise different liquid-liquid systems an image analysis technique was developed. The image analysis technique was used to determine phase separation rates in liquid-liquid systems. The technique was used in the lab on multiple samples at once with minimal change to the algorithm input parameters. The analysis technique was tested on both fast and slow settling systems with different phase ratios. In order to demonstrate the value of the imaging technique a selection of systems were scaled up to 20 Litres so that the separation rate of the scaled up mixtures could be compared to the 10 ml samples. The scaled up systems showed good correlation with the small scale counterparts which showed that the small scale experiments could be used to predict separation behaviour at a larger scale.
A laboratory scale continuous separation device was then developed which utilised nonwoven coalescing filter media to rapidly separate liquid phases. The device has an integrated control scheme that relies on conductivity measurements and downstream valve or pump control. The user is able to specify different flow rates and phase ratios and the system adapts automatically to different solution conductivities. The device’s performance was compared with a commercially available separation device based on different flow rates, phase ratios and liquid pairs. The performance depending on what filter media was used and the batch separation rate (determined by the aforementioned image analysis technique) was also considered.
The separation device was then developed further so that it could be used as a multistage extraction platform, allowing the testing of complex extraction processes at a laboratory scale. Two extraction systems were tested, an Acetone extraction from water and an extraction of Benzoic acid derivatives. Both systems provided challenges for the system such as emulsion formation and large changes in phase ratio. The device enabled the study of these two systems at laboratory scale, providing valuable insight into the system behaviour at low cost and with a small footprint.