Utilization of milli-scale coiled flow inverter in combination with phase separator for continuous flow liquid–liquid extraction processes

Abstract

Process-design intensification situated under the umbrella of Novel Process Windows heads for process integration and here most development is needed for flow separators. The vision is to achieve multi-step synthesis in flow on pilot scale. This calls for scale-up of separation units. This study is rare and thus conducted here. The coiled flow inverter (CFI) was considered as the right tool to work at higher flow rates. A milli-scale CFI with tube internal diameter of 3.2mm and tube length of 210cm was used where partitioning takes place in slug flow. Phase separation was achieved with PTFE membrane flow separator or slit shaped flow separator composed of glass and Teflon rectangular capillaries. The microextraction unit was tested for model systems of toluene–water–acetone and n-butyl acetate–water–acetone. High extraction efficiency close to thermodynamic equilibrium was achieved for both systems. The CFI setup was also compared with straight tube and CFI showed about 20% higher extraction performance with the increase in flow rate. In straight tube, parallel flow developed at higher flow rates whereas the CFI kept operating in the slug flow regime. Membrane separator could be used up to 20ml/min, however pure organic phase was attained throughout. With slit shaped separator, for the butyl acetate–water–acetone system, 20% breakthrough occurred at a flow rate of 32ml/min. For the model system of toluene–water–acetone flow rate up to 120ml/min (7.2l/h) was achieved at same breakthrough level indicating the influence of interfacial tension on the operating window of separator. It is important to point out that slug flow regime that is limited to microfluidic systems was maintained even at such pilot scale (58m3/y).