An improved liquid–liquid separator based on an optically monitored porous capillary

Abstract

We report an easily assembled, high performance liquid/liquid separator constructed from a drilled-out block of aluminium, a short length of porous polytetrafluoroethylene tubing, and a small number of off-the-shelf components and 3D-printed parts. The separator relies on the two incoming liquids having different wettabilities to the wall of the porous capillary, with the more strongly wetting liquid leeching through the porous wall while the other liquid passes unhindered through the interior channel. To achieve complete separation of the two phases, the fluid streams at the separator outlets are monitored optically, and the back-pressure at one outlet is iteratively adjusted using a motorised needle valve until smooth time-invariant signals are recorded at both outlets. The separator may be applied to many pairings of immiscible liquids over a broad range of flow rates, automatically establishing complete separation within minutes of activation and adjusting dynamically to subsequent changes in the flow conditions. The separator – whose performance is competitive with far costlier commercial systems – is released here as open hardware, with technical diagrams, a full parts list, assembly instructions, and source code for its firmware.