In this work, we developed a biphasic designer solvent system for enzymatic biotransformation, to demonstrate automatic purification and enzyme reuse, in the frame of a new process concept reported recently (solvent-enabled factory, One-Flow project). “Automatic” refers to instantaneous operation by preferential solubility between two immiscible phases, which does not require (sophisticated) process control (“automated”). The reaction studied is lipase-catalyzed hydrolysis of 4-nitrophenyl acetate. As a designer solvent, the class of ionic liquids (ILs) has been chosen, and their usage is largely documented in the biocatalysis literature. Three ILs are chosen; all with the 1-butyl-3-methyl-imidazolium cation and differing in their anions, being tetrafluoroborate, bis(trifluoromethylsulfonyl)-imide, and hexafluoro-phosphate. The first IL forms a monophasic system and thus was left out of consideration. The other two form the desired biphasic system, when being contacted with water, respectively. The operation of that system is hampered by foaming, that is, the formation of an interfacial emulsion layer as the third phase, which makes phase separation difficult. Therefore, we investigated in detail the phase behavior of the batch and flow-processed fluid systems under various process conditions. Batch processing, which causes tremendous foaming, needs intense stirring because of the high IL viscosity. Continuous-flow reactors provide an alternative because they stir more softly by their shear-enforced convection in their liquid slugs. As a result, they do not show foaming, and therefore, separation in phases is facile. With that issue solved, we report here for the continuous-flow biocatalytic reaction that we achieved high-level product purification and (three times) recycling of the enzyme.