Using monoclonal antibodies in a cell culture harvest as an example for complex biomolecules, a mini-plant-scale aqueous two-phase purification process was studied. The results of this study indicate that antibodies can be concentrated and purified in a single extraction step employing a small phase ratio. Following the extraction step, a multi-stage wash-extraction for further purification was investigated. Starting at a test tube-scale cross-current wash, the process was advanced towards a continuous counter-current mixer-settler and column wash process. It was shown that a test tube cross-current extraction operation can predict the multi-stage purity reasonably well. The hydrodynamic process performance for the multi-stage wash column was evaluated and related to the separation performance.