Kenics static mixers enhance mixing under laminar flow conditions. The ideal static mixer achieves efficient mixing at a low pressure drop. A modified design of the Kenics static mixer is analyzed, featuring gaps between the mixing elements, which can achieve the same level of mixing as the conventional design but with fewer mixing elements and a substantially lower pressure drop. The mixing effects at the entrances and exits of the mixing elements are enhanced by the introduction of gaps between the elements. The performances of mixers based on the right−left and right−right configurations with different gap lengths are characterized in terms of pressure drop, coefficient of variance of concentration, residence time distribution, and extensional efficiency with computational fluid dynamics simulations. Furthermore, the coefficient of variance of concentration is measured experimentally with several three-dimensional (3D) printed devices. The gaps reduce the mixing length when the design is based on the right−right configurations, and the gap-to-diameter ratio is 0.5 or 1.0 compared to the corresponding conventional design. Furthermore, Taylor dispersion is suppressed with the introduction of gaps, which enables a narrower residence time distribution. The presence of gaps between mixing elements introduces an additional degree of freedom, which can be utilized to strike a compromise between the required mixing length and pressure drop.

Crystallization is an attractive separation and purification technique for proteins. However, protein crystallization often suffers from long batch times due to slow crystallization kinetics. Furthermore, brittle protein crystals may be subject to attrition in conventional crystallizers. An airlift crystallizer is fabricated using three-dimensional (3D) printing and characterized for crystallization of lysozyme. The desupersaturation profile is substantially shorter in the airlift crystallizer compared to a conventional stirred tank crystallizer for all tested conditions. Furthermore, the crystals from the airlift crystallizer are larger and less agglomerated. Finally, the biological activity of the product indicates that the airlift crystallizer preserves the functionality of the protein well. The increased throughput and larger crystals with reduced agglomeration demonstrate that an airlift crystallizer is well suitable for crystallization of a protein. This work also demonstrates how 3D printing can be used to fabricate innovative crystallizers rapidly and at a lower cost, which is especially important for early learning during process development.

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