Design and characterization of Kenics static mixer crystallizers

• Static mixers can approximate plug-flow behavior for continuous crystallizers. • Gapped Kenics and standard Kenics static mixer crystallizers are tested. • Numerical and experimental characterization of the static mixer crystallizers. • 3D printing for the fabrication of customized tubular crystallizers. • Gapped Kenics mixer leads to lower pressure drop and less segregation of crystals. Tubular crystallizers are desirable for continuous operations because they can approach plug flow conditions, achieve higher throughputs, and can be easy to control. However, the possible limitations of tubular crystallizers may include settling of crystals, fouling and higher pressure drops at longer residence times. The performance of a tubular crystallizer with gaps between the Kenics type mixing elements is characterized and compared with a standard Kenics static mixer and a hollow tubular crystallizer for the crystallization of lysozyme from solution. The gapped Kenics static mixer crystallizer provides an attractive trade-off between the standard Kenics static mixer and the hollow tubular crystallizer in terms of mixing length, shear rate, residence time distribution, pressure drop and segregation or settling of crystals. Furthermore, the gapped Kenics static mixer crystallizer and the standard Kenics static mixer crystallizer exhibit a similar crystallization performance in terms of desupersaturation profile and mean crystal size at the outlet for different initial lysozyme concentrations and seed loadings. The advantages of the gapped Kenics static mixer crystallizer in terms of pressure drop and minimization of crystal settling allow for lower flow rates and longer residence times under plug flow conditions, which has important practical benefits for continuous crystallization.