Continuous Crystallization of Proteins in a Stirred Classified Product Removal Tank with a Tubular Reactor in Bypass

A lab-scale stirred tank with a cooled tubular reactor in bypass was applied for continuous crystallization of lysozyme and a full-length therapeutic monoclonal antibody. The stirred tank was operated as a mixed suspension classified product removal crystallizer. Lysozyme was crystallized by a combination of cooling crystallization and salting-out. The antibody was crystallized by a combination of cooling crystallization and isoelectric crystallization. It was deduced that nucleation rates were enhanced when the protein solutions passed through the cooled tubular bypass. It was further deduced that crystal growth rates were enhanced in the stirred tank which was operated at a higher temperature compared to the tubular reactor. Classified product removal was possible by controlled sedimentation of protein crystals. The continuous crystallization system allowed a targeted control of crystal morphology and size. No sedimentation occurred in the tubular reactor and precipitation was avoided at all times. High crystallization yields of more than 90% were obtained. Crystals of the monoclonal antibody were continuously produced for the first time with a space-time yield of up to 12 g L^-1 h^-1.