No abstract

The influence of mechanical stress on the crystal size distribution of lysozyme crystal slurries in a dynamic cross-flow device is discussed. The reduction of crystal size may have an influence on mass and resistance of the fouling layer. A filter test device with a filter area of 130 cm 2 is used for thickening. After thickening, a model impurity, namely bovine serum albumin, is washed out of the suspension. A reduction of crystal size due to stirring and a reduced fouling layer with increasing stirrer speed is observed. Furthermore, a higher stirring speed increases the specific filtrate flux. In the presence of the impurity, more crystal aggregates than single isometric crystals are formed and, hence, the decrease of crystal size due to shear forces is more pronounced than without impurity.

Research Article Downscaling cake filtration-Correlations between compressibility of lysozyme crystal filter cakes and filter areaCrystallization is a commonly used method for the purification and formulation of proteins. In order to harmonize crystallization with the mechanical separation process, it is necessary to estimate early the separation conditions of protein crystals. To fulfill this requirement, the feed material for filtration is minimized by reducing the filter area. The filtration behavior of lysozyme crystals in pressure filters with two different filter areas was compared. Crystal slurries with different mean crystal sizes and shapes were produced and the influence of the size and shape on the scalability of filtration data was examined. It was found that for different aggregated crystal structures and isometric crystals, the larger the compressibility of the cake was, the larger were the deviations for the two considered filter areas. For needle-shaped crystals, the compressibility was not subject to deviations, but the absolute filter cake resistance was. Furthermore, the deviations of the cake resistances increased with higher pressures for all product systems. It was indicated that upscaling from the small filter area is possible for low compressible product systems and at low pressures. With high compressible products and for needle-like crystals, the filtration time is underestimated with the small filter area.

No abstract