Study on the influence of lysozyme crystallization conditions on crystal properties in crystallizers of varied sizes when temperature is the manipulated variable

In this work, crystallization experiments were conducted in three different sizes of crystallizers (5 and 100 ml, and 1 L) to study the influence of temperature on the crystallization of lysozyme. Lysozyme solutions with concentrations of 40 and 30 g L−1 and 10% (w/w) NaCl were used. The temperature was reduced from 20 to 0 °C with various cooling rate and stirring speed. The data indicated that crystallization with cooling but without agitation or with agitation but without cooling led to low yield and inconstancy between batches, whereas that with combined cooling and agitation resulted in tetragonal crystals with high yields. Parameters, including crystallization onset, crystal morphology, crystal size distribution, concentration, supersaturation, and yield were examined by in situ and ex situ observations. The observations within small cooling rate range of 0.030-0.111 °C min−1 indicated that minor changes in cooling rate could cause significant differences in these parameters. The comparison with thermostatic experiment showed that cooling could cause the crystal sizes to be widely dispersed. While high cooling rate lead shorter crystallization onset time and higher supersaturation, thereby result in larger crystal size, higher tendency of aggregation and wider crystal size distribution, low cooling rate can pose a great challenge to the temperature control in scale-up crystallization. The work also demonstrated that the crystallization conditions obtained from 5- to 100-ml crystallizers, from which well-defined crystals with high yields were obtained, could successfully be reproduced in 1-L crystallizer.