Making large, flowable particles of protein or disaccharide in a mini-scale spray dryer

A mini-scale spray dryer, the ProCept 4M8, with a 1.4 m or 2.1 m drying chamber length has been used to prepare large, flowable particles of catalase, trehalose or lactose. A 25 kHz ultrasonic nozzle or a Rayleigh breakup mono-disperse droplet generator was used for atomization. The ultrasonic nozzle produced dried particles of average diameter ≥30 µm that show incipient flow behavior when measured with the vibrating spatula method. A high solute concentration of 69% w/w in the liquid feed was required, which is readily achievable with trehalose but not with the viscous catalase solution. At lower solute concentrations, e.g. 20% w/w, the mono-disperse droplet generator was able to produce well flowable particles of approximately 50 µm diameter, although with a low yield. This is a result of collisions between the droplets falling through the drying chamber when then coalesce. It is possible to produce dried, flowable particles in milligram quantities on a mini-scale spray dryer such as the ProCept using the 25 kHz ultrasonic nozzle. With the mono-disperse droplet generator the long drying chamber ensures a residence time of a number of seconds, but this also allows droplet coalescence at fall heights >40 cm.