Moving toward continuous manufacturing in the pharmaceutical industry offers new possibilities, such as reducing costs and improving flexibility and product quality. However, this paradigm change requires new small-scale continuous manufacturing technologies. Since drying is one of the crucial elements of pharmaceutical production, we performed an evaluation of existing drying technologies suitable for continuous production. We focused on small-scale equipment for handling preconcentrated slurries at the kg/h scale. Lactose (soluble) and ibuprofen (poorly soluble) suspensions were dried, first, in two fluidized bed spray dryers, second, in a small-scale spray dryer, third, in a spin flash dryer, fourth, in a paddle dryer, and, finally, in a corotating twin-screw extruder. During these trials we evaluated the performance of the equipment and its advantages and disadvantages with regard to pharmaceutical production. An analysis was performed to compare the different technologies. Our findings confirm that there is a need for improved continuous small-scale systems for drying crystalline products without causing agglomeration and/or attrition in order to preserve crystal properties originating from careful engineering during the crystallization phase. The aim of this study was to provide information regarding operational capabilities of continuous small-scale drying equipment.

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In a previous study, a small-scale dynamic filtration device (SFD) was analyzed and the basic mechanisms governing the filtration process were characterized. The present work aims at improving the device's performance in terms of actual production. Various operation modes were tested in order to increase permeate flow and concentration factors (CF), while maintaining a fully continuous production mode. Both, a vacuum-enhanced and a pulsating operation mode, proved to be superior to the currently implemented open-operation mode. For example, for lactose, an increase of the CF could be achieved from 1.7 in open mode to 7.6 in pulsating operation mode. The investigated operation strategy enables process control systems to rapidly react to fluctuating feeds that may occur due to changes in upstream manufacturing steps. As a result, not only filtration performance in terms of permeate rate but also process flexibility can be significantly increased. Overall, vacuum-enhanced operation was shown to be most promising for integration into an industrial environment. The option to elevate achievable concentration factors, ease of flow monitoring as well as the ability to react to changes in the feed conditions allow for effective and efficient continuous small-scale filtration.

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