(284f) Continuous Drying of Powders and Slurries in an Extruder without Changing Product Particle Size Distribution

Academia, industry and regulators have increasingly demonstrated and addressed the advantages of continuous manufacturing during recent years. Slowly, this is leading to a change in mindset for pharmaceutical manufacturing, moving towards advanced continuous processing based on real-time quality assurance and away from batch processing.

Greater interest is being shown in the pharmaceutical industry for linking primary and secondary manufacturing into a single continuous manufacturing line. This demand is driven by the need of a cost-efficient process development and upscaling phase, which occurs during phase two and three of drug product development. Within the framework of continuous manufacturing, several techniques are commonly used for producing drugs. These include filtration, drying, milling/blending, granulation, and tableting, among others.

Drying is one of the most challenging process steps, if linking primary and secondary production. Not only does drying consume a vast amount of energy, but moreover, particle properties can significantly change during drying. Since the particle structure is carefully considered during continuous crystallization, it is highly desirable to avoid any changes in the particle properties while drying. Two counteracting forces, attrition and agglomeration, constantly occur during the drying of wet powder by shear movement.

When considering continuous manufacturing, not only must the product quality be considered, but also the processability. Therefore, the residence time distribution must be taken into account. Ideally, the residence time distribution should be narrow and no material should be stuck to walls and in dead spaces. Using an extruder helps to overcome many of the challenges normally faced during drying. Agglomeration can be avoided and the residence time distribution can be very narrow if using a twin-screw extruder with forced-feed and self-cleaning screws.

This paper will highlight successful efforts for drying wet powders or slurries, with high solid content, in a twin-screw extruder (Leistritz 27mm twin-screw). This work is focused on the processability of a test substance with a particle size below 100 µm. The screw configuration was optimized to best suit the needs of the drying process. Different process settings where tested and some showed very promising results. Products with different starting moisture contents were also tested. The percent reduction in moisture observed following the drying procedure was 99% with a residual moisture below 0.1% and there was no agglomeration observed during drying.