Understanding the effect of screw design on continuous particle isolation performance within a continuous vacuum screw filter

Continuous manufacturing (CM) provides high potential for the pharmaceutical industry, for instance in terms of elimination of batch-to-batch variability, increased space-time yield and reduced waste. Therefore, there is an increasing demand for CM equipment. Since crystallization is involved in about 90 % of the manufacturing processes of active pharmaceutical ingredients, several technologies for continuous crystallization are already available. However, the particle isolation within a crystal process chain represents a bottleneck for end-to-end continuous pharmaceutical manufacturing. We developed and patented the continuous vacuum screw filter (CVSF) for continuous filtration, washing and drying in a modular setup to address the lack of CM equipment for continuous particle isolation. In this study, we focus on the performance and robustness of the particle isolation process in the CVSF according to needs predetermined by the crystallization process, i.e. varying volume flows or suspension densities, by the adaptation of screw design. By increasing the pitch distance of the screw, particle backslip is reinforced, which impairs particle traceability. Nevertheless, we demonstrate that screw design within the CVSF is key to enable efficient filter cake deliquoring and particle purification, and to tune the residence time within the apparatus in a desired way. • Varying screw designs enables tuning of particle residence time for varied screw speeds at constant filling degree. • At a filling degree of 50 %, the requirements for continuous particle isolation are met for each tested screw design. • Filtration and washing performance depend on filter cake thickness and fluid dynamics, both influenced by screw design. • By increasing the pitch distance of the screw, particle backslip is reinforced, which impairs particle traceability.