Case Study – Stryker Biotech

Scaling Down to Scale-up Shear Sensitive Mixing Process

Situation

A medical product company needed to perform an 8X scale-up of a particle reaction/washing process. Mixer vendors had already specified recommended equipment and operating conditions based on their standard calculations and orders were placed to meet tight time constraints. However, it was unknown how the particles would behave at this large scale under the vendor recommended conditions and whether or not attrition would lead to yield losses or poor product quality. Additionally, the existing 1X pilot system had been dismantled and was no longer available for parameter testing.

Approach

IMPACT elected to scale the process down to a volume that could be easily facilitated by readily available equipment and small volumes of materials. In this case, the process was scaled down to 0.05X in the laboratory. This allowed the recommended operating conditions from the mixer vendor to be studied prior to plant startup.

Results

Based on this approach, particle attrition was studied (using a Lasentec FRBM in-line particle monitoring device) and found to be a prevalent contributor to yield loss (~30%) at the vendor proposed tip speed and resulting shear rates. Optimal conditions were subsequently determined at the small scale that achieved negligible attrition due to lower shear rates while still maintaining other process requirements such as full off-bottom suspension of particles and foam re-entrainment. These new operating conditions were then later tested and confirmed at IMPACT’s Development Center during a second 0.75X scale experiment.

These scale-down experiments were critical in giving engineers a platform to study and understand the fundamental parameters that would govern the scale-up and to recommend operating conditions at full scale that would avoid attrition. This knowledge insured both a smooth start-up of the commercial process and also allowed the client to immediately achieve significantly higher product yields and profitability.