Identifying Optimal Stirrer Geometries for Aqueous Textile Suspensions Using Material Extrusion Based Rapid Prototyping

Increasing amounts of textile waste require rapid implementation of novel recycling technologies. Biocatalytic degradation via enzymatic hydrolysis can be used to separate blends, which are otherwise inaccessible. However, the complex nature of the substrate and narrow operating window of the reaction necessitates process optimization but also complicates computational approaches. The reaction is performed in aqueous suspension at ambient pressure and temperatures well below boiling. Due to the gentle process conditions, preliminary assessment of ideal stirrer geometries can be performed in water under ambient conditions, using stirrers produced from commodity plastics using material extrusion-based 3D-printing at both bench (2 L) and semi-pilot (30 L) scale. Eight geometries were assessed using suspension activity (via cloud height), mixing energy consumption, and mixing time assessment via tracer addition at the bench scale. Four of these geometries were chosen for scale-up in a 30 L conical vessel. While large, especially close-clearance mixing equipment performed well at both sizes, an increase in performance of the pitched-blade turbine was observed at 30 L. This highlights the necessity of experimental scaleup procedure as well as optimized stirrer geometries for enzymatic hydrolysis.