Effect of material properties and design parameters on the final blend uniformity using experimental and simulation results

• Effect of material properties and parameter design on final blend uniformity
• Relationship between the MRT and the feeding position
• DEM simulations were used to study continuous mixing processes.

One of the most important operations in the food, chemical, and pharmaceutical industries is powder mixing. In the pharmaceutical industry this operation is currently performed mainly in batch mode. However, the Food and Drug Administration (FDA), using the Process Analytical Technology (PAT) initiative, has been working on the promotion of the application of continuous processes in the pharmaceutical industry. The main goal of this study was to understand the powder phenomena inside the mixer and monitor mixing uniformity using experiments and simulations by Discrete Elements Methods (DEM). The experimental results showed highest relative standard deviation (RSD) using the lowest active pharmaceutical ingredient (API) concentration (2.5%), and after using image analysis part of this effect was attributed to the position of the feed inlet. The two experiments with the highest RSD (50 and 70 RPM) were replicated using a new feeding position (25°). The RSD values for the new feeding position demonstrated an improvement in mixing uniformity. The new feed position was studied in more detail using DEM by performing a simulations set that included simulations at two mixer speeds (50 and 70 RPM), three concentrations (2.5%, 10.5%, and 50%), and two different material properties (with and without cohesion). Values of hold-up, velocity profile, mean residence time (MRT), and mixing uniformity were compared for both feed positions. Also the blend uniformities inside the tumble, at each tumble exit, and at the final exit of the system were compared. The results show a positive effect of the angle in the uniformity inside the mixer, in the exit points, and at the exit of the system. Additionally, a relationship between RSD and concentration was found.

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