Etude comparative du mélange granulaire à écoulement libre dans un mélangeur en V et un mélangeur simple cône

This work is part of a research project involving the granular mixing group of the department of chemical engineering of École Polytechnique de Montréal and ratio-pharm operations. There is a trend in the pharmaceutical industry to shift from the V-blender, one of the most common tumbling blenders (Alexander et al., 2004b; Kuo et al., 2005), to the bin-blender when developing new mixing processes or scaling up existing ones. However, industrial experience has shown that this trend cannot generally be done in a straightforward manner since such a change may have a significant impact on the powder blend uniformity. The main objective of this work consists of investigating the influence of process parameters such as the fill level, the loading profile and the rotational speed on the granular mixing of two 8-qt. lab-scale versions of industrial V- and conical bin-blenders using spheronized microcrystalline cellulose granules (&phis; = 500 μm) as free-flowing material. To achieve this goal, two strategies were followed: (1) Granular mixing experiments involving three loading profiles (front-back or FB, right-left or RL, and top-bottom or TB), three rotational speeds (15, 30 and 45 rpm) and three fill levels (35, 50 and 65%v/v _tot) on both mixing systems were done. The experiments results, obtained by analyzing thief probe sampling and image analysis, were analyzed on the basis of residual standard deviation (RSD) curves. (2) Discrete element simulations involving three loading profiles (FB, RL and TB), two rotational speeds (15 and 45 rpm) and two fill levels (35 and 65%v/v _tot) were carried out. These simulations involved 420 000 or 800 000 2-mm particles, depending on the fill level. The numerical results, which were compared to the experimental results on the basis of mixing time, were analyzed using mixing dynamics, mean velocity, granular temperature and RSD curves.

This study showed that the mixing performance of the bin-blender is similar or slightly better than that of the V-blender for the FB and the TB loading profiles for all cases. As for the RL loading profile, the V-blender outperformed the bin-blender. This better performance of the V-blender could lead to a significant increase of the mixing time when changing from a V-blender to a bin-blender if the free-flowing material is not equally loaded on each side of the axial plane of symmetry. However, the addition of a baffle within the shell of the bin-blender was shown to increase significantly its performance in the case of the RL loading profile. Finally, the effect of the operating parameters was found to be qualitatively similar for both systems.