Granulated particles, mechanical strength

In contrast to common belief, compaction/granulation is well suited for the manufacturing of easily degradable carrier particles since one of the main binding mechanism, molecular forces (van-der-Waals), diminishes by a factor of 10 in the presence of water. Therefore, if rain or dew wet the granules they lose strength, readily degrade, and liberate the active substance. 

Adsorbents are practically used in the granular form. The performance of an adsorption process critically depends on the size, shape, pore texture and mechanical strength of the support body used. Sol-gel process has commonly been employed for preparation of ceramic films, fibers and powders. This section reports our work on synthesis and properties of the sol-gel derived alumina granular particles. The principle of the sol-gel derived granulation process should be applicable to preparation of granular particles of other ceramic materials discussed in the preceding section. 

A major quaUty feature of particles is their mechanical strength. This parameter depends mainly on the material properties but also, as discussed in Section 7.3.2, on the microstructure of the particles. Microscopic changes in the structure, porosity or surface properties of the granules occur under the influence of different process parameters and can lead to major changes in properties on a macroscopic scale, for example breakage and attrition resistance. 

To demonstrate the effect of different process parameters on the mechanical strength, granulation experiments were performed in a cylindrical fluidized bed unit with an inner diameter of 250 mm and a fluidization chamber height of about 500 mm. The pilot plant (Fig. 7.26) can be operated with superheated steam or air in batch or continuous mode. The experiments presented here were batch, with 5 kg of synthetic zeolite particles with a Sauter diameter of 2.18 mm as the starting material. 

During the granulation experiments samples were taken at constant time intervals. For each sample the particle size distribution was analyzed by means of a Camsizer (see Section 5.2.2 in Volume 2 of this series). Additionally, the mechanical strength was determined per uniaxial compression (see Chapter 6 in Volume 2 of this series). The results are visualized by plotting the breakage probability versus the breakage energy, similarly to the plot of Fig. 7.12 of Section 7.3.1. 

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