Sol-gel granulation process

Buelna, G. Lin, Y.S. Preparation of spherical alumina and copper oxide coated alumina sorbents by improved sol-gel granulation process. Microporous Mesoporous Mater. 2001, 42, 67-76. 

One of the key steps in this sol-gel granulation process is the formation of the sol droplets. There are basically two ways for droplet formation gravity-force assistant method [63] and shear-force assistant method [64]. In both cases, the orifice of the dropper is immersed in the paraffin oil. In the second case, the shear-force is created by either moving the paraffin oil (orifice is fixed) or moving the orifice in the paraffin oil. When the sol is continuously pushed out through the orifice, the sol in the oil experiences the gravity force or drag-force (in the shear-force assistant method) that acts to separate the drop from the orifice. 

In 1998, Avnir and coworkers patented the interfacial polymerization process in which the mild sol-gel production of silica glass is combined with emulsion chemistry to form sol-gel spherical microparticles in place of irregular granules. In brief, the emulsion droplets provide a microreactor environment for the hydrolysis and condensation reactions of Si alkoxides. All sorts of molecules can be entrapped and stabilized in similar ceramic microparticles with broad control over the release rate for a range of applications (such as drug delivery, release of specialty chemicals and cosmeceutical/ nutraceutical, and beyond, Figure 18.1), with no need for reformulation for different molecules. 

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. 

The granulation process included generating sol droplets by the droppers, shaping and partially gelating the droplets into spherical wet-gel granules in a paraffin oil layer, and consolidating the structure of the wet-gel granules in a 8 wt.% ammonia solution layer. The device used to prepare the gel particles is schematically shown in Fig.7. The temperature of the paraffin oil layer (white... 

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