Solid shear mills

The high-speed impeller or shear mixer is the most eommon equipment to prepare dispersions of solids in liquid. High speed shear mills and kinetie shear mills have retained their usefulness beeause of their ability to deagglomerate material that is not adequately dispersed in the premixing step. A high-speed shear mill is eomposed of two elements - a container and an impeller. These factors are important in the design ... 

One of the most efficient techniques for physical cell disruption is the grinding of the cells in a ball mill (solid shear). These mills consist of either a vertical or a horizontal cylindrical chamber with a motor-driven central shaft supporting a collection of off-centred discs or other agitating elements. In this process, cells are agitated in suspension with small abrasive particles. Cells break because of shear forces, grinding between beads and collisions with beads. The beads disrupt the cells to release biomolecules but do not break the target molecules. The kinetics of biomolecule release by this method is a first-order process. 

Liquid shearing, such as high pressure homogenization, solid shear, such as bead milling and the extrusion of frozen cells are the most common mechanical methods for cell disruption (D souza and Killedar, 2008 Hatti-Kaul and Mattiasson, 2003). These methods are mainly based on the use of mechanical force to disrupt the cell. Some of these techniques, such as bead milling, have already found applications on a large scale (Prasad, 2010). 

Geotrichum candidum is a well-known catalyst for asymmetric ketone reductions, and different cell-disintegration methods were used to liberate inuacellular CREDs from these cells. Solid shear (bead milling) proved best. Next, various solid supports were examined for the immobilization of the purified enzyme. The CRED was immobilized on silica with an optimized protein loading of 4 mg/g support. Cross-linking vwth glutaraldehyde rendered the preparation more stable and suitable for use in consecutive batches. This immobilized enzyme was found to be a highly efficient biocatalyst formulation for the production of S(-)-l-(10-naphthyl)ethanol [49]. 

Liquid and/or solids Droplet/solid size Colloid mill, tandem shear pipeline... 

Fig. 10 relates the composite extraction index (see above) obtained in the low-shear aqueous test system for these Tween surfactants, and adhesion tensions measured against various solids. Adhesion tensions against platinum and bitumen saturated pyrophyllite are irregularly related to tar sand extraction, while the adhesion tension against a fresh pyrophyllite surface is linearly (inversely) related to tar sand extraction. This is the first linear correlation between a measurable property of a surfactant solution and tar sand extraction which we have been able to obtain, and there appears to be no such finding in the literature. Fig. 11 gives the relations between extraction of bitumen with the paddle mill, solvent-aqueous-surfactant extraction and adhesion tensions measured against platinum, bitumen saturated pyrophyllite and hydrated (48 hours in water) pyrophyllite. 

Feed material in ball mills is nsnally smaller than about 50 p.m, and the solids contents of slurries range from 30% to 70%. The size of the spherical grinding media is in the range of 0.5-5 mm. Very rapid attrition is produced in ball mills by the intense combination of compression and shearing forces and the frequency of collisions, which is very high. 

Comminution, or particle size reduction of solids, is considerably different from that of the breakup of one liquid by dispersal as small droplets in another. Particle size reduction is generally achieved by one of four mechanisms (1) compression, (2) impact, (3) attrition and (4) cutting or shear. Equipment for particle size reduction or milling includes crushers (which operate by compression, e.g., crushing rolls), grinders (which operate principally by impact and attrition, although some compression may be involved, e.g.,... 

Figure 3.5 The critical Weber number for disruption of droplets in simple shear flow (solid curve), and forthe resulting average droplet size in a colloid mill (hatched area) as a function ofthe viscosity ratio for disperse to continuous phases. Redrawn from data in Walstra [131].

A surfactant used in froth flotation to adsorb onto solid particles, make them hydrophobic, and thus facilitate their attachment to gas bubbles. See also Froth Flotation. A high-shear mixing device used to prepare colloidal dispersions of particles or droplets by size reduction (comminution). Also termed dispersion mill . 

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