Disperser Disk

Another typical radial flow impeller is the disperser disk, also known as the toothed disk or dissolver disk. The EKATO MIZER disk belongs to this category, and consists 

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In the past two decades quite a few new techniques have emerged for the treatment of aqueous samples prior to organic analysis. Perhaps the most important development is that of solid-phase extraction (SPE), which has successfully replaced many off-line steps. This technique can be considered to have introduced a genuine new era in sample handling [1]. The many varieties in which the technique is available and can be applied have made it the key step in handling of aqueous samples. Among the successful varieties are solid-phase microextraction (SPME), matrix solid-phase dispersion, disk extraction and immunosorbent extraction. Several reviews covering these topics have appeared in the literature in the past decade (see e.g. Refs. [2,3] for nonylphenol... 

Fig. 5. Disperser disk. (Reprinted with permission from the publisher, VCH Publishers, Inc., after Zlokarnik and ludat, 1988.)...

To disperse gas, the gas is usually injected into the liquid from the bottom of the tank or near the impeller to enhance dispersion. Disk style turbines are found to be most convenient for gas dispersion because the disk disturbs the freely rising gas bubbles. The turbines with flat blades give radial flow and are very useful for gas dispersion where the gas is introduced just below the impeller at its axis and drawn up to the blades and chopped into fine bubbles. 

The formulations described in this paper were prepared using a dispersion disk and degassed In vacuum. The basic formulation of the resin matrix consisted of 33 parts of cycloaliphatic diepoxid, 33 parts of cresolnovolac epoxide, 33 parts of cycloaliphatic epoxy diluent, 0.5 parts of silane and 0.5 parts of photolnltlator (resin A). In addition fused silica 150 parts (resin B), 186 parts (resin C), 233 parts (resin D) was added. In the toughened mixture (resin E) the cycloaliphatic epoxide of resin D was substituted by 41.7 parts of a dispersion of 20Z silicone elastomer In epoxy resin. In the flexlbilized modification (resin F) 33 parts of epoxldlsed soya bean oil were added to resin D. 

For specifically difficult applications, special combinations of anchors/helixes and anchor/turbines can be used. For example, a helical ribbon impeller can be supported on an anchor for providing both top-to-bottom material movement and folding action. For dispersing powder into a viscous liquid, a high-speed dispersing disk is used in combination with the helix. Intermeshing cone helical ribbon impellers also exist for self-cleaning action and for viscous plastic masses, which may accumulate on the impeller blades. 

Other high-shear impellers include the tapered blade ChemShear impeller and dispersing disks such as the Cowles impeller. These provide excellent shear, but far less flow than the RDT. They are used primarily in small scale batch applications where dispersion time is not critical. Pitched blade tmbines (PBT) are used when large density differences could lead to a suspension problem. They require higher speed to create the same drop size as the RDT, since they have a lower power number. The flow discharge angle for PBTs varies with Reynolds number and blade angle. 

Several modifications of the design have appeared. Modifications of the rotors include perforation of the disk [Krishnara et al., Br Chem. Eng., 12, 719 (1967)] and radially supported arc plates [Nakamura and Hiratsuka, Kagaku Kogaku, 30, 1003 (1966)]. An asymmetric modification, with off-center rotors and arrangement of settling spaces for the liquids between dispersions (Misek, loc. cit.) is available in Europe. 

Colloid mills which are employed for dispersion or for emulsification fall into four main groups the hammer or turbine, the smooth-surface disk, the rough-surface type, and valve or orifice devices. 

FIG. 23"37 Equipment for liquid/liquid reactions, a) Batch stirred sulfonator. (h) Raining bucket (RTL S A, London), (c) Spray tower with Loth phases dispersed. (d) Two-section packed tower with light phase dispersed, (e) Sieve tray tower with light phase dispersed, (f ) Rotating disk contactor (RDC) (Escher B V, Holland). (g) Oldshue-Rushton extractor (Mixing Equipment Co. ). 

FIG. 23-38 Efficiency and capacity range of small-diameter extractors, 50 to 150 mm diameter. Acetone extracted from water with toluene as the disperse phase, V /V = 1.5. Code AC = agitated cell PPC = pulsed packed column PST = pulsed sieve tray RDC = rotating disk contactor PC = packed column MS = mixer-settler ST = sieve tray. (Stichlmair, Chem. Ing. Tech. 52(3), 253-255 [1980]). 

This dispersion of the gas passes through several stages depending on the gas feed rate to the underside of the impeller and the horsepower to the impeller, varying from inadequate dispersion at low flow to total gas bubble dispersion throughout the vessel. The open, without disk, radial flow type impeller is the preferred dispersing unit because it requires lower horsepower than the axial flow impeller. The impeller determines the bubble size and interfacial area. 

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