Agitated Suspension

Draft tubes are often used in crystallizers as they are particularly effective and efficient at imparting a good degree of vertical mixing. They are discussed in detail below. However, they are 

Not all crystallizers are agitated with impellers in the vessel itself in agitated tank configuration. A common arrangement is to use a pump (or an axial flow impeller in an external pipe) to generate flow in a loop external to, but drawing from, and discharging to the main vessel. Such crystallizers are known as forced circulation crystallizers. These are widely used, for example, in sodium chloride crystallization (see Chapter 5, section 

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Suspension Polymerization. Suspension polymerization is carried out in small droplets of monomer suspended in water. The monomer is first finely dispersed in water by vigorous agitation. Suspension stabiUzers act to minimize coalescence of droplets by forming a coating at the monomer—water interface. The hydrophobic—hydrophilic properties of the suspension stabiLizers ate key to resin properties and grain agglomeration (89). 

For agitated suspensions, however, reeent work suggests that miero-attrition of parent erystals ean oeeur in agitated suspensions (Synowiee etai, 1993). Sueh breakage via miero-attrition will result in many fine erystals generated and a relatively unehanged parent partiele (ef. seeondary nueleation, see below) with a eorrespondingly more eomplex distribution funetion (Hill and Ng, 1995, 1996). These alternative attrition models are eonsidered in more detail later. 

The experimental results are eonsistent with erystal attrition oeeurring via both erystal-impeller impaets and turbulent disruption with no signifieant effeet of erystal-erystal eollisions on the number of fine fragments produeed in the dilute agitated suspensions. 

Synowiec, P., Jones, A.G. and Shamlou, P.A., 1993. Crystal break-up in dilute tur-bulently agitated suspensions. Chemical Engineering Science, 48, 3485-3495. 

Wojcik, J. and Jones, A.G., 1998b. Particle disruption of precipitated CaC03 crystal agglomerates in turbulently agitated suspensions. Chemical Engineering Science, 53, 1097-1101. 

M Bisrat, C Nystrom. Physicochemical aspects of drug release. VIII. The relation between particle size and surface specific dissolution rate in agitated suspensions. Int J Pharm 47 223-231, 1988. 

Hypochlorous acid is obtained by dissolving chlorine in water, or by adding bleaching powder or sodium hypochlorite to water. A better method of production is passing chlorine gas into a well-agitated suspension of mercuric oxide ... 

Scaling up of the deposition-precipitation procedure does not present any difficulty with urea or sodium nitrite. The preparation of tin oxide on silica catalysts has been scaled up from 11 to a vessel of 2 m3 without any difference in the final catalyst. The injection procedure has been scaled up by recirculating the suspension of the support from a large vessel through a small vessel in which the alkaline solution was injected into the vigorously agitated suspension. Provided the flow of the fluid being injected was kept slow and continuous, excellent results have thus been obtained. 

The other HOX compounds are also unstable. In water their dissociation constants are HOC1, 3.4 x 10 8 HOBr, 2 x 10"9 HOI, 2 x 10"u. As can be readily seen, reaction of halogens with water does not constitute a suitable method for preparing aqueous solutions of the hypohalous acids owing to the unfavorable equilibria. A useful general method is interaction of the halogen and a well-agitated suspension of mercuric oxide ... 

The simplest procedure is to extract samples from an agitated suspension for less robust materials a procedure detailed in reference [3] may be used in which an air jet circulates the suspension through a sampling tube that can be closed and withdrawn to provide samples for analysis. Slides may be of three main types dry, temporary and permanent. For very easily dispersed material, the particles may be... 

Effectiveness of deflocculants in dilute suspensions may be studied by light absorption. If the optical density of an agitated suspension falls with time this is an indication of either floeculation or dissolution, whereas an increasing optical density indicates breakdown of floes. 

Three other methods of electrode preparation include photopolymerization of vinyl-saturated zeolites on a Pt electrode [163], direct synthesis of zeolite films on metal supports [164] (although electrochemical studies on this system have not been reported) and the use of agitated suspensions of zeolite, where zeolite particles contact the electrode at random [165]. 

Hypochlorous acid (HOCl) is produced by bubbling chlorine through an agitated suspension of mercury(II) oxide in water. The chemical equation for this process is... 

A solution of 13.5 g (0.64 mol) pure propyl isocyanate in 15 ml anhydrous N, N-dimethylformamide was carefully added into a previously chilled and well-agitated suspension of 20.25 g (0.42 mol) dry para-chlorobenzene sulphonamide taken up in... 

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