Multistage process

It is usual to degas demineralized water produced by weak base anion schemes, but the presence of dissolved carbon dioxide helps suppress the pH across the anion loading cycle thereby assisting ionization of the free base form functional groups. Therefore it is preferred to position the degasser downstream, not upstream, of the weak base anion column especially if the raw water has a low EMA value. 

As discussed in Chapter 7 (Column Breakthrough and Leakage ) counterflow regeneration designs not only provide for better operational efficiencies compared with coflow systems but leakage residuals are virtually eliminated such that the column effluent quality only begins to deteriorate as the resin begins to truly exhaust. 

Consider the following simple fully counterflow system  

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The principle of solvent extraction in refining is as follows when a dilute aqueous metal solution is contacted with a suitable extractant, often an amine or oxime, dissolved in a water-immiscible organic solvent, the metal ion is complexed by the extractant and becomes preferentially soluble in the organic phase. The organic and aqueous phases are then separated. By adding another aqueous component, the metal ions can be stripped back into the aqueous phase and hence recovered. Upon the identification of suitable extractants, and using a multistage process, solvent extraction can be used to extract individual metals from a mixture. 

In general, high selectivities can be obtained in liquid membrane systems. However, one disadvantage of this technique is that the enantiomer ratio in the permeate decreases rapidly when the feed stream is depleted in one enantiomer. Racemization of the feed would be an approach to tackle this problem or, alternatively, using a system containing the two opposite selectors, so that the feed stream remains virtually racemic [21]. Another potential drawback of supported enantioselective liquid membranes is the application on an industrial scale. Often a complex multistage process is required in order to achieve the desired purity of the product. This leads to a relatively complicated flow scheme and expensive process equipment for large-scale separations. 

Nitration of dinitrophenol. This is a multistage process. First chlorobenzene is nitrated to chlorodinitrobenzene as shown schematically below ... 

While the manifolds were fabricated by a plain molding process, the microchannels substrate fabrication was quite complicated and was achieved by a multistage process. The following main stages were used in the process (1) double side oxidation of a 525 pm (1 0 0) silicon substrate to 1,000 A, (2) single side 1,200 A silicon nitride deposition, (3) silicon nitride channels template opening by reactive... 

Increase synthesis. This may be achieved by giving the precursor, if it crosses the blood-brain barrier. Whether this works will depend on (i) how many neurons remain to synthesise the NT, unless this can be performed extraneuronally and (ii) the availability of synthesising enzymes. Thus if synthesis is a complicated multistage process or is controlled by the availability of enzymes that are already reduced or working maximally in remaining neurons, this approach may prove difficult. 

In the multistage process described on Fig. 20-14 feed enters one of several crystallizers installed in series. Crystals formed in each crystallizer are transferred to a hotter stage and the liquid collected in the clarified zone of the crystallizer is transferred to a colder stage and eventually discharged as residue. At the hot end, crystals are transferred to a vertical purifier where countercurrent washing is performed by pure, hot-product reflux. TSK refers to this multistage process as the countercurrent cooling crystallization (CCCC) process. In... 

This chapter covers the design of separating columns. Though the emphasis is on distillation processes, the basic construction features, and many of the design methods, also apply to other multistage processes such as stripping, absorption and extraction. 

Material and energy balance equations can be written for any stage in a multistage process. 

Compared to animal assays, CTA is faster and cheaper. In vitro CTAs have been shown to involve a multistage process that closely resembles some stages of in vivo carcinogenesis and have the potential to detect both genotoxic and non-genotoxic carcinogens. 

CTAs are possible in vitro alternatives to the standard approach for the assessment of carcinogenicity (the 2-year bioassay in rodents), which have been shown to be a multistage process able to model the most important stages of in vivo carcinogenesis [50]. CTAs are faster and more economic than in vivo assay and they could be a valid and useful screening tool for chemicals. 

Cholesterol biosynthesis is a multistage process in general, it may be divided into three steps ... 

Activation of the arachidonic acid cascade during ischemia-reperfusion is a multistage process 586... 

The formation of latent images is a multistage process, involving the Frenkel defect population. The major steps in the formation of the latent image follow a path similar to that originally suggested by Gurney and Mott (1938) ... 

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