Continuous stirred tank crystallizer

Figure 16.7. Material balancing of continuous stirred tank crystallizers (CSTC). (a) The single stage CSTC. (b) Multistage battery with overall residence time t = (lIQ) Si Ki-...

Analysis of Size Distribution Data Obtained in a CSTC Differential distribution data obtained from a continuous stirred tank crystallizer are tabulated. 

A high degree of control can also be achieved in continuously stirred tank crystallizers. Temperature differences between feed and crystallizer can be regulated as necessary. The seed is the product and will normally be present at the slurry concentration as determined by the feed rate, concentration, and solubility differences achieved. However, in cases in which this amount of seed is not sufficient, cross-flow filtration on the discharge of the crys-tallizer(s) can be used to increase the slurry density. See Example 7-4 for a discussion of the resolution of ibuprofen lysinate. 

Crystallization in a Continuous Stirred Tank with Specified Predominant Crystal Size... 

The reactor system may consist of a number of reactors which can be continuous stirred tank reactors, plug flow reactors, or any representation between the two above extremes, and they may operate isothermally, adiabatically or nonisothermally. The separation system depending on the reactor system effluent may involve only liquid separation, only vapor separation or both liquid and vapor separation schemes. The liquid separation scheme may include flash units, distillation columns or trains of distillation columns, extraction units, or crystallization units. If distillation is employed, then we may have simple sharp columns, nonsharp columns, or even single complex distillation columns and complex column sequences. Also, depending on the reactor effluent characteristics, extractive distillation, azeotropic distillation, or reactive distillation may be employed. The vapor separation scheme may involve absorption columns, adsorption units,... 

Impurities, added or unintentional, can have a major effect on rates of nucleation and crystal growth. Table 4-1 shows the effect of an impurity, structurally similar to the crystallizing solute, added to an all-growth crystallization (separation of stereoisomers. Examples 7-6 and 11-6). The data for a continuous stirred tank (CSTR) operation show a sevenfold decrease in the first order growth rate constant as a result of addition of this impurity to prevent nucleation of the undesired isomer. 

Impinging jet crystallization was discussed in Section 9.11 above. One configuration of this type of operation is shown in Fig. 9-22. The impinging jet contacting device delivers its product to an age vessel (either batch or continued stirred tank CSTR) to provide an age time, required for most compounds, to allow diffusion of mother Uquors from the droplets (actually nucleated solids with trapped... 

Fluorophenylacetic acid was transformed into the unsaturated acid 48 by reaction with 2 mol equiv. of i-PrMgCl, followed by acetone addition, dehydration, and crystallization. The tetra-substituted double bond was then hydrogenated under high pressure in an ad hoc designed continuous-stirred tank reactor system and in the presence of the Ru complex 49 (substrate/catalyst ratio =1000) to afford (.5)-acid 50 in 93.5% e.e. Crystallization of its sodium salt upgraded the e.e. to 98%. 

The majority of applications of crystal population balance modeling have assumed that the solution and suspension in the crystallizer are homogeneous, i.e., the Mixed-Suspension Mixed-Product Removal (MSMPR) approximation (Randolph and Larson 1988). (This is simply the analog of the Continuous Stirred Tank (CSTR) (Levenspiel 1972) approximation for systems containing particles. It means that the system is well mixed from the standpoint of the solute concentration and the particle concentration and PSD. In addition, the effluent is assumed to have the same solute concentration, particle concentration, and PSD as the tank.) This approximation is clearly not justified when there is significant inhomogeneity in the crystallizer solution and suspension properties. For example, it is well known that nucleation kinetics measured at laboratory scale do not scale well to full scale. It is very likely that the reason they do not is because MSMPR models used to define the kinetic parameters may apply fairly well to relatively uniform laboratory crystallizers, but do considerably worse for full scale, relatively nonhomogeneous crystallizers. 

Feed purification generally involves absorption, adsorption, extraction, and/or distillation. Reaction involves agitated batch, agitated semibatch, continuous stirred tank, or continuous flow reactors. The continuous flow reactors may be empty or contain a mass of solid catalyst. Product separation and purification involves distillation in the petrochemical industry or extraction and crystallization in the extractive metallurgy and pharmaceutical industries absorption is used to a lesser extent. 

Crystallizing, batch processing design calculations, 99-100 CSTR (continuous stirred tank reactor) external heat exchanger, 714 reactor performance, 706-712 single-phase transfer medium, 714 Cumene catalyst, replacing, 721-726 Cumene process feed section, troubleshooting, 784-787 Cumene reactor... 

The flow of slurry within all the agitated crystallizer vessels illustrated is clearly complex and mixed to a greater or lesser extent at the microscopic level. In order to ease theoretical analysis a new type of vessel therefore had to be invented This idealized vessel has become known as the continuous MSMPR crystallizer, after Randolph and Lawson (1988). The MSMPR is the crystallization analogue of the CSTR (continuous stirred tank reactor) employed in idealizations of chemical reaction engineering. 

Section 6.4 covers continuous stirred tank separators. Section 6.4.1 studies equilibrium separation processes most of this section is devoted to crystallization, with additional coverage of liquid extraction. Membrane separation processes/devices are sometimes modeled as CSTRs. Section 6.4.2 touches upon a few of these examples, encountered, for example, in ultrafllUation and gas permeation. There are brief treatments of batch systems that are well-stirred in Sections 6.4.1 and 6.4.2 for both equilibrium based and membrane separation processes. 

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