Tank crystallizers

A glass stirred tank crystallizer with 350 ml volume was used, which had a marine type propeller located near the bottom. The rotational speed was 200 rpm throughout the experiments. The crystallizer had a filter at the center of the bottom to quickly separate the solution... 

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. 

Kureha Double-Screw Purifier [Fig. 16.16). This unit employs a double screw with intermeshing blades that express the liquid from the crystal mass as it is conveyed upward. The melt is formed at the top, washes the rising crystals countercurrently, and leaves as residue at the bottom. A commercial unit has an effective height of 2.6 m and a cross section of 0.31 m2. When recovering 99.97% p-dichlorbenzene from an 87% feed, the capacity is 7000 metric tons/yr. The feed stock comes from a tank crystallizer and filter. Data on other eutectic systems are shown, and also on separation of naphthalene and thiophene that form a solid solution a purity of 99.87% naphthalene is obtained in this equipment. 

Cooling of the mother liquor, such as in tank crystallizers... 

Although unagitated tank crystallizers arc quite commonly used, they are greatly limited with respect to control of desired crystal product characteristics. The only variables are the initial and final temperatures and initial concentration, which determine the product yield. Rate of cooling may be controlled to some extent by the use of insulation or a tempered water jacket. The only liquor circulation which takes place is due to natural convection currents. As crystals grow and settle to the bottom of the vessel, agglomeration and occlusion of mother liquor may take place. Serious difficulties arise from the inability to control crystal product size and quality. 

A tank crystallizer is the simplest type of industrial crystallizing equipment. Crystallization is induced by cooling the mother liquor in tanks, which may be agitated and equipped with cooling coils or jackets. Tank crystallizers are operated batch-wise and are generally used for small-scale production. 

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. 

Stirred tank crystallizers, see Section 16.11.4.6 and reactors. Sections 16.11.6.23 through 16.11.6.25. Liquid fluidized bed reactors. Section 16.11.6.26 hquid adsorption, Section 16.11.4.12 ion exchange, Section 16.11.4.13 backwash fixed-bed operations such as deep-bed filters. Section 16.11.5.13 liquid adsorbers. Section 16.11.4.12 and ion exchangers. Section 16.11.4.13. 

In the slurry scrubbing process, limestone dissolves at pH A to 6 and 55°C in both absorber and the hold tank/crystallizer. Because of HC1 accumulation from the flue gas, typical scrubbing solution contains 0.01 to 0.2 M CaCl2 C02 partial pressure can vary from near zero with forced oxidation to one atmosphere with CO2 evolution from the hold tank and is typically 0.1 atm in the absorber. Sulfite/bisulfite buffer can be present in concentrations up to 0.1 M. CaS03 and/or CaS04 crystallization must occur simultaneously with limestone dissolution. Buffer additives such as adipic acid should enhance both SO2 removal and CaC03 dissolution at concentrations of 3 to 10 mM (5). 

The oldest and simplest representative is the tank crystallizer. It consists of an open tank, either rectangular or circular in section, exposed to the atmosphere, which provides the necessary cooling. Frequently, ropes, rods, or lead strips are suspended in the bath to provide a base... 

The effects of the preparation methods and the number of recrystallization were examined experimentally by the use of the threonine (TTir.) - water system. The supersaturation of D-77tr., for example, will slightly increase during the crystallization of L-Thr since for this system a < 2. This may lead to a conclusion that the possibility of primary nucleation to occur would also slightly increase as the progress of the resolution. Small stirred tank crystallizers were used both for preparation of... 

A schematic diagram of the experimental apparatus is shown in Figure 1. This apparatus has some similarity to the apparatus u in the previous paper (7), A glass stirred tank crystallizer with 125 ml effective volume was used, which had a flat... 

The installation of an agitator in an open-tank crystallizer generally results in smaller, more uniform crystals and reduced batch time. The final product tends to have a higher purity because less mother liquor is retained by the crystals after filtration and more efficient washing is possible. Vertieal baffles may be fitted inside the vessel to induce better mixing, but they should terminate below the liquor level to avoid excessive encrustation. For the same reason, water jackets are usually preferred to coils for cooling purposes and, where possible, the internal surfaces of the crystallizer should be smooth and crevice-free (section 9.5). 

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