Batch crystallization industrial

Girolami, M.W. and Rousseau, R.W., 1985. Initial breeding in seeded batch crystallizers. Industrial and Engineering Chemistry Research, 25, 66-70. 

Tavare, N.S., Garside, J. and Chivate, M.R. (1980) Analysis of batch crystallizers. Industrial and Engineering Chemistry Process Design and Development, 19, 653-665. 

Several features of secondary nucleation make it more important than primary nucleation in industrial crystallizers. First, continuous crystallizers and seeded batch crystallizers have crystals in the magma that can participate in secondary nucleation mechanisms. Second, the requirements for the mechanisms of secondary nucleation to be operative are fulfilled easily in most industrial crystallizers. Finally, low supersaturation can support secondary nucleation but not primary nucleation, and most crystallizers are operated in a low supersaturation regime that improves yield and enhances product purity and crystal morphology. 

Batch Crystallization Batch crystalhzation has been practiced longer than any other form of ciystaUization in both atmospheric tanks, which are either static or agitated, as well as in vacuum or pressure vessels. It is still widely practiced in the pharmaceutical and fine chemical industry or in those applications where the capacity is veiy small. The integrity of the batch with respect to composition and history can be maintained easily and the inventoiy management is more precise than with continuous processes. Batch ciystalhzers can be left unattended (overnight) if necessary and this is an important advantage for many small producers. 

Batch crystallizers are widely used in the chemical and allied industries, solar saltpans of ancient China being perhaps the earliest recorded examples. Nowadays, they still comprise relatively simple vessels, but are usually (though not always) provided with some means of agitation and often have artificial aids to heat exchange or evaporation. Batch crystallizers are generally quite labour intensive so are preferred for production rates of up to say 10 000 tonnes per year, above which continuous operation often becomes more favourable. Nevertheless, batch crystallizers are very commonly the vessel of choice or availability in such duties as the manufacture of fine chemicals, pharmaceutical components and speciality products. 

Brown, D.J. and Boyson F., 1987. Modelling of fluid flow in a batch crystallizer. In Industrial Crystallization 87. Eds. J. Nyvet, S. Zacek, Bechyne, Czechoslovakia, September 1987. Academia Prague and Elsevier, 1989, pp. 547-550. 

The design and operation of industrial crystallizers is where developments in the laboratory are confirmed and their practical significance determined. In recent years, crystallization processes involving specialty chemicals and pharmaceuticals have increased. This has led increased interest in batch crystallization operation, optimization and desigrt At the same time, the advent of powerful computers and their routine avaUabilily has stimulated interest in the area of on-line control of crystallization process (both batch and continuous). Progress in batch crystallization is surrunarized in a number of recent papers and reviews 173-801. In this section I will discuss two areas which I think will have an impact in the next decade. 

Batch crystallizers are used primarily for production of fine chemicals and pharmaceuticals at the rate of 1-100 tons/week. The one exception is the sugar industry that still employs batch vacuum crystallization on a very large scale. In that industry, the syrup is concentrated in triple- or quadruple-effect evaporators, and crystallization is completed in batch vacuum pans that may or may not be equipped with stirrers [Fig. 16.11(g)]. 

A common approach in the pharmaceutical industry for the development of a batch crystallization process... 

Trends in the crystallization process development in the pharmaceutical industry is to carry out measurements at a small scale in addition to utilizing automation and high throughput systems as exemplified by the use of automated metastable zone measurement for 1 mL samples. It is expected that the future batch crystallization recipes will be designed based on the data collected from much smaller scale crystallizers than what is currently used in industry. 

In the pharmaceutical industry most solid compounds are crystallized in batch operations, i.e., the crystalline product is isolated at the end of the operating cycle. Many bulk chemicals, such as table sugar, are prepared through continuous processes, in which the product is collected throughout the crystallization cycle. Batch crystallization produces a narrower range of particle size and may afford better control for the efficient crystallization of molecules from complex mixture [14]. 

PuEL, F., Fevotte, G. Klein, J. P. 2003b Simulation and analysis of industrial crystallization processes through multidimensional population balance equations. Part 2 a study of semi-batch crystalization. Chemical Engineering Science 58, 3729-3740. 

A critical control aspect common to all batch crystallization is controlling the initial population of crystals. Control action intended to produce large crystals may be insufficient to compensate for the massive generation of nuclei that results from spontaneous nucleation. Industrial experience supports the copious academic documentation that seeding with a defined mass and size range of crystals permits the growth of larger crystals with a narrower size distribution. 

Laboratory batch crystallizers have been used successfully to develop crystallization kinetic expressions and to measure the effects of process conditions on the kinetics in realistic crystallization environments approximating those in industrial practice. Laboratory data are needed to help decide what mode of crystallization to use and to determine the features of design that will produce to the greatest degree the crystal properties and yield desired. 

Although most of the industrial crystallizers described in the literature (e.g., Bamforth 1965 Bennett 1984 Moyers and Rousseau 1987) are continuous crystallizers, they often can be operated in a batch mode. For capacity requirements less than 500kg/h, batch crystallization is usually more economically advantageous. Furthermore, if the product requires a relatively narrow CSD, a batch crystallizer clearly has the advantage. Several industrial batch crystallizers are deseribed here. 

Fines Destruction. In the operation of industrial crystallizers, one would usually want to avoid the fines (i.e., small crystals) since they may cause difficulties in downstream processing equipment (e.g., filtration) and affect both product quality and process economics. Excessive fines may also require a relatively long batch run time to achieve the desired final size of the product crystals. Karpinski (1981) proposed a controlled dissolution of secondary nuclei in order to improve CSD from fluidized bed crystallizers. Jones et al. (1984) first described the application of fines destruction in batch crystallization of potassium sulfate solutions. Their study demonstrated the experimental feasibility of this technology to dramatically reduce the amount of fines in the final product CSD. Their theoretical predictions, obtained from population balance models, agreed with the experimental results. 

Figure 10.16 Effect of fines destruction on cumulative number distribution in a batch crystallizer. (Reprinted with permission from Zipp G.L., and Randolph A.D. (1989), Industrial Engineering and Chemical Research, vol, 28, p. 1447. 1989 American Chemical Society.)...

Batch crystallization has several desirable features and advantages in laboratory and industrial applications. Industrial batch crystallizers are commonly used to manufacture a wide variety of crystalline materials with desirable product features and quality. Laboratory batch crystallizers are often used to characterize crystallization kinetics and CSDs and to determine the effects of process conditions on these kinetics and CSDs. 

There are several common problems encountered in the use of crystallization in the pharmaceutical industry (1) the control of supersaturation (and PSD) in a batch crystallizer (2) the effective use of seed (3) efficient measurement of solubilities in multiple solvent systems to maximize purification and yield and (4) identification and retention of the most stable polymorphic form. 

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