Crystallization design data

Mulliii, J.W. and Garside, J., 1967. Crystallization of aluminium potassium sulphate a study in the assessment of crystallizer design data I Single crystal growth rates, II Growth in a fluidised bed. Transactions of the Institution of Chemical Engineers, 45, 285-295. 

Table 2.1 shows the crystal structure data of the phases existing in the Mg-H system. Pnre Mg has a hexagonal crystal structure and its hydride has a tetragonal lattice nnit cell (rutile type). The low-pressure MgH is commonly designated as P-MgH in order to differentiate it from its high-pressure polymorph, which will be discussed later. Figure 2.2 shows the crystal structure of p-MgH where the positions of Mg and H atoms are clearly discerned. Precise measurements of the lattice parameters of p-MgH by synchrotron X-ray diffraction yielded a = 0.45180(6) mn and c = 0.30211(4) nm [2]. The powder diffraction file JCPDS 12-0697 lists a = 0.4517 nm and c = 0.30205 nm. The density of MgH is 1.45 g/cm [3]. 

With the advancement of online measurement techniques such as focused beam reflectance measurement (FBRM) and Fourier transform infrared (FTIR), it is now possible to obtain particle size distribution and solution concentration information rapidly through these in-situ probes. In one experiment, hundreds of data points can be generated. With proper experiment design, the model-based experimental design for crystallization is capable of obtaining high-quality crystallization kinetic data with a small number of experiments. This approach can thus save significant experimental effort and time in the development of crystallization processes. 

Now, having discussed the theory, the equipment, the required design data, and the special considerations, an actual design vvill be considered. Crystallization of monosodium glutamate shall be used for this example. The first step is to gather the design data. 

The development and operation of industrial crystallization processes can be made significantly easier if some data on the kinetics of crystal growth are available. This information can be incorporated in process models, can be used in process and crystallizer design, and can shed light on the observed behavior of the system. 

By far the widest area of application of molecular mechanics and related methods toward the design of metal ion selective ligands is the calculation of the hole size of macrocyclic ligands. The simplest method for determining the hole size R, is to measure from crystal stmctural data the mean distance J h of the donor atom positions from their centroid, and to correct it with the covalent radius for the size... 

Undercooling data obtained from unseeded solutions have little or no industrial relevance. In fact it is often impossible to obtain consistent unseeded values for many aqueous solutions, e.g. sodium acetate, sodium thiosulphate and citric acid. For crystallizer design purposes, the lowest seeded value should be taken as the maximum allowable undercooling, and the working value of the undercooling should be kept well below this. 

The processes of growth and nucleation interact in a crystallizer, and both contribute to the crystal size distribution (CSD) of the product (see section 9.1). Kinetic data needed for crystallizer design purposes (effective growth and nucleation rates) can be conveniently measured on the laboratory scale in a mixed-suspension, mixed-product removal (MSMPR) crystallizer operated continuously in the steady state Figure 9.3). The assumptions made are that no crystals are present in the feed stream, that all crystals are of the same shape, that crystals do not break down by attrition, and that crystal growth rate is independent of crystal size. 

Table 8.5-1 Approximate design data of industrial crystallizers (valid for products with the...

The number and nature of potential non-toxic co-crystal formers (or co-formers) that can be co-crystallized with an API is numerous. The last chapter is an attempt to hst promising ones. Even if each API must be examined and evaluated on a case-by-case basis in terms of molecular structure, we are confident that this listing could serve as a valuable companion for both screening and retrosynthetical design approaches to co-crystallization. The data provided should help chemical intuition to assist the process of selection of co-crystal formers. 

The design equations may also be used to infer nucleation kinetics from continuous crystallizer performance data. 

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