Crystal design

Nucleation. Crystal nucleation is the formation of an ordered soHd phase from a Hquid or amorphous phase. Nucleation sets the character of the crystallization process, and it is, therefore, the most critical component ia relating crystallizer design and operation to crystal size distributions. 

A fines removal system is installed on the crystallizer designed in the first example. Assuming that the cut size for the fines removal system is 50 im and the ratio of mean residence times for product and fines, rp/rp( = 7), is 10, calculate the mean product residence time now required to produce the same dominant size of 600 pm at the same production rate and suspension density. 

Dye, S.R. and Ng, K.M., 1995. Bypassing eutectics with extractive crystallization design alternatives and tradeoffs. American Institute of Chemical Engineers Journal, 41, 1456. 

Larson, M.A. and Garside, J., 1973. Crystallizer design techniques using the population balance. Chemical Engineer, London, June, p. 318. 

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. 

First, the use of higher dimensional robust networks (such as the two-dimensional GS network) simplifies crystal engineering because is reduces crystal design to the last remaining dimension. The use of two-dimensional supramolecular modules, in particular, provides an easily conceptualized mechanism for topological adaptation (in the case of GS networks the arrangement of the pillars). 

One learns from these molecular complexes that equivalent synthons can lead to virtually identical crystal structures. Synthons in, V and VI are chemically and geometrically equivalent though they originate from different molecules, a nitrile, an N-oxide and a nitro compound. These three synthons are used in crystal design in almost the same way. So, different molecules may yield similar crystal structures if they are capable of forming equivalent synthons. This is a powerful concept because it establishes a many-to-one correspondence between molecular and crystal structures. 

The past 30 years have seen great advances in our understanding of the fundamentals of crystallization and has resulted in improved crystallizer design and operation. A dominant theme during this period was the analysis and prediction of crystal size distributions in realistic industrial crystallizers. This led to the development and refinement of the population balance technique which has become a routine tool of the crystallization community. This area is best described in the book of Randolph and Larson (1) which has been an indispensable reference and guide through two editions. 

Figure 11. Standard Dupont Draft tube crystallizer design which was developed in the early sixties.

The main processing options open to the crystallizer designer are the solubility gap (transition temperature, acid content), the operating temperature and the values of the rate coefficients (affected by Impurities) and crystal surface areas (eg. altering crystal content). The computer model generated In this study allows these effects to be evaluated. 

Braga D, Grepioni F (2003) In Desiraju GR (ed) Crystal design, structure and function. Perspectives in supramolecular chemistry, vol 7. WUey, Chichester... 

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