Crystallization design example

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. 

The many technological innovations in melt crystal growth of semiconductor materials all build on the two basic concepts of confined and meniscus-defined crystal growth. Examples of these two systems are shown schematically in Figure 1. Typical semiconductor materials grown by these and other methods are listed in Table I. The discussion in this section focuses on some of the design variables for each of these methods that affect the quality of the product crystal. The remainder of the chapter addresses the relationship between these issues and the transport processes in crystal growth systems. 

This kind of crystal design is more often a failure than a success, and crystal structure prediction, particularly hard crystal structure prediction is still extremely difficult (Section 8.8). Generally, a large majority of the currently known host structures discussed in Chapter 7, for example, were discovered by accident rather than design. However, as our knowledge of the factors involved grows, in tandem with more powerful computational and modelling tools, more successes may be expected. 

That having been said, their deliberate application in crystal design and specifically in inorganic crystal design has been much more limited. There are nevertheless some interesting examples of D-H tt hydrogen bonds in inorganic systems... 

The circulating-magma design describes equipment in which crystals are intentionally transported with the liquor to the region where supersaturation is being created. Swenson-Walker, Wulff-Bock, and doublepipe crystallizers are examples of this type. Forced-circulation design is common. 

Examples in this chapter include sterile crystallization of a labile compound, yield enhancement by crystallization, yield and selectivity enhancement, removal of low-level impurities via crystallization from the melt, crystal formation in vials in a freeze drier, and non-equilibrium resolution of stereoisomers by crystallization. These examples represent unique crystallization processes designed for specific purposes. One lesson to be learned from examination of these nonmainstream applications is that understanding of principles can lead to inventive solutions to problems. For instance, in Examples 11-2 and 11-3, the solubility difference between starting material and desired product is used to optimize the reaction yield/selectivity by crystallizing the product and protecting it from overreaction. 

In the fledgling field of super- and supra-molecular liquid crystals, many different terms have been introduced which describe some of the same structures. Figure 1 shows some classical molecular architectures that can be used to describe the gross structures of super- and supra-molecular liquid crystals. For example, two mesogenic units, i.e., molecular entities that can be deployed in material design in order to induce mesophase formation, can... 

Germanium ATR crystals were coated with thin polymer films by spin-coating techniques. A commercially available spin coater (Headway Research, Inc., Model EC-101) with a specially designed Teflon chuck was used to hold the Ge crystal. For example, Biomer--the medical polyurethane supplied by Ethicon (Somerville, NJ)--was applied in three to four coats in a 1.5 percent solution of cyclohexanone to produce stable films with thickness less than the depth of penetration of the IR field. 

---