Distillation and its companion processes, azeotropic and extractive distillation, are by far the most widely used separation processes for mixtures that can be vaporized. Distillation is a process for isolating components from a mixture based on differences in boiling points. Vapors are generated from liquids or solids by heating and are then condensed into liquid products. In azeotropic distillation, a compound is added to form an azeotrope with at least one of the components of the mixture. That component can then be more readily separated from the mixture because of the increased difference between the volatilities of the components. Extractive distillation combines continuous fractional distillation with absorption. A relatively high-boiling solvent is used to selectively scrub one or more of the components from a mixture of components with similar vapor pressures. Distillation processes are widely used for the separation of organic chemicals and for the separation of gases, usually at cryogenic temperatures, as in the production of oxygen and nitrogen from air.

Crystallization is one of the oldest unit operations in the portfolio of separation techniques used for industrial and laboratory processes. Crystallization is used to achieve several functions: separation, purification, concentration, solidification, and the production of a crystal that can be used to determine molecular structure. Because the heat of crystallization is typically much lower than the heat of vaporization, considerable energy savings can be realized in applications where crystallization is an effective means of separation.

Solutes can be recovered from solutions by reducing the solubility through cooling, heating, evaporation, chemical reaction, or by adding a nonsolvent to the mixture. Alternatively, separation of a chemical species from a mixture of similar compounds may be achieved by melt crystallization. In such operations, the mixture is cooled and the species allowed to solidify differentially according to their melting points. Melt crystallization is an important means of separating para-xylene from ortho-and meta-xylene. An example of the purification of a chemical species is the manufacture of L-isoleucine, in which the material crystallized from a fermentation broth that has been filtered and subjected to ion exchange may contain undesirable impurities. The crystals are then redissolved and recrystallized to enhance purity. Concentration of a solution can be accomplished by crystallization of the solvent. For example, fruit juice is concentrated via the crystallization of ice.

Product requirements are the criteria for determining the success of the crystallization process. These requirements are based on how the product will be used and the processing steps between crystallization and the recovery of the final product. Key determinants of product quality are size distribution (including mean and

Front Matter (R1-R14)

Executive Summary (1-5)

1 Introduction (6-12)

2 Chemical Industry (13-27)

3 Petroleum Industry (28-35)

4 Cross-Cutting Issues for the Chemical and Petroleum Refining Industries (36-50)

5 Aluminum Industry (51-58)

6 Steel Industry (59-67)

7 Metal Casting Industry (68-73)

8 Glass Industry (74-78)

9 Forest Products Industry (79-86)

10 Cross-Cutting Issues for the Materials Processing Industries (87-96)

11 Conclusions and Recommendations (97-104)

References (105-110)

Appendix A: Biographies of Panel Members (111-113)