Page 34 - Separation process principles 2

Chapter 1

Separation Processes

The separation of chemical mixtures into their constituents This book presents the principles of large-scale com-
has been practiced, as an art, for millennia. Early civiliza- ponent separation operations, with emphasis on methods
tions developed techniques to (1) extract metals from ores, applied by chemical engineers to produce useful chemical
perfumes from flowers, dyes from plants, and potash from products economically. Included are treatments of classical
the ashes of burnt plants, (2) evaporate sea water to obtain separation methods, such as distillation, absorption, liquid-
salt, (3) refine rock asphalt, and (4) distill liquors. The liquid extraction, leaching, drying, and crystallization, as
human body could not function for long if it had no kidney, well as newer methods, such as adsorption and membrane
a membrane that selectively removes water and waste separation. Separation operations for gas, liquid, and solid
products of metabolism from blood. phases are covered. Using the principles of separation
Separations, including enrichment, concentration, purifi- operations, chemical engineers can successfully develop,
cation, refining, and isolation, are important to chemists and design, and operate industrial processes.
chemical engineers. The former use analytical separation Increasingly, chemical engineers are being called upon
methods, such as chromatography, to determine compositions to deal with industrial separation problems on a smaller
of complex mixtures quantitatively. Chemists also use scale, e.g., manufacture of specialty chemicals by batch
small-scale preparative separation techniques, often similar processing, recovery of biological solutes, crystal growth
to analytical separation methods, to recover and purify of semiconductors, recovery of valuable chemicals from
chemicals. Chemical engineers are more concerned with wastes, and the development of products (such as the
the manufacture of chemicals using economical, large-scale artificial ludney) that involve the separation of chemical
separation methods, which may differ considerably from mixtures. Many of the separation principles for these
laboratory techniques. For example, in a laboratory, chemists smaller-scale problems are covered in this book and
separate and analyze light-hydrocarbon mixtures by gas- illustrated in examples and homework exercises.
liquid chromatography, while in a large manufacturing plant
a chemical engineer uses distillation to separate the same
hydrocarbon mixtures.

1.0 INSTRUCTIONAL OBJECTIVES

After completing this chapter, you should be able to:
Explain the role of separation operations in an industrial chemical process.
Explain what constitutes the separation of a chemical mixture and enumerate the five general separation
techniques.
Explain the use of an energy-separating agent (ESA) and/or a mass-separating agent (MSA) in a separation
operation.
Explain how separations are made by phase creation or phase addition and list the many separation operations that
use these two techniques.
Explain how separations are made by introducing selective barriers and list several separation operations that
utilize membranes.
Explain how separations are made by introducing solid agents and list the three major separation operations that
utilize this technique.
Explain the use of external fields to separate chemical mixtures.
Calculate component material balances around a separation operation based on specifications of component
recovery (split ratios or split fractions) andlor product purity.