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A with challenges from other technologies, distillation

substantial number of unit operations of chemical engineering are concerned
with problem of changing the composition of solutions and mixtures. Usually
these operations are directed towards separating a substance into its component
parts. If the operations involve changes in composition of mixtures, they are
known as the mass transfer operations. Sadler, 2009. Mass transfers
operations include drying, liquid-liquid extraction, crystallization, leaching,
adsorption, absorption, distillation etc Geankoplis, 2003. Commonly drying means
the removal of moisture from a substance. It is so slackly and incompatibly
applied that some constraints in its meaning is necessary in the treatment for
further significance. The mixture is brought into
contact with a solvent in which the substance of interest is soluble, but the
other substances present are insoluble the way to separate a desired substances
are known as extraction. Leaching is the preferential solution to one or
more constituents of solid mixture by contact with a liquid solvent. This unit
operation is one of the oldest in the chemical industries. When all the
constituents are present in both phases at equilibrium we have the operation of
fractional crystallization. The adsorption operations exploit the ability of
certain solids preferentially to concentrate specific substances from solution
on to their surfaces. In this manner, the components of solid, liquid or
gaseous mixtures can be separated from each other. Gas absorption is an
operation in which a gas mixture is contacted with a liquid for the purposes of
preferentially dissolving one or more components of the gas and to provide a
solution of them in to the liquid. Ordinarily these operations are used only
for solute recovery or solute removal. Separation of solutes from each other to
any important extent requires the fractionation techniques of distillation.
Treyball. Certainly, distillation is the most widely applied separation
technology and will continue as an important process for the foreseeable future
because there is simply no industrially viable alternative around. Also,
confronted with challenges from other technologies, distillation improves and
from time to time breakthroughs are made which move this technology to a higher
level of sophistication Z. Oluijiae,
B. Kaibel. Distillation is a method of separating the components of a
solution which depends upon the distribution of the substances between a gas
and a liquid phase, applied to cases where all components are present in both
phases. It is concerned with the separation of solution where all the
components are appreciably volatile. J.m Smith. The primary advantages of distillation
are potential for high throughput, any feed concentration, and high purity.
Many of the alternatives to distillation carry out only partial separation and
cannot produce pure end-products. Thus, several of the other alternative
separation methods can be used only in combination with distillation, while
distillation itself can be used as a stand-alone operation. The distillation
technique itself is a mature technology, that is, we have confidence in its
design, operation and control, in contrast to other promising technologies.
Because of these advantages compared with other thermal separation processes,
distillation is used in 90% of cases for the separation of binary and multicomponent
liquid mixtures Gmehling, 1994. Familiar examples include fractionation
of crude oil into useful products such as gasoline and heating oil etc.
It is a very frequent separation process in the pharmaceutical industry and in
wastewater treatment units.
The distillation columns consume more than 95% of the total energy used in
separations in chemical process industries worldwide Ognisty,
The capital
investments for distillation as a function of capacity scales according to the
“six-tenths power rule”, membranes tend to scale linearly with capacity Kunesh,
1995. Thus, distillation often has a distinct economic advantage at
large throughput. The major disadvantage of distillation is that the cost of
operation depends almost entirely on energy costs. Major efforts are under way
to improve the energy efficiency of distillation or to use alternative, less energy-intensive
separation steps Luben, 2009.
Hence design of distillation columns is a major concern of chemical engineers.


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