Distillation successful because fluids are handled easily and energy can be used efficiently

Cutaway section of tray column shows highly-developed column internals that help make distillation successful.

Cutaway section of a tray column

a) Downcomer;
b) Tray support;
c) Sieve trays;
d) Manway;
e) Outlet weir;
f) Inlet weir;
g) Side wall of downcomer;
h) Liquid seal [1]

Distillation successful because fluids are handled easily

…only fluid phases, which can be handled very easily, are involved.

A further advantage is a high density difference between the coexisting phases. High density differences enable high velocities in the equipment and make the separation of the phases easier.

Distillation successful because energy can be used efficiently

Disadvantages of distillation and rectification are a risk of thermal degradation of substances and, even more importantly, a high energy demand.

This high energy demand, however, can be drastically reduced by special measures, e.g., by material and thermal coupling of the equipment, by implementing heat pumps or by complete heat integration of the process.[2] …this energy frequently can be in the form of exhaust steam from turbine drives or other waste heat that has a relatively low value. In fact, reboilers may provide a utility service by using heat that otherwise might be wasted.[3] …the theoretical work can be closely approached by actual work after known inefficiencies are identified and… the dominant driving force losses are in pressure drop and temperature difference.[4]

Process data and column internals are highly developed

Rectification [distillation] is a highly developed technology with respect to thermodynamic fundamentals (e.g., vapor–liquid equilibrium, thermodynamics) as well as design and construction of the equipment. Rectification columns can be safely constructed and operated up to diameters of 10 m and heights of 100 m.

Column internals (e.g., trays, packings) are very effective in enhancing the interfacial mass transfer

All these advantages often make rectification the separation technology of choice. Whenever a fluid mixture can be fractionated [separated into components] by rectification then rectification is in most cases the winner of a comparison of several separation techniques…[2]

  1. Stichlmair, Johann. “Distillation and rectification.” Ullmann’s Encyclopedia of Industrial Chemistry, Wiley-VCH, 2005, p. 74.
  2. Mersmann, Alfons, Matthias Kind, and Johann Stichlmair. Thermal separation technology: principles, methods, process design. Springer Science & Business Media, 2011, p. 231.
  3. Kunesh, J. G., et al. “Distillation-Still Towering over Other Options.” Chemical Engineering Progress 91.10 (1995): 43-54.
  4. Steinmeyer, Dan. “Process Energy Conservation.” Kirk-Othmer Encyclopedia of Chemical Technology. 5th ed., Wiley-Interscience, 2004-2007, p. 6.

Distillation is the benchmark separation for reliability and efficiency

Distillation process flow diagram for a binary mixture of benzene and toluene

Distillation of a binary mixture of benzene and toluene [1]

Distillation is the dominant separation worldwide

…the unit operation rectification [distillation]… is the only technology which is capable to separate fluid mixtures into all pure substances.[2]

For more than 5,000 years distillation has been used as a method for separating binary and multicomponent liquid mixtures into pure components. Even today, it belongs to the most commonly applied separation technologies and is used at such a large scale worldwide that it is responsible for up to 50% of both capital and operating costs in industrial processes. It moreover absorbs about 50% of the total process energy used by the chemical and petroleum refining industries every year. Given that the chemical industry consumed 19% of the entire energy in Europe (2009), distillation is the big driver of overall energy consumption.[3]

Distillation scales up efficiently and reliably

The capital investment for distillation scales as a function of capacity to about the 0.6 power. Some other methods such as membranes tend to scale linearly with capacity. Thus, distillation often has a distinct economic advantage at large throughputs.[4]

…distillation is the benchmark separation method to which all other methods must be compared. Distillation should always be the first method considered for any separation. Moreover, when other methods give comparable results to distillation, the reliability and efficiency of distillation make it the likely choice.[5]

Of all factors influencing the decision to choose one process in preference to another, design reliability is the most important. Regardless of any other considerations, the plant, when constructed, must work properly to produce an acceptable product that can be sold at a profit.

Reliable design methods for distillation have been developed over many years of industrial experience and extensive testing of commercial-scale equipment by Fractionation Research, Inc. A competent engineering firm usually can design a distillation process given a knowledge of the pertinent physical properties of the components and vapor-liquid equilibrium information on the significant binary-pair components of the mixture to be separated. Occasionally, some small-scale testing is required, but scale-up methods for distillation are the most reliable of all the separation methods.[6]

  1. Seader, J. D., Ernest J. Henley, and D. Keith Roper. Separation process principles: chemical and biochemical operations. 3rd ed., John Wiley & Sons, 2011, p. 259.
  2. Mersmann, Alfons, Matthias Kind, and Johann Stichlmair. Thermal separation technology: principles, methods, process design. Springer Science & Business Media, 2011, p. 231.
  3. Górak, Andrzej. “Preface to the Distillation Collection.” Distillation: fundamentals and principles. Edited by Andrzej Górak and Eva Sorensen, Academic Press, 2014. pp. vii-viii.
  4. Kunesh, J. G., et al. “Distillation-Still Towering over Other Options.” Chemical Engineering Progress 91.10 (1995): 43-54.
  5. Barnicki, Scott D., and James R. Fair. “Separation system synthesis: a knowledge-based approach. 1. Liquid mixture separations.” Industrial & engineering chemistry research 29.3 (1990): 421-432.
  6. Null, H. R. “Selection of a separation process.” Handbook of separation process technology. Edited by Ronald W. Rousseau, John Wiley & Sons, 1987, pp. 982-995; p. 984.