DISTILLATION- HISTORY& BASIC PRINCIPLE

INTRODUCTION TO DISTILLATION

1. The first clear evidence of distillation comes from Greek alchemists working in Alexandria in the first century AD. 

2. Distilled water has been known since 200 AD, when Alexander The Great described the process. Arabians learned the process from the people Egypt and used it extensively in their chemical experiments.

3. Clear evidence of the distillation of alcohol comes from the School of Salerno in the 12th   century. Fractional distillation was developed by Tadeo Alderotti in the 13th century.

4. In1500, German alchemist Hieronrymus Braunschweig published Liber de arte destillandi (The Book of the Art of Distillation) the first book solely dedicated to the subject of distillation, followed in 1512 by a much expanded version.

5.As Alchemy evolved into the science of chemistry, vessels called retorts became used for distillations. Later, copper alembics were invented. These were called pot stills. Today, those stills have been largely supplanted by more efficient distillation methods in most industrial processes.

6. In the early 19th century the basics of modern techniques including pre-heating and reflux were developed, particularly by the French, and then in 1830 a British Patent was issued to Aeneas Coffey for a whiskey distillation column, which worked thoroughly and may be regarded as the archetype of modern petrochemical units.

7. In 1877, Ernest Solvay was granted a United State Patent for a tray column for ammonia distillation and the same and subsequent years saw developments of this theme for oil and spirits.

With the emergence of chemical engineering as a discipline at the end of the 19th century, scientific rather than posteriori methods could be applied.

The developing industry of petroleum in the early 20th century provided the impetus for the development of accurate design methods such as the McCabe-Thiele method and the Fenske equation.

     

     Basic Principles of Distillation

  Separation of components from a liquid mixture via distillation depends on the         differences in boiling points of the individual components. Also, relying on the             concentrations of the components present, the liquid mixture will have various boiling  point characteristics. Therefore, distillation processes rely on the vapour pressure  characteristics of liquid mixtures.

  

  The vapour pressure of a liquid at a particular temperature is the equilibrium pressure   exerted by molecules leaving and entering the liquid surface.

  

     Below are some important points about vapour pressure:     

1. Energy input raises vapour pressure

2. Vapour pressure is related to boiling

3. A liquid is said to ‘boil’ when its vapour pressure equals the surrounding pressure

4. The ease with which a liquid boils depends on its volatility

5. Liquids with high vapour pressures (volatile liquids) will boil at lower temperatures

6. The vapour pressure and hence the boiling point of a liquid mixture depends on the relative amounts of the components in the mixture

7. Distillation occurs because of the differences in the volatility of the components in the liquid mixture

    

     The distillation equipment to achieve the desired aims will generally consist of:

     1. Heating system to evaporate the solvent;

     2. Condensers and coolers;

     3. Fractionating column

     4. Storage both as part of the plant as a still kettle and to hold residue, products and          feed.