steam distillation questions....?

Question

--The main advantage of steam distillation as a method of purification is the compounds insoluble in water may be distilled below their boiling point. Explain clearly why this is possible.

--Why are compounds boiling below 100degCelsius not subjected to steam distillation? Give at least three characteristics of a compound suitable for steam distillation.

Answer 1

For example, the isolation of aniline, C6H5NH2, by steam distillation. At 100C, the vapor pressure of water is 760mmHg. The vapor pressure of aniline is "x" at 100C. The vapor pressure of the mix is (760-x) + (x) at 100C. "x" is the vapor pressure of aniline if it were boiling at a much lower temperature. It is like vacuum distillation without the vacuum.

It is important that aniline is "insoluble" in water. Because after the steam distillation, one can extract the aniline from the water with organic solvents.

I do not know three characteristics, but I can point out one example: ortho-nitrophenol and para-nitrophenol. One separates them by steam distillation. The ortho-isomer is hydrogen bonded internally and so volatile with steam. The para-isomer is not, and so stays behind.

Answer 2

Distillation Of Aniline

Answer 3

Steam distillation is a special type of distillation (a separation process) for temperature sensitive materials like natural aromatic compounds. Many organic compounds tend to decompose at high sustained temperatures. Separation by normal distillation would then not be an option, so water or steam is introduced into the distillation apparatus. By adding water or steam the boiling points of the compounds are depressed, allowing them to evaporate at lower temperatures, preferably below the temperatures at which the deterioration of the material becomes appreciable. If the substances to be distilled are very sensitive to heat, steam distillation can also be combined with vacuum distillation. After distillation the vapors are condensed as usual, usually yielding a two-phase system of water and the organic compounds, allowing for simple separation. Steam distillation is employed in the manufacture of essential oil, for instance, perfumes. In this method steam is passed through the plant material containing the desired oils. It is also employed in the synthetic procedures of complex organic compounds. Eucalyptus oil and orange oil are obtained by this method in industrial scale. Steam distillation is also widely used in petroleum refineries and petrochemical plants where it is commonly referred to as "steam stripping"

Answer 4

I used to distill sea water. 100 deg C is boiling point of water. Anything less will not boil the water into steam. The compound requires some impurities that when temp is at 100, they don't vaporize. The water vaporizes and moves to a different chamber where it can be cooled without the impurities. Compound needs to be a liquid.