Steam Distillation

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Steam Distillation
6.6.12

Aim: To isolate and extract citrol from lemongrass oil using steam distillation.

Theory: Impure chemicals are usually purified using distillation, allowing the changes in boiling points to separate the substances. Chemicals with high boiling points decompose before reaching the temperature necessary for separation, leading to the invention of steam distillation. The contamination is separated at lower temperatures and allows the separation of chemicals from their contaminants. Lower boiling temperatures are achieved when immiscible compounds are mixed together and heated. Two immiscible liquids exert pressure on the common external pressure and boil at a temperature lower than usual as a result of the sum of partial pressures. Boiling point remains constant throughout steam distillation as long as the organic compound being heated has a steady, and sufficient supply of water to saturate the vapor space and uphold the pressure. Dalton’s law explains that the molecular proportion of one volatile substance to the other is the ratio of their vapor pressures (p) in the boiling mixture. Water insoluble chemicals like lemongrass oil, is immiscible in water, and therefore not able to be purified by distillation. Its boiling temperature is ˚229 and is prone to polymerization, oxidation, and decomposition during boiling which makes it a candidate for steam distillation when purifying to get citral because its distillation occurs below the boiling point of water. Adding t-butyl methyl ether to the distillate and shaking creates a distinct layer separation which when dried leaves purified citral.

Materials and Equipment:
Spatula, syringe, syringe needle, short-neck round bottom flask, digital thermometer, pipette, pipette bulb, ice, lemongrass oil, beaker, electric hot plate, t-butyl methyl ether, saturated sodium chloride, anhydrous calcium chloride, stopper, boiling chips, sand bath, distillation column, air condenser, clamp,...
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