Cite this Article Format. Helmenstine, Anne Marie, Ph. Fractional Distillation Definition and Examples. How to Separate Salt and Sand — 3 Methods. What Is Distillation? Chemistry Definition. Pure Substance Definition in Chemistry. Methods for Protein Purification in Biotechnology.
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We and our partners process data to: Actively scan device characteristics for identification. I Accept Show Purposes. The mixture boils , forming vapor gases ; most substances go into the vapor phase. The vapor enters the bottom of a long column fractional distillation column that is filled with trays or plates. The trays have many holes or bubble caps like a loosened cap on a soda bottle in them to allow the vapor to pass through.
They increase the contact time between the vapor and the liquids in the column and help to collect liquids that form at various heights in the column. There is a temperature difference across the column hot at the bottom, cool at the top. The vapor rises in the column. As the vapor rises through the trays in the column, it cools.
When a substance in the vapor reaches a height where the temperature of the column is equal to that substance's boiling point, it will condense to form a liquid. The substance with the lowest boiling point will condense at the highest point in the column; substances with higher boiling points will condense lower in the column. The trays collect the various liquid fractions. The collected liquid fractions may pass to condensers, which cool them further, and then go to storage tanks, or they may go to other areas for further chemical processing.
The resulting vapour then rises through the vertical column. As the gases rise through the tower, the temperature decreases. As the temperature decreases, certain hydrocarbons begin to condense and run off at different levels. Each fraction that condenses off at a certain level contains hydrocarbon molecules with a similar number of carbon atoms.
After this rough refinement, individual fuels may undergo more refinement to remove any contaminants or undesirable substances, or to improve the quality of the fuel through cracking. There are several ways of classifying the useful fractions that are distilled from crude oil.
One general way is by dividing into three categories: light, middle, and heavy fractions. Heavier components condense at higher temperatures and are removed at the bottom of the column. The lighter fractions are able to rise higher in the column before they are cooled to their condensing temperature, allowing them to be removed at slightly higher levels.
However, there are two major components that are not accounted for in these three categories. Fractional distillation is more efficient than simple distillation in separation due to a high number of theoretical plates. It is an important process in chemistry, industry and food science. Uses of fractional distillation include processes such as desalination, crude oil refining and chemical purification. While keeping the pressure constant, one can generate a temperature-composition diagram.
After the first vaporization-condensation cycle, the percentage of pentane has increased from 48 percent to 73 percent. L 2 then vaporizes into V 2 , resulting in a further enrichment in pentane. L 5 , which is the liquid obtained after four cycles, is almost pure pentane. Each vaporization-condensation cycle, also called theoretical plate , yields a purer solution of the more volatile component. In a fractional distillation setup, a fractionating column is typically placed between the distilling flask and head to increase the separation of liquids from the mixture.
These columns have a larger surface area on which liquid-vapor equilibria can occur and thus more theoretical plates.
Examples of fractionating columns are Vigreux and glass beads columns, which have six to eight theoretical plates. In a simple distillation, a fractionating column is not used, and vapor from the distilling flask goes straight into condensation.
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