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Vacuum Distillation

Mixture is the combination of more than one substance which may or may not be in same phase.  On the basis of phases, mixture can be classified as homogenous and heterogeneous mixtures. All the constituents of a homogenous mixture remain in same phase like ethanol in water or acetic acid in water. On the other hand, heterogeneous mixtures have different phases like sand in water. It’s easy to separate the components of a heterogeneous mixture as they are in separate phase therefore can easily separate by filtration or separating funnel. Homogenous mixtures cannot separate by normal filtration methods as all components remain in same phase.

Today we have several methods to separate the components of homogeneous mixtures. In this article we will discuss one of the most common methods of separation of components called as distillation. It is a method which is based on the boiling point of components of mixture. In distillation process, the mixture is taken in a round bottom flask. The flask is heated with the help of a Bunsen burner. As temperature increases, the component with low boiling point converts first in vapour and will go up the flask.

Distillation Process

The mouth of flask is connected with adapter and condenser where vapour condenses to convert into liquid. Another component with high boiling point will remain in the flask and separate out from other.

 

Vacuum Distillation Definition

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Distillation process can be used to separate all the liquids in the mixture. Fractional distillation is very common to separate the components of crude oil and to separate nitrogen and oxygen from liquid air. Unlike fractional distillation, vacuum distillation is mainly the components with very high boiling points.

The instrumental set up is almost same as of a micro-scale or semi-macro scale distillation. However in a vacuum distillation, a spin vane or spin bar has to be used instead of boiling stones as it cannot work in vacuum.

Vacuum Distillation Process

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In the setup of vacuum distillation, the spin bar is connected to the vacuum source through thick-walled tubing. A vacuum adapter or a drying tube on the top of the air condenser can be used for this purpose. All the glassware should fitted nicely to ensure the vacuumed of the system. All glassware should be crack-free and fitted with metal clamp. In a vacuum distillation process, all volatile solvents are evaporated off at ambient pressure by using the rotary evaporator and remaining liquid must be cool down at room temperature. Later we have to transfer into the flask. The stirrer must be on and setup is slowly evacuated without heating and cooling. Because of this the low boiling components evaporate away first. With stirring and vacuum, the temperature is slowly raised.

The water flow in the water-jacketed condenser condensed the vapors and transfer to the receiving flask. Once the receiving flask fills up, the setup is raised from the hotplate for cooling. Later it can disconnect from the vacuum source to remove the liquid. The vacuum setup is re-assembled and the distillation continued until entire compound is distilled.

Vacuum Distillation Method

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Vacuum distillation method is mainly used in refineries. It involves expanding oil to produce high surface area that facilitates the vaporous extraction of water and other contaminants.  The distillation includes heating, vaporization, condensation and cooling of vapors. It separates all the components of a liquid mixture with the help of partial vaporization. It results the separation of vapor and liquid residue.

In this process, the more volatile components like water vaporized and less volatile components remain in the oil. The water vapors can be condensed and back to liquid state. Various properties of components of mixture and efficiency of the distillation process will determine the completeness of separation of components.

Principle Vacuum Distillation

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The distillation process that occurs below one atmosphere and in vacuum is called as vacuum distillation. Low pressure permits vaporization at low temperatures. For example at 1 atm, the boiling point of water is 212°F (100°C) whereas under vacuum at 27" Hg it boils at 135°F or 57°C. Hence vacuum distillation involves the thermal decomposition and degradation of the fluid. Its additives are avoided. Due to this, heating and cooling both requires less energy and make it energy efficient process.

Vacuum Distillation Column

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Vacuum distillation involves dehydration and also used for lubricants and hydraulic fluids. The vacuum distillation column is applied in one of three process configurations. First application involves simple transfer from one unit to another through the vacuum distillation unit. Because of this, treated and untreated oil do not mix with each other. 

Vacuum Distillation Column

Second application involves the multi-passing of fluid from a tank or the reservoir of a static through the vacuum distillation unit. Third application involves online recirculation on an operating fluid system through a vacuum distillation unit. It can be a paper machine main lube oil system, a hydraulic system or turbine-generator lubrication.

Vacuum Distillation Ethanol

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We know that the boiling point of ethanol is 79°C which drops to 34°C under vacuum. In the presence of vacuum, distillation can take place at lower temperatures which attain higher alcohol concentrations. At low pressure azeotrope moves towards 100 % and below 0.1 atmospheres it disappears that helps us to get 100% alcohol.
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