We have already said that the simple distillation is less efficient at separating liquids, because there is a smaller surface area inside the column, but it is usually much faster. This means that the fractions obtained are impure, and often contain traces of the other liquids found in the original mixture.

It is impossible to get pure ethanol by distilling any mixture of ethanol and water containing less than 95.6% of ethanol. This particular mixture of ethanol and water boils as if it were a pure liquid. It has a constant boiling point, and the vapor composition is exactly the same as the liquid.

A boiling point composition curve (Figure 2) can be used to predict the number of theoretical plates needed to achieve a desired separation.

For example, liquid ethanol can be separated from a mixture of ethanol and water by fractional distillation. This method works because the liquids in the mixture have different boiling points. When the mixture is heated, one liquid evaporates before the other.

Figure 1: Fractional distillation scheme of a 1:1 mole ratio mixture of liquids A and B, with B being the most volatile. In this example, the distillation column has three theoretical plates; the condensate and vapor that constitute the same plate number are coded with the same color.

A theoretical plate is an area in the column where the recondensing liquid and the rising vapor come into equilibrium with one another. The Height Equivalent to the Theoretical Plate (HETP) is the distance (length) between theoretical plates, and it is a measure of separation power in such systems.

The number of theoretical plates is the number of discrete distillations that would have to be performed to obtain an equivalent separation of a discrete plate. This number is commonly used as a measure of separation efficiency and is a useful when comparing the performance of various chromatographic columns.

In other words, having more theoretical plates increases the efficiency of the separation process be it either a distillation, absorption, chromatographic, adsorption or similar process.

A compound must satisfy three conditions to be successfully separated by steam distillation. It must be stable and relatively insoluble in boiling water, and it must have a vapor pressure in boiling water that is of the order of 1 kPa (0.01) atmosphere.

It has very high levels of acidity. Distillation should not be considered as a method of water softening because one might end up having unwanted elements in the distilled water. For example, liquids that have a boiling point equal to water will not be separated but will condense with the water.

List of Disadvantages of Fractional Distillation

• It can be expensive. On an industrial level, fractional distillation is expensive because it requires large structures, heavy-duty materials, and specialized machinery.
• It comes with operational hazards.
• It can contribute to environmental pollution.

The Disadvantages of Simple Distillation

• Impurities. Since the mixture in simple distillation is only boiled and recondensed once, the final composition of the product will match the composition of the vapor, which means it may contain significant impurities.
• Azeotropic Mixtures.
• Energy Consumption.
• Chemical Reactions.

Distillation is used to purify a compound by separating it from a non-volatile or less-volatile material. This method is used whenever there is enough of the compound to perform a distillation. The distillation method of boiling point determination measures the temperature of the vapors above the liquid.

If it is too low, it will be too close to the boiling liquid and will read higher than the true vapor temperature. If it is positioned too high, it will be out of the path of the vapors and read lower than the true temperature.

Distillation is used to separate liquids from nonvolatile solids, as in the separation of alcoholic liquors from fermented materials, or in the separation of two or more liquids having different boiling points, as in the separation of gasoline, kerosene, and lubricating oil from crude oil.

Distillation effectively removes inorganic compounds such as metals (lead), nitrate, and other nuisance particles such as iron and hardness from a con- taminated water supply. The boiling process also kills microorganisms such as bacteria and some viruses. Distillation removes oxygen and some trace metals from water.

Cost is one of the main reasons why few bottlers use distillation. The major cost factor is equipment. The cost of energy required to heat the water to boiling in the water distillation process has made even the cost of producing a gallon of distilled water a lot more expensive than RO.

Answer: The principle of fractional distillation is that different liquids boil at different temperature. The miscible liquids boil at different temperature and evaporate at different temperature. When the mixture is heated, the liquid with lower boiling point boils and turns into vapours.

Sublimation is a process in which a solid turns directly into gas without passing into liquid state. It works on the principle that solids have a weak intermolecular force hence a higher vapour pressure which converts it into directly vapour state.

Below, we will discuss some of the practical applications of distillation.

• Creating CBD Oil Products. Distillation processes such as steam distillation are widely used to extract CBD from the hemp plant.
• Purifying Water. Another practical application of distillation is purifying water.
• Producing Gasoline.
• Recycling Oils.

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