INTRODUCTION:

Evaporation can be defined as the process where a liquid is converted to a gaseous state. Evaporation can only take place when water is available. Evaporation requires that the humidity of the atmosphere be lower than the evaporation surface.¹Evaporation occurs when the liquid is converted into gas. The process begins when the liquid molecules receive energy in the form of heat. They turn into a vapour after this gaining of energy.²Evaporation is the most important environmental process that can reduce the quality and quantity of water available for industrial, agricultural and domestic use.³Evaporation is the release of vapor from the surface of a liquid below its boiling point. Evaporation can also occur at room temperature. The vapor atmosphere that produces steam reduces the pressure that causes changes in temperature. The vapor pressure is highest at the boiling point of the liquid as vapor is formed throughout the liquid. The liquid vapor pressure is equal to the atmospheric pressure at its boiling point.⁴

Objectives of Evaporation:

1. To get concentrate products.⁵

2. To remove water from an aqueous solution.⁵

3. To evaporate Seawater for developing drinking water.⁵

4. To obtain solid free water which is used for chemical processing in boilers.⁵

Applications:

1. Evaporation is used to make salt from aqueous solution in concentration and recovery of dissolved solvents like sodium chloride.⁶

2. Evaporation is commonly used in the pharmaceutical industry, chemical industry for the manufacture of bulk of drugs.⁵

3. It is used to prepare galencial preparation.⁵

4. It is also used in the concentration of solutions.⁷

5. It is used to concentrate pharmaceutical herbal extracts in the herbal industry.⁶

6. It is used in the pharmaceutical industry to remove excess moisture, facilitate handling of products, and improve product stability.⁶

7. It is used to preserve long-term activity or to stabilize enzymes in laboratories.⁶

8. Evaporation is used in the manufacture of organic products. For example, insulin, enzymes, hormones.⁶

9. It is used in the demineralization of water for drinking purposes.⁵

10. It is also used in the concentration of chromatographic fractions, glucose and fructose syrup.⁶

11. Evaporation can be used for a variety of purposes, including dehydration, separation.⁸

12. Evaporation is especially useful for the treatment and disposal of specific high-power, low-volume process waste streams.⁸

13. Evaporation is used for blood product. For example, plasma and serum.⁵

Factor Affecting Evaporation:

Evaporation from water and other wet surfaces is a continuous process. The rate per unit area of water vapour released on a wet surface depends on the properties of the excess air and the heat supply to the evaporating surface. Evaporation occur owing to diffusion, convection or wind or wind action. Propagation will continue as long as the air vapour pressure is below the saturated vapour pressure at the corresponding water temperature. Convection occurs when water is hotter than air. Sensitive loss is usually associated with wind action which is most effective when the wind flow is turbulent.⁹ The following are the Factor which affect the rate of evaporation:

1. Temperature

2. Surface area

3. Humidity of the surroundings

4. Vapour pressure

5. Type of product required

6. Density of liquid

7. Temperature and time of evaporation

8. Economic Factors

9. Temperature and Moisture Content

10. Air circulation or wind speed

11. Boiling point of liquid

1. Temperature:

The rate of evaporation is directly proportional to the liquid temperature. Evaporation is accelerated by an increase in temperature, but this leads to the disintegration of the heat-sensitive elements of many drugs. Many glycosides and alkaloids decompose at temperatures below 100°C. Due to the high heat-sensitive content of hormones, vitamins, enzymes and antibiotics, special treatment is required to prevent disintegration e.g. Malt extract is concentrated by evaporation under reduced pressure so as not to deplete the enzyme.⁴

2. Surface area:

Evaporation is a surface phenomenon, indicating that the process takes place only on a liquid surface. During evaporation, the molecules of the liquid present on its surface overcome the interstitial force of attraction to separate from the liquid and escape into the atmosphere as gas (or vapour).

Liquids are known to not have any definite shape - they assume the size of their container. Therefore, the surface area of the container (or more than the surface occupied by the liquid), the higher the number of liquid molecules present on the surface. The larger the number of liquid molecules on the surface, the greater the number of molecules that will separate and form gas at a given time, which will contribute to an increase in the rate of evaporation.¹⁰

3. Humidity of the surroundings:

There is a limit to how much water vapour can be in the atmosphere. This limit is related to temperature (which means that hot air can hold more water vapour than cold air). Evaporation can be seen as an equilibrium process by which the amount of water vapour in the atmosphere reaches the equilibrium of the liquid surface water. Therefore, the higher the amount of water vapour in the atmosphere, the lower the rate of evaporation. Also, it can also be noted that an increase in temperature with constant humidity contributes to an increase in the rate of evaporation as hot air can cause excessive water vapour.¹⁰

4.Vapour pressure:

A liquid that evaporates at low boiling points due to high vapour pressure.⁵

5. Type of product required:

Solid liquid, semisolid and solid are formed after liquid evaporation. The choice of method and equipment required for evaporation depends on the type of product required.⁴

6. Density of liquid:

As the density increases, the rate of evaporation decreases. Liquid evaporation with high density has a low rate. For example, honey has a lower evaporation rate than water, which has a lower evaporation rate than alcohol. This is because honey is thinner than water and water is lower than alcohol.⁶

7. Temperature and time of evaporation:

It has been observed that exposure to relatively high temperatures for a short period of time may be less harmful to the active ingredients of a drug with a lower temperature over a shorter period of time. Based on this fact, the liquid in the film evaporates withstands high temperatures for a short period of time.⁴

8. Economic Factors:

Economic factors are important when choosing a method and equipment. Evaporators is designed to give maximum heat transfer to a liquid.⁵

9. Temperature and Moisture Content:

Some drug components decompose more rapidly in the presence of moisture when heated to high temperatures. This is due to the hydrolysis of the active ingredient. Evaporation is carried out at the temperature of the law to prevent the decomposition of the active ingredients of such materials and then the final drying is done at a high temperature when it has little moisture left.⁴

10. Air circulation or wind speed:

Evaporation increases the humidity of the atmosphere which is immediately around the liquid. This moist air takes some time to merge with the rest of the atmosphere. The presence of a breeze, a strong wind or some other type of air circulation can speed up this process and make the liquid atmosphere less humid. Therefore, by reducing the humidity of the surrounding atmosphere, a strong wind or wind can increase the rate of liquid evaporation.¹⁰

11. Boiling point of liquid:

Liquids evaporate rapidly with a low boiling point. Mercury hardly evaporates at room temperature as it has a boiling point of 357°C.⁶

CONCLUSION:

The aim and purpose of this article is understand the evaporation process and other related concept and uses in pharmaceutical industry. Evaporation a portion of the solvent concentrates the solute into a more viscous liquid product. Evaporation is mainly used in pharmaceutical industry for getting the pure form of product to increase their self life and maintain the concentration of products.

REFERENCES:

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Received on 30.09.2020 Modified on 27.10.2020

Asian Journal of Pharmacy and Technology. 2021; 11(2):163-165.

DOI: 10.52711/2231-5713.2021.00027