i)Mixing: Mixing is carried out for producing simple mixtures, accomplishing dispersions and promoting chemical reactions. It is a process in which two separate materials such as two different fluids, a fluid and a powdered solid or two different or same solids are taken and forced them to be randomly distributed through one another by some mechanical means. Mixing involves gases, liquids and solids in any possible combination. For liquid- liquid mixing agitated vessels are used, for solid-solid mixing kneading machines, ribbon blenders are used.
ii) Drying: Drying is an operation in which the moisture of a substance is removed by means of thermal energy. In this operation, moisture is removed by circulating hot air or gas over the material in order to carry away the water vapour. In this operation, heat and mass transfer occur simultaneously. Heat is transferred from the gas phase to the solid phase and mass is transferred from the solid phase to the gas phase. Usually a solid or nearly solid materials are processed in dryer. Drying operations may be carried out for i)reducing the transportation cost, ii)making materials more suitable for handling and storage, iii)preventing corrosion arising due to the presence of moisture and iv)providing definite properties to materials. Eg: Drying of pharmaceuticals, dyes, paper, cloth
iii) Evaporation: It is a unit operation in which a weak solution is concentrated by boiling off the solvent. The product is concentrated solution. In this operation, the solvent to be evaporated is generally water and concentrated solution or thick liquor is the product. Evaporation is carried out by supplying heat to a solution to vaporize the solvent. A common heating medium is low pressure steam. The heat is utilized to increase the temperature of the solution to its boiling point and supply the latent heat of vaporization of the solvent.
iv) Gas Absorption:
-This operation is used to separate the components of gas mixture .
-It is carried out for the recovery or the removal of a soluble components of a gas mixture depending upon the situation.
-Absorption is an operation in which a gas mixture is contacted with a liquid solvent for the purpose of dissolving a definite component of the gas mixture in the liquid.
Example:
1) Absorption of ammonia from an air- ammonia mixture by water
2) Removal of hydrogen sulfide from naturally occurring hydrocarbon gases.