BASICS OF MASS TRANSFER -:Guided by:- Proff. Bhoomika Domadia Dept. of Chemical Engg. Pacific School of Engg. Surat.

Prepared by.. SR.NONAMEENROLLMENT NO. 1TAPRE MUKESH RANA KARAN TARSARIYA JAYDEEP PALAVWALA HARDIK KALSARIYA BHAUTIK SHAIKH UVESH

Introduction of Mass transfer  The mass transfer is defined as “The transport of one constitute from a region of higher concentration to that of lower concentration”.  The primary driving force for the mass transfer is concentration difference, when a system contains two or more component whose concentration varies from point to point, there is a natural tendency for mass to be transfer.  Mass transfer requires the presence of two regions at different chemical composition and mass transfer refers to the moment of chemical species present in the medium.  The transfer of mass within a fluid mixture or across a phase boundary is a process that plays a major role in many industrial process.

 There are some examples of such type of processes are, 1.Dispersion of gases from slash. 2.Removal of pollutant from plant discharge stream by absorption. 3.Stripping of gas form waste water. 4.Neutron diffusion within nuclear reactor.  Many of our day by day experiences also involve mass transfer for example, 1.Lumet of sugar added to a cup of coffee eventually dissolves and then eventually diffuses to make concentration uniform. 2.Water evaporated from ponds increase humidity from passing air stream. 3.Perfume present a pleasant fragrance which is imparted throughout the surrounding atmosphere.

 Mass transfer may occur in a gas mixture, a liquid solution or solid.  Mass transfer occurs whenever there is a gradient in the concentration of a species.  The basic mechanisms are the same whether the phase is a gas, liquid, or solid.

Types Of Mass Transfer Operation On a very broad basis all the mass transfer operation can be classified into four major part : 1.Direct contact Of Two immiscible phases 2.Phases Separated by a Membrane 3.Direct contact of visible phases 4.Use of surface Phenomena

 Direct contact Of Two immiscible phases: This category is by the most important of all and includes the bulk of the mass-transfer operation. We take advantage of the fact that in two-phase system of several components at equilibrium, with few expectation the compositions of the phase are different. The various components, in other words, are differently distributed between the phases. Operations are : Gas-Gas, Gas-Liquid, Gas-Solid, Liquid-Liquid, Liquid- Solid, Solid-Solid.

 Gas – Gas :  Since with very few exceptions all gases are completely soluble in each other, this category is not practically realized.  Gas – Liquid :  In this category we can include the Gas absorption,Distillation,Desorption, Humidification and dehumidification, Striping. Gas Absorption : A solute gas is absorbed from an inert gas into a liquid. Example: Removal of ammonia from a mixture of ammonia-air by means of liquid water. Ammonia is transferred from gas to liquid phase

Distillation : Separation of a liquid mixture of miscible and volatile substances into individual components or group of components by vaporization. Example: 1. Separation of ethanol and water into its components. 2. Crude petroleum into gasoline, kerosene, fuel oil. Desorption : A desorption involves the transfer of mass from the solid surface (adsorbents) to the gas or liquid medium (adsorbates).

Striping : The stripping is the separation of gas solute from the liquid phase. The separation of ammonia from an air-ammonia mixture by means of water is a typical example of absorption. The solute is then recovered from the solution by distillation.  Gas – Solid :  If diffusion take place from gas to solid so this operation can happen Drying, Adsorption. Adsorption : A solute is removed from either a liquid or a gas through contact with solid adsorbent. Adsorbent has surface of which has a special affinity for the solute. Example: Removal of dyes using activated carbon as adsorbent.

 Liquid – Liquid :  Separation involving the contact of two insoluble liquid phases are known as liquid extraction operations. Liquid extraction : A mixture of two components is treated by solvent that preferentially dissolves one or more of the components in the mixture. Example; 1. recovery of penicillin from fermentation broth solvent: butyl acetate 2. recovery of acetic acid (b.p c) from dilute aqueous (b.p c) solutions solvent: ethyl-acetate

 Liquid – Solid :  When all the constituents are present in both phases at equilibrium, we have the operation of fractional crystallization. Other examples are Leaching, Adsorption. Crystallization : Crystallization is a process of formation of solid from a liquid solution based on difference in solute concentration and its solubility at a certain temperature. In crystallization, transfer of a solute occurs from the liquid solution to a pure solid crystalline phase. When solute concentration becomes higher than its solubility at certain temperature, the solute comes out of the solution and forms a crystal. Leaching : is a treatment of a finely divided solid with a liquid. Some examples of leaching operations are oilseed extraction, extraction of sugar beets with hot water and extraction of medicinal compounds from plant roots, leaves and stems.

 Solid – Solid :  Because of the extraordinarily slow rates of diffusion within solid phases, there is no industrial separation operation in this category.