In the previous post, we talked about the basics of mass transfer. That article was a bit theoretical. So in this post, we are going to learn about practical aspects of the mass transfer subject which is mass transfer operations.
Mass transfer operations are very important to a set of unit operations that follow the principles of mass transfer.
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So let's start by defining mass transfer operations.
What are Mass Transfer Operations?
Mass Transfer Operations are operations based on mass transfer. Mass transfer operations mean operations in which molecules transfer from higher concentration region to lower concentration region.
There are various mass transfer operations carried out in the chemical industry which you might be aware of. Also, there are many mass transfer operations types of equipment that can be equipped for various applications.
Most mass transfer operations are also separation processes that are concentration-driven.
So let's start by classifying the mass transfer operations:
Types of Mass Transfer Operations
Mass Transfer Operations are classified according to phases involved in the mass transfer operation. This classification is like this:
- Gas-Liquid Contact Mass Transfer Operations: Gas Absorption, Stripping, Distillation, Humidification, and Dehumidification
- Liquid-Liquid Contact Mass Transfer Operations: Liquid-Liquid Extraction
- Solid-Liquid Contact Mass Transfer Operations: Solid-Liquid Extraction (Leaching) and Crystallization
- Gas-Solid Contact Mass Transfer Operations: Drying, Adsorption, Desorption and Ion-Exchange
Gas-Liquid Contact Mass Transfer Operations
- Gas Absorption and Stripping: Gas absorption is a gas-liquid contact mass transfer operation in which solute transfers from the gas phase (carrier gas) to the liquid phase (solvent) by dissolving into it. An example of gas absorption is the absorption of CO2 from reformed gas with the help of a mono-ethanol amine solvent. Stripping is the opposite operation of gas absorption. Stripping is a gas-liquid mass transfer operation in which solute transfers from the liquid phase (carrier liquid) to the gas phase (stripping medium). An example of a stripping operation is the separation of absorbed CO2 by stripping it with steam.
- Distillation: Distillation is a gas-liquid contact mass transfer operation in which separates less volatile liquid and high volatile liquid by application of heat. An example of distillation is the separation of various petroleum products from crude oil.
- Humidification and dehumidification: Humidification is a gas-liquid contact mass transfer operation in which process gas is humidified by spraying liquid over it. Dehumidification is the reverse operation of humidification in which gas is dehumidified by cooling it. Removal of moisture from the air by cooling it to lower temperatures is an example of dehumidification.
Read also: Distillation
Liquid-Liquid Contact Mass Transfer Operations
- Liquid-Liquid Extraction: Liquid-Liquid Extraction is a liquid-liquid contact mass transfer operation in which solute molecules transfer from one liquid (carrier liquid) to another liquid (liquid solvent) having a difference in solubility. An example of liquid-liquid extraction is the separation of the aromatic compound from gasoline reformation. Another example of liquid-liquid extraction is penicillin from fermentation broth.
Read also: Liquid-Liquid Extraction
Solid-Liquid Contact Mass Transfer Operations
- Solid-Liquid Extraction: Solid-Liquid Extraction is a solid-liquid contact mass transfer operation in which solute molecules transfer from solid (carrier solid) to liquid (solvent) by dissolving it. Another name of solid-liquid extraction is Leaching. An example of solid-liquid extraction is the extraction of aroma from coffee by hot water.
- Crystallization: Crystallization is a solid-liquid contact mass transfer operation in which solid crystals are generated by the cooling of supersaturated solutions of solute and solvent. An example of crystallization is separation wax from crude oil by dewaxing carried out in petroleum.
Read also: Solid-Liquid Extraction
Gas-Solid Contact Mass Transfer Operations
- Drying: Drying is a solid-gas contact mass transfer operation in which moisture is removed from wet solid by dry air. An example of drying is the drying of fruits, polymers, ceramic items, etc.
- Adsorption, Desorption, and Ion-Exchange Process: Adsorption is a solid-gas contact mass transfer operation in which solute molecules from gas are adsorbed on the surface of the solid. An example of adsorption is the separation of various components of air in their pure form. The opposite operation of adsorption is desorption. The separation of adsorbed gases on solid by decreasing pressures is an example of desorption. Ion exchange is another similar operation to adsorption. In ion exchange, dissolved gases and impurities are separated by ion exchange resins. Demineralization of water is an example of an ion-exchange process.
Read also: Adsorption