What is Unit Process and Unit Operation?

Question

Accepted Answer

Unit process and unit operation are terms used in chemical engineering to describe different stages of a chemical process.

Unit process refers to a single chemical transformation or reaction that takes place in a process.
Unit operation refers to a physical change or separation that occurs in a process.
Examples of unit processes include distillation, crystallization, and chemical reactions.
Examples of unit operations include filtration, evaporation, and centrifugation.

Accepted Answer

Unit Operations

A unit operation is defined as a process which does not involve any chemical reaction. Unit operations only deal with physical changes of the materials involved in the process. They are equipments which cause the materials to undergo physical changes. The physical changes are carried out for variety of purposes. Generally unit operations steps are carried out before subjecting the materials to chemical reactions so

that chemical reactions happen smoothly.

The physical changes can imply phase changes such as evaporation,condensation, crystallization etc. Thus Distillation is a unit operation step because condensation and evaporation happens inside the

column. Evaporators, and crystallisers are also unit operations equipment.

Unit Process

Chemical reaction is at the heart of the unit processes. A chemical reactor is an equipment which falls under the category of unit processes. Literal chemical change takes place inside the equipment wherein the the chemical structure of the material changes and it transforms and forms an entirely new material.

All kinds of chemical reactions carried out in industrial equipments comes under this category. Some examples of such chemical reactions are, sulphonation, nitration,halogenation, alkylation, hydrolysis, hydrogenation,polymerization, oxidation, reduction, etc. The examples

can be innumerable as there can be innumerable compounds which can be formed by reaction of two or more materials or by decomposition of the material itself. Thus classification can be similarly endless.Most of the chemical reactions are irreversible in nature.

A chemical reaction step in a process forms the heart of the process, often governing the economics of the entire

process. Thus the unit processes are often subject of optimization.

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