Unit operation and Unit Process | Difference between

Chemical engineering is a vast subject and if you are an engineering student, you will encounter various concepts. There are some terms that are considered basic and one should know them at least. The first thing that will encounter you if you start studying chemical engineering is what is unit operation and unit process.

Chemical engineering is all about chemical reactions and elements, factors, and optimization of those to understand the mechanics of chemical reactions and production products. The combination of both unit operation and the process is called the manufacturing process or chemical process.

Today, in this article, we will learn what is unit operation and unit process with examples that will clear all your doubts. We will also see the difference between unit operation and unit process which is considered the most basic question that fresher chemical engineers face in on-campus interviews or open interviews. So without wasting more time, let’s jump into the article and learn in detail.

Unit Operation

Unit operation is a basic step in a process that involves physical change or chemical transformation during the process like polymerization separation, evaporation crystallization, filtration, isomerization, and other reactions. 

Example of Unit operation

Example 1 – Distillation of Methylene Di Chloride with water

Explanation – In a process, the separation of Methylene Di Chloride with water using a liquid-liquid separation technique can be called a unit operation. Only separation is taking place which will be done based on density difference. This is a physical change and no chemical reaction taking place, hence this process is considered a unit operation.

Example 2 – Distillation of acetone and water

Explanation – The distillation of acetone from the water is an example of unit operation. In the distillation process, acetone is separated and that is due to boiling point difference or volatility of the components. This is also a physical change and no chemical reaction is carried out. Hence distillation is a unit operation.

Classification of Unit Operation

Now we have seen the definition of unit operation and hereby learned what is unit operation. There are 4 classifications of unit operation. The classification of unit operations is listed below.

1. Material handling, transportation / Fluid flow process
   Pumping
   Compression
   fluidization
2. Mechanical unit operations
   Size reduction
   Size enlargement
   Mixing, agitation, blending, etc
3. Mass transfer operations
   Evaporation
   Distillation
   Absorption
   Extraction
   leaching.
4. Heat transfer operations
   conduction
   convection
   radiation

We recommend you read When vacuum distillation is selected – Purpose of vacuum distillation

Unit Process

The unit process is a process in which chemical changes take place to the material present in the reaction and result in the chemical reaction is known as the Unit process. This consists of a reaction between two or more chemicals which results in another chemical and can also be defined as a unit process. Sulphonation, nitration, oxidation, halogenation, and many more.

Example of Unit process

Example 1 – Electrolysis of sodium chloride solution

As I currently work in a Chlor Alkali industry where we do electrolysis of sodium chloride solution, we will take this as an example of a Unit process.

Explanation – Here, electrolysis of NaCl is done and the concentration of sodium chloride is taken as 305 (around) GPL (gram per liter) concentration is fed to an electrolysis cell in which electricity is passed and sodium hydroxide is produced. In this reaction, a decomposition reaction takes place hence, this is a unit operation. If you are interested, you can read Fundamentals of Electrolysis

Example 2 – Production of Hydrogen

Hydrogen is produced using a very popular method i.e. Steam-methane reforming reaction. In this method, methane reacts with steam at a pressure under 3–25 bar pressure in the presence of a Nickel catalyst at about 750 to produce hydrogen.

In this Steam-methane reforming reaction, a chemical reaction under pressure and temperature is conducted to react Methane with steam and generate Hydrogen. As the reaction is conducted, this process comes under the unit process.

What is the Manufacturing Process | What is chemical Process?

The manufacturing process consists of a combination of various unit operations and unit processes which being conducted considering factors like optimization, design of equipment and selection of equipment, use of suitable utilities, and many more to make the product is known as the Manufacturing process/chemical process.

Example – Manufacturing process of cement

Cement is considered a product that is a result of unit operation and unit process. There are various unit operations and unit processes involved in the manufacturing process of cement. We will not go in-depth into the manufacturing process and will consider the relevant things only. For the manufacturing process of cement.

The main raw material of cement is limestone which is present in the hard solid rock form. It is crushed into a fine powder using a jaw crusher. Using a Jaw crusher, only physical changes will be conducted hence it is a unit operation. In the chemical process, limestone is heated and decomposes into lime, and carbon dioxide is released which is a unit process.

Difference between unit operation and unit process

FAQ (Unit process and unit operation)

Wrapping Up

This was a detailed tutorial on the unit operation and unit process and concerning that, we also covered the difference between unit operation and unit process with examples.

If you have any doubts related to the topic then drop your question in the comment section, we will help you and explain to you in detail. Till then if you are a chemical engineering professional or a chemical engineering student then do check out the chemical engineering article.

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