Solvay Process - JEE Important Topic

VSAT 2022

Industrial Synthesis of Sodium Carbonate

Several chemical reactions are used in industries to synthesise a variety of useful industrial products. One such process is the ‘Solvay process’, which is used majorly for the formation of sodium carbonate, a key ingredient used in the formation of soaps, detergents, household cleaners, glass, paper, and in the wool industry. In this topic, we will learn about the Solvay process, its steps, the chemical reactions it involves and also its effects on the environment.

What is the Solvay Process or the Ammonia Soda Process?

The Solvay Process, also known as the Ammonia Soda Process or the Solvay Ammonia Process, was developed by the Belgian chemist Ernest Solvay in 1861. The raw materials used in the Solvay Process are inexpensive and easily available. They include brine, limestone and ammonia.

  • Sodium chloride solution, also known as brine, provides the sodium ions in the formation of sodium carbonate. Seawater and underground water are some of the few sources of brine.

  • Limestone or calcium carbonate is the source of carbonate ions in the synthesis of calcium carbonate. It can be obtained from mining.

  • The ammonia used is synthesised in the industries using Haber’s process. It is expensive but is recycled in the Solvay process.

Solvay Process Steps

  1. Firstly, brine is saturated using ammonia, followed by CO2 and is cooled later. The NaHCO3 gets precipitated out of the solution. 

NaCl + NH3 + CO2 + H2O → NaHCO3 (s) + NH4Cl

This is the Solvay Process reaction equation.

  1. The precipitates of NaHCO3 are filtered, dried, and heated. This results in the formation of sodium carbonate, carbon dioxide and water vapours.

2 NaHCO3 + Heat → Na2CO3 + H2O(g) + CO2(g)

This is the second Solvay process equation.

  1. The carbon dioxide used in the process is produced by heating limestone.

CaCO3 + Heat CaO + CO2

Lime dissolves in water to form calcium hydroxide.

CaO + H2O → Ca(OH)2

This calcium hydroxide is then reacted with the solution left after the precipitation of NaHCO3. Later, NH3 is recycled.

Ca(OH)2 (s) + 2 NH4Cl (aq)  →  2NH3 (g) + CaCl2 (aq) + 2 H2O (l)

This recycled ammonia is used in the process again for the production of NaHCO3. Therefore, the only byproduct formed during the Solvay process is calcium chloride.

Environmental Issues Caused by the Solvay Process

There are several environmental issues associated with the Solvay Process, including mining, thermal pollution, disposal of by-products, etc. 

  1. One of the raw materials for the Solvay Process is limestone, which is obtained by mining. Mining leads to pollution and destroys natural habitats. 

  2. The Solvay Process is exothermic. As a result, an excess amount of heat is liberated into the atmosphere during the Solvay Process, causing a rise in the temperature, followed by thermal pollution. The increased temperature in the waterways affects aquatic life and destroys fish eggs.

  3. The main by-product of the Solvay Process is calcium chloride. The high amount of calcium chloride produced is difficult to dispose off without affecting the ecosystem. The high chloride ion concentration affects the vegetation of an area. A small amount of ammonia is released during the Solvay Process, which can cause respiratory problems if inhaled.

Conclusion

Sodium carbonate is synthesised in industries using the Solvay Process. The raw materials used in the Solvay Process include brine, limestone and ammonia. The Solvay process is a multi-step process and involves many chemical reactions. In the first step, the brine solution is saturated using ammonia and CO2​, the carbon dioxide used is produced by heating limestone. The precipitates of NaHCO3 are formed. The precipitates are collected by filtering and are dried, followed by heating to produce sodium carbonate.

The lime produced by heating limestone is dissolved in water to form a base, which is calcium hydroxide. It is then reacted with the solution left after the precipitation of NaHCO3 and the ammonia is recycled, which can be used in the process again. The Solvay process has some environmental issues associated with it, like thermal pollution, mining, disposal of by-products, etc.

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FAQs on Solvay Process - JEE Important Topic

1. Why is the Solvay Process important?

The Solvay Process is used to produce sodium carbonate in industries. Sodium carbonate is in great demand due to its applications in the glass industry, textile industry and paper industry. Other than that, it is used in the manufacture of soaps, detergents and numerous other chemicals. It is also used in petroleum refining as a water softener.


As the Solvay process uses easily available and inexpensive raw materials, it is cost-effective as compared to other methods. Hence, it is widely used in industries to produce sodium carbonate.

2. Can potassium carbonate be synthesised using the Solvay Process?

Potassium carbonate can not be synthesised by using the Solvay Process. In the case of sodium carbonate formation by Solvay process reaction, sodium bicarbonate gets precipitated out of the solution, as it is insoluble in water and gives sodium carbonate on heating. However, in the case of potassium carbonate formation by the Solvay process, when carbon dioxide is passed through KCl saturated with ammonia, potassium bicarbonate is formed. This is soluble in water and thus, can not be precipitated out of it.

3. What is the purpose of burning coke in the Solvay Process

Calcium carbonate or limestone is commonly known as coke. Coke is one of the Solvay process raw materials. Coke provides energy by burning and the heat generated is used to decompose calcium carbonate to provide carbon dioxide for the process.

4. What is ammoniacal brine?

Ammoniacal brine is used in the Solvay or ammonia soda process. It is a commercially important chemical and can be formed by bubbling ammonia gas through a saturated sodium chloride solution. The chemical formula of the ammoniacal brine solution can be given as, NaCl + NH3 + H2O Ammoniacal brine can be used to make sodium carbonate and other chemicals.

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