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