Sodium carbonate manufacturing process, solvay process

Sodium carbonate (washing soda) is a white crystalline solid. It exists as decahydrate ( Na2CO3.10H2O). Sodium carbonate is manufactured by solvay process in industrial scale and have very industrial and domestic uses.


In this tutorial, we first discuss about sodium carbonate manufacturing process, solvay process. Then study about uses, applications and reactions of Na2CO3. Also NaHCO3 and it's reactions, uses are explained later.


Prepare sodium carbonate in the laboratory

Sodium chloride and calcium carbonate reaction

Sodium chloride react with calcium carbonate and give sodium carbonate and calcium chloride. This reaction is reversible and create many other problems. Therefore we have to use more chemicals to separate desired product.

Sodium chloride and calcium carbonate reaction


Washing soda, soda ash, baking soda

  • Washing soda - Na2CO3
  • Baking soda - NaHCO3
  • Soda ash - Na2CO3


Solvay process steps or ammonia-soda process

Solvay process has five main steps on sodium carbonate manufacturing.

  1. Ammonia absorber - saturation of brine with ammonia
  2. Carbonation tower
  3. Filtration
  4. Calcination of sodium bicarbonate
  5. Ammonia recovery tower

The solvay process is an excellent example for a closes cycle chemical process where the byproducts are efficiently reused in the manufacturing process.


Raw materials of sodium carbonate manufacturing

  • Brine solution (NaCl)
  • Limestone (CaCO3) for CO2
  • Ammonia gas
  • water

Like above materials, ammonia(NH3) is also contributed in sodium carbonate manufacturing. But it does not contain in the final product. Therefore ammonia gas is recycled completely in the solvay process..


Principles of solvay process of sodium carbonate manufacturing


common ion effect

The main psysicochemical principle is that when a saturated solution of sodium chloride (NaCl) is saturated with ammonia and carbon dioxide, then sodium bicarbonate gets precipitated. Sodium bicarbonate is generally soluble in water, but in a concentrated solution of NaCl its solubility gets lowered. Therefore sodium bicarbonate gets precipitated. This is called the common ion effect. What this state is that the solubility of an electrolyte is lower in a medium where there is an excess of a common ion. In sodium bicarbonate manufacturing process, sodium ion is the common ion.



Counter current principle

The counter current principle is used in sodium carbonate manufacturing process. Brine is saturated with ammonia gas and slowly passed through solvay tower from top to bottom. Carbon dioxide is sent from bottom to top. Inside the tower, there are a number of mushroom shaped perforated plates.

counter current process of solvay process of sodium carbonate manufacturing


Steps of Sodium carbonate manufacturing process

Below figure shows outline of solvay process. sodium carbonate manufacturing plant
Figure 1: sodium carbonate manufacturing plant outline


Ammonia absorber tower

Brine solution (NaCl, 30% solution) is pumped into the ammonia absorber tower. Ammonia and small amount of carbon dioxide from ammonia recycling tower is bubbled through brine solution. Solution gets saturated with ammonia and form sodium bicarbonate.
Calcium and Magnesium ions(in brine solution) are removed as carbonates in the filter.

ammonia absorber tower
Figure 2: reactions of ammonia absorber tower

Carbonation tower

Carbon dioxide is entered from the bottom of the tower.brine solution comes down.
Both reacts and form insoluble (due to common ion effect) sodium bicarbonate.

carbonation tower
Figure 3: reactions of ammonia carbonation tower

Solution coming from the carbonation tower contain ammonium chloride and small amount of ammonium bicarbonate. They are pumped to ammonia recovery tower.

Sodium bicarbonate is heated.

Then sodium carbonate, carbon dioxide gas and water form.

Sodium bicarbonate is heated

Ammonia recovering tower

Filtered ammonium chloride ,ammonium bicarbonate are pumped into ammonia recovering tower and mixed with calcium hydroxide. Then mixture is heated. Ammonia gas, calcium chloride (CaCl2), and water are given as products. This is an economical advantage because ammonia is recovered. Ammonia is a relatively expensive material.

ammonia recovery tower
Figure 4: reactions of ammonia recovery tower

Lime kiln

Lime(CaCO3) is heated to produce CO2 and CaO.
CaO is mixed with water to produce Ca(OH)2.
HEAT + CaCO3 → CaO + CO2
CaO + H2O → Ca(OH)2

sodium carbonate manufacturing process
Figure 6: sodium carbonate manufacturing process

By-products of solvay process

Ammonium chloride(NH4Cl) formed as a byproduct. It reacts with calcium hydroxide to regenerate ammonia. To produce carbon dioxide gas, limestone (CaCO3) is heated. CaO formed as a byproduct in this reaction. CaO is slaked with water to produce calcium hydroxide (Ca(OH)2) which is used to regenerate ammonia from ammonium chloride.



Environmental pollution due to solvay process

Ammonia is a very toxic material. If ammonia gas is leaked into water or air from plant, it pollutes the environmental. Therefore plant should be carefully operated.

To produce carbon dioxide gas and heat, limestone is heated. This heat increases the temperature of the environment around the plant. If limestone is taken from coral, it will cause to coastal erossion.

Uses of sodium carbonate

Sodium carbonate is used in domestic purposes and industrial productions.

  • for softening the hard water
  • for washing purposes in the laboratory
  • in textile industry
  • in petroleum refining industry
  • to produce soap, glass, paper, borax, caustic soda, etc.
  • A mixture of Na2CO3 and K2CO3 is used as a fusion mixture.
  • Na2CO3 is used as a reagent in the laboratory.
  • For paint and dye stuffs.
  • For metal refining

Sodium carbonate in qualitative analysis

Sodium carbonate is used to identify cations in qualitative analysis. It precipitates insoluble carbonates of calcium, barium and strontium.

Ammonia can be reused while other raw materials are cheap. Only calcium chloride(CaCl2) is not sent back to the process. CaCl2 is used to manufacture gypsum from the mother liquor of salterns.



Requirements to build a solvay process plant

Ability of getting limestone easily. Limestone is used in two ways in solvay process for heating purpose and obtaning carbon dioxide gas.



Why ammonia is used in solvay process?

The equilibrium reaction of carbon dioxide and water give H+ ions. Ammonia reacts with these H+ ions. Therefore equilibrium reaction of carbon dioxide and water shifts to the right according to the Le Chatelier principle.

This results more carbon dioxide dissolving in the medium. Therefore more NH4+ ions are generated and it drive the reaction to produce more Na2CO3. Finally ammonia is recoverd again by CaCl2 in the solvay process.

Cannot manufacture potassium carbonate by solvay process?

Potassium carbonate (K2CO3) cannot be manufactured by solvay process because potassium bicarbonate (KHCO3) fairly soluble in water. In sodium carbonate manufacturing, firs,t sodium bicarbonate is precipitated, then Na2CO3 is produced. But due to higher solubility of KHCO3, K2CO3 is unable to manufacture by solvay process.



Sodium carbonate reactions



Sodium carbonate and acid reaction

When dilute acid(HCl, H2SO4) is added to a solid sodium carbonate(Na2CO3) , carbon dioxide gas is generated.

Sodium bicarbonate and acid reaction

Sodium carbonate and carboxylic acid reaction

Sodium carbonate and carboxylic acids (RCOOH) react to give CO2 and RCOO-Na+ and water. Also sodium bicarbonate reacts with carboxylic acid to give CO2.

Sodium carbonate and carboxylic acid reaction

Note : Alcohols and phenol do not react with sodium carbonate and sodium bicarbonate.



Sodium carbonate and milk of lime reaction

With hot milk of lime (Ca(OH)2), sodium carbonate react to form sodium hydroxide and calcium carbonate. Calcium carbonate exist as a precipitate.

Sodium carbonate and milk of lime reaction - Na2CO3 + Ca(OH)2


Sodium bicarbonate or baking soda, NaHCO3

Sodium bicarbonate( baking soda, sodium hydrogen carbonate) is obtained as an intermediate product in solvay process for the manufacturing of sodium carbonate.

Preparing sodium bicarbonate in the laboratory

Passing carbon dioxide to a cold concentrated solution of sodium carbonate will give sodium bicarbonate(NaHCO3).

Preparing sodium bicarbonate in the laboratory

Properties of sodium bicarbonate

  1. Sparingly soluble in water
  2. A white crystalline solid
  3. When heating(373K), it decomposes into sodium carbonate, carbon dioxide and water. sodium bicarbonate decomposition
  4. Aqueous solution of sodium bicarbonate is alkaline in nature. aqueous sodium bicarbonate


Uses of sodium bicarbonate

  1. to make baking powder. Baking powder contains sodium hydrogen carbonate and an acid like tartaric acid or citric acid.
    Baking powder should be added to cakes. If baking powder is not added, the obtained cake will be comparatively hard and small in size.
  2. sodium bicarbonate is used in medicines as an antacid to remove the acidity of stomach.
  3. to prepare aerated water(soda water)
  4. sodium bicarbonate is used in fire extinguishers. Soda acid fire extinguishers contains a solution of sodium bicarbonate and sulfuric acid. These two substances can be brought in contact by pressing a knob or by inverting the extinguisher. Then carbon dioxide is released and surrounds the combustible substances and cut off the supply of air to put out the air.

Uses of calcium chloride (CaCl2)

  1. To prepare gypsum.
  2. As a dehydrator


How sodium carbonate is used to remove hardness of water?

There are two types of hardness of water as temporary hardness and permanent hardness. Na2CO3 can be used to remove both temporary hardness and permanent hardness.


Remove temporary hardness of hard water

HCO3- of Ca2+ and Mg2+ cause to temporary hardness. Adding Na2CO3 will form CaCO3 and MgCO3 precipitates by removing HCO3-.

Remove temporary hardness of hard water

Remove permanent hardness of hard water

SO42- and Cl- of Ca2+ and Mg2+ cause to permanent hardness. Adding Na2CO3 will form CaCO3 and MgCO3 precipitates by removing Ca2+ and Mg2+ from water.

Remove permanent hardness of hard water


More to learn about sodium carbonate and solvay process


Reactions of sodium carbonate preparing


Urea and NaOH reaction

Ammonia and sodium carbonate are given as products by the reaction of urea and NaOH.

Urea and NaOH reaction

Questions and answers of Na2CO3 and solvay process


What are the other names of sodium carbonate?

Soda ash



Is sodium carbonate acidic or basic?

sodium carbonate is a basic compound. sodium carbonate dissociates completely in the water to Na+ ion CO32- ion. Na+ ion is stable in the water. But CO32- is not stable in the water and is hydrolyzed in the water.

carbonate ion hydrolysis

By the hydrolysis of carbonate ion, OH- ions are released.

carbonate ion hydrolysis reactions

Due to release of OH-, sodium carbonate solution is weak basic.



How brine solution is taken in solvay process?

Brine solution is taken to the solvay process from sea.



What is soda ash?

Sodium carbonate is a white crystalline solid which exists as a decahydrate (Na2CO3.10H2O). This is called washing soda. When decahydrate gets heat, it looses the water of crystallisation to form monohydrate ( Na2CO3.H2O). Above 373K, the monohydrate becomes completely anhydrous and changes to a white powder called soda ash.


What will happen when calcium chloride aqueous solution is added to sodium carbonate solution?

With addition of calcium chloride (CaCl2), there are Na+, CO32-, Ca2+ and Cl- ions in the water. We know CaCO3 is a precipitate. Therefore in higher concentrations of Ca2+ and CO32- ions in aqueous solution, a white precipitate (CaCO3) is formed.

sodium carbonate and calcium chloride


At what temperature, sodium bicarbonate is precipitated in solvay process?

At a temperature about 150C, sodium bicarbonate is precipitated and separated from the solution. Because this precipitation reaction is exothermic, the reaction tower is cooled by spraying water.



Molecular mass of sodium carbonate

MNa2CO3 = 23*2 + 12 + 16*3

MNa2CO3 = 106 g mol-1



What is the solubility of sodium carbonate ?

Solubilty - 30.7 g/100 g water at 250C



Are there any exothermic reactions in solvay process?

Separating and precipitaing NaHCO3 is exerthormic reaction. Therefore reaction tower is cooled by spraying water.


Why there is a counter current principle in solvay process?

In counter current principle, reactants are collided with each other very well. Therefore it makes higher reaction rate to produce products.