Sodium carbonate manufacturing process, solvay process

Sodium carbonate (washing soda) is a white crystalline solid. It exists as a decahydrate ( Na2CO3.10H2O) compound . 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, and applications of Na2CO3. Also NaHCO3 and it's uses are explained later.

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 closed 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 obtaining 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.

Why 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, first sodium bicarbonate is precipitated, then Na2CO3 is produced. But due to higher solubility of KHCO3, K2CO3 is unable to manufacture by solvay process.

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.

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

Questions and answers of Na2CO3 and solvay process

solvay’s process is very economical, why?

Your purpose of operating an industrial plant is earning profits. You have to buy raw materials when you are doing a production. In solvay's process, brine solution (sea water) is used as raw material. For this, plant has to spend very low amount of money. Therefore their production cost is low.

Why do solvay plant situated near water mass?

Water is used as a raw material in two steps in solvay process. In ammonia absorber tower, brine solution (sea water) is fed to tower. Brine solution is a highly concentrated aqueous NaCl solution. Therefore, there is water in this stream.

To reproduce ammonia gas from ammonium chloride, calcium hydroxide is used. In the process calcium oxide is produced in the carbon dioxide generation section. Water is added to calcium oxide to produce calcium hydroxide.

Now, you can see water is a must for a solvay plant and plant should be located near a water source. Usually, these locations are situated close to the sea

How brine solution is taken in solvay process?

Brine solution is taken to the solvay process from sea.

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.

substances that are react to re generate ammonia gas in the solvay process and the chemical equation

Ammonium chloride is reacted with calcium hydroxide to regenerate ammonia.

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

Are there any exothermic reactions in solvay process?

Separating and precipitating NaHCO3 is exothermic reaction. Therefore reaction tower is cooled by spraying water.

economical features of the solvay process

Solvay process is a cery economical because cost for raw materials is low.

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.