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.
Solvay process has five main steps on sodium carbonate manufacturing.
The solvay process is an excellent example for a closed cycle chemical process where the byproducts are efficiently reused in the manufacturing process.
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..
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.
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.
Below figure shows outline of solvay process.
Figure 1: sodium carbonate manufacturing plant outline
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.
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.
Solution coming from the carbonation tower contain ammonium chloride and small amount of ammonium bicarbonate.
They are pumped to ammonia recovery tower.
Then sodium carbonate, carbon dioxide gas and water form.
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.
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
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.
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.
Sodium carbonate is used in domestic purposes and industrial productions.
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.
Ability of getting limestone easily. Limestone is used in two ways in solvay process for heating purpose and obtaining carbon dioxide gas.
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.
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( baking soda, sodium hydrogen carbonate) is obtained as an intermediate product in solvay process for the manufacturing of
Brine solution is taken to the solvay process from sea.
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.
Ammonium chloride is reacted with calcium hydroxide to regenerate ammonia.
2NH4Cl(aq) + Ca(OH)2(aq) → 2NH3(g) + CaCl2(aq) + 2H2O(l)
Separating and precipitating NaHCO3 is exothermic reaction. Therefore reaction tower is cooled by spraying water.
In counter current principle, reactants are collided with each other very well. Therefore it makes higher reaction rate to produce products.
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