Industrial preparation of Sodium carbonate

This presentation will help you in the conceptual understanding of commercial and industrial preparation of washing soda, also known as soda ash.

1. Commercial Production of Sodium Carbonate By Mr. Muhammad Ullah Afridi Institute of Chemical Sciences, University of Peshawar.

2. Na 2 CO 3

3. Sodium carbonate (molecular formula: Na 2 CO 3 ), is the water soluble sodium salt of carbonate. The pure product appears as a white, odorless powder with a strong alkaline taste.

4. Strong electrolyte Density 2.532 g/cm 3 Melting point 851 C Boiling point1600 C Weak acid slightly soluble in ethanol Insoluble in alcohol

5. Solvay process Labnac process Dual process(modified solvay process) Electrolytic process

6. I n 1861,lab n a c p roces s failed a s i t p rove d to have polluting impacts to environment Belgian industrial chemist Ernest Solvay introduced Solvay process in which ammonia recovered in reaction for re-use, which reduced the polluting impacts. 1874 is a year which forced to set up industries of sodium carbonate after success Solvay process and 1890 was a dominant year of soda ash production worldwide.

7. PROCESS FLOW DIAGRAM

8. Ammoniation tower(ammonia absorber) Solvay tower(carbonation tower) Lime kiln Ammonia recovery tower

9. Sodium chloride ( NaCl) Lime stone(CaC O 3 ) Ammonia (NH 3 ) Coal for fuel/coke

10. Ca 2+ ( a q ) + CO 2- → CaCO 3 (a q ) 3(s) Mg 2+ + 2OH - → Mg(OH) Fe 3+ (aq) - (aq) 2(s) (aq) + 3OH (aq) → Fe(OH) 3(s) PREPARATION OF BRINE First of all saturated solution of N a C l is made called as brine PURIFICATION OF BRINE As metal impurities present in water such as calcium, magnesium and iron are removed by precipitation, eg,

11. AMMONIATION TOWER Brine solution is then filtered and passed through an ammonia tower to dissolve ammonia. This process is exothermic, releases energy, so the ammonia tower is cooled.

12. Carbon dioxide is produced by the thermal decomposition of limestone, CaCO 3(s) , in the lime kiln: CaCO 3(s) → CO 2(g) + CaO (s)

13. SOLVAY TOWER Carbon dioxide is bubbled through the ammoniated brine solution in the carbonating tower. The carbon dioxide dissolves to form a weak acid: CO 2(g) + H 2 O (l) --------- HCO - 3 (aq) + H + (aq) + The ammonia in the brine reacts with H to form ammonium ion: NH 3( aq ) + H + (aq) NH + 4 (a q) - The HCO 3 then reacts with the Na + to form a suspension of ( a q ) ( a q) sodium hydrogen carbonate : HCO 3 - + Na + NaHCO 3(s) 4 (a q)

14. SOLVAY TOWER - NaHCO 3 precipitates because of the large excess of Na + present in the brine The overall molecular equation for the formation of sodium hydrogen carbonate in the carbonating tower is : NH 3( aq ) + CO 2(g) + NaCl (aq) + H 2 O (l) → NaHCO 3(s) + NH 4 Cl (aq) The net ionic equation for the formation of sodium hydrogen carbonate in the carbonating tower is: NH 3( aq ) + CO 2(g) + Na + (aq) + H 2 O (l) → NaHCO 3(s) +NH + 4 ( a q )

15. Suspended sodium hydrogen carbonate is removed from the carbonating tower and heated at 300 o C to produce sodium carbonate: 2NaHCO 3(s ) → Na 2 CO 3(s) + CO 2(g) + H 2 O (g) The carbon dioxide produced is recycled back into the carbonating tower.

16. When CaCO 3 is heated, CaO is obtained along with CO 2 . CaO is treated with water to form Ca(OH) 2 . CaO + H 2 O Ca(OH) 2 Quick lime is heated with NH 4 Cl to form NH 3 and calcium chloride (by product) . Ammonia is used again in this process. 2NH 4 Cl + Ca(OH) 2 CaCl 2 + 2NH 3 + 2H 2 O

17. CaO is formed as a by-product of the thermal decomposition of limestone in the lime kiln. This CaO enters a lime slaker to react with water to form calcium hydroxide: CaO (s ) + H 2 O (l) → Ca(OH) 2( aq ) The calcium hydroxide produced here is reacted with the ammonium chloride separated out of the carbonating tower by filtration: Ca(OH) 2(aq) +2NH 4 Cl (aq) →CaCl 2(aq) +2H 2 O (l) + 2NH 3