Manufacturing Processes

• Many salt-tolerant "halophyte" plant and seaweed species were the main source of sodium carbonate until the early of nineteenth century. Sodium carbonate occurs naturally as dry deposits in the lakes of many arid regions such as East Africa, Egypt and California. On a commercial scale, sodium carbonate is prepared by three processes: the ammonia-soda, or Solvay process; the electrolytic process; and the Leblanc's process. The Solvay process yields most sodium carbonate for industrial use, while the Leblanc's process is almost obsolete now, although it was the first commercially successful process for making sodium carbonate, and played an important role in the Industrial Revolution.
  
  

Solvay Process

• The Solvay process was invented by a Belgian industrial chemist, Ernest Solvay, in 1861. This process involves a reaction between sodium chloride and ammonium bicarbonate when sodium bicarbonate precipitates out due to its low solubility in sodium chloride solution. The precipitation is filtered off and heated to give normal sodium carbonate.
  
  

Saturating or Ammoniation Tank

• A saturated solution of sodium chloride and ammonia is introduced into the top of a large hollow iron tower, and allowed to flow downwards. The temperature is maintained below 30 degrees C for maximum saturation. At the bottom of the tower, calcium carbonate or limestone is heated to give off carbon dioxide. When the clear ammonium solution of sodium chloride flows downward and meets a current of carbon dioxide traveling upwards. The ammonium bicarbonate, first formed, reacts with sodium chloride, resulting in the precipitation of sodium bicarbonate. Sodium bicarbonate separates out as tiny crystals. The crystals are dried and heated strongly when sodium bicarbonate decomposes into sodium carbonate, releasing carbon dioxide and steam.
  
  

Ammonia Recovery Tower

• The ammonia is produced again from the byproduct ammonium chloride, treating it with soda lime or calcium hydroxide left over at the bottom of the iron tower from carbon dioxide generation. The Solvay process allows regeneration of ammonia, and it consumes only brine, i.e., sodium chloride solution, and leaves calcium chloride as its waste product, which made the Solvay process more economical than other manufacturing processes. Today, more than 85 percent of sodium carbonate is produced from the Solvay process worldwide.
  
  

Leblanc's Process

• In 1791, the French chemist Nicolas Leblanc invented the first successful commercial process for making sodium carbonate from salt, lime stone, coal and sulfuric acid. First, sea salt or sodium chloride is boiled in a sulfuric acid solution, forming sodium sulfate and liberating hydrogen chloride gas. Next, sodium sulfate is mixed with ground limestone or calcium carbonate, and coal. The mixture is heated, producing calcium sulfide while sodium carbonate is extracted using water from the ashes, and collected by the evaporation of water.