1. Bran alkali process: In ancient times, people extracted potassium carbonate from plant ash, and later obtained sodium carbonate from saline-alkali land, salt lake and other natural resources, but the amount was too small. It is far from meeting the needs of chemical production. In 179 1 year, French doctor Lubran first obtained a patent for alkali production, and made salt into alkali, which is called Lubran alkali production method. The method is divided into three parts:
① Sodium sulfate is prepared by the reaction of sodium chloride and sulfuric acid: 2 NaCl+H2SO4 = Na2SO4+2 HCl;
(2) Reducing sodium sulfate with coke to obtain sodium sulfide: Na2SO4+4C = Na2S+4Co =
③ Sodium sulfide reacts with limestone to generate sodium carbonate: Na2S+CaCO3=Na2CO3+CaS.
Disadvantages:; This method needs high temperature for production, sulfuric acid corrodes the equipment seriously, CaS waste accumulates for a long time, smells everywhere and costs high, so it is replaced by ammonia-alkali method.
2. Ammonia-alkali method, that is, solvay alkali preparation method, was invented by solvay 1862 in Belgium. Salt, ammonia and carbon dioxide are used as raw materials, and the reaction is also divided into three steps:
①NH3+CO2+H2O=NH4HCO3
② ammonium bicarbonate+sodium chloride = sodium bicarbonate+ammonium chloride
③2NaHCO3=Na2CO3+CO2↑+H2O
CO2 produced by the reaction can be recycled, and NH4Cl can react with quicklime to regenerate ammonia.
2NH4Cl+CaO=2NH3↑+CaCl2+H2O
Disadvantages: this method realizes continuous production, improves the utilization rate of salt, greatly reduces the price of soda ash, and the product quality is pure, so it is called soda ash.
Thirdly, Hou's alkali production method greatly improved the above method. The biggest feature of this method is that ammonia is not absorbed from solid ammonium bicarbonate (NH4HCO3), but is absorbed from brine first, and then carbonated for continuous production. The principle of this method is that at low temperature, carbon dioxide (CO2) can be introduced into saturated brine saturated with ammonia, and sodium bicarbonate (NaHCO3) can be precipitated. At this time, Na+ in the mother liquor decreases and Cl- is relatively high, and then it is added. Due to the same ion effect, the solubility of low-temperature ammonium chloride (NH4Cl) suddenly decreased, while the solubility of salt (NaCl) changed little, so ammonium chloride (NH4Cl) precipitated but salt did not, and then it was saturated with ammonia, and then carbon dioxide (CO2) was introduced. Thus, NaHCO3 and NH4Cl are precipitated back and forth, in which ammonia is obtained by hydrogenation of nitrogen and water, and CO2 is a semi-water gas by-product of extracting hydrogen and nitrogen, thus skillfully combining nitrogen production industry with alkali production industry. The alkali produced by this method is of excellent quality and pure as snow, and won the "World Expo Gold Award" in Philadelphia, USA 1926. Specifically, it is like this:
1 Introduce carbon dioxide into ammoniated saturated brine.
NH3+H2O+CO2+NaCl=NH4Cl+NaHCO3 (precipitation)
2. Heating sodium bicarbonate to obtain sodium carbonate.
Sodium bicarbonate = sodium carbonate +H2O+ carbon dioxide
3. Sodium hydroxide is prepared by introducing lime water into sodium carbonate.
Sodium carbonate+calcium hydroxide = 2 Sodium hydroxide+calcium carbonate
And 4, roasting calcium carbonate to obtain carbon dioxide circulation.
CaCO3=CaO+CO2
Calcium oxide +H2O = calcium hydroxide
5. When excessive salt is added to the mother liquor of 1 step reaction, ammonium chloride will crystallize out to make fertilizer.
After thousands of experiments, Mr. Hou successfully studied the combined alkali process in 1943. This method combines synthetic ammonia with soda ash, which improves the utilization rate of salt, shortens the production process, reduces the pollution to the environment and reduces the cost of soda ash.