Sodium carbonate
Sodium carbonate or sodium carbonate is a white, translucent salt with the chemical formula Na2CO3, used among other things in the manufacture of soap, glass, and dyes. It is commonly known as barrilla, natron, Solvay soda, Solvay soda, Ash soda >, soda ash and anhydrous sodium carbonate or simply soda , (not to be confused with caustic soda, which is a derivative of sodium carbonate, through a process known as causticization). It is the most common alkaline substance known and used since ancient times.
It can be found in nature or obtained artificially, thanks to a process devised and patented in 1791 by the French doctor and chemist Nicolás Leblanc. The Leblanc process involved the following chemical reactions:
- Common salt reaction with sulfuric acid: 2 NaCl + H2SO4 → Na2SO4 + 2 HCl
- Na calcining reaction2SO4 with limestone and coal: Na2SO4 + CaCO3 + 2 C → Na2CO3 + CaS + 2 CO2
This method was later replaced by the Solvay method devised by the Belgian chemist Ernest Solvay. Solvay founded the Solvay company in 1863, where he extensively used his method, which made the process even cheaper and eliminated some of the problems presented by the Leblanc method. This method uses sodium chloride (common salt), ammonia and calcium carbonate (limestone) as raw materials. In 1915 the last Leblanc soda factory was closed.
Uses
Sodium carbonate is used to roast (heat under a blast of air) chrome and other extractives and lowers the sulfur and phosphorous content of cast iron and steel. In the manufacture of detergents, sodium carbonate is essential in the formulations in order to ensure the correct functioning of the rest of the substances that compose it, enzymes, surfactants, etc. during the different phases of washing. The use of sodium carbonate is no less important in those processes in which the pH of different solutions must be regulated, we are referring to industrial water treatment, as well as in flotation processes. Ceramics, soaps, cleaners, hard water softener, oil refining, aluminum production, textiles, pulp and paper. Metallurgical processing, preparation of pharmaceuticals, caustic soda through the causticizing process, sodium bicarbonate, sodium nitrate and various other uses. Sodium carbonate and its derivatives are used to lower the melting point of silicon and to be able to work it better, it also provides the necessary solid to form the network.
Production
Mining
Trona, also known as trisodium hydrogen carbonate dihydrate (Na3HCO3CO3-2H2O), is mined in various areas of the US and provides nearly all of US sodium carbonate consumption. Large natural deposits found in 1938, such as the one near Green River, Wyoming, have made extraction cheaper than industrial production in North America. There are significant reserves of trona in Turkey; Two million tons of soda ash have been extracted from reserves near Ankara. It is also extracted from some alkaline lakes, such as Lake Magadi in Kenya, by dredging. Hot saline springs continually replenish salt in the lake, and therefore as long as the rate of dredging is not greater than the rate of replenishment, it could be considered sustainable.
Barilla and seaweed
Several halophilic (salt-tolerant) plant species and marine algae can be processed into an impure form of sodium carbonate, and these sources were prevalent in Europe and elsewhere until the early 19th century. Terrestrial plants (generally of the Salicornia genus or of the Salsola and related genera) or marine algae (typically Fucus species) were harvested, dried, and burned. The ashes were leached (washed with water) to form an alkaline solution. This solution was boiled dry to create the final product, which was called a "barrilla"; This very old name refers to the Arabic word soda, applied in turn to salsola soda, one of the many species of coastal plants harvested for its production. "Barilla" is a trade term applied to an impure form of potash obtained from shore plants or kelp-like algae.
The concentration of sodium carbonate in soda ash varies widely, from 2-3% of the kelp-derived form, to 30% of the best barilla produced from salicornia plants in Spain. Vegetable and algae sources for soda ash, and also for the related alkali 'potash', became increasingly inadequate in the late 18th century, and the search for commercially viable ways to synthesize soda ash from salt and other chemicals.
Leblanc Process
In 1792, French chemist Nicolas Leblanc patented a process for producing soda ash from salt, sulfuric acid, limestone, and coal. In the first step, sodium chloride is treated with sulfuric acid in the Mannheim process. This reaction produces sodium sulfate (salt cake) and hydrogen chloride:
2NaCl + H2SO4 → Na2SO4 + 2HCl
Salt cake and crushed limestone (calcium carbonate) are reduced by heating with coal. There are two parts to this conversion. The first is the carbothermic reaction whereby coal, a carbon source, reduces sulfate to sulfide:
Na2SO4 + 2C → Na2S + 2CO2
The second stage is the reaction to produce sodium carbonate and calcium sulfide:
Na2S + CaCO3 → Na2CO3 + CaS
This mixture is called black ash. Soda ash is extracted from black ash with water. Evaporation of this extract produces solid sodium carbonate. This extraction process is called leaching.
Hydrochloric acid produced by the Leblanc process was a major source of air pollution, and the calcium sulfide byproduct also presented disposal problems. However, it remained the main method of producing soda ash until the late 1880s.
Solvay Process
In 1861, Belgian industrial chemist Ernest Solvay developed a method for making sodium carbonate by first reacting sodium chloride, ammonia, water, and carbon dioxide to produce sodium bicarbonate and ammonium chloride:
NaCl + NH3 + CO2 + H2O → NaHCO3 + NH4Cl
The resulting baking soda turned into sodium carbonate on heating, releasing water and carbon dioxide:
2NaHCO3 → Na2CO3 + H2O + CO2
Meanwhile, ammonia was regenerated from the by-product ammonium chloride by treating it with the lime (calcium oxide) left over from carbon dioxide generation:
2NH4Cl + CaO → 2NH3 + CaCl2 + H2O
The Solvay process recycles its ammonia. It only consumes brine and limestone, and calcium chloride is its only waste product. The process is substantially cheaper than the Leblanc process, which generates two waste products, calcium sulfide and hydrogen chloride. The Solvay process quickly came to dominate the production of soda ash around the world. By 1900, 90% of sodium carbonate was produced by the Solvay process, and the last Leblanc process plant closed in the early 1920s.
The second step of the Solvay process, heating baking soda, is used on a small scale by home cooks and in restaurants to make baking soda for culinary purposes (including pretzels and alkaline noodles). The method is attractive to these users because sodium bicarbonate is widely sold as sodium bicarbonate, and the temperatures required (250°F (121°C) to 300°F (149°C)) to convert sodium bicarbonate in soda ash are easily achieved in conventional kitchen ovens.
Hou process
This process was developed by Chinese chemist Hou Debang in the 1930s. The earlier by-product of steam reforming, carbon dioxide, was pumped through a saturated solution of sodium chloride and ammonia to produce bicarbonate of soda. sodium by these reactions:
CH4 + 2H2O → CO2 + 4H2 3H2 + N2 → 2NH3 NH3 + CO2 + H2O → NH4HCO3 NH4HCO3 + NaCl → NH4Cl + NaHCO3
The sodium bicarbonate was collected as a precipitate due to its low solubility and then heated to approximately 176 °F (80 °C) or 203 °F (95 °C) to produce pure sodium carbonate, similar to the latter step of the Solvay process. More sodium chloride is added to the remaining sodium and ammonium chloride solution; more ammonia at 30-40 °C is also pumped into this solution. The solution temperature is then reduced to less than 10 °C. The solubility of ammonium chloride is greater than that of sodium chloride at 30°C and less at 10°C. Due to this temperature-dependent difference in solubility and the effect of common ions, ammonium chloride precipitates out of sodium chloride solution.
The Chinese name for the Hou process, lianhe zhijian fa (联合制碱法), means "alkaline coupled manufacturing method": The Hou process is coupled to the Haber process and offers better economy of atoms by eliminating the production of calcium chloride, since it is not necessary to regenerate the ammonia. The ammonium chloride byproduct can be sold as a fertilizer.