Sesquicarbonate

Trona Purification Processes. Two processes, named the monohydrate and sesquicarbonate according to the crystalline intermediates, are used to produce refined soda ash from trona. Both involve the same unit operations only in different sequences. Most ash is made using the monohydrate process. Eigure 2 shows simplified flow diagrams for each. 

FMC makes sodium bicarbonate at the Green River complex by reaction of sesquicarbonate (Na2 CO3 -NaHC03 -2H2 O) with carbon dioxide recovered from a sodium phosphate plant. This fairly recently patented process avoids the energy intensive heating step (33). 

Bronze disease necessitates immediate action to halt the process and remove the cause. For a long time, stabilization was sought by removal of the cuprous chloride by immersing the object in a solution of sodium sesquicarbonate. This process was, however, extremely time-consuming, frequentiy unsuccesshil, and often the cause of unpleasant discolorations of the patina. Objects affected by bronze disease are mostiy treated by immersion in, or surface appHcation of, 1 H-henzotriazole [95-14-7] C H N, a corrosion inhibitor for copper. A localized treatment is the excavation of cuprous chloride from the affected area until bare metal is obtained, followed by appHcation of moist, freshly precipitated silver oxide which serves to stabilize the chloride by formation of silver chloride. Subsequent storage in very dry conditions is generally recommended to prevent recurrence. 

The dissociation of hypochlorous acid depends upon pH and, to a much lesser extent, temperature (6). At 25°C, it is - 0% at pH 5, about 50% at pH 7.5, and - 100% at pH 10, see Figure 1. Because of the acidity formed by chlorine gas, addition of soda ash (Na2C02) or sodium sesquicarbonate (Na2C03-NaHC03) is necessary to maintain the proper pH and to replenish alkalinity. 

A hydrate CO2.8H2O can be crystallized from aqueous solutions at 0° and p C02) 45 atm. There is also evidence for a hydrogen-bonded sesquicarbonate ion, H3C20s this was originally suggested to have the sandwich... 

In 1864 Ernest Solvay, a Belgian chemist, invented his ammonia-soda process. A few years later the soda ash price was reduced one third. The Solvay process had completely replaced the LeBlanc method by 1915. The Solvay method is still very popular worldwide. However, in this country large deposits of natural trona ore were found in the 1940s in Green River, Wyoming. In the last few years there has been a tremendous conversion from synthetic to natural soda ash. The first and last Solvay plant in the U.S. closed in 1986 (a large Allied Chemical plant in Solvay, NY). Trona ore is found about 500 m below the surface. It is called sodium sesquicarbonate... 

C. L. Berthollet, and J. J. Berzelius 11 found that when an aq. solji. of potassium hydrocarbonate is boiled, and then cooled, crystals of potassium sesquicarbonate... 

J. Black s investigation 3 of 1756 is the first contribution to the chemistry of the carbonates of ammonia, and he pointed out the chemical difference between the aqua ammonia and the solid carbonate of commerce. J. Priestley also, in 1774, dwelt on the same subject. T. Bergmann analysed the commercial carbonate in 1774 H. Davy emphasized the variable nature of the compounds of carbon dioxide and ammonia in 1799 while C. L. Berthollet (1806) and J. Dalton (1819) demonstrated that there are several different carbonates of ammonia. In his paper On the combinations of carbonic anhydride with ammonia and water (1870), E. Divers showed that there are at least three well-defined ammonium carbonates—the normal carbonate, the hydrocarbonate, and the sesquicarbonate. On the other hand, in his paper Ueber die Verbindungen des Ammoniaks mit der Kohlensaure (1839), H. Rose claimed to have shown that an indefinitely large number of these compounds can be prepared, and he described twelve of them. He said ... 

H. St. C. Deville also succeeded in preparing only the two crystalline carbonates— viz. the sesquicarbonate and the acid carbonate. 

In 1839, H- Rose said that the ordinary commercial carbonate liquefied when slowly heated in a retort whereas, in 1870, E. Divers found scarcely any liquefaction. The older carbonate when distilled with anhydrous calcium chloride gave ammonium chloride, calcium carbonate, and carbon dioxide, whereas the newer carbonate gave in addition ammonium carbamate. The solubility of the newer carbonate is about twice as great as the old and the aq. soln. is not charged with carbon dioxide. R. Phillips and E. Divers have also reported as rare the occurrence of the hydrocarbonate in commercial carbonate. In consequence of these differences it is necessary to know whether the old or the new carbonate is in question when discussing the properties of the commercial carbonate. Sometimes the sesquicarbonate is to be understood. 

The ordinary method of determining the solubilities cannot be applied to the commercial carbonate because a sat. soln. decomposes any fresh carbonate added to it. F. Riidorlf found the temp, fell from 15 3° to 3 2° when 25 parts of salt are dissolved in 100 parts of water. E. Divers found that 100 parts of water at 15° dissolve 25 parts of the commercial salt, and at about 65°, 66 7 parts. When the sat. soln. is cooled, it furnishes crystals of the hydrocarbonate. T. J. Pelouze and E. Fremy 2 said that the sesquicarbonate separates under these conditions, but in E. Divers opinion this statement is wrong. According to J. J. Berzelius, 100 parts of water at 49° dissolved 50 grms. of the old carbonate of commerce. In a general way, E. Divers has shown that the solubility of the commercial carbonate approximately accords, with the hydrocarbonate it contains—viz. one of the salt in two of water. G. Lunge measured the sp. gr., D, of soln. of ammonium sesquicarbonate and found this constant rose from 1-005 with 1 66 per cent, of salt to 1144 with 44 90 per cent, of salt, at a temp. 12°. Some intermediate values are ... 

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