Economic feasibility of the ammonia-soda process for soda ash production

This post was last edited by zgj2405 on September 1, 2011, at 13:57. I. The ammonia-soda process (also known as the Solvay process) This is a method for producing soda ash invented in 1892 by the Belgian engineer Solvay (1838–1922). He used table salt (sodium chloride), limestone (which, when calcined, produces quicklime and carbon dioxide), and ammonia as raw materials to produce soda ash. First, ammonia gas is passed into saturated brine to produce ammoniated brine; then carbon dioxide is introduced, resulting in the precipitation of sodium bicarbonate, which has low solubility, and an ammonium chloride solution. The principle of the chemical reaction is: NaCl + NH3 + H2O + CO2 = NaHCO3↓ + NH4Cl. The tiny NaHCO3 crystals obtained after filtration and washing are then heated and calcined to produce soda ash products. 2NaHCO3 = Na2CO3 + H2O + CO2↑ The carbon dioxide gas released can be recovered and recycled. The filtrate containing ammonium chloride is mixed with lime milk and heated; the ammonia gas released can be recovered and recycled. CaO + H2O = Ca(OH)2, 2NH4Cl + Ca(OH)2 = CaCl2 + 2NH3↑ + 2H2O. The simple process for its industrial production is shown in the figure. The advantages of the ammonia-soda process are: the raw materials (table salt and limestone) are inexpensive ； The purity of the product, soda ash, is high ； Both by-products, ammonia and carbon dioxide, can be recovered and reused ； The manufacturing steps are simple, making it suitable for mass production. However, the ammonia-soda process also has many drawbacks: firstly, only half of the components of both raw materials are utilized. The sodium ions (Na⁺) from salt and the carbonate ions (CO32−) from limestone combine to form sodium carbonate. Yet the chloride ions (Cl−) from salt and the calcium ions (Ca2⁺) from limestone combine to form calcium chloride (CaCl2), which has little practical use. Therefore, how to dispose of calcium chloride becomes a major burden. The biggest drawback of the ammonia-soda process is that the utilization rate of raw salt is only 72%–74%; the remaining salt is discarded as waste liquid along with the calcium chloride solution, which represents a significant loss. II. The combined soda ash process (also known as the Hou’s process) was developed in 1943 by Hou Debang (1890–1974), a Chinese chemical engineering expert. It is a method that combines the ammonia-alkali process and the synthetic ammonia process to produce both soda ash and ammonium chloride. The raw materials are table salt, ammonia, and carbon dioxide—a byproduct generated when hydrogen is produced from water gas in ammonia synthesis plants. The principle of its chemical reactions is: C + H2O = CO + H2; CO + H2O = CO2 + H2. The combined soda-making process consists of two steps: The first step is the same as in the ammonia-soda process—ammonia is introduced into saturated brine to form ammoniated brine, which is then treated with carbon dioxide to produce sodium bicarbonate precipitate. After filtration and washing, tiny NaHCO3 crystals are obtained; these are then calcined to produce soda ash. The filtrate obtained is a solution containing ammonium chloride and sodium chloride. The second process is the crystallization and precipitation of ammonium chloride crystals from the filtrate containing ammonium chloride and sodium chloride. Since ammonium chloride has a higher solubility at room temperature than sodium chloride, its solubility is lower at low temperatures. Moreover, the solubility of ammonium chloride in concentrated solutions of sodium chloride is much lower than its solubility in water. Therefore, under low-temperature conditions, by adding fine powdered sodium chloride to the filtrate and introducing ammonia gas, ammonium chloride can be precipitated as a separate crystal; after filtration, washing, and drying, the ammonium chloride product is obtained. At this point, the filtrate obtained after filtering off the ammonium chloride precipitate is essentially saturated with sodium chloride and can be recovered for reuse. The simple process of its industrial production is shown in the figure. Compared to the ammonia-soda process, the greatest advantage of the combined soda process is that it raises the utilization rate of table salt to over 96%; using the same amount of salt, it produces more soda ash than the ammonia-soda process. Additionally, it makes comprehensive use of carbon dioxide from ammonia plants and chloride ions from alkali plants; at the same time, it produces two valuable products—soda ash and ammonium chloride. The carbon dioxide from the exhaust gases of ammonia plants is converted into a primary raw material for soda ash production in alkali plants, thereby eliminating the need for the large lime kilns used in alkali plants to produce carbon dioxide ； The useless component chloride ion (Cl-) in the alkali plant is used to replace the more expensive ammonia in the sulfuric acid fixed ammonia plant to produce nitrogen fertilizer ammonium chloride. As a result, calcium chloride—which is of little use and difficult to handle—is no longer produced, thereby reducing environmental pollution. Moreover, it **lowers the costs of soda ash and nitrogen fertilizers**, fully demonstrating the advantages of large-scale integrated production.

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It’s necessary to comprehensively consider the favorable factors affecting a project; it’s not the case that any resource alone is sufficient to launch a project

This post was last edited by amand on 2010-8-20 at 14:37. Economic advantages must be considered comprehensively. Firstly, there are advantages in terms of raw materials; soda ash production requires lime, NaCl, NH3, and CO2. There are also issues such as the market and transportation. Currently, the production process for soda ash has become mature; however, the entry barriers for the soda ash industry have been raised. Therefore, its economic advantages must be considered comprehensively.

This topic involves far too many aspects: craftsmanship, environmental protection, safety, market, raw materials, etc

Calcium carbonate is insoluble; to participate in a reaction, it must be converted into calcium oxide. Currently, calcium chloride has many uses; however, it causes significant pollution and requires numerous storage yards.

This post was last edited by Qingtan Xiaolong on 2010-9-26 at 18:51.  The ammonia-soda process for producing soda ash and the Hou’s soda-making process. Anhydrous sodium carbonate is commonly known as soda ash or baking soda. It is an important raw material for industries such as glass, papermaking, soap, detergents, textiles, and leather processing. It is also commonly used as a water softener for hard water, as well as in the production of sodium compounds. Its industrial production methods mainly include the ammonia-soda process and the combined soda process. I. Ammonia-soda process (also known as the Solvay process) It is a method for producing soda ash invented in 1892 by the Belgian engineer Solvay (1838–1922). He used table salt (sodium chloride), limestone (which, when calcined, produces quicklime and carbon dioxide), and ammonia as raw materials to produce soda ash. First, ammonia gas is passed into saturated brine to produce ammoniated brine; then carbon dioxide is introduced, resulting in the precipitation of sodium bicarbonate, which has low solubility, and an ammonium chloride solution. The chemical reaction principle is: NaCl (saturated) + NH3 + H2O + CO2 = NaHCO3↓ + NH4Cl. The tiny NaHCO3 crystals obtained after filtration and washing are then heated and calcined to produce soda ash products. 2NaHCO3 = Na2CO3 + H2O + CO2↑ The carbon dioxide gas released can be recovered and recycled. The filtrate containing ammonium chloride is mixed with lime milk and heated; the ammonia gas released can be recovered and recycled. CaO + H2O = Ca(OH)2; 2NH4Cl + Ca(OH)2 = CaCl2 + 2NH3↑ + 2H2O. The advantages of the ammonia-soda process are: the raw materials (table salt and limestone) are inexpensive ； The purity of the product, soda ash, is high ； Both by-products, ammonia and carbon dioxide, can be recovered and reused ； The manufacturing steps are simple, making it suitable for mass production. However, the ammonia-soda process also has many drawbacks: firstly, only half of the components of both raw materials are utilized. The sodium ions (Na⁺) from salt and the carbonate ions ( ) from limestone combine to form sodium carbonate. Meanwhile, the chloride ions ( ) from salt and the calcium ions (Ca2⁺) from limestone combine to form calcium chloride (CaCl2), which has little practical use. Therefore, figuring out how to dispose of calcium chloride becomes a major problem. The biggest drawback of the ammonia-soda process is that the utilization rate of raw salt is only 72%–74%; the remaining salt is discarded as waste liquid along with the calcium chloride solution, which represents a significant loss. II. The combined soda ash process (also known as the Hou’s process) This is a method developed by Hou Debang, a chemical engineering expert in China. It combines the ammonia-soda process and the synthetic ammonia process to produce two products simultaneously: soda ash and ammonium chloride. The raw materials are table salt, ammonia, and carbon dioxide—a byproduct generated when hydrogen is produced from water gas in ammonia synthesis plants. The principle of its chemical reactions is: C + H2O = CO + H2; CO + H2O = CO2 + H2. The combined soda-making process consists of two steps: The first step is the same as in the ammonia-soda process—ammonia is introduced into saturated brine to form ammoniated brine, which is then treated with carbon dioxide to produce sodium bicarbonate precipitate. After filtration and washing, tiny NaHCO3 crystals are obtained; these are then calcined to produce soda ash. The filtrate obtained is a solution containing ammonium chloride and sodium chloride. The second process is the crystallization and precipitation of ammonium chloride crystals from the filtrate containing ammonium chloride and sodium chloride. Since ammonium chloride has a higher solubility at room temperature than sodium chloride, its solubility is lower at low temperatures. Moreover, the solubility of ammonium chloride in concentrated solutions of sodium chloride is much lower than its solubility in water. Therefore, under low-temperature conditions, by adding fine powdered sodium chloride to the filtrate and introducing ammonia gas, ammonium chloride can be precipitated as a separate crystal; after filtration, washing, and drying, the ammonium chloride product is obtained. At this point, the filtrate obtained after filtering off the ammonium chloride precipitate is essentially saturated with sodium chloride and can be recovered for reuse. Compared to the ammonia-soda process, the greatest advantage of the combined soda process is that it raises the utilization rate of table salt to over 96%; using the same amount of salt, it produces more soda ash than the ammonia-soda process. Additionally, it makes comprehensive use of carbon dioxide from ammonia plants and chloride ions from alkali plants; at the same time, it produces two valuable products—soda ash and ammonium chloride. The carbon dioxide from the exhaust gases of ammonia plants is converted into a primary raw material for soda ash production in alkali plants, thereby eliminating the need for the large lime kilns used in alkali plants to produce carbon dioxide ； Chloride ions ( ), which are useless components in alkali plants, are used to replace the more expensive sulfuric acid in fixing ammonia in ammonia plants, thereby producing the nitrogen fertilizer ammonium chloride. As a result, calcium chloride—which is of little use and difficult to handle—is no longer produced, thereby reducing environmental pollution. Moreover, it **lowers the costs of soda ash and nitrogen fertilizers**, fully demonstrating the advantages of large-scale integrated production.

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