Ammonia-soda Process
   HOME

TheInfoList



OR:

The Solvay process or ammonia-soda process is the major industrial process for the production of
sodium carbonate Sodium carbonate, , (also known as washing soda, soda ash and soda crystals) is the inorganic compound with the formula Na2CO3 and its various hydrates. All forms are white, odourless, water-soluble salts that yield moderately alkaline solutions ...
(soda ash, Na2CO3). The ammonia-soda process was developed into its modern form by the Belgian chemist
Ernest Solvay Ernest Gaston Joseph Solvay (; 16 April 1838 – 26 May 1922) was a Belgian chemist, industrialist and philanthropist. Born in Rebecq, he was prevented by his acute pleurisy from going to university. He worked in his uncle's chemical factor ...
during the 1860s. The ingredients for this are readily available and inexpensive: salt
brine Brine is a high-concentration solution of salt (NaCl) in water (H2O). In diverse contexts, ''brine'' may refer to the salt solutions ranging from about 3.5% (a typical concentration of seawater, on the lower end of that of solutions used for br ...
(from inland sources or from the sea) and
limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
(from quarries). The worldwide production of soda ash in 2005 was estimated at 42 million tonnes,Kostick, Dennis (2006)
"Soda Ash"
chapter in ''2005 Minerals Yearbook,'' United States Geological Survey. See Table I.
which is more than six kilograms () per year for each person on Earth. Solvay-based chemical plants now produce roughly three-quarters of this supply, with the remaining being mined from natural deposits. This method superseded the
Leblanc process The Leblanc process (pronounced leh-blaank) was an early industrial process for making ''soda ash'' (sodium carbonate) used throughout the 19th century, named after its inventor, Nicolas Leblanc. It involved two stages: making sodium sulfate from ...
.


History

The name "soda ash" is based on the principal historical method of obtaining alkali, which was by using water to extract it from the ashes of certain plants. Wood fires yielded potash and its predominant ingredient
potassium carbonate Potassium carbonate is the inorganic compound with the formula K2 CO3. It is a white salt, which is soluble in water. It is deliquescent, often appearing as a damp or wet solid. Potassium carbonate is mainly used in the production of soap and gl ...
(K2CO3), whereas the ashes from these special plants yielded "soda ash" and its predominant ingredient
sodium carbonate Sodium carbonate, , (also known as washing soda, soda ash and soda crystals) is the inorganic compound with the formula Na2CO3 and its various hydrates. All forms are white, odourless, water-soluble salts that yield moderately alkaline solutions ...
(Na2CO3). The word "soda" (from the Middle Latin) originally referred to certain plants that grow in salt solubles; it was discovered that the ashes of these plants yielded the useful alkali soda ash. The cultivation of such plants reached a particularly high state of development in the 18th century in Spain, where the plants are named ''barrilla''; the English word is "
barilla ''Barilla'' refers to several species of salt-tolerant (halophyte) plants that, until the 19th century, were the primary source of soda ash and hence of sodium carbonate. The word "barilla" was also used directly to refer to the soda ash obtained ...
". The ashes of
kelp Kelps are large brown algae seaweeds that make up the order Laminariales. There are about 30 different genera. Despite its appearance, kelp is not a plant - it is a heterokont, a completely unrelated group of organisms. Kelp grows in "underwat ...
also yield soda ash, and were the basis of an enormous 18th century industry in Scotland. Alkali was also mined from dry lakebeds in Egypt. By the late 18th century these sources were insufficient to meet Europe's burgeoning demand for alkali for soap, textile, and glass industries. Online version archived at WebCite fro
this original URL
on 2008-03-12.
In 1791, the French physician
Nicolas Leblanc Nicolas Leblanc (December 6, 1742 – January 16, 1806) was a French chemist and surgeon who discovered how to manufacture soda ash from common salt. Earlier days Leblanc was born in Ivoy le Pré, Cher, France on 6 December 1742. His fathe ...
developed a method to manufacture soda ash using salt,
limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
,
sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...
, and
coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when dea ...
. Although the
Leblanc process The Leblanc process (pronounced leh-blaank) was an early industrial process for making ''soda ash'' (sodium carbonate) used throughout the 19th century, named after its inventor, Nicolas Leblanc. It involved two stages: making sodium sulfate from ...
came to dominate alkali production in the early 19th century, the expense of its inputs and its polluting byproducts (including
hydrogen chloride The compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colourless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hydrogen chloride ga ...
gas) made it apparent that it was far from an ideal solution. It has been reported that in 1811 French physicist
Augustin Jean Fresnel Augustin-Jean Fresnel (10 May 1788 – 14 July 1827) was a French civil engineer and physicist whose research in optics led to the almost unanimous acceptance of the wave theory of light, excluding any remnant of Isaac Newton, Newton's co ...
discovered that sodium bicarbonate precipitates when carbon dioxide is bubbled through ammonia-containing brines – which is the chemical reaction central to the Solvay process. The discovery wasn't published. As has been noted by Desmond Reilly, "The story of the evolution of the ammonium-soda process is an interesting example of the way in which a discovery can be made and then laid aside and not applied for a considerable time afterwards." Serious consideration of this reaction as the basis of an industrial process dates from the British patent issued in 1834 to H. G. Dyar and J. Hemming. There were several attempts to reduce this reaction to industrial practice, with varying success. In 1861,
Belgian Belgian may refer to: * Something of, or related to, Belgium * Belgians, people from Belgium or of Belgian descent * Languages of Belgium, languages spoken in Belgium, such as Dutch, French, and German *Ancient Belgian language, an extinct languag ...
industrial chemist
Ernest Solvay Ernest Gaston Joseph Solvay (; 16 April 1838 – 26 May 1922) was a Belgian chemist, industrialist and philanthropist. Born in Rebecq, he was prevented by his acute pleurisy from going to university. He worked in his uncle's chemical factor ...
turned his attention to the problem; he was apparently largely unaware of the extensive earlier work. His solution, a gas absorption tower in which carbon dioxide bubbled up through a descending flow of brine. This, together with efficient recovery and recycling of the ammonia, proved effective. By 1864 Solvay and his brother Alfred had acquired financial backing and constructed a plant in Couillet, today a suburb of the Belgian town of
Charleroi Charleroi ( , , ; wa, Tchålerwè ) is a city and a municipality of Wallonia, located in the province of Hainaut, Belgium. By 1 January 2008, the total population of Charleroi was 201,593.
. The new process proved more economical and less polluting than the Leblanc method, and its use spread. In 1874, the Solvays expanded their facilities with a new, larger plant at Nancy, France. In the same year,
Ludwig Mond Ludwig Mond FRS (7 March 1839 – 11 December 1909) was a German-born, British chemist and industrialist. He discovered an important, previously unknown, class of compounds called metal carbonyls. Education and career Ludwig Mond was born i ...
visited Solvay in Belgium and acquired rights to use the new technology. He and John Brunner formed the firm of Brunner, Mond & Co., and built a Solvay plant at
Winnington Winnington is a small, mainly residential area of the town of Northwich in Cheshire, England. Industry Winnington is the home to Brunner Mond UK chemical works, where soda ash is created. Polythene, the material used in many plastic items (e.g ...
, near
Northwich {{Infobox UK place , static_image_name = Northwich - Town Bridge.jpg , static_image_caption = Town Bridge, the River Weaver and the spire of Holy Trinity Church , official_name = Northwich , country ...
,
Cheshire Cheshire ( ) is a ceremonial and historic county in North West England, bordered by Wales to the west, Merseyside and Greater Manchester to the north, Derbyshire to the east, and Staffordshire and Shropshire to the south. Cheshire's county t ...
, England. The facility began operating in 1874. Mond was instrumental in making the Solvay process a commercial success. He made several refinements between 1873 and 1880 that removed byproducts that could slow or halt the process. In 1884, the Solvay brothers licensed Americans William B. Cogswell and Rowland Hazard to produce soda ash in the US, and formed a joint venture (
Solvay Process Company The Solvay Process Company was an American chemical manufacturer that specialized in the manufacture of soda ash. A major employer in Central New York, the company was key in the origin of the village of Solvay, New York, where it was headquarter ...
) to build and operate a plant in
Solvay, New York Solvay is a village located in the town of Geddes, Onondaga County, New York, United States, and a suburb of the city of Syracuse. According to the 2010 census, the village had a total population of 6,584. The village is named after the Solvay ...
. By the 1890s, Solvay-process plants produced the majority of the world's soda ash. In 1938 large deposits of the mineral
trona Trona (trisodium hydrogendicarbonate dihydrate, also sodium sesquicarbonate dihydrate, Na2CO3•2NaHCO3•3H2O) is a non- marine evaporite mineral. It is mined as the primary source of sodium carbonate in the United States, where it has replace ...
were discovered near the
Green River Green River may refer to: Rivers Canada * Green River (British Columbia), a tributary of the Lillooet River *Green River, a tributary of the Saint John River, also known by its French name of Rivière Verte *Green River (Ontario), a tributary of ...
in
Wyoming Wyoming () is a U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. It is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the south ...
from which sodium carbonate can be extracted more cheaply than produced by the process. With the closing of the original Solvay, New York plant in 1986, there is currently a Solvay plant in operation in the city of Longview, Washington. It supplies the areas paper mills. Throughout the rest of the world the Solvay process remains the major source of soda ash.


Chemistry

The Solvay process results in soda ash (predominantly
sodium carbonate Sodium carbonate, , (also known as washing soda, soda ash and soda crystals) is the inorganic compound with the formula Na2CO3 and its various hydrates. All forms are white, odourless, water-soluble salts that yield moderately alkaline solutions ...
(Na2CO3)) from
brine Brine is a high-concentration solution of salt (NaCl) in water (H2O). In diverse contexts, ''brine'' may refer to the salt solutions ranging from about 3.5% (a typical concentration of seawater, on the lower end of that of solutions used for br ...
(as a source of
sodium chloride Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g ...
(NaCl)) and from
limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...
(as a source of calcium carbonate (CaCO3)). Online version archived at WebCite fro
this original URL
on 2008-03-12.
The overall process is: : 2NaCl + CaCO3 -> Na2CO3 + CaCl2 The actual implementation of this global, overall reaction is intricate."Process Best Practices Reference Document (BREF) for Soda Ash,"
report produced by th
European Soda Ash Producer's Association
March 2004. Archived at WebCite fro
this original URL
on 2008-03-01.
A simplified description can be given using the four different, interacting chemical reactions illustrated in the figure. In the first step in the process,
carbon dioxide Carbon dioxide (chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is transpar ...
(CO2) passes through a concentrated
aqueous solution An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, or sodium chloride (NaCl), in water would be re ...
of sodium chloride (table salt, NaCl) and
ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...
(NH3). : NaCl + CO2 + NH3 + H2O -> NaHCO3 + NH4Cl ---(I) In industrial practice, the reaction is carried out by passing concentrated brine (salt water) through two towers. In the first, ammonia bubbles up through the brine and is absorbed by it. In the second, carbon dioxide bubbles up through the ammoniated brine, and
sodium bicarbonate Sodium bicarbonate (IUPAC name: sodium hydrogencarbonate), commonly known as baking soda or bicarbonate of soda, is a chemical compound with the formula NaHCO3. It is a salt composed of a sodium cation ( Na+) and a bicarbonate anion ( HCO3−) ...
(baking soda) precipitates out of the solution. Note that, in a
basic BASIC (Beginners' All-purpose Symbolic Instruction Code) is a family of general-purpose, high-level programming languages designed for ease of use. The original version was created by John G. Kemeny and Thomas E. Kurtz at Dartmouth College ...
solution Solution may refer to: * Solution (chemistry), a mixture where one substance is dissolved in another * Solution (equation), in mathematics ** Numerical solution, in numerical analysis, approximate solutions within specified error bounds * Soluti ...
, NaHCO3 is less water-soluble than sodium chloride. The ammonia (NH3) buffers the solution at a basic (high) pH; without the ammonia, a
hydrochloric acid Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid Acid strength is the tendency of an acid, symbol ...
byproduct would render the solution
acid In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...
ic, and arrest the precipitation. Here, NH3 along with ammoniacal brine acts as a "mother liquor". The necessary ammonia "catalyst" for reaction (I) is reclaimed in a later step, and relatively little ammonia is consumed. The carbon dioxide required for reaction (I) is produced by heating ("
calcination Calcination refers to thermal treatment of a solid chemical compound (e.g. mixed carbonate ores) whereby the compound is raised to high temperature without melting under restricted supply of ambient oxygen (i.e. gaseous O2 fraction of air), genera ...
") of the limestone at 950–1100 °C, and by calcination of the sodium bicarbonate (see below). The calcium carbonate (CaCO3) in the limestone is partially converted to
quicklime Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline, crystalline solid at room temperature. The broadly used term "''lime''" connotes calcium-containing inorganic ma ...
(calcium oxide (CaO)) and carbon dioxide: : CaCO3 -> CO2 + CaO ---(II) The sodium bicarbonate (NaHCO3) that precipitates out in reaction (I) is filtered out from the hot ammonium chloride (NH4Cl) solution, and the solution is then reacted with the
quicklime Calcium oxide (CaO), commonly known as quicklime or burnt lime, is a widely used chemical compound. It is a white, caustic, alkaline, crystalline solid at room temperature. The broadly used term "''lime''" connotes calcium-containing inorganic ma ...
(calcium oxide (CaO)) left over from heating the limestone in step (II). : 2 NH4Cl + CaO -> 2 NH3 + CaCl2 + H2O ---(III) CaO makes a strong basic solution. The ammonia from reaction (III) is recycled back to the initial brine solution of reaction (I). The sodium bicarbonate (NaHCO3) precipitate from reaction (I) is then converted to the final product, sodium carbonate (washing soda: Na2CO3), by
calcination Calcination refers to thermal treatment of a solid chemical compound (e.g. mixed carbonate ores) whereby the compound is raised to high temperature without melting under restricted supply of ambient oxygen (i.e. gaseous O2 fraction of air), genera ...
(160–230 °C), producing water and carbon dioxide as byproducts: : 2 NaHCO3 -> Na2CO3 + H2O + CO2 ---(IV) The carbon dioxide from step (IV) is recovered for re-use in step (I). When properly designed and operated, a Solvay plant can reclaim almost all its ammonia, and consumes only small amounts of additional ammonia to make up for losses. The only major inputs to the Solvay process are salt, limestone and
thermal energy The term "thermal energy" is used loosely in various contexts in physics and engineering. It can refer to several different well-defined physical concepts. These include the internal energy or enthalpy of a body of matter and radiation; heat, d ...
, and its only major byproduct is
calcium chloride Calcium chloride is an inorganic compound, a salt with the chemical formula . It is a white crystalline solid at room temperature, and it is highly soluble in water. It can be created by neutralising hydrochloric acid with calcium hydroxide. Ca ...
, which is sometimes sold as
road salt Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g ...
. After the invention of the Haber and other new ammonia-producing processes in 1910s-1920s its price dropped, and there was less need in reclaiming it. So in the modified Solvay process developed by Chinese chemist
Hou Debang Hou Debang (; 9 August 1890 – 26 August 1974), also known as Hou Qirong () and Hou Te-Pang, was a Chinese chemist and chemical engineer. He was born in Taijiang District of Fuzhou (then known as Houguan County). Graduating from Tsinghua Prepa ...
in 1930s, the first few steps are the same as the Solvay process, but the CaCl2 is supplanted by ammonium chloride (NH4Cl). Instead of treating the remaining solution with lime, carbon dioxide and ammonia are pumped into the solution, then sodium chloride is added until the solution saturates at 40 °C. Next, the solution is cooled to 10 °C. Ammonium chloride precipitates and is removed by filtration, and the solution is recycled to produce more sodium carbonate. Hou's process eliminates the production of calcium chloride. The byproduct ammonium chloride can be refined, used as a fertilizer and may have greater commercial value than CaCl2, thus reducing the extent of waste beds. Additional details of the industrial implementation of this process are available in the report prepared for the European Soda Ash Producer's Association.


Byproducts and wastes

The principal byproduct of the Solvay process is
calcium chloride Calcium chloride is an inorganic compound, a salt with the chemical formula . It is a white crystalline solid at room temperature, and it is highly soluble in water. It can be created by neutralising hydrochloric acid with calcium hydroxide. Ca ...
(CaCl2) in aqueous solution. The process has other waste and byproducts as well. Not all of the limestone that is calcined is converted to quicklime and carbon dioxide (in reaction II); the residual calcium carbonate and other components of the limestone become wastes. In addition, the salt brine used by the process is usually purified to remove magnesium and calcium ions, typically to form carbonates ( MgCO3, CaCO3); otherwise, these impurities would lead to scale in the various reaction vessels and towers. These carbonates are additional waste products. In inland plants, such as that in
Solvay, New York Solvay is a village located in the town of Geddes, Onondaga County, New York, United States, and a suburb of the city of Syracuse. According to the 2010 census, the village had a total population of 6,584. The village is named after the Solvay ...
, the byproducts have been deposited in "waste beds"; the weight of material deposited in these waste beds exceeded that of the soda ash produced by about 50%. These waste beds have led to water pollution, principally by calcium and chloride. The waste beds in Solvay, New York substantially increased the salinity in nearby
Onondaga Lake Onondaga Lake is a lake in Central New York, immediately northwest of and adjacent to Syracuse, New York. The southeastern end of the lake and the southwestern shore abut industrial areas and expressways; the northeastern shore and northwestern ...
, which used to be among the most polluted lakes in the U.S. and is a
superfund Superfund is a United States federal environmental remediation program established by the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA). The program is administered by the United States Environmental Pro ...
pollution site. As such waste beds age, they do begin to support plant communities which have been the subject of several scientific studies. At seaside locations, such as those at Saurashtra, Gujarat, India, the CaCl2 solution may be discharged directly into the sea, apparently without substantial environmental harm (although small amounts of heavy metals in it may be a problem), the major concern is discharge location falls within the Marine National Park of Gulf of Kutch which serves as habitat for coral reefs, seagrass and seaweed community. At
Osborne, South Australia Osborne is a suburb in the Australian state of South Australia located on the LeFevre Peninsula in the west of Adelaide about north-west of the Adelaide city centre. Description Osborne is bounded to the south by the suburb of Taperoo, to the ...
, a settling pond is now used to remove 99% of the CaCl2 as the former discharge was silting up the shipping channel. At
Rosignano Solvay Rosignano Solvay is a ''frazione'' (detached borough) of Rosignano Marittimo, Tuscany, Italy, located some 25 km from Livorno. It houses the White Beaches (Italian: ''Spiagge bianche''), whose sand is formed by limestone ( calcium carbonat ...
in Tuscany, Italy the limestone waste produced by the Solvay factory has changed the landscape, producing the "Spiagge Bianche" ("White Beaches"). A report published in 1999 by the United Nations Environment Programme (UNEP), listed Spiagge Bianche among the priority pollution hot spots in the coastal areas of the Mediterranean Sea.


Carbon sequestration and the Solvay process

Variations in the Solvay process have been proposed for
carbon sequestration Carbon sequestration is the process of storing carbon in a carbon pool. Carbon dioxide () is naturally captured from the atmosphere through biological, chemical, and physical processes. These changes can be accelerated through changes in land ...
. One idea is to react carbon dioxide, produced perhaps by the combustion of coal, to form solid carbonates (such as sodium bicarbonate) that could be permanently stored, thus avoiding
carbon dioxide emission Greenhouse gas emissions from human activities strengthen the greenhouse effect, contributing to climate change. Most is carbon dioxide from burning fossil fuels: coal, oil, and natural gas. The largest emitters include coal in China and larg ...
into the atmosphere. The Solvay process could be modified to give the overall reaction: : 2 NaCl + CaCO3 + + → 2NaHCO3 + CaCl2 Variations in the Solvay process have been proposed to convert carbon dioxide emissions into sodium carbonates, but carbon sequestration by calcium or magnesium carbonates appears more promising. However, the amount of carbon dioxide exhausted by mankind as compared to the amount which can be used for carbon sequestration with calcium or magnesium is very low. Moreover, variation on the Solvay process will most probably add an additional energy consuming step, which will increase carbon dioxide emissions unless
carbon neutral Carbon neutrality is a state of net-zero carbon dioxide emissions. This can be achieved by balancing emissions of carbon dioxide with its removal (often through carbon offsetting) or by eliminating emissions from society (the transition to the "p ...
energy sources like
hydropower Hydropower (from el, ὕδωρ, "water"), also known as water power, is the use of falling or fast-running water to Electricity generation, produce electricity or to power machines. This is achieved by energy transformation, converting the Pot ...
,
nuclear energy Nuclear energy may refer to: *Nuclear power, the use of sustained nuclear fission or nuclear fusion to generate heat and electricity * Nuclear binding energy, the energy needed to fuse or split a nucleus of an atom *Nuclear potential energy ...
, wind or
solar power Solar power is the conversion of energy from sunlight into electricity, either directly using photovoltaics (PV) or indirectly using concentrated solar power. Photovoltaic cells convert light into an electric current using the photovoltaic e ...
are used.


See also

*
Chloralkali process The chloralkali process (also chlor-alkali and chlor alkali) is an industrial process for the electrolysis of sodium chloride (NaCl) solutions. It is the technology used to produce chlorine and sodium hydroxide (caustic soda), which are comm ...


References


Further reading

* The minimum energy required to calcine limestone is about per tonne.


External links


European Soda Ash Producer's Association (ESAPA)

Timeline of US plant at Solvay, New York

Salt and the Chemical Revolution

Process flow diagram of Solvay process
{{DEFAULTSORT:Solvay Process Ammonia Chemical processes Belgian inventions