The contact process is the most widely used method of manufacturing tetraoxosulphate(vi) acid, otherwise called sulphuric acid on a commercial scale. The main reaction in the manufacturing process of this very important compound is the catalytic combination of sulphur(IV) oxide and oxygen to form sulphur(VI) oxide. Sulphur(IV) oxide is made by burning sulphur in dry air or by roasting sulphide ores.
2SO2(g) + O2(g) 2SO3(g) + heat
S(s) + O2(g) SO2(g)
Below is a concise description of a simple procedure in the industrial preparation of sulfuric acid, otherwise known by its IUPAC name is tetraoxosulphate(VI) acid using the contact process.
Sulphur(IV) oxide is mixed with excess air and passed through an electric chamber in order to remove impurities and dust which might poison the catalyst. The gaseous mixture is then passed through concentrated tetraoxosulphate(VI) acid to be dried before it is taken to the reaction chamber or contact tower. Here, the sulphur(IV) oxide combines with oxygen in the presence of pellets of a catalyst, vanadium(V) oxide to yield sulphur(VI) oxide.
The contact process is carried out at an atmospheric pressure and at a temperature of about 450 -500oC with excess air or oxygen to ensure that all the sulphur(IV) oxide has reacted. Around 98% of the possible yield of sulphur(VI) oxide is obtained.
The sulphur(VI) oxide is cooled and passed into an absorption tower where it dissolves in concentrated tetraoxosulphste(VI) acid to produce a very thick liquid called oleum. Note that the oxide, sulphur(VI) oxide, is not dissolved directly in water because the heat evolved during the process would cause the acid solution to boil and producing a mist of acid droplets which could spread throughout the factory.
SO3(g) + H2SO4(aq) → H2S2O7(aq)
The Oleum, H2S2O4 is then diluted with appropriate amounts of water to produce the 98% tetraoxosulphate(VI) acid often used in the laboratory and also into other desired concentrations.
Stages Involved in the Contact Process
Production of tetraoxosulphate(vi) acid, commonly known as sulfuric acid on a commercial scale is done by the contact process. This is the main method of preparing this strong acid industrially.
Sulphur(IV) oxide is combined with oxygen in a reaction chamber or contact tower. The gaseous mixture is passed through an electric chamber to remove impurities and dust that may poison the catalyst, vanadium(V) oxide, V2O5. It is then dried.
Tetraoxosulphate(vi) acid, also known as sulphuric acid is produced industrially by the contact process. It is very strong acid and has many important uses. It is used in production of fertilizers, cleaning metals before electroplating and as a drying agent. It is very corrosive and can burn if it comes into contact with skin. It can oxidize some metals and non-metals, and it is moisture sensitive.
The preparation of sulphuric acid by the contact process involves three steps. The first step is the oxidation of sulphur dioxide gas to produce oleum, the second step is the formation of tetraoxosulphate(vi) acid by the catalytic reaction and the third step is the purification of tetraoxosulphate dihydride. The oleum is then treated with water to form sulphuric acid of the required concentration.
A solution of sulphuric acid has a pH below 7. It is very corrosive and can cause burns on contact with skin. It oxidizes some metals and some non-metals, including iron. It is a strong acid and has many important uses.
The contact process is the most common method for preparing tetraoxosulphate(vi) acid on a commercial scale. The sulphur dioxide (SO2) from the air is catalytically oxidized to sulphur trioxide (SO3) in an electric contact chamber with platinum as catalyst at 4500C temperature and 2 atm pressure. The SO3 is then absorbed by quartz or acid proof stone in an absorption tower and 98% H2SO4 is sprayed over it to give concentrated sulfuric acid. This is called the contact process because the catalyst is placed close to the SO2 vapor in order to facilitate the reaction. This is the only way to get a pure sulphuric acid without using large quantities of expensive precious metals like platinum.
Sulphur(IV) oxide exists as white needle-like crystals at room temperature and is very soluble in water. It is corrosive and can burn the skin. It vaporizes on warming and has a pungent odor. It reacts with many oxidizing agents, such as acidified KMnO4, acidified K2Cr2O7, FeCl3, HNO3 and chlorine gas to form tetraoxosulphate(vi) acid and other salts. It is used as a germicide and a fumigant especially for destroying termites. It is also an excellent bleaching agent for straw, silt and wood.
The sulphur(IV) oxide formed is passed through an electric chamber to remove impurities which might poison the catalyst to be used and then through H2SO4 to dry it before being passed into the reaction chamber. This solution is then reacted in the presence of vanadium (VI) oxide to produce sulphur (VI) sulfate and Oleum.
A salt is a substance that forms when all or part of the replaceable hydrogen ions in an acid are replaced by metal (Na+, Mg2+, Ca2+, Cu2+) or ammonium (NH4+) ions. All acids have their corresponding salts. There are five major types of salts namely normal, acid, basic, double and complex.
3. Catalytic Reaction
The raw materials for the manufacture of tetraoxosulphate vi acid by the contact process are sulphur and air/oxygen. Sulphur (IV) oxide can be produced by burning sulphur in dry air or by roasting sulphide ores such as pyrite, FeS2. The gaseous mixture is passed through an electric chamber to remove any dust which might poison the catalyst used. Then it is dried with H2SO4. It is then taken to a reaction chamber, called a contact tower, where the sulphur (IV) oxide reacts with oxygen to yield sulphur (VI) oxide. This reaction is catalysed by pellets of the catalyst vanadium (VI) oxide, V2O5.
The reaction is reversible but the conditions in the reactor can have a huge impact on the position of equilibrium, and optimum conversion of reactants to products is desired. Like the Haber process for the production of ammonia, the reaction for the manufacture of tetraoxosulphate acid by the contact process is a catalytic one.
The sulphur(VI) oxide does not dissolve directly in water because this would give off too much heat, but it can be dissolved in concentrated sulphuric acid (H2SO4). As the acid is a strong acid, it can replace hydrogen ions from other molecules in solution and this will change their chemical properties. This is why it can be used to make artificial pigments, extract metals, as an electrolyte in lead-acid storage batteries and in some chemical reactions. It is also used as a drying agent. Because of its basicity, tetraoxosulphate (VI) acid can form salts with alkalis. This can be exploited by the pharmaceutical industry in the production of some antibiotics. This is why the term Oleum is used to describe a solution of the acid, not its pure form.
4. Formation of Oleum and Other Uses of Tetraoxosulphate(vi) Acid
Tetraoxosulphate(vi) acid is one of the most widely used chemicals in industrial processes. Almost all manufacturers use it directly or indirectly at some stage. This chemical is widely manufactured by the contact process which is an efficient way of producing high quality sulphuric acid.
In the contact process, raw sulfur is combined with oxygen to produce sulphur dioxide and then combined with water to form sulphuric acid. This is the most common method of producing sulphuric acid on a large scale. It is far more economical than the older lead chamber method and also produces sulphur trioxide and oleum, both of which are useful products.
The air and sulphur dioxide produced in the process are passed through an electric chamber to remove any impurities such as dust, which might poison the catalyst to be used. It is then passed through concentrated tetraoxosulphate(vi) to dry it before being fed into the reaction chamber. The gaseous mixture is then fed into a contact tower (reaction chamber) where it is combined with oxygen in the presence of pellets of vanadium(v) oxide, V2O5 which catalyses the reaction. This is done at atmospheric pressure and a temperature of 450-500oC.
This reaction forms a thick liquid called oleum, H2S2O4. This is then diluted with water to produce 98% tetraoxosulphate(vi) acid which can be used in the manufacture of many different things including cellulose film, artificial and natural fabrics, plastics and explosives. It is also used as an electrolyte in lead accumulators and batteries, as a dehydrating agent in nitration and for cleaning metals prior to plating. Calcium tetraoxosulphate(vi) forms plaster of Paris which is used to set broken bones and iron tetraoxosulphate(vi) is useful in the production of some dyes.
More Uses of Tetraoxosulphate(vi) Acid
Tetraoxosulphate(vi) acid, also known as sulfuric acid, is a strong mineral acid with the chemical formula H2SO4. As stated above, it is manufactured industrially in large quantities using the contact process. This is a two-stage reaction which converts sulphur dioxide to sulphuric acid via the catalytic oxidation of a mixture of nitrates and oxides of other metals. It is used in a variety of applications, especially for the manufacture of fertilizer such as ammonium tetraoxosulphate(vi), NH4SO4, and superphosphates. It is also employed in the manufacture of paints and pigments, for example to produce sulphuric red and blue colours. It is also used in the manufacture of glass and some plastics, as well as detergents, dyes, explosives and drugs. It is used in the extraction of metals, for example in pickling iron and steel before plating them with tin or zinc. It is also employed as an electrolyte in lead-acid storage batteries.
Concentrated tetraoxosulphate(vi) acid is a dehydrating agent, removing water molecules from compounds such as sugar, ethanol and methanoic acid C 12 H 22 O 11 (s) – C 12 H 17 O 15 CHO (s). It is also a strong oxidising agent, destroying many organic compounds and forming complexes with metals, for example magnesium, aluminium, chromium and zinc. It is also used to prepare sodium tetraoxosulphate(vi) sulphate, a useful anti-corrosive.
Tetraoxosulphate(vi) acid forms a variety of salts with other substances, such as potassium trioxoiodate(v) and potassium iodide. It is also capable of reacting with cyanide salts to form cyanuric acid, which is used in treating textile waste water. It is also used as a disinfectant and for the destruction of termites and moulds.