The contact process is one of the most widely used methods to manufacture sulphuric acid. Peregrine Phillips, a British merchant, invented the contact process and patented it in 1831. It is not only the economical process to manufacture sulphuric acid, but also produces sulphur trioxide and oleum. Here is an in-depth explanation of the contact process.
Sulphuric Acid (H2SO4)
It is said that the amount of sulphuric acid produced in a country is directly proportional to the industrial growth of that country. Sulphuric acid is an essential raw material for almost everything that is industrially made and is commonly used in fertilizer manufacturing, oil refining, mineral processing, wastewater processing, domestic acidic drain cleaners, and electrolytes in lead-acid batteries, as a dehydrating agent, etc.
In brief, sulphuric acid is one of the strong mineral acids and has a density of 1.83 g/cm3. The chemical formula of sulphuric acid is H2SO4 and is characterized by its strong dehydrating and oxidizing nature. It is transparent and gives a pungent smell. When contacted with water it completely gets dissolved and releases heat. It is corrosive to metals and other organic matters like tissue, wood, etc.
Properties of Sulphuric Acid
The properties of Sulphuric Acid are listed below,
Chemical formula: H2SO4
Molar mass: 98.079 g/mol
Appearance: Clear, colourless liquid
Density: 1.8302 g/cm3
Melting point and boiling point: 50.560 F and 6390F
Solubility in water: Exothermic, miscible
Viscosity: 26.7 cP
Manufacturing of Sulphuric Acid by Contact Process
Generally, sulphuric acid can be manufactured in several ways and varies in the effort, cost, and purity of the sulphuric acid that is produced. Among all of these, the most common process is the contact process. The manufacturing of sulphuric acid by contact process is done using a four-step process, They are
Extraction of sulphur.
Preparation of sulphur dioxide.
Conversion of sulphur dioxide to sulphur trioxide.
Conversion of sulphur trioxide to sulphuric acid.
Extraction of Sulphur
For the production of sulphur dioxide gas, pure sulphur is required. Sulphur can be extracted using various sources, among these the recovery from natural gas and oil is most important. To obtain sulphur, the organic or mineral parts get removed.
Apart from the extraction of pure sulphur, sulphur dioxide can also be extracted using certain ways. One among them is metal refining. In soil, many metal ores occur as sulphides, they get roasted to obtain their respective oxide and sulphur dioxide.
For example, in the extraction process of lead:
Similarly, sulphur dioxide can be obtained from the metallurgy of copper, nickel, zinc, etc.
Preparation of Sulphur Dioxide
By burning pure sulphur in the presence of excess air sulphur dioxide can be prepared. This results in the formation of dioxide of sulphur.
The preparation process of sulphur dioxide is as follows:
In a stationary atomizer, the molten sulphur is pumped in, resulting in the formation of atomized sulphur. It is then applied to the hot furnace. Using a sulphuric acid dehydrator, the air is preheated, dried and is also applied to the hot furnace. At one end of the hot furnace, air and atomized molten sulphur are kept. On the other end, due to the reaction, sulphur dioxide is produced.
S (solid)⟶ S (gas) on heating at 450 degree celsius
S(g) + O2 ⟶ SO2(g) +Δ
Conversion of Sulphur Dioxide to Sulphur Trioxide
This is an elegant step in the contact process. This step is partial because it produces corrosive sulphur trioxide and can be reversed and involves different reaction parameters to obtain maximum output.
Inside a lead chamber, sulphur dioxide and oxygen are combined in a 1:1 ratio. At temperature 400 – 450 degrees Celsius the temperature is set with 1 to 2 atm. By the vanadium pentoxide catalyst, the process is catalysed.
Conversion of Sulphur Trioxide to Sulphuric Acid
Sulphuric acid can be yielded by diluting sulphur trioxide in water. This is a very dangerous method and not followed. Adding sulphur trioxide to water is highly exothermic and causes the fuming of sulphuric acid. Further dissolution of sulphur trioxide in water is prevented by the fumes.
The widely used method is to dilute the sulphur trioxide in sulphuric acid, which produces oleum.
SO3 (g) + H2SO4 ⟶ H2S2O7 (1)
Oleum is then diluted in water to produce concentrated sulphuric acid.
H2S2O7 (1) + H2O (1) ⟶ 2H2SO4 (1)
Applications of Sulphuric acid
The major applications of sulphuric acid are,
Preparation of fertilizers ((NH)2SO4).
Paper, and sugar bleaching.
Amino and intermediates.
Regeneration and ion-exchange resins.