These figures relate to - It was expected that by , the World production would be over million tonnes mcgroup. The process for producing sulfuric acid has four stages: a extraction of sulfur b conversion of sulfur to sulfur dioxide c conversion of sulfur dioxide to sulfur trioxide d conversion of sulfur trioxide to sulfuric acid.
Easily the most important source of sulfur is its recovery from natural gas and oil. These contain sulfur compounds , both organic and hydrogen sulfide both of which must be removed before they are used as fuels or chemical feedstock.
Another important source of sulfur is as sulfur dioxide from metal refining. Many metal ores occur as sulfides and are roasted to form an oxide and sulfur dioxide, for example, in the manufacture of lead :. Other metals manufactured from their sulfide ores include copper , nickel and zinc. In particular, China makes most of its sulfuric acid from pyrites, an iron sulfide ore. Sulfuric acid is also obtained from ammonium sulfate, a by-product in the manufacture of poly methyl 2-methylpropenoate and also recovered from 'spent' i.
If sulfur is the feedstock, it must first be converted to sulfur dioxide. Molten sulfur is sprayed into a furnace and burnt in a blast of dry air at about K. The sulfur burns with a characteristic blue flame:. The gases are very hot and so are passed through heat exchangers waste heat boilers.
The gases are cooled to about K and the water in the surrounding boiler pipes is converted into steam. In manufacturing one tonne of sulfuric acid, one tonne of high pressure steam is also produced. A typical plant contains one cylindrical vessel which acts as a fixed bed reactor with four separate beds of catalyst, known as a converter, heated to K, through which the sulfur dioxide and air pass:. The catalyst, vanadium V oxide on silica, is generally in the form of small pellets, to which caesium sulfate has been added as a promoter Figure 2.
The function of the promoter is to lower the melting point of vanadium V oxide so that it is molten at K. Figure 3 A flow diagram of the Contact Process. As shown above, it is an exothermic reaction so, for a satisfactory yield of sulfur trioxide above Thus, heat is removed from the gas leaving each bed using heat exchangers.
The sulfur trioxide produced is removed between the third and fourth beds and flows to the next stage, the conversion of sulfur trioxide to sulfuric acid. However, a small amount of the sulfur dioxide is not converted and is passed through the fourth bed of catalyst and the resulting gases, mainly sulfur trioxide, flow to the next stage. Based on diagram given by Mike Sellars.
The sulfur trioxide formed from the third bed and the small amount from the fourth bed are now converted to sulfuric acid. Sulfuric acid is the largest-volume industrial chemical produced in the world million tons per year.
The starting material for sulfuric acid manufacture is clean, dry sulfur dioxide SO2 gas. This can be obtained by burning molten sulfur, from metallurgical off-gases or by decomposing spent sulfuric acid.
Over the last decades the contact process has been used to produce sulfuric acid, replacing the traditional «Lead Chamber» process dating back to the 18th Century.
SO3 then is dissolved in concentrated sulfuric acid forming fuming sulfuric acid oleum. This can then be reacted safely with water to produce concentrated sulfuric acid.
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