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Sulfuric acid king of chemicals production using - contact process

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Sulfuric acid king of chemicals production using - contact process

Post  bejoy on Wed Feb 12, 2014 1:05 am



sulfuric acid molecular formula written as H2SO4, with other names includes oil of vitriol, battery acid, and king of chemicals. Sulfuric acid composed of hydrogen, oxygen, and sulfur and available forms include dilute sulfuric acid, concentrated sulfuric acid.

Sulfuric acid is formed naturally by the oxidation of sulfide minerals, such as iron sulfide. On earth, sulfuric acid does not exist in a natural form. But on the planet Venus, there are lakes of the sulfuric acid exist. The sulfuric acid from lakes will evaporate to form clouds, leading to sulfuric acid rain on the Venerean surface.

sulfuric acid is the largest volume industrial chemical produced in the world i.e., 200 million tons per year. 93-98 per cent (concentrated) sulfuric acid is used in the manufacture of fertilizers, explosives, dyes, petroleum products, domestic acidic drain cleaner, lead-acid batteries, mineral processing, fertilizer manufacturing, oil refining, wastewater processing, and chemical synthesis.

International commerce of sulfuric acid, lists sulfuric acid under Table II of the convention as a chemical frequently used in the illicit manufacture of narcotic drugs or psychotropic substances.

In laboratories or industries if you spill a drop of sulfuric acid on your hand, it will burn tissue instantly. It also causes skin dehydration. Other severe effects of sulphuric acid are fumes cause blindness, and damage the lungs if inhaled. Even dilute sulfuric acid is dangerous.

While handling sulfuric acid following precautionary steps need to be follow

Always wear thick gloves
Wear a lab coat or apron
Never handle it on an open bench
Never pour it / through out from the bottle
Never pipette out with mouth
Always use a thick glass pipette with a rubber bulb
Sulfuric acid is often stored in concentrated form
Sulfuric acid has following properties
Sulphuric acid is a powerful protonating agent.
Sulphuric acid is also a powerful dehydrating agent and is used to remove a molecule of water from many organic compounds.
Dilute sulphuric acid is a strong dibasic acid forming two series of salts.
Sulfuric acid reacts with most bases to give the corresponding sulfate.
It can oxidize non-active tin and copper metals

Sulfuric acid production process

The production of sulfuric acid has come to be accepted throughout the world as a reliable barometer of industrial activity. Its universal use has made it indispensable, in the widest sense of the world, in chemical and process industries. Sulfuric acid is a strong acid i.e. is in aqueous solution it’s largely changed to hydrogen ions and sulfate ions. Each molecule gives 2 hydrogen ions and thus sulfuric acid is dibasic acid.

The preparation by burning sulfur with saltpeter was first described by Valentinus in the fifteenth century. Later its preparation by distilling niter with green vitriol was mentioned by Persian alchemist Abu-Bekr-Ahhases, who died in 940.The weathering of iron pyrites was usually the source of green vitriol. Sulfuric acid has been an important item of commerce for at least 250 years and has been known and used since the Middle Ages.

In the eighteenth and nineteenth centuries, it was essentially and entirely produced by chamber process, in which oxides of nitrogen (as nitrosyl compounds) were used as homogeneous catalysts for the oxidation of sulfur dioxide. The product made by this process was of rather low concentration not high enough for many commercial uses.

In 1746, Roebuck of Birmingham, England produced successfully on commercial scale by burning sulfur and potassium nitrate in ladle suspended in a large glass partially filled with water.

The contact process was first discovered in 1831 by Phillips, an Englishman whose patent included the essential features of the modern contact process namely the passing of the mixture SO2 over a catalyst followed by absorption of SO3 in 98 to 99 per cent H2SO4. Later it was demonstrated that excess of oxygen in the gaseous mixture for contact process was advantageous. The contact process has been improved in all details and at the current scenario is one of the low cost industries and is almost wholly automatic continuous process for the manufacture of sulfuric acid.

Primary impetus for the development of the contact process came from a need for high strength acid and oleum to make synthetic dyes and organic chemicals. The contact process employing platinum catalysts began to be used on large scale for this purpose late in the nineteenth century. Its development accelerated during the World War I to provide the concentrated mixtures of sulfuric and nitric acid for the production of explosives.

Contact process




The contact process is the current method of producing sulfuric acid in the high concentrations needed for industrial processes. Platinum was formerly employed as a catalyst for the reaction, but as it is susceptible to poisoning by arsenic impurities in the sulfur feedstock, vanadium oxide (V2O5) is now preferred.

The sulfur dioxide is obtained by burning sulfur or by roasting sulphide ores in air. Purification of air and SO2 is necessary to avoid catalyst poisoning. The sulfur dioxide, mixed with an excess of air, is purified and dried then passed through a series of converters where the catalyst is stored on shelves in a way which exposes the maximum possible surface area to the reacting gases.

The oxidation is exothermic and operating temperature is maintained without external heating by using heat exchangers.

After passing through the converters the gases are cooled and passed into an absorption tower where the sulfur trioxide dissolves in concentrated sulfuric acid. The product leaving the absorption tower is normally 100 per cent sulfuric acid. Some of it is diluted with water, cooled, and reirculated through the absorption tower. By controlling the dilution the contact process can be adapted to produce fuming sulfuric acid.

Reactions involved in contact process

S(l) + O2(g) → SO2 (g)
2SO2(g) + O2(g) ↔ 2SO3 (g)
SO3(g) + H2SO4(l) → H2S2O7 (l)
H2S2O7(l) + H2O(g) → 2H2SO4(l)

Double Contact Double Absorption process

Another significant change in the contact process occurred in 1963, when Bayer AG announced the first large scale use of Double Contact Double Absorption process and granted several patents.

In this process the product gases SO2 and SO3are passed through absorption towers twice to achieve further absorption and conversion of SO2 to SO3and production of higher grade sulfuric acid.

SO2 rich gases enter the catalytic converter, are converted to SO3, achieving the first stage of conversion. The exit gases from this stage contain both SO2and SO3 which are passed through intermediate absorption towers where sulfuric acid is trickled down packed columns and SO3reacts with water increasing the sulfuric acid concentration. Unreactive SO2 comes out of the absorption tower.

This stream of gas containing SO2, after necessary cooling is passed through the catalytic converter bed column again achieving up to 99.8 per cent conversion of SO2 to SO3 and these gases are again passed through the final absorption column thus resulting high conversion of SO2but also enabling production of higher concentration of sulfuric acid.

bejoy

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