SULFURIC ACID (H2SO4): PROPERTIES, STRUCTURE AND USES - CHEMISTRY - 2025

The sulfuric acid (H ₂ SO ₄₎ is a liquid, oily, colorless chemical compound, soluble in water with release of heat and corrosive to metals and fabrics. It charres wood and most organic matter on contact with it, but is unlikely to cause a fire.

Sulfuric acid is perhaps the most important of all heavy industrial chemicals and its consumption has been cited many times as an indicator of the general state of a nation's economy.

Sulfuric acid 96% extra pure

Long-term exposure to low concentrations or short-term exposure to high concentrations can result in adverse health effects. By far the most important use for sulfuric acid is in the phosphate fertilizer industry.

Other important applications are in petroleum refining, pigment production, steel pickling, non-ferrous metal extraction, and manufacturing of explosives, detergents, plastics, man-made fibers, and pharmaceuticals.

Vitriol, the antecedent of sulfuric acid

In medieval Europe sulfuric acid was known as vitriol, vitriol oil or vitriol liquor by alchemists. It was considered the most important chemical substance, and it was tried to be used as a philosopher's stone.

Sulfuric acid skeletal formula

Already the Sumerians had a list of various types of vitriol. In addition, Galen, the Greek physician Dioscorides and Pliny the Elder raised its medical use.

On the left: «The Alchemist, in search of the Philosopher's Stone» by Joseph Wright, 1771 / On the right: Anagrammatic figure representing the vitriol, according to the alchemist motto “Visit interiora terrae; rectifying invenies occultum lapidem ”(“ Visit the inner parts of the earth, rectifying you will find the hidden stone ”). Stolzius von Stolzembuirg, Theatrum Chymicum, 1614

In Hellenistic alchemical works the metallurgical uses of vitriolic substances were already mentioned. Vitriol refers to a group of glassy minerals from which sulfuric acid can be obtained.

Formula

-Formula: H ₂ SO ₄

-Number Cas: 7664-93-9

Chemical structure

In 2D

Sulfuric acid

In 3d

Sulfuric Acid / Ball and Rod Molecular Model

Sulfuric acid / Molecular model of spheres

characteristics

Physical and chemical properties

Sulfuric acid belongs to the reactive group of strong oxidizing acids.

Reactions with air and water

- The reaction with water is negligible unless the acidity is above 80-90%, then the heat of hydrolysis is extreme, it can cause severe burns.

Inflammability

- Strong oxidizing acids are generally non-flammable. They can accelerate the combustion of other materials by providing oxygen to the combustion site.

- However, sulfuric acid is highly reactive and capable of igniting finely divided combustible materials when in contact with them.

- When heated, it emits highly toxic fumes.

- It is explosive or incompatible with a huge variety of substances.

- It can undergo violent chemical changes at high temperatures and pressure.

- It can react violently with water.

Reactivity

- Sulfuric acid is strongly acidic.

- Reacts violently with bromine pentafluoride.

- Explodes with para-nitrotoluene at 80 ° C.

- An explosion occurs when concentrated sulfuric acid is mixed with crystalline potassium permanganate in a container containing moisture. Manganese heptoxide is formed, which explodes at 70 ° C.

- The mixture of acrylonitrile with concentrated sulfuric acid must be kept well refrigerated, otherwise a vigorous exothermic reaction occurs.

- Temperature and pressure increase when sulfuric acid (96%) is mixed in equal portions with any of the following substances: acetonitrile, acrolein, 2-aminoethanol, ammonium hydroxide (28%), aniline, n-butyraldehyde, chlorosulfonic acid, ethylene diamine, ethyleneimine, epichlorohydrin, ethylene cyanohydrin, hydrochloric acid (36%), hydrofluoric acid (48.7%), propylene oxide, sodium hydroxide, styrene monomer.

- Sulfuric acid (concentrated) is extremely dangerous in contact with carbides, bromates, chlorates, priming materials, picrates, and powdered metals.

- May induce violent polymerization of allyl chloride and reacts exothermically with sodium hypochlorite to produce chlorine gas.

- By mixing chlorosulfuric acid and 98% sulfuric acid, HCl is obtained.

Toxicity

- Sulfuric acid is corrosive to all body tissues. Inhalation of vapor can cause serious lung damage. Contact with the eyes can result in total loss of vision. Contact with the skin can cause severe necrosis.

- Ingestion of sulfuric acid, in an amount between 1 teaspoon and a half ounce of the concentrated chemical, can be fatal for an adult. Even a few drops can be fatal if the acid gets into the windpipe.

- Chronic exposure can cause tracheobronchitis, stomatitis, conjunctivitis and gastritis. Gastric perforation and peritonitis can occur and can be followed by circulatory collapse. Circulatory shock is often the immediate cause of death.

- Those with chronic respiratory, gastrointestinal or nervous diseases and any eye and skin diseases are at higher risk.

Applications

- Sulfuric acid is one of the most widely used industrial chemicals in the world. But, most of its uses can be considered indirect, participating as a reagent rather than an ingredient.

- Most sulfuric acid ends up as spent acid in the production of other compounds, or as some type of sulfate residue.

- A number of products incorporate sulfur or sulfuric acid, but almost all of them are special low-volume products.

- Around 19% of the sulfuric acid produced in 2014 was consumed in about twenty chemical processes, and the rest was consumed in a wide variety of industrial and technical applications.

- The growth in the demand for sulfuric acid worldwide is due, in decreasing order, to the production of: phosphoric acid, titanium dioxide, hydrofluoric acid, ammonium sulfate and in uranium processing and metallurgical applications.

Indirect

- The largest consumer of sulfuric acid is by far the fertilizer industry. It represented just over 58% of total world consumption in 2014. However, this share is expected to decline to approximately 56% by 2019, mainly as a result of higher growth in other chemical and industrial applications.

- The production of phosphate fertilizer materials, especially phosphoric acid, is the main market for sulfuric acid. It is also used for the manufacture of fertilizer materials such as triple superphosphate and mono and diammonium phosphates. Smaller amounts are used for the production of superphosphate and ammonium sulfate.

- In other industrial applications, substantial amounts of sulfuric acid are used as an acid dehydration reaction medium, in organic chemistry and petrochemical processes involving reactions such as nitration, condensation and dehydration, as well as in the refining of the petroleum, where it is used in the refining, alkylation, and purification of crude distillates.

- In the inorganic chemical industry, its use in the production of TiO2 pigments, hydrochloric acid and hydrofluoric acid is notable.

- In the metal processing industry, sulfuric acid is used for the pickling of steel, the leaching of copper, uranium, and vanadium ores in the hydrometallurgical processing of minerals, and in the preparation of electrolytic baths for the purification and plating of Nonferrous metals.

- Certain processes of the manufacture of wood pulp in the paper industry, in the production of some textiles, in the manufacture of chemical fibers and in the tanning of hides, also require sulfuric acid.

Direct

- Probably the largest use of sulfuric acid in which sulfur is incorporated into the final product is in the organic sulfonation process, particularly for the production of detergents.

- Sulfonation also plays an important role in obtaining other organic chemicals and minor pharmaceuticals.

- Lead-acid batteries are one of the best-known sulfuric acid-containing consumer products, accounting for only a small fraction of total sulfuric acid consumption.

- Under certain conditions, sulfuric acid is used directly in agriculture, for the rehabilitation of highly alkaline soils, such as those found in the desert regions of the western United States. However this use is not very important in terms of the total volume of sulfuric acid used.

The development of the sulfuric acid industry

Vitriol process

copper (II) sulfate crystals that form blue vitriol

The oldest method of obtaining sulfuric acid is the so-called "vitriol process", which is based on the thermal decomposition of vitriols, which are sulfates of various types, of natural origin.

The Persian alchemists, Jābir ibn Hayyān (also known as Geber, 721 - 815 AD), Razi (865 - 925 AD), and Jamal Din al-Watwat (1318 AD), included vitriol in their mineral classification lists.

The first mention of the "vitriol process" appears in the writings of Jabir ibn Hayyan. Then the alchemists Saint Albert the Great and Basilius Valentinus described the process in more detail. Alum and chalcanthite (blue vitriol) were used as raw materials.

At the end of the Middle Ages, sulfuric acid was obtained in small quantities in glass containers, in which sulfur was burned with saltpeter in a humid environment.

The vitriol process was used on an industrial scale from the 16th century due to a greater demand for sulfuric acid.

Vitriol of Nordhausen

The focus of production was in the German city of Nordhausen (which is why the vitriol began to be called “Nordhausen vitriol”), where iron (II) sulfate was used (green vitriol, FeSO ₄ - 7H ₂ O) as raw material, which was heated, and the resulting sulfur trioxide was mixed with water to obtain sulfuric acid (oil of vitriol).

The process was carried out in galleys, some of which had several levels, in parallel, in order to obtain greater quantities of vitriol oil.

Galley used in the production of vitriol

Lead Chambers

In the 18th century, a more economical process for the production of sulfuric acid was developed known as the “lead chamber process”.

Until then, the maximum concentration of acid obtained was 78%, while with the "vitriol process" concentrated acid and oleum were obtained, so this method continued to be used in certain sectors of the industry until the appearance of the "process of contact ”in 1870, with which concentrated acid could be obtained cheaper.

Oleum or fuming sulfuric acid (CAS: 8014-95-7), is a solution of oily consistency and dark brown color, with a variable composition of sulfur trioxide and sulfuric acid, which can be described by the formula H ₂ SO ₄. xSO ₃ (where x represents the free molar content of sulfur oxide (VI)). A value for x of 1 gives the empirical formula H ₂ S ₂ O ₇, which corresponds to disulfuric acid (or pyrosulfuric acid).

Process

The lead chamber process was the industrial method used to produce sulfuric acid in large quantities, before being supplanted by the “contact process”.

In 1746 in Birmingham, England, John Roebuck began to produce sulfuric acid in lead-lined chambers, which were stronger and less expensive than previously used glass containers, and could be made much larger.

Sulfur dioxide (from the combustion of elemental sulfur or metallic minerals containing sulfur, such as pyrite) was introduced with steam and nitrogen oxide in large chambers lined with lead sheets.

The sulfur dioxide and nitrogen dioxide dissolved and, over a period of about 30 minutes, the sulfur dioxide was oxidized to sulfuric acid.

This allowed for the effective industrialization of sulfuric acid production and, with various refinements, this process remained the standard method of production for nearly two centuries.

In 1793, Clemente and Desormes achieved better results by introducing supplemental air into the lead chamber process.

In 1827, Gay-Lussac introduced a method of absorbing nitrogen oxides from the waste gases in the lead chamber.

In 1859, Glover developed a method for the recovery of nitrogen oxides from newly formed acid, by stripping with hot gases, which made it possible to do the nitrogen oxide catalyzing process continuously.

In 1923, Petersen introduced an improved tower process that allowed it to be competitive with the contact process until the 1950s.

The chamber process became so robust that in 1946 it still represented 25% of the world's sulfuric acid production.

Current production: contact process

The contact process is the current method of producing sulfuric acid in high concentrations, necessary in modern industrial processes. Platinum used to be the catalyst for this reaction. However, vanadium pentoxide (V2O5) is now preferred.

In 1831, in Bristol, England, Peregrine Phillips patented the oxidation of sulfur dioxide to sulfur trioxide using a platinum catalyst at elevated temperatures.

However, the adoption of his invention, and the intensive development of the contact process, began only after the demand for oleum for the manufacture of dye increased after about 1872.

Next, better solid catalysts were searched, and the chemistry and thermodynamics of the SO2 / SO3 equilibrium were investigated.

The contact process can be divided into five stages:

1. Combination of sulfur and dioxygen (O2) to form sulfur dioxide.
2. Purification of sulfur dioxide in a purification unit.
3. Addition of excess dioxygen to sulfur dioxide in the presence of the vanadium pentoxide catalyst, at temperatures of 450 ° C and pressure of 1-2 atm.
4. The sulfur trioxide formed is added to the sulfuric acid which gives oleum (disulfuric acid).
5. The oleum is then added to the water to form sulfuric acid which is highly concentrated.

Scheme of the production of sulfuric acid by the contact method using pyrite as raw material

The fundamental disadvantage of nitrogen oxide processes (during the lead chamber process) is that the concentration of the sulfuric acid obtained is limited to a maximum of 70 to 75%, while the contact process produces concentrated acid (98 %).

With the development of relatively inexpensive vanadium catalysts for the contact process, coupled with the increasing demand for concentrated sulfuric acid, the global production of sulfuric acid in nitrogen oxide processing plants declined steadily.

By 1980, virtually no acid was being produced in nitrogen oxide processing plants in Western Europe and North America.

Double contact process

The double contact double absorption process (DCDA or Double Contact Double Absorption) introduced improvements to the contact process for the production of sulfuric acid.

In 1960, Bayer applied for a patent for the so-called double catalysis process. The first plant to use this process was started in 1964.

By incorporating a preliminary SO ₃ absorption stage before the final catalytic stages, the improved contact process allowed a significant increase in SO ₂ conversion, substantially reducing its emissions to the atmosphere.

The gases are passed back through the final absorption column, obtaining not only a high conversion efficiency from SO ₂ to SO ₃ (of approx. 99.8%), but also allowing the production of a higher concentration of sulfuric acid.

The essential difference between this process and the ordinary contact process is in the number of absorption stages.

Starting in the 1970s, the main industrial countries introduced stricter regulations for the protection of the environment, and the double take-over process became more widespread in new plants. However, the conventional contact process is still used in many developing countries with less stringent environmental standards.

The major impetus for the current development of the contact process is focused on increasing recovery and utilization of the large amount of energy produced in the process.

In fact, a large modern sulfuric acid plant can be viewed not only as a chemical plant, but also as a thermal power plant.

Raw materials used in the production of sulfuric acid

Pyrite

Pyrite was the dominant raw material in the production of sulfuric acid until the middle of the 20th century, when large amounts of elemental sulfur began to be recovered from the oil refining process and the purification of natural gas, becoming the main material industry premium.

Sulfur dioxide

Currently, sulfur dioxide is obtained by different methods, from various raw materials.

In the United States, the industry has been based since the early years of the 20th century on obtaining elemental sulfur from underground deposits by the “Frasch Process”.

Moderately concentrated sulfuric acid is also produced by reconcentration and purification of large amounts of sulfuric acid obtained as a by-product of other industrial processes.

Recycling

The recycling of this acid is increasingly important from the environmental point of view, especially in the main developed countries.

The manufacture of sulfuric acid based on elemental sulfur and pyrite is, of course, relatively sensitive to market conditions, since the acid produced from these materials represents a primary product.

In contrast, when sulfuric acid is a by-product, manufactured as a means of removing waste from another process, the level of its production is not dictated by conditions in the sulfuric acid market, but by market conditions for the primary product.

Clinical effects

-Sulfuric acid is used in industry and in some household cleaning products, such as bathroom cleaners. It is also used in batteries.

-Deliberate ingestion, particularly of highly concentrated products, can cause serious injury and death. These ingestion exposures are rare in the United States, but are common in other parts of the world.

-It is a strong acid that causes tissue damage and protein coagulation. It is corrosive to the skin, eyes, nose, mucous membranes, respiratory tract and gastrointestinal tract, or any tissue with which it comes in contact.

-The severity of the injury is determined by the concentration and duration of contact.

-Lower exposures (concentrations less than 10%) only cause irritation of the skin, upper respiratory tract and gastrointestinal mucosa.

-Respiratory effects of acute inhalation exposure include: irritation of the nose and throat, coughing, sneezing, reflex bronchospasm, dyspnea, and pulmonary edema. Death can occur from sudden circulatory collapse, glottis edema and airway involvement, or acute lung injury.

-Sulfuric acid ingestion may cause immediate epigastric pain, nausea, salivation, and vomiting of mucoid or hemorrhagic material that looks like "coffee grounds." Occasionally vomiting of fresh blood is observed.

-Ingestion of concentrated sulfuric acid can cause corrosion of the esophagus, necrosis and perforation of the esophagus or stomach, especially in the pylorus. Occasionally, injury to the small intestine is seen. Later complications can include stenosis and fistula formation. After ingestion, metabolic acidosis may develop.

-Severe skin burns can occur with necrosis and scarring. These can be fatal if a large enough area of ​​the body surface is affected.

-The eye is especially sensitive to corrosion injury. Irritation, tearing, and conjunctivitis can develop even with low concentrations of sulfuric acid. Splashes with sulfuric acid in high concentrations cause: corneal burns, loss of vision and occasionally perforation of the globe.

-Chronic exposure may be associated with changes in lung function, chronic bronchitis, conjunctivitis, emphysema, frequent respiratory infections, gastritis, erosion of tooth enamel, and possibly cancer of the respiratory tract.

Safety and Risks

Hazard statements of the Globally Harmonized System of Classification and Labeling of Chemicals (GHS)

The Globally Harmonized System of Classification and Labeling of Chemicals (GHS) is an internationally agreed system, created by the United Nations designed to replace the various classification and labeling standards used in different countries by using consistent criteria at the global level (Nations Nations, 2015).

The hazard classes (and their corresponding GHS chapter), the classification and labeling standards, and the recommendations for sulfuric acid are as follows (European Chemicals Agency, 2017; United Nations, 2015; PubChem, 2017):

GHS hazard classes

H303: May be harmful if swallowed (PubChem, 2017).

H314: Causes severe skin burns and eye damage (PubChem, 2017).

H318: Causes serious eye damage (PubChem, 2017).

H330: Fatal by inhalation (PubChem, 2017).

H370: Causes damage to organs (PubChem, 2017).

H372: Causes damage to organs through prolonged or repeated exposure (PubChem, 2017).

H402: Harmful to aquatic life (PubChem, 2017).

Precautionary statement codes

P260, P264, P270, P271, P273, P280, P284, P301 + P330 + P331, P303 + P361 + P353, P304 + P340, P305 + P351 + P338, P307 + P311, P310, P312, P314, P320, P321, P363, P403 + P233, P405, and P501 (PubChem, 2017).

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