Sulfuric Acid

General background:

Sulfuric acid is a chemical compound H2SO4 that is colorless, odorless, extremely corrosive, oily liquid and is sometimes called oil of vitriol. Balanced equation: H2SO4  H2 + SO42−


Uses of sulfuric acid:

1. Serves as electrolyte in lead-acid storage battery.
a. Acid for this use, containing about 33% H2SO4 and with specific gravity about 1.25, is often called battery acid.
b. Commonly used in motor vehicles.
2. Crucial in the production of fertilizers.
a. Examples: Superphosphate of lime (CaCO3) and ammonium sulfate (NH4)2SO4, which is formed when rock phosphate is treated with sulfuric acid.
3. Used to remove oxides and rusts from iron and steel before plating them with tin or zinc.
4. Dehydrating agent to remove water (only for concentrated sulfuric acid).
a. It has a tendency to form hydrates such as H2SO4.H2O, H2SO4.2H2O, etc.
5. Used to dry neutral and acidic gases.
a. Examples: Nitrogen gas N2, Oxygen gas O2, Carbon dioxide CO2, Sulfur dioxide SO2 etc.
6. Remove water from carbohydrates and some other organic compounds which contain oxygen and hydrogen.
a. Examples: React with sucrose or cane sugar C12H22O11(s) to produce a spongy mass of carbon:
i. C12H22O11(s) + 11H2SO4 12C(s) + 11H2SO4.H2O
7. Used in production of nitroglycerine, an inorganic ester and organic nitrate.
a. Used as an explosive.
b. Used as a vasodilator that is a substance that dilates blood vessels and can be used in the treatment of certain types of heart disease.
8. Used in petroleum refining to wash impurities out of gasoline and other refinery products.
9. Used to make rayon.
10. Use in the manufacturing of other chemicals.
a. Examples: hydrochloric acid, nitric acid, sulfate salts, synthetic detergents, dyes and pigments, explosives, and drugs.


Manufacture of sulfuric acid:

General background: There are two major processes in the manufacturing and production of sulfuric acid, namely the Lead Chamber Process and the Lead Contact Process, with the Lead Chamber Process being the older of the two. The Lead Chamber Process is used to produce much of the acid used to make fertilizers and produces a relatively dilute acid of 62%–78% sulfuric acid whereas the contact process produces a much purer, more concentrated acid but requires purer raw materials and the use of expensive catalysts. Both processes are similar in the oxidized of sulfur dioxide and the dissolving of sulfur dioxide in water.

1. Lead Chamber Process

History

In 1746 John Roebuck developed the Lead Chamber Process for the manufacture of sulfuric acid. Prior to this time, sulfuric acid had been produced in glass bottles several pounds at a time. But the lead chamber process could produce sulfuric acid by the ton. However, this manufacturing process was a batch process and resulted in the consumption of potassium nitrate. In 1835, Joseph Gay-Lussac improved the manufacturing process.


Process

John Roebuck’s Lead Chamber Process:
a) In the original lead chamber process, sulfur and potassium nitrate are ignited in a room lined with lead foil. Potassium nitrate, or saltpeter is an oxidizing agent oxidizes the sulfur to sulfur trioxide.
a. Chemical equation: 6 KNO3(s) + 7 S(s) -----> 3 K2S + 6 NO(g) + 4 SO3(g)
b) The floor of the room was covered with water. When the sulfur trioxide reacted with the water, sulfuric acid was produced.
a. SO3(g) + H2O(l) -----> H2SO4(aq)

Joseph Gay-Lussac’s improvement:
a) A process for recovering the nitrogen in nitrogen monoxide and recycling it to replace the saltpeter as a source of nitrogen was invented.
a. Chemical equation: 4 NO(g) + O2(g) + 2 H2O(l) -----> 4 HNO2(l)
b. Chemical equation: 4 HNO2(l) + 2 SO2(g) -----> 2 H2SO4(aq) + 4 NO(g)
b) Reduced the dependence on expensive saltpeter and sharply reduced nitrogen monoxide emissions.

Lead Chamber Process after improvements:
a) Hot sulfur dioxide gas enters the bottom of a reactor called a Glover tower where it is washed with nitrous vitriol (sulfuric acid with nitric oxide and nitrogen dioxide dissolved in it) and mixed with nitric oxide and nitrogen dioxide gases.
a. Two functions of the Glover tower:
i. Concentration of the chamber acid (62% to 68% H2SO4) is achieved by the hot gases entering the tower which evaporate water from the acid. Some of the sulfur dioxide is oxidized to sulfur trioxide and dissolved in the acid wash to form tower acid or Glover acid (about 78% H2SO4).
ii. Dissolved nitrogen oxides are stripped from the acid and carried with the gas out of the Glover tower into the lead chambers.
b) From the Glover tower, a mixture of gases – including sulfur dioxide and trioxide, nitrogen oxides, nitrogen, oxygen, and steam – is transferred to a lead-lined chamber where it is reacted with more water.
a. Lead-lined chamber: A large, boxlike room or an enclosure in the form of a truncated cone.
b. Sulfuric acid condenses on the walls and collects on the floor of the chamber.
c. The gases pass through each in succession of the three to twelve chambers in a series.
d. The acid produced in the chambers, often called chamber acid or fertilizer acid, contains 62% to 68% H2SO4.
e. Chemical equation: 2 SO2 + O2 + 2 H2O -----> 2 H2SO4
c) After the gases have passed through the chambers they are passed into a reactor called the Gay-Lussac tower where they are washed with cooled concentrated acid from the Glover tower.
a. The nitrogen oxides and unreacted sulfur dioxide dissolve in the acid to form the nitrous vitriol used in the Glover tower.
b. The waste gases exiting the Guy-Lussac tower are usually discharged into the atmosphere.
d) Product acid at a concentration of 78% H2SO4 is drawn from the cooled acid stream that is circulated from the Glover tower to the Guy-Lussac tower. Nitrogen losses are made up with nitric acid which is added to the Glover tower.



2. Contact Process: A process involving the catalytic oxidation of sulfur dioxide, SO2, to sulfur trioxide, SO3.

History

The first observation of a “contact” or heterogeneous catalytic reaction seems to have been made by Edmund Davy in 1817. He noted that heated platinum wire introduced into a mixture of oxygen or air with hydrogen, carbon monoxide, or ethylene became hotter and finally glowed with rapid combustion of the mixture. In 1831 Peregrine Phillips, a vinegar manufacturer in Bristol, England, patented a new process in British Patent No. 6096. The patent described the instantaneous union of sulfur dioxide with atmospheric oxygen when passing the mixture over platinum which had been heated to a strong yellow heat, with the sulfur trioxide formed rapidly absorbed when contacted with water to form sulfuric acid. In spite of the obvious advantages of the contact process over chamber plants for the production of high strength sulfuric acid and oleum used for dyes and nitrocellulose (smokeless powder), the commercial development of the process was extremely slow. Chemical technology of the time, especially involving catalytic reactions, was limited.

Process

a) Solid sulfur, S(s), is burned in air to form sulfur dioxide gas, SO2.
a. Chemical equation: S(s) + O2(g)  SO2(g)
b) The gases are mixed with more air then cleaned by electrostatic precipitation to remove any particulate matter.
c) The mixture of sulfur dioxide and air is heated to 450oC and subjected to a pressure of 101.3 - 202.6 kPa (1 -2 atmospheres) in the presence of a catalyst, which is often platinum on a silica/ asbestos carrier/ vanadium pentoxide on a silica carrier (vanadium oxide) to produce sulfur trioxide, SO3(g), with a yield of 98%.
a. Chemical equation: 2SO2(g) + O2(g)  2SO3(g)
d) Any unreacted gases from the above reaction are recycled back into the above reaction.
e) The sulfur trioxide is cooled and passed through two towers.
a. In the first tower, sulfur trioxide, SO3(g) is dissolved in 98% sulfuric acid, H2SO4, to produce disulfuric acid or pyrosulfuric acid, also known as fuming sulfuric acid or oleum, H2S2O7.
i. Chemical equation: SO3(g) + H2SO4 ------> H2S2O7
ii. This is done because when water is added directly to sulfur trioxide to produce sulfuric acid.
iii. Chemical equation: SO3(g) + H2O(l) -----> H2SO4(l)
iv. The reaction is slow and tends to form a mist in which the particles refuse to coalesce (bond).
v. Note: This cannot be done by simply adding water to the sulphur trioxide – the reaction is too uncontrollable that it creates a fog of sulphuric acid.
b. Water is added to the disulfuric acid, H2S2O7, to produce sulfuric acid, H2SO4
c. Chemical equation: H2S2O7(l) + H2O(l) -----> 2H2SO4(l)
d. Note: This can then be reacted safely with water to produce concentrated sulphuric acid - twice as much as you originally used to make the fuming sulphuric acid.



References:
http://www.ausetute.com.au/sulfacid.html
http://www.infoplease.com/ce6/sci/A0861350.html
http://www.infoplease.com/ce6/sci/A0861351.html
http://www.chemguide.co.uk/physical/equilibria/contact.html
www.aiche-cf.org/Clearwater/2008/Paper2/8.2.7.pdf
http://en.wikipedia.org/wiki/Sulfuric_acid
http://web.fccj.org/~ethall/h2so4/h2so4.htm
http://scifun.chem.wisc.edu/chemweek/sulf&top/sulf&top.html
http://www.factmonster.com/ce6/sci/A0861351.html
http://www.factmonster.com/ce6/sci/A0861350.html
http://www.buzzle.com/articles/sulfuric-acid-uses.html