Chemical of

 the Week

SULFURIC ACID

Sulfuric acid is the product of the U.S. chemical industry produced in largest quantity in terms of mass. About 40 million tons are produced annually. There are two major processes used in the production of H2SO4, lead chamber process and contact process. The lead-chamber process is the older of the two processes, and its product is aqueous sulfuric acid containing 62% to 78% H2SO4. The contact process yields pure sulfuric acid. In both processes, sulfur dioxide, SO2, is oxidized to sulfur trioxide, SO3, and the SO3 is dissolved in water.

Sulfur dioxide is obtained by burning sulfur,

S(s) + O2(g) SO2(g)

by roasting pyrite (iron sulfide) or other metal sulfides prior to smelting,

4 FeS(s) + 7 O2(g) 2 Fe2O3(s) + 4 SO2(g)

or by burning hydrogen sulfide,

2 H2S(g) + 3 O2(g) 2 SO2(g) + 2 H2O(g)

The sulfur dioxide is oxidized to sulfur trioxide catalytically.

2 SO2(g) + O2(g) catalyst 2 SO3(g)

Without the catalyst the oxidation of SO2 is quite slow. In the old lead-chamber process, the catalyst is nitrogen dioxide gas. In the contact process, the catalyst is vanadium(V) oxide, V2O5, mixed with an alkali metal sulfate. The mixture is supported on small silica beads, and at the high temperature inside the reactor, the mixture is a liquid. The product SO3 is dissolved in 98% sulfuric acid. The dissolved SO3 reacts with the 2% water, forming H2SO4.

SO3(g) + H2O(l) H2SO4 H2SO4(l)

Pure sulfuric acid is a colorless, odorless, oily liquid. It freezes at 10.5C. It fumes when heated, because some of the H2SO4 decomposes to H2O and SO3. The H2O is retained in the liquid, while SO3 gas is released. Therefore, the concentration of H2SO4 decreases, reaching a concentration of 98.33%. This solution boils at 338C and is the material sold as "concentrated sulfuric acid." Concentrated sulfuric acid, which is 18M, has a strong affinity for water and is sometimes used as a drying agent. It can be used to chemically remove water from many compounds. It dehydrates sucrose (table sugar), C12H22O11, leaving a spongy black mass of carbon and diluted sulfuric acid. Concentrated sulfuric acid reacts similarly with skin, paper, and other animal and plant matter. When it is mixed with water, a highly exothermic reaction occurs, and the energy released can be enough to heat the mixture to boiling. Therefore, concentrated sulfuric acid must be diluted by adding the acid slowly to cold water while the mixture is stirred to dissipate the heat.

Sulfuric acid has a wide range of uses and plays a part in the production of nearly all manufactured goods. About 65% of the H2SO4 produced annually is used in the production of agricultural fertilizers.



TOP 20 CHEMICALS

This list includes the most recent figures for the United States chemical industry. These figures are obtained from government, trade associations reports, and industry estimates. The list includes chemically homogeneous finished products. It does not include minerals which do not require processing, such as salt and sulfur, and petrochemical feedstocks, such as ethane and butane, which are considered products of oil companies.

2000 RANK
(by mass)
CHEMICAL 2000 PRODUCTION
(in 109 kg)
FORMULA PRODUCTION
(in moles)
RANK
(by moles)
1 Sulfuric acid 39.62      
2 Ethylene 25.15      
3 Lime 20.12      
4 Phosphoric acid 16.16      
5 Ammonia 15.03      
6 Propylene 14.45      
7 Chlorine 12.01      
8 Sodium hydroxide 10.99      
9 Sodium carbonate 10.21      
10 Ethylene chloride 9.92      
11 Nitric acid 7.99      
12 Ammonium nitrate 7.49      
13 Urea 6.96      
14 Ethylbenzene 5.97      
15 Styrene

5.41

     
16 Hydrogen chloride 4.34      
17 Ethylene oxide 3.87      
18 Cumene 3.74      
19 Ammonium sulfate 2.60      
20 1,3-Butadiene 2.01      
 
Compiled from Chemical and Engineering News, June 25, 2001.

EXERCISE: For the first ten chemicals in the table, write the formula of the substance in the fourth column. (Look up in the textbook the formulas you don't know. Ethylene dichloride is the trade name for 1,2-dichloroethane.) Then, calculate the number of moles of each of the top ten chemicals. Record these amounts in the fifth column. Then, rank the top ten in order of moles produced, writing this rank in the last column.