Sulfuric acid manufacture, contact process

Industrial manufacture of sulfuric acid - the Contact process Uses of sulfuric acid Properties of sulfuric acid... 

Sulfuric Acid. Essentially all sulfuric acid manufactured in this industry is produced by the contact process, in which SO2 and oxygen contact each other on the surface of a catalyst (vanadium pentaoxide) to form SO3 gas. Sulfur trioxide gas is added to water to form sulfuric acid. The sulfur dioxide used in the process is produced by burning elemental sulfur in a furnace. 

Figure 2.3 Contact process for sulfuric acid manufacture.

The contact process has evolved to become the method of choice for sulfuric acid manufacture because of the ability of the process to produce stronger acid. 

Fig. 25.9. Schematic flow diagram of a double absorption contact process for sulfuric acid manufacture.

Manufactured in greater amounts than any other chemical, sulfuric acid is usually produced by the contact process, which is described in Chapter 3. About 60% of the sulfuric acid manufactured in the United States is used to produce fertilizers from phosphate rock (see Section 19.3). The other 40% is used in lead storage batteries, in petroleum refining, in steel manufacturing, and for various other purposes in the chemical industry. 

The emission of sulfur dioxide from sulfuric acid plants is strongly reduced with the double contact process. If all the sulfuric acid manufactured in the Federal Republic of Germany were produced by modern plants using the double contact process, the resulting emission of sulfur dioxide would account for only 0.32% of the total emission from human activities. 

In early times hydrogen cyanide was manufactured from beet sugar residues and recovered from coke oven gas. These methods were replaced by the Castner process in which coke and ammonia were combined with Hquid sodium to form sodium cyanide. If hydrogen cyanide was desired, the sodium cyanide was contacted with an acid, usually sulfuric acid, to Hberate hydrogen cyanide gas, which was condensed for use. This process has since been supplanted by large-scale plants, using catalytic synthesis from ammonia and hydrocarbons. 

Miles, F. D., The Manufacture of Sulfuric Acid by the Contact Process, Gurney Jackson, London, 1925. 

N2(g) + 3H2(g) 2NH3(g) AH° = —92 kj/mol Because the reaction is exothermic, heat is released as the reaction proceeds. Le Chatelier s principle predicts that the yield of ammonia is greater at lower temperatures. Just as in the contact process for manufacturing sulfuric acid, however, high yield is not the only important factor. The rate of reaction for ammonia synthesis is too slow at low temperatures. 

We begin our discussion with what is by far the largest volume chemical produced in the United States sulfuric acid. It is normally manufactured at about twice the amount of any other chemical and is a leading economic indicator of the strength of many industrialized nations. Since about 80% of all sulfuric acid is made by the contact process which involves oxidation of sulfur, we will examine this raw material in detail. The average per capita consumption of sulfur in the United States is a staggering 135 Ib/yr. 

The contact process was invented by Phillips in England in 1831 but was not used commercially until many years later. Today 99% of all sulfuric acid is manufactured by this method. It was developed mainly because of the demand for stronger acid. All new contact plants use interpass absorption, also known as double absorption or double catalysis. This process will be described in detail in Fig. 2.3. 

Late 1800s The lead chamber process for manufacturing sulfuric acid was prevalent in this period. Arsenic was a common contaminant in the pyrites used as a source of sulfur for this process. Now the cleaner contact process is used and most of the raw material is elemental sulfur. 

Sulfuric acid is manufactured by two processes namely, the chamber process and the contact process. The chamber process was discovered in 1746 and was used to produce sulfuric acid for over a century. This process was replaced hy the contact process which has a lower production cost and yields a more concentrated acid needed for most industrial applications. The chamber process is obsolete now but for historical interest it is outlined below. 

Sulfur trioxide is produced as an intermediate in manufacturing sulfuric acid by the contact process (See Sulfuric Acid). The process involves catalytic oxidation of sulfur dioxide to trioxide. 

Dermal/Ocular Effects. No skin lesions or dermatitis were reported in an early review of the dermatological problems associated with the manufacture of coumarone-indene resin (a polymer made from 2,3-benzofuran and indene) however, the manufacturing process essentially prevented contact with monomers (Schwartz 1936), so the significance of these negative findings is questionable. Workers continuously exposed to wood varnished with coumarone-indene resin developed dermatitis, but the sensitivity was attributed to the sulfuric acids in the varnish (Schwartz 1936). 

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