Sulfuric acid: Pumping up the volume An 18th-century English physicians lead cathedrals helped launch a chemical industry. French chemist J.-L. Gay-Lussac improved the lead chamber process.

NATIONAL LIBRARY OF MEDICINE Sulfuric acid is the workhorse chemical of the industrial world. It is made in greater volume than any other product of the chemical industry. In the United States alone, well over 40 million tons of the colorless, viscous, relatively low-cost liquid are produced each year. Its use is so widespread that during the last half of the 19th century and the first half of the 20th century, fluctuations in its output were considered a good barometer of overall business conditions. It is, moreover, the first chemical to have been made on an industrial scale. The origins of sulfuric acid are lost in the obscurity of aniquity. There is evidence that it was known prior to the 10th century. In the late 15th century, Basilius Valentinus described two ways to prepare sulfuric acid; one was by burning sulfur with potassium nitrate, or saltpeter, and the second was by distilling the acid from a mixture of silica and ferric sulfate (vitriolhence the name oil of vitriol used by alchemists). Until the 18th century, demand for sulfuric acid was slight; small amounts were consumed in preparing nitric and hydrochloric acids for use in treating or assaying nonferrous metals. It was produced, for the most part, by burning sulfur in bell-shaped earthenware vessels, with the resulting sulfur dioxide absorbed in water. In the 17th century, saltpeter and sodium nitrate were found to enhance the reaction; they served as catalysts, unbeknownst to the chemical producers of that time. By the 18th century, wide-necked glass jars replaced the fragile earthenware containers. The 18th century also brought an even more basic change to the process. Glass was expensive and easily broken, and the size of the jars was limited. In 1746, John Roebuck, an English physician, came up with a much better method. In Birmingham, Roebuck built a boxlike chamber from riveted sheets of lead, the only inexpensive metal known at the time that was resistant to sulfuric acid. In such a lead chamber, Roebuck could produce a hundred pounds or more of sulfuric acid at a time, compared with only a few pounds possible in a glass jar. Soon Roebuck established a manufacturing facility near Edinburgh in Scotland. Roebuck mixed sulfur with a small amount of saltpeter on a ladle, ignited it, and placed it on a tray in the lead chamber. Water on the floor of the chamber absorbed the gases. This operation was repeated several times, and then he withdrew the acidulated liquor, which contained about 3545% sulfuric acid. The acid could be concentrated by boiling. Although Roebuck sought to keep his process secret, during the latter part of the 18th century similar plants were put up elsewhere in Britain, as well as in France. By the end of the century, Roebucks Scottish plant consisted of more than 100 chambers (often dubbed lead cathedrals), each about 10 ft square and 12 ft high. The acid was sold for making dyes and hydrochloric and nitric acids; it was also used as a substitute for sour milk by cloth bleachers. Even more important in spurring demand for the acid was the invention by the French surgeon Nicolas Leblanc in 1791 of a process for producing soda ash (sodium carbonate), used in the production of glass, soap, and dyes and for bleaching textiles. The first step of the Leblanc process involves treating sodium chloride (common salt) with sulfuric acid to form salt cake (sodium sulfate) and hydrochloric acid. Because sulfuric acid is difficult to ship, soda ash manufacturers usually established their own acid plants. Gay-Lussacs Towers

The 19th century brought major improvements in lead-chamber units. Blowing supplemental air into a chamber increased production by adding oxygen. In 1827, the French chemist Joseph-Louis Gay-Lussac devised a tower that recovered most of the nitrogen oxide gases formed, thereby reducing consumption of saltpeter. The first Gay-Lussac tower was installed at a plant in France in 1837. But its use was not widespread until John Glover invented a second type of tower, patented in England in 1859, in which the acid was concentrated and more of the nitrogen oxides were recovered. By the 1870s, the GloverGay-Lussac system was used with lead chambers in Britain and throughout Europe. Meanwhile, starting in the 1840s, acid makers had increasingly turned to roasting pyrites (iron and copper sulfide ores) as a source of sulfur dioxide. Most sulfur was mined in Sicily, and the monopoly there kept the price high. Pyrites not only were a less expensive raw material but also could be used to produce iron and copper once their sulfur content had been extracted. In the latter part of the 19th century, the demand for sulfuric acid expanded further as ammonium sulfate (used as a fertilizer) began to be made from ammoniacal liquors formed as a byproduct of gas works. In the 1840s, too, British fertilizer firms started to produce superphosphates by treating phosphorus-rich rocks with sulfuric acid. In Britain, output of the acid nearly tripled between 1860 and 1900 to about 1 million tons. Harrisons Plant

The lead chamber was introduced to the United States when John Harrison, then only 20 years old, set up a plant in Philadelphia in 1793. Harrison had earlier studied chemistry with Joseph Priestley in England. Initially, he made only about 45,000 lb of sulfuric acid a year, but by 1804 his plant was 18 ft high, 18 ft wide, and 50 ft long and could turn out nearly 500,000 lb annually. The company Harrison formed, which also manufactured various salts and paint pigments, remained in business until 1917, when it was sold to DuPont. Other lead-chamber units were put in place in Philadelphia, the New York City area, New England, and Baltimore. In Cincinnati, OH, German immigrant Eugene Grasselli erected the first lead chamber west of the Alleghenies in 1839. Acid produced in a lead chamber cannot be concentrated to greater than 78% purity, even with distillation. This was not a drawback for such heavy-duty applications as making soda ash or fertilizers. But the rise of the German organic dyestuff industry in the 1870s created a demand for stronger acid. A way to prepare concentrated acid had been developed in the 17th century in Saxony. The process began with iron pyrites, which could be converted to a material containing about 50% ferrous sulfate, which in turn could be calcined to form ferric sulfate. Heating in a retort changed the sulfate to ferric oxide and sulfur trioxide. Absorbing the trioxide in water resulted in concentrated sulfuric acid; absorbing it in normal sulfuric acid formed the fuming oil of vitriol needed to produce dyes. It was a complex, difficult process; yields were low and costs were high. Output totaled merely a few tons a year. In the early 19th century, a ton of fuming sulfuric acid cost $100 or more. The German dye makers of the last half of the 19th century were not long saddled with such burdensome costs, however. A rival to the lead-chamber process had been developed that could generate acid that was more concentrated (98100% pure). In 1831, Peregrine Phillips, a British vinegar merchant, patented a method by which sulfur dioxide that had been diluted with air was passed through a heated tube containing finely divided platinum. The sulfur dioxide converted to sulfur trioxide, which was then absorbed in water to form concentrated sulfuric acid. At that time, the demand for such acid was so slight that Phillips catalytic contact process did not make any inroads against the lead-chamber method. But in 1875, a contact-process acid plant was started up at Freiberg in Germany, using lead-chamber sulfuric acid decomposed by heat as a source for pure sulfur dioxide. From the mid-1880s on, the output of acid produced by the contact process grew rapidly. By then, gases from pyrites had replaced sulfuric acid as a source of sulfur dioxide. During the early 20th century in Germany, development of vanadium catalysts to replace platinum encouraged the use of the catalytic contact process. Vanadium is stronger, less expensive, and less likely to have impurities. Stateside Production

Sulfuric acid makers in the United States did not immediately switch to the catalytic contact technique. Until the 1880s, in fact, they had not adopted the GloverGay-Lussac towers or shifted to pyrites, in part because domestic sources were not available at a reasonable price. After the Civil War, though, consumption of sulfuric acid grew, especially for making superphosphate fertilizers and refining petroleum. Output of the acid expanded from 60,000 tons in 1863 to about 700,000 tons in 1890. The first U.S. contact-process plant was built at Mineral Point, WI, in 1899 and used sulfur dioxide from an adjacent zinc smelter. Other, similar facilities quickly followed. By the start of World War I, the annual U.S. output of sulfuric acid, at 4 million tons, led the world. With improvements in design and engineering, production from contact-process plants gradually eclipsed that from lead-chamber plants (where the units were no longer necessarily built as boxlike chambers but as towers). In 1910, about 80% of the sulfuric acid made in Europe and North America came from the chamber process. By 1930, it had dropped below 75%. By 1960, chamber-process acids share of total output was only about 15%. Probably no new chamber-process plants have been built since the 1950s. Meanwhile, an increasing share of the sulfur dioxide used in contact-process plants has come from the off-gases of smelters, waste (spent) sulfuric acid, and other environmentally harmful wastes. These sources have largely replaced pyrites. But whatever the raw material, sulfuric acids world ranking as the volume leader among industrial chemicals remains secure. David M. Kiefer, former assistant managing editor of Chemical & Engineering News until his retirement in 1991, is a consulting editor for Todays Chemist at Work. Send your comments or questions regarding this article to tcaw@acs.org or the Editorial Office 1155 16th St N.W., Washington, DC 20036.