Indian Journal of Chemical Technology Vol. 9, May 2002, pp. 263-271

Educator

The history of bromine from discovery to commodity

Jaime Wisniak*

Department of Chemical Engineering, Ben-Gurion University of the Negev, Beer-Sheva, Israel 84105

The discovery of bromine represents one of the first experimental evidences that elements could be grouped in families of similar properties. Transformation of the new element and its derivatives into a commercial reality had to wait until automobiles begun to be mass-produced. The pattern end use of bromine has reflected the changes in social appreciation of environmental protection and safety. From a strong initial use as gasoline additive and agricultural chemical, the end uses are changing drastically into flame-retardants and sanitary uses. From a strictly initial European industrial activity it has turned into an important chemical activity for the United States, Jordan, and Israel.

Presently, most of the bromine produced in the world is obtained from oil well brines and from the end brines from the Dead Sea. Although iodine and bromine were discovered from the same source, iodine became very rapidly a major chemical commodity while bromine commanded a very modest production until the beginning of the 20th century when car manufacturers started adding ethylene dibromide as a lead scavenger to gasoline.

Today, more than 80% of bromine world consumption comes from brines processed in the United States and Israel (Table 1) using a steam blowing-out process.

Discovery of bromine Bromine was discovered in 1826 by Antoine­

Jerome Balard (1802-1876) a young student of pharmacy at the Faculte des Sciences in Montpellier. Balard observed that after treating a solution of the cinders of Fucus (an algae that contains iodine) that contained starch, with aqueous chlorine, there appeared two coloured zones, an upper blue one indicating the presence of iodine and a lower one of intense yellow colour. Balard had previously observed the appearance of the same yellow-orange colour when treating the mother liquid of marsh brines with aqueous chlorine. He had also noticed that the tint was more intense the more concentrated the brine was and that the appearance of the hue was always accompanied by a particular odor1.2.

Balard proceeded to separate the source of the colour and study its properties. His results led him to

*For correspondence (Fax: 972-8-6472916; E-mail: wisniak@bgumail.bgu .ac.il)

believe that he had discovered a new element, which on the advice of Joseph Anglada (1775-1833) he named, on first instance, muride (from the Latin Muria, brine; in Greek, almuris, almuridos) because it reflected its origin besides being euphonic.

Balard's results were presented to the Academie des Sciences as a memoir entitled "Sur une substance particuliere contenue dans I' eau de la mer" (About a particular substance present in sea water)!. Jean Baptiste Andre Dumas (1800-1884), the permanent secretary of the Academie, commented that the new element had been discovered in the provinces by a young student of pharmacy, not by an act of hazard but as the legitimate fruit of scientific research3

. The memoir presented to the Academie had 13 parts and constituted a chemical and physical study of the element. It described the procedure for extracting bromine from seawater, the physical properties of the element, of hydromuridic acid (HBr), its salts, the reactions with chlorine, iodine, phosphorus, sulphur, carbon, and certain organic substances. In this memoir the name muride was changed to brome, as suggested by Joseph-Louis Gay-Lussac (1778-1850).

Balard concluded his paper indicating that he had also identified bromine in seawater and bitterns, marine plants and animals, and certain mineral waters obtained from the Pyrenees.

Balard's paper was followed by a report prepared by a committee appointed by the Academie des Sciences to verify Balard's claim to have discovered another substance similar to iodine and chlorine. The commission certified Balard's claims as well as his experimental results favorably and suggested, however, that the new element be called brome

Educator

(bromine) from the Greek word bromos (bad smell) rather than muride, which was Balard's name for it4 .

Bromine was the third of the halogen family to be discovered and separated, after chlorine in 1774 and iodine in 181l.

Bromine sources Bromine does not appear in nature as the free

element, it is always combined with other elements. It is not abundant in quantity in nature although it is well distributed in rocks, soils, waters, plants, animal ti ssues, and foodstuff. The most common salts are the bromides, organic and inorganic. A few substances such as seaweeds, sponges and corals, contain it in relatively large quantities. The largest reservoirs are underground waters from certain deep oil-well brines, mineral springs, and the Dead Sea. The richest brines (besides the Dead Sea) are found in Arkansas and Michigan (United States) with bromide contents ranging from 2 to 5 giL.

Bromine is the third in the halogen group and accompanies frequently the most abundant of the group, chlorine. The total bromine content in the crust of the earth has been estimated to be 1015_10 16 tons or 0.00016% bromine; present in rocks. There are only a few bromine containing minerals, all silver ores such as bromyrite (AgBr), embolite [(Ag(Cl, Br)), and iodobromite [Ag(Br, Cl, I)]. The bromine from weathered rocks are dissolved and transported into the hydrosphere. They concentrate in the oceans and may move back into the lithosphere through deposition from parts of the sea separated from the main water­body of the ocean5

.

Bromine is usually found at very low concentration in fresh waters, but in seawater it is generally considered to be a major element. Its concentration in full-strength seawater is 65 mg/L or 0.81 IlM, and essentially all of that is in the form of bromide ions. The chlorine:bromine ratio in ocean water fluctuates a little around the value 292. Bromine in seawater is in the state of bromide ion .

Bromide ions are activated by the bromoper­oxidases enzymes that use hydrogen peroxide to activate bromide into a reactive form. The activated bromide then attacks and attaches into an organic molecule. Many of these reactions are highly specific so that bromine ends up at certain special positions in special molecules. Some of the enzymes use a vanadium cofactor and other an iron cofactor.

Brominated indole alkaloids have been isolated from the marine tunicate Pseudodistoma arborescens;

264

Indian J. Chern. Techno!.. May 2002

brominated molecules have been isolated from the marine tunicate Eudisoma album. Brominated phospholipids and fatty acids have been found in the sea anemone Stiochactis helianthus. A significant fraction of the horny core of black corals consists of brominated and iodinated molecules with these two elements accounting for several per cent of the total mass of this part of the coral. Sponges are probably the best known of the sea species with bromine derivatives such as brominated tyrosine derivatives, brominated alkaloids and guanosidine derivatives, indole alkaloids, benzcyciooctane. The brominated fatty acids seem to play the role of toxic and predator deterrent6

•

Dibromotyrosine is found in corals, algae and sponges. Dibromoindigo, the well-known Tyrian purple, is found in the body of two species of snails, Murex brandaris and Murex purpureus.

Oil field brines contain variable amounts of iodine (present as iodide) and bromine depending on the location and strata tapped. For example, in California, the iodine content may vary from 10 to 160 ppm. Analyses show that the bromine content of these brines is roughly twice that of iodine. This is in markedly contrast with seawater that contains approximately 65 ppm of bromine but less than 0.1 ppm of iodine.

Like other substances, bromine is part of a natural cycle involving the atmosphere, the oceans, and the ground, with most bromine in nature being present in the ocean and derived water deposits . At the beginning it is probable that the primitive soil contained bromine salts, which because of their solubility were little by little carried by rivers, rains, and floods into the sea. The principal source of atmospheric bromine is methyl bromide produced in large quantities by marine biota like macroalgae (seaweed) and plankton. Bromide in the atmosphere is returned to the soil by rain. The bromine-containing gases cross the sea-air interface and enter the atmosphere where their bromine is released into the so-called reactive bromine pool by the action of sunlight and other chemicals. Similar to fluorine and chlorine, the chemistry of bromine in the atmosphere is extremely complex and plays a part in the destruction of ozone (see below).

The most concentrated natural reservoir of bromine is the Dead Sea, a hypersaline lake located at the deepest part of the Jordan-Arava rift, in the East African Rift Valley . It is the world saltiest natural lake, with an average salinity of 280 g/kg compared

Wisniak: History of Bromine

with the ocean's average of 35 grams. It is unique in the nature and amount of the ions it contains. It is very concentrated in cr and also contains an abnormally high amount of B(. The CI: Br ratio is 35: 1, only about one third that of the tributary springs and rivers, and only one eighth that of the ocean. The total amount of bromine now present in the Dead Sea is estimated at about 900 million tons.

An interesting comparison is between the Dead Sea brines and the nitrate fields (caliche) present in the Atacama Desert in the North of Chile. The Dead Sea is rich in magnesium, chlorides and bromides and has very large chlorine to bromine ratio. The Chilean deposits are very rich in sodium nitrate and a number of other unusual salts such as iodates, perchlorates, chromates, and dichromate, and have an exceptionally high iodinelbromine ratio of greater that 10 to 1, which is the reverse of the relative abundance of these elements in other saline deposits and in rock, water, and air. The origin of the salt composition of both sites is unclear, particularly, the reason for their unusual ratios Cl: Br and I: Br7.

Bentor8 has elaborated extensively on the possible origins of the unusual salt composition of the Dead Sea. According to him, existence of organic material may lead to bromine enrichment. It is well known that most oil waters carry considerable amount of bromine and iodine. Since the Br:I ratio in the Dead Sea water is larger than 105, it is almost certain that the origin of the bromine is not organic. Consequently, it is most likely that bromine in the Dead Sea originated from the concentration of fossil residual salt brines, which formed during the Tertiary.

Bromine is at least one order of magnitude more abundant that iodine in nearly all inorganic materials, including the ocean and the thermal springs associated with the volcanism in the northern Chilean Andes, whereas it occurs only as traces « 0.01 %) in the nitrate deposits. In as much as iodine and bromine have similar chemical and physical properties, it would be expected that they become concentrated in the nitrate deposits in proportions similar to those of the source material.

Development of the manufacturing process The bromine industry had its origin in 1865 when

Adolf Frank (1834-1916) successfully isolated the element from the mother liquor remaining after the crystallization of potassium chloride from the Stassfurt carnallite deposits (which contained about 2.5 kg bromine/ton). Originally, he obtained bromine

Educator

by a batch process in which a brine containing about 3 g brominelL and heated to 60°C, was treated with manganese ore and sulphuric acid, according to the following reaction:

The original Frank process had the disadvantage of requiring a mineral acid (sulphuric) and a solid phase (Mn02), which made it unsuitable for continuous production. It had also a very low productivity, about 2.5 kg of bromine per batch. Chlorate (soluble in water) was tested as a replacement for Mn02, without much successs.

In 1877 Frank patented an improved continuous process9 in which he substituted the oxidizing agent (Mn02) with chlorine, acting on Stassfurt brine containing (per cent per weight) KCl, 1.4%; MgS04 5%, MgCIz 34.8%; NaCI 1.2%, and MgBr2 0.3 to 0.5%. The concentrated mother-liquor, heated to 80°C, was trickled down a 3 to 4 meter high tower packed with earthenware balls. Chlorine entered the tower from below, and reacted with the solution, liberating the bromine and forming magnesIUm chloride, according to the reactions

... (2)

.. . (3)

Other reactions took place too

.. . (4)

... (5)

Live steam was then introduced and bromine, some chlorine (most of it combined with bromine in the form of bromine chloride), and water vapour, distilled off. Any bromine left in the liquor was expelled by steam.

The vapours were condensed and the two phases, aqueous bromine and bromine highly contaminated with chlorine, were collected and separated by decantation. The gas leaving the condenser was led into a small tower packed with moist iron fillings in which any further bromine was absorbed. The crude bromine phase contained about 2.5% of chlorine and had to be refined to contain less than 0.2% of the latter.

265

Educator

It can be seen that the process patented by Frank represents, in a way, a return of his original method to that developed by Balard to prepare bromine.

The intermediate step of preparing FeBr2 was eventually replaced by a continuous distillation step in a special tower designed by Konrad Kubierschkyl o. ll.

Oxidation-reactions (2) and (3) are possible because chlorine has a higher reduction potential (+1.356 V) than bromine (1.065 V). Thermodynamic calculations show that the difference of about 290 m V in the oxidation potential of the two couples CI2/Cr and Br21B( is enough for driving Eq. 2 to almost complete conversion. Some bromine is always left non-oxidized to ensure full use of chlorine in its reaction with bromine. However, the residence time of the reactants in the tower is not sufficient and therefore the liberated bromine contains a few per cent of unreacted chlorine, probably in the form of bromine chloride, BrCI [see Eqs (4 and 5»).

During the early development of bromine production electrolysis was tested as an alternative to chlorine, to oxidize bromides. Electrochemical oxidation of bromide is essentially similar to that of chloride. The theoretical amounts of current per equivalent of the halogen are the same but the theoretical amount of energy required is smaller for bromine due to the fact that the decomposition voltage is lower by 0.29 volt. Two industrial processes were introduced in Germany at about the beginning of the 20th century. The Wtinsche process l2

was based on the use of membranes to assure a better current efficiency; the carbon cathodes were separated from the carbon anodes by porous clay cylinders, which allowed ion diffusion. The cathode reaction produced hydrogen and magnesium hydroxide, which created a major problem of clogging the membranes5

.

The Kossuth process l3 used a cell with bipolar carbon electrodes shaped in the form of plates and each served on one side as cathode and on the other as anode. Magnesium hydroxide was dislodged from the cathodes by switching the current periodically.

Despite this advantage the Kossuth process required 3000 kW/ ton bromine against 2000 kW needed by the Wtinsche process. In the long run both process were abandoned because they were less economical than the ones using chlorine.

As mentioned before, bromine occurs in the form of bromide in seawater and in natural brine deposits and the different processes that have evolved continue to be based on modification of Balard's original process. Actual processes may be considered formed

266

Indian J. Chern. Techno!., May 2002

by four operations (1) oxidation of bromide to bromine; (2) stripping bromine from the aqueous solution; (3) separation of bromine from the vapor: and (4) purification of the bromine. Most of the differences between the various bromine manufacturing processes are in the stripping step.

The standard processes use steam or air for stripping. Steam is used when the concentration of bromine in brine is greater than 1000 ppm and has the advantage that bromine can be condensed directly from the steam. Air is used when seawater is the source of bromine because very large volumes of stripping gas are needed and steam would be too expensive. When ai r is used the bromine needs to be trapped in an alkaline or reducing solution to concentrate it5

.

The hot or steaming-out process, as it is applied now with certain modifications, was developed by KubierschkyIO. It consists of simultaneous chlorination and steam blowing. The brine is preheated before its introduction into a tower, usually to 75-80°C, and heated inside the tower by means of live steam to near boiling. A small amount of the steam supplied is used to distil the liberated bromine continuously. Heating of the brine to near boiling reduces the partial pressure of bromine (and bromine chloride) in the effluent brine to nearly zero and in this way improves stripping of the brine of its bromine content.

In the blowing process, invented by Herbert Henry Dow (1866-1930) in 1889 for Midland, Michigan, brines 14 the bromine in the exiting air mixture was stripped with an alkaline carbonate solution. The Dow process is able to recover 95% of the bromine content of the natural brines. Dow was able to make bromide production, (the process did not produce bromine) a technologically and financial success. In the following 30 years the Dow process was improved to a level at which his company made one-half of the total 650 tons produced then in the United States. The total world production at this time did not exceed 2,500 ton/year and probably would not have been much greater today had it not been for the selection of ethylene dibromide as a lead scavenger in automobile engines.

Both Kubierschky and Dow may be considered the developers of the two technologies used nowadays to produce bromine (blowing out and steaming-out).

11 We will now describe the processes used to produce bromine from seawater, oil well brines, and from the Dead Sea.

Wisniak: History of Bromine

From seawater'5 - Nowadays bromine is extracted from sources in which the concentration of bromide ion may be as small as 65 mglL or as much as 14 gIL.

As mentioned before, the low concentration of bromine in seawater requires using the blowing-out process where air is used to strip bromine from the solution. Before stripping, enough sulphuric acid is added to the seawater to reduce the pH to 3-3.5. Seawater is slightly alkaline (PH = 7.2) so that addition of an acid is necessary to obtain a satisfactory yield of bromine by oxidation with chlorine. At the pH of seawater the liberated bromine hydrolyzes to hypobromous acid and bromide. Bromine traps bromine as the tribromide ion and little bromine are released.

The exiting gas in the blowing-out process is passed through an absorption tower were it meets a recirculating sodium carbonate solution to form a solution of sodium bromide and bromate according to the reaction

3Na 2C03 + 3Br2 -7 5NaBr + NaBr03 + 3C0 2 t ... (6)

At proper intervals the strong bromide-bromate solution is transferred to the next stage where it is treated with sulphuric acid to liberate the bromine, according to

NaBr03 +5NaBr+3H 2S0 4 -73Br2 +3Na 2S0 4

+ 3H 20 ... (7)

The free bromine vapors are then steamed out of the acidified solution and condensed into pure liquid bromine.

In a modification of the process, which was used for time at Freeport, Texas, halogens blown from the sea were reduced with S02 and absorbed in water

... (8)

BrCl -7 +S02 + 2H 20 -7 HBr + HCl + H 2S0 4

... (9)

The resulting aqueous solution of mixed acids was treated with chlorine in a conventional steam-out tower and the bromine recovered. The remaining mixture of HCI and H2S04 was used for acidifying the raw ocean water.

Educator

Nowadays, bromine IS purified to market specifications by treatment with sulphuric acid followed by fractional distillation. It is especially important to reduce the water content to less than 30 ppm to prevent corrosion of metal transportation and storage containers.

From the Dead Sea-According to Picard'6, at the beginning of the 20th century the German commercial attache in Turkey proposed to several German capitalists the establishment of a chemical plant in the north end of the Dead Sea. His suggestion was based on the expected large growth in the use of bromine in the manufacture of ethylene dibromide as a lead scavenger. General Motors Corporation requested in 1924 from the German Potash Company (which produced bromine from the Zechstein evaporates) to explore the possibility of utilizing Dead Sea brine for the production of bromine. However, the project was discarded because of the remoteness of the area at that time and the lack of proper infrastructure for industry : In the next step it was the Palestine Potash Company that established in 1931, a small plant to extract bromine from the residual brines using the steaming­out process.

The process used at the Dead Sea utilizes the end brine from the carnallite pans, which contain 11-12 gIL of bromine in the form of bromide salts. This is the highest concentration of bromine found in the world and compares favourably with other sources of bromine such as salt brines in the United States (3-4 gIL) and seawater (70 ppm).

The end brine is sent to the top of the blowing-out packed tower where it flows counter current to live steam and chlorine and bromine is liberated according to Eq (2). The brine is usually heated to near-boiling point to reduce the partial pressure of bromine to nearly zero.

The exit top stream contains excess steam and impure bromine. After cooling it separates into two phases, the bromine phase is distilled to remove the dissolved chlorine and then dried with concentrated sulphuric acid. The water content must be less than 30 ppm to prevent corrosion of metal transportation and storage containers.

Owing to the large halide concentration in the brine, no hydrolysis of the free bromine occurs, but complex formation leading to ions such as Br2Cr and BrCl2 - results in the incomplete removal of the bromine during the steaming out process, and the effluent brine contains about 01-0.2 gIL of elementary bromine 17

.

267

Educator

From oil well brines- In the 1950s bromine was discovered in south Arkansas brines, which became the only significant source of bromine in the United States. Bromine is present in abnormally high concentrations in salt brines of the Smackover formation (Jurassic) in south-central Arkansas. Bromine concentration ranges from 4000 to 4600 ppm, or about 70 times the bromine concentration of normal ocean water. Between 1.5 to 1.8 pounds of bromine are recovered from every barrel of brine processed. Typical brines received at an Arkansas bromine plant have 3-5 gIL bromide, 200-2150 giL chloride, 0.15-0.20 gIL ammonia, 0.1-0.3 giL bromide, 0.01-0.02 gIL iodide, and additionally may contain some dissolved organics. The bromide­containing brine is first treated to remove natural gas, crude oil, and hydrogen sulphide prior to introduction into the contact tower where it is steam-blown according to the same procedure described for Dead Sea brines.

Patterns of use and historical development of the market

It seems appropriate to start the analysis of bromine's market development by quoting from the eulogy that Jean Baptiste Andre Dumas (1800-1884) delivered at the Academie des Sciences, three years after Balard' s death (March 30, 1876). Dumas asked3

:

what is the benefit of having discovered bromine? Dumas answered the question by stating that "shortly after bromine's discovery two different fields of chemistry found it to be indispensable for their chores : (a) The art of image fixation that was based on the chemical action of light on certain combinations containing silver. Chlorine, bromine, and iodine formed with silver white compounds that were coloured by the action of light. A compound of silver and chlorine yielded a black colour that the physician Jacques Alexandre Cesar Charles (1746-1823) had used for reproducing the gross silhouette of objects. Using silver iodide Jacques Daguerre (1787-1851) succeeded in fixing images using a camera, images that the public considered as astounding scientific marvel. Use of silver chloride required that the objects to be reproduced be exposed to the sun for several ours; silver iodine many minutes. With silver bromide the process took place in fraction of a second. It was thus possible to obtain instant images of the passage of a heavenly body, a galloping horse, Venus penetrating the disk of Apollon, the fugitive expression of a face, or a rapid light play. (b) The

268

Indian J. Chern . Techno!. , May 2002

second application was in the area of organic analysis and synthesis. Up to that time chemical analysis were usually done by combustion, generating water, tar, combustible gases, and a solid residue of charcoal or coke. The new derivatives of bromine would make these tasks much easier."

A third argument was related to basic chemistry. The discovery of bromine constituted the departing point between two epochs of chemistry. Before, the elements were considered independent entities, with no relations among them. Now it was seen that they arranged themselves in natural families and in those families that were incomplete it was possible to predict not only the existence of the unknown elements but also their properties.

From Dumas' arguments it could be inferred that development of bromine' s market was a sure thing, as it had occurred with iodine, which was extracted from the same raw material. Unfortunately, Dumas' was too optimistic, the needs for bromine developed very slowly and it took almost a century, until World War I (WWI), to achieve the status of a major chemical commodity.

Discovery of bromine and invention of photography were made at about the same time. In 1840 the use of silver bromide was introduced in photography and through this bromine became a small-scale industrial chemical. Bromine requirements followed closely the development of photography science and techniques. Improvement of the photographic technique, progress from a plate to film, motion picture, and X-ray photography, resulted in substantial increases in the requirements for silver bromide. The first medical use was in 1857 when bromides were used for the treatment of epilepsy. Another early and significant application of bromine was in the preparation of bromine-containing dyes such as eosin (tetrabromofluorescein).

As mentioned before, up to WWI the bromine production was rather small, 500 tons in the period 1865-1890, 800 tons in the period 1891-1900, 9000 tons between 1901 and 1911, and 2500 ton in the year 1912 alone'S. The main client was the pharmaceutical industry, followed by intermediates for the organic industry and photography. All the requirements were completely met by German and American facilities.

The bromine industry in the United States developed a little differently from that of Germany. The first plant in Freeport, Pennsylvania, was operated in the years 1846-1856. The total output was of the same order as the German production, a few

Wisniak: History of Bromine

hundreds of tons yearly . All of this was produced using manganese oxide and steaming out until Dow introduced electrolytic oxidation, which was later replaced by chlorine5

.

WWI and the years thereafter brought a considerable development of the automobile industry, especially in the United States. Automobiles became more numerous and their engines more powerful. With the increasing compression ratio of the engine' s cylinders, knocking became an acute problem that limited further development. Several additives were found to reduce the problem, but they were either expensive (iodine) or they had a very low efficiency (aniline). In 1922 Charles F. Kettering and Thomas Midgley demonstrated that tetraethyllead was an excellent and cheap antiknock additive, although it deposited lead oxides in the engine. It was then found that ethylene dichloride, ethylene dibromide, and mixtures of both compounds transformed the lead oxide deposit into lead halides that were sufficiently volatile to be expelled together with the hot exhaust gases. In 1925 production had already increased to 6,000 ton/yearI8.

Eventually ethylene dichloride was discarded in favour of pure ethylene dibromide and resulted in a tremendous increase in the demand for bromine; at one time 80% of all bromine was used to produce ethylene dibromide. This situation continued until 1974 when the Environmental Protection Agency (EPA) mandated the phase down of leaded gasolines. In spite of this, in 1981 the use of ethylene dibromide still amounted to 35 to 40% of the United States total consumption of bromine.

The development of antiknock compounds and the conflict between public health, environment, and commercial interests are very well described in a short paper by Hilleman 19. Auto firms initially considered using either ethanol or tetraethyllead. Ethanol was considered the additive of choice but it had the drawback that it could not be patented. Sales of ethanol would not be as profitable as sales of the lead derivative and General Motors Company, owned 36% by DuPont, chose tetraethyllead.

The first step in the diversification of bromine uses was made in the 1930s when ethylene dibromide and ethyl bromide were found to be efficient grain fumigants. Subsequently both materials as well as dibromochloropropane were found to be good soil fumigants. The use of bromine compounds in the baking and brewing industries and, more recently, in flame extinguishing and flameproofing, in shrink

Educator

proofing of wool and disinfection and catalysis represent further examples of diversification5

.

The high-density characteristics of bromine compounds are advantageously applied in hydraulic fluids, gage fluids, ore flotation , and drilling fluids. Calcium bromide, 53% in aqueous solution and having a density of l.70 g/mL, was introduced in 1972 as a dense fluid product for use as oil well packs and completion fluid.

Today, bromine has a wide range of uses in the chemical and allied industries. Bromine-containing chemicals are used in swimming pools and industrial cooling towers to control algae, bacteria and odours. The main bromine compounds used in biocide applications are sodium bromide and bromochlorodimethylhydantoin. Methyl bromide is a highly effective soil fumigant and fumigant for stored grain and produce. Historically methyl bromide has been used to treat insect and nematode infestations in high value crops, including strawberries, tomatoes, melons and tobacco. Some bromine-containing pesticides are used in the production or storage of food crops.

A high percentage of the initial use of bromine lies in the production of intermediates, which are frequently marketed as such. A break down of world bromine consumption for 1999 suggests that 27% was used in flame retardants, 15% in the manufacture of ethylene dibromide, 15% in agricultural chemicals, 10% in well drilling fluids, and 5% for water treatment. Other minor uses are the bromides of potassium, sodium, calcium, etc., as sedatives, potassium bromate as additive to wheat flour to improve baking characteristics, inks and colorants, photographic chemicals, laboratory reagents, motor fuels , and lubricants.

The fastest growing application of bromine is as the building block for some of the most effective flame­retarding agents available to the plastics industry today. They are used to protect against the risk of accidental fire in such as computers, televisions, radios, video, and in products made of textiles and woods. Brominated compounds are also used to improve the fire safety of foam padding used in upholstered furniture, in the plastic coating on electrical wire, and even in carpeting. Brominated flame-retardants, as all flame-retardants , act to decrease the risk of fire by reducing the risk that an object will ignite. The inhibitory action of brominated compounds is though to involve both the bromine atom and hydrogen bromide, although the halogen

269

Educator

atom is believed to be the active species. In the late 1950s pentabromobiphenyl oxide was the first aromatic bromine flame retardant to gain commercial significance. Since then the development of new flame retardants has focused on products with increased molecular mass, such as tetrabromobisphenol A (TBBA), decabromodiphenyl oxide (deca DPO), terabromophthalic anhydride, and pol y( tri bromostyrene).

Flame-retardants are of two types: (a) additive­type, which is physically blended into thermoplastic polymers, and (b) the reactive-type, which chemically reacts during the formation of a thermosetting polymer.

Bromine compounds are also used in fire extinguishers.

Total world production stands today at more than 500,000 ton/year, distributed as shown in Table 1. The United States and Israel produce more than 80% of the total.

Environmental impact of bromine and its compounds

Ozone has a critical role in the Earth ' s ecological balance owing to its strong absorption of biologically damaging incoming ultraviolet light21

• It has long been recognized that chlorine can destroy stratospheric ozone, and that the use of chlorofluorocarbons has led to a pronounced increase in the stratospheric chlorine content.

Reactions involving the coupling between chlorine and bromine also contribute to the ozone destruction rate, particularly through the reaction cycle:

CIO + BrO ~ Br + Cl0 2

Indian 1. Chern. Techno!., May 2002

Although the contemporary burden of stratospheric bromine is believed to be largely natural (surface releases of methyl bromide), anthropogenic emissions of b~omine-containing compounds (mainly methyl bromIde and halons) are rapidly increasing. Halons and methyl bromide are scheduled to phase out under the Montreal Protocol, and their rate on increase in the atmosphere has been slowed by a factor of three since 1989. Unlike the CFCs, a complete phase-out of which will not purge these compounds from the atmo~phere for hundreds of years, atmospheric methyl ?romide abundances will drop to background levels in Just a few years following a phase-out, and the potential recovery of the ozone will be almost immediate.

Algae in seawater, ice algae, or phytoplankton, emit brominated organic compounds such as CH)Br, CH2BR2 and CHBr3 that have tropospheric lifetimes from several days to several months.

Methyl bromide is probably the largest reservoir of gaseous bromine in the Earth ' s atmosphere. The World Meteorological Organization estimates that the major sources of methyl bromide are the oceans, fumigation, and biomass burning, and that these contribute respectively 60-160; 20-60, and 10-50 kton/year to the atmosphere22

. It is estimated that five to ten percent of the current loss of stratospheric ozone is attributed to methyl bromide alone23.

Consequently, this compound has been the recent target of aggressive regulation.

Bromine photochemistry is believed to be similar to that of chlorine, except that the reactive forms Br and BrO represent a larger fraction of the budget due to the relative photochemical instability of the reservoirs HBr and BrON02, despite the much lower mixing

Table 1 Crude bromine: World production by country (tons/year)20

270

Country

Azerbaijan

France

China

Israel

Japan

Ukraine

England

United States

TOTAL

1996

2,000

2,024

41 ,400

160,000

\5 ,000

3,500

30,600

227,000

478,374

1997

2,000

1,974

50,100

180,000

20,000

3,000

35,600

247,000

539,674

1998 1999 2000

2,000 2,000 2,000

1,950 2,000 2,000

40,000 45 ,000 45 ,000

185,000 185,000 \85,000

20,000 20,000 20,000

3,000 3,000 3,000

30,000 28,000 30,000

230,000 239,000 229,000

511,950 524,000 512,600

Wisniak: History of Bromine

ratio of only a few ppt of bromine. Bromine concentration in the stratotosphere is 150 times smaller than chlorine concentrations. However, atom for atom, bromine is 10 to 100 more effective than chlorine in destroying ozone. The smaller bond energy in BrO than in CIO, results in the fast reformation of the Br atoms and aggravation of the stratospheric ozone depletion. In addition, there is no stable reservoir for bromine in the stratosphere; HBr and BrN02 are very easily photolyzed so that nearly all of the bromine is in a form than can react with ozone.

Current estimates for the atmospheric lifetime of methyl bromide put it at 0.8-1.7 years and its ozone depletion potential to be about 0.6. However, recent laboratories and field experiments indicate that soil bacteria consume large amounts of methyl bromide. This would reduce the atmospheric lifetime down to the lower limit of 0.8 years and reduce the ozone depletion potential to 0.424

.

References I Balard A J, Ann Chim Phys, 32 (1826) 337. 2 Wisniak J, Educ Quim, (200 1) submitted. 3 Dumas M J -B, Memoire.l' de IAcademie des Sciences [2], 41

(1879) Iv.

Educator

4 Vauquelin L N, Thenard L J & Gay Lussac J L, Ann Chim Phys, 32 (1825) 382.

5 Jolles Z E, Bromine and its Compounds (Academic Press, New York) 1966.

6 Faulkner D J, Tetrahedron~ 33 (1977) 1421. 7 Wisniak J, The Dead Sea - A Living Pool of Chemicals,

Indian J Chem Technol , 9 (2002) 79. 8 Bentor Y K, Geochim Cosmochim Acta, 25 (1961) 239. 9 Frank A, Ger Pat, 2251, September 20, 1877.

10 Kubierschky K, Ger Pat, 103644, May 23 , 1897. 11 Kubierschky K, Kolonnenapparat, Zeit Chem

Apparatenkunde, 3 (1908) 212. 12 Wilnsche A, Ger Pat, 140274, January 18, 1902. 13 Kossuth H, Ger Pat, 103644, May 23,1897. 14 Dow Chemical Co, US Pat, 460 370 (1891). 15 Stewart L C, Ind Eng Chem, 26 (1934) 361. 16 Picard L Y, Econ Forum, 11 (1954) 10. l7 Epstein J A, Hydrometallurgy, 2 (1976) 1. 18 DeLong, Ind Eng Chem, 18 (1926) 425. 19 Hilleman, B, Chem & Eng News, (2000) 29. 20 U S Geological Survey, Mineral Commodity Summaries,

Washington, DC January 2001. 21 Solomon, S, Nature, 347 (1990) 347. 22 Khalil M A K, Rasmussen R A & Gunawardena R. J

Geophys Res, 98 (1993) 2887. 23 Mana S & Andreae M 0, Science, 263 (1994) 1255.

24 Shorter J H, Kolb C E, Crill PM, Kerwin R A, Talbot R W, Hiner ME & Harriss R C, Nature, 377 (1995) 717.

271