SULFUR. I11 WILLIAM A. CUNNINGHAM, Chemical
Engineen ..
San Anpelo, Texas
0
RDINARY solid sulfur is not "solid sulfur at all in the sense of being homogeneous, but is usually a mixture of at least two modifications, the nature of which depends on its previous history. Solid sulfur exists in both crystalline and amorphous forms; the latter is known as plastic or y sulfur, and the two most common crystalline forms are rhombic or or sulfur and monoclinic or B sulfur. Rhombic sulfur is the modification which is stable at ordinary temperatures, and hence all other forms gradually change over to this form. Native sulfur, of which some 36 crystalline varieties have been recognized, is all rhombic sulfur. Monoclinic or p sulfur, which is produced when molten sulfur is allowed to crystallize, exists in two distinct crystallme forms. At ordinary temperatures the usual long needle-like crystals of monoclinic sulfur gradually change over to the stable rhombic forms. The transition point is 96'C. and the transformation is reversible. Rhombic sulfur melts at 112.8°C. while monoclinic sulfur melts at 119.25°C.
Molten sulfur also exists in sev+ different varieties, dependmg primarily upon the temperature. Just above the melting point, say 120°C., it is a brownish-yellow, transparent liquid known as SA. As the temperature is increased the liquid gradually darkens in color; it also becomes more fluid until it reaches about 150°C., above which temperature it rapidly becomes quite viscous. At about 160°C. it is dark red and has the consistency of thick sirup. At this point the sulfur exists in several forms, Sp, SA, ST, and possibly S+. At 230°C. the color has changed to black and the liquid is still very viscous; it is practically all in the form of Sp. Upon further heating the viscosity slowly decreases, but the color remains black and the liquid boils at 444.6"C. This boiling point is very constant at atmospheric pressure, and is one of the calibration points for high-temperature thermometers. All of the above-desaibed changes are reversible, and when boiling sulfur is allowed to cool slowly, it passes through the entire series of color and viscosity changes and will finally solidify as monoclinic sulfur.
Even sulfur vapor is known to exist in several states which are dependent upon the temperature and pressure. Although pure or refined sulfur is a bright yellow, native sulfur may range from a straw yellow to black, depending on the amount of carbonaceous matter present. Massive sulfur is the most predominant form of native sulfur. Some of the most important properties are listed below: Insoluble in water. Insoluble in most acids. Tensile strength approximately 200 pounds per square inch. Heat conductivity only slightly greater than that of cork1.72-2.0 B.t.u. per square foot per hour per 1°F. per inch thichess. Electrical conductivity about the same as hard rubber. Melting point depending on conditions, 112.&119.0°C. (235-246°F.). Ignition temperature-261'C. or 501.S°F. Boiling point-444.BDC.or 832.3'F.
As would be expected from its position in the periodic table, sulfur unites directly with all elements except gold, platinum, and the inert gases. However, it is relatively inert and stable at ordinary temperatures. Sulfur unites with hydrogen and oxygen, forming gaseous hydrogen sulfide and sulfur dioxide, and with carbon to form the liquid carbon bisulfide. I t reacts at ordinary temperatures with all the halogens except iodine. Lithium, potassium, sodium, copper, silv&, and mercury form sulfides at ordinary temperatures, while arsenic, phosphorous, antimony, and bismuth react by simply melting them in sulfur. Magnesium, zinc, cadmium, and aluminum will scarcely react at ordinary temperatures; tin and lead will combine with sulfur at the melting point, but calcium and strontium must be heated to 400°C. before they react. Chromium, tungsten, uranium, iron, cobalt, and nickel are comparatively resistant to sulfur. Sulfur is slowly oxidized in air at.uormal temperatures, forming sulfur dioxide. Most acids do not affect sulfur, though hydrochloric acid in the presence of large quantities of iron will react with' it and concentrated sulfuric acid at 200°C. reacts with it to form sulfur dioxide. Aqueous solutions of the alkali hydroxides react with sulfur to form pentasulfides and thiosulfates. Carbon bisulfide and sulfur monochloride are the best solvents for sulfur, though the latter is seldom used. Other good solvents are benzene, phenol, dichloro-benzene, turpentine, olive oil, linseed oil, toluene, dipheuyl methane, bromo-benzene, naphthalene, chlorinated naphthalene, and the chlorinated diphenyls. Very few people realize that sulfur is used, either directly or indirectly, in the manufacture of approximately one-half of the commodities used by mankind. Table 1, taken from the November, 1930, issue of Chemical Markets, lists some of the iudustries and products in which sulfur is used.
1 2 3 4 5 6 7 8 9 10 11 12 13 14
20 21 22 23 24 25 26 27 28 29
alcohol alum aniline artificial fertilizer% artificial silk (rayon) beltingr binderr bleaching celluloid cements ehernicalr dyer ebooite elastics
,
TABLE l 30 leather 31 liquid fuel 33 lubricants 32 livestock food
food preservative. fumigaofs fungicides glau glue glymzin illumioaots inorganic and organic:acids insecticides laboratory reagent3
34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 60 51 52 53 54 55 56 57 58
matchen medicine metallurgy motor fuel. motion picture film paint. paper paper bleaching petroleum products photography plastic3 poiraos refrigerating ageota rodent exterminaton rubber goodr shoe polish soap
sod; solvents steel pickling and galvanizing rtormge batteries sugar
farming textile3 wafer purification
Of course not all these industries can be classed as "major consumers," but they do show the wide diversity of the uses of sulfur. The consumption of the leading sulfur-using industries in the United States in 1929 is shown in Table 2. Since that time there has been a marked decrease in the total amount of the sulfur used, but the relative amounts used by the various industries has remained about the same. TABLE 2
Lonn Ton,
............................... Fertilizer. and insecticides.. ....................... Pulp and paper.. ................................
Heavy ehemiealr..
Explosive Dyen and Rubber Eleetroehemie~b Fine chemicals.. Paint and varni Food products Miscellaneous ....................................
................................... ,...... ..................................
Total .........................................
560,000 415,000 265,000 67.000 47,000 43.000 23,000 15,000 5.000 5,000 137.000 1,582,000
In addition to this domestic consumption, foreign shipments through the Sulfur Expdrt Corporation totaled 855,500 long tons, during the same time. Approximately 70% of all sulfur sold is used in the manufacture of sulfuric acid, which is a basic necessity in many industries. Sulfuric acid is made by oxidizing sulfur dioxide to sulfur trioxide and then absorbing the latter in water. The sulfur dioxide may be formed by the burning of elemental sulfur or by the roasting of some of the metallic sulfides, usually iron pyrites or "fool's gold" which contains from 42% to 48% sulfur. The use of the latter frequently has the serious disadvantage of requiring an additional source of heat and of enforced disposal of large quantities of waste materials from which the sulfur bas been removed. In some cases however, this waste material is of more value than the sulfur dioxide which it produces. The use of elemental sulfur has the decided advantage of producing its own heat, of burning clean and leaving no waste products, and of being constantly available.
Originally, the oxidation of the sulfur dioxide to sulfur trioxide was accomplished by the chamber process in which an oxide of nitrogen was used as the catalytic agent. However, this process is being gradually replaced by the contact process in which very finely divided platinum, and lately vanadium, is used as a catalyst to bring about the direct oxidation of the sulfur dioxide by atmospheric oxygen. The sulfur trioxide is then combined with water in any desired ratio to form sulfuric acid. The majority of commercial acid is from 90% to 96% sulfuric acid, though it may be obtained as strong as 125y0 acid, based on the content of sulfur trioxide. The latter, known as "fuming sulfuric a c i d or "oleum," is made possible by the fact that sulfur trioxide gas is quite soluble as such in 100% sulfuric acid. Oleum is a powerful oxidizing and dehydrating agent. TABLE 3
Consrrmplian of Sulfur* Acid in :ha UniUd Slolcr d w i n g 1929, in Lag Tons of 50' Boumd Acid. Fertilizers ....................................... 2,360,000 Petroleum refining. ............................... 1,570,000 Chemicals....................................... 820.000 Coal products. ................................... 820,000 Iron and steel. ................................... 770,000 Other metnllurgieal industries.. .................... 625,000 Paints and pigments.. ............................ 215,000 Exolorives ....................................... 195.000 ~ a k o .......................................... n 145:000 Textiles ......................................... 85,000 Mirdlaneoun .................................... 320,000 Total
7,925,000
The largest user of sulfuric acid is the fertilizer industry, which annually consumes some 30% of the total sulfuric acid produced. Practically all the acid thus used is for the treatment of phosphate rock to make the "water-soluble" phosphate which constitutes a large portion of all commercial fertilizers. The treatment is comparatively simple and consists essentially of "cooking" the ground phosphate rock, known as "floats," with sulfuric acid, thus rendering the phosphate available as plant food. The petroleum refining industry is rapidly coming to the front as a user of sulfuric acid. ,Much of the naphthas, gasolines, kerosenes, light burnmg oils, and lubricating oils require treatment with 96% to 98% sulfuric acid to remove certain impurities and to give them the desired color. The quantity of acid used is quite variable, but in most cases the gasolines and lighter oils require from one to eight pounds of acid per barrel and the heavier lubricating stocks from eighteen to sixty-five pounds per barrel. Despite the widespread research work which has beeu done on the acid treating of petroleum products, exact chemical control of the process has never beeu developed. In general, an increase in the quantity of acid used will produce an oil of lighter color. However, to many a refinery superintendent's sorrow, such is not always the case, and "trial and error" methods must still be relied upon to give the desired results. Sulfuric acid is used by the iron and steel industries as a "picMig" agent. All the iron or steel products which are to be galvanized or plated must have the
mill scale or oxide coating removed before entering the plating bath. This is very effectively done by passing the rolled steel plate, the drawn wire, or casting through a dilute sulfuric acid solution to which has been added an inhibitor which permits the acid to dissolve the oxide and leave the metal untouched. The manufacture of nitroglycerin and its products affords an example of an industry in which sulfuric acid enters indirectly. The nitration of the glycerin must be accomplished in the absence of moisture, and yet the reaction itself produces water as one of its end.. products. Consequently, the glycerin is treated with a mixture of 44% nitric acid and 56% sulfuric acid. The nitric acid reacts with the glycerin and the sulfuric acid absorbs the moisture. But not all the sulfur is used in the manufacture of sulfuric acid. A very considerable quantity goes into the manufacture of automobile tires and other rubber articles. The vulcanization of rubber involves the addition of a small amount of sulfur to the soft gum rubber, transforming it into a tough, elastic, wearresisting solid. This phenomenon was discovered and announced independently by Hancock in England, Ludersdorf in Germany, and Charles Goodyear, a "Connecticut Yankee," about 1840, but it was not until about 1900 that the industrial application of the .. discovery began to be realized.
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Very finely divided sulfur is coming into wider use as a fertilizer and as an insecticide. The lime-sulfur spray has become quite renowned as a means of combating the Sau Jose scale. Sulfur, mixed with a small amount of flour as a retaining agent, serves very effectively in the treatment of many plant diseases and in the elimination of insects. Recent investigation by federal and state agricultural agencies has proved that the direct addition of sulfur to many types of soil is quite beneficial. It serves to counteract the alkalinity of the soil, is a plant food in itself, and is a "catalyst" to make other plant foods available. Crops to which sulfur has been particularly beneficial are alfalfa, sweet potatoes, cotton, and tomatoes. There are two commercially important processes for
the manufacture of paper, the sulfite process and the sulfate process, both of which require the use of sulfur in one form or another. The wood paper stock is composed of cellulose, which part is later used to make the paper, and various substances, including resins, which must be removed. The sulfite method utilizes calcium and magnesium sulfite and bisulfite, formed by passing sulfur dioxide into limewater. The sulfate process utilizes sodium sulfate or "salt cake" and is used primarily to make wrapping paper, or kraft paper, from pine woods of the South. At present, the greater part of the sodium sulfate on the market is a by-product of the manufacture of hydrochloric acid, which involves the treating of sodium chloride, or common salt, with sulfuric acid. Although the total sulfur used in the manufacture of explosives amounted to only 67,000 tons in 1929, in times of war the use for this purpose is increased enormously. Sulfur, usually in the form of sulfuric acid, is used in the preparation of nearly all munitions of war, explosives, gases of nearly all sorts, metals to be used for shells and guns, in addition to the uses elsewhere described. So important was the source of sulfur during the World War that the mines of the Freeport Sulphur Company of Bryan Mound were practically taken over by the United States Government. A company of soldiers was stationed there and very rigid restrictions were made and enforced regarding those who should be allowed to enter the vicinity of the mines. All workmen were issued passes and no one was allowed to enter the area without having in his possession an authorized pass. So strict was this regulation that a t one time the general manager of the company was not allowed to enter when he had left his pass a t home. In spite of all precautions one or two attempts were made to destroy the plant but were discovered before any damage was done. As a further assurance that the mining operations should not be stopped, "standby" equipment consisting of boileis, pumps, heaters, etc., in quantities sufficient to build arcomplete new plant was purchased and kept in large tanks of oil to prevent corrosion. There was thus available enough equipment to erect a new plant within a short time in event the one in operation should be destroyed. However, this emergency did not arise, and the machinery was later installed and is now in operation a t Hoskins Mound. In addition to the traditional uses of sulfur, there are many novel and interesting- uses being. - developed by its producers. A mixture of 40% sulfur and 60% sand, by weight, makes --- - an - excellent acid and alkali-resistant "cement." Such a mixture has a very good compressive strength and has a tensile strength of some 400 pounds per square inch. It is being used to line acid tanks, to make sewer pipe, to calk ceramic ware pipe carrying corrosive liquids, to grout in pumps, motors, etc., and in manv other more or less novel wavs. A numb& of new products are being made and new
properties imparted to old products by impregnating porous or semiporous materials with liquid sulfur and then allowing it to solidify. Cured portland cement concrete will absorb approximately 17% by weight of molten sulfur. The resultant product is impervious to moisture, is very resistant to destructive agencies, and is enormously stronger than the original concrete. Tests made by the Bureau of Standards show that the impregnation of cured concrete with molten sulfur increases both compressive and tensile strength from two to ten times over that of the untreated concrete, the percentage of increase of strength being greater in the case of lean mixtures. The increase in compressive strength may be accounted for by the filling of the voids, but the increased tensile strength seems to indicate that there is some chemical action between the set portland cement and the molten sulfur.
Sandstone treated with molten sulfur shows increase in compressive strength of only two or three times that of untreated sandstone. However, the treated stone has excellent heat and electrical insulating properties and makes a good building stone. . Artificial board fabricated from various fibrous materials may be treated with liquid sulfur to make surprisingly strong acid-proof and moisture-proof insulating board. This field is just opening up and promises the future use of a considerable quantity of sulfur as a building material. Other fields are continually being opened up to the use of sulfur, such as the manufacture of objects of art, the preservation of wood by impregnation with molten sulfur, as a possible insulating material, etc. The properties of sulfur are such that its uses will continually increase. The ever-increasing use of sulfur quite naturally brings up the question of the future supply. The three companies operating in Texas have been producing approximately SOYo of the world's sulfur from five mines, two of which are nearing depletion. The Texas Gulf Sulphur Company has practically abandoned its original mine a t Gulf and is now concentrating its operations a t he former has an New Gulf and a t Long Point.
estimated maximum life of forty years at the normal rate of production of 4000 tons per day. No data are available concerning the extent of the deposit at Long Point, but it is reported to be as large as that a t Hoskins Mound. The Freeport Sulphur Company is operating mines at Bryan Mound and at Hoskins Mound, both in Brazoria County. The deposit at Bryan Mound was very recklessly exploited during the World War and now, although there is much sulfur remaining, the supply available by present mining methods can last only a few years longer. Hoskins Mound has an estimated life of from fifteen to twenty years with a daily production of 3000 tons per day. The Duval Sulphur Company which is operating at Palangana Dome, although producing sulfur of a somewhat inferior quality, is reported to have a large reserve supply available. Very little information is available concerning the two proved deposits in Louisiana. The Jefferson Lake O i l Company apparently has a very good deposit at its Iberia Parish mine, and the Freeport Sulphur Company intimates that its deposit in Plaquemines Parish is even better than that of the Texas Gulf Sulphur Company at New Gulf. There are several known deposits of sulfur which are reputed to be rich enough to warrant their exploitation when the demand is sufficiently great. Although there is no official confirmation of the reports, jt is currently "rumored that there are sulfur deposits at Damon Mound and Stratton Ridge in Brazoria County, Texas, and at Vinton Dome in Louisiana. In addition there are several smaller deposits of sulfur scattered around over the country, hut, so far as is known publicly, none of these is sufliciently rich to permit its being mined. The Italian and Japanese mines are comparatively small, and the sulfur supplied by them may be considered negligible in terms of the world demand. The Sicilian mines still have an estimated reserve supply of some 30,000,000 tons in sight. It may be that there is much moie than that which will be available ultimately, but that i s doubtful. Be that as it may, the Sicilian deposit could not supply the world's demand for sulfur at the present rate of consumption for a very long period of time. Thus it appears that while the sulfur deposits now being operated cannot be called inexhaustible there is a potential reserve great enough to meet the demand for many years. The successful exploitation of the newer deposits will depend upon improved mining operations whereby under-water deposits and very deep deposits can be economically obtained. Even though the supply of elemental sulfur should become exhausted, there is no prospect of a shortage of pyrite ores from which both elemental sulfur and sulfuric acid can be produced. The author wishes to express his sincere appreciation to Mr. A. D. Potter, Austin, Texas, who aided in preparing the manuscript, and to Mr. W. T. Lundy, Vice President and General Manager of the Freeport Sulphur Company, who co6perated by furnishing the pictures for this article.
