17. RAW MATERIALS FOR TAR-ACID RESINS

The first tar-acid resins were made from phenol and formaldehyde. As a result this group of resins is frequently spoken of as phenolic resins. This is true despite the fact that coal-tar acids other than phenol, particularly the cresols and xylenols, are used in large volume today.

The term coal-tar acids is applied to certain organic compounds either obtained from or known to be present in coal tar. Probably the best known is phenol or carbolic acid, produced in large quantities in the United States and abroad. Others of commercial importance are ortho, meta, and para cresol and the xylenols. All of these are definite chemical compounds available as such or in mixture with other tar acids. Cresylic acid is a term widely used in commerce for almost any mixture of tar acids. Formerly it was used to designate a mixture of ortho, meta, and para cresols in the proportions in which they are found in coal tar. The higher boiling tar acids (listed in table56below the xylenols) have little or no commercial importance at this time.

Table56lists the tar acids by commercial name, chemical name, boiling point of the pure compound, and average percentage present in coal tar. Boiling point is shown because the several tariff classifications covering tar acids under the acts of 1922 and 1930 (pars. 27 and 1651) depend upon distillation range (boiling points) for classification and assessment of duty (see pp.119and124).

Table 56.—Tar acids: Commercial and chemical names, boiling points and average percentage present in coal tar

Source: Ellis, Chemistry of Synthetic Resins.

Since the quantities of tar acids present in coal tar are small (see table56), it is usually uneconomical to distill coal tar completely unless the creosote oil and pitch can be marketed profitably. Beginning in 1936, production of tar acids in the United States was increased by the practice of topping. Topping is the recovery in tar distillation of the light fractions only, leaving a residual thin enough to flow through the pipe lines to supply fuel to open hearth and other type furnaces. These light fractions contain the naphthalene and tar acids. The practice permits recovery of these products from tar to be used as fuel, thus providing a new alternative intermediate between the two older practices of either complete distillation or using the undistilled tar as fuel.

In the United States, consumption of most of the tar acids greatly exceeds the quantities extracted from tar, necessitating large production of synthetic phenol and importation of large quantities of the cresols and xylenols. The calculated amount of these tar acids present in the tar produced in this country vastly exceeds present day requirements. Table57shows the approximate amounts of the several tar acids contained in the coal tar produced and distilled in 1936. These estimates are based on a 1936 production of coal tar of 560,385,578 gallons and a distillation of 292,140,249 gallons. The calculation is made by using the percentage of tar acids in tar shown in table56and converting the gallons to pounds in accordance with the specific weights of the pure tar acids. Actual production of all tar acids in the United States in 1936 was about 29 million pounds.

Table 57.—Tar acids available in coal tar produced and distilled in 1936

1560,385,578 gallons.2292,140,249 gallons.

1560,385,578 gallons.

2292,140,249 gallons.

The several tar acids are discussed in detail under the following heads:

(a) Phenol.

(b) The cresols, xylenols, and cresylic acid.

Phenol (commonly called carbolic acid) is a tar acid obtained from two sources: (a) From one of the fractions recovered in the distillation of coal tar, a byproduct resulting from the manufacture of coke in byproduct ovens, and from the manufacture of coal gas; (b) from benzol, by synthesis. The second source has been the more important since 1923. Phenol, when pure, is a colorless substanceof interlaced or separate needle-shaped crystals with a characteristic aromatic odor. It is corrosive to the skin and to mucous membrane. When pure it is water white, melts at about 42° C., and boils at about 181.5° C. It was discovered in 1834 by Runge.

Phenol is used today chiefly as a component of tar-acid resins. It is also widely used as an antiseptic and disinfectant, in the manufacture of explosives (picric acid and ammonium picrate), and as an intermediate for certain dyes and medicinals. Salicylic acid and its derivatives—aspirin, salol, and methyl salicylate (artificial oil of wintergreen)—are important medicinals made from phenol. Another use is in the extraction of lubricating oils. The relative importance of these various uses in recent years is indicated by table58, which gives the estimated domestic consumption of phenol by uses in 1936-37.

Table 58.—Phenol: Estimated consumption by industries, 1936-37

Prior to 1914 United States production of phenol averaged about a million pounds a year and was entirely the natural product obtained from distillates of coal tar. Increased demand during the World War was met by several synthetic phenol processes, which utilized in part the vast quantities of benzol available. Our output of phenol reached 64 million pounds in 1917 and 107 million pounds in 1918. When the armistice was signed stocks on hand in the United States totaled between 35 million and 40 million pounds, estimated at three times the annual consumption at that time for nonmilitary purposes. As a result the price dropped from about 45 cents to 6 cents a pound, and the synthetic plants were closed.

The limited quantities of phenol available to synthetic resin makers prior to and during the World War caused much concern to that industry and led to research work for substitutes, work resulting in the development of many new and modified types of resins in which tar acids other than phenol were used. But notwithstanding the use of these other tar acids the increased demand for synthetic resins used up the accumulated stocks of phenol sooner than was expected.

Of the phenol produced in the United States from 1919 through 1923 a large part was natural phenol but the rapid increase in demand and the improvement of processes for synthetic phenol had by 1923 resulted in four companies beginning production of the synthetic article. The rapid increase in output, from about 3 million pounds in 1923 to about 15 million pounds in 1925, was almost entirely in synthetic phenol. Since then a large part of the domestic production has continued to be synthetic, although the production of natural phenol since 1935 has been about four times that of 1929.

Adequate quantities of coal tar are usually available to produce sufficient natural phenol to meet a substantial part of our requirements, if it were all recovered, but the quantity actually produced is determined in part by the demand for other coal-tar products, and in part by the value of the tar as fuel. More than 50 percent of the tar produced has been burned as fuel, principally at the coke ovens or nearby steel mills.

The domestic production and sales of phenol, natural and synthetic combined, are shown in table59.

Table 59.—Phenol: United States production and sales, in specified years, 1918-37

Source: Compiled from annual reports of the Tariff Commission on dyes and other synthetic organic chemicals in the United States.

Grades produced for resins.—Increased production of phenol in recent years is largely due to the demand from makers of synthetic resins. A number of grades are regularly produced for this purpose, though it is believed that the technical grade is the principal one used in resins. The several grades are as follows:

(1) USP.—Either natural or synthetic. This grade contains not less than 98 percent phenol.

(2) Technical.—Various grades containing from 80 to 95 percent phenol, of which the two most important are 82-84 percent and 90-92 percent.

(3) Mixtures.—Containing from 30 percent to 80 percent phenol and the remainder of the isomeric cresols.

Producers.—Natural phenol is obtained in the distillation of coal tar and to a smaller extent in the purification of ammonia liquors in coke and gas plants. In 1937 there were four producers of natural phenol with plants located at Philadelphia, Pa., Follansbee, W. Va., Indianapolis, Ind., and Pittsburgh, Pa. All these are tar distillers recovering creosote oil, pitch, cresylic acid, naphthalene, and other crudes from coal tar.

Synthetic phenol is made from benzene, either by sulfonation followed by alkaline fusion, or by chlorination and subsequent heatingunder pressure with caustic soda. It is produced in large quantities by two firms, one at Midland, Mich., and the other at St. Louis, Mo. A third producer is building a plant at North Tonawanda, N. Y., using a process recently developed in Germany. Operation of this unit will probably start late in 1938.

Natural phenol is recovered in practically all European countries and in Japan. Germany and the United Kingdom are the principal producers and have also been the leading exporters. Synthetic phenol was made in Germany as early as 1900, and during the World War. Plants for synthetic phenol recently installed are now in operation in Germany, Great Britain, Belgium, and Italy.

Table60shows the average annual world production of phenol in recent years by countries. Half of the total was produced in the United States.

Table 60.—Phenol: Estimated average annual production, by countries, 1933-35

Source: Consular reports.

In the United Kingdom, where tar distillation is a well developed and highly organized industry, large quantities of gas-works tar, rich in phenol and other tar acids, are available. Prior to the World War the United Kingdom was the principal source of phenol, and of the other products of tar distillation. During the war several synthetic processes of commercial importance were developed, but they were discontinued after its close. A new synthetic unit has recently been installed in England and is now in operation. Increasing consumption of phenol in synthetic resins during the last decade, particularly in the last several years, has changed the United Kingdom from an exporter to an importer of phenol. Estimated consumption of phenol in the United Kingdom is given as 20 million pounds annually—principally in synthetic resins, and in lesser quantities in dyes, intermediates, antiseptics, and disinfectants.

In Germany the phenol recovered in 1936 amounted to about 20 million pounds, and recently three commercial units have been installed for the production of synthetic phenol, one with a reported daily output of 11,000 pounds.

Natural phenol is also recovered in Belgium, France, the Netherlands, Czechoslovakia, Poland, Italy, and Spain. Synthetic phenol has recently been produced for the first time in Belgium and Italy. The quantities normally produced in these countries are small and are supplemented by imports from Great Britain and Germany.

The production of phenol in Japan has increased rapidly and has been sufficient since 1930 to meet domestic requirements. The estimated output increased from 300,000 pounds in 1927 to more than 3 million pounds annually in recent years. The Miike Dyestuffs Works is reported to be producing synthetic phenol.

Rates of duty.—Prior to September 6, 1916, phenol was imported free of duty. Since that date it has been dutiable at the various rates shown in table61. Under the act of 1930 the rate of duty is 3½ cents per pound and 20 percent ad valorem on the American selling price (the wholesale price of a similar competitive article manufactured in the United States).[21]

Table 61.—Phenol: Rates of duty upon imports into the United States, 1916-37

1As defined in subdivision (f) of section 402, title IV, act of 1922.2As defined in subdivision (d) of section 402, title IV, act of 1922.3As defined in subsection (g) of section 402, title IV, act of 1930.4As defined in subsection (e) of section 402, title IV, act of 1930.

1As defined in subdivision (f) of section 402, title IV, act of 1922.

2As defined in subdivision (d) of section 402, title IV, act of 1922.

3As defined in subsection (g) of section 402, title IV, act of 1930.

4As defined in subsection (e) of section 402, title IV, act of 1930.

Import statistics.—Imports for consumption are shown in tables62and63. Table62shows imports of phenol or carbolic acid and table63imports of “all distillates of tars yielding below 190° C. an amount of tar acids equal to or more than 5 percent.” Imports under the latter classification prior to 1928 were probably chiefly phenol. Phenol imports consist entirely of the natural product.

Table 62.—Phenol: United States imports for consumption, 1910-37

1Fiscal year.215 percent ad valorem and 2½ cents per pound effective Sept. 9, 1916.355 percent ad valorem and 7 cents per pound, effective Sept. 22, 1922.4Ad valorem based on American selling price or United States value under acts of 1922 and 1930.5Ad valorem reduced to 40 percent effective Sept. 22, 1924.6Duty reduced to 20 percent ad valorem and 3½ cents per pound effective Nov. 30, 1927.7Preliminary.Source: Foreign Commerce and Navigation of the United States.

1Fiscal year.

215 percent ad valorem and 2½ cents per pound effective Sept. 9, 1916.

355 percent ad valorem and 7 cents per pound, effective Sept. 22, 1922.

4Ad valorem based on American selling price or United States value under acts of 1922 and 1930.

5Ad valorem reduced to 40 percent effective Sept. 22, 1924.

6Duty reduced to 20 percent ad valorem and 3½ cents per pound effective Nov. 30, 1927.

7Preliminary.

Source: Foreign Commerce and Navigation of the United States.

Table 63.—All distillates of tar yielding below 190° C. an amount of tar acids equal to or more than 5 percent: United States imports for consumption, 1918-37

155 percent ad valorem and 7 cents per pound, effective Sept. 22, 1922.2Ad valorem based on American selling price or United States value under acts of 1922 and 1930.3Ad valorem reduced to 40 percent, effective Sept. 22, 1924.4Duty reduced to 20 percent ad valorem and 3½ cents per pound, effective Nov. 30, 1927.Source: Foreign Commerce and Navigation of the United States.

155 percent ad valorem and 7 cents per pound, effective Sept. 22, 1922.

2Ad valorem based on American selling price or United States value under acts of 1922 and 1930.

3Ad valorem reduced to 40 percent, effective Sept. 22, 1924.

4Duty reduced to 20 percent ad valorem and 3½ cents per pound, effective Nov. 30, 1927.

Source: Foreign Commerce and Navigation of the United States.

Exports of phenol have not been separately shown in official statistics since 1924. In that year they went chiefly to Panama, Japan, Cuba, and Mexico. Table64shows exports from 1918 to 1924, inclusive, as furnished by the Department of Commerce.

Table 64.—Phenol: United States exports, 1918-24

Source: Commerce and Navigation of the United States.

Appreciable quantities of phenol have been exported in recent years to Japan and China, and to Great Britain and other European countries. Export statistics, collected by the U. S. Tariff Commission from the several domestic producers, show the following quantities exported in recent years.

Table 65.—Phenol: United States exports, 1934-36

Source: Data obtained by the U. S. Tariff Commission through questionnaires.

In 1934, the principal destinations in order of importance were China, Italy, and Canada; in 1935 Germany, China, Japan, and Belgium; and in 1936 China, Belgium, and the Netherlands.

Before the World War our average annual consumption of phenol was 5 million pounds, of which about 80 percent was imported from Great Britain and Germany. These countries produced phenol in excess of their consumption, and phenol was on the free list in the United States.

In September 1916 phenol became dutiable. The demand was increasing rapidly because of the use of phenol in the manufacture of picric acid, an explosive. To meet the wartime demand at home and abroad large scale production of synthetic phenol sprang up in the United States. But the end of the war not only shut off the largest part of the demand but left the producers with large stocks on hand. The price dropped sharply and the production of synthetic phenol ceased.

Since 1922 there has been a gradually increasing demand for phenol in the United States, chiefly for use in the manufacture of synthetic resins, and production has increased to meet this demand as shown in table66.

Table 66.—Phenol: United States production, imports, exports, and apparent consumption in specified years, 1918-37

1From table59.2From tables62and63.3From tables64and65.4Production plus imports minus exports.5Not calculated because of importance of stocks on hand.6Not available.7Not available because of absence of export figures. Exports probably negligible up to 1929; substantial in 1933.

1From table59.

2From tables62and63.

3From tables64and65.

4Production plus imports minus exports.

5Not calculated because of importance of stocks on hand.

6Not available.

7Not available because of absence of export figures. Exports probably negligible up to 1929; substantial in 1933.

The manufacture of synthetic phenol was revived about 1923. Imports were quite small as compared with production, especially after 1927. At first this was probably due primarily to the protection given by the duty which had been increased in 1922.[22]But with the increase in volume of production in the United States the price decreased and since 1933 the United States producers have enjoyed a substantial export business. It may therefore be doubted that in recent years there would have been any substantial imports even if phenol had been free of duty.

Reference to table56, page109, will show that, as distillation of coal tar proceeds and the temperature of distillation is increased, the phenol fraction is followed in order by the three cresols and then by the six xylenols. Each of these tar acids is a definite chemical compound with definite physical properties. Consideration of them as raw materials for synthetic resins is complicated by the fact that they are generally used in mixtures and that the commercial term, cresylic acid, applied to many of these mixtures has no definite relationship to the precise chemical terminology. Yet since the term cresylic acid is so widely used in commerce, since the tariff provides for imports under that name, and since the statistics available are in part in terms of cresylic acid and in part in terms of cresols and xylenols it is impossible to present the complete picture on the basis of the correct chemical terminology.

The cresols.—The cresols are isomeric tar acids obtained from coal tar by fractional distillation. Their combined content averages about 1 percent of domestic coal tar. The total cresol content is divided in about the following proportions: 40 percent metacresol, 35 percentorthocresol, and 25 percent paracresol. The cresols are marketed in a number of types and grades including mixtures of ortho, meta, and para; mixtures of meta and para; separated ortho, meta, and para; and also in mixtures with phenol and the xylenols.

Metacresol(chemically, 3-methyl phenol) is a colorless to yellow liquid with a phenol-like odor. When pure, it melts at 11° C., boils at 202.8° C., and has a specific gravity of 1.03. It is used in the manufacture of synthetic resins, photographic developers, explosives, disinfectant soaps, paint and varnish removers, to remove ink from newsprint, to soften and reclaim rubber, and in intermediates for dyes and perfume materials.

Orthocresol(chemically, 2-methyl phenol) is a colorless, crystalline product with a phenol-like odor, melting at 30° C., boiling at 190.8° C., and having a specific gravity of 1.04. It is used in the manufacture of coumarin (flavor), antiseptics, disinfectants, and fumigants. It is not used to any extent in synthetic resins.

Paracresol(chemically, 4-methyl phenol) is a colorless, crystalline substance with a phenol-like odor, melting at 35° C., boiling at 201.8° C., and having a specific gravity of 1.03. It is used in the manufacture of intermediates, dyes, disinfectants, and fumigants, in medicine, and in mixture with metacresol in synthetic resins. Domestic production of synthetic paracresol was announced early in 1938 by Swann & Co., Birmingham, Ala.

Metaparacresolis a combination of approximately 60 percent meta and 40 percent para cresol obtained in the fractional distillation of mixed cresols. The ortho isomer is distilled off, leaving a residue of metaparacresol. It is widely used in the manufacture of synthetic resins.

Cresol.—The term cresol used without further qualification indicates a mixture of the three isomers in substantially the same proportions in which they are found in coal tar. The United States Pharmacopoeia describes cresol, a mixture of isomeric cresols obtained from coal tar, as a colorless or yellowish to brownish-yellow or a pinkish, highly refractive liquid, becoming darker with age and on exposure to light. It is widely used in synthetic resins, antiseptics and disinfectants, and in medicine.

The xylenols.—Shortly after the original patents on Bakelite resins expired extensive research was begun for raw materials that would give different properties to the resultant resins. This work led to a study of the high-boiling tar acids, and methods of recovery for some of them were commercially developed. Among those obtained from coal tar are the six isomeric xylenols, methylethyl phenol, and one of the trimethyl phenols (see table56). Coal tar contains about 0.2 percent xylenols and 0.5 percent other high-boiling tar acids.

The principal uses for these products have been in the preparation of high-phenol coefficient disinfectants, and recently in the replacement of phenol and cresols in synthetic resins. It was found, for example, that 3: 5 xylenol reacts with formaldehyde faster than either metacresol or phenol. Numerous patents have been granted on the use of these high-boiling acids in the production of synthetic resins.

The xylenols, when pure, are colorless, crystalline substances boiling between 211° and 225° C. They are usually marketed in mixtures containing from 50 to 80 percent xylenols and 20 to 50 percentcresols. There is commercial production of at least one of the separated xylenols (3: 5). An appreciable part of our imports of crude cresylic acid and of our production of cresylic acid contains high percentages of the xylenols.

Other high-boiling tar acids.—The other high-boiling tar acids are ortho ethylphenol, meta ethylphenol, para ethylphenol, methyl ethylphenol, and the three isomeric trimethyl phenols. Several of these have been isolated from coal tar. All of them, when pure, are crystalline compounds with boiling points ranging between 206° and 235° C. There has been little, if any, commercial production of this group up to this time. They are known, however, to have very high phenol coefficients, a property which would make them suitable for use in disinfectants. Little is known as yet concerning their application in synthetic resins.

Cresylic acid.—Cresylic acid is a generic term now applied to mixtures of tar acids in widely varying proportions. As defined in the literature and as formerly used in commerce the term identified a mixture of ortho, meta, and para cresols in the proportions in which they occur in coal tar. This proportion is approximately 40 percent metacresol, 35 percent orthocresol, and 25 percent paracresol. But in recent years the designation cresylic acid has been applied to all sorts of mixtures of tar acids boiling above 190° C. Practically every maker of synthetic resins, antiseptics, and disinfectants has his own specifications for cresylic acid; it may be any mixture in almost any proportions of the three cresols, the six isomeric xylenols, and the higher boiling tar acids. Imports of crude cresylic acid are understood to be largely xylenol mixtures containing low percentages of the cresols. This loose application of cresylic acid in recent years is due to the increased commercial application of the high-boiling tar acids, especially the xylenols.

Under the Tariff Act of 1930 refined cresylic acid, that having a purity of 75 percent or more, is dutiable under paragraph 27 at 3½ cents per pound and 20 percent ad valorem based on American selling price or United States value; while crude cresylic acid, that having a purity of less than 75 percent, is free under paragraph 1651. The provision in paragraph 27 reads, “cresylic acid which on being subjected to distillation yields in the portion distilling below two hundred and fifteen degrees centigrade, a quantity of tar acids equal to or more than 75 per centum of the original distillate.” Under this provision cresylic acid may include an endless number of combinations of tar acids and may or may not contain any of the isomeric cresols. Of the 17 or more tar acids known to exist in coal tar (see table56), only 8 have boiling points above 215° C. It would seem to be more accurate and more in line with present day usage to have the tariff drop the designation cresylic acid in favor of more definite terms based on composition, such as cresols and cresol mixes, xylenol and xylenol mixes, etc.

About 60 percent of our consumption of cresylic acid is in synthetic resins and the remainder in the manufacture of insecticides, antiseptics, disinfectants, and other coal-tar products, such as intermediates for dyes, plasticizers for nitrocellulose, etc.

The cresols.—There is large production of cresol, metaparacresol, and orthocresol in the United States. Commercial production of paracresol was reported for the first time in 1934, and of metacresol in 1935.

Statistics of domestic production and sales are publishable only for the year 1934 because of the small number of producers. The output in that year is shown in table67. Production has increased appreciably since then.

Table 67.—Meta, ortho, and para cresols: United States production and sales, 1934

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