Animal Fats and Oils in Industry

Daniel Swern, Waldo C. Ault, A. J. Stirton.

For a long time we have used inedible animal fats and oils and products made from them in a wide variety of industrial applications, many of which Nave been modified only a little since they were first developed.

But now the industry is entering an, era of expansion and development, comparable to periods passed through by both the petroleum and coal-tar industries, in which emphasis is being placed on isolating and preparing chemically homogeneous substances.

This approach opens a tremendous field for fundamental and applied research and for the manufacture of many new products. Such a trend promises increased income to the farmer, industrialist, and wage earner, as well as many products to add to the public comfort and health.

As industrial raw materials, it is the inedible grades of animal fats and oils that are used almost exclusively. Inedible tallow and grease comprise about 90 percent of these materials, with pork fat and neatsfoot oil making up the rest. Factory consumption of inedible animal fats and oils in 1947 to 1950 was about 2 billion pounds a year.

Inedible tallow comes mostly from cattle and sheep as trimmings from meat-packing plants or as scrap fats obtained from meat trimmings in butcher shops or saved in the kitchen and sold to commercial renderers for processing. A large amount of inedible pork fat is marketed as grease, an average of about 5 pounds of grease being produced for each hog slaughtered. Other sources of grease are city garbage, waste fat from restaurants and hotels, and bones. When production of lard exceeds the demand, a part of this edible fat is diverted to grease.

Although grease is ordinarily considered to be hog fat, and tallow the fat of cattle and sheep, the commercial distinction between greases and tallows is made entirely on the basis of the titer (the temperature at which solidification occurs) of the fatty acids obtained from the fat. If the titer is below 40 C., the fat is a grease; above 40 C., the fat is a tallow.

Inedible tallows and greases are graded on the basis of color, content of free fatty acids, and general quality flavor and odor. The important grades of tallow, in order of quality, are: Prime (Packers') Tallow, produced from the choicest inedible stock; Number One Tallow, the most widely used industrial grade; and Number Two Tallow. The important grades of grease are A White Grease, B White Grease, Yellow Grease, and Brown Grease.

For most uses, the materials have to be modified chemically. The only important exception is neatsfoot oil, which is prepared from the feet and shinbones of cattle and is used in lubricants and dressings for leather. Only 3 million to 4 million pounds of neatsfoot oil is produced annually, a relatively small percentage of the total quantity of inedible animal fats consumed by industry.

The most important outlet for inedible animal fats is in making soap, a chemical process that has been conducted for hundreds of years and for a long time was almost the only outlet for inedible animal fats. Soap accounts for about 80 percent of the inedible animal fats, or about 1.5 billion pounds (1943 to 1950), consumed in the United States annually. Saponification of fats with alkali yields glycerol as well as soap.

Some of the many uses of glycerol are in the preparation of explosives and synthetic resins, as a moistening agent, and in the food, cosmetic, and pharmaceutical industries.

Everybody uses soap because of its detergent properties. Soap is an excellent detergent in soft water and at an alkalinity greater than pH 8, but not in hard water. For use where water is hard, synthetic detergents, which are said to be equal or superior to soap, are now available, the result of intensive industrial research. The production and consumption of synthetic detergents have increased tremendously and will probably continue as new uses for these products, based on certain of their properties, are found.

The production and consumption of soap have remained substantially constant (1943 through 1949), despite the active competition from the newer detergents in a field that until recently was reserved almost exclusively for fat derivatives. The use of inedible fats in the preparation of synthetic detergents is increasing, but chemicals from petroleum and coal tar are still by far the most important source materials in synthetic-detergent manufacture. Production of synthetic detergents was about 300 million pounds in 1947, 500 million in 1948, 800 million in 1949, and about 1 billion in 1950.

Another important industrial outlet for inedible animal fats and oils is in the preparation of lubricants and lubricating greases, which account for somewhat less than 5 percent of the annual consumption, or approximately 100 million pounds.

Most of the remaining inedible animal fats and oils (10 to 15 percent of the total, or 200 million to 300 million pounds) go into the preparation of free fatty acids, of which about 50 percent are used in the preparation of stearic acid and red oil. The remainder are used in the preparation of soap (10 to 20 percent) , lubricants and greases (about 10 percent), rubber, and miscellaneous products.

Minor applications for inedible animal fats and oils (5 percent of the total,. or about 100 million pounds) are in the manufacture of synthetic detergents, leather, illuminating oils, cutting oils for metal-working operations, printing inks, and paints and varnishes.

Although most inedible animal fats and oils are converted by simple procedures to end products, which are then used up (soap, lubricants, greases) , the fatty acids represent an intermediate stage in the consumption of inedible animal fats and oils, and find their way into a surprisingly wide variety of products.

FREE FATTY ACIDS obtained by hydrolysis of inedible tallow and grease consist of 40 to 50 percent saturated acids (mainly palmitic and stearic acids), as much as 10 percent polyunsaturated acids (mainly linoleic acid), and 40 to 45 percent of oleic acid, the monounsaturated acid. For many years this mixture was separated into solid and liquid fractions by pressing, to yield so-called stearic acid, originally employed in the preparation of candles, and red oil (or commercial oleic acid), originally considered to be of little value and occasionally discarded or burned.

Commercial stearic acid consists of about equal parts of stearic and palmitic acids and it is contaminated with unsaturated acids, depending on the number and efficiency of the pressing operations. Thus, the terms single-, double-, and triple-pressed grades of stearic acid were introduced, the last-named containing the smallest proportion of unsaturated acids, occasionally as little as 2 percent, and having the highest melting point and the best color, odor, and stability to oxidation.

Red oil, or commercial oleic acid, is a yellow to dark-brown liquid that contains 60 to 75 percent oleic acid. The remainder is saturated and polyunsaturated acids in about equal quantities. Because of this composition, the conventional analytical values for red oil agree with those calculated for pure oleic acid. Many investigators thus assumed that red oil was chemically homogeneous. As a result, a great deal of research with red oil, rather than purified oleic acid, as the starting material has led to erroneous conclusions. By redistillation, the color of commercial oleic acid can be improved, but, because the composition remains almost the same, its stability of color and odor and resistance to oxidation are only slightly improved. The residue from this and other distillation operations in the preparation of fatty acids is called fatty acid pitch, or stearine pitch. It is used in electrical-insulating and roofing materials and in other materials that require a product with pitchlike properties.

Separation of solid- and liquid-acid fractions by pressing is mainly a hand operation. The process is slow, and labor costs are high. Other disadvantages are limitations in the quantity of fatty acids that can be separated, excessive product losses due to handling, and cost of remelting, chilling, repressing, and recycling. About 1945, however, a commercial solvent-crystallization process, the Emersol process, was developed for the separation of the solid from the liquid acids. The process separates the acids efficiently and it is continuous. Operating costs are said to be only about 35 percent of those for pressing. The composition of the solid and liquid fractions is about the same as that obtained by pressing. Because the process is efficient, the iodine number of the solid-acid fraction can be easily reduced below the value usually obtained by conventional cold- and hot-pressing operations.

Despite this lack of chemical homogeneity, the fatty acid fractions obtained by pressing or crystallizing operations have a good industrial position. Their use is widespread and increasing. The use of fatty acids in organic synthesis, however, can be expected to increase greatly when pure individual fatty acids are available.

The most important use for stearic acid is in compounding rubber. About 15 million pounds were used in 1949, out of a total of about 50 million pounds of stearic acid consumed. Stearic acid is also used in cosmetics, ointments, and shaving creams and in other pharmaceutical and toilet preparations. As shown by the number of pounds used in 1949 (in parentheses), it was used largely in the form of soaps (6 million), lubricants and greases (4 million), chemicals (7 million) , candles (3 million) , paints, varnishes, and resins (1.5 million) , metal-working operations (1 million), textiles (1.5 million), and many miscellaneous applications (11 million).

Approximately 45 million pounds of commercial oleic acid were consumed in 1949. About 16 million pounds of that amount went into liquid, or low-melting, soaps intended primarily for use in textile-scouring operations. Commercial oleic acid is also used as a textile lubricant (10 million pounds) , in the manufacture of chemicals (8 million) , in lubricants and greases (2.5 million) , sulfonated oils (3 million) , rubber (1.5 million), protective coatings (1 million), resins (1 million) , metal-working operations (1.5 million), and many miscellaneous industrial applications.

The instability of color and odor of commercial oleic acid and the ease with which it forms gummy polymerization and oxidation products are serious drawbacks to many industrial uses. It has been impossible to eliminate the disadvantages by the use of inhibitors or antioxidants. The undesirable characteristics can be attributed to the high percentages of polyunsaturated acids in the commercial product, which oxidize and polymerize faster than oleic acid. Textiles lubricated with red oil and stored for long periods may burst into flame as a result of spontaneous combustion, caused by the evolution of heat during oxidation of the polyunsaturated acids. The gummy de-posits formed on textiles lubricated with red oil cannot be removed by scouring and may cause uneven dyeing and unpleasant odors in the finished fabric.