UTILIZATION OF AGRICULTURAL WASTES* CHARLES GERALDALBERT, THECOLLEGEOF WOOSTER, WOOSTBR. OHIO
Undoubtedly one of the greatest services of chemistry to mankind is the utilization of waste materials which are absolutely worthless without treatment, but which are often transformed by chemistry into valuable by-products. In many industries this chemical use of wastes has, for several years, been highly developed; nevertheless, there is a chance for greater development as scientists make progress. Especially is this true of agriculture, perhaps the most important of all industries. Recently the advances of chemists in their research for profitable uses for such now worthless things as straw, corncobs, peanut shells, and cornstalks are interesting scientifically minded America. All over the world, in fact, research men are attempting t o find profitable uses for the great agricultural by-products. By far the most common use of corncobs a t the present time is as a fuel. But analysis shows the cobs i o contain a great deal of moisture and to possess little heating value. Clearly some better use should be made of them. Many farmers grind up their corncobs and feed them to the cattle, but such a use is uneconomic, because corncobs have almost no food value. Chemists, attempting to find a use for this waste product, discovered that if the corncobs were heated in a closed retort and the resulting liquids distilled, the final products obtained would be approximately the same as those from a similar treatment of wood. Such a discovery is important in face of the fact that the supply of wood for distillation is decreasing rapidly. But by far the most interesting treatment of corncobs is that by which furfural is produced. Furfural has been known for a long time as a light yellow, oily substance, the chief value of which was as a laboratory curiosity. Until experimenting proved that it could easily be derived from corncobs and oat hulls it sold for $30 a pound, and often for more. The number of practical uses for furfural is now almost infinite. Embalming fluid, for instance, may be manufactured with furfural employed as a substitute for formaldehyde. The fabric so often used on airplane wings must be treated chemically with "dope," a substance which can be manufactured from furfural. This golden furfural makes a fine antiseptic for the treatment of seeds. It features in the making of several anesthetics. Recently chemists have found that i t is a good ingredient for the popular quick-drying lacquers. Aqueous solutions of furfural are very fine preservatives for anatomical specimens. It is found to be a possible new raw material for the dye industry, and, by itself, it is a very good varnish remover. It is also an excellent solvent for such materials as nitro-cellulose. * Fist prize-winning college essay, 1929-30. This is one of the five specific titles prescribed under the general topic, "The Relation of Chemistry t o Agriculture or to Forestry." 1563
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During the last few years, a series of hard plastics produced from phenol and formaldehyde have come upon the market and practically revolutionized certain industries. These substances are sold under trade names such as Bakelite and Redmanol. Almost no change is found in the plastic if furfural is used to replace the formaldehyde. All such plastics demand some inactive filler in order to keep the price from becoming excessive. In the laboratory, ground corncobs have been used for the filler, together with furfural for the formaldehyde, and excellent results have been obtained. A very inexpensive process is used. It is a simple treatment of the ground corncobs with hydrochloric acid and phenol. The hydrochloric acid liberates furfural from the cobs; the furfural reacts with the phenol to form the final product; and the final product contains the excess of ground cobs as a filler. Some furfural compounds are used in anti-knock gasoline, and furfural by itself may sometimes become an extensive gasoline substitute, although its present price, fifteen cents per pound, makes this use impractical. If all the corncobs, peanut shells, and cottonseed hulls in the United States were, each year, made into furfural, we should never he faced with a gasoline shortage. Other furfural compounds are used in rubber curing, where they act as accelerators. These varied and extensive uses of only one of the many products obtainable from corncobs, not to mention the many other agricultural wastes, show the immense importance of such chemical research. Fnrfural is by no means the only product that can be obtained from corncobs. A strong glue is made by digesting the cohs with water under pressure. The substitution of dilute mineral acids for the water changes the resulting product to xylose, which is a sugar. Xylose is particularly valuable as a sweetening agent in the diet of diabetic patients, since it is not assimilated to any extent in the body. Lactic acid, acetic acid, alcohol, and succinic acid may all he easily obtained by fermenting the xylose sirup. Another valuable derivative of corncobs is oxalic acid, obtained by the fusion of the cohs with caustic soda. Oxalic acid has a multitude of uses, being employed in the dye, tanning, explosive, ink making, and laundry industries, the production of artificial silk, celluloid, and other things. Corncobs may be used in place of spent tan bark in the manufacture of white lead. Ground cobs also make a suitable substitute for ground cork in the production of linoleum. A flour obtained by grinding the cohs extremely fine makes a good filler for diabetic food, plastic wood, and many similar substances. Besides these, there are a great many minor uses for corncobs, such as in the manufacture of sweeping compounds, in the curing of concrete, in making punk and incense, in the smoking of meat, and in an almost limitless variety of rather unimportant processes.
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Next to corncobs, possibly the greatest waste product on our great Middle Western farms is the cornstalks. Scientists have proved that cornstalks have little or no beneficial effect when they are plowed under the soil, and that, as a food, they may be harmful to cattle. If the stalks are shredded, beaten, and cut up into small fiber bundles almost like pulp, and then cooked, a sticky substance is secreted; which substance, when the material is run through rollers, holds i t together in the form of wall board. This wall board is very light in weight; it is an excellent heat insulator; and i t is thus extremely useful in the building industry. It has every advantage over the old-time wood lath; i t also makes a fine sheathing, not only because of its insulating properties, but because it makes a stronger wall than the older sheathing process. This insulating value is equal to that of the sheet cork now used in refrigerator constrnction. The yield per ton of cornstalks is quite high, and the cost of production promises to be reasonably low; therefore, it appears that cornstalks may become an economic good of no mean importance. By slightly varying the manufacturing process for this wall board, we obtain a very hard, strong material. This denser material can be used for many things where the softer insulating board would be quite unsuitable. A few possible applications are for paneling in automobile bodies, Pullman cars, and truck bodies. The cost of production for this type of board is somewhat higher than that for the first type. If gypsum is used as one of the ingredients in the manufacture of the wall board, the resulting product is almost perfectly fireproof. It has advantages over the pure gypsum board, since it is lighter in weight and is somewhat easier to nail into. The pulp used in making these wall , boards may be molded into a variety of shapes while wet, and will become hard and quite strong upon drying. The sale for novelties made in this way is large, and the resulting papier machi industry is rather important. Another simple change in the process causes the pulp to dry out to a hard, dense substance not unlike vulcanized fiber. This material can be either molded or machined, and is used to make knife handles, gears, and knobs. It is a good electrical insulator, and possesses surprising strength, so that it can well be used in the manufacturing of switch buttons and similar electrical apparatus. This material is on the market under the trade name of maizolith or cellulith. But there is one use for cornstalks which easily eclipses all others. It is ihe manufacture of paper. Attempts to use cornstalks in this industry date back as far as the seventeenth century. At present, because wood pulp is becoming rather scarce, the production of cornstalk paper is assuming a new importance. Under quite a high steam pressure, the stalks are digested with a regular paper chemical. Then the pulp is beaten and the fibers which are too large are removed. The final steps
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are bleaching the pulp with a solution of white powder and rolling it into sheets. All types of paper, from coarse, thick filler for egg cases to fine, bleached writing paper have been produced. Most efforts are being bent toward the economic production of newsprint. Cornstalk paper pulp has proved very satisfactory, and the paper is already used quite extensively in some localities. Alpha cellulose, an important raw material in the manufacture of rayon, or artificial silk, is obtained by especially purifying the cornstalk pulp. The rayon manufactured from this pulp is perfect, and alpha cellulose is now being produced commercially from cornstalks in a factory in Illinois. This cornstalk cellulose suggests a great field of possibilities. A gunpowder company is using it in the manufacture of smokeless powder. Another explosives manufacturer is experimenting with the fibers as an absorbent for dynamite. Like the corncob products, cornstalk cellulose may he incorporated into special foods for diabetic patients. Clay mixed with cornstalk fibers has been found to make an excellent building material. Ordinary brick is heavier than this new building block, and considerably more expensive. In addition to these products, there are many things now made from derivatives of other celluloses which could just as easily be made from the cornstalk cellulose. But cornstalks and cobs are by no means the only agricultural waste products which chemistry has made valuable to man. This limited space will not be sufficient to deal as extensively with the other accomplishments of science in this field, but a few of them should be mentioned. The cheese, or casein, industry is steadily becoming more and more important in the United States. Formerly almost all of the milk from our great dairy herds was skimmed, the cream, or butter fat, hauled away to the creameries, and the skim milk used wastefully without getting the maximum utility from the chemicals contained in it. But cow's milk contains almost as much casein as it does butter fat, and this casein is an extremely valuable by-product if i t is treated properly. By means of coagulating the casein with a dilute acid a precipitate is formed, which precipitate, after being washed and pressed, becomes our modern cheese. This cheese has a very high food value. The remainder of the milk, mixed with the washing water and called whey, is fed to the hogs just as the skim milk was before chemistry came along to make use of the casein. By treating this casein with different chemicals, we obtain glues, cements, putty, and paints. Casein, together with formaldehyde, is used in a treatment for waterproofing paper. Containers made from this treated paper are used for the products of many present-day industries. In the meat-packing industry, chemistry has made possible the profitable use of many wastes which otherwise would be absolutely worthless. Meat packers, with the help of science, can thus produce glue, soap, and a
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variety of other products. Thus a Midas-like touch has transformed the scraps of an industry into common and important articles. Chemistry takes beef fat, formerly a financial loss, and makes from it oleomargarine, an important butter substitute. It takes the wastes of the fruit-growing industry and turns them into lemon extract, cider, vinegar, and similar products. It takes the unsalable potatoes and makes alcohol from them. It makes the same valuable product from the waste of the cane sugar industry, a t an almost negligible expense. The number of agricultural by-products made with the aid of chemistry is too great to he gone into any more extensively here. Suffice it to say that almost anything from face powder to varnish can be made from the wastes of the corn farmer alone, and the possibilities in the other branches of the industry are equally great. Up t o the present, experimenters have barely touched the possibilities of chemistry as a salvager in agriculture. The main body of the work is yet to he done. It has a romantic appeal which should call to any one who is interested in voyaging into the unknown, and returning with the golden fleece of worthwhile information for his fellowman. We can powder our faces and run our automobiles with peanut shells now! With the aid of chemical research, materials we even now consider worse than useless may, sometime, sustain the whole human race. Bibliography "Chemistry in Industry," H. E . Howe, Editor, The Chemical Foundation, Inc., 1924, Volume I, pp. 37-57. Bulletin 99, Engineering Extension Department, Iowa State College, Ames, Iowa, pp. 2-15. "Dictionary of Applied Chemistry," Thorpe, Longmans, Green& Co., 1921, Volume IV, pp. 72S34. "Smith's College Chemistry," Kendall, The Century Co., New York City, 1929, pp. 506, 513.
