Furfural shipped abroad *Intank steamers
INDUSTRIAL DEVELOPMENT OF F HAROLD J. BROWNLEE QUAKER OATS LTD., SOUTHALL. MIDDLESEX, ENGLAND
C A R L S. MINER T H E MINER LABORATORIES. CHICAGO. ILL.
T
H E furfural project did not originate from an effort to produce chemicals from farm by-products, and certainly when the project was set up, no one connected with it had thought of furfural production as a possible result of the research. The project was initiated a long while before the invention of the word “chemurgy” and at a time when, except for ethyl alcohol and a few other fermentation processes, farm by-products were thought of almost exclusively as raw materials for animal feeding. At the time when the research was started, oat hulls had a good but not wholly satisfactory, market position as a component of mixed feed. I n those days, the early ’twenties, the mixed feed industry had not gained the tremendous market which it now enjoys. The Quaker .Oats Company mill a t Cedar Rapids, Iowa, was producing 50,000 to 60,000 tons per year of oat hulls, and in seasons of favorable crop yields the demand for this feed material, of only medium digestibility, sometimes ran far below the current supply, which’resulted from the demand for rolled oats, not oat hulls. Consequently, there were times when oat hulls accumulated a t the factory in inconvenient quantities. I n one period it was necessary to use a circus tent to store them. At another time they were burned under the boiler. Consequently, the officials of the company established a research fellowship to investigate the possibility of improving the market position of oat hulls. The oat hulls market as a livestock feed was limited primarily by the comparatively low digestibility of the hulls. The oat hull is about 50% digestible, and it seemed that the most likely way of getting larger returns from the hulls would be to increase their digestibility through chemical treatment. This company was not the first to undertake the job of improving the nutritive value of a roughage material, but the methods which had been developed 20 1
abroad for the treatment of straw involved the use of large quantities of sodium carbonate or of sodium hydroxide which had to be washed out of the treated product before it could be fed. The result was a process expensive not only because of the cost of the chemicals, but also because of the substantial loss of material made soluble and removed a b n g with the soda in the washing operation. These difficulties were avoided by the use of lime, which was effective, cheap, and could be neutralized and left in the feed as calcium sulfate. The resulting product had a digestibility close to 70%, and the initial feeding tests were fairly satisfactory. However, the product was lacking in palatability and in certain other desirable characteristics; consequently various forms of acid treatment of the hulls were investigated. It was soon found that an acid treatment would produce a much more palatable feedstuff since the considerable quantity of sugar products formed gave a desirable sweet taste to the material, and it was possible to separate and refine the sugars into a reasonably palatable sirup. This sirup was, however, too expensive and would probably have shown a comparatively low digestibility for man as its pentose content was high. These results encouraged a continuation of the investigation of the acid treatment; but since it had been found that a substantial loss of dry material resulted from the process, it was considered important to determine the nature of the volatile products formed in order to reduce their quantity and increase the yield of feed. From the beginning of our study of the acid treatment it was known that a t least a small percentage of furfural wa8 being formed, for its odor is unmistakable, but the substantial quantities being formed were surprising. When we compared our figures for possible production with the current price of furfural-$6.50 per pound-we got a very
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great thrill, but it was short-lived, for when we began to investigate the demand for furfural, we discovered that one ton of oat hulls would probably supply the annual demand of the world for this commodity. That changed our problem in magnitude only; instead of merely having to find a way of making furfural, we had to find a market for it, and for a while this looked like more of a problem than finding a market for the hulls themselves. Furfural, once we had started to work on it, gave such stimulating symptoms that we have never seriously investigated any other phase of the oat hull problem since the day we got the first report of the yield v e were accidentally getting in our feed process. That was the beginning of a tremendous number of experiments. Bt the time when this work was begun, the method of determining pentosan by distilling with hydrochloric acid to form furfural and precipitating the furfural with phloroglucin had been used for many years. Several methods of manufacturing furfural had been suggested, and in that general period La Forge and Mains (9) of the Bureau of Chemistry, and Sweeny and his group at Iowa State College, were workiflg on methods for producing furfural from corn cobs. We studied all the known processes. None of them seemed satisfactory for large scale manufacturing, so a study was undertaken of this phase of the problem. The essentially simple process consists in treating oat hulls with acid at an elevated temperature, and it is practically impossible to do this without getting a t least a little furfural. Since the problem, however, was to produce furfural at the lowest possible cost per pound, and this meant getting the largest yield from oat hulls with the least expenditure for equipment, chemicals, power, and labor, an exhaustive investigation was carried out of the effect of various factors-time, temperature, percentage of acid, ratio of water to hulls, fineness of hulls, steam flowv,etc. Curves were plotted and optimum points determined and gradually an initial process mas developed which has been continually improved. The improvement in the process is reflected in the downward curve of the prices, beginning at $1.00 in 1922 and going down gradually to the current price of 9l/2 cents. The step from the laboratory to the plant is usually a long and expensive one. The first pilot plant equipment poses a great number of problems, solution of which is essential before the full scale plant can be built. This company never had a pilot plant for furfural; work moved directly from the laboratory experiments to what was essentially a full scale unit. This was the result of the fact that The Quaker Oats Company had available in the plant a t Cedar Rapids, where the first furfural process plant was to be operated, a number of iron pressure cookers about 8 X 12 feet, which had been used in the manufacture of a cereal product which did not prove profitable. Since these cookers were available and since the process was to consist of the treatment of oat hulls with acid under pressure, it seemed advisable to try to use these digesters at least for the first attempts at large scale operation. There was an additional reason for utilizing the cookers which were then available at Cedar Rapids. At the period when this work was being undertaken, research budgets were not so liberally interpreted by management as they frequently are today, and it was highly advisable not to ask for a larger expenditure than was thought absolutely essential. Since these digesters were available and could be lined with acidproof material-at least that seemed probable-it seemed inadvisable to pick that time to design and have built a cooker of ideal characteristics. The chronological order of equipment was glass jars in an aluminum pressure cooker, followed by a small cast-iron pressure cooker; then experimental work was carried on briefly in an enamel-lined steamjacketed cooker at the Forest Products Laboratory through the courtesy of the director of that laboratory. These were the pieces of equipment that had been used for the production of furfural on a gradually ascending scale up to the time when production was begun at the Cedar Rapids plant.
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When the decision was reached to line the iron digester a t C e dar Rapids with an acid-resistant material, a study was made of a number of metals. A consultation with the various purveyors indicated the use of 20-gage Monel, the edges being turned up and welded. The digester lining was finished, and the first digestion made in Kovember 1921. Prior to the actual experiment, a blank test was run on the Monel metal lining by applying steam pressure of 60-75 pounds, blowing off the steam, and putting on a vacuum immediately following; but when the cooker was opened for inspection after this test, the lining had caved in badly. Apparently there were a few pinholes n-hich permitted air and steam to seep slowly behind the lining while the cooker was under pressure. This permitted pressure to develop behind the lining, which caved the lining in when pressure on the cooker was released. This experience was repeated a t least once before this method of installing a tight lining was abandoned. Finally one hole was left in each end of the cooker in the Monel shell to act as a breather and equalize the pressure on both sides of the liner. This prevented further cave-ins but had the disadvantage that the corrosive vapors from the cooked hulls penetrated behind the Monel metal and eventually corrodcd the iron badly. The lining served, however, for much of the prcliminary work on furfural but never proved wholly satisfactory. Later liners were made of copper, but they were never quite satisfactory, and ultimately linings were used of carbon brick with acidproof cement, which is the type still in use in the furfural plants today. Once the problem of obtaining a reasonably resistant metal lining had been solved, the digester was operated as a regular routine manufacturing process. The process (10) consisted of introducing into tho digester 5000 pounds of finely ground oat hulls and sufficient dilute sulfuric acid to dampen them. The digester was then closed and steam introduced, the digester being rotated from this point until the end of the process. When the pressure in the digester had been raised to the proper point (about 60 pounds), the exit valve was opened and steam was blown through the digester to carry off the furfural as soon as possible after it was formed, this steam being introduced through a large number of orifices to allow as complete contact with the hulls as possible. Initially the total distillate was condensed and then fractionated. h little later the mixture of steam and volatile reaction products went directly to a rectifying column where, with the aid of one piece of auxiliary equipment, it was separated into three fractions, one mainly water with traces of organic acids and practically free from furfural, one containing low boiling materials including acetaldehyde, and one consistingof 98 to 9970 furfural. This process differed in at least two essentials from earlier processes proposed for furfural manufacture. Since steam was one of the most important elements of cost, the steam utilization had been reduced by the expedient of operating in a reaction mass of merely dampened oat hulls ( 1 ) instead of in a fluid medium as had previously been proposed, So far as we have been able to learn, the manufacture of furfural at Cedar Rapids was the first factory-scale production of this compound. The second important modification of older proposals was the use of a relatively voluminous flow of steam to carry off the furfural as rapidly as possible after its formation. Thi3 step was introduced because experimental work had shown that furfural formed nonvolatile products readily when exposed to high temperatures under acid conditions and that this reaction was catalyzed by the presence of certain metals. In line with a policy of keeping the expense of the project at a minimum, a very simple type of rectifying column was developed which consisted of an iron pipe filled x-ith gravel from the nearby river. I t worked efficiently for a considerable length of time and is recommended for use in emergencies where more satisfactory equipment is not available.
February 1948
INDUSTRIAL AND ENGINEERING CHEMISTRY
The process was operated commercially for a number of years, using first the Monel-lined and then the copper-lined cooker along with the simple rectifying column just described. During this early period there was a substantial production of furfural running into a good many thousands of pounds. HOWever, at that time the sponsors of the project, cereal millers who had never had any direct connection with the chemical industry, were hesitant to allow the name of their company to be used in connection with the sale of furfural, and for that reason the sales were made by the laboratory which was responsible for the research project. The first commercially produced furfural was offered for sale by this company a t $1.00 a pound. Shortly after that the price was reduced to 50 cents, then to 35 cents. Finally in 1922 the price came down to 25 cents a pound in 1000-pound lots. During this early period the largest single item of expense of furfural production was the repairs, mostly due to corrosion of iron equipment. However, the management agreed that repairs were likely to .be greatly reduced as suitable and well designed equipment was introduced, and the effect of that item on cost was to some extent ignored in the fixing of a price. It is not to be understood that research was abandoned during this early period when a good deal of time was taken up with mere details of the manufacturing process and sales of products. ACtually, research went on actively during that time, although it waa only on a part-time basis. Beginning in 1930 there was a period when the depression almost resulted in the termination of the furfural project. But just about the time when the project was ready for formal burial, some of the sales outlets began to show pleasing signs of activity, and it was decided to lay out a new unit from the ground up, a building of six stories was planned, and new e q u i p ment came in for full discussion. At this time globe-shaped, 14foot-diameter digesters were adopted, and these were lined with carbon brick, which proved, after some period of experimentation with cements, a satisfactory lining still in use today. When the idea of a continuous digester took hold, a vast amount of work went into the planning and producing of such a machine (a),which was based on the principle of the oil expeller and forced the hulls into a closed vessel against pressure. It was built of acid-resistant metal, and the pressure was held by plugs of the hulls formed a t the inlet and outlet. This development ultimately had to be scrapped, as a succession of disasters ultimately showed that this was not a satisfactory method of operation. Although the system was made to work at times, abrasion and corrosion ate away the flights in the feeder at the rate of about one quarter of an inch a week; this was considered to justify the scrapping of that part of the project. The question of the disposition or utilization of the residue left after the treatment of the hulls with acid in furfural production is important. This residue consisted of about 70% of the original weight of the hulls and was in a finely divided state, slightly carbonized, so it seemed that this might be an excellent raw material for the production of an activated carbon. A great deal of work was expended in the effort to utilize this digester residue successfully as activated carbon for dry distillation, dextrose production, as filler for plastics, and for other purposes, but for many years no better use was found than the utilization of this material for the fuel value it had under the boilers. Lately, however, a market has been found for the residue as a soil conditioner. The production of a new chemical compound is only the beginning of the project, since the development of a market may be a much more difficult problem than the manufacture of the compound itself. Certainly that has been true in the case of furfural. In some instances the increased sales result primarily from decreased cost, but in the case of furfural this is not true, although decreased cost has contributed to the expansion of markets. The most important markets for furfural have not been developed by research directly concerned with this ob-
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jective, but have been the result of research work directed toward the solution of specific industrial problems, such as the refining of rosin, petroleum, vegetable oils, and butadiene, and the search for raw materials for nylon production. This does not mean that no research effort of those responsible for furfural production was directed toward the finding of uses for the product, but the early history of those direct efforts is, on the whole, a record of frustration rather than success. Furfural was early found useful in resins, as a refining agent for rosin and lubricating oils, as insecticide, herbicide, cellulose ester solvent, and a raw material for other furan compounds. The history of these early developments, up to 1936, has already been reviewed by Peters (11). The period since 1936 has been marked by steady and, a t some times, spectacular increases in the consumption of furfural. The oil industry continues to install furfural refining plants, and today there are twenty units in operation and ten more in the planning stage. Although the war delayed the installation of a number of furfural selective solvent plants, it was directly responsible for the erection of three furfural extractive distillation units designed to recover pure 1,3-butadiene from cracked refinery gases. These plants were operated by Phillips Petroleum Company near Borger, Tex., by Neches Butane Products Company a t Neches, Tex., and by Sinclair Rubber, Inc., at Houston, Tex. Descriptions and technical information regarding the process are given by Buell and Boatright (3) and Happel et al. (6). The extractive distillation separations made in these plants were three in number: n-butane from 2-butenes, isobutane from 1butene, and butadiene from 1-butene. To supply the demand for furfural for these plants, the already existing furfural capacity was tripled by building another plant at Memphis, Tenn. (4). The demand for furfural has far outstripped the supply of oat hulls, so now corncobsare a major source of the aldehyde. It has always been believed that furfural eventually would find a large outlet in the synthetic resin field, but it was not until war-caused shortages of formaldehyde, cresol, and phenol developed that manufacturers in great numbers seriously considered furfural. As a result, during the past few years the volume of furan resins has greatly increased. These uses include the substitution of furfural for formaldehyde, but within the past few years entirely new types have developed, such as furfuryl alcohol-formaldehyde (7, 1.8) and furfuryl alcohol-phenol (8). There are also resins in which furfuryl alcohol is combined with melamine and with dimethylolurea. Several successful pharmaceutical products have appeared within the past few yearsfor example, furmethide, which is a quaternary ammonium furan compound (furfuryltrimethylammonium iodine) and Furacin, which is an excellent antiseptic and may be used at times in place of penicillin or streptomycin. This compound is 5-nitrofurfural semicarbaaone (6). The latest and possibly largest potential use for furfural is as a chemical intermediate. Products such as furan, tetrahydrofurfuryl alcohol, methyltetrahydrofuran, dihydropyran, and others, are available in experimental or pilot plant quantities. What could better portend the future of furfural than its growth? The first drum of furfural was shipped in 1922 and the first tank car in 1927, and in 1947 furfural was first shipped in a tank steamer. However, the use curve, as'indicated by sales, has been far from smooth. There have been no serious dips except in 1931-32, but there have been plateaus where it seemed that the limit of the market might have been reached. Yet always these plateaus have been followed by sharp upward trends, with the result that today the production of furfural is approaching the point where 500 million pounds per year of farm by-products are utilized in its production. The demand has far outstripped the supply of the oat hulls, wh.ose limited market furnished the impetus that was responsible for the birth of the furfural industry. It has
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been necessary lately to utilize both cottonseed hulls and corn cobs, and other raw materials must be taken into consideration in connection with further expansion of the industry. Before World War I1 it seemed reasonable to consider that even the cheapest by-product of the annual crops could not compete successfully with petroleum as a source of raw material for the chemical industry. Now, in the face of depleted petroleum resources, it is conceivable that the price of petroleum may increase more rapidly than the cost of farm by-products. Consequently, the outlook for a chemical industry, based on annual crops, appears encouraging. One of the serious drax backs to theii use in this field is the expense of transporting cheap, bulky materials to a central plant for chemical processing, and consequently one of the problcms on nhich interested research workers will concentrate effort ~ ~ 1 1 1 be the development of processes and equipment by means of which intermediate and crude chemicals may be produced on the faim itself, in order to reduce the bulk of the material that must be transported to the plant nhere ultimate reaction or purification is to take place.
Vol. 40, No. 2
Under all the circumstances, even with the threat of a flood of by-product chemicals from the petroleum industry, the long future of the industrial production of chemicals from farm byproducts may be considered sufficiently hopeful to justify continued and increasing expenditure for research in that field. LITERATURE CITED
(1) Brownlee,H. J., IND.ENG.CHEM.,19,422 (1927). (2) Brownlee, H. J., U. S. Patent 1,919,875 (1933). ENG.CHEM.,39, 695 (3) Buell, C. K., and Boatright, R. S., IND. (1947). (4) Chem. h M e t . Eng., 52, 132 (1945). (5) Dodd, M. C., J . Pharmacol. Ezptl. Therap., 86, 311 (1940). (6) Happel, J., et al., Trans. Am. Inst. Chem. Eagrs., 42, 180 (lQ46). ( 7 ) Harvey, M., C . 9. Patent 2,343,972 (1944). (8) Korten, E., I h i d . , 2,321,493 (1943). and Mains, G. H., ISD. Exti. CH (9) La Forge, F. B.. (1923). (10) Miner, C. S., andBrownlee, H. J., U. S. Patent 1,735,084 (1929). ENG.CHEM.,28, 755 (1936). (11) Peters, F.N., IND. (12) Zerweck, W., Schuhert, hf., Heinrich, E., and Pintcn, P..1'. S. Patent 2,306.924 (1942). RECEIVED January 9, 1948.
A . P.D U N L O P T H E QUAKER OATS COMPANY, CHICAGO, ILL
The kinetics of formation of furfural are discussed briefly. The stability of furfural is considered i n some detail, attention being given to such factors as autoxidation, and decomposition by acids and heat. I'arious stabilizing agents are evaluated. Deaeration of the system is recommended in all processes employing furfural at elevated temperatures. From the standpoint of its chemical behavior, furfural is considered as an aldehyde and as a heterocyclic compound. The etheric, dienic, and aromatic properties of the nucleus are discussed with appropriate illustrations.
choice of a particular raw material. Jointly they detcrmine the amount of furfural which can be produced per cycle in a digester of given volume. Consider, for example, the case of rice hulls; the potential furfural content is relatively low by comparison with that of oat hulls or of corn cobs, The higher bulk density of the rice hulls, however, permits a greater weight to be charged to the digester, so that, from the standpoint of pounds of furfural produced per charge, there is comparatively little penalty in using rice hulls as a source of furfural. This is not true of several other potential ran' materials. K I N E T I C S OF F O R M A T I O N
P
ENTOSAK-containing agricultural residues are known to be the raw materials from which furfural is produced. Little discussion of this general subject is needed, except to point out some of the factors which influence the selection of one particular source in preference to another. From a theoretical standpoint furfural might be made from a great many agricultural materials, but in practice, economic considerations limit the choice to a comparatively small number. Cost is the most important factor; the yield of furfural averages only about 10% of the processed raw material. Low-priced furfural is therefore dependent upon low-cost raw material and such items as collection, handling. and shipping charges. In general, a suitable source of furfural should be available in large tonnages within a convenient shipping radius of the producing plant. Today the major raw materials are those listed in Table I, which also includes the potential furfural content of each. The latter represents the amount of furfural which can be obtained in the -4.O.A.C. ( 1 ) analytical procedure for determination of pentoses and pentosans. Actually, it is only SS-90y0 of the theoretical amount if all the pentose is xylose, since the analytical method gives only this yield of furfural from pure xylose. The potential furfural content, average nat;ral moisture content, and bulk density are three additional factors which influence
In the process employed today for the production of furfural, the pentosan-containing raw material and dilute sulfuric acid are charged to a large, spherical, rotary digester which is then set in rot,ation. Steam is introduced to bring the charge to a selected conversion temperature, a t which point a vapor outlet valve is opened to permit removal of furfural in the form of a steam distillate which passes directly to the recovery syst,em. Steaming is continued until the furfural content of the vapors from the digester decreases below the practical level dictated by economic factors. By appropriate adjustment of operating temperature and acid concentration, the digestion cycle can be varied over wide limits of time. This brief description of the commercial process shows that the conversion of pentosan to furfural is handled a.s a one-step procedure. Holyever, it, is recognized that there are several intermediate steps in the over-all reaction. The first of these TABLE I. MAJORSOURCES OF FURFURAL Raw Material
Potential Furfural, % on Dry Basis
Corn cobs Oat hulls Cottonseed hull bran Rice hulls
23-24 21-23 20-23 12-13
