Hydrogenation A Demonstration for the Classroom1 JAMES W. KERCHEVALP and LLOYD A. ARMBRUSTERa Michlgan State Normal College, Ypsilanti, Michigan
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ORE THAN a billion pounds of refined cottonseed oil are produced each year in the United States (1). The principal use for the refined oil is found in the preparation of shortenings, which consumes about 65 per cent of the annual production. Margarine manufacture accounts for about 8 per cent of the total refined oil produced, and miscellaneous food products such as salad oil, mayonnaise, and salad dressing use an additional 17 per cent. The remaining. - 10 per . cent is used for nonfobd purposes (2). Thus the major portion, or approximately 80 per cent, of the cottonseed oil used for food in this country is used not as the liquid oil, but in the form of a hardened fat in shortenings such as Crisco or Spry, and in margarines. The hardening is brought about by the process of hydrogenation which involves the addition of hydrogen atoms to the unsaturated linkages in the cottonseed oil. According to the analyses of cottonseed oils by Jamieson and Baughman (3) and Hilditch and Jones (4) the oil consists of the glycerides of the fatty acids shown in Table 1.
tion of the saturated glyceryl tristearate does not occur until the final stages of hydrogenation. Also triolein disappears more rapidly than the tristearate is produced. This fact is interpreted to mean that only one double bond of the triolein is hydrogenated during one contact with the catalyst. The sequence of reaction is thought to be: trioleates
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dioleomanostearates + mono-oleodistearates tdstearate-q (6)
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Refined cottonseed oil has a solidification point ranging from - 13O to 4-12'C. and an iodine number of 103 to 111 (7). When completely hydrogenated, it melts a t approximately 62" to 63'C. The shortenings made in the United States from the refined oil melt from 35O to 43'C. and have an iodine number of 60 to 75. The saturated acid content has been increased until it is 27 to 33 per cent and the liioleic acid reduced to 5 to 12 per cent. The lower the liioleic acid content, the better the keeping qualities of the product will be (8). Even though hydrogenation of vegetable oils is an important commercial process, very little has been published concerning the possibility-of demonstrating TABLE 1 om^ Formde P ~ ~hydrogenation ~ ~ in the ~ classroom, I ~ under ~ atmospheric ~ ~~~~~~t conditions. Haub (9) describes such a project, but bePalmitic CHt(CHduC0OH 19 to 22 cause one and one-half to two hours are required to obOleie CHs(CHdrCH CH(CH>)rCOOH 24 to 34 tain a hardened product, the project as described is imL ~ ~ O I ~ CHI(CH.),CH ~ C = CHCH.CH = CH(CHdrCO0H 39 to 50 1.5 to 2.5 practical for lecture demonstrations. With this objecstea& CHI(CH.~~~COOH M F ~ S ~ ~ C CHI(CH,I~,COOH smallamount tion in mind the authors set about to devise a method Amchidie CHI(CH~~~COOH Small amovnt which could be carried out during a single lecture Practically all of the palmitic acid is associated with period of 50 minutes. In the experimentation both vapor and liquid ~ h a s e unsaturated fatty acids in mixed glycerides. Only were considered. phase about 1.5 per cent of fully saturated glycerides are present. ~h~ remainder of the oil appears to consist of genation a t atmospheric pressure gave results indieatfor use as a 'lassabout 60 per cent monopalmito glycerides, 15 per cent of ing that this method was room demonstration. In an atmosphere of hydrogen, dipalmito glycerides, and 24 per cent of mixed triglydecomposition was considerable a t the temperatures cerides of oleic and liuoleic acids (5). ~h~ hydrogenation of these unsaturated glycerides necessar~for the vaporization of the oil. On the other proceeds in a stepwise manner. The more unsaturated hand, liquid phase hydrogenation yielded a product glycerides are hydrogenated to a considerable extent quite similar to that obtained commercially. It was before the less unsaturated glycerides begin to react. found that good results could be obtained within the Reduction of glyceryl trilinoleate, with hydrogen in the 50-minute period. The main the liquid phase pmcedure presence of nickel on kieselguhr as the catalyst, results in a nearly complete conversion to glyceryl trioleate are: (1) the apparatus needed; (2) the attention rebefore the latter is further hydrogenated. ~h~ forma- quired for temperature control; and (3) the necessity of a freshlv , *nrenared catalvst. These obiections are of 1 Presented before the Science Section at the annual meeting small significance in co&parison with he results obof the Michigan Schoolmasters' Club, Ann Arbor, Michigan, tained by this method. The most complex part of the April 16, 1943. k 'Present address: Big Spring Army Air Field. Big Spring, setup is the stirring unit. However, once this is made it Texas. Canbe left for future a Present address: Tennessee Eastman Cqoration, &oxIn the liquid phase hydrogenation, the heated oil is ville, Tennessee. 12
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agitated in an atmosphere of hydrogen with freshly reduced nickel on charcoal as the catalyst. The catalyst can be made in a number of ways; the one adopted was the most easily performed and least time consuming. The procedure followed is similar to the method used in the hydrogenation industry (10) and that described by Adkins (11). The catalyst is prepared in the following manner. A mixture of 50 g. of medium fine granular animal charcoal and 150 cc. of distilled water are boiled for 15 minutes, after which 58 g. of Ni(NOa)z.6Hz0are added and completely dissolved. To this hot mixture is slowly added, with stirring, a solution of 24 g. of (NH&COa dissolved in 100 cc. of distilled water. The resulting mixture is again heated to boiling. After cooling the solids are filtered off by suction, thoroughly washed with distilled water. and finallv dried in air a t room temperature. The reasons for using the nitrate of nickel and the ammonium carbonate are: (1) the nitrate residues are more easily washed out of the precipitate than are the sulfates or chlorides; (2) when the precipitated catalyst is ready to use, the carbonate is easily decomposed to the oxide which is then reduced to the free nickel. After reduction the nickel is mostly in the colloidal state and is dispersed on the charcoal which acts as the catalyst carrier. Other carriers, such as fuller's earth, diatomaceous earth, and kieselguhr can be used if preferred. To reduce the nickel carbonate on the camer, a 5-g. sample of the above air-dried residue is introduced into a simple reducing chamber consisting of an 8-inch pyrex test tube with hydrogen inlet and exit tubes. This amount is sufficientto catalyze a 20- to 30-cc. charge of oil. A continuous stream of washed, dry hydrogen is supplied while the contents of the tnbe are heated uniformly a t a temperature range of 300' to 325"C., or in a partially luminous flame for 15 minutes. A longer reduction time is required for catalyst charges of more than 5 g. At the end of the reduction period, the tube and contents are heated thoroughly to redness and then allowed to cool. Hydrogen is supplied continuously during the cooling period. Because age and contact with the air tend to make the nickel inactive, the catalyst should not be reduced more than a few hours prior to its use, and then should be kept well stoppered in the test tnbe in an atmosphere of hydrogen. This method of dry reduction has been found to be better suited to the small scale lecture demonstration than the more timeconsuming wet reduction. Both methods are used in industry, the wet reduction method being in more common use (12). The arrangement of the hydrogenation apparatus is shown in Figure 1. Hydrogen is obtained from a Kipp generator and is washed in a concentrated solution of sodium hydroxide, passed through concentrated sulfuric acid and then through a calcium chloride drying tube filled with glass wool., Hydrogen in coal or water gas cannot be used for the reduction of the nickel carbonate or for the hydrogenation process because the carbon monoxide in the gas will poison the catalyst and make it
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FIGURE 1
inactive. Fmm the drying tube the hydrogen is led to the hydrogenation chamber, which consists of a 250-cc. wide-mouth pyrex Erlenmeyer flask enclosed in an oven constructed of an asbestos-lined burner guard. The flask and its stopper hold inlet and exit tubes, a 360°C. thermometer, and a stirrer, which is run by a small laboratory motor. The stirrer, thermometer, and tubes should be mounted in the rubber stopper in such a manner that the unit may be inserted through the neck of the flask with ease. The inlet tube is turned so the incoming hydrogen will not come in contact with the thermometer bulb. The stirrer shaft is introduced through the stopper by a glass bearing and a mercury seal shown in detail in Figure 2. The mercury seal unit is made from glass rod and tubing of sizes common to all laboratories. The oil to be hydrogenated will serve as a lubricant for the glass-tube bearing. The exit tnbe is led into a bottle trap for condensation of low-boiling-point materials distilled over during the operation. This, in turn, is connected to another bottle containing water, the purpose of which is to help regulate the flow of hydrogen, allowing the gas to pass through a t the rate of about 60 bubbles per minute. From this bottle the gas should be disposed of through the hood or a vent where there is no danger of an explosion from the hydrogen. To begin the hydrogenation, a 25-cc. sample of reh e d cottonseed oil is put into the hydrogenation chamber, the freshly prepared catalyst charge is added, and the apparatus is assembled as shown in Figure 1. The air is washed out by the flow of hydrogen, and the flask in the heating oven is fitted with an asbestos collar to cover the oven. The agitator is started, the hydrogen flow regulated, and then heat applied from the
number of lard varies from 60 to 75. After 30 minutes hydrogenation proceeds rapidly, giving in 40 minutes a solid product with an iodine number of 42 which is comparable to mutton tallow. The time required for the hydrogenation, includ'mg chilling of the product, is less than an hour, provided the apparatus has been set up and the catalyst reduced prior to the time of demonstration. This demonstration, as described, has proved very satisfactory in presenting to a class some of the principles of bydrogenation as they are carried out in industry. Furthermore, it illustrates the close relationship existing between industrial processes and the theoretical chemistry which lies behind them. The above procedures may be varied to some extent to fit the needs and facilities of the individual, but in the main the described procedure has been shown by experimentation to give the most satisfactory results. The authors wish to express their appreciation to Dr. P. S. Bmndage and Mr. K. D. Conn of the Michigan State Normal College chemistry staff, and to Mr. G . W. Reed for their helpful suggestions and aid. Bunsen burner. The temperature is allowed to rise to 190°C. and then held between 190' to 200°C. for a period of 30 minutes. At the end of this time the flask is immediately removed and the oil-catalyst mixture is filtered by suction through a small Biichner funnel containing a dry asbestos mat inch thick. If the funnel has been heated, the filtering takes only a matter of seconds. The filtered oil is chilled in ice water to hasten solidification. If cottonseed oil is not available, corn oil, soya oil, or olive oil may be used in its place. Corn oil can be hydrogenated in approximately the same period of time as the cottonseed oil, whereas the soya and olive oil require 5 to 10 minutes longer. Refined cottonseed oil has a usual iodine number range of 103 to 111. The particular sample used by the authors was 115. The 30-minute hydrogenation run gave a solid fat with an iodine number of approximately 65, and was about the consistency of lard. The iodine
LITERATURE CITED (1) "Commodity Year Bmk, 1941," Commodity Research Bureau, Inc., New York, 1941, p. 218. (2) Ibid., p. 210. AND BAUGHMAN, Oil and Fat Industries, 4, 131 (3) JAMIF~EN (lYZ/J.
(4) HILD~TCH AND JONES, J.SOC.C h m . Ind., 51,202 (1932). (5) Ibid., 53, 13T (1934). (6) GILMAN,"OTganic Chemistry." 2nd ed., John Wiley and Sons, Inc., New York, 1942, Val. I, p. 802. (7) LANCE."Handbook of Chemistry," 3rd ed., Handbook Publishers, Inc., Sandusky, Ohio, 1939, p. 518. (8) JAMIESON. "Vegetable Fats and Oils," A. C. S. Monograph No. 58, Chemical Catalog Co., New York, 1932, pp. 189-
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(9) HAuB, "A novel high-scbwl experiment in hydrogenation of oils," J. C ~ MEDUC., . 8, 1856-7 (1931). (10) FURNAS,"Rogers Manual of Industrial Chemistry," 6th ed., D. Van Nostrand Co., Inc., New York, 1942. Val. 11. p. 1524. (11) ADKINS."Reactions of Hydrogen," University of Wisconsin Press, Madison, Wisconsin, 1937. (12) WUR~TER, "Hydrogenation of fats," Ind. Eng. Chm., 32, 1194 (1940).
