-
Schwarzenbach G., Fischer. A., Mb. Chim. Acta, 43, 1365 (19601: Chem. Abstr.,.55, 9020(1961). Siedlewski. J.. Roczniki Chem.. 38 (716). 1151 (1964): Chem Abstr., 62,
8435 (1965).
Siedelewski. J.. Trawinski, S.,ROczniki Chem., 40 (61, 1083 (1966):Chem. Ab&, 85. 19351 (19661: h t . Chem. Eng., 8 (41, 663) (1966). Sreeramemurthy. R.. Menon, P., J. Catal.. 37,287 (1975). SteenberQ. L. R.. Swanson, W. M.. presented at the American Institute of Chemical Engineers. National Meeting. New Orleans, La., Mar 16-20,
Tedder, A,, SvenskPappemtidning.72,294 (1969). Valensi. 0.. Camite intern. Themndynam. et Cinet. Electmchim, Compt. Rend Reunion, 51-68 (1950). Walker. P., Jr.. Shelef. M.. Anderson. R.. "Chemistry and Physics 01 Carban:' Voi. 4, Marcel Dekker, Inc.. New York. N.Y., 1968. Yamato. M., Watkins, C. H.. Hydr-rbon pTocess.. 47 (51, 131 (1968).
1969. "Sulfur." VoI. XIiI. p 1053 Nouvean Traite' de Chimie Minerale Mason el Cie., Paul Pascal, Ed.. 1960.
Receiued for reuiew March 10,1975 Accepted August 27,1975
Hydrogenation of Jojoba Oil Jaime Wlsnlak. and Michael Holin Department oi Chemical Engineering. Ben Gurion University of the Negev, Beer-Sheva. $rad
1 Dr. J a i m e Wisniak is a professor a t the Department of Chemical Engineering, Ben Gurion University of the Negev, Beer", oneva, Israel. n e receruea his B.Sc. degree from Universidad Catolica. Chile. in 1957 and a Ph.D. degree from Purdue University in
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md. Eng. Chem.. Prod. Res. mv.. VOI. 14. NO. 4. 1975
Introduction Hydrogenation is a standard technique for improving the properties of vegetable and animal oils. By hydrogenation, liquid oils such as cottonseed oil and soybean oil are converted into plastic fats, which are used in the manufacture of shortenings, margarine, soaps, and a variety of other edible and industrial fat products. In addition to increasing the softening and melting point of the fats, the hydrogenation process also improves their color, odor, and stability. Two excellent reviews of hydrogenation theory and techniques have been presented by Swern (1964) and Markley (1968). The catalysts are generally based on nickel which is sometimes mixed with copper, aluminum, andfor silicon oxides as promoters. Impurities in the oil or catalyst may poison the catalyst surf ace (Miirk. 1972). In the manufarture of most products, however, softer'fats are required, tydrogenated. The objective in parquently to hydrogenate selectively d not others. Selectivity in a chemias the preferential reduction of the ,;ules in the fatty oil. The ratalvtic hydrogenation of an unsaturated fat produces isomeric unsaturated fats (Swern, 1964), and several investigators have shown that not only the douhle bonds undergo a geometrical isomerization from the cis to the trans form but in addition the double bonds migrate along the chain forming positional isomers. In the last few years several investigators have contributed information reeardine the mechanism of the reaction and the effect of operatinivariahles on the rate of hydrogenation, isomerization, and selectivity of hydrogenation. I t is generally agreed that the reaction proceeds by a series of mass transfer and adsorption-desorption steps and that under proper conditions the main resistance may be concentrated on the chemical reaction a t the catalyst surface (Wisniak and Alhright, 1961; Eldib and Alhright, 1957). Regarding the effect of operating variables, it is agreed that selectivity and isomerization are favored by low hydrogen pressure, low agitation, high temperature, and increased catalyst concentration. Simmondsia californica, or jojoba, is an evergreen shrub of the Buxaceae family that grows in semidesertic areas and yields a nut that contains ahout 50% of an oil composed of the Czo and CZZalcohols and acid, each with one double bond. Simmondsia oil resembles sperm oil in chemical composition and behavior, and it can probably find use
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Jojoba oil was hydrogenated with several nickel and also copper-chromite catalysts under a wide range of temperature, pressure, catalyst concentration, and agitation rates. The reaction was pseudo first order and with nickel catalysts it was controlled by the surface reaction between atomic hydrogen and adsorbed unsaturate. Activation energies varied between 12.8 and 29.5 kcal/mol. Severe poisoning was. observed with one of the catalysts tested. Copper-chromite catalysts were not able to hydrogenatethe oil, but substantial isomerization was observed.
as a substitute for sperm oil and high priced waxes such as carnauba and beeswax. Partial hydrogenation yields a soft wax which, like the liquid and completely hydrogenated product, has unusual stability during long storage. The literature on the hydrogenation of jojoba oil is sparce and superficial. In a patent assigned to Taussky (1946) an example is given where jojoba is hydrogenated a t 225'F and 250 psig using a mixed catalyst consisting of ?$ nickel and % copper. The final product is a color and odor free hard jojoba oil which resembles a spermaceti-like crystalline wax. Warth (1956) reports that jojoba seed oil can be easily hydrogenated by a process similar to hydrogenation of cottonseed oil and that the resulting product consists of highly lustrous pearly white crystalline laminae that are very hard and melt at 70'. Among the uses suggested for the solid wax are ingredient in polish waxes, carbon paper, and penicillin drugs, for the waxing of fruit, and the impregnation of paper containers. It is said that candles made from it burn with a brilliant flame and do not smoke. In a paper by Knoepfler et al. (1959) a comparison was made of the hydrogenation characteristics of jojoba oil obtained by extracting the oil with solvents such as carbon tetrachloride, benzene, heptane, hexane, isopropyl alcohol, and tetrachloroethylene. Samples of the oil were hydrogenated in glass equipment using l%weight nickel catalyst at 190' and 2.5 psig, for 3 hr. It was found that the iodine value of some samples dropped to less than 1.0 while with others this was not achieved. No explanation could be found for this behavior. All samples that had iodine values of less than 1.0 had melting points between 65 and 68' and hardness values of 90 on the trionic gauge. Hydrogenated wax of a batch provided by the University of Arizona was analyzed by a commercial firm and found to have a penetration value of 1 mm/lO at 77'F and 3 mm/lO at 100°F, insolubles were 55% weight, the total acid number 1.7, and the tensile strength 225 psi. These figures make jojoba oil a good substitute for candelilla and carnauba waxes (Haase, 1974). The solubility of hydrogen in jojoba oil has been measured by Wisniak and Stein (1974) at temperatures between 50 and 250' and pressures between 100 and 800 psig. The system behaved according to Henry's law with a heat of solution of 1240 cal/mol and entropy of solution of 2.9 cal/K mol. The partial volume of dissolved hydrogen varied between 24.6 and 62.9 ml/mol in the temperature range considered. Equipment and Materials Hydrogenation runs were made in a dead-end Y4-gal batch hydrogenator, Model AF 150, manufactured by Autoclave Engineers for a working pressure of 5000 psi a t 650OF. Details of the basic experimental setup as well as of the operating procedure have been reported previously (Wisniak et al., 1974). Samples were taken through a heated line connected to the bottom of the reactor, so that no blocking by solid wax would take place. Proper control of the heating and cooling operations allowed temperature control to f2'. The jojoba seeds used in this work were obtained from
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shrubs grown at the Negev Institute for Arid Zone Research, now a part of t h e Ben Gurion University of the Negev. Cold-pressing produced a medium color oil that had the following characteristics: refractive index (20') 1.4652; iodine value (Wijs), 83.2; melting point, 13.0; acid number, 6.7; saponification number, 107. The gas chromatographic analysis was performed according to the method suggested by Miwa (1971), namely 3% OV-1 on Gas Chrom Q, 100200 mesh, stainless steel column 100 cm long and 0.2 cm i.d., temperature programming of 3'/min between 275 and 300°, injection port 350°, flame ionization oven 380°, Packard-Becker Model 417 chromatograph. The following results were obtained: c34 0.1%; c36 1.6%; c38 7%; c4032%; C42 49%; C44 9%; c46 0.9%; c48 0.1%. The oil was bleached by adding 2% of active earth, heating to 80°C for 3 hr, and filtering. Hydrogenation catalysts were obtained from Girdler-Sudchemie Katalysator Gmbh, Munich, Germany (G22, G-53, and G-70) and the Harshaw Chemical Co. (Nysel and Cu-1106P). The G-22 catalyst is a barium promoted copper-chromite catalyst which contains about 35% Cu, 28% Cr, and 10%Ba. The G-53 and G-70 products are nickel on kieselguhr catalyst with a nominal composition of 25% nickel, 10%kieselguhr, and 65% protective medium. The Cu-1106P catalyst is also a barium promoted copper-chromite catalyst with a nominal composition of 39% CuO, 44% Cr2O3, and BaO. All the catalysts were used as received without prior treatment. In all the following figures percentage and weight of catalyst refer to bulk catalyst per 1000 ml of oil. The electrolytic hydrogen was reported by the vendor to be 99.9% pure. The infrared absorption of the samples was measured by the AOCS method Cd-14-61 (1964) on a Perkin-Elmer Model 457 spectrophotometer with a 1-mm sodium chloride cell, and elaidic and brassidic esters methyl esters Ind. Eng. Chem., Prod. Res. Dev.. Vol. 14, No. 4, 1975
227
Table I. Main Runs and Kinetic Constants
Run no.
Pressure, psig
120 10 10 120 130 10 140 10 10 100 110 10 10 110 140 10 110 10 140 10 10 140 10 110 12.5 110 15 110 30 110 10 110 10 100 10 110 10 110 10 100 10 110 10 100 10 100 10 100 10 110 10 100 5 100 5 100 700 5 100 5 600 100 500 5 100 5 400 100 5 100 300 5 100 100 90 200 5 110 200 5 5 120 200 130 200 5 100 200 2.5 10 100 200 20 100 200 a Runs 1-31:G-70;runs 37-51: G-53. 1 2 3 4 5 6 7 8 9 10 11 12 18 19 20 21 22 23 24 25 26 27 28 29 30 31 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51
200 200 200 200 200 200 200 200 200 200 200 200 200 200 200 400 700 800 700 790 300 600 400 300 600 500 200 800
CataAgitaTemp, lyst," tion, k X lo3/ OC g/l. of oil rpm 2.30,min-' 920 920 920 920 920 1050 1200 1200 550 550 740 920 920 920 920 920 920 920 920 920 920 920 920 920 920 920 920 920 920 920 920 920 920 920 920 920 920 920 920 920 920
6.63 25.0 32.3 55.0 1.76 3.28 3.04 59.6 3.29 14.3 20.3 3 .oo 3.12 5.80 3.49 9 .oo 8.55 9.12 11.24 7.61 7.11 16.34 6.89 3.78 20.19 8.28 7.75 23.16 20.50 14.75 19.67 14.80 14.45 19.83 6.99 17.27 25.85 26.84 5.59 5.29 93.70
standards (Applied Science Laboratories), using the correction suggested by Scholfield et al. (1956). Iodine values were determined by the AOCS method Cd-1-25 (1964). Refractive indices were measured at 75OC with a Zeiss Abbe3L precision refractometer which gave direct readings to four significant figures. Results Eighty hydrogenation runs were made a t pressures 100 to 800 psig, temperatures 100 to 140°, catalyst weight 5 to 30 g/1000 ml of oil, and agitation rates 550 to 1200 rpm. Eight pressure levels were selected and the effect of the remaining three variables was studied at each level. The hydrogenation reaction was followed in each case by plotting the logarithm of the Wijs iodine value (I.V.) of the oil vs. the time (t) of the reaction. For most of the catalysts studied these plots were essentially straight lines after initial induction periods, so that the overall rate could be represented by the pseudo-first-order reaction 228
Ind. Eng. Chem., Prod. Res. Dev., Vol. 14, No. 4, 1975
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Figure 3. Influence of agitation on isomerization.
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The first-order reaction constant could thus be used to characterize a particular set of variables. Figure 1 shows some typical results and Table I summarizes the main runs. The advance of the reaction was controlled qualitatively through the decrease in refractive index at 75OC. It was found that this parameter varied more or less linearly with the iodine value, between 1.4391 for the fully hydrogenated wax and 1.4469 for the raw oil. Mass Transfer Effects. All runs were made using 1 1. of oil which corresponded to the impeller being located at about two-thirds of the liquid height and to the optimum dispersion of the hydrogen in the oil (Wisniak et al., 1971). Hydrogenation runs made under variable agitation regimes a t 110 and 14OOC showed that the rate of reaction was independent of the impeller speed above 900 rpm (Figure 2). These results, together with those obtained at different catalyst loadings, indicated that the chemical resistance predominated in most of the runs. Figure 3 indicates that
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Figure 5. Hydrogenation with Nysel catalyst. isomerization was not affected significantly by the rate of agitation, although a t lower agitation rates somewhat more trans isomers were formed. Catalyst Nature and Concentration. Substantial differences in behavior were observed with the different catalysts tested. All the copper chromite catalysts failed to hydrogenate the oil even under the severest conditions. This result is not so extraordinary when one considers that the accepted mechanism of hydrogenation with copper chromite catalysts involves a step that requires the presence of two double bonds capable of conjugation (Koritala, 1970). Although no hydrogenation took place, some isomerization was observed together with a green coloring of the oil. Best results were obtained with the G-53 and G-70 nickel on kieselguhr catalysts. Figure 4 reports some typical results for these catalysts. It is seen that the G-53 material is substantially better than G-70. The G-70 catalyst was active only above a loading of 5 g/lOOO ml of oil and this was attributed
to partial poisoning. It is a known fact that most oils contain sulfur and phosphorus compounds that are strong poisons for nickel catalysts. Coenen and Linde (1970) have estimated that one sulfur atom occupies about two surface nickel atoms; hence 1 mg of sulfur corresponds to a sulfur poisoned area of 2.38 m2. According to Mork (1972) the sulfur poison present in fish oils corresponds to about 0.00996 nickel; in the present case it is about 0.05% nickel. In order to test the presence of poison the following experiment was performed: 1 1. of oil was mixed with 5 g of G-70 catalyst and treated with hydrogen a t 160' and 200 psig. No drop in iodine value was observed during 2 hr. The oil was filtered, 5 g of fresh catalyst added, and the treatment reinitiated. Reaction did occur this time at a rate somewhat smaller than that of the run with the full 10 g of catalyst. The Nysel catalyst tested showed a large induction period and a break in the iodine value/time of reaction curve at about an iodine value of 40, indicating a change in the reaction mechanism (Figure 5). In Figures 6 and 7 are reported the influence of catalyst nature and concentration on isomerization, and it is seen that isomerization was not affected by catalyst concentration and that the Nysel catalyst produced substantially more trans isomers. Temperature. The values of k have been plotted in Figure 8 for the G-53 and G-70 catalysts at 200 psig. Within Ind. Eng. Chem., Prod. Res. Dev., Vol. 14. No. 4, 1975
229
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the range studied it is seen that both catalysts present typical behavior and that the straight segment is limited to a very small temperature range; below and above it reaction control probably passes from the chemical reaction to the physical steps associated with mass transfer of the components. Figure 9 represents the Arrhenius plot and indicates that the activation energy of the G-53catalyst is 12.8 kcal/ mol and 29.5 kcal/mol for the G-70catalyst. Operation of the reactor a t 120' with the G-70catalyst was characterized by thermal instability. The runs plotted in Figure 10 for this case show the upper and lower operating limits obtained. The rate of heat production and heat elimination differed substantially for small temperature variations about 12OOC so that the system would readapt itself to a lower or higher rate. This phenomenon is charac230 Ind. Eng. Chem., Prod. Res. Dev., Vol. 14, No. 4, 1975
o
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HYDROGEN
500
600
PRESSURE
loo
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Figure 11. Pressure effect on hydrogenation rate, G-70 catalyst.
teristic of the particular reactor used in this study and does not indicate that it will occur a t the same temperature with reactors of different geometry. Isomerization effects are shown in Figure 11 for the G-53catalyst and indicate that the temperature level does not influence the trans isomer content. Similar results were obtained with the G-70catalyst. The difference in energy of activation for the G-53and G-70catalysts is probably indicative of the relative degree of coverage by hydrogen atoms. Beek's (1950) results for ethylene hydrogenation indicate that hydrogen adsorbs readily on catalytic films of nickel prepared by evaporation of nickel in vacuum. The heat of chemisorption is about 30 kcal/mol for a sparsely covered surface and decreases to a value of about 18 kcal/mol when the surface is completely covered. The energy of activation for the G-53catalyst is within the range reported by Eldib and Albright (1957) for Rufert nickel catalysts.
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with the chemisorbed n bond. With G-70 this competitive reaction must be significant, particularly at high pressures. It can be expected that for the same reason the curve for G-53 will eventually bend down. The change of isomeriza7 tion with pressure is shown in Figures 13 and 14 for catalysts G-53 and G-70. The behavior of the latter catalyst is the normal one, that is, lower pressures are inducive of larger percentages of trans isomers. Catalyst G-53 behaved somewhat differently a t all the temperature levels studied. The trans content decreased with increased pressures up to 300-400 psig; a t the next pressure level the trans content went up again to continue afterward the normal decrease for increased pressures. This is probably due to a change in the structure of the hydrogen adsorbed at the catalyst surface, with part of the active layers accepting more than a monomolecular coverage by the gas.
PRESSURE, P.S.LA.
Figure 12. Pressure effect o n hydrogenation rate, G-53catalyst. 15 7 0
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Literature Cited I O IODINE
40 VALUE
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Figure 13. Influence o f pressure o n isomerization, G-53catalyst. Pressure. The effect of pressure on the overall constant is shown in Figures 12 and 13 and serves as an additional example of the differences in behavior between catalysts G-53 and G-70. With half of the concentration of the G-70 catalyst, G-53 achieves the same rate of reaction a t about 600 psig and continues to accelerate the rate with increasing pressure. The accepted mechanism of double hydrogenation on nickel catalysts (Wisniak and Albright, 1961) assumes that the controlling step is the surface reaction between atomic hydrogen and unadsorbed oil. At the site of reaction the r-bond of the oil is chemisorbed on the catalyst, allowing only cis-addition of the atomic hydrogen across the double bond. Competition between the desorbed atomic hydrogen is not affected by the pressure of the molecular hydrogen because these are different moieties. Competition between the desorbed atomic hydrogen and the molecular hydrogen for sites on the chemisorbed n-bond would not be significant unless the molecular hydrogen can somehow react
American Oil Chemist's Society, "Official and Tentative Methods", 2nd ed, Chicago, Ill., 1964. Beek, O., Adv. Catal., 2, 151 (1950). Coenen, J. W. E.,Linsen, B. G.. "Physical and Chemical Aspects of Adsorbents and Catalysts", B. G. Linsen. Ed., Academic Press, New York. N. Y., 1970. Eldib, I. A,, Albright, L. F., lnd. f n g . Chem., 49, 825 (1957). Haase. E. F., Office of Arid Land Studies, University of Arizona, personal communication, 1974. Knoepfler, N. B., McCourtney, E. J., Molaison, L. J., Spadaro, J. J.. J. Am. Oil Chem. Soc.,36, 644 (1959). Koritala, S.,J. Am. OllChem. Soc., 47, 463 (1970). Markley, K. S.,"Fatty Acids", Part 1 (1960), Part 5 (1968), Interscience, New York. N. Y.. 1960, 1968. Miwa, T. K., J. Am. OilChem. Sot., 48, 259 (1971). Mork, P. C., J. Am. Oil Chem. Soc., 49, 426 (1972). Scholfield, C. R., Butterfield, R. O., Dutton, H. J., Anal. Chem., 38, 1694 (1966). Swern, D., "Bailey's Industrial Oil and Fat Products", Interscience. New York, N. Y., 1964. Taussky, I., U. S.Patent 2,413,009 (1946). Warth, A. H., "The Chemistry and Technology of Waxes", p 172, Reinhold. New York, N. Y., 1956. Wisniak, J., Albright, L. F., hd. f n g . Chem.. 5 3 , 375 (1961). Wisniak, J., Hershkowitz, M., Leibowitz. R., Stein, S., hd. Eng. Chem., Prod. Res. Dev., 13, 75 (1974). Wisniak, J., Stefanovic, S.,Rubin, E., Hoffman, S..Talmon, Y., J. Am. Oil Ch8m. SOC., 46, 379 (1971).
Received for review January 13,1975 Accepted September 4,1975 Supported in p a r t by a research g r a n t f r o m t h e U n i t e d States-Isr a e l B i n a t i o n a l Foundation.
Ind. Eng. Chem., Prod. Res. Dev., Vol. 14, No. 4, 1975
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