Catalytic Isomerization of
Vegetable Oils IVICKEL CATALYSTS S. B . Radlovel, If. -\I. Teeter, TV. H . Bondz, .J. C. Cowan, and J . P . ICass3 NORTHERY REGIONAL RESEARCH LABORATORY. U. S. DEPARTIIEYT OF 4GRICULTURE, PEORI 1. ILL.
Catalysts have been found which are effectite in the isomerization of vegetable oils to conjugated forms. These catalysts include active surface materials such as diatomaceous earth and carbon black, nickel on kieselguhr, and nickel on carbon black. Since these catalysts are neutral, they do not split ester linkages, and no further chemical treatment of the isomerized oil is required. The nickel-on-carbon catalyst is the most effective,particularly H hen i t is prepared by reduction of a suitable nickel salt on Nuchar XXX or Nuchar C-190. When 6 to 8% of reduced catalyst is heated for 6 hours at 170' C. with alkalirefined soybean or linseed oil, 30 to %yo conjugation is obtained. A sample of catalyst may be used to isomerize five to ten batches of oil before its activity is lost. The treated oils dry in substantially less time than the untreated, and the water and alkali resistances of their films are appreciably improved. A process is proposed for conjugating vegetable oils by the nickel-on-carbon catalyst.
T
HE shortage of tung oil during World War I1 emphasized the need for the development of an economical process for the isomerization of domestically available nonconjugated oils to conjugated forms. While the alkali isomerization processes described by Kass and Burr (6, 12) and Bradley and Richardson ( S , 5 ) offer considerable promise, they are relatively cumbersome. Moreover, the properties of these isomerized oils have not met the expectations based upon the amount of conjugation achieved by alkali isomerization (18). The partial hydrogenation of linolenates and linoleates, or even oleates, yields a considerable proportion of the so-called iso-oleic acids. These are now known to be mixtures of elaidic acid and mono-unsaturated acids in which the double bond is not in the usual 9-10 position. Sabatier ( 1 7 ) called attention t o the effects of hydrogenation catalysts other than promoting reductions. Moore ( 1 6 ) noted the effects of temperature, pressure, and the nature of the catalyst on the formation of these "iso-oleic" acids. H e observed t h a t palladium a t 180" C. was effective in the isoinerization. Copper powder was also cited (14) in this connection. Subsequent studies by Bauer, Hilditch, Waterman, and co-workers (2, 9, 10, 22) definitely established t'hat the production of "iso-oleic" acids IS a t a maximum under the conditions of selective hydrogenation-that is, when hydrogenation is effected by the agitation process a t high temperatures (200" C. or above), low pressures, in the presence of a moderate concentration oi powdered hydrogenation catalyst. The isomerization of linoleates and linolenates under conditions of selective hydrogenation in the absence of hydrogen might therefore be expected. Waterman and van Tussenbroek (28) and van Dijk ( 7 ) found t h a t soybean oil a n d ethyl linoleate showed a rise in refractive index and a fall in iodine value on heating with nickelcatalysts for 5 hours a t 250" C. in a vacuum, whereas ethyl oleate and stearic 1
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Present address, Interchemical Corporation, N e a Tork, N . Y.
' Present address, R . F. D. No. 2. Oaktarvn, I n d .
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997
acid sho\ved no change. \ ~ a t e r m a ni t n c t van Vlodrop ( 2 4 ) later inferred the formation of conjugaticn in the linoleic acid fraction of tlie oils, since a high refractive index and a lon. iotline value are charactcJristic of conjugated systems. Hon crnian lice of and ~ a 1 1Vlodrop offered no direct evidence for conjugation in their isomerized materials, nor tiid they make comparisons in the drying rates of the ran. and treated oils. I n a later paper (26) they mentioned t h a t , a t high tempcraturcs (290' C.), hydrogenation catalysts in the absence of hJ tlrogcn produced elaidinization in ethyl oleate. Recently Turk and ro-workers (20, 21) reportcd the isomerization of linseed fat acids, linseed oil, and menliric!en oil by heatiug for 2-4 hours a t 290-300" C. with siliceous materials, such as floridin, bentonite, and kieselguhr, or with metallic oxides, such as aluminum oxide and oxides of groups IVand VIA of the periodic system. Their results must be accepted with reservation because proof of conjugation Kas based upon exaltation of molecular refraction rather than upon the well-established spectrophotometer method, and the criterion of exalted molecular refraction has not proved satisfactory when applied to such a complicated system as a vegetable oil derivative. Furthermore, no data are presented which would eliminate other possible causes of increased refractive index, such as polymerization, anhydride formation, or cracking. l f a t t i l ( 1 5 ) reported the production of small amounts of conjugation (2.57, or less) when soybean oil was heated with a nickel catalyst a t 400' F. The expired patent of Levey ( I S ) , which describes a process for heating oils with various metallic catalysts after partial hydrogenation, indicates t h a t hydrogenation catalyst5 may improve the drying properties of oils, Levcy claimed that the improvement was due to dehydrogenation. However, in their work n-ith isolated saturated and oleic acids, Suzuki arid Kurita (19) and Forbes and Seville (8) failed to find any significant dehydrogenation by a large number of catalysts. Kcvertheless, the catalytic approach to isomerizat,ion appeared feasible and methyl esters were chosen for our first work because of the ease of differentijiting b e b e e n isomerization and polymerization by distillation. CONJUGATIOX WITH NICKEL-KIESELGUHR CATALYST
Preliminary experiments disclosed that a small amount of conjugation could be achieved by heating either vegetable oils or their methyl esters with platinum, palladium, and nickel catalysts. Consequently an investigation of a nickel-on-kieselguhr catalyst, prepared according to -4dliins ( I ) , was conducted. hfethyl esters of soybean fat acids were treated in an inert a b mosphere for various periods a t 210-220' C . with 307, of their weight of a catalyst containing 0.2 gram of nickel per gram of kieselguhr. ilfter isomerization the methyl esters were distilled a t 0.5 to 1.0 mm. until the pot temperature reached approximately 250' C. The amount of nonvolatile material iyas determined, and spectrophotometric estimates of tlie amount of conjugatioii were obtained for the original reaction mixture and the volatile fraction obtained on distillation. These values were
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INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLEI. EFFECTOF NICKELKIESELGUHR CATALYST o s SOYBEAN M E T 3 Y L ESTERS TREATED AT 210-220" c. Measurement Nonvolatile, yo Diene conjugation of reeationmixture, % Diene conjugation of distillate. %
Controls 0 hr. 16 hr. 5.5 7.0
Duration of Treatment with Catalyst 8 hr. 12 hr. 16 hr. 9.9 15.7 17.7 19.5
4 hr.
0.54
1.82
12.2
13.6
15.7
18.1
1.06
0.98
12.0
14.5
15.7
17.3
TABGE 11. ISOMERIZATION OF SOYBEAN METHYLESTERSWITH ACTIVESURFACE MATERIALS Amount, Catalyit Nons Acid-w*ihed kieselguhr Activatsd alumina (200
meah)
% I
.
23
Xonvolatile Matter,
Diene Conjugation of Distillate,
%
%
5.5 14.4
1.0 11.3
23
13.2
5.0
3.4 18.5
4.7 12.8
10
5.4
28.9
3.9
23
Activated carbon Florex XXF (A1 iilicats clay)
Diene Conjugation of Reaction Mixtureu, 0 5 10.9
After 16 hours a t 210-220° C.
TABLl
111.
IBOMERIZATION O F ALKALI-REFIXED LINSEEDOIL WITH ACTIVE SURFACE hfATERI.4LS Amount,
Catalyst h i d - w a s h e d kieielguhr Activated carbon Florsx XXF
%
23
23
30
Diene Conjugation', 70 3.1 8 5 1.9
Viscosity a t 2.5' C. (Gardner)
Color (Gardner)
A F
6
T-U
4 l l b
'A h r
1 6 h o u n at 210-220° C. under carbon dioxide. b Q r e m fluoreacence present.
compared with similar data obtained in corresponding control experiments. T h e results are given in Table I which, for brevity, lists control data for heating periods of 0 and 16 hours only. The results indicate t h a t the nickel-kieselguhr catalyst produces significant amounts of conjugation in soybean methyl esters. The duration of heating had little effect on the diene conjugation of the reaction mixture because of increasing amounts of polymerization. This result may be due to specific polymerizing activity of the catalyst, or i t may be caused by polymerization a t 210-220" C. of the conjugated methyl esters. Only minor decomposition was noted during these experiments. I n these experiments conjugation was determined (4, 11) by means of a Beckrnan quartz spectrophotometer, Model D. Purified Skellysolve F and n-hexane were used as solvents for the analytical samples, and values were taken as 1150and 1850 a t 2320 b. and a t 2705 .&., respeotively, for 1007, diene and 100% triene conjugation.
about 0.1 to 0.3 (Table V). The catalysts were effective with oils as v d as with methyl esters, and exerted only a limited polymerization action if employed under the proper conditions. These catalysts are required in comparatively small amounts, usually 6 to 8% of reduced catalyst based on the weight of oil treated. Xany commercial grades of activated carbon were tested as components of the catalyst (Table VI), but isomerizing aetivity was found only when t h e activated carbon n-as selected from the group called Suchars, a t l pe of carbon prepared from thc residues of sulfite viaete liquors. Suchars C-190 and XXX were exceptionally satisfactory in this respect. One sample of Xriciiar 2A was received which \vas equally satisfactory, and several cxperiments are included in m-hich this carbon was used; subsequent samples were unsatisfactory. Four types of nickel-carbon catalyst compositions w r e developed. Each gave an active isomerization catalyst after reduction with hydrogen. The catalysts Tvere: Type A, nickel formate deposited on activated carbon; type B, nickel chloride deposited on activated carbon, followed by treatment with sodium bicarbonate; type C, nickel nitrate deposited on activated carbon, folloTved by treatment with ammonium carbonate; and type D, nickel nitrate deposited on activated carbon. The catalysts were prepared as folloivs:
TYPEA. A filtered solution of 192 grams of nickel formate [Ki(HC02)2.2H20]in 5 liters of distilled water is mixed with 210 grams of activated carbon. Water is then evaporatcd from the mixture until a paste is formed. The paste is dried overnight a t 90" C., and is ground to a powder and stored. T h e ratio of nickel to carbon in this catalyst is 0.291. TYPEB. A solution of 95.2 grams of nickel chloride (Sicla. 6HzO) in 160 ml. of distilled water is ground with 100 grams of activated carbon in a mortar. A solution of 67.2 grams of sodium bicarbonate in 500 ml. of hot water is added, and the ingredients are mixed thoroughly until the evolution of gas ceases. The mixture is filt,ered, and the filter cake is washed with about 200 ml. of Lvater in small portions. The moist cake is dried a t
TABLEIT. ACTIVITY O F I N D I V I D r A L CATALYST IS ISOUERIZIXG LISSEEDOIL Yeight, Component Nuchar 2Aa Reduced nickelb C a t a l \ s t A (Nuchar 2A) N i x t u r e S u c h a r 2A a n d reduced nickel
9
Time, Hr. 8 4 6
12
8
'-i
g 5 a
CO\lPOiYESTS
COIIJUR~tlon, 7*
Tcnrp., O C 17 0 210-220 170
0 0
0 0 3-1 3
165
8 0
T h e S u c h a r 2.1 used was from a very active sample; subsequent samples were not active (Table VI). b Prepared by tne dr). reduction of nickel formate. a
TABLEy.
CONJUGATION WITH ACTIVE SURFACE MATERIALS
During experiments t o determine whether the activity of nickel-kieselguhr was additive or cocatalytic in nature, the activity of kieselguhr alone as an isomerization catalyst n-as determined and compared with the activity of several other active aurface materials (Tables I1 and 111). Both oils and methyl esters were heated with these substances. All of the active surface materials possessed definite isomerising activity. Methyl esters Rere more readily isomerized than were the oils. Activated carbon was the most active isomerization catalyst of the materials tested.
Vol. 38, No. 10
Ratio Si/C
EFrECT O F T A R Y I S G
R ~ T I OOF
S I C h C L TO
CAItBON
os C %TALE ST A C T I \ I T I ~ Total Catalyst, %b
Coniugation,
R
Ratio Si/C
Total Catalpt,
Coniugation,
70
D/cb
a Alkali-refined linseed oil was m e d ; catalyst was t y p e C ( S u c h a r SXX) Experiments were conducted f o r 6 hours a t 165' C . b Based on t h e weight of oil used.
OF CHOICEOF CARBOX ON ANOCNTO F TABLE VI. EFFECT
COXJTGATIOS
Conjugation-,
CONJUGATION WITH NICKEL-CARBON CATALYSTS
Because of the isomerizing ability of activated carbon, catalysts composed of nickel on carbon reduced with hydrogen were prepared. A striking augmentation of isomerizing activity was observed (Table IV). The most active catalysts were obtained when the ratio of nickel to carbon in the reduced catalyst was
Group Carbon 1 Piuchars SSS,C-190, '2-750, C-1000, 2Ab 2 S u r h a r s G L C-115 N IT D S u r h a r s 2Ad, GFO. 2 (alkaline), 00 Oil, 00 N , \VA; 3 S o r i t SG 11: Darco G-60 4 Nuchars 3 Oil, Aqua F a n : Korits .IG-NC, A After 6 hours a t 170' C.
5'0
>30 20-28 10-20
