APRIL, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
the changes in physical properties of the coke brought about by oxidation. Using Figure 4 and the ultimate and proximate analyses of a new coal, the sensitivity of the coal toward oxidation can be estimated. If tests on other coals should confirm this relation, it will be valuable in that it establishes a norm from which deviations due to differing petrographic constitution, sulfur content, etc., can be considered.
Aclrnowledgment The authors are indebted to H. ill. Cooper for chemical analyses, to D. A. Reynolds for carbonization tests, and to W. A. Selvig and W. H. Ode for agglutinating-value tests. They also wish to thank H. 8. Buvil for assistance in reviewing the manuscript,
Literature Cited (1) Am. SOC. Testing Materials, 1938 Supplement t o A. S. Standards, pp. 157-62, D388-38.
T. M.
5.55
Fieldner, A. C., and Davis, J. D., U. S. Bur. Mines, Monograph 5 (1934). Holmes, C. R., Brewer, R. E., and Davis, J. D., IXD.EXG. CHEM.,to be published. Jiippelt, -4., and Steinman, A , , Oel Kohle,Erdosl Teer, 13,1027-30 (1937) : Feuerungstech., 26, 169-72 (1938) ; Steinman, a,, Braunkohlenarch., No. 49-50, 3-29 (1938). Lambris, G., and Boll, H., Brennstoff-Chem., 19,177-84 (1938). Lesher, C. E., and Zimmerman, R . E., Coal Age, 44, S o . 3, 45-9 (1939).
Porter, H. C., and Ovitz, F. K., U. 9. Bur. Mines, BulZ. 136 (1917), Tech. Paper 16 (1912). Rose, H . J., and Sebastian, J. J . S., T r a n s . Am. Inst. Mining Met. Engrs., 88, 556-84 (1930); Fuel, 11, 284-97 (1932). Schmidt, L. D., and Elder, J. L., ISD. ESG. CHEnr., 32,249-56 (1940).
Schmidt, L. D., Elder, J. L., and Davis, J. D., Ibid., 28, 1346-53 (1936).
Tancey, H.F., and Zane, R. E., U. S. Bur. Mines, Rept. Investigations 3215 (1933) ; Colliery Guardian, 147,343-5 (1933). PRESENTED before t h e Division of Gas and Fuel Chemistry a t the 98th Meeting of the American Chemical Society, Boston, Zllass. Published b y permission of t h e Director, U. S.Bureau of Mines. ( N o t subject t o copyright.)
Catalytic Methods for Increasing
the Unsaturation of Long-chain Fattv Compounds J
DEHYDRATION OF CASTOR OIL The dehydration of castor oil is investigated with a great variety of catalysts. Their relative effectiveness is determined by means of the water evolved in the process and by the iodine number (Wijs) of the product. The mechanism of the catalytic dehydration is discussed, and several lines of evidence are presented to prove that the product contains a considerable proportion of molecules having conjugated double bonds. The catalytic dehydrogenation of oleic acid is briefly considered as an alternative process. WO general methods suggest themselves for increasing by catalytic means the unsaturation of long-chain fatty acids and esters-namely, dehydration and dehydrogenation. Both methods were used but only dehydration gave the desired large increases in unsaturation. Castor oil is an ideal starting material for the dehydration experiments since it is readily available in a high degree of purity, and contains a hydroxyl group and a double bond in each chain. An examination of the E formula for the triglyceride
T
WILLIAM C. FORBES AND HARVEY A. NEVILLE Lehigh University, Bethlehem. Penna. (molecular weight 926) reveals that if the hydrogens removed with the hydroxyls are the ones indicated, the resulting product will have a conjugated system of double bonds.
If the other possible hydrogens-i. e., those to the left of the hydroxyls as written-were removed, the resulting product would contain an isolated system of double bonds. From practical considerations the conjugated system would be preferable because of its readiness to form films. Evidence that the product obtained actually contains a considerable percentage of the conjugated system is presented in this paper. The dehydration of ricinoleic acid was carried out by Fokin (4) with phosphorus pentoxide in benzene solution, by Boeseken and Hoevers (3) under vacuum distillation with active alumina, and by Scheiber (IO) who combined the product with glycerol. Castor oil was dehydrated according to Ufer ( I S ) by heating it in the presence of a small percentage of an acid compound of the nonoxidizing mineral acids containing oxygen. Yamada (14) accomplished this by heating castor oil to 200250" C. in the presence of Japanese acid earth as a catalyst.
INDUSTRIAL 9 N D ENGINEERIKG CHEMISTRY
556
I. DEHYDRATIOK O F CASTOR
TABLE
Catalyst
Conditions
c.
207, bentonite 20Y0 kaolin 1670 kaolin 10% kaolin 4% White Bond clay 4T0 S o . 1 Ware clay (kaolin: l\lgSOa = 95:5) (NaHSOa: Ware clay = 9:l) Cellite 4 7 pumice 10% KHS04 20% KHSOa 5% KHSOr 5% KHSOa (added later) ? % KHSOI a % NaHSOI 2 % LiHS04
+
KHSOp
+ 1%
{
KaHGOr
NaHSO4.HnO NaHSOa.Hn0 Chromium acid sulfate
4%
230-240 225-240 229-235 230-240 230-240 240-250 230-240 235-240 230-240 -236 240-250 -254 200-237 200-223 230-240 230-240 240-250 -240 180-185 -263 250-276 240-255 230-250 240-250 240-250 230-250 240-253
otassium alum powder ferric ammonium alum powder
-230
Room temp -250 170-180 '
sample.
86.4"
% Increase
Iodine T o .
Min. 45 50 30 30 30
in Unsatn.
12G.4 146.2 149.1 137.7 135.0 129.5 133.6 139.4 129.1 127.6
46.3 69.2 72.5 59.4 57.0 49.9 54.6 61.4 49.4 47.7
30
116.4 117.9 113.7 117.1 97.8O 127.6 122.0= 94.1a 130.0" 108.1" 132.2 O 134.gn 122.7
3i:7 36.5 31.6 35.5 13.2 47.7 41.2 8.9 50.5 25.1 53.0 5G. 1 42.0
60 34
132.2a 135,Oa
53.0 56.3
12
117.ja 128.1 130.5 113.8 110.0" 133.8; 137.5 1?8.0U 116.0'' 129.8"
3610 48.2 51.0 31.7 27.3 54.9 59.2 48.2 29.6 43.4
89.50
3.1
60
50 75 60
.. ..
11
30 45 105 30 30
.. ..
30 80 60
4,5 GO
-250
160-155 -260 230-240 230-240 -260 -260 220-257 -240 250-252 230-240 -27 1 -280 -244 230-240 -260 230-255 -265 -265 230-255 240-257 240-250 235-263 -250 -245 -250
O I L O F I O D I X E XUMBER
VOL. 32, NO. 4
11 40
.. ..
30
6 15
.... ..
19
.... ....
....
85.0 93,'3a
....
100
145.0
53 60 30 42
119.2a 143.3'3 148.8a 127.3n
..
..
.. .. .. .. ..
..
Schwarcman (11) dehydrated castor oil by heating it with a small amount of sulfuric acid adsorbed on an inert earthy carrier such as fuller's earth. RIiinzel (9) claims freshly precipitated tungstic acid anhydride as the catalyst for this process. H e also mentions the use of thorium oxide, uranic acid anhydride, molybdic acid anhydride, and a mixture of iron oxide, zinc oxide, and aluminum hydroxide, all freshly precipitated.
Experimental Procedure The catalysts used were those which a comprehensive survey of the subject of dehydration suggested as potentially active. The increase in unsaturation of the oil was measured by determining the iodine number of the product. The standard procedure for the Wijs method, calling for a standing interval of 30 minutes, was used ( 1 ) . After many determinations had been made, it was found advisable to standardize on a sample weight of 0.1 gram. The iodine numbers obtained with this weight of sample are marked a in Table I. In most of the ex eriments a sample of 50 grams of castor oil was used, containeg in a 500-ml. round-bottom, short-necked flask. After the catalyst was added, a three-hole rubber stopper was inserted which contained an inlet tube for the inert gas used for agitation, a thermometer, and a delivery tube; the flask was then heated by a bath of molten Wood's metal. The delivery tube was connected to an air condenser which delivered to a graduate. If completely dehydrated, a 50-gram sample should yield a little less than 3 ml. of water. The extent of dehydration, therefore, could be roughly estimated by the amount of water collected in the graduate, although a few droplets usually adhered
....
....
.... .... .... ....
..
,
..
S.'O
67:s
..
38:O
65.9 72.2 47.4
85.85
.. .. .. .. ..
99.on
14:6
....
Comments Difficult t o separate Difficult t o separate Cerit ri f uged hrir
Such Clay 'i.0. Such Clay Co. Slightly c l o d y Dark, clear N o water N o water Clear, slightly darker
....
Color Color Color Color
.... .... ....
very dark dark liglit dark
....
Mechanical ztirrer Color lighter t h a n with either alone Color li$l;t' ' N o water Color dark Color fairly light Color very dark
Color l i i i t ' ' Color dark Brown color Color very dark Color fairly light Color dark
....
N o water S o water
....
S o water Colored product S o water K o water Colored prodiict Mechanical stirrer l\lechanical stirrer RIechanical stirrer N o water No water N o water N o water N o water N o water
....
to the condenser and some was carried away as vapor by the inert gas. Foam formation on the surface of the oil was another indication of catalytic activity, beginning a t a much lower temperature v-ith some catalysts than with others. As a rule, the temperature was increased rapidly to about 200" C., after which it was allowed to increase a t a more moderate rate to about 230" C. The active range of the majority of catalysts was 200-280" C., the latter half being much the more effective. Above 250' C., with an active catalyst, some waxy or oily substance was usually carried over and deposited in the condenser. The range of temperature used in each experiment is indicated in Table I under "conditions". Where the flask and its contents were merely raised to some particular temperature, this is indicated by a dash before the temperature. In all the experiments temperature proved to be an important variable. In general, the reaction was more pronounced at an elevated temperature, but in many experiments, especially tvith the strongly acid catalysts, this had to be avoided because of charring. Table I reveals that those catalysts which were especially effective belonged to the following groups-clays, acid derivatives of sulfuric acid, phosphoric acid, and oxides of certain metals. When the clays were used as catalysts, the extent of dehydration increased roughly with the amount used; rather large amounts were required to obtain products with the highest iodine numbers. At the end of the reaction the bulk of the clay formed a puttylike mass in the bottom of the flask. The remainder of the clay was so finely dispersed that it was extremely difficult to obtain enough clear sample, by
INDUSTRIAL AND ENGINEERING CHEMISTRY
,\PRIL, 1940
sedimenting and centrifuging, for iodine number determinations. K h e n such a separation was made, the oil obtained was very light yellow. The "fines" of one sample of clay were floated off before use, but 110 visible improvement resulted since aggregates of fine particles broke down during heating to give dispersions just as difficult to filter or settle. Figure 1 shows the rate a t which water was evolved on a larger scale where it could be more accurately measured. I n another attempt to improve the settling of the clays, a catalyst was prepared by mixing the clay with a solution of a n electrolyte to form a paste which was then dried and powdered. Wherever any great improvement in clarity was noted, the activity of the catalyst was greatly impaired. A silicate of the glassy type such as pumice, with little or no affinity for water, had no catalytic activity for this reaction. Several determinations starting with larger amounts of castor oil, using 4 per cent of Xo. 1 Ware clay as a catalyst and a temperature range of 230-240' C., permitted the percentage increase in unsaturation to be calculated both on the basis of the water evolved and of the iodine number: Grams of Oil 822.0 813,O
737.3
Iodine No. 133.2 131.3 129.7
Theoretical hZ1. HzO H20, 311. Collected 47.9 31.0 47.4 31.4 43.0 27.0
yo Increase in Unsatn. On H20 evolved 64.7 66.3 62.8
On iodine h'o. 54.2 52.0 50.2
The higher value based on the water evolved may be due to linkages being formed not leading to unsaturation, or the difference in the two values may result from failure to obtain the maximum or true iodine number-an error characteristic of a conjugated system of double bonds. Both factors are probably involved. The acid sulfates as a class were effective in this reaction and had the distinct advantage over the catalysts previously mentioned that they could be easily separated from the product. They settled to the bottom of the flask, and the clear oil, slightly darker in general due to charring, could be poured off. From a practical point of vie\T, sodium acid sulfate was the most satisfactory of these. A concentration
557
of 5 per cent gave a dark product, but that obtained with 2 per cent was light in color and greatly increased in unsaturation. Part of its activity may be due to the fact that it is a solid a t the temperature of reaction. It is inkresting to note the activity of the acid sulfates of the first group of the periodic table in this reaction: Iodine No. Yo Increase of Product 122.0 135.0 130.0 117.1 94.1
Acid sulfate
in Vnsatn. 41.2 56.3
50.5 35.5 8.9
Their activity is no doubt clue to their tendency to liberate sulfuric acid or to the amount of sulfuric acid with which they are in equilibrium a t the temperature of the reaction. This tendency decreases with increase in molecular weight. Lithium acid sulfate is the most active in that it begins to liberate water a t a lower temperature, but it chars so much that an elevated temperature cannot be employed. Sodium acid sulfate has already been discussed. Potassium acid sulfate is less active, and larger amounts may be used without excessive charring. Ammonium acid sulfate, due to decomposition, gives a dark product which remains tacky when spread on glass, even after weeks. A peculiarity encountered with mixtures of sodium and potassium acid sulfates was the fact that, although the iodine numbers of the product 1%-erealways intermediate between those obtained with either acid sulfate alone, in every case the color was distinctly lighter. Of the acids, sulfuric was too active in the amount used and caused great charring. Phosphoric acid in low concentration ( 2 per cent) was effective and did not discolor excessively. The alums and sulfates evidently owe their activity to their tendency to break down into sulfuric acitl. For example, ferric sulfate on heating in the preeenccl of water reacts:
+ 3HzO
Fe2(S0d)3
+ 3H,S04
Fe203
As would be expected, phosphorus pentoxide IS quite active. the color becoming dark when 2 per cent is used. Boric anhydride, however, has only a slight effect. Only two metallic oxides, both in the same group of the periodic table, showed any activity in this reaction. That of molyb40 denum was moderate but that of tungsten, especially vhen mechanical stirring replaced agitation by inert gas, was marked. The mode of preparation of the latter was important since high iodine numbers were obtained 30 0 only when the yellow oxide, W03.H20(J. T. 0 Baker Chemical Company), was dissolved in sodium hydroxide, heated to the boiling al P point, and precipitated by aqua regia. This ri precipitate was washed with water by de20 W cantation until a colloidal solution formed 0 which was then evaporated to dryness. This d residue ground in a mortar proved effective ri as a dehydrant. However, it became active i?10 only after it changed during the heating to the blue oxide, WsOa. It is difficult to remove the last traces of this catalyst from the oil, It was expected that some of the acid phosphates would be effective as dehgdrants, by 0 analogy to the acid sulfates, but this result was not found, Time, min. The only organic compound tried, p-toluene FIGURE1. RATEOF EVOLUTION OF WATER DUE TO ACTIONOF 4 PER CENT sulfonic acid, showed a definite action, even KAOLINON 952.2 GRAMSCASTOR OIL a t the moderate temperature (170-180° C.) Temperature prevailing is indicated by the dotted curve. which had to be used.
.
'c(
:
INDUSTRIAL AND ENGINEERING CHEMISTRY
558
Ricinoleic acid when dehydrated with catalysts which had been found to be effective with castor oil gave definitely lower results. When the low- and high-melting forms of 9,lO-dihydroxystearic acid (8,6) were dehydrated with 2 per cent sodium acid sulfate, the high-melting form gave a product with more than twice the degree of unsaturation of the low-melting form (iodine numbers, 79 us. 37). This could be due to water splitting out from the two adjacent hydroxyl groups, or other condensation reactions could have intervened. Both products contained a solid phase which might have been due t o polymerization.
Mechanism of Dehydration For those compounds which are derivatives of sulfuric acid the most plausible mechanism is as follows :
OH -CH-CH2-CHaCH-
1
+
H20
That involving phosphoric acid is no doubt analogous. To explain the action of tungstic oxide, the mechanism of Sabatier and Mailhe given by Green (6) for the dehydration of alcohols appears satisfactory:
+
-CH=CH-CH=CH-
The clays probably owe their activity to their extremely fine particle size, approaching colloidal dimensions. (Tungstic oxide was found to be much more active when its particle size was in this range.) I n addition, their ratio of silica to alumina is a factor as well as their affinity for water.
Type of System Formed The possibility of obtaining, on theoretical grounds, either
a conjugated or isolated system of double bonds has already been mentioned. There are three lines of evidence which indicate that the product contains a considerable percentage of the conjugated system. DIENE NUMBER. I n the Diels-Alder synthesis, maleic anhydride is known t o add 1,4 to conjugated systems. Therefore, if the dehydrated oil adds maleic anhydride, the conclusion is that it contains conjugated double bonds. At the same time, a comparable experiment was made with the original castor oil to determine to whht extent, under the conditions of the experiment, maleic anhydride would react with the hydroxyl group. The procedure was that given by Kaufmann and Baltes (7). The following diene numbers were obtained : Castor oil
After this determination had been completed, confirmation was found in the work of Boeseken (3) who concluded from a Diels-Alder reaction that the product he obtained from dehydrating ricinoleic acid contained 75 per cent of 9,11linoleic acid, the conjugated isomer. IODINE NUMBERS.The fact that the iodine numbers of the product vary greatly with the size of the sample used for analysis is another convincing evidence that conjugated double bonds are present. The basis for this evidence is presented by the authors in another article (4A). FILMFORMATION. Most of the products with the higher iodine numbers gave nontacky films after a short time. This, in conjunction with the two lines of evidence already given, indicates the presence of conjugated double bonds.
Dehydrogenation of Oleic Acid Levey (8) indicated that the dehydrogenation of oleic acid was entirely practical, but the work of Suzuki and Kurita ( l a )with a great many catalysts did not check this conclusion. I n the present work liquid phase experiments were carried out using different percentages of Raney nickel and freshly precipitated chromic oxide, the latter giving a product with slightly increased unsaturation (3 per cent). Vapor-phase experiments with copper gauze as catalyst and temperature ranges up t o 360” C. were unsuccessful. A similar experiment with freshly precipitated chromic oxide on coke a t 475’ C. gave a product in which the unsaturation had increased 9 per cent. If the oleic acid was first heated with 1 or 2 per cent sulfur and the heating continued a t 200-250’ C.in the presence of 1 per cent sodium acid sulfate, hydrogen sulfide was evolved. Heating periods of 1 to 1.5 hours led to increased unsaturation: with 1 per cent sulfur, 10.5 per cent, and with 2 per cent sulfur, 12.5 per cent. Since hydrogen sulfide was evolved throughout the heating, further increases in unsaturation would no doubt have been obtained if the heating had been prolonged.
Literature Cited
J.
-C€I=CH-CH=CH-
Castor oil dehydrated with 16% kaolin
VOL. 32, NO. 4
2.21 16.66
(1) Assoc. Official Agr. Chern., Official and Tentative Methods of Analysis, 4th ed., 1935. (2) Bauer, K. H., “Die trocknenden Ole”, Stuttgart, Wissenschsftliche Verlagsgesellschaft m. b. h., 1928. (3) Boeseken, J., and Hoevers, R., Rec. trav. chim., 49, 1163, 1165 (1930). (4) Fokin, S., J . Russ. P h y s X h e m . Soc., 46, 224-6, 1031-2 (1914). (4A) Forbes, W. C., and Teville, H. A., IND.ENQ. CHEM.,Anal, Ed., 12, 72 (1940). Green, S. J., “Industrial Catalysis”, New York, Macmillan Go., 1928. Hilditch, T. P., J . Chem. Soc., 1926, 1828. Kaufmann, H. P., and Baltes, J., Fette u. Seifen, 43, 93-7 (1936). Levey, H. A., U. S. Patent 1,374,589 (1921). Munzel, F., Swiss Patent 193,931 (1937): French Patent 830,494 (1938). Scheiber, J., U. S. Patents 1,942,778 and 1,979,495 (1934). Schwarcman, A . , Ibid., 2,140,271 (1938). Suzuki, T., and Kurita, T.,Sei. Papers Inst. Phgs. Chem. ReseaTch (Tokyo), suppl., 9, 5-6 (1928). Ufer, H., U. S. Patent 1,892,258 (1932). Yamada, T., J . SOC.Chem. Ind. Japan, 38, Suppl. Binding, 120-3 (1935). PRESENTED before the Division of Paint and Varnish Chemistry a t the 98th hIeeting of the American Chemical Society, Boston, Mass. W. C . Forbes is Research Assistant a t Lehigh University of Devoe and Raynolds Company, Inc.
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