Mav. ‘1924
IND USTRIAL A iVD ENGINEERIATG CHEMISTIZ Y
519
Heterogeneous Catalysis’ I--Selective Action of Catalytic Nickel in Hydrogenation of Certain Vegetable Oils By A. S. Richardson, C. A. Knuth, and C. H. Milligan THEPROCTER & GAMBLBCo., I V O R Y D A L E , ‘ ~ H I O
T
H E term “selective hydrogens t i o n ’ ’
The previous literature on selective hydrogenatioq is reviewed and new evidence presented to show that the hydrogenation of cottonseed. peanut, and SOY bean oils with the use of nickel catalyst is daracterized by the preferential conversion of linoleic acid to oleic acid and its isomers. The selective hydrogenation of linoleic acid appears to be more marked with use of increasing amounts of catalyst and with increasing temperature up to an optimum in the neighborhood of 2000 ,-.
might appropriatelY be used to describe the prefe w ~ t i a lsaturation of any group of double bonds ~ h i c h@anbe structurally distinguished from the remaining double bonds in a reaction mixture. As a matter of fact, the term has been most often used to describe the preferential of linoleicto oleic acid mixtures where both these unsaturated free Or combined, are subjected to the action of hydrogen in the pres@nee of‘ a nickel or other metallic catalyst. By a logical extension of this Common usage, selective hydrogenation may be defined as the conversion of more highly unsaturated fattv acids to acids of corresnonding molecular weight contain\ng one double bond, withLut thgformation of sucstantial of completely saturated fatty acids, the extreme case of selective hydrogenation, Probably never to be realized in practice, the last trace of fatty acid containing two or more double bonds would be entirely eliminated, by conver;rion to oleic acid or its analogs, without any conversion of the latter to saturated fatty acids. PREVIOUS WORK
Bomer,2 from a study of the iodine value of the liquid fatty acids isolated from a few samples of hydrogenated oils, concluded that the fatty acids containing two or more double bonds are completely saturated more readily than is oleic acid. Bomer apparently did not consider the possibility of the preferential hydrogenation of linoleic acid to the oleic acid stage. The first extensive investigation of the problem of selective hydrogenation appears to have been t h a t of H. K. Moore, Richter, and Van Arsdel.3 These investigators undertook to follow the course of the hydrogenation of cottonseed oil, the unsaturated fatty acids of which are linoleic and oleic acids. The conditions of hydrogenation were varied and the composition of the partially hydrogenated product was estimated from the iodine value of the oil and the iodine value of the liquid fatty acids. The separation of solid from liquid acids was effected by the well-known method of extracting the lead soaps of the mixed acids with ether and subsequently liberating the liquid acids from the soluble lead soaps. This method gives a fairly satisfactory separation of the saturated from the unsaturated fatty acids of raw cottonseed oil and most other fats and oils other than those that have been hydrogenated. L,ewkowitsch4 had prrviously pointed out that hydrogenation results in the formation of solid, unsaturated fatty acid, designated as “isooleic” acid. The lead soap of this solid unsaturated acid is practically insoluble in ether, and consequently H. K. Moore, Richter, and Tan Arsdel obtained neither the whole of the unsaturated acids of any of their hydrogenated samples nor a representative sample of the unsaturated portion. The work of these authors does show beyond question that the hydrogenation of linoleic acid to the oleic acid stage proceeds with much greater velocity than the hydrogenation of oleic to stearic, but their conclusions regarding the effect of different conditions of hydrogenation 1 Presented before the Division of Physical and Inorganic Chemistry at the 60th Meeting of t h e American Chemical Society, Milwaukee, Wis., September 10 t o 14, 1923. * Seifenensieder-Ztg., 39, 977, 1004 (1912). Tnrs JOURNAL. 9, 451 (1917). 4 “Chemical Technology and Analysis of Oils, Fats and Waxes,” Vol. 1, 1913, p. 192.
upon the character of the partially or little hydrogenated no value, onOil account are Of of their failure to obtain a “liquid iodine value” that was representative of the ~ ~ in ~
Armstrong and Hilditch6 found that the rate of hydrogenation of cottonseed, linseed, and whale oils was approximately constant a t the beginning of hydrogenation. The constant rate of hydrogenation persisted to a point a t which apparently only 10 to 20 per cent of the glycerides present was derived from acids less saturated than oleic. A natural interpretation of this result is that these more unsaturated glycerides are selectively hydrogenated to the oleic stage. This conclusion is supported by data in the recently published Paper of Hilditch and C. W. Moore,O who examined the composition of various samples of partially hydrogenated oil by the same method as that used by H. K. Moore. Richter. and Van Arsdel. Hilditch and C. W. Moore were familiar with the defects of their method, the latter’ having previously investigated the nature of the solid unsaturated fatty acids formed during hydrogenation. Since these solid unsaturated acids are isomers of oleic acid, and since these acids are retained by the solid saturated acids in the method of separation used by Hilditch and C. W. Moore, it is clear t h a t the unsaturated acids actually isolated by these observers contain a greater proportion of linoleic acid relative to oleic acid than was present in the hydrogenated sample. Consequently, their analytical method gives results too high in linoleic acid. N o criticism can be made of their final conclusions, however, whlch emphasize the selective nature of the hydrogenation in spite of an experimental method which tends to overestimate the proportion of linoleic acid present in the hydrogenated oil. Ubbelohde and Svanoes likewise studied the course of the hydrogenation of cottonseed oil by means of the separation of the solid and liquid acids after hydrogenation to varying degrees. These investigators extracted the lead soaps of the mixed fatty acids with ether, and determined the weight and the iodine value of both solid and liquid fatty acids. Unfortunately, in the pursuit of minor advantages, they prepared their mixed lead soaps from a solution so rich in alcohol that precipitation was inevitably incomplete-a fact t h a t doubtlessly explains why their total recovery of solid and liquid acids showed a loss varying from 3 to 21 per cent. Ubbelohde and Svanoe were of the opinion that hydrogenation of cottonseed oil proceeds in stages, linoleic acid being first converted into a solid isomer of oleic acid, which is more slowly reduced to stearic acid. This conclusion regarding the source of the solid, unsaturated acid formed during hydrogenation is contrary to the opinion of C. W. Moore,, who has maintained that the formation of isooleic acid can occur only during the actual hydrogenation of oleic acid.
PRESENT PROBLEM The whole problem of selective hydrogenation is closely connected with the problem of the kinetics of the hydrogenation reaction, on which the evidence is conflicting. Some investigators have maintained that the velocity of hydrogenation is essentially that of a unimolecular reaction. If this is true of all the unsaturated components of a reaction mixture, then each of these components should be hydrogenated from the very beginning a t rates proportional to the product of the concentration and the reaction constant of each such component (assuming, of course, a constant amount of cataProc. Roy. SOC. (London), 96A, 137 (1919). J . SOC.Chem. I n d . , 42, 15T (1923). 7 Ibzd., 38, 320T (1919). 8 Z . angew. Chem., 32 ( I ) , 278 (1919).
8
e
vel. 16,'No. 5
IdYD UXTRIAL AhTD ENGINEERING CHEMISTRY
520
lyst, a constant temperature, and a constant pressure of hydrogen). On the other hand, mention has already been made of cases in which a constant rate of hydrogenation was observed over a considerable period. According to this view, the concentration of the reacting unsaturated component on the surface of the active catalyst is not proportional to its concentration in the reaction mixture as a whole, but is practically constant over the greater part of the reaction. It is quite consistent with this view, although not a necessary consequence, that one of several unsaturated components in the same reaction mixture should be selectively absorbed upon the surface of the catalyst and, in consequence, be preferentially hydrogenated to the point of almost complete disappearance. Further discussion of this matter will be undertaken after the presentation of experimental evidence. From their own work on the rate of hydrogen absorption by oils under varying conditions, the writers can readily understand that conflicting observations may have been made and that different observers, or even the same observer under different conditions, may have obtained rates of hydrogenation varying from constant to the unimolecular type or even higher order of reaction. They have not, therefore, placed great dependence upon observations of the rate of hydrogenation, but have undertaken to follow the hydrogenation of the glycerides containing more than one type of unsaturation by means of a study of the composition of the reaction product and, in particular, by means of a method free from the errors inherent in the method of previous investigators.
EXPERIMENTAL For the separation of solid from liquid acids the method of Twitchell,g in which the lead soaps of the solid acids are fractionally precipitated from an alcoholic solution of the mixed fatty acids, was followed without essential modification. It is believed that this method gives a sharper separation and more consistent results than the widely used method of extracting the lead salts of the mixed fatty acids with ether. Instead of examining the liquid fatty acid fraction, the 9
THISJOURNAL, 18, 806 (1921).
writers determined, for each sample examined, (1) the weight of the solid fatty acid fraction, (2) the iodine value of the solid fraction, and (3) the iodine value of the mixed fatty acids, preferably by calculation from the iodine value of the more stable glycerides. It is possible to estimate from the foregoing experimental values the composition of the fatty acids in terms of (1) solid saturated acids, (2) solid unsaturated acids or isooleic acid, (3) oleic acid, and (4) linoleic acid, provided the sample under examination contains no unsaturated acids other than oleic and linoleic (or their isomers) and contains no saturated acid of lower molecular weight than palmitic. (The lead salts of myristic acid and acids of lower molecular weight are appreciably soluble in alcohol.) Let s = per cent solid acids in total fatty acids a = iodine value of solid acids b = iodine value of total fatty acids
Oil
49.4 51.7 45.4 , 47.6 a Original oil.
Mixed 011 Acids 94.2 90.la 79.8 76.3 75.0 71.7 68.7 71.9 64.1 67.1 61.6 64.3 59.4 56.8 51.9 54.3 44.2 46.2 n Original oil.
.
VALUE Solid Acids 1.7 37.2 42.1 38.0 41.1 35.1 29.4 27.2
-
Liquid Acids 148.6 102.5 100.5 97.9 95.3 88.9 89.3 88.0
TABU 11-REFINED PEANUT IODINE VALUB Liquid So!id Acids Acids 4.9 113.0 98.2 29.5 94.3 36.1 92.4 39.5 90.6 39.5 90.9 40.2 38.9 89.9 35.3 90.0 29.3 87.5
Solid Acids Per cent 23.1 42.3 47.6
44.2 52.2 03.5 02.5 65.8 OIL
O S
Per cent solid saturated acids = s
as -90
The percentage of linoleic and oleic acids can be calculated In a number of ways. For instance, if u c per cent total unsaturated acids (induding isooleic), and c = iodine value of total unsaturated acids, then 24
= 100
c = -
Per cent linoleic acid = Per cent oleic acid
-
- (. -
E)
lOOb U
- 9O)u 91 s (181 - a90 91 (c
C)U
These conditions are fulfilled in the case of cottonseed oil, peanut oil, and partially hydrogenated soy bean according to the best available information on the composition of these oils. Marine oils will require special consideration. The samples of hydrogenated oils were prepared in the laboratory under carefully controlled conditions. All samples of cottonseed oil described in the present paper were 10 According to Baughman and Jamieson, J . Am. Chem. SOC.,44, 2947 (1922),bean oil contains a small amount of linolenic acid. This, however, is eliminated in the first stages of hydrogenation.
OIL HYDROGENATED WITH 0.2 P E R TABLE I-REFINED COTTONSEED IODINE
Mixed Acids
90
Per cent isoiileic acid =
CENT
-COMPOSITION
Saturated Acids 22.7 24.8 25.4 25.5 28.4 38.7 42.1 45.9
HYDROGENATED WITH 0.1 P E R Solid -COMPOSITION Acids Saturated Per cent Acids 16.6 17.6 18.7 27.8 20.5 33.6 22.2 39.5 25.9 46.1 29.3 52.9 33.9 59.7 39.7 65.3 47.2 70.0
NICKEL AT 175' c. O F MIXEDACIDS, P E R Oleic 27.1 47.5 43.9 49.4 43.7 36.5 37.5 34.2
CENT
NICKEL AT 200' c. OF MIXEDACIDS,P E R Oleic 61.4 65.0 62.7 58.5 53.5 46.5 40.3 34.7 30.0
CENT-
Isoiileic 0.40) 17.5 22.2 18.7 23.8 24.8 20.4 19.9
Linoleic 49.8 10.2 8.5 6.4 4.1 0 0
B
CENT-
Isooleic 1.0(?) 9.1 13.1 17.3 20.2 23.6 25.8 25.6 22.8
TABLE 111-REFINBD SOY BEANO I L HYDROGENATED WITIi 0.15P E R CENT NICKEL AT 203°-2050 c. Solid COMPOSITION OF MIXEDACIDS,P E R
,-____-IODINE VALUE-----
'
Mixed Oil Acids 128.7 123.00 93.3 89.2 89.7 85.8 85.9 82.1 82.4 78.8 79.4 75.9 75.2 71.9 68.1 65.1 Original oil.
Solid Acids 6.9 48.5 50.2 52.7 53.0 55.2 53.6 50.2
Liquid kcids 146.1 109.1 105.8 102.1 99.5 96.9 94.9 92.9
Acids Per cent 12.9 31.5 34.3 38.3 41.9 46.8 51.4 60.4
Saturated Acids 11.9 14.5 15.2 15.9 17.2 18.1 20.8 26.7
Linoleic
21.0 7.2 3.7 2.0 0.4 0.6 0 0 6)
CENT-
Oleic
IsoBleic
Linoleic
5b:7 51.1 50.6 49.6 47.1 44.4 37.3
1i:o 19.1 22.4 24.7 28.7 30.6 33.7
li:S 14.6 11.1 8.5 6.1 4.2 2.3
I N D CSTRIAL AA-D ESGI,YEERISG CHEMISTRY
May, 1024 Nickel Per cent 0 05
0 1 0 2 0 5 0 05 0 1 0 2
0 5
-
---Oil 74 3 74 7 73 3 73.4 69.9 70.0 71.0 70.7
TABLEIT-REFINED COTTONSEED OIL HYDROGENATED AT 153' C. WITH DIFFERENT AUOUNTSOII CATALYST -COMPOSITION O F MIXEDACIDS,PER CENT-Solid IODINEVALUE-Mixed Solid Liquid Acids Saturated Isooleic Linoleic Oleic Per cent Acids Acids Acids Acids 16.8 12.3 44.7 43.0 26.2 35.1 105.3 77.7 78.1 z6 7 16.8 73.1 73.2 74.2 74.0
32.7 30.4 39.6 37.5 37.6 33.2 42.4
104.8 103.3 101.7 101.1 99.6 101 2 95.3
40.1 39.0 43.8 47.4 45.5 42.1 46.6
TABLEV-REFINED COTTONSEED OIL HYDROGENATED AT 175' IODINE VALUE-------Solid -Mixed Solid Liquid Acids hcids Acids Acids Per cent
,---------
Nickel Per cent 0.05 0 1 0 2 0 05 0 1
0 2
Nirkel Per cent 0 95 0 1 0 2 0 5
Oil
52 1
74.3 73.8 73.7 71.8 69.4 69.7
77.7 77.2 77.1 75.1 72.6 72.9
29.0 30.5 37.2 28.0 31.1 38.0
108.1 105.8 102.5
106.6 101.4 97.9
77.3 77.7 78.1 76.6
73.9 74.3 74.7 73.2
104.5 102.9 102.8 100.8
38.4 35.4 39.8 41.3
14.6 13.2 19.3 19.7 19.0 15.5 21.9
12.0 10.8 9.6 8.7 7.6 9.0 6.8
c. WITH
DIFFERENT AMOUNTS O F CATALYST -COMPOSITION OF MIXED ACIDS,PER CENT-Saturated Acids Oleic Isoaleic Linoleic
41.4 40.8 42.3 41.9 43.3 44.2
TABLE VI-REFINED COTTONSEED OIL HYDROGENATED A T 198' Solid ---------IODINE VALUEMixed Solid Liquid Acids Acids Per cent Oil Acids Acids
47.9 50.2 46.6 43.9 46.9 48.9 46.6
25.5 25.8 24.5 27.7 26.5 26.6 24.7
44.4 46.7 47.5 46.0 47.8 49.4
28.1 27.0 24.8 28.9 28.4 25.5
13.3 13.8 17.5
14.2 12.5 10.2 12.1 8.9 6.4
13.0
14.9 18.7
c. WITH
DIFFERENT AMOUNTS O F CATALYST ---COMPOSITION OF MIXEDACIDS,PER CENTSaturated Acids Oleic Isoo1ei c Lindeic
45.3 40.4 43.1 44.3
26.0 24.5 24.0 24.0
43.0 49.0 46.3 46.8
19.3 15.9 19.1 20.3
11.7 10.6 10.6 8.9
TABLEVII-REFINED COTTONSEED OIL HYDROGENATED AT 217' C. WITH DIFFERENT AMOUNTS OF CATALYST IODINE VALU? Solid ---COMPOSITION O F MIXED.%CIDS, PER CDNT----Mixed Solid Liquid Acids Saturated Acids Acids Acids Per cent Acids Oleic Isobleic Lindeic
7 -
Nickel Per cent 0.05 0 1 0 2 0.05 0 1 0 2
Oil 73.3 74.3 73.4 69.3 69.6 69.7
76.7 77.7 76 8 72.5 72.8 72.9
36.4 37 9 41.8 34.6 38.9 41.6
106.8 104 7 101.9 101.7 99.2 97.1
from the same original lot of raw oil, so that possible errors due to variations in the raw oil are eliminated. The same is true of the other oils studied. The results have, of course, been checked a t times with different raw material. Hydrogenation was carried out in a vertical copper cylinder. Temperature control was maintained in nearly all cases by means of a jacket containing a constant boiling liquid. For agitation, a small propeller on a vertical shaft was used in the case of the cotton oil samples; for the other oils a modified Witt centrifugal stirrer was used. The catalyst consisted of partially reduced nickel on kieselguhr. Storage over carbon dioxide proved a satisfactory means of insuring constant and uniform activity of catalyst throughout the experiments. The amount of catalyst is expressed as the percentage of total nickel on the basis of the oil used in each experiment. Table I shows the composition of cottonseed oil hydrogenated to varying degrees a t constant temperature and with constant amount of catalyst. The first, second, and fourth samples of hydrogenated oil shown in this table were taken successivzly from the same charge of oil. The other samples in this series were hydrogenated separately. Table I1 shows the composition of peanut oil hydrogenated to varying degrees, and Table I11 shows similar results for soy bean oil. I n the case of each of these oils, the samples analyEed were withdrawn successively from the same charge of oil, which was hydrogenated a t constant temperatures and otherwise under uniform conditions. If hydrogenation were strictly selective, the percentage of solid saturated acids would not sensibly change before the complete conversion of linoleic to oleic acid, the theoretical disappearing point of linoleic acid for the three samples bf oil in question being as follows: Iodine Value Cottonseed oil
Peanut oil Soy bean oil
66.5 71.6 75 8
47.3 44.5 45.9 46.6 46.8 46.3
28.2 25.8 24.6 28.7 26.6 24.9
39.6 43.6 44.4 44.3 45.9 47.9
19.1 18.7 21.3 17.9 20.2 21.4
13.1 11.9 9.7 9.1 7.3 5.8
Examination of Tables I, 11,and I11 shows that, as a matter of fact, hydrogenation of these three oils is to a high degree selective. This fact is better seen in Fig. 1, which shows a sharp break in the increase in saturated acids a t approximately the theoretical iodine value a t which the linoleic acid in each oil should disappear. This apparently selective action is not due, as might be suspected, merely to the more rapid rate of hydrogenation of linoleic as compared with oleic acid. I n the case of refined cottonseed oil, the rate of hydrogen absorption is practically constant down to the point a t which solid saturated acids begin to accumulate in a substantial amount. After the complete disappearance of linoleic, the reaction rate again becomes almost constant for a considerable period. These approximately constant rates of hydrogenation may be regarded as a measure of the rate of hydrogenation of the linoleic and of oleic acids, respectively.
I20
110
100
90
80
70
60
50
Jodine Va/ue of O i l
FIG. ]-CHANGE SEED
I N COMPOSITION DURING HYDROGENATION OF ( A ) COTTONOIL, ( B ) PEANUTOIL, A N D ( C ) SOY BBAN Ou.
522
INDUSTRIAL AND ENGINEERING CHEMISTRY
I n a number of experiments the initial rate of hydrogenation of cottonseed oil is somewhat less than four times the rate of hydrogenation subsequent to the disappearance of the linoleic acid. By no stretch of the imagination can this difference in rates account for the relative amounts of the two acids hydrogenated during the first stage of the reaction. On the contrary, we are forced t o believe that the result is due to the selective action of the nickel catalyst, probably to the preferential adsorption of linoleic acid on the surface of the catalyst. Although hydrogenation appears in the main to be selective, the saturated acids begin to build up in appreciable amount before the linoleic acid is entirely eliminated. It becomes of interest, therefore, to inquire into the effect of reaction conditions upon the composition of the hydrogenated product. For this purpose cottonseed oil was selected for study and this oil was hydrogenated under various conditions to iodine values of approximately 74 to 70, both of which lie within the critical range within which appreciable increase in saturated acid content occurs without entire elimination of linoleic acid. The principal factors studied were temperature of hydrogenation and amount of catalyst. The- results obtained are shown in Tables IV, V, VI, and VII. I n order to determine the effect of amount of catalyst upon the selective character of hydrogenation, either the percentage of saturated acids or of linoleic acid present in samples hydrogenated to a common iodine value under the same conditions except as to amount of nickel may be compared. Tables IV to VI1 are arranged in such a manner as t o make this comparison convenient. Since the actual iodine values are only approximately those which the writers attempted to obtain-namely, 74 and 70-small corrections should be made before comparing the actual percentages of saturated acids or of linoleic acid. The correction is approximately 1 per cent linoleic acid for each unit by which the iodine value of the actual sample differs from the desired value 74 or 70. The correction is practically negligible in the case of the saturated acids. The experimental values show that increasing amounts of nickel favor selective hydrogenation a t all temperatures studied. If the percentages of saturated acids or of linoleic acid in samples hydrogenated to the same iodine value with the same amount of catalyst are compared, certain irregularities are encountered. Of the temperatures studied, however, 198" C. was found to be the most favorable for selective hydrogenation regardless of amount of catalyst. The writers feel justified in stating that the optimum temperature for selective hydrogenation is in the neighborhood of 200" C. for cottonseed oil, although the effect of temperature is in general by no means so marked as the effect of quantity of catalyst within the range investigated. In addition to ,temperature and amount of catalyst, the effect of agitation and of hydrogen pressure upon selective hydrogenation has also been investigated to some extent. For the present it can only be stated that these factors, although of considerable importance in regard to speed of reaction, are of relatively small importance with regard to their effect upon the composition of the hydrogenated product.
DISCUSSION OF RESULTS While no claim to originality is made in emphasizing the selective action of catalytic nickel in the hydrogenation of vegetable oils, the writers believe that their results are based upon a much more reliable analytical method than the results of previous investigators in this field. Certainly they show that hydrogenation is selective to a greater extent than has been previously indicated.
Vol. 16, X o . 5
The conclusion that increasing temperature up to about 200" C. favors selective hydrogenation is in fair agreement with previous investigators. On the other hand, the evidence in favor of the view that increasing amount of catalyst favors selective hydrogenation is new, being contrary to the view of H. K. Moore, Richter, and Van Arsdel, whose conclusions are questioned for reasons already explained, & to the reason why the conditions of hydrogenation should have the particular effects described, no explanation can be offered at present, The extent to which hydrogenation is selective does not directly confirm, but is extremely compatible with, the view of Armstrong and Hilditch6.l1 that hydrogen absorption by a given unsaturated component in the presence of nickel proceeds normally a t a constant rate of reaction, and the writers' results suggest that those investigators who have observed apparently unimolecular rates of hydrogenation have in reality observed the effect of conditions interfering with the normal course of reaction. With this point in mind, they have reexamined some of the evidence in favor of the unimolecular type of reaction. The most frequently quoted investigator in this connection is Fokin,I2 whose results, for instance, have been quoted by Armstrong and Hilditch as conflicting with their own evidence in favor of the linear rate of reaction. Fokin's experimental results, so far from contradicting the subsequent results of Armstrong and Hilditch, afford the very strongest evidence in favor of the essentially linear rate of hydrogenation. I n a majority of hydrogenations of various compounds Fokin obtained for more than half of the reaction period a substantially constant rate of hydrogen absorption. Such experimental results are much more impressive than Fokin's own conclusion (with reservations) that hydrogenation is essentially a unimolecular reaction. The work of Thomas13 also merits serious attention as an example of an investigation which apparently demonstrated the unimolecular rate of hydrogenation, but Armstrong and Hilditch have already shown that the gradually decreasing reaction rates observed by Thomas were probably caused by the use of a closed system for hydrogen absorption and the consequent accumulation of gaseous impurities. On the whole, it seems to be well established that the normal course of hydrogenation of a single unsaturated component of a liquid mixture involves a constant rate of hydrogen absorption as long as the concentration of that component exceeds a more or less well defined critical value, and that, owing to the selective action of the catalyst, a constant rate of hydrogen absorption is not uncommon even when the reaction mixture contains a variety of unsaturated components. J . SOC.Chem. Ind , '79, 120 (1920). 2.angew. Chem., 22. 1496 (1908). 18 J . SOC.Chem. I n d . , 39, 10T (1920).
11 I*
Lead in 1923 The following statistics, compiled in the United States Geological Survey by C. E. Siebenthal and A. Stoll, show the status of the lead industry in the United States in 1923. PRODUCTION OF REFINED PRIMARY L ~ A IN D
1921 (Short tons) Domestic desilverized lead 187 962 Domestic soft lead 157:513 Domestic desilverized soft lead 52,747
398,222
Foreign desilverized lead Total refined primary lead Antimonial lead Apparent consumption Average selling price in cents per pound
THE UNITEDSTATES 1922 1923 (Short tons) (Short tons) 185,191 304 595 209,250 190:749 61,364 74,305
-
-
50,367
468,746 63,916
556,708 61,300
448,589 10,064 444,872
532 662 8:075 492,705
618 008 14:190 573,729
4.5
5.5
7.0
-
