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was Bushed out several times with fresh oil and the washings were thoroughly mixed with the used oil before sampling for analysis. The laboratory in which the engine tests were run was remarkably clean and free from dust and dirt. These tests indicate an increased rate of wear occurring at dilutions in excess of 15 per cent. The tests on Engine 2 (Figure 4) were conducted in a manner similar t o those on Engine 1 with the exception that the crank case was removed for thorough cleansing after each run, and the tests were of 10 hours’ duration instead of 7 as in the previous runs. The first series of tests indicates a greatly increased rate of wear at about 10 per cent dilution. After this series the engine was opened up for examination, but no evidences of excessive wear were found. The engine was reassembled and a second series of runs made, with the results also indicated in Figure 4. A change was not,ed in the behavior of the engine in that its equilibrium dilution under the existing conditions increased from about 5 per cent for the first series to 9 per cent for 6he second series. The results show a marked increase in wear a t dilutions above 10 per cent. The fact that the same wear was observed a t both 20 and 30 per cent dilutions may be accounted for by the small change
in viscosity for this range.
VoI. 17, No.3 This is shown by the plot of wear
vs. viscosity in the second part of Figure 4. Conclusions
1-Road tests under ordinary conditions in which wear is estimated from oil analysis, although indicating increased wear with dilution, are inconclusive because of settling of the metallic particles. 2-Liability to increased wear caused by excessive amounts of suspended matter is considerably lessened by this settling. 3-As shown by the dynamometer tests, rate of wear increases with dilution. Furthermore, rate of wear increases much more rapidly than dilution and, above a dilution of 10 or 15 per cent, percentage increase in wear is much greater than the percentage dilution. Acknowledgment
The writer wishes to express his appreciation to C. W. Stose and E. R. Barnard, whose theses furnished the data given in this paper, to B. A. Fides and H. M. Meyers of the Institute staff for their invaluable assistance, and to the Standard Oil Company of New Jersey for their generosity in supplying the oils used in the tests.
A New Type of Silica Gel’ By Harry N. Holmes and J. Arthur Anderson OBERLIN COLLEGE,OBERLIN,OHIO
A method is described for the preparation of silica gels of different degrees of porosity. Some of the gels so prepared are much more adsorbent for certain substances than are any gels previously known. For example, addition of a dilute solution of ferric chloride to a dilute solution of sodium silicate yields a gel or gelatinous precipitate composed of a n intimate mixture (formed in the act of precipitation) of hydrated ferric oxide with hydrated silicon dioxide. Previous custom has called for washing out by-product salts while gels are rather soft. In this paper it is pointed out that is it far better to dry gels to a rigid structure before washing in order to prevent collapse of capillary walls. T o secure still greater porosity the hydrated ferric oxide is removed from the ferric oxide-silica mixture by
soaking the dried product in dilute hydrochloric acid. Soluble ferric chloride is washed out leaving a chalkwhite hydrated silica. When this is dried and activated it contains all the capillaries expected from removal of water and, in addition, a network of larger capillaries due to the removal of ferric oxide. In the preparation of such gels nickel chloride, or other salts, may be substituted for the ferric chloride. Owing to the presence of coarser capillaries a “gel from iron” was able to decolorize completely a sample of Lima crude oil, whereas ordinary silica gel could not do so. Furthermore, the “gel from iron” was decidedly more effective in removing objectionable sulfur compounds from Lima crude than was ordinary silica gel.
AN Bemmelen2 observed in 1897 that dried silicic acid improved the methods of drying silicic acid (to “activate” adsorbs various vapors and gases and even removes it), and studied its use in the separation and recovery of vasome material from solution. Marcus3records the use pors and gases. Wilson and Parsons dried and activated a of silica gel as an adsorbent in taking up undesirable constitu- precipitate of ferric hydroxide, obtaining a good adsorbent ents from gases and liquids. Patrick4and his a ~ s o c i a t e s ~ ~gel. ~~~~* Since hydrated silica and hydrated ferric oxide represented 1 Presented under the title “The Preparation of Highly Adsorbent Gels.” acids and bases, it was thought that an intimate mixture of before Section 2-Colloids, of the Division of Physical and Inorganic Chemthe two might be interesting as an adsorbent. The writers istry a t t h e 65th Meeting of the American Chemical Society, New Haven, Conn., April 2 t o 7, 1923. Received October 23, 1924. secured this intimate mixture by adding a solution of ferric 2 Z . anorg. Chem., 13,296 (1897). chloride to a solution of sodium silicate. The gelatinous * British Patents 17,873 (August 5 , 1911); 25,220 (February 5, 1912); precipitate was probably not ferric silicate, for hydrolysis of German Patents 263,388 (June 13, 1912); 268,057 (March 26. 1912); 279,such a salt must be practically complete. An X-ray study of 075 (February 20, 1914); 283,882 (March 8, 1913); French Patent 465,569 (December 1, 1913). the dried gel9 failed to indicate any crystalline structure. 4 Inaugural Dissertation, Gottingen, 1914. This evidence, however, is not conclusive. 6 McGavack and Patrick, J . A m . Chem. Soc., 41, 946 (1920). Although this work was begun with a mixed gel of hydrated Davidheiser and Patrick, I b i d . , 44, 1 (1922). silica-hydrated ferric oxide, it turned out to be merely the 7 Miller, Chem. Met. Eng., 23, 1155 (1920). 8 U. S. Patent 1,297,724 (March 18, 1919); 1,335,348 (March 30, 1920); introduction to an improved method of making an unusually British Patent 136,543 (December 6, 1919); 137,284 (December 24, 1919); porous silica gel.
V
159,508 (February 26, 1921); Canadian Patent 200,912 (June 15, 1920); 217,365 (March 28, 1922).
0
Made by Wheeler Davey of the General Electric Company.
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Improved Method of Washing Gels
Acid Treatment
According to the patents of Patrick and his associates, the soft jelly-like lumps of freshly precipitated silicic acid were washed free from the sodium chloride formed as a byproduct of the reaction between sodium silicate and hydrochloric acid. It was thought that it might be advantageous to dry the gel to a rigid solid before washing. Then, on washing, the soluble salts would diffuse out, leaving capillary spaces previously occupied by these salt molecules or aggregates. The rigid structure of the dried gel would prevent collapse of the capillary walls. The tests were made on a sample of Silica Gel, on a product prepared by the writers according to Patrick’s patents, and on a product prepared in exactly the same way except that it was washed after drying to a hard solid. In obtaining the values in Table I a stream of 150 CC. of air per miniite was saturated with benzene a t 30” C. and passed through 10 grams of the gel for a few hours, until no more benzene was adsorbed.
The writers’ success in forming new capillary spaces by washing out soluble salts from the dried gel led to speculation on the possibility of removing the ferric oxide from the red ferric oxide silica gel. It seemed certain that this would yield a vast number of capillary spaces previously occupied by the molecules or aggregates of ferric oxide. To remove the insoluble iron oxide the dried gel was soaked overnight in 6 N hydrochloric acid. It speeded up the action to have the acid hot a t first. By this treatment the ferric oxide was converted into soluble ferric chloride, which was readily washed out leaving a hard, white gel of hydrated silica. The product was washed with hot water until free from chlorides. The ease with which even 2 N hydrochloric acid removes the ferric oxide strengthens the theory that the red gel is not ferric silicate but an intimate adsorption mixture of hydrated ferric oxide with hydrated silica formed in the act of precipitation. Furthermore, the silica left after removal of the ferric oxide is not colloidally dispersed in the solution, nor is it gelatinous, for it retains the bulk and rigidity of the original mass. After the usual activation the “gel from iron” showed a capacity to adsorb 50 per cent of its own weight of benzene from a stream of air (132 cc. per minute) saturated at 30’ C., compared with 32.5 per cent for Silica Gel (although chemically the same) under the same conditions. Table I1 shows also an interesting difference for gasoline.
Table I-Benzene
Adsorbed i n Gels Per cent of weight of gel 32.5 33.0 44.3
ADSORBENT GEL Silica Gel According to Patrick’s patents Washed after drying
After this treatment of the dried gel had been developed the writers read a paper by Briggs,lo in which he stated that he heated a silica gel to 300’ C. and plunged it into hot water. He offered no theory as to collapse of capillary walls. The writers found no advantage in drying much above room temperatures. There is a slight gain in first steaming the dried gel and then immersing in hot water, larger fragments being secured by this procedure than when the gel was plunged directly into water.
f r o m a S t r e a m of Air Saturated w i t h Gas or Vapor a t 30’ C. Silica Gel “Gel from Iron” SUBSTANCE ADSORBED Per cent Per cent
Table 11-Adsorption
Preparation of Ferric Oxide Silica Gel
When a dilute solution of ferric chloride is poured slowly, with stirring, into a dilute water-glass solution, some precipitate is formed on addition of each drop until a maximum amount of precipitate is obtained. Near this maximum the mixture is neutral. Ferric chloride should be added beyond the neutrality point, however, until there is obtained a slowsetding yellow precipitate showing a slight reddish tint. The writers used a white water glass of 1.375 density with a ratio of NazO to SiOz of 1:3.5. They added 1440 cc. of 2 N ferric chloride solution to 500 cc. of the concentrated water glass which had previously been diluted to 10 liters. This involved the use of a greater excess of ferric chloride than was really necessary for reaction. About 1000 cc. of 2 N ferric chloride is sufficient to make the solution approximately neutral. It was found advisable to allow the mixture to stand from 2 to 3 days before filtering. The color became a dark red-brown. After filtering, the wet mass was spread out in cloth-bottomed trays and dried in a warm room with the aid of a fan. After a few days the lumps became hard and brittle. They were then steamed and later washed in hot water until free from chlorides. After drying a t room temperatures the red gel mas activated by heating to 135”-145” C. for about 12 hours. Just before use the gel was given a final activation at 150’ C. by passing a slow stream of dry air through to constant weight. Such a red gel of hydrated ferric oxide-silica adsorbed 43.2 per cent of its own weight of benzene from a stream of air (150 cc. per minute) saturated with benzene at 30” C. This compared favorably with the 32.5 per cent adsorption by Silica Gel. The preparation of a similar red gel was claimed by Patrick in a patent. His gel was washed while soft and was very inferior as an adsorbent. Io
Proc. R o y Sor. (London), 100A,88 (1921).
Other Metallic Oxide Silica Gels
Gels containing oxides of aluminium, chromium, calcium, and copper mixed with silica were prepared by adding 0.22 of an equivalent of the metallic chloride in 500 cc. of solution to 50 cc. of the concentrated water-glass sirup diluted to 1 liter. These proportions gave the maximum amounts of precipitates and the solutions were nearly neutral. They were dried, steamed, treated with acid, washed, dried, and activated as described above. A nickel oxide silica gel was also prepared, but in this case a better gel was obtained by adding 1 liter of the diluted water glass to 110 cc. of 2 N nickel chloride. These gels were then compared in their capacity to adsorb benzene from a stream of air (132 cc. per minute) saturated at 30” C. In the case of the nickel product the rate was 236 cc. per minute. Table 111-Benzene Gel, more or less hydrated (A1zOs)t (SiOdU (CaOIz (SIOZ)Y (Crz0s)z (Si0z)y. (CuO)r (SiOz)” (NiO)z (Si0du
Adsorption b y Various Metallic Oxide Silica Gels Gel washed after dryAcid-treated gel, meing without acid tallic oxide removed Per cent weight of gel Per cent weight of gel 4.1 24.5 8.6 21.2 23.2 37.8 26.1 37.9 60.0 96.8
The chromium and nickel products could have taken up a little more benzene. Since the “gel from nickel” surpassed all others in respect to benzene adsorption, it was decided to make further comparisons of the Silica Gel, “gel from iron,” and “gel from nickel.” It seemed probable that the average capillary diameter would be different in each of the three gels. The experiments were carried out as before with an air stream saturated at 30” C. Apparently, the only explanation of Table IV is the theory that there is an optimum size of capillary for each gas or vapor. Even though these three gels are chemically the
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282
same, pure silica, no single gel is consistently the best adsorbent for all gases. T a b l e IV-Comparison of A d s o r p t i o n in V a r i o u s G e l s (Air stream saturated a t 30’ C.) “Gel from “Gel from Silica Gel iron” nickel” Per cent weight Per cent weight Per cent weight SUBSTANCE ADSORBED of gel of gel of gel Carbon disulfide 42.5 81.2 18.6 Carbon tetrachloride 46.6 91.5 69.2 Chloroform 50.7 88.3 57.2 Ether 24.6 66.2 25.8 Benzene 32.5 50.0 96.8
Effect of Silica Gels on Petroleum
Silica Gel was successfully used to remove objectionable sulfur compounds from petroleum fractions. The writers tried filtration of Lima crude oil containing 0.96 per cent sulfur through “gel from iron,” and found it decidedly more eficient in sulfur removal than the ordinary type of silica gel prepared according to Patrick’s patents. Both gels were powdered so that half passed through screens between 40 and 100 mesh and half between 100 and 200 mesh. Ten grams of powder were well shaken with 40 grams of oil and the mixture was thrown on a filter bed of 10 grams of powdered gel in a tube 1.6 cm. in diameter. Filtration was hastened by air pressure equal on both tubes so as t.0 secure 10-gram filtrates for analysis. T a b l e V-Removal
of S u l f u r C o m p o u n d s f r o m L i m a C r u d e Oil b y Different Types of S i l i c a G e l
CIULFUR CONTENT OF OIL-
ADSORBENT GEL Silica Gel “Gel from iron”’
Before filtering Per cent 0.96 0.96
After filtering Per cent 0.67 0.33
A little more sulfur could have been removed by longer filtration, but the results indicate clearly that a silica gel with larger capillaries can be more efficient in sulfur removal than the usual type containing only those capillaries left by evaporation of water. Analysis of duplicate samples checked within 0.02 per cent. The first fractions filtered through “gel from iron” were as colorless as water, the next fractions gradually taking on a clear yellow, then a deeper color, until finally the coarser capillaries were clogged with colloidal material. The usual type of silica gel removed no color whatever from Lima crude oil. Adsorbed material may be burned out and the gels used again. Nitrogen Adsorption at Low Temperatures
R. B. Moore, of the Bureau of Mines, compared “gel from iron” with Silica Gel as to capacity to separate nitrogen from helium a t liquid air temperature. The time period for Silica Gel was 26.0 minutes, whereas for “gel from iron” it was 35.5 minutes. By “time period” he meant the point a t which the break in the adsorption of nitrogen took place. Chloropicrin Test
Galloway and Hall, of the Pittsburgh Station, Bureau of Mines, reported a chloropicrin test on “gel from iron.” The tube test showed 21.03 minutes with an activity of 20.03 per cent. This is evidently not equal to the “40-minute carbon” prepared by the Bureau of Mines. Toluene Retentivity
Katz and Hall, of the Bureau of Mines, compared the writers’ silica gel with the bureau’s best carbon in toluene adsorption and in retentivity. By their saturation test they mean the amount of toluene adsorbed per gram of activated adsorbent when exposed to saturated toluene vapor at 25’ C . By retentivity they mean the amount of adsorbed gas held apparently in a form not readily removed. The carbon took
Vol. 17, KO.3
up only 42.1 per cent of toluene and retained 21.5 per cent, whereas the silica gel prepared by the writers adsorbed 56.25 per cent and came out again cleanly, as it should, with only 3.9 per cent retained. Discussion
The loss of water molecules in the drying process gives capillarity to the usual silica gel. I n the writers’ gels are found all of these capillaries and, in addition, coarser ones formed by removal of ferric oxide or other metallic oxide. It is well known that the best gas-adsorbent charcoals contain very fine capillaries whereas the best decolorizing charcoals contain coarser capillaries. I n this connection it is noteworthy that Lima crude oil is perfectly decolorized by “gel from nickel” and by “gel from iron,” while the better known Silica Gel fails to remove any color. Our acid-treated gel is chalk-white and less dense than the clear, glassy Silica Gel. Fortunately for the economy of the process, the ferric chloride used is all recovered by the treatment of the red gel with hydrochloric acid. Nickel chloride and other metallic salts may be recovered in the same way and used againin precipitation of the gel. The effort to secure porosity by mixing with any gel some soluble material which may later be washed out after drying the gel did not yield very satisfactory results. I n an application for patent the writers pointed out that superior porosity is obtained by securing an intimate mixture of a hydrated metallic oxide with hydrated silica in the act of mutual precipitation; then drying to a rigid solid and later removing the metallic oxide by treatment with a suitable acid. Patrick states that when ferric chloride, for example, precipitates silicic acid it is the acid of hydrolysis of the ferric chloride that really precipitates silicic acid from the sodium silicate. That this accounts for only part of the action is evident. When enough acid to equal that liberated by complete hydrolysis of the ferric chloride used was added to the water glass no precipitation occurred. The trivalent positive ferric ions must have a strong precipitating effect on the colloidal silicic acid always found in a solution of sodium silicate. The porosity of these gels is greatly affected by the rate of drying-the slower the better. The composition of the water glass is also a factor, as is the amount of excess (beyond neutrality) of ferric chloride used. The intermediate dry red gel used in preparation of white “gel from iron” showed a ratio of Fez03 to Si02 of 1:3. The uses of these various forms of silica gel must include solvent recovery, drying of air for the blast furnace and for the vacuum ice process, recovery of sulfur dioxide and oxides of nitrogen, removing offensive odors from air, removing sulfur compounds from petroleum fractions, decolorizing certain liquids, recovery of gasoline from natural gas, and other uses to be developed. Nok-Since writing this paper the authors prepared a more efficient “gel from iron” b y slower drying of a thicker layer. The final product adsorbed 67 per cent of its own weight of benzene from a n air stream saturated at 30’ C.
Decrease in Production of Sulfur in 1924 The production of sulfur in the United States in 1924 dropped to 1,220,600 long tons from 2,036,097 long tons in 1923, a decrease of 40 per cent, as shown by figures compiled in the Geological Survey. The shipments also decreased, but only to the extent of 5 per cent. The shipments in 1924 were thus the second largest on record and for the first time since 1920 were greater than the production. The estimated value of the shipments in 1924 was $25,000,000, compared with $26,000,000 in 1923, at approximately the same rate per ton. About 300,000 tons (10 per cent) of the stocks in hand at the end of 1923 were shipped in 1924.
