IND VSTRIAL A S D EA'GIXEERING CHEMISTRY
May, 1930
lose (soluble cotton) is the base for such important products as pyroxylin plastics (celluloid), photographic films, lacquers, nitro-rayon, artificial leather, and explosives. Lacquers and safety glass, involving the use of transparent sheet pyroxylin, have been recent outstanding factors in the growth of the nitrocellulose industry. The making of cellulose acetate is a very complicated process and requires a cellulose of high purity and reactivity. Cotton cellulose is treated with acetic anhydride and acetic acid in the presence of a catalyst, usually sulfuric acid. During the acetylation the temperature is carefully controlled. When the reaction is completed the cellulose acetate is precipitated by addition of water into the form of white flakes. It is washed to remove free acid and carefully dried. The principal product of cellulose acetate is acetate rayon although it is also gaining recognition for molded articles and lacquers. In the preparation of the solution by the acetate process for rayon manufacture the dried cellulose acetate is dissolved in a suitable volatile solvent, usually acetone. After filtering, the spinning solution is forced through fine openings into warm air. Coming in contact with the air, the volatile solvent evaporates and coagulates the solution, forming a filament. The filaments are wound upon a cone or spool. The estimate of chemical cotton
47 1
produced in 1929 for manufacture of cellulose acetate rayon is 6000 tons. Approximately 60 per cent of this quantity was exported. The use of chemical cotton in products of viscose and cuprammonium solution is also closely affiliated with the rayon industry. Since the leading producer of rayon by the viscose process is the largest consumer of chemical cotton and also owing to the increasing demand by other large viscose rayon manufacturers, this division of the industry is outstanding in the consumption of cotton cellulose. Searly 40,000 tons of chemical cotton are estimated to have been produced in the United States during 1929 for the manufacture of rayon. The use of rayon fibers in articles of wearing apparel is now generally known. The fact that chemical cotton, made from linters, is the base for various other outstanding products, such as toilet and other celluloid articles, photographic and moving-picture films, non-shatterable glass, automobile lacquer finishes, and artificial leather, indicates the diversity of its uses and its importance as a chemical raw material. Literature Cited (1) Committee on Viscosity of Celliiloqe 1 , 4 9 (1929)
ISD
EXG CHFM indl Ed
,
Vanadium Compounds as Catalysts for the Oxidation of Sulfur Dioxide' Harry N. Holmes and A. L. Elder SEVERAXCE CHEMICAL
I
3 A previous publication
H o l m e s , Ramsay, and Elder (3) studied t h e conversion of sulfur dioxide to sulfur trioxide using platinized silica gel as the catalyst. In that article they stated that the study of the oxidation of sulfur dioxide was to be continued using vanadium cornpounds as the contact masses.
LABORATORY, OBERLIN
COLLEGE, OBERLIN, OHIO
A new method for preparing extremely intimate mixtures of catalysts containing vanadium compounds, promoters, and supports is described in detail. The best of these shows a 98 per cent conversion of sulfur dioxide to sulfur trioxide without any decrease in efficiency even after 60 hours of continuous use. Intimate mixtures of vanadates with silicates, hydrated silica, and promoters such as compounds of iron, calcium, copper, cobalt, and nickel were made and tested.
Previous Work
Several attempts have been made to use vanadium compounds as catalysts for increasing the conversion of sulfur dioxide to sulfur trioxide. The early experiments were cited by Alexander (1) and Nickel1 (9). Recently Jaeger and his associates claimed remarkable advantages, in the catalytic oxidation of sulfur dioxide, for the use of vanadium compounds associated with certain promoters as effective catalytic mixtures. Using vanadium in the non-exchangeable nucleus of non-siliceous base-exchange bodies, Jaeger (4) claims to have an excellent catalyst which is immune to the common poisons of platinum catalysts. Spangler (IO) predicts that the contact mass developed by Jaeger will replace to a large extent other active masses used in sulfuric acid manufacture. I n fact, it is now in considerable use in this country. It is of interest to note that 35 per cent of the 8 million tons of sulfuric acid produced in 1929 in this country was manufactured by contact processes. 1 Received iMarch 7, 1930. Presented before the Division of Industrial and Engineering Chemistry at the 79th Meeting of the American Chemical Society, Atlanta, Ga , April 7 to 11, 1930.
The patent literature relating t o the use of vanadium compounds as catalysts has been reviewed by Waeser ( I d ) . Another survey is to be found in a journal published by the V a n a d i u m Corporation of America (11). The most important patents of recent date p e r t a i n i n g to the use of vanadium compounds in the contact process for making sulfuric acid are those by Jaeger and his associates (5,6). It would appear from these patents that many of the known elements in some form are promoters for vanadium catalysts. Few figures are available in the patents on actual rates of conversion. Jaeger does state that with one catalyst 135 liters of 7 per cent burner gas may be passed per hour over 200 cc. of the contact mass. This is equivalent to 0.067 gram of sulfur per hour per cubic centimeter of catalyst on the basis of perfect conversion, which was, of course, not attained. In one patent he claims a conversion efficiency of 98 per cent on a 6 to 9 per cent sulfur dioxide mixture, but he fails to disclose the actual weight of vanadium in the catalyst used. Neumann (8) and his associates have published some very valuable data on the use of vanadium catalysts and have included curves showing the effect of temperature variation on the per cent conversion when using different catalysts. Comparisons were made of the catalytic value of silver vanadate, vanadium pentoxide, copper vanadate, tungstic oxide, silver, ferric oxide, ferric oxide and bismuth oxide, strontium oxide and ferric oxide, tin oxide, chromium oxide, and titantium oxide. One of the best catalysts prepared
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INDUSTRIAL A X D ENGINEERING CHEMISTRY
Yol, 22, No. 5
producing a t one time a precipitate containing both the catalyst and the support seemed attractive. As an example of this procedure we may cite the addition of potassium metavanadate to a solution of ferric chloride in equivalent quantities with formation of a precipitate. The addition of an excess of ferric chloride causes the precipitate first formed to be peptized or colloidally dispersed. If this solution is then added to water glass, a single precipitate containing catalyst, promoter, and support is obtained. The final precipitation is, of course, due to the reaction between the acid of hydrolysis of the excess ferric chloride solution with the silicate solution and to the coagulating effect of the ferric ions. Twelve different catalysts were prepared for this investigation. A brief description of the method for preparing the catalyst follows. The potassium metavanadate used in the catalytic mixtures was prepared by the addition of an equivalent amount of potassium hydroxide to ammonium metavanadate, followed by heating the solution to drive off the ammonia.
Figure 1-Apparatus for Measuring C o n v e r s i o n of S u l f u r Dioxide to S u l f u r Trioxide A-Calcium chloride tube B-Bottle of sulfuric acid C-Mercury manometer D-Flowmeter E-Air-pressure regulator F-Calcium chloride tube G-Bottle of sulfuric acid H-Flowmeter I-Three-way stopcock for sampling mixtures before they reach converter
J-catalyst K-Ground-glass joints L-Bottles of sulfuric acid for absorbing sulfur dioxide -if-Bottles of Iz f o r absorbing sulfur dioxide >‘-Thermocouple 0-Stopper which may be removed when catalyst is inserted
was silver vanadate. Keumann believes that adsorption catalysis plays an important role in the catalysis of sulfur dioxide to sulfur trioxide. Some metals appear to be much better activating agents than others. Either silver oxide or vanadium oxide alone is a poor catalyst, but silver vanadate has shown as high as 97 per cent conversion of sulfur dioxide to the trioxide. Neumann believes that when V ~ O Sis the catalyst, VOSOl is formed, and the intermediate reactions probably are:
Preparation of Catalysts
A typical method of forming catalysts, as found in the patents of Jaeger, by processes incorporating a vanadium compound into the final product consists in mixing a solution of ferric chloride or ferric sulfate with a solution of potassium metavanadate in such quantities that the ferric vanadate is precipitated either alone or mixed with other materials. The precipitate is then mixed with a solution of a silicate, such as potassium or sodium silicate. Further precipitation or the production of a gel is obtained by the addition of an acid or any suitable precipitating substance. All such methods in which one precipitate is first produced and another precipitate is later produced on the first have the disadvantage that a thoroughly homogeneous material cannot be obtained. In the present investigation it was decided that an attempt should be made to distribute the vanadium compounds more evenly through the catalytic mass and to follow this with a study of the efficiency of the catalyst. The possibility of
Catalyst 1 . Mix 60 cc. of potassium metavanadate solution (0.166 gram vanadium per cc.) with 3660 cc. of ferric chloride solution (0.05 FeC13.6H20per cc.). Add 475 cc. of 1 : l O commercial sodium silicate. Allow the precipitate which forms to settle several hours, and then filter on cheesecloth. Dry the precipitate slowly a t room temperature to a moisture content of 30 to 50 per cent. After being ground to particles between 10 and 20 mesh and activated by passing air over it a t 2OC-300” C. for 2 hours it is ready for use as a catalyst. During such use its efficiency gradually increases for several hours to a maximum constant value, maintained for 40 to 60 hours, which was the usual duration of the experiment. Catalyst 2 Same procedure as for catalyst 1 only less vanadium is used. Catalyst 3 . Same procedure as for catalyst 1 only potassium silicate is substituted for sodium silicate. Catalyst 4 . Mixtures of solutions of cupric chloride, cobaltous chloride, nickel chloride, and ferric chloride instead of ferric chloride alone as in catalyst 1 The elements copper, cobalt, nickel, iron, and vanadium are present in ratio of 5:5:5:12:2. Sodium silicate is added until neutral to litmus. Catalyst 5. Same procedure as for catalyst 1, except copper sulfate is substituted for ferric chloride. Catalyst 6 . Mix 50 cc. of potassium metavanadate solution (1 cc. contains 0.091 gram of vanadium) with 4800 cc. of chromic chloride (110 grams CrC13.6H~0per 800 cc. of H20). Add 1 : l O commercial sodium silicate until the resulting mixture is neutral to litmus. Catalyst 7. Mix 8.1 grams of vanadium pentoxide with 5.15 grams of potassium hydroxide in 300 cc. of water. Add hydrochloric acid until neutral to litmus. Add 1200 cc. of water, 140 cc. of sodium silicate, and 70 grams of Celite (grade “F.C.”). Warm to 60-70’ C. Add just enough dilute hydrochloric acid to leave the mixture slightly alkaline. Catalyst 8. Same procedure as for catalyst 1, except that aluminum sulfate is substituted for ferric chloride. Catalyst 9. Mix 1000 cc. sodium tungstate (50 grams) with 450 cc. of ferric chloride solution (containing 225 grams of PeCl3.6HZ0)and 10 liters of water. Add sodium silicate diluted to 1 : l O till neutral to litmus. Catalyst 10. Carnotite (K20.2U03.Vz0~3Hz0). Catalyst 11. Platinum deposited on silica gel ( 3 ) . Catalyst 12. Same procedure as for catalyst 1 except that calcium chloride is substituted for ferric chloride.
A necessary precaution in making catalysts of this type is to use very dilute solutions so that the precipitate obtained by adding the water glass by no means makes a solid gel. In preparing these catalysts the writers used an amount of water such that a precipitate settled to the lower half of the container. The quantity of peptizing agent used was in all cases sufficient, not only to react with the precipitate first formed and to peptize it, but also to form a gel when water glass was added. The degree of drying depends upon the desired hardness of the final product. The excess of ferric chloride used in making up these gels peptizes the precipitate first formed and then upon addition of sodium silicate mutual
INDUSTRIAL A N D ENGINEERING CHEMISTRY
May, 1930
precipitation of hydrated silica and ferric oxide takes place while releasing from solution the originally precipitated ferric vanadate. Any peptizer or dissolver that itself forme a precipitate with water glass may be used to form complex mixtures. For instance, aluminum chloride and certain other salts are effective as are the common acids. Apparatus
A diagram of the apparatus used in this investigation is shown in Figure 1. The preheater used in the preT7ioua work (3) was replaced by two Hoskins furnaces each 32 cm. long. The temperature needed for maximum conversion of sulfur dioxide using platinum catalysts was found to be about 450" C. For conversion using vanadium catalysts the temperature of the furnaces was kept a t 500" * 10" C. This temperature range appeared to be optimum for maximum conversion to sulfur trioxide. Experimental Procedure
The previous procedure of estimating the efficiency of the catalysts by determining the sulfur dioxide content of the gases entering and leaving the catalytic chamber by means of the Reich iodine test was used. The volume of catalytic mass used in each experiment was 75 cc., with a gas flow (8 per cent sulfur dioxide) of 12 liters per hour. It was found, however, that less catalyst than this could be used and the same maximum conversion obtained. The exact minimum was not determined. I n these experiments it seemed better to use an excess of catalyst rather than to overload it. Calculations made from these data will then indicate maximum quantities of catalyst which would be needed. Experimental Data
Table I gives the results using twelve different catalysts. Analyses were made of the vanadium content of the catalysts a t the close of the experiments by the procedure of Keefer ( 7 ) . The maximum conversion obtained-98 per cent-was with the catalyst containing vanadium with calcium as the promoter. Table I-Conversion of Sulfur Dioxide to Sulfur Trioxide Using Vanadium, Tungsten, and Platinum Catalysts on Mixture of 8 Per Cent Sulfur Dioxide with 92 Per Cent Air VANADIUM
CATA-METALLIC IONS USEDIN LYST
1 2 3 4 5
6 7 8 9 10
SUPPORT
PREPARING CATALYSTS
Fe, V, K , Na
Fe V K, Na Fe: V: K Cu, Co, Ni, Fe, V, K , N a Cu, K , Na, V Cr, K , Na, V K , Na, V Al, K , N a , V Fe, N a , W K, U, V
CONVERSION
SiOz.xHz0 SiOa.xHz0 SIOz.xHz0 SiOz.xHz0 SiOz.xHz0 SiOz.xHzO Celite and Si02 .xHnO SiOz.xHz0 SiOz.xHz0 I....
.....
93" 96.5 95.5 93.5 83 75 95 75 50 66
Mixtures of vanadium pentoxide, potassium hydroxide, Celite, and water glass made an effective catalyst, Tungsten was not so efficient as vanadium. Carnotite was a poor catalyst. According to the data of Chase and Pierce ( 2 ) approximately 1 part of platinum is needed per 1000 parts of sulfur converted to sulfur trioxide per 24 hours. Using catalyst 7 for calculation, 1 part of vanadium is needed per 48 parts of sulfur converted to sulfur trioxide per 24 hours. There is no doubt that large-scale installation would diminish the quantity of vanadium needed. The fact that platinum costs about two thousand times as much as vanadium indicates that the cost of making a vanadium catalyst should not be more than 1 per cent of that of making a platinum catalyst of equivalent capacity. Unless the volume of vanadium catalyst can be decreased, larger contact space would be needed than if platinum catalysts were used. These data indicate that,, if vanadium catalysts operate with as long life as platinum catalysts and resist poisons effectively, there should be a future for vanadium catalysts in this process, The successful preparation of ext'remely homogeneous vanadium catalysts of the highest efficiency appeared to warrant application for patents on the process. Literature Cited (1) (2) (3) (4) (5)
(6) (7) (8) (9)
(IO) (11) (12)
Alexander, J . Sot. Chem. I n d . , 48, 871 (1929). ENG.CHEM., 14, 498 (1922). Chase and Pierce, J. IND. Holmes, Ramsay, and Elder, I b i d . , 21, 850 (1929). Jaeger, I b i d . , 21, 627 (1929). Jaeger, U. S. Patents 1,657,754 (January 31, 1928); 1,675,308 (June 24, 1928); 1,675,309 (June 26, 1928); 1,685,672 (September 25, 1928); 1,694,123 (1928); 1,694,620 (December 11, 1928); 1,696,546 (December 25, 1928); 1,701,075 (February 5, 1929). Jaeger and Bertsch, U. S. Patent 1,660,511 (February 28, 1928). Keefer, "Methods of Non-Ferrous Metallurgical Analysis," p , 273 (1928). Neumann et al., Z . Elektrochen., 54, 696, 734 (1928); 56, 42 (1929). Nickell, Chem. Mel. Eng., 56, 153 (1929). Spangler, IND.ENG.CHEM., 21, 417 (1929). Vancoram Review, 1, 42 (1930). Waeser, Metallbmsc, 19, 1349 (1929).
Note on Explosion of Cracked Gasoline in Oxygen'
PER CC OF
CATALYST S AN example of abnormally low autogenous ignition Gram the explosion that occurred recently, in connection 0.005 0.014 with an accelerated test for gum formation, may be of interest. 0.012 An Emerson double-valve bomb was charged with 50 ml. 0.006 0.010 of a vapor-phase cracked gasoline which was forwarded to 0.028 0,006 the Bureau of Standards by the War Department, Wright 0.003
A
...
11% by wt.
P t on silica gel 96 Ca, K , Xa. V Si02 xHzO 98 0' 009 a Conversion by either VzOs alone or FezOa alone is said to range from 60 to 70 per cent. 11 12
473
Interpretation of Data
The best catalyst obtained thus far was made by mixing potassium metavanadate with an excess of calcium chloride to peptize the precipitate first formed and then neutralizing the excess calcium chloride with sodium silicate. Of course the peptized calcium vanadate was promptly precipitated, intimately mixed with the calcium silicate. This gel converted 98 per cent of the sulfur dioxide to sulfur trioxide when catalyzing 8 per cent mixtures. With the commercial mixtures containing only 7 per cent sulfur dioxide it is quite probable that conversion would be higher. Catalysts in which the calcium was replaced by ferric iron were very good. Copper, cobalt, nickel, chromium, and aluminum were not such effective promoters in these experiments as calcium and iron.
Field, Dayton, Ohio. Oxygen was admitted until 20 atmospheres was registered on the gage, a t room temperature. The bomb was then placed on the steam bath, and covered with a proper guard, vented so that it was entirely surrounded by steam at atmospheric pressure. After about 11/* hours an explosion occurred in which the expansion member of the gage failed in two places, the reaction having sufficient energy to force the gage dial through the copper guard. The heavy brass connection tube between the gage and bomb was broken off flush with its seat in the bomb. Solder at the base of the expansion tube of the gage was melted, and the inside of the upper half of the bomb was heavily coated with carbon black. A second explosion occurred several days later with the same material and similar results. Fortunately in this case the indication of a thermocouple in the vapor space was obtained within 1 minute before the explosion occurred. A t the time the temperature was not over 105" C.
1 Publication approved by the Director of the Bureau of Standards of the U. S. Department of Commerce.
