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17. This installation, designed by the h'iagara Blower Company, is used for handling both coarse and moist material and dry powders of extreme fineness in a plant making fruit concentrates and pectins. The material is passed into the air stream by a screw conveyor located under the floor of the storage room. It is raised from the floor of the building to the roof, where it enters a battery of cloth screen collector units. Reduced air speed a t this point permits the separation of all fine dusts which are dropped into a hopper. The hopper has a swinging spout to discharge the material into storage tanks. The screen is cleaned by reversing the air flow. This installation has a capacity of from 7 t o 8 tons per hour. The suction system used by the Dust Recovering and Conveying Company was described in Part I of this series. Figure 18 shows the method of unloading box cars by means of a flexible hose connection that can be made a t various points in the line. The operator's principal duty is to keep the end of the hose submerged in the material being moved. Other Types of Mechanical Handling Equipment
There are other types of conveying equipment somewhat less commonly used but with an important field, such as drag scrapers, skip hoists, monorail systems, trucks of various types, and cranes. Figure 19 shows a drag scraper installation for handling sulfur in storage. This system is operated by one man and can handle about 50 tons per hour. The drag scraper is widely used in out-door storage yards of comparatively large area for concentrating and loading purposes. Because of low initial and maintenance costs they can be economically used on materials that are abrasive or destructive. The skip hoist is very widely used for handling coal in power plants but is being increasingly used in chemical plants
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for loading and unloading operations. It consists, essentially, of a large bucket which a t the bottom of the run trips a hopper gate and loads itself. The bucket is then automatically hoisted to the top of the tower, where it empties into a distributing hopper or chute. I n handling coal in power plants, the coal tar is emptied into a hopper, from which it is raised to the upper storage bins in the plant. For loading operations the reverse takes place, the material being taken from a hopper a t the lower floor and elevated to the mouth of the loading chute. Conclusion
Each of the various material handling systems described in these articles has various advantages and limitations controlled, not only by the type of equipment itself, the initial cost, and the cost of operation, but also by the material to be handled and the necessity, in many cases, of adapting the equipment to the layout of a building already constructed and to the process of manufacture. Which system to use can be determined only by a careful study of individual plant conditions and requirements. Whenever there is a constant flow of materials in unloading, processing, packing, or shipping, mechanical handling can show labor savings of from 50 to nearly 100 per cent, with a consequent large reduction in handling costs. By enabling the chemical plant to purchase and store raw materials in bulk, they can reduce the cost of supplies. The merchandising and shipping of goods are also vitally influenced by the material handling equipment. Literature Cited (1) Burditt and Schaphorst, IND ENG CHEM, 21, 489 (1929) (2) Liddell, Handbook of Chemical Engineering, Vol I, p 1
Platinized Silica Gels as Catalysts for the Oxidation of Sulfur Dioxide' Harry N. Holmes, James Ramsay, and A. L. Elder SEVERANCE CHEMICAL LABORATORY OF OBERLIN COLLEGE, OBERLIN. OHIO
OLMES and Williams ( 5 ) have discussed in detail a simple method for obtaining uniform distribution of catalysts throughout porous solids. Using their procedure, platinum was deposited on three different supports-the Holmes porous chalky gel, Patrick's gel, and long-fibered asbestos. Their method of depositing platinum on supports is more convenient than that recommended by Reyerson (1I), which consists in reduction of the platinum compound with adsorbed hydrogen. The procedure of Holmes and Williams used in preparing the catalysts for this investigation begins with the moistening of the supports with a slightly basic solution of HQPtC14 6H20. The porous gel (or asbestos) is then dried at 100" C., cooled, and carefully moistened with ordinary formalin solution. Inasmuch as reduction with formaldehyde is slow a t room temperature, thorough penetration by formaldehyde is obtained before any reduction takes place. When the temperature is raised to 100" C., there results a rapid production of metallic platinum. The platinized porous support is then carefully washed m-ith warm water and dried.
H
1 Received April 1, 1929 Presented before the Division of Industrial and Engineering Chemistry at the 77th Meeting of the American Chemical Society, Columbus, Ohio, April 29 to May 3, 1929.
Using the three catalysts described above, a studyiwas made of the rates of oxidation of sulfurLdioxide to the trioxide. Apparatus
A diagram of the apparatus used in this investigation is shown in Figure 1. The sulfur dioxide used was obtained in cylinders and was guaranteed by the manufacturers to be of high purity. Any moisture in the sulfur dioxide was removed by means of the calcium chloride-sulfuric acid drying chain. The source of the oxygen used for oxidation of the sulfur dioxide was compressed air. The air which entered the converter was also dried as shown in Figure 1. During the first experiment the preheater shown in the diagram was not used, but difficulty in obtaining constant temperature lcd to its installation in later experiments. Use of the side outlet I on the three-way stopcock made it possible t o obtain samples of the reaction mixture before it entered the converter. It also facilitated the calibration of the flowmeters, which were of the type described by Reisenfeld ( I O ) . The difficulty encountered in obtaining satisfactory connections between sections of the apparatus, due to the hot sulfur dioxide and sulfur trioxide, led to the adoption of
September, 1929
I Y D USTRIAL A LYD ELVGI NEERING C H E X I S T R Y
ground-glass joints held together by spring clamps, as shown in Figure Z S 2 These joints are very easy t o make. and for this purpose were as satisfactory as the ball-and-socket joints described by Lewis ( 7 ) . The joint was made a little better by a drop of phosphoric acid. The temperature was determined by means of a Hoskins pyrometer and chromel-alumel thermocouples. The error in temperature reading was considered t o be less than * l o o C. The temperatures of the furnaces were controlled by placing in the furnaces Pyrex air-bulb thermoregulators operating secondary resistances.
851
the apparatus was kept constant in all experiments. An excess of oxygen over the theoretical quantity needed for the converFion of sulfur dioxide to sulfur trioxide was thus present a t all times. Lewis and Ries (9) and Benton (1) have shown that an excess of oxygen has no deleterious effect on the conversion of sulfur dioxide to sulfur trioxide. Experimental Data
The first study was a comparison of the percentage conversion of sulfur dioxide to sulfur trioxide a t 395" C., a temperature below that for maximum conversion for the>e cataCatalysts lysts. The preheater was not used during the time these The grow volume of the catalyst support used in each determinations were made. Table I gkes the data for these determination was arbitrarily chosen as 5 cc., with parti- determinations. From these data it appears that a t 395" cles about the size of wheat grains. I n those experiments C. platinum distributed on the Holmes chalky gel makes a more efficient catalyst than in which asbestos was used _ _ _ ~ does platinum on Patrick's as the support, 5 cc. of glassy gel. long-fibered asbestos (0.635 A t temperatures slightly below those for maximum These experiments mere gram) were taken. This conversion of sulfur dioxide to sulfur trioxide, platinum c o n d u c t e d with 5 cc. of asbestos h a d p r e v i o u s l y deposited on the Holmes chalky silica gel is more efficatalyst. The length of the been treated with hot hycient as a catalyst than platinum on Patrick's glassy reaction tube occupied by drochloric acid and washed silica gel. A t temperatures for the maximum conwas 5 to 8 cm. the catalyst until nearly all acid-soluble version in each case little difference is noted in the So little time elapsed bematerial had been removed. efficiency of the two gels as supports for platinum catatween the entrance of the The sample of Patrick's gel lysts. Under similar conditions platinum deposited gas into the reaction chamwas obtained from the Silica on either gel is more efficient as a catalyst than platiber and its contact with the Gel Corporation and adnum on asbestos. catalyst that it was impossisorbed 33.8 per cent of its The temperature found for maximum conversion in ble without a preheaFing deown weight of benzene from these experiments is approximately that found in vice to heat the gas to the a stream of air saturated previously reported data in the literature. Within the t e m p e r a t u r e needed for with benzene a t 30" C. The limits studied the percentage conversion at the optimaximum conversion. It sample of the Holmes chalky mum temperatures increases with the platinum conwas therefore decided that gel was prepared i n t h i s tent of the catalyst, although the optimum temperabefore conducting further laboratory according to the tures decrease with increasing richness of catalyst. experiments, a preheater as d i r e c t i o n of Holmes and The Reich iodine method was found sufficiently shown in Figure 1 should be others (3 and 4). It adaccurate for determining sulfur dioxide in gas mixtures. sorbed 115 per cent of its installed. By use of this The Holmes-Williams method for depositing platinum own weight of benzene unarrangement the gas entered uniformly throughout silica gel particles was found to der similar conditions. A the reaction chamber a t a be satisfactory. standard solution containing uniform temperature, which 1 g r a m of H2PtClo.6H20 was approximately that reper 10 cc. of w a t e r w a s quired for maximum conused as a basis for coating the supports. The desired amount version. To simulate more nearly the customary plant pracof platinum solution was drawn with a 1-cc. graduated pipet tice, it was decided to install equipment which would make and diluted to the volume necessary to wet evenly 5 cc. of it possible to expose the sulfur dioxide first to a catalyst of low platinum content and then to a catalyst of higher platithe gel. num content. Experimental Procedure
The standard procedure for estimating the efficiency of t h e catalysts was used. It consisted in determining the sulfur dioxide content of the gases entering the catalytic chamber, by means of the familiar Reich iodine test, then completely absorbing the catalyzed sulfur trioxide in 98 per cent sulfuric acid (in equilibrium with sulfur dioxide), and finally determining, by means of the Reich test, the percentage by volume of unabsorbed sulfur dioxide left in the gases leaving the reaction chamber. Lewis and Ries (8) have objected t o the use of this method on the basis that it was inaccurate for low concentrations of sulfur dioxide. The prment writers have obtained check results with the Reich method and have found the error of this determination to be no greater than that of measuring the rate of flon- of gas through the apparatus. Sulfur dioxide a t the rate of 16 cc. per minute and air a t the rate of 184 ec. per minute (an 8 per cent mixture) entered the apparatus. The rate of flow of gases entering T h e authors are indebted t o A. F. 0. Germann for suggesting these joints, and t o B. J Smythe for the design of t h e metal clanips which have proved so satisfactory.
Table I-Percentage Conversion of Sulfur Dioxide t o Sulfur Trioxide (at 395' C.) Using Holmes Chalky Gel and Patrick's Glassy Gel upon Which Varying Quantitles of Platinum Have Been Deposited THEHOLMESCHALKYGEL Catalyst 90.
H- 1 H-2 H-3
Pt per 5 cc. of gel
Co?version
ME.
Per cent
117.5
91.4 68 2 53.5
5S.S 39.2
1
PATRICK'SGLASSYGEL Catalyst No.
P t per 5 cc. of gel
Conversion
Jlg. 117.5 58.8 39.2
Per cent
P- 1 P-2 P-3
% 64 6
I-YDrSTRIAL dAVDE S G I S E E R l S G CHEJIISTRY
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caine in contact with the catalyst, nor did it produce an ideal condition for reaction in the first chamber during the twostage conversion experiments. The results with the different catalysts were, however, directly comparable. I n Table I1 are given the data on the percentage conversion obtained by use of one- and two-stage converters, using platinum deposited on the Holmes chalky gel, Patrick's glassy gel, and platinum on longfibered asbestos. The temperature for maximum conversion is recorded for each experiment. Interpretation oi Data
F i g u r e 1 - - A p p a r a t u s for M e a s u r i n g C o n v e r s i o n of Sulfur Dioxide t o Sulfur Trioxide
d -Calcium
chloride tube R-Bottle of H Q . S O.I ?--Mercury manometer D-Flowmeter E-Air pressure regulator F-Calcium chloride tube G-Bottle of HzSOa H-Flowmeter I-Three-way stopcock for sampling mixtures before they reach converter J-Preheater ..~ . . .~ . K-Ground-glass joint connecting- preheater and furnace in which conversion of SO2 t o SO8 takes place L-First-stage catalyst L'-Second-stage catalyst M-Connection between two tubes containing catalyst N,N'-Stoppers which may be removed when catalysts are being inserted 0,O'-Ground-glass joints P,P'-Bottles of HzSOa for absorbing so8 Q,Q'-Bottles of Iz for absorbing SO%. When one-stage conversion is measured t h e stopcock above 0' is closed and the one above 0 is opened. For two-stage conversion the stopcock above 0 is closed and the one above 0' is opened. ~
sion to 96-97 per cent. I n all the experiments activation was secured by passing air through the catalyst for 1 hour a t 450" C. Sulfur dioxide and air were then passed through it a t approximately the temperature for maxiinum conversion for 1 hour. The temperature of the furnace was then lowered to 300" C. and measurements of percentage conversion were recorded as the temperatures of the two furnaces were raised. Two to three hours elapsed during the raising of the temperature of the furnace from 300" C. to a little above the point of maximum conversion. It should be mentioned that the end of the reaction tube extended outside the second furnace as shown a t 31 in Figure 1. The gas thus passed out of the furnace from the first coni-erter and then back into the furnace to the second catalyst. By adjusting the amount of mineral wool around this projecting end of the furnace, it was possible to compensate the heat of reaction of sulfur dioxide to sulfur trioxide by heat loss through the small part of the tube extending from the furnace. Both catalyst sections mere thus kept at the same temperature during the two-stage conversion experiments. This arrangement did not prevent or eliminate "hot spots" a t the points where the higher concentrations of sulfur dioxide
I n Figure 3 are plotted the data recorded in Table 11. These ciirves show that there is practically no difference in the efficiency of the Holmes gel and Patrick's gel when they are working under optimuln temperature ~ i 2 -g ~ ~ ~ ~~ j ~o i~n~t conditions. Both of these gels appear someiyhat more efficient as a catalyst support than does long-fibered asbestos. A relatively small quantity of platinum is needed t o convert 80-83 per cent of sulfur dioxide to sulfur trioxide, but relatively large quantities are needed to catalyze the conversion of the remaining 15-20 per cent of sulfur dioxide. Figure 4 shows the effect of increase in platinum content on the temperature needed for maximum conversion. ,4s the quantity of platinum on the porous support was increased, the percentage conversion also increased, provided that the temperature was decreased to the optimum under those conditions. This is in agreement with the work of Knietsch, who found that increase in gas flow not only lowered the percentage conversion but also required a rise in temperature to maintain the optimum per cent conversion. The curve in Figure 4 was obtained from conversion experiments with all three supports.
F i g u r e 3-Percentage C o n v e r s i o n of Sulfur Dioxide t o Sulfur Triokide Using H o l m e s C h a l k y Gel, P a t r i c k ' s G l a s s y Gel, a n d Asbest o s a s M a t e r i a l s o n W h i c h P l a t i n u m W a s Deposited Temperature in each case was optimum for maximum conversion. the curves coincide above 90 per cent conversion.
Two of
The effect of change in temperature on the rate of coiiversion of sulfur dioxide to sulfur trioxide is shown in Figure 5. These curves are typical of the curves obtained by the use of any of the catalysts studied. They are of the same general shape as those recorded by Knietsch, and show that after an optimum temperature is reached for a given rate of gas flow any further increase in temperature causes a
d
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ISDCSTRIAL A S D ESGIAYEERISG CHEJIISTRY
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rapid decrease in percentage conversion, due to the dissociation of some of the sulfur trioxide produced. Table 11-Conversion of Sulfur Dioxide t o Sulfur Trioxide Using P l a t i n u m on Asbestos, Platinum on Holmes Silica Gel, a n d Platinum o n Patrick's Silica Gel a s Catalvstsa
SERIAL S O .
COXVERqIq3x
PLATINUM P E R 5 cc. OB CATALYST Stage I
~
OoNVERS1oN
~~
A- 1 A 2 .4-3 .A-4
A-5 .A-6 H-1 H-2 H-3 H-4 H-5 H-6 H-7
H-8 H-9
H-10 H-11
Ppr c p n t 63.2 86 2 Si 1 88 88 68.8 ti6 Si
89 2 88 4 89 89 91 3 94.7 94
95
P- 1
?!,.. ..
P-3 P-4 P-5 P-6 P-7
56 81.3 3s 00 90 93
5.;
LI
Stage I I
TEMPERATURE FOR MAXIMUM
31g.
.\le.
4.7
..
9.4 12.5 12.5 9 4 37.6
3.i
,. 4
4%
_35 - 1 iS.2
48'7 470
486
-, a- . 2
1.8
3.7
1.8 19.6
460 493 490 493 480
.. ..
l l i .5 29 4 11; 5
7 4 19 6 i.4
smaller quantities of catalysts. Using one-half the usual quantities of catalyst did not loner the percentage conver>ion (1 part platinum to 450 parts sulfur), but less than this much catalyst decreased the efficiency. This apparent lack in efficiency is due, no doubt, t o the extremely short time of contact when gases pass a t the rate of 200 cc. per minute through such small quantities of catalyst. The larger contact masses used in induqtry afford longer time contact between gases and catalyst.
490
..
3.7 19.6 29.4 14 7 19 6 l l i .5 7.4 117 5 29 4
1 . 8_
c.
853
i.4
..
473 4% 472
3912 58.8
457 446 450
, .
440
m n. ~. 488
..
484 482 473 466 460
29'4 5s 8 58.8
T h e arrangement of I hese items follows the order of increasing amounts
5
of platinum used, either in a single stage or a s t h ? sum of both stages.
Tetnperatur e
According t o the data of Chase and Pierce (i?), approximately 1 part of platinum is needed per 1000 parts of sulfur converted to sulfur trioxide per 24 hours; or 1.5 troy ounces
Figure 4-Effect of Change of P l a t i n u m Content of Catalyst on Temperature Needed for Maximum Conversion of Sulfur Dioxide to Sulfur Trioxide
of platinum are sufficient t o convert 100 pounds of sulfur t o sulfur trioxide (96-97 per cent conversion) per 24 hours. I n the laboratory experiments, using catalyst H-40 for the first-stage and catalyst H-10 for the second-stage comer.ion, 1 part of platinum converted 225 parts of sulfur (9607 per cent conversion) per 24 hours, using the rate of flow of sulfur dioxide as 16 cc. per minute and of air 184 cc. per minute. -4s this was approximately the maximum rate of flow of gases which could be obtained with the apparatus as constructed, a few experiments were conducted using
Figure 5-Effect of Change i n Temperature on Percentage Conversion of Sulfur Dioxide t o Sulfur Trioxide Using Holmes Chalky Catalysts Containing 14.7 and 146.0 mg. ot Platinum, Respectively
In conducting experiments with platinized asbestos as catalyst, great difficulty was encountered in maintaining a constant flow of gas through the apparatus due t o the high resistance to gas flow offered by the 5 cc. of platinized asbestos. The resistance t o the flow of gases offered by silica gels of wheat-sized particles was much less. No conversion of sulfur dioxide t o sulfur trioxide vias noted when unplatinized silica gels were tested for catalytic effects. The authors plan to carry on similar research with vanadium compounds supported on gels of varying porosit,p. L i t e r a t u r e Cited (1) Benton, IKD. E-vc. CHEX?.. 19, 494 (1927). (2) Chase and Pierce, I b i d . , 14, 498 (1922). (3) Holmes and Anderson, I b i d . , 17, 280 (1925). (4) Holmes, Sullivan, and Metcalf, I b i d . , 18, 386 (1926). (5) Holmes and Williams, Colloid Symposium Monograph, 1'01.11, p. 283 (1924). (6) Knietsch, Bev., 34, 4069 (1901). ( 7 ) Lewis. Chemistry I n d u s i v y , 47, 1238 (1928). (8) Lewis and Ries, ISD. EKG.CHEI., 18, i 4 i (1926). (9) Lewis and Ries, I b i d . , 19, 830 (1927): 17, 593 (1925). (10) Reisenfeld, Chem.-Ztg., 51, 678 ( 1 9 2 7 ) . (11) Reyerson and Thomas, Colloid Symposium hionograph, Vol. 111, p. 99 (1925).
Self -Extinguishing Cigarette and Fireproof Match Invented A t the request of Representative Edith Nourse Rogers of Massachusetts, scientists a t the Bureau of Standards, in a sixmonth test of nine popular brands, have evolved a "safety cigarette." Its fire-protection factor lies in an inch-long cork tip, lined with water-glass, air-excluding sodium silicate. The scientists also have developed a fireproof match, coated with waterglass within a half-inch of its head. Tossed aside as a fag-end, the self-extinguishing cigarette was found in tests to go out quickly enough to reduce the fire hazard some 90 per cent, as compared with the untreated cigarette. Possibility of accidental fires was reduced approximately one-third by the fireproofed matches. An annual fire loss of approximately $90,000,000 from carelessness of smokers prompted Representative Rogers to ask scientific aid. P. D. Sale and F. M. Hoffneins, under the super-
vision of s. H. Ingberg, chief of the fire-resistance laboratory, attacked the problem. They studied discarded cigarette stubs in highways, by-ways. and building corridors. By scientific measurements, they learned that a one and one-quarter inch cigarette stub is the one most frequently discarded, and that two-thirds of the smokers will toss aside a stub between one and one and one-half inches long. Laboratory experiments showed that cigarettes had a 40-to-1 fire hazard as compared to cigars. It was learned that five seconds is the time most frequently taken for lighting cigarettes, ten seconds for cigars and pipes. The scientists then computed the percentage of water-glassing with the greatest safety factor while retaining the fiery usefulness of the match.
