I N D U S T R I A L A N D ENGINEERING CHEMISTRY
74
maintained at the same rate for 20 minutes, when the temperature of the nitrating liquor should be in the neighborhood of 125" C. From this time on the nitric may be added as rapidly as possible and should have completely entered the nitrating pot within 1 hour. The foregoing is only general, as the rate of flow of the nitric is best determined by practice. The procedure outlined above has given yields as high as 220 pounds of picric acid having a solidification point of 120" + C. to every 100 pounds of phenol used. The average yield should exceed 180 pounds.
Vol. 16, No. 1
If nitric acid is manufactured at the plant where the picric is being produced, it is better to nitrate with straight nitric. If, however, the nitric has to be shipped in, it is better for transportation and handling reasons to substitute mixed acid for the nitric. The mixed acid should have the composition of sulfuric acid 1part, water 2 parts, and nitric acid 7 parts. The ratio of phenol to 66" BB. sulfuric for sulfonation should be changed t o 1:3.
Catalyzers for t h e Oxidation of Ammonia' By Wilfred W. Scott COLORADO SCHOOL
OF
MINES,GOLDEN,COI.0.
A list offifty-two substances, elements or compounds, used by the author for catalytic oxidation of ammonia to nitric acid are gioen in their order of efficiency. The influence of certain substances added as accelerators is indicated and seoeral additional examples are gioen of substances used, showing a marked increased eficiency due to their presence. Cobalt has proved to be one of the most eficient elements, and in combination with small amounts of added substances rioals platinum in efficiency as a catalytic agent f o r oxidation of ammonia. T h e e&ts of beryllium, cerium, bismuth, thor i u m , nickel, ascertained in recent experiments, are shown and a comparative table given. Bismuth appears to be the most efficientaccelerator f o r cobalt; the amount, howeoer, should be kept within certain limits, as large amounts of bismuth will f o r m a n easily fusible alloy andamounts less than 0.1 per cent are not eficient. A good combination is 97 parts by weight of cobalt oxide and 3 parts by weight of
bismuth oxide, though this m a y be varied within fairly broad limifs. Several substances apparently improoe with use and are not so easily poisoned as is platinum. The fixation of nitrogen is one of the most important achievements of modern chemistry. T h e demand of the f o r m of fixation will depend upon the state of war or peace. I n time of war the balance will swing towards nitric acid o n account of its use in explosives; in peace the proportional demand f o r ammonia and its compounds will exceed that for nitric acid and explosioes. Whether in peace or in war we are dependent upon the products of fixed nifrogen-ammoniacal nitrogen f o r the production of our food supply, nitric acid and its derivatives f o r our national security. T h e great source of raw materials f o r the making of either has n o monopoly-free air and water, available fuel, and catalysts that can be obtained in abundance and at low cost.
URIKG the first two years of the World War the au-
Many of these tests, where pumice was used, may be in error from the light of more recent work, since silica combinations occurring under the intense heat of the reaction undoubtedly influenced results. It is worthy of notice that conversions as high as 93 per cent were obtained with metallic platinum a t a temperature of 200" C., which is far below the temperatures used a t the Government plants in their experimental work. Platinized asbestos was found to be a poor catalyst. A short duration of contact of the gases with platinum was necessary for good yields (0.007 second or less). The influence of small amounts of substances in increasing the activity of catalytic substances has been noted by a number of investigators. In previous work on this interesting feature of the subject the writer tested out the effect of added substances as promoters for iron, nickel, and cobalt, the following elements being added in small amounts to each of the elements mentioned: aluminium, antimony, arsenic, barium, bismuth, calcium, chromium, copper, lead, lithium, magnesium, manganese, molybdenum, osmium, ruthinium, strontium, tin, titanium, thorium, tungsten, uranium, vanadium, and zinc. I n the majority of cases the addition was of very little effect and in some cases actually detrimental. The following combinations, however, gave good results : Iron with bismuth resulted in an increased efficiency of more than 20 per cent over the oxide of iron alone; bismuth added to nickel increased the efficiency of nickel oxide 63 per cent, added to cobalt it increased the fficiency of the CObalt oxide over 8 per cent; aluminium h d very little effect as a promoter for iron or nickel, but it increased the efficiency
D
thor was engaged in researches relating to products used by the Allies, and more especially in investigating various substances for ascertaining their efficiency as catalysts in the oxidation of ammonia. During this period a large number of substances were compounded and tested. Pumice was used as a carrier where it was not possible to use the substances direct or where bulk was desired. A list of the more important of these substances based as catalyzers is given in the order of their efficiency as found by the writer: Bright metallic platinum gauze Cobalt metal (surface oxidized) Cobalt oxide Iron oxide Metallic silver Metallic nickel Silver vanadate Copper uranate Cobalt chromate Palladium metal Iron manganate Platinum-coated iron gauze Nickel chromate Stannic oxide Vanadium oxide Silver manganate Iron arsenate Silver arsenate Nickel vanadate Nickel manganate Copper molybdate Silver chromate Cobalt manganate Chromium oxide Iron vanadate Silver molybdate
Nickel oxide Manganese dioxide Silver oxide Copper vanadate Copper tungstate Metallic copper gauze Silver uranate Copper vanadate Iron molyhdate Iron tungstate Copper arsenate Nickel arsenate Cobalt arsenate Nickel molybdate Copper chromate Copper molyhdate Oxides of copper Gold Titanium Uranium Barium Lead Iron uranate Nickel wanate Cobalt uranate Nickel tungstate
1 Received April 30, 1923. Extract from thesis presented in partial fulfilment of the requirements fcir the degree of doctor of science.
P
January, 1924
I N D USTRIAL A N D EATGINEERINGCHEMISTRY
75 Sigh! Glass
Globe
FIG.I-APPARATUSFOR
CONVERStON O F AXbSONXA TO NITRIC
of cobalt oxide over 15 per cent. This latter catalyst was considered so good that it was decided to get patents2 for the combination in the leading countries of the world. This paper deals with promoters of cobalt oxide. Omitting combinations which were found to be of little value, by the process of elimination the selection has been limited to the few substances giving promising results as promoters and those untried which would be of commercial value. The cobalt nitrate salt used was of the highest purity obtainable. A trace of nickel was present, but the amount was exceedingly small, a large amount of the salt being necessary to obtain ~ttest for nickel.
APPARATUS I n the author’s previous work on catalysts, the air and ammonia were carefully measured, the latter even being weighed to obtain the exact amount in the run. The resulting oxides of nitrogen were adsorbed and oxidized by means of a complicated system of absorption towers down which water was run or sprayed. The exit gases from the converter were cooled by means of a silica coil immersed in a tank of water. The system involved the use of meters, delicate scales for ammonia cylinders of special construction, and necessitated the determination of the total acid formed. More recent developments of methods for determination of convwsion, notably the method of Gaillard, have enabled the writer greatly to simplify the apparatus by elimination of gas meters, scales for weighing ammonia, and the elaborate absorption system, since an accurate determination of conversion may be made by obtaining samples of the inlet and exit gases of the converter and analyzing each for the total combined nitrogen by weight, in the entering gas combined as ammonia, and in the exit gas combined as oxides of nitrogen. The proportions of ammonia and air were regulated by means of two flowmeters or differential gages. The gases were combined in a mixing bottle, then were conducted into a 2-liter bottle before entering the converter. Samples were drawn from this bottle for determining the percentage of ammonia in the gas. The gas entered the top of a silica tube converter through a glass bulb, through which the *Scott, U. S. Patent 1,399,807 (December 13, 1921), assigned t o Atmospheiic Nitrogen Corporation, New York
ACID
9
glow of the catalyst could be seen during the run. The upper part of the tube was cooled by air, and by means of a wet cloth one end of which dipped in a beaker of water to prevent overheating of the rubber stopper connecting the upper part of the tube with the bulb. Temperatures were obtained by means of a thermocouple. Converter dimensions were asfollows: length, 30 cm.; bore, 3-em. constricted tube a t lower end 13 cm. long; diameter of bore, 0.8 om. This thermocouple was connected with a second tube 30 em. long. The gas leaving the converter entered a 3-liter separatory funnel serving as a reservoir for sampling. The rubber stopper had two gas outlets-one passing into a hood, where the oxides and remaining air escaped continuously during the run; the other tube, from which samples of the hot exit gas were taken, was kept closed when not i n use. Cooling of the gases was unnecessary, and for purposes of sampling was not desired, since the steam formed by the reaction, as well as the oxides of nitrogen, had to be taken into the sampling bulb. The sample was drawn from the center of the separatory funnel where the temperature was sufficient to prevent condensation. Fifty grams of catalyzer were taken in each This amount of material occupied about 40 cc. of space in the lower end of the silica tube, forming a column the diameter of the bore and 5 to 6 em. long. The gas was conducted through this material a t a n average rate of 11 liters per minute, unless otherwise stated. I n addition t o needle valves for regulating the flow of the air and the ammonia, by-passes for relieving any sudden rise in pressure were attached to each line just before entering the flowmeters. A mercury seal maintained the desired pressure in each case. The converter was electrically heated by means of two elements of a combustion furnace, such as are commonly used in furnaces for determining carbon in steel. Heat ra8
Exceptions to this amount taken wilt receive special mention later.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
76
diation was largely prevented by surrounding the elements with a casing of sheet iron packed with asbestos. The writer had in mind the countercurrent flow method for maintaining the temperature in the converter after the reaction had started, but unfortunateIy could not procure the necessary equipment. In practice the countercurrent principle should be used, thus doing away with the necessity of heating the converters throughout the run with outside energy. DETERMINATION OF CONVERTER EFFICIENCY In place of determining the total ammonia used and the total products of oxidation, samples may be taken, during the operation, of gases entering and leaving the converter and analyzed according to the following simple and accurate procedure suggested by Gaillard;4 a method successfully used by the American Cyanamide Company at Warners, I?. J., and by the United States nitrate plants a t Sheffield and Muscle Shoals, Ala.
F I G . 2-EVACUATING
AND WEIGHING
BULBS
PRINCIPLE-The gas to be analyzed is drawn into an evacuated bulb which has previously been weighed, and the increased weight due to the sample is obtained. The ammonia or nitrogen oxides in the bulb are then absorbed and titrated, and the percentage by weight of combined nitrogen in the gases is determined. The efficiency is the ratio of the combined nitrogen in the exit and inlet gases. SOURCES OF ERROR-Error may be caused by: (a) Water condensation in the sampling tube during sampling.
( b ) Air leakage into the tube during sampling. (c) Ammonia escaping oxidation being drawn into the bulb. In presence of ammonia a cloudiness is readily observed. (d). Changes in temperature, barometric pressure, and moisture conditions between successive weighings of the same bulb.
These errors are rendered negligible by careful manipulation. (The writer would suggest that a similar bulb tare weight be used and the procedure for weighing recomqended in combustion carbon determinations be followed.)
PREPARATION OF THE CATALYSTS In the preliminary work it was thought to be necessary to add starch paste to the powdered oxides in order to make the material adhere and form a granulated, porous product. The writer found, however, that the product thus made crumbled easily into a powder and that it was preferable to evaporate the mixed nitrate crystals without the addition of water or starch. Upon heating, the crystals dissolved in their own water of crystallization forming a homogeneous solution. The evaporation was conducted over a sand bath, heated on an electric plate (or over a MBker gas burner) 4
THISJOURNAL, 11, 745 (1919).
Vol. 16, KO.1
until the water was expelled and the brown fumes of nitrogen oxides were freely evolved, The temperature was then increased and heating continued until a hard residue (or cake of oxides) was obtained. The cooled material was broken down to about 0.6 to 0.2 cm. lumps and the fine dust screened out through a 40-mesh screen. The granular material was placed in the silica tube and ignited at red heat, air being passed through the product until no fumes of nitric oxides were evident. After 2 hours of this last treatment the material was dumped into a beaker, any fines less than 40 mesh were again screened out (this fine powder offered too great resistance to the passage of gas), and 50 grams were weighed and placed in the silica tube converter, a clean perforated porcelain disk being placed in the bottom of the tube to prevent any material from entering and blocking the constricted portion of the converter. The converter tube was placed in the tubular electric furnace and connected up with the inlet and exit system. The heat was turned on and the air-ammonia gas passed through as soon as the temperature had risen to the conversion heat. The action was allowed to proceed for an hour or more before tests of the inlet and exit gases were made. For connecting up the exit, lower end of the converter, to the silica tube that entered the 3-liter separatory funnel, wet, fine-fibered asbestos was found to be a very satisfactory packing material, as it formed a tight seal, was not attacked by the corrosive oxides of nitrogen, and resisted the heat. The exit gas in the funnel was well above the condensing temperature of steam (150' C.), so that the gases swept into the sampling bulbs contained all the products of the converter reaction, including the water vapor. I n making up new catalysts it was deemed advisable to use different casseroles for carrying on the evaporation, so that there was no chance of contamination of one mixture by another, After the run the converter was cleaned out carefully and any adhering oxide was dissolved from the mall by action of hydrochloric and nitric acids. The acids were washed out carefully before the tube was again placed in service. Frequently, the proportions of the cobalt oxide and the promoter were varied to ascertain whether there was a maximum efficiency ratio. In this case it was deemed unnecessary to observe the foregoing precautions regarding a change of casseroles and acid treatment of the convert&. The proportions are statedin terms of the oxides rather than the elements, since the percentageof the FIG. 3-EXPERIMENTAL CONVERTER F O R OXIDATTON OF AMMONIA TO NITRIC ACID oxides was ascertained by evaporation and ignition of the crystallized nitrate salts, the oxides thus obtained being in the form used in the process. The percentages thus obtained were used in the caIculations for making up the mixtures. Five-gram samples were taken for making this analysis, the evaporation and
INDUSTRIAL AND ENGINEERING CHEMIJTRY
January, 1924
ignition being conducted in porcelain crucibles in a manner similar to that used in the preparation of the catalysts. The following results were obtained in the analysis used in the experiments: CRYSTALLIZED SALT Bkmuth nitrate Beryllium nitrate Cerium nitrate Nickel nitrate Cobalt nitrate Thorium nitrate
Oxide from 5 Grams Grams
Per cent
2.350 0.674 2.170 1.260 1.368 2.450
47.00 13.50 43.40 25.20 27.36 49.00
Oxide
Grams Salt Required per Gram Oxide
2.13 7.48 2.31 3.97 3.66 2.04
STANDARDIZATION OF THE FLOWMETER TUBES The rate of passage of the gas was measured by means of a standard gas meter, a stop watch being used. The time required for the passage of 10 liters was ascertained by half a dozen tests each, a t different pressures (differentials 8.5, 12, and 18 em.), and an average was taken of the readings. From the data thus obtained the rate of gas flow per minute for each capillary tube under the fixed pressures was calculated and B chart plotted. These flowmeter capillary tubes were exceedingly important, since they enabled one to obtain the correct proportions of gas mixtures and maintain these proportions during tests of inlet and exit gases. For example, suppose two tubes were selected, the one used in the flowmeter for air delivered 10 liters of gas per minute at a differeatial pressure (water) of 18 cm., and the other more constricted tube delivered 1 liter of gas per minute under a differential pressure of 16 cm. If the proportion of 10 volumes of air to 1 volume of ammonia gas was desired, the gas pressures were regulated so that the gages showed throughout the tests exactly 18 em. and 16 em. columns of water, respeclively. The upper and lower limits were marked and the water columns in the U-tubes were kept a t these points during the sampling of the inlet and exit gases, so that the inlet air-ammonia mixture was exactly the same during the period of the sampling. The importance of this can be appreciated, since the accuracy of calculation of conversions depended upon these proportions remaining constant. The gas pressures were regulated by means of needle valves. The fluctuation of temperature in the air and ammonia lines was negligible since the lines remained a t the uniform temperature of the room. This was shown by tests of the gas entering the reservoirs preceding the flowmeters.
77
EXPERIMENTAL DATA
COBALTOXIDES w z
3s
$8
Inlet Exit Inlet Exit Inlet Exit Inlet Exit Inlet Exit Inlet Exit Inlet Exit Inlet Exit Inlet Exit Inlet Exit lnlet Exit Inlet Exit Inlet Exit Inlet Exit Inlet Exit
*R
0.5060 0.4493 0.5200 8.4734 0.4873 0.4783 0.4873 0.4509 0.5091 0.4603 0.5048 0.5024 0.5665 0.4998
5.2 8.1 6.6 13.5 10.1 12.0 8.2 12.2 10.1 13.0 10.2 15.8 13.1 13.5
0.0073 0.0013 0.0092 0.0189 0.0141 o.0168 0.0115 0.0171 0.0141 0.0182 0.0143 0.0211 0.0183 0.0189
1.40 2.52 1.78 4.00 2.91 3.30 2.40 3.80 2.80 4.00 2.80 4.20 3.20 3.80
..
71
..
72
.. . . ... . 1:12
1:17
ilik
.... .. .... 70 1:11 . . 1:lO ... . 76 .. .... 82 1:12 J $2 74 74
1:12
680i
AVERAGE76.6 = reagent in all the tables.
The actual weights of the bulbs used varied from 60 to 75 grams. The removal of the balance pan, watch glass, and hanger reduced the weights over 55 grams, making the weighings more sensitive. The inlet and exit samples were taken as close together as possible and the proportions were calculated from the following facts: 1 liter of air weighs 1.293 grams. 1 liter of ammonia weighs 0.76 gram. The nitrogen in ammonia is equivalent to 0.62 gram per liter of ammonia. Keeping NHs = 1 and varying the volumes of air, the following were calculated: Volumesof air CC. 8 9 10 11 12 13 14 16 18 20 25 Per cent com: bined nitrogen 5.6 5.0 4.5 4.1 3.8 3.5 3.3 2.8 2.6 2.3 1.8
Temperatures are approximate.
COBALT-BERYLLIUM OXIDES Cobalt Oxide 97.1 Per cent, Berpllium Oxide d.9 Per cent
CRECKON METHOD FOR ASCERTAINING CONVERSION I n the author’s previous work on catalysts the efficiency of cobalt as a catalytic substance was ascertained by carefully measuring the ammonia used during an entire run, obtaining the total oxides of nitrogen by absorption, and determining the same by analysis. An average of six runs extending over a period of nearly 10 days gave an efficiency for cobalt of 74.3 per cent. The tests obtained were as follows: 76.3, 68.5, 77.6, 72.0, 67.6, 83.7 per cent; average, 74.3 per cent. An average of the last fifteen tests by analysis of the inlet and exit gases during the use of the cobalt oxide catalyst, following the procedure as previously outlined and adopted for this present investigation, gave 76.6 per cent-a remarkable check on the conversion average of this previous work. The tests obtained are given in the following table. The first four were obtained during the adjustment for obtaining correct conditions for conversion, and are not included in the average. The fifteen tests obtained during a period of a day’s run have been arranged in order of percentages. The extremes of these are in fair agreement with the extremes given above.
..
....
.. .. .. .. ..
.... ’
....
..
....
1:9 17 5.05 48 8 800 0.4712 9.0 2.44 0.5176 47 1 : 10 15.5 4.55 8 0.4770 2.12 0.4995 7.5 ki 1: 10 11 7 60 4.58 16.4 0.4815 2.26 8.2 0.5078 1:9 5.12 17.0 66 0.4790 3.39 12.5 0.5164 ilii 4.20 13.5 77 700 0.4482 3.24 11.0 0.5092 9 82 1:10 b 4.48 13.0 0.4071 .... 3.60 13.5 0.5160 1: 12 3.95 85 13.5 0.4783 3.36 12.0 0.4997 ilii 4.20 86 13.5 0.4490 .. < 3.50 12.8 0.5104 93 1: 13 3.45 12.2 0.4964 3.I9 12.0 0.5254 89 1:13 ? 11 3.45 13.0 0.5240 Exit 0.4714 10.4 3.10 .. Inlet 0.4843 12.2 3.73 93 iIii Exit 0.5261 13.1 3.48 Five runs omitted from record a Average ol last eight runs 84 per cent. of average.
..
....
....
.. I,
Cobalt Oxide 91 Per cent, Beryllium Oxide 9 Per cent In a preliminary run the catalyst became packed in the con-
verter. The material was removed, powdered, and again mixed with starch. After drying in an oven a t 110’ C. until thoroughly
,778
INDUSTRIAL A N D ENGINEERING CHEMISTRY
hard and dry, the catalyzer w$s placed in a covered beaker over the flame and ignited. This material was then placed in the silica tube and carbon burned out by passing oxygen through the tube heated to redness. The catalyst weighed 50 grams and occupied a column of 8 cm. in the silica tube converter. The following results were obtained. The record given is in the order obtained during the run. FIXED Weight NITRO-of Gas 0.1 N R Per cent Per cent GEN Gram Cc. Nitrogen Conversion Inlet 0.4669 13.5 4.00 70 Exit 0.4977 9.8 2.8 .. 14.0 Inlet 0.4511 4.3 60 Exit 0.4948 9.4 2.6 4.2 53 Inlet 0.4485 13.5 Exit 0.4936 7.5 2.14
.. ..
Ratio 1:11
iIio ilio
..
"emRate peiature Liters/ C. Min. 700 7
i i
7%
si0
..
It is interesting to note that the catalyzer, poor a t first, improved after several hours' run, giving conversions over 90 per cent. The run was started a t 9 A . M. and completed at 6 P. M. The first four runs were made on the previous day. The catalyzer was dried and roasted in a closed beaker. The following day the catalyzer was placed in the converter, heated t o redness, and oxygen passed through. Immediately following this the run was begun with air-ammonia mixture. Average conversion = 90 per cent (4 determinations omitted). The increased temperature undoubtedly caused a drop in conversion. The catalyst was removed from the tube, about 5 grams of the fines were screened out and the remaining 45 grams returned to, the tube. The temperature was gradually raised to a dull red heat, air only passing through the material. Finally, ammonia was also passed in. The rate of flow was 7 liters per minute of mixed gases. Considerable care was taken to keep the flow and proportions of ammonia and air constant, as well as to hold the temperature a t about 700' C . I n the last of this series the temperature was again increased to a bright red heat (850' t o 900' C.). A decided drop in conversion was evident. FIXED NITROGEN
Weight of Gas Gram
0.1 N R Cc.
Per cent Nitronen --- 3.5~
3.24
The temperature was now raised. Inlet Exit Inlet Exit
0.4680 0.5104 0.4483 0.5193
10.4 9.0 12.5 4.0
Per cent Conversion Ratio 88 1:12
..
Temperature 700
..
3.1 2.47 3.9 1.7
80
1:14
800
53
iIii
91%
..
..
The material was examined and was found to be much lighter in color. Air was again passed through the material heated to dull red heat. Strict attention was directed to keeping the ammonia and air flow constant, as'well as the temperature, which was held to 690" C. (0.25 inch below surface of the catalyst) and 480' C. exit gas (I inch below the material). The latter temperature was taken with thermocouple in contact with the outside of constricted portion of tube, the couple being covered with asbestos. The inlet gas was found to contain 4.15 per cent of nitrogen. The air and ammonia proportions being kept constant, additional tests were considered unnecessary. The results follow: FIXED Weight Per cent NITRO-of Gas 0.1 N R Per cent ConverGEN Gram Cc. Nitrogen sion Inlet 0.4621 13.7 4.15 Exit 1 0.4723 12.2 3.62 Exit2 0.4783 12.5 3.66 14.2 3.90 Exit 3 0.5096 14.0 3.99 96 Exit 4 0.4912 14.3 3.96 95 Exit6 0.5102
Temperature Ratio
Inlet
1:11
690
and the procedure for preparation of the material t h a t has been outlined was adopted for this and subsequent catalysts. The evaporation was conducted over a sand bath in a casserole of 500 cc. capacity and the product taken to dryness, strong fumes of nitric oxides being freely evolved. The heating was then continued for about 2 hours over the sand bath before the final ignition in the silica tube, air being conducted through the broken up material until the nitric oxides had been completely expelled from the catalyst heated to redness. This final roasting required about 2 hours. Proportion ammonia to air = 1: 12. Weight of Gas
Per cent remRate Per cent Copver- pera- Liters per Cc. Nitrogep sion ture C. Minute 0.4465 12.2 3.82 0.5022 13.2 3.68 96 0.5231 13.8 3.69 96 700 10 0.4934 12.1 3.44 90 0.4577 3.85 12.6 0.6261 3.78 14.2 99 710 10 0.4974 3.52 12.5 92 Average conversion = 94.6 per cent
GASTESTED Gram Inlet Exit Exit Exit Inlet Exit Exit
c.
Exit 480
The average of these five runs is 92 per cent. The average of the last three runs is 95 per cent, which can undoubtedly be obtained with careful regulation of temperatures and gas
0.1 N R
..
1
During the tests the gas flow was carefully kept constant.
Cobalt Oxide 91 Per cent, Cerium Oxide 9 Per cent The proportion of the ammonia to air was kept a t approximately 1: 10. Rate of flow = 10 liters per minute. Temperature, 720" C. GASTSSTED Inlet Exit Inlet Exit Exit Exit
Weight of Gas 0.1 N R Per cent Gram Cc. Nitrogen 0.4547 14.0 4.31 0.4790 13.5 3.95 0.4592 14.1 4.34 0.5147 14.1 3.86 0.4917 14.0 3.99 0.5264 14.3 3.87 Average conversion = 9 0 . 5 per cent
Per cent Conversion
.. .. 89 91
..
90
The conversion was good from the start. The gas flow was increased t o 11liters per minute. Temperature fell t o 710' C. Proportions of ammonia t o air held a t about 1: 10. Conversions based on average of ammonia tests,
..
Slight change in proportions.
Vol. 16, No. 1
GASTESTED Inlet Exit Exit Exit Inlet Exit Exit Exit
Weight of Gas 0.1 N R Per cent Gram cc. Nitrogen 4.35 0.4560 14.2 14.2 3.87 0.5146 14.1 0.5178 3.81 3.95 14.5 0.5134 14.4 0.4874 4.14 14.7 0.5198 3.94 14.9 0.5200 4.01 4.1 15.1 0.5162 Average conversion = 93 per cent
Per cent Conversion
..
91 90 93
..
93 94 96
CERIUMOXIDE, 100 PERCENT In the previous work on catalysts for the oxidation of ammonia the writer tested out cerium oxide, using pumice as a carrier for the purpose of giving bulk to the material. The following test was made to ascertain whether the pumice was the cause of the poor results obtained by this oxide. Cerium has been shown by the writer's recent results to be a good promoter for cobalt oxide. The oxide was made in the usual way by heating the crystallized nitrate salt of cerium. Rate of flow, 8 liters per micute. Temperature, 110' C. Weight of Gas 0.1 N R Per cent Per cent GASTESTED Gram cc. Nitrogen Conversion Inlet 0.4654 12.0 3.61 Exit 0.4976 10.0 2.80 7610 Exit 0.4946 10.5 2.98 82.0 Exit 0.5072 10.8 3.00 . 82.0 Inlet 0.4572 11.9 3.64 Exit 0.5265 11.2 3.00 8i:O Average conversion, approximately 81 per cent
proportions.
Increasing the proportion of beryllium appears t o be beneficial. The material in this active condition appears a bluish black. The irregular lumps are brittle, but fairly firm.
COBALT-CERIUX OXIDES Cobalt Oxide 97 Per cent, Cerium Oxide S Per cent Direct evaporation of the nitrate salts of cobalt and cerium
in the proportions necessary for this proportion was found to give a firmer product.
The addition of starch was abandoned,
The rate of gas flow was now increased to 11 liters per minute. The exit gave a decided fume showing t h a t with a rapid flow the cerium gave poor conversion. Only one test was made of this run. GASTESTED Inlet Exit
Weight of Gas Gram 0.4806 0.525
0.1 h T R cc. 15.2 12.6
Per cent Nitrogen 4.4 3.3
Per cent Conversion
Cerium alone cannot be considered a good catalyst.
..
75
INDUSTRIAL A N D ENGINEERING CHEMISTRY
January, 1924
COBALT-BISMUTH OXIDES Cobalt Oxide 9Y Per cent, Bismuth Oxide S Per cent The product was made by mixing 363 grams of cobalt nitrate with 6.6 grams of bismuth nitrate, approximately 100 grams of cobalt oxide and 3.1 grams of bismuth oxide resulting after expulsion of the water and nitric acid. Fifty grams of the product broken into small lumps, approximately 0 6 to 0.2 cm , were used as a catalyst in the following tests. Beginning with a gas flow of 8 liters, the rate was increased t o 11 liters per minute with a ratio of ammonia t o air of 1: 10. The temperature ranged between 710" to 720" C. GASTESTED Inlet Exit Exit Exit Exit Inlet
Weight of Gas Gram 0.4722 0.5217 0.5305 0.5417 0.5435 0.4676
0 1N R cc. 14.5 14.9 15.8 16.2 16.5 14.4
Per cent Nitrogen 4.29 4.00 4.16 4.19 4.25 4.30
Weight of Gas 0.1 N R Per cent Gram cc. h-itrogen 15.6 4.61 0.4739 4.3 0.5112 15.7 4.35 0.5030 15.6 4.3 0.5088 15.6 17.6 4.55 0.5417 4.35 0.5067 15.7 Average conversion, 95+ per cent
GAS TESTED Inlet Exit
0.1 N R cc.
Per cent Nitrogen
GASTESTED
..
Per cent Conversion
..
93 94 93 98 94
Per cent Conversion
0.1 N R cc.
Per cent Xitrogen
Per cent Conversion
Fourteen grams (0.5 ounce) of cobalt-bismuth catalyst 97:3 in a 3.18 cm. (1.25 inch) tube will handle 22 liters of air-ammonia mixture, but preheating of the gas mixture is necessary. efficiency of the catalyst is remarkable.
The
Cobalt Oxide 99.9 Per cent, Bismuth Oxide 0.1 Per cent The following test was made to ascertain whether small amounts ol bismuth, such as 0.1 per cent of the oxide, would make a n appreciable difference in cobalt oxide as a catalyst for the oxidation of ammonia t o oxides of nitrogen. The calculated amounts of the crystallized salts, which would give the foregoing proportions of the oxides of cobalt and bismuth, were mixed by melting the few crystals of bismuth in the large bulk of cobalt salt, evaporating, and finally igniting as usual. The temperature ranged from about 600' t o 750' C. The appearance of the surface of the catalyst was a dull red. Fifty grams of material were taken and the air-ammonia mixture was passed through a t a rate of 11 liters per minute. The color of the exit gas was the characteristic red obtained in good conversions and the gas was free from fumes. GAS TESTED
Weight of Gas Gram
0 1 A' R cc.
Per cent Nitrogen
Per cent Conversion
0.4734 0.5410 Average conversion, 94.5 per cent
Average conversion, approximately 81 per cent
The efficiency of the catalyst is equally as good as it was with half the amount of gas used in the first experiments. I n testing out the efficiency of platinum with a similar converter, the writer obtained a n efficiency of 93 per cent conversion with a gas volume of 20 liters per minute, 8 grams of t::e platinum gauze being employed.
Averages of the first and last tests of the inlet gas were taken in making the calculation of yields. The gas flow was kept constant. The following tests were made after the action had continued for a n additional 4 hours, as i t was desired to learn whether the material improved or became a poorer catalyst through use.
Cobalt Oxide 97 Per cent, Bismuth Oxide 3 Per cent The catalyst demonstrated its efficiency as shown in the foregoing tabulated results. Fifty grams of material were able to give a high conversion at the rate of gas flow used with other materials tested. It showed an equal efficiency when the gas volume was doubled. Twenty-two liters per minute taxed the apparatus t o its limit-the heat of the exit gas was sufficient t o crack the large separatory funnel, and the pressures were considerably increased. It was unwise to attempt an increase of gas volume. The alternative was t o reduce the quantity of catalyst. This was cut down t o 20 grams while the gas flow was held at 22 liters per minute. GAS TESTED Inlet Exit Inlet Exit Inlet Exit
Weight of Gas Gram
..
93 97 97 99
It was decided to double the volume of the gas t o ascertain whether the 50 grams of material would be effective in handling larger amounts. A new set of flowmeters were installed for adjusting the proportions of ammonia and air, which were held betweer 1: 10 and 1: 11. The temperature taken in the middle of the catalyst, half way down the column, was 730' C. Speed of gas flow, 22.5 liters per minute. Weight nf Gas Gram
by the rapid flow of the gases. A preheater of the gases would do away with this cooling effect. It is evident that 20 grams of the material are as effective in conversion as the larger 50-gram sample. A further cut in the amount of catalyst t o 14 grams (approximately 0 5 ounce) was now made. Volume, 14 cc. Rate of flow, 22 liters per minute. Temperature, 800' t o 950' C. At 700" C. a destinct fume was evident, the surface of the catalyst not being sufficiently hot for effectiveness. When the temnow perature was raised to 800' C. the fume was faintly evident. At 900" C. no fume appeared.
'
Per cent Conversion
The following tests were made 4 hours later, the proportion ofithe ammonia being increased slightly, as shown by the inlet gas: GAS TESTED Inlet Exit Exit Exit Exit Exit
79
Weight of Gas 0.1 A' R Gram cc. 0.5165 19.8 0.5350 20.5 0.4732 16.4 0.5341 17.8 0.4664 14.4 0.5133 15.7 Temperature, 710' to 730'
Per cent Nitrogen 5.367 8.365 4.855 4.666 4.324 4.263 C.
Per cent Conversion
1 1
1
GAS TBSTED Inlet Inlet Exit Exit Exit Exit
Weight of Gas Gram 0.4670 0.4793 0.5117 0.5041 0.5193 0.6070
0.1 N R Cc. 15.2 15.7 15.3 14.4 15.1 15.0
Per cent Nitrogen 4.5 4.6 4.2 4.0 4.1 4.1
Per cent Conversion
..
92 89 90 90
The tests gave much more nearly uniform results, with an average of about 90 per cent conversion. This is better than is obtained by the pure cobalt oxide, but is not so good as was obtained with a larger proportion of the bismuth oxide. It is evident that the material improves as a catalyst after a few hours of use. It is a remarkable fact that very small percentages of bismuth oxide have a marked promotive action on cobalt oxide as a catalyst.
99 96 97
The proportions of the air and ammonia were purposely varied to ascertain whether there would be a difference in conversion. This difference is but slight. A stronger ammonia gas has evidently a n advantage, since the te,mperature of reaction is greater and there is less tendency t o the cooling of the catalyst
Cobalt Oxide 75 Per cent, Bismuth Oxide 25 Per cent Bismuth oxide has been shown t o be an active promoter for cobalt oxide when present in small amounts. This experiment was undertaken t o find out whether it increased the activity of cobalt oxide as an oxidizer of ammonia when present in comparatively large proportion. The necessary amounts of cobalt nitrate and bismuth nitrates were mixed and heated by the adopted procedure and the ignited oxides used in the test. Gas flow, 11 liters per minute. Temperature, 650" to 710' C.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
80 GAS TESTED Inlet Exit
Weight of Gas Gram
0.1 N R cc.
Per cent Fixed Nitronen
Percent Conversion
..
0.4631 0.4904 0.4940 0.4994 0.4972 0.4959
13.4 4.05 11.1 3.19 11.7 3.32 12.5 3.50 12.0 3.40 12.2 3.44 Average conversion, 76 per cent
71 74 79 77 78
Cobalt Oxide 60 Per cent, Bismuth Oxide 50 Per cent The proportion of bismuth oxide was increased to 50 per cent. The nitrate salts OF cobalt and bismuth calculated t o give the foregoing proportion of oxides were evaporated and heated as usual and the oxides produced were used in the experiment. When the mixed gas of ammonia and air was passed through this material a dense white fume resulted with the temperature at 650" C. The temperature was gradually raised to 750' C. and the rate of gas flow cut down from 11 to 8 liters per minute. The exit gas gradually turned a light brown, but a fume was still evident. Only one test was made of the gas, as it was necessary to shut down shortly after this test owing t o the fusion of the mixture. GASTESTED Inlet Exit
Weight of Gas Gram
0.1 N R
cc.
Per cent Fixed Nitrogen
Per cent Conversion
0.4491 0.5320
12.1 2.8
3.77 0.61
17
..
It is evident that bismuth has its limits of usefulness. Large proportions are inadvisable, giving a detrimental action on cobalt and, as in case of bismuth alloys, causing a lowering of the fusion point.
COBALT-NICKEL OXIDES Cobalt Oxide 97 Per cent, Nickel Oxide 3 Per cent Nickel is invariably present in cobalt nitrate, in appreciable quantities in the commercial product and in small quantities in the purified salt. The following experiment was undertaken t o ascertain whether the presence of nickel in cobalt nitrate in an appreciable quantity would lower its efficiency as a catalyst agent for the oxidation of ammonia to nitric acid. The crystallized nitrates of cobalt and nickel were mixed in the necessary quantities to give the above proportion of oxides, the oxides being prepared according to the procedure outlined in the fore part of this paper. A 50-gram sample of the material was used. Rate of gas flow, 11 liters per minute. Temperature, 690' to 720' C. GASTESTED ( A ) Inlet Exit ( B ) Inlet Exit
Weight of Gas Gram
0.1 N R cc.
Per cent Nitrogen
0.4642 0.5163 0.4522 0.5009
14.5 14.7 14.2 14.4
4.37 3.99 4.87 4.00
Per cent Conversion
..
91
..
92
Rate of gas flow increased to 22 liters per minute. ture, 680' C. a t surface of catalyst. ( A ) Inlet Exit (8) Inlet Exit
0:4456 0.4929 0.4520 0.5054
8.2 7.9 8.8 7.2
2.58 2.23 2.73 2.00
Tempera-
may be used as a catalyst for the oxidation of ammonia to oxides of nitrogen. The average yield by this cobalt-nickel combination is 89 per cent.
Cobalt Oxide 3 Per cent, Nickel Oxide 76 Per cent This catalyst was made up so that cobalt itself became the promoter for nickel. In the writer's previous work of this subject nickel oxide had proved to be a poor catalyst, being well down in the list, as is shown in a previous part of this paper. Rate of gas flow, 11 liters per minute.
800" C.
GASTESTED Inlet Inlet Average . Exit Exit Exit Exit
0.5069 0.5014
0.1 N R
81
cc.
Per cent Nitrogen
Per cent Conversion
17.1 16.3
4.72 4.53
96
..
The following tests were made using a fresh batch of product and a new converter tube: GAS TESTED Infet Inlet Exit Exit EXlt Exit
Weight of Gas Gram
0.1 N R
0.4726 0.4638 0.6160 0.5004 0.6287 0.5490
15.5 15.4 14.3 14.2 14.6 17.6
cc.
Per cent Nitrogen 4.59 4.59 3.89 3.94 3.89 4.48
0.1 N R cc.
0.4876 0.4716 0.4795 0.5005 0.5139 0.5140 0.5033
Per cent Per cent Nitrogen Conversion
...
15.3 15.1 4.02 15.2 10.5 2:ii 12.7 3.46 12.8 3.48 11.9 3.31 Average conversion, 82 per cent
.. .. ..
73 86 87 82
The presence of 3 per cent of cobalt oxide considerably improves nickel as a catalyst for the oxidation of ammonia, more than doubling its efficiency.
COBALT-NICKELBISMUTH OXIDES Cobalt Oxide 94 Per cent, Nickel Oxide 3 Per cent, Bismuth Oxide 3 Per cent A mixture of the crystallized nitrate salts in the proportion required to give these proportions was made and the catalyst prepared by the procedure outlined in previous descriptions. The purpose of this experiment was to ascertain the effect of two good promoters in conjunction on cobalt. Temperature, 690' to 720' C. Amount of catalyst, 50 grams. Gas flow, 11 liters per minute. Ammonia-gas mixture, approximately 1:10. GAS TESTED Inlet Exit
Weight of Gas Gram
0.1 N R cc.
Per cent Nitrogen
0.4749 0.5167
17.1 17.5
5.04 4.74
Per cent Conversion
..
94
In the following tests the temperature was increased as indicated. Weight
GASTESTED Inlet Exit Exit Exit Inlet Exit
Check tests were repeated with same bulbs in A and E .
Weight of Gas Gram
Weight of Gas Gram
Temperature, 700" to
of Gas
0.1 N R
Gram
Cc.
0.4704 0.5154 0.5242 0.5273 0.4792 0.5361
15.9 15.6 15.4 14.5 16.2 15.1
Per cent Nitrogen
Per cent Cdnversion
..
4.73 90 4.24 87 4.11 80 3.70 4.71 3.90 83 Average conversion, 87 per cent
..
Temperature
c.
750 850 900
..
With this rate of gas flow high temperatures are not desirable. The gas flow was now increased to 22 liters per minute. Temperature held between 750" and 850" C.
89
The following tests were made after the catalyst had been used 6 hours: GAS TESTED Inlet Exit
Vol. 16, No. 1
Per cent Conversion
.. ..
84 85 84 97
These results were a surprise, as it is evident that nickel itself is a promoter for cobalt. From a commercial standpoint this is an important factor, for it means that commercial cobalt nitrate for which no special effort has been made to eliminate nickel
GAS T~CSTED Inlet Inlet Exit Exjt Exit Exit
Weight of Gas Gram
0.1 N R
0.4854 0.4936 0.5004 0.5257 0.5216 0.4977
16.9 17.1 17.5 16.7 17.0 15.8
Cc.
Per cent Per cent Fixed ConverNitrogen sion
.. ..
4.89 4.85 4.64 95 4.66 95 4.57 94 4.47 92 Average conversion, 94 per cent
Temperature
..c.
7bO 800 850 850
From these results it is evident that the presence of nickel up to 3 per cent does no harm to the bismuth-cobalt combination as a catalyzer for oxidation of ammonia.
COBALT-THORIUM-CERIUM OXIDES Cobalt Oxide 90 Per cent, Thorium Oxide 9.9 Per cent, Cerium Oxide 0.1 Per cent Cerium has proved to be an excellent promoter for cobalt. Low suggested that thorium be added, making the thorium and cerium in the proportion used in the Welsbach mantles-99 per cent thorium and 1 per cent cerium. The ratio decided upon by the writer is given above. The necessary amounts of crys-
January, 1924
INDUSTRIAL AND ENGINEERING CHEMISTRY
tallized nitrate salts were mixed and the oxides obtained by evaporation and ignition by the regular procedure. Thorium nitrate upon evaporation and ignition swells t o several times its original volume. In analysis of the salt to ascertain the oxide that could be obtained per unit weight, it was found necessary to use a large crucible for the 5-gram sample analyzed. In the preparation of the oxides, thorium caused the entire mass to swell and boil over. Of the total 100 grams, about 65 remained in the casserole, a 15-gram excess of what was desired for the experiment. The writer found that the mass that ran over into the sand of the sand bath was exceedingly porous but its texture was firm. This material was placed in a separate bottle for later investigation. It is believed that the porous material will make a very good product for converter use and this mode of preparation of catalysts may be a desirable one. The sand can easily be removed. Rate of gas flow, 11liters per minute. Temperature, 680' to 750" C. Ratio ammonia to air varied as indicated. GASTESTED Inlet Exit Inlet Exit Exit Inlet Inlet Exit Exit Exit Exit
;i;
Weight Per cent Per cent of Gas 0.1 N R Fixed ConverGram Cc. Nitrogen sion 4.68 0.4957 16.6 4.18 0.5054 15.1 0.4385 11.6 3.70 0.4753 11.1 3.27 0.5003 3.28 11.8 4.00 0.4709 13.5 0.4723 4.10 13.7 3.66 91 0.4972 13.0 3.69 91 0.5083 13.7 3.86 95 0.5106 14.1 3.68 91 0.5022 13.2 Average conversion, 91 per cent
Ratio 1 : 10
1: 12
1: 11
The cobalt-thorium-cerium combination is a very good catalyzer for oxidation of ammonia to nitrogen oxides.
The work of the present investigation was concluded by this experiment. The experiments as given are in the order in which they were taken in hand and in the majority of cases the tests are recorded in the order in which they were made. , CONCLUSION
A glance a t the comparative table shows that bismuth is the best of the substances tested as a promoter for cobalt as a catalyst for the oxidation of ammonia t o oxides of nitrogen. The oxide of this element, added in small quantity, increases the effectiveness of cobalt oxide over 20 per cent. Fourteen grams, or half an ounce, of the mixed oxides in the proportion of 97 parts of cobalt oxide and 3 parts of bismuth oxide by weight are sufficient to oxidize a mixture of ammonia and air Containing over 10 per cent of ammonia by volume flowing a t the rate of 22 liters per minute with a conversion of over 94 per cent. With a suitable preheater for the entering ammonia-air mixture, the rate of gas flow per minute could, no doubt, be increased. Basing the calculation on an actual result obtained (500 cc. a t 200' C. of gas in the exit containing an equivalent of 20.5 cc. 0.1 N nitric acid) and calculating back to the original volume entering the converter a t the rate of 22 liters per minute at 18" C., we obtain approximately 330 cc., which will give (20.5 x 0.0063) 0.1292 gram nitric acid, or approximtttely 0.39 gram nitric acid per liter, or 8.36 grams of the acid per minute per 14 grams of catalyst (approximately 0.5 ounce). I n terms of an ounce of the catalyst we should obtain double the above amount-i. e., 16.72 grams per minute, or 1440 x 16.72 = 22,076.8 grams of acid per day, or about 48 pounds per day. Metallic platinum according t o experiments by the U. s. Governments will produce about 100 pounds of nitric acid per ounce of platinum per day. The cost of the cobalt-bismuth oxide would be less than 50 cents per ounce, while platinum is about $116 a n ounce, imore than two hundred times as much, and its efficiency per weight is just about double that of the cobaltbismuth catalyst. I n actual efficiency in conversion the cobalt-bismuth catalyst gives higher results than does platinum. With a 6
Parsons, THISJOURNAL, 11, 541 (1919)
81
similar apparatus the writer obtained 93 per cent conversioh with platinum. Parsons states that an average conversion of 90.7 per cent was obtained by Government practice, using a gas containing 10.57 per cent of ammonia by volume. COMPARATIVE TABLE Rate of Flow Proportion Liters per No. CATALYST-OXIDES OF: of Mixture Minute Cobalt 1 ~ ~ . . 11 100% 2 Cobalt and beryllium 97:2.9 11 3 Cobalt and beryllium 97:2.9 22 4 Cobalt and beryllium 91:9 11 Cobalt and cerium 5 97:3 10 Cobalt and cerium 6 91:9 10 Cobalt and cerium 7 91:9 11 Cerium 8 8 100% Cerium 9 11 100% Cobalt and bismuth 11 (50 grams) 97:3 11 10 Cobalt (50 grams) and bismuth 97:3 22 Cobalt and bismuth 12 (20 grams) 97:3 22 13 Cobalt and bismuth 99.9:O.l (50 arams) 11 14 Cobalf and. bismuth (50 grams) 99.9:O.l 11 15 Cobalt and bismuth (50grams) 75:25 11 16 Cobalt and bismuth (50grams) 50: 50 17 18 I9
20
21
Cobalt and nickel Cobalt and nickel Cobalt bismuth, nick& Cobalt bismuth, nick61 Cobalt, thorium, cerium
Temperature
Per cent Copversion 680 to 700 76.6 84.0 700 90.0 700f 92.0 690 94.6 700 90.5 720 93.0 710 81.0 710 75.0 720 O
c.
710 to 720 730
95.0 94.5
710 to 730
97.0
710 to 730
81 .O
710 to 730
90.0
690 to 710
76.0
..
Material
11 22
69b-i6-720 700 to 800
91.0 89.0
94:3:3
11
750 to 900
87.0
94:3:3
22
750 to 900
94.0
90:9.9:0.1
11
97:3 3: 75
f1,arrl
750
17 .n -.
91.0
Notes-Catalyst 7 improves upon use. Catalyst 12 is all right provided temperature is sufficiently high for conversion. The amount cut down to 14 grams gave good conversion for gas flow of 23 liters until a drop in temperature occurred. Catalyst 14 improves upon use. Catalyst 15 is about the same as cobalt alone, apparently the limit for bismuth. Catalyst 16 shows what occurs with too much bismuth. In the majority of cases the best conversion temperatures range between 650° and 750° C.; this may go to 900' C., but above this a decomposition apparently results as conversions drop. Catalyst 21 is good, apparently due to cerium, since cobalt and thorium, by previous investigation, proved to be poor.
The slight increase of the size of the converter to accommodate double the weight of cobalt-bismuth material over platinum would be an item of minor importance, since the added cost of construction and the additional space necessary would be negligible. It is evident that with the vast supply of the necessary materials for making this efficient catalyst, and the comparative cheapness of the product, a scarcity of platinum will not effect the synthetic production of nitric acid. Losses in conversion are generally attributed to the following causes: 1-To a secondary decomposition of the oxides of nitrogen formed by too long a contact of the gases with the catalyzer. 2N0 Na 4-0 Too great an increase of gas flow, however, would lead t o the second cause of loss.
2-A part of the ammonia escapes contact with the catalyst. The loss thus entailed is double the amount of nitrogen that the ammonia contains, decomposition of the nitrous acid made taking place. s"4 6N0 = 5N2 6Hz0 We would expect this reaction with a thin layer of catalyzer, such as the platinum gauze, the chances being less with a granular column of material, such as the cobalt catalysts, with which this paper deals. 3-In the case of these experiments, where an efficient preheating was not attempted, loss occurs due to the cooling of the catalyst to below its efficient temperature. (See 2 above.) 4-Comrnercially, loss occurs due to incomplete absorption and oxidation. 5-In an improperly constructed converter, loss may also occur due to a preliminary decomposition of ammonia before it comes in contact with the catalyst of the system. There is an
+
+
INDUSTRIAL A N D ENGIATEERINGCHEMISTRY
82
abundance of evidence which shows that there is a serious decomposition of ammonia by almost all bodies except silica a t temperatures favorable to the catalytic oxidation of ammonia. 2"s 3 0 = Nz 3Hz0
+
+
Imison and his eo-authors6 give the following figures : Ammonia decomposed at 350' C.by: Wrought iron.. Nickel Aluminium ..................................... Silver.. ........................................ Silica less than.. ................................
................................. .........................................
Per rent 81.47 35.25 10.8 3.85 1.0
The writer found that ammonia was completely decomposed when passed through pumice heated to 750" C. Parsons gives the results obtained by G. B. Taylor in his work on this subject. Per cent NHa Destroved
..
Pieces of pure aluminium sheet.. 0.0 Vitrified silica.. . . . . . . . . . . . . . . . . . 0 . 8 Nickel wire 2 mm. diam. staples., 1.4 Nickel wire' 2 mm. diam. staples.. 11.3 Nickel wire' 2 mm. diam. staples.. 22.0 Porcelain, $ieces from dish. . . . . . . 0 0 34.0 2.3 Alundum cement, briquets
........{
Temperature
c.
550 880 500 580 890 700 710
590
The selection of silica tubing for the experimental work of this paper was for the purpose of eliminating as far as 6
Imison. A. Russel and Russel, J . SOC.Chem. Ind., 41, 371 (1922).
Vol. 16, No. I
possible any preliminary decomposition of ammonia, the gases coming in contact with silica alone when heated to conversion temperature. On the commercial scale silica-lined iron tubes may be used. Imison suggests a coat of paint made by mixing barium sulfate with a solution of sodium silicate. The action of iron is prevented by this protective covering. From Taylor's results it is evident that aluminium may be used without any deleterious effect on the preheated gases. The temperature withstood by this metal has the upper limit of 650" C., so that the metal is not suitable for the converter itself. The production of nitric acid from ammonia is a comparatively simple process and the apparatus required can be made up easily with comparatively little expense. Since synthetic ammonia has passed its experimental stage, it is a question of but a short time when 50 per cent nitric acid may be made a t an exceedingly low cost per pound. Cheap ammonia will also be obtained from the cyanamide process. The Kahn bill pending in Congress for the U. S. Army control of Muscle Shoals, Alabama, makes a demand for twelve million dollars, two million for repairs of the plant, which originally cost 70 million. Ten million dollars are sought for operative costs. The yearly output of 200,000 tons of cyanamide equivalent to 35,000 tons of ammonia is the beginning of a great enterprise
Smoke Screen and Bombing Tests Official photographs, publzshed by permission of the U. S. A r m y Air Service
1-A half-mile smoke screen from titanium tetrachloride laid from an airplane in eighteen seconds. This screen remained opaque for 4 or 5 minutes and then began t o be broken up by the wind as shown here. ' 2-A 1200-pound bomb of T N T dropped from about 3000 feet and striking an obsolete battleship, passing through the ship and emerging at the water line as indicated. This took place during the bombing experiments off the
Virginia capes in September 1923. 3-The result of the 1200pound bomb. Note that the decks have been ewept clear of all superstructures and that the vessel is rapidly filling. Shortly after this photograph was taken, the vessel turned turtle and sank. These experiments again demonstrated the community of interests which exists for the h'avy, the Air Service, and the Chemical Warfare Service in both offense and defense.
