June, 1918
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
457
EFFECT OF ACETYLENE ON OXIDATlON OF AMMONIA TO NITRIC ACID1
cables connected the aluminum electrodes to a lowvoltage transformer which furnished the current for B y GUY B . TAYLOR AND JULIAN H . CAPPS heating the gauze. Ammonia mixed with air was adReceived May 13, 1918 mitted a t the top and the reaction products issued a t I n experiments on t h e oxidation of ammonia to the bottom. A perforated aluminum plate was fixed nitric acid carried out in the laboratories of t h e Bureau j in. above the gauze t o serve as a bame for securing of Mines, some attention has been given t o the question uniform distribution of the gas flow through the gauze. of the effect of such impurities as normally occur in The mica window shown in the figure afforded an unammonia gas derived from commercial sources. It obstructed view of the entire gauze surface. has been found t h a t high-grade ammonia liquor deThe ammonia-air mixture was obtained by bubbling rived from carbonization of coal contains no deleterious air through two metal drums in series containing pure impurity whatever and t h a t conversion efficiencies of ammonia liquor of such strength as to secure a suitable g j per cent are easily obtained with platinum as concentration of ammonia in t h e mixture. The feed catalyzer. mixture then passed into a n empty jo-gal. drum to An important source of ammonia is calcium prevent pressure fluctuations and then through I O cyanamide. Since this material is manufactured from f t . of rubber hose to the top of the converter. The carbide, small amounts of which remain in the finished arrangement of the rest of the apparatus has been product, the ammonia gas derived from it almost previously described. always contains acetylene. The object of the experiAcetylene, with its accompanying impurities, was ments described in this paper has been t o determine the generated in a Kipp apparatus from high-grade calcium effect of acetylene in the ammonia gas upon catalytic carbide and water, washed through water, and careoxidation with platinum. fully measured. It was passed into the ammonia-air EXPERIMEKTAL mixture in the rubber hose line connecting the ammonia The oxidizer or converter consisted of two rectangu- saturator t o the converter, about 8 f t . from t h e latter. lar aluminum boxes, 6 b y 3 by 1 2 in., bolted together The acetylene-bearing gas came into contact with iron only through a T-connection and short nipple. The composition of t h e gas entering the oxidizers was calculated from the rates of flow of the acetylene and of the air through the ammonia vaporizer, together with analysis of the ammonia-air mixture for ammonia. The acetylene present in the gas could thus be determined more accurately than by analysis a t the small concentrations qmployed. The gauze used in these experiments was made of pure platinum wire 0.003 in. diameter, 80 wires to the linear inch. Platinum is never fully active when first placed in the converter but is “activated” b y the reaction itself so t h a t the conversion efficiencyZ rises with use, increasing from day t o day until the maximum efficiency is reached. Gauzes vary widely in the time required t o reach their full activity. The particular gauze used in these experiments reached its full activity unusually quickly. I n Table I are presented results showing the performance of this gauze with pure ammonia. The converter was operated several hours continuously each day over the j-day period. OF PUREPLATINUM GAUZEFROM BAKER& Co., 80 MESH, 0 0 0 3 IN. WIRE, USINGPURE AMMONIA NHz ~. cu. ft. mixture in air Yield Test of air No. Der hr. Amperes Per cent Per cent DATE 92.4 9.10 Feb. 6 . . . . . . . . . . . 341 93.2 9.58 Feb. 6 . . , . , , , , , , . 342 9 3.5 8 . 4 0 Feb. 7 . . . . . . . . . . . 343 94.6 8.78 Feb. 8 . . . . . . . . . . . 344 9 6.0 8 . 7 3 Feb. 8 . . . . . . . . . . . 345 9.80 94.6 Feb. 8 . . . . . . . . . . . 346 9 4 .4 9 . 8 0 Feb. 8 . . . . . . . . . . . 347 95.0 7.48 Feb. 9 . . 348 9 4 .0 7 . 4 9 Feb. 9 . . . . . . . . . . . 349 94.8 8.50 Feb. 11 . . . . . . . . . . . 350 9 4 . 3 8 . 5 5 Feb. 1 1 . . . . . . . . . . . 351 Average yield 94.6 per cent, excluding Nos. 341 and 342. Ammonia escaping oxidation, 0.3 per cent.
TABLE I-TESTS
.........
LUI
FIG.I
with a platinum gauze between (Fig. I ) . The gauze was crimped into two pieces of aluminum sheet at either end and held between “Janos” gaskets. Heavy 1
Published by permission of Director of IJ. S. Bureau of Mines.
The result of the addition of acetylene is shown i n . detail in Table 11. The poisoning effect a t concentraTaylor, Capps and Coolidge, THISJOURNAL, 10 ( 1 9 1 8 , 270. The vacuum bottle method was used in determining efficiencies, see Tcylor and Davis, THISJOURNAL, 9 (1917), 1106. 1
2
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
458
TABLE 11-EFFECTS OF ACETYLENE ON YIELD, 170 Cu. FT.AIR PER HOUR Intake Gas NHa CzHz Yield Test Amp- Per Per Per Map of DATE Time No. eres cent cent cent Gauze March 2 368 165 7.50 0.0 96.0 March 2 369 165 7.50 0.0 96.5 .. March 4 10':'20 150 8.0 0.0 Clear March 4 10 : 30 ... 150 8.0 1.12 March 4 10 : 32 150 8.0 1.33 Sei'Map March 4 10 : 38 150 8.0 1.54 See Map March 4 10 : 53 150 8.0 0.53 March 4 1 1 : 20 150 7.9 0.21 See Map March 4 1 1 : 45 150 7.8 0.13 March 4 12: 10 150 7.7 0.13 Clear March 4 12: 22 370 155 7.7 0.13 7i:S Clear March 4 12 : 27 371 155 7.7 0.13 75.0 Clear 155 7.7 0.04 Clear March 4 1 : 00 Clear March 4 2 : 00 ... 155 7.6 0.04 March 4 2 : 20 . . . 155 7.5 0.0 Clear 155 7.5 0.21 See Map March 4 2 : 23 &larch 4 2: 45 155 7.5 0.13 Clear March 4 2 : 50 372 150 7.5 0.0 90:4 Clear March 4 2 : 55 373 150 7.5 0.0 92.5 Clear
...
..
... ... ... ... ... ... ...
... ... ... ... ... ...
...
... ... ...
...
...
... ...
A n g . I1 B: Fig. I1
C, Fig. I1
D, Fig. I1
Fig"
DATE March 5 March 5 March 5 March 5 March 5 March 6 March 6 March 6 March 6 March 6 March 7 March 7 March 7 7
March March March
March March March March March
7 7 8 8 8 8 8 8 8 8 9 9 9 9
Intake Gas NHa CnHn Test Am- Per Per Time No. peres cent cent 10 : 30 0 1 : 00 jik iio 9.35 o 1 : 05 375 140 9.35 0
...
3 : 35 3 : 38 9 : 10 10 : 40 10 : 43 2 : 53 2 : 56 9 : 10 1 1 : 05 11 : 08 1 : 40 2 : 30 3 : 19 10:40 1 1 : 25 1 1 : 45 12 : 15 1 : 10 3 : 08 3 : 12 3 : 19 9 : 05 9 : 57 10 : 00 1 : 55
March March March March March
11 11 11 11
1 : 9: 11 : 2: 2:
March March March March March March March
12 12 12 12 12 12 12
1 1 : 00 1 1 : 43 1 1 : 46 2 : 45 2 : 55 4 : 15 4 : 20
March March March March March March March March March March March March March March March March March March
13 13 13 13 13 13
9 : 10 10 : 22
9
376 150 8.92 0 377 150 8.92 0
......
0
150 s : i o 0 150 8.80 0 150 9.06 0 150 9.07 0 0 382 165 ?:io o 383 165 7.43 0 . . . . . . 7.0 0.12 385 160 6.70 0 09 386 165 6.40 0:16 378 379 380 381
......
Ammonia Escaping OxiYield dation Per Per cent cent WMARKS Start 9i:k 0.5'
92.5 0.7 92.2 0.6 92.5 0.6
...
Shutdown 3 : 45 Start
0.k'
94.2 95.0 93.5 94.0
0.6 0.6 0.6
9i:9 95.0
..
.. ..
Start
387 160
389 150 8.05 0.04 85.6 390 150 7.52 0.05 87.3
...... 391 150
......
58 395 125 30 . . . . . . 00 396 160 50 397 140 53 398 140
1.5 1.1
0
;:54
o
0
392 150 i:is o 393 150 8.21 0 394 125 9.42 0 9.38 0
0 i:iS 0 9.32 0 9.32 0
9i:i 0:7
si16
0:7 92.0 0.7 89.7 0.8
Start Shutdown4 : 15
...-. ma#
89.4 0.8 9i:j 0:6 93.6 0.5 93.4 0.5
Start Shutdown4 : 15 D M -.-I
jg4
0
iio i0:js o
10.75 9.50 8.70 10.35 404 130 10.50
0 0 0 0
96:0 89.6 91.7 93.8 92.4 92.6
..........
0
...
400 401 402 403
110 120 120 130
iii
10 : 30 40s 11 : 00 406 125 11 : 52 407 133 2 : 25 408 150 13 2 : 45 409 140
0.03 ... i0:i.s 0.03 93.0 9.90 0.03 90.0 9.40 0.03 89.4 8.37 0.03 88.4 8.37 0.03 86.6 8.40 0,025 87.3
3 : 37 410 146 9 : 10 9 : 15 10 : OS 10 : 15 11 : 23 1 : 08 1 : 16 1 : 33 2 : 43 2 : 45 Speed was 205 cu. ft. air.
13 14 14 14 14 14 14 14 14 14 14
0
0:7 0.7 0.5 0.5 0.6 0.6
Start
Shut down 4 : 22 P.M.
Start
6:6 0.6 0.9 1.2 1.2
.. ... .. ...
IO,
No. 6
tions above 0 . 2 per cent in the mixture is immediately optically apparent on the gauze. Black inactive areas appeared which are shown b y maps of the gauze. If the electric current is shut off, when running on pure ammonia, the gauze remains dull red from the heat of reaction. Under t h e same conditions with 0.1 per cent acetylene black areas immediately appeared tending t o spread over the entire gauze. These areas are difficult t o clear u p and it is our opinion t h a t oxidizing ammonia from sources which may even occasionally contain acetylene, would give unlimited trouble from development of black spots, which could not be cleared u p readily without electric heating. No black area appeared after March 4. The tests showed t h a t t h e yield was a function of the concentration of acetylene and t h a t when the acetylene was shut off the yield immediately rose t o within 3 or 4 per cent of its original value, b u t required many hours running on pure ammonia t o restore i t completely. A gauze t h a t has been rendered active by oxidizing pure ammonia has a distinctive gray appearance t o the naked eye. Under t h e microscope the wires appear t o be covered with platinum sponge. Examination of the gauze a t the conclusion of the tests on March 4 showed a n entirely different appearance. It had a speckled crystalline appearance t o t h e naked eye and the wires appeared rough b u t shiny under t h e microscope. Re-activation with pure ammonia returned the gauze t o its original gray. At t h e conclusion of the experiments on March 14, t h e gauze was less different from the gray than t h e previous examination had showed.
Shut down 3 P . M . Start
69:O 2.'5 46.5 5.4(a) Shut down 3 : 25
. . . .... . . . . . . +:is 0o 91.4 ...... 0.04 388 150 8:65 0.05 9i:i 0:s
Vol.
Start
68.3 2:2 68.7 2.4 77.5 63.0 i:9
...
88.4 i:o 87 .O 1 .o 88.7 0.8
An increase of velocity of this order (a) causes a decrease when running on pure ammonia of less than 2 per cent.
REMOVAL OP ACETYLENE F R O M A M M O N I A
These results show so conclusively t h e poisoning action of acetylene or its accompanying impurities t h a t some method for its removal seems imperative if cyanamide ammonia is t o be successfully oxidized with high efficiency. Several methods for accomplishing this result suggest themselves. Removal by scrubbing the gas with ammoniacal cuprous solutions might be managed. Cuprous acetylide was found t o be readily precipitated from ammonia gas by bubbling i t through ammoniacal copper nitrate solution containing metallic copper. Such a process involves complicated procedure for recovery of copper. Scrubbing with organic solvents appears t o be impracticable on account of their volatility. A thoroughly practical method is t o convert the ammonia into liquor by dissolving i t in water. Water dissolves its own volume of acetylene. I t s solubility in strong ammonia liquor as shown b y our experiments is of the same order. On this basis one liter of liquor containing 300 g. NHs would hold in solution 440 liters of ammonia gas and only I O cc. acetylene if saturated with ammonia gas containing I per cent acetylene. Such a liquor when vaporized with air t o form a I O per cent ammonia mixture should yield a gas for the oxidizer containing about 0.0002 per cent acetylene
June, 1918
T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
or I part by volume in 500,ooo. Acetylene a t this concentration would probably not poison platinum. The calculation made above is based on Henry's law. Since t h e acetylene is only I per cent of the ammonia, its partial pressure is 0.01atmosphere and i t follows therefore t h a t I liter of liquor will dissolve a t equilibrium one liter of acetylene a t 0.01 atmosphere, or I O cc. a t normal pressure. I n dissolving ammonia-acetylene in water, the former is absorbed quite rapidly, thereby increasing t h e partial pressure of the acetylene so t h a t the concentration of acetylene in solution is a t first quite high. The gas must be passed in some time after all absorption of ammonia has ceased in order t h a t equilibrium may be established and the acetylene concentration in the liquor reach its minimum value. Laboratory experiments show conclusively t h a t the deductions arrived a t b y application of Henry's law are correct. Ammonia gas containing I t o 2 per cent acetylene was passed into water until the ammonia reached a concentration of 28 per cent. The acetylene in solution was then determined by precipitation as AgzCz with standard silver nitrate, and found t o be 130 cc. C2Hz per liter. T h e ammonia-acetylene mixture was then continued through the solution until it passed freely and no more ammonia was being absorbed. The liquor now contained I O cc. C2H? per liter. The application of this scheme industrially should offer no difficulties. Ammonia absorption apparatus is simple. Two or more absorbers would have t o be employed since equilibrium conditions must be established by blowing t h e gas freely through the first absorber after t h e liquor is saturated. The temperature of the absorber could be adjusted so t h a t t h e strength of the liquor would not be too high after cooling, t o avoid loss of "3. This temperature in winter would probably be in the neighborhood of 35' C. and warmer in summer. The heat of solution makes such a n adjustment easy. Should i t be desirable t o make a liquor absolutely
I
free from acetylene, pure ammonia gas could be blown through the absorber a t t h e end of the operation. About 5 per cent of this very pure liquor could be reserved a s a source of pure gas t o treat the next batch. An ammonia liquor free from all non-reacting foreign gases may be prepared in this way. SUMMARY
I-As little as 0 . 0 2 per cent acetylene in the ammoniaair mixture has a distinctly deleterious effect. The yield drops from about 95 per cent t o 89 per cent or less. 11-The effect of 0.1 per cent acetylene, or its accompanying impurities, is disastrous. The yield may drop as low as 6 5 per cent. 111-A small quantity of acetylene will render t h e platinum so inactive t h a t t h e yield on pure ammonia will be reduced 2 t o 4 per cent for several hours. This means t h a t the ammonia used for manufacture of nitric acid should be free from acetylene a t all times. IV-Operation of oxidizers working on the principle of a self-sustaining reaction without electric heating or preheating, and utilizing sources of ammonia t h a t contain acetylene, is probably impracticable. V-Ammonia gas may be freed from acetylene and other non-reacting gases by dissolving i t in water t o make a strong ammonia liquor. Such procedure involves no difficulty industrially, nor any considerable expense in operating a commercial oxidizing plant. ACKNOWLEDGMENT
The experiments described herein are a part of a n extensive investigation on commercial ammonia oxidation and t h e production of nitric acid thereby, conducted by the Bureau of Mines and the Semet-Solvay Company in co6peration with the General Chemical Company and the Ordnance Department, under the . direction of the Chief Chemist, Dr. Charles L. Parsons. B U R E A U O F MINES WASHINQTON, D.C.
LABORATORY AND PLANT A ROCKING ELECTRIC BRASS FURNACE' By H. W. GILLETT AND A. E. RHOADS Received M a y 15, 1918
It seems inevitable t h a t t h e next few years will see electric furnaces largely replacing crucible furnaces in t h e brass industry, a development comparable t o t h a t which the last few years have seen in t h e steel industry. With Klingenberg clay not available and Ceylon graphite requiring shipping needed for other purposes, crucibles, despite t h e good work done on the problem by crucible manufacturers, the Bureau of Standards, and others, are still, speaking generally, of much poorer quality and many times more costly t h a n they were under pre-war conditions. T h e time is ripe for t h e practical elimination of t h e crucible from the brass industry. 1
Published by permission of the Director of the Bureau of Mines.
459
I
With t h e huge tonnage of brass required for war 200 purposes, the use of t h e small units-averaging lbs. per charge-in which crucible melting is done b y the brass rolling mills, seems, and is, a n anachronism. Besides the avoidance of crucibles and the ability t o melt larger charges, electric melting (in a suitable type of furnace) decreases the loss of metal b y oxidation and by volatilization, prevents the taking up of sulfur from the fuel, gives better and more healthful working conditions, and has many minor advantages such as freedom from handling and storing fuel and ash. Electric furnaces give crucible quality of metal without using crucibles. However, not every t y p e of electric furnace can be used for brass melting. If brass did not differ materially from steel in its behavior during melting, electric furnaces would long ago have superseded crucible
