Commercial Oxidation of Ammonia to Nitric Acid. - ACS Publications

Apr 30, 2018 - important problem before the world, both for the production of food in time of peace and of munitions in time ofwar, than the fixation ...
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J u n e ) 1919

T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y

541

ORIGINAL PAPERS COMMERCIAL OXIDATION OF AMMONIA TO NITRIC AClD By CHARLESL. PARSONS Received May 8 , 1919

I t is realized by all chemists and all economists t h a t there is no more important problem before t h e world, both for t h e production of food in time of peace and of munitions in time of war, t h a n t h e fixation of atmospheric nitrogen. All civilized countries are deeply interested and many are actively engaged in scientific and industrial research for its solution. There are two distinct methods of procedure: One is t o produce t h e combined nitrogen primarily in t h e form of nitrates, t h e other is t o obtain i t directly or indirectly in t h e form of ammonia. The methods which produce nitric acid without first producing ammonia, while applicable t o t h e production of munitions, do not lend themselves readily t o the production of fertilizers in a form acceptable t o t h e agriculturist and are, therefore, subject t o great economic disadvantage in time of peace. Those which first produce ammonia, or from which ammonia and ammonia compounds can readily be obtained, are particularly applicable t o use as fertilizers and have distinct commercial advantages. As immense sums for construction and maintenance of plants are involved, it therefore becomes almost a necessity t o base the production of fixed nitrogen on some process which yields ammonia. Accordingly if nitrogen fixation plants used for fertilizers in time of peace are t o be depended upon for munitions in time of war, some method for converting ammonia into nitric acid, essential t o all explosives, is imperative. This paper, therefore, deals with t h e methods and apparatus which have been used or are being used for t h e oxidation of ammonia t o nitric oxide which, absorbed in water, yields nitric acid. The importance of t h e oxidation of ammonia t o nitric acid was early realized in t h e United States. North America has no resources of natural nitrates, b u t the United States does produce and has produced large quantities of ammonia as a by-product in t h e coking of coal. Although other sources of nitrates were available for war, it was, nevertheless, imperative t o be able t o utilize by-product ammonia, should America be cut off from Chile. Statements had been made broadcast in this country t h a t coal-tar ammonia could not be successfully oxidized on account of impurities Accordingly two months previous t o the passage of the National Defense Act of June 3, 1916,the Secret a r y of t h e Interior had, on April 7, 1916,offered t o the Secretary of War t h e aid of t h e Interior Department in any capacity t h a t would be usefulin t h e study of methods and materials necessary for large-scale manufacture of nitrogen products. During April and May 1916, t h e writer had several informal conferences with officials of the War Department and on June 6, 1916, by request of Brig. Gen. William Crozier, made a 1 Paper read before the Washington Section of the American Chemical Society May 8 1919.

tentative report on the fixation of atmospheric nitrogen b y methods then known. As a result of recommendations then made, an agreement was signed on August IO, 1916, whereby t h e Semet-Solvay Company, in cooperation with t h e Bureau of Mines and with t h e approval of General Crozier, undertook t o erect a t Syracuse a plant t o demonstrate whether by-product ammonia could be successfully oxidized on a commercial scale t o nitric acid. It was through this agreement t h a t t h e writer became interested in ammonia oxidation. HISTORICAL

RBSUMB

I t is not t h e purpose of this paper t o go extensively into the literature of ammonia oxidation. Those interested in detail will find excellent bibliographies on the subject.’ The discovery of t h e general principle of oxidation of ammonia belongs t o Kuhlman, a. French chemist,’who as far back as 1 8 3 9 ~found t h a t ammonia could be oxidized t o nitric acid and t h a t platinum, as well as other metallic and non-metallic substances, would catalyze this reaction. At t h a t time, however, there was no possibility of commercially applying t h e process and i t remained for Wilhelm Ostwald t o study and develop t h e reaciion for commercial purposes.3 While Ostwald obtained patents in foreign countries, such as France, England, Switzerland, and America, he was unable t o hold them in Germany on account of Kuhlman’s former work and the process was, therefore, developed as a secret one in his own country. As early as 1909 a small plant was installed a t Gerthe in Westphalia for t h e conversion of by-product ammonia into nitric acid, using platinum as a catalyzer. This plant continued operations a t least until 1913 for in 1912 and 1913 i t paid dividends t o its stockholders. A second plant using t h e Ostwald process was erected a t Vilvorde, Belgium, b y a n English company. The first published sketch of an ammonia oxidizing plant with estimates of cost4 probably refers t o this plant and its operations. The Vilvorde plant was erected in t h e chemical products factory of M. Duch6, a Frenchman who was president of the French Chamber of Commerce of London. This plant was captured by t h e Germans early in t h e war b u t neither i t nor t h e plant a t Gerthe, nor indeed t h e Ostwald process as developed by Ostwald, appear t o have been used t o any extent during the war in Germany itself. The process used a t Vilvorde was installed during t h e war a t AngoulBme, France, and Dagenham, England. The writer visited both of these plants in October and November 1916. The general features of this process are now known and were first publicly described by W. S. Landis in a lecture given before t h e Electrochemical Society in New 1 Helen R . Hosmer, “Literature of Nitrogen Industries, 1912-1916,” THISJOURNAL, 9 (1917), 424; John C. Boyce, “Bibliography of the Production of Synthetic Nitric Acid and Synthetic Ammonia,” Met. b Chem. Eng., 17 (1917), 228. 2 A n n . , 29 (1839), 281. 8 Berg. u. Huttenm. Rundschau, 3 (1906), 71; also, Schmidt u. BScker, Ber., 1906, p. 1366 4 Iron and Coal Trades Review, May 23, 1913.

542

T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y

York on April 3, 1919.' The plant is made up of a large number of small units, in principle much t h e same as described in Ostwald's original patent and illustrated in Fig. I.

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process consisted essentially of a cross section of platinum gauze placed in an iron pipe, t h e ammoniaair mixture being preheated b y mixing hot air with ammonia just before it reached t h e catalyst, thus largely avoiding t h e decomposition of the mixed gases which takes place if they are passed through iron pipes a t an elevated temperature. Very high efficiencies, much over I O O per cent, were claimed for this process, b u t the results obtained were found t o be due t o faulty methods of analysis. With modifications t h e process is capable of commercial application b u t cannot compete with more modern apparatus. It was apparently t h e first plant which used platinum in t h e form of platinum gauze. A discussion of t h e operation of this process and its capacity will be found in a controversy printed in Chem.-Ztg., 1916,p. 14. M O D E R N METHODS

FIG.1-OSTWALD METHOD. DOUBLE UNIT

The mixed gases pass up the outer tube, being preheated by t h e hot inner nickel tube, so t h a t they come i n contact with t h e platinum catalyzer a t a temperature not far from 600' C. The mixed gases come in cont a c t with the only known materials, namely, nickel a n d silica lining, which will withstand t h e temperature necessary and also themselves have little decomposing effect on t h e ammonia previous t o its coming in contact with t h e platinum catalyst. The inner tube might be constructed of aluminum t o even better advantage, if the aluminum would only withstand the temperatures involved, as nickel does have a tendency t o decompose ammonia even a t 500'. The plant at Angoulbme produced many thousands of tons of nitric acid during the last years of the war, b u t is reported t o have been severely handicapped in its efficiency by t h e phosphine present in t h e ammonia used. During t h e later years of t h e war t h e reason for t h e low results was found and by blowing out the phosphine from t h e autoclaves t h e efficiency of t h e plant was very greatly increased. Dr. Karl Kaiser, a professor in t h e University of Heidelberg, had patented previous t o t h e war a modified method of procedure for oxidizing ammonia and had installed a small plant a t Spandau, near Berlin. This plant, as early as 1912,was operating on a n experimental basis and was shown during t h a t year and 1913 t o representatives,of French and American firms with an idea of its adoption in these countries. The 1

Chsm. b' Met. Eng., 20 (1919), 471.

I t is interesting t o note t h a t while Germany knew she could successfully oxidize ammonia before she began t h e European war in August 1914,nevertheless t h e methods known a t t h a t time for t h e oxidation of ammonia do not appear t o have been extensively used during t h e war itself. The war had scarcely begun when t h e Frank-Car0 interests, representing t h e cyanamide industry, began extensive investigation on ammonia oxidation and also developed t h e commercia1 conversion of cyanamide nitrogen into ammonia gas in order t h a t it might be used for t h e production of nitric acid. They gathered together near Berlin some of t h e best chemical engineers of Germany and of t h e Scandinavian countries. Fortunately, W. S. Landis, a representative of the American Cyanamid Company, was also present. He obtained much important information and secured autoclaves and other machinery which, in spite of great difficulty, he succeeded in bringing t o this country. During the early part of 1915 he installed these autoclaves in an American munitions plant. The Berlin Anhaltische Maschinenbau A. G., which obtained t h e rights t o t h e Frank-Caro oxidation process, had already during 191; installed some 3 0 projects of a yearly capacity of more t h a n 12,000,000 kg. of ammonia and had in process of erection projects capable of oxidizing I 7,000,000 additional ki1ograms.l The apparatus which they used in t h e early part of 1915and which at t h a t time was confined chiefly t o t h e production of nitric oxide for sulfuric acid plants is described in detail, together with t h e method of operation, by Schuphaus.2 It is hard t o conceive how t h e German government could have allowed t h e publication of this article, for i t gives all t h e essential details of the Frank-Car0 process as first developed on a commercial scale. It is true t h a t a t the time of its publication (early 1916) t h e B. A. M. A. G. had already abandoned electric heating and were using a multiple gauze, as may be easily deduced from t h e discussion above referred t 0 . 3 But i t is hard t o conceive how t h e German government could have allowed t h e publication in such great detail of a method which, 1

2 8

Chem.-Ztg., 1916, p. 14. Metall u. Erz, [ 2 ] 13 (1916),22. Chem.-Ztg , 1916, p . 14.

June, 19x9

T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y

FIO 2

except for the abandonment of elect use of multiple gauze, and the passa gases downward instead of upward, in silica-lined apparatus, is essential that used in the huge German pla method at the time the armistice Illustrations of the apparatus described by Schuphaus are reproduced in Figs 2 . 3 , and 4. The apparatus used an electrically-heated platinum gauze "of a silky fineness." I n the spring of 1916 the American Cyanamid ComDanv erected a t Niarara Falls, Ont., an electricallyheated platinum gauze apparatus for experimental purposes. As a result of these experiments, they erected in the summer of 1916 a plant at Warners, N. J., in connection with a large sulfuric acid plant being built there. This plant supplied a 60,000-ton sulfuric acid plant with nitric oxide' and was the erst oxidizing plant established in America. The nitrate plant erected by the Air Nitrates Corporation, an agent of the American Cyanamid Company, at Sheffieid, Ala., installed this process with the intent

543

given excellent illustrations of the oxidizers used by the American Cyanamid Company in the photographs reproduced in his article. Through the courtesy of VI. S. Landis, which is gratefully acknowledged, the writer was accorded the privilege of a visit t o the Warners plant in August 1916, with the distinct understanding that although plans and details of the process would not he revealed to him, nevertheless he was a t liberty t o use anything that he saw in the development oi the experimental plant t o be built by the Bureau of Mines in cooperation with the Semet-Solvay Company a t Syracuse. However, having already studied the description of the Frank-Caro process as published by Schuphaus seven months before, a detailed explanation of the construction and operation of the plant was scarcely necessary. The company also kindly allowed H. W. Gillett and G. B. Taylor, of the Bureau of Mines, to visit this plant with another party of chemists, including the writer, who inspected it a t the time of the meeting of the AMERICAKCHEEICALSOCIETY in New Yorli in September 1916.

' .

Fro. 3

of producing approximately 90,ooo tons of nitric acid per year,2 employing for t h a t purpose, according t o Fairlee,J 696 catalyzer units arranged in 6 catalyzer buildings each 50 X z z o ft. Each building contained 4 rows of catalyzers, 2 9 t o a row, with 4.6 troy ounces of platinum for each catalyzer. Fairlee bas also I

E. 3. Pranke, C k n . bl iWd. En#., 19 (1918). 396.

* Ibid.

*IUd..20(1919),6.

PIC. 4

D E V E L O P M E N T OF 'THE B U R E A U O F MINES COXVERTER

The work of the Bureau of Mines and the SemetSolvay Company really began in August 1916, the writer together with L. C. Jones being placed in charge thereof and having associated with them G. B. Taylor and J. H. Capps, who undertook laboratory studies of oxidation methods, and J. D. Davis and later G. A. Perley, who were assigned t o the plant development and operation a t Syracuse where they were assisted by advice from the chemists of the Semet-Solvay Company, and also by the active help of Bryan Handy of the same company. Another chemist, of the Bureau of Mines, and a representative of the Bureau of Soils of the Department of Agriculture also went t o Syracuse but remained there only a short time, being assigned t o other work. Valuable assis; tance and suggestions were received throughout the work from Dr. L. C. Jones, chief chemist of the SemetSolvay Company. G. E. Perley was afterwards commissioned by the Ordnance Department and assigned t o the work of the Bureau of Mines until the Nitrate

THE JOURSAL

INUL'STRIAL A N D ESGIiVEERING CEIEMISTRY

Vol.

11.

So. 6

girc high eficiency and which are extremely cheap in thcmselves, nevertheless the large amount of material that has t o be used, the consequent size of the apparatus t h a t has t o be constructed, the labor cost of installing the catalyzer and removing i t when i t deteriorates, the difficulties of granulation and of avoiding local ovcrheating will even with the cheapest catalyst render it uneconomical when platinum can he procured. The platinum used for catalysis is chiefly a capital charge, as most of it can be recovered and reworked into new gauze whenever such recovery becomes necessary. Its effective life, the smallness, cheapness, and simplicity of the apparatus, its high esciency, and its ease of replacement will probably maintain platinum as by far the best catalytic agent for ammonia oxidation. Much detailed information was obtained from the

FIG. s--GIPER,MGNT*L

AIMON,,,

OXLDLllN

HRAIEI)

Division was established some months later. The writer wishes t o ackiiowledge the valuable assistance of all of these chemists and, without going into the details of their individual accomplishment, wishes t o state that it was due t o their efficient efforts t h a t the worli was successfully accomplished. Before leaving for Europe to view the European operations, early i n October, the writer, assisted by others, prepared gene,ral plans for the erection of a small plant a t Split Rock near Syracuse. While this plant was being erected, experiments were directed chiefly to an attempt to develop a catalyzer, metallic or non-metallic, other than platinum. After three or four months' work with a large number of nom-metallic catalyzers and some metallic gauzes. details of which will be published later, i t was concluded t o confine further work to platinum. Other materials, while hastening the reaction, worked with a lower conversion of ammonia t o nitric oxide. All non-metallic catalysts, although some showed high efficiency, involved such high cost for material and construction of apparatus t h a t their use was found t o he impracticable. The writer is still of the opinion that although non-metallic catalyzers are known which wili

Fro, 6 -Axrrusia

Oxioizr~c.APPARATUS OP L h ~ o l Typs s

.~~ .

June,

3939

1 ” E J O U R N A L OF I N D U S l R I A L A N D E N G I N E E K I K G C H E M I S T K Y

...

545

laboratory. A small, electrically-heated converter, having a platinum gauze with a n exposed 3 X 6 in. gauze surface, was used t o determine in the laboratory many of the factors having t o do with ammonia oxidation. This apparatus is illustrated in Fig. 5. rimental apparatus similarly constructed and patterned from memory on the apparatus used in the Warners, N . J., plant was built at Syracuse in connection with the necessary cooling and absorption towers. It was first electrically-heated, using various sizes of platinum gauze, the gauze itself being 13 X 2 6 in., of nrhich 1 2 X 24 in. were effective, the balance being taken up betpreen the sheets of the asbestor insulation. The gauze finally adopted was of 80mesh, 0.0026 in. wire, the electricity for heating being carried t o the apparatus by silver tubes 13 in. lone a t each end of the gauze. The apparatus worked well and it was earlv determined that, with the high “A” grade by-pro

in order t o save electric power and expensive electrical apparatus. This was accomplished by using three gauzes superimposed on each other, each being first activated separateiy. I n this form the cost of electrical heating was done away with and details of this apparatus were sent, with permission of the Government, by the Semet-Solvay Company t o their English correspondent,s, Brunner hlond and Company, and formed the basis of an experimental plant erected by that company in England, using, however, a much smaller ’cross section of platinum gauze. The first commercial-sized apparatus installed a t Syracuse is shown YiO. 7 in Fig. 6. Although this apparatus functioned with Semet-Soivay Company, there was no difficulty what- multiple gauzes with a fair degree of success, the temever in oxidizing ammonia with this apparatus a t a perature could not be adequately maintained a t all high degree of efficiency. I t seemed t e s t early in the times without preheating, and it was later abandoned work t o do away with the electrical heating altogether on the development of the cylindrical converter.

.

,."

546

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T B E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y

1'01.

11,

NO. 6

P I G .9

The work on the flat m uze converter showed that the heat was t o by the gas stream. An att made to design a converter w of the heat of reaction. This plished in the cylindrical co section in Fig. 7 , while a phot t h e first rough converter is shown in Fig. 8. built up from pipe sections on hand in the Semet-Solvay Company. In this co platinum gauze is so arranged in cylind four superimposed layers of gauze t h a t the inside surface is always reflecting against another red-hot surface, while on the outside the fire brick lining of the converter soon reaches a red heat and reflects this heat back against the outer walls of the cylinder. By this method a much larger amount of heat is retained in the converter and with pure ammonia and proper catalyst the converter is entirely self-sustaining and needs no outside heat of any kind except t h a t generated by the reaction itself. Preheating of the gas is not necessary, but a heat regenerator is readily and easily installed and was recommended t o the Nitrate Division for the first installation in Chemical Plant No. I a t Muscle Shoals t o meet any possible exigencies, such as unduly cold weather, which mighf arise. The installation of this apparatus in Plant No. I a t Muscle Shoals is shown, by courtesy of the Nitrate Division of the Ordnance Department, in Fig. 9. This installation is essentially as recommended by t h e Bureau of Mines, except that the Bureau recommended the installation of a preheater and also the

exclusive use of aluminum pipes for all gases before they reached the converter. After the gases have passed through the converter, iron pipes are perfectly satisfactory so long as the gas temperature is above 175' t o zoo'. Much below this temperature corrosion takes place. This converter has the advantage of very low cost of construction, very high unit capacity, and very low cost of operation. It works with as high efficiency as any apparatus made and is easily constructed out of the simplest materials. The apparatus is built out of cast iron or boiler iron lined with fire brick. The pipes conducting the ammonia-air mixture t o the apparatus should be made of aluminum, the entrance chamber, designed by G. -4. Perky, shown on the illustration, having some minor advantages. A simple aluminum L or T works equally well if there is a gas holder in the line t o take up pulsations. The platinum gauze is attached t o a nickel or quartz entrance cylinder and the end of the q-ply platinum cylinder is closed with a nickel or quartz plate. Quartz is preferable and can now be readily obtained. Quartz and silicates in gciicral have less tendency t o decompose an ammonia-air mixture than any metals. Nickel, quartz, an.d aluminum are the only three substances which have been found t o be suitable for this purpose, other substances tending t o cause the ammonia t o burn to nitrogen and water Aluminum is better than nickel in this respect except for its much lower melting point. Porcelain would work as well as quartz except for its contraction and expansion under heat a n d consequent tendency t o fracture. A platinum wire is much t o be preferred to a nickel

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

547

LOG O F

CONVERTER N O . 4. APRIL 25-MAY 18, 1918 Gauze 0.0026 in. wire, 80 mesh, activated in electrically-heated apparatus NHs Per cent

GASFLOW Cu. f t . YIELD per Min. Per cent

GASFLOW RUN

10.18 10.08 ll.,37 8.22 8.79 10.15 9.46 9.42 9.42 8.90 8.90

180 180 180 180 180 200 200 200 200 200 200

92.9 93.7 93.5 89.0 89.4 87.6 91.2 94.4 93.9 85.2 83.4

Davis Davis Cawley Davis Davis Davis Perley Perley Perley Davis Davis

9.16 9.07 9.07 8.93 9.28 9.28 9.61 9.61 9.27 9.08 9.86 9.86 10.15 10.10 9.93 10.13 10.13

205 205 205 197 197 197 200 200 203 203 203 203 200 200 ? ? ?

96.3 95.1 96.8 87.2 86.4 84.0 86.1 86.6 88.6 90.6 92.5 90.2 84.1 84.2 97.0 97.8 98.0

Perley Perley Perley Perley Perley Perley Davis Davis Cawley Cawley Cawley Cawley Davis Davis Perley Perley Perley

9.90 10.00 9.87 10.02 10.15 9.53 9.73 9.81 9.90 9.90

200 200 200 200 200 205 205 205 205 205

90.8 91 .O 90.6 94.7 92.6 93.0 91.0 90.9 87.2 91.5

Perley Perley Perley Cawley Cawley Perley Perley Perley Cawley Cawley

10.93 11.08 9.84 10.34 10.21 10.22 10.30 10.56 11.18 10.68 11.11 11.11 10.93 10.98 10.41 10.38 10.38

202 202 198 198 198 198 198 197 197 197 197 197 197 197 197 197 197

90.6 91.3 95.1 87.0 86.0 96.0 89.5 89.8 86.8 88.3 89.1 91.2 83.0 88.7 84.6 85.7 87.6

Davis Davis Perley Perley Perley Cawley Cawley Perley Davis Perley Davis Davis Cawley Cawley Davis Davis Davis

9.11 9.18 9.18 9.48 9.49 10.27 10.30 10.21 10.38

185 185 185 185 185 196 196 196 196

84.6 85.5 84.3 87.6 89.0 85.0 86.6 88.5 87.7

Davis Davis Davis Perley Perley Cawley Cawley Davis Davis

10.53 10.53

190 190

93.2 90.4

Cawley Cawley

1

11.27 11.19 11.02 10.99 10.99 11.60 11.60 11 35 11 38 11 38 11 55 11.48

180 180 180 180 180 178 178 178 178 178 178 178

89.8 89.2 88.8 89.8 89.7 90.8 91.0 92.2 91.2 91.2 90.9 91.2

Cawley Cawley Davis Davis Davis Davis Davis Davis Davis Davis Cawley Cawley

11.38 11.40 10.99 10.99 11.43 11.45

190 190 190 190 187 187

89.2 90.2 90.4 90.6 94.8 93.2

Cawley Cawley Davis J Davis Cawley Cawley

11.22

11.36 11.22 11.18

190 180 180

93.5 91.1 91.2

Cawley Cawley Cawley

11.18 11 13 10.95 10.95 11.35 10.35 10.45 10.50 11.28 11.28

175 175 247 247 247 247 250 250 250 250

88.3 88.5 88.5 85.8 86.4 lost 86.4 87.2 88.0 86.5

Cawley Cawley Davis

Davis Davis Brush Brush

11.87 11.87 10.02 10.45 10.45 ? ?

150 150 150 190 190 190 190

89.6 89.7 89.8 85.0 93.3 90.2 91.8

Davis Davis Davis Brush Brush Brush Blush

11.38 10.64 10.64 10.38 10.38 10.60 10.60 11-18 11.06

160 170 170 170 170 170 170 170 170

94.4 89.3 89.6 91.6 88.8 89.4 90.0 89.5 89.9

April 28

11.01 11.01 11.01 11.01 10.95 11.10 10.37 11.39 11.39 11.20 11.20

170 170 170 170 170 170 170 170 170 170 170

92.8 93.6 92.2 93.2 91.0 90.9 90.2 89.6 91.0 89.5 89.5

RUN

YIELD Per cent

May 1 a/, cm. suction May 2 Slight pressure on system Slight vacuum on system '/a

May 3 cm. pressure

I/t

cm. pressure on system

All samples taken with suction on ;Qste",t,'m".

1

May 4 1 cm. suction on system 11/2

cm. suction

May 6 1 cm. suction

DATEAND RBMARES May 6

BY

cm. suction

1/1

t t

J

May 7 1 cm. pressure

21/2

cm. pressure

May 9 1 cm. pressure

2 cm. pressure (?)

M a y 10 1 cm. suction

1 cm. pressure

Davis Davis Davis Davis Davis Davis Davis Brush Brush Brush Brush

M a y 11

>

1/2

cm. suction

,

M a r 12 Found some leaks around bottom plate OF silica holder. These were patched. M a y 13 94.5 10.48 175 I cm. suction 94.6 10.48 175 M a y 14 Davis 11.15 185 93.4 11.15 185 93.2 11.11 185 89.9 90.1 Brush 11.11 185 88.8 11.35 175 2 cm. pressure 89.4 11.10 175 Davis 90.6 11.57 185 Davis 1 cm. suction 91.4 11.57 185 87.52 Cawley 11.66 185 Davis 11.45 180 90.7 11.45 180 90.9 1/2 cm. pressure 96.2 11.05 180 92.5 Brush 11.32 180 Brush 11.32 180 92.2 Cawley 1 cm. suction 91.0 11.29 195 90.5 Cawley 11.33 195 M a y 15 95.1 Davis 10. IO 175 Davis 94.5 10.10 175 94.1 10.10 175 Davis 1/2 cm. suction Davis 94.5 9.94 170 Davis 94.0 9.90 170 93.0 Davis 9.90 170 Cawley 9.86 170 91.5 Brush 11.21 162 Normal feed pressure 86.7 Brush 11.21 162 88.5 Davis 10.93 172 90.6 Davis 10.93 172 90.8 Pressure about atmosBrush 92.1 11.03 159 pheric Brush 11.03 159 91.1 Cawley 11.30 165 90.7 M a y 16 hTo yield tests made. M a y 17 Davis 10.32 170 92.2 Davis 10.32 170 92.9 Davis 10.35 170 91.9 Cawley 90.8 10.65 180 Cawley 10.70 180 92.5 M a y 18 Perley 94.2 Perley 93.0 Cawley 92.2 Davis 91.9 Davis 93.0 Cawley 91.6 Cawley 90.7 Cawley 90.3 Cawley 87.6 Cawley 87.8

]

z:$seY ]

E:$ey

Davis Davis Davis Davis Davis

Davis Davis Davis Cawley

APril 26

Aprel 30

86.0 86.5 86.0 91.3 92.2

94.9 94.3 93.5 90.0

c u . ft. per Min.

~~~~~

190 190 190 190 190

190 190 190 I90

NHs Per cent

I

April 29

10.65 10.65 10.65 10.94 10.74

10 71 10.71 10 71

DATBAND RSMARKS April 25

BY

t

1 i

548

T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y

wire for fastening t h e gauze in place and is simply a capital charge, as its value is not lost. The holder is so arranged t h a t it can be easily removed a t a n y time if necessity arises. There are peep-holes in t h e top of t h e aluminum entrance cap and in the outer sides of t h e apparatus so t h a t t h e platinum gauze may be viewed both from t h e inside and from t h e outside of t h e platinum cylinder. The gauze is lighted, after being activated, b y simply applying a torch for a moment through one of t h e peep-holes. When t h e ammonia-air mixture is started t h e apparatus almost immediately begins operation and after coming t o heat, which it does in a few hours, will continue witho u t interruption for months if supplied a pure gas mixture . The cost of t h e converter, exclusive of platinum, should not exceed $ 2 0 0 . It contains a platinum gauze 13 in. wide and 1 1 3 ~ / 2 in. long wound in 4 layers into a 9 in. cylinder. The cylinder when completed, if made of 80 mesh gauze, 0 . 0 0 2 6 in. wire, weighs 1 6 l / ~oz., and has a capacity of about 2’/2 tons of IOO per cent nitric acid per day and works with an efficiency, above 90 per cent, with a gas flow of zoo cu. f t . per min. of I O t o 11 per cent ammonia-air mixture. If t h e gas flow is increased, t h e capacity can be easily brought up t o 3 tons per day b u t the efficiency a t t h e same time drops off z or 3 per cent. The best results obtained for any single run of this converter during t h e experimental work operated on a commercial scale gave t h e following: 208 lbs. of nitric acid per hr or 21 7 lbs per sq. ft. of gauze surface, or 14.1 Ibs per oz of platinum

with t h e gas containing IO^/^ per cent of ammonia being run a t the rate of 2 0 0 cu. ft. of mixed gases per minute, with a n efficiency of 94 per cent. The converter was also run a t a capacity of 2 5 0 lbs. of nitric acid per hr., b u t under these conditions t h e efficiency dropped below 90 per cent. Careful measurements show t h e temperature of t h e gauze itself in this converter, when running with pure ammonia of 11 per cent ammonia content, t o be approximately 82s0 c. The exit gases a t t h e bottom of t h e converter are above 600’ C. Ammonia from cyanamide will not work well in this apparatus unless first purified from t h e phosphine which is always present, although much more in some cyanamide ammonias t h a n in others. This purification is simple and easy a n d may be accomplished either b y first making aqua ammonia under proper conditions, or by passing the mixed gas through gas-mask charcoal or whetlerite which immediately oxidizes phosphine t o phosphoric acid which is retained as ammonium phosphate in the mass. Patents for this method of purification have been applied for Also, a patent has just been granted b y J. D. Davis. t o W. S. Landis1 for t h e elimination of most of t h e phosphine by first blowing air through t h e ammonia autoclaves before turning on t h e steam for ammonia production. With “A” grade coal-tar ammonia, hav1

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ing an organic number’ of 50 or less, t h e apparatus has always worked with high efficiency a n d without difficulty of any kind so long as t h e gauze was kept free from iron oxide or from oil of any kind. I t s efficiency with “B” grade ammonia having a n organic number of 200 or over is lower, t h e temperature of t h e gauze falling off exactly as it does with phosphine, although not t o so great a n extent. If, however, t h e gases are preheated before entering t h e converter, as can easily be accomplished b y the waste heat from t h e reaction, t h e temperature of t h e platinum can undoubtedly be held even with these lower grade materials. While it is not t o be expected t h a t impure ammonia can be oxidized with as high an efficiency as pure ammonia, nevertheless there can be little doubt t h a t better results will be obtained even with impure ammonia, whether in this or in an electrically-heated apparatus, if t h e gauze is kept up t o a proper operating temperature. To accomplish this desired result, either electric heating or preheating should serve equally well. Regenerative heating has the advantage of costing nothing. OPERATING EFFICIENCY

A number of converters were installed a t Syracuse both for experimental purposes and plant operation. At t h e time of t h e installation t h e production of nitric acid and sodium nitrite needed by t h e Semet-Solvay Company was so profitable t h a t t h e converters were run, both old style and new style, day and night in order t o obtain output. At t h a t time it was profitable t o run the converters even with some of t h e poorer gauzes, t o be mentioned later, which were so contaminated t h a t they gave low efficiency. The report on page j 4 7 b y J. D. Davis on Converter No. 4, which was run for experimental purposes with varying conditions from April 2 5 t o May 18, 1918, shows results obtained b y three observers running t h e apparatus independently and making efficiency determinations by two different methods which checked each other. SUM M A R Y

1-Al1 these d a t a are representative except some 4 or 5 determinations known t o be off. The average is t h e best criterion available for publication for t h e work of this converter and gauze. One hundred and sixty determinations were made b y four different chemists using two different methods of determination. Average per cent ammonia, 10.57. Average yield, 90.7 per cent. The air flow was always noted and was varied from 159 t o zoj cu. f t . of mixed gases per minute, one trial day being run a t 2 5 0 cu. f t . b u t not included in t h e average. This rapid flow of gas gave a capacity of 5880 lbs. of nitric acid per day, but t h e efficiency dropped off t o 8 7 per cent. 2-If we average t h e results by periods excluding only t h e results taken a t a flow of 2 j o cu. f t . per min. we obtain t h e following figures: 1 T h e “organic number” here referred to is the number of cubic centimeters of N/100 potassium permanganate which are decolorized by 100 cc. of the ammonia water under consideration.

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PERIOD No. of Av. Percentage Efficiency No. Tests of NHa Per cent 1 21 9.44 90.0 2 20 10.11 91.4 20 10.27 87.4 3 (a) 4 20 10.96 90.0 5 17 11.20 91.2 6 20 10.87 91.1 7 19 11.16 91.0 8 19 10.71 92.2 9 13 10.64 91.9 (a)Most of the low results were in this period, during which leaks developed around the quartz bottom.

The last results are t h e best and a 92 per cent efficiency with 10.5 per cent ammonia and with zoo cu. f t . per min. capacity can easily be reached with this converter. 3-One can pick out sets of results obtained under conditions considered favorable which will make a better showing. However, t h e above represents more nearly what a good works operator would obtain with ordinary care, given the proper design of furnace, good ammonia, and good platinum. Another of these cylindrical converters was run continuously by the Semet-Solvay Company for commercial purposes without repairs or alterations from February 23 t o September 15, 1918,when t h e gauze was injured by an accident which caused caustic from t h e sodium nitrite absorption towers t o back up into t h e burner. The analytical control of this converter was not as continuously conducted as the experimental burner since it was being run purely for commercial purposes in the hurry of war production. The average of all tests, forty in all for this period, made by t h e Semet-Solvay Company was 91.4 per cent. Further work with this converter has been carried o n at Plant No. I by Captain G. E. Perley, of t h e Nit r a t e Division, Ordnance Department. Important results have been obtained b y him which he will publish later. SOME GENERAL PRINCIPLES O F AMMONIA OXIDATION

Mr. F. G. Liljenroth,’ in an article on “The Starting and Stability Phenomena of Ammonia Oxidation and Similar Reactions,” has theoretically considered some of t h e phenomena accompanying and influencing ammonia oxidation, basing his curves on the hypothetical figure of 7 5 0 ° C., as the temperature a t which maximum efficiency is obtained. While this temperature is, undoubtedly, low, the conclusions are unaffected thereby. The curves are decidedly interesting and it seems well to consider here also some of t h e factors which apply t o all forms of apparatus using platinum as a catalytic agent for the oxidation of ammonia. I t is impossible in this paper t o more t h a n summarize the results obtained in the laboratory and in the plant. Given a definite concentration of pure ammonia gas a t a definite temperature with a given catalytic agent, in this case platinum, the amount of conversion or capacity of any apparatus or converter is dependent upon the surface of platinum exposed t o t h e reaction. The object, then, is t o bring as large a surface of platinum as possible into contact with the ammonia t o be oxidized and t o bring pure ammonia t o this surface up t o its capacity t o bring about chemical change. JChem.& Met. Eng., 19 (1918), 208

549

A. Q U A L I T Y OF PLATINUM-The platinum should be as pure as possible, consistent with strength. Fine wire cannot be drawn from platinum unless i t contains some hardening element. Iridium is t h e best for this purpose, and iridium in the necessary quantity t o allow platinum t o be drawn into fine wire has not proved harmful in our experiments. This is also true of palladium. Pure palladium gauze is as active as or even more active t h a n platinum, but has no life, falling t o a powder of palladium black within a few hours. Ten t o 2 0 per cent palladium in platinum apparently in no wise injures the oxidizing efficiency of the gauze, but the gauze is harder to activate and has not given as much satisfaction as a platinum gauze with a small amount of iridium, which meets every need. Iron in t h e platinum, even in small quantities, is a very serious impurity, as much as 0.2 per cent seriously affecting the efficiency of t h e operation. One large gauze used commercially containing this amount of iron never functioned well. Iron, however small in amount, should be entirely eradicated; even t h a t added through drawing by steel dies should be removed by washing in strong hydrochloric acid. Any iron in t h e wire gradually works t o t h e surface where iron oxide is formed. Every precaution should be taken to keep iron out of t h e platinum and iron oxide from its surface, whether the iron comes from t h e platinum itself or is carried mechanically from iron pipes with the gas. Rhotanium gauze (an alloy of palladium and gold) was tried b u t was found t o have no catalytic effect so far as conversion of ammonia into nitric oxide was concerned. The ammonia gas burned almost wholly t o nitrogen and water. B. SIZE OF W I R E A N D MESH O F GAUZE-In the gauzes actually tried by the Bureau of Mines, namely, 7 0 mesh 0 . 0 0 2 6 in. wire, 80 mesh 0 . 0 0 2 6 in. wire, and I O O mesh o . o o I j in. wire, the 80 mesh gauze gave by far the best results. It is, however, improbable t h a t this size of gauze is t h e best. Mr. Alvan Allen Campbell, of t h e Newark Woven Wire Cloth Company, Newark, New Jersey, which company has woven most of the gauzes used by the Government, has published a paper1 on platinum gauzes used as a catalyzer for the oxidation of ammonia, giving a table of weights, active surfaces of platinum, air space, etc., of various meshes of gauze made from various diameters of wire. His figures would indicate t h a t a finer mesh and a finer wire give a much larger surface of platinum per gram of platinum and t h a t in all probability more efficient results for the platinum used would be obtained from a platinum-iridium alloy of 99 per cent platinum and I per cent iridium, if a I jo mesh gauze with 0.0015 in. wire were used. Although this gauze may be mechanically weak, it is highly desirable t h a t it should be tried out commercially and t h a t a I Z O mesh 0 . 0 0 2 in. and a 1 5 0 mesh 0.00~ in. wire should also be experimented with. C. A C T I V A T I O N O F P L A T I N U M GAUZE-Fresh, smooth platinum wire shows comparatively little catalytic activity. If, however, it is exposed around 800’ t o a 1

THISJ O U R N A L , 11 (1919), 468.

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Fro. IO--~~.ITINVI WIRE S C X ~ B N100 , Muse, NBW,Nor ACIIY~TSD

Fro. L I . - - - ~ ' L ~ I N Uwin% D~ Scanen, 100 M~ssx, AC'IIVITSD FOE AMSONU OxroArrow. JULY 25, ~P.II..TFAoEDsTI?,~~.M.,~~I~

rather rich ammonia-air mixture it takes on in a few hours a gray appearance, the wire becoming covered with spongy platinum, Whether this simply increases the effective surface or changes the nature of the platinum is hard t o judge. Certainly, however, the platinum must first be activated before it is successfully used. I n an electric apparatus this takes place simply b y operation, particularly if the ammonia concentration is increased for a few hours. With the cylindrical converter, however, it is necessary t o first activate the platinum gauze two feet a t a time in a flat electrically-heated convcrter before i t is worked up to the cylindrical form. One electrically-heated converter should be kept on hand in any large plant for this purpose. Otherwise the inner layers of this platinum cylinder become activated from the rich ammonia hut the outer layers take weeks or even months t o activate, even if they become notably changed a t all. The results of this activation are shown in Figs. 10, 11, and 12. D. CATALYTIC P O I S O N ~ - A S already pointed out in this paper, phosphine is a very serious catalytic poison. It has been elsewhere shown' t h a t as little as z or 3 parts in ~oo,ooo,ooo has a distinct effect. Also, as previously stated, iron oxide and grease, oil or tar of any kind must be kept away from the platinum gauze or dark spots showing inefficient catalytic action will appear. A new gauze should be washed x i t h pure gasoline or ether before being activated. I t is undouhteclly due t o some volatile tar-like bodies t h a t the temperature of a self-heating gauze falls 08 %\-hen ammonia with a high organic number is burned. Fortunately, all of these impurities are casily removed and there should be no excuse for any of them reaching the gauze in a properly constructed ammonia oxidation plant. Hydrogen sulfide or organic bodies which burn without leaving a residue on the gauze have little deleterious action, a t least when present in small quantities. Acetylene itself is not harmful, and cyanogen and hydrocyanic acid are oxidized t o nitric oxide apparently as easily as pure ammonia itself.

'

G. 14. Taylor and Iuiian 11. CWPI. "i!Reet of Acetylene 022 Oxidation of Ammonia i o h'itric Acid," ?'iris Jurranl~,10 (1918), 457; "EtTeci of Phosphine mnd Iiydiosce SulRdr on the Oxidelion ai hiimonixi to Nitric A c i d , " I b i d . 11 ( , g i g ] , 2 7 .

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Fio. IZ-I'LA~~IIUMWixs S c n l l s ~io0 , MESH, OxloanoN. JULY. 2.3, 3~,~.,r0A0~~~~17,91.~.,1917 ACIIYdTED POX AMHONIA

E. T E X P E R A T U K E O F REACTION-The temperature at which platinum best oxidizes ammonia is certainly above 825' C. All results obtained by the Bureau indicate that the temperature should nevcr be allowed t o fall below 7 5 0 ' and that the efficiency of operation increases with the temperature above this point and certainly docs not fall OR below 900" or 925'. The increase in efficiency above S q " , however, is r slow as the temperature rises. A few definite measurements were made by Taylor during his laboratory experiments, all indicating increased efficiency as the temperature rose, hut the number is too small t o warrant the publication of a temperature curve. The cylindrical converter certainly worked best around 82j0, the highest temperature a t which it could be maintained with pure ammonia at efficient concentration a,ithout regenerative heating. All the experiments with the small laboratory apparatus previously described gave better results as the heat of the gauze was increased. An operating temperature of at least 82jo is recommended. This should apply t o all apparatus using platinum as a catalyzer. F. CONCENTRATION OF MIXED cnsas-Eficiency at a proper operating temperature undoubtedly varies within limits inversely with the amount of ammonia present, although not necessarily proportionate thereto. With a self-heating gauze and pure ammonia, I O t o I Z ~ / per ~ cent of ammonia in the gases is desirable to keep the gauze t o proper temperature. While a slightly lower efficiency obtains with the higher concentrations of ammonia, nevertheless there is a compensation in actual operation in the fact that the nitric oxide gases produced vary directly with the concentration of the ammonia in the gas burned, and these higher concentrations of nitric oxide absorb much more readily in the absorption towers and yield a higher concentration of nitric acid. With percentages lower than IO per cent, regenerative heating or electric heating is advisable, the regenerative heating having the advantage that it utilizes the waste heat of the reaction, while electric heating is costly both from the standpoint of power and the electric apparatus be constructed required' Any preheater of aluminum or of silicate material, if the gas mixture

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a n d not simply the air alone is preheated, for otherwise a considerable proportion of t h e ammonia will be converted into nitrogen and water before i t reaches the platinum gauze. Numerous experiments carried out by t h e Bureau and also results obtained by others’ indicate t h a t great care must be exercised in regard t o the substances which come into contact with the mixture of ammonia and air if decomposition is not t o take place a t elevated temperatures. The following unpublished *experiments by G. B. Taylor illustrate these points. I n these experiments the material was filled into a porcelain tube which was heated while the ammoniaairamixture was slowly passed through. MATSRIA~

Temp. Deg. C. 550

.................. ............. 680

Pieces of pure aluminum sheet.. Vitrified silica (pieces of broken tube). Nickel wire, 2 mm. diameter in form of small staples Nickel wire, 2 mm. diameter in form of small staples Nickel wire, 2 mm. diameter i n form of small staples Porcelain (pieces of broken dish glazed on one side) .Alundum cement briquettes.. Alundum cement:,~ briauettes. ................... a 1.8 per cent oxidized t o NO. b 1.0 per cent oxidized t o NO.

..................

500 580 690 700 710 590

NHs Destroyed Per cent 0.0 0.8 1.4

;;:%j 0.0 34.0 2.3

{I

Electric heating or regenerative heating will undoubtedly enable lower concentrations of ammonia gas t o be burned with slightly increased efficiency, an efficiency offset, however, as already pointed out, b y t h e lower concentration of t h e nitric oxide obtained. It is the writer’s opinion t h a t a concentration of approximately I volume of ammonia t o 9 volumes of air will be found t o be an excellent basis of operation under ordinary conditions, but t h a t when a heavy output is Tequired a concentration of from I I t o 1 2 per cent by volume of ammonia may be burned t o distinct advantage. G. E F F I C I E N C Y O F CONVERSION-In speaking Of efficiency of conversion, it is necessary t o point out t h a t efficiency of operation of the converter has been a n d must be determined on the basis of gas analysis. I n t h e determination of the total efficiency of a plant actual weights of ammonia used and nitric acid obtained will give an over-all commercial efficiency which is independent of such analysis, but such efficiency of operation includes not only t h e losses involved in the catalytic reaction but also involves mechanical losses. The methods used by the Bureau of Mines in its experimental work for t h e determination of the efficiency of reaction are two: one described by 6. B. Taylor and J. D. Davis,2 the other being the method used by the American Cyanamid Company which is soon t o appear in THISJ O U R N A L in an article b y Capt. D. P. Gaillard entitled “Analytic Method of Determining Efficiency of Ammonia Oxidation,” an advance copy of which has been furnished t o the writer by the courtesy of Capt. Gaillard. These two methods have been used side by side for months in t h e investigations of the Bureau of Mines and the Ordnance Department a n d have closely checked each other.

5.51

On the other hand, the method used in England for the determination of t h e efficiency of ammonia oxidation, as used in American hands, yields results notably higher. As the early published d a t a on t h e efficiency of ammonia processes by Kaiser and others often ran above I O O per cent, presumably owing to t h e actual burning of nitrogen and oxygen, but really due t o t h e inaccuracy of the method employed, great care should be exercised in efficiency determinations. There is no reason t o believe t h a t t h e efficiency of any apparatus using t h e same platinum as a catalyzer will vary notably from the efficiency of any other apparatus if t h e same condition of temperature, gas concentration, purity of gas, and absence from premature decomposition are observed. With proper precaution, a commercial plant using the Frank-Car0 apparatus, the apparatus of t h e American Cyanamid Company, or t h e cylindrical converter should yield efficiencies above 91 per cent, and i t is believed, with further refinements, t h a t oxidation efficiencies of 95 t o 96 per cent are quite possible. ELECTRIC HEATING V S . S E L F HEATING OR R E G E N E R A T I V E HEATING

The chief advantage of t h e cylindrical converter over an electrically heated converter is one of cost. With a pure gas and a definite temperature, held by retaining heat in the converter itself or obtained through preheating, the same surface of platinum gauze should and will give t h e same output of nitric oxide no matter which form is used. Electrical units take up very much more space for a given output. Each unit, although having approximately one-fifth of t h e capacity, costs more t h a n the cylindrical unit of five times the capacity, and the difference in cost of construction and operation are very considerable factors. T h e electrical unit for a given output requires a heavy additional expenditure for converter units, for dynamos, electrical meters, transformers, switchboards, a n d wiring, a large amount of extra piping, extra land, extra buildings for installation, and extra platinum. Also a considerable enlargement has t o be made t o any power plant required. The amount of electricity used is no small item, being 5,500 continuous horse power for a plant t h e size of Plant No. 2 a t Muscle Shoals, employing, as before stated, 696 converters. T o this must be added additional cost for repairs, overhead, interest, and amortization, a n d for labor. Small units always require more labor for a given output t h a n large ones in almost any form of chemical operation. COST OF NITRIC ACID PRODUCTION

While the present paper has simply t o do with the oxidation of ammonia t o nitric oxide and scarcely touches upon the cooling, absorption, and concentration t o nitric acid, nevertheless these divisions of the subject are none the less important and require the W. Ramsay and S. Young, “The Decomposition of Ammonia by greater part of plant outlay both for construction and Heat,’’ J . Chem. Soc., 45 (1884), 88; E. P. Perman and G. A. S. Atkinson, operation. “The Decomposition of Ammonia by Heat,” Proc. Roy. SOC.,74 (1904). 110; A. H. White and W. Melville, “The Decomposition of Ammonia,” In these times of change, unsettled conditions, and J . A m . Chem Soc., 27 (1905), 373. * “Analytical Control of the Ammonia Oxidation Process,” THIS high prices, any chemist would be rash t o make JOUR“&, 9 (1917), 1106. predictions of cost of construction and operation with

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plants would save money by its immediate adoption, t h a t 3 6 O Be. nitric acid can a t present prices of ammonia be made as cheaply as from sodium nitrate even if i t drops t o pre-war prices, and t h a t ammonia has t o drop in price only a few cents per pound in order t o have concentrated nitric acid also made competitively b y t h e oxidation of ammonia. BUREAUO F M I N E S WASHINGTON, D. C.

STUDIES ON THE OFFICIAL METHOD FOR PYRIDINE I N AMMONIUM NITRATE By R. M. LADD Received September 17, 1918

I-From

FIG.13-Cosr Ammonia, by Oxidation

NITRICACID 11-From

OR

Sodium Nitrate

claims t o exactness. The following figures should, therefore, be considered simply as an "order of magnitude." They are round figure averages between t h e (1917-18) costs of one actual plant and t h e estimates of a reliable and experienced engineering and constructing firm for the erection and operation during 1918 of another To these figures in t h e case of acid costs, $3.00 per ton has been arbitrarily added as estimates of late have always proved low. It is, accordingly, t h e opinion of t h e writer t h a t t h e following figures may be considered high for 19191920. They include cost of vaporizing, oxidizing, cooling, absorption, weighing, and concentration systems with buildings and foundations, and an addition of 20 per cent t o operating costs for repairs, interest, and depreciation. P L A N T CONSTRUCTION COSTS

Plant for 25,000 tons As 50 per cent "0s.. As 94 per cent "0s..

"03

(100 per cent) per year

. . . . . . . . . $45.00 per ton year

.........

60.00 per ton year

PLANT OPERAT~ON COSTS

As NO gas.

Per ton HNOa (100 per cent) $ 5.00 plus cost of NHa . . . . . . . . . 15 00 plus cost of NHa 30.00 plus cost of NHs

................... .........

As 50 per cent "08.. As 94 per cent "0s..

I n order t o make a comparison with t h e cost of 94 per cent acid from sodium nitrate, $48.00 may be taken as fabrication cost per ton of nitric acid (100 per cent basis) and add thereto t h e cost of 2800 lbs. of commercial Chile saltpeter. Fig. 13 will then make plain the relation between t h e costs of the two methods of producing nitric acid on t h e basis above adopted. A study of Fig. 13 should give at a glance an idea as t o when t h e production of nitric acid by ammonia oxidation can compete commercially with the old methods from Chile nitrate. It is evident t h a t sulfuric acid

The original government directions for t h e determination of pyridine in ammonium nitrate read as follows : Dissolve a known weight, approximately IOO g., in IOO cc. of distilled water, using a I liter Kjeldahl distilling flask. A few drops of methyl orange and 5 cc. of normal sodium hydroxide solution are added. The pyridine and ammonia are then distilled into IOO cc. of sodium hypobromite solution (100g. sodium hydroxide dissolved in 500 cc. of water, 2 5 cc. bromine added, and the solution made up t o 1000 cc.) contained in an Erlenmeyer flask of approximately 800 cc. capacity. The ammonia is decomposed by the hypobromite solution while the pyridine passes unaffected into a second receiving flask containing I O cc. of N / I O sulfuric acid. From the acid used the pyridine is calculated. One cc. N / I O sulfuric acid is equivalent t o 0.0079 g. pyridine. Twenty minutes' boiling is sufficient. At first glance i t appears t h a t different analysts would interpret this test in different ways and hence would obtain different results. I n our laboratory we first set up t h e apparatus without any condenser. We found t h a t a t one of t h e other plants belonging t o t h e company a condenser was being used as shown in Fig. I. The inspector when he came advised t h e use of a condenser. Since t h a t time we have set up t h e apparatus as shown in the figure. But this is only one of t h e difficulties. The series of results in Table I will show what widely differing results can be obtained b y different interpretations of the method. TABLG I VOl. of Grams Distillate Pyridine SAMPLE Used Method1 Cc. Per cent A. 100 Ia ? 0.0000 300 Ib 40 0.0020 100 I C 75 0.0210 ? B . . . . . . . . . . . 300 Ia 0.0005 100 Ib 40 0.0150 100 IC 0.0350 50 0.0003 100 la J 500 Ib 100 0.0020 300 IC 100 0.0169 200 IC 75 0.0166 1 Method I a calls for 20 min. of slow boiling in hypobromite flask. Method I b calls for the destruction of the ammonia before boiling starts in the hypobromite flask, then rapid boiling until the required amount of distillate has been collected. Method IC calls for 20 min. rapid boiling in the hypobromite flask, without preliminary slow heat t o destroy the ammonia. Ammonia was invariably carried over by this method, hence the results were always too high.

..........

............

Table I1 shows a series of results which would seem t o indicate t h a t not all t h e pyridine is carried over by this method, even when the time of boiling is counted from the start of rapid boiling in t h e hypobromite flask.