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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 CHEMISTRY
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NOTES AND CORRESPONDENCE TWO LETTERS ON THE CHEMICAL CONTROL OF AMMONIA OXIDATION Editor of the Journal of Industrial and Engineering Chemistry: In a paper on the “Analytical Control of the Ammonia Oxidation Process”1 Messrs. Guy B. Taylor and Joseph D. Davis refer to the present writer’s article2 and a brief statement seems necessary by way of reply or further elucidation. Taylor and Davis assert that the “statements of Schonbein, Weith and Weber are not to be taken to mean that ammonia is oxidized by hydrogen peroxide abundantly under all conditions.” But there is nothing in our paper that says they are so to be taken. We said that hydrogen peroxide abundantly oxi‘dizes ammonia-which is true. We did not say that it happened under all conditions. The course of this chemical reaction, and for that matter, all chemical reactions, is determined by the conditions of temperature, concentration, etc. This is a sort of Theorem I of chemical dynamics, and is presumed in any discussion. It may well be true that under the conditions of analysis as used by Taylor and Davis no such oxidation occurs; we should be the last t o dispute it as we have no data to dispute i t with. It does not appear to us, however, that the evidence brought forward to show absence of oxidation is sufficient to prove the case, under all conditions of analysis. In the same paper the authors state (p. I 109) that “the reaction z N O iO2 = 2N02 occurs in measurable time.” That is, it requires a measurable time for the specified equilibrium to be reached. To prove this, they cite five journal articles, most of which are very long and full of data having no relevancy to the issue. They give, however, no particular references; in fact they might as well have cited the literature en masse. Let us see what the literature says. In the first paper cited,$ on p. 2135, we find the statement: “these experiments show that two volumes of NO and one volume of oxygen of different origins (i. e., made by different manufacturing processes) a t atmospheric pressure are practically completely transformed into NO2 and Nz04.” On p. 2134 is given a curve of time against pressure decrease, which shows that the reaction practicaIly runs its course in half a minute or less. Thus with only the theoretical amount of oxygen (which Holwech used) the reaction is practically complete in less time than would be required to go through our apparatus, but our method of course requires a decided excess of oxygen. Perhaps the most important paper for the case on hand is that of Foerster and Blich,4 and the issue amounts to thiswhen the mixture of air or oxygen and NO is run into a dilute caustic: soda solution, does the reaction take place as follows? 2N02 zNaOH = NaNOz f NaN03 H20 The answer is, that it all depends on Theorem I above, and there is nothing in the article bearing on our work because Foerster and Blich did not duplicate our conditions. However the results given in the table on p. 2019 “Versuchsreihe” Experiment ( 6 (where the gases are dilute) and in Experiment 42 on p. zoz I come as near as any in the paper to being, comparable. I n both instances the reaction runs practically as specified in the equation above. We do not base anything, however, on these statements from the literature. What is said in our paper was based on the fact that the amount of nitrite found in the first absorber was close enough to the reaction given to justify the calculation. The fact is, that so far from being in the sense of
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(1917), 737. a Holwech, “uber die Reaktion zwischen Stickoxyd und Sauerstoff,” 2.ongew. Chem., 2 1 (1908). 2131. 2. angew. Chem., 2s (1910), 2017. 9
more nitrite as would be presumed from Taylor and Davis’s supposition, there was invariably less, i. e., more than half the acid was nitric. The writer thought there might be a little ozone in the oxygen but as the corrections involved were small, he did not think the point worth pursuing. Doubtless the amount of nitrite and nitrate are much influenced by the concentration of the alkaline solution into which they are led. In the writer’s apparatus certainly all the N O yielded NO2 and a little NzOs. However, Taylor and Davis admit that by our procedure all the nitrous gases are absorbed, and all their contention would amount to, even if valid, would be that the formula would have to be modified. One does not adjust his testing to a mathematical formula, but calculates what he wants to know from the data he can get most conveniently and accurately. Curiously enough, Taylor and Davis in their literature citations overlooked the only paper that could have been cited with any effect. We refer t o that by Mandl and Russ’ who found that with some kinds of oxygen (e. g., that from electrolysis and also that from barium superoxide, bichromate and sulfuric acid, but not that from liquid air) the reaction between NO and 0 2 did not go to completion.2 The objection would apply of course to any methods requiring oxygen, including those of Taylor and Davis. However, we were fortunate enough not to get hold of any such oxygen. Mandl and Russ think that the differences in oxygen of different origin may explain the contradictory statements in the literature on the behavior of KO and oxygen. Method I of Taylor and Davis amounts substantially to our method in that they have added oxygen to the gases before absorption, the difference being that they omit the precautions to prevent the oxidation of ammonia by the hydrogen peroxide. The main fact is t h a t nitric oxide (NO) is not nearly completely absorbed by alkaline hydrogen peroxide. Sufficient oxygen must be present to convert it into NOs(N204). The writer proved this repeatedly, when nitric oxide would go through three absorbers, two of them filled with alkaline peroxide and beads, only to burst into brown fumes on coming into contact with the air. The essential features of our method are to insure by previous addition the presence of the necessary oxygen, and to avoid the oxidation of ammonia which takes place under not well-understood conditions. Now, Taylor and Davis have previously added the oxygen but there is no certainty that it would be enough; this difficulty is avoided by adding an additional dose in the large (1200 cc.) displacement vessel after the absorption is completed. This plan, while not specially appealing to us on account of the double titration and the necessity of getting the acid out of the large container, will doubtless get all the nitrous gases provided the mixture coming from the catalyzer contains enough oxygen already to oxidize practically all the NO to NO*. In fact, with the saturators a t 7 or 8 per cent ammonia (as mentioned in the article) we suspect that little or no oxygen would be necessary. Supposing, however, that the gases from the catalyzer contain all the combined nitrogen as KO, with little or no oxygen, then only limited absorption3 will take place in K”, and, especially in a cool place, there would be ample opportunity in an hour for part of it to dissolve in the displacement water and get lost. We see then that the method is available only for a highly special manner of operating the catalyzer, and will be satisfactory only so long as there is sufficient excess of oxygen present. The writer was never able to get complete Z. angew. Chem., 2 1 (1908), 486. These results have not been confirmed by later workers, without, however, disproving them. Holwech, Z. angew Chem., 21 (1908), 2131. 8 Probably also irregular. See the reference to Schdnbein in the writer’s original paper. 1 2
T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY absorption with only one absorber, but possibly the absorber K “ is better than his. The use of a manometer is not very convenient. The same criticism applies t o the evacuated bottle method as described. A sufficiency of oxygen is not assured, except under special conditions. Moreover, a pump capable of evacuating to 2 mm. is necessary as well as connections and capillary stopcocks so well ground that they will retain the vacuum mentioned. Fortunately a concession is made in the matter of ground glass connections. What all these mean, it is unnecessary t o state. The statement that it is the only method permitting the determination of ammonia escaping oxidation presumably applies only to the procedures described in the paper, for it is perfectly feasible by our method. We are convinced that anyone trying the vacuum bottle method will find it exceedingly elaborate. Presumably the plan could be modified by adding a measured amount of oxygen first to the vacuum bottle, but it then becomes even more complicated. A larger bottle will also be required to cover all cases of gas mixture. Messrs. Taylor and Davis present a method for eliminating titrations because “the principle involved offers possibilities for development of a rapid method of works control.” The essential novelty of the principle however-the running of a gas into a definite volume of liquid stained by an indicator until the indicator turns-had been stated already by the present writer in the second and third paragraphs of his paper. They have added an elaborated glass apparatus which would impress us as being a great deal more troublesome than half a dozen titrations. Finally, and this a crucial point, catalyzers do not work uniformly and the taking of a sample should extend over considerable time, in fact should be continuous. It seems to the present writer that his is the only process which has this advantage; i t is also free from limitations on the composition of the gases. He hopes to publish shortly an account of an improved and more compact form of his apparatus, together with a new method of approximate factory control requiring less skill than any of the proposed methods. PAULJ. Pox 1605 E. CAPITOL STREET WASHINOTON, D. C. December 11, 1917
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Editor of the Journal of Industrial and Engineering Chemistry: I n reply to criticisms of Mr. Paul J. Fox, on our paper “Analytical Control of the Ammonia Oxidation Process.” In regard to the oxidation of ammonia by hydrogen peroxide in alkaline solutions, we are convinced that no such oxidation occurs in any method used by us and would not occur in the method proposed by Mr. Fox, even if hydrogen peroxide were contained in his first absorption vessel. No experimental evidence of such oxidation is presented by Mr. Fox, and certainly none in the reference quoted by him.’ However, the question is relatively unimportant since little or no ammonia is allowed t o pass the oxidizer in commercial operation. In regard to the second point a t issue, the completeness of the oxidation of NO to NOS, the literature cited by us and confirmed by our own experiments shows that this reaction is not a n instantaneous one and has a negative temperature coefficient. The latter is important. If the gas is not cooled to room temperature even with a large excess of oxygen, there is no assurance that the reaction will complete itself unless a large reaction space is provided before the gases enter the alkaline absorbing solution. The apparatus sketched by Mr. Fox shows that the only reaction space provided is the narrow tube conducting the gases to the bottom of the absorption vessel. Since the gases must be kept hot till they enter this tube to prevent moisture condensation, it appears likely to us that the reaction does not complete 1
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itself before the acid oxides are absorbed by the alkali. But if Mr. Fox obtained practically equal quantities of nitrate and nitrite in his absorbers from the hot oxidizer gases, we withdraw the objection in our original paper. We quite agree that NO is not absorbed by alkali or alkali containing hydrogen peroxide. But a mixture of NOz and NO in any proportions such that NO does not exceed that of NOz is more readily absorbed by alkali than NO2 alone.’ I n our aspiration method a partial reaction of NO to NO% was all that was required. The use of oxygen was t o clear absorption vessel K ” of air a t the beginning of the test and of the oxidizer gases a t the end of the test and not to assist in the absorption as assumed by Mr. Fox. In our opinion no aspiration method is very satisfactory. We do not agree that it is desirable to draw continuous samples, or samples over a period of time. I n fact, to the authors’ knowledge, a commercial plant using an aspiration method similar to that advocated by Mr. Fox, has recently discarded i t in favor of the vacuum method which they have recommended. The vacuum bottle method has been in use over a year under all‘ kinds of experimental conditions and in actual plant operation, where i t has proved satisfactory. When high concentrations of ammonia are being oxidized it is necessary to introduce a little pure oxygen after taking the sample, but it is not necessary to measure i t and is 60 trouble whatever. One man with a little experience can make a complete efficiency test including calculation of results in half an hour if determination of the free ammonia escaping oxidation be neglected. BUREAU OF MINES G w B. TAYLOR WASHINGTON, D. C. J. D. DAVIS January 3, 1918
AVOIDABLE WASTE IN THE PRODUCTION OF SULFURIC ACID BY THE CHAMBER PROCESS Editor of the Journal of Industrial and Engineering Chemistry: I n connection with the subject of the increased production of sulfuric acid called for on account of explosives requirements, it is interesting to consider one phase which seems to have escaped general observation. In the United States we make some four million tons of acid by the chamber process each year. Very few chamber plants are run on a scientific basis; in fact, most of them operate by rule of thumb, this being particularly true of the acid plants attaehed to fertilizer factories. While there has never been a survey made of the average operating conditions in the chamber plant acid industry, I am reasonably sure from the data I have gathered during the past five years that the average chamber plant space obtained by combining all the plants in the country would be of the order of 1 3 cu. f t . per pound of sulfur burned. With proper analytical control of the gases, and with exact control of the volume and temperature of the acid circulated over the towers there is no reason why the chamber space used should not be cut down to I I f t . per pound OF sulfur burned per 24 hours. Suppose, however, the average improvement is no more than a reduction to 1 2 cu. ft., we would have an increased output. without the construction of additional plant, of some 300,000 tons of 50’ Be. sulfuric acid per year. A questionnaire sent to the acid manufacturers covering chamber acid output and chamber space per pound of sulfur, would soon show the possibilities of increasing our acid production in the way I have indicated, but, of course, such a query t o result in answers of real value would have to be sent out b y some department of the Government. A. E. MARSHALL BALTIMORE, MD. Chemical Engineer January 4, 19 18
