March 1948
397
INDUSTRIAL AND ENGINEERING CHEMISTRY
(carbonated to a composition corresponding to ethylenediamine 56%, carbon dioxide 15%, water 29%). At a temperature of 235’ C., and a pressure of 600 pounds per square inch, an 85%
conversion of the carbon dioxide in this mixture will be obtained in a cycle of 30 minutes. If 90% diamine is available, a solution containing 25% carbon dioxide could be prepared. I n a cycle of 10 minutes about 95% conversion could then be effected. The efficiency of this system is much higher than the aqueous diamine system; three to four times as much ethylene urea would be produced in the same unit time. Because, as shown above, a carbonated mixture of diamine and water can be dehydrated to almost any desired extent by fractionation, the selection of an input composition is a matter of economics. The figures cited in the flow diagram are merely representative of one set of operating conditions as obtained with small scale equipment. With the composition given, 75% of the preseure coil effluent must be recycled. This condensate from the stripping column, fortified with fresh diamine and carbon dioxide, is partially dehydrated in the still. A 55% aqueous diamine solution is thereby raised to a 66y0 solution suitable for introduction to the reactor. The losses in this process are very low and occur chiefly in distillate from the fractionating still. The data cited show that 2.7 pounds of diamine and 3.9 pounds of carbon dioxide were lost for every 56.8 pounds of ethylene urea produced. These figures are considerably higher than necessary, since they were taken from laboratory data obtained on a rather inefficient column. With the figures as given the-over-allyield is still 94%. The molten ethylene urea runs continuously from the flash boiler to the flaker. The product as obtained was sufficiently pure to meet all government specifications. SUMMARY
By the process described here, the cost of production of ethylene urea on a large scale is about equal to the cost of ethylenediamine. Diamine and carbon dioxide are the only raw materials. Relatively simple equipment is needed and the process can be made almost completely automatic. Heretofore a laboratory curiosity, cheap ethylene urea has been developed as a direct, result of the war emergency. It is to be expected that many uses will be found for ethylene urea.
Various uses have already been reported in the literature (1,2,6, fO),particularly in the field of high polymers. Condensation polymers with polyhydroxy compounds are claimed as finishing agents for textiles and leather. Alkoxymethyl derivatives are claimed to be useful as creaseproofing and waterproofing agents for textiles. Certain derivatives are cited as pharmaceutical intermediates (If). Other unpublished information indicates the usefulness of ethylene urea in the formulation of plasticizers, lacquers, and adhesives. ACKNOWLEDGMENT
The authors wish to express their thanks to Joseph Kalish, Gerald OJConnor, Samuel Sklarew, John Pretka, and Charles Cook for their valuable assistance during the course of this work. They are especially indebted to L. R. Littleton of the Office of the Chief of Ordnance for his original suggestion of the problem and his constant advice and encouragement. LITERATURE CITED (1) Burke, W. J., and Hoover, F. W. (to E. I. du Pont de Neinours & Co.), U. S. Patent 2,374,647 (May 1, 1945). (2) Burke, W. J., and Werntz, J. H. (to E. I. du Pont de Nemours & Go.), U.S. Patent 2,370,839 (March 6, 1945). (3) Chemisohe Fabrik auf Actien, German Patent 123,138 (July 30, 1901). (4) Dittmar, H. R., and Loder, D. J. (to E. I. du Pont de Nemours & C o . ) ,U. S. Patent 2,416,046 (Feb. 18, 1947). (5) Fischer, E., and Koch, Ann., 232, 227 (1886). (6) Hoover, F. W., and Vaala, G. T. (to E. I. du Pont de*Nemours& Co.), U. S. Patent 2,373,136 (April 10, 1945). (7) Klut, Arch. Pharm., 240, 677 (1887). (8) Larson, A. T., and Loder, D. J. (to E. I. du Pont de Nemours & Co.), U. S. Patent 2,416,057 (Feb. 18, 1947). (9) Loder, D. J. (to E. I. du Pont de Nemours & Co.), U. S. Patent 2,425,627 (Aug. 12, 1947). (10) Maxwell, R. W. (to E. I. du Pont de Nemours & Co.), U. S. Patent 2.373.135 (Am. 10. 1945). (11) Muskat, I.’E.,’and Strain, F. (to’pittsburgh Plate Glass Co.), U. 9. Patent 2,379,250 (June 26, 1945). (12) Pierron, P., Ann. Chirn., [Q]11, 363 (1919). (13) Puschin, N. A., and MitiO, R. V., Ann., 532, 300 (1937). (14) Tafel, J., and Reindl, L., Be?., 34, 3288 (1901). ENG.CHEM.,27, 867 (1935). (15) Wilson, A. L., IND.
.
RECEIVED January 5, 1948. The material of this paper is the subjeot of a patent application by the authors, assigned to the Secretary of War.
CATALYTIC OXIDATION OF AMMONIA TO NITROUS OXIDE Kenneth A. Kobe and Paul D. Hosman ’
UNIVERSITY OF TEXAS, AUSTIN, TEXAS
AMMONIA was oxidized to nitrous oxide over a manganese oxidebismuth oxide catalyst. A maximum yield of 71% was obtained at 200’ C. at a space velocity of 5 to 6 ml. of gas per ml. of catalyst per minute, using a gas mixture containing approximately 10% ammonia and 90% oxygen. After about 40 hours of use the catalyst activity decreases rapidly. This reaction should receive further consideration for the preparation of nitrous oxide for increased industrial utilization. c
ITROUS oxide, used for many years as an anesthetic, is prepared by the thermal decomposition of ammonium nitrate, a method which gives a gas of high purity. Recently, nitrous oxide has been used as a low temperature refrigerant a t Oak Ridge, Tenn. (8). It also has been used as an immersion refrigerant for the quick freezing of foods (2, 9) and for the ex-
trusion of whipped cream (16). I n the field of refrigeration nitrous oxide has been compared to carbon dioxide for use as a low temperature refrigerant; Table I shows a comparison of common refrigerants, using approximate values in English engineering units 10,12,1C, 17). As the triple point pressure of nitrous oxide is below atmospheric, it can exist as a liquid a t atmospheric pressure. This property permits the direct introduction of foodstuffs into the liquid nitrous oxide bath and gives the greatest possible rate of heat transfer between the substance immersed and the bath. Nitrous oxide must be produced a t a lower cost than a t present if it is to be used more extensively in the fields of refrigeration and food preservation and for other industrial purposes. The economical oxidation of ammonia to nitrous oxide rather than nitric oxide depends mainly on having a relatively cheap source of oxygen. This has been made possible by recent advances (1,18).
398
INDUSTRIAL A N D ENGINEERING CHEMISTRY
The catalytic oxidation of ammonia was patented by the I.G. Farbenindustrie in 1928-30 (5, 6, 11, 15). Nothing has been done in this country to verify or extend this work, though one paper was published in Russia (IS). The general specifications call for a mixture of ammonia with an excess of oxygen to be passed over a catalyst for the reaction a t a temperature below 530" C. and a t space velocities sufficiently low that nitrous oxide and nitrogen are the principal oxidation products. Some of the catalysts stated to be suitable for this oxidation are platinum, iron oxide with bismuth oxide or manganese oxide, and mixtures of copper oxide with manganese oxide with or without silver (5). It is the purpose of this work to verify this reaction, using a manganese oxide-bismuth oxide catalyst.
~~
b
175
200
225
TEMPERATURE *
F i g y r e 1.
27
250 'C
Vol. 40, No. 3
The nitrous oxide was determined by the catalyst tube method of Kobe and MacDonald ('i'), in which the hydrogen and nitrous oxide were made to react on platinized silica gel a t 515" C. When this method is used the catalyst tube is first filled with hydrogen, then brought to 515 ', and the pressure is adjusted to atmospheric pressure. The hydrogen used later in the analysis is passed over the catalyst several times to remove all oxygen and then stored in a contact pipet until needed in the analysis. The nitrous oxide in the gas mixture is calculated from the decrease in volume due to the reaction N1O H? ----f Nz HLO. The nitrogen in the sample is calculated by difference.
+
+
EXPERIMENTAL RESULTS
For the particular cataylst used in this work, the process variables studied xere temperature, space velocity, ammonia concentration in the ammonia-oxygen mixture, and catalyst life. The effects of these variables are shown in Figures 1, 2, 3, and 4. The efTect of temperature on conversion to nitrous oxide is shown in Figure 1. A gas containing approximately 11% ammonia and 89% oxygen was passed through the catalyst at a space velocity of 3 ml. of gas per ml. of catalyst per minute. Unconverted ammonia and other oxides of nitrogen varied from 0.0 to 2.07,, the balance of the ammonia was converted to nitrogen. A second series of experiments showed a lower conversion than the first series, as shown on Figure 1, indicating that the catalytic activity decreases with time of operation. The effect of space velocity (millimeter of gas per millimeter
Effect of T e m p e r a t u r e on Conversion to Nitrous Oxide
EXPERlMENTAL METHOD
.
The reaction chamber was a 26-mm. Pyrex tube wound with resistancc wire for heating and covered with magnesia insulation. The temperature of the reactor could be varied by changing the electric current in the resistance wires by means of a variable transformer. A 1-mm. Pyrex tube was inserted inside the reaction chamber and passed through the bed of catalyst. An ironconstantan thermocouple could be moved within the small tube to measure the temperature at any central point in the reaction chamber. The catalyst, 20 ml. in amount, was supported on a perforated aluminum plate in the annular space between the two glass tubes. The reaction products from the reactor passed through a glass, water-cooled condenser to cool the gases and remove most. of the water vapor before the gases passed into the sampling bulb. The ammonia and oxygen were from commercial cylinders of the gascs. Their flow rates were measured with small glass orifice mtaters equipped with inclined manometers. CATALYST.The catalyst was prepared by mixing 180 grams of manganese nkratt! with 5 grams of bismuth nitrate and dissolving the salts in dilute nitric acid. The solution was then made basic with ammonium hydroxide and the precipitat,e was spread o n a glass plate in a layer about 0.125 inch thick and divided into small squares. The plates were placed in an oven a t 100" C. until the precipit.ate was dry. The dried precii)itate was heat,ed i n an electric oven a t 375" C. until it attained a characteristic metallic-gray color; this process is supposed to decrease the ability of the catalyst to produce higher osides of nitrogen (13). The catalyst was then screened to pass 6-mesh and be retained on an 8-mesh screen. GAS ANALYSIS.Samples of the reactmionproducts were taken by plaring a gas-sampling bulb in the line carrying the gases from the reactor. Onc hour was allowed for tht! displacement of the stir from the bulb. The gas sample containvd oxygen, nitrogen, nitrous oxide, higher oxidw of nitrogen, arid unretxted ammonia. A 100-ml. mine air type of buret, was used; mercury was the confining liquid and a small quantity of water was kept on the surface of the mercury to ensure saturat,ion with water vapor. A 100-ml. sample of the reaction products was drawn into the buret and passed first to an absorption pipet cont>aining78% sulfuric acid to remove higher oxides of nitrogen and utireacted .ammonia, then to a pipet containing alkaline pyrogallol to remove the osygen. Because of the small voluine of gas remaining, the absorption of the oxygen could not be completed without increasing the volume of the gascs. This was done by adding a measured volume of oxygen-free hydrogen, about 75 ml., after which the gases. were again passed through the pyrogallol. This final volume of gas minus the volume of hydrogen added was the volume of nitrous oxide and nitrogen in the sample.
SPACE VELOCITY
Effect of Space Velocity on Conversion t o Nitrous Oxide
Figure 2.
TABLE I. COMPARISON O F P H Y S I C A L AND REFRIGERANT PROPERTIES OF NITROUS OXIDEASD Conrnrox REFRIGERANTS Critical temperature, e F. Critical pressure, lb./sq. inch Triple point Temperature, F. Pressure, lb./sa. inch abs. Latent heat of fusion Normalboilingpoint, OF.
N2O
cot
SO2
97 8 1054
88.0 1072
315.4 1143
-131.5 12.74
-69.9 75.1
-103.4 0.24
-107.9 0.9
81.5 -109.3
49.7 -14.0
151 -28.0
167.5
589.3
63.8 -127.2 161.7
Vapor pressure a t standard condensaLion, temperature, 86' F., Ib./sq. inch Latent heat of vaDoriaa-
~
-, - -. - _. ,
(sublimes)
.. . . ..
"3
271.4 1657
303
332.4
11.7
34.3
917
1045.9
66.2
169.2
0.308
0.267
0.154
0.1227
March 1948
INDUSTRIAL A N D ENGINEERING CHEMISTRY
of catalyst per minute) is shown in Figure 2. These experiments were conducted a t 200" C. and with a gas containing from 9.7 to 11.4% ammonia. Unconverted ammonia and higher oxides of nitrogen increased from 2.6% at a space velocity of 3.05 ml. to 17.9% a t a space velocity of 6-80 ml. Undoubtedly, this was largely ammonia passing unreacted through the catalyst.
399
than the 90% claimed for an iron oxide-bismuth oxide catalyst a t 275" to 300" C., space velocity of 1000 liters of gas per liter of catalyst per hour for a gas containing 10% ammonia (15), and for which a yield of 87y0 is reported when air is used. Postnikov and co-workers ( l a )report yields of 80 to 88% with a manganese oxide-bismuth oxide catalyst under conditions similar to some used in this work. Undoubtedly, many factors concerning catalyst activity remain to be investigated, for no p r e v h w workers report decreased activity with time of use.
% N< IN GAS MIXTURE
Figure 3.
z
Effect of A m m o n i a C o n c e n t r a t i o n on Conversion to Nitrous Oxide
The effect of ammonia concentration in the gas mixture is shown in Figure 3. These experiments were conducted a t 200" C. and a constant space velocity of 0.5 ml. of ammonia per ml. of catalyst per minute, which is the value corresponding to the maximum in Figure 2. The conversion in gas mixtures containing 9.95 and 11.2y0 ammonia were identical but at higher concentrations the conversion decreased markedly. Again, unreacted ammonia and higher oxides increased with increasing concentration of ammonia in the gas. Air was used as the oxidizing agent under a set of conditions corresponding to the maximum yield obtained with oxygen. The temperature was 200 O C., ammonia concentration was 10% of the ammonia and oxygen present, and the space velocity was 5 ml. of ammonia and oxygen (in the air) per ml. of catalyst per minute. The conversion was 10% lower than when an ammoniaoxygen mixture was used. Although this yield probably could be increased by lowering the space velocity, thereby decreasing the linear velocity of the total gases through the catalyst, another factor must be considered. The product gases from the oxidacost of contion with air are so dilute in nitrous oxide that the * centration and recovery might be prohibitive. As shown in Figure 1, the total time of operation of the catalyst has an effect on its activity. This is shown in Figure 4 for a freshly prepared catalyst operating at 200" C. with a 10% ammo$a gas a t a space velocity of 5 ml. per ml. of catalyst per minute. An attempt was made to reactivate the used catalyst by heating it a t 375' C. for 15 hours, but no improvement in yield was obtained after this treatment. The maximum yield of 71% obtained in this work is lower
\
'
LITERATURE CITED (1) Anon., Chem. Eng., 54, No. 1, 123-31; No. 3, 126-41 (1947). (2) Anon., Refrig. Eng., 52, No. 3, 235,260 (1946). (3) Giauque, W. F., and Stephenson, C. C., J . Am. Chem. SOC.,60, 1389-94 (1938). (4) Hoge, H. J., J. Research Nut. Bur. Standards, 34, 281-93 (1945). (5) I. G. Farbenindustrie, British Patent 325,475 (Nov. 12, 1928). (6) I. G. Farbenindustrie, French Patent 679,541 (July 30, 1929). (7) Kobe, K. A,, and MacDonald, R. A., IND.ENQ.CHEM.,ANAL. ED.,13,457-9 (1941). (8) McFarlan, A. I., Power, 89,365-7 (1945) ; 90, 249 (1946). (9) McFarlan, A. I., Frosted Food Field, 3, No. 2, 2 , 4 (1946). (10) Meyers, C. H., and Van Dusen, M. S., J. Research Nut. Bur. Standards: 10,381-412 (1933). (11) Nagel, A,, and Schlecht, L., German Patent 498,808 (May 28. 1930) ; 503,200 (July24, 1930). (12) Natl. Bur. of Standards, Circ. 142 (1923). (13) Postnikov, V. F., Kuz'min, L. L., an8 Tsal'm, N. K., J. Chem. Ind. (U.S.S.R.), 13,1348-50 (1936). (14) Rynning, D. F., and Hurd, C. O., Trans. Am. Inst. Chem. Engrs., 41,265-81 (1945). (15) Schlecht, L., and Nagel, A., U. S. Patent 1,946,114 (Feb. 6, 1934). (16) Smith, G. F., private communication. (17) Strobach, W., Compressed Gas Mfrs. Assoc. @-oc.,Ann. Rept., 31,49-58 (1943). (18) Sze, M. C., and Wu, C., Chem. Eng., 53, No. 8, 113-5 (1946), RECEIVED
December 26,1947.
END OF SYMPOSIUM
