1090
INDCSTRI.4 L AND ENGINEEli‘I.VG CHEMISTRY
materials the primary or secondary products,6 as the case may be, are dense, adherent, and resistant to diffusion. Increasing the concentrations of sodium chloride in general increases the corrosion rate of the nonferrous metals, while the rates in the cases of iron and steel reach maximum values at a fairly low salt concentration. I n the presence of salt the relative degree of protection afforded by chromates is considerably higher, providing sufficient quantities are used to prevent localized action due to a weakening of the film by the chloride ions. Where the films produced by chromate are only partially protective in distilled water better results are not to be expected in chloride solutions. This statement is borne out by the results which show that, in general, more retarder is required for the same protection as the chloride concentration increases. The effect of temperature on the corrosion in treatment by sodium chloride solutions was investigated for only three materials-namely, iron, steel, and zinc. I n all cases the corrosion rate reaches a maximum a t some temperature between that of the room and the boiling point, At higher temperatures in the stronger salt solutions the use of dichromate is of little use in the case of zinc; for iron and steel adequate protection is obtainable by using more chromate than was used in the same salt solution a t the low temperature. Conclusions
From this investigation it may be concluded that: Soluble chromates may be used for the practically complete protection of iron and steel in distilled water and sodium chloride solutions of all concentrations a t all temperatures up to the boiling point of the solution and for protection of aluminuni in dilute salt solutions a t room temperatures. Chromates may be used for partial protection of copper, 6 The secondary product of corrosion on lead seems to be a film of precipitated lead chromate 7%hich forms a t the anodic points in the porous priman product
Vol. 23, S o . 10
brass, lead, zinc, and galvanized iron in sodium chloride solutions a t room temperatures. Care must be exercised in choosing the chromate concentrations for particular conditions desired, since insufficient quantities of the retarder tend to accelerate the localized corrosion of the metal. (Particularly true in the cases of iron, steel, zinc, and aluminum.) The use of chromates for the protection of zinc in water and in sodium chloride solutions a t elevated temperatures is of litt’le value except in distilled water and very dilute salt solutions. Literature Cited (1) Allen, U. S . Patent 1,287,605 (1918). (2) Bennett and Burnham, T r a n s . A m . Electrothem. .So< , 29, 217 (1916). (3) Byers, J . A m . Chem. Soc., 30, 1718-42 (1908). (4) Callendar, Engineering, 1’20, 340-2 (1925). (5) Cushman, Trans. .Im. Electrochem. Soc., 12, 403-9 (1907). (6) Cushman, E n g i n e e r i w , 87, 710-48 (1908). (7) Cushman and Gardner, “Corrosion and Preservation of Iron and Steel,” pp. 44-111, McGrarv-Hill, 1910. (8) Evans. Chem. Zentr., 11, 238 (1925). (9) Evans, J . Soc. Chem. I d . , 44T, 163 (1925). (10) Evans, I b i d . , 46T, 347-55 (1927). (11) Evans, Am. Inst. Mining Met. Eng., Tech. Publ. 206 (1929). (12) Evans, J . Chem. Soc., 1929, 92-110. (13) Friend, “Corrosion of Iron and Steel.” pp. 161-7, Longmans, 1911. 114) Furney and Young, S a t . Petroleum S e a s , 19, 81, 83-4 (1927). (15) Goudriaan, Chem. TI-eekblad, 16, 1270-85 (1919). r16) McKelvey and Isaacs, Bur. Standards, Tech. Paper 180 (1920). (17) Ornitz, Rrfrigerating Eng., 13, 65-7 (1926). (18) Roberts, Forrest, and Russell, I b i d . , 14, 173-82 (1927). (19) Rohland, Z . Elektrochem., 15, 865-6 (1909). (20) Rohland, Farber-Z., 19, 1123-4 (1914). (21) Rohland, Elektrochem. Z . , 21, 2036 (1914). (22) Russell, Roberts, and Chappell, Refrigerating Eng., 13, 309-16 (19266). (23) Thompson, I r o n and Steel Inst. (London), 1, 232-98 (1916). (24) Thompson, Refrigerating Eng., 19, 87-90 (1930). (25) Tinkler and Masters, A f r a l y s t , 49, 30-2 (1924). (26) Whitman, Chappell, and Roberts, Refrigerating Eng., 12, 158-65 (192,;) (27) Zschokke, Rea. mblal., 20, 165-74 (1923).
Poisoning of Platinum Catalysts for Oxidation of Ammonia’ J . Y. Yee and P. H. Emmett FERTILIZER A N D FIXED NITROGEN IXVESTIGATIONS, BUREAU OF CHEMISTRY A N D SOILS, DEPARTMENT OF AGRICULTURE, Wr\sIiI”Xox, D. C.
Four-tenths per cent of acetylene and 0.07 Per cent catalyst operating a t 700” C. EVERAL investigators have studied the inof hydrogen sulfide are found to exert no injurious effected a conversion of 94.4 fluence of various gaseeffect on a platinum catalyst used in ammonia oxidaper cent of the ammonia in tion when passed continuously for 2.5 and 4.5 hours, an ammonia-air mixture to ous poisons on the activity of platinum catalysts used respectively, into an ammonia-air mixture. Two nitric oxide when operating parts of phosphine per 100 million parts of ammoniaon a gaseous mixture conin the oxidation of ammonia air mixture are enough to lower the Conversion Several taining 0.38 per cent acetyTaylor (,& to nitric 5 ) found t h a t p h o s p h i n e Percent. lene, 0.02 per cent hydroThe apparent conversion of ammonia into nitric gen s u l f i d e , a n d 0.00002 p r e s e n t in a concentration oxide is increased about 3.5 to 4 per cent by the ad&per cent phosphine; and 70.9 as low as 3 parts per 100 tion of 0.07 per cent of hydrogen sulfide either in the per cent when the 0.02 per million had a definite injuripresence or absence of 0.00002 per cent of phosphine. cent h y d r o g e n sulfide was 0 ~ effect s upon the activity An increase of only 1.4 per cent is accounted for by removed, leaving only 0.38 of the c a t a l y s t , b u t t h a t assuming all the hydrogen sulfide to have been quantiper cent acetylene and acetylene and hydrogen sui0.00002 per cent phosphine. tatively oxidized to sulfuric acid. fide had no appreciable influence. Decarriere and his I n view of t h e u n e x p e c t e d co-workers (Z), on the other hand, claimed that both acety- nature of this last mixed-poison experiment and of the defilene and hydrogen sulfide were somewhat toxic. Further- nite disagreement between the authors as to the toxic effects more, the latter authors reported a peculiar protective effect of acetylene and of hydrogen sulfide, a reinvestigation of of hydrogen sulfide against phosphine poisoning. Thus a the influence of the single and mixed poisons has been carried out a t this laboratory. These poisoning studies are a part Received May 21, €931.
S
1
Ii1-D USTRIAL AiYD EiVGINEERI,VG CHEMIXTR Y
October, 1931
of a larger prograin on the catalytic oxidation of ammonia; they are reported a t this time because of a necessary indefinite postponement of the remainder of the program. Preparation of Gases
Acetylene was generated by adding water to calcium carbide prepared from purified calcium oxide and Acheson graphite. The gas was shaken in a bottle containing a saturated solution of copper sulfate and then allowed to stand oyer this solution for 2 days before it x a s condensed in a liquid-air bath. fractionally distilled, and dried over phosphorus pentoxide. Hydrogen sulfide was generated by adding water to aluminum sulfide that was prepared by igniting a mixture of pure aluminum powder and flon-ers of sulfur in theoretical proportion to give A1& The gas iyas collected over water and then twice liquefied in a solid carbon dioxide-alcohol bath, fractionally distilled, and dried over phosphoruh pentoxide.
SL Figure 1-Apparatus
for Oxidation of A m m o n i a
Phosphine, generated from aluminum phosphide with water in an apparatus thoroughly flushed out with nitrogen, was passed through a tube of phosphorus pentoxide and then through a coil kept in a carbon dioxide snow bath to remove traces of liquid phosphine, which, when present, cause the gas to be self-inflammable, The gas obtained was analyzed and diluted with nitrogen to a few parts per 100 thousand parts before being admitted into the air stream at a very slow rate controlled by a flowmeter. All these gases were stored in flasks over mercury. Ammonia was obtained from anhydrous synthetic ammonia. Compressed air was purified by passing it through a furnace containing platinized asbestos a t about 800" C., soda lime, and phosphorus pentoxide towers, and then through a coil immersed in a solid carbon dioxide-alcohol bath.
1091
of the platinum gauze. Samples were sucked into the bulb a t such a low rate as to prevent any possibility of sucking in gas from the scrubbing tower. When the sampling was finished, the bulb was weighed, the contents shaken, and the excess alkali titrated with standard acid. The average m i g h t of the samples was about 0.36 gram. The analytical procedure for determining the per cent conversion is sensitive enough to give an accuracy in individual experiments of less than *I per cent. At first all gas impurities were introduced into the air stream before reaching the mixing chamber but, after a few experiments with hydrogen sulfide, a thin layer of white deposit was found in the mixing chamber, so tube N was added t o introduce this gas into the mixture a short distance from the gauze. The probable nature of the obsewed white deposit was established in the following way: Since mixing dry ammonia and hydrogen sulfide together in a tube showed no reaction, some oxygen or air was introduced, and white fumes appeared in the tube and soon deposited on the walls. This deposit was identified as sulfur. It is probable, accordingly, that the white deposit in the mixing chamber was sulfur. An 80-mesh platinum gauze with 0.003-inch wires was used in the experiments. The gauze temperature was maintained between 800" and 900" C. It was measured by means of a platinum-platiniim rhodium couple in conjunction with a Leeds and Yorthrup Type K potentiometer, and was recorded to the nearest 5" C. The junction of the thermocouple mas electrically welded on to the center of the gauze. With the gas mixture and rate of flow used in these experiments, the conversion of ammonia to nitric oxide is not very sensitive t o temperature change ( 1 ) . Results of Poisons
Acetylene did not seem to cause any injurious effect on the catalyst as shown by the results in Table I. Table I-Effect
of Acetylene o n A m m o n i a Oxidation TOTAI
CONVER- ELAPSED PION TIME^ REMARKS O C c%, Minutes ," 143 870 91.2 70 144 860 0 91.2 225 850 0.2 90.6 345 CzHz introduced at 145 263 min. 146 850 0.2 90 1 370 CzH2 increased t o 0.4% at 387 min 147 560 0 4 91.7 425 CzH? turned off a t 435 min. 148 845 0 91.0 495 0 Experiments started a t 0 time
TEST
TEMP
CnH2 T" 0 ,I
I n Table I1 are shown the results of experiments in which phosphine was used as a poison. As is evident, even 2 parts The platinum gauze ii, Figure 1, was held in place at the of phosphine per 100 niillion parts of gas mixture were tapered end of a quartz tube, B, having an inside diameter of enough to cause a distinct lowering of the conversion, but 6 mm., by slipping over it a small porcelain tube, C. The the effect was only temporary, for the normal conversion was quartz tube was placed in a porcelain tube D, heated by a fur- obtained again soon after the poison had been removed. This was true with 7 or 12 parts per 100 million. With 22 parts nace. Since the reaction took place a t atmospheric pressure, the per 100 million, however, as shown in Table 111, phosphine joints between the Pyrex and porcelain tubes were easily seemed to have a permanent injurious effect on the catalyst. made gas-tight by packing them with moistened soft asbestos The latter Tvould not recover completely after removing the cord. poison from the gas mixture. This gauze, when examined Ammonia and air at flows of 25 and 225 cc. per minute were under the microscope, was seen to be covered with shiny black passed from flowmeters through tubes E and F , respectively, spots. into the mixing chamher G, and then into the catalyst tube. It is also interesting to note that although the conversion The products of the reaction were absorbed in a water scrubbing was lowered by 16 per cent by the addition of phosphine, as tower, K , to prevent the Contamination of the laboratory at- shown in Table 111,only a trace of ammonia was found in the mosphere. samples taken; this also holds true in the experiments in The reaction product was analyzed by Periey's method ( 3 ) . which unpoisoned ammonia-air mixtures were used. A 500-cc. evacuated bulb of known weight containing some Results in Tab!e 111show the combined effect of phosphine standard alkali was attached to tube H , the other end of which and hydrogen sulfide on the catalyst. I n these experiments, was fitted with a quartz tip, L, reaching to within a centimeter the hydrogen sulfide mas introduced through tube .If. dddiApparatus and Procedure
INDUSTRIAL AND ENGINEERING CHEMISTRY
1092 Table 11-Effect
of Phosphine on A m m o n i a Oxidation AVERAGE TOTAL CONVERCONVER-ELAPSED SION SION T I M B ~ REMARKS ~~
~~
TEST
TEMP
187 188 189 190
840 825 825 820
PHa P 0.m 0 0 0.02 0.02
191 192 193
810 805 807
0.02 0.02 0.02
87.3 85.9 87.4
194 195 196 283 284 285
820 820 820 885 885 875
0 0
0 0 0 0.07
89.0 90.3 90.0 91.0 90.3 86.5
286 287 288
875 880 880
0.07 0.07 0.07
84.8 85.0 86.1
289 290 291 292 293 294 295
885 885 880 880 880 875 880
0.07 0.07 0 0 0
85.1 85.1 88.9 88.4 91.1 91.0 91.0
296 297 298
880 880 885
0
0.12
90.2 90.2 84.4
299 300 301 302
875 875 880
880
0.12 0.12 0.12 0.12
83.6 83.1 84.0 83.6
8317
303
885
0
90.1
, .
c.
0 0
0
%
%
90.7 90.0 90.1 88.3
90:3
~~~
Minutes
New pt. gauze
65 85 215 240
..
..
PHa. added 3t 162 min.
270 320 345
87:s
..
..
420 445 475 58n 87 200
.,
230 255 310
80.7 90:6
335 365 410 435 510 535 600
s5:2
..
90: 1
660 690 750
90:2
i75 795 84 5 945
..
.. 0 90.0 885 90.7 0 885 90.4 90:3 0 885 a Experiments started a t 0 time.
304 305 306
1035 1060 1085 1205
PHs turned off a t 365 min
New pt. gauze PHa, added a t 150 min. PHa turned off and expt. stoppedovernight a t 380 min
Expt. stopped overnight a t 600 min. PHI. added at 720 min.
PHn turned off a t 960 min. Expt. stopped overnight a t 945 min.
Effect of Phosphine a n d Hydrogen Sulfide on A m m o n i a Oxidation Av. Av. CHANGE CON- CON- O N ADD- TOTAL VER- ING 0 07% ELAPSED PHa VERSION SION H2S TIME
Table 111-Combined
TEsT
TsrrrP. HIS
% P.P. m.
%
%
0
0
0 0
90.6 .. 90.3 90.4 90:4
o 07 0.07
n 0
94.1 94.2
..
885 885
0.07 0.07
0 0
93.5 94.0
..
362 363 364
885 875 875
0.07 0 0
0 0
0
93.5 93.8 89.8 90.6 9012
365 366 367
880 885 8S5
0 0 0
0.22 0.22 0.22
72.9 74.3 73.6
368 369
880 880
0
0.22 0.22
75.0 75.0 7412
370 37 1 372 373 374 375
880 880 880 875 875 870
0 0 0 0
0
84.8 .. 88.7 .. 89.4 .. 88.3 .. 88.2 88.8 S S '
376 377 378 379
885 880 880 885
0 0
0 0
0.22 74.8 .. 0.22 73.7 .. 0.22 72.5 0.22 7 3 . 1 7 3 : s
380 381 382
885 885 885
0.07 0.07 0.07
0.22 0.22 0.22
383 384
890 885
0.07 0.07
0.22 78.6 0.22 78.0
385 386 387
885 880 875
0 0 0
0.22 0.22 0.22
388 389 390
875 880 880
0.07 0.22 79.7 0.07 0.22 80.8 0.07 0.22 79.4 80'
OC.
354 355 356
890 885 880
0 0
357 359
885 885
360 361
0
0 0
0 0 0
0
0
76.2 78.0 78.6
75.0 76.9 76.2
7*
+3.4
.. , .
..
.. .. ,.
7?:8
+4.3
.. 70'
.. +4
Minities 65 New pt. gauze 90 120 HIS added a t 135 min. 200 265 HzS turned off a t 405 min. 310 360 Expt. stopped overnight a t 405 min. 405 450 470 PHr added a t 475 min. 535 560 585 PHs turned off at 705 min. 635 680 Expt. stopped overnight a t 680 min. 815 935 950 970 1030 1055 PHI added at 1055 min. 1145 1170 1190 1220 HIS added at 1230 min. 1280 1300 1325 PHa and HIS turned off a t 1375 min. 1355 1375 Expt. stopped overnight a t 1375 min. 1430 1450 1475 HnS added at 1490 min. 1540 1555 1570
Vol. 23, No. 10
tion of 0.07 per cent of this gas to the ammonia-air mixture caused an absolute increase of 3.4 per cent in the conversion. Next, the combined effect of phosphine and hydrogen sulfide on the catalyst was determined. After an average efficiency of 73.7 per cent had been obtained by the addition of 22 parts of phosphine to 100 million parts of the gas mixture for 2.5 hours, 0.07 per cent of hydrogen sulfide was added. During this experiment, which lasted for 2 hours and 25 minutes, the average conversion was 77.8 per cent, shoning an increase of 4.3 per cent. This experiment was repeated and the results showed an increase of 4 per cent. This increase is, within experimental errors, the same as that observed when 0.07 per cent hydrogen sulfide alone was added. Discussion of Conversions The 3.5 to 4 per cent increase in apparent conversion from the presence of 0.07 per cent hydrogen sulfide is in good agreement with the 3.5 per cent increase obtained by Taylor and Capps ( 5 ) using the same amount of the gas. The 0.07 per cent hydrogen sulfide would, however, if completely oxidized to sulfuric acid, result in an apparent increase of 1.4 per cent in the conversion rather than the 3.4 to 4 per cent actually observed. The calibration of the hydrogen sulfide flowmeter was finally checked in two separate determinations by collecting the samples in gas burets by the displacement of water. The apparatus was so arranged that copper sulfate solution could be added t o precipitate all of the collected gw. Precautions were taken to prevent any possible escape of hydrogen sulfide. The precipitated copper sulfide, after being washed free of copper sulfate, was ignited in air to the oxide. This was then dissolved in acid and the cogper was determined electrolytically. The calibration showed that the hydrogen sulfide flow used in the experiments corresponded to 0.0718 per cent and 0.0711 per cent of the total gas flow. It seems, accordingly, that the hydrogen sulfide in some way effects a definite increase in the conversion of ammonia to nitric oxide compared to that obtained on ammonia-air mixtures. This increase, contrary to the results of DecarriBre and his co-workers, seems to be the same in the presence as in the absence of phosphine in the ammonia-air mixture. The course or mechanism of this apparent increase in conversion brought about by the addition of hydrogen sulfide is not clear and has not been established in the present work. Results of the present authors agree with those of Taylor and of Decarriere as regards the effect produced by 0.00002 per cent phosphine, The conversion changed in all cases from between 90 and 95 per cent to between 70 and 75 per cent in the presence of the above phosphine concentration. Acknowledgment The writers wish to express their appreciation to Miss E. Z. Kibbe, who made all the analytical determinations except those for nitrogen oxides. Literature Cited (1) (2) (3) (4) (5)
Andrussow, Z. angew. Chem.. 40, 166 (1927). DecarriLre, Compl. rend., 173, 148 (1921); 174, 460 (1922) Perley and Smith, IND. ENG. CHEM., 17, 258 (1925). Taylor and Capps, Ibid., 10, 457 (1918) Taylor and Capps, Ibid., 11, 27 (1919).
Oil Pollution of Waters Decreases-Pollution of inland and coastal waters in the United States is decreasing. Of the fortyfour states questioned by the American Engineering Council's Joint Committee on Oil Pollution, twenty-five reported improvement. I n eleven states oil pollution was believed t o be on the increase.
