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Hydrogen from Water Gas' Catalysts for Its Production By R. M. Evans and W. L. Newton FIXEDNITROGES RESEARCH LABORATORY, WASHINGTON, D. C.
HE interest in the commercial production of pure I n the absence of a catalyst the reaction between steam hydrogen has been greatly stimulated in the last few and carbon monoxide is very slow, even a t 550" C., and for years by the rapid growth of two relatively new rapid reaction a t 400' C. a very active catalyst is required. industries, the catalytic hydrogenation of oils and the manu- The success of the process is, therefore, dependent upon facture of synthetic ammonia. As a result of this new int,er- finding a cheap catalytic material sufficiently active to est the patent literature, since 1912 especially, has contained permit operation below 500" C. and at the same time hard a great many proposals for new or improved processes and and rugged enough to withstand long-time operation. Many apparatus for the large-scale production of hydrogen. I n catalysts have been suggested, in most of which the oxides most of these processes hydrogen is made either by the of iron or iron group metals are the active constituents. I n electrolytic decomDosition addition to these, promoters of water or by one of the are suggested, which when water-gas processes. Of the present in small amounts A study has been made of the activity at 444' and methods proposed, the one enhance the activity of the 380' C. of certain precipitated oxides as catalysts for which seems best suited to p r i n c i p a l catalytic subthe catalytic water-gas process. Cobalt oxide and the production of hydrogen stance. Because of the exiron oxide were found to be the best single-component for large-scale a m m o n i a cess of steam in the gas catalysts. Mixtures of these with the oxides of alumimanufacture is the catalytic mixture only noble metals num, chromium, manganese, and potassium as prowater-gas, or Bosch, process. can be used in the metallic moters were also tested. Mixtures of cobalt, alumiI n this process a mixture state. Of these palladium num, and potassium oxides, and of iron, aluminum, of w a t e r g a s and excess and rhodium on asbestos and potassium oxides were found to be best suited to s t e a m i s p a s s e d over a have been proposed. Allow-temperature operation. catalyst a t temperatures though many catalytic maIn the production of hydrogen by the catalytic waterbelow 550" C. and the carterials have been suggested, gas method the sulfur compounds present in water bon monoxide of the water very little has been written gas must be removed by some suitable method of purig a s i s c o n v e r t e d by the a b o u t t h e i r comparative fication if the gas is to be used for the synthesis of steam into a n equivalent efficiency or of the effect of ammonia. The effect of the three forms of sulfur presamount of hydrogen and various materials as proent in water gas, hydrogen sulfide, carbon disulfide, carbon dioxide, according m o t e r s . Taylor2 has reand carbon oxysulfide, upon the activity of the waterto the well-known waterp o r t e d a c t i v i t y tests on gas catalysts, together with the changes occurring in gas reaction, twelve quite different patthese sulfur compounds during the catalytic converented materials. CO HzO Cog -tH2 sion, has been investigated. At this laboratory a study After condensation of the of the catalytic water-gas excess steam the gas mixture process has been made which thus produced contains about 30 per cent of carbon dioxide has so far been mainly a laboratory-scale test of the activity and between 1and 4 per cent of carbon monoxide, which must of various catalyst materials, the object of which has been be removed by subsequent purification. This has usually the development of a catalyst which would be at the same been accomplished by scrubbing with water and cuprous time cheap, rugged, resistant to the action of poisons, and ammonium solutions under pressure. sufficiently active to permit its efficient operation a t relaI n the water-gas reaction a t 500" C. about 10,000 calories tively low temperatures. are given off per mol of carbon monoxide reacting. It is Activity of Catalysts under Standard Testing Conditions possible, therefore, by proper use of heat interchangers to make the reaction autothermal. As the reaction is exotherThe method of testing consisted in passing measured volmic the complete elimination of carbon monoxide is favored umes of steam and water gas over a catalyst a t constant by low temperatures. The values of the .equilibrium con- temperature and analyzing the exit gases for carbon monoxide. stant for the reaction The apparatus used is shown in Figure 1. Water gas was made by blowing steam through an externally heated tube containing willow charcoal, and was comare roughly 4, 8, and 16 at 550°, 4 4 5 O , and 380" C., respec- pressed to about 4 kg. per sq. cm. (65 pounds per square tively. With a ratio of steam to water gas of 3 volumes to inch) for storage. It was a relatively low temperature water 1, the corresponding concentrations of carbon monoxide in gas, containing on the average 33 per cent of carbon monoxide. the equilibrium mixture after the condensation of the water The water gas was purified by passage over a copper deare about 2 per cent a t 550" C., 1 per cent a t 445" C., and oxidizer, through a solution of chromic acid in concentrated sulfuric acid to remove oil vapors from the compressor, and 0.5 per cent at 380" C. finally through a tube of dry soda lime to remove acid spray. 1 Presented before the joint session of the Divipions of Industrial and Very little carbon dioxide was removed by the dry soda Engineering Chemistry and Cellulose Chemistry and the Section of Paint lime. The flow of water gas was maintained at 100 cc. per and Varnish Chemistry a t the 70th Meeting of the American Chemical minute and was measured by means of an ordinary flowmeter. Society, Los Angeles, Calif., August 3 to 8, 1925. Subtitle not included in meeting title. Received March 19, 1926. * "Industrial Hydrogen," 1921. Chemical Catalog Co., New York.
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The flowmeter was recalibrated and the purified gas analyzed in an Orsat apparatus every time a new batch of water gas was made. Steam was generated electrically and the volume introduced was measured by means of a flowmeter with a mercury manometer kept hot by a toluene vapor bath. The steam flow was maintained at 300 cc. per minute, or three times the flow of water gas. Water gas and steam Were mixed and led through a spiral preheating tube into the bottom of the catalyst tube. I n most of the work 10 cc. of 10- to 14-mesh catalyst material was employed. This corresponds to a space velocity of 600 volumes of water gas per volume of catalyst per hour. I n some of the earliest work a space velocity of 1000 was maintained by the use of G cc. of catalyst. I n the first tests the temperature of the catalyst was maintained by means of an electric furnace and measured by a thermocouple within the catalyst mass. Vapor baths mere soon substituted, however, as the boiling points of sulfur and anthraquinone, 444" and 380" C., respectively, were found to be very satisfactory temperatures for the activity tests. After leaving the catalyst, the gas was freed from the excess of steam by cndensatiun, the volume of condensate serving asa check upon the operation of the steam flowmeter. Carbon dioxide was removed by bubbling through strong caustic potash solution and the remaining carbon monoxide and hydrogen were burned with oxygen over copper oxide a t a dull red heat. The carbon monoxide was estimated by dissolving the carbon dioxide formed in a given time, usually 3 minutes, in standard 0.05 N barium hydroxide and titrating back with standard oxalic acid, using phenolphthalein as an indicator. As the measurement of gas flow was made upon the initial water gas because of its constant composition, the analysis gave the volume of carbon monoxide per Yolume of unconverted water gas. However, from the original analysis of the water gas the percentage of carbon monoxide in the dry effluent gas can be calculated readily.
venient'ly added. During kneading a considerable amount of water is removed from the gel and it is usually necessary to refilter. The catalyst is dried, first a t about 100" C. and finally a t about 150" C. Cobalt catalysts were best made by precipitating with potassium hydroxide and boiling until a pink precipitate of cobalt hydroxide was obtained. The use of ammonium hydroxide produced a much softer and less reproducible catalyst. Promoters were added either by precipitating from a solution of mixed salts or by mixing in the desired quantity of promoter during the kneading of the precipitate. The results by both methods were apparently the same. The presence of 5 to 10 per cent of aluminum hydroxide was found to improve the hardness of both iron and cobalt catalysts. Catalysts made by the procedure described were firm gels and did not powder appreciably when squeezed between the fingers. A few catalysts were made in which the iron was precipitated as hydrated magnetite by adding the theoretical mixture of ferrous and ferric salt solutions t o either ammonium or potassium hydroxide. The oxides of pure metals were first tested. As iron and cobalt oxides were the only ones offering any promise as lowtemperature catalysts, the subsequent work was confined to mat,erials having one of these as the principal constituent and containing ot'her oxides as promoters. Of the promoted catalysts tested, a few are listed in Table I which contain varying amounts of the oxides of iron, cobalt, aluminum, potassium, chromium, and manganese. Most other combinations-for example, iron and copper oxides-were found to be poorer catalysts than ferric oxide alone. Table I-Catalytic Activity of Precipitated Oxides Ratio steam to water gas: 3 to I C O in dry Temp. Space Val. C O in exit effluent gas ,\fetal c. velocity 100 vol. water gas Per cent co 444 600 1.5 1.2 300 1000 0.6 0.5 Fc 444 ti00 1.4 1.1 380 600 5.0 3.9 Fen 444 600 1.2 0.9 380 600 7.0 5.6 Cr 444 600 8.1 6.5 380 600 17.0 14.8
Preparation of Catalysts Most of the catalysts tested were gels made by precipitating and drying the metallic hydroxides. A few were made by direct ignition of metallic nitrates, by impregnating refractory materials with very light coatings of active materials, and by the method of Larson and Richardson3 for making ammonia catalysts by electrical fusion of the oxides. The fused catalysts are very hard and rugged, but have very low catalytic activity and offered little promise as low temperature catalysts. The same is true of the materials impregnated with superficial coatings of active material. The precipitated catalysts and those made by direct ignition of the nitrates are about equally active, but it seems possible to prepare a more rugged material by precipitation. The catalysts described in this paper were all made from C. P. chemicals with distilled water. The activity of a precipitated catalyst and its physical ruggedness depend largely upon the method of preparation. I n a comparison of the activity of various catalysts and the effect of promoters it was necessary to adopt a standard procedure for their preparation. The following method has proved most satisfactory in making pure or promoted iron catalysts: A dilute solution of metal salts, usually the nitrates, is heated t o about GO" C. and the hydroxides are precipitated with ammonium or potassium hydroxide. The precipitate is washed well five or six times by decantation and filtered. It is then kneaded either by hand or in a kneading machine. During this kneading process certain promoter materials, especially soluble substances such as potassium hydroxide, may be cons THISJ O U R N A L , 17, 971 (192.5)
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: ; I CU i vi }
450
1000
Practically no conversion
w ! _. V I a
Precipitated as FeaOa.
Table 11-Catalytic Activity of Promoted Precipitated Oxides Ratio steam t o water gas: 3 to 1 Space velocity: 600 4' 2 ' .-380' C.-CO in dry C O in dry vel. co in exit e f f l u ~ ~ g a sco ~ oin~ exit . Material and aowox. compn. 100 vol. water gas cent 100 vol. water gas Per cent 0.5 0.7 1.2 0.9, 9 9 7 Co 1 % K 0.P 0.3" 1.1 1.4= 97g Co: ?YOAI, 1 % K 0.6: 0.8 1.0 1.3 94% C o , 0% AI, 1% K 5.2 6.5 1.2 1.6 99'/ Fe l Y c K 2.3 3.0 1.2 1.6 9 9 g Fe' 1 % Kb 7.4 9.2 1.1 1.5 90% Fe: ;Oh A1 2.3 1.7 1.0 1.3 94y0 Re, 2% AI, 1% K 2.1 1.6 1.1 1.4 97% Fe, 2 % AI, 1% K b 4 .3 5 . 5 0.9 65% Fc, 25% Co, !0% AI 1 . 2 3.0 3.9 1.1 1.5 S5L7 Fe 10% Co 9 % A1 6 4 g Fe: 25% Co,' 10% AI, 0.7 0.9 1.0 1.3 1% K 84% Fe, 10% Co, 5 % AI, 1.9 2.5 1.3 1.7 1% K S 4 T Fe, 10% Co, 5% AI, 0.9 1.2 0.9 1.2 12 K b 2.0 2.6 1.0 1.3 9 4 7 Fe 5 % C o 1% K 1.3 1.0 0.9 S 9 G Fe: 10% Cb, 1% K5 1 . 2 2 .3 3 . 0 1.8 2 . 3 94Yo Fe. 6 7 , Cr 3.2 4.2 1.1 1.4 S 5 7 0 Fe, 15% Cr 5.6 7.0 1.0 97% Fe, 2.5% Cr, '/z% Ce 1 . 3 4.6 5.8 1.0 1.3 95% Fe, 5% M n 3.8 4.9 0.9 1.2 94% Fe, 5% Mn, 1% K
__
b
Tested at 450' and 350' C. with 1000 space velocity. Iron precipitated as FesOd.
May, 1926
INDUSTRIAL A N D ENGINEERING CHEMISTRY
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I
Figure 1
Of all the catalysts tested, those of pure and promoted cobalt oxide were by far the best low-temperature catalysts, in that they alone were sufficiently active to give as low as 0.5 per cent of carbon monoxide in the effluent gas. All the catalysts listed in Table I1 are capable of giving approximately the equilibrium conversion of carbon monoxide a t 444' C. The only basis for comparison is, therefore, their activity a t 380' C., a t which temperature differences between various compositions are clearly indicated. Even a t this temperature a too rigorous comparison of the effectiveness of the various promoters should not be made because in some cases a difference of l per cent of carbon monoxide is about the limit of reproducibility for two different preparations of a catalyst of essentially the same conipositions. As has already been stated, it is particularly difficult to reproduce catalysts containing cobalt oxide when ammonia is used as the precipitating agent. The results do show the value of aluminum and potassium oxides as promoters. Somewhat better results appear to be given by iron catalysts if the iron is precipitated as hydrated magnetite instead of ferric hydroxide. One important property of the catalysts which i t has been impossible to study completely, owing to the length of time required, is their physical ruggedness and length of life. Small changes in catalyst composition have very little effect in this regard compared with that due to changes in the method of preparation. Cobalt catalysts are as a rule softer than the iron catalysts, but, as has already been noted, may be obtained in a fairly satisfactory condition by precipitation with potassium hydroxide and the addition of a small amount of aluminum hydroxide. Although a used catalyst is softer than a freshly prepared one, none of the iron catalysts tended to powder during the normal testing treatment. Activity Tests in the Presence of Sulfur Compounds
In order to make predictions concerning the operation of water-gas catalysts in commercial practice, it is necessary
to consider the effect of impurities in the water gas. As the principal impurity in industrial water gas is sulfur, its effect upon the activity of the various water-gas catalysts must be taken into account. Experience with metallic catalysts for ammonia synthesis has shown them to be poisoned by even minute concentrations of sulfur in any form. At some stage during the production or subsequent purification of hydrogen by the catalytic water-gas process, these impurities must be completely removed if the hydrogen is to be used for the production of synthetic ammonia. Finally, side reactions are known t o occur between the reactants of the water-gas reaction and certain sulfur compounds, which have an important bearing upon their ultimate elimination from the gas. This paper presents data for the effect of hydrogen sulfide, carbon disulfide, and carbon oxysulfide in various concentrations upon the operation of water-gas catalysts. From the work it was hoped to learn, first, the effect of each sulfur compound upon the activity of the water-gas catalyst; and second, the completeness with which these sulfur compounds are converted to hydrogen sulfide under the conditions of the water-gas conversion. For these tests a definite procedure was chosen arbitrarily. Ten-cubic centimeter samples of the catalysts were tested a t 444' C., with a space velocity of 600 volumes of water gas per hour per volume of catalyst, and with a fixed ratio of 3 volumes of steam to 1 of water gas. The same apparatus was used as in the efficiency tests with pure water gas, and the volume of carbon monoxide in the dry effluent gas was again used as a measure of the activity of the catalyst.. . The desired quantity of hydrogen sulfide, carbon disulfide, or carbon oxysulfide was added to the purified water gas before its mixture with steam. Considerably larger amounts of each gas were added than would be expected in technical water gas, in order to be able to obtain a definite effect in a shorter test, and also in order that by the simpler analytical methods the completeness of the side reactions with carbon
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disulfide and carbon oxysulfide might be followed. An iron catalyst and a cobalt catalyst were used in the tests. Their approximate compositions were:
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drogen sulfide the time of activation was about 30 minutes, while with 3 per cent hydrogen sulfide it was between 1 and 1.5 hours. The amount of sulfur which had been taken up by the Catalyst No. 1 catalyst when exposed to various concentrations of hydrogen 95 parts b y weight of Fe precipitated as Fe(0H)a 5 parts by weight of A1 precipitated as Al(0H)a sulfide was obtained by analysis. The results of three analy1 part by weight of K as K O H Precipitated with NH40H from nitrates and KOH added ses gave 0.16, 0.49, and 2.19 per cent sulfur in the catalyst Catalyst N o . 2 after continued treatment with, respectively, 0.5, 1.0, and 99 parts by weight of Co precipitated as Co(0H)z 3 per cent of hydrogen sulfide in the water gas. 1 part b y weight of K as K O H Precipitated with KOH from the nitrates and boiled The nature of the reaction between an iron catalyst and hydrogen sulfide can be explained from these results. As A third catalyst was used in the tests with hydrogen sulfide. the concentration of hydrogen sulfide increases the amount It was similar to the first catalyst except that the iron was of sulfur retained by the catalyst increases and the efficiency precipitated as hydrated Fe304 instead of Fe(OH)3, and the of the water-gas catalyst decreases, but soon reaches a aluminum content was 2 per cent instead of 5 per cent. No constant value for any fixed concentration of hydrogen sulfide. difference could be noticed between the results with this At any given concentration a steady state must be attained catalyst and the first one. at which a virtual equilibrium is established between the Eflect of Hydrogen Suljide catalyst and the hydrogen sulfide, steam, and water gas of Hydrogen sulfide was made from ferrous sulfide and the gas mixture. The cobalt catalyst (No. 2) was tested with from 0.2 to sulfuric acid in a Kipp generator. It was diluted with hydrogen to make the measurement of small quantities of 0.5 per cent of hydrogen sulfide in water gas. The activity it by means of a flowmeter more accurate and was kept over of the catalyst remained unchanged for a 7-hour treatment dilute sulfuric acid. The mixture was analyzed from time with 0.2 per cent hydrogen sulfide, the catalyst giving equilibrium conversion during the entire period. Analysis of the to time during the experiments. I t was found with samples of the iron oxide (No. 1) that effluent gas showed no trace of hydrogen sulfide leaving the its activity on gas containing a definite concentration of catalyst, and a zone of discoloration could be seen moving hydrogen sulfide soon reached a constant value lower than up the catalyst bed, showing the progress of the sulfur conthat for pure gas. The efficiency measurements were fairly tamination. From this time on continued treatment with reproducible with different samples of the same catalyst gas containing hydrogen sulfide caused a steady decrease and with approach to a given concentration of hydrogen in the activity of the catalyst. By the time the first trace sulfide from a higher or lower one. On treatment with pure of hydrogen sulfide was detected in the effluent gas the catagas the efficiency of the poisoned catalyst rose quickly to its lyst was not giving more than 50 per cent conversion. The initial pure gas value. This behavior is illustrated by the test was stopped at this time and the catalyst was found by analysis to have gained sulfur equal to 4.5 per cent of its data shown in Figure 2. weight. The experiment was repeated with another sample of the catalyst, with the same results; and an attempt was made to reactivate the catalyst by treatment with pure water gas and steam, which was unsuccessful, the catalyst showing no tendency to regain its initial activity. The results indicate that a cobalt catalyst will ultimately be rendered inactive, even by very small concentrations of hydrogen sulfide, the time required depending upon the initial activity of the sample. I n the present experiments the period of unimpaired activity a t the start was due to the fact that, a t the arbitrarily chosen testing conditions of 445' C. and I 8 /O I2 /4 600 space velocity, the catalyst was initially active enough Ti'me in Hours to give equilibrium conversion, even after a considerable Figure 2-Effect of Hydrogen Sulfide on Activity of Iron Oxide portion of the sample was rendered inactive by the action Catalyst of the hydrogen sulfide. The activity of the iron oxide catalysts with varying Effect of Carbon Disulfide concentrations of hydrogen sulfide is shown in Table 111. The catalyst was operated with a constant amount of hyThe carbon disulfide was introduced into the gas stream drogen sulfide in the gas for a t least 3 hours in order to be by leading the water gas through a bubbler containing liquid sure that the efficiency of the catalyst had reached its con- carbon disulfide, which was kept a t a desired temperature by stant value for the concentration of hydrogen sulfide present a liquid ammonia or alcohol-carbon dioxide bath. The and did not decrease with time. amount was varied in this way from approximately 0.1 per cent to 1.8 per cent. Table 111-Efficiency of Catalyst 1 in Presence of Hydrogen Sulfide In the tests with the iron oxide catalyst the presence of CO in HsS in gas effluent gas from 0.6 to 1.8 per cent of carbon disulfide in water gas was Per cent Per cent found to be very deleterious. The activity of the catalyst 0.0 1.0 0.5 1.3 fell off very rapidly and a catalyst once poisoned responded 0.8 1.9 very slowly and incompletely to reactivation with pure gas. 1.0 2.9 1.3 3.2 The first tests were made with water gas containing be3.0 3.7 tween 1.7 and 1.8 per cent of carbon disulfide to ascertain When a poisoned catalyst was again operated with pure the completeness of the reaction between carbon disulfide water gas, the time necessary for reactivation was found to and steam to give hydrogen sulfide and carbon dioxide, which vary with the concentration of hydrogen sulfide to which it is known to occur in the presence of oxide catalysts of this had been subjected. After running with 0.8 per cent hy- kind.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
The gas leaving the catalyst was tested qualitatively for carbon disulfide by means of the copper zanthate test, but none was detected. The exit gas was also analyzed for hydrogen sulfide by bubbling the gas through standard iodine solution and titrating back with thiosulfate solution. At first most of the sulfur was retained by the catalyst and the activity of the catalyst fell off rapidly. The evolution of hydrogen sulfide increased as the testing Continued, but by the time the amount, was equivalent to the carbon disulfide added the catalyst’s efficiency had dropped almost to zero. On analysis the catalyst was found to contain 21.8 per cent of sulfur a t the inlet end of the catalyst tube and 14.3 per cent of the sulfur a t the exit end. A second sample of the catalyst retained some catalytic activity after treatment with water gas containing from 0.6 to 0.9 per cent of carbon disulfide for 29 hours, a t which time the concentration of hydrogen sulfide was again equivalent to the amount of carbon disulfide added. The reactivation of this catalyst was studied by operating with pure water gas and steam. The efficiency of the catalyst increased quite rapidly a t first but more and more slowly as time went on, and a t the end of 50 hours the carbon monoxide leakage was still 3.2 cc. per minute as compared with 1.3 cc. per minute before the catalyst was poisoned. About 1000 cc. of hydrogen sulfide were given off by the catalyst during the entire test, and the catalyst was found by analysis still to contain 3.9 per cent or 0.42 gram of sulfur. A third sample of the catalyst was run with water gas containing between 0.1 and 0.15 per cent of carbon disulfide, an amount more comparable with what is probably the maximum concentration of carbon disulfide, about 0.02 per cent, to be expected in commercial water gas. In one hour the carbon monoxide leakage past the catalyst rose from the pure gas value of 1.3 cc. per minute to 2.1 cc. per minute. As no further decrease in the activity of the catalyst occurred on continuing the test for 8 hours, and as the amount of hydrogen sulfide in the effluent gas was approximately equivalent to the amount of carbon disulfide added, i t appeared that the catalyst had reached a steady state. The above figure was taken, therefore, as the true value for the activity of the catalyst with gas containing 0.1 per cent of carbon disulfide. On again passing pure gas over the catalyst for 2 hours, its activity rose to substantially its initial value. The effect of carbon disulfide upon an iron oxide catalyst may be summarized as follows: The difference between the action of hydrogen sulfide and of carbon disulfide is merely one of degree, the poisoning action of a small concentration of carbon disulfide being as serious as roughly ten times as much sulfur as hydrogen sulfide. With the cobalt oxide catalyst the effect of the carbon disulfide was cumulative and ultimately destroyed its catalytic activity, but the amount of sulfur in this form necessary to poison completely the catalyst was again less than was the case with hydrogen sulfide. With about 0.15 per cent of carbon disulfide in the water gas, the catalyst gave only about 50 per cent conversion when analysis showed it to have retained only 0.75 per cent of sulfur. The exposed catalyst was distinctly changed both as to the color and general appearance of the granules. No carbon disulfide was in the effluent gas, but a t the end of the test a trace of hydrogen sulfide could be detected. Once poisoned, the catalyst showed no improvement in activity on operation with pure water gas and steam. Effect of Carbon Oxylsuljde Carbon oxysulfide was made by acidifying a solution of potassium thiocyanate with about 15 N sulfuric acid. The gas was freed from carbon dioxide and hydrogen sulfide by bubbling it through 30 per cent NaOH solution in which
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concentrated carbon oxysulfide is the least rapidly dissolved.
It was diluted with water gas in order to facilitate its introduction through a flowmeter. The testing conditions were the same as for the tests with hydrogen sulfide. The gas leaving the catalyst tube was tested for both hydrogen sulfide and carbon oxysulfide by dissolving out the hydrogen sulfide in an iodine solution made acid with hydrochloric acid, by which carbon oxysulfide is not readily dissolved, and then dissolving the carbon oxysulfide in a solution of lead acetate in potassium hydroxide. I n the tests upon the iron oxide catalyst approximately 0.5 per cent of carbon oxysulfide was present in the water gas and the effect upon the activity of the catalyst could not be distinguished from that of a same amount of hydrogen sulfide. After 1 hour the amount of carbon monoxide in the effluent gas had risen from 1.2 cc. per minute with pure gas to 1.8 cc. per minute with the gas containing carbon oxysulfide. From this point no further decrease in the activity of the catalyst was detected, although one test was continued for 19 hours. No carbon oxysulfide was detected in the gas leaving the catalyst, although hydrogen sulfide was found in increasing amounts as the experiment continued. As before, the catalyst soon regained its initial activity upon shifting back to pure gas. With the cobalt oxide catalyst the addition of carbon oxysulfide again caused a rapid falling off in efficiency and resulted finally in the complete poisoning. The fact that the effect of carbon oxysulfide upon an iron oxide catalyst was indistinguishable from that of hydrogen sulfide in the same concentrations indicates the readiness with which carbon oxysulfide is decomposed by steam. This reaction is known to take place slowly a t room temperature to give hydrogen sulfide and carbon dioxide. Under the conditions of these tests the carbon oxysulfide may have been completely decomposed before ever reaching the catalyst, or at least by a small portion of the catalyst present. From the results of the experiments it is obvious that the removal of sulfur compounds from water-gas hydrogen will depend upon the type of catalyst employed. For the use of a cobalt oxide catalyst in an attempt to obtain a nearly complete low-temperature conversion of the carbon monoxide in water gas, it would be necessary to remove sulfur compounds prior to the water-gas conversion. With an iron oxide catalyst, on the other hand, it is doubtful if any preliminary removal of sulfur is either necessary or justified. The activity of the catalyst would not be seriously affected by the total sulfur content of water gas made from a good grade coke, probably never more than 1 1 mg. per liter (50 grains per 100 cubic feet), and carbon disulfide and carbon oxysulfide would be converted into hydrogen sulfide by interaction with steam in the presence of the catalyst. All of the hydrogen sulfide in the gas following catalytic conversion could then be removed along with the carbon dioxide by whatever method was employed to remove the latter. No attempt was made to determine the *effect upon the water-gas catalysts of the organic sulfur compounds known to be present in small amounts in water gas such as thio ethers, mercaptans, and thiophene. Their effect should be no more serious than an equal amount of carbon disulfide and their catalytic conversion into hydrogen sulfide by steam can be reasonably expected.
Organic Rubber Accelerators-Correction In the list of patents in the article under this title, THIS JOURNAL, 18, 316 (1926), Mr. Cadwell is the inventor of the patents attributed to Caldwell.
