Sept., 1921
775
T H E J O C R X A L OF INDCSTRIL4L A N D E N G I N E E R I N G C H E M I S T R Y
The Preparation of Ethylene by Hydrogenation of Acetylene l S 2 B y William H. Ross, James B. Culbertson and J. P. Parsons CHEMICAL LABORATORY, EDGBWOOD .\RSBS.4L,
The earliest work on the hydrogenation of acetylene was done by Sabatier and Senderens during the course of their general investigations on the hydrogenation of organic compounds by catalysis." It was obserred that when one volume of acetylene and three volumes of hydrogen were passed through a tube containing reduced nickel the temperature rose to 100" to 150°, and tlie recorered gas consisted almost entirely of ethane and hydrogen. When the proportion of hydrogen was reduced to two volumes, the recovered gas consisted of 5.3 per cent acetylene, 15.0 per cent ethylene, and 79.1 per cent ethane. On reducing the proportion of hydrogen still further, the nickel became hotter, aromatic hydrocarbons were formed, and the recovered gas analyzed as follows: acetylene, 23.0 per cent, ethylene 18.3 per cent, ethane 61.0 per cent, and hydrogen 2.5 per cent.& A similar result was obtained with platinum, but a t the same temperature this catalyst is slower in its acti0n.j Reduced copper a t temperatures of 150" or above also acts as a catalyst in bringing about the combination of hydrogen and acetylene to form ethylene mixed with other hydrocarbons, I t was found, however, that when the mixture contained half its volume of acetylene the reaction was attended by the formation of cuprene and that this metal was therefore less promising than nickel for the hydrogenation of acetylene.6 Paal and his eo-workers found that combination of hydrogen and acetylene occurs when a mixture of these gases is shaken with a colloidal solution of platinum or palladium in ~ a t e r . ~Using . equal volumes of the gases mentioned, there was recorered in this way a gas which analyzed 80 per cent ethylene.s The reaction between the gases in this process is a relatirely slow one, however, and when an excess of hydrogen is used ethane is formed, as in the case of nickel catalyst. The present paper describes experiments t h a t were undertaken to increase the yield of ethylene in the hydrogenation of acetylene by means of nickel.
PREPARATION OF SICKEL CATALYST The catalyst was prepared from pure nickel nitrate, ac~ oxide cording t o the method of Sabatier and E ~ p i l . The preparecl from the nitrate was reduced to metallic nickel with hydrogen in the apparatus represented in Fig. 1. I n order to remove the last traces of moisture and of oxygen from the hydrogen it was passed through sulfuric acid in the wash bottle E, over copper gauze, G, heated t o redness in the electric furnace F?,and finally over sticks, H, of solid potassium hydroxide. At this point the flow of hydrogen was divided and directed into teach of four tubes, I, containing the nickel oxide to be reduced. The tubes were placed in an electric furnace, F z , and during he reduction were maintained at a temperature of 3000, a s inclicated by a thermometer placed in one of the tubes. The reduction of the oxide to metallic nickel was assumed to be complete when the moisture which first formed on the walls of the tubes leading to the absorption traps had conilKeceived J u n e 15, 1921. 2PuBlished b y permission of the Director of t h e Chemical Warfare Service. Paul Sabatier, '' La catalyse en chimie organique." * C o m p t . rend., 128 (1899), 1173. C o m p t . rend., 131 (1900), 40. 6 C o m p t . ?end., 130 (1900), 1.569. ' B a r . , 48 119161, 276, 1196, 1202. 8 Cham.- Z t y . , 26 (1912), 60. Cowapt. vend., 158 (19141, 668.
EDGEWOOD, 3IARYLARD
pletely disappeared. When the furnaces were shut off for the night or a t the elid of the reduction, the outlets of the traps J were closed, the hydrogen cylinder was shut off, and in its place there was joined in with the apparatus by means of the 3-way stopcock the reservoir of hydrogen, D. I n this way the catalyst could be cooled in hydrogen without any decrease in pressure occurring in the tubes.
i
FIG.
1
Each tube in which the nickel oxide was reduced was about 30 em. long and 2 em. in diameter, and was sealed at each end to a coarse capillary tube about 10 em. long. The nickel oxide was placed in the tube after one of the capillary tubes had been sealed on. The quantity of oxide taken amounted to about 20 g., sufficient t o fill the tube about onethird full. This was spread out in a train covering the whole length of the tube when placed horizontally. Metallic nickel deposited on 20-mesh pumice was also used. APPARATUS AKD METHOD
In testing out the action of nickel catalyst on mixtures of hydrogen and acetylene use was made of the apparatus represented in Fig. 2. The two gases were measured and mixed in tlie graduated gas buret C, of 300-cc. capacity. The tube containing the reduced nickel is represented at G in the figure. P is a manometer in connection with the tube, and H is a graduated receiver in which the gases could be collected over mercury after passing through or over the catalyst.
i7
b
FIG.2
Before introducing the hydrogen-acetylene mixture into the catalyst tube, the hydrogen remaining in the tube after the reduction of the nickel was pumped out to a pressure of about 6 em., as indicated by the manometer. This was done by closing the stopcock A, and opening A,. The leveling bottle of the receiver H: was then lowered BO as to create a
'
776
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
decrease in pressure within the catalyst tube. The gas withdrawn into H was discharged through the outlet B,, and the process was repeated if necessary until the desired vacuum was obtained. B y cautiously turning stopcock A, the gaseous mixturc from the buret C could be passed over the catalyst at any desired rate, as indicated by the mercury trap D; or by opening stopcocks E and A, the mixture could be passed quickly into the catalyst tube to normal pressure and left in contact with the catalyst as long as desired. This latter procedure was followed in most of the experiments. When equal parts of hydrogen and acetylene combine to form ethylene a reduotion in volume occurs to one-half of the original mixture, while a still greater decrease in volume occurs if the reaction proceeds to paraffin forniation. Any reaction which takes place when a mixture of hydrogen and acetylene is quickly passed t o normal pressure into a n evacuated catalyst tube will therefore be iiidioated when connected with the apparatus of Fig. 1 by a rise of the mercury in the manometer F. The time taken f o r the mercury t o rise any given height will likewise inclicate the rapidity at which the reaction takes place. With a n active catalyst at room temperature and in a tube holding about 75 cc. of free gas, the column of mercury in the manometer after adding a mixture of equal volumes of hydrogen and acetylene was often observed to rise to a height of 38 em. in 1.5 min. With an inactive catalyst, on the other hand, no change took place in the level of the mercury.
ADSORPTION OF HYDROGEN St the end of the first day's experiments the hydrogenacetylene mixture that had been in contact with the catalyst was pumped out, and hydrogen was added to normal pressure, with a view to decreasing the danger of any leak into the apparatus while standing over night. Instead of the pressure remaining constant a s was expected, the manometer indicated almost as great a degree of exhaustion within the tube as before the hydrogen was added. A similar result was also observed, but to a less marked extent, when acetylene was passed into a n evacuated tube that had previously contained hydrogen. However, when a tube containing freshly reduced nickel was exhausted in the same way and hydrogen was introduced again, no decrease in pressure occurred. These results could be explained if active nickel has the power of adsorbing a n appreciable amount of hydrogen o r acetylene, which is retained on the surface of the finely divided metal after the free gas within the tube had been pumped out. Experiments were accordingly undertaken to measure the extent of such adsorption of hydrogen, acetylene, and ethylene as occurred in the catalyst used in the experiments. This work has not yet been completed, but the preliminary results indicate t h a t a t ordinary temperature hydrogen is adsorbed in active nickel to a considerably greater extent than in coconut charcoal.' The fact being established that the active nickel used in these experiments contained adsorbed hydrogen, a further study was made of its action by exhausting a tube containing active catalyst and then quickly passing in acetylene alone to normal pressure. Reaction at once took place, as indicated by a rapid rise of the mercury in the manometer. The tube was then pumped out as before, and acetylene was again added. On repeating this treatment a number of times it was found that acetylene could be left in con* C f Id. Troast and P Hautefeullle Oampt v m d 80 (18'711) 7 8 8 ' P 'Baxter Am Uh&, J 22 (i800) dCil. ;r'dolf Sieveit# I;: pkyeiL C h e d 60 '(1907 lg9 : 77 ( I d ) , CiOi : M. Mayer and V. Altma'er Be;. 4 1 (I90d' 8062: 0 , Neuman and .'E Streintzl, Nonatah f2 (189,$, 642' I ,Rlrhards and A, B, Cuahman, Proo, Am. &cad,, 84 (18 ), 88'5,
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Vol. 13, No. 9
tact with the catalyst indefinitely without any change taking place in its composition. That the catalyst still remained active was shown by pumping out the acetylene and filling the tube with hydrogen. A marked reduction of pressure quickly took place, hydrogen disappeared, and the recovered gas consisted largely of ethane. By repeating the treatment with hydrogen, the acetylene in turn was eliminated and hydrogen could then be left in contact with the catalyst without any reduction in pressure taking place. These results indicate that acetylene will react with the hydrogen adsorbed in nickel catalyst; that the adsorbed liydrogen in a n active catalyst can be removed by repeated treatment with acetylene without destroying its activity ; that an active catalyst from which the adsorbed hydrogen has been removed has no action on acetylene; and that acetylene as well as hydrogen is adsorbed in active nickel. MEASURENEXT OF RELATIVE ACTIVITYOF CATALYSTS These results suggested a simple method of measuring the relative activity of different nickel catalysts by connecting each tube in turn in the apparatus, exhausting t o a given pressure, quickly passing in a mixture of equal parts of hydrogen and acetylene to normal pressure, and noting the time taken f o r the mercury to rise to a given height while the tube was maintained at constant temperature. The activity of the different catalysts was assumed to be proportional to the r a t e a t which the mercury rose in the manometer. Having made these determinations in portions of different catalysts, steps were also taken t o determine the adsorbed hydrogen by combustion in the remaining portion of each, with a view to ascertaining if the activity of a catalyst in t h e hydrogenation of acetylene is proportional t o its capacity for adsorbed hydrogen. This work has not yet been completed.
FORMATIOX OF ETHANE Since reduced nickel contains adsorbed hydrogen it will follow that a catalyst tube that has been evacuated and filled with a hydrogen-acetylene mixture of equal parts will actually contain a n excess of hydrogen over that required for ethylene. Reduction of the latter to ethane would therefort be expected. This was found to be the case in a set of experiments in which a mixture of equal parts of hydrogen and acetylene were passed over a new catalyst at ordinary temperature a t the rate of 2 cc. per min. The recovered gas was found to contain only a trace of acetylene, 8.7 per cent of ethylene, and over 80 per cent of paraffins. The experiments were repeated with the reacting tube maintained a t a temperature of -10" by surrounding it with a freezing mixture. I t was thought that a t this temperature the reduction of ethylene to ethane might possibly be diminished o r entirely inhibited. A t the lower temperature the activity of the catalyst was found to have decreased somewhat. By regulating the flow of the gas, samples were sometimes recovered containing upwards of 50 per cent ethylene, but in every case a considerable percentage of ethane was also present. Mixtures of equal volumes of ethylene and hydrogen were substituted f o r the acetylenehydrogen mixtures and passed over the catalyst at the same temperature as before. It was found that when the flow of the gas was sufficiently reduced almost complete conversion into ethane took place. This shows that ethylene as well as acetylene will undergo hydrogenation at a temperature as low as -10". Since there is a reduction in volume to one-half when equal parts of hydrogen and acetylene combine t Q form ethylene while the decrease in volume is still greater if the reaction proaeeds to paraffln formation, it was thought that p a e ~ i b l ythe preeaure of the gases in the catalyd tube might
Sept., 1921
777
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
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YIELDOF ETHYLENE The experiments were repeated with a freshly reduced ,..talyst from which all adsorbed hydrogen was removed by repeated treatment with acetylene. The tube was then exhausted, and equal volumes of hydrogen and acetylene were passed in quickly to normal pressure and allowed t o remain until the pressure decreased t o half an atmosphere. The resulting g a s was then pumped out and analyzed. By this treatment there was obtained a marked increase in the percentage of ethylene formed. Results of analyses of composite samples collected over several days a r e given in Table I. F r o m the results give11 in Table I it is seen that a comparatively small variation in the proportion o f hydrogen to acetylene in the mixture taken produces a marked change in the composition of the recovered gas. Best results seem to be attained when the hydrogen in the mixture is slightly in excess of the acetylene. A further increase in the proportion of hydrogen, however, results in a decrease of ethylene with a corresponding increase of ethane. When a considerable excess of acetylene is taken, no hydrogen is found in the recovered gas and very little ethane. In a series of experiments in which the proportion of acetylene to hydrogen in the mixture w r i e d u p to two parts of the former to one of the latter it was found that the acetylene and ethylene in the recovered gas amounted to 91.5 per cent. The impurities in the gas which came from that occurring in the original mixture amounted to 5.4 per cent, which leaves a total of only 3.1 per cent for the ethane and other constituents which make u p the balance of the gas. The acetylene used in these experiments was obtained from an ordinary acetylene cylinder. An analysis of the gas at the beginning of the experiments showed 94.7 per cent of acetylene which later increased to 96.4 per cent, and finally to 98.1 per cent. The purity of the hydrogen amounted to 99.3 per cent. I f one volume of hydrogen were to combine with one volume of acetylene to give one volume of ethylene, then the impurities in the product, which owe their source t o that occurring in the original mixture, would amount a t first to 6.0 per cent, and with the gases finally used, to 2.6 per cent. The excess of the nonabsorbable and noncombustible components found in the recovered gas, orer what was to be expected from the impurities in the original mixture, was no iloubt due to a
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have some effect on the reaction as suggested by Le Chatelier's principle. The experiments were accordingly repeated by passing the gaseous mixture over the catalyst a t room temperature but a t different pressures below normal. It was not noticed, howerer, that the change in pressure, which was varied from normal t o one-twelfth of a n atmosphere, had a n y appreciable effect, under the conditions of the experiment, in decreasing the proportion of ethane formed.
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slight leak of air through the stopcock A, (Fig. 2 ) as the apparatus was being pumped out. To determine if any slight decomposition of acetylene occurs when in contact with active nickel, an analysis was made for carbon and hydrogen in a catalyst that had been in almost constant use f o r a period of several weeks. Mixtures of equal parts of hydrogen and acetylene were passed over the nickel before being taken from the tube. The analysis as determined by combustion showed the presence in the nickel of 1.09 per cent of carbon and 0.41 per cent of hydrogen by weight. The ratio of hydrogen to carbon in the sample was therefore even greater than that corresponding to methane. I f the carbon occurred in the sample analyzed in the free state, then the hydrogen would have a volume under standard conditions of about 400 cc. per unit volume of the nickel. This is greatly in excess of the quantity found adsorbed in a freshly prepared catalyst. It must therefore be concluded that no appreciable amount of carbon was deposited on the nickel and that the carbon and hydrogen found owe their source to free hydrogen and to hydrocarbons which are either adsorbed in, o r deposited on, the nickel. A-RUBBER BAG GASOMETER F-BY-PASS w / r H STOP COCK a-WATER OUr"LET.9 6-CArA'YSr C.TWO+VAY STO+COCKS H-NANOMETER PYS m L b r €-M€ncuAY TRAP J-COh'7A/NER / - G A S ounErs FOR SYPPIIINC WATER-HfAD
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LARGE-SCALE APPARATTJ~ I n order to collect larger quantities of ethylene than could conveniently be done with the equipment shown in Fig. 2, use was made of a second apparatus as represented in Fig. 3. The hydrogen and acetylene mixture was stored in tlic rubber b a g of the gasometer AI, of 2000-cc. capacity. By means of the pressure supplied by the head of water in the aspirator bottle J, the gas in the bag could be passed a t any rate through the stopcock C,, the mercury trap E, and the catalyst G, and be collected in the bag of the gasometer A,. The water of this gasometer was displaced through B,. The rate a t which the gas was passed over the catalyst coulcl be roughly measured by counting the
778
T Z E JOURNAL OF I N D U S T R I A L A N D EA-GINEERING C H E M I S T R Y
bubbles per second passing through E. On an average each bubble had a volume of 0.06 cc. To remove the adsorbed hydrogen from a freshly prepared catalyst, the tube in which it was contained was evacuated through the outlet I,, after closing C, and opening C,. The latter stopcock was then closed, and the pressure within the tube was brought to normal again by passing in a portion of the hydrogenacetylene mixture from A, through the by-pass F. When the mercury rose to a constant height in the manometer the gas was again pumped out, and tlie process was repeated until the composition of the recovered gas became constant. The same mixture was now passed slowly at practically normal pressure over the catalyst, and the procluct of the reaction was collected i n the gasometer A,. TVith an arrangement of this kind the reaction could be allowed to proceed a t night, as the flow of water from J automatically stopped when the bag in the gasometer A, became empty. Sample A, Table I, represents the average of several unples collected while the rubber bag of the gasometer A, was suspended in the air. The analysis would seem to indicate that a slight exchange of gas had taken place through the walls of the bag. Sample B represents the mean of several collected with the bag in the gasometer as shown.
METHODSOF ATALYSIS I n the preliminary experiments described in the early part of this work, use was made of the Tucker and Moody method f o r determining ethylene in the presence of acetylene.' This method consists in passing the gases through a n ammoniacal silver nitrate solution, which is claimed to remove the acetylene completely, but only a relatively small amount of ethylene. It was found, however, that the quantity of ethylene absorbed so varied with different conditions, particularly with the time the mixture was shaken with tlie silver nitrate solution, as to make the method impractical f o r determining the degree to which the composition of the recovered gas was affected by any modification in the conditions of the experiment. Tests were made with a method developed during the course of this work by Ross and Trumbull,2 of this laboratory. This method, which is based on the volumetric determination of the nitric acid set free when acetylene is precipitated with excess of silver nitrate solution, was found to be rapid, accurate, and simple of manipulation, and it therefore greatly facilitated the progress of this investigation. In the analysis of samples containing ethylene, a s well as acetylene, the percentage of the former present was taken as the difference between the total percentage absorption in fuming sulfuric acid and the value obtained for the percentage of acetylene in the sample. F o r the determination of the other components in the sample analyzed use was made of the usual methods of gas analysis as described in Dennis' '' Gas Analysis." EXPERJMESTS WITH FILCHAR AS CATALYST Since charcoal is known to act as a catalytic agent in bringing about reactions between different gases, as f o r eyample in tlie combination of carbon monoxide and chlorine to make phosgene, it was thought advisable to test any effect which the material might have on the hydrogenation of acetylene. The material selected f o r the experiments consisted of screened filchar of medium-sized grains. This was placed in a Pyrex glass tube similar to that used in the experiments with nickel catalyst. The tube was heated 'J. ;lm. Chem. S o o . , 23 (1901),6 7 1 ; see also Dennis, ysis," p. 249. 2 J . A??%,@~p)72. Soc., 41 (1919), 1180.
"
Gas -4nal-
Vol. 13, No. 9
to 700°, and chlorine was passed through until tlie charcoal had undergone complete chlorination and all tarry matter present in the pores of tlie material had been destroyed. Nitrogen was then passed through the tube at the same temperature as before, followed by enough hydrogen i o drive out the nitrogen, after which the tube was allowed to cool down in an atmosphere of hydrogen. The tube containing the filchar was then placed in an apparatus simil a r to t h a t represented in Fig-. 2. The g a s was pumped out to 6 em. of mercury, and a mixture of hydrogen and acetylene in equal volumes was added a t normal temperature. After standing for several hours the rise of mercury in the manometer amounted to only a few millimeters. A t 50" and even at 100" the rise of mercury was still less than at normal temperature. This shows, as was also confirmed by an analysis of the gas, that under the conditions of the experiment filcliar is without action in bringing about the combination of hydrogen ancl acetylene. ACKKOWLEDGMENT This investigation was suggested by Major TTm. L. Evans, in charge of the Chemical Laboratory of Edgewood Arsenal a t t h a t time, and the authors wish gratefully t o acknowledge the courtesy and kind assistance which was tendered them a t all times during the course of this work. SUMMARY Metallic nickel reduced from the oxide a t 300" has a greater capacity than coconut charcoal for adsorbing hydrogen a t ordinary temperature. When a mixture of equal volumes of hydrogen and acetylene is passed into an evacuated tube about one-third filled with freshly reduced nickel, the hydrogen adsorbed in the nickel, together with that added, map be sufficient to bring about the complete reduction of the acetylene to ethane. By repeating the process of evacuating the tube and passing in tlie hydrogen-acetylene mixture until the excess of hydrogen is used up, a product may be obtained which contains upward of 80 per cent of ethylene. A comparatively small variation in the composition of the mixture taken produces a considerable change in the coinposition of the recovered gas. Best results seem to be obtained when the hydrogen in the mixture is slightly in excess, but a s this is further increased the ethylene decreases, with corresponding increase of ethane. As the acetylene in the mixture is increased the ethane in the product decreases, and the sum of the ethylene and acetylene increases. The adsorbed hydrogen in an active nickel catalyst may be eliminated without destroying its activity by repeated treatment with acetylene. The catalyst is then without action on either ethylene o r acetylene. A simple apparatus is described f o r measuring the relstive activities of different nickel catalysts.
VULCANIZATION O F RUBBER A new method f o r the vulcanization of rubber is described in a recent article by Professor Bruni of the Pirelli Research Laboratories, Milan, Italy. H e states t h a t if certain accelerators such as thiocarbanilide which a r e formed by the action of a n organic amine and carbon bisulfide a r e produced relatively t o the rubber in the nascent state, particularly in the presence of zinc oxide, curing takes place a t ordinary temperatures.
