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INDUXTRIAL AND ENGINEERING CHEMISTRY
Vol. 20, No. 5
Synthesis of Higher Hydrocarbons from Water Gas' David F. Smith, J. D. Davis, and D. A. Reynolds PITTSBURGH EXPERIMENT STATION, U. S. BUREAUOF MINES.PITTSBURGH, PA.
EPORTS by Fischer and Tropsch2 and by Elvins and product could be accurately determined. Gas analyses NashS of the production, from water gas a t atmos- of the incoming and exit gases were made at intervals. pheric pressure, of higher hydrocarbons resembling Preparation of Catalysts those of natural petroleum, led the present writers to start an investigation of the process. I n view of the meagerness IRoru-This was the ordinary ammonia (1) PROMOTED of the data as yet available it has seemed desirable to present catalyst kindly supplied by the Fixed Nitrogen Research the results thus far obtained in this work. Laboratory. It was made by the reduction of artificial Although Fischer mentions various substances as possible magnetite promoted with potassium and aluminum oxides. catalysts, he does not give definitely the composition or (2) COBALT-COPPER-CHROMIUM OXIDE-A solution conmethod of preparation of the various catalysts he uses, or taining 400 grams Co(N0&.6HzO, 246 grams CrCla, and the corresponding yields. He states that he has obtained 16 grams CuS04.5Hz0was precipitated with NaOH. The 100 arams of product from a cubic meter of water gas on precipitate of the mixed hydroxides was washed, dried at several passes- of the gas 100" C. in air, and reduced over the catalyst, but he with hydrogen at 300-350" does not specify the catalyst, C. Qualitative tests have been made on the efficiency its volume, the rate of gas (3) COBALTCHROMATE of various catalytic materials in the production of flow, the number of passes, -A solution of CoC12 was liquid hydrocarbons from water gas at atmospheric the exact temperature, or precipitated with an excess pressure. A more extended study has been made of the relative amounts of the of NazCrOd. The precipithe action in this process of a catalyst coxfsisting of various products obtained. tate was washed, dried at metallic cobalt and manganese oxide with a small The work of Elvins and 100" C., and reduced as beamount of metallic copper. Both saturated and unNash was not very extenfore. saturated hydrocarbons ranging from methane up sive. They have neglected (4) COBALT-COPPER-A to solid paraffins have been produced. The nature to give the proportions of solution containing CoCl2 and amounts of the various products formed under the three constituents in the a n d Cu(C2H302)Z i n t h e definite conditions have been indicated. proportions to contain equal c a t a l y s t they use. They On the basis of the recovery in small-scale experiatomic weights of cobalt and have also not obtained the ments, it is shown that with the cobalt-copper-manrelative yields a t different copper was p r e c i p i t a t e d ganese oxide catalyst at the most favorable temperawith KOH. The precipitate temperatures nor have they ture it would take about 1400 cubic feet of water gas made very clear the nature was washed, dried, and reto make 1 gallon of liquid fuel. This corresponds to duced as above. and amounts of all the prod66 grams of liquid hydrocarbons per cubic meter of ucts obtained. ( 5 ) C o B A LT - C o P P E R water gas. URANIUM OXIDE-A soluExperimental Method The gas remaining after removal of liquid hydrotion containing 296 grams carbons, carbon dioxide, and water would be of equal C o ( N 0 8 ) ~6. H 2 0 and 20 The apparatus is shown or higher calorific value than an equal volume of the g r a m s CuS04.5H20 w a s in Figure 1. The gas was original water gas. p r e c i p i t a t e d with KOH. made by passing steam a t a From the commercial standpoint it would be deThe precipitate was washed uniform rate into activated sirable to obtain more product per volume of catalyst free of sulfate. Two hunc h a r c o a l in a silica tube in a given time. dred grams of U02(CzH3heated to about 950" C. The 02)2.2H20 were heated to gas thus obtained, after pas300" C. until all but a trace sage through soda lime and activated charcoal, was a mixture of nearly pure carbon mon- of the acetic acid had been driven off. The resulting uranium oxide and hydrogen in about equal volumes. It was passed oxide was first ground in a mortar with water and then through a gas meter, over calcium chloride, and into the thoroughly ground together with the moist cobalt and copper catalyst tube. The exit gases passed into a receiver cooled hydroxides. The mixture was dried and reduced as usual. in liquid air and provided a t the bottom with a tip of small (6) COBALT-COPPER-MANGANESE OXIDE-A solution conbore, and then through another gas meter. After an experi- taining 370 grams Co(NO&. 6Hz0, 85 grams MnClz. 4Hz0, ment the receiver was allowed to warm up to room tempera- and 76 grams Cu(N03)~. 3Hz0 was precipitated with NaOH. ture, the escaping gas was collected for analysis, and the The precipitate was washed, dried, and reduced as usual. liquid products were distilled into the tip. The volumes of water and of oily products were determined by measureExperimental Results ment with a small cathetometer of the heights of the columns CATALYST No. 1-It was reported by Fischer2 that iron of liquid in the tip (t, Figure 1) which had been previously calibrated. I n this way the volumes of small amounts of possesses some activity as a catalyst for this process. The promoted ammonia catalyst was tried since i t seemed likely 1 Published by permission of the Director, U. S. Bureau of Mines (not to present an active iron surface. With about 150 cc. of subject to copyright). Presented under the title "The Formation of Liquid Hydrocarbons from Water Gas" before the Division of Gas and Fuel this catalyst in an experiment at 300" C., using 4 cubic Chemistry at the 74th Meeting of the American Chemical Society, Detroit, feet (113.2 liters) of gas, we were unable to detect any liquid Mich., September 6 to 10,1927. condensate or any odor of higher hydrocarbons. The exit * Brcnnsfof-Chcm., 7, 97 (1926). gas, however, contained a small amount of carbon dioxide I Fuel, 0, 263 (1926).
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May, 1928
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C4HI0,1.6; higher hydrocarbons, 2.5 per cent. The remainder was air from the receiver, CO, Hz,and CHd. No alcohols were detected. From an experiment a t 285" C . in which 2.6 cubic Activated charcoal feet (73.6 liters) of water gas were used and 0.5 cc. of liquid hydrocarbons remained, about 10 Electric furnace liters of gas boiled out between - 180" and -80" C. and about 4.4 liters between -80" and +25" C. A calculation from these data shows that there was lost in the evaporation from the receiver an amount of hydrocarbons from pentane up equal to about 22 per cent of the weight of the total ,er liquid hydrocarbons recovered-from butane up, about 58 per cent. The total amount of hydroL'quid carbons above methane is equal to about 2.3 times the total weight of liquid hydrocarbons actually Figure 1-Apparatus for Catalytic Formation of Higher Hydrocarbons f r o m recovered. At the lower temperatures, where Water Gas the quantity of gas evaporated from the reand methane (about 0.5 per cent of each). A small amount ceiver was less, the loss would be somewhat less. The quantitative separation of all of these various products from the of slightly acid, watery condensate was obtained. CATALYSTNo. 2-Qualitative tests in which about 3 receiver is, of course, a troublesome matter in small-scale excubic feet (85 liters) of gas were passed over 150 cc. of catalyst periments. The above analyses show that the hydrocarbons obtained a t 300" C. showed this catalyst to be fairly active. The exit gas had a strong odor of hydrocarbons and a film of oil are varied in nature, consisting of both saturated and uncollected on the surface of the watery condensate. The saturated products ranging from ethylene and ethane up to exit gas contained 4.4 per cent COZ and 7.6 per cent CH4. hydrocarbons which are liquid at ordinary temperature. CATALYSTNo. 3-This catalyst seemed completely in- With this catalyst, however, there was no evidence of very heavy products. active. The temperatures were measured by means of a thermoCATALYSTNo. 4-This catalyst gave, in qualitative tests, about the same results as in the case of catalyst No. 2. couple attached to the outside wall of the catalyst tube a t No. 5-This catalyst seemed somewhat more about the middle. The recorded temperatures represent CATALYST active than catalyst No. 2. After a considerable amount the maximum temperatures at the exterior of the tube. of gas had been passed over the catalyst in qualitative tests, The temperature in the furnace toward the ends was somea deposit of a substance resembling white vaseline was pro- what lower. The whole mass of the catalyst was thus not duced in the connecting tubes. This deposit was not no- a t the measured temperature. It is also possible that, under some conditions, local overheating of the catalyst ticed in the case of any other of the catalysts used. The only attempts a t quantitative measurement were may have occurred owing to the heat of the reaction. made using the cobalt-copper-manganese oxide catalyst (No. 6). I n each experiment in Figure 2, 1 cubic foot (28.3 liters) of water gas a t a rate of flow of 200 cc. per minute was passed over a single sample of about 18.5 grams (gross volume about 20 cc.) of catalyst in the form of a powder which had been mixed with glass wool to cut down resistance to the flow of gas. flthough this catalyst was originally used in the form of pellets, it was found that during reduction with hydrogen and subsequent use it powdered and tended to swell. A combustion analysis of the catalyst after considerable use showed the presence of a large amount of carbon and perhaps some hydrocarbons. I n spite of this, however, the activity of the catalyst did not seem to have largely changed. The carbon dioxide analyses were made on the gas before it had passed into the receiver. The recorded contractions in gas volume included the contraction due to the condensation of carbon dioxide, methane, and other condensable gases, as well as to the occlusion of some of the lighter gas in the liquid air condensate. TEUPERATLRE ' C A typical analysis of the gas boiling out of the condensate Figure 2-Results with 18.5 Grams (Gross Volume 20 c c . ) Catalyst from liquid air to carbon dioxide snow temperatures is: No. 6, a t 200 cc. per Minute COZ, 10.4; illuminants, 2.1; CO, 13.7; CHI, 44.7; HP, 3.4 per cent. The remainder was air from the receiver. From Figure 2 we see that a maximum yield of oil is obF. E. Frey very kindly made an analysis by his method of tained a t about 275" C. With rising temperature the confra~tionation,~ of the gas boiling between COe snow and traction in volume and the amount of carbon dioxide and room temperatures. The analysis of a sample from which water formed slowly rise. The amount of methane in the a content of about 80 per cent COZhad been removed was: effluent gas does not change markedly in this temperature CzH4, 1.8; CzHe, 8.0; C3H6, 7.6; GHs, 3.7; CkHs, 4.5; range, increasing from about 4 per cent at 260" C. t o about ' Prey and Yant, IND.ENG.CHBM.,19, 492 (1827). 7 per cent a t 300" C. Heating coils
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VOl. 20, No. 5
Figure 3 records the results of experiments in each of which hydrogen, and methane, would be as valuable as or more 1 cubic foot (28.3 liters) of water gas was passed over 70 valuable than the original water gas. g r a w (gross volume about 75 cc.) of catalyst No. 6 a t 275 O C. From the fractionation analysis given above it has been The catalyst in these experiments, after a preliminary calculated that the total yield of all hydrocarbons higher than reduction, was moistened with water and molded into pellets methane would be about 2.3 times the yield of liquid hydroout of contact with air. I n this case the pellets did not carbons actually obtained. This would bring the yield powder up as before. The figure shows how the yields of of total higher hydrocarbons up to about 124 grams per cubic the various p r o d u c t s meter of water gas. Or, if all hydrocarbons from butane up 0.7 ,50 vary as the rate of flow were retained with the liquid product, we would have about of gas is changed at con- 85 grams of liquid hydrocarbons per cubic meter of water stant temperature. gas. The cost of the water gas to produce 1 gallon of liquid From Fimre 3 we find fuel would then be 22 cents instead of 28 cents. If the t h a t , t o Form 0.68 cc. value of the hydrocarbons lower than butane and higher (0.46 gram) of oil, there than methane were taken into account, this figure could has been 0.37 cubic foot probably be further reduced to about 15 cents. (10.7 liters) of water gas A rough estimate shows that about 2 to 3 per cent of the a c t u a l l y used. This carbon monoxide in the original gas appears as carbon figure, c o r r e c t e d f o r deposited on the catalyst. The process would be much methane caught in the improved if this could be avoided. Doubtless much of this receiver and for carbon deposition of carbon occurs a t the higher temperatures. monoxide and hydrogen Theoretically the only way to improve the yields of liquid occluded in the con- hydrocarbons would be to eliminate the formation of any lower hydrocarbons. From the commercial standpoint, densed p r o d u c t s, be comes about 0.3 cubic of course, it would be desirable to obtain more product per foot (8.5 liters). After volume of catalyst in a given time. extraction of liquid hyI n conclusion, the difficulties inherent in these experiments drocarbons, carbon di- must be emphasized. First, as mentioned before, a strictly oxide and water, there quantitative separation of all the various products formed remains a gas containing, in these small-scale experiments is very difficult. Further, FATE OF FLOW OF GAS, C. C. PER %llNUTE the relative results a t different temperatures may be inbesides carbon Figure 3-Results w i t h 70 Grams and hydrogen, fluenced to some extent by changes in the activity of the (Gross Volume 75 cc.) Catalyst No. 6, atn275* C. Der cent of methane in ad- catalyst during use. The apparently large effect of temperadition to small amounts ture on these reactions makes non-uniformity of the catalyst of low-boiling saturated and unsaturated hydrocarbons. Us- temperature a disturbing factor. This work is being continued and recent experiments on a ing a more efficient fractionating condenser, which would recover all hydrocarbons from pentane up, the yield of liquid larger scale with a much more active catalyst and more hydrocarbons could be brought up to about 0.56 gram per accurately controlled conditions give promise of more favor0.3 cubic foot (8.5 liters) of water gas. This corresponds to a able results. Acknowledgment yield of about 66 grams per cubic meter. On this basis i t would take 1400 cubic feet of water gas to make 1 gallon of The authors wish to take this opportunity to express their oil. At 20 cents per 1000 cubic feet the water gas actually appreciation to A. C. Fieldner, whose interest and encourageused to make 1 gallon of oil would cost 28 cents. In actual ment as chief chemist of the Bureau of Mines made this work practice the unused gas, consisting of carbon monoxide, possible.
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Design of Fractionating Columns’ D. B. Keyes, Roy Soukup, and W. A. Nichols, Jr. UNIVBRSITY OF ILLINOIS, URBANA, ILL.
HE estimation of the theoretical number of plates required to separate a binary liquid mixture into its com-
T
ponents has received considerable attention in recent years. An excellent review of the various methods has been given by Shirk and Montonna.2 They show quite conclusively that the most practical method is the graphical scheme devised by McCabe and Thiele.s This method requires as data the composition in mol per cent of the feed, the product, and the residue, also the reflux ratio. Equilibrium is necessary between vapor and liquid on each plate. This is, of course, never attained in 1 Received 1
January 30, 1928.
IND. ENO. CHBM., 19, 907 (1027).
* Ibid., 17, 605 (1925). See also Walker, Lewis, and McAdams, “Principles of Chemical Engineering,” 2nd ed.
practice, for many reasons. The most evident reason is faulty plate design. A safety factor, known as the plate efficiency, is applied to the theoretical number of plates in order to determine the actual number necessary. This safety factor varies greatly with changing conditions, and cannot be determined in advance. It is quite probable, therefore, that a still simpler graphical method can be devised which will give practical results of equal accuracy. I n many cases it is merely a question of choosing one of four columns-a lo-, a 20-, a 30-, or a 50-plate column. Obviously, the column chosen will be the one with the fewest number of plates that will operate under the specified conditions and with a reasonable reflux ratio (5 to 1 or less). The practlical application of the McCabe and Thiele method using the proper safety factor (found by experience) would
