JANUARY, 1937
19
INDUSTRIAL AND ENGINEERING CHEMISTRY
(26) Jones, Yant, and Berger, Bur. Mines, Repts. Investigation8 2539 (1923). Jordan, J. IND.ENQ.CHEM.,8, 812 (1916). Kinney, Univ. Ky., Coll. Agr., Extension Div. Circ. 230 (Sept., 1930). Koperina, Biochem. Z.,256, 134 (1932). League of Nations Yearbook, 1935. Ludwig, J . Am. SOC.Botany, 5 , 171 (1918). Mulinos and Osborne, N . Y . State J . Med., 35,590(1935). Mulinos and Osborne, Proc. SOC.Exptl. Biol. Med., 32, 241 (1934). Neuberg and Kobel, Biochem. Z . , 206,240 (1929). O'Shes, "Tobacco and Mental Efficiency," New York, Macmillan Co., 1925. Posey, Univ. Md., Extension Service Bull. 65 (Dec., 1932). Pucher, Leavenworth, and Vickery, IND.ENO. CHEM.,Anal. Ed., 2,191 (1930). Rolleston, Lancet, 1926,I, 961. Rowe, "Tobacco under the A. A. A.," Washington Brookings Inst., 1935. Schmalfuss and Barthmeyer, 2. Untersuch. Lebensm., 63, 283 (1932). Schrumpf-Pierron. "Tobacco and Physical Efficiency," New York, Paul B. Hoeber, 1927. Schweitzer, Paper, 27,No. 27,14,36 (1921). Shedd, Ky. Agr. Expt. Sta., Bull. 258 (April, 1925). Ibid., 308 (July, 1930).
(45) Shirokaya, State Inst. Tobacco Investigations (U. S. S. R.), Bull. 90, 67 (1932). (46) Shmuk and Kolesnik, Ibid., 81, 45 (1931). (47) Statistical Abstracts of the U. S., Govt. Printing Office, 1935. (48) Symons, Can. Chem. Met., 19,259 (1935). (49) Tech. Assoc. Pulp Paper Industry, Standard Methods, 1932. (50) Thurston, Agr. Comm. Ohio, Bur. Drugs, Bull. 2 (Nov., 1914). (51) Thurston, J . Am. Pharm. Assoc., 4 , 435 (1915). (52) U.S.CommissionerInternal Revenue, Ann. Repts. (53) U.5. Dept. Agr. Yearbook, 1934. (54) Ibid., 1935. (55) U.S.Dept. Commerce, Biennial Census of Manufactures, 1935. (56) Vickery and Pucher, IND.ENG.CHEM.,Anal. Ed., 1, 121 (1929). (57) Vickery and Pucher, J . Bid. Chem., 83,1 (1929). (58) Ibid., 84,233 (1929). (59) Ibid., 90,179 (1931). (60) Wallace, Reinhard, and Osborne, Arch. Otolaryngotouy. 23, 300 (1936). (61) Waser and Stahli, 2. Untersuch. Lebensm., 67,280 (1934). (62) Wenusch, Biochem. Z., 273, 178 (1934). (63) Wenusch, Fachl. Mitt.Oestrr. Tabak-Regie, 3, No.6 (1932). (64) Wenusch, Z . Untersuch. Lebmnsm., 69,81 (1935). (65) Ibid., 70,201 (1935). REomIvmn August 27, 1936. The authors are Industrial Fellows of the Philip Morris 8 Company, Ltd., Ino., Industrial Fellowship at Mellon Institute.
Vapor-Phase Hydration of Ethylene R. HARDING BLISS1 AND BARNETT F. DODGE Yale University, New Haven, Conn.
A
PREVIOUS paper from this laboratory by Sanders and Dodge (7) gave the first definite proof that
ethanol could be synthesized in significant quantities by the purely catalytic, vapor-phase hydration of ethylene. An approximate value for the equilibrium constant for the reaction a t one temperature was established, and new data on catalysts were presented. Calculation of the equilibrium constant by thermodynamic methods yielded widely discrepant results, depending on the particular thermal data chosen. It appeared desirable, therefore, to continue the investigation of the equilibrium in this reaction in order to obtain a more accurate value of the constant at some one temperature and also to secure values over a range of temperatures. This paper presents values for the equilibrium constant, K,, for the vapor-phase hydration at 7 to 11 atmospheres and 320", 350°, and 378" C., along with some new observations on catalysts which were obtained incidental to the main problem. After the work to be reported was well started, two papers (3,9) appeared which overlap somewhat the work done in this laboratory, However, inasmuch as results in this field have been scanty and very conflicting, checking results by independent investigators are desirable.
Thermodynamic Calculation of Equilibrium Constant Sanders and Dodge (7) reviewed the situation on the thermodynamic calculation of the equilibrium constant and 1
Preaent addresa, Rlihm L Ham Company, Philadelphia, Pa.
Equilibrium in the hydration reaction has been investigated at 7 to 11 atmospheres pressure and at 320°, 350°, and 378" C. The results agree well with those of Stanley, Youell, and Dymock, and both sets of data are well represented by the equations : loglo Kp = AF' =
2100/T 28.20T
-- 6.170 9600
which refer to the reaction :
+ HzO (g) = CzH@H (g)
CzHi (9)
Some new observations on the behavior of various catalysts €or the dehydration of ethanol are also presented.
came to the conclusion that this method was of little value because of the widely divergent results obtained. The present authors have made further calculations using other combinations of. thermal data, some of which became available after the earlier paper was published. The results confirm the conclusions already reached. Calculated values for AF" (standard free energy change) for the vapor-phase hydration reaction a t 298" K. varied from -3025 calories per mole to +1168, corresponding to a K , variation from 164 to 0.14 or 1170 fold. Furthermore this variation is due wholly to differences in the ethylene data since the same values for the free energies of formation of ethyl alcohol and water were used throughout. Comparison of these calculated values with experimentally measured ones necessitates the use of specific heat data to bridge the gap from 25" C. up t o the temperatures a t which the reaction becomes sufficiently rapid to permit an experimental approach to equilibrium. Since these data, are rather
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CHEMICAL ENGINEERING LABORATORY, YALE UNIVERSITY meager for ethanol and ethylene, a further uncertainty is introduced. This unsatisfactory state of affairs prompted the writers to undertake further experimental work to determine directly the constant as a function of temperature.
Previous Work Sanders and Dodge (7) review work done prior to their investigation, both on equilibrium and on catalysts for the reaction. They studied the activity of twenty-five different catalysts for the dehydration of ethanol and presented a number of new facts about catalysts for this reaction. They investigated equilibrium in the vapor phase using a flow method and alumina catalysts, a t a pressure of 70 atmospheres and a temperature of 380" C., approaching equilibrium from both sides. They made a careful study of analytical methods and were the first to prove incontrovertibly (by fractionation and by preparation of a solid derivative) that ethanol could be formed in this way. Their values for K , to 0.51 X lod3a t 380" C. with an varied from 2.35 X average value of 1.07 X 10-3. Stanley, Youell, and Dymock (9)'using a flow method a t atmospheric pressure, approached equilibrium from both sides over the temperature range 145" to 250" C. They used a silver sulfate-sulfuric acid catalyst at 145" C. and a manganese borate-phosphoric acid catalyst a t the higher temperatures. The equation which they recommended as expressing their results,
a t 380" C. in almost exact agreegives K , = 1.06 X ment with Sanders and Dodge's average value (7).
Gilliland, Gunness, and Bowles (2) recently investigated the equilibrium simultaneously in both the liquid and gas phases by a static method. The catalyst was a dilute aqueous solution of sulfuric acid. Pressures were varied from 83 to 264 atmospheres and temperatures from 176' to 307' C. The following equation was stated by them to express their experimental results: AFo = -7780 26.27' (2)
+
which may be transformed to logm K , = 1700 -
T
5.73
(3)
They also state that the following equation correlates all available experimental data for the vapor phase, including their own, AF"
=i
26.9T
- 8300
(4)
which can be transformed to loglo K , =
T - 5.890
(4'4)
The equations of Parks and Huffman (6)and of Francis and Kleinschmidt ( I ) , based on thermodynamic data, were in poor agreement with Equation 4.
Apparatus and Procedure for Studying Catalysts Catalytic activity was investigated by means of the reverse reaction-namely, the dehydration of ethanol-at atmospheric pressure and 360" C., with flow rates sufficiently
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INDUSTRIAL AND ENGINEERING CHEMISTRY
high so that equilibrium was not approached. The apparatus adopted for measuring the extent of dehydration was essentially the same as that used by Huffman and Dodge (3) and Sanders and Dodge (7). Ethanol was boiled in an adiabatic boiler, so arranged that all heat of vaporization was supplied by an electric coil which allowed an easy calibration of alcohol vaporized us. coil current. The vapors passed over the catalyst supported in a Pyrex glass tube which was heated in a n electric resistance furnace provided with a n aluminum core for smoothing out temperature variations. From the catalyst the vapors were led to a water condenser and thence t o a coil condenser immersed in a mixture of solid carbon dioxide and ethanol where last traces of water and certain low boiling materials were removed. The gas was then conducted through a flowmeter (for indicating constancy of flow) and measured by water displacement. I t s ethylene content was determined by absorption in fuming sulfuric acid on an Orsat apparatus. I n operating this apparatus, the two principal variables were the rate of alcohol ebullition per unit volume of catalyst and the catalyst temperature. These should be fixed so that even the best catalysts do not produce complete dehydration, in order that differentiation and comparison may be made easier. A temperature of 360" C. and an alcohol rate of 23.5 grams per hour (corresponding to a space velocity, for 5 cc. of catalyst, of 2300 volumes of gas a t standard conditions per volume of catalyst per hour) satisfied this requirement. The usual operating procedure was to bring the catalyst chamber to the desired temperature and then to start the vaporization of alcohol. This immediately produced a change in the catalyst temperature, and considerable time was required to adjust the heater to its proper setting. It was found, in the case of some catalysts, that the activity changed markedly in this period. Therefore, it was necessary to make these adjustments in as short a time as possible; at least 10 minutes were required. The run proper was then divided into 15-minute periods, the average activity being determined for each period. Thus the change of activity could be followed, and this was found to be quite noticeable in some cases.
Catalyst Preparation
21
as indicated by red coloration of litmus paper. The precipitate was transferred t o a 5-gallon (19-liter) bottle and washed seven times by decantation with distilled water. A part of it was filtered by suction and dried at 105". 2. ALUMINA-TUNQSTIC ACID. The remainder of the settled sludge of catalyst 1 was analyzed for alumina; 500 cc. of this sludge (corresponding to 17.7 grams of alumina) were stirred and heated. During this process 0.354 gram of tungstic acid was added. It was finally evaporated to dryness in an oven at 105" C. and sized to the proper dimensions. This corresponds to 2 per cent of tungstic acid based on the anhydrous alumina. 3. ALUMINA-SULFURIC ACID. To another 500 cc. batch of sludge from catalyst 1, 0.354 gram of sulfuric acid was added, and the same treatment was given as for catalyst 2. 4. ALUMINA-POTASSIUM HYDROXIDE.Same as catalyst 2, except that 0.354 gram of potassium hydroxide was added. 5. ALUMINA-PHOSPHORIC ACID. Same as catalyst 2, except that 0.354 gram of phosphoric acid was added. 6. TTJ-NGSTIC ACID. Twenty-five grams of powdered tungstic acid (Merck technical grade) were mixed with one per cent of its weight of graphite and pressed into pellets. Since these were a little large to feed into the catalyst tube easily, they were broken up to 8-14 mesh size. 7. TUNGSTIC ACID. Sixty grams of tungstic acid were dissolved in a solution of 26 grams of sodium hydroxide in 200 cc. of water. This solution was added to a boiling solution of 190 cc. hydrochloric acid, 190 cc. nitric acid, and 235 cc. water. It was diluted t o 3 liters and washed four times by decantation. Further washing was prevented by the fact that, at this stage, the precipitate tended to become almost entirely colloidal. It was filtered by suction and dried at 105" C. 8. ALUMIKA.Twenty grams of aluminum turnings were amalgamated by dipping them into a solution of mercuric chloride. The resultant amalgam was transferred to a beaker containing water, and the alumina formed was washed into a 5-gallon bottle, every few hours at first and every day thereafter, for one week. The alumina so formed was washed seven times by decantation, filtered, and dried at 105" C. 9. ALUMINA.Ninety grams of aluminum turnings were dissolved in a solution of 175 grams of sodium hydroxide in 2 liters of water. The resultant solution was filtered and diluted to 9 liters. The consequent treatment was the same as for catalyst 1, since the prime purpose was to learn how easily duplicable these catalysts were. 10. ALUMINA.One hundred and twenty-five grams of Al(NO&.9H20 were dissolved in 1.5 liters of water and heated t o 85" . Ammonium hydroxide (diluted 4 to 1) was added until recipitation was complete, as evidenced by blue coloration to Etmus It was diluted to 3 liters, washed seven times by decantation, filtered, and dried at 105" C. 11. ALUMINUM BORATE. Two hundred grams of potassium alum were dissolved in 1.5 liters of water. One hundred grams of borax were dissolved in 1.5 liters of water and the solution added to the previous one with stirring a t 60" C. It was transferred to a 5-gallon bottle and washed by decantation five times. It was then filtered by suction and dried at 105" C.
The method by which a catalyst is prepared is often of prime importance in determining its activity. In general, the best grades of chemically pure reagents were used throughout, the various steps were carried out in glassware, and the washings were made with distilled water unless otherwise specified. Precipitated cataTABLD I. SUMMARY OF DATAFROM CATALYST TESTS lysts were ground and screened Per Cent on s t a n d a r d Tyler screens, Run CatalystPer Cent Dehydration after Ethanol Flow for: Ethylene No. No. Type 20 min. 40 min. 60 min. 80 min. 100 min. 120 min. in Gas Notesb only the 8 to 14 mesh size be1 1 AlzOa (aluminate) 745 52a 40a 33" 28" 25" NA ing used. Powdered catalysts 2 2 90 44 AlzOa-WOa 81 71 62 53 98.'15 ... 3 6 WOa (pellets) 69 66 were made into small pills, 61 59 56 64 96.94 ... 4 8 Alto3 (amalgam) 77 76 73 71 68 66 97.9 ... utilizing graphite as a binder. 5 9 Ah08 (aluminate) 51 71 41 .. .. 94.9 7 6 Wos (pptd.) 94" 84a iia 77a 68a .. NA All catalysts were dried in an 11 7 AlzOa,~BzOa 87 81 76 73 70 68 9 s : b7 8 1 Alp08 (aluminate! 63 67 65 oven at about 105" C. and no 69 71 .. 97.34 A' 9 1 Same 100 99 98 96 92 .. 99.11 B additional heat treatment was 10 3 61 &Oa-&4804 66 56 52 48 .. 96.22 ... 11 4 AlzOa-KOH 59 75 41 48 34 29 98.34 ... given to the catalyst unless 12 1 AhOa (aluminate) 75" 575 45" .. ... NA 13 7 wos ( ptd ) 74 79 noted in Table I. The details 70 66 61 ii 94.6 C 14 10 A1203 ?nitrite) 17 16 .. .. .... 96.5 ... of manufacture are as follows: 15 10 Same 35 36 si 38 .. 97.8 B 16 8 AizOa (amalgam) 88 88 88 89 89 89 97.9 B 17 11 A120a.ZBz08 56 52 49 48 .. 65 98.4 .. B 1. ALUMINA. S i x t y - t w o 19 12 AlzOa (aluminate) 61 63 62 63 64 97.5 B grams of aluminum t u r ni n g s 20 12 Same 77 79 81 83 85 97.95 87 D 21 5 Alz08-HsPO4 92 72 45 were dissolved in a solution of 56 38 97.45 .. .. * 22 12 Ah08 (aluminate) 69 75 73 67 .. 9 6 . 6 .. E 120 grams of sodium hydroxide 23 12 Same 36a . . . . .. . . .. ... NA in 600 cc. of water. The resulta Assumes 100% ethylene in exit gas. ing solution was filtered, diluted b Notes: NA gas not analyzed. A, used in run 1 and reactivated at 500' C with air for 2 hours. B preaotit o 6 liters, and heated t o 85" C. vated at 500' b. with air for 2 h;urs* C, preactivated at 450' C. with a 2 to'l Hz-CO mixture for'2 $ours. D Sulfuric acid, diluted 4 t o 1with used in equilibrium runs 13, 14. and i5, reactivated for 2 hours at 500' C. with air, and used in equilibrium ;un; 17-28; E, same aa B but for 4 hours. water, was added with stirring until precipitation was complete ~
~~~~
--
..
INDUSTRIAL AND EN XNEERING CHEMISTRY
22
12. A L U M I N A . Three hundred and ten grams of aluminum- turnings were dissolved in a solution of 600 g r a m s sodium hydroxide in 4 liters of w a t e r . The resulting solution was filtered, and 45 liter: and heated t o 8 5 C. i n a n
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20. ALUMINUMBORATE.Twelve hundred grams of potassium alum were dissolved in 20 liters of water, diluted to 45 liters, and heated to 85" C. in an enamel-lined steam kettle. To this a solution of 650 grams of borax in 12 liters of water was added until litmus turned faintly blue. It was transferred to a 50gallon barrel and washed seven times by decantation with tap water, filtered by suction, and dried at 105' C. 21. TUNQSTIC ACID. Five hundred grams of this material were pressed into pellets in the same way as catalyst 6.
Data and Conclusions
The criterion of catalyst activity was the extent of dehydration or, more specifically, the percentage of ethanol passing over the catalyst which undergoes decomposition to ethylene. This will be denoted by the term "per cent dehydration." It is also important to determine the specificity of the catalyst for this particular reaction and this may be judged by the ethylene content of the gases produced. With all the catalysts studied, the ethylene content was 94 per cent or higher, indicating that dehydration was the predominating reaction. Since it was almost impossible to obtain exactly the same prerun period for each test, the variation of catalyst activity 105" c. 13. A L U M I N A with time was plotted and the results given in Table I were A E R O G E L . This read from the curves. The most significant results are also catalyst was kindly presented graphically in Figure 1, using the smoothed data. s u p p l i e d by 8. S. Comparisons of runs 1 and 12 made on the same catalyst Kistler of the Norton and runs 1and 5 made on catalysts prepared in the same way Company. indicate that both the methods of catalyst preparation and 14. ALCOA ACTIVATED A L U M I N A . the testing procedure are reasonably reproducible. The folThis catalvst is a lowing conclusionsmay also be drawn from the data presented: commercial" adsorb\ ent marketed by the (1) All of the catalysts, if not given any special activation treatment, showed a continued diminution of activity with Aluminum Company I I I I I 41' of America. time during use. This behavior was more pronounced with TIME ELxPSPD (M~ONUTL) ' 15. MANGANOUS the alumina than with the tungstic oxide catalysts and there FROM START OF ETHANOL OXIDE- BORICANwere differences in the alumina catalysts in this respect, H Y D R I D E - PHOSFIGURE 1. COMPARISON OF CATAPfIORIC ACID. depending on the method of preparation (for example, runs LYSTS FOR DEHYDRATION OF ETHANOL 1 4 , 6, 7). Twenty-three grams of manganous car(2) Treatment of an alumina catalyst with air for a short bonate, 12.4 grams of boric acid, and 47 cc. of 85 per cent phosperiod a t a temperature well above its normal operating phoric acid were intimately mixed with about 100 CC. of water. temperature (500' C. used in most cases) not only increased The mixture was evaporated with stirring and then baked in an the initial activity but stabilized the catalyst so that decrease oven for 4 hours at 240' C. The resulting material was then ground and screened to 8-14 mesh size. This has the approximate in activity with use was either prevented entirely or greatly molecular formula Mn0.B0.31/2H3P04and was made t o conminimized (compare runs 1, 8, and 9; 14 and 15; 4 and 16). form t o a catalyst used by Stanley, Youell, and Dymock (9). (3) Addition of B small percentage (about 2 per cent) of 16. SILVER SULFATE-SULFURIC ACID. Sixty-five cubic centltungstic oxide or phosphoric acid to an alumina catalyst inmeters of sulfuric acid were added to 35 cc. of water, and 5 grams of silver sulfate were dissolved in the acid solution with heating. creased its initial activity somewhat but had no effect on the In this solution 8-14 mesh pumice was soaked for 3 hours, filtered stability. A small amount of sulfuric acid reduced initial on glass wool, and dried at 105" C. This also was an attempt to activity but lessened the rate of decrease of activity, whereas duplicate a catalyst suggested by Stanley, Youell, and D p o c k a small percentage of potassium hydroxide was without (9). 17. ALUMINUMSULFATE.Fifty grams of ammonia alum significant effect on either property (compare runs 1 and 2; were calcined slowly at 400' C. for 20 minutes. The material was 1 and 10; 1 and 11; 1 and 21). then removed, and the hardened bubbles formed by the calcina(4) Alumina made by ammonium hydroxide precipitation were broken. It was returned for 10 minutes more. It tion was a less active catalyst than alumina made either from was then removed, powdered, and heated again for 30 minutes at a slightly lower temperature. After cooling, it was mixed with aluminate or from aluminum amalgam (confirms results of 2 per cent of its weight of graphite and pressed into pellets. Sanders and Dodge, 7 ) . Heat treatment a t 500' C. improved 18. CADMIUM PHOSPHATE. One hundred and fifty-four grams its activity greatly but still left it inferior to the other two of Cd(NO&4H2O were dissolved in water and precipitated with (compare runs 1 and 14; 4 and 15). sodium hydroxide. The cadmium oxide was washed by decantation four times, made up to a slurry of 1200 cc., stirred, and (5) An aluminum borate catalyst is somewhat more acheated. Sixty-four grams of phosphoric acid were added, and tive initially than the best alumina catalysts, but heat treatheating was continued until most of the water had evaporated. ment a t 500' C. reduced its activity and did not make it as It was then transferred to an oven where final evaporation to stable as the pure alumina catalysts (runs 7 and 17). dryness took place at 130" C. This was an attempt to duplicate a catalyst su gested in a patent granted to the Imperial Chemical (6) Tungstic oxide is more active initially and more stable Industries (47. than the best unactivated alumina catalysts, but treatment 19. ALUMINA.Four hundred and ten grams of powdered with a reducing gas a t 450" C. reduced the activity and did aluminum were dissolved in a solution of 820 grams of sodium not stabilize the catalyst. The lower activity of catalyst 6 hydroxide in 6 liters of water. The resulting solution was filtered, diluted t o 45 liters, heated t o 85' C. in an enamel-lined steam as compared to 7 was probably due to the fact that the tungstic kettle, and precipitated with one t o one sulfuric acid until fitmus oxide was simply a technical grade used without further turned red. The resultant mixture was diluted to 50 gallons treatment whereas catalyst 7 had been precipitated (compare and washed seven times by decantation with tap water. It was runs 4, 6, and 13). filtered by suction and dried at 105" C. enamel-lined steam kettle. It was precipitated with a 4 to 1 solution of sulfuric acid until l i t m u s turned red, and the sludge was diluted to 50 gallons (189 liters) in a b a r r e l . The latter was washed seven times by decantation with tap water, f i l t e r e d by suction, and dried at
.
JANUARY, 1937
INDUSTRIAL A N D ENGINEERING CHEMISTRY
In view of the large number of variables and the small number of tests, these conclusions are tentative but should prove a useful guide to anyone who is. starting work with catalysts of this type. The results of a few other tests were poor or negative and are not recorded in Table I, but a record of them may prove useful to others. An alumina aerogel (catalyst 13) gave only 8 per cent dehydration and a gas containing only 88 per cent ethylene. Catalyst 15, a manganese borate-phosphate catalyst made according to the directions of Stanley, Youell, and Dymock (Q),was active initially but soon became wholly inactive. Distinct tests for phosphate in the liquid product indicated that the loss of activity was probably due to the volatilization of phosphoric acid. However, this catalyst was used successfully by Stanley, Youell, and Dymock a t a temperature a t least 100" C less than that of the present experiment, which may account for the difference in behavior. Cadmium phosphate catalyst 18, made according to directions in a patent (4), was wholly inactive. Commercial activated alumina (Alcoa) exhibited slight activity, and aluminum sulfate, prepared as directed by Senderens (8), was of low activity, giving 15 per cent dehydration a t 360" C.
Equilibrium Measurements As mentioned a t the beginning, the chief aim of this work was the evaluation of the equilibrium constant. For this purpose a n apparatus had to be designed and a procedure chosen so that the amounts of reactants and products a t equilibrium could be measured. There are two general methods of accomplishing this end-a static method and a ,dynamic one; in this work the latter
23
Two methods were used to indicate that an approach to true equilibrium was being attained. The first was to vary the space velocity and the second was to add ethanol to the reactants in excess of the approximate equilibrium amount so that the direction of the reaction was reversed. If the same value for K , is obtained, confidence that equilibrium has been reached is justified. Another equally important consideration essential to the accuracy of results is the elimination of appreciable side reactions. Provision has been made in the analytical scheme to determine the amounts of ethyl acetate, acetic acid, and acetaldehyde so formed and to remove any ether from interference with the ethanol analysis. All results (with the exception of those obtained with tungstic acid catalysts) show that these materials are formed in negligible amounts. There is, however, one other side reaction which is very troublesome-namely, the polymerization of ethylene. This reaction consumes ethylene, thus continually disturbing the equilibrium sought, and the polymer so formed interferes with determining water in the product by difference. It cannot be analyzed by any simple means, and it is of such complex structure that estimation of its molecular weight is impractical. Therefore, in order to make equilibrium results of value, it is absolutely essential to avoid this side reaction. The conditions chosen for the investigation were temperatures of 320' to 380" C., pressures of 7 to 11 atmospheres, space velocities of 3 to 75, and ethylene-steam ratios of 0.25 to 9. Temperature was limited on the low side by the activity of the catalysts and on the high side by side reactions. Although the yield of ethanol increases nearly in proportion
24
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thermocouple inserted in a steel well which projected into the catalyst bed and was controlled by manual adjustment of the current. The equilibrium runs varied in length from 2 to 18 hours and were receded by a prerun period of 5 to 7 hours which was necessary Kr the adjustment of the operating conditions to the values desired. During this period, traps H and I (Figure 2) were bypassed. At the completion of a run, these traps were removed and weighed to determine total material condensed, and the contents combined for analysis. Analysisof the gas sample was conducted on an Orsat apparatus using a mercury-sealed compensated buret, and absorbing the ethylene in fuming sulfuric acid. Carbon dioxide, oxygen, carbon monoxide, and in some cases hydrogen and hydrocarbons, were also determined. The liquid condensate, freed from any nonaqueous layer, was analyzed for ethanol and water by the method of Sanders and Dodge (7).
Discussion of Results
FIGURE2.
DIAQRAM OF EQUILIBRIUM APPARATUS
to the pressure, this was kept a t a relatively low value to minimize polymerization and to simplify the apparatus. Space velocity and ethylene-steam ratio were varied within wide limits, mainly because it was not possible to predict in advance the best conditions to use and because the steam ratio was not under close control.
Apparatus and Procedure The moderate pressure permitted the use of a simple apparatus constructed of ordinary pipe and fittings and modeled after that used by Newton and Dodge (6) in their work on the methanol equilibrium. The complete assembly is shown in Figure 2: The ethylene, stored in cylinder A , passes through pressure re g u 1a t i n g varve B, and then through a quarterinch (6.25-mm.) copper tube to purifier C, which i s m a d e of 1-inch (2.5-cm.) iron pipe a n d c o n t a i n s about 100 cc. e a c h of a c t i v a t e d silica gel and activated c h a r c o a 1. From here the gas goes through a check valve, which prevents flow of water from the saturator back to the purifier during pre- and afterrun periods, to saturator D where water vapor is added t o the gas by allowing it to bubble through iwater maintained at a constant temnerature bv an oil thermostat (dilu
