April 1953
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INDUSTRIAL AND ENGINEERING CHEMISTRY
The equipment consists of a standard Orsat provided with the usual combustion tube. A 1000-ml. buret and a Krassel tube filled with 20/48 mesh activated charcoal are added as extra equipment and connected in series with the 100-ml. buret of the Orsat. A three-way stopcock is provided a t the outlet of the charcoal tube to permit evacuation, purging, and introduction of the gas sample. Prior t o making a determination, the charcoal tube is submerged in a bath a t room temperature. Residual gases are removed by evacuating the tube t o a pressure of less than 1 mm. of mercury and the tube is then filled with nitrogen. Approximately 1000 ml. of sample are taken into the larger buret, the connection t o the charcoal tube is opened, and approximately one half of the sample is vented t o the air through the .charcoal. This allows the charcoal to become essentially saturated with respect t o hydrogen but not t o the heavier hydrocarbons. After an accurate reading has been taken on the large buret, a sufficient volume of the process gas sample is passed through the charcoal tube to give approximately 100 ml. of hydrogen-rich gas in the small buret. A volume reading is again taken on the large buret in order t o obtain the volume of the sample being analyzed. The sample in the small buret is essentially free of the heavier interfering hydrocarbons and after removal of the acidic gases, olefins, and oxygen, the remaining gas concentrate is handled in the usual manner for hydrogen. This method has been repeatedly checked against results from low temperature fractional analyses and has proved to be accurate within 2%. Use of Method for Testing Pelleted Catalyst
855
equipment and procedure for testing both powdered and pelleted catalysts would simplify the testing problem for owners of several types of catalytic crackers. Acknowledgment The authors wish to express their appreciation to the Phillips Petroleum Co. for permission t o publish this work. They also wish to acknowledge the valuable assistance of Karl Meixner for his work on constructional details, L. G. Larson for his development work on the hydrogen determination method and on the electronic control systems used, and J. H. Rainwater for his work in the early development of the catalyst test method. Literature Cited (1) Am. Petroleum Inst., Proc. Am. Petroleum Znst., (111) 27, 9 (1947).
(2) Grote, H. W., Hoekstra, J., and Tobiasson, G. T., IND.ENG. CHEM.,43,545 (1951). (3) Katz, D. L., and Brown, G. G., I b X , 25, 1373 (1933). (4) McReynolds, H., Proc. Am. Petroleum Znst., (111)2 7 , 78 (1947). ENQ.CHEM.,42, 182 (1950). (5) Mills, G. A., IND. (6) Mills, G. A., and Shabaker, H. A.,Petroleum Refiner, 30, 97 (1951).
(7) Shankland, R. V., and Schmitkons, G . E., Proc. Am. Petroleum Inst., (111) 27, 57 (1947). ( 8 ) Smith, H. M., Bur. Mines, Tech. Paper 610 (1940). (9) Thomas, C . L., and Hoekstra, J., IND.ENG.CHEM.,37, 332 (1945).
The method has been adapted to the testing of pelleted catalyst. Preliminary experimental work has shown that the equipment described in this paper can be used with only minor.alterations for testing TCC pelleted catalyst. The use of the same
(10) Voorhies, A.,Zbid., 37, 318 (1945). RECEIVED for review December 31,1951. ACCEPTED December 4, 1952. Presented at the Seventh Southwest Regional Meeting of the AMERICAN CHIMICAL SOCIETY, Austin, Tex., December 6 to 8, 1951.
0
Dehydration of Ethyl Alcohol over Alumina 0
HANS FEILCHENFELD' Deparfmenf o f Chemisfry, Northwesfern Universify, Evansfon,
T
HE dehydration of ethyl alcohol to diethyl ether in the
. *
.
vapor phase over a n alumina catalyst has been extensively studied (1, 3, 4, 6 , 7, 9). I n general, the conversion of ethyl alcohol t o ether increased with increasing contact time (or, in flow systems, with decreasing space velocity), passed through a maximum, and decreased. This decrease was explained by the formation of ethylene, e i d e r in competition with ether or by further dehydration or disproportionation of ether. I n this investigation the conversion of ethyl alcohol to ether has been studied under superatmospheric pressure which suppressed ethylene production. If even then the rate of production of ether a t low space velocities leveled off to zero, this could not be due to ethylene formation but either to the thermodynamic equilibrium between the reactant and the products or to inactivation of the catalyst.
111.
The liquid feed was pumped from a pressure charger; the gaseous feed was introduced by water displacement a t a predetermined rate; and the reactants were passed through the catalyst tube from the bottom instead of from the top, the preheater and spacer having been interchanged. The products were passed consecutively through a water-cooled trap and a dry ice-acetone trap. Absolute alcohol waa used as the standard feed. Water, ether, and ethylene were added t o it in order to determine their influence upon the reaction. I n order t o reduce the effect of the small but varying amounts of ethylene formed a t different feed rates, the absolute alcohol was always saturated with ethylene a t 1 atmosphere gage pressure; the amount of ethylene produced was measured. The composition of the li uid product was determined by fractional distillation, the me%od of Hodgson and Glover (6) having proved unsatisfactory, probably because of the presence of dissolved ethylene in the liquid product. The catalyst was in all cases alcoa F-10 alumina and was not further pretreated.
Experimental Work
Results and Discussion
The apparatus was arranged according to the continuous flowtype system (IO), but with the following changes:
To determine the conditions under which a reasonable amount of ether could be produced without the formation of appreciable amounts of ethylene, a preliminary reaction was run a t 20 atmospheres and varied temperature. No temperature was found
1 Present
address, Research Council of Israel, Jerusalem, Israel.
,
856 Table 1.
INDUSTRIAL AND ENGINEERING CHEMISTRY Conversion of 9570 Ethyl Alchol over 50 MI. of Alumina Catalyst
(At a teniperatuie of 355' C. and pressure of 20 atmospheiss) Partial Pressure Duration of LHSV, Conversion, Experiment, of Water, Jfin. ( M I . Cat.) (Hr.) Ether E t h y G At 111, 8.55 1.3 70 4.4 7.6 2.1 2.7 56 6.6 44 1.9 4.1 23 0.5 4.6 6.6 3.2 3.2 56 7.7 6.1 9.35 1.2 72 59 8.0 4.7 1.4 5.4 67 8.9 1.1 8.2 64 9.2 0.7 13.5 8.1 48 0.4
r0
Table II.
Vol. 45, No. 4
Conversion of 100% Ethyl Alcohol over 30 of Alumina Catalyst
MI.
(.4t temperature of 335' C a n d pressure of 40 atmospheres) LHSV Conversion of Ethyl .4ge of Alcohol, 7" Catalyst, .~ 311 * lhn ( M I . Cat ) ( € I r ) ' Ether Ethylene 155 1.1 49.5 215 1.1 44 0:33 350 1.1 50 0.70 475 1.1 48 0.61 730 0 6 46 1.09 790 0 6 44 1.13 905 0 6 50 1.05 1030 0 6 48.5 0.96 1255 0.6 49 .. 1365 2.3 30.5 0.53 1355 2.3 33.5 0.53 1515 2.3 36 0.53 1545 2.3 35.5 0.53 1635 1.9 44 0.67 1666 1.9 43 0.67 1710 1.9 38 0.59 1785 1.9 38 0.54
Duration of Experiment, Min 155 215 350 475 256 315 430 555 780 110 140 260 290 90 120 165 240
I n order to test whether the falling off of the conversion rate to zero (as witnessed by the horizontal parts of the curves in Figure 2 ) is due to an equilibrium between reactant and products, the partial pressures of the gases at maximum conversion have been calculated on the assumption that they are ideal. The value ' Figure 1. Conversion of 95% Ethyl Alcohol over Alumina Catalyst
50 MI. of
At temperature of 355' C. and pressure of 20 afmospheres
which suited the requirements. Typical results are given in Table I. I n Figure 1 the conversion of alcohol under these conditions is illustrated graphically as the function of the inverse space velocity. The shape of the curves is similar to that found by other investigators working at atmospheric pressures. The dispersion of the points around the curve is thought to be due to failure to allow sufficient time to attain conditions of steady state. In order to suppress the formation of ethylene it was found necessary to raise the pressure to 40 atmospheres. The data for one series of experiments at 335" C. are given in Table 11. A steady state is reached after spans of time varying from 90 minutes a t a liquid hourly space velocity of 3.6 to 430 minutes at 0.6. The conversion of ethyl alcohol to ethylene is less than 1% even at the lowest feed rates encountered. I n Figure 2 the conversion of ethyl alcohol to ether is graphically shown as a function of the inverse space velocity in (milliliters of catalyst)(hours)/(millimole). This unit allows for easier correlation of feeds of different composition than the inverse liquid hourly space velocity. The results obtained show that after a sharp rise the conversion reached a constant value with increasing inverse space velocity (contact time). After a certain contact time has been passed, no further ether is formed, nor does ether disappear, as no ethylene is formed under the given conditions. On addition of ether to give a feed of 13.5 molar % in alcohol, the conversion of ethyl alcohol was 44.37, a t an inverse space velocity of 0.048 (milliliters of catalyst) (hours)/(millimole), only slightly lower than that of pure alcohol feed. Similarly, feeding 3.7 and 15 molar % ethylene-alcohol mixtures influenced the conve,rsion of ethyl alcohol but little. The influence of water to the feed was, however, surprisingly large. I n Table I11 the conversions of different water-alcohol feeds are compared to the conversion of pure alcohol.
P e t h e r ?)water
p 2 sloohol
for 9570 alcohol feed is 0.17, which is considerably l o ~ e r o feed. Moreover, all values than the mean 0.28 for 1 0 0 ~ alcohol are low compared to the equilibrium values of other authors. Unfortunately, there are considerable variations in the published data. It seems that the more reliable value is that of Newitt and
Figure 2.
conversion of Alcohol to Ether
At tempereture 01 335' C. and pressure of 40 atmospheres
Semerano (8),who approached equilibrium from both sides a t 10 atmospheres and from one side at 50 atmospheres, and found K p to be 7.75 a t 266' C. The most recent values are 3.51 at 219' C. and 3.86 at 236' C. determined by Valentin ( I S ) ; by his formula this would extrapolate to a value of 20 a t 338" C. Alvarado ( I ) , who disproved the values of Pease and Yung (9), agreed with Clark et al. ( 4 ) that at 300" C. K1, is greater than 5 . The values a t 355' C. and 20 atmospheres, calculated from Table I of the present investigation, would indicate a value greater than 2.5. Thermodynamic equilibrium had, therefore, not been reached a t 40 atmospheres and at 335" C. in this investigation. It was, therefore, thought that the falling off of the conversion
INDUSTRIAL AND ENGINEERING CHEMISTRY
April 1953
rate was due to a deactivation of the catalyst by water either iormed in the reaction or added in the feed, the aytive ?-alumina being hydrated to or-alumina monohydrate. This would also explain the strong inhibiting effect of water, which could not be explained on kinetic grounds. This hypothesis seemed the more likely, since Bentley and Feachem ( 8 ) reported the ?-alumina to pass into an inactive boehmite (a-alumina monohydrate) between 154' and 256' C. at 1 atmosphere water vapor pressure. Recently Stumpf et al. ( I d ) , who have studied the transition of the different phases of alumina by x-ray diffraction, found that aalumina monohydrate passed into ?-alumina between 400' and 600" C. By following the transition by weight loss and surface area increase, Russel and Cochran (11) have shown that a-alumina monohydrate (either gelatinous or prepared by steam digestion of trihydrate a t 200' C.) passed into a practically anhydrous form a t about 400' C.; 30 hours' heating time was sufficient for total conversion of the hydrate. On the other hand, the same authors found that the monohydrate from trihydrate decomposition started to decompose a t or below 250" C. Unfortunately, the true decomposition pressure of the alumina hydrate has never been determined. To test the hypothesis that the catalyst is deactivated by water produced in the reaction, a fresh catalyst was run a t conditions of cpnstant conversion corresponding to the flat part of the curves in Figure 2. The actual conditions of the run were as follows: Feed Running time hours Volume of oaialyat ml. LHSV, (mlJ/(ml. ;st.) (hr.) Conversion,
Table 111.
857
Influence of Addition of Water to Feed on Conversion of Ethyl Alcohol
Inverse Space Velocity, (MI* Cat.) (Hr.) (Mmole.) 0.036 0.026 0.058 0.070 0.074 0.157
Water Added, Wt.
Conversion, % < 3 13
20.4 15 5 5 5
23
28.5 30.5 39
5
Conversion of Pure Alcohol, % 40 35 49 49 49 49
Ratio of
Conversions
