March 1948
INDUSTRIAL AND E N G I N E E R I N G CHEMISTRY
hydride ratio 2 to 1; temperature 325" F., reaction time 5 minutes, and catalyst concentration 1.33% based on total reactants by weight. The conversion obtained was essentially 100%. TREATMENT OF PRODUCT STREAM
\
In all the experimental runs the acetic acid, unreacted acetic anhydride when present, and phosphoric acid were water-washed from the product and last traces removed with ammonia solution. The thiophene was then topped out, first at atmospheric pressure and last traces a t about 20 inches of vacuum. The product was distilled under vacuum (20 mm. absolute pressure) in a 30gallon glass and glass-lined column. The purity of the final constant-boiling product was 99% or better. Transition cuts were rejected t o redistillation. No materials heavier than acetyl thiophene were distillable under these conditions. After a 20gallon batch of product had been run, a small amount of black tarry material remained in the still pot. This amounted to approxymately 0.470 of Dhe crude topped product and contained some acetyl thiophene because of column holdup. This residue was not analyzed but probably consists partly of polymers of thiophene. Commercially it would be desirable to recover the by-product acetic acid either to convert to acetic anhydride for re-use in the process or to market as the acid. Figure 9 is a flow sheet for a possible commercial unit. I n the operation of the process, using excess thiophene and converting all the acetic anhydride, the reaction, assuming a charge ratio of 2 moles of thiophene to 1 of acetic anhydride, may be written:
2C,TT,S
-
+ (CH,CO),O + 1% &PO4 CdH3SCOCH3 + CH,COOH + CaH4S + 1%
Hap04
Thus the product stream contains three major components and IL small amount of phosphoric acid. The main physical
389
properties of the products along with those of acetic anhydride are given in Table IV. Because of the wide differences in boiling points, the product components are readily separable by distillation. A study of the binary system thiophene-glacial acetic acid revealed an azeotrope boiling at 182' F. containing 4.5% by weight of acetic acid. However, this composition returned to the process as recycle thiophene has no undesirable effect on the reaction. Actually, in the operation of the process, because of limitations of column efficiency, thiophene containing 6% acetic acid is returned to the process. In the proposed scheme the separations are carried out in two columns. The thiophene and acetic acid are stripped overhead in a first column operating under slight vacuum, and the crude product and phosphoric acid withdrawn as bottoms. In the second column operating a t atmospheric pressure, the thiopheneacetic acid azeotrope is taken overhead to recycle, and the acetic acid withdrawn as bottoms. A third column may be used to distill the acetylthiophene for the production of pure grades after phosphoric acid hae been caustic-washed and density-separated from the crude product. LITERATURE CITED
(1) Goodloe, P.,IND.ENO.CHEM., ANAL. ED.,9,527(1937). (2) Hartough, H., and Kosak, A., J. Am. Chem. Soc., 68, 2639 (1946). (3) Ibid., 69, 1012 (1947). (4) Hartough, H.:Kosak, A., and Sardello, J., Ibid., 69,1014 (1947). (5) Radcliffe, L. G., and Medofski, S., J. 8 0 0 . Chem. Ind., 36, 628 (1917). (6) Rasmusgen, H. E., Hansford, R. C., Sachanen, A. N., IND.ENG. CHEM.,38,376 (1946). (7) Rasmussen, H. E., and Ray, F. E., Chent. Inds., 60,593(1947). (8) Steinkopf, W.,"Die Chemie des Thiophen," p. 73,Verlag von Theodor Steinkopf, Dresden andsleipsig, 1941. R E C E I V ~September D 22, 1947.
VAPOR-PHASE HYDRATION OF ETHYLENE OXIDE .
R. R. Cartmell', J. R. Galloway2, R. W. Olson, and J. M. Smith PURDUE UNIVERSITY, LAFAYETTE, IND.
THEincreased demand for ethylene glycol, chiefly for use
P
as an antifreeze, has stimulated investigation of new methods of manufacture. One of these is based on the vapor-phase oxidation of ethylene with air, followed by the liquid-phase hydration of the ethylene oxide to glycol in weakly acidic, aqueous solutions. In this investigation a study was made of the possibility of carrying out the second step (the hydration reaction) i n the vapor phase by passing ethylene oxide and steam over a solid catalyst, thereby eliminating the purification difficulties encountered in the acidic liquid-phase process. Over a temperature range from 150' to 250' C. with acid-type catalysts, such as phosphoric acid on alumina, silica gel, thoria, etc., no glycol was obtained, although considerable quantities of aldehydes were formed in some instances. Silver oxide on an alumina carrier was found to be effective, conversions to glycol ranging from 20 to 30oJ,, with corresponding yield figures of about 80 and 40%. This yield is affected by catalyst age, increasing to an approximately constant value of 80% after about 5 hours of operation. The results suggest that, with a new catalyst, significant quantities of ethylene oxide are converted to a by-product which is held on the solid catalyst surface.
D
URING the last few years the demand for ethylene glycol has increased at a rapid rate, the total production reaching over 200,000,000pounds in 1944 (8). As a result there has been considerable interest in the development of new methods of manufacture to compete with the conventional 'Dhlorohydrin process (2, 3, 11). I n one'of these ethylene is first oxidized to ethylene oxide by passing air and ethylene over a silver oxide catalyst, on a suitable carrier, at temperatures from 200-300° C. (6, 6). I n the second step glycol is obtaihed by hydration of the oxide. This reaction has been investigated in the liquid phase; it was found to take place slowly when ethylene oxide is dissolved in pure water and much more rapidly in the presence of a small amount of acid (IO). Since the presence of acid in the liquid phaseprocess may make extensive purification necessary, it seems desirable to investigate the possibility of avoiding its use by carrying out the hydration in the vapor phase. This paper presents the results of a preliminary investigation of the vapor-phase process. The reaction C~H40(g) HnO(g)+(CH20H)2(g)is exothermic. The heat of reaction is +23,000 calories per gram mole a t 25 C. using Bichowsky and Rossini's (1)values for the heats of formation of the three compounds.' 1 Present addresa, California Research Corboration, Whittier, Calif. 9 Present address, Riohmond, Ind.
+
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INDUSTRIAL AND ENGINEERING CHEMISTRY
To evaluate the equilibrium constant, the entropy change for the reaction was computed from the data tabulated by Wenner (9) at 25 C. : S, HnO(g) = 45.1 cal./g. mole O C. S, C2H40(g) = 64.0 cal./g. mole ' C. S, (CH,OH)2(1) = 39.9 cal./g. mole ' C. AH of vaporization S, (CHsOH)&) 39.9 298 = 84.2 cal./g. mole" C. A S o = -24.9 cal./g. mole' C. O
Vol. 40, No. 3
The constant temperature bath, 16 (Figure 1) consisted of a 4 . 5 inch id., 7.5-inch 0.d. steel cylinder equipped with two 2550watt Nichrome heaters. The fino1 heating medium was well agitated with a 2-inch propeller, 17, and maintained a t constant temperature, +0.5" C., with a mercury-in-glass regulator, 18. An 8foot coil of copper tubing, 19, through which cold water could be passed was available for rapid lowering of the bath temperature.
+
The standard free energy change and the equilibrium constant at 25' C. are A F o = A H " - TAS" = -15,800 cal./g. mole K = 4 X 10" (at 25" C.) Assuming as an approximation that AH is independent of ternperature, K a t 300" C. is
K = 3 X lo3 (at 300" C.) Even at 300' C. the equilibrium constant is high enough so that almost complete conversion is expected for the vapor-phase process at equilibrium. Since this temperature has been found to be above that a t which it is desirable to operate'(because of side reactions), the problem is reduced to one of finding a satisfactory catalyst. Consequently, the experimental apparatus described in the next section was constructed to facilitate catalyst testing. APPARATUS
Figure 1 is a drawing of the apparatus used during the experiments. Ethylene oxide from the cylinder, 1, was vaporized in the copper U-tube, 2, which was inserted in the constant temperature bath, 3. The rate of flow m s adjusted by means of needle valve 4 and measured in flowmeter 5. The steam rate was regulated and measured by needle valve 6 and flowmeter 7. Both the steam and ethylene oxide meters were calibrated at the conditions used in thg experimental work, but with the catalyst chamber empty. The reactant stream joined a t 8, and passed through a md OF copper tubing mound around the reaction chamber whose purpose wm to ensure uniform mixing of the reactants a t the bath Bsrnperature. All the lines were of '/,inch outside diameter capper tubing, except the flowmeters and manometers.
Figure 2. Reaction Vessel
The reaction products leaving the top of the reaction chamber were collected in two flasks, 20 and 21, placed in the ice bath, 22. The copper tubing condenser was divided into two sections, an initial short length (1 foot), 23, before the first flask and a 3-fOOt section, 24, before the final flask. I t was found that a single long condenser coil would frequently become rlogged, presumably because of the formation of hydrates of ethylene oxide. The outlet tube Fas vented to the atmosphere through a mercury seal, 25. When the apparatus was oper?ting satisfactorily there was no escape of vapors from the seal. OPERATION AKD ANALYTICAL METHODS
The operation of the equipment wm simple. After the reaction chamber had been brought to the desired temperature, the steam flow was started and adjusted to the proper value. The ethylene oxide rate was then set and a measured run begun. The usual run time was 1 hour, after which the material collected in the two condensate flasks was combined and analyzed. The unreacted ethylene oxide was determined by weighing the total product, fractionating in a glass column to separate the ethylene oxide, and reweighing. The method was tested by distilling synthetic mixtures of known quantities of ethylene oxide, ethylene glycol, and water. It was found that the ethylene oxide could be determined within 1%. This result indicates that there is no appreciable hydration of the unreacted oxide during the analytical process. Probably this is due to the fact that the major part of the ethylene oxide is vaporized while the solution is relatively cold and that
TABLEI. RESULTS WITH USSATISFACTORY CATALYSTS
Figure 1. Flow Diagram
Figure 2 is a detailea drawing of the reaction vessel. The outside chamber, 9, was a tube of brass, 1.75 inches in inside diameter and 11.5 inches high. The reactants entered the bottom of the chamber at 10 and left a t the side outlet at 11. In order to replace the catalyst without dismantling the reaction chamber, a 16-gage brass sleeve, 12, 10.5 inches long was used as a catalyst holder. This sleeve fit snugly in the reaction chamber. A thin, drilled brass plate, 13, was brazed to the bottom of the sleeve, and a brass screen, 14, placed in the top to hold the catalyst in place. The brass disk, 15, screwed to the top of the outer chamber, was equipped with a thermometer well which extended into the catalyst bed. The volume occupied by the catalyst was 325 ml.
Phosphoric acid on silica gel (12-20 mesh) Silicagel(6-12mesh) Same Alumina (3-6 mesh) 3%= thoria o n 3-6
Same Same 6.8% * silver on alumina (3-6 mesh) a
b
167
2.0
3
61
208 253 175 175
4.0 2.0 2.0 3.0
10 2 3 2
89 66
47 0
5
7 34 23
212 185
6.0
2.0
3 3
70 67
1 26
29 7
180
1.5
4
80
0
20
105
1.0
100
9
86
2.0 1.0
14 21 5
0 0 5
163
7 19
Represents per cent by weight of carrier. Aldehydes v i t h a boiling range from 30-98O C.
46 72
79 90
12 11
27 0
March 1948
IN D U S T R I A L A N D E N G IN E E R IN G 'CH E M I S T R Y
the entire distillation requires but a few minutes. The remainder of the product was analyzed for ethylene glycol and water by fractionating into separate components and measuring the volume of each.
391
,
CATALYST PREPARATION AND TESTING
Since hydrogen ion has been found to be an effective catalyst for the liquid-phase hydraticm, it appeared worthwhile to try an acidic type of catalyst, such as phosphoric acid, for the vapor-phase process. Twelve- to twenty-mesh silica gel was soaked in 85% phosphoric acid solution for 4 hours, the excess acid drained off, and the wet silica gel heated for 1.5 hours at 225" C. When this catalyst was tested a t 160" C. with a contact time of 2 seconds and a ratio of steam to ethylene oxide of 3, the product contained no ethylene glycol but 30% (by volume) of an aldehydewater mixture having a boiling range of 90-98" C. Several other catalysts-silica gel, alumina, thoria, and silver-were also tried, without success with respect to the hydration reaction. The results with these catalysts are shown in Table I, and the method of preparation is described in the following paragraphs. SILICAGEL. Six- to twelve-mesh silica gel, absorpCatalyst Age Hours . tion grade, from the Davison Chemical Company was used without further treatment. Figure 3. Comparison of Acidic and Basic Silver Oxide: Catalysts ALUMINA. Three- to six-mesh Alorco activated alumina from the Aluminum Ore Company was used without further treatment. Although the conversion is essentially the same, the yield is sigTHORIA ON ALUMINA. Thoria was dissolved in fuming sulfuric nificantly higher with the basic catalyst. acid and the solution evaporated to dryness. Water was added forming a white flocculent precipitate. The alumina carrier was introduced and the mixture evaporated to dryness. The material EFFECT OF CATALYST AGE AND ATTEMPTED REGENERATION was heated for 3 hours at 600' C. T H O R I A ON SILICAGEL. Thorium nitrate was dissolved in The yield curves in Figure 3 indicate that with a new catalyst water. Silica gel was soaked in the solution for 2 hours and the the major part of the ethylene oxide is converted to substances mixture evaporated to dryness. The catalyst wm heated a t other than glycol. However, the product analysis shows nothing 600" C. for 6 hours. but unreacted ethylene oxide, ethylene glycol, and water, so that SILVERON ALUMINA.Silver nitrate was dissolved in water, the by-product must be held in the reaction chamber. To investiand alumina added and soaked for 24 hours. The mixture was gate further the effect of catalyst age, runs were made for longer evaporated to dryness and heated for 6 hours at 550 O C. periods of time and regeneration with steam and air attempted. The results in Table I show that any of the catalysts were efI n theee tests operating conditions were maintained constant at fective in causing aldehyde formation a t sufficiently high temper170-172° C., 1.8 seconds contact time (referred to the volume of atures, but that alumina was the most active. *Sincethe investithe empty catalyst chamber), and a steam-ethylene oxide molal gation of the aldehyde reaction was not the object of this work, no ratio of 13.5. The results are shown in Figure 4 and Table 11. further study was made of the catalysts in Table I. However, These data show, as in Figure 3, that the yield first increases and further investigation might be warranted for the purpose of anathen tends toward an equilibrium value of 80-85'% after about 4 lyzing this method of obtaining aldehydes from ethylene. Some hours. After 7 hours of operation with catalyst 4, superheated work has been reported on the isomerization of ethylene oxide to steam a t 195" C. was passed through the bed for 1 hour. The acetaldehyde in German (7) and English ( 4 )patents. effect of this was to reduce the yield but not affect appreciably SILVER OXIDECATALYST.It was found that silver oxide on an the conversion of the subsequent run. Regeneration with air alumina carrier was yln effective catalyst for the hydration reachas the same result, equivalent to returning the catalyst to its origtion. In the early work this material was prepared by the decominal condition (zero catalyst age). These results lead to the position of silver oxalate. Three- to six-mesh alumina was soaked conclusion that the by-product reaction, which is predominant on for 24 hours in a 10% silver nitrate solution and evaporated to a fresh catalyst surface, falls off and reaches an equilibrium value dryness. A 10% oxalic acid solution was added, the mixture evapocorresponding to 15-20% of the total ethylene oxide. The atrated to dryness, and the precipitate washed with water. The tempted regenerations with steam and air were harmful rather oxalate was decomposed by heating for 24 hours at 200 " C. Later than helpful since, as a result, the conditions of fresh catalyst surit was noted that a more effective catalyst could be obtained by face were reproduced. During the air regeneration runs a highly the simpler procedure of precipitating silver oxide directly from exothermic reaction occurred, presumably the burning of the bythe nitrate by adding a 10% sodium hydroxide solution. The preproduct adhering to the catalyst surface. The temperature of the cipitate was washed with water and heated at 200' C. for 24 hours reaction chamber rose to nearly 300 " C. during the air runs. as before. In all cases the silver oxide constituted 8.7 weight % REACTION MECHANISM.The material adhering to the catalyst of the inert carrier. surface was recovered by collecting the condensate from t h e Figure 3 shows a typical yield and conversion curve for both steam regeneration runs. Vacuum fractionation of this condenthe first, or acidic type, and the second, or basic type, of catalysts. sate (after the water was distilled off at atmospheric pressure) inConversion is considered to be the per cent of the total ethylene dicated that' the major portion was ethylene glycol, with small1 oxide that is converted to ethylene glycol. The yield is the per amounts of diethylene and triethylene glycol. Since the hydracent of the reacting ethylene oxide that is converted to glycol, tions runs were carried out at conditions such that the partid
5
-
"11
x
INDUSTRIAL AND E N G I N E E R I N G CHEMISTRY
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Vol. 40, NO. 3
The presence of considerable ethylene glycol on the catalyst surface, and the low yield obtained with fresh catalyst and immediately following regeneration, indicate that Equation 3 is sufficiently slow to affect the over-all reaction rate. It may be that this is a case of the reaction product retarding the process by covering a significant part of the active catalyst surface. The fact that the yield approaches a constant value after a few hours (Figures 3 and 4) suggests the existence of a dynamic equilibrium where the fraction of the catalyst surface occupied by adsorbed glycol molecules does not change. EFFECT O F TEMPERATURE. The effect of temperature has not as yet been fully investigated. However, preliminary results a t 1.8-seconds contact time, a steam-ethylene oxide ratio of 10-15, and a catalyst age of 3 9 IO hoursindicate that the yieldis negligible C A T A L Y S T AGE - H O U R S below 105’ C., amounts to about 5% a t 110’ C., and increases to Figure 4. Effect of Catalyst Age and Regeneration about 80% at 170” C. It has also been observed that, a t temperatures much above 200” C., the yield of glycol decreases and the aldehyde reaction becomes significant. pressure of ethylene glycol in the vapor phase would not exceed its vapor pressure, glycol must be adsorbed on the catalyst SUMMARY surface. Since no ethylene oxide was discovered in the condensate from the regeneration with steam, it would appear that it is Phosphoric acid, silica gel, alumina, thoria, and silver were not necessary for the oxide to be adsorbed to produce glycol and found to be inactive as catalysts for the hydration of ethylene oxthat it is not adsorbed by the silver oxide catalyst. This suggests ?de over the range of conditions studied. However, considerable that the activity of the catalyst is due to its ability to adsorb waquadtities of aldehydes were formed in some cases. It appears ter vapor. The next step is the reaction of this adsorption comlikely that steam did not take part in these reactions. Silver oxplex with one molecule of ethylene oxide to regenerate the cataide on alumina was effective in catalyzing the hydration reaction. lyst surface. The reactions might be written, The only products collected were water, unreacted ethylene oxide, and glycols, although the yield is reduced because of the deposition AgzO HzO(g) = AgzO[HzOl (1) of a by-produkt on the catalyst surface. The extent of this side reaction decreases with catalyst age. The adsorbed by-product CzHaO = [(CHzOH)z]AgzO AgaO[HzO] (2) can be removed by regeneration with air or steam, but this reduces rather than increases the glycol yield for the first 3-4 hours after regeneration. The fact that silver oxide has been found to be an effective cataTo determine with more certainty whether water vapor Was lyst for both the oxidation of ethylene and the hydration of ethyladsorbed, the reactor was evacuated after a hydration run and ene oxide suggests the possibility of converting ethylene to glycol the evacuation product collected in a dry ice-acetone condenser. in one reactor by introducing steam, air, and ethylene. If this Vacuum distillation of this material yielded no ethylene oxide and process proved t o be feasible it would have many advantages over consisted chiefly of water, ethylene glycol, and small quantities existing methods of glycol manufacture. of polyethylene glycols. Temperature Contact Time
= =
170-172.C. I 8 Sec
+ +
LITERATURE CITED
AGEAND REGENERATIOX TABLE 11. EFFECTOF CATALYST (Operating conditions: temperature, 170-172’ C.; contact time, 1 . 8 secondsa; molal ratio of steam to ,ethylene oxide, 1 3 . 5 ; pressure, atmospheric; basic type catalyst) Catalyst 4 Catalyst. age, hr. 1 2 3 4 5 6 7 8 9 1 0 1 1 30 25 27 24 22 32 24 22 24 23 22 Conversion, % 80 60 30 53 78 .. Yield, % p P P P P P R8 P , R n P P P Type of run b
..
Catalyst 7 1 2 3 4 5 6 Catalyst age, hr. 41 31 23 22 24 23 Conversion, % 48 66 75 37 52 79 Yield, % P P P,Ro P P P Tvue .. of runb a Contact time is based on volume of empty catalyst chamber 325 CC. b Type of run: P, hydration: Rs,steam at 195O C. was’pas$ed over the catalvet for 1 hour: R., air initlally at 170” C. was passed over the catalyst for 1 -hour.
(1) Bichowsky, F. R., and Rossini, F. D., “The Thermochemistry of Chemical Substance,” New York, Reinhold Pub. Corp., 1939. (2) Curme, G. O., U. S. Patent 1,422,184 (1922). (3) Curme, G. O., and Young, C. O., Ibid., 1,456,916 (1918). (4) I. G. Farbenindustrie A,-G., Brit. Patent 331,185 (1930). (5) Lefort, T. E., U. S. Patent 1,988,878 (1929). (6) McBee, E. T., Hass, H. B., and Wiseman, P. A., IXD.ENQ. CHEW,37, 432 (1945). (7) Rheinische Kampfer-Fabrik G.m.b.H., German Patent 547,641 (1931).
U. S. Tariff Commission, R e p t . 155 (1944). Wenner, R. R., “Thermochemical Calculations,” New York, McGraw-Hill Book Co., 1941. (10) Whitmore, F. C., “Organic Chemistry,” New York, D. Van Nostrand Co., 1937. (11) Young, C. O., U. S. Patent 1,456,959 (1922) (8) (9)
RECEIVED September 22, 1947.
