VAPOR PHASE VINYLATION OF ALIPHATIC MONOHYD RIC ALCOHOLS VICTOR A. S I M S A N D J A M E S F. V l T C H A Central Research Laboratories, Air Reduction Co., Inc., Murray
Hill,N . J .
The vapor phase addition of aliphatic monohydric alcohols to acetylene over alkaline fixed-bed catalysts was investigated. O f the evaluated catalysts, potassium hydroxide specifically supported on magnesia (periclase) or lime (calcium oxide) gave the best results with respect to production of aliphatic vinyl ethers and catalyst life. Primary alcohols, in general, were vinylated more easily than secondary alcohols. The reaction with 2-methyl-2-propanol went with extreme difficulty. Marked exotherms, characteristic of these reactions, often had a deactivating effect on the catalysts.
commercial methods for the manufacture of vinyl ethers had been developed in Germany in the l930's, these ethers became available in this country only after World War I1 (8). Vinyl ethers have potential value as chemical intermediates and as monomers but thus far have not been fully exploited. Numerous substances can be readily added across the double bond to produce ether derivatives that often cannot be obtained by any other means (7,8). Addition polymers. ranging from viscous, sticky liquids to elastomeric solids, are formed under influence of certain acid catalysts (8). These ether polymers find industrial applications in plastics and lacquers and as plasticizers, adhesives, and impregnation agents. The most satisfactory method for preparing simple aliphatic vinyl ethers is by the direct addition of alcohols to the triple bond of acetylene (7, 3:5. 6, 8 ) . I n this vinylation reaction as developed by Reppe and his associates (61, diluted acetylene under pressure reacts with the alcohol at 120' to 185' C.?in the presence of a strongly alkaline medium, to give the corresponding aliphatic vinyl ether:
A
L'rHoucH
CH-CH
+ ROH
-t
CHz=CH-OR
Although the above reaction has been studied extensively and numerous vinyl ethers have been prepared by the liquid phase process (51, few useful data have appeared for comparable reactions conducted in the vapor phase. In a 1936 patent (7). Reppe and Wolff reported successful vinylation of 1-butanol a t 265' C. in the presence of a soda-lime catalyst. No detailed information, however, has been published with respect to reaction conditions and catalysts, except for the vinylation of methanol. That study is limited to two catalyst systems, commercial soda lime ( 4 ) and potassium hydroxide supported on charcoal (2). The reported yields are good, but catalyst life is short and the catalysts do not respond to regeneration ( I ) . Surprisingly, nothing is mentioned, in the open literature, on the vapor phase vinylation of more complex alcohols than simple primary alcohols. The present work was undertaken to find more efficient alkaline catalysts that would be better suited for the vapor phase vinylation of alcohols in general. Also? the effects of catalyst composition, reaction conditions, and structure of alcohol were investigated to obtain a more comprehensive knowledge of this potentially useful vinylation process.
Experimental
Catalysts. I t was found that the nature of the catalyst support used in conjunction with potassium hydroxide was critical. Of the supports tested, magnesia (Westvaco Mineral Products Division, periclase-base pebbles consisting of 94 to 977, MgO) and lime (Fisher Scientific Co., S . F . pure calcium oxide lumps) were crushed into 4- to 10-mesh particles; activated charcoal (Columbia Carbon Co.. C-1038) was purchased as 4- to 6-mesh pellets. The general procedure for catalyst preparation was to heat the catalyst support a t 130" C. under vacuum (5 mm. of Hg) and then impregnate with a minimum amount of an aqueous or alcoholic solution of the dissolved basic catalyst. While being stirred under vacuum, the impregnated catalysts were slowly dried using moderate heat (to 140' C . ) . Before evaluation, all catalysts were heated in the reactor under nitrogen a t 250' to 300' C. (or about 50' higher than expected maximum reaction temperature). Commercial soda lime (Fisher Scientific Co., S-196 or S-200, 8- to 14- or 4- to 8-mesh) was used as purchased except for vacuum drying and heating in nitrogen before catalyst evaluation studies. Feed Streams. Prepurified grade cylinder nitrogen and purified acetylene (Airco gases) were metered through capillary floivmeters. Commercial acetylene was purified by passing the gas through a dry ice-cooled trap and then through a tall tower of alumina. A pressure-relief tube was also incorporated in the gas manifold system (not shown in Figure 1). Commercial, anhydrous alcohols were metered by a Brewer automatic pipetting machine (Model 120, Baltimore Biological Laboratories, Inc.) into the top of an electrically heated vaporizer tube. Acetylene, nitrogen, or acetylene-nitrogen mixtures: entering at the bottom of the vaporizer, carried the vaporized alcohol into the reaction zone (see Figure 1). Reaction Procedure. The arrangement of the major components of the laboratory-scale vapor phase vinylation apparatus is illustrated in Figure 1. The 18-inch-long reactor tube of 1-inch 0.d. borosilicate glass was normally packed with 100 ml. of test catalyst, which was centrally positioned over a IO-inch length. In this position, the catalyst bed was in an even temperature zone. Bed temperatures were measured by a n internal sliding thermocouple to follow the path of the hot spot. A temperature gradient of the catalyst bed was measured a t intervals of 15 minutes or less during a run. In a successful run, the hot spot moved very slowly downward through the catalyst bed a t a constant rate. Alcohol feed was started in a nitrogen atmosphere, and acetylene was then introduced in increments as the nitrogen VOL. 2
NO. 4 D E C E M B E R 1 9 6 3
293
I C A L I B R A T E D LlOUlO F E E D SYSTEM 2 M I C R O PUMP 3 C A P I L L A R Y FLOW M E T E R 4 PREHEATER A N 0 M I X E R 5 ELECTRIC FURNACE 6 BERL S A D D L E S 7 SLIDING T H E R M O C O U P L E TO T E M P E R A T U R E CONTROLLER 8 REACTOR 9 CATALYST B E 0 IO C O N D E N S A T E RECEIVER I I I C E CONDENSER 12 D R Y ICE TRAPS 13 WET TEST M E T E R
I
I
"
I
1
I
_.---
HOURS
Figure 1 .
IO
Vapor phase vinylation apparatus
stream was being shut down. Since the resulting reaction was often highly exothermic, bed temperatures had to be controlled by heat input and occasionally by an air stream applied on the exterior wall. Lack of an exotherm and poor acetylene take-up signified an inactive or a spent catalyst. Condensable products, coming out of the reactor, were collected in a receiver and when needed in dry ice-cooled traps. For example, methyl vinyl ether is a gas a t ordinary temperatures and pressures (b.p. 5.5' C.), but was easily condensed in the apparatus shown in Figure 1. Exit gas was measured by a wet-test meter and was designated as recovered acetylene in our calculations. Liquid products were analyzed for alcohol content by acetylation and for alkyl vinyl ether by the iodoacetal method. Products were also separated by distillation for the most important runs. O n this basis, conversion and yields were calculated (see footnotea, Table I). Results and Discussion
Catalyst Evaluation. Fixed-bed alkaline catalysts were evaluated for the vapor phase vinylation of methanol and 2-propanol in order to compare their effectiveness for producing alkyl vinyl ethers from a primary and a secondary alcohol. The results pertinent to the present discussion are shown in Table I. Potassium hydroxide was found to be the best catalyst; but to make the catalyst system highly effective, the
- I 5
OF
T E M P E R A T U R E OF HOT ZONE MeOH TO C 2 H 2 M O L E - RATIO L . / H R / L SPACE VELOCITY
Figure 2. Comparison of catalyst activity and life for vapor phase vinylation of methanol
alkali had to be impregnated on a specific type of support. For example, activated charcoal proved to be a poor support because it had to be heavily laden with alkali (40 to 50% KOH on C) to display a reasonable degree of activity. Acidic or amphoteric supports are unsatisfactory for alkalies, because of pronounced degradation (2). Basic supports have apparently been tried in a few instances (3, 7) but with limited success. We felt, however, that a suitable alkaline catalyst support for potassium hydroxide not only would prevent catalyst degradation and loss of porosity but might also function as a cocatalyst or promoter. Magnesia (periclase MgO) or lime (pure CaO) as a carrier for 5 to 15% potassium hydroxide by weight proved to be the most outstanding vinylation catalyst system found in our work (Tables I and 111). This combination of alkaline materials produced a highly active and selective catalyst, as verified by the many aliphatic vinyl ethers prepared in high yields. Magnesia or lime used by itself exhibited virtually no catalyst activity. Sodium hydroxide as tested on several carriers was less active as a vinylation catalyst for methanol (2) and 2-propanol than potassium hydroxide. Commercial soda lime, contrary to reports (4, 7). had poor catalyst properties in our tests, as evidenced by low conversions and rapid deactivation. Other
+
+
on M e 0 10% N a S H on MgO
a
294
5 conu.
=
Trace 70 24 60 c:
moles of e t h f i X 700. molps of acetylene f e d
CaO
... 90
157,KOH on CaO Soda lime 507, KOH on C
45 90 ...
ycyield
=
moles of ether X 700. moles of acetylene reacted
l&EC PRODUCT RESEARCH A N D DEVELOPMENT
H
OPERATION
Table 1. Initial Activity of Vapor Phase Vinylation Catalysts A B CH30H CzHz + CHa--O-CH=CH2 (CH3)2CHOH C2H2 + (CHa)sCH--O-CH=CHz Mole ratio of ROoH to C?H2 1.1-1.4 1.1 Hot zone temp., C. 2 10-260 180-230 Space velocity (N.T.P.)., l./hr./l. 50-100 75-100 Reaction time, hr. 3-6 3-5 Results Based on Acetylene Results B a e d on Acetylenea Catalyst System 7, conv. 7, yield Catalyst System yGconu. %yield. 4 . . . 0 ... MgO MgO 34 1Yc KOH on MgO 60 47, KOH on MgO 20 45 676 KOH on MgO 70 90 7 % KOH on M e 0 40 60 157, KOH on MgO 74 15% KOH on G g o 85 65 80 25 60 10% K-OCH(CH3)g
Ca(OH)2 15Y0 KOH on CaO Soda lime 507, KOH on C 15% KOH on C
I
% KOH ON C a O r 5 0 % KOH ON CARBON C O N D I T I O N S FOR V I N Y L A T I O N
VAIN'
50 - 200
I2
I
\
1 I
I2
I
r 10% KOH ON M g O
21O'-26O0C
13
I
Table II. Catalyst Attrition and Activity during Vapor Phase Vinylation of Methanol Acetylene Conversion Hours to Methyl Final Catalyst Vinyl Ether of Initial Catalyst Reaction Composition Initial Final Composition
so
154 KOH on MgO 6Yc KOH on M g O 50yo KOH on C
8 30 15
0.5% KOH on MgO 2YC K O H o n M g O 257, KOH on C
34 70 60
4
65 10
common bases such as alkali metal cyanides: acetates, and carbonates when impregnated on magnesia or charcoal had poor activity as vin)-lation catalysts. Catalyst Activity and Life. To demonstrate the outstanding performance of the potassium hydroxide-magnesia catalyst system. a plot of catalyst activity has been made for the extended vinylation of mrthanol. Several other catalysts have been included for comparison. Figure 2 readily shows that the t\vo reported vinylation catalysts-soda lime (4, 7) and 50% potassium hydroxide on charcoal (2)-are inferior in activity and catalyst life to either the K O H - M g O or K O H C a O system. More exactly? potassium hydroxide on magnesia produced methyl vinyl ether in 707, conversion and 85 to 1007, yield during the entire 30-hour intermittent reaction period (Table I). Potassium hydroxide on lime gave equivalent activity but displayed shorter life. The broken lines in Figure 2 indicate the projected catalyst life based upon the rate of movement of the hot spot in the catalyst bed. During this time, conversions to methyl vinyl ether remained almost constant. As the exotherm reached the end of the bed, the vinylation rate dropped rapidly. The hot spot effect was observed only for active catalyst systems and when the exotherm was carefully controlled. With a poor catalyst such as soda lime, the reaction exotherms were slight and movement of the hot spot was erratic. Catalyst Deactivation. Spent alkaline catalysts could not be reactivated by heating in air, nitrogen, or steam or by washing with solvents. This seemed to indicate that catalyst deactivation was probably due to other factors than usual surface adsorption of contaminants (4). A possible explanation is that the alkali w a s being gradually converted to a n acid salt during the vinylation, as occurs in the liquid phase vinylation process (3).
A number of simple experiments were devised to substantiate the disappearance of potassium hydroxide as the vinylation of methanol progressed. Table I1 shows the extent of alkali attrition us. reaction time. and the effect of the modified catalyst composition on the vinylation results. A synergistic effect is apparently displayed by the combination of potassium hydroxide-magnesia (or lime). A few per cent of this alkali deposited on magnesia-base pebble produces a n active cataly-st with long life. By comparison, a n unusually heavy concentration of potassium hydroxide (40 to 50%) on carbon is needed to achieve comparable vinylation activity for a much shorter period of time. Magnesia (periclase pebbles), by itself, is not a vinylation catalyst. Reaction Conditions for Vinylation. O u r present studies Xvere concerned only with conditions for effective vinylation in the presence of fixed beds of potassium hydroxide on magnesia or lime. IVith these highly active catalysts, reaction temperature was the most important process variable. Although space velocity and mole ratio of alcohol to acetylene were held constant. reaction temperature could not be contained within narrow limits as reported by other authors using less active catalysts (2, 4 ) . Vapor phase vinylation of alcohols over active catalysts was found to be highly exothermic, and heat of reaction was difficult to remove efficiently. I n general, bed temperatures for low molecular weight alcohols (to C,) were set at 160' to 200' C. with the hot zone or "reaction temperature" averaging about 10" to 75' C. higher; intensity of the exotherm was dependent on type of alcohol (primary. secondary, or tertiary) vinylated and nature of support (MgO or CaO) used with ROH. Much higher reaction temperatures were needed for longer chain alcohols (see Table 111). I n our studies, proportion of reactants was confined to mole ratios of alcohol to acetylene of 1 to 1.5. An excess of acetylene caused rapid catalyst deactivation, and a large excess of alcohol afforded no noticeable increase in aliphatic vinyl ether production. Best space velocities, under our conditions, appeared to be 50 to 150 liters of gaseous reactants per liter of catalyst (N.T.P.). Effect of Alcohol on Vinylation Results. Base-catalyzed addition of methanol to acetylene produces methyl vinyl ether, the simplest member of the alkyl vinyl ether family. Surprisingly. the detailed study of gas phase vinylation. in the literature, is limited to methanol ( 2 , 4). This might be due to the fact that methanol is probably the easiest alcohol to vinylate in the vapor phase and alkaline catalysts seem to be less prone to deactivation with this alcohol. We proved that structure of
-
Table 111. Vinylation of Various Alcohols over Active Catalysts Reaction. ROH CHECH R-O--CH=CH2 Mole ratio of ROH to CZHZ. 1.O-1.3 Space velocity (NTP). 70-100 liters/hr./liter
+
Alcohol Vinylated
CH30H CHsOH CHzCHzOH CHaCHzOH H?N-CHzCHzOH n-CH3( CH2)iOH n-CHz(CH2)110H Cyclohexanol (CHz)zCHOH (CH3)zCHOH (CH3)zCOH (CH313COH Sue footnote a in Table I .
Catalyst Composition 5-15yc KOH on MgO 15% KOH on CaO
5-iS70 KOH on MgO 5-15% KOH on CaO
Acetylene to Alkyl Vinyl Ethera 7oyield 70 85 72 90
Average Hot Zone Temp., "C.
Tc con&.
250 21 5 200 190 220 245 285 240 185 225 210 21 5
69 56 40 67 38 50 40-65 53 20 25
VOL. 2
NO.
83
73 87 95 100 83 60-80 70 40 40
4 DECEMBER 1 9 6 3
295
the alcohol that was vinylated had a pronounced effect on reaction rate and also on catalyst life. As shown in Table 111, the general trend of vapor phase vinylation with the most active catalysts goes best with primary alcohols, such as methyl. ethyl, n-octyl, n-dodecyl. and 2-aminoethyl. Poorer results were obtained with secondary alcohols. Vinylation of tertiary alcohols, as typified by 2-methyl-2-propanol. proceeded at a much lower rate than secondary alcohols. .411 results reported are based on acetylene. M’hen Iields of methyl, ethyl. and isopropyl vinyl ethers are calculated on the alcohol. they are higher than the yields shown in Table 111. In these experiments, the alkyl vinyl ether plus alcohol totaled 95 to 98y0 of the reaction product, which indicated very little by-product formation. The material balance based upon weight in and out was usually 95 to 10070. Catalyst life with the most active catalysts (Table 111) was found to be much longer during the vinylation of methanol than ethanol or 2-propanol. Vinylation of 2-methyl-2-
propanol was difficult to achieve and catalysts were prone to rapid and often immediate deactivation. Similarly, phenol which contains an acidic hydroxyl group, was found to vinylate poorly in the presence of basic catalysts. literature Cited
(1) Copenhaver, J. W., Bigelow, M. H., “Acetylene and Carbon Monoxide Chemistry,” p. 32, Reinhold, New York, 1949. (2) Ghosh, J. C., Bhattacharyya, S. K., Chaudhuri, D. K. R.: Petroleum (London) 19, 358 (1956). (3) Hanford, W.E., Fuller, D. L., Ind. Eng. Chem. 40, 1171 (1948). (4) Harshman, R. C., Dtssertation Abrtr. 18, 538 (1958). (5) Reppe, W.,Ann. 601, 81 (1956). (6) Reppe, W. (to I. G. Farbenindustrie), L.S. Patent 1,959,927 (May 22, 1934). (7) Reppe, W., Wolff, W. (to I. G. Farbenindustrie), Ibzd., 2,066,076 (Dec. 29, 1936). (8) Schildknecht, C. E., “Vinyl and Related Polymers,” p. 593, Wiley, New York, 1952. RECEIVED for review May 23, 1963 ACCEPTED August 19, 1963
VINYL ETHERS OF DIETHYLENE GLYCOL R . L. Z I M M E R M A N , G. D. JONES, A N D W. R. NUM-MY The Dow Chemical Co., Midland, Mich.
Diethylene glycol was made to react with acetylene in the presence of a basic catalyst; by operating a t low conversion and separating the mixture by distillation and extraction with water, both the monovinyl ether and the divinyl ether of diethylene glycol were obtained in good purity and characterized. Additives for inhibition or stabilization were investigated. Reactions of the vinyl ether group were investigated, including the free radical-catalyzed addition of hydrogen sulfide, which in the case of the divinyl ether of diethylene glycol yields a tetraethylene glycol dithiol. Homopolymers and copolymers of the monovinyl ether of diethylene glycol were produced by free radical initiation and a series of rubbery copolymers was cured with a rubber vulcanization recipe. Copolymers of the divinyl ether of diethylene glycol were prepared wherein the second vinyl ether group was available for secondary reaction.
synthesis of vinyl ethers of glycols by the reaction of Tacetylene with glycol (Equation 1) HE
HC=CH
+ HOROH
KOH
+
CHe=CHOROH CH2=CHOROCH=CH?
(1 )
in the presence of a basic catalyst is a n attractive reaction from the standpoint of utilization of glycols and acetylene and the production of potentially cheap and unique monomers. Interest by the authors in the possibility of large scale commercialization resulted in the present review and investigation of the synthesis, reactions, and polymerization of diethylene glycol vinyl ethers. Divinyl ether of diethylene glycol is now being sold as a chemical specialty, whereas the monovinyl ether is not known to be available commercially. Monovinyl ether of ethylene glycol was first reported by Hill and Pidgeon ( 6 ) , and using the vinylation reaction, later by Reppe (72-74), who also reported the divinyl ether and synthesized the vinyl ethers of 1,4-butanediol and diethylene glycol. Isomerization of vinyloxyethanol to methyldioxolane (Equation 2) 296
l & E C P R O D U C T RESEARCH A N D D E V E L O P M E N T
CHFCHOCHZCHZOH
-
/O-CH?
CHICH \O--bHt
(2)
was found by these authors to occur in the presence of acidic substances with explosive violence and also occurred during vinylation and distillation. Walling and Faerber (78) employed a process which removed the glycol monovinyl ether of ethylene glycol, 1,3-methylene glycol, or diethylene glycol from the reaction zone with excess acetylene or an inert gas to avoid cyclization. \$‘hen four or more atoms separate the hydroxyl groups, the cyclization tendency is greatly reduced, so that diethylene glycol (DEG) was selected in the present work for the development of a process to produce both the monovinyl ether (MVE) and the divinyl ether (DVE). Preparation
The vinylation of diethylene glycol proceeds smoothly a t temperatures in the range of 160’ to 200’ C. a t acetylene partial pressures of 25 to 200 p.s i. (72, 73, 78). Since acetylene can
