OXYPROPYLATION OF GLYCEROL A Study of Variables CARL W. Y O S T , ' C .
A. P L A N K , A N D E. R. G E R R A R D
Department of Chemical Engineering, University of Louisville, Louisville, K y .
The oxypropylation of glycerol in the presence of alkaline catalyst has been studied in a semibatch operation. Initial catalyst concentration was varied from 0.22 to 2.3 weight % KOH, temperature was varied from 220" to 270" F., and agitation speed was varied from 50 to 200 r.p.m. The rate of reaction was shown to increase with increase in all three variables. The most significant variable was catalyst concentration, which gave a fourfold increase in reaction rate.
glycol is a major raw material for polyThe rapid growth of foam usage in the furniture, automotive, and construction industries has resulted in the development of a new major chemical industry during the past decade and has created a challenge for industry to improve the productivity of existing facilities. This investigation was concerned with the base-catalyzed reaction of propylene oxide and glycerol to yield the poly(oxypropylene) derivative of glycerol, a triol. Previous work on base-catalyzed reactions of propylene oxide with low molecular weight triols has been reported in the patent literature (De Groote, 1953; Lundsted, 1954; Pruitt and Rogers, 1960; Saunders and Frisch, 1962; Union Carbide Corp., 1960). Typical reactions for glycol and triol formation are reported (Bender, 1965). The exothermic reaction is usually carried out in a stirred tank reactor jacketed to remove the heat of reaction. The initiator and catalyst are charged to the reactor and heated to reaction temperature. Propylene oxide is added a t the maximum possible rate while maintaining constant temperature and pressure until the desired molecular weight product is formed. The final product will require 110 to 115% of the theoretical amount of propylene oxide because of side reactions and molecular weight distribution. OLYPROPYLENE
Purethane foam.
Raw Materials
The glycerol and propylene oxide used in these experiments had the following properties: Property
The catalyst used was 85% reagent grade potassium hydroxide. Experimental Apparatus
The experiment was carried out in a 5-gallon reactor constructed from 10-inch 304 stainless steel pipe. The essential components of the reactor were : An outer jacket for cooling and heating the reactor contents. An internal agitator fitted with a double mechanical seal cooled by circulating glycerol. An injection ring to assure uniform distribution of the propylene oxide feed. Two internal baffles to prevent vortexing. Sampling ports and temperature and pressure measuring and controlling instruments. The complete experimental system is shown in Figure 1. I n addition to the reactor, the system contained a propylene oxide weigh tank, preheater, condensers, nitrogen supply, and the necessary control valves and instruments (Yost, 1966). Operating Procedure
The reactor was initially purged with nitrogen. The catalyst was dissolved in the glycerol and the mixture added to the reactor. Agitation was started and a vacuum (29.9 inches of Hg) applied to the apparatus to remove the nitrogen. The glycerol and catalyst were then preheated to the desired temperature. The temperature and pressure controllers were set and preheated propylene oxide was added as rapidly as possible until the desired reactor temperature and pressure were obtained. During the reaction, the propylene oxide feed rate was measured and samples of the reacting mixture were taken and analyzed for hydroxyl number, volatile content,
Limits
PROPYLENE OXIDE Water, wt. 7, Aldehyde, wt. 7, Organic chloride, w t . 70 Color APHA Ethylene oxide, wt. 7,
0.030 max. 0.010 max. 0.008 10 max. 0.010 max.
GLYCEROL
Glycerol, wt. 7, Spec. gravity 25 O / 2 5 C. Color APHA Appearance Total chlorine, wt. 7, Sulfates, p.p.m. Ash, wt. 7 0 Arsenic, p.p.m. O
99.570 min. 1 ,2607 min. 20 max.
Clear
0.0005 20 max. 0.017, 2 max.
Present address, Olin Mathieson Chemical Corp., Brandenburg, Ky.
Figure 1 ,
Experimental system VOL. 6
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and catalyst concentration over the average molecular weight range of 260 to 3000. Accordingly, the propylene oxide reacted was obtained by subtracting the propylene oxide in solution from the amount added. The slope of a plot of propylene oxide reacted us. time was constant after steady conditions were established. This value, calculated as moles of propylene oxide reacted per hour per mole of glycerol charged, is referred to as the rate of reaction. Variables studied were catalyst concentration, temperature, and agitation.
3.0
0.0
1.0
0
I .o
0.5
1.1
0.0
W1.X K O H
Figure 2.
Effect of Catalyst Concentration
Effect of catalyst concentration
The most significant variable was catalyst concentration, which was studied at 250' F., 55 p.s.i.g., and a 120-r.p.m. agitator speed (Figure 2). The catalyst concentration is defined as the weight per cent KOH in the original glycerol charged. The reaction rate increased fourfold as the catalyst concentration was varied from 0.22 to 2.3 weight %. The curve appears to become asymptotic at the higher catalyst concentrations. Effect of Temperature
220
230
240
260
050
270
A value of approximately 210' F. is needed to initiate this reaction in the catalyst concentration range studied. Since temperature control is difficult, the upper temperature was limited to 270' F. because of the heat transfer characteristics of the apparatus. Data were obtained at 220°, 230', 250°, and 270' F. for a catalyst concentration of 0.85 weight %, 120 r.p.m,, and 55 p.s.i.g. (Figure 3). The data point at 250' F. on this plot was taken from the smoothed curve of Figure 2.
260
TEMPERATURE 'F
Figure 3. 3.0
Effect of reaction temperature
I
-I 0
*E
2.0
au
./-:
/.Ad&y---=40
02.
',:
23O.F 220
1.0-
0
F
IP.S.I.G. 0.65 % K O H
I O
1
OF
*F
4.-
wA & w
2:
270
10
100 AGITATOR
Figure 4.
150
Only one type of impeller was used and its speed was varied from 50 to 200 r.p.m. Data \yere taken at 0.85 weight % catalyst, 55 p.s.i.g., and 220', 230°, 250', and 270' F. (Figure 4). The most significant data, obtained at 230" F., indicate an approximately 60% increase in reaction rate upon varying the speed from 50 to 200 r.p.m. Data a t other temperatures were drawn to parallel this effect.
200
R.P.M.
Effect of agitation
and alkalinity. Hydroxyl number was used to characterize molecular weight. The volatile content is a measure of the unreacted propylene oxide. Results
The propylene oxide feed rate was measured. Charge tank weight decrease provided usage rate. A recording orifice meter provided continuous information. Part of the propylene oxide accumulated in the reactor vessel and the remainder reacted with the glycerol and later with the triols. Usually 15 to 30 minutes were required for satisfactory temperature and pressure control to be established. During this time most of the glycerol reacted to form the lower molecular weight triols. After steady operations were obtained, samples showed that the propylene oxide in solution was a t the vapor-liquid equilibrium value for the particular temperature and pressure. These vapor-liquid equilibrium data have been reported (Plank and Yost, 1967). The propylene oxide concentration, in weight per cent, is independent of triol molecular weight 114
Effect of Agitation
I & E C P R O D U C T RESEARCH A N D D E V E L O P M E N T
Discussion
Since both catalyst concentration and agitation were significant variables, it would appear that some mass transfer resistance existed. I n particular, it seems necessary to get enough catalyst to the reacting sites. Dispersion of propylene oxide did not appear to be a serious problem, since its concentration was found to be equal to its vapor-liquid equilibrium value, once the low molecular weight triol was formed. The reaction rate with the original glycerol is probably different from the values reported here for the triol but could not be readily determined. I n considering the effect of agitation, only shaft speed was varied. The effects of impeller design or placement and physical properties of the solution were not investigated. No optimum operating conditions were established. I n general, an increase in temperature, agitation speed, and catalyst concentration increased the reaction rate. However, at all times a balance must be maintained between reaction rate and the ability to remove the exothermic heat of reaction. Acknowledgment
Appreciation is expressed to the Olin Mathieson Chemical Corp., Brandenburg, Ky., for the use of equipment and ma-
terials used in this work. also acknowledged.
Its cooperation and assistance are
Plank, c. A,, Yost, c. w.9 Chem. Processing, in Press. Pruitt, M. E., Rogers, W. A., Jr. (to Dow Chemical Corp.), U.S. Patent (ALP. ~. 9. 1960). .. ..,_ - ~ 2.948.757 ~ --- ,. ._ Saunders, J. H., Frisch, K. C., “Polyurethanes, Chemistry and Technology,” Interscience, New York, 1962. Union Carbide Corp., Belgian Patent 584,738 (March 16, 1960). Yost, C. W., M. S. thesis in chemical engineering, University of Louisville, Louisville, Ky., September 1966. -I-
literature Cited Bender, R. J., “Handbook of Foamed Plastics,” Lake Publishing Corp., Libertyville, Ill., 1965. DeGroote, M. (to Petrolite Corp.), U.S. Patent 2,626,910 (Jan. 77 -.,
IC)$?)
L. G.
~
.I
-_I-
Lundsted,
(to W andotte Chemicals Corp.), U.S. Patent
RECEIVED October 28, 1966. ACCEPTED March 8, 1967
264,619 (April 6, 19547.
QUATERNIZATIONS OF TRIETHYLAMINE AND TRIETHANOLAMINE WITH EPICHLOROHYDRIN JOHN B. M c K E L V E Y , R U T H
R. BENERITO, AND T R U M A N
L.WARD
Southern Regional Research Laboratory, New Orleans, La. An investigation of cellulose-epoxide reactions, many of which are catalyzed by Lewis bases, necessitated a study of the reactions between epichlorohydrin and triethylamine or triethanolamine at room temperature. Preparation of the simple glycidyl quaternary chlorides has not been found to be feasible because triethylamine continues to react to form 2-hydroxytrirnethylene-l,3-bis(triethylammonium chloride), which has been isolated for the first time in good yield. The triethanolamine, while initially quaternizing with epichlorohydrin, dimerizes to form [2,5-p-dioxanylenebismethylene]bis[tris(2-hydroxyethyl)ammonium chloride], which was isolated in high yield. Physicochemical data have been used as the basis of mechanisms postulated for both reactions.
PIcHLoRoHYDRiN has found wide usage in polymer chemis-
E try because of its uniqueness in possessing both a labile
chlorine and an oxirane group. The authors’ interest has been in mechanisms of epichlorohydrin-amine reactions because of their importance in the chemical modifications of cellulose. Of particular interest are reactions catalyzed by tertiary amines. The relatively few literature reports give conflicting views of mechanisms of reactions between epichlorohydrin and triethylamine, possibly because reaction products were not isolated. Reboul (77, 78) claimed formation of a simple glycidyl quaternary chloride such as N-(2,3-epoxypropyl)trimethylammonium chloride (I). Later, Schmidt and Hartmann (22) reported formation of diquaternary salts, 2-hydroxytrimethylene-1,3-bis(trimethylammonium chloride) chlo(11) or 2-hydroxytrimethylene-l,3-bis(triethylammonium ride (111) and the presence of I-chloro-2-hydroxypropyltrialkylammonium chloride as a by-product. A patent (4) also claims preparation of simple glycidyl quaternary chlorides, More recently, Burness ( 2 ) reported that in acetonitrile, trimethylamine and epichlorohydrin form N-(3-hydroxy-lpropeny1)trimethylammonium chloride (IV) rather than the expected I. However, I has been synthesized by undisclosed methods and has been available for several years in research quantities ( 2 4 ) . Most recent information on the reaction comes from the Noguchi patent (74),which reports on the formation of N-(3-chloro-2-hydroxypropyl)trimethylammonium chloride (V) in almost theoretical yield when epichlorohydrin reacts with trimethylamine hydrochloride rather than with the free amine. While the latter method has been successful in the authors’ hands with the compounds men-
tioned, application of the reaction to triethylamine hydrochloride (VI) or to dimethyloctadecylamine hydrochloride has been unsuccessful. A linear diquaternary compound, 111, was obtained by use of V I as indicated in the experimental, and the quaternary obtained with the dimethyloctadecylamine hydrochloride contained no glycidyl group. The isolation of simple glycidyl quaternaries was doubted, since others (8, 20) had shown that aqueous secondary amines such as diethylamine or morpholine react with epichlorohydrin to form a tertiary amine which is also a chlorohydrin. The net result was reported to be a formation of substituted p dioxane derivatives. A similar observation was made by the writers (7 I ) with diethanolamine and epichlorohydrin in nonaqueous media. Ross, Baker, and Coscia (79) disagreed with this explanation of reactions with secondary amines and showed in one case, a t least, that an azetedinium compound could be isolated. The effectiveness of chloride ions of amine salts as catalysts for epoxide ring openings has been known for some time (27, 28). Consideration of a third type of reaction based on epichlorohydrin as an alkyl halide should take into account the findings of Semb and McElvain (23) and Noller and Dinsmore (75). They demonstrated that a tertiary amine not only forms a quaternary salt by reaction with a primary halide, but also a hydrohalide of the amine and an unsaturated compound as well. Lohmann (9) and McKelvey, Webre, and Benerito (77) noted the complexity of the reaction between triethanolamine and epichlorohydrin in the absence of solvents at 25’ C., but nothing has been reported on this reaction. The use of a 3 to 1 molar ratio of epichlorohydrin to tertiary amine was suggested VOL. 6 NO. 2
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