-z5giProduct -_ and Process Development ,
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A section devoted to information on the development of products 'and the processes for making them on any scale with industrial implications, and including economics and market development
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Long-chain Vinyl Esters and Ethers Preparation from Commercial Raw Materials L.
E. CRAIG,l R. F. KLEINSCHMIDT,2 E. S. MILLER,
AND
J. M. WILKINSON, JR.
Central Research Laborafory, General Aniline and Film Corp., Easfon, f a .
R.
w.
DAVIS AND
c.
F. MONTROSS
General Aniline and Film Corp., Linden, N. J.
N
WILLIAM S. PORT Earfern Regional Research Laboratory, Philadelphia 18, Pa.
EARLY all monomers of commercial interest have been,
until now, compounds of low molecular weight. Recently, considerable attention has been directed toward the preparation and polymerization of monomers derived from long-chain fatty acids and alcohols, particularly vinyl esters and ethers. Polymers and copolymers of these materials are of potential commercial interest because the monomers can be prepared from inexpensive and readily available raw materials-acetylene and tallow, for example. In the copolymers of long-chain compounds &ndolefinic monomers of low molecular weight, the long chain is chemically bound in the polymer molecule and the resulting intramolecularly modified polymers should retain their original properties indefinitely (except for the long-time oxidative, hydrolytic, and photochemical changes to which all plastics are subject). Thus problems of exudation, evaporation, and leaching, commonly encountered with plasticized polymer compositions, are eliminated. Investigations in recent years have shown that vinyl esters and vinyl ethers of long-chain fatty materials can be homopolymeriaed (9, 17-19) to give polymers useful as coating materials, adhesives, softening and plasticizing agents, and agents for improving the viscosity index and depressing the pour point of lubricating oils ( I C , 24, 68,30, 44, 46). Poly(viny1 oleyl ether) was manufactured in Germany as a pour point depressant and marketed under the name of Pour-point Depressor PVO. Poly(vinyl octadecyl ether), marketed in Germany under the name I. G. Wax V, was used as a wax substitute in polishing and dressing agents. 1 Present address, Grand River Chemical Division, Deere and Co., Pryor, Okla. 2 Present address, Phillips Petroleum Co., Bartlesville, Okla.
1102
Long-chain vinyl esters and ethers also have been shown to copolymerize readily with a variety of monomers of low molecular weight, such as vinyl chloride, vinyl acetate, acrylonitrile, acrylic acid and esters, and maleic anhydride and esters (10, 11, 19-61, 23-66, B9, 41, 4 3 ) . Copolymers having widely varied properties can be prepared. Copolymers containing vinyl esters of fatty acids have been suggested for use as adhesives, coating materials, chewing gum bases, textile assistants, and lubricating oil additives (10, 19). Waterproofing compositions for fabrics have been formulated from copolymers of vinyl stearate or octadecyl vinyl ether with maleic anhydride (16, 16, 42). Synthetic rubber of increased tear resistance is reported to result from incorporation of small amounts of vinyl fatty esters in butadienestyrene emulsion polymerizations (96, @). One of the major obstacles in the past to the commercial development of polymers and copolymers of long-chain compounds has been the unavailability of pure materials. In recent years, however, long-chain fatty acids and alcohols of relatively high purity have become available. The work described herein had two objectives: the study of the commercial feasibility of preparing vinyl esters and ethers of long-chain fatty acids and alcohols by vinylation with acetylene, and the preparation of sizable quantities of vinyl stearate, vinyl oleate, octadecyl vinyl ether, and oleyl vinyl ether of sufficiently high purity for use in extensive polymerization and copolymerization studies. Vinyl esters of long-chain acids have been prepared by two methods: (1) mercuric salt-catalyzed interchange reactions between acids and vinyl acetate ( 1 , id, is,i 7 , 18, 34-36, 39) and ( 2 ) vinylation of acids with acetylene in the presence of zinc salts (8, 7, 9, 67). The reported yields in the vinylation method have been good and it would appear the more economically feasible
INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 47, No. 9
.
PRODUCT AND PROCESS DEVELOPMENT square inch gage, and the pressure was released. While being stirred, the charge was heated to 165' C., and the pressure increased to 70 pounds per square inch gage with propane and then to 200 pounds per square inch gage with acetylene. This mixture of gases contained 65 yo acetylene which previous tests had shown to be nonexplosive at the usual temperature range encountered in vinylation. With these conditions of temperature and catalyst, vinylation was complete in 8.5 to 9.5 hours. Control of the reaction was maintained by following the consumption of stearic acid by determining the acid number of samples taken through the blow leg. Vinylation was halted with 3 to 5y0 of the stearic acid left unreacted (acid number 4 to 8). If a higher conversion was attempted, there was obtained an overvinylated product which could not be purified to meet the polymerization specifications, [These impurities have not been isolated, but they may be polyunsaturated compounds, since the overvinylated monomer had a deep yellow color and a strong sharp odor. A concentrate of the inhibitor (which may be the same as those due to overvinylation) in "crude" vinyl stearate exhibited strong absorption a t 1712 and 988 em.-]] A product of lower conversion of stearic acid also gave problems in purification, special techniques being required t o remove the unreacted stearic acid (22). Isolation and Purification. When the acid number had fallen to 4 to 8, heating and agitation were stopped, and the autoclave was vented and purged with nitrogen. The reaction mixture was cooled to 120" C., discharged, and filtered to remove the catalyst. (The product freed from catalyst but not further purified is denoted in this paper as "crude" vinyl stearate.) The yield of crude vinyl stearate was 5860 grams. The catalyst was extracted twice with 10 liters of acetone, and another 1800 grams of crude vinyl stearate were recovered from the acetone solution for a total yield of 7660 grams or 91.5y0 of theory. At this point, the dry weight of the catalyst exceeded the starting weight by 480 grams. If this is assumed to be vinyl stearate, the conversion based on stearic acid was 97y0 of theory. In 11 vinylation runs, the average yield of crude vinyl stearate was 94.1%. The extracted catalyst was recycled twice with no effect on the yield. In one case, the catalyst was recycled without extraction without loss of yield.
method. Of the various methods reported in the literature for preparing vinyl ethers, the one which appears the best suited for the preparation of vinyl ethers of long-chain alcohols on a large scale involves vinylation with acetylene in the presence of alkali catalysts. Such vinylations have been carried out previously with octadecyl (stearyl) and oleyl alcohols (9, 8, 9, 26, 46). The products described in this paper were prepared by vinylation of the appropriate acid or alcohol with acetylene. Because one of the objectives of this work was to test the commercial feasibility of the method of preparation, commercially available acids and alcohols were used. Pure acids and alcohols are not commercially available, but functionally pure (consisting of only saturated fatty derivatives) stearic acid and octadecyl alcohol are obtainable. As functional purity is the important criterion for polymerizability, such raw materials were used. Purification of oleic acid and oleyl alcohol was necessary because functionally pure (monounsaturated) compounds were not available. Vinyl stearate i s made from stearic acid and acetylene, with zinc stearate catalyst
Starting Materials. The stearic acid used was Hystrene 5-97, obtained from Atlas Powder Co., and contained about 95% stearic acid and 5% palmitic acid. Samples consistently had iodine numbers below 1 and were suitable for vinylation without further purification. From a practical, commercial point of view the important specifications for the stearic acid are the absence of polyunsaturated fatty acids and a low content of monounsaturated fatty acids. If polyunsaturated acids are present, the resulting vinyl stearate will be contaminated with the vinyl esters of these acids which are polymerization inhibitors. Vinyl oleate, when present in amounts greater than about 1070, is also an inhibitor for the polymerization of vinyl stearate. For most purposes, an increased amount of palmitic acid will have no adverse effect. The zinc stearate (catalyst) was Baker and Adamson U.S.P. grade. It contained practically no unsaturated fatty acid salts and only a trace of free acid, Acetylene was obtained from cylinders in which it was stored as an acetone solution. Vinylation Equipment. The vinylation reactor consisted of a 5-gallon, Blaw-Knox, stainless steel autoclave having a working pressure a t 25" C. of 3000 pounds fitted with an anchor-type stirrer, pressure gage, thermowell, blow-out disk rated a t 300 pounds, and blow leg. The equipment was rated to provide stirring a t 330 r.p.m. for a maximum operating pressure of 3000 pounds and a maximum operating temperature of 250' C. Heat and temperature control were provided by elements in the body of the autoclave. Pressed asbestos gaskets were employed in the head set. Copper and its alloys were rigorously excluded. The blow leg was connected through a T-valve directly to the incoming acetylene line. The third side of the T-valve enabled the operator to obtain samples of the reaction mixture. All external lines and valves were steam traced to prevent solidification of zinc stearate, A high pressure trap was inserted between the autoclave and the pressure regulator of the acetylene tank. The trap was cooled to - 5 to -8' C. to remove as much acetone as possible while avoiding explosion hazards due to liquefaction of acetylene which would occur a t a lower temperature-e.g., -20" C.-at the pressure employed. Vinylation Procedure. The autoclave was preheated to 90' to 100" C. and was charged with 7680 grams (27.0 moles) of stearic acid and 1120 grams (1.77 moles, 6.5 mole yo)of zinc stearate. The size of the charge was selected to fill the reactor to 65% of capacity at the vinylation temperature. After being charged, the autoclave was sealed, pressure-tested with dry nitrogen a t 300 pounds per square inch gage, vented, and purged twice with nitrogen a t 200 pounds per square inch gage followed by two purges with propane a t 100 pounds per O
September 1955
Table 1.
Expt.
No.
-
1 2 3 4 5 6 ' 7 8 9 10 11 Av,
Reaction Time, Hr. 7.5 9.0 8.75 8.25 13.5 16.0 26.5 10,25 13.0 8.25 9.5 11.77
Crude 94.6 94.8 97.1 97.0 93.5 93.0 87.5 91.5 94.8 94.9 95.8 94.0
Vinyl Stearate
Yield, % FlashRecrystaldistilled lized (technical (pure grade) grade) 67.0 84.4 68.4 86.0 68.0 88.5 68.2 87.7 85.8 70.0 67.6 83.6 61.6 76'.0 61.8 82.5 70.2 84.6 70.2 84.3 69.5 83.8 84.3 67.5
Properties of Pure Grade Iodine polYmerizaNO. tion (theory = 81.7) n6g 81.2 1.4540 80.0 1 4650 78.7 1 ,4543 78.1 1.4550 1.4535 79.2 1.4548 79.2 1.4564 79.0 1.4533 79.9 1.4510 77.8 78.7 1 ,4549 78.9 1.4548 79.1 1.4542
a All products had initial n'J 1.4360 i 0.0002. These values are refractive indices of the solution of monomer and polymer after 4 hr. at 70° C. with 0.25% by weight benzoyl peroxide (93).
The next stage in purification was provided by flash distillation a t 155' to 160" C. and 0.5-mm. pressure. (The product free from catalyst and purified by flash distillation only is denoted in this paper as "technical" vinyl stearate. A typical sample assayed 96% vinyl stearate, 4y0 stearic acid.) Overheating of the monomer was avoided by continuously dripping in the crude and providing a large surface for evaporation in the form of a packing of stainless steel turnings. An oil bath maintained
INDUSTRIAL AND ENGINEERING CHEMISTRY
1703
PRODUCT AND PROCESS DEVELOPMENT a t 210' to 220" C. was used as the heat reservoir. The average yield in the distillation step was 88.50J0. Technical vinyl stearate was further purified by crystallization from 3.2 parts of acetone a t 0" C. (The products so obtained denoted in this paper as "pure" vinyl stearate.) The average yield in the crystallization step was 80.1%. An over-all average yield of 67.2y0 was thus obtained. The results of the series of eleven vinylations are summarized in Table I.
*" Y, v)
RECRYSTLLLIZED FLASH DISTILLED
t 4 1 X W
n
z
- 1 W
z
-I
V
a nI !A
W
a 0
2
I TIME,
3
4
HOURS
Figure 1. Rate of polymerization of vinyl stearate at 70' C. with 0.2570 benzoyl peroxide Specifications and Polymerizability. Pure vinyl stearate was a white, waxy solid, which was essentially colorless when molten. The refractive indices of the products were 1.4360 f 0.0002 (55" C.) and the iodine number ranged from 78.1 to 81.2. Chemical analysis was frequently an inadequate measure of purity because analytically undetectable amounts of inhibitor could entirely prevent polymerization, the iodine number on repeatedly purified vinyl esters was low, and samples which had low iodine values were frequently readily polymerized. A more sensitive test for purity was based on rate of polymerization. Studies on the mass polymerization in vinyl stearate showed that the presence of inhibitors could be detected from the shape of the curve obtained by plotting percentage polymerized (as measured by the refractive index) against time. A simple, practical test and specification was developed when it was observed that samples of vinyl stearate containing 0.2570 benzoyl peroxide when heated a t 70' f 2" C. under a nitrogen atmosphere attained a minimum refractive index at 55" C. of 1.4540 and showed no inhibition period ( 3 3 ) . [Similarly, vinyl oleate gave a copolymer with vinyl stearate (90% vinyl stearate, 10% vinyl oleate) having a minimum refractive index ( n g )of 1.4470 when heated 12 hours under nitrogen a t 70" f 2" C. with 0.5 weight yo of benzoyl peroxide. ] Such samples which showed an inhibition or retardation period invariably failed to reach the specified refractive index during the test time. While it is recognized that a truer measure of absence of inhibitor could be achieved by more refined tests, such as showing the linear dependence of rate of polymerization on the square root of the initiator concentration, the pragmatic test outlined is more suitable for the purpose for which it was intended. Mass polymerization was carried out by agitating a 6-gram sample containing 0.2570 by weight of benzoyl peroxide at 70" i 2" C. under a nitrogen atmosphere. The polymerization was followed by change in refractive index. The curves in Figure 1 show the typical polymerization behavior of the three grades of vinyl stearate. No period of inhibition is observable for the pure grade. Further examination of the technical vinyl stearate showed that a higher catalyst concentration effected an increased 1704
rate of polymerization (see Figure 2), and it seems probable that this material would be suitable for many uses, particularly in copolymerizations involving low ratios of vinyl stearate. Crude and technical vinyl stearate contained significant amounts of vinyl pamitate, but this was absent in pure vinyl stearate.
Crystallized oleic acid is the basis of vinyl oleate Pure oleic acid is not a t present commercially available. The commercial product used in these investigations, Emersol 233 LL Elaine (Emery Industries, Inc.), contains 4 to 5% polyunsaturated acids, some trans-octadecenoic acid (elaidic acid), and some saturated acids. After a number of the methodti reported (S, 6, 39, S6, 38, 40) for purifying oleic acid were examined, the method adopted consisted of a single low-temperature (-55' t o -50" C.) crystallization from acetone to remove the bulk of the polyunsaturated acids. The removal of the elaidic acid did not appear practical, but the vinyl esters of the lower saturated acids were removed as foreruns in the fractional distillation of the vinylation product. The single crystallization gave oleic acid containing 0.8 to 1.2y0polyunsaturated acids (4,6)in an average yield of 77%. Vinylation of crystallized oleic acid was carried out by the procedure described above for stearic acid. The catalyst, however, was prepared from zinc acetate and crystallized oleic acid. A mixture of 2000 grams of crystallized oleic acid, 480 grams of zinc acetate, and 350 ml. of toluene was heated with agitation, water and acetic acid being removed azeotropically. After the toluene had been removed in vacuo, the residue, along with another 5800 grams of crystallized oleic acid, was charged into the 5-gallon autoclave, and vinylation was carried out to an acid number of 5 to 10.
V
1.455
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In v)
+ U
1.450-
X W
n
z
-
1.445-
4
W
a
