PRODUCT AND PROCESS DEVELOPMENT re-used, as its only “contaminant” is vinyl stearate, the product being made in the first place. Elimination of the acetone wash step significantly lowers the costs of equipment and processing, and also cuts down on the over-all operating time. At a n annual production of 5,000,000 pounds, elimination of the acetone wash reduces the selling cost of vinyl stearate t o about 42 cents per pound and at 10,000,000 pounds t o about 31 cents. Acknowledgment
T h e authors would like to thank Sidney Siggia and his staff
at the Central Research Laboratory, General Aniline and Film Corp., Easton, Pa,, for all analytical determinations. literature cited
Adelman, R. L., J . Org. Chem., 14, 1057 (1949). Beller, H., Christ, R. E., and Wuerth, F., U. S. Patents 2,472,084, 2,472,086 (June 7, 1949); Brit. Patent 641,438 (Aug. 9, 1950). Bertram, S. H., Rec. trau. chim., 46, 397 (1927). Brice, B. A.. and Swain, hf. L., J . Opt. Soc. Amer., 35, 532 (1945). Brice, B. A., Swain, hl. L., Schaeffer, B. B., and Ault, W. C . , Oil and Soap, 22, 219 (1945). Brown, J. B., and Shinowara, G. Y . , J . Am. Chem. SOC., 59, 6 (1937). Cirpenter, G. B., FIAT Final Report 935, PB 52163 (1946). Ibid., 936, PB 58441 (1946). Copenhaver, J. W., and Bigelow, M. H., “Acetylene and Carbon Monoxide Chemistry,” Reinhold, New York, 1949. Mkentscher, H., Kuko Report 106 (ilpril 1937), PB A 76327, listed in BSIR 5. No. 10. 850 (June 1947). Fikentscher, H., U. S. Patent 2;016,490 (Out. 8, 1935); Ger. Patent 634,408 (Aug. 26, 1936). Harrison, S. A., and Wheeler, D. H., J . ’Am. Chem. Soc., 73, 839 (1951). Herrmann, W. O., and Haehnel, W., U. S. Patent 2,245,131 (June 10, 1941). Kollek, L., Ibid., 2,045,393 (June 23, 1936). NBsslein, J., and Finck, G. von, Ibid., 2,168,535 (Aug. 8 , 1939), 2,234,501 (March 11, 1941). Nusslein, J., Finck, G. von, and Stlirk, H., Ibid., 2,168,534 (Aug. 8, 1939). Paloheimo, O., Suomen Kemistilehti, 23, 71 (1950). Port, W. S.,Hansen, J. E., Jordan, E. F., Dietz, T. J., and Swern, D., J . Polymer Sci., 7, 207 (1951). Port, W. S., Jordan, E. F., Hansen, J. E., and Swern, D., Ibid., 9, 493 (1952). Port, W. S.. Jordan, E. F., Jr., Palm, W. E., W-itnauer, L. P., Hansen, J. E., and Swern, D., IND.ENG.CHEM.,47, 472 (1955).
(21) Port, W. S., Jordan, E. F., Jr., Palm, W. E., Witnauer, L. P., ‘ Hansen, J. E., and Swern, D., U. S. Dept. Agr., Bur. Agr. Ind. Chem., AIC-366 (1953). (22) Port, W. S., Jordan, E. F., and Swern, D., U. 9. Patent 2,586,860 (Feb. 26, 1952). (23) Port, W. S., Kincl, F. A., and Swern, D., Ofic.Dig., Federation P a i n t & Varnish Clubs, 26, 408 (1954). (24) Port, W. S., O’Brien, J. W., Hansen, J. E., and Swern, D., IND. ENG.CHEM.,43, 2105 (1951). (25) Powers, P. O., Ibid., 38, 837 (1946). (26) Reppe, W., U. S. Phtent 1,959,927 (May 22, 1934) ; Ger. Patent 584,840 (Sept. 7, 1933). (27) Reppe, W., U. S. Patent 2,066,075 (Dec. 29, 1936); Ger. Patent 588,352 (Nov. 2, 1933). (28) Reppe, W., and Schlichting, O., U. S. Patent 2,104,000 (Dee. 28, ,1937). (29) Reppe, W., Starck, W., and Voas, A., Ibid., 2,118,864 (May 31, 1938); Ger. Patent 593,399 (Feb. 8, 1934). (30) Rosen, R., and Sparks, W. J., U. S. Patent 2,468,516 (April 26, 1949). (31) Siggia, S., and Edsberg, R. L., Anal. Chern., 20, 762 (1948). (32) Skellon, J. H., J . Soc. Chem. Ind., 50T, 131 (1931). (33) Swern, Daniel, Eastern Utilization Research Branch, Philadelohia. Pa.. orivate communication. (34) Swern, D., Billen, G. N., and Knight, H. B., J . Am. Chem. SOC., 69, 2439 (1947). (35) Swern, D., and Jordan, E. F., Ibid., 70, 2334 (1948). (36) Swern, D., and Jordan, E. F., Org. Syntheses, 30, 106 (1950). (37) . . Swern. D., Knight, H. B., and Findley, T. W., Oil and S o a p , 21, 133.(1944). (38) Swern, D., Scanlan, J. T., and Roe, E. T., Ibid., 23, 128 (1946). (39) Toussaint, W. J., and MacDowell, L. G., U. S. Patent 2,299,862 (October 27, 1942). (40) Twitchell, E., J. IND.ENQ.CHEM.,13, 806 (1921). (41) Voss. A., and Dickhauser, E:, U. S. Patent 2,047,398 (July 14, 1936). (42) Voss, A., and Stark, H., Ibid., 2,160,375 (May 30, 1939). (43) Weber, K. H., and Powers, P. O., Ibid., 2,518,509 (dug. 15, 1950). (44) Wulff, C., and Breuers, W., Ibid., 2,020,714 (Nov. 12, 1935); Ger. Patent 600,722 (Feb. 15, 1936). (45) Ziegler, K., ed., “Preparat,ive Organic Chemistry,” by Hecht, O., and Kroeper, H., in Field Information Agencies Technical, U. S. Dept. Commerce, PB 99207, pp. 6-24 (1948). ACCEPTED March 25, 1955. RECEIVEDfor review August 11, 1954. Presented before t h e Division of Industrial and Engineering Chemistry a t CHEMICAL SOCIETY, Kansas City, Mo., the 125th Meeting of the AMERICAN 1954. Report of work done in part under contract with the U. S. Department of Agriculture and authorized by the Research and Marketing Act of 1946. Contract supervised by Eastern Utilization Research Branch, Agricultural Research Service. Reference to commercial products in this paper is not intended t o be a recommendation of these products by the U. s. Department of Agriculture over others not mentioned. The Eastern Regional Research Laboratory is 8 laboratory of the Eastern Utilization Research Branch. Agricultural Research Service, U. S. Department of Agriculture.
Pentaerythritol Production Yields M.
S. PETERS
AND
J. A. QUI“‘
Universify of Illinois, Urbana, Ill.
P”
NTAERYTHRITOL is a n important chemical produced by reacting acetaldehyde with formaldehyde in a n alkaline medium under rigorously controlled conditions. One of the major factors in the economic production of this material is the attainment of high over-all yields and good grade product. Yield losses can occur in the chemical reactions involved in the process and in the physical operations necessary for separating the pentaerythritol from the reaction mixture. The published information relating t o the synthesis of pentaerythritol is found almost entirely in United States patents. Among these patents, there are considerable differences in the procedure followed and in the yields claimed. However, the main differences center on two topics 1 Present
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address, Princeton University, Princeton, N. J.
1. The type and amount of alkaline catalyst used 2. The time and temperature of the reaction
Other variables of importance in the process are the ratio of formaldehyde t o acetaldehyde in the reaction mixture, water content of the reaction mixture, choice of acid t o neutralize the excess alkali, method of separating the pentaerythritol from the reaction mixture, and purity of the reactants. I n this work, all these variables have been taken into consideration, and results are presented showing the effect of time, temperature, and type of catalyst on production yields. T h e first stage in the stepwise reactions producing pentaerythritol is a n aldol condensation of acetaldehyde with formaldehyde in the presence of alkali t o form pentaerythrose as shown by
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PRODUCT AND PROCESS DEVELOPMENT
The second stage consists of a Cannizzaro reaction involving the pentaerythrose and produces monopentaerythritol as shown by the equation where sodium hydroxide is used as the alkali
The final product is obtained by evaporating part of the water from the reaction mixture and permitting the pentaerythritol to crystallize from the concentrated solution. Smaller amounts of other hydroxylated substances are also formed. One of these, which is formed in a considerable amount, is dipentaerythritol, a n ether having the structure
HOCHt-
ZiHzoH
CHzOH
-CHz-0-CH
&HpOH
I I
C-CHzOH 2-
CHzOH
Any excess formaldehyde reacts by a further Cannizzaro reaction 2 HCHO
+ NaOH
CHsOH
+ NaCOOH
The catalyst, amount of alkali, reaction time and temperature, ratio of formaldehyde to acetaldehyde, reaction mixture, water content, and neutralizing acid affect yield
Type of Catalyst. A variety of different catalysts have been used in the preparation of pentaerythritol. Calcium hydroxide, sodium hydroxide, barium hydroxide, magnesium oxide, potassium hydroxide, and an anion exchange resin have been employed. No single catalyst of the preceding group has qualities greatly superior to the others. Therefore, barium hydroxide, potassium hydroxide, and the anion exchange resin may be eliminated because of their excessive cost. Considerable recovery difficulties are encountered with magnesium oxide, and it is not desirable. This reduces the possibilities t o calcium hydroxide or sodium hydroxide, the alkalies most commonly employed in commercial practice, and the ones used in this work. Amount of Alkali Used. According t o the chemical reactions for the synthesis of pentaerythritol, one equivalent of alkali is consumed for each mole of pentaerythritol formed or for every 4 moles of formaldehyde entering the reaction. The Cannizzaro reaction involving the excess formaldehyde requires one half an equivalent of alkali for each mole of excess formaldehyde. The amount of alkali used in the process has varied with two schools of investigators. The older processes used about a 200% excess of alkali. This was reasonably satisfactory when the reaction was carried out a t a low temperature and when several weeks were allowed for the reaction t o take place. I n such cases, the presence of the large excess makes the removal of alkali more difficult. When higher temperatures are used, such large excesses of alkali are undesirable due t o side reactions which occur, with resulting adverse effects on the yield. The more recent processes use only a slight excess of alkaliapproximately 10%-over the amount theoretically necessary for the complete chemical reaction, including the excess-formaldehyde reaction. This slight excess permits the attainment of good over-all yields with reasonable reaction times. I n this work, 8 % excess alkali waa used in all runs. Reaction Time and Temperature. The reactions involving alkali, acetaldehyde, and formaldehyde are exothermic. If these materials are mixed with no attempt to control the temperature, the heat of the reactions will cause the temperature to increase t o the point where multiple side reactions occur. Therefore, it is extremely important t o control the temperature t o prevent the reactions from proceeding too far. The time of the reaction is closely related to the temperature by the reaction rate. Some investigators ( 3 ) recommend a reaction time of 16 to 20 hours a t temperatures as low as 15' C., September 1955
while others ( 4 ) operate a t temperatures of 80" t o 85" C. with a corresponding reaction time of 2 hours or less. There is no general agreement in the literature on the recommended temperature or time of reaction within the extremes cited. Ratio of Formaldehyde to Acetaldehyde. An excess of formaldehyde should be used if good yields are to be obtained. Molar ratios of formaldehyde to acetaldehyde varying from 4.0 to 5.5 have been reported in the literature, A molar ratio of 5.0 gives the best results (8, 6),and this ratio has been used in the experimental tests in this work. Water Content of Reaction Mixture. To obtain high yields, a considerable amount of water must be present in the reaction mixture. However, too much water is undesirable, because the reactions then require a n undue amount of time for completion, and the evaporation load becomes excessive. It is convenient t o express the amount of water present on the basis of the initial formaldehyde concentration, considering only the total weight of water and formaldehyde a t the start of the reaction. On this basis, formaldehyde concentrations varying from 2 to 37% have been used in the production of pentaerythritol. At the high concentrations, large amounts of dipentaerpthritol are fcrmed and poor yields are obtained. At the low concentrations, excessively long reaction times are required for completion of the reactions. The optimum value for the formaldehyde concentration is in the range of 12 t o 20% (1, 6). A value of 13% was used in this work. Choice of Neutralizing Acid. Sulfuric, hydrochloric, oxalic, formic, and other acids have been used for neutralizing the excess alkali remaining a t the end of the reaction. Sulfuric and formic are the two acids most commonly employed. I n this work, formic acid was used for the neutralization. Yields. Yields in pentaerythritol production are based on the amount of pentaerythritol which theoretically could have been obtained if all the acetaldehyde were converted t o pentaerythritol. Percentage yields varying from 50 to 90% have been reported in various patent claims. Claims using calcium hydroxide as the alkali run t o approximately 80% while those using the sodium hydroxide process are as high as 90%. Acetaldehyde i s reacted with formaldehyde under controlled conditions in presence of either calcium hydroxide or sodium hydroxide
The reaction was carried out in a 5-liter, three-necked Bask suspended in a temperature-regulating bath. T h e contents of the flask were agitated continuously with a variable-speed, motor-driven Rtirrer. Liquid acetaldehyde of 99% grade was added beneath the surface of the mixture of reagent grade formaldehyde, alkali, and water, keeping the temperature below 25" C. The time required for the addition of the acetaldehyde was approximately 5 minutes, and the temperature of the reaction mixture was easily maintained below the desired level. When the acetaldehyde addition was completed, the temperature was gradually increased to the test value. The reaction mixture was sampled periodically and analyzed for alkali and formaldehyde content. After a given reaction time, the mixture was neutralized with formic acid and concentrated under vacuum to a specific gravity of about 1.28 (50" C.) in the calcium hydroxide runs and 1.22 (50" C.) in the sodium hydroxide runs. When calcium hydroxide was used, the insoluble calcium formate produced by the reaction was removed by filtration a t a temperature of 95" C. The concentrated liquor was cooled a t 5' t o IO" C. for 24 hours, during which time pentaerythritol crystallized from solution. The pentaerythritol was separated from the mother liquor with a small, basket-type centrifuge, dried, and analyzed. Additional product pentaerythritol was obtained from the mother liquor by further concentration and separation. The overall percentage yield for each run was calculated from a knowledge
INDUSTRIAL AND ENGINEERING CHEMISTRY
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PRODUCT AND PROCESS DEVELOPMENT of the amount of acetaldehyde charge, the amount of dry firstcrop pentaerythritol, t,he analysis of the dry product, the amount of mother liquor, and the solubility of pentaerythritol in the mother liquor. Yield losses occur in chemical reactions and in physical separation of product
Yield Losses in Separational Operations. The pentaerythritol lost in the separational operations is that which cannot be recovered from the motor liquor plus any lost in the filtration steps. In the standard separational procedures, the aqueous reaction mixture is concentrated and a first crop of pentaerythritol crystals is obtained by allowing the hot, filtered reaction mixture to cool from approximately 95' to 10" C. The mother liquor remaining after the crystallization can be concentrated still further, yielding additional crops of crystals. Finally, after three or four concentrations, there remains a residue containing the formate salt of the alkali, small amounts of pentaerythritol, and sirupy polyhydroxy materials. No further product can be recovered from this residue by crystallization.
Reaction-mixture temperature affects product yield and grade
The runs made with calcium hydroxide were characterized by a so-called second reaction or carmelization reaction. This second reaction was evinced by a sudden rise in temperature followed shortly by the development of a yellow color in the reaction mixture.
a w
W
2
!-
z
Y
CL W
a i
ea
I
tu
REACTION TIME,MINUTES
Figure 2. Effect of reaction time at constant temperature on sodium hydroxide concentration in reaction mixture
W
a z
I-
W
a
8
50-
I
a
J -I
7
U
I
40
~
-
__-
I
I
I
I
I
CONSTANT REACTION T I M E 95 MIN. SODIUM HYDROXIDE PROCESS
W
By careful treatment of the mother liquor and re-use of wash water, product losses in the mother liquor can be reduced to a negligible amount. Therefore, except for several check runs, the pentaerythritol in the mother liquor was not recovered in this investigation. The reaction mixture was concentrated, and a first crop of pentaerythritol was obtained. Knowing the solubility of pentaerythritol and the volume of the mother liquor, the amount of pentaerythritol remaining in the mother liquor was calculated. This value was included in determining the over-all yield. I n these tests, approximately 75% of the total product was recovered in the first-crop crystallization. The only other loss of product t h a t could have occurred in the separational operations was in the runs with calcium hydroxide in which the calcium formate was removed by filtration before the pentaerythritol crystallization step. Analysis of the calcium formate filter cake indicated essentially pure calcium formate with a negligible amount of pentaerythritol present. Therefore, the over-all yield of pentaerythritol was less than the theoretical amount because of losses involved in the chemical reactions. 1112
After the formaldehyde, acetaldehyde, and calcium hydroxide had been mixed, the temperature of the reaction mixture increased gradually to about 25' C. During this time, the reaction vessel was suspended in a n ice bath. On reaching 25' C., the temperature stopped climbing and the mixture was then heated to 45' C. At this point the temperature increased very rapidly t o 53" t o 57" C., and the color of the reaction mixture then changed sharply from white t o yellow. The reaction was stopped by neutralizing the reaction mixture with acid. A number of tests were carried out under these conditions in which a good grade product pentaerythritol was obtained. The overall yields obtained in all these runs were essentially constant at67%'0(12%). I n all runs with calcium hydroxide, when the reaction was stopped before the temperature reached 45' C., no appreciable amount of pentaerythritol was obtained. On the other extreme, it was not feasible t o raise the temperature above that a t which the color change occurred because the color became progressively darker, being bright orange in a short interval of time. This darkening color was due t o the formation of strongly colored resinlike compounds and yielded a n unsalable trade of product. Some commercial installations, using calcium hydroxide and the same concentrations as in this work, indicate 42" t o 4.5' C. as the maximum temperature t o which the reaction mixture can be heated. According to the results of this investigation, this temperature would not be adequate to give a n appreciable yield. However, in this work, rapid agitation of the reaction mixture was maintained so that a true over-all temperature was obtained. I n the commercial installations, the agitation is not so effective, and hot spots undoubtedly occur in the reaction mixture. I n the runs made with sodium hydroxide, the yield of pentaerythritol varied with the temperature of the reaction as indicated in Figure 1, which shows the effect of reaction temperature on over-all yield a t a constant reaction time of 95 minutes. A
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PRODUCT AND PROCESS DEVELOPMENT maximum over-all yield of 77% was obtained a t 84" C. The rate of the reaction varied considerably with the temperature as can be seen in Figure 2 in which the percentage of unreacted sodium hydroxide is shown as a function of the reaction time a t various temperatures. It should be realized t h a t part of this increase in reaction rate a t the high temperatures would be caused by the Cannizzaro reaction between formaldehyde and alkali. Effect of Reaction Time. The majority of the tests were carried out a t a total reaction time of 95 minutes. To determine the effect of reaction time, a run was carried out with sodium hydroxide at 60" C. using a total reaction time of 330 minutes. Under these conditions, an over-all yield of 64% was obtained compared t o a 587, yield obtained at 61" C. using a reaction time of 95 minutes. Thus, an increase in reaction time of nearly 3
