‘2538
INDUSTRIAL AND ENGINEERING CHEMISTRY
cotton linters. In other words, the uniform distribution of cotton linters leads to a rayon having a more uniform chain length distribution than one prepared from wood pulp. The total over-all degradation during the viscose process appears to be greater for the more heterogeneous pulp. CONCLUSIONS
A summative method for the fractional analysis of cellulose is described, and the advantages and disadvantages of the process are discussed. A mathematical interpretation of sumniative data is given, and the conversion of summative distribution data to more common integral and differential distribution plots is illustrated. Differential distribution curve8 are given for several rayons and rayon wood pulps. The rayon wood pulps examined did not possess a distribution of chain lcngths that approached the homogeneity of the chain length distribution of cotton linters pulp. The distribution of chain length in the original pulps, however, has a pronounced effect on the chain length distributione of the rayons made from these pulps. LITERATURE CITED ( 1 ) Battista, 0. A., IND.ENG.CHEM., ANAL.ED.,16, 351-4 (1944). (2) Battista, 0. A., and Sisson, W. A , , J . Am. Chem. Soc., 68, 915
(1946).
Vol. 42, No. 12
BeaJ1, G., J . PoZymer Sci., 4, 483-513 (1949). Cragg, L. H., and Hammeischlag, Hanna, Chem. Reus., 39, 1, 79135 (1946). Davidaon, G. F., J. TertileInst., 25, T174-96 (1934). Ibid., 27, T112-30 (1936). Dolmetsch, H., and Reinecke, F., ZeZZzuoZZe u. Deut. KunstseidenZtg., 5, 219-27 (1939). Ibid., pp, 299-307. Ekenstam, A. af., Suensk Papperstidn., 45, No. 5, 81-9 (1942). Jgrgcnsen, L., “Studies on Partial Hydrolysis of Cellulose,” Oslo, Trykt Hos Emil hloestue A/S, 1950. Kumichel, W., Papier-Fahr., 36, Tech. TViiss. T-1, 497-508 (1938). Mark, H., Paper Trade J . , 113,3440 (1941). Mark, H., and Simha, R., Trans. Faraday SOC.,36,611-18 (1940). Morey, D. R., and Tsmblyn, J. W., J . Phys. Cheni., 50, 12-22 (1946). Neumann, R., Obogi, R., and Rogovin, Z., CeZZuZosechemie. 17, 57-91 (1936). Purves, C. B., in “High Polymers,” Vol. 5, pp. 85-100, N r w York, Interscience Publishers, 1943. Schieber, W.F., Angew. Chem., 52, 487-8 (1939). Schieber, TV. F., Papier-Fabr., 37, 245-50 (1939). Strauss, F. L., and Levy, R. RI., Paper Trade J . , 114, No. 18,237 (1942). Tasman, J. E., and Corey, A. J., P u l p & Paper M a g . Can., 48, NO. 3, 166-70 (1947). Tyden, H., Suensk. K e m . T i d . , 51, 100-1 (1939).
RECEIVED March 24, 1950. Combination of three papers presented before the Division of Cellulose Chemistry a t the 106th Meeting of the A M E R I C A N CHEVICAL SOCIETY, Pittsburgh, Pa.
DRYING OILS AND RESINS Segregation of Fatty Acids and Their Derivatives by Extractive Crystallization with Urea HERBERT A. NEWEY, EDWARD C. SHOKAL, ALBERT C. MUELLER, AND THEODORE F. BRADLEY S h e l l Development Company, Emeryville, Calif.
LLOYD C. FETTERLY University of Washington, Seattle, Wash.
A
new method for fractionating mixtures of fatty acids
o n the basis of their degree of unsaturation has been found
in extractive crystallization with urea. When the fatty acids are admixed with a saturated aqueous or alcoholic solution of urea or ground with solid urea a crystalline adduct is formed with the more saturated fraction of the acids. This can be filtered off leaving a raffinate of high iodine value. The adduct can be decomposed readily with excess water t o recover the extracted fraction. The method also successfully segregates such mixtures as the unsaturated alcohols obtained by reducing linseed oil, the nitriles derived from soybean acids, and tall oil. In each
T
HE advantages of separating vegetable and marine oils or their fatty acids into at least two fractions having different
degrees of unsaturation have long been recognized. The separation makes possible the more efficient use of the fatty acids or glycerides. The more unsaturated fraction is valuable for the drying properties imparted to the poly01 esters by the acid radicals having two or more double bonds. The more saturated fraction, while detracting from the drying properties of a mixture, is in itself a valuable product for other t~pplications. Many processes for bringing about this separation both on the free fatty acids and the naturally occurring mixed glycerides have been proposed. The majority of such processes are based on either fractional crystallization or selective extraction with an
case the urea removes stearic and oleic acids or their derivatives through adduct formation, while the linoleic and linolenic acids or their derivatives concentrate in the raffinate. While the present work delineates some of the possible uses of the method rather than establishes optim u m conditions for any specific use, the new method does appear to offer numerous advantages. I t is simple, relatively inexpensive, and operates a t room temperature. The efficiency of separation compares favorably with processes using fractional crystallization or selective extraction, perhaps excelling them in the separation of oleic from polyene fatty acids.
organic solvent. The Emersol process (5, 16), in which the free fatty acids are fractionally crystallized from an organic solvent at low temperature, is a commercial example of the first type of process. Laboratory data on similar low temperature crystallizations have been published by several authors (1, 4, ’?’, 11-13’, 10, 68). Eckey has recently described a separation process involving direct.ed interesterification of glycerides and fractional precipitation of the solid glycerides formed (6). Perhaps the two best known selective extraction processes are the extraction with furfural patented by Freeman (8) and operated by the Pittsburgh Plate Glass Company (9) and the liquid propane cxtraction patented by Hixson and Millw (14, 16),and commercialized under the name of thc Solexol proccss by the M. W. Kellogg Company.
INDUSTRIAL AND ENGINEERING CHEMISTRY
December 1950
Other methods such chromatographic absorption (24.6) and preferential neutralization (17) have also been described. Extractive crystallization with urea provides a means for a new simple and efficient separation of fatty acids on the basis of their degree of unsaturation. Bengen (3, 23) in Germany, tirst found that when a saturated aqueous solution of urea is shaken with a straight chain c o m p o u n d a u c h as a hydrocarbon, an alcohol, or an acici-a crystalline adduct is readily formed. On the other hand, with most branched or cyclic compounds no adduct is obtained. Apparently the urea molecules form interpenetrating spirals around the long chain molecules; hydrogen bonding between the adjacant urea molecules and the van der Waals' force between the long chain molecule and the urea molecules account for the stability of the structup (19, 91). Such adducts are easily broken by dissolving the urea with excess water. Extensive experiments have been performed using this adduct formation for removing straight chaio alkanes and alkenes from mixtures of hydrocarbons such as petroleum fractions (9, 18, 19, 26). The present authors have found that extractive crystallization with urea can be used not only to separate straight chain compounds from branched or cyclic compounds, but can also be used on mixtures of polar compounds to separate a more saturated fraction from a more unsaturated one. Apparently the double bonds cause the chains to deviate from the linear form by a sufficient amount so that they no longer fit easily into the urea crystal structure. Thus, when a mixture of fatty acids is shaken with a concentrated aqueous urea solution, the more saturated portion of the fatty acids forms a crystalline adduct, which can be filtered from the more unsaturated fraction. Under proper conditions urea adducts can be formed with stearic, oleic, linoleic, or linolenic acids. However, the separation is possible because the equilibrium among the more saturated acids, the adduct, and the urea favors adduct formation to a greater extent than the corresponding equilibrium involving unsaturated acids. EXPERIMENTAL METHODS
To illustrate the general experimental procedure used in this work, a typical extraction of linseed fatty acids is described. A 250-gram sample of linseed fatty acids was dissolved in 250 grams of methyl isobutyl ketone and stirred into 2 liters of saturated a ueous urea a t 23" C. (This contained 1200 grams of urea.) I n &e course of 5 minutes, a copious, white crystalline precipitate was formed. Stirring was continued for 0.5 hour, and the adduct was then filtered off and carefully washed with 500 ml. of methyl isobutyl ketone. The crystalline adduct was decomposed by stirring into 1 liter of water a t 60' to 80" C., which dissolved the urea and left the exact and residual methyl isobutyl ketone as an u per layer. This was washed with water, separated, and the m e t h 3 isobut 1 ketone was removed under vacuum. The extract was a solid meLing a t 46" C. The methyl isobutyl ketone layer of the combined filtrate and washings, which contained that, portion of the acids not forming an adduct, was separated and washed with water The solvent was removed under vacuum. The results were as follows: Original Linseed Acids Grams % b y wt. of original acids Iodine value (Wijs)
250
i io
Extract
Itaffinate
Losa
40 16 54
192 77 199
18
..7
Here the urea removed 16% of un extract composed mainly of stearic and oleic acid (iodine value 0 and 90, respectively). It concentrated in the raffinate the linoleic and linolenic acids (iodine values 181 and 273, respectively). The adducts formed from the fatty acids were crystdliiie and were easily filtered. They contained approximately 12 moles of urea to each mole of fatty acid and were about 72y0 urea and 28% fstty acid by weight. While the use of an aqueous solution of urea is preferred and has been used in most of the present work, other solvents for the urea, such as methanol, or solid urea itself, are also effectivc in
2539
N SOYBEAN FATTYACIDS TABLE I. UREAE X T ~ ~ W I OOF AND THEIR METHYLESTERS
Weight % Yield
Wijs Iodine Value ExRa5-Feed tract nate
Raffi-
EX-
tract nate Loss Soybean f a t t y acids 40 58 2 182 Soybean f a t t y acids" 50 47 3 132 Methyl esters of soybean f a t t y acids 42 52 6 139 0 Using urea dissolved i n methanolinstead of mater.
77 90
169 177
97
175
the separation. The use of solid urea is illustrated by the following experiment:
A 200-gram sample of the methyl esters of soybean fatty acids and 100 grams of crystalline urea were ground in a ball mill overnight. Methyl isobutyl ketone was then added to aid in filtering and washing the crystalline adduct formed. As before the adduct was decomposed in warm water. The extract and rahnate were worked up as in the general procedure above. The results were as follows: Original Esters
% b y wt. of ori inal esters Iodine value (&tils)
...
141
Extract 22
78
Raffinate
70
160
Loss
.8.
Even though methyl isobutyl ketone was generally used as a solvent for the fatty acid or ester, its use was not absolutely necessary. It was used mainly to speed the formation and filtering of the adduct. Partial separation was obtained also. by merely stirring urep, with the fatty acid or ester and filtering off the crystalline adduct. I n subsequent experiments this new method of fractionation was tried in several separations. APPLICATIONS
One of the most attractive commercial uses for a separation on the basis of unsaturation is found in soybean acids. Soybean oil, while p1ent)ifuland cheap, dries slowly and forms a film with considerable aftertack. Typical soybean oils contain acids of approximately the following composition: Saturated acids Oleic acid Linoleic acid Linolenic acid
10-16% 22-29 % 50-55 7-10%
The iodine value ranges from 120 to 141. Between 35 and 45y0 of the acid radicals contribute little to the drying of the oil. Removal of this fraction should greatly improve the drying properties of the remainder. The results, of various extractions of soybean acids and their methyl esters are shown in Table I. The general procedure described above using aqueous urea was employed in two of the experiments while urea dissolved in methanol was used in the third. In each case stearic and oleic acids or thcir esters concentrated in the extract while the linoleic and linolenic acids concentrated in the raffinate. The unsaturation in the r a f i a t e approached an average of two double bonds per molecule. (This would be an iodine value of 181 for the acids i t i d 173 for the methyl esters.) In the third experiment, Table I, of a raflinate was obtained which actually avcraged more than two double bonds per molecule. To illustrate the usefulness of the urea separation, the drying properties of a triglyceride prepitred from a raffinate of soybean methyl esters were compared with thosc of soybean, linseed, and dehydrated castor oil. The raffiiitttr, with an iodine value of 173, was converted to the triglyceride by carefully reacting it with glycerol triacetate in the prcwncc o f sodium methoxide. The same method was used to coiivcrt tht. methyl esters of soybean acids, linseed acids, and dehvdruted c:istor acids to the corresponding triglycerides. Films of thcw oils were tested for their air-drying properties after addition of 0.025% cobalt and 0 25%,
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
2540
Vol. 42, No. 12
relatively p u r dryirrg properties. Removal of the nondrying acids ~houldniaterially improve t,lw drying propertiea of tall oil raters. R'hik improvement of the drying propertlea of fatty acids is probably the most pmmising application of such a separation process, other types of comp,untls were investigated to see if they too could iK. separated by this mothod. Two such nlixtures were tried-the unsaturated alwhols obtained by roduciog liaseed oil with sodium and methyl isobutyl carbinol (10); and Armour's Arneal SI), which is a mixture of riitriles apparontly obtained fmm mybtwi acids, In both ernes tile extraction removed the derivatives of stearic and oleic acid arid conoentreted the derivatives of linoleic arid linolenic acid i n the raffiate. The results are shown i r k Taljle
1. Oil rrum "res ra1iinarr or aoylaa.. methyl 11. Soybean Oil 111. Linseed Oil IV. Uehydratrd FUX~UI oil V. Alkali-refined l i n s ~ odi l
Icild its the metal cx:twtes. Siricc all of ttx oils were "reconstit u t 4 ds"--i.e., prepared via the methyl estels-it natural oiln:mely, nlkali-refined linsrd oil&- w m included ~3 B contml. tt'ats were carried out by two methods ( I ) the wnventioeal finger touch method and (2) by means of the Sarrriemm dr.ying time meter. Thc rcvultv arc eompiled in Ti~hleIT, and photogrilpliir. rcprodoctions of the Sandawn disks sre presented in Figure 1. 111 this teat thc glau; disk is coated with the: drying oil and rotatr,.
