PREPARATION OF DRYING OILS Recent Developments DALE V. STINGLEY Armour and Company Auxiliaries, Chicago, ill
America'b diynmdence on foreign sourceb of drying oils is a pressing subject, and conbideralion must be given to the practical possibilities of utilizing domestic semidrying oils as raw material for the chemical production of new drying oils. By employing the fractional distillation process for the separation of the fatty acids of bemidrying oils into drying and nondrying fatty acid fractions, and by subsequent re-esterification of these drying f a t t y acid fractions w i t h glycerol or pentaerythritol, new and valuable drying oils can be produced. Domestic oils, such as marine and soybean oils, are well suited to serve as raw m a terials for this process. In the commercial field unsaturated CZO fatty acids from marine oils with iodine values of 235 to 250 are available, as are also drying oils synthesimd from these acids. Field and laboratory data have been obtained which evaluate the commercial unsaturated C ~ O glyceride in terms of linsepd and tung oils. Fractionated soybean fatty acids with iodine values of 150 to 160 have been produced commercially.
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HERE has probably never heen a time wlicii the economic need for the development of domestic sources of necessary raw materials has been as great as it is today. Chemical developments have, to some extent, aided in solving this problem, but in many fields, particularly drying oils, the major portion of our supplies must be imported (7). Efforts have been and are being made to develop domestic sources of these commodities (S,4, but climatic and economic consiilera.tions have retarded any rapid increase in our agricultural production. The seriousness of this situation is reflected daily in the drying oil market, and iinsettled price levels as well as uncertain supplies have caused grave concern among American consumers. Although the foregoing statements are true for drying oils in general, and for such oils as tung, perilla, and linseed oils in particular, it does not follow that we are confronted with an impossible situation in increasing domestic production of oils of this type. Oils such as soybean, castor, and various marine oils can he produced in this country, and although they cannot he classed as good drying oils, it is possible by newly developed methods to produce oils from these materials which are ac-
coptable replacements and even miprtivements over natural drying oils. Established procedures such as blowing, heat bodying, wintering, or similar treatments are not referred to in this respect, and should not b confused with entirely new methods of production, such as the catalytic dehydration of castor oil (5, 6) or the production of synthetic glycerides hy the reesterification of fractionally distilled fatty acids. Oils produced by these new methods are uniform materials because of their synthesized origin and possess properties not present in natural oils. It is important to realize that such synthesized oils are not merely substitutes for exixting drying oils but are actual additions to the drying oil field, and proper study and care must be devoted to their utilization.
Synthetic G1yceridc.s One of the most recent developments of consequence in this new field of drying oils bas been the production of syntlietic glycerides from fractionally distilled fatty acids. In the past
1218
the practice has been to employ straight distillatiuns only in the production of distilled fatty acids which have substantially the same composition as the natural oil from wliich the crude fatty acids were obtained. An entirely new type of distillation has been made possible in part by the introduction of special alloy vacuum fractionating columns. These columns permit the use of special processes whereby separat.ion of the various fatty-acid componcnts can be achieved. Then hy the subsequent re-esterifiration of suitable fractions, drying oils vith a maximum degree of desired properties can he produced. Although this process is not limited in scope to any specific class of raw materiala. marine oils have been found excellent for this purpose. Xatural fats and oils of marine oriein are sharnlv . - differentiated from all other classes of fats and oils because of their high content of highly unsaturated acids containing 20 and 22 carbon atoms. The physical properties of these oils are also differentin many respects fmm other oils, and in general these differencesare directly traceahle to their unusual composition. Although little is actually known concerning the basic glyceride make-up of marine oils, Dean (2) showed that probability to a large extent governs glyceride structure in oils; and we can postulate from the fatty acid composition that marine oils
drying and nondrying fatty acid fractions. For example, from sardine oil it is possible to produce nondrying fatty acids comparable to tallow fatty itcids and drying fat.ty acids with extremely high unsaturation. “Neofat No. 19” fatty acid is a representative commercial product of this type of processing. Some mention was previnusly made concerning the fatty acid composition of marine oils in general. Specifically, however, the fatty acids which comprise the major constituent of Neofat No. 19 fatty acidnamely, the unsaturated acids of 20- and 22-carbon chain length, are a rather specialized group. From the information now available these acids are believed to include monoand diethylenic as well as tri- and tetraethylenic fatty acids. Unfortunately, acids of the Goand Cn group are difficult to isolate; many have not been identified or studied and must of riecessity be referred to simply as unsaturated Cm and unsaturated Cpl fatty acids. For our present purpose this is a satisfactory designation, inasmuch as our interest is essentially with their properties a s a group. -4 pertinent point concerning these acids is that in their entirety they fall almost oompletely in the nonconjugated system. Considering this fact and also their high degree of unsaturation, i t is possible to predict rather unusual physical and chemical properties for both these acids and their derivatives.
SEPTEMBER, 1940
INDUSTRIAL AND ENGINEERING CHEMISTRY
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do not stand overcooking, and a finishing temperature of not over 450" F. (232" C.) is recommended. In addition to alkyds, various other derivatives of unsaturated C20 acids have been prepared and studied. Pentaerythritol esters, for example, are worthy of note and closely approach tung oil in many ways. I n the commercial field the glycerol ester of unsaturated Czoacids is known as Neofat No. 19 triglyceride and its average chemical and physical characteristics are as follows: Sa onification value Ioxine value Acid value Absolute viscosity a t 25' C., poises Color
177.0 205.0 6.0
2.0 Pale yellow
Unsaturated Czofatty acids with an iodine value of approximately 250 are used in the production of Neofat No. 19 triglyceride. The drop from 250 to 205 iodine value in the SOYBEAN N E D - F A T 14 G L Y C E R I D E OIL -DRY; finished product is caused first by the change ,' ' -_---*I I */--/I ,: in molecular weight due to formation of the I ** I ester, and secondly to some polymerization ; ,I I' ' c occurring during esterification. I " f DUST- I/ /I i '1 The properties of Neofat No. 19 triglyceride i-----;.'--___--,' are exactly those to be expected from a highly unsaturated nonconjugated oil, free from satu/ .* ,' rated acids. It is a rapid drying material, ,," FIG.2 - F I L M forms clear glossy films, has good adhesion, I' F 0 R M AT1 0 N but shows some tendency toward brittleness CURVES on aging. Figure 1 shows clearly how i t com0 , I I ; ,,' I' t L A 5 S PLATES -70'F pares with other commonly known oils in /' 0.207.PB. 0.02"l.CO. drying characteristics. Extensive tests have been conducted for 0 5 10 I5 20 25 30 the purpose of evaluating Neofat No. 19 triglyceride in the varnish and enamel field. Comparison with linseed and tung oils were made by preparing varnishes of lo-, 30-, and 50-gallon oil lengths, by using various resins, such as pure phenolic, modified phenolic, copal, ester gum, and limed rosin, and by subjecting these varnishes to standard tests, inNeofat No. 19 Fatty Acid cluding exposure. Results of these tests, as well as subsequent commercial application, make it possible to evaluate Neofat Neofat No. 19 fatty acid is composed chiefly of acids of the No. 19 triglyceride in terms of better known natural oils. To Ci0 and Cn series as described above, with certain unsaturated summarize briefly, i t was found with most resins, particularly C,, acids also present. Its average chemical and physical rosin and ester gum, that unless soybean oil, dehydrated castor constants are as follows: oil, tung oil, or some other plasticizing material was present in suitable amounts, brittleness would develop. On the other Titer, C . 20 Iodine value (Wijs) 235 hand, proper formulation produced superior varnishes in every Neutralization value 184 respect. I n drying time, adhesion, surface hardness, hot and Mean molecular weight 305 Color Pale yellow cold water resistance, gas checking, alkali resistance, and alcoI
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When first introduced to the trade Xeofat No. 19 fatty acid had an average iodine value of 250, but experimental results soon indicated that for commercial applications in the production of alkyd resins this degree of unsaturation produced heatreactive alkyds which frequently gelled in the cooking equipment; consequently it was found advisable to lower the iodine value to the present standard. Neofat No. 19 fatty acid produces excellent air-drying and baking alkyds. These alkyds have good color retention, and air-dried or baked Ums are practically odorless. Straight alkyds produced from Keof a t No. 19 fatty acid may show signs of brittleness, and in practice soybean fatty acids or dehydrated castor fatty acids are included in the resin to impart plasticity. Some precautions must be observed in formulating these acids; i t should be mentioned specifically that Neofat No. 19 fatty acid alkyds
OF MARINE OILS (1) TABLE I. COMPOSITION
Whale Oil Saturated acids 8.0 Myristic, CuHzeOz 11.0 Palmitic, C~sHazOz 2.5 Stearic. CieHosOz Unsaturated acids 1.5 Myristoleic, CiiHisOz Palmitoleic, CiaH~aOz 17.0 Oleic, ClsHsaOz 34.0 Linoleic C18Haz0z 9.0 Linoleni'c ~ l a ~ a o ~ ? Trace Czoacids,'CznH?(z0-=)0z 5.0 Czz acids, CzzHz(zz - z)Oz 12.0 Titer ' C. 22-24 1odin)e value 110-136 Saponification value 185-195
Menhaden Oil
Sardine Oil
7.0 16.0 1.0
14.0 3.0
Trace
Trace
Trace
Trace
17.0 27.0
5.0
Herring Oil 7.0 8.0
15.0
18.0 9.0 13.0
20.0 12.0
22.0 19.0
20.0 25.0
31-33 148-186 189-193
28-34 170-190 189-193
23-27 130-144 179-194
Trace
...
12.0 10.0
...
...
INDUSTRIAL AND ENGINEERING CHEMISTRY
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hol resistance, Neofat No. 19 varnishes, in general, are equal to tung-linseed oil varnishes, except for the fact that brittleness develops on aging. It was found that this difficulty could be completely overcome by using a mixture of dehydrated castor oil and Neofat KO. 19 triglyceride in approximately equal parts, with but little sacrifice of most of the desired properties. Further tests also showed that substituting Neofat No. 19 triglyceride for all of the linseed oil and half of the tung oil in better quality varnishes, gave results superior to the linseed-tung oil varnishes alone. It wa8 also demonstrated that a mixture of approximately 65 per cent soybean oil and 35 per cent Neofat Xo. 19 triglyceride was comparable to linseed oil. Varnishes, enamels, lacquers, printing iiiks, linoleums, oilcloth, patent leather, putty, quick-drying paints, aluminum vehicles, core oils, and the fortifying of slower drying oils are all applications for this versatile material. Much that has been said about the chemical processing of marine oils is also applicable to soybean and other semidrying oils. For example, the fractional distillation of crude soybean fatty acids produces fractionated soybean fatty acids with iodine values of 150-160, and with characteristics similar to linseed oil when used in alkyd resins. Fractionated soybean fatty acids are now available commercially, and laboratory investigations of both the glycerol and pentaerythritol esters of these acids have been made, Figure 2 shows how these derivatives compare with regular linseed and soybean oils in drying characteristics.
VOL. 32. N O . 9
These products appear promising in the laboratory, and i t is possible that soybean derivatives such as these may soon supplement our drying oil supply. In any event a practical means is at hand for the production of a great variety of drying oils from domestic sources; although future developments in a field as new as this cannot be foreseen: there seems to be no logical reason why we cannot expect continued progress in the production of drying oils from domestic sources.
Acknowledgment The author wishes to acknowledge the assistance of the staff of the Development Department of Armour and Company Auxiliaries in the preparation of this paper and also the cooperation of Armour and Company in granting permission to present the data.
Literature Cited Armour and Co., unpub. laboratory data. Dean, H. K., “Utilization of Fats”, 1st ed., pp. 105-7, New York, Chemical Publishing Co. of N. Y . ,1938. Holton, J. C., Paint Oil. Chem. Rev., 99, 29-30, 141-2 (1937). Lawson, P. F., I b i d . , 99, 142-3, 147-8 (1937). Scheiber, Johannes, U. S. Patent 1,942,778 (Jan. 9, 1934). Schwarcman, Alexander (to Spencer Kellogg and Sons), Ibid., 2,140,271 (Dec. 13, 1938). U. S. Dept. Commerce, “Animal and Vegetable Fats and Oils”, Washington, U. S. Govt. Printing Office, 1935. PRESENTED before the Division of P a i n t and Varnish Chemistry a t the 99th Meeting of the American Chemical Society, Cincinnati, Ohio.
MULTICOMPONENT RECTIFICATION Estimation of the Number of Theoretical Plates as a Function of the Keflux Ratio’ E. R. GILLILAKD Massachusetts Institute of Technology, Cambridge, Mass.
A graphical method for estimating the number of theoretical plates required for a given separation as a function of the reflux ratio is presented in Figures 4 and 5. The values of the limiting conditions of the minimum number of plates at total reflux and the minimum reflux ratio are needed to use the method.
FTEK it is desirable to obtain a rapid estimate of the number of theoretical plates required for a given separa-
0
tion as a function of the reflux ratio. The most accurate method of making such calculations is the stepwise procedure outlined by Lewis and Matheson ( 5 ) , but this method requires several hours to determine the number of theoretical plates required for each reflux ratio considered. However, because of the confidence that can be placed in the results, this stepwise plate-to-plate method is to be recommended for the final detailed calculations; but a more rapid method is desirable for making preliminary surveys of separa1 Previous papers in this series appeared in July (page 918) andlAugust (page 1101). 1940.
tion problems and for orienting the designer for his detailed calculations. A number of approximate methods have been published, but in most of these procedures the approximations employed make the accuracy of the results so uncertain that the’designer can have little faith in them. For example, a t reflux ratios near the minimum reflux ratio the results of these approximate methods are very erratic and often give a finite number of plates when actually an infinite number would be required, or vice versa; however, the reflux ratios in this region are important since the most economic design usually occurs at values of the reflux ratio, O / D , equal to 1.2 to 1.5 times the minimum reflux ratio, (O/D),. T H I S paper presents an empirical method of plotting results that has been used for the past year in conjunction with courses in distillation a t M. I. T. The plot can be used to estimate the number of theoretical plates required for a given separation as a function of the reflux ratio, and the method has the advantage that it is most accurate near the limiting conditions of the minimum reflux ratio and the minimum number of theoretical plates a t total reflux. Thus i t is particularly satisfactory in the economic design region. One of the most common methods of presenting the results of distillation calculations is to plot the number of theo-
