US3396182A - Process for recovery of purified saturated higher fatty acid from fatty acid fractions - Google Patents

Description

United States Patent 3,396,182 PROCESS FOR RECOVERY OF PURIFIED SATU- RATED HIGHER FATTY ACID FROM F A'ITY ACID FRACTIGNS Dwight E. Leavens and John M. Derfer, Jacksonville,

Fla, assignors, by mesne assignments, to SCM Corporation, New York, N.Y., a corporation of New York No Drawing. Filed Jan. 21, 1966, Ser. No. 522,039 Claims. (Cl. 260-419) ABSTRACT OF THE DISCLOSURE A process for purifying and recovering crude fatty acids comprising: (1) recrystallization of the crude acids from liquid normal alkane solution, (2) further purifying the recrystallized acids, in liquid normal alkane solution, with an acidic reagent such as boron trifluoride, (3) removing the acidic reagent, and (4) recrystallizing the purified fatty acids from the liquid normal alkane solution.

The present invention relates to purified saturated higher fatty acid and more particularly relates to a process for recovering purified fatty acid from crude fatty acid fractions.

The invention is advantageous in that it provides a process by which saturated higher fatty acid of a greater purity and color and heat stability than that heretofore obtainable from fatty acid fractions from natural sources such as tall oil can be economically produced.

The term saturated higher fatty acid as used herein is intended to mean and to include saturated C -C aliphatic fatty acids and mixtures thereof having an iodine value of 3 or less.

Saturated fatty acid, recovered from natural sources such as tall oil by conventional processes, generally has an undesirable odor and brown color, both of which often persist during and after extensive processing. Actually, the odor intensity and brown color of the saturated higher fatty acid tend to increase during storage even after short periods of time (e.g. several days) under ambient conditions. Such odor and color in saturated higher fatty acid detracts from its usefulness in commerce.

The present invention provides a process by which saturated higher fatty acid having improved color and odor and improved stability can be readily obtained from natural sources, particularly tall oil. The process is for recovering purified saturated higher fatty acid from a hereinafter defined crystalline fatty acid fraction obtained from natural sources such as tall oil heads which comprises the steps of:

(A) Dissolving the fatty acid fraction in a non-aromatic liquid hydrocarbon;

(B) Crystallizing saturated higher fatty acid from the hydrocarbon and separating the crystals therefrom;

(C) Re-dissolving the crystals in additional liquid nonaromatic hydrocarbon;

.(D) Treating the resultant solution with an acidic reagent, insoluble in the hydrocarbon, at a temperature and for a time sufiicient to remove impurities from the solution, the acidic reagent employed being incapable of undergoing a reaction with the fatty acid and the hydrocarbon;

(E) Separating the acidic reagent from the solution;

(F) Re-crystallizing the saturated higher fatty acid 3,396,182 Patented Aug. 6, 1968 from the solution and separating the resultant crystals therefrom;

(G) Removing residual hydrocarbon from the crystals so obtained.

By so proceeding, substantially pure saturated higher fatty acid having a low odor, color and an iodine value of 3 or less is obtained which does not undergo a significant intensification of odor and color when subjected to accelerated stability tests or when stored under ordinary conditions for prolonged periods (e.g. three months or longer).

The saturated higher fatty acid obtained by the processes of this invention have a color (1933 Gardner standard) of one or less and maintain a color of below one when subjected to storage for prolonged periods of time or when subjected to accelerated storage procedures as hereinafter described.

Although saturated higher fatty acid fractions from natural sources such as animal fat, corn, cottonseed and soya oils may be employed as the starting materials in the process of this invention, an advantageous fatty acid fraction is a tall oil distillation heads-cut comprising from about 25 to 45 weight percent of dark colored crude crystalline saturated higher fatty acid solids consisting preponderantly of palmitic acid. The heads-cut is a semisolid viscous mass at room temperature and, if desired, can be further concentrated by conventional means such as centrifugation, distillation, filtration, decantation, cold pressing or the like to provide a starting material containing from about to weight percent of dark colored, crude, crystalline saturated higher fatty acid.

Generally when the starting material is a tall oil distill-ation heads-cut, the crude saturated higher fatty acid fraction will consist primarily of palmitic acid. Small quantities of lauric and stearic acid and substantially larger quantities of higher unsaturated fatty acids such as oleic and linoleic acids and of an unsaponifiable material of varied and undetermined composition are also often present in the fraction.

As previously noted, the crystalline fatty acid fraction is dissolved in a liquid non-aromatic hydrocarbon. Almost any liquid non-aromatic hydrocarbon which is relatively inert and which is a solvent for higher saturated fatty acid may be employed. Since the process involves subsequent fatty acid crystallization, liquid non-aromatic hydrocarbons boiling between about 40 C. and 200 C. have been found to be especially advantageous. Aromatic liquid hydrocarbons are usually undesirable because of the high solubility of the fatty acid in these solvents resulting in low crystal yield.

Aliphatic liquid hydrocarbons having the above described properties may be employed. Examples of liquid aliphatic hydrocarbons include lower alkanes and mixtures thereof having a boiling point within the above defined range (e.g. mixtures of alkanes having between 5 and 15 carbon atoms). Cyclic liquid aliphatic hydrocarbons such as cyclopentane, cyclohexane, and mixtures thereof may also be used. Advantageous commercially available liquid hydrocarbons include white spirits, mineral spirits, textile spirits and ligroin having a boiling temperature between about 40 C. and 200 C.

The crystalline fatty acid fraction can be suitably dissolved in the liquid aliphatic hydrocarbon by mixing one volume part of fatty acid fraction with from about 2 to about 4 volume parts of the liquid hydrocarbon and heating the mixture at a temperature below the boiling point of the hydrocarbon usually between about 50 C. to about 75 C., when preferred hydrocarbons such as mineral or textile spirits are used, until solution occurs. If less than about 2 volume parts of liquid hydrocarbon per volume part of fatty acid fraction is used, undesirable quantities of colored, odoriferous material and unsaturated fatty acids will contaminate the recovered higher fatty acid crystals. On the other hand, if more than about 4 volume parts of liquid hydrocarbon per volume part of fatty acid fraction are employed, the yield of fatty acid crystals obtained will be unnecessarily low.

If temperatures below about 50 C. are employed to dissolve the fatty acid fraction in the liquid hydrocarbon, an unnecessarily large volume of liquid aliphatic hydrocarbon will often be required. If temperatures above the boiling point of the solvent are employed, there is danger of loss of liquid hydrocarbon unless pressures above atmospheric pressure are used.

After dissolving the fatty acid fraction in the hydrocarbon, fatty acid crystals are obtained by cooling the solution to a temperature in the range of from about to +10 C. Although temperatures below about 10 C. may be employed, some of the impurities in the solution (present in the starting fatty acid fraction) can often crystallize concurrently with the saturated fatty acid resulting in color and odor instability in the purified product. On the other hand, if temperatures above about 10 C. are employed, unduly large quantities of saturated higher fatty acid will remain in the mother liquor resulting in low product yield.

After crystallization from the liquid hydrocarbon, the saturated higher fatty acid crystals are separated from the liquid by conventional means such as filtration, centrifugation, decantation, etc. It is desirable to wash the crystals with cold liquid hydrocarbon and the higher fatty acid crystals will then be substantially white and will have a faint characteristic fatty acid odor. However, if crystals so treated are stored at room temperature for several weeks, they will darken and take on a more intense and rancid fatty acid odor (presumably due to the presence of unknown chromophoric and osmophoric compounds and other impurities). Thus the crystals, while initially white and of low odor, will often undergo chemical changes, an increase in odor, and Will also form color bodies upon storage.

The supernatant liquid hydrocarbon from which the fatty acid crystals are recovered (e.g. the mother liquor) is brown in color and contains unsaturated fatty acids and colored compounds which are unknown but are believed to be phenolic in character.

The separated crystals are then re-dissolved in additional liquid hydrocarbon in the concentrations and within the temperature ranges employed in forming the previously described solution. For economic reasons, it is preferred to use the same kind of liquid hydrocarbon and it has also been found advantageous to mix a portion of the mother liquor previously obtained with quantities of fresh liquid hydrocarbon. Usually the hydrocarbon employed in the second solution step may contain up to 50% by volume of such mother liquor.

As afore-noted, the second solution is then treated with a small amount of acidic reagent, preferably of the Lewis acid type, which is substantially insoluble in the hydrocarbon solvent and which is also incapable of undergoing a chemical reaction with the higher fatty acid and the liquid hydrocarbon solvent. Useful acidic reagents include mineral acids, certain hereinafter-defined acidic metal salts and organic derivatives thereof, acidic clays and mixtures thereof. Additionally, as will be hereinafter evident, the above acidic reagents can also be employed in conjunction with a lower aliphatic aldehyde.

Examples of suitable mineral acids which may be used as acidic reagents include sulphuric and phosphoric acids and mixtures thereof; examples of acidic metal salts include the halides and sulfates of tin and boron, particularly boron triliuoride; examples of organic derivatives of acidic metal salts include the etherates and other complexes of the above metal halides; a specifically advantageous etherate being that of boron trifluoride; examples of acidic clays include acid activated montmorillonite such as acid activated bentonite and fullers earth, acid activated attapulgite and acid activated china clays such as kaolin. Although not critical, it has sometimes been found advantageous and desirable to use an aliphatic aldehyde such as formaldehyde, paraformaldehyde, acetaldehyde, etc. in conjunction with the acidic reagent The employment of such aldehydes in conjunction with the aforedescribed acidic reagents makes it Possible to obtain a more stable end product.

The clays which can be employed as acidic reagents in the processes of this invention are Well known in the art and usually consist of activated montmorillonite clay minerals. The method of activation which is old in the art is accomplished by treating a slurry of clay and water with a mineral acid such as hydrochloric or sulfuric acid in an amount of about 35% of the total dry weight of the clay. The mixture is then treated with steam at a temperaure of about 200-210 F. for a period of about 5 to 6 hours and is thereafter washed and filtered. US. Patents 1,397,- 113, 1,642,871, 1,776,990, and 1,796,799 relate to montmorillonite clays and the acid treatment thereof and the teachings of these patents are incorporated herein by reference. Specific examples of acid activated clays that can be prepared according to the prior art referred to are various grades of commercially available trademarked products such as Filtrol and the Bennett Clark clays. The acid activated clays are finely divided, that is, they are supplied as fine white powders -95% of which pass through a 20 mesh screen. Particular preferred clays are those acid activated montmorillonites having a pH when dispersed in water from about 2 to about 5.0. They function as selective adsorbents for impurities in the fatty acid hydrocarbon solution.

The solution, consisting primarily of the higher fatty acid and the liquid hydrocarbon, may be treated with the acidic reagent in a variety of conventional ways depending upon the particular acidic reagent used. Since the acidic reagent, whether liquid as in the case of mineral acid or solid as in the case of acid activated clay, is substantially insoluble in the liquid hydrocarbon solution, treatment can be effected by dispersing the reagent in the solution, thus forming a dispersion comprising a solution phase and a reagent phase, and agitating the dispersion preferably by mechanical means. i

In order to efficiently effect treatment of the solution with the acidic reagent, it has been found desirable to heat the dispersion during agitation to a temperature of from about 30 C. to just below the boiling point of the solvent, preferably a temperature in the range of from about 60 C. to about 70 C.

Alternatively, when an acidic clay is employed, the acid treatment may be effected by contacting the solution with a fixed bed of the acidic clay. When an acidic clay is used in conjunction with an aldehyde and a fixed bed is employed, it is desirable (as will be hereinafter evident) to add the aldehyde to the clay bed prior to contact of the solution with the fixed bed.

The amount of acidic reagent employed may vary considerably depending upon the volume of solution, the concentration of fatty acid dissolved therein, the residual impurities initially present and the pa ticular reagent employed. Generally, from about /4 to about 10% by weight, based on the weight of the fatty acid, of acidic reagent can be used. Thus, for example, when a mineral acid or a mixture of mineral acids such as for example a mixture of sulfuric and phosphoric acids is employed from about 1 to about 4% by weight, based on the weight of the fatty acid, will be contacted with the hydrocarbon solution. When an acidic metal salt or an etherate of an acidic metal salt is employed, from about 1 to 4% by weight of acidic reagent will be required. When an acidic clay is used, from about 1 to weight percent, based on the weight of the fatty acid is usually required. When an aldehyde is used in conjunction with the acidic reagent, from about 0.05 to about 0.15 percent by weight of aldehyde, based on the weight of the fatty acid, will usually be used in addition to the acidic reagent. The reason for the effectiveness of the aldehyde is not known with certainty. However, since it is consumed during the acidic reagent treatment of the solution, its effectiveness is believed to be due to re-activity with chromophoric (i.e. color-forming bodies), osmophoric (odor-forming bodies), and other impurities dissolved in solution. Such re-activity is selective and does not involve reaction with the higher fatty acid dissolved in the hydrocarbon.

The treatment time of the hydrocarbon solution with the acidic reagent may vary considerably depending upon the amount of impurities (e.g. chromophoric bodies and odor producing materials) in the solution as well as the quantity (volume) of the solution employed. Generally, the time will be from about 30 to about 180 minutes, the longer treatment times corresponding to larger quantities of solution and more impure solutions. As the treatment of the solution with the acidic reagent proceeds, the impurities which result in the instability of color and odor in the final product are removed from the solution phase and transferred to the reagent phase.

After completion of the treatment, the reagent phase is separated from the solution phase by conventional means such as filtration, centrifugation, decantation, and the like.

In one advantageous embodiment of the treatment of the hydrocarbon solution with an acidic reagent, from about 3% to about 5% by weight, based on the weight of the fatty acid in the solution, of acid activated montmorillonite clay is dispersed in a solution containing from 2 to 4 volumes of lower alkane per volume part of crystallized saturated higher fatty acid. To the resultant dispersion there is added from about 0.05 to about 0.15 weight percent basis the weight of the dissolved fatty acid of an aldehyde such as formaldehyde, paraformaldehyde or-acetaldehyde. Dispersion is accomplished and maintained by mechanical agitation and while the dispersion is heated to a temperature from between 6070 C. for three hours after which agitation is ceased and the solution is separated from the clay by filtration. By so proceeding, a colorless, brilliant, clear solution containing higher fatty acid is obtained. Alternatively, there may be added to the solution in place of the clay from about 1% to about 4% by weight of either boron trifiuoride, boron trifiuoride etherate or complexes, or a mixture thereof and the same procedure followed as that above described.

In another embodiment, the acidic clay may be replaced with from about 1% to about 10% by weight, based on the weight of the fatty acid, of a mixture of mineral acids consisting substantially of 60 weight percent H SO and 40 weight percent of phospholeum (e.g. l02l05% H PO the time and temperature of treatment being substantially identical to that above described.

After the treatment of the solution by the acidic reagent has been completed and the acidic reagent separated from the solution, re-crystalliz'ation of the fatty acid is effected by cooling the liquid hydrocarbon to a temperature within the range of -l0 to about +10 C. The fatty acid crystals are then conventionally separated from the liquid hydrocarbon and thoroughly washed with fresh cooled (e.g. l0+l0 C.) liquid hydrocarbon. Thereafter, the crystals are heated either at atmospheric pressure or in vacuo to remove residual hydrocarbon. By so proceeding, the fatty acid product (palmitic acid when the starting material is a tall oil fatty acid fraction) of greater than 96% purity is usually obtained. The material has a white color and an extremely faint characteristic odor, which upon storage under ambient conditions for prolonged periods of time (e.g. up to three months or longer) does not darken or undergo an increase in odor.

The following specific examples are intended to illustrate the invention, but not to limit the scope thereof, parts and percentages being by weight unless otherwise specified.

Example 1 Five kilograms of a tall oil heads-cut containing 63.3 of palmitic acid (as measured by vapor phase chromatography) was centrifuged to remove excess liquid. After decantation of the liquid, a crude, brown, wet crystalline solid weighing 4.2 kilograms was obtained. One kilogram of the solids was dissolved in three kilograms of textile spirits having a boiling point of 79 C. by mixing the solids with the spirits and heating the mixture to about 75 C. until complete solution occurred. The resulting solution was then cooled with gentle stirring to 5 C. in an ice bath until no further crystallization occurred. The mother liquor was filtered off and 826 grams of crystalline palmitic acid (analyzed at 96% pure by vapor phase chromatography) were obtained. The crystals were then dissolved in 2.5 liters of additional textile spirits consisting of one liter of mother liquor and 1.5 liters of fresh textile spirits, by heating the textile spirits and dispersed crystals to a temperature of 65 C. To the resultant solution there was added, with agitation provided by a mechanical stirrer, 32.5 grams of Piltrol, a finely divided acid activated montmorillonite clay having the formula, (MgCa) OAl .5SiO .H O and 0.9 gram of paraformaldehyde to form a dispersion containing the solution of palmitic acid dissolved in the textile spirits in which there was dispersed a finely divided acid activated clay and the paraformaldehyde. The heating and agitation were continued for minutes after which the dispersion was cooled to a temperature about 40 C. The clay was separated from the solution by filtration through a Buchner funnel. The solution, which was a water white color, was then cooled to -10 C. to crystallize the palmitic acid. The textile spirits were decanted from the palmitic acid crystals and the crystals were washed with cold (5 C.) fresh textile spirits. The excess residual textile spirits were then removed from the palmitic acid by distillation at reduced pressure (10 mm.Hg) at 40 C. A yield of 750 grams of palmitic acid, which analyzed (using vapor phase chromatography) at 98% purity was obtained. The crystals were white and had a faint characteristic fatty acid odor and an iodine value of 0.1. Upon storage for three months at 30 C., no significant change in the color and odor of the crystals was detected.

When the above process was repeated using white mineral spirits in place of textile spirits substantially the same results were obtained. However, the yield of palmitic acid was reduced by 30%. The white spirits employed had a boiling point of C.

Example 2 One hundred grams of the crystals obtained from the first crystallization step of Example 1 were washed with cold textile spirits employed in Example 1, dried, and heated in vacuo at reduced pressure and at a temperature of 30 C. to remove residual hydrocarbon. Upon storage of two Weeks, the crystals, which were originally white, noticeably darkened and the fatty acid odor had intensified. The crystals had an iodine value of 3.1.

Example 3 The palmitic acid products obtained in Examples 1 and 2 had Gardner scale color of below one when freshly prepared. Each of these materials in flake form was added to respectively separate 1" by 8" test tubes, blanketed with nitrogen, and immersed in an oil bath at 205 C. in accordance with AOCS Test No. Td 3a-64. The level of the palmitic acid in each tube was adjusted to the level of the oil bath. The tubes remained in the bath 7 for 2 hours after which they were removed, cooled, and poured into separate Gardner color tubes and read on a Gardner Color Comparator. The color of the palmitic acid obtained from Example 1 was less than 1. However, the color of the palmitic acid obtained from Example 2 had intensified to a Gardner color value of 4 indicating the presence of substantial chromophoric impurities even after the single crystallization of the palmitic acid from the textile spirits.

Example 4 The process of Example 1 was repeated except that 9 grams of boron trifluoride etherate were employed as the acidic reagent in place of Filtrol and paraformaldehyde employed in that example. The yield of palmitic acid was substantially the same as the yield obtained in Example 1. The product had a Gardner color value of less than one and a faint characteristic fatty acid odor. The crystals were then stored at 30 C. for three months and re-examined. The Gardner color value was still less than one and no appreciable change in odor could be detected.

Example 5 The process of Example 1 was repeated except that an acidic reagent consisting of 50 grams of a mixture of 60% by weight H 50 and 40% by weight of phospholeum (105% H PO was employed in place of the Filtrol used in that example. A palmitic acid product having the same purity and the same color and odor properties of the product of Example 1 was obtained. Storage stability test conducted as in Example 1 showed the product to have the same stability characteristics as the product in Example 1.

When a hydrogenated cottonseed oil fatty acid or a hydrogenated soya oil fatty acid fraction or a hydrogenated tall oil fatty acid fraction is used in place of the tall oil distillation heads-cut employed in Example 1 and the process of that example is repeated, purified fatty acid products having good color and odor characteristics and good stability characteristics are obtained.

Example 6 Five kilograms of a tall oil heads-cut containing 63.3% of palmitic acid (as measured by vapor phase chro matography) were centrifuged to remove excess liquid. After decantation, 4.3 kilograms of a crude, brown, crystalline solid were obtained. One kilogram of this solid was dissolved in 3.5 kilograms of mineral spirits having a boiling point of 180 C. by mixing the solid with the spirits and heating the mixture to about 150 C. until complete solution occurred. The resulting solution was then cooled with gentle stirring to C. in an ice bath until crystallization occurred. The mother liquor was filtered off and 819 grams of crystalline palmitic acid (analyzed at 95.9% pure by vapor phase chromatog* raphy) were obtained. The crystals were dissolved in 2.7 liters of additional mineral spirits consisting of 1 liter of mother liquor and 1.6 liters of fresh mineral spirits by heating the spiirts and dispersed crystals to a temperature of 170 C. To the resultant solution there were added 32.5 grams of Filtrol, a finely divided acid activated montmorillonite clay having the formula (MgCa) OA1 -SiO -H O and having admixed therein 0.9 gram of paraformaldehyde. The clay mixture was dispersed in the solution by means of a mechanical stirrer to form a dispersion containing palmitic acid dissolved in the mineral spirits and containing, in dispersed form, the finely divided acid activated clay in the paraformaldehyde. The heating and agitation were continued for 150 minutes after which the dispersion was cooled to 50 C. The clay was separated from the solution by filtration through a Buchner funnel. The solvent which was water white in color was then cooled to l0 C. to crystallize the palmitic acid. The mineral spirits were then decanted from the palmitic acid crystals and the 8 i crystals were washed with cold (-5 C.) fresh miner'a spirits. The excess residual mineral spirits were then removed from the palmitic acid by distillation at reduced pressure (10 mm.-Hg) at 60 C. A yield of 720 grams of palmitic acid which analyzed (using vapor phase chromatography) at 97.5% purity was obtained. The crystals were white, had a faint characteristic fatty acid odor, and an iodine value of 0.2. Upon storage for 13 weeks at 30 C., no significant change in the color and odor of the crystals could be detected.

What is claimed is:

1. -A process for recovering purified saturated higher fatty acid from a crude crystalline fatty acid fraction which comprises the steps of:

(A) dissolving said fraction in a liquid saturated aliphatic hydrocarbon;

(B) crystallizing saturated higher fatty acid from said hydrocarbon and separating the crystals therefrom;

(C) redissolving said crystals in additional liquid aliphatic hydrocarbons;

(D) treating the resultant solution with an acidic reagent substantially insoluble in said hydrocarbon and selected from the group consisting of boron trifluon'de, boron trifluoride etherate, and finely divided activated clay, phospholeum and a mixture of phospholeum and sulfuric acid, at a temperature and for a time sufficient to remove impurities from the solution; said reagent being incapable of undergoing a reaction with said fatty acid and said hydrocarbon;

(E) separating said acidic reagent from said solution;

(F) re-crystallizing said saturated higher fatty acid from said solution and separating saturated higher fatty acid crystals therefrom; and

(G) removing residual liquid non-aromatic hydrocarbon from the last mentioned crystals.

2. The process of claim 1 wherein the crystalline fatty acid fraction is a tall oil distillation heads-cut containing a preponderant amount of crude palmitic acid crystals.

3. The process of claim 1 wherein the liquid hydrocarbon is a mixture of lower alkanes containing from about 5 to about 15 carbon atoms having a boiling point between about 40 and 200 C. and one volume part of crystalline fatty acid is dissolved in from about 2 to about 4 volume parts of said hydrocarbon at a temperature in the range of from about 30 to about C.

4. The process of claim 1 wherein the dissolved fatty acid is crystallized from said hydrocarbon at a temperature in the range of from about 10 C. to about +10 C.

5. The process of claim 1 wherein the treatment of the solution by said acidic re-agent is effected by dispersing said reagent in said solution and agitating the resultant dispersion at a temperature of from about 60 C. to about C. for from about 30 to about minutes.

6. The process of claim 5 wherein said treatment with the acidic reagent is done in the presence of :from about 0.05 to about 0.15 weight percent, basis the Weight of saturated higher fatty acid in the solution, of a lower aliphatic aldehyde.

.7. The process of claim 5 wherein the acidic reagent used is from about 2 to about 5 weight percent, basis the weight of the fatty acid in the solution, of a finely divided acid activated mineral clay and said treatment is done in the presence of from about 0.05 to about 0.15 percent by weight basis the weight of the fatty acid in the solution of paraformaldehyde.

8. The process as in claim 7 wherein the acidic reagent in the dispersion is separated from the solution by filtration.

9. The process as in claim 7 wherein the re-crystallized saturated higher fatty acid is recovered from the solution by cooling the solution to a temperature of between about -10 C. to about +10 C.

10. The process of claim 9 wherein the recovered saturated fatty acid is washed with fresh liquid hydrocarbon at a temperature of from about 10 C. to about -0 C.

and the residual hydrocarbon is removed in vacuo by heating the crystals to just above their melting point. 1

References Cited UNITED 10 3,052,701 9/1962 Hampton 260-419 3,066,160 11/1962 Hampton 260419 OTHER REFERENCES STATES PATENTS 5 Vogel, A.I.: Practical Organic Chemistry QD 251, 3rd Edition (1957), Longmans, Green & Co., V6, New York S32? 3313:3313: 22MB 122-11304,

Huif 260-419 Leaders et a1 260419 ALTON D. ROLLINS, Przmary Examiner.

Terry et 1 260-419 10 R. V. RUSH, Assistant Examiner.