US3052701A - Refining fatty acids - Google Patents

Description

3,052,701 Patented Sept. 4, 1962 3,052,701 REFINING FATTY ACS Burt L. Hampton, Port St. Joe, Fla., assignor to The Glidden Company, Cleveland, Ohio, a corporation of Ohio No Drawing. Filed Nov. 12, 1959, Ser. No. 852,232 1 Claim. (Cl. 260-419) This invention relates to a process for refining unsaturated fatty acids. The invention relates more particularly to an improved method for treating mixtures comprising mostly unsaturated fatty acids to improve their color and heat stability. Reference will be made hereinafter mostly to the treatment of tall oil fatty acids although this should not be construed as a limitation of the process of this invention. Examples will be offered showing treatment of other fatty acids such as soya oil, cottonseed oil, etc. in accordance with the teachings herein.

Tall oil is made from black liquor soap, a product of the sulfate paper mills. The soap skimmings from the mill contain about 60% solids and yields about 50 to 56% of tall oil upon acidulation.

Crude tall oil has a disagreeable odor. This odor generally can be improved for example by heating and blowing with steam or an inert gas, but some of the ingredients of the tall oil decompose upon standing and the oil again develops a disagreeable odor.

The viscosity of tall oil varies with the percent rosin acids which range from 37% to about 55%. Tall oil has a very wide variation in properties depending on the source, care in acidulation, etc. Tall oil generally made throughout the southern United States has the following variations in properties:

Acid number 150-174 Saponification number 160-178 Rosin acids percent 3 8-5 3 Fatty acids do 3 8-5 3 Unsaponifiables do 6.5-10

In recent years the industry has developed eflicient fractionating units for the separation of rosin and fatty acids. The initial step in fractionation is to separate the volatile fraction of crude oil from the non-volatile or pitch. This first step in a continuous system is carried out in a flash tower, the volatile fraction being fed to a fractionating column which separates rosin from the bottom and fatty acids and unsaponifiables from the upper plates. A third column can also be utilized to further remove rosin and unsaponifiables from the fatty acids. Even in the most efficient systems, however, all of the impurities which contribute to poor color, heat-stability, and poor odor cannot be removed completely. Commercial grades of tall oil fatty acids therefore, contain from 0.3% to 6% rosin acids and from 0.3% to 4% unsaponifiables.

The nature of the bodies that contribute to poor color and poor heat-stability is not known, but it is suspected that unsaponifiables which consist largely of phenolic bodies, alcohols and unsaturated hydrocarbons are responsible.

In commercial practice in order to obtain a finished fatty acid of around Gardner 3 color (1933 Gardner Standard) it is necessary to refractionate more highly colored acids or to remove a much larger overhead or first fraction cut. Either way results in the loss of large quantities of C-18 fatty acids to a lower grade product giving a poor economical picture. Thus, prolonged fractionation in a blocked operation results in a Gardner 3-4 colored fatty acid containing about 0.5% rosin acids and about 0.5% unsaponifiables. However, even this product has poor heat-stability. By heat-stability I mean the ability of the fatty acid composition to retain a light color when subjected to a temperature of 205 C. for a period of one hour. There is no standard heat-stability test adopted by the industry, but one test generally used is as follows: Add fatty acids to a 1 x 8" test tube and immerse in an oil bath at 205 C. Adjust the level of the acids to the level of the oil bath. After one hour remove from the bath, cool, fill a Gardner color tube and read the color on a Gardner Comparator (1933 varnish scale). This is the test referred to in this work. The following table records the original Gardner color and color after this test of different commercially available tall oil fatty acids which will be identified throughout this specification as A, B, C, etc. Other analytical data is recorded for comparison.

TABLE I Commercial Color Color Rosin Unsaps.,

Tall Oil Before After Acid N o Acids, Percent Fatty Acid Heat Test Test Percent 'It is evident from the table that even though a tall oil fatty acid may have a fairly good initial color, the color does not stand up very well when the acids are subjected to the heat-test. For many uses good heat-stability is a prerequisite.

It is well known that manufacturers of fatty acids have strived to improve the color, odor and heat-stability of fatty acid products. For example, fatty acids. and vegetable oils have been bleached with natural absorbents such as fullers earth and activated absorbents such as the sub-bentonite type clays. Fullers earth is by far the most Widely used of natural occurring unactivated clays. This mineral is chiefly a magnesium aluminum silicate present in attapulgite and montmorillonite. Fullers earth usually has a pH in the range of 6.5-7.5.

Most raw clays show some ability to decolorize oils and most of these can be improved to some extent by acid treatment. However, only a few types can be activated by acid treatment to produce eflicient adsorbents. The types usually used for activation are bentonrites, consisting chiefly of montmorillonite clay minerals. Activated clays and the art of making them are old in the art. Activation is accomplished by treating a slurry of clay and water with a mineral acid such as hydrochloric or sulfuric in an amount of about 35% of the total dry weight of the clay. The mixture is then treated with steam to a temperature of about 200 to 210 F. for a period of about 5 to 6 hours and is thereafter washed and filtered. The teachings of US. Patents 1,397,113, 1,642,871, 1,776,990 and 1,796,799 are incorporated herein by reference. Patent 1,776,990 relates to the acid activation of sub-bentonite type clays and the example presented therein is illustrative of the method used for the preparation of the acid activated clays applicable to the process herein described. Reference is also made to Kirk and Othmer, Encylopedia of Chemical Technology, vol. 4, p. 55 (1954), for a further description of acid activated clays.

In decolorizing oil by the contact process, the finely ground adsorbent is intimately mixed with the oil to be processed, and the slurry is heated to the desired temperature until adsorption is complete. The decolorized oil is separated from the clay by filtration, and the filter cake is washed and steamed to recover oil soakage. The used adsorbent is discarded; recovery of contact grade clay seldom being practiced. Although acid-activated adsorbents are more expensive than natural clays, they usually exhibit much greater decolorizing power, which makes their use economical. Examples of acid activated clays that can be prepared according to the prior art referred to are the various grades of commercially available trademarked products such as Filtrol and The Bennett-Clark clays. The Filtrol trademark identifies a group of acid-activated adsorbents and catalysts from the mineral montmorillonite,

The acid-activated materials are supplied as fine white powders, 85-95% passing through a ZOO-mesh screen. The examples presented below illustrate the use of these acid activated adsorbents and will be referred to as acidactivated crystalline clay(s) or simply as clay(s).

In working toward the improved process of this invention I found that clays, especially the activated clays were the only practical substances for this purpose. More specifically acidic crystalline clay minerals of a pH of from about 2 to 7.5 are applicable herein. I found that it is possible to decolorize tall oil fatty acids to a Gardner 2 color or better if a sufiicient amount of clay is used. However, this type of decolorized fatty acid has poor heat-stability. For example, the commercial tall oil fatty acid designated as B above, color to 6, can be decolorized to a 2 to 3 color by stirring with 2% of an acid-activated crystalline clay for one hour at 90 C. The tall oil fatty acid designated D of a color 3 to 4, when subjected to the same treatment did not decolorize, and the heat-stability tests showed little improvement on both products. The following table compares:

When 4% acid activated crystalline clay is used to decolorize the above fatty acids, a 1 to 2 colored product can be obtained but the heat-stability is still poor, yielding around a 7 to 8 color product.

Accordingly, an object of the present invention is to refine fatty acids to improve their color and heat-stability.

A further object of this invention is to improve the color and heat-stability of distilled tall oil fatty acids. Distilled tall oil may contain relatively large amounts of rosin acids ranging from 15-65%, while tall oil fatty acids now commercially produced may contain from traces of rosin acids up to about 6%. p A still further object of this invention is to refine other fatty acids such as those from soybean oil, corn oil, cottonseed oil, and the like to improve the color and heatstability of these mixtures of fatty acids.

A still further object of this invention is to improve the odor of the tall oil fatty acids. Such products, some more than others, have a disagreeable odor representing cation color of 5-6 (Gardner).

a slight carry over from the foul smelling crude tall oil from which they are manufactured.

In accordance with the objects of my invention above, I have found that when fatty acids are first treated with a crystalline clay mineral, and then distilled, the distilled products are reduced in color and improved in heat stability. Thus in Table 11 above, when the treated fatty acids B and D are distilled, the color is reduced to 1 to 2 from 3 to 4 and the heat-stability tests degrade the products only to a 3 to 4 color in both instances.

It is well known that acids and oils that have been in storage for some time, may be only a few days, do not decolorize with clays as readily as oils that have been freshly prepared. This difliculty is overcome in the case of fatty acids by my new distillation after clay-treating step. Thus an old acid which has absorbed a small amount of oxygen can be clay treated, showing little or no improvement in color, but if the product is distilled, both the color and heat stability are greatly improved.

Most of the experimental work described herein was performed, employing the commercial tall oil fatty acid, designated as B above. An analysis of this fatty acid is as follows: Acid No. 196-l97.8; rosin acids, percent, 0.8-1.4; unsaponifiables, percent, 0.8-1.5; iodine value, 133-135; color 5-6 (Gardner 1933 Standards).

The procedures for carrying out these laboratory experiments was to heat about 500 grams of the fatty acids to the desired temperatures in a l-liter, 3-neck round bottom flask fitted with a stirrer, a thermometer and a nitrogen gas inlet tube. The desired amount of clay was then added all at once and the mixture stirred vigorously for the desired time. The clay was then removed by filtration using a Buchner funnel at a temperature not greater than around C. The filtrate was then distilled at 1-3 mm. absolute pressure (a range of from 1 to 25 mm. can be used) with no fractionation. To insure removal of most of the volatile acids a flame was played over the top of the flask toward the end of the distillation.

Example 1 Table III below records an experiment on a relatively fresh sample of fatty acid B, that is the sample was only about 24 hours old when used after taking from a regular plant sampling connection. This sample had the specifi- The Gardner color was 8-9 after the heat-test described above. The sample was treated with 2% of an acid-activated crystalline clay for .the specific time at 90 C.

TABLE III Color Color Color Time In Minutes After After Heat Color of After Heat Filtering Test On Distillate Test On Filtrate Distillate Good initial color is had rather quickly, but there is some improvement by allowing the reaction to continue. It will be noted that the heat-stability appears to be poorer after the longer period of heating, but the distilled product is superior to the product obtained after the shorter period.

By distillation alone, without clay, the color of the tall oil fatty acid is improved very little, color 5-6.

Example 2 Table IV below records the results using tall oil fatty acid B and different percentages of an acid-activated crystalline clay at diflerent temperatures.

Table IV Color Color Clay, Color of Fil- Color of Dist. Experi- Per- Temp., Time, of Filtrate of After ment cent C. Mins. trate After Dist. Heat- Heat- Test Test NOTE-Experiment 19 Week old tall oil fatty acid, color 6; experiment 20 fresh tall oil fatty acid, color 5-6.

Example 3 A fresh sample of tall oil fatty acids having a color of 8-9, acid number 196, unsapo-nifiables 0.66%, rosin acids 1.4% (500 grams), was treated with 3% of an acid-activated crystalline clay at 90 C. for 60 minutes. After filtering, the color was 5-6, with a heat stability of 9-10. The distillate had a color of 2-3. The heat-stability test yielded a color of 4-5. Distillation alone of the original sample yielded a color of 5-6.

Table V records the results of refining tests on commercial tall :oil fatty acids designated as D, E, and F above. See Table I for properties of these acids.

Two 500 gram samples of tall oil fatty acid B, Gardner color 6 were stirred with 2% each of two different grades of an acid activated crystalline clay at 90 C. for 30 minutes. After filtering the samples were distilled. Exactly the same results were obtained with each sample: Color after filtering, 3-4 color after heat-stability test 8. Color after distilling l-2; color after heat-stability ttest 3-4.

Example 5 Tall oil fatty acid B, color 5-6 (500 grams), was stirred under nitrogen at 90 C. for 30 minutes with 4% of fullers earth. The color after filtering was 4-5; color after the heat-stability test 8-9. The color after distilling was 3-4; color after the heat-stability test was 4-5.

Example 6 Five hundred grams of tall oil fatty acid B was stirred with 1.6% of an acid-activated clay and 0.4% of Nori-te A, a commercial decolorizing carbon, at 90 C. for 1 hour. The color of the fatty acids after filtering was 3-4; color after the heat-stability test 6. The color after distilling was 2-3; color after the heat-stability test 3-4.

Example 7 Crude tall oil is fed to a column and the pitch removed by simple flash =dis't1llation. The volatile fraction sample used in this experiment had the following analysis. Acid No. 181; rosin acids unsaponifiables 6%; Gardner color 10-11. This sample was treated with 2% clay as above at 90 C. for 20 minutes. The color of the filtrate was 9-10 with a heat-stability color of 12; the original material had a heat-stability color of 12-13. The distillate after clay treating had a color of 8-9 and a color after heat-stability test of 9.

Example 8 Distilled tall oil is a product normally made as more or less of a by-product in the fractionation of tall oil. Plant sidestrearn distilled tall oil (in this case) usually contains about 25 to 30% rosin acids and about 1.5% unsaponifiables, the remainder being fatty acids. A sample of this material with the following analysis: Rosin acids 27%, acid number 190, unsaponifia-bles 1.4%, Gardner color 7-8, was treated with 2% acid-activated crystalline clay at 90 C. for 20 minutes. The product after filtering had a color of 5-6 with a color after the heatstability test of 8-9. The original sample had a color after the heat-stability test of 9-10. The distilled fitrate had a color of 4-5 and a color after the heat-stability test of 5-6. The odor was considerably improved. In all of these examples, the color referred to is Gardner color, 1933 Gardner Standard.

Example 9 An old sample of a double distilled cottonseed oil fatty acid original Gardner color of 1-3 had colored to 4-5. On a straight distillation with no fractionation the color improved to 0-1 with a color after the heat-stability test of 4-5. On treating the original old sample with 2% acid-activated crystalline clay at 90 C. for 30 minutes and filtering, there was no improvement in color. The distillate had a color of 0-1 with a color after the heatstability test of 3-4. The only improvement here then by treating with clay Was an improved heat-stability on the distilled product.

Example 10 In this experiment crude tall oil fatty acids were clay treated. The crude tall oil fatty acids of this sample 45 contained 5.2% unsaponifiables and 1.6% rosin acids.

after the heat-stability test of 12-13.

5 test.

7 stability test.

The color was 8-9; color after the heat-stability test 13-14, and the acid number 190. One sample was treated with 2% of an acid-activated crystalline clay at C. for one hour. The filtrate had a color of 8-9 with a color The distillate had a color of 6-7 with a color after the heat-stability test of 7-8. A second sample treated in the same way with 4% clay and filtered had a color of 8-9 and a color after the heat-stability test of 11-12. The distillate had a color of 6-7 and a color after the heat-stability test of 8.

Example 11 PART A A sample (400 grams) of distilled cottonseed oil fatty acids of Gardner color 6-7 with a color of 12-13 after the heat-stability test; AN. 202 was distilled at 1-2 mm. absolute pressure. The distillate had an acid number of 204, a color of 2-3 and a color of 5 after the heat-stability Yield 97.4%.

PART B A 500 gram sample of the same cottonseed oil fatty acids was stirred with 2% acid activated crystalline clay at 90 C. for one hour and filtered. The filtrate had a color of 5-6 and a color of 9-10 after the heat-stability test. A sample (400 grams) of the filtrate was distilled at 1-2 mm. absolute pressure. The distillate had an A.N. of 206, a color of 2 and a color of 4 after the heat- Yield 97.6%.

Example 12 PART A A sample (400 grams) of distilled soya oil fatty acids of Gardner color 4-5; color after heat-stability test 10-11; AN. 200, was distilled at 1-2 mm. absolute pressure. the distillate had an acid number of 202, Gardner color 1-2 and a color of 5 after the heat-stability test. Yield 97.5%.

PART B A 500 gram sample of soya oil fatty acids (as in part A) was stirred with a 2% acid-activated crystalline clay at 90 C. for 1 hour and filtered. The filtrate had a color of 4-5 and a color of 8-9 after the heat-stability test. A portion of the filtrate (400 g.) was distilled at 12 mm. absolute pressure. The distillate had an acid number of 203, a Gardner color of 1 and a color of 3-4 after the heat-stability test. Yield 97.4%.

The results of the above Examples 11 and 12 show that a clay treatment followed by a distillation yields more highly refined soya or cottonseed oil fatty acid than either a clay treatment or a distillation alone. Products of an improved color and improved heat stability are obtained.

From the foregoing experiments it can also be seen that the clay bleaching alone of tall oil fatty acids can improve the color, but the acids have poor heat stability. Furthermore, in cases where there is no improvement of color by clay-bleaching alone I can obtain a product of both improved color and improved heat stability by the process of my invention which includes a final distillation. There is some evidence that freshly made fatty acids do bleach more readily with clay, but by the process of my invention I can use a fatty acid that has been in storage for days, weeks or even months and still obtain very good results.

I can use as little as 0.2% clay if activated, and as much as 20%. From a practical economic standpoint, however, I prefer to use from 0.5% to 4%. The amount is not critical.

I have found that a somewhat elevated temperature is better and yields a final distillation product of good heat stability. However, the conditions are not critical and I can operate at temperatures which involve cooling, say from 0 C.'to 25 C. A preferred temperature is from 50 C. to 110 C. although I can employ temperatures of up to 150 C. I have found that at 150 C. I obtain an improved product, but I also obtain a 6% yield of non-volatile residue. At preferred temperature the nonvolatile residue amounts to only 1 to 1.5% which is about the same as in a blank distillation. I can treat the products from minutes at the higher temperatures to 24 hours at lower temperatures, but prefer from 30 minutes to 3 hours at 50 C. to 110 C.

Practically I desire to use from 0.5 to 4% of an acidactivated crsytalline clay in carrying out the process of this invention, as previously mentioned, but it should be pointed out that in addition to activated bentonites other clay-like materials such as glauconite, nontornite, beidellitic clays, halloysite, and some kaolinitic clays have been successfully acid activated but the relative efliciencies of the products are not equal to those obtained from high grade-sub-bentonites in which the clay mineral montmorillonite predominates.

Analytical results, including infrared anaylsis, indicate there are no significant changes in the products resulting from the treatment of my invention. The acid numbers, percent unsaponifiables, percent rosin acids remain approximately the same, within experimental error, as those of the starting materials.

The acid number possibly tends to be slightly higher and the unsaponifiables slightly lower, but from a practical standpoint there is litlte change.

However, it is obvious that some changes have occurred not measurable by our standard methods of analysis except that in some cases the iodine number is lowered by 23 units and the conjugated diene reduced about 1%. It is apparently necessary to remove only traces of certain types of material to improve color and heat-stability.

Beds of granular clays can be used, instead of stirring with powdered clays.

From the foregoing experimental part it is seen that I have achieved all of the objects of this invention. By treating tall oil fatty acids with clay and distilling, I have obtained a product of better color and better heat-stability than by clay treating alone. By the process of this invention I can make a fatty acid product of a color of 2 (Gardner) or a color no higher than the original color, or better after the heat-test by treating with clay and distilling. Treating with clay alone, as noted, does not result in a product of good heat-stability and the color depends on the age of the sample, etc.

I have achieved the same results with fatty acids containing high percentages of rosin acids and unsaponifiables.

The odor of all products is better after clay treatment, but still improved considerably by the final distillation.

Having thus described my invention I claim:

An improved process for upgrading a tall oil fatty acid distillate fraction without substantially changing the com position of said fraction which consists essentially of suspending in said fraction /24% of finely-divided, acidactivated montmorillonite clay solids, agitating the resulting suspension for /2-3 hours at 501l0 C., filterably separating said suspension into clay solids and filtrate, distilling said filtrate and collecting the resulting redistillate of improved heat-stable color.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. AN IMPROVED PROCESS FOR UPGRADING A TALL OIL FATTY ACID DISTILLATE FRACTION WITHOUT SUBSTANTIALLY CHANGING THE COMPOSITION OF SAID FRACTION WHICH CONSISTS ESSENTIALLY OF SUSPENDING IN SAID FRACTION 1/2-4% OF FINELY-DIVIDED, ACIDACTIVATED MONTMORILLONITE CLAY SOLIDS, AGITATING THE RESULTING SUSPENSION FOR 1/2-3 HOURS AT 50*-110*C., FILTERABLY SEPARATING SAID SUSPENSION INTO CLAY SOLIDS AND FILTRATE, DISOF IMPROVED HEAT-STABLE COLOR.