US2182179A - Treatment of glycerin lyes and of crude glycerin - Google Patents

Description

Des., 5, 1939, R. H. Por'rs ET AL TREATMENT 0F' GLYCERIN LYES AND OF CRUDE GLYCERIN Filed Nov. 8, 1937 WOHQVO nmmwfmm Oa im? juz, W CO/7h,

@Uv-mk @www Patented Dec. 5, 1939 UNITED STATES PATENT OFFICE TREATMENT F GLYCERIN LYES AND 0F CRUDE GLYCERIN Application November 8, 1937, Serial No. 173,539

Claims.

This invention relates to the treatment of glycerin-containing materials such as soap lyes, soap lye ciudes, and similar materials, and it comprises processes whereinlsuch glycerin-containing materials, prior to the recovery of glycerin therefrom, are acidified and then extracted with a solvent for caprylic and caproic acids, or

other organic materials therein, without, however, dissolving the glycerin, in order to remove lo caprylic and caproic acids and other organic impurities from the glycerin-containing material before subjecting the material to processes for the recovery of glycerin therefrom.

In the manufacture of soap, animal and vegetable fats, or mixtures thereof, are saponiied with a solution of an alkali, usually caustic soda, and the soap salted out of the reaction mixture. The liquid from which the soap has been salted out is commonly referred to as a soap lye. Soap lyes contain all the products of the soap kettle that are not thrown out by the salt, and, consequently, these lyes are aqueous solutions of salt, caustic soda, and glycerin associated with relatively small amounts of impurities. The impur- ,5 ities are mainly sodium salts of low molecular weight fatty acids, namely those fatty acids containing from 6 to 10 carbon atoms, such as sodium caproate, caprylate and caprate, and sodium salts of low molecular weight hydroxy and similar oxidized acids. These salts are not thrown out of solution when common salt (sodium chloride) is added to salt out the soap. Other complex organic materials may also be present. An average soap lye may contain about 0.11% of normal aliphatic acids (as sodium salts) having an average molecular weight corresponding to straight-chain aliphatic acids of 10 carbon atoms, and a similar amount of hydroxy or otherwise oxidized acids having an average molecular weight corresponding to about 8 carbon atoms in the molecule. These lyes, however, vary considerably in the nature and quantity of impurities, depending upon the kind of fats being saponied. It has been recognized in the art that before glycerin is recovered from the soap lye the impurities in the lye should be removed to the highest possible vdegree consistent with practical plant operations. Their presence materially affects the yield of glycerin which can be obtained from 50 the lye. Since the average amount of glycerin in a soap lye is about 5%, traces of low molecular weight aliphatic acids materially reduce the amount of glycerin recovered. The quality of the glycerin is also affected by the presence of these fatty acids, most of which are quite volatile and distil over with the glycerin.

Hitherto the glycerin manufacturer has treated soap lyes with chemical reagents to precipitate the soluble fatty acid salts as insoluble salts. 5 Ferrie chloride, for example, will form insoluble iron salts of caprylic, caproic and capric acids. Some of the ferrie chloride may also hydrolyze to insoluble ferrie hydroxide which may carry down much of the other organic impurities also. 10 'I'his has, of course, necessitated filtration of the lye and the glycerine lost in the press-cake is significant. The thus treated lye is then evaporated to give a crude glycerin, most all of the salt used for salting-out being thrown out of 15 solution at this stage, and the crude glycerin is then distilled to give a distillate of substantially pure glycerin. In the ferrie chloride or other precipitation method, there is a relatively large press-cake loss of available grlycerin. Much available glycerin is also lost during the distillation of the crude.

We have set ourselves to the problem of developing improved ways of treating soap lyes prior to recovery of the glycerin therefrom, so as to reduce the glycerin loss and to improve the quality of the glycerin, and we have discovered that relatively low molecular weight fatty acids, namely those having from 6 to 10 carbon atoms, either simple aliphatic acids or oxidized forms thereof, existing in the original soap lye as sodium salts, can be extracted from the lye with solvents provided the lye is rst acidiiled to liberate the free fatty acids from their salts.

The sodium salts of the Ce to Cio fatty acids only amount to about 0.2% to 0.3% of the soap lye and they are thus soluble in the lye in spite of its high salt concentration. Before we can extract the soap lye with our solvents, it is necessary that the C6 to Cio fatty acids be liberated from their sodium salts. Consequently, we first acidify the soap lye with any suitable acid. Hydrochloric acid is the best because it forms sodium chloride coincident with the liberation of free fatty acid. Sulfuric acid, which would form 45 sodium sulfate, can, of course, be used instead of hydrochloric, and we do not wish to be limited to any particular acid so long as' it is one which will displace the aliphatic acids from their sodium salts. This acidification step is advantageously such that the pH of the acidied lye lies between about 3 and 4. 'Ihe pH value can be decreased below 3 but this requires additional acid which for economic reasons should be avoided.

In broad aspects then. our process comprises the steps of acidifying soap lye and then extracting the acidled lye with solvents for the Cs to Cio acids and other organic impurities present, which solvents do not dissolve signicant amounts of glycerin. That is our major contribution to the art. Thereafter, we neutralize the acidity of the extracted lye and recover its glycerin content therefrom. The extracted, acidied lye is neutralized to avoid any danger of corroding the stills. This step is readily performed by simply adding enough alkali to the acidied extracted lye until its pH is 6 or higher. Recovery of the glycerin from the treated lye is done in the manner usual in this art.

In consequence of our discovery we are able to markedly increase the yield of available glycerin. We avoid the press-cake loss which is inherent in any type of precipitation process, such as the ferric process method. We are also able to recover more glycerin from the evaporated lye. In addition, our process permits us to recover commercial quantities of the valuable low molecular Weight acids, namely, caprylic, caproic and capric acids.

There are many solvents which we can use in our process. All of them should be waterinsoluble and have the property of dissolving low -molecular Weight fatty acids, such as caprylic,

caproic and capric without, however, dissolving any substantial quantity of glycerin. These solvents include aliphatic solvents, such as ethyl ether, chloroform, trichlorethane and petroleum ether. Aromatic solvents, such as benzene, toluene and xylene can also be used. We have further discovered that one particularly advantageous group of solvents is fatty acids having molecular weights higher than the molecular weights of the fatty acid impurities in the acidii'led lye. Thus, for example, vif the acidied lye contains mostly caproic acid, extraction of the lye with any fatty acid having a higher molecular weight than caproic will remove the caproic acid and leave an extracted lye substantially free of organic acid impurities. If the lye, after acidification contains caprylic acid as an impurity then any fatty acid having a molecular weight higher than caprylic will remove caprylic acid. For most purposes We flnd it best to use fatty acids having sixteen or more carbon atoms as the extraction agent. These acids can be palmitic, stearic, oleic and linoleic, or mixtures thereof. All of these acids are insoluble in the acidified lye and are readily availv able commercially. But, more broadly, our invention comprises the extraction of the lye with a fatty acid, or mixtures thereof, having a molecular weight higher than that of the acid in the lye.

Neutral oils, namely triglycerides, are also insoluble in the acidied lye and can be used instead of the fatty acids. A triglyceride of any fatty acid, or mixtures of fatty acids, will work regardless of the molecular weight of the fatty acid radical, since these are all relatively insolublein the acidifled lye, and will not dissolve the glycerin therein under the conditions'of our process. Since the extraction is in liquid phase the extraction liquid or solvent should be one which is normally iiuid or can be made so at moderately elevated temperatures. The temperature of extraction is not a factor, and we can operate at temperatures as high as 180 F. or up'to a temperature just below the boiling point of the mixture being treated. Pure stearic acid, while it can be used as the extraction liquid, would have to be liquefledvby the application of heat, and, of course, the soap lye would have to be treated while hot. For this reason we prefer to use solvents which are normally fluid at room temperature or slightly above.

One very advantageous mixture of fatty acid for use as the solvent is that obtained as a fraction in the distillation of cottonseed fatty acids. On the average such a fraction will contain about 5% palmitic acid, 55% of llnoleic acid and 40% of oleic acid. Or We can use ordinary oleic acid of commerce, commonly referred to as red oil. For greater convenience in processing operations, it is best that the extraction liquid be either a normally liquid fatty acid, such as oleic, or, when normally solid fatty acids are used,

`they can be rst mixed with enough oleic or linnoleic so that the nal mixture is liquid. One of the major advantages of our process is that the extraction liquid can be a common product of the soap works. Fats can be split to liberate free fatty acids, such as mixtures of oleic with palmitic and stearic, and these mixtures can be used as the extraction liquid. If the split fatty acids contain large quantities of normally solid acids they can be fractionally distilled to get a fraction which is normally liquid, or enough of the solid fatty acids can be pressed from the fatty acid mixture so that the mixed acids used for extraction are fluid. However, as stated, We do not intend to be limited to the use of only normally liquid mixtures because mixtures which may be solid or pasty at, for example,70 F. may be fluid enougth for use at extraction temperatures of 180 F. or higher.

With respect to fatty acids asv extraction liquids, our invention, however, is not limited to the use of palmitic, stearic, oleic and linoleic acids. Caprylic acid will remove caproic acid from the lye and, although caprylic acid is very slightly soluble in the acidified lye, the amount thereof in the lye will be less than myristic, palmitic, stearic and the unsaturated fatty acids are entirely insoluble and these are best for commercial purposes.

Most all of the triglycerides We use are liquid at room temperature or can be made so at moderately elevated temperatures. Cottonseed oil is one such triglyceride which works well. VTriolein, tripalmitin, and like triglycerides or mixtures thereof are operative.

In order that our invention may be more clearly understood, we have, on the appended ow-sheet indicated a suitable apparatus setup for practising our process.

Referring to the drawing, the hot aqueous soap lye is first collected in a storage tank I. The average composition of this lye may be about 5% glycerin, 12% salt, 0.2% to 0.4% of a mixture of sodium salts of Cs to C fatty acids and sodium salts of oxidized fatty acids having approximately this carbon chain length. The hot soap lye is pumped from tank I by pump 2 through line 3 to a filter 4 wherein suspended dirt and other insolubles are removed. Since the amount of material removed is very small there is practically no press-cake loss of glycerin. The filtrate is then passed by line 5 to a mixing vessel 6 in which it is mixed with hydrochloric or other suitable acid. Advantageously the amount the amount of caproic in the lye prior to extraction. Laurie,

of acid added canbe carefully controlled by` means of hydrogen ion control devices not shown. Enough acid is added until the pH of the soap lye is reduced to between 3 and 4 although, as stated above, the acidification can be more drastic. It should not be less than sufcient to give a pH of about 4.5 to 5 since at higher pH values there is relatively little conversion of these sodium salts of the organic acids to free acids.

The acidied lye then passes by line 'I to a storage tank 8 from which it is withdrawn by line 9 and pumped by pump I0 to the upper part of the extraction tower II through line I2.

The extraction liquid or solvent maintained in storage tank I3 flows by line I4 to pump I5 by which it is pumped into the lower part of tower II through line I6.

'Ihe extration liquid, advantageously the mixture of palmitic, oleic and linolec acids referred to above, meets the down-coming stream of acidiiied soap lye and the extraction process is thus countercurrent. Since the specic gravity of the fatty acids is less than that of the acidied soap lye, the fatty acids naturally rise in the tower and collect at the top thereof. The fatty acids which we use are, of course, substantially insoluble in the soap lye. Countereurrent extraction is especially advantageous because of its high emciency. We can, however, use other extraction methods, either batch or multi-stage methods wherein lye extracted in one vessel passes to another and so on through a series of vessels, and extraction iiuid passes through the series of vessels in the opposite direction.

The extracted lye leaves the,bottom of the tower Ii by lines I'I and I8 and passes to a storage vessel I9 from which it flows to a centrifuge 20 for the removal of any fine suspended globules of fatty acid extraction iiuid. In the centrifuge, hydroxy fatty acidsvin the original lye also separate out. We have discovered that although the extraction liquid will effect 100% removal of normal acids, such as caproic, caprylic and capric, it only removes about 50% to 70% of the oxidized acids. But as the normal fatty acids are removed from the soap lye the solubility of the oxidized acids in the acidiiied lye decreases, consequently, any remaining quantities of oxidized acids tend to separate out in the centrifuge. Or we can alternatively filter the lye from storage tank I9 prior to further treatment since filtration at this stage will remove any remaining traces of oxidized acids. The point at which line I 8 is set with respect to the column of liquid in tower I I determines the position of the fatty acid-lye interface. During the extraction the acidied lye can be the continuous phase and the yiextracting liquid the discontinuous phase, or the extracting liquid can be the continuous phase and the acidied lye the discontinuous phase. By maintaining the intrface 'at some intermediate level both methods can be employed.

The use of a centrifuge or a lter for the treatment of lye flowing from storage tank I9 is optional and depends entirely on whether the extracted lye coming from the bottom of tower II needs the further treatment stated. In any event, the lye from storage tank I9 passes by line 2l to a mixing vessel 22 wherein it is substantially neutralized with any suitable alkali, such as caustic soda, prior to passing to the evaporators for the recovery of glycerin and salt. The amount of alkali added, such as caustic soda, should be enough to raise the pH value to about 6 or 7, or even higher if desired. Advantageously the neutralized lye is conducted to a further storage tank 23 from which it passes as required to the evaporators. The extraction process indicated on the drawing is continuous.

The fatty acid, or triglyceride, extraction fluid with its content of dissolved impurities extracted from the lye leaves the top of the tower by way of discharge outlet 24 to a settling vessel 25. In this vessel any occluded lye is given an opportunity to separate out. The extraction liquid then passes byline 26 to a stripping column 21 which can be of any conventional type wherein the volatile organic acids, such as caproic, caprylic, and capric can be stripped with steam and vacuum from the extraction liquid. These volatile acids are then condensed and collected, and the higher fatty acid extraction liquid is returned to container I3 for reuse by way of line 28.

The above description, together with the drawing indicates the principles of our invention. There are many modifications possible. For example, we can recycle a portion of the contents of separator 25 after it leaves settling device 25 back to the tower by way of line 29, pump 30 and mixer 3l. Various other recycling features common in the art of extraction generally can, of course, be employed.

The amount of extraction uid necessary is not' critical. Ordinarily we use from about 2 to 4 volumes of fatty acid or triglyceride extraction liquid for each 100 volumes of soap lye since this quantity appears to be adequate for all purposes.

Our process of treating soap lyes for the removal of impurities prior to distillation enables us to increase markedly the yield of glycerin which can be obtained from the soap lye, and we are also able to get a better glycerin distillate with respect to quality. Moreover, We' are able to recover from the lye sizeable amounts of caproic, caprylic and capric acids which have a market value.

Our process is also adaptable to the treatment of soap lye crudes and residues from the distillation of glycerin. A soap lye crude consists largely of glycerin about 80%, salt about 12%, and about 1% of fatty acid salts, such as sodium caproate. These crudes are the product of evaporating most of the water and removing most of the common salt from the original lye prior to distilling glycerin from the crude. Our process can be used to further purify crudes which have been partially purified by other methods. The crudes are i'lrst diluted with an equal quantity of water, then acidied to liberate the free fatty acids, and then extracted as described above for the soap lye. When treating crudes it is better to increase the amount of extraction liquid to about 7.5% based on the volume of diluted crude. In addition to getting a higher yield of good quality glycerin we also are able to recover the valuable Ce to Cio acids therein. The residues from the distillation of glycerin commonly contain glycerin that is not recoverable in the presence of large quantities of salt and organic impurities. These residues contain large quantities of organic impurities because the impurities in the original soap lye or soap lye crude tend to concentrate in the residue during distillation of the residue from the crude. If the impurities have been but partially removed from a soap lye, and the thus treated soap lye evaporated to get a crude, and

the crude then distilled for the recovery of glycerin, the residue from the distillation of the glycerin can be extracted by our invention to effect removal of organic impurities and the thus puried residue again distilled to recover more glycerin therefrom. By our process, we can recover more glycerin of better grade from these residues vand in treating these materials we first dilute them with water, then acidify to liberate free fatty acids, and then extract as described above.

Since our process can be used for the treatment of soap lyes, soap lye crudes, and residues prior to the distillation thereof for the recovery of their glycerin content, these materials in the appended claims.

In the above more specific description of our invention we have described the use of fatty acids and triglycerides as the extraction fluid or solvent. It is to be understood that our other solvents can be used in exactly the same manner as we have described above.

Having thus described our invention, what we claim is:

1. The process of treating glycerin-containing materials of Athe class of acidified soap lyes, acidified soap lye crudes and acidied residues prior to the recovery of glycerin therefrom which comprises the step of extracting material of the class described with a water-insoluble solvent for organic impurities therein which solvent does not substantially dissolve glycerin in said material.

2. The process as in claim 1 wherein the acidity of the glycerin-containing material during the extraction is about 3 to 4 expressed in pH units.

3. The process of recovering caprylic and caproic acids from glycerin-containing materials of the class of soap lyes, soap lye' crudes and residues which comprises acidifying such glycerincontaining material and then extracting the acidified material with a water-insoluble solvent for said acids, which solvent does not substantially dissolve glycerin in said material.

4. The process as in claim 3 wherein the solvent is a fatty acid having a molecular weight greater than caproic acid.

5. The process of treating glycerin-containing materials of the class of acidied soap lyes, acidied soap lye crudes and acidied residues prior to the recovery of the glycerin therefrom which comprises the step of extracting material of the class described with a fatty material chosen from the group consisting of water insoluble triglycerides and fatty acids having a molecular weight higher than that of the fatty acids in the acidied material.

6. The process of treating glycerin-containing materials of the class consisting of acidied soap.

lyes, acidied soap lye crudes and acided residues prior to recovery of glycerin therefrom which comprises the step of extracting such material while-at a pH of about 3 to 4 with a fatty material chosen from the group consisting -of water insoluble triglycerides and fatty acids having a molecular weight higher than that of the fatty acids in the acidified material.

7. The process as in claim 5 wherein the fatty material is at least one water insoluble fatty acid.

8. The process'as in claim 6 wherein the fatty material is at least one water insoluble fatty acid.

9. The process of treating soap lyes which comprises acidifying the lye until the pH thereof is not more than about 4 and then extracting the acidied lye with a fatty material chosen from the group consisting of water insoluble triglycewe wish to cover all of 'fatty material comprises rides and fatty acids having a. molecular weight higher than that of the fatty acids in the acidified material. l

10. The process of treating soap lyes which comprises acidifying the lye until the pH thereof is not more than about 4 and then extracting the acidied lye with at least one water insoluble fatty acid. y

1l. 'I'he process of treating soap lyes which comprises adding hydrochloric acid to the lye until the pH thereof is about 3 to 4 and then extracting the acidied lye with a liquid'mixture of palmitic, oleic and linoleic acids.

12. In the recovery of glycerin from soap lyes the steps which comprise acidifyingthe lye, extracting the lye with a fatty material chosen from the group consisting of lwater insoluble triglycerides and fatty acids having a molecular weight higher than that of fatty acids in the acidied material, neutralizing the acidied extracted soap lye and recovering glycerin therefrom.

13. In the recovery of glycerin from soap lyes the steps which comprise acidifying the lye to a pH of about 3 to 4, extracting the lye with a fatty material chosen from the group consisting of water insoluble triglycerides and fatty acids having a molecular weight higher than that of fatty acids in the acidified material, neutralizing the acidied extracted lye and recovering glycerin therefrom.

14. In the recovery of glycerin from soap lyes the steps which comprise acidifying the soap lye with hydrochloric acid, extractingthe acidied lye with a fatty material chosen from the group consisting of water insoluble triglycerides vand.

fatty acids having a molecular weight higher than that of fatty acids in the acidied material, neutralizing the acidied extracted lye and recovering glycerin therefrom. l

15. In the recovery of glycerin from soap lyes the steps which comprise acidifying the lye with hydrochloric acid until the pH of the lye is about 3 to 4, extracting the acidi-fied lye with a fatty material chosen from the group consisting of water insoluble triglycerides and fatty acids having a molecular weight higher than that of fatty acids in the acidified material, neutralizing the acidied extracted lye and recovering glycerin therefrom.

16. The process as in claim fatty material comprises at least one water insoluble fatty acid.

17. The process as in claim 13 wherein the at least one water insoluble fatty acid. l

18. The process as in fatty material comprises soluble fatty acid.

19. The process as in fatty material comprises soluble fatty acid.

20. The process as in claim l2 wherein the fatty material comprises a liquid mixture of palmitic, oleic and linoleic acids.

claim 14 wherein the at least one water inclaim 15 wherein the at least one water in- RA I.|PH H. POTTS. EDWIN W. COLT.

12 wherein the y

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