US2651646A - Liquid-liquid extraction process - Google Patents

Description

Patented Sept. 8, 1953 UNI TED PATENT OFFICE LIQUID-LIQUID EXTRACTION PROCESS .Henry Arnold-Goldsmith, Long Island city, N. :Y., assignor to fiolgaz e-Palmolivc-reet Company, Jersey City, 1,, a corporation of Delaware No Drawing. Application March 4, 1950, Serial No. 147,761

6 Claims.

- 1 Thi invention relates to liquideliquid extraction methods for separatin components of a mixture to prepare concentrates of the same, and more particularly to a liquid-liquid extraction process for treating a mixtureiof lower and higher acylated esters of ,polyhydric alcohols and fatty acids to obtain an extract phase in which the lower acylated esters areconcentrated and .a raffinate phase in which the higher acylated esters are concentrated, and from which "the respective concentrates may be separately recovered.

The discovery of the superior surface-active and emulsifying proper-ties possessed by the less hi h y .acylated partial esters of fatty acids and polyhydric alcohols, such as the sglycer l mono esters as compared with the more highlyacylated glyceryi di and .tri-esters, has brought about .a demand for the production of thesepartialresters, especially the less highly ,acylated esters, in concentrated form. Various methods have been used for obtaining such partial esters in concentrated or purified form comprising molecular distillation, fractional crystallization, and the like, which processes are either time-consuming, and produce poor yields, or, as in the case of molecular distillation, require the use'of special high vacuum equipment. The resultant cost of preparing the product is accordingly, high.

It has now been found that the above disadvantage and drawbacks of'prior methods can be obviated for all practical purposes by employing a liquid-liquid solvent extraction process in accordance with this invention, and which process is admirably suited 'for commercial application as either a continuous or batch method.

In accordance withthe invention, compositions containing principallya mixture of less completelyacylated esters, .e. .g. monoslycerides, hereinafter referred to as iless completely lacylated esters, and morecompletely acylatedesters, e. g. diand tri-glycerides, hereinafter referred to as more-completely acylated esters of fattylacids and polyhydric alcohols are subjected .toa;liquid' liquid extraction treatment using a .tWOWDhB/SE solvent system comprising a so vent phase such as an aqueous lower aliphatic alcohol in which the less completely acylated esters arepreferentially soluble and a solvent phase such .as a hydrocarbon which is immiscible with the firstmentioned liquid phaseand in which the more completely acylated esters are preferentially .so'luble. After commingling of the liquids to effect the extraction the two liquid phases are separated as distinct'liquid fractions which are drawn off and which can be trea'tedto recover the solute Although the invention will be described with particular reference to the preparation of concentrates of "fatty acid monoesters of polyhydri-c alcohols, and especially esters of saturated and unsaturated iattyacids containing from about 8 to about 20 carbon :atoms per molecule, it will be understood that the process of the invention is'applicable generally to the preparation of separable ziiquid :fractions in which :cer-tain acyla-tcd esters are respectively concentrated, and from which the said esters may be recovered by removal ofthe solvent. The term esters of polyhydric alcohols further will lbe understood to include esters of 'pol-yhydricethers of polyhydric alcohols such :as polyethylene -gly-col, polyglycerols, etc.

In the treatment 20f -fattylacid pol-yhydric alco hol esters containing less completely acylated esters and more completely acylated esters which are to be ;concentrat.ed, an aqueous alcoholhydrocarbon solvent system is preferably emplayed, :it having-been round that the alcohol solubility :of the ,fatty esters of polyhydric .alcohols decreases with increased fatty acid substitution the -molecule. Employing such an aqueous alcohol-hydrocarbon solvent system, the less completely acylated esters which are preferentially soluble in the aqueousaalcoholic phase can be concentrated in this phase and separated as animmiscible vliquid from the remainin 11yclrocarbon solvent phase in which themore cornpletely acylated esters are preferentially soluble. The reaction products obtained by esterifyihg lycerol, for exam le, with iatty acids, or by the lvcerolysis of iglycerides, .are usually mixtures of mono e, (11-, and minor amounts of .tri-glycerides even when the excess of glycerol .used is considerable. Such mixtures are known and sold n the various trades as "imonog1ycerides even though their actual monoglyceride content generally ranges .onlyirom about 30 to The recognized superiority, however, of monoglycerides over ,diglycerides ,as surface-active agents, as Well as their known value in the preparation Ql lnonwsoap detergents, has increased th desirability of obtaining monoglycerides of the fatty acids in concentrated form. 7

The liquid-liquid extraction process of the present invention provides a method for effecting this, the extraction preferably being carried-out in repeated stages with fresh solvent, in a continuous countercurrent extraction flow, or as a batch counter-current method, as desired.

The alcohols employed in the solvent system for-effecting the liquid-liquid extraction of Iatty acid monoglycer'ides from mixtures containing v mono-, diand tri-glycer'ides, are preferably the water-soluble lower aliphatic alcohols :(e. g. conincorporating suitable amounts of water in the alcohols the resultant liquid mixture is caused to separate into two phases, one containing prin-- cipally aqueous alcohol in whichthe mono ester 1 is dissolved and another containing essentially the hydrocarbon solvent in which are dissolved a major part of the diand triglycerides. Al-

though the two liquid phases do not consist of pure solvents, the aqueous alcohol phase functions as a preferential solvent for the mono esters whereas the hydrocarbon solvent forming the raflinate phase functions as a preferential solvent for the diand triglycerides.

The proportion of water required in any particular case depends upon the solvents'used, the material being treated, as well as the yield and purity desired. In concentrating glycerol monostearates from mixtures containin principally monoand di-stearates of glycerol, the purest monoglycerides were obtained using approximately 100 volumes of ethyl alcohol to 20 volumes of water. In the case of lower fatty acid esters such as glyceryl monolaurates, approximately 55% ethyl alcohol and 45% water by volume has been found to be the most efficient for effecting the preferential liquid separation of the monolaurates. With the application of the process to the recovery of other monoglycerides and mono ester of glycols and fatty acids the water content of the alcohol will vary and can be readily determined by trial methods so as to provide for proper liquid phase separation. In multiplestage extractions, preferably somewhat more than the minimum amount of water is used which will cause the liquid phase'separation to be accomplished at the temperature of treatment, particularly where a high extract yield is desired. The process is readily effected at room temperature, that is between about 20 and 30 C. Higher or lower temperatures may of course be used, and in some cases may be desirable, but in general the process will be carried out at ordinary room temperatures.

In successive five-stage extraction treatments employing a system consisting of n-octane-ethanol and water, it was observed that in the treatment of a mixture of lauric acid glycerides, comprising 80% by weight monoglyceride, it required a solvent system containing about 27% or more (by volume) of water to yield extracts of a purity of over 90% by weight mono ester. Somewhat less water may be used, however, in the case where methyl alcohol is employed in place of ethyl alcohol. In a similar system, the extraction of a mixture of myristic acid glycerides containing 57.9% by weight mono myristin, produced extracts of an optimum purity of 86% monomyristin when the system contained 20% (vol.) of water. Beyond this dilution, the purity of the extract in mono ester decreased. With a mixture of palmitic acid glycerides containing 55.6% by weight monopalmitin, the extract reached an optimum purity of 88% monopalmitin wherethe system contained approximately 11% (vol.) of water. In the case of a mixture of stearic acid glycerides containing 52.5% monostearin, the extracts of the monoglyceride were 90% pure where the system contained above about 9% (vol.) of water.

Where the ester mixture being treated contains appreciable amounts of free glycerol the mixture is best pretreated to remove the free glycerol. If this i not done, the amount of water must b correspondingly reduced in order to compensate for the presence of glycerol. The following examples illustrate how the process may be utilized, the'percentage parts given having reference to weight unless otherwise stated. The monoglyceride content in the examples given was determined by the periodic acid oxidation method.

' Example 1 Twenty-two and a half grams of a commercial stearic acid mixed glyceride, composed of 57.3% monoglyceride and 42.7% diglyceride (together with minor amounts of triglyceride) is dissolved in 100 ml. of n-heptane, the commercial stearic acid being composed of a mixture of 43% stearic, 51% palmitic, and 6% oleic acids. To the resultant solution is introduced 100 ml. ethyl alcohol and 20 ml. water, and the solutions shaken. Upon separation of the phases, and evaporation of solvent from the separated phases, the extract in the aqueous alcohol phase was found to contain 26.2% of the monoglyceride present in the form of a mixture of 83.3% monoglyceride and 16.7% diglyceride of the commercial stearic acid. Although, as will be observed, the yield is low employing a single stage treatment the purity of the extract in monoglyceride is relatively high.

Example 2 To 18 grams of a mixed glyceride, composed of 59.2% monoglyceride and 40.8% diglyceride (with minor amounts of triglyceride) of the commercial stearic. acid of Example 1, dissolved in ml. octane, a mixture of 100 ml. 95% ethyl alcohol and 12 ml. water was added, the solutions shaken, allowed to separate into phases, and the solvent from each of the phases evaporated. The aqueous alcohol extract was found to contain 52.2% of the monoglyceride present in the form of a mixture of 81.1% monoglyceride and 18.9% diglyceride of the commercial stearic acid. In this example by the use of a lesser proportion of water than in Example 1 the yield of mono ester was increased but the purity of the extract in monoglyceride was lowered.

Example 3 A 22.5 gram sample of the mixed glyceride described in Example 1 was dissolved in 100 ml. of commercial n-heptane and extracted by shaking outwith a mixture of 100 ml. 95% ethyl alcohol and 20 ml. water. The aqueous alcohol phase was separated and extracted with 4 successive 100 ml. portions of fresh n-heptane; the n-heptane phase was extracted with 4 successive ml. portions of aqueous alcohol, and each alcoholic extract was shaken out successively with the successive portions of n-heptane mentioned above. Thus, every one of the aqueous alcohol portions are extracted by each of the n-heptane portions, and vice versa. The combined aqueous alcohol extracts contained 80.3% of the monoglyceride present in the form of a mixture of 91.2% monoglyceride and 8.3% diglyceride of the commercial stearic acid.

A 54.6 gramsampleota mixedglyceride, composed .of 47.6% :monoglyceride and 52.4% of diglyceride .(containing minor proportions of ltriglycerides) of coconut oil .iatty .acids =was .ex tracted with live200 .mLmort-ions :of commercial n-hep-tane ,and five .portions each of .200 .ml. methanol .and 40 .ml. water, proceeding as .described in Example 3. The combined aqueous methanol extracts iconta-ined 185.4%- .of the monoglyceride present .in the form of .a mixture-of 75.6% 'monoglyceride .and.24.4% or diglycerideof coconut oil .fatty .acids.

' Example 5 .A 22.6..gram a p-1e are mixed .glyceride. composed .of 56.2%,monoglycer'ideand 433% dig'lyc- .eride of .a commercial .oleic .acid Ki. .e. .a mixture of .85 -:O1BiC., 3% .linoleic. and .7 palmitic acids.) was .extracted with five .100 ml. portions or commercial .n.-heptane and .fiveportions. each of 100 ml- 95% ethyl alcohol and .30. ml. water proceeding as described in Example 3. The combined aqueous alcoholiextractscontained 78.4% .of the monoglyceride present in .theiorm of .a mixture oI:93.-4% monoglyceride and-6.6.% diglycer-ide of the connnercial oleic acid.

Example fi dissolved in 200 ml. of commercial n-heptane was placed inside a simple =4-foot glass column of 24 mm. .inner diameter which .was packed in its centralsection (33 inches high) with flfliserl saddles. Amixture of '600 m1.95.% ethyhalcohol and 150 ml. water was pumped through "Zthe column, from the top, at the'rate of 600nil.per hour, and the aqueous alcohol phase emerging at the bottom was drained and evaporated. The extract thus obtained contained 85.17% of the monoglyceride present in the form of a mixture of 92.5% monoglyceride and 7.5% diglyceride of the commercial stearic acid.

Example 8 A twelve-stage, agitated, counter-current column essentially as described by E. G. Scheibel (Chemical Engineering Progress 44, 681-90; 771-82, 1948) was employed as a convenient counter-current device in the extraction treatment of a commercial mixed glyceride composed of 59.2% monoglyceride and 40.8% diglyceride of commercial stearic acid, as described in Example 2. During the counter-current treatment, a 26.1% by weight solution of this glyceride mixture in the extraction system (47.16 volume percent of commercial n-octane, 47.16 volume percent of 95% ethyl alcohol, and 5.68 volume percent of water) was fed into the column at the eighth mixing zone upward, thus dividing the column into seven stages below and four stages above the feed stage. The glycerideisohition' forms a. clear liquid which permits the glyceride to be -easily introduced into thecolumn and which solution will readily separate "into two "liquid phases -=upon dilutionwith more solvent. "To bring this liqu-i'd phase -separation about and provide the desired selective solvent phases, octane was fed into the columnat the bottom, and a 100912 by volume mixture of 95% ethyl alcohol and water, respectively, fed at the top by means of small pumps. A'stirring rotational speed'of 1200 R. '1. M. ;;provided -=eificient agitation of the col-umn contents. The best extraction results were obtained by setting the pumping ratesof the three feed pumps in such aratioas to producean'equilibrium concentration'of Elite 46 grams of glyceridesper liter' of solutions at the-topand bottom 'ofthe-cdlumn. Carrying outtheextractionas described employ ing an equil'flrrium concentration of '46 grams glyc eride per liter, 89.5% of the :mon'oglycerideifed into the "mixture "was extracted by the aqueous alcohol phase and in :theform of amixture of 92%monog'lycerideand 8 of diglyceride ofthe commercial "s'tearic acid.

The "results, as measured by extraction yield and extract fipurity, may be varied "by changing. the concentration of the -mixed 'glyceride feed, the pumping'rates,'the rotational speedo'f the'column agitation, and the solvent composition. Also the mixed .g'lyceride may befedtnto themixture in the .form of a melt where suitable designed extraction equipment is utilized.

Example 9 ethyl alcohol and "8 ml. water. The alcoholic extract contained 360% .of the diethylene glycol monoester presentin the [form of a mixture of monoester and 20% diesterlcalculated from .the saponification value of the extract) Example :10

.A;210.gram,sarnple of an .ester mixture obtained .=by.readting one .mole of a polymerized glycerol -.(.conihiriing weight 186; approximately 75% of .dig1ycerol,.25,% of f triglycerol and small :amounts oIt-lii gherpolyglycerols') with two moles ofcommercial stearic acid was dissolved'in 200 m1. 'c'om-' mercial n-octane, and the solution extracted with a mixture of 200 ml. 95% ethyl alcohol and 8 ml. water. The alcoholic extract contained 49.5% of the sample as a soft, tough solid which swelled up in hot water and could be dispersed by adding some alcohol; the raflinate in the octane phase was a brittle, and comparatively hard solid which did not disperse in water at all. The saponification values of the starting material, the extract, and the rafiinate were 166, 153 and 181 respectively, indicating that the extract was poorer and the raflinate richer in fatty acid than the material subjected to extraction.

Example 11 A 40 gram sample of an ethylene glycol ester of a commercial oleic acid composed of 73.5% monoester and 26.5% diester (refractive index at 25 0., 1.56202) was dissolved in 200 m1. of commercial n-octane, and the solution extracted with a mixture of 200 ml. methanol and 8 ml. water. The methanolic extract contained 45.2% of the sample in the form of a mixture of 78.5% monoester and 21.5% diester (refractive index at, 25 (3., 1.46170).

, The process of the invention provides many advantages over prior methods of obtaining these partial esters in concentrated form, particularly as regards simplicity of operation and commercial adaptability. As heretofore pointed out, the process is not only capable of wide variation with respect to the ester mixtures which may be refined, but also the operating procedure and arrangement may be varied to suit the particular conditions and uses to which the invention may be put. 7

As many widely difierent embodiments of the invention may be made without departing from the spirit and scope thereof, it is to be understood that the same is not limited to the specific examples or embodiments hereinbefore setforth except as defined in the following claims.

What is claimed is:

1. A process of treating an ester product containing principally a mixture of less completely and more completely acylated esters of fatty acids and polyhydric alcohols which comprises contacting said ester product with water, a water miscible lower aliphatic alcohol, and a low boiling aliphatic hydrocarbon, said alcohol and hydrocarbon being miscible and said water being present in an amount sufficient to cause the formation of two immiscible liquid phases, one phase comprising aqueous alcohol in which a major proportion of said less completely acylated esters are dissolved and one phase comprising the hydrocarbon in which a major proportion of said more completely acylated esters are dissolved, and

separating said two liquid phases.

r 2. A process as set forth in claim 1 in which said ester product is subjected to liquid-liquid extractionwith said water, alcohol and hydrocarbon by continuous countercurrent flow.

I 3. A process of treating a glyceride product containing a mixture of monoand diesters of fatty acids and glycerine to produce a liquid extract in which the glyceryl mono fatty acid ester is concentrated and a liquid raflinate in which said glyceryl di fatty acid ester is concentrated which comprises intermingling the glyceride product with water, a lower aliphatic monohydric alcohol containing about 1 to 4 carbon atoms, and a low boiling aliphatic hydrocarbon, said alcohol and water being miscible and said Water being present in an amount sufiicient to cause the for- 8 mation of an aqueous alcohol extract phase in which said monoesters preferentially are dissolved and a hydrocarbon rafiinate phase immis cible therewith in which said diesters preferentially are dissolved, and separating said extract and raffinate phases.

4. A process as defined in claim 3 in which the glyceride product treated consists principally of a mixture of glyceryl monostearate and glyceryl distearate.

5. A process of extracting a liquid fraction containing monoesters of fatty acids and glycerol from a fatty acid glyceride mixture comprising said monoesters together with fatty acid diesters which comprises contacting said glyceride mixturewith water, a lower aliphatic monohydric alcohol containing about 1 to 4 carbon atoms, and a low boiling aliphatic hydrocarbon, said alcohol and hydrocarbon being miscible and said water being present in an amount suflicient to form two immiscible liquid phases, said monoesters be-'- ing dissolved selectively in one of said immiscible liquid phases, withdrawing said liquid phase containing said monoesters dissolved therein, and removing the solvent to recover the monoesters substantially free of said diesters.

6. A process of treating a mixture comprising mono-, diand triglycerides resulting from reacting fatty material with glycerine to separate the monoglycerides therefrom which comprises subjecting the glyceride mixture to liquid-liquid extraction with water and a mixture of miscible solvents comprising ethyl alcohol and n-heptane, said water being present in an amount suflicient to produce a liquid extract phase comprising principally said monoglycerides dissolvedin said ethyl alcohol and water and a liquid raflinate phase immiscible with said extract phase comprising principally said diand triglycerides dissolved in said n-heptane, withdrawing said 'extract phase, andremoving the alcohol and water therefrom to recover said monoglycerides substantially free from said (111- and triglycerides.

' HENRY ARNOLD GOLDSMITH.

References Cited in the. file of this patent UNITED STATES PATENTS Number Name Date 2,200,391 Freeman May 14, 1940 2,290,609 Goss July 21, 1942 2,553,288 Young et al May 15, 1951

Claims (1)

1. A PROCESS OF TREATING AN ESTER PRODUCT CONTAINING PRINCIPALLY A MIXTURE OF LESS COMPLETELY AND MORE COMPLETELY ACYLATED ESTERS OF FATTY ACIDS AND POLYHYDRIC ALCOHOLS WHICH COMPRISES CONTACTING SAID ESTER PRODUCT WITH WATER, A WATER MISCIBLE LOWER ALIPHATIC ALCOHOL, AND A LOW BOILING ALIPHATIC HYDROCARBON, SAID ALCOHOL AND HYDROCARBON BEING MISCIBLE AND SAID WATER BEING PRESENT IN AN AMOUNT SUFFICIENT TO CAUSE THE FORMATION OF TWO IMMISCIBLE LIQUID PHASES, ONE PHASE COMPRISING AQUEOUS ALCOHOL IN WHICH A MAJOR PROPORTION OF SAID LESS COMPLETELY ACYLATED ESTERS ARE DISSOLVED AND ONE PHASE COMPRISING THE HYDROCARBON IN WHICH A MAJOR PROPORTION OF SAID MORE COMPLETELY ACYLATED ESTERS ARE DISSOLVED, AND SEPARATING SAID TWO LIQUID PHASES.