US2348970A - Process for the separation of acids contained in tall oil - Google Patents

Description

. centration of neutralized resin acids.

Patented May 16, 1944 P cs 1 PROCESS FOR THE SEPARATION OF ACIDS CONTAINED IN TALL on.

Frederick H. Gayer and Charles E. Fawkes, Chicago, Ill., assignors to Continental Research Corporation, Chicago Heights, 111., a corporation of Illinois No Drawing. Application April 7, 1942. Serial No. 438,005

Claims.

This invention relates to an improved process for the separation'and recovery ofthe major constituents of organic mixtures or oils containing both resin acids and fatty acids, and particularly the clean, sharp and economic separation and recovery of the resin acids and the fatty acids from such mixtures or oils, and particularly from tall oil.

Tall oil is a by-product of sulphate or kraft paper manufacture, and is obtained by acidification of the black liquor soap, which is salted out and rises to the surface of the black liquor on standing. The 'main constituents of tall oil in clude fatty acids, resin acids, and unsaponifiable substances. While the bulk of the unsaponifiablematter consists of hydrocarbons, it also contains a considerable proportion of high-molecular Weight cyclic alcohols belonging to the group of phytosterols.

Tall oil as such has found relatively little commercial use. It is not suited for soap making on account of its dark color, its odor and its high resin acid content, nor can it be used as a substitute for resin or other natural resins on account of its fatty acid content. On the other hand, the componentsof tall oil, especially the resin acids,

first esterify the fatty acids by reacting them with a low molecular weight, aliphatic, monohydric alcohol, as for example methyl and ethyl alcohol,

' or the isomeric propyl, butyl or amyl alcohols.

We effect the esterification at atmospheric pressure. as for example by refluxing the tall oil with the alcohol in the presence of a catalyst. Or we may esterify at a superatmospheric pressure in the absence of a catalyst, as proposed in our copending application Serial No. 427,536. In either case, the esterification can be controlled in such a way as to include only the fatty acids, leaving 1 tent of the esterified mixture is, by necessity,

fatty acids and phytosterol are of considerable commercial value. Therefore, a process for the sharp separation of the tall oil would be of great commercial value, especially in view of the vast potential supply of tall oil, resulting from the increasing importance of the sulphate process for paper making. .Due to its low commercial value,

found that if the concentration of the resin acids,

as defined hereinafter, is higher than approximately we can effect a substantially com-' plete separation of the mixture into fatty acid esters and resin acid soaps by extracting with a We have slightly lower than that found by the usual analytical methods in the tall oil before esterification.

In the second stage of our process we neutralize the resin acids with an aqueous alkali such as, for example, sodium or potassium hydroxide or carbonate. Substantially complete neutralization of the resin acids is required, although slight deviations on either the acid or alkaline side are permissible and do not materially affect the refneutralization, we :have a mixture which consists essentially of the alkali soaps of the resin acids. fatty acid esters, unsaponifiable and water. Depending on the proportion of water present, the

esters and unsaponifiable might form a transparent solution with the resin acid soap solution, or, as the proportion of water is increased, the mixture assumes the appearance of an ordinary, coarse emulsion in which at least a portion. or the esters and unsaponifiable are dispersed in fine droplets.v We found that the proportion of water to the resin acid soap dissolved in it is the critical factor which determines the colloid chemical behavior of the neutralized esterified mixture and makes a' strictly quantitative expression of the elements entering into our process possible;

The quantitative relationship between water and resin acid soaps is expressed in a convenient form by the concentration of the resin acids pres ent in water solution as soaps. -This concept of resin'acid concentration altogether disregards the presence of fatty acid esters and unsaponifiable. More specifically, this concentration is defined as the relationship of the weight of the resin acids before neutralization to the volume of the aqueous soap solution resulting after neutralization. The volume of the soap solution will be approximately equal to the volume of the resin acids and the volfied showed an acid number of '76. On the basis of an equivalent weight of 302 for the resin acids, this acid number corresponds to a resin acid content of 41% by weight on the esterified mixture.

" One hundred grams of the esterified mixture con- To obtain a resin acid concentration of, for example, 40% we obviously have to use an alkali strong- =23% resin acids I or than normal In this case the 41 grams resin acids would be contained in 98 cc. of soap solution and the alkali would have to be contained in 98-41=58 cc. aqueous solution. As a rule we use a stronger alkali than is required to obtain the exact resin acid concentration and then dilute the mixture with water until the desired resin acid concentration is reached. We are aware that in a strictly scientific sense the volume of the soap solution is not the exact sum of the volume of the resin acids and the alkali solution. However, we have found that for our purpose the approximation introduced is suiliciently precise and permits rapid calculation of the volume conditions involved. In the following specification and claims, the term Resin acid concentration" is always used in the sense as here defined, namely, to denote the concentration of the resin acids (present as soaps) in the aqueous soap solution, or the number of grams of resin acid contained in 100 cc. of soap solution.

It is known to those skilled in the art that extraction of soap solutions with hydrocarbon solvents is invariably effected in the presence of demulsiiying agents, such as, for: example, alcohols. In the laboratory determination of unsaponifiable matter the presence of alcohol in the soap solution is always required to avoid emulsification oi the soap solution with the hydrocarbon solvent. We are also aware of United States Patent No. 1,736,802. The method disclosed in that patent consists to esterifying thei'atty acids in tall oil using an excess of alcohol, neutralizing the mixture andtreating the neutralized mixture with benzene to remove the fatty acid esters and unsaponifiable. At this point the alcoholoriginally used in excess over that necessary for the esterificationof the fatty acids is still present in the mixture and according to the disclosure is recovered from the aqueous-alcoholic soap. solution only after the extraction of the fatty acid esters. We consider the use of an alcohol as a de-mulsifyins agent in the extraction of a neutralized esterifixed mixture of tall oil as far too expensive since it necessitates recovery and re-concentration of the alcohol so used. It is an essential feature of our process to remove the excess'oi alcohol used in the esterification immediately after esteriilcation is completed and before the esterifled mixture is neutralized. We have found that if an esteri- 5 fled mixture 'so obtained is neutralized and extracted with a hydrocarbon solvent to remove the fatty acid esters, invariably troublesome emulsions are produced unless the concentration of the resin acids is approximately or higher.

- As is known to those skilled in the art, soap solutions, when extracted with awater immiscible ,solvent, invariably retain a quantity of that solvent which can be removed only by decomposing the soap with acid. On beginning the extraction solvent will be retained in the soap solution until the latter is saturated with the solvent and only then will efficient extraction begin. We have, therefore, found that the smoothness and the speed of the extraction are greatly increased, if, before starting the extraction, we dissolve in the soap solution a suflicient amount of the extracting solvent to saturate the soap solution. This is of. a particular advantage its. continuous liquid-liquid extraction method is used where the quiescent extraction mixture is scrubbed by droplets of the extracting solvent.

'Summarizing, our method of preparing an esterified mixture for extraction comprises neutralizinz the esterified mixture with a strong alkali solution, adding water until the desired resin acid concentration is obtained. and adding solvent in excess of that required for saturating the soap solution, or we may reverse this order and add first the solvent to the esterified mixture and then neutralize. After thorough mixing, the excms solvent together with a small quantity of extracted matter rapidly separates out as an upper layer, the mixture to be extracted forming the lower layer. At resin acid concentrations of approximate- 0 1y 30% or'higher separation occursfrapidly at concentrations of approximately 30 to 40%, more slowly at higher concentrations.

The table I illustrates the volume conditions found in the extraction of 100 grams esterified.

mixture with benzol.

not

272 18 270 m 268 I 261 H 225 I) m7 9 29.5

I No solvent separation.

It is quite obvious from these figures that the resin acid concentration most favorable for extraction is at or slightly above 30%. At this concentration the volume of the'layer to be extracted is at a minimum which coincides with a miniimum for the solvent dissolved. At this concen- 7 trationthe volume capacity of the extraction equipment can be utilized more emciently the total quantity of solvent required is less than at any other concentration. Since in the course 2,348,970 removal of a small quantity of soap by the sol vent it is desirable to start the extraction at a resin acid concentration somewhat above 30%.

For the reasons just given, our preferred range of resin acid concentration in the extraction of the fatty acid esters from neutralized esterified mixtures of tall oil is at approximately 32 to 40%. Our process, however, includes the use of any other concentration within the limits previously given. For example in the extraction of the unsaponifiable matter from. rosin for which the present process is eminently suited, higher resin acid concentrations might be found to give better results than for a tall oil mixture.

The'last traces of esters and unsaponifiable are very tenaciously held by the soap solution and v are extracted rather slowly. We have found that their extraction can be speeded up considerably by adding toward the end of the extraction, a small quantity of free resin acids to the mixture which is being extracted or to the solvent'before it enters the extractor. For this purpose we can either use resin acids dissolved in the extracting solvent or we can use a small portion of fresh, not neutralized esterified mixture. Most of the resin acids added in either form no doubt go over into the extract but their presence brings about a rapid and complete removal of the esters from the soap solution. The resin acids obtained from such a soap solution are of a high acid number, hard and of a high melting point, whereas even small traces of fatty acid esters in the resin acids cause a considerable depression of the melting point.

For extraction we prefer the continuous liquidliquid extraction method using any suitable apparatus. This method requires a much smaller quantity of solvent than. the batch method. While extraction at or somewhat below room temperature is possible, we prefer to keep the mixture to be extracted at approximately from 30 to 50 C. I

As solvents for the extraction, we use petroleum solvents such as gasoline or naphtha fractions or aromatic hydrocarbons. Our preferred solvent is benzol.

The extract is a rather concentrated solution of the fatty acid esters and the major portion of the unsaponifiable in the extracting solvent. It

also contains small quantities of free resin acids and resin acid soaps. After removing the solvent by distillation the free resin acid is neutralized and the resin acid soap either washed out with water or removed by separation according to the process of our co-pending application Serial No.-

438,004, filed April 7, 1942.

This latter separation process comprises the general steps of adjusting the resin acid concentration of the soap solution to from about 30 to about and heating at a superatmospheric temperature to cause a formation of two layers, the soap solution comprising the lower layer. By this procedure we obtain soap-free and resin acid-free fatty acid esters which contain the maior proportion of unsaponifiable matter original- 1y present in the esterified mixture.

Acidification of the extracted soap solution sets free the resin acids and releasesthe solvent dissolved in the soap solution. The solvent is dis tilled and resin acids of a high acid number are recovered.

-The starting material for our process may be either crude or refined tall oil. In using esterified mixtures made from crude tall oil, we obtain both the fatty and resm acid portion in a crude form, the fatty acid ester portion containwere free of resin acids.

ing a major portion of the total unsaponifiable matter. The esters and unsaponifiable may then be subjected to a refining treatment with sulphuric acid in accordance with the process of our Patent No. 2,223,850 to obtain valuable phytosterol and refined esters containing only a fraction of the original unsaponifiabl matter. We may also remove the phytosterol with a mild treatment with sulphuric acid and distill the esters to separate them from the major portion of the unsaponifiable. The crude resin acids also can be refined in accordance with the teachings of our aforesaid patent or any other known meth. ad for refining rosin.

If our starting material is refined tall oil, we obtain both the fatty acid and resin acid portions in a refined form. The fatty acid esters in this case will contain the major portion of the unsaponifiable matter. For this reason, it is desirable to start with a refined tall oil containing a low proportion of unsaponifiable.

The following examples are introduced to further illustrate our process, but are not to be construed as limiting the broad scope thereof.

Example 1 In a crude tall oil which contains 33.5% resin acids, 59% fatty acids and 7.5% unsaponifiable, the fatty acids were esterified with methanol in the absence of a catalyst at a gauge pressure of approximately pounds per square inch. The excess of methanol used was removed by distillation. The esterified mixtur obtained had an acid number of 60, corresponding to a resin acid content of 32.3

113.5 kilograms of the esterified mixture, containing 36.7 kilograms resin acids, were charged into an extractor of approximately 400 liters capacity and neutralized with 34.6 liters 3.5 normal sodium hydroxide. To obtain. a resin acid concentration of 34%,'36.7 liters water were added. The neutralized mixture was stirred with liters benzol and the temperature adjusted to 30 C. After separation of the layers the extraction was started and continued at a temperature of 30 to 45 C. until the solvent leaving the extractor was only slightly colored. Now 11 kilograms of fresh esterified mixture were added in small portions to the solvent entering the extractor in order to extract the last traces of esters, and the extraction continued until the solvent leaving the extractor was colorless. The benzol was now distilled and an extract obtained which contained small proportions of resin acid soap and 5% resin acids. The soap and resin acids were removed and 83 kilograms of fatty acid esters and unsaponifiable obtained which The esters and unsaponiflable were treated with a small quantity of sulphuric acid to remove the phytosterol and purified. The extracted soap solution was acidified with dilute sulphuric acid, the resin acidbenzol solution charged into a still, th benzol distilled and crude dark colored, micro-crystalline resin acids recovered.

Example 2 A medium grade rosin of acid number 165 was dissolved in sodium hydroxide and theresin acid concentration adjusted to 38% by the addition We claim as our invention:

1. A process for the separation and recovery of the tall oil resin acidsand fatty acids which comprises converting the fatty acids into their alkyl esters, removing excess alcohol remaining from said esterification, substantially completely neutralizing the resin acids with an aqueous alkali in dilution to provide a resin acid concentration greater than about 30% of the resin soap solution present in the mixture, and extracting the fatty acid esters from the resulting mixture with a hydrocarbon solvent.

2. A process of separating fatty acids from resin acids contained in tall oil which comprises, converting the fatty acids into their alkyl esters, removing excess alcohol remaining from said esterification, substantially completely neutralizing the resin acids with an aqueous alkali in dilution to provide a resin acid concentration not lower than about of the resin soap solution present in the mixture, and extracting the fatty acid esters from the resulting mixture with a hydrocarbon solvent.

3. A process of separating fatty acids from resin acids contained in tall oil which comprises, converting the fatty acids into their alkyl esters, removing excess alcohol remaining from said esterlflcation, substantially completely neutralizing the resin. acids with an aqueous alkali in dilution to provide a resin about 30 to about 50% present in the mixture,

of the resin soap solution and extracting the fatty acid concentration of from acid esters from the resulting mixture with a hydrocarbon solvent.

4. A process of separating fatty acids from .resin acids contained in tall oil which comprises, converting the fatty acids into their alkyl esters, removing excess alcohol remaining from said esterification, substantially completely neutralizing the resin acidswith an aqueous alkali in dilution to provide a resin acid concentration of from about 32 to about 40% of the resin soap solution present in the mixture, and extracting the fatty acid esters from the resulting mixture with a hydrocarbon solvent.

5. A process of separating fatty acids from resin acids contained in tall oil which comprises, converting the fatty acids into their alkyl esters, removing excess alcohol remaining from said esterification, substantially completely neutralizing the resin acids with an aqueous alkali-arid adjusting the aqueous content of the resulting soap solution to" provide a resin acid concentration not lower than about 30% of the resin soap solution present in themixture, extracting the fatty acid esters from the resulting mixture with a hydrocarbon solvent, and recovering the resin-acids from the extracted soap solution.

6. A process of separating fatty acidsfrom resin acids contained in tall oil which comprises, converting the fatty acids into their alkyl esters,

removing excess alcohol used in the esterificae tion reaction, substantially completely neutralizing the resin acids with an aqueous alkali and adjusting the aqueous content of the resulting soap solution to provide a resin acid concentration of from about 30 to about 50% of the resin soap solution present in the mixture,-ext ractlng the fatty acid esters from the resulting mixture with a hydrocarbon solvent, and, acidifying the extracted soap solution to set free the resin acids and to release dissolved solvent.

7. A process of separating fatty acids from resin acids contained in tall oil which comprises, converting the fatty acids into their alkyl esters, removing excess alcohol used in the esterification reaction, substantially completely neutralizing the resin acids with an aqueous alkali and adjusting the aqueous content of the resulting soap solution to provide a resin acid concentration of from about 30 to about of the resin soap solution present in the mixture, and extracting the fatty acid esters from the resulting mixture with a hydrocarbon solvent after pre-saturation of the soap solution with said solvent.

8. A process of separating fatty acids from resin acids contained in tall oil which comprises,

converting the fatty acids into their alkyl esters, removing excess alcohol used in the esterification reaction, substantially completely neutralizing the resin acids with an aqueous alkali and adjusting the aqueous content of the resulting soap solution to provide a resin acid concentration of from about 30 to about 50% of the resin soap solution present in the mixture, mixing therewith a hydrocarbon solvent in excess of the amount required to saturate the soap solution, extracting the fatty acid esters from the soap solution by continuous liquid-liquid hydrocarbon solvent extraction, and acidifying the extracted soap solution to set. free the resin acids and to release dissolved solvent.

9. A process of separating fatty acids from resin acids contained in tall oil which comprises, converting the fatty acids into their alkyl esters, removing excess alcohol used in the esterification reaction, substantially completely neutralizing the resin acids with an aqueous alkali and adjusting the aqueous content of the resulting soap solution to provide a resin acid concentration of from about 30 to about 50% of the resin soap solution present in the mixture, saturating the soap solution with a hydrocarbon solvent, subjecting it to continuous liquid-liquid hydrocarbon solvent extraction to extract the fatty acid esters, and adding to the soap solution a relatively small amount of free resin acid near the end of the extraction period to facilitate rapid and complete removal of the esters from the soap solution.

10. 'A process of separating fatty acids from resin acids contained in tall oil which comprises, converting the fatty acids into their alkyl esters,

removing excess alcohol used in the esteriflcation reaction, substantially completely neutralizing. the resin acids with an aqueous alkali and adJusting the aqueous content of the resulting soap solution to provide a resin acid concentration of from about 30' to about 50% of the resin soap solution present in the mixture, saturating the soap solution with a hydrocarbon solvent, subjecting it to continuous liquid-liquid hydrocarbon solvent extraction to extract the fatty acid esters, adding to the soap solution a relatively small amount of free resin acid near the