US2411536A - Method for producing alkyl esters of higher fatty acids - Google Patents

Description

" Patented Nov. 26,

METHOD FOR PRODUCING ALKYL ESTER or means FATTY ACIDS y Frederick H. Gayer and Charles E. Fawkes, Chicage, lll., assignors to Continental Research Corporation, Chicago tion of Illinois Heights, Ill., a corporav No Drawing. Application January 21, 1942, x

Serial No. 427,536

14 Claims. (01. zed-97.5)

This invention relates to an improved method for producing alkyl esters of higher fatty acids, and particularly to the esterification'of fatty acids tin, mixtures thereof with resin acids, and

is a continuation-impart of our copendingapplication Serial No. 284,915, filed, July 17, 1939.

Our improved method is especially useful as a tion could be'eifected without the use of a'icatalyst, would be of great practical value. The present application discloses such a process.

. Briefly our process comprises subjecting a"mixture of tall oil and a monohydrlc aliphatic alcohol, in the absence of a catalyst, to treatment preliminary step in processes for the separation of the constituents of organic mixtures contain ing both fatty and resin acids,'as for example tall oil. ent No. 2,166,812 and. in the following copending applications? Serial Nos: 284,917, new Patent No- 2,288,946, and 284,918, new Patent No. 2,288,947, both filed July 1'7, 1939. These processes comprise esteriflcation of the fatty acids, transform- "ing the resin acids into resinates, and separating the esters from-the resinates. The present application discloses a method whereby the fatty acids can be quantitatively esterifled in such a way' that the esterification reaction is sharply Such processes are set forth in our Pat-v under pressure by heating to a suitable temperature and discontinuing such treatment at a point where the fatty acids are completely esterified and at. which point esterification of the resin acids has not yet begun. The important'elements entering into our process are: The kind of alcohol Y used, the quantity of alcohofused, the time re quired for the treatment and the'temperature at which the treatment is efiected.

The alcohols we use in our process are members of the monohydric aliphaticalcohol series restricted'to the fatty acids and does not at all extend to the resin acids.

Esterification ofithe'fatty acids is usually accomplished by reacting the mixture with an excess of an alcohol irrthe presence of a catalyst.

Due to the greater reactivity of the fatty acids and include methyl, ethyl, propyl, butyl, and

alcohols and which are hereinafter, and particularly in the claims termed, fl'ow molecular weight monohydric aliphatic alcohols. The choice of the alcohol depends on the ,type of fatty acid ester desired as one of the end products. If our object is only the separation of the fatty and resin acid portion of tall oil regardless of the type of esters obtained, we prefer, for simple reasons, the use of methyl alcohol.

The quantity of alcohol we use is always in excess of the calculated quantity required for the esterification of the fatty acids. In calculating the theoretically required quantity of alcohol, we

assume the figure of 282 for the average molecwill be extended to the resinacids if the catalyst concentration is materially increased (Patent No. 1,829,481).

Numerous catalysts for the esterification reaction have been described in the literature and in patents. By far the most active catalysts are strong acids such as hydrochloric or sulfuric. They have the disadvantage that their action on the equipment is rather destructive and that they cause discoloration of the reaction" product. Sulfonic acids have a milder action on the equipment but also cause discoloration. Anhydrous metallic chlorides and sulfates, metallic soaps and finely divided metals also have been recommended as catalysts. They are much less active catalysts than mineral acids. All catalysts have the added disadvantage in common that they must be removed after the reaction has proceeded to the desired point, which means an additional operation.

Considering the disadvantages connected with the use of catalysts, a process whereby esteriilca ular weight of the fatty acids contained in tall oil. For example, 100 parts by weight of a tall oil containing 52% fatty acids will require 5.9 parts of methyl alcohol for the esterification of the fatty acids. In practice'we may use from slightly more than thecalculated quantity up to 4 or more times that quantity of alcohol. The

' excess used depends on the particular nature or source of the tall oil treatedfidifferent oils requiring different proportions of excess-alcohol for esterification in the same period of time. With the same tall oil, the time needed for esterification of its fatty acids is shorter when the proportionof excess alcohol present is higher. For example, in the above tall 011 the fatty acids were esterified in 8 hours when using 3.2 times the calculated quantity of methyl alcohol, whereas at the same temperature, 22 hours were required when only 1.35 times the calculated quantity of alcohol was used. After esterification of the fatty acids is complete, the excess of alcohol is removed by distillation. Together with the alcohol we also distill off the water formed in the esteriflcation reaction.

The alcohols are preferably used in a'rather concentrated form but our process does not re quire the use of anhydrous alcohols. We have successfully used, for example. methyl alcohol of 80% strength by volume, or the constant boiling mixture of isopropyl alcohol with water which contains only 91% by volume of anhydrous isopropyl alcohol.

The temperature for esterificatlon, according to our process, ranges between the following limits. The lower limit is the temperature at which the mixture of tall oil and alcohol would boil at at= mospherlc pressure. This corresponds closely to the boiling point of the alcohol used which is 66 C. for methyl alcohol and 140 C. for n-amyl alco hol. The upper limit of temperature is approximately 200 C. The corresponding pressures range from atmospheric to approximately 500 pounds per square inch. Esterification is extremely slow on refluxin a mixture of tall oil and an alcohol in the absence of a catalyst at atmospheric pressure. If, however, the mixture is heated in a closed system to a temperature above its boiling point at atmospheric pressure, the reaction Velocity increases as the temperature is raiscdj We have found that the effect of the temperature on the velocity of the esterification reaction conforms to the general rule according to which a rise of C. approximately doubles the rate of reaction. In the following Table I the velocity of the reaction is expressed as the time required to reduce the initial acid number of 173 of a refined tall oil to the sam extent on heating it with four times the theoretical quantity oi methyl alcohol in experiments made at different temperatures. With this particular oil, a decrease of 106 points in acid number corresponds to a complete esterification of acids duringwhich period the acid number stays constant. This inhibition period may be of a duration from about one-half hour to several hours. Its existence enables us to-stop the reaction sharp- 1y at a point at which the fatty acids are completely esterifled and before commencement of esteriflcation of the resin acids. This is an important requirement of the usefulness of our process since our ultimate purpose is to enable a sharp separation of the fatty acid component of tall oil from the resin acids to be made by methods such as those set forth in our aforesaid patent and copending applications.

According to our process, the esterification is efiected in a pressure vessel which may be constructed of any metal reasonably corrosion-proof against tall oil, such as stainless steels, Monel metal, aluminum, etc. We charge the tall oil together with an excess of the alcohol into the pressure vessel and raise the temperature to the desired level. The progress of the esteriflcation can be easily followed by withdrawing samples from time to time and, after evaporating the excess alcohol and the water formed during the reaction determining the acid number of the oil. At the point where the fatty acids will be completely es terifled, the acid number will be entirely due to the resin acids. The acid number expressing the quantity of resin acids present varies with different oils depending on their resin acid content and has to be determined previously by analytical laboratory methods. When the acid number indicates complete esterification of the fatty acids, the heatin is discontinued and the excess alcohol and the water formed in the reaction are removed by distillation, at first at atmospheric pressure and then finished in vacuo. We obtain an esteri fication mixture of good color, unharmed by sidereactions which are liable to occur in processes in the fatty acids. so which catalysts are used. The use of pressure Table i a Egg: Pressure, Decrease Time Decrease Time Decrease Time tum lbs/1n. of acid recgilred, of acid re mood, of acid relglired,

0G Ga. 0. rs. No. re. No. rt.

72 Atm. 9 6 100 9 0.5 89 22 108 86 180 120 89 3 10d 8 l 146 iso s9 1 106 3.5

The foregoing table clearly shows the time element involved, and indicates that with four times the theoretical quantity of methyl alcohol a temperature of approximately 130440" C. insures a sumciently high reaction velocity for commercial operation. With lower ratios of excess alcohol the temperature must be correspondingly raised if esterirlcation is to be effected in the same time, and we may use temperatures up to approximately 200 C. Thus within the limits of.our invention we can control the time factor by either the temperature or the excess of alcohol used or by both.

While the esterification of resin acids becomes of an important magnitude only at temperatures above 200 C. (Patent No. 1,924,934) we have found that the resin acids may undergo a slow esterification even between the temperature limits of our process. So slow are the resin acids to react, however, that the beginning of their reaction is always preceded by the complete esterification of the fatty acids. We have actually found an inhibition period between the point of th completion of the esterification of the fatty acids and the beginning of the esterification of the resin equipment at first appears to be a complication as compared to processes using catalysts at atmospheric pressure. Actually, however, it is a great simplification, since materials can be used for the construction of the pressure equipment which under the influence of active catalysts would disintegrate in a short time. Whatever corrosion action free fatty and resin acids have at higher temperatures on most metals is greatly reduced due to the presence of the alcohol. Instead of using a pressure vessel and working by the batch method. our process may also be carried out in a continuous manner by supplying a mixture of tall oil and alcohol into one end of a reaction chamber kept at a suitable temperature and continuously discharging the reacted mixture at the other end of said reaction chamber.

The following Table II shows the change of the acid number with time for two different tall oils reacted with methyl alcohol. Oil No. 1 was a crude tall oilcf acid number 166, containing 55 per cent fatty acids and 38 per cent resin acids. Oil No. 2 was a tall oil refined according to our Patent No, 2,223,850, of acid number 173, con- S taining 57 per cent fatty acids and 37 per cent resin acids. The table clearly indicates the 111- hibition periods of approximately 1 hour and 1% hour respectively after which a further slow decrease of the' acid number indicates a slow esterification of the resin acids.

Table II fined. z

Example 1 Five hundred grams of a'reiined tall oil of acid number 173, containing fatty acids 57 percent,

resin acids 3''! per cent and 160 cc. of methyl al ounces alcohol at a temperature 167-167 (3., thepresof the fatty acids was complete in 23 hours.

l in the absence of a catalyst, at a superatmosas the fatty acids are completely esterified and before esterification of the resin acids begins.

: sence of a catalyst, at a superatmospheric prescohol are" charged into a steel'pressure bomb lined with aluminum and equipped with a sampling valve. The bomb is heatedin an oily bath which is kept at a constant temperature of 180 C. After 6 hours'heating, the acid'number of the oil as determined von samples withdrawn, decreases to 68,. which figure does not change on further heating for one-half hour.

Heating is stopped, the excess methyl alcohol and the-water. formed distilled off. We obtain flvehundred and fifteen grams esteriiled mixture oi good color.

' Example 2 200 pounds of a crude tall oil containing resin acids and 50 pounds methyl alcohol were heated in a steel pressure tank under a pressure of 170 pounds. After 13 hours, the acidnumher was 63 and remained constant for the next 4 hours. The heating was now stopped and the excess alcohol and the water distilled off.

Exampl 3 250 grams .of a crude tall oil containing 42% resin acids and cc. of 80% methyl alcohol by 'volume were charged into a pressure vessel and heated 23 hours at a temperature of l'70-5 C. when the acid number became constant at '78.

Example 4 300 grams of a crude tall 011 containing 42% resin acids were treated with 30 cc. methyl alcohol (corresponding to an excess of approximately at a. temperature of 166-170 C., the pressure rising to about 210 pounds. The acid number became, constant at '78 after 20 hours heating when the excess methyl alcohol and the water were distilled off.

Example 5.

v tained in tall oil, which comprises heating a mixture consisting of at all oil and a low molecular and below approximately 200 C. for a period sumcient to effect esteriiicaticn of only the fattycacids sence of a catalyst, at a superatrnospheric presand below approximately 200 C. for a "period ture consisting of a tall oil and an excess of a low Example s 300 grams of a crude tall oil song 42% resin acids were reacted with cc. normaly amyl sure rising up to about 2'1 pounds. Esterification We claim as our invention: a

1. The process of esterifying the fatty. acids contained in a tall oil mixture of fatty acids and resin acidawhich comprises treating a mixture consisting of said tall oil and an excess of a low molecular .weight monohydric aliphatic alcohol.

pheric pressure and a temperature of from about the boiling point or the mixture to approximatei 200 C. and discontinuing the reaction as soon 2. The process of esterii'ying fatty acids conweight monohydric aliphatic alcohol. in the absure and a temperature or from abov that at which the mixture boils at atmospheric pressure and discontinuing the reaction before esterificot ion of the resin acids occurs.

3. The process of esterifying fatty acids contained in tall 011, whichcomprises heating a mixture. consisting of a tall oil and a low molecular weight monohydric aliphatic alcohol, in the absure and a temperature of from above that atwhich the mixture boils at atmospheric pressure sufllcient to effect. esterification. of only the fatty acids, the said alcohol being in molal excess of the fatty acid content of the tall 011 and before esterification or the resin acids begins.

4. vThe process of esterifying fatty acids ,contained in tall oil, which comprises heating a ture consisting of a tall oil and a low molecular weight monohydric aliphatic alcohol, in the sbsence of a catalyst, at a superatmospheric pressure and a temperature of from about the boiling point of the mixture at atmospheric pressure to apprately 200 C. and discontinuing the reaction as soon as the fatty acids are completely esterified and before esterincation of the resin acids begins. v v I 5. The process of esterifying fatty acidscon tained in tall 011, which comprises heating a mix-- molecular weight monohydric aliphatic alcohol, in the absence of a catalyst, at a superatmospheric pressure of from about atmospheric to about 500 pounds per square inch, and at a temperature of from about the boiling point of the mixture at atmospheric pressure to approximate- 1y 200 C. and discontinuing the reaction as soon as the fatty acids are completely esterifled and before esterification of the resin acids begins.

6. The process of esterii'ying fatty acids contained in tall oil, which comprises heating a mixture consisting of a tall oil and a. low molecular weight monohydric aliphatic alcohol, in the ab sence of a catalyst, at a superatmospheric pressure and a temperature of from above the boiling point of the mixture at atmospheric pressure to approximately 200 C. and discontinuing the ra action as soon as the fatty acids are ccmpletel esterified and before the esteriflcation of the to! oil resin acid content begins.

7. The process of esterifying fatty acids con tained in tall oil, which comprises reacting a mixture consisting of tall oil and an excess of a low molecular weight monohydric aliphatic alcohol, in the absence of a catalyst, at a superatmospheric pressure and a temperature of from above.

the boiling point of the mixture at atmospheric pressure to approximately 200 C. and discontinuing the reaction as soon as the acid number of the tall oil becomes constant and before esterification of the resin acids begins.

8. The process of esterifying fatty acids contained in tall oil, which comprises reacting a mixture consisting of a tall oil and an excess of a low molecular weight monohydric aliphatic alcohol, in the absence of a cataylst, at a superatmospheric pressure and a, temperature of from above the boiling point of the mixture at atmospheric pressure to approximately 200 C. and discontinuing the reaction as soon as the acid number of the tall oil becomes constant for at least one hour and before esterification of the resin acids begins.

9. The process of esterifying fatty acids contained intall oil, which comprises reacting a mixture consisting of a tall 011 and an excess of a methyl alcohol, in the absence of a catalyst, at a superatmospheric pressure and a temperature of from above the boiling point of the mixture at atmospheric pressure to not in excess of approximately 200 C. and discontinuing the reaction as soon as the fatty acids are esterified and before esteriflcation of the resin acids begins.

10. The process of esterifying fatty. acids contained in tall oil, which comprises reacting a mixture consisting of a tall oil and an excess of an ethyl alcohol, in the absence of a catalyst, at a superatmospheric pressure and a temperature of from above the boiling point of the mixture at atmospheric pressure to not in excess of approximately 200 C. and discontinuing the reaction as soon as the fatty acids are esterified and before esterification of the resin acids begins.

11. The process of esterifying fatty acids contained in tall oil, which comprises reacting a mixture consisting of a tall oil and an excess of an iso-propyi alcohol, in the absence of a catalyst,

at a superatmospheric pressure and a temperature of from above the boiling point of the mixture at atmospheric pressure to not in excess of approximately 200 C. and discontinuing the reaction as soon as the fatty acids are esterifled and, before esterification of the resin acids begins.

12. In a process for separating the fatty acid and resin acid constituents of tall oil, the step of esterifying the fatty acids, which consists in reacting a mixture of a tall oil with a monohydric aliphatic alcohol, in the absence of a catalyst, at a superatmospheric pressure and a temperature of from above the boiling point of the mixture at atmospheric pressure torapproximately 200 C. and discontinuing the reaction after'the fatty acids are completely esterifled and before esterification of the resin acids begins.

13. In a process for producing fatty acid esters from fatty acids contained in a tall 011 in admixture with resin acids, the step which consists in reacting said. mixture with a low molecular weight monohydric aliphatic alcohol, in the absence of a catalyst, at a superatmospheric pressure and a temperature of from above the boiling point of the mixture at atmospheric pressure to approximately 200 C. and discontinuing the reaction after the fatty acids are completely esterified and before esterification of the resin acids begins.

14. The process of producing a mixture of fatty acid esters and resin acids, which comprises treating a mixture consisting of a. tall 011 and a low molecular weight monohydric aliphatic al- 001101, in the absence of a catalyst, at a superstmospheric pressure and at a temperature of from above the boiling point of the mixture at atmospheric pressure not in excess of approximately 200 0., discontinuing the reaction as soon as the fatty acids are completely esterified and before esteriflcation of the resin acids begins, and removing the excess oi alcohol and water formed duringthe reaction.

FREDERICK H. GAYER. CHAS. E. FAWIGLS.