US2319929A - Treating natural oils and fats - Google Patents

Description

Patented May 25, t 1943 TREATING NATURAL OILS AND FATS Harold D. Hoffman, Park Ridge, and Albert R.

Zeigler, Evanston, Ill., assignors to Armour and Company, Chicago, 111., a corporation of Illinois I o .7 Claims.

This invention relates to a methodfor treating natural'oils and fats.

In the treatment of natural oils and fats where the material is split to separate the fatty acids and the fatty acids .aie subsequently distilled, considerable difficulty has been encountered by No Drawing. Application November 22, 1940, Serial No. 366,706-

reason of impurities within the fats and oils which tend to induce pitch formation and low distillate yields. With some stocks, there are found to be saturated components.

In the treating methods now employed prior to the distillation step, it is customary to hydrolyze the material eitherby autoclaving or by twitchel- In autoclaving an oil, the usual procedure is to add a catalyst, which may be zinc oxide, calcium oxide or caustic soda, etc. However, the

amount of alkali, metal used for this process is relatively small and is not suiiicient to react with an of the fatty acids which result from the splitting operation. The catalyst is used only in an,

amount suflieient to'promote the hydrolyzatio'n. If a sufllciently high temperatureis employed and the operation carried on for a sufficient lengtho'f "time, the catalyst may beentir'ely omitted. As

already stated, the above, treating operations now employed result in a somewhat inferior product, in a relatively low yield in the final distillation step and in' a reductionorloss of some unsaturateds present in the original stoc An object of the present invention is to combine with the distillation or fractional distillation step anearlier treating operation which results in a better distillate yield, a product of better more unsaponification of the mass, the soap is acidulated to liberate the fatty acids and the fatty acids are then subjected to fractional distillation.

Following the first step of saponification, we find that the product can be improved and better yields obtained if the resulting soap is grained with salt or with alkali in a manner similar to the customary method of settling a soap during the manufacture'of soap. The lye (lower phase) is removed and water. and salt added to the soap and one or more similar washes repeated. The impurities are more soluble in salt solution than is the soap and effective separation results from this process. The settled soap is removed, acidulated, and the fatty acids stock subjected to distillation. v

'The product resulting from the distillation has a much better color and the yields are substantially greater than those obtained by the old methods as will be shownlater by reference to specific examples. Further, in the treatment of stockscontaining a large amount-of unsaturated fatty acids, and where it is desired to obtain in color, and with less destruction of unsaturateds in the distillation operation. While in some respects, the two main steps of the new process are old, the combination thereof in the manner which will be described result in extremely important and new results.

Instead of autoclaving in the presence of catalysts or twitchellizing the natural oils or fats,

we find that far better results can beobtained by completely saponifying with an alkali'the oils and fats as the first step, the saponiflcation being the final product-a high yield of the unsaturated fractions, the new method considerably increases the yield of such product over that heretofore obtained. v Byway of example, the application of the proc- -ess to low grade fats,- such as cotton seed and soybean oil foots, may be discussed in detail. Cotton seed foots, for example, are normally handled" in one of the following methods: the foots are aeidulated and the resulting black stock subjected .to distillation without treatment. Usually the still bottoms" are subsequently hydrolyzed and the resulting black stock subjected the second time to distillation. In an alternative method, the foots are hydrolyzed, eitherby autoclaving or by twitchellizing, and the resulting split stock subjected to distillation. In either of these normal methods of preparing and distilling the acids from cotton seed foots, the overall distillation yield has been of the order of 88 percent. Thelowyield is due to impurities. Cotton seed foots containvery substantial amounts of impuriti es which are found to induce 'pitch formation.

It is well known that distillation yield is related to the eflfciency of the splitting or hydrolyzing of the oils. The methods heretofore used result iii splits of percent or thereabouts. It i generally known that raising the split to about 97 to 98 per cent will increase the overall distillation yield. Obviously the unsplit portion is not distillable and this portion remains as a component of the pitch. However, the amount of grained with salt or with alkali in a manner similar to the customary method of settling a soap kettle during the manufacture of soap. The lye (lower phase) is removed and water and salt added to the soap, and one or more similar washes repeated. The washings are found to remove asubstantial portion of the impurities which are more soluble in salt solution than is the soap. The settled soap is removed, acidulated, and the prepared black stock subjected to distillation.

The "split on the black stock prepared in this fashion will run around 98 to 99 percent, which is substantially better than that secured by the I other methods now in use.

The salting or graining operation removes proteins, mucilaginous substances, oxidized fatty acids, coloring matter and other impurities.

The distillation yield on the black stock prepared as above set forth is 95 percent, and the quality of the distillate is measurably better than that obtained by the other methods. For example, in fractionally distilling cotton seed fatty acids, we find that the proposed method produces a palmitic acid fraction having a color reading of 4.41%, Y, through 1 on the Lovibond scale compared to B, 1003! by the previous methods.

If, in the above process, the graining step is omitted, we find that there is a reduction in the yield and a lowering in the quality of the distillate. For example, cotton seed fonts that were completely saponiiled but not grained showed a distillationyield of only 92 percent, as compared with a yield of 95 percent where the graining step was employed. Likewise, the color of the Cu unsaturated fraction of the stock which was not grained was 3.58, 91?. This was considerably darker than the 1.23., 5!! that was obtained on grained stock.

As a second example of the process, the application to highly unsaturated oils, such as sardine oil and menhaden oil, may beset forth in detail. In the treatment of highly unsaturated oils such as sardine oil, the prime object is to obtain a fraction which possesses very high unsaturation and hence can be used advantageously in the paint and resin industry. The important consideration is to obtain the highest possible yield of fatty acid distillate having the desired degree of unsaturation. It is-also desired to obtain such a distillateof the bestpcasible color.

In the-methods now employed. th first step is to hydrolyze or split the fish oil by autoclaving or twitchellizing. In autoclaving, the usual procedure is to add a catalyst such as zinc oxide, calcium oxide, caustic soda, etc. The amoimt of the alkali metal used is kept as low as possible, it being used only in sumcient amounts to promote hydrolysis. Where a sufficiently high temperature is had and sufficient length of time is employed, the catalyst may be entirely omitted. When sardine oil is split by either of these conventional methods, i. e. autoclaving or twitchellizing, and the resulting acids subjected to distillation, it is found that an iodine balance on theory the total products resulting from distillation falls considerably short of the iodine value of the acids in the original oil. In other words,-considerable destruction to the carbon-to-carbon double bonds has resulted along the way.

We have found that when sardine oil is completely saponifled in a kettle with caustic soda in a manner similar to that in which ordinary soap is made and the soap is then acidulated to liberate the fatty acids from the soap, and these fatty acids are then subjected to distillation, the products resulting from the distillation show a much higher iodine balance as compared to the original starting material than is the case when the sardine oil is hydrolyzed according to methods previously employed.

Under the old methods we obtained a 35 percent yield of fatty acids, having an iodine value of 240 when sardine oil, having been either autoclaved or twitchellized, was tractionally distilled.

Under the new method of preparing the fatty acid feed stock before distillatirm, the yields of fatty acid distillate having an iodine value of 240 jumped to 50 percent. When the bottoms were subjected to a redistillation process, there was recovered from it 31.8 percent of fatty acid having an iodine value of 241. An overall yield of 55.7 percent having an iodine value of 236 was obtained.

We are not able to set forth positively a reason for the unexpected improvement in yield of the high iodine fraction. It may be due to factors as to which we have no information. We are inclined to attribute the improvement to the lack of damage to the carbon-to-carbon double bonds during the splitting operation. Our experiments indicate that autoclaving high iodine oil, such as sardine oil, does bring about some kindofdamagetothedoublebmdstructureof thefatty acid. The higher thepremureatwhich autoclavingiscarriedomthegreaterthedamage.'lnthecaseottwitchellising,damageappearstolieinthesulfonationofthedoublebond. althoughtheresultingspiitacidsmly ppearto beundamagetasindicatedbytheiodinevalue, the inferior distillation yield su sts that some sulfonation may'haveoccm'redandthstthi organicsulfatelinkagemamatthetunperatureof distillation. produce polymerization of the more unsaturatedcomponents.

In addition to the great improvement in yield ofthehighiodinetractiomthecolorofthercsuiting distillate is foundtobemueh better-than that obtainedundertheoldmethods.

The surprising increase in yleldof distillate canhardlybeexplainedonthegroundofdiiier enceinspiitsobtainedbythenewmethod. Since the split onsardine oil twitchellhedwasfl percent, compared with the split on the saponiiied oil, which was 98.7 percent, we believe that the y suggested above may be thetrue expla- Athirdexampleoftheprocessistbemtionthereoftorefractoryoilsmchaaforexample,refuse palmoil. Thisoilisdiscardedoilobtained from tin platers. Tin platers uselll'le quantitiesofpalmoiltoquenchtinplatebefore exposureofthehotmetaltoaii'. Thetempera turesatwhichtheoilisheatedareupwardsof 500' llandtheycauseconsiderabiedamageto theoil. Damagedoilisconstantlyremovedmid' the bath replenished with freshpalm oil. Inan effort to obtain salvagevalne tromthe vastqmtityor damagedpalm oil availablaattemptshave beenmadetolwdrolyseitandsuhicctthereniltimpure oils.

ing fatty acids to distillation. Extreme difllculties have been encountered in splitting or hydrolyzing such oil due to extremely persistent emulslons whichresult from the usual methods of splitting. surmount this difficulty, including treatment with fuming sulfuric acid, centrifuging of the emulsion, etc. The results have been far short of the desired results,

Unless the emulsion is broken, it i impossible togseparate the fatty acids from the glycerine. Furthermore, it is impossible t separate cata-' lysis and mineral acids from the fatty acid feed stock. The iron and tin which contaminate the refuse palm oil cannot be removed from the feed stock. Further, when the feed stock which has not been completely freed from water emulsion and the above objectionable impurities, is fed to the still, blocking of the heaters almost invariably occurs and both yield and quality of the distillate are disappointing. Under the circumstances, yields of 50 percent have heretofore been felt satisfactory, and seldom has a yield exceed-- ed 70 percent.

When under the present process the refuse palm oil is completely saponified with caustic soda and grained in the manner well known to the soap manufacturer, the wash waters remove very substantial quantities of oxy-acids, which we findare responsible for the above emulsion difficulties, and they remove also substantial quantities of the metallic impurities. Soaps of oral-fatty acids are quite soluble in brine solution as contrasted with the soaps of normal fatty acids which are completely salted out of solution. The assembly of fatty acids as solubles in the washing operation enables the complete separation of the fatty acids to be accomplished during Thus there is a substantial improvement both inthe yield and quality. The invention is applicable to tall oil and to a number of other highly The above examples are believed to be exemplary of the steps to be followed and the results which may be obtained through the new combination of steps, such combination including complete saponification and acidulation, together with the final fractional distillation operation. Similar benefits may also be obtained with straight distillation. We prefer, however, to em- Various expedients have been used to important in reducing and eliminating impurities which interfere with the subsequent high distillation yield.

While in the foregoing specification we have set forth certain specific steps and certain specific exemplary operations for the purpose of illustrating the invention, it will be understood that great variation may be made in such steps and in the substitution of chemical equivalents, without de- 'with caustic soda and at atmospheric pressure,

graining the resulting soap with an aqueous solution of the substance of the class consisting of salts and alkalies, separating the solution and the soap, acidulating the soap to free the fatty acids, and distilling the fatty acids.

3. In a process for treating low grade fats of a class consisting of cotton seed and soy-bean oil oil foots, the steps of completely saponifying with an alkali the fats, grain ing the resulting soap with an aqueous solution of a substance of the class consisting of salts and alkalies, separating the solution and the soap, acidulating the soap to free the fatty acids, and distilling the fatty acids.

4. In a process for treating low grade fats of a class consisting of cotton seed and soybean oil foots, the steps of completely saponifying the fats with caustic sodaand at atmospheric pressure, graining the resulting soap with an aqueous solution of a substance of the class consisting of salts and alkalies, withdrawing said solution, recovering the settled soap and acidulating it to liberate the fatty acids, and distilling the fatty acids.

5. In a process for treating highly unsaturated fish oils, the steps of completely saponifying the oil with an alkali at atmospheric pressure, graining the resulting soap with an aqueous solution of a substance of the class consisting of salts and alkalies whereby the soap and the solution form two phases, with the solution and the materials'soluble therein ln-the lower phase, withdrawing the lower phase, recovering the settled soap and acidulating it to free the fatty acids, and distilling the fatty acids.

6. In a process of the character set forth for treating refuse palm oil, the steps of completely saponifying the oil with an alkali, graining the resulting soap with an aqueous solution of a substance of the class consisting of salts and alkalies whereby the soap and the solution form two phases, with the solution and the materials soluble therein in the lower phase, removing the lower phase, acidulating the settled soap to free the fatty acids, and distilling the fatty acids.

7. In a process of the character set forth for treating refuse palm oil, the steps of completely saponifying the oil with caustic soda and at atmospheric pressure, graining the resulting soap with an aqueous solution of a substance of the class consisting of salts and alkalies whereby the soap and the solution form two phases, with the solution and the materials soluble therein in the lower phase, removing the lower phase, washing the soap, acidulating the settled soap to liberate the fatty acids, and distilling the fatty acids.

, I HAROLD D. HOFFMAN.

. ALBERT H. ZEIGLER.