US2259540A - Purification of hydrogenated fatty oils - Google Patents

Description

Patentecl Oct. 21,

PURIFICATION OF HYDROGENATED FATTY OILS I Arthur U. Ayres, CheStnutfiill,fiPa., assignor to The Sharples Corporation, Philadelphia; Pa, a.

corporation of Delaware No Drawing. Application Serial No. 362,796"

tater 25.1940,

7 cream-s. (or. 2604425 The present invention pertains to the treatment of fatty oils, such as the familiar vegetable oils, which have been hydrogenated in order to reduce the degree of unsaturation of such oils and to render the product suitable for use as a vegetable oil shortening.

In the treatment of fatty oils, of which cottonseed oil may be taken as an example, the crude oil is subjected to treatment with an alkaline solution of appropriate strength, the alkaline solution being employed in anamount which represents a very substantial molecular excess over the free fatty acid content of the oil. The alkaline solution reacts with the fatty acid of the oil to produce soap stock, and this soap stock is separated from the neutral oil by centrifugation or gravity settling, entraining undesired gums and coloring matter, and thereby producing a yellow refined oil.

The refined oil is then subjected to water washing and vacuum drying operations, and the dried product is bleached by mixing with it a small quantity of a suitable bleaching clay, "such as fullers earth, and separating the clay with associated impurities from the bleached oil. The clay acts as an adsorbent for the coloring matter, removing most of the remaining coloring matter. After the conclusion of the bleaching operation, the oil is subjected to hydrogenation, if an oil which is suitable for use as shortening is to be the ultimate product of the process. While the hydrogenation process produces a normally solid product by addition of hydrogen to the unsaturated bonds of the product under treatment, with production of more saturated products having higher melting points from the normally liquid constituents of the oil under treatment, the hy drogenation treatment ordinarily has an undesired effect, in that a certain amount of splitting of the neutral oil occurs incident to the hydrogenation step, thereby producing a small amount of fatty acid, and undoing a part of the useful effect of the initial treatment with alkali.

The specifications for acceptable shortening products require that these products contain practically no free fatty acid, a fatty acid content in excess of 0.05% being highly undesirable. In View of this fact, it will be seen that the splitting of the neutral glycerides to form free fatty acid in the hydrogenation process often creates a condition which must be corrected by subsequent treatment. In prior art practice, free fatty acids have been removed from the hydrogenated oil by first mixing with this hydrogenated oil a small amount of alkaline solution (e. 'g:, sodium hydroxide). This operation resultsinneutralization ofthe free fatty acids, but at the same time it results inthe dispersion ofthe r-esultingsoap through the oil in a form which is exceedingly difficult to separate. The oil is ordinarily subjected to a succession of washing. operations with water and brine in order to remove this finely dispersed soap but a certain amount of soap remains in the oil in spite of very intensive efiorts to remove the last traces, and the oil is ordinarily subjected to a final step of :filtration in the presence of'clay in order to free-it adequately of the soap.

The ,above' steps of treatment of the hydrogenated oil with alkali, washing with water and brine; and filtration, result in the loss of a very substantial quantity of the neutral oil. Consideration of the fact that the hydrogenated oil contains only a very small proportion of free fatty acid and that thisioil contains no coloring matter, gums or other foreign matter to be removed, would lead one to the belief that the residual fatty acid could be removed with ease. As

, a matter of fact, however, the loss of oil encountered .in neutralizing this fatty acid is considerably greater'than would be the loss of oil in treatingflcru'de oil having a comparable fatty acid content, even though the function of the alkali treatment of such crude oil would include the steps of removing the red coloring matter and gums, in addition to neutralization of the fatty acidsof the highly impure crude product.

The present invention rests upon the discovery that, by addition'of a very large excess of alkali to the hydrogenated oil, followed by prompt and intensive centrifugation of the resulting mixtureof oil and'soap, the'fatty acid may beneutralized and'the resulting soap adequately removed from the oil with a saving of at least 50% of the oil previously lost in connection with the neutralizing, washing and filtering steps. In the practice of these operations, it is preferable that the centrifuging operation be performed at an elevated temperature (e. g., between and F.). It is preferable that the rate of flow of oil through the mixing and centrifuging apparatus be such that it requires ten minutes or less for any given particle of oil to pass through the system. In the practice of the invention, an enormous molecular excess of alkali should be used. Best results have been obtained in cases in which alkali metal hydroxides (e. g., sodium hydroxide) have been used in aqueous solutions containing between 8 and 20% of alkali metal hydroxide, and in which the molecular excess of alkali iiietal hydroxide over free fatty acid amounted to at least 600%.

In a number of typical runs involving comparison of the results of the practice of the pres- 'ent invention (using a 14% caustic soda solution) with operations of batch neutralizing, washing and filtering as discussed above, a loss of 3% of the neutral oil, as entailed in the batch process, was cut down to 1.5%. At the same time, the acidity of the finished oil was lower in practicing the centrifugal treatment than in practicing the batch treatment.

While I do not Wish to be limited by any theory as to the reasons for the results obtained in the practice of the present invention, it is my opinion that the combination of the electrochemical effects obtained by the use of an enormous excess of alkali, together with the substitution of an enormously stronger force for the force of gravity, results in the separation of soap which cannot be otherwise separated except by elaborate and time-consuming processing which further reduces the yield of neutral oil because of saponification which occurs during the prolonged contact of the oil with soap, alkali and water at the temperatures employed. It may be that the superior results of the present invention are also partially attributable to sharp reduction in the time of contact between the oil and alkali, since the prolonged contact involved in batch procedure results in formation of emulsions which are very difficult to resolve. In any case, it has been discovered that the oil may be more thoroughly neutralized, and the resulting soap adequately removed from the oil, by the sequence of first mixing the oil with a quantity of alkali which is at least seventimes the quantity required for neutralization, and then subjecting the resulting mixture of oil and soap to a centrifugal force which should be at least 5000 times the force of gravity, and in actual practice of the invention has been 15,000 times the force of gravity.

Example A refined and hydrogenated cottonseed oil was subjected to a batch neutralizing and soap removing treatment in accordance with the best known prior art procedure of batch treatment with caustic soda, gravity settling and clay filtration, as discussed above. In this operation, the free fatty acid was reduced from 0.090% to 0.047%, with a loss of 3% of the oil treated.

In a comparative test in which a sample of the same oil was treated in accordance with the present invention by mixing 2 /z% of 20 B. lye with the oil and centrifuging to remove the resulting soap, the free fatty acid was reduced from 0.090% to 0.038%, with a loss of 1.47%.

Modifications will be obvious to those skilled in the art, and I do not therefore wish to be limited except by the scope of the following claims,

I claim:

1. In the separation of free fatty acid from refined, hydrogenated fatty oil, the process comprising mixing the oil with an alkaline solution containing an amount of alkali at least seven times the amount required to neutralize the free fatty acid content of the oil, and thereafter subjecting the resulting mixture of oil and soap to prompt centrifugation to remove the soap from the oil.

2. In the separation of free fatty acid from refined, hydrogenated fatty oil, the process com- ..prising mixing the oil with an alkaline solution containing an amount of alkali metal hydroxide at least seven times the amount required to neutralize the free fatty acid content of the oil, and thereafter subjecting the resulting mixture of oil and soap to prompt centrifugation to remove the soap from the oil.

3. In the separation of free fatty acid from refined, hydrogenated fatty oil, the process comprising rnixing the oil with a sodium hydroxide solution containing an amount of sodium hydroxide at least seven times the amount required to neutralize the free fatty acid content of the oil, and thereafter subjecting the resulting mixture of oil and soap to prompt centrifugation to remove the soap from the oil.

4. A process as defined in claim 2, in which the total period of treatment of the oil by the alkali amounts to not over ten minutes.

5. A process as defined in claim 2, in which a centrifugal force of at least 5000 times the force of gravity is applied to the mixture of the oil and soap to remove the soap from the oil.

6. A process as defined in claim 2, in which the alkali employed to neutralize the free fatty acid of the oil is a sodium hydroxide solution of approximately 14% concentration.

'7. In the separation of free fatty acid from refined, hydrogenated fatty oil, the process comprising mixing the oil with a sodium hydroxide solution of approximately 14% concentration containing an amount of sodium hydroxide at least seven times the amount required to neutralize the free fatty acid content of the oil, and thereafter subjecting the resulting mixture of oil and soap to centrifugation at a centrifugal force of over 5000 times the force of gravity and a temperature of at least F. to remove the soap from the oil, the entire sequence of mixing and centrifuging steps being performed in a period of not more than ten minutes.

ARTHUR U. AYRES.