US2657224A - Refining of fatty oils, especially vegetable oils - Google Patents

Description

Oct. 27, 1953 s. F. N. BIERKE 2,657,224

REFINING 0F FATTY OILS, ESPECIALLY VEGETABLE OILS Filed Sept. 9, 1950 INVENTOR 5vome FHf/viof Ni/ason Bferke Patented Oct. 27, 1953 REFINING OF FATTY OILS, ESPECIALLY VEGETABLE OILS Svante F. N. Bierke, Lidingo, Sweden, assignor to Aktiebolaget Separator, Stockholm, Sweden,

a corporation of Sweden Application September 9, 1950, Serial No. 183,970 In Sweden September 29, 1949 6 Claims.

The present invention relates to the refining of fatty oils, especially vegetable oils, in a continuous process.

The difierent working operations used when refining fatty oils, especially vegetable oils, are already known, and the literature in this art shows that these operations can be arranged in varying sequence with varying temperatures and reaction times for the diiferent operations. Depending upon which of the known methods is used, special advantages are gained, such as a simple plant with subsequent low investment costs, low operating expenses, and the like. The common aim, however, is to obtain as a final product pure oil of good quality.

The process of the present invention differs from previous processes for refining fatty oils, particularly in the temperature ranges, pressures and reaction times used, and in the steps of the process where they are used.

The object of the invention is to provide a continuous process which, in a short time and without interruption, changes crude fatty oil into pure oil with the smallest possible loss of neutral oil; to provide such a process which requires a minimum of neutralizing agent for changing the content of free fatty acids in the oil into soapv stock; and to provide such a process which may be practiced with simple, low-priced apparatus.

The invention is characterized chiefly as follows: Crude fatty oil and water, possibly with some acid or carbohydrate added, are fed continuously into a mixer where they are thoroughly blended, and then, during a reaction time (differing in length with different oils) sufiicient for de-sliming the crude oil, the mixture is led through a vessel so designed that slimy substances are prevented from settling in it, whereupon the mixture is fed through a centrifugal separator in which it is split into a water phase rich in slimy substances, which are led away, and

an oil phase of a slime-free or nearly free nature, which is de-aerated. During this first stage of the process, heat is applied so that the wateroil mixture when entering the separator has a temperature of at least 70 C. After this centrifugal separation, the oil phase, with its temperature principally maintained, and a solution of a substance neutralizing the free fatty acid content of the oil phase, such as caustic soda or other alkali or a product comparable with it in its action, are passed under pressure into a mixer in which, during the lapse of 2 to 5 seconds, they are rapidly and intimately mixed with each other. The ,mixture is then introduced, still in a con- 2 tinuous flow, into a hermetic separator of centrifugal type, in which the mixture is split into a soapstock phase and a refined oil phase, both of which are led away separately. A maximum lapse of time of approximately 40 seconds is allowed from the moment the oil is mixed with the neutralizing agent until the refined oil is led away from the separator.

The de-sliming step, the first step in the refining process, is not in itself novel. It is old, in de-sliming and de-gumming, to mix oil with water in a cold state or at max. 30 C. and, after mixing, pass the mixture through a heating apparatus which raises the temperature to a maximum of C., and then to separate the mixture in a centrifugal separator and thus obtain oil which is mainly slime-free. It is also known in the art that the refining of oil thus obtained can be continued by mixing cold oil with a solution of a neutralizing agent for the free fatty acid of the oil, subsequently heating the mixture to C. during gentle or diminishing stirring, and finally separating it in a centrifugal separator with two outlets, one for the soapstock andone for refined oil.

However, the water requires a certain reaction time to act upon the slimy substances, and during this time a considerable amount of slimy substances will normally precipitate. In order to feed to the centrifugal separator a homogeneous mixture of oil and slime substances and to help bring about a continuous operation, I avoid precipitation of slime substances during a period suitable for the reaction, by conveying the wateroil mixture through a vessel specially installed for this purpose and in which an even flow is maintained, for example, in a vertical direction. The centrifugal separator will then operate smoothly with a constant or nearly constant level between the two liquid components which are separated in the bowl. This condition for the de-sliming constitutes an essential part of the present invention.

After the de-sliming operation, the method of mixing cold oil with a neutralizing medium for the free fatty acid of the oil, heating the mixture during mild turbulence, and separating it in a centrifuge, has proved less advantageous. The cooling of the oil before mixture and the subsequent heating before separation means loss of time and heat. It has been found of more advantage to de-aerate the oil, while maintaining the high temperature of the oil or even raising it further, and then to mix it rapidly and intimately with the neutralizing medium in a closed tank, for 2 to seconds under a pressure of preferably 4-5 l g./cm. While maintaining the pressure, the mixture is led through a hermetic centrifugal separator in which the mixture is split into a soapstock phase and a phase of refined oil, both of which are discharged separately, a maximum period of approximately 40 seconds being allowed to elapse from the moment the oil is mixed with the neutralizing medium until the purified oil is discharged from the separator.

By this method, there is a saving of time and also of part of the heat which, in the prior processes, are required for the cooling and repeated heating of the oil. Also, the apparatus will be simple to use and the initial cost low. Another advantage of this part of the new process is that the mixing of the still hot oil (the temperature of which is slightly below the initial temperature of preferably HP-80 C.) rapidly and intimately with the neutralizing agent in a period of 2 to 5 seconds, and the subsequent centrifugal separation in a hermetic separator, during a maximum period of 40 seconds, results in the neutralizing medium reacting rapidly with the free fatty acids of the hot oil and neutralizing them. By effecting the separation in a hermetic separator immediately after the reaction, the soapstock is separated from the neutral oil as rapidly as it was formed, so that neither the soapstocli nor the neutralizing agent will have time to aifect the neutral oil, at least in any degree worth mentioning, and saponify it. The slime and color substances which may remain in the oil after de-sliming are also attacked by the neutralizing agent and are discharged with the soapstock. The mixture, when introduced into a hermetic separator, is not subjected to a splitting action by the separator, and therefore the formation of inseparable emulsions is prevented. The high pressure and temperature enable the soapstock to be discharged from the separator as a soft sausage-like p'ulp without necessitating special means of dilution. Although the neutralizing medium is used in excess, 1. e. more of it than should be theoretically necessary, its total requirements are, however, small due to the crude oil having first been de-slimed with water, a stage known by itself but used to particular advantage in the present process.

Special importance is attached to the rapid mixingof hot, de-slim'edoil With the neutralizing medium, followed by arapid separation in a hermetic separator. The same good result in the quality and quantity of the oil is not obtained by mixingat lower temperatures and in the usual manner for a period up to minutes duration with subsequent heating and separation in an ordinary separator, or by a slow mixing operation at successively rising temperature, until the stated temperature range is reached, followed by separation in an ordinary separator.

The importance of the rapid and'intimate'mixing of de-slimed oil with the solution of neutralizing agent followed by a separation in a hermetic separator during a maximum period of 40 seconds, can be explained theoretically in the following way:

Each finely divided drop of lye in the oil forms a globule in intimate contact with the free fatty acids of the oil and with the neutral oil. In the first place, the lye in the surface film of the globule reacts with the free fatty acids and forms a soapstock envelope around the globule, while the core'of the'latterconsists of pure lye. In

other words, the free fatty acids diffuse through the envelope of the globule toward its center and are changed into soapstock. Due to the fact that both the soapstock and the lye are alkaline, they are capable of affecting the neutral oil and saponifying it. Of these two, however, the lye has the stronger saponifying action. If there is a long period of reaction between the lye globules, on the one hand, and the free fatty acids and the neutral oil, on the other hand, the lye content of the globule is almost entirely neutralized and a saponification of neutral oil takes place with the soapstocl; and the lye, if the latter is present in excess. If, after the dispersion of the lye drops in the oil, the mixture is subjected to vigorous stirring or a turbulence rendering it possible for a globule surrounded by soapstock to burst into smaller-sized globules, this means that lye comes in contact with the oil already nearly free of free fatty acid, and saponifies it. Each bursting of the lye globules, once they are dispersed in the oil, is therefore detrimental, as is each prolongation of the reaction time beyond a fixed length of time. Accordingly, it is essential that the lye is dispersed in the oil, from the start, as rapidly and in as small globules as possible so that the reaction may set in immediately and simultaneously in the entire cross section of the oil flow and continue during the fixed length of time without the risk of the globules bursting. The reaction is then rapidly interrupted by separation, and part of the reaction may take place in the separator itself, which is of the hermetic type so that it will not cause the globules to burst.

A process according to the invention, for continuously refining vegetable oil, is described in detail in the following, reference being made to the attached drawing in which the single illustration is a diagrammatic view of an apparatus for use in practicing the process.

Referring to the drawing, the oil to be refined is led by pump E through pipe 2 to and through heater 3, in which the oil is heated to a temperature of -80 C. In counter-current to the oil, a heating medium flows into the heater via pipe i and out through pipe 5. From the heater 3, the hot oil fiows through a hand-regulated valve ii into a mixer '7. Water at the prevailing temperature is led into mixer 7 through pipe 8, which is fitted with a hand-regulated valve =9. The quantity of water added to the oil in mixer l amounts to 2 to 5% by volume of the oil and is preferably in excess of the quantity required theoretically for de-sliining the oil. Due to the water quantity being so "small, its addition means but a small reduction in the temperature of the mixture in relation to the temperature of the oil before mixing. The mixing is effected quickly and efficiently in'the mixer "i, which conveys the mixture to the top part of a vessel it. The latter comprises a closed vertical tube of a diameter and height calculated so that the mixture will flow continuously from the top part to the 'bottompart'of thetube during the required reaction time between the water and the slime 'matter :of the oil and at a speedat least egual to the settling speed of the slime substances (information or already formed) 'in .the oil. The reaction time varies for different oils, and the time of sojourn in vessel H3 is as a rule about 30 minutes, "not more. From vessel '5 ii, the mixture is'led through ashort'pipe "II to separator 12, which is'o'fthe centrifugal type. "In the latter, the mixture is separated into a water-phase of -s1imysubs'tances,

discharged through pipe I3, and a substantially slime-free oil phase, which flows out through pipes M and i5 to a heater IS. The oil passes through heater I6 in counter-current relation to a heating medium fed in through pipe I! and discharged through pipe is. While the heater i6 is not necessary, in certain cases it is advantageous and brings the oil to a temperature of between 70-80 C. and substantially compensates for the fall in temperature in the previous apparatus. From heater I6, the oil flows to a de-aeration unit l9, where it is freed from possible air bubbles and other gases. The de-aerator l9 may be arranged in advance of the heater I6, if any. In certain cases, the unit Hi can be dispensed with, if de-aeration is eifected in some other way at this point in the process. The oil is then conveyed by a pump 20, under a pressure of 4.-5 kg./cm. into a mixer 2| fitted with a pipe 22 through which, at the same pressure, a pump 23 feeds to the mixer 2| a solution of a neutralizin medium for the free fatty acids of the oil. The neutralizing agent may be caustic soda or some other alkali or comparable product of the desired neutralizing quality. The neutralizing agent is added in a quantity fixed in relation to the quantity of oil flowing per unit of time and its free fatty acid content, but the quantity of neutralizing agent is in excess of that required theoretically. In the mixer 2|, the oil and the neutralizing agent are mixed rapidly and thoroughly for 2 to 3 seconds while the temperature is maintained. There may, however, be a slight reduction of temperature caused by the neutralizing agent, which is generally added at normal temperature. The mixture is then passed through a short pipe 24 into a hermetic separator 25 of the centrifugal type, where it is separated into a soapstock phase within a period not exceeding 30 seconds, and a refined oil phase. The soapstock is discharged through p'pe 26 and the oil through pipe 21.

The purified oil produced according to the invention has proved to be fully comparable to the oils produced from the same initial material with the best current methods, but it is produced more quickly and simply with lower installation and operating costs.

As with other methods used for refining oils of the kind under consideration, the oil obtained by the present method can be further refined by subsequent treatments.

I claim:

1. A method of refining fatty oils in a continuous flow, which comprises feeding a stream of the crude oil and a stream of Water to a mixing zone and there effecting an intimate mixture of the oil and water, feeding the mixture from said zone through a reaction zone for a period suflicient to de-slime the crude oil and while maintaining the mixture continuously in motion to prevent settling of slimy substances in said mixture, passing the mixture from the reaction zone to a centrifugal separator at a temperature of at least C. and there separating it into a water-phase rich in slimy substances and a substantially slime-free oil-phase, separately discharging said phaSes from the separator, deaerating the oil-phase, feeding to a second mixing zone, under pressure, a stream of the oilphase at substantially said temperature and a stream of a neutralizing agent for the free fatty acids in the oil, quickly and intimately mixing said agent and oil phase in the second mixing zone under a superatmospherie pressure for a period not exceeding 2 to 5 seconds, passing the mixture from said last zone through a closed path into a hermetic centrifugal separator and there separating it into a soapstock-phase and a refined oil phase, and separately discharging said last phases from the hermetic separator, the maximum period elapsing from the moment the oil is mixed with said agent until the refined oil phase is discharged from the hermetic separator being approximately 40 seconds.

2. A method according to claim 1, in which the water is added to the oil in the first mixing zone in an amount in excess of the amount theoretically required for de-sliming the oil.

3. A method according to claim 1, in which the crude oil is heated to 7080 C. before it is mixed with the water in said first zone.

4. A method according to claim 1, in which the mixture of crude oil and water is led through said reaction zone in a generally vertical direction at a speed at least equal to the settling speed of the slimy matter in the oil.

5. A method according to claim 1, in which the de-slimed oil-phase from the first separator is heated to at least 70 C. before it is mixed with said neutralizing agent.

6. A method according to claim 1, in which the de-slimed oil and said agent are mixed together in the second mixing zone under a pressure of 4 to 5 kg./cm. the de-slimed oil and agent being introduced separately under pressure into the second mixing zone.

SVANTE F. N. BIERKE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,157,069 Clayton May 2, 1939 2,182,755 Clayton Dec. 5, 1939 2,219,968 Thurman Oct. 29, 1940 OTHER REFERENCES M. K. Schwitzer, Ind. Chemist. 25,352-53 (1949).

Bailey, Industrial Oil and Fat Products (2nd Edition) 1951, pages 638-39.

Claims (1)

1. A METHOD OF REFINING FATTY OILS IN A CONTINUOUS FLOW, WHICH COMPRISES FEEDING A STREAM OF THE CRUDE OIL AND A STREAM OF WATER TO A MIXING ZONE AND THERE EFFECTING AN INTIMATE MIXTURE OF THE OIL AND WATER, FEEDING THE MIXTURE FROM SAID ZONE THROUGH A REACTION ZONE FOR A PERIOD SUFFICIENT TO DE-SLIME THE CRUDE OIL AND WHILE MAINTAINING THE MIXTURE CONTINUOUSLY IN MOTION TO PREVENT SETTLING OF SLIMY SUBSTANCES IN SAID MIXTURE, PASSING THE MIXTURE FROM THE REACTION ZONE TO A CENTRIFUGAL SEPARATOR AT A TEMPERATURE OF AT LEAST 70* C. AND THERE SEPARATING IT INTO A WATER-PHASE RICH IN SLIMY SUBSTANCES AND A SUBSTANTIALLY SLIME-FREE OIL-PHASE, SEPARATELY DISCHARGING SAID PHASES FROM THE SEPARATOR, DEAERATING THE OIL-PHASE, FEEDING TO A SECOND MIXING ZONE, UNDER PRESSURE, A STREAM OF THE OILPHASE AT SUBSTANTIALLY SAID TEMPERATURE AND A STREAM OF A NEUTRALIZING AGENT FOR THE FREE FATTY ACIDS IN THE OIL, QUICKLY AND INTIMATELY MIXING SAID AGENT AND OIL PHASE IN THE SECOND MIXING ZONE UNDER A SUPERATMOSPHERIC PRESSURE FOR A PERIOD NOT EXCEEDING 2 TO 5 SECONDS, PASSING THE MIXTURE FROM SAID LAST ZONE THROUGH A CLOSED PATH INTO A HERMETIC CENTRIFUGAL SEPARATOR AND THERE INTO A HERMETIC CENTRIFUGAL SEPARATOR AND THERE FINED OIL PHASE, AND SEPARATELY DISCHARGING SAID LAST PHASES FROM THE HERMETIC SEPARATOR, THE MAXIMUM PERIOD ELAPSING FROM THE MOMENT THE OIL IS MIXED WITH SAID AGENT UNTIL THE REFINED OIL PHASE IS DISCHARGED FROM THE HERMETIC SEPARATOR BEING APPROXIMATELY 40 SECONDS.

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