US2035589A - Process for refining vegetable and animal oils and fats - Google Patents

Description

Patented Mar. 31, 1936 UNITED STATES PATENT OFFICE .rnoosss Fon REFINING VEGETABLE AND on.s AND FATS No Drawing.

Application September 9, 1933,

Serial No. 688,861. In Germany April 28, 1933 8 Claims.

This invention relates to a process for refining vegetable and animal oils and fats, and more particularly to that stage in the refining of said oils and fats which is designed to separate the impurities-mucins, phosphatides, bitter principles and so forth-present in the crude oils, and to remove the free fatty acids. r

The processes hitherto employed for this purpose have the defect in practice that the losses of neutral oil are comparatively heavy. Said losses are chiefly due to the circumstance that the resulting soapstock contains large quantities of neutral oil, or that much of e neutral oil is decomposed during neutralization. In resolving such soapstocks with acids, it usually happens that mixtures of neutral oil and fatty acids-often termed soap oils-are formed, which contain large quantities of neutral oil. Since high-grade distillation fatty acids have been successfully produced by the process of distillation in a. high vacuum, there has been an increasing tendency in practice to subject soap oils-which are usually dark coloured and often extensively contaminated by impurities-to distillation. In order to render the soap oils, with a high content of neutral oil, more suitable for distillation, it is necessary to split the contained neutral oil by the Twitchell process, or in an autoclave. This splitting is expensive and in addition, it transformsthe more valuable neutral oil into less valuable free fatty acids.

In order to reduce or prevent this expense and loss, endeavours should be made in refining fats and oils, to recover as much as possible of the neutral oil as such, so that only a minimum amount of neutral oil is retained in the soapstock. If possible, this soapstock should be of such a character that it will furnish, when resolved with acid, high grade fatty acids which are directly suitable for distillation without expensive splitting. In order to prevent saponification of the neutral oil in refining, the neutrallization should be performed at the lowest possible temperature.

It is known that the neutral oil can be recovered from the soapstock by dissolving the soap in aqueous alcohol. In so doing, however, a certain amount of neutral oil also dissolves in the aqueous alcohol, and moreover, a portion of the impurities in the soapstock passes into the recovered oil. Consequently, impure oils are obtained, which have to be refined again. It is also known that fatty acids can be separated from oils and fats by means of alcohol, but at the same time large quantities of neutral oils and fats also dissolve in the alcohol. When aqueous alcohol is employed, considerable difiiculties also arise in separating the alcoholic solution of the fatty acids from the undissolved neutral oil, owing to the small difference in their specific gravities and to the presence of mucinous substances and the like. There is moreover, the further disadvantage that alcoholic solutions of caustic alkalis extensively and quickly saponify neutral oil as well as the fatty acids.

In consequence of these diflicuties neither the refining of oils and fats by means of alcohol nor with alkalis in alcoholic solution and the recovery of the neutral oil from the soapstock by means of alcohol has made headway in practice.

It is also known to effect the neutralization of oils or fats by means of a solution of ammonia in aqueous alcohol, which is stated to separate the oil and soap solution rapidly and in welldefined layers and to furnish comparatively pure fatty acids after the water, alcohol and ammonia have been driven off by distillation. It was also proposed to effect the decolorization of the oils and fats at the same time, by the addition of small quantities of ammonium chloride to a neutralizing agent of the above type. On the other hand, the addition ,of small-quantities of sodium sulphate is said to neutralize and demucinize the oils and fats more rapidly and thoroughly when a solution of ammonia. in aqueous alcohol is employed as the neutralizing agent. Nevertheless, the use of ammonia has the drawback of requiring a closed apparatus for the neutralization. In consequence of these and other drawbacks,

plants operated in accordance with such processes have had to close down.

It has now been ascertained in accordance with the present invention that a strong, preferably saturated, solution of salts, for example metallic salts such as common salt and sodium sulphate, inmore particularly. aqueousalcohol (for example, of 50 to 80% strength), does not dissolve either neutral oil or fatty acids, whereas thesoaps formed in neutralizing oils and fats with alkali solutions are dissolved by such an alcoholic solution of salts (salts of alkali metals especially) which do not form with fatty acids any compounds that are insoluble in water, alcohol or aqueous alcohol. Moreover, alcoholic soap solutions are able to dissolve considerable quantities of alkali salts, without any separation of soaps. This solubility is particularly good when the temperature is raised somewhat higher than room temperature, for example to 35 to C. Finally, it has transpired that mucinous substances, phosphatides, bitter principles and the like, which have been separated from oils and fats by preliminary refining processes-such as heating, or by treatment with acids, electrolytic saline solutions and similar substances--are not redissolved during the subsequent neutralization of the free fatty acids by means of alkali, and during the separation of the soaps from neutral oil by means of alcoholic solutions of salts that do not form compounds insoluble in fatty acids, the said impurities remaining in suspension, in the same, or nearly the same, flocculent condition in the soap solution-not in the neutral oilin which they were separated out in the preliminary refining process.

On the basis of these discoveries, the refining of vegetable or animal fats and oils is effected according to the present invention, by intimately mixing the soaps produced by neutralization with alkalis, with alcohol containing in solution a salt that does not form insoluble compounds with oils and fatty acids. The alcohol may contain larger or smaller amounts of water, a consideration which apart from the question of cost, has also the advantage of increased capacity for dissolving salts and fatty-acid soaps. The chief salts to be considered are alkali salts (including ammonium salts) such as sodium sulphate, common salt, saltpetre, or also salts (such as alkali acetates) of organic acids. The treatment may be performed at ordinary temperature, but preferably at 25 to 70 C., and is continued until the soap is dissolved and the mixture of neutral oil, soap solution and (if necessary) any other substances present, such as mucinous substances, phosphatides, bitter principles, and like impurities, resembles an emulsion. On being then left to stand, the neutral oil separates very quickly from the soap solution and a pure neutral oil is obtained together with a soap solution that contains practically the whole of the impurities present. The neutral oil and soap solution can be efliciently separated for example, by clecantation and the losses ofneutral oil occurring in the process of the present invention are incomparably small.

The following methods of carrying out the present process show that it can be modified in many respects and thereby adapted most favourably to suit the special requirements of practice in all cases.

In order to refine crude oils or fats, the first step consists in separating the impurities, such as mucinous substances, phosphatides, bitter principles and so forth, present in colloidal solution, by means of acids, electrolytic saline solutions or the like. The granular; flakes fioat in the refined oil. The free fatty acids are then neutralized with alkalis. When acids are employed for separating the mucinous substances and the like, they must be borne in mind in calculating the amount of alkali needed for neutralization. During the neutralization, small granular flakes of soap are formed. The oil is next actively stirred with a mixture of aqueous alcohol and a saline (especially electrolytic) solution which does not form solid compounds with fatty acids and neutral oil, the amount of said solution being sulficient to dissolve the soap flakes at the Working temperature selected. After stopping the stirrer mechanism, the separated impurities are taken up by the alcoholic soap solution, whilst this latter separates from the neutral oil. Since alcohol also dissolves bitter principles, such of these 1atter as have not already been rendered insoluble neutral oil.

by the alkali treatment are also separated from the neutral oil. Any small quantities of phosphatides and the like which have not been eliminated from the neutral oil by the preliminary refining also pass into the alcoholic solution, whereas on the contrary, neutral oil is not dissolved by the alcoholic solution employed according to the invention. The specific gravity of the alcoholic soap solution is increased by the saline content, thus also tending to improve and accelerate the separation between the soap solution and the The liquid alcoholic solution of soap and salts, in which the impurities separated from the crude oil are also present, separates definitely from the neutral oil and contains only very small quantities of the latter. Consequently, the present process furnishes an excellent yield of pure, high-grade neutral oil, and a soapstock that is almost entirely free from neutral oil. After the alcohol has been distilled off and the soap resolved with acid, this soapstock yields a very high-percentage fatty acid, directly suitable for distillation. The alcohol is recovered from the soap solution either directly by distillation or the alcoholic soap solution is resolved with mineral acid, into a mixture of soap and fatty acid, the alcohol being then distilled off. The conditions in each case will determine which method is preferable-for recovering the alcohol, in respect of yield, safety and convenience in operating and so forth.

After being separated by a known process of preliminary refining, the impurities contained in the crude oil may also be removed from the oil at once. Thereupon, the free fatty acid contained in the refined oil is saponifiedwith an alkali solution and the soap flakes are brought into solution in a suitable alcoholic saline solu tion according to the invention. After separating the soap solution from the neutral oil, distilling off the alcohol and decomposing the soap with acid, a pure and very high-grade fatty acid is then obtained, which can also be satisfactorily employed in the soap industry, directly that is, without any previous distillation.

The crude oil may also be neutralized with an alkali solution, without any previous refining, and the soap fiakes-which will have absorbed most of the impurities of the crude oil,can be brought into solution by an alcoholic'saline solution. The yields of neutral oil are also still very good though not so high as in the firsttwo operative methods.

Crude oil, or pre-reflned oil from which the separated impurities such as mucinous substances and the like have been removed or are still remaining therein, can also be neutralized with a mixture of alkalis and alcoholic saline solution. In such case, the soaps formed in the neutralization of the free fatty acids are brought into solution at once. To minimize decomposition of the neutral oil, it is advisable, in these circumstances, to employ an alkali carbonate, or a mixture of alkali carbonate and hydroxide, as the neutralizing agent. In this case, also, the yields of neutral oil are better when pre-refining processes have been applied.

Another method of carrying out the invention consists in first treating the crude or pre-refined oil with the alcoholic saline solution and neutralizing with an alkali solution afterwards.

Alternately, after being neutralized with alkali solution, the oil may first be treated with the alcohol, the salt being then added, for example,

Again, the crude or Dre-refined oil can first be crude or pre-refined oil are neutralized with sodium carbonate solutions in conjunction with or succeeded by the application of. a vacuum or high vacuum, the object of which is to render the neutralization as extensive as possible, and to dry the soap (German specification No. 437,520). After relieving the vacuum, the soap flakes floating in the oil are brought into solution in a mixture of aqueous alcohol and saline solution and the neutral oil is separated from the soap in the manner hereinbefore described. In addition to providing an important increase in the yields of neutral oil, this procedure offers the advantage Over the known neutralization in vacuo, that the troublesome and expensive separation of the soap by filtration, and blowing the soap out of the filter press with air-which may oxidize the soap-are avoided.

In many processes for distilling-off the free fatty acids contained in oils and fats, oils are obtained which still contain a certain quantity of free fatty acids and hydroxy-fatty acids, which latter moreover, cannot be eliminated from oils and fats by distillation. According to the pres-- ent invention, the fatty and hydroxy-fatty acids still present in such oils and fats, are neutralized with alkali solutions, the soap being brought into solution by an alcoholic saline solution and after separation, from the neutral oil, subjected to further treatment.

The process according to the invention can also be applied to the treatment of the soapstocks resulting from the neutralization of the oils and fats, after the same have been separated from the neutral oil by decantation, filtration, centrifuging and the like. With this object, the soapstocks are well mixed with a mixture for example, of dilute alcohol and alkali-salt solution, in order to bring the soap into solution. The neutral oil that was contained in the soapstock separates cleanly above the heavy alcoholic soap solution and is then removed from the latter, which for further treatment, can be decomposed with acid, either before or after the alcohol is distilled oiT. In this case, also, very high-percentage fatty acids are obtained.

The expression alcoholicv saline solution frequently used in the foregoing, is of course, not to be construed as meaning saline solutions generally, but as being restricted to the definition hereinbefore given, namely, alcoholic solutions of salts which do not form insoluble compounds with neutral oils and fatty acids, these solutions containing considerable amounts of salts or even being saturated therewith.

Furthermore, "alcoholic solution must be regarded as comprising not only a solution in pure ethyl alcohol, but also those in other alcohols such as methyl alcohol, that dissolve soaps, but not neutral oil, or in mixtures of alcohols which satisfy the same conditions. As already mentioned, it is advisable in many cases to employ alcohol diluted with water, since the water-content further reduces the solubility of the neutral oils in alcohol and improves the solubility of the soap together in many instances, that of the saltemployed according to the invention.

Example I 1500 grms. of raw cottonseed oil having an acid value of 4.0, are heated to 25 C. in a. glass beaker, and 6 cc.' (0.4% by volume) of 50% sulphuric acid and 6 cc. of a concentrated solution of Glauber salt are stirred in. The impurities such as phosphatides, mucinous substances and the like, in colloidal solution in the oil, soonseparate out in the form' of granular flakes which float in the oil. A Be solution of caustic soda is thereupon stirred-in in sufficient quantity to neutralize both the excess of sulphuric acid still present in the oil, and the free fatty acids. Small granular soap flakes are formed. The oil is then heated to 50 to 55 C., stirring being continued and is treated with 150 cc. of a mixture consisting of 90 cc. of 50% alcohol and 60 cc. of a'coldsaturated solution of Glaubers salt.- Active mix ing is continued for 15 minutes, the soap flakes passing into solution. After stopping the stirring mechanism, the alcoholic solution of Glaubers salt and soapcontaining also the separated impurities-settles down in the bottom of the beaker as a layer with a sharp line of demarcation in relation to the neutral oil and almost free from any of the latter. This solution is separated from the neutral oil and is treated either before or after the alcohol has been distilled off, with acid in order to decompose the fatty acid soaps.

Example II 6400 kgs. of demucinated ground-nut oil, containing' 3.6% of free fatty acids, is drawn into a vacuum apparatus and heated to 35 C. under a good vacuum and being stirred the while. 162 kgs. of sodium carbonate solution, containing 54 kgs. of NaaCOs are then drawn into the oil, active stirring being continued. After the solution has been drawn in, a high vacuum is generated in the apparatus and the temperature of the oil is raised to 45 C. After "stirring for half an hour longer, the vacuum is relieved. The fine-grained soap flakes float in the clear oil. which is next treated with an addition of 805 kgs. of a mixture consisting of 460 kgs. of aqueous (50%) alcohol and 345 kgs. of a concentrated solution of common salt, and thoroughly mixed According to the present invention, the alcoholic saline solution is preferably employed in a concentrated form, for example, cold-saturated or nearly so. The concentration may be so high that salts or soaps separate out when the alcoholic solution of salt and soap is cooled below the temperature at which the soap was dissolved. It is namely, possible to separate the neutral oil from the soap solution without further measures before such cooling and its accompanying depositions occur. If, in such event, deposits are found in the soap solution separated from the neutral oil, these deposits are no longer a cause of trouble, being easily rendered harmless by-known means, such as decompositionof the soaps, distilling-01f the alcohol, or the like.

contains 40-60 percent of alcohol.

3. Process according to claim 1, in which the salt solution is nearly saturated.

4. Process according to claim 1, wherein the oil or fat mixture is dried in a vacuum before dissolving the soaps.

5. In a process of purifying vegetable and animal oils and fats involving neutralization of the free fatty acids therein with a basic alkali metal compound with resultant formation of soaps, the step which comprises dissolving the soap from the mixture of oil or fat and soap with a mixture of alcohol and a concentrated aqueous solution of such alkali metal salts as do not form insoluble fatty acid compounds allowing the mixture to stratify into two layers and separating the layer of soap solution from the layer of neutral oil or fat. a

6. The process of purifying vegetable and animal oils and fats which comprises precipitating the albuminous and mucilaginous substances and similar impurities, separating the precipitated substances and the precipitating agent from the oil or fat, neutralizing the free fatty acids with a basic alkali metal compound, dissolving the resulting soaps in a mixture of alcohol and a concentrated aqueous solution of such alkali metal salts as do not form insoluble fatty acid compounds, allowing-the mixture to stratify into two layers and separating the layer of soap solution from the layer of neutral oil or fat.

7. A process of purifying vegetable and animal oils and fats which comprises mixing therewith alcohol, a concentrated aqueous solution of such alkali metal salts as do not form insoluble ,fatty acid compounds and a quantity of a basic alkali metal compound sufiicient to neutralize the free fatty acids whereby a solution of the resulting fatty acid soaps is formed, allowing the mixture to stratify into two layers and separating the layer of soap solution from the layer of oil or fat.

8. Process according to claim 1, wherein the constituents of the solvent are added individually.

o'rro BRI'icKE.