Process for extracting fatty acids from triglyceride oils

Abstract

A process which can extract a fatty acid from a triglyceride oil includes (a) contacting a triglyceride oil T1 made of a fatty acid with an aqueous solution W1 made of a quaternary ammonium salt and an aliphatic diol having 1 to 8 carbon atoms, where a triglyceride oil phase T2 and an aqueous phase W2 are obtained, where T2 has a reduced content of fatty acids compared to T1 and W2 has an increased content of fatty acids compared to W1; and (b) separating the triglyceride oil phase T2 from the aqueous phase W2. The quaternary ammonium salt includes a quaternary ammonium cation and a basic anion selected among hydroxide, alkoxide, alkyl carbonate, hydrogen carbonate, carbonate, serinate, prolinate, histidinate, threoninate, valinate, aspartate, taurinate, and lysinate.

Description

This application claims priority to European Patent Application No. 17201077.9, filed on Nov. 10, 2017.

The invention relates to an improved process for extracting fatty acids from triglyceride oils. The extraction of the triglyceride oil is carried out in this case with an aqueous solution comprising at least one quaternary ammonium salt and at least one aliphatic diol comprising 1 to 8 carbon atoms. The process according to the invention is characterized by high efficiency.

BACKGROUND OF THE INVENTION

Natural fats and oils have various undesirable components such as metals, free fatty acids and phospholipids and therefore have to be refined. In the refining of natural fats and oils, a distinction is made between physical and chemical refining.

In the case of chemical refining, which is used predominantly for triglyceride oils having a low fraction of free fatty acids, the free fatty acids are separated off by reaction with a base. So-called soapstocks are formed in this case, an aqueous mixture of base, free fatty acids, the salts of the free fatty acids and also oil. These soapstocks are an undesired by-product of chemical refining which are of low value and limited use.

In the case of physical refining, which is used predominantly for triglyceride oils having a relatively high fraction of free fatty acids, the free fatty acids are in contrast separated off thermally. In this way, the formation of soapstocks may be avoided, but at the same time high temperatures (up to 260° C.) have to be applied in order to be able to separate off the free fatty acids from the oil by distillation.

In addition to chemical and physical refining, other methods are described in the prior art by which free fatty acids may be separated off or soapstocks may be processed. For example, liquid-liquid extraction techniques are used here (C. E. C. Rodrigues, C. B. Gonçalves, E. Batista, J. A. Meirelles, Recent Patents on Engineering 2007, 1, 95-102).

WO 2016/149692 A1 describes the acidification of aqueous solutions which originate from saponification reactions and comprise lipids. The lipid-containing raw material is mixed with base (especially sodium or potassium hydroxide) and saponified. CO₂ is then injected, reacted with the reaction mixture and the aqueous phase is removed.

In addition, U.S. Pat. No. 2,771,480 also describes the regeneration of fatty acids by means of ion exchangers. This, however, is very costly.

CN 106281672 A describes the treatment of triglyceride oils with antioxidants (e.g. tocopherol, lactate) and alkali metal salts thereof for removing trichloropropanol and derivatives thereof.

WO 2012/031176 A1, WO 2016/189114 A1, WO 2016/189115 A1 and WO 2016/189328 A1 describe the treatment of triglyceride oils with quaternary ammonium salts and solutions thereof for removing free fatty acids, metals and other undesirable components.

In WO 2016/189114 A1, a triglyceride oil is extracted with an aqueous solution of a basic quaternary ammonium salt in order to remove fatty acids therefrom. After extraction, the phases are separated. To regenerate the aqueous solution, which is necessary in order to be able to use this in a new extraction step of the process, this aqueous phase, charged with fatty acid salts from the triglyceride oil, is pressurized with CO₂. Free fatty acids are formed from the fatty acid salts as a result, which may be separated off from the aqueous phase.

Although WO 2016/189114 A1 discloses a reliable method for extracting free fatty acids from triglyceride oils, this method has a problem, especially in industrial scale applications. Quaternary ammonium salts are surface-active and are frequently used as cationic surfactants in soaps and fabric softeners. Their removal after treatment of triglyceride oils is therefore technically very demanding right from the start since they emulsify with water and oil and complicate the phase separation. The quaternary ammonium salts used in the extraction of the fatty acids from the triglyceride oil can therefore only be removed with difficulty, or not completely removed, from the triglyceride oil.

This is especially disadvantageous when using the extracted triglyceride oils as edible oils: not only are some quaternary ammonium salts of concern to health, quaternary ammonium salts, and especially choline, also have the tendency to a foul smell and sometimes even dark-colored deposits. This causes a distinct reduction in quality of the extracted oil. It is therefore desirable to further improve the extraction technique of the prior art (e.g. WO 2016/189114 A1).

It is therefore an object of the present invention to provide a process for extracting fatty acids from triglyceride oils which does not have the aforementioned disadvantages.

Above all, a process should be provided which allows reuse of the phases and at the same time ensures high quality of the extracted triglyceride oil.

DETAILED DESCRIPTION OF THE INVENTION

It has now been found that, surprisingly, when extracting triglyceride oils with ammonium salts, the fraction of quaternary ammonium salt in the extracted oil can be lowered significantly if an aliphatic diol having 1 to 8 carbon atoms is added to the quaternary ammonium salt, wherein ethylene glycol and propanediols, especially ethylene glycol and 1,2-propanediol, are most suitable.

Accordingly, the invention relates to a process for extracting fatty acids from triglyceride oils comprising the following steps:

(a) contacting a triglyceride oil T₁ comprising fatty acids with an aqueous solution W₁ comprising at least one quaternary ammonium salt and at least one aliphatic diol having 1 to 8 carbon atoms, whereby a triglyceride oil phase T₂ and an aqueous phase W₂ are obtained, wherein T₂ has a reduced content of fatty acids compared to T₁ and W₂ has an increased content of fatty acids compared to W₁;(b) separating the triglyceride oil phase T₂ from the aqueous phase W₂:wherein the quaternary ammonium salt comprises at least one quaternary ammonium cation and at least one basic anion selected from hydroxide, alkoxide, alkyl carbonate, hydrogen carbonate, carbonate, serinate, prolinate, histidinate, threoninate, valinate, aspartate, taurinate, lysinate.

In the context of the invention, the term “quaternary ammonium cation” means a cation having at least one nitrogen atom and one positive charge, in which said nitrogen atom is only bonded to carbon atoms. The nitrogen atom may be saturated and may be bonded to 4 carbon atoms by single bonds, or it may be unsaturated and be bonded to two carbon atoms by a single bond and to a third carbon atom by a double bond.

If the nitrogen atom is unsaturated, it may also be part of a heteroaromatic ring such as, for example, an imidazolium cation or a dialkylimidazolium cation (e.g. 1-methyl-3-ethylimidazolium cation, 1,3-dimethylimidazolium cation, 1,3-diethylimidazolium cation).

If the nitrogen atom is saturated, it may also be part of an alicyclic ring, for example a pyrrolidinium ring or piperidinium ring.

Advantageously, the nitrogen atom is bonded to 4 substituted or unsubstituted hydrocarbon groups having 1 to 12 carbon atoms, wherein these hydrocarbon groups may bear further substituents, wherein these substituents are preferably on carbon atoms which are not bonded to the positively charged nitrogen atom.

In the context of the invention, hydrocarbon group preferably means alkyl, cycloalkyl, alkenyl, alkynyl or aryl.

The quaternary ammonium salt in the present invention is advantageously and preferably used as a liquid which comprises the salt. It is not volatile and exists as part of the liquid only in its ionic form.

The liquid is preferably the solution of the salt in a solvent, for example water.

Possible solvents are selected from polar solvents such as water, ethanol, methanol or mixtures thereof for example. Preference is given to using water as solvent. The quaternary ammonium salt may be an ionic liquid.

The expression ionic liquid is known to those skilled in the art and is described, for example, in U.S. Pat. No. 7,638,636 B2.

The quaternary ammonium cation is preferably selected from a compound according to the structure[N(R^a)(R^b)(R^c)(R^d)]⁺,where R^a, R^b, R^c and R^d are each independently selected from C₁ to C₈ alkyl, wherein one or more of the radicals R^a, R^b, R^c and R^d may optionally be substituted on one carbon atom, which is preferably not bonded directly to the positively charged nitrogen, by a group selected from: C₁ to C₄ alkoxy, C₂ to C₈ alkoxyalkoxy, C₃ to C₆ cycloalkyl, —OH, —SH, —CO₂R^e, and —OC(O)R^e, where R^e=C₁ to C₆ alkyl. For example, it may be substituted by one to three OH groups.

The quaternary ammonium cation is more preferably selected from a compound according to the structure[N(R^a)(R^b)(R^c)(R^d)]⁺,where R^a, R^b, R^c and R^d are each independently selected from C₁ to C₄ alkyl, including methyl, ethyl, n-propyl, isopropyl, n-butyl, se-butyl, isobutyl and tert-butyl, wherein at least one of the radicals R^a, R^b, R^c or R^d may be substituted on one carbon atom, which is not bonded directly to the positively charged nitrogen, by an OH group. Substituted radicals R^a, R^b, R^c or R^d are preferably 2-hydroxyethyl, 2-hydroxypropyl or 2 hydroxy-2-methylethyl.

The quaternary ammonium cation most preferably used is choline: (CH₃)₃N⁺CH₂CH₂OH.

The quaternary ammonium salt comprises in addition at least one basic anion selected from hydroxide, alkoxide, alkyl carbonate, hydrogen carbonate, carbonate, serinate, prolinate, histidinate, threoninate, valinate, aspartate, taurinate, lysinate.

In one embodiment, the basic anion is selected from alkyl carbonate, hydrogen carbonate, carbonate, hydroxide, alkoxide. More preferably, it is selected from alkoxide, hydrogen carbonate, alkyl carbonate and carbonate; most preferably hydrogen carbonate.

If the basic anion is selected from alkoxide or alkyl carbonate, the alkyl group is unbranched or branched and substituted or unsubstituted. It is preferably unbranched and unsubstituted.

An alkyl group in accordance with the invention preferably comprises 1 to 10 carbon atoms, more preferably 1 to 8, most preferably 1 to 4 carbon atoms. The alkyl group may be selected from methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl. Also usable are branched alkyl groups such as isopropyl, isobutyl, sec-butyl, tert-butyl. The alkyl group is particularly preferably selected from methyl, ethyl, propyl, butyl, more preferably selected from methyl, ethyl.

Particularly preferred in the process according to the invention is a quaternary ammonium salt which comprises a choline cation.

Very particular preference is given to using in the process according to the invention a quaternary ammonium salt which is selected from choline hydrogen carbonate: (CH₃)₃N⁺CH₂CH₂OH HOCOO⁻; choline hydroxide: (CH₃)₃N⁺CH₂CH₂OH OH⁻, choline alkyl carbonate: (CH₃)₃N⁺CH₂CH₂OH ROCOO⁻ where R is an alkyl group having in particular 1 to 4 carbon atoms and more preferably 2 to 3 carbon atoms. Most preference is given to using choline hydrogen carbonate: (CH₃)₃N⁺CH₂CH₂OH HOCOO⁻.

The solution W₁ used in step (a) of the process according to the invention also comprises at least one aliphatic diol having 1 to 8, in particular 1 to 6, preferably 1 to 5, more preferably 1 to 4, even more preferably 1 to 3 carbon atoms, wherein said diol is particularly preferably selected from the group consisting of ethylene glycol (=1,2-ethanediol), propanediols, and more preferably from ethylene glycol and 1,2-propanediol.

In accordance with the invention, “propanediol” means any propane bearing 2 OH groups, no matter on which of the carbon atoms, preferably 1,2-propanediol or 1,3-propanediol.

An aliphatic diol having 6 carbon atoms is preferably 1,6-hexanediol.

By way of preference, in the aqueous solution W₁ in step (a) of the process according to the invention, the proportion of aliphatic diol relative to quaternary ammonium salt is such that the molar amount of all aliphatic diols having 1 to 8 carbon atoms, based on the molar amount of all quaternary ammonium salts, wherein the quaternary ammonium salt comprises at least one quaternary ammonium cation and at least one basic anion selected from hydroxide, alkoxide, alkyl carbonate, hydrogen carbonate, carbonate, serinate, prolinate, histidinate, threoninate, valinate, aspartate, taurinate and lysinate, is in the range from 0.0001% to 99.9%, preferably 0.01% to 50.0%, more preferably 0.1% to 40.0%, even more preferably 1.0% to 30.0%, most preferably 10.0% to 20.0%, especially preferably 15.3% to 18.8% and at best 17.6%.

In a preferred embodiment, the process according to the invention includes step (c):

(c) adding CO₂ and optionally an organic solvent to the aqueous phase W₂, whereby an aqueous phase W₃ having a lower content of fatty acids compared to W₂, and a fatty acid-containing organic phase, are obtained.

In an even more preferred embodiment, a further step (d) follows on:

(d) separating off the aqueous phase W₃ from the fatty acid-containing organic phase obtained in step (c).

It has now been found that, surprisingly, the problems arising in the prior art, i.e. the elevated content of quaternary ammonium salt in the triglyceride oil freed from fatty acids, by adding an aliphatic diol having 1 to 8 carbon atoms instead of the ionic liquid alone, as described in the prior art (in particular the choline salt from WO 2016/189114 A1), leads to improved quality of the extracted triglyceride oil.

The feature “triglyceride oil” in accordance with the invention comprises any oil or fat of which the main constituent are triglycerides to an extent of >50% by weight. Besides the main constituent of triglycerides, the oil or fat may also comprise mono- and diglycerides.

The triglyceride oil is preferably of natural origin and more preferably of animal or vegetable origin. The triglyceride oil is more preferably a fat or oil of vegetable origin.

Contemplated as fats and oils of vegetable origin and comprising aroma chemicals are in particular (latin names which may be indicated in brackets refer to the plant species from which the relevant oil may be derived): algae oil, apricot kernel oil (Prunus armeniaca), argan oil (Argania spinosa), avocado oil (Persea americana), babassu oil (Attalea speciosa), cottonseed oil (Gossypium), ben oil (Moringa oleifera), borage oil (Borago officinalis), nettle seed oil (Urtica pilulifera or Urtica dioica), beech oil (Fagus), cashew shell oil (Anacardium occidentale), oil from plants of the genus Citrus (for example lemons, oranges, grapefruit, limes), cupuaçu butter (Theobroma grandiflorum), safflower oil (Carthamus), peanut oil (Arachis hypogaea), rosehip seed oil (Rosa), hemp oil (Cannabis), hazelnut oil (Corylus avellana), jatropha oil (Jatropha curcas), jojoba oil (Simmondsia chinensis), coffee bean oil (Coffea), cocoa butter (Theobroma cacao), tea seed oil (Camellia), acai palm (Euterpe oleracea), coconut oil (Cocos nucifera), pumpkin seed oil (Cucurbita), false flax oil (Camelina sativa), linseed oil (Linum), corn oil (Zea mays), macadamia oil (Macadamia integrifolia, Macadamia tetraphylla), almond oil (Prunus dulcis), mango butter (Mangifera indica), corn oil (Zea mays), poppyseed oil (Papaver), evening primrose oil (Oenothera biennis), olive oil (Olea europaea), palm oil (oil obtainable from a plant of the genus Elaeis), especially Elaeis guineensis, Elaeis oleifera), papaya seed oil (Carica papaya), pecan nut oil (Carya illinoinensis), perilla oil (Perilla frutescens), pine nut oil (plants from the genus Pinus), pistachio oil (Pistacia vera), rapeseed oil (Brassica napus), rice bran oil (Oryza sativa), castor oil (Ricinus communis), sea buckthorn kernel oil (kernels of Hippophae rhamnoides), sea buckthorn oil (flesh of Hippophae rhamnoides), black caraway oil (Nigella sativa), mustard oil (Brassica nigra), sesame oil (Sesamum indicum), shea butter (Vitellaria paradoxa), soybean oil (Glycine max), sunflower oil (Helianthus annuus), grapeseed oil (Vitis vinifera), tung oil (Vernicia, Aleurites), walnut oil (Juglans regia), watermelon seed oil (Citrullus lanatus), wheat germ oil (Triticum). The fats and oils of vegetable origin are preferably selected from coconut oil, corn oil, cottonseed oil, olive oil, palm oil, peanut oil, rice bran oil, soybean oil, sunflower oil, rapeseed oil, castor oil, safflower oil. The fat and oil of vegetable origin is most preferably palm oil.

Contemplated as fats and oils of animal origin and comprising aroma chemicals are in particular. Marmot fat, butter fat, fish oil, oil obtainable from crustaceans (for example krill), cod liver oil, milk fat, pork lard, duck lard, goose lard, beef tallow, wool wax.

In the context of the invention, “fatty acids” include saturated and mono- or polyunsaturated fatty acids. In accordance with the invention, this term also includes (unless referred to otherwise in a specific case) both the protonated and the deprotonated form of the relevant fatty acid.

Examples of unsaturated fatty acids are myristoleic acid, palmitoleic acid, sapienic acid, oleic acid, elaidic acid, vaccenic acid, linoleic acid, linolelaidic acid, α-linolenic acid, arachidonic acid, eicosapentaenoic acid, erucic acid and docosahexaenoic acid. Examples of saturated fatty acids are caprylic acid, capric acid, undecanoic acid, lauric acid, tridecanoic acid, myristic acid, palmitic acid, margaric acid, stearic acid, nonadecanoic acid, arachidic acid, heneicosanoic acid, behenic acid, lignoceric and cerotic acid.

“Palm oil” signifies an oil obtainable from a plant of the genus Elaeis (part of the family of the palm-like or palms Arecaceae or Palmae), especially Elaeis guineensis, Elaeis oleifera or hybrids thereof. The palm oil may be obtained for example from the fruit or the seed of the plants.

The triglyceride oil, in particular the palm oil used in step (a), may be unrefined or at least partially refined. This also includes fractionated triglyceride oil, for example fractionated palm oil, especially stearic acid fractions or oleic acid fractions of the palm oil.

“Unrefined” triglyceride oil signifies triglyceride oil according to the invention which has not been subjected to any refining step. For example, unrefined triglyceride oil has not been passed through any of the following refining steps: degumming, deacidification, bleaching, depigmentation, deodorizing, winterization.

“Refined” triglyceride oil has been passed through at least one refining step, for example at least one selected from degumming, deacidification, bleaching, depigmentation, deodorizing, winterization.

In step (a) of the process according to the invention, a triglyceride oil T₁ comprising fatty acids is contacted with an aqueous solution W₁ comprising at least one quaternary ammonium salt and at least one aliphatic diol having 1 to 8 carbon atoms.

The temperature in step (a) of the process according to the invention is not further restricted. In particular, step (a) of the process according to the invention is conducted at a temperature <100° C., preferably at a temperature of 25° C. to 90° C., more preferably at 40° C. to 90° C. yet more preferably at 70° C. to 90° C., most preferably at 80° C.

The pressure in step (a) of the process according to the invention is likewise not further restricted. In particular, step (a) of the process according to the invention is conducted at a pressure of 1 bar to 100 bar, especially at standard pressure of 1 bar.

The triglyceride oil T₁ comprising fatty acids can be contacted with an aqueous solution W₁ comprising at least one quaternary ammonium salt and at least one aliphatic diol having 1 to 8 carbon atoms by methods known to those skilled in the art. The contacting may also take place in a vessel in which T₁ and W₁ are mixed with each other. It will be apparent that the contacting is to be carried out such that as many fatty acids as possible migrate from the triglyceride oil T₁ into the aqueous phase W₁. For this purpose, for example, a mechanical mixer (such as, for example, a stirred tank which may be operated in batchwise mode or continuously), an ultrasonic mixer or an electromagnetic mixer is used. During the contacting, an inert gas can be bubbled through the resulting mixture. Alternatively, T₁ and W₁ may also be mixed in a static mixer such as a Sulzer mixer or Kenics mixer.

It is also possible to mix T₁ and W₁ continuously in countercurrent flow, for example in a column, or in cocurrent flow. The column may be a sieve tray column, a structured packing column or an agitated column such as, for example, a Kühni column or a Scheibel column.

In the continuous processes in cocurrent flow, for example, T₁ and W₁, prior to contacting thereof, may each also be passed through a tube with the aid of a pump, at the end of which they meet and mix together, in order then to be passed through a flow tube R.

In the continuous processes in countercurrent flow in a column, for example, the trigylceride oil T₁ is introduced at or at least close to the bottom end of the column and the aqueous solution W is introduced at or at least close to the top end of the column.

The aqueous phase W₂, which has an increased content of fatty acids compared to W₁, is then discharged at or close to the bottom end of the column, and a triglyceride oil phase T₂, which has a reduced content of fatty acids compared to T₁, is then discharged at or close to the top end of the column.

The column preferably also has a bottom region in which a secondary stream may be collected, and more preferably the trigylceride oil T₁ is then fed in directly above this bottom region.

Naturally, two or more such countercurrent columns may also be used, for example 2 to 6, or 3 to 5 or 4.

It is preferable that the column also has a structured packing, for example a packing of Raschig rings or several trays.

Further possible apparatuses for mixing in cocurrent flow are mixer settlers, which can be arranged in a countercurrent cascade. Centrifugal extractors also exist, as described further below, in which steps a) and b) of the process according to the invention may be carried out in one go.

Step a) is preferably carried out in which T₁ and W₁ are mixed in cocurrent flow, more preferably in at least one mixer settler.

The ratio by volume of T₁ and W₁ in step (a) of the process is likewise not further restricted. The ratio of the volume of the triglyceride oil T₁ to the volume of the aqueous phase W₁ in this case is in particular in the range from 10:1 to 1:100, more preferably from 1:1 to 1:10, yet more preferably from 1:1.5 to 1:4, yet still more preferably 3:7.

The mixing, such as for example the contacting in the column in the case of continuous contacting, may be adjusted by a person skilled in the art such that as large a fraction as possible of the triglyceride oil phase T₁ migrates into the aqueous phase W₁. Accordingly, the contacting is carried out, for example, for 1 second to 2 hours, particularly 30 seconds to 1 hour, preferably 1 to 50 minutes, more preferably 10 to 40 minutes, most preferably 20 to 30 minutes.

In step (a) of the process according to the invention, the fatty acids contained in the triglyceride oil T₁ are neutralized by the quaternary ammonium salts contained in the aqueous phase W₁. In particular, the molar amount of all quaternary ammonium salts contained in the aqueous phase W₁ is at least equal to the molar amount of all fatty acids contained in the triglyceride oil T₁. The ratio of the molar amount of all quaternary ammonium salts contained in the aqueous phase W₁ to the molar amount of all fatty acids contained in the triglyceride oil T₁ is preferably in the range from 1:1 to 500:1, more preferably from 2:1 to 200:1, yet more preferably from 10:1 to 100:1, most preferably from 30:1 to 70:1.

The fraction of fatty acids in the triglyceride oil may be determined by methods known to those skilled in the art, for example by titration with potassium hydroxide and a phenolphthalein indicator. Following determination of the fractions of fatty acids in the triglyceride oil T₁, the person skilled in the art then also knows how much the desired molar amount of all quaternary ammonium salts in the aqueous phase W₁ must be, which can then be adjusted accordingly.

In step (a), an aqueous phase W₁ comprising at least one quaternary ammonium salt and at least one aliphatic diol having 1 to 8 carbon atoms is used. The aqueous solution may also comprise further solvents in addition to water, for example acetone, ethyl acetate, alcohols, preferably methanol or ethanol. The aqueous phase W₁, however, preferably does not contain any other solvents besides water, which signifies in accordance with the invention that the proportion by weight of the sum total of all quaternary ammonium salts and all aliphatic diols having 1 to 8 carbon atoms and of the water in W₁ is at least 95% by weight, preferably at least 99% by weight, more preferably at least 99.9% by weight, and the remainder thereof of W₁ are various chemical substances such as organic solvents.

The total concentration of all quaternary ammonium salts in the aqueous phase W₁ is not further restricted and is preferably in the range of 70 to 80% by weight, preferably 75% by weight, based on the total mass of the phase W₁.

On contacting a triglyceride oil T₁ comprising fatty acids with an aqueous solution comprising at least one quaternary ammonium salt and at least one aliphatic diol having 1 to 8 carbon atoms W₁, the fatty acids migrate from the triglyceride oil T at least partially into the aqueous phase W₁. Therefore, in carrying out step (a), a triglyceride oil phase T₂ and an aqueous phase W₂ are obtained, wherein T₂ has a reduced content of fatty acids compared to T₁ and W₂ has an increased content of fatty acids compared to W₁.

In step (b) of the process according to the invention, the triglyceride oil phase T₂ is then separated off from the aqueous phase W₂.

This separation may also be carried out by methods known to those skilled in the art, for example with the aid of gravity in a Settler unit. In general, the trigylceride oil phase T₂ is the upper phase here, whereas the aqueous phase W₂ is the lower phase. The separation of the triglyceride oil phase T₂ from the aqueous phase W₂ may alternatively also be carried out in a decanter, a hydrocyclone, an electrostatic coalescer, a centrifuge or a membrane filter press. In step (b) of the process according to the invention, the triglyceride oil phase T₂ is preferably separated off from the aqueous phase W₂ in a centrifuge.

If a salt should at least partially precipitate in W₁ during the contacting in step (a) and be present as a solid in the triglyceride oil phase T₂, it may also be removed by centrifugation or filtration. Solvent or water may also be added to the triglyceride oil phase T₂ containing the solid in order to bring the solid into solution, and to separate off the aqueous solution comprising the corresponding salt as described above.

In a preferred embodiment of the present invention, step (a) and step (b) of the process according to the invention, i.e. the contacting and separation, may be carried out in a centrifugal separator, such as is described for example in U.S. Pat. Nos. 4,959,158, 5,571,070, 5,591,340, 5,762,800, WO 99/12650 and WO 00/29120. In this case, T₁ and W₁ are firstly fed into the separator as separate streams and mixed in a circular mixing zone. The mixture is then conveyed to the separating zone where the phases are then separated with the aid of a centrifuge.

A series of centrifugal separators is preferably used, for example 2 to 6, 3 to 5 or 4, and the triglyceride oil T₁ is introduced into the first separator of the series, and the aqueous phase W₁ is introduced into the last separator of the series, such that triglyceride oil flows through from the first to the last separator of the series with decreasing content of fatty acids, while the aqueous phase flows through the separators in the opposite direction with increasing content of fatty acids. The aqueous phase W₂ is then withdrawn from the first separator of the series and the triglyceride oil phase T₂ is withdrawn from the last separator of the series.

In each case, the triglyceride oil phase T₂ may also be fed to a coalescing filter in order to remove last drops of aqueous solution from the fat or oil phase. A coalescing filter of this kind is known to those skilled in the art and comprises for example a filter material, which is wetted by the aqueous phase and by the oil phase, for example a filter material composed of glass or cellulose.

After separating off the triglyceride oil phase T₂ from the aqueous phase W₂ in step (b), the triglyceride oil phase T₂ may then be fed to a further workup or processing. A step of this kind may be one or more selected from degumming, deacidification, winterization, bleaching, depigmentation, deodorization. These steps are known to those skilled in the art and have been described in WO 2016/189114 A1 for example.

It will be apparent that the triglyceride oil phase T₂ after the separation in step (b) may be fed again once or more than once, for example twice up to ten times, to a contacting step (a), in which the triglyceride oil phase T₂ is used as triglyceride oil T₁ and in each step is contacted with a fresh charge of aqueous phase W₁ comprising alkali metal/alkaline earth metal (hydrogen)carbonate(s), in order to lower still further the fraction of fatty acids in the triglyceride oil phase T₂.

The aqueous phases W₂ obtained in these additional steps may then be be fed entirely or partially to the subsequent step (c) and so on.

Optionally, the following step (c) may then be carried out in which the aqueous phase is regenerated.

In this step (c), CO₂ and optionally an organic solvent is added to the aqueous phase W₂, whereby a fatty acid-containing organic phase, and an aqueous phase W₃ having a lower content of fatty acids compared to W₂, is obtained. The appropriate conditions are known to those skilled in the art and have been described in WO 2016/149692 A1 for example.

The contacting of the aqueous phase W₂ with CO₂ and optionally an organic solvent can be carried out by methods known to those skilled in the art. The contacting can be effected in a gas-tight sealable pressure vessel, in which W₂ and CO₂ and optionally an organic solvent may be mixed together. For this purpose, CO₂ may be introduced via a capillary or a gas-treatable stirrer. It will be apparent that the contacting is intended to be carried out such that as much CO₂ as possible is introduced into the aqueous phase W₂. For this purpose, for example, a mechanical mixer or an electromagnetic mixer is used.

If an organic solvent is added in step (c) of the process according to the invention, the ratio by volume of W₂ and the organic solvent in step (c) is not further restricted in this case. The ratio of the volume of W₂ to the volume of the organic solvent is then in particular in the range from 1:100 to 100:1, preferably from 1:5 to 5:1, even more preferably from 1:2 to 2:1.

If an organic solvent is used in step (c), preference is given to diisopropyl ether, n-butyl acetate, ethyl acetate, hexane, 1-hexanol, preferably n-butyl acetate.

The pressure and temperature in step (c) of the process according to the invention are not further restricted.

In particular, the pressure during the addition of CO₂ is in a range from 0.1 to 55 bar, preferably 1 to 20 bar, more preferably 5 to 10 bar.

The temperature is preferably in the range from 0° C. to 120° C., more preferably 5° C. to 100° C., yet more preferably 10° C. to 90° C., even more preferably 20° C. to 80° C., still more preferably 40° C. to 60° C., most preferably 50° C.

The CO₂ used in step (c) may originate from a combustion process or blast furnace process and may comprise other constituents such as N₂O, SO₂, H₂S, NO₂. These constituents may further acidify the aqueous phase W₂ which further promotes the formation of a fatty acid-containing organic phase.

At the end of step (c), a fatty acid-containing organic phase and an aqueous phase W₃, which has a lower content of fatty acids compared to W₂, are obtained.

In the further optional step (d) in the process according to the invention, the aqueous phase W₃ may be separated off from the fatty acid-containing organic phase obtained in step (c).

This may be carried out by processes familiar to those skilled in the art, as also described for step (b) of the process according to the invention.

After completion of step (d), a phase W₃ is obtained which may be added to a new cycle with a fresh batch of triglyceride oil.

Therefore, in an optional further step (e), at least part of the aqueous phase W₃ is contacted with further triglyceride oil T₃ comprising at least one quaternary ammonium salt and at least one aliphatic diol having 1 to 8 carbon atoms, whereby a triglyceride oil phase T₄ and an aqueous phase W₄ are obtained, wherein T₄ has a reduced content of fatty acids compared to T₃ and W₄ has an increased content of fatty acids compared to W₃.

This further step (e) is preferably carried out as described for step (a). The process according to the invention is especially suitable for always recycling the aqueous phase W₁ and for its use in a new extraction run.

I will be apparent that the triglyceride phase T₂ obtained in step (b) of the process according to the invention may be subjected to one or more further refining steps which is/are selected, for example, from degumming, deacidification, bleaching, depigmentation, deodorizing, winterization.

The examples which follow are intended to elucidate the invention, but without restricting it thereto.

EXAMPLES

Measurement Methods Used:

The choline content in the triglyceride phase was determined by HPLC-ESI-MS on an Infinity II with QQQ-6430 from Agilent. For this purpose, ca. 50 mg of sample were diluted in 10 mL of water acetone 1:1 (v:v) and analyzed by the HILIC separation method, ESI pos. detection. The results were evaluated via two calibration functions. The correlation coefficient was determined where R₂=0.9997/0.9999.

Comparative Example C1

To 30 g of palm oil (5.5% free fatty acids, determined by titration by DGF method DGF-C-V 2) were added 70 g of an aqueous choline hydrogen carbonate solution (75.0% by weight, density ca. 1.16 g/mL; ˜5.3 mol/L) and the mixture was stirred at 80° C. for 1 hour. After reaction was complete, the aqueous phase and the organic phase were separated in a separating funnel. The content of fatty acids in the triglyceride phase obtained was determined by titration as 0.11% by weight. This corresponds to a reaction of free fatty acids of 98.2%. The choline content in the triglyceride phase was determined by HPLC-ESI-MS as 113 646 ppm.

Comparative Example C2

To 30 g of palm oil (5.5% free fatty acids, determined by titration by DGF method DGF-C-V 2) were added 70 g of an aqueous choline hydrogen carbonate solution (80.0% by weight, density ca. 1.17 g/mL; ˜5.7 mol/L) and the mixture was stirred at 80° C. for 1 hour. After reaction was complete, the aqueous phase and the organic phase were separated in a separating funnel. The content of fatty acids in the triglyceride phase obtained was determined by titration as 0.08% by weight. This corresponds to a reaction of free fatty acids of 98.6%. The free choline content in the triglyceride phase was determined by HPLC-ESI-MS as 6405 ppm.

Inventive Example E1

To 30 g of palm oil (5.5% free fatty acids, determined by titration by DGF method DGF-C-V 2) were added 66.5 g of an aqueous choline hydrogen carbonate solution (75.0% by weight, density ca. 1.16 g/mL; molar concentration of choline hydrogen carbonate ˜5.3 mol/L; corresponds to 0.30 mol of choline hydrogen carbonate) and 3.5 g (56.4 mmol) of ethylene glycol and the mixture was stirred at 80° C. for 1 hour. After reaction was complete, the aqueous phase and the organic phase were separated in a separating funnel. The content of fatty acids in the triglyceride phase obtained was determined by titration as 0.16% by weight. This corresponds to a reaction of free fatty acids of 97.2%. The free choline content in the triglyceride phase was determined by HPLC-ESI-MS as 389 ppm. The triglyceride phase obtained was subsequently treated with 1.5 g (0.5% by weight based on the triglyceride phase) of Tonsil Supreme 118 F bleaching earth and wet-bleached at 95° C. for 5 minutes and dry-bleached for 15 minutes under vacuum. After filtration of the bleaching earth, the triglyceride phase was decolorized at 240° C. for 10 min under vacuum and steamed at 200° C. with dist. water for a further 90 minutes The oil obtained was virtually colourless and had a neutral taste and odour.

Inventive Example E2

To 30 g of palm oil (5.5% free fatty acids, determined by titration by DGF method DGF-C-V 2) were added 66.5 g of an aqueous choline hydrogen carbonate solution (80.0% by weight, density ca. 1.17 g/mL; molar concentration of choline hydrogen carbonate ˜5.7 mol/L; corresponds to 0.32 mol of choline hydrogen carbonate) and 3.5 g (56.4 mmol) of ethylene glycol and the mixture was stirred at 80° C. for 1 hour. After reaction was complete, the aqueous phase and the organic phase were separated in a separating funnel. The content of fatty acids in the triglyceride phase obtained was determined by titration as 0.13% by weight. This corresponds to a reaction of free fatty acids of 97.8%. The free choline content in the triglyceride phase was determined by HPLC-ESI-MS as 2442 ppm.

Inventive Example E3

To 30 g of palm oil (5.5% free fatty acids, determined by titration by DGF method DGF-C-V 2) were added 66.5 g of an aqueous choline hydrogen carbonate solution (75.0% by weight, density ca. 1.16 g/mL; molar concentration of choline hydrogen carbonate ˜5.3 mol/L; corresponds to 0.30 mol of choline hydrogen carbonate) and 3.5 g (46.0 mmol) of 1,2-propanediol and the mixture was stirred at 80° C. for 1 hour. After reaction was complete, the aqueous phase and the organic phase were separated in a separating funnel. The content of fatty acids in the triglyceride phase obtained was determined by titration as 0.11% by weight. This corresponds to a reaction of free fatty acids of 98.2%. The free choline content in the triglyceride phase was determined by HPLC-ESI-MS as 4853 ppm.

Inventive Example E4

To 30 g of palm oil (5.5% free fatty acids, determined by titration by DGF method DGF-C-V 2) were added 66.5 g of an aqueous choline hydrogen carbonate solution (75.0% by weight, density ca. 1.16 g/mL; molar concentration of choline hydrogen carbonate ˜5.3 mol/L; corresponds to 0.30 mol of choline hydrogen carbonate) and 3.5 g (29.6 mmol) of 1,6-hexanediol and the mixture was stirred at 80° C. for 1 hour. After reaction was complete, the aqueous phase and the organic phase were separated in a separating funnel. The content of fatty acids in the triglyceride phase obtained was determined by titration as 0.13% by weight. This corresponds to a reaction of free fatty acids of 97.8%. The free choline content in the triglyceride phase was determined by HPLC-ESI-MS as 8924 ppm.

The results of the experiments are summarized in Table 1 below.

TABLE 1
		FFA	Conversion	Choline
Example	Diol	content [%]	[%]	content [ppm]	Separation time
C1	—	0.11	98.2	11364	120 min, cloudy
					aqueous phase
C2	—	0.08	98.6	6405	30 min, cloudy
					aqueous phase
C3	3.5 g glycerol	0.11	98.2	6855	120 min, cloudy
					aqueous phase
E1	3.5 g ethylene glycol	0.16	97.2	389	30 min, clear phases
E2	3.5 g ethylene glycol	0.13	97.8	2442	45 min, clear phases
E3	3.5 g 1,2-propanediol	0.11	98.2	4853	45 min, clear phases
E4	3.5 g 1,6-hexanediol	0.13	97.8	8924	45 min, clear phases

Accordingly, it has been shown that, surprisingly, a clear phase could only be obtained when using the diol. In addition, the undesired residue of free choline in the resulting extracted oil was significantly reduced only upon combination with an aliphatic diol such as ethylene glycol or 1,2-propanediol.

Claims

1. A process for extracting a fatty acid from a triglyceride oil, the process comprising: (a) contacting a triglyceride oil T1 comprising the fatty acid with an aqueous solution W1 comprising at least one quaternary ammonium salt and at least one aliphatic diol having 1 to 8 carbon atoms, whereby a triglyceride oil phase T2 and an aqueous phase W2 are obtained, wherein T2 has a reduced content of fatty acid compared to T1 and W2 has an increased content of fatty acid compared to W1; and(b) separating the triglyceride oil phase T2 from the aqueous phase W2;wherein the quaternary ammonium salt comprises at least one quaternary ammonium cation and at least one basic anion selected from the group consisting of hydroxide, alkoxide, alkyl carbonate, hydrogen carbonate, carbonate, serinate, prolinate, histidinate, threoninate, valinate, aspartate, taurinate, and lysinatewherein said quaternary ammonium cation is at least one cation according to the structure [N(Ra)(Rb)(Rc)(Rd)]+,wherein Ra, Rb, Rc and Rd are each independently a C1 to C8 alkyl, andwherein one or more of the radicals Ra, Rb, Rc and Rd is optionally substituted on one carbon atom by a group selected from the group consisting of: C1 to C4 alkoxy, C2 to C8 alkoxyalkoxy, C3 to C6 cycloalkyl, —OH, —SH, —CO2Re, and —OC(O)Re,wherein Re=C1 to C6 alkyl.

2. The process according to claim 1, wherein the quaternary ammonium cation is choline.

3. The process according to claim 1, wherein the basic anion is at least one member selected from the group consisting of alkyl carbonate, hydrogen carbonate, carbonate, hydroxide, and alkoxide.

4. The process according to claim 3, wherein the basic anion is hydrogen carbonate.

5. The process according to claim 1, wherein the aliphatic diol comprises 1 to 4 carbon atoms.

6. The process according to claim 5, wherein the aliphatic diol is at least one member selected from the group consisting of ethylene glycol and propanediols.

7. The process according to claim 1, wherein said a) contacting is conducted at a temperature of 70° C. to 90° C.

8. The process according to claim 1, wherein a ratio of the volume of the triglyceride oil T1 to the volume of the aqueous solution W1 is in the range from 10:1 to 1:100.

9. The process according to claim 1, wherein, in the aqueous solution W1 in said a) contacting, a proportion of aliphatic diol relative to quaternary ammonium salt is such that the molar amount of all aliphatic diols having 1 to 8 carbon atoms, based on the molar amount of all quaternary ammonium salts, andwherein the quaternary ammonium salt comprises at least one quaternary ammonium cation and at least one basic anion selected from the group consisting of hydroxide, alkoxide, alkyl carbonate, hydrogen carbonate, carbonate, serinate, prolinate, histidinate, threoninate, valinate, aspartate, taurinate, and lysinate, is in the range from 0.0001% to 99.9%.

10. The process according to claim 1, wherein, a total concentration of said at least one quaternary ammonium salt in said aqueous solution is 70 to 80% by weight.

11. The process according to claim 1, wherein, a proportion of aliphatic diol relative to quaternary ammonium salt is 0.0001 to 99.9%.

12. The process according to claim 1, wherein, a proportion of aliphatic diol relative to quaternary ammonium salt is 0.01 to 50.0%.

13. The process according to claim 1, wherein, a proportion of aliphatic diol relative to quaternary ammonium salt is 0.1 to 40.0%.

14. The process according to claim 1, wherein, a proportion of aliphatic diol relative to quaternary ammonium salt is 1.0 to 30.0%.

15. The process according to claim 1, further comprising (c) adding CO2 and optionally an organic solvent to said aqueous phase W2, whereby an aqueous phase W3 having a lower content of fatty acids compared to W2 and a fatty acid-containing organic phase are obtained.

16. The process according to claim 1, wherein a molar ratio of all quaternary ammonium salts contained in said aqueous phase W1 to all fatty acids contained in said triglyceride oil T1 is 1:1 to 500:1.

17. The process according to claim 15, wherein a pressure of CO2 during said adding is from 0.11 to 55 bar.

18. The process according to claim 1, wherein said triglyceride oil further comprises at least one glyceride selected from the group consisting of a monoglyceride and a diglyceride.

19. The process according to claim 1, wherein said triglyceride oil is at least one oil selected from the group consisting of coconut oil, corn oil, cottonseed oil, olive oil, palm oil, peanut oil, rice bran oil, soybean oil, sunflower oil, rapeseed oil, castor oil and safflower oil.