WO2012116820A1

WO2012116820A1 - Process for obtaining organic carboxylic acids from aqueous mixtures

Info

Publication number: WO2012116820A1
Application number: PCT/EP2012/000896
Authority: WO
Inventors: Karlheinz Bretz
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
Priority date: 2011-03-02
Filing date: 2012-03-01
Publication date: 2012-09-07
Also published as: DE102011012857A1; EP2681184A1

Abstract

A process is specified for obtaining organic carboxylic acids from aqueous mixtures, for example fermentation broths, comprising the following steps: A) providing the aqueous mixture with a pH of 1 to 10, B) contacting the aqueous mixture with particles of a metal oxide and/or metal hydroxide, in the course of which the organic carboxylic acid is adsorbed onto the particles, C) contacting the particles obtained in step B) with an alkaline solution, in the course of which the carboxylic acid is desorbed, and removing the metal oxide/metal hydroxide particles from the resulting mixture.

Description

Patent Application:

Process for the recovery of organic carboxylic acids from aqueous

mixtures

The invention relates to a process for obtaining organic carboxylic acids, for example succinic acid, from aqueous mixtures, for example from

Fermentation broth, in which the acids to be separated are brought into contact with a metal oxide, so that an adsorption of the acids takes place on the metal oxide and separation from the aqueous mixture is possible.

According to the state of the art, the recovery of carboxylic acids from mixtures is either costly in terms of apparatus or cost-intensive for other reasons. In particular, high energy costs, chemical costs or waste disposal costs arise.

The production of fermentatively produced succinic acid can be carried out for example by means of bipolar electrodialysis, which, however, requires a high expenditure of energy. Furthermore, the succinic acid can be precipitated by means of calcium hydroxide; the resulting calcium succinate is subsequently treated with sulfuric acid to isolate the succinic acid. Caicium sulfate must be disposed of costly.

The purification of organic carboxylic acids by means of ion exchange resins permits selective extraction of the organic acids, for example from

Fermentation broths. The disadvantage here, however, is the resulting high salt load and the biofouling occurring and the complex regeneration of

Ion exchanger, so that the cost of this process are considerable. Furthermore, an interfering influence of anions such as sulfate, phosphate or carbonate but also of other chemical substances such as glucose is recorded. An object of the invention is to provide a method by which organic carboxylic acids can be obtained from aqueous mixtures which is improved over the prior art, for example because it is less expensive or requires less use of auxiliary materials for separation or sufficient egenerierbarkeit guaranteed this auxiliary materials.

This object is achieved by the process for the recovery of organic carboxylic acids from aqueous mixtures according to the independent claim. Further

Embodiments and developments of the method are the subject of

Subclaims and continue to be apparent from the following description. A process for the recovery of organic carboxylic acids and / or

Carboxylic acid salts from aqueous mixtures comprises the following steps:

A) providing the aqueous mixture containing at least one organic

Containing carboxylic acid and / or a carboxylic acid salt, wherein the aqueous mixture has a pH of 1 to 10;

B) contacting the aqueous mixture with metal oxide particles and / or

Metal hydroxide particles such that the organic carboxylic acid and / or the carboxylate is at least partially adsorbed to the particles;

C) contacting the particles obtained after step B) with an alkaline

Solution so that a desorption of the carboxylic acid and / or the carboxylate occurs and separation of the metal oxide particles and / or metal hydroxide

Particles from the resulting mixture.

According to the invention, it has been observed that the use of a metal oxide and / or metal hydroxide for obtaining carboxylic acids / carboxylic acid salts from aqueous mixtures is very suitable. As a rule, the metal oxide / metal hydroxide particles can be regenerated well since step C) can be carried out in such a way that a substantially complete desorption takes place. Furthermore, the process does not generate large amounts of waste, as for example in the precipitation of

Carboxylic acids with calcium hydroxide is the case. Finally, the

Metal oxide / metal hydroxide particles can also be added to ongoing reactions, for example, reactions in which carboxylic acids or carboxylates are formed, the metal oxide / metal hydroxide particles running the reaction equilibrium Carboxylate / carboxylic acid withdraw without the reaction itself by the

etaiioxid / Metaiihydroxid- Partikei is impaired. For example, with a suitable choice of the pH in step A), carboxylic acid can be continuously recovered from fermentation broths. This has the positive side effect that moderately salt-tolerant strains can be used for the production of carboxylic acids, since the salt load of the fermentation broth is constantly reduced and thus no high salt concentrations, which can be caused by neutralizing agents according to the prior art, are recorded.

The process according to the invention can be carried out according to step A) both at alkaline and at acidic pH. Accordingly, whether a given carboxylic acid in the form of the carboxylic acid or in the form of the

Corresponding carboxylate anion is in solution or what ratio of acid and corresponding anion in solution. If in the context of the present application of organic carboxylic acids and / or

Carboxylic acid is spoken, it is to be understood that depending on the pH, the carboxylate groups of the present in the aqueous mixture of organic compounds may be in the protonated or in the deprotonated form. The same applies to those obtained after carrying out step C)

Carboxylic acid-containing or carboxylate-containing solutions.

Are in the aqueous mixture compounds containing a plurality of carboxylate groups as

Substituents present, so may be present in one and the same molecule (again, depending on the pH), both the protonated and the deprotonated form. Also intermediate forms in which, for example, the proton is coordinated via a hydrogen bond to two carboxylate groups, are conceivable. According to the invention, an aqueous mixture is understood to mean any mixture in which a carboxylic acid or a carboxylate in dissolved or else only partially dissolved form is present in water as solvent or an aqueous solvent mixture. In particular, alcohols, e.g. Ethanol, into consideration. Often, in the aqueous mixture, in addition to water, there is either no further (in particular organic) solvent or ethanol as organic

Solvent present. Furthermore, regardless of this - as a rule, in addition to the Carboxylate or the carboxylic acid further inorganic and / or organic compounds are present, in particular also inorganic and / or organic

Compounds in dissolved form. Salts such as phosphates and / or carbonates (which may also be present in partially protonated form depending on the pH) and nitrates, halides and / or sulfates present in the solution may be mentioned here as inorganic compounds. As organic compounds, for example, carbohydrates, such as saccharides, proteins, lipids, and DNA or components thereof, such as purines and Pyrimidines.zu call.

According to one embodiment of the invention, the aqueous mixture may also be a fermentation broth; In particular, in this case, the aqueous mixture in addition to inorganic and / or organic components and biomolecules, especially bacteria contain. The latter can - but need not - be easily separated from the aqueous mixture by conventional methods. The measures required for this purpose are known to the person skilled in the art. In general, the aqueous mixture can be present according to the invention as a suspension or as a true solution; also in fermentation broths and the like, if the biomolecules are disregarded as a suspension or as a true solution.

According to the invention, any aqueous mixture which is basically suitable as an aqueous mixture from the pH value is suitable for the process according to the invention; if, however, the pH is <1 or> 10, the pH of the mixture must be brought to a value of 1 to 10 before carrying out the process by adding a base or an acid, wherein As bases in particular alkali metal hydroxides and as acids in particular dilute mineral acids into consideration.

According to the invention, a metal oxide or a metal hydroxide is understood as meaning a chemical compound which contains "oxide ions" and / or hydroxide ions (ie, O ^{2 "} and / or OH-ions) in addition to the metal, and which as a rule does not contain any metal ions In this context, a metal is understood to be a true metal, but not a semi-metal, and metals are therefore in particular not the elements boron, silicon, germanium, arsenic, antimony or tellurium to understand. Frequently, the metal is a transition metal or a metal of the 2nd or 3rd main group, which is usually present in an oxidation state> 0.

Furthermore, it should be noted according to the invention that the organic carboxylic acid and / or the carboxylate in step B) is adsorbed on particles of the metal oxide and / or metal hydroxide. Accordingly, the metal oxide according to the invention and / or

Metal hydroxide in the aqueous mixture is not or only slightly soluble. To a lesser extent, this may mean that the solubility product L of the metal oxide and / or metal hydroxide in pure water at room temperature is less than 1.10 × 10 ^-6 . Adsorption on the particle does not mean that the metal oxide and / or metal hydroxide have reacting the carboxylic acid and / or the carboxylate to form a Metallcarboxylats which precipitates from a solution as a solid, but in particular that on the solid (undissolved) particles adsorption of carboxylic acid and / or carboxylate (on the surface of the particle) takes place.

In step C) of the process, the adsorbed carboxylic acid molecules and / or carboxylates by alkaline solution of the metal oxide and / or

Metal hydroxide particles desorbed; as a rule, a regeneration of the

Metal oxide and / or metal hydroxide is accompanied. In particular, compounds suitable as metal oxides and / or metal hydroxides are those which allow adsorption at low pH values and desorption of carboxylic acid and / or carboxylate groups at high pH values. In particular, the metal oxide and / or metal hydroxide particles may therefore comprise or consist of compounds having an isoelectric point. The isoelectric point is often referred to as point of zero charge (PZC). The PZC then indicates the pH at which the

Surface charge of the metal oxide / metal hydroxide is zero. Thus, if an adsorption of carboxylic acids and / or carboxylates is intended, then the PZC of the

Metal oxide / metal hydroxide usually be greater than the pH of the aqueous mixture. Accordingly, in step A), the pH is usually chosen to be lower than the PZC of the metal oxide / metal hydroxide.

The pH of the alkaline solution added in step C) will generally be above the pH of the aqueous mixture. This is usually required to ensure separation. However, too - depending on the aqueous mixture and the alkaline solution from step C), which normally contains no further substances in addition to the alkaline compound - also sufficient pH values between 7 and 10, for example, when the aqueous mixture and the alkaline solution are basically different from each other and attack The hydroxide ions of the alkaline solution on the particles with adsorbed carboxylic acid / carboxylate can therefore be made easier than the attack of basic components that in the aqueous

Mixture are present.

As the alkaline solution according to step C), basically any aqueous bases (or even bases in other solvents than water) can be used,

In particular, however, simple amines, alkali metal hydroxides or NH _{3 will be used} as the alkali component for the sake of simplicity.

According to one embodiment, particles are used in step B)

Metal oxide and / or metal hydroxide or consist of a metal oxide and / or metal hydroxide, wherein the metal is selected from one or more metals of the group consisting of beryllium, magnesium, calcium, aluminum,

Gallium, lanthanum, scandium, chromium, manganese, iron, cobalt, nickel, copper and zinc. Oxides or hydroxides with one, two or more metals from this group as the only cationic component or in combination with other metals as cationic components generally have a PZC, which is in the relevant pH range of pH 1 to 12 here. For example, the binary oxides of trivalent aluminum,

Iron or chromium has a PZC between about pH 7 and pH 8.5 (see GA Parks, Journal of Physical Chemistry 1962, 66, 967-973, which is also referred to in the measurement of PZC). Corundum (a-AI203) has a PZC at pH 9.1, γ-ΑΙΟΟΗ a PZC at pH 8.2, goethite (α-FeOOH) a PZC at pH 7.8, hematite (a-Fe203) a PZC at pH 8.5, Fe (OH) ₃ a PZC at pH 8.5, ß-Mn02 a PZC at pH 7.2 and

Hydroxyapatite a PZC at pH 7.6.

According to a further embodiment, in step B) particles of a metal oxide and / or metal hydroxide are used in which the or a contained therein

Metal oxide and / or metal hydroxide forms a layered structure. This has the advantage that the particles have a particularly large surface at which the

Carboxylic acids / carboxylates can adsorb. According to another embodiment, in step B) metal oxide and

Metallhydroxid Partikei used which form a Doppeisaiz- structure or

Metal hydroxides and / or metal oxides containing such a double salt structure. By means of a compound having such a double-salt structure, the PZC can be tailored by selecting the at least two different metals. For example, it is possible to use metals which are present in the same oxidation state, in particular +2; Alternatively or simultaneously, metals may also be present in different oxidation states; for example in the oxidation states +2 and +3 or also +2 and +4. Under a double salt structure is understood that a regular structure with the at least two metal ions is formed or that in a

Metal oxide / metal hydroxide structure of a first metal lattice sites of the first metal are replaced by the second metal. Under a double salt structure is in particular not understood that in a particle two different metal oxides or

Metal hydroxides are present side by side, without the one component has an influence on the structure of the other component or without (metal) cations of the one component are incorporated into the structure of the other.

According to a further embodiment, the metal oxides / metal hydroxides

Double layer hydroxides, in particular double layer hydroxides of the formula

[M ¹ ₍₁ _×) M ² _× (OH) ₂ ] ^{n +} n / z [A] ² -y H ₂ 0.

Herein M ^{1 is} a divalent metal and M ^{2 is} a trivalent metal; A is a singly or multiply charged anion, whereby a mixture of singly charged or singly and / or multiply charged anions may also be present. For the index x, 0 <x <1, but as a rule x lies in the following interval: 0, 1 <x <0.5, x can be between 0.2 and 0.4, y is any number greater than or is 0 and may be 0 to 10 in particular; where y is not limited to integer numbers, but can also be a decimal number, z is an integer or decimal number for which 1> z <3. If there is only one sort of anions, z is an integer. Often, z will hold: 1 <z <2, in particular 1 <z <1, 5. When only one kind of anions is present, z is often 1, but even with anion mixtures, there will often be substantially simply negatively charged anions A). Essentially means more than 75%, and usually more than 90% of the anions are simply negatively geiads.

Bilayer hydroxides according to the present invention are two-dimensional inorganic polycations with intracrystalline charge compensation by mobile interlayer anions A). Particularly noteworthy are bilayer hydroxides, which derive their structure from the mineral brucite, the divalent metal ions are partially replaced by trivalent metal ions. The anions are accordingly required for charge balancing. A naturally occurring double layer hydroxide of this type is hydrotalcite, in which the divalent magnesium ions are partially replaced by aluminum ions. Frequently, the charge balance is carried out by carbonate anions. In addition, there is water of crystallization between the bilayers. The double-layer hydroxides are described many times in the literature and can be prepared, for example, according to DE 40 34 305 A1 or DE 198 36 580 A1 and the literature cited therein. The use of double layer hydroxides has the advantage that solid particles with a relative to the carboxylic acid / carboxylate adsorption very relevant

Surface can be provided. Furthermore, the choice of the divalent and the trivalent metal can also influence the PZC. Natural hydrotalcite, for example, has a PZC in the basic pH range, so that for aqueous media with a pH <7 a suitability for the adsorption of carboxylic acids / carboxylates is present.

According to a further embodiment, the divalent metal M ^{1 is} selected from one or more of the metals beryllium, magnesium, calcium, manganese, iron, cobalt, nickel, copper and zinc. Independently, the trivalent metal M _{2 is} selected from one or more metals of the group boron, aluminum, gallium, lanthanum, scandium, titanium, chromium, manganese, iron, cobalt, nickel. As a rule, the double-layer hydroxides will contain both one of the abovementioned divalent metals and one of the abovementioned trivalent metals.

According to a further embodiment, the anion A of the bilayer hydroxides is selected from the group consisting of halides, perchlorate, nitrate, nitrite, sulfate, Sulfonate, carbonate, bicarbonate, hydroxide and borate or mixtures thereof. Chlorides, bromide and iodide are to be mentioned in particular as halides. A monovalent anion, in particular a halide ion such as chloride (or even bromide) or a nitrate ion as anion A) is particularly common. Especially with monovalent anions, it has been observed that a very effective adsorption of the carboxylic acids / carboxylates is observed, presumably because of easier exchangeability.

In another embodiment, the organic carboxylic acid recovered from the aqueous mixture is selected from aromatic and / or

aliphatic carboxylic acids having 1 to 12 carbon atoms. It is decisive

According to the invention, that the carboxylic acids should have good water solubility in order to be able to be recovered from an aqueous mixture. Although acids with poor solubility in water can in principle also be obtained, they can often be separated well by crystallization processes.

Accordingly, carboxylic acids having more than 12 carbon atoms are generally less suitable. However, it is known that the water solubility can be increased by customary substituents such as, for example, hydroxyl groups, so that, in principle, carboxylic acids having more than 12 carbon atoms may also be suitable.

Suitable aromatic and / or aliphatic carboxylic acids according to the invention are carboxylic acids having one, two, three or more than three carboxylic acid groups. Furthermore, the aliphatic and / or aromatic radicals can also carry functional groups, for example hydroxy groups, as are contained, for example, in many naturally occurring carboxylic acids. However, the substituents are not limited to hydroxyl groups, but rather any functional groups can be present on the aromatic and / or aliphatic radicals of the carboxylic acid groups, in particular amino groups, ester groups, keto groups, thiol groups, To name ether groups, thioether groups and phosphate groups, As aromatic radicals hereby mono- and polycyclic aromatic compounds may be present, including in addition to the known homocyclic compounds and the heterocyclic aromatics may be mentioned. Aliphatic groups can be branched, unbranched and / or cyclic and also be saturated or unsaturated.

According to a further embodiment, the organic carboxylic acid is made

Dicarboxylic acids, in particular oxalic acid, malonic acid, maleic acid,

Fumaric acid, oxaloacetate, succinic acid, glutaric acid, adipic acid, tartaric acid,

Malic acid, itaconic acid, glutamic acid or aspartic acid. Of the acids mentioned, succinic acid, for example, is of interest, since it can be obtained as a C _{4 building} block, for example by means of fermentation processes, and then can serve as a valuable starting material for organic syntheses by derivatization or reduction. In addition to the dicarboxylic acids, however, the monocarboxylic acids, for example acetic acid, propionic acid, butyric acid, lactic acid, glycolic acid, acrylic acid, levulinic acid and also the natural amino acids are to be mentioned in principle. As important

Tricarboxylic acid is the citric acid to mention.

According to a further embodiment, the process according to the invention is carried out with an aqueous mixture which has a pH of from 5.5 to 7.5, preferably from 6 to 7. Often, the pH can be 6.5 to 7. In the case of mixtures which have such a pH, it is generally possible to continuously separate carboxylic acid or carboxylates formed during ongoing chemical reactions from the mixture, without the chemical reaction proceeding as a result of a particularly high or particularly low pH is impaired.

By way of example, an aqueous mixture in the form of a fermentation broth may be mentioned, with which carboxylic acids or carboxylates are prepared.

According to a further embodiment, the process according to the invention is carried out under atmospheric pressure and at a temperature between 20 and 100.degree. C., in particular 20 to 60.degree. In principle, however, other temperatures and increased or reduced pressures are conceivable. As an aqueous mixture, however, one

Used fermentation broth, it is - depending on the bacteria used - often a temperature in this temperature range makes sense. Frequently, a temperature between 35 and 45 ° C in fermentation broth prevail, but also extremely thermophilic bacteria are known in which the fermentation process at significantly higher temperatures, for example, at temperatures between 45 ° C and 90 ° C can be performed. Thus, if the carboxylate or the carboxylic acid are obtained from the ongoing fermentation process, the process according to the invention is accordingly also at the temperatures of the

To carry out fermentation process.

The process according to the invention is furthermore generally carried out at atmospheric pressure. Regardless of this, aerobic or anaerobic conditions may prevail.

According to a further embodiment, at least step B) during the

Fermentation process performed. Step A) is then usually also a process step of the fermentation process, because the provision of the aqueous

Mixture is to a certain extent the provision of the starting materials required for the fermentation process. As a rule, the contacting of the particles obtained in step B) with an alkaline solution (according to step C)) is not carried out in the fermentation broth in which the reaction continues. It makes sense to first separate the particles with the absorbed carboxylate or the adsorbed carboxylic acid from the fermentation broth. However, in the individual case, the complete separation of the fermentation broth outside the

continue fermentation reaction carried out when the separation is carried out so that with the particles having the carboxylic acid or the carboxylate, also some fermentation broth is separated. However, before step C), this should be removed to ensure a high degree of purity of the desorbed carboxylic acid.

According to a further embodiment, the inventive method is not only used for the separation of carboxylic acids but also for separation

different carboxylic acids contained in the aqueous mixture used.

In particular, this is possible, on the one hand, when carboxylic acids with different numbers of carboxylate groups in the molecule are present in the aqueous mixture, because they have different binding affinities to the metal oxide / metal hydroxide particles, and, secondly, when the carboxylic acids contain, in addition to the carboxylic acid groups, further functional groups which are attached to the carboxylic acid groups the particles can coordinate and thereby the

Increase binding capacity included (for example, hydroxide groups) and finally when the carboxylic acids have a greatly different pKs value. In all of these Cases, the inventive method can be used to the more coordinating carboxylic acid or the acidic carboxylic acid of the other

Separate carboxylic acids. The further separation of two or more remaining carboxylic acids after separation of the first carboxylic acid from a mixture with at least three carboxylic acids is analogously possible.

In particular, it should be emphasized that according to this embodiment of the method according to the invention, the oligo- or polycarboxylic acids of

Monocarboxylic acids can be easily separated. As a rule, the process according to the invention is suitable for obtaining, from mixtures with a plurality of carboxylic acids, the carboxylic acid separated off as specified above substantially pure. Essentially pure means that in addition to the carboxylic acid to be isolated at most 10 wt .-% (based on the total amount of carboxylic acids) of a further carboxylic acid are included, in particular less than 5% and often even less than 1%.

According to a further embodiment, not only an alkaline solution is added in step C) but additionally an inorganic salt. Here are in particular simple inorganic salts of the formula M ⁺ X \ where M is a monovalent cation, in particular a metal cation or an ammonium cation (wherein organically substituted ammonium cations are included), and X is any monovalent anion, for example, alkali halides or alkali metal nitrate. By means of such salts can - especially in the use of

Double layer hydroxide-containing particles regeneration of the particles occur simultaneously with the desorption of the carboxylic acid / carboxylate. It has also been observed that, in general, easier desorption of the carboxylic acid / carboxylate can also take place. According to a further embodiment, a double-layer hydroxide is used in step B), in which the anion A) is not, at least but not exclusively

Carbonate anion is (not exclusively means that at least 10 mol% of another anion, usually more than 50 mol% of another anion and often more than 90 mol% of another anion is included). Of course, depending on the synthesis of the double layer hydroxide, it is also possible from the outset

Material are used, which has no carbonate anions. Will, however Commercially available double layer hydroxide, for example commercial hydrotalcite used, this is often in the carbonate form. To here the

Accordingly, before carrying out step B), the carbonate anion can be exchanged for another anion. In particular, the carbonate ion can be driven off by addition of an acid, for example a mineral acid (for example aqueous hydrochloric acid), or thermally (for example by heating to 300 ° C.) and released in the form of carbon dioxide. In principle, however, other ways of removing the carbonate are conceivable, for example by complex formation with correspondingly strong complexing agents, which then to some extent wash out the carbonate from the double-layer hydroxide.

Further advantages and advantageous embodiments and further developments of

The invention will become apparent hereinafter - without limiting the generality - from the examples.

EXAMPLE 1 1.5 g of hydrotalcite (Synthal 969 from Sudchemie - a magnesium- and aluminum-containing talcite) are treated with a 1 molar HCl solution in order to drive off the bound carbonate. Subsequently, the material is washed twice with distilled water and dried at 105 ° C.

The aqueous mixture used here is a solution of succinic acid in water which has a concentration of 10 g / l. To this solution, 1 g of the pretreated hydrotalcite is added and incubated on the shaker. In a further experiment, the abovementioned succinic acid solution (which has a pH of 2.5) is brought to a pH of 6.5 by means of sodium hydroxide solution and likewise incubated on the shaker. By means of an ion chromatograph from Metrohm the concentration of succinic acid in the remaining solution is determined and thus determines the amount of adsorbed carboxylate or the adsorbed acid. At an incubation time of 3 hours, an adsorption of 50 ± 3.4 mg / ^' g hydrotalcite results at pH 2.5 and 37.8 ± 3.4 mg / pH at pH 6.5 / g of hydrotalcite. If an incubation of 24 hours on the shaker, at a pH of 2.5, an adsorption of 69.8 ± 1, 6 mg / g hydrotalcite and at a pH of 6.5, an adsorption of 61, 7 ± 4.8 mg / g talcitol. Accordingly, the adsorption can be greatly increased by prolonged incubation time; By reducing the pH, it is true that during short incubation times an increased adsorption, which, however, is no longer so pronounced at long adsorption times. FIG. 1 shows a bar graph of the measured values on the left with an incubation time of 3 hours, on the right with an incubation time of 24 hours, wherein the left bar in each case relates to the pH 2.5 and the right bar to the pH 6.5.

Example 2:

In a further experiment, the influence of anions on the adsorption of succinic acid is determined. Sodium carbonate and / or potassium hydrogen phosphate, which are also constituents of the nutrient medium of

Fermentation processes may be added.

5 g / l Na ₂ C0 ₃ and 3 g / l K ₂ HP0 ₄ are additionally added to the succinic acid solutions with pH 6.5 from Example 1. Furthermore, in each case a solution is prepared in which either only 5 g / l Na ₂ C0 ₃ or only 3 g / l K ₂ HP0 _{4 are} included. 1 5 ml of these solutions are mixed with 1 g of the hydrotalcite from Example 1 and incubated for 4 hours on the shaker.

Figure 2 shows the results obtained as a bar chart. The results show that the addition of hydrogen phosphate does not affect the adsorption of the

Succinic acid has. While succinic acid solution without further additives (referred to in Figure 2 BS) shows approximately an adsorption of 53 mg / g hydrotalcite, the adsorption in the presence of hydrogen phosphate (in Figure 2 P0 ₄ called) even slightly increased. In contrast, carbonate ions have a negative influence on the adsorption. Both the solutions, which contain only carbonate ions in addition to succinic acid (in 1 C0 ₃ denotes - measured value 30.1 ± 2.9 mg / g hydrotalcite) as well as the solutions which contain both hydrogen phosphate and also carbonate (in FIG. 2 P0 ₄ + C0 ₃ - measured value 22.9 mg / g hydrotalcite) show a clear

Reduction of adsorption in the presence of carbonate. Example 3:

In Example 3, the selective separation of a dicarboxylic acid in the presence of a monocarboxylic acid is carried out using an aqueous mixture which is a fermentation broth.

By means of the fermentation process according to Lee et al. 1999a "Effects of medium components on the growth of anaerobiospirillum succiniciproducens and succinic acid production" Proc Biochem. 35: 49-55 and Lee et al. 1999b. "Succinic acid production by Anaerobiospirillum succiniciproducens: Effects of the H2 / CO2 supply and glucose concentration" Enzymes Microbiol Technol 24: 549-554 a fermentation broth was obtained from which the biomass was separated by centrifugation. After centrifugation, 10 ml of the supernatant were added to 1 g of hydrotalcite according to Example 1 and incubated on the shaker for 3 hours. By means of ion chromatography before and after treatment with hydrotalcite, the concentrations of

Succinic acid and acetic acid.

Figure 3 shows the concentration of succinic acid and acetic acid before treatment with hydrotalcite and of succinic acid and acetic acid in the remaining solution after treatment with hydrotalcite. The succinic acid concentration decreased by the adsorption from 22.8 ± 1.0 g / l to 10.7 ± 0.1 g / l, while the concentration of acetic acid remained constant at 6 g / l. Accordingly, selective adsorption of succinic acid on hydrotalcite occurs. To obtain the free succinic acid, the centrifuged hydrotalcite was re-eluted by means of a solution containing 3 mol / L of common salt and 3 mol / L of NaOH. From the eluate, the succinic acid crystallized in the freezer.

Example 4: Isolation of a functionalized tricarboxylic acid:

A solution of 10 g / l citric acid in water is adjusted to pH 6.5 by means of sodium hydroxide solution. To 10 ml of this solution, 1 g of hydrotalcite are added according to Example 1 and incubated for 3 hours with shaking. The supernatant aqueous phase after incubation contains only a concentration of 3 g / l citric acid.

Example 5:

Use of a functionalized monocarboxylic acid.

A solution of 10 g / l lactic acid in water is brought to pH 6.5 by means of sodium hydroxide solution. 10 ml of this solution are mixed with 1 g of hydrotalcite according to Example 1 and incubated for 3 hours with shaking. In the supernatant aqueous phase, only a concentration of 4 g / l of lactic acid could be determined after incubation.

Example 6:

Use of Goethite: A solution of 10 g / l succinic acid in water is brought to pH 2.5 using sodium hydroxide solution. 10 ml of this solution are mixed with 1 g of goethite and incubated for 3 hours with shaking. In the supernatant aqueous phase, only a concentration of 8 g / l of succinic acid could be determined after incubation.

The invention is not limited by the description with reference to the embodiments. Rather, the invention includes every new feature and every combination of features, which in particular any combination of features in the

Claims, even if this feature or combination itself is not explicitly stated in the claims or exemplary embodiments.

Claims

claims

1 . Process for the recovery of organic carboxylic acids and / or

Carboxylic acid salts from aqueous mixtures comprising the following steps:

A) providing the aqueous mixture containing at least one organic carboxylic acid and / or one carboxylic acid salt, wherein the aqueous mixture has a pH of 1 to 10,

B) contacting the aqueous mixture with particles of a metal oxide and / or metal hydroxide, wherein the organic carboxylic acid and / or the carboxylate is at least partially adsorbed on the particles,

C) contacting the particles obtained in step B) with an alkaline solution, wherein a desorption of the carboxylic acid and / or the carboxylate takes place, and separating the metal oxide and / or metal hydroxide particles from the resulting mixture.

2. Method according to the preceding claim, wherein

the particles contain or consist of a metal oxide and / or metal hydroxide whose metal is selected from one or more metals of the group consisting of metals of the 2nd and 3rd main group and the

Transition metals, and in particular is selected from one or more metals of the group consisting of beryllium, magnesium, calcium, aluminum, gallium, lanthanum, scandium, chromium, manganese, iron, cobalt, nickel, copper and

Zinc.

3. The method according to any one of the preceding claims, wherein

the particles contain a metal oxide and / or metal hydroxide containing a

Layer structure formed, or consist of such a metal oxide and / or metal hydroxide.

4. The method according to any one of the preceding claims, wherein

the particles contain a metal oxide and / or metal hydroxide containing a

Forms double salt structure, or consist of such a metal oxide and / or metal hydroxide.

5. The method according to the preceding claim, wherein

the particles are a double layer hydroxide of the formula

[M ¹ ₍ _{x, x)} M ² _x (OH) ₂ ] ^{n +} · η / ζ [Α] ^{ζ '} · y H ₂ O contain, in which

M ^{1 is} a divalent metal,

M ^{2 is} a trivalent metal,

A is an anion,

0 <x <1, in particular 0, 1 <x <0, 5, is

1 <z <3 and

y is a number greater than or equal to 0, in particular 0 to 10.

6. The method according to the preceding claim, wherein

M ^{1 is} selected from one or more ions of the group of divalent cations consisting of beryllium, magnesium, calcium, manganese, iron, cobalt, nickel, copper and zinc, and

M ^{2 is} selected from one or more of trivalent cations of aluminum, gallium, lanthanum, scandium, chromium, manganese, iron, cobalt, nickel.

7. The method according to one of the two preceding claims, wherein

A is one or more anions selected from the group consisting of halides, especially chloride, bromide and iodide, perchlorate, nitrate, nitrite, sulfate, sulfonate, carbonate, bicarbonate, hydroxide and borate.

8. The method according to any one of the preceding claims, wherein

the organic carboxylic acid is selected from aromatic and / or aliphatic carboxylic acids having 1 to 12 carbon atoms.

9. The method according to the preceding claim, wherein

the organic carboxylic acid is a dicarboxylic acid, in particular oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, tartaric acid, malic acid, itaconic acid, glutamic acid or aspartic acid.

10. The method according to any one of the preceding claims, wherein

the pH of the aqueous mixture is 5.5 to 7.5, preferably 6 to 7.

1 1. Method according to one of the preceding claims, wherein

the aqueous mixture is a fermentation broth.

12. The method according to the preceding claim, wherein

Step B) during the fermentation process.

13. The method according to any one of the preceding claims, wherein

the aqueous mixture at least one organic monocarboxylic acid and at least one further organic carboxylic acid having more than one

Having carboxylic acid group and wherein in steps B) and C), the at least one further organic carboxylic acid is substantially separated from the at least one organic monocarboxylic acid.

14. The method according to any one of the preceding claims, wherein

in step C) the alkaline solution additionally comprises an inorganic salt.

A method according to any one of claims 5 to 14, wherein

the anion A of the bilayer hydroxide comprises or consists of carbonate and wherein, before carrying out step B), the carbonate anion is exchanged for another anion and in particular the carbonate-containing bilayer hydroxide is treated with an acid in order to drive out carbonate.