Process for the production of an organic acid

Description

1 / 13 “PROCESS FOR THE PRODUCTION OF AN ORGANIC ACID” FIELD

[001] The present invention relates to the conversion of salts of organic acids into organic acid by means of electrodialysis. BACKGROUND

[002] Methods for converting salts of organic acids into their organic acids by means of electrodialysis are described in several publications. The organic acid salt is often obtained by fermentation. During this fermentation, an alkaline salt is usually added as a neutralizing agent to prevent a decrease in pH to such an extent that the activity of the microorganism is inhibited. As a result, an organic acid salt is obtained instead of the organic acid itself. The organic acid salt can be converted into its acid by electrodialysis, optionally after an intermediate cation exchange reaction and / or a purification step.

[003] Document WO98 / 22611 discloses a process for the production of organic acids, such as lactic acid. The process includes the steps of producing lactic acid by fermentation of a carbohydrate source, resulting in an aqueous fermentation broth containing lactic acid, and adding a calcium base, such as calcium carbonate, to the fermentation broth, thereby producing calcium lactate in the broth. The biomass is removed from the broth, leaving an aqueous solution or dispersion of calcium lactate. The calcium lactate reacts with a source of ammonium ions, such as ammonium carbonate, or a mixture of ammonia and carbon dioxide, thus producing ammonium lactate. Contaminating cations can be removed by ion exchange. Free lactic acid or a derivative thereof can be separated from the ammonium ions, preferably by salt-splitting electrodialysis.

[004] Document no. WO 98 / 28433 refers to a method of lactic acid fermentation from a fermentation liquid containing sugar in a fermenter by means of lactic acid fan bacteria, in which whey protein is present or added as a nutritive substrate for the Petition 870250088345, dated 09 / 29 / 2025, pp. 56 / 76 2 / 13 lactic acid fan bacteria, in which at least one protease is added to the fermenter during fermentation, so that the hydrolysis of the protein into amino acids occurs simultaneously with the fermentation of the sugar into organic acid, and in which the lactic acid resulting from the fermentation is isolated from the fermentation liquid. Ammonia is preferably added to result in the formation of ammonium lactate, and lactic acid is preferably isolated by a process comprising ultrafiltration, ion exchange, conventional electrodialysis, and electrodialysis with bipolar membranes.

[005] Document no. WO2011 / 95631 discloses a process for the preparation of lactic acid comprising the steps of: a) providing an aqueous medium comprising magnesium lactate; b) adding to the aqueous medium comprising magnesium lactate a monovalent base to form an aqueous medium comprising a water-soluble monovalent lactate salt and a solid magnesium base; c) separating the magnesium base from the aqueous medium comprising the water-soluble monovalent lactate salt; d) adjusting the concentration of the monovalent lactate salt in the aqueous medium to a value between 10% and 30% by weight; (e) subjecting the aqueous medium comprising the monovalent lactate salt to electrodialysis by water division, to produce a first solution comprising monovalent base and a second solution comprising lactic acid and monovalent lactate salt, the electrodialysis being carried out to a partial conversion of 40% to 98% by mole;f) separate the second solution comprising lactic acid and monovalent lactate salt into lactic acid and a solution comprising monovalent lactate salt by vapor-liquid separation; g) recycle the solution from step f) comprising the monovalent lactate salt to step d).

[006] Despite the various publications describing the electrodialysis of organic acid salts, prior art processes leave much to be desired with regard to membrane fouling, product purity, yield, processing time, water consumption and subsequent water evaporation, or energy consumption throughout the process as a whole, or combinations of these aspects. Petition 870250088345, dated 09 / 29 / 2025, p. 57 / 76 3 / 13

[007] Other documents relating to electrolysis are: - Document No. US 2008 / 0272001 refers to a method for treating an aqueous stream containing an organic material, wherein the method comprises: providing a feed stream that includes a target desired organic product, a large molecule / protein material, a soluble mineral material, and a non-ionized material to a second compartment of a three-compartment electrodialysis unit; passing the target desired organic product to an adjacent third compartment of the three-compartment electrodialysis unit; passing at least part of the soluble mineral material to an adjacent first compartment of the three-compartment electrodialysis unit; and passing the remainder of the feed stream through the second chamber; - Document No. WO 2020 / 077917 discloses a multi-stage treatment device for the treatment of wastewater with high salt content, comprising a clarification pool, a softening pool, an ultrafiltration device, a weakly acidic cationic bed, a medium-pressure membrane concentration device, a high-pressure membrane concentration device, a nanofiltration device, a first electro-actuated membrane device and a sequential bipolar membrane electrodialysis device; - Document No. CN 112237845 discloses a method for preparing an acidic system with a pH value of 3.0 to 4.0 using bipolar membrane electrodialysis technology. Specifically, it involves using brine / seawater as a liquid feedstock and employing bipolar membrane electrodialysis technology to produce an acidic system with a pH value of 3.0 to 4.0 as a medium for extracting bromine by air blast. SUMMARY

[008] The present invention relates to a process for the production of an organic acid comprising the steps of: a) provide a feed stream comprising an aqueous medium of a monovalent salt of an organic acid, Petition 870250088345, dated 09 / 29 / 2025, pp. 58 / 76 4 / 13 b) divide the feed stream into at least a first and second stream; c) subjecting the flows to multicompartmental bipolar electrodialysis comprising: an acid flow compartment (1) defined by a bipolar membrane and a cation or anion selective membrane (6), a base flow compartment (2) defined by a bipolar membrane (6) and a cation or anion selective membrane (6), wherein the acid and base compartments are arranged between a positive electrode (4) and a negative electrode (5), which are separated by a cation or anion selective membrane (6), wherein the first flow is supplied to the acid flow compartment (1) and the second flow is supplied to the base flow compartment (2), d) after which an aqueous acid stream comprising an organic acid exiting the acid stream compartment and an aqueous base stream comprising a base and a monovalent salt of the organic acid exiting the base stream compartment.

[009] Surprisingly, it was found that the process of the present invention provides a reduction in water consumption, allowing work within a concentration window for the monovalent salt that is ideal with regard to conductivity.

[010] In one embodiment, step (c) ideally comprises subjecting the flows to bipolar electrodialysis in a plurality of acid flow compartments (1) and base flow compartments (2), wherein the acid and base flow compartments alternate adjacent to each other and are separated from each other, on the one side, by a cation or anion selective membrane (6) and, on the other side, by at least one bipolar membrane (3), which forms an electrodialysis unit, wherein the first flow is supplied to the acid flow compartments and the second flow is supplied to the base flow compartments.

[011] With this modality, therefore, a so-called stack of units of Petition 870250088345, dated 09 / 29 / 2025, page 59 / 76 5 / 13 electrodialysis is used, forming an electrodialysis unit.

[012] The process according to the invention is preferably carried out with the first flow of the aqueous medium of the monovalent salt of the organic acid comprising a volume percentage of at least 45%, preferably at least 50% of the monovalent salt of the organic acid based on the total volume of the flow.

[013] Preferably, a concentration of the monovalent salt should be maintained so as to ensure that the monovalent salt is in solution. In general, the concentration of the monovalent organic salt of the acid in the first and second flows can be chosen to be between 2% and 99% of the solubility, measured in grams per liter, of the monovalent organic salt, preferably between 10% and 90%, and more preferably between 30% and 40%.

[014] The process of the present invention has been found to be very efficient. The amount of organic acid that exits the acid flow compartment can be between 1% and 100%, preferably between 85% and 99%, more preferably between 92% and 94% of the molar equivalent of organic salt that enters the acid flow compartment.

[015] The aqueous acid stream exiting the acid flow compartment may contain organic acid at a concentration of at least 20% by weight, preferably at least 25% by weight.

[016] In another embodiment of the process, according to the present invention, the organic acid is produced in an array of sequentially arranged electrodialysis units, wherein the first flow is supplied to the acid flow compartment of the first electrodialysis unit and the aqueous acid flow exiting the acid flow compartment of the electrodialysis unit is supplied to the acid flow compartment of the subsequent electrodialysis unit, while the second flow is supplied to the base flow compartment of the last electrodialysis unit and the aqueous base flow exiting the base flow compartment is supplied to the base flow compartment of the previous electrodialysis unit, after which an aqueous acid flow comprising an organic acid exits the Petition 870250088345, dated 09 / 29 / 2025, pp. 60 / 76 6 / 13 acid flow compartment of the last electrodialysis unit and an aqueous base flow comprising a base and a monovalent salt of the organic acid exits the base flow compartment of the first electrodialysis unit.

[017] The number of electrodialysis units can vary from 2 to more than 500 units. This configuration with more units offers the possibility of increasing the concentration of organic acid resulting in the aqueous acid stream and the concentration of metal salt in the aqueous base stream through several stages to obtain the desired concentrations.

[018] Furthermore, the stack size of an electrodialysis unit is limited by the voltage that can be applied to the electrodes. By arranging several electrodialysis units in series, as described above, the desired yield and final concentration of both the organic acid and the monovalent acid salt can be easily adjusted, minimizing the risk of fouling, lower acid purity and / or current leakage.

[019] Optionally, the aqueous acid stream exiting the last acid flow compartment is further evaporated and distilled under vacuum.

[020] In another embodiment of the present invention, at least part of the aqueous base stream exiting the base stream compartment is recycled upstream of the feed stream. The recycled stream can, for example, be supplied to a fermentation step or a cation exchange reaction step in the production of organic acid salt.

[021] The organic acid, according to the present invention, may be chosen from the group consisting of lactic acid, glycolic acid, malic acid, acetic acid, citric acid, propionic acid, pyruvic acid, oxalic acid. Preferably, the organic acid is lactic acid.

[022] The monovalent salt may be chosen from the group consisting of sodium, potassium, lithium, ammonium, monoalkylammonium, dialkylammonium, trialkylammonium or tetraalkylammonium salt. Preferably, the monovalent salt is potassium.

[023] The preferred monovalent salt of the organic acid is potassium lactate. In Petition 870250088345, dated 09 / 29 / 2025, pp. 61 / 76 7 / 13 In another embodiment of the present invention, the aqueous medium comprising a monovalent organic salt of the acid is provided by fermentation, wherein a carbohydrate source is fermented by means of a microorganism to form an organic acid, after which a base is added as a neutralizing agent during fermentation to provide a divalent organic salt of the acid, wherein the divalent organic salt of the acid is subsequently converted into a monovalent organic salt of the acid by a double substitution precipitation reaction or an ion exchange step. Suitable carbohydrate sources are known in the art. Examples include sugars such as glucose or sucrose, starch, and the like.

[024] After the isolation of lactic acid, other modifications or purification steps known in the field can be performed. Examples include distillation, such as vacuum distillation, clean film evaporation, absorption, extraction, ion exchange, crystallization, conversion into oligo or polymers. DESCRIPTION OF THE DRAWINGS Figures 1a and 1b provide a schematic view of a bipolar electrodialysis unit with a cation-selective membrane and an anion-selective membrane, respectively; and Figure 2 provides a representation of a possible bipolar electrodialysis process with three stages. DETAILED DESCRIPTION

[025] The present invention relates to a process for the production of an organic acid comprising the steps of: a) provide a feed stream comprising an aqueous medium of a monovalent salt of an organic acid, b) divide the feed stream into at least a first and second stream; c) subjecting the flows to bipolar electrodialysis in an acid flow compartment (1) defined by a bipolar membrane (3) and a cation or anion selective membrane (6) and Petition 870250088345, dated 09 / 29 / 2025, pp. 62 / 76 8 / 13 a basic flow compartment (2) defined by a bipolar membrane (3) and a cation or anion selective membrane (6), wherein the compartments are arranged between a positive electrode (anode) (4) and a negative electrode (cathode) (5) and are separated by a cation or anion selective membrane (6), wherein the first flow is supplied to the acid flow compartment and the second flow is supplied to the base flow compartment, d) after which an aqueous acid stream comprising an organic acid exiting the acid stream compartment and an aqueous base stream comprising a base and a monovalent salt of the organic acid exiting the base stream compartment.

[026] The process of the present invention provides a reduction in water consumption, allowing work within a concentration window for the monovalent salt of the organic acid that is ideal with respect to conductivity.

[027] Ideal conductivity is determined by the solubility of the monovalent salt of the organic acid, the process conditions used and their constraints, and the specific electrodialysis equipment used. To conduct an effective process, the concentration of the feed for bipolar electrodialysis generally needs to be increased. In the process according to the present invention, the monovalent salt of the organic acid is also supplied to the base flow compartment, whereas in processes according to the prior art the base flow compartment is supplied with water, introducing additional water into the system. The water needs to be evaporated in other stages of the process. This is avoided with the process of the present invention; therefore, the process of the present invention provides an improved water consumption profile.

[028] The bipolar membrane provides H+ ions in the acid flow compartment and OH- ions in the base flow compartment.

[029] The process can be carried out with a cation-selective membrane or an anion-selective membrane. In the case of a cation-selective membrane, the ion Petition 870250088345, dated 09 / 29 / 2025, pp. 63 / 76 9 / 13 of the monovalent salt's cationic component is transferred from the acid flow compartment across the cation-selective membrane. In the case of an anion-selective membrane, it is the organic carboxylate ion that moves from the basic flow compartment across the membrane.

[030] In one embodiment of the present invention, step (c) ideally comprises subjecting the flows to bipolar electrodialysis in a plurality of acid flow compartments (1) and base flow compartments (2), wherein the acid and base flow compartments alternate adjacent to each other and are separated from each other, on the one hand, by a cation or anion selective membrane (6) and, on the other hand, by at least one bipolar membrane (3) that forms an electrodialysis unit, wherein the first flow is supplied to the acid flow compartments and the second flow is supplied to the base flow compartments.

[031] With this method, therefore, a so-called electrodialysis unit stack is forming an electrodialysis unit. A bipolar electrodialysis process with multiple units improves the process yield. However, this stack size is limited by the maximum voltage that can be applied between two electrodes. Too high a voltage will create a risk of leakage and / or flow diversion.

[032] The process is generally carried out at a temperature between 20 -50 °C. Ideally, the process is conducted at the highest possible temperature that does not damage the spacers and cell membranes. A spacer, as defined in the present invention, provides the flow space in the acid and base flow channels, separating the membranes from each other, typically in the form of a mesh. It has been found that the process according to the description provides the best yield when conducted with the first flow of the aqueous medium of the monovalent salt of the organic acid, comprising a volume percentage of at least 45%, preferably at least 50%, of the monovalent salt of the organic acid of the total flow volume.

[033] Preferably, a salt concentration should be maintained Petition 870250088345, dated 09 / 29 / 2025, pp. 64 / 76 10 / 13 monovalent in order to ensure that the monovalent salt is in solution. In general, the concentration of the monovalent organic salt of the acid in the first and second streams can be chosen to be between 2% and 99% of the solubility, measured in grams per liter, of the monovalent organic salt, preferably between 10% and 90%, and more preferably between 30% and 40%.

[034] Electrodialysis performs best when the feed stream does not contain insolubles, as this can cause fouling of the membranes.

[035] The process was considered very efficient. The amount of organic acid exiting the acid flow compartment can be between 1% and 100%, preferably between 85% and 99%, more preferably between 92% and 94% of the molar equivalent of organic salt entering the acid flow compartment. It was found that with a feed stream containing 35% by weight of potassium lactate based on the total weight of the feed stream, an acid stream of 28% by weight of lactic acid could be obtained based on the total weight of the acid stream.

[036] The aqueous acid stream exiting the acid flow compartment can contain organic acid at a concentration of at least 20% by weight, preferably at least 25% by weight.

[037] In another embodiment of the process, according to the present invention, the organic acid is produced in an array of sequentially arranged electrodialysis units, wherein the first flow is supplied to the acid flow compartment of the first electrodialysis unit and the aqueous acid flow exiting the acid flow compartment of one electrodialysis unit is supplied to the acid flow compartment of the subsequent electrodialysis unit, while the second flow is supplied to the base flow compartment of the last electrodialysis unit and the aqueous base flow exiting the base flow compartment is supplied to the base flow compartment of the previous electrodialysis unit, after which an aqueous acid flow comprising an organic acid exits the acid flow compartment of the last electrodialysis unit and an aqueous base flow comprising a base and a monovalent salt of the organic acid exits the Petition 870250088345, dated 09 / 29 / 2025, pp. 65 / 76 11 / 13 base flow compartment of the first electrodialysis unit.

[038] The number of electrodialysis units can vary from 2 to more than 500 units.

[039] This configuration offers the possibility of continuously increasing the resulting organic acid concentration in the aqueous acid stream and the metallic salt concentration in the aqueous base stream through several stages to obtain the desired concentrations.

[040] As mentioned above, the number of units between a pair of electrodes is limited by the voltage that can be applied to the electrodes. With increasing voltage, the risk of current leakage and / or drift increases. This risk is mitigated by the use of a series of sequential electrodialysis units.

[041] Optionally, the aqueous acid stream exiting the last acid flow compartment is further evaporated and distilled under vacuum.

[042] In another embodiment, at least part of the aqueous base stream exiting the base stream compartment is recycled to the feed stream. Recycling part of the base stream avoids the need to add water to the feed stream to create the desired acid concentration in the feed stream. This improves water consumption and subsequent evaporation in the process as a whole. Recycling is not expected to negatively affect the final purity and yield of the product, while no additional fouling of the membranes is expected.

[043] The organic acid may be chosen from the group consisting of lactic acid, glycolic acid, malic acid, acetic acid, citric acid, propionic acid, pyruvic acid, oxalic acid, preferably lactic acid.

[044] The monovalent salt may be chosen from the group consisting of sodium, potassium, lithium, ammonium, monoalkylammonium, dialkylammonium, trialkylammonium or tetraalkylammonium salt, preferably potassium lactate. These salts are less likely to foul the membranes and electrodes in the process. Acids prepared from fermentation are often in their divalent salt form. The salts Petition 870250088345, dated 09 / 29 / 2025, pp. 66 / 76 The 12 / 13 monovalent compounds mentioned above can be easily obtained from them by a cationic ion exchange reaction.

[045] In one embodiment, the aqueous medium comprising a monovalent organic salt of the acid is provided by fermentation, wherein a carbohydrate source is fermented by means of a microorganism to form an organic acid, after which a base is added as a neutralizing agent during fermentation to provide a divalent organic salt of the acid, wherein the divalent organic salt of the acid is subsequently converted into a monovalent organic salt of the acid by an ion exchange step.

[046] The description of the drawings below serves only to illustrate the process according to the description and should not be interpreted as limiting the invention. DESCRIPTION OF THE DRAWINGS

[047] Figure 1a shows a bipolar electrodialysis unit (BPED) (cell), wherein the dashed line encloses the repetitive cell unit composed, from left to right, of a base flow compartment, a cation-selective membrane, an acid flow compartment, and a bipolar membrane. The cell unit (or cell units) is between a cathode, shown as (-), and an anode, shown as (+). Entering the base flow compartment is shown an aqueous solution containing a monovalent acid salt (MA); exiting the base flow compartment is shown an aqueous solution containing a base (MOH) and a monovalent acid salt. Entering the acid flow compartment is shown a solution containing a monovalent acid salt; exiting the acid flow compartment is shown an aqueous solution containing an organic acid (HA) and a monovalent acid salt.

[048] Figure 1b shows a bipolar electrodialysis (BPED) unit (battery) similar to figure 1a, with the cation-selective membrane being replaced by an anion-selective membrane.

[049] Figure 2 shows a possible three-stage BPED process, that is, with a matrix of 3 electrodialysis units arranged sequentially. Each Petition 870250088345, dated 09 / 29 / 2025, pp. 67 / 76 13 / 13 One of the stages can have any number of stacks, represented here as rectangles within each stage. At least one stage containing at least one stack is required; there are no maximums. The feed stream (1) contains an aqueous solution of a monovalent organic salt (MA) which is split into a first (a) and a second (e) stream. Leaving each stage is an aqueous solution of monovalent organic salt (MA) and organic acid (HA) or base (MOH). Streams a, b, c and c represent streams entering or leaving the acid flow compartments, while streams e, f, g and h represent streams entering or leaving the base flow compartments. The concentration of organic acid leaving the acid flow compartments is increased from stage 1 to stage 3. The concentration of organic acid salt leaving the acid flow compartments is reduced from stage 1 to stage 3.The concentration of base exiting the base flow compartments is increased from stage 3 to stage 1. The organic salt entering and exiting the base flow compartments is considered inert.

[050] This configuration shows that using an aqueous solution of a monosalt of the organic acid as a diluent for feeding the base flow compartment increases the concentration of the monovalent salt of the organic acid in the final base stream that is recycled upstream of the organic acid production process. As a result, evaporation to the ideal feed concentration for bipolar electrodialysis can be reduced or avoided completely. Petition 870250088345, dated 09 / 29 / 2025, pp. 68 / 76

Claims

1 / 4 CLAIMS 1. Process for the production of an organic acid characterized by comprising the steps of: a) providing a feed stream comprising an aqueous medium of a monovalent salt of an organic acid, b) dividing the feed stream into at least a first and second stream;c) subjecting the flows to a multicompartmental bipolar electrodialysis comprising: an acid flow compartment (1) defined by a bipolar membrane and a cation or anion selective membrane (6) and a base flow compartment (2) defined by a bipolar membrane (6) and a cation or anion selective membrane (6), wherein the acid and base flow compartments are arranged between a positive electrode (4) and a negative electrode (5), which are separated by a cation or anion selective membrane (6), wherein the first flow is supplied to the acid flow compartment (1) and the second flow is supplied to the base flow compartment (2), d) after which an aqueous acid flow comprising an organic acid is exiting the acid flow compartment and an aqueous base flow comprising a base and a monovalent salt of the organic acid is exiting the base flow compartment.

2. Process, according to claim 1, characterized in that step c) comprises subjecting the flows to bipolar electrodialysis in a plurality of acid flow compartments (1) and base flow compartments (2), wherein the acid and base flow compartments alternate and are adjacent to each other, being separated from each other, on one side, by a cation or anion selective membrane (6) and, on the other side, by at least one bipolar membrane, which forms an electrodialysis unit, wherein the first flow is supplied to the acid flow compartments and the second flow is supplied to the base flow compartments.

3. Process, according to claim 1 or 2, characterized in that the first flow of the aqueous medium of the monovalent salt of the organic acid comprises a volume percentage of at least 45%, preferably at least 50% based on the total feed flow.

4. Process, according to any one of claims 1 to 3, characterized in that the concentration of the monovalent organic salt of the organic acid in the first and second stream is between 2% and 99% of the solubility of the monovalent organic salt, preferably between 10% and 90%, more preferably between 30% and 40%.

5. A process according to any one of claims 1 to 4, characterized in that the amount of organic acid exiting the acid flow compartment is between 1% and 100%, preferably between 85% and 99%, more preferably between 92% and 94% of the molar equivalent of organic salt entering the acid flow compartment.

6. A process according to any one of claims 1 to 5, characterized in that the aqueous acid stream exiting the acid flow compartment contains organic acid at a concentration of at least 20% by weight, preferably at least 25% by weight.

7. Process, according to any one of claims 1 to 6, characterized in that the organic acid is produced in an array of sequentially arranged electrodialysis units, wherein the first flow is supplied to the acid flow compartment of the first electrodialysis unit and the aqueous acid flow exiting the acid flow compartment of one electrodialysis unit is supplied to the acid flow compartment of the subsequent electrodialysis unit, while the second flow is supplied to the base flow compartment of the last electrodialysis unit and the aqueous base flow exiting the base flow compartment is supplied to the base flow compartment of the preceding electrodialysis unit, after which an aqueous acid flow Petition 870250088345, dated 09 / 29 / 2025, p.74 / 76 3 / 4 comprising an organic acid is exiting the acid flow compartment of the last electrodialysis unit and an aqueous base flow comprising a base and a monovalent salt of the organic acid is exiting the base flow compartment of the first electrodialysis unit.

8. A process according to any one of claims 1 to 7, characterized in that the aqueous acid stream exiting the last acid flow compartment is further evaporated and distilled under vacuum.

9. A process according to any one of claims 1 to 8, characterized in that at least part of the aqueous base stream exiting the base stream compartment is recycled upstream of the feed stream.

10. Process, according to any one of claims 1 to 9, characterized in that the organic acid is chosen from the group consisting of lactic acid, glycolic acid, malic acid, acetic acid, citric acid, propionic acid, pyruvic acid, oxalic acid.

11. Process according to claim 9, characterized in that the organic acid is lactic acid.

12. Process, according to any one of claims 1 to 10, characterized in that the monovalent salt of the organic acid is chosen from the group consisting of sodium, potassium, lithium, ammonium, monoalkylammonium, dialkylammonium, trialkylammonium or tetraalkylammonium salt.

13. Process according to claim 11, characterized in that the salt is a potassium salt.

14. Process, according to any one of claims 1 to 13, characterized in that the monovalent salt of the organic acid is potassium lactate.

15. Process, according to any one of claims 1 to 14, characterized in that the aqueous medium comprising a monovalent organic salt of the acid is provided by fermentation, wherein a carbohydrate source is fermented by means of a microorganism to form an organic acid, after which a base is added as a neutralizing agent during fermentation to provide a divalent organic salt of the acid, wherein the divalent organic salt of the acid is subsequently converted into a monovalent organic salt of the acid by an ion exchange step.

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