Process for preparing an aqueous solution of potassium lactate, use of the aqueous solution of potassium lactate and process for manufacturing lactic acid

Description

1 / 17 “PROCESS FOR PREPARING AN AQUEOUS SOLUTION OF POTASSIUM LACTATE, USE OF THE AQUEOUS SOLUTION OF POTASSIUM LACTATE AND PROCESS FOR MANUFACTURING LACTIC ACID”

[001] The present invention relates to a process for preparing an aqueous lactate solution from a medium comprising magnesium lactate. The invention also relates to further processing of this solution to generate lactic acid.

[002] Lactic acid (LA), also known as 2-hydroxypropanoic acid, has many commercial applications, including use in the food industry and as a monomer for the manufacture of biodegradable and / or renewable polymers.

[003] Most commercial processes for the preparation of lactic acid are based on the fermentation of carbohydrates by microorganisms. These processes require strict control of temperature and pH. A common characteristic of all fermentation processes is the need to neutralize the acids excreted by the microorganisms in the process. A drop in pH below a critical value, depending on the microorganism used in the process, can damage the microorganism's metabolic process and interrupt the fermentation process. Therefore, fermentation processes generally result in the formation of lactic acid in the form of a salt, i.e., the salt of the base added to maintain the pH of the fermentation medium within the acceptable pH range for the microorganism.

[004] Despite many efforts in the field, it remains a challenge to generate high-purity lactic acid from the aqueous medium comprising the lactate salt. The challenge lies not only in achieving high purity but also in obtaining it in a way that can be operated reliably and consistently with energy efficiency. The latter is necessary, among other characteristics, to make lactic acid an attractive monomer for polymer manufacturing.

[005] An example of a process for the preparation of lactic acid is described in document WO98 / 22611. This patent publication describes a process for the production of lactic acid through the steps of producing acid. Petition 870250086776, dated 09 / 25 / 2025, pp. 55 / 76 2 / 17 lactic acid by fermentation, addition of an alkaline earth base, such as calcium base, to form alkaline earth lactate, such as calcium lactate, removal of biomass, reaction of the alkaline earth base with an ammonium source to form ammonium lactate, and recovery of lactic acid by electrodialysis of salt splitting.

[006] Document WO2005 / 123647 describes a process for the production of lactic acid from a medium comprising magnesium lactate which may be supplied by fermentation. The magnesium lactate is reacted with a sodium, potassium, calcium and / or ammonium hydroxide to form magnesium hydroxide and the corresponding monovalent and / or divalent lactate salt. As a means of converting the lactate salt to lactic acid, the document suggests bipolar electrodialysis or the addition of a strong mineral acid. However, these conversions are not included in the processes exemplified in this document.

[007] Document WO2011 / 095631 describes a process for the preparation of lactic acid comprising the steps of: a) providing an aqueous medium comprising magnesium lactate; b) adding a monovalent base to the aqueous medium comprising magnesium lactate 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 water-split electrodialysis to produce a first solution comprising monovalent base and a second solution comprising lactic acid and monovalent lactate salt, the electrodialysis being carried out at a partial conversion of 40 to 98% by moles;f) separate the second solution comprising lactic acid and monovalent lactate salt into lactic acid and a solution comprising monovalent lactate salt by liquid-vapor separation; g) recycle the solution from step f) comprising monovalent lactate salt to step d).

[008] It was found that, although water splitting electrodialysis is, in Petition 870250086776, dated 09 / 25 / 2025, pp. 56 / 76 3 / 17 principle, an attractive method for generating high-purity lactic acid, is not easy to perform in an economically attractive way due to its sensitivity and inherent energy requirements. This is even more true if the starting material is a lactate solution derived from a fermentation process, which is associated with the possible presence of a wide variety of organic and inorganic contaminants that can interfere with water-splitting electrodialysis, such as divalent cations.

[009] There is a technical need for a manufacturing process for a lactate solution that results in an economically attractive process for the production of lactic acid when the lactate solution is subjected to water-splitting electrodialysis. The present invention offers such a process.

[0010] The invention relates to a process for preparing an aqueous solution of potassium lactate with a magnesium ion content of less than 50 ppm, the process comprises the steps of: - In a first reaction step, react solid magnesium lactate in an aqueous suspension of magnesium lactate with KOH to form a first suspension of solid magnesium hydroxide in a first potassium lactate solution comprising magnesium ions, the reaction occurring under conditions such that the amount of excess OH- ions in the suspension is in the range of 20 to 300 ppm, - subject the first suspension to a solid-liquid separation step to separate the solid magnesium hydroxide from the first potassium lactate solution, - In a second reaction step, subject the first potassium lactate solution resulting from the solid-liquid separation step to a new reaction with KOH to form a second suspension of solid magnesium hydroxide in a second potassium lactate solution, the reaction occurring under conditions such that the amount of excess OH- ions in the suspension is greater than 300 ppm. - subject the second suspension to a solid-liquid separation step Petition 870250086776, dated 09 / 25 / 2025, pp. 57 / 76 4 / 17 to separate the solid magnesium hydroxide from the second potassium lactate solution, wherein the second potassium lactate solution has a magnesium ion content of less than 50 ppm.

[0011] The present invention is based on a number of important features combined.

[0012] A first important feature of the process according to the invention is that it aims at the manufacture of a potassium lactate solution instead of a sodium lactate solution. Potassium lactate solutions have been found to be more attractive for processing in water-split electrodialysis than sodium lactate solutions. In chemistry, sodium salts are the generally preferred metallic alkaline salts for reasons of cost, safety and availability.

[0013] Another important characteristic of the process is the excess of OH- ions in the first reaction step of 20 to 150 ppm and the excess of OH- ions in the second reaction step of more than 300 ppm, combining the two reaction steps with a separation of intermediate products. It has been found that these combined characteristics result in a final KOH solution with a very low content of divalent alkaline earth metal components, especially magnesium and calcium, while ensuring that magnesium hydroxide can be recovered from the process efficiently and economically.

[0014] The process according to the invention can be used, in particular, for the manufacture of lactic acid. Therefore, the invention also relates to the use of an aqueous solution of potassium lactate with a magnesium content of less than 50 ppm obtained according to any of the preceding claims in the manufacture of lactic acid.

[0015] Finally, the invention relates to a process for the manufacture of lactic acid, comprising the steps of: - to prepare an aqueous solution of potassium lactate with a magnesium content of less than 50 ppm according to the invention, - provide an aqueous solution of potassium lactate with a content of Petition 870250086776, dated 09 / 25 / 2025, pp. 58 / 76 5 / 17 magnesium less than 50 ppm for a reaction step in which potassium lactate is converted to lactic acid, for example, by reacting potassium lactate with a strong inorganic acid or by electrodialysis.

[0016] The invention will be discussed in more detail below.

[0017] The starting material in the process according to the invention is magnesium lactate in the solid state. The magnesium lactate can be supplied in the form of a fluid paste, but it is also possible to supply it in the form of a solid, for example, in the form of a filter cake or in the form of dry crystals. The magnesium lactate in the solid state can be suspended in water, where part of the magnesium lactate will be dissolved in the water and part will remain as a solid. Alternatively, the magnesium lactate in the solid state can also be suspended in the potassium lactate solution derived from the first or second filtration.

[0018] Both forms (magnesium lactate in solid form or magnesium lactate in aqueous suspension) will henceforth be referred to as magnesium lactate.

[0019] Magnesium lactate is combined with KOH to form a reaction medium. To facilitate processing, KOH is usually supplied in the form of a solution. The concentration of the KOH solution will depend on how the magnesium lactate is supplied. If the magnesium lactate is supplied in the form of a filter cake or dry crystals, a more dilute KOH solution may be desirable. Conversely, if the magnesium lactate is supplied in the form of a relatively dilute, flowing paste, a highly concentrated KOH solution will be desirable. Alternatively, KOH can be supplied in solid form, such as pellets. The reaction of magnesium lactate with KOH then results in the first suspension of solid magnesium hydroxide in a first solution of potassium lactate.

[0020] In one embodiment, the aqueous magnesium lactate suspension has a magnesium lactate content (calculated as magnesium lactate anhydrate) of at least 15% by weight. Preferably, the magnesium lactate content is at least Petition 870250086776, dated 09 / 25 / 2025, p. 59 / 76 6 / 17 20% by weight and, in particular, at least 25% by weight. Preferably, the aqueous magnesium lactate suspension has a magnesium lactate content (calculated as magnesium lactate anhydrate) of no more than 50% by weight of the total weight of the suspension.

[0021] In one embodiment, magnesium lactate in solid form comprises at least 60% by weight, preferably 70% by weight, more preferably 80% by weight, and in particular at least 85% by weight of magnesium lactate (calculated as magnesium lactate anhydrate) of the total weight of the solid.

[0022] Preferably, the first step of the reaction is carried out under agitation. In this way, it is possible to avoid high local concentrations of hydroxide in the suspension.

[0023] In the first step of the reaction, magnesium lactate is reacted with KOH to form a first suspension of solid magnesium hydroxide in a first solution of potassium lactate. The amount of KOH supplied is such that the amount of excess OH- ions in the first suspension is in the range of 20 to 150 ppm. It has been found that selecting an amount of excess OH- ions within the stipulated range during this step of the reaction ensures the obtaining of crystals with good filtering properties. These crystals can be easily removed from the potassium lactate solution without, for example, using excessively large separation equipment and / or using a large amount of water to wash the potassium lactate from the Mg(OH)2 crystals.

[0024] It is preferable that the amount of excess OH- ions in the first suspension be at most 125 ppm, more preferably at most 100 ppm and, in some embodiments, at most 70 ppm. In addition, or in combination, it may be preferable that the excess of OH- ions be at least 25 ppm, in particular at least 30 ppm and, more specifically, at least 35 ppm.

[0025] The excess of OH- ions in the solution is determined by potentiometric titration as follows: the liquid part of the suspension is withdrawn using a syringe fitted with a 0.45 μm filter to remove any residual solid from the sample. 5 to 10 g of the filtered samples are weighed, with precision Petition 870250086776, dated 09 / 25 / 2025, pp. 60 / 76 7 / 17 of 0.0001 g is placed in a titration vessel. 70 mL of Milli-Q water is added to the sample. The sample is titrated with 0.01 M hydrochloric acid, and the electrical potential difference is measured at different volumes of hydrochloric acid addition. The first equivalence point is determined by finding the maximum slope of the titration curve. The hydroxide concentration in the sample is then calculated using the following formula: volume of HCl at the 1st equivalence point [mL]x0.01 [^^]x17.007[-^]x1030H [PPm]=-------------------sample weight----~-----““-

[0026] It is preferable that the vast majority of the magnesium present in the system be recovered from the process after the first reaction step. In particular, it is preferable that, of the total amount of magnesium lactate in the initial aqueous magnesium lactate suspension, at least 75% be converted to potassium lactate and magnesium hydroxide in the first reaction step, in particular, at least 85%, more particularly, at least 90%, even more particularly, at least 95%, even more particularly, at least 98%. This conversion can be achieved by controlling the pH and obtaining an excess concentration of OH ions, as described in the present embodiments. Reaction time is typically between 30 and 60 minutes, with a minimum of 10 minutes.

[0027] The conversion can be calculated from the amount of magnesium lactate present in the recovered solid magnesium hydroxide. This value can be determined based on the amount of magnesium lactate supplied in the first reaction step and the amount of residual magnesium lactate present in the Mg(OH)2 filter cake recovered after separating the solid magnesium hydroxide from the first potassium lactate solution.

[0028] The magnesium hydroxide suspension in potassium lactate solution is subjected to a solid-liquid separation step to separate the solid magnesium hydroxide from the first potassium lactate solution. The solid-liquid separation step can be carried out in ways known in the art. Since the magnesium hydroxide product has good filtration properties, conventional filtration using vacuum, high pressure, and centrifugal forces, such as a filter of Petition 870250086776, dated 09 / 25 / 2025, pp. 61 / 76 An 8 / 17 horizontal belt, a pressurized belt filter, or a peeling centrifuge will be suitable for separating the solid magnesium hydroxide from the initial potassium lactate solution.

[0029] The amount of excess OH- ions in the range of 20 to 150 ppm in the first suspension is adequate to provide crystals with good filtering properties, but will also result in a first potassium lactate solution containing residual magnesium ions. To make the lactate solution more suitable for electrodialysis, the first potassium lactate solution is subjected to a further reaction with KOH to form a second suspension of solid magnesium hydroxide in a second potassium lactate solution. It has been found that when the amount of excess OH- ions in the second suspension is greater than 300 ppm, a second potassium lactate solution with a magnesium ion content of less than 50 ppm is obtained.The second potassium lactate solution is separated from the solid magnesium hydroxide by a solid-liquid separation step, thus providing a lactate solution that is more suitable for electrodialysis, resulting in a lactic acid production process with less downtime and therefore a more economically attractive lactic acid production process.

[0030] It is preferable that, in the second step of the reaction, the excess of OH- ions in the second suspension be above 400 ppm, in particular above 500 ppm, more particularly above 650 ppm and, in general, above 800 ppm. In this way, a second potassium lactate solution with a lower magnesium ion content is obtained. Preferably, the excess of OH- ions in the second suspension in the second step of the reaction is at most 10,000 ppm, since the magnesium hydroxide crystals obtained at relatively high levels of excess OH- ions have lower filtering capacity and are therefore more difficult to remove from a suspension by filtration. With the use of excess OH- ions above this concentration, the magnesium ion content in the second potassium solution would hardly decrease further.

[0031] In one embodiment, the difference between the excess of OH ions in the first Petition 870250086776, dated 09 / 25 / 2025, pp. 62 / 76 9 / 17 suspension in the first reaction step and the excess of OH- ions in the second suspension in the second reaction step is at least 100 ppm, in particular at least 200 ppm, more particularly at least 300 ppm, even more particularly at least 400 ppm and at most 1,200 ppm, in particular at most 1,000 ppm, more particularly at most 850 ppm, even more particularly at most 700 ppm, even more particularly at most 10,000 ppm. Thus, the greater excess of OH- ions in the second suspension in the second reaction step compared to the suspension in the first reaction step leads to a stronger reduction in the magnesium ion content of the first potassium lactate solution. Therefore, a second potassium lactate solution with a magnesium ion content of less than 50 ppm is obtained.

[0032] The concentration of OH- ions in the first suspension in the first reaction step and in the second suspension in the second reaction step depends on both the temperature and the pH of the respective suspension. At a higher temperature, the ionization of water increases, thus increasing the concentration of OH- ions and increasing the pH. On the other hand, the addition of OH- ions to the suspension in the form of a base also increases the concentration of OH- ions and the pH. Thus, a greater excess of OH- ions in the second suspension, compared to the first suspension, can be obtained by carrying out the second reaction step at a higher temperature than the temperature at which the first reaction step is carried out, by carrying out the second reaction step at a higher pH than the pH of the first reaction step, or by carrying out the second reaction step at a higher temperature and pH than the temperature and pH of the first reaction step.

[0033] To obtain a difference between the excess OH- ions in the first reaction step and the excess OH- ions in the second reaction step of at least 100 ppm, it is preferable that the second reaction step be carried out at a temperature that is at least 20°C higher than the temperature at which the first reaction step is carried out and / or that the second reaction step be carried out at a pH that is at least 0.5 higher than the pH at which the first reaction step is carried out. Petition 870250086776, dated 09 / 25 / 2025, pp. 63 / 76 10 / 17 completed.

[0034] In one embodiment, the second reaction step is carried out at a temperature that is at least 25°C higher and at most 75°C higher than the temperature at which the first reaction step is carried out. In this way, the excess of OH- ions in the second reaction is increased compared to the first reaction step, and a second potassium lactate solution with a magnesium ion content of less than 50 ppm is obtained.

[0035] Preferably, the first and second steps of the reaction are carried out at a temperature in the range of 20-100°C, especially 25-90°C, more specifically 30-80°C, the temperature in each step being selected individually. Preferably, the first step of the reaction is carried out at a temperature in the range of 20-70°C and the second step of the reaction is carried out at a temperature in the range of 40-90°C. If the temperatures of the first and second steps of the reaction are chosen so that the difference in excess OH- ions between the first and second steps of the reaction is less than a desired value, the difference in excess OH- ions may be increased by adding a base in the second step of the reaction.

[0036] In one embodiment, the pH in the second reaction step is at least 0.7 above the pH in the first reaction step, in particular at least 0.8. The pH in the second reaction step is generally at most 2.5 above the pH in the first reaction step, in particular at most 2. Preferably, the first and second reaction steps are carried out to obtain a pH in the range of 9.5 to 14, in particular in the range of 10 to 12.5, the pH in the two steps being selected individually. If the pH of the first and second reaction steps is chosen so that the difference in excess OH- ions between the first and second reaction steps is less than a desired value, the difference in excess OH- ions may be increased by carrying out the second reaction step at a higher temperature than that of the first reaction step.

[0037] Preferably, the second step of the reaction is carried out at a Petition 870250086776, dated 09 / 25 / 2025, pp. 64 / 76 11 / 17 temperature at least 20°C higher than the temperature at which the first reaction step is carried out, and the pH of the second reaction step is less than 0.5 above the pH of the first reaction step. Alternatively, the pH in the second reaction step is at least 0.5 above the pH in the first reaction step, and the second reaction step is carried out at a temperature that is at most 20°C higher than the temperature at which the first reaction step is carried out. In this way, it is not necessary to substantially increase the pH and temperature in the second reaction step compared to the first reaction step to increase the excess of OH- ions in the first reaction step compared to the second reaction step.Since only temperature and pH are substantially modified between the first and second reaction steps, this results in a more economically attractive way to obtain the increased excess of OH- ions in the second reaction step compared to the first reaction step.

[0038] It is preferable that the second potassium lactate solution have a magnesium ion content of less than 25 ppm, in particular less than 15 ppm, more particularly less than 10 ppm, even more particularly less than 5 ppm, or even less than 2 ppm. In this way, the lactate solution is even more suitable for a subsequent electrodialysis step in the manufacture of lactic acid.

[0039] Preferably, the process of preparing an aqueous solution of potassium lactate with a magnesium ion content of less than 50 ppm is carried out continuously.

[0040] An aqueous solution of potassium lactate with a magnesium content of less than 50 ppm is especially useful in the manufacture of lactic acid. Therefore, the invention relates, in other respects, to the use of the aqueous solution of potassium lactate with a magnesium content of less than 50 ppm, according to the invention, as a starting material in the manufacture of lactic acid and to a process for the manufacture of lactic acid.

[0041] Water splitting electrodialysis is a common way to convert potassium lactate into lactic acid and potassium hydroxide. Water splitting electrodialysis Petition 870250086776, dated 09 / 25 / 2025, pp. 65 / 76 A solution of 12 / 17 water, in particular, allows the direct conversion of a lactate salt into lactic acid and base. In this type of electrodialysis, bipolar membranes are generally used to split water into H+ and OH-, respectively, which combine with the anion and cation of the lactate salt, respectively, resulting in the production of separate solutions of lactic acid and base. However, the presence of divalent cations, such as magnesium, in the dialysis process can result in membrane fouling and decreased energy efficiency. Thus, the electrodialysis equipment needs to be cleaned regularly, which results in interruption of electrodialysis and decreased efficiency of lactic acid production. The aqueous potassium lactate solution with a magnesium content of less than 50 ppm, according to the invention, is less likely to affect the electrodialysis equipment. Thus, less equipment maintenance is required and, therefore, less interruption of electrodialysis.Lactic acid and potassium hydroxide can therefore be manufactured in a more economically attractive way.

[0042] In one embodiment, a lactic acid manufacturing process comprises the following steps: - to prepare an aqueous solution of potassium lactate with a magnesium content of less than 50 ppm according to the invention, - To provide an aqueous solution of potassium lactate with a magnesium content of less than 50 ppm for a reaction step in which potassium lactate is converted to lactic acid and potassium hydroxide by means of electrodialysis.

[0043] As an alternative to water-splitting electrodialysis, potassium lactate can be converted to lactic acid by reacting potassium lactate with a strong inorganic acid.

[0044] The potassium hydroxide produced by the electrodialysis of potassium lactate is preferentially recycled to the first reaction step and / or to the second reaction step for reaction with magnesium lactate. In this way, a more economical process is obtained. As the potassium hydroxide produced by electrodialysis generally has a temperature of around 40°C, the first and second steps Petition 870250086776, dated 09 / 25 / 2025, pages 66 / 76 13 / 17 of the reaction is preferably carried out at least at 40°C, in order to provide an even more economical process.

[0045] Lactic acid is normally produced by the fermentation of a carbohydrate source into lactic acid in the presence of a microorganism. To neutralize the fermentation medium, a base is added to the medium as a neutralizing agent, resulting in the formation of an aqueous fermentation medium comprising lactate. Thus, the process for the manufacture of lactic acid preferably comprises the step of fermenting a carbohydrate source into lactic acid in the presence of a microorganism, with the addition of magnesium hydroxide as a neutralizing agent, to form an aqueous fermentation medium comprising magnesium lactate. This aqueous medium can then serve as a base for the preparation of the aqueous potassium lactate solution according to the invention. Optionally, the aqueous medium is subjected to a biomass removal step before the preparation of the aqueous potassium lactate solution in order to substantially remove the microorganism used in the fermentation process.Optionally, the aqueous medium is concentrated before preparing the aqueous potassium lactate solution to provide a fluid magnesium lactate paste that can be fed to the first stage of the reaction. Optionally, a liquid-solid separation step is performed to obtain solid magnesium lactate. Optionally, the magnesium lactate dissolved in the aqueous fermentation medium is crystallized to obtain solid magnesium lactate. In this way, the magnesium lactate yield from the fermentation is increased. The solid magnesium lactate can then be used to prepare the aqueous magnesium lactate suspension.

[0046] Preferably, magnesium hydroxide recovered from the first and / or second suspensions, as obtained by subjecting the first and / or second potassium lactate suspensions to solid-liquid separation for the fermentation step, as a neutralizing agent. This results in a more economical lactic acid production process.

[0047] Preferably, the fluid magnesium lactate paste has a content of Petition 870250086776, dated 09 / 25 / 2025, pp. 67 / 76 14 / 17 Magnesium lactate (calculated as magnesium lactate anhydrate) of at least 30% by weight based on the total weight of the fluid paste. This concentration of magnesium lactate is advantageous for preparing a potassium lactate solution with a relatively high concentration of potassium lactate, which, in turn, can be used to produce a relatively high amount of lactic acid. This magnesium lactate content can, for example, be obtained by heating the aqueous medium to remove water and concentrate the aqueous medium.

[0048] The following example will illustrate the practice of the present invention in some of its preferred embodiments. Other embodiments within the scope of the claims will be apparent to a person skilled in the art. EXAMPLES

[0049] Examples 1 and 2 show the effect of relatively low or relatively high amounts of excess OH- ions in the first and second reaction steps on the filtering capacity of magnesium hydroxide (Mg(OH)2) particles and on the moisture content, potassium (K) content, and magnesium lactate (Mg) content of the Mg(OH)2 cake obtained after the first reaction step. Furthermore, Examples 3 to 5 show the effect of relatively low amounts of excess OH- ions in the first step and relatively high amounts of excess OH- ions in the second step on the magnesium ion content of the second potassium lactate (KL) solution.

[0050] In a first reaction step, the fluid paste of magnesium lactate (as anhydrate) of 42-47% by weight was reacted continuously for 1 hour in a first reactor with a KOH solution of 11-12% by weight at 50°C and at the pH indicated in Table 1 below, resulting in the formation of a first suspension of solid magnesium hydroxide (MgOH2) and a first solution of potassium lactate. After one hour of residence time in the first reactor, the Mg(OH)2 was separated from the first potassium lactate solution by filtration with a 7 μm mesh.

[0051] The first potassium lactate solution was then sent to a second reactor and, in a second reaction step, reacted continuously for 0.5 Petition 870250086776, dated 09 / 25 / 2025, pages 68 / 76 15 / 17 hours with an 11-12% by weight KOH solution at a higher temperature than that of the first reaction step or at a higher pH than that of the first reaction step, as indicated in Table 1 below. The second reaction step resulted in the formation of a second suspension of solid Mg(OH)2 and a second potassium lactate solution. After 0.5 hours of residence time in the second reactor, the Mg(OH)2 was separated from the first potassium lactate solution by filtration through a 1 µm mesh filter cloth.

[0052] After the first stage of the reaction, the filtering capacity of the Mg(OH)2 particles and the moisture content, potassium content and magnesium lactate content of the Mg(OH)2 cake were determined as shown in Table 2.

[0053] After the second stage of the reaction, the magnesium ion content of the second potassium lactate solution was determined as shown in Table 3.

[0054] Table 1 Example Reactor 1 Reactor 2 T °C PH [OH] PPm T °C PH [OH] PPm 1 50 11.4 322 50 12 675 2 50 10.8 38 50 10.8 50 3 50 10.8 54 50 12 666 4 50 11.1 65 50 12 675 5 50 11.1 65 80 11.2 721 Results

[0055] The results show that when the amount of excess OH ions in the first reactor was relatively high, as in example 1, the filtering capacity of Mg(OH)2 formed in the first reaction step exhibited a filtering capacity of 109 kg of dry solids / m2h, indicating that it was relatively difficult to separate the Mg(OH)2 formed under these conditions from the potassium lactate solutions.

[0056] When the amount of excess OH ions in the first and second reactors was <100 ppm, as shown in example 2, the filtering capacity of Petition 870250086776, dated 09 / 25 / 2025, pp. 69 / 76 16 / 17 The Mg(OH)2 formed in the first reaction step exhibited a filtration capacity of over 150 kg of dry solids / m2h, while the second potassium lactate solution contained more than 50 ppm of Mg.

[0057] However, when the amount of excess OH- ions in the first reactor was less than 150 ppm, as in examples 3-5, the Mg(OH)2 formed in the first reaction step has a filtration capacity of > 150 kg dry solids / m2h, indicating that the Mg(OH)2 formed in the first reaction step can be separated from the potassium lactate solutions with relative ease. Since the separation of Mg(OH)2 from the first potassium lactate solution is necessary before sending the first potassium lactate solution to the second reactor to produce the second potassium lactate solution with less than 50 ppm of magnesium ions, a relatively easy separation of Mg(OH)2 from the first potassium lactate solution after the first reactor contributes to a more efficient production of the second potassium lactate solution.

[0058] Furthermore, the Mg(OH)2 cake under the conditions of experiments 3-5 contains a relatively low amount of potassium, which makes the Mg(OH)2 obtained after the second reaction step suitable to be supplied as a neutralizing agent in a fermentation step.

[0059] Table 2 Example: Filtration capacity (kg ds / m2h) Mg in KL (ppm) Residual component in the Mg(OH)2 cake Moisture (% by weight) K (ppm) (Mg) Lactate (% by weight) 1 109 57 73.5 2015 0.7 2 188 169 71.3 436 1.7 3 169 138 75.9 338 1.2 4 314 145 71.2 786 1.0 5 314 145 71.2 786 1.0 Petition 870250086776, dated 09 / 25 / 2025, pp. 70 / 76 17 / 17

[0060] Furthermore, as can be seen in Table 3 below, the second potassium lactate solutions obtained in the processes under the conditions of Examples 3-5 contained less than 50 ppm of magnesium ion. In fact, when the first reaction step occurred at an excess of OH- ions less than 150 ppm and the second reaction step occurred at an excess of OH- ions greater than 150 ppm, the second potassium lactate solution contained between 0.7 and 3.7 ppm of magnesium ions. These Mg concentrations are much lower than the 490 and 100 ppm magnesium ion concentrations obtained in Example 6 of document WO2005 / 052800.

[0061] Due to the low concentration of magnesium ions, the second potassium lactate solutions obtained according to the processes in Examples 3 to 5 are very suitable for application in electrodialysis for the production of lactic acid.

[0062] Table 3 Example Mg in KL (ppm) 1 2.1 2 82 3 3.7 4 2.1 5 0.7

[0063] Thus, an excess amount of OH- ions in the first reaction step of less than 150 ppm and an excess amount of OH- ions in the second reaction step of greater than 150 ppm result in a second potassium lactate solution with a magnesium ion concentration of less than 50 ppm, while the process is more efficient because the Mg(OH)2 formed in the first reaction step is more easily separated from the first potassium lactate solution. Petition 870250086776, dated 09 / 25 / 2025, pp. 71 / 76

Claims

1 / 4 CLAIMS 1. Process for preparing an aqueous solution of potassium lactate with a magnesium content of less than 50 ppm, characterized in that it comprises the steps of - in a first reaction step, reacting magnesium lactate in the solid state or an aqueous suspension of magnesium lactate with KOH to form a first suspension of solid magnesium hydroxide in a first potassium lactate solution comprising magnesium ions, the reaction occurring under conditions such that the amount of excess OH- ions in the first suspension is in the range of 20 to 150 ppm, - subjecting the first suspension to a solid-liquid separation step to separate the solid magnesium hydroxide from the first potassium lactate solution, - in a second reaction step,The first potassium lactate solution resulting from the solid-liquid separation step is subjected to a further reaction with KOH to form a second suspension of solid magnesium hydroxide in a second potassium lactate solution, the reaction occurring under conditions such that the amount of excess OH- ions in the second suspension is greater than 300 ppm; the second suspension is subjected to a solid-liquid separation step to separate the solid magnesium hydroxide from the second potassium lactate solution, the second potassium lactate solution having a magnesium ion content of less than 50 ppm.

2. Process according to claim 1, characterized in that the second potassium lactate solution has a magnesium ion content of less than 25 ppm, in particular less than 15 ppm, more specifically less than 10 ppm, even more specifically less than 5 ppm, or even less than 2 ppm.

3. Process according to any of the preceding claims, characterized in that the aqueous magnesium lactate suspension has a magnesium lactate content (calculated as magnesium lactate anhydrate) of at least 15% by weight, preferably at least 20% by weight and, in particular, at least 25% by weight of the total weight of the suspension, and the aqueous magnesium lactate suspension has a magnesium lactate content (calculated as magnesium lactate anhydrate) of at most 50% by weight of the total weight of the suspension.

4. Process according to claim 1 or 2, characterized in that the magnesium lactate in solid state comprises at least 60% by weight, preferably at least 70% by weight, more preferably at least 80% by weight and, in particular, at least 85% by weight of magnesium lactate (calculated as magnesium lactate anhydrate) of the total weight of the solid.

5. A process according to any one of the preceding claims, characterized in that, in the first step of the reaction, the excess of OH- ions in the first suspension is, in particular, in the range of 20-125 ppm, more particularly in the range of 25-100 ppm, and even more particularly in the range of 30-70 ppm.

6. A process according to any of the preceding claims, characterized in that, in the second step of the reaction, the excess of OH- ions in the second suspension is, in particular, above 400 ppm, in particular above 500 ppm, more particularly above 650 ppm, generally above 800 ppm and, at most, 10,000 ppm.

7. A process according to any of the preceding claims, characterized in that: - the second step of the reaction is carried out at a temperature that is at least 20°C higher than the temperature at which the first step of the reaction is carried out, or - the pH in the second step of the reaction is at least 0.5 higher than the pH in the first step of the reaction.

8. Process according to claim 7, characterized in that the second step of the reaction is carried out at a temperature that is at least 25°C higher than the temperature at which the first step of the reaction is carried out and at most 75°C higher.

9. Process according to claim 7, characterized in that the pH in the second step of the reaction is at least 0.7 above the pH in the first step of the reaction, in particular at least 0.8, and in that the pH in the second step of the reaction is at most 2.5 above the pH in the first step of the reaction, in particular at most 2.

10. A process according to any of the preceding claims, characterized in that the first and second reaction steps are carried out at a temperature in the range of 20-100°C, in particular 20-90°C, more particularly 30-80°C, the temperature in the two steps being selected individually.

11. Use of an aqueous solution of potassium lactate with a magnesium content of less than 50 ppm, obtained as defined in any of the preceding claims, characterized by the fact that it is used in the manufacture of lactic acid.

12. A process for manufacturing lactic acid, characterized in that it comprises the steps of - preparing an aqueous solution of potassium lactate with a magnesium content of less than 50 ppm as defined in any of the preceding claims, - supplying the aqueous solution of potassium lactate with a magnesium content of less than 50 ppm to a reaction step in which potassium lactate is converted to lactic acid and KOH by means of water-splitting electrodialysis.

13. A process for manufacturing lactic acid according to claim 12, characterized in that the KOH obtained after electrodialysis is recycled for the first and / or second steps of the reaction.

14. A process for manufacturing lactic acid according to claim 13, characterized in that an aqueous solution of potassium lactate with a magnesium content of less than 50 ppm is obtained by a process comprising the steps of: - fermenting a carbohydrate source into lactic acid in the presence of a microorganism, with the addition of magnesium hydroxide as a neutralizing agent, to form an aqueous fermentation medium comprising magnesium lactate; - optionally, subjecting the aqueous medium to a biomass removal step; - optionally, performing a concentration step to provide a fluid paste of magnesium lactate; - optionally, performing a liquid-solid separation step to obtain solid magnesium lactate; - optionally, crystallizing the dissolved magnesium lactate to obtain solid magnesium lactate.

15. Process according to claim 13, characterized in that the lactic acid manufacturing process comprises a step of recycling magnesium hydroxide obtained from subjecting the first and / or second potassium lactate suspensions to solid-liquid separation for the fermentation step of a carbohydrate source. Petition 870250086776, dated 09 / 25 / 2025, pp. 75 / 76