JP2020045349A - Recovery of carboxylic acids from their magnesium salts by precipitation with hydrochloric acid, useful for fermentation broth treatment - Google Patents

Abstract

An efficient and complete method for the production of carboxylic acids using magnesium carboxylate, which can be produced by fermentation, as a starting material.
A method for preparing a carboxylic acid, the method comprising preparing a magnesium carboxylate, wherein the carboxylic acid corresponding to the carboxylate is 2,5-furandicarboxylic acid, fumaric acid, adipic acid Selected from the group consisting of: itaconic acid, citric acid, glutaric acid, maleic acid, malonic acid, oxalic acid, and a fatty acid having more than 10 carbon atoms; acidifying the magnesium carboxylate with hydrogen chloride (HCl); Thereby obtaining a solution comprising a carboxylic acid and magnesium chloride (MgCl ₂ ).
[Selection diagram] None

Description

The present invention relates to 2,5-furandicarboxylic acid, fumaric acid, adipic acid, itaconic acid, citric acid, glutaric acid, maleic acid, malonic acid, oxalic acid, and a group consisting of fatty acids having more than 10 carbon atoms. It is directed to a method for preparing the carboxylic acid of choice.

The production of the above carboxylic acids leads to various undesirable by-products, especially when produced by fermentation. Fermentation processes where carboxylic acids are excreted by microorganisms result in a decrease in pH. It is common practice to add a base to the fermentation medium to neutralize the pH, as such a decrease in pH can impair the metabolic processes of the microorganism. As a result, the carboxylic acid produced in the fermentation medium is typically present in the form of a carboxylate.

A disadvantage of obtaining the carboxylic acid from the fermentation process in the form of a carboxylic acid salt is that one or more of the carboxylic acid is separated from the salt, ie, to convert the salt to a carboxylic acid. Additional steps are required, which typically result in the loss of carboxylic acids and / or carboxylate salts, and thus, a decrease in the overall fermentation or process yield.

A further disadvantage of such processes is that they typically result in considerable salt waste. For example, the separation step often involves acidification of the carboxylate with sulfuric acid, resulting in sulfate as waste.

It is an object of the present invention to provide a separation step in which the carboxylic acid is separated from the salt solution with a suitable conversion yield.

It is a further object of the present invention to provide a method that is free or substantially free of salt waste.

At least one of these objectives is directed to 2,5-furandicarboxylic acid, fumaric acid, adipic acid, itaconic acid, citric acid, glutaric acid, maleic acid, malonic acid, oxalic acid, and fatty acids having more than 10 carbon atoms A method for preparing a carboxylic acid selected from the group of
2,5-furandicarboxylic acid, fumaric acid, adipic acid, itaconic acid, citric acid, glutaric acid, maleic acid, malonic acid, oxalic acid, and magnesium carboxylate selected from the group of fatty acids having more than 10 carbon atoms The process of preparing
Acidifying the magnesium carboxylate with hydrogen chloride (HCl), thereby obtaining a solution comprising a carboxylic acid and magnesium chloride (MgCl ₂ );
Optionally, a thickening step, wherein the solution comprising carboxylic acid and MgCl ₂ is thickened,
It precipitated the carboxylic acid from the solution containing the carboxylic acid and MgCl _2, thereby filled by providing the method comprising the step of obtaining a carboxylic acid precipitates and MgCl ₂ solution.

Fermentation processes can also result in impurity profiles that are difficult to process in further downstream purification steps. The fermentation process depends in principle on the carboxylic acid to be produced and can thus produce a different impurity profile (for example, not only at the concentration level, but also at the type of impurities potentially present). That is, downstream processing steps for further enrichment and purification can also vary with the carboxylic acid. In particular, for the carboxylic acids mentioned according to the invention, the process according to the invention starts not only from magnesium carboxylate which can be produced by a chemical synthetic processing route, but also, if applicable, from magnesium carboxylate which can be produced by fermentation. It has been found that it is an efficient and complete method for the production of these carboxylic acids used as materials.

We have found that the addition of HCl to the magnesium salt of the selected carboxylic acid and subsequent precipitation of the carboxylic acid from the solution results in a very efficient separation of the carboxylic acid from the magnesium carboxylate solution. Has been found to bring.

In particular, it has been found that the selected carboxylic acids precipitate with very high efficiency from carboxylate solutions acidified by HCl. Without wishing to be bound by any theory, we predict that the high efficiency of the precipitation is due to a particularly high salting-out effect of MgCl _{2 in} the solution. In particular, the salting out effect is expected to be caused by the specific combination of HCl, magnesium and the selected carboxylic acid of the present invention. The particular high salting-out effect for these acids observed in the process of the invention was surprising to the inventors, as the salting-out effect is generally difficult to predict.

That is, when using the method of the present invention for the carboxylic acids specifically mentioned above, carboxylic acid precipitates can be obtained in high yields from magnesium carboxylate solutions, which are obtained, for example, in fermentation processes. Fermented mixture. Furthermore, the carboxylic acid precipitate obtained has a relatively high purity. This is because the precipitation step in the method of the present invention does not result in a large amount of precipitation of compounds other than carboxylic acid. Furthermore, a magnesium chloride solution is obtained. This solution can be further processed as described below.

In addition, certain choices for HCl and magnesium carboxylate provide reduction of salt waste, especially when combined with a pyrolysis step.

Preferably, the method further comprises the following steps:
Subjecting the MgCl ₂ solution to a pyrolysis step at a temperature of at least 300 ° C., thereby decomposing the MgCl ₂ to magnesium oxide (MgO) and HCl;
Optionally, dissolving the HCl formed in the pyrolysis step in water, thereby obtaining an HCl solution; and, optionally, contacting the MgO with water, thereby obtaining Mg (OH) ₂ , Wherein the Mg (OH) ₂ is optionally recycled for use in a fermentation process, preferably the fermentation process provided with the magnesium carboxylate from the first step.

An advantage of these additional steps is that a process can be obtained that is free or substantially free of salt waste. The HCl solution can be reused for the acidification step of the method of the invention. The Mg (OH) ₂ can be recycled for use in the fermentation process.

The term "carboxylate", as used in the present specification refers to a conjugate base of a carboxylic acid, which is generally represented by the formula RCOO ^- can be represented by. The term "magnesium carboxylate" refers to the magnesium salt of the carboxylic acid to be prepared in the method of the invention.

The term "carboxylic acid corresponding to the carboxylate" refers to a carboxylic acid obtained by acidifying the carboxylate. Therefore, it can also be referred to as acidified carboxylate. The carboxylic acid corresponding to the carboxylate may generally be represented by the formula RCOOH.

The term "precipitating" as used herein refers to the formation of a solid starting from a completely dissolved state. The carboxylic acids can be precipitated in crystalline or amorphous form. By precipitating the carboxylic acid according to the method of the invention, the carboxylic acid can also be purified. If the magnesium carboxylate solution contains dissolved impurities, precipitation of the carboxylic acid typically separates the carboxylic acid from such impurities.

The term "solution to be precipitated" as used herein refers to a solution that will be subjected to precipitation. Typically, the term refers to a solution containing the carboxylic acid and MgCl ₂ obtained after acidification, optionally subjecting the solution to a thickening step and / or a step where extra MgCl ₂ is added. Refers to a solution containing carboxylic acid and MgCl ₂ obtained after the reaction. However, in the case of a second or further precipitation step, the term “solution to be precipitated” refers to the MgCl ₂ solution obtained after the last or last precipitation step, optionally wherein this solution is a thickening step and / or Alternatively, it refers to a MgCl ₂ solution obtained after being subjected to a step of adding extra MgCl ₂ . Such a MgCl ₂ solution may still contain a carboxylic acid, which may be obtained by subjecting it to a second or further precipitation step.

The method of the present invention provides 2,5-furandicarboxylic acid, fumaric acid, adipic acid, itaconic acid, citric acid, glutaric acid, maleic acid, malonic acid, oxalic acid, and a group of fatty acids having more than 10 carbon atoms. Has been found to work efficiently for carboxylic acids selected from Thus, the magnesium carboxylate may be selected from the magnesium salts of these carboxylic acids. Good results have been obtained with carboxylic acids selected from the group consisting of adipic acid, itaconic acid, 2,5-furandicarboxylic acid, and fumaric acid.

The magnesium carboxylate provided in the method of the present invention can be obtained in a fermentation process.

The magnesium carboxylate may be provided in a solid (eg, crystalline form). Alternatively, the magnesium carboxylate may be in dissolved form, for example, as part of a solution or suspension. Such a solution or suspension containing dissolved magnesium carboxylate may be aqueous, and in particular may be obtained in a fermentation process. An example of a suspension can be, for example, a suspension containing dissolved magnesium carboxylate and insoluble biomass, such as a fermentation broth. When the magnesium carboxylate is provided in dissolved form, the magnesium carboxylate solution or suspension is 1-700 g, preferably 100-600 g, more preferably 200 g per liter of solution or suspension. It may have a concentration of 500500 g of magnesium carboxylate.

When the carboxylate is provided as a solution or suspension, the concentration of magnesium carboxylate at which the carboxylic acid precipitates upon acidification can depend on the HCl concentration. For example, if the carboxylate is acidified with an HCl solution having a high HCl concentration (eg, 20-30% by weight), the carboxylic acid precipitates at a relatively low carboxylate concentration (eg, 1-10% by weight or Around 1-10% by weight). However, if lower HCl concentrations (eg, 10-20% by weight) are used, higher carboxylate concentrations (eg, 10-50% by weight) may be required for precipitation to occur. For practical reasons, the upper limit of magnesium carboxylate concentration in magnesium carboxylate solution is the maximum solubility of magnesium carboxylate at a maximum temperature of 75 ° C. This concentration is typically about 20% by weight magnesium carboxylate or lower, based on the total weight of the solution. However, it can vary for the particular carboxylate used. To bring the magnesium carboxylate into a completely dissolved form, a concentration higher than 20% by weight may require that the solution have a temperature of 75 ° C. or higher. This temperature is bad for the equipment with regard to the corrosion susceptibility of the materials used in the presence of HCl.

In order to obtain as much carboxylic acid as possible after acidification and precipitation, the carboxylate concentration going to the acidification is preferably as high as possible. When the magnesium carboxylate is provided as a solution, the upper limit of magnesium carboxylate concentration is determined by the solubility of magnesium carboxylate and the temperature at which the device is still sufficiently resistant to corrosion due to HCl. When the carboxylate is provided as a suspension, typically the suspension's agitation determines the upper limit. If the carboxylate is provided as a solid cake, the solid-liquid separation and the resulting attached water will typically determine the upper limit. To support high carboxylic acid yields after acidification and precipitation, the HCl concentration is preferably as high as economically feasible. This is because the introduction of extra water dilutes the system. Carboxylate and combinations of the above mentioned was put concentration of HCl is preferably shall result a situation where MgCl ₂ is the number of carboxylic acids as possible and remains left in the solution precipitates during the precipitate step . One skilled in the art can vary the two concentrations to achieve the desired result. For example, good results have been obtained at 40-75 ° C. with a combination of HCl of 15-25% by weight and magnesium carboxylate concentration of 20-50% by weight.

If the magnesium carboxylate solution or suspension is obtained from a fermentation process that does not have a sufficiently high magnesium carboxylate concentration, the solution may be thickened, for example, by evaporation.

In a preferred embodiment of the invention, magnesium carboxylate is produced directly, in contrast to first fermentation and then addition of base to form magnesium carboxylate, making the treatment as simple as possible. And in order to prevent the use of additional processing steps, the magnesium carboxylate is obtained in a fermentation using a magnesium-based base for neutralization. The method of the present invention further preferably comprises a magnesium carboxylate fermentation at 25-60 ° C., wherein the carboxylate solution obtained when adding the base in the fermentation comprises 1-30% by weight of magnesium carboxylate. So that the magnesium carboxylate as a fermentation product does not precipitate directly. Precipitating magnesium carboxylate directly in the fermentation broth during fermentation requires rather extreme fermentation conditions, such as magnesium carboxylate concentrations of more than 40% or even more than 50% by weight, which Not preferred for the microorganism, fermentation yield and / or equipment. To precipitate the magnesium carboxylate from the fermentation broth after fermentation, preferably another precipitation step is applied. Such a precipitation step is, for example, a thickening step as described above or a cold precipitation as described further below. The precipitate thus obtained may then be dissolved in water to form an aqueous magnesium carboxylate solution or suspension.

The method of the present invention further includes the acidification step, which in the magnesium carboxylate is acidified by HCl, thereby obtaining a solution containing a carboxylic acid and MgCl _2. The present inventors have, HCl is other acids found that preferred example H ₂ SO acidifying agent than like _4. First, the use of HCl provides for efficient precipitation, such as the advantageous salting-out effects described above. In particular, the presence of MgCl ₂ reduces the solubility of the carboxylic acid, which results in more efficient precipitation of the acid. Furthermore, the reaction of the magnesium carboxylate and HCl are also compared to the particular other and as compared to the magnesium salt of a number of carboxylic acids containing MgSO _4, and salts having a relatively high solubility of (MgCl ₂₎ Results . A high solubility of the salt obtained by acidification is desirable, since as little as possible this salt should precipitate in the precipitation step. Therefore, the maximum concentration of carboxylic acid in the solution to be precipitated is determined in part by the solubility of the salt obtained in the acidification step. That is, if the salt has a high solubility, a high carboxylic acid concentration can be obtained without precipitation of the salt, which results in an efficient precipitation of the carboxylic acid.

Acidification is typically performed with an excess of HCl. The excess is preferably low, so that the MgCl ₂ solution obtained after precipitation is not highly acidic, which may be undesirable in view of further processing such a solution. For example, the excess of HCl used may be such that the resulting MgCl ₂ solution after precipitation has a pH of 1 or higher, such as a pH of about 1.5. One skilled in the art knows how to calculate the maximum allowable excess for such one or higher pH based on reaction stoichiometry. In order to obtain a sufficiently complete acidification, MgCl ₂ solution is該得is preferably lower than 4, more preferably a pH lower than 3.

HCl acidification can be, for example, by contacting the magnesium carboxylate with HCl, for example, by contacting the magnesium carboxylate (in solid, suspension or solution) with an aqueous HCl solution or by adding a magnesium carboxylate solution or suspension. This can be done by contacting the turbid matter with HCl gas.

If an HCl solution is used in the acidification step, it preferably comprises at least 5%, more preferably at least 10%, even more preferably at least 20% by weight of HCl. Such a concentration is generally sufficient to acidify the magnesium carboxylate. A high HCl concentration is desirable because of the salting out effect mentioned above. Due to the low boiling point of HCl and the HCl / H ₂ O azeotrope, the HCl concentration in the HCl solution will typically not be higher than 40%, especially when the HCl solution is used at atmospheric pressure. Preferably, the HCl concentration is used at an HCl concentration of 15 to 25% by weight, based on the total weight of the HCl solution. Nevertheless, HCl concentrations up to 100% may also be used, in which case the HCl solution will typically be at elevated pressure (eg, above atmospheric pressure) and optionally at a lower temperature (eg, less than 20 ° C.). Low).

If HCl gas is used, the HCl gas can be contacted by contacting it with a carboxylate solution or suspension. In particular, HCl gas can be blown through the solution or suspension. If HCl gas is used, the HCl may be obtained from a pyrolysis step, such as, for example, those described further below.

Preferably, the acidification is performed at a temperature of 75 ° C or lower. At higher temperatures, adapting the device to its harsh conditions becomes uneconomical. Taking into account the freezing point of the water, the acidification is typically carried out at a temperature above 0 ° C. Temperatures above 20 ° C. are preferred to avoid using cooling machines. Temperatures of 40 ° C. or higher, or even 60 ° C. or higher, are even more preferred, since more magnesium carboxylate can be dissolved at these higher temperatures. The temperature of the magnesium carboxylate solution or suspension is typically determined by and corresponds to the temperature at which the acidification is performed.

The method of the invention may comprise a thickening step, in which the solution obtained after acidification with HCl is thickened. Higher concentrations of carboxylic acid in the solution will increase the efficiency of carboxylic acid precipitation. The thickening step can be performed by evaporation. In the thickening step, 10-90% of the total amount of water present in the solution can be removed. However, preferably MgCl ₂ is not precipitated as a result of the enrichment. Therefore, the solution obtained after acidification is preferably thickened lower MgCl ₂ concentration than or equal the saturation point and the saturation point of MgCl _2.

The method of the invention further comprises precipitating the carboxylic acid from the solution obtained in the acidification step, or, if present, from the solution obtained in the thickening step. This step may be referred to as the (first) precipitation step. The precipitation may be by any precipitation method known in the art, such as by reactive precipitation, or by cooling, thickening and evaporating the solution to be precipitated, or by the solution to be precipitated. By adding an anti-solvent to the mixture.

Precipitation is preferably established by acidifying the magnesium carboxylate with HCl. This type of precipitation can be referred to as reactive precipitation. In reactive precipitation, precipitation occurs during acidification. As a result, the acidification of the magnesium carboxylate and the precipitation of the carboxylic acid thus obtained are performed as one step. Accordingly, the method of the present invention comprises the steps of optionally providing a magnesium carboxylate obtained in a fermentation process (as described above); and acidifying the magnesium carboxylate with HCl (eg, an aqueous HCl solution); This would include the step of obtaining a carboxylic acid precipitate and a MgCl ₂ solution. It is noted that the precipitation step actually results in a suspension with the carboxylic acid precipitate present in the MgCl ₂ solution.

Reactive precipitation can be performed by choosing conditions in the acidification step such that immediate precipitation of the carboxylic acid can occur. Those skilled in the art know how to establish such conditions. In particular, the magnesium carboxylate concentration can be selected such that acidification with HCl results in a carboxylic acid concentration above the saturation point of the carboxylic acid. As the skilled person will know, the value for the saturation point depends on the carboxylic acid used.

The precipitation step can also be carried out by cooling the solution to be precipitated, for example the solution formed in the acidification step or, if present, the solution obtained in the thickening step. This type of precipitation can be referred to as cold precipitation. The cooling step may require that the solution to be the precipitate is first heated to substantially the temperature at which all of MgCl ₂ and carboxylic acid are dissolved. The solution to be precipitated can be cooled from a temperature above the nucleation temperature of the carboxylic acid in the solution to a temperature below the nucleation temperature of the carboxylic acid in the solution. The nucleation temperature is the highest temperature at which a solid, especially a precipitate, is formed. This temperature depends, inter alia, on the concentration of MgCl ₂ , the carboxylic acid and the presence of other components. It is therefore not possible to give a single temperature value for the nucleation temperature. However, in general, the solution to be precipitated is cooled from a temperature of at least 35 ° C to a temperature of less than 30 ° C, preferably to a temperature of at least 40 ° C to less than 25 ° C. Larger temperature differences make it possible to increase the yield of the carboxylic acid precipitate. In the case of cold precipitation, the carboxylic acid concentration before cooling is preferably as close to the solubility as economically feasible. The carboxylic acid concentration may be equal to the saturation point of the carboxylic acid or may be up to 5 g / L below the saturation point of the carboxylic acid, preferably up to 10 g / L.

Furthermore, precipitation, the solution containing the carboxylic acid and MgCl _2, preferably by evaporation, by thickened, can be established. Evaporation of a portion of the solvent of the solution containing the carboxylic acid and MgCl ₂ results in a higher concentration of the carboxylic acid and a stronger salting out effect, which increases precipitation.

Further, precipitation can be established by adding an anti-solvent to the solution to be precipitated. Examples of anti-solvents are alcohols, ethers and ketones.

Preferably, the MgCl ₂ solution obtained after precipitation may be subjected to a second and / or further precipitation step, thereby forming an additional carboxylic acid precipitate and a second and / or further MgCl ₂ solution I do. It said second or further precipitation step is performed in order to recover at least a portion of the carboxylic acid remains in the MgCl ₂ solution obtained in the previous precipitation step. In this case, the previous precipitation step of the present invention may be referred to as a first precipitation step. The MgCl ₂ solution obtained in the first precipitation of the method may still contain small amounts of carboxylic acids. A second precipitation step can be performed to recover at least a portion of the carboxylic acid. Such second precipitation step may be conducted under conditions similar to said first precipitation step may include the addition of thickening step and / or MgCl ₂ is carried out before the precipitate process.

In a preferred embodiment, the method of the invention comprises a first precipitation reaction, which is a reactive precipitation step, after which the MgCl ₂ solution obtained in this step is subjected to a cooling and / or evaporation step. Is done. The cooling and / or evaporation step is a further precipitation step, in which additional carboxylic acid is precipitated, and the loss of carboxylic acid and the process yield are thus improved.

Before any precipitation step, magnesium chloride may be added to the solution to be precipitated or to the HCl solution. This solution to be precipitated can be a solution containing the magnesium carboxylate solution (for example in the case of a reaction precipitation) or a solution containing the carboxylic acid and magnesium chloride (as obtained in the acidification step). Such added magnesium chloride may increase the salting out effect, thereby increasing carboxylic acid precipitation.

Preferably, the method further comprises:
Subjecting the MgCl ₂ solution to a pyrolysis step at a temperature of at least 300 ° C., thereby decomposing the MgCl ₂ to MgO and HCl; and dissolving the HCl formed in the pyrolysis step in water. Obtaining a HCl solution therefrom; and contacting the MgO with water, thereby obtaining Mg (OH) ₂ .

As described above, an advantage of these additional steps is that a process can be obtained that has no or substantially no salt waste.

Pyrolysis as described herein may also be suitably applied in the method of the invention. Therefore, thermal decomposition used in the present invention can be carried out by contact with a hot gas stream by spraying the MgCl ₂ solution. The temperature of the hot gas is equal to the temperature at which pyrolysis takes place, as described below.

The combination of pyrolysis in the acid / salt separation of magnesium carboxylate from the fermentation process has not been previously described to the applicant's knowledge. We have found that MgCl ₂ can be pyrolyzed by pyrohydrolysis at relatively low temperatures (as opposed to, for example, CaCl ₂ which begins to decompose at about 800 ° C. or higher). understood. This is advantageous, because the MgO formed still has a sufficiently high reactivity, which can be used effectively, for example, in fermentations.

Apparatus suitable for performing pyrolysis are known in the art. Pyrolysis may be performed using a roaster, such as a spray roaster or a fluidized bed roaster. Such a device can be obtained, for example, with SMS Siemag. The use of a spray roaster is preferred. Spray roasters have low energy costs (as compared to fluidized bed roasters) because they require relatively low temperatures (as described below). Spray roasters have also been found to produce reactive MgO particles, which are very suitable for use as neutralizing agents in fermentations.

Preferably, the pyrolysis is performed at a temperature of at least 300 ° C., which is the lowest temperature at which MgCl ₂ decomposes. Preferably, the pyrolysis is performed at a temperature of at least 350C, for example 350-450C. Due to energy costs, the temperature is preferably below 1000 ° C, more preferably below 800 ° C. For example, the temperature at which the pyrolysis takes place can be 350-600 ° C or 300-400 ° C. In addition, it is undesirable to use a temperature that is too high for the pyrolysis step, since it reduces the reactivity of the MgO formed, so that it is less suitable for use as a neutralizing agent in fermentation. It is not suitable.

Pyrolysis as applied in the present invention is preferably carried out at a pressure of 0.1 to 10 bar. However, the use of elevated pressure is undesirable because of the increased risk of corrosion by the HCl, which cannot condense. Preferably, the pyrolysis is performed at atmospheric pressure, especially when using a roaster, to avoid unnecessary energy costs and the need for expensive high pressure equipment.

Magnesium oxide (MgO) is one of the products of the pyrolysis and is typically obtained in powder form. The magnesium oxide hydrates the water, for example by quenching the MgO with water, thereby forming a magnesium hydroxide (Mg (OH) ₂ ) suspension. The magnesium hydroxide suspension is preferably recycled for use in the fermentation process. For example, the Mg (OH) ₂ can be used as a neutralizing agent in a fermentation process. In this case, the Mg (OH) ₂ can be first washed with water to remove chloride ions, typically to a content of less than 1000 ppm. The presence of chloride ions is undesirable because they can cause corrosion problems when added to the fermentation vessel. Since Mg (OH) ₂ has low solubility in water, such a washing step will typically not result in a significant loss of Mg (OH) ₂ . Alternatively, the Mg (OH) ₂ is first converted to magnesium carbonate (MgCO ₃ ), which is then used as a neutralizing agent in the fermentation process. Also, combinations of these two steps may be applied, it in Mg (OH) part of the _two is being cleaned and reused, and the second portion is converted into MgCO ₃ and then the process Reused in Some of the MgO can even be used directly in the fermentation. The HCl obtained in the pyrolysis step may be dissolved in water, thereby forming an aqueous HCl solution. Preferably, the HCl obtained in the pyrolysis step is recycled by using it in the acidification step in the process of the invention, for example as HCl gas or an aqueous HCl solution.

The magnesium carboxylate provided in the method of the present invention can be obtained in a fermentation process. In such fermentation processes, the carbohydrate source is typically fermented by microorganisms to form carboxylic acids. Next, a magnesium base is added as a neutralizing agent during the fermentation to provide the magnesium salt of the carboxylic acid. Examples of suitable magnesium bases, magnesium hydroxide (Mg (OH) _2), magnesium carbonate (MgCO ₃₎ and magnesium bicarbonate _{(Mg (HCO 3) 2)} . An advantage of using Mg (OH) ₂ as a base is that this compound can be provided by the method of the present invention. The use of MgCO ₃ is also desirable and can easily be obtained by converting the Mg (OH) ₂ obtained in the process of the invention. Furthermore, the use of MgCO ₃ or Mg (OH) ₂ is desirable, since hydroxides and carbonates are not expected to have a detrimental effect on the salting out effect of the process of the invention (neutralization may leave solution as CO ₂ in either carbonate also gas remaining after).

In one embodiment, the fermentation process may include a purification step, wherein the magnesium carboxylate obtained during crystallization is crystallized from a fermentation broth, which is then subsequently dissolved in water to form an aqueous solution. A solution may be formed, which typically has a higher carboxylate concentration than the fermentation broth. Such a purification step may have the advantage that, due to the higher concentration of the magnesium carboxylate, a higher yield can be obtained in the first precipitation step.

However, as described above, the magnesium carboxylate preferably remains in dissolved form when the magnesium base is added as a neutralizing agent. This has the advantage that the magnesium carboxylate is pumpable and can be used directly in the acidification step. Further, the acidification step is easy to control when the magnesium carboxylate is in a dissolved form. In particular, the magnesium carboxylate present in the magnesium carboxylate solution or suspension obtained after addition of the magnesium base comprises at least 90% by weight, preferably at least 95% by weight, more preferably at least 99% by weight of magnesium. Contains carboxylate in dissolved form. Small amounts of solids (at most 10% by weight) may still not have the adverse effects mentioned above.

The crystallization can include at least one thickening step, such as a water evaporation step, a cooling step, a seeding step, a separation step, a washing step, a recrystallization step, and the like. The thickening can be performed as a separate step or together with crystallization (eg evaporative crystallization).

The present invention is further described by the following examples.

Preparation of magnesium dicarboxylate

Magnesium hydroxide was added to the aqueous solution of the dicarboxylic acid and heated until complete dissolution. Four different carboxylic acids were used: adipic acid, fumaric acid, itaconic acid, and 2,5-furandicarboxylic acid. The amounts of each component are given in Table 1. The resulting dicarboxylate solution was meant to resemble the magnesium dicarboxylate solution obtained in the fermentation process. Although the magnesium dicarboxylate solution obtained in the fermentation process generally contains compounds other than magnesium dicarboxylate, such as relatively large amounts of impurities, the magnesium dicarboxylate solution prepared for this example may be used in the fermentation process. It was sufficiently similar to the resulting magnesium dicarboxylate solution and was considered to be proof of the principle that the present invention works.

Dicarboxylic acid precipitation

An amount of an aqueous solution of HCl was added to the magnesium dicarboxylate solution from Example 1, as shown in Table 2. The temperature of the mixture thus obtained is also given in Table 2. The mixture was cooled to 20 ° C. and a precipitate formed. During cooling, a sample of the solution was taken for each 10 ± 1 ° C. The composition of the sample and the total amount of precipitate formed were determined.

The sample was taken only from the solution (for sampling, the stirrer was stopped for a few seconds and after the crystals had settled, the sample was taken from the upper layer). Magnesium and dicarboxylic acids in the solution were analyzed and expressed as g / g water. The amount of crystals formed was calculated as the difference between the mass of dicarboxy initially and the mass of dicarboxy remaining in solution.

The results are shown in Tables 3 to 6 for adipic acid, fumaric acid, itaconic acid and 2,5 furandicarboxylic acid, respectively.

These results correspond to a total recovery of more than 97% for adipic acid, more than 72% for fumaric acid, more than 80% for itaconic acid, and more than 96% for 2,5-furandicarboxylic acid.

This example shows that adipic, fumaric, itaconic and 2,5-furandicarboxylic acids can be obtained efficiently using the method of the present invention. During precipitation, substantially all of the magnesium ions remain in solution while the majority of the dicarboxylic acid precipitates. It is concluded that acidification with HCl and subsequent crystallization results in a very efficient separation of the dicarboxylic acid from the magnesium dicarboxylate solution.

Precipitation of citric acid

In the first experiments with citric acid, citric acid 5 g, it was added to a saturated solution of MgCl _2.

In a second experiment with citric acid, 15 g citric acid were added to a saturated solution of MgCl _2.

In a third experiment with citric acid, 5 g of magnesium chloride was added to a saturated solution of citric acid.

In a fourth experiment with citric acid, 15 g of magnesium chloride was added to a saturated solution of citric acid.

A precipitate formed in all four experiments. The citric acid and Mg content of the precipitate was analyzed using HPLC. The results are shown in Table 7.

This experiment shows that citric acid can be precipitated from a magnesium chloride solution.

Claims (18)

A method for preparing a carboxylic acid, comprising:
Step of preparing magnesium carboxylate, wherein the carboxylic acid corresponding to the carboxylate is 2,5-furandicarboxylic acid, fumaric acid, adipic acid, itaconic acid, citric acid, glutaric acid, maleic acid, malonic acid, Oxalic acid and selected from the group consisting of fatty acids having more than 10 carbon atoms;
Acidifying the magnesium carboxylate with hydrogen chloride (HCl), thereby obtaining a solution comprising a carboxylic acid and magnesium chloride (MgCl ₂ );
Optionally, a thickening step, wherein the solution comprising carboxylic acid and MgCl ₂ is thickened;
Step from the solution containing the carboxylic acid and MgCl ₂ precipitated the carboxylic acid, to obtain thereby a carboxylic acid precipitates and MgCl ₂ solution,
The method comprising: Subjecting the MgCl ₂ solution to a pyrolysis step at a temperature of at least 300 ° C., thereby decomposing the MgCl ₂ to magnesium oxide (MgO) and HCl; and converting the HCl formed in the pyrolysis step to water. dissolved in, thereby obtaining a HCl solution; re and the MgO in contact with water, thereby obtaining a Mg (OH) _2, the Mg (OH) ₂ is for use in any manner fermentation process Used,
The method of claim 1, further comprising: The method according to claim 2, wherein the pyrolysis is performed using a spray roaster. 4. The process according to claim 2, wherein the pyrolysis is carried out at a pressure of 0.1 to 10 bar, preferably at atmospheric pressure. The method according to any one of claims 2 to 4, wherein the pyrolysis is performed at a temperature of 300 to 450C. Mg (OH) ₂ is converted to MgCO _3, which is used as a neutralizing agent in the next fermentation process, the method according to any one of claims 2-5. Thermal decomposition, by spraying the MgCl ₂ solution is effected by contacting a flow of hot gas, the method according to any one of claims 2-6. 8. The method according to any one of claims 1 to 7, wherein acidifying the magnesium carboxylate and precipitating the carboxylic acid thus formed are performed in one step or as one step. the method of. MgCl ₂ solution as in the MgCl ₂ solution or concentrated is subjected to a second precipitation step, recovering at least a portion of the carboxylic acid remains in the MgCl ₂ solution obtained in the first precipitation step, A method according to any one of the preceding claims. It said second precipitation is preferably to at least 30 ° C. temperature from a temperature below 25 ° C., is carried out by the MgCl ₂ solution is cooled and / or thickening method of claim 8. Prior of the second precipitation, additional MgCl ₂ is added to the MgCl ₂ solution, The method of claim 8 or 9. The method according to any one of claims 1 to 11, wherein the carboxylic acid is selected from the group consisting of adipic acid, itaconic acid, 2,5-furandicarboxylic acid, and fumaric acid. The method comprises a thickening step, wherein the solution comprising the organic acid and MgCl ₂ is at or above the saturation point of the carboxylic acid, at most 5 g / L, preferably at most 10 g / L. 13. The method according to any one of the preceding claims, wherein the method is concentrated to a low organic acid concentration. Magnesium carboxylate is acidified with an HCl solution, said solution preferably comprising at least 5% by weight, more preferably at least 10% by weight, even more preferably at least 20% by weight of HCl. Item 2. The method according to item 1. 15. The method according to any one of the preceding claims, wherein the carboxylic acid is provided in dissolved form, as part of an aqueous solution obtained in a fermentation process or as part of an aqueous suspension. Aqueous solutions or aqueous suspensions of at least 10 wt% based on the total weight of the solution or suspension, preferably at least 15 wt% magnesium carboxylate, and, said containing the carboxylic acid and MgCl ₂ 15. The method according to claim 14, wherein the solution comprises at least 5% by weight, preferably at least 10% by weight, based on the total weight of the solution comprising the carboxylic acid. The magnesium carboxylate is obtained in a fermentation process, the process comprising a purification step, wherein the magnesium carboxylate is crystallized from the fermentation broth and then optionally dissolved in water to form an aqueous solution; The method according to any one of claims 1 to 16. The magnesium carboxylate is obtained in dissolved form in a fermentation process, the process comprising a purification step wherein the carboxylic acid is neutralized by adding a magnesium base during which the magnesium carboxylate is 17. The method according to any one of the preceding claims, wherein the method remains in dissolved form.