Formic acid extraction

Abstract

The invention is in the field of formic acid production. In particular the present invention is directed to a method and system for the production of a concentrated aqueous formic acid solution. The process comprises the steps of: - providing a first aqueous solution comprising formate ions and one or more metal ions, - subjecting the first solution to bipolar membrane electrodialysis, thereby obtaining a second aqueous solution comprising formic acid, - extracting formic acid from the second solution using an organic solvent, thereby forming a formic acid poor aqueous phase and a formic acid rich organic phase, and - distilling the formic acid rich organic phase, thereby obtaining a concentrated aqueous formic acid solution.

Description

[0001] P137472PC00

[0002] Title: Formic acid extraction

[0003] BACKGROUND OF THE INVENTION

[0004] The invention is in the field of formic acid production. In particular the present invention is directed to a method and system for the production of a concentrated aqueous formic acid solution.

[0005] Formic acid is a chemical that is expected to play an important role in the energy transition. Among others, formic acid can serve as a hydrogen carrier for e.g. fuel cells, or as an intermediate for the production of combustion fuels. Formic acid can be produced from non-fossil sources, for instance using electrochemical reduction of aqueous carbon dioxide solutions. Therefore, the use of formic acid in fuel applications can prevent release of carbon dioxide from fossil sources into the earth’s atmosphere, thereby contributing to a more sustainable future.

[0006] A challenge associated with electrochemical reduction of carbon dioxide to formic acid is that the electrochemical process typically produces an aqueous stream with relatively low concentrations of ionic product such as potassium formate. The concentration of formate is typically ca. 1-2 M. For further use or downstream processing of formic acid, the ionic product is typically treated in order to convert formate (e.g. in the form of potassium formate) to formic acid and subsequently concentrated.

[0007] In the art, different approaches for converting formate salts to formic acid are used in order to obtain a formic acid stream. For instance, a formate solution can be acidified with HC1, followed by chromatographic separation. However, acidification with HC1 leads to further dilution of the product stream and the process results in large amounts of waste. For instance, acidification of potassium formate with HC1 produces KC1, which needs to be regenerated or treated as a contaminated wastewater stream, which is a disadvantage in terms of energy efficiency and environmental impact.

[0008] Another approach for acidification is the use of ion exchange resins which can exchange the K+ in potassium formate for H+ in order to obtain formic acid. However, the use of ion exchange resins is not economically viable for large scale processes. In addition, regeneration of the ion exchange resins leads to a stream containing both HC1 and KC1, which are difficult to separate and to regenerate.

[0009] Concentrating an aqueous formic acid solution is difficult, because formic acid and water form an azeotrope. In such situations, special distillation processes such as extractive distillation, in which a solvent (e.g. toluene, MIBK, n-octanol) is added to aid separation between water and formic acid, or pressure swing distillation can be applied. However, these distillation methods are typically not energy efficient or need additional steps in order to obtain the concentrated formic acid.

[0010] An object of the present invention is to provide an energy-efficient process to obtain a concentrated formic acid solution from a dilute formate salt solution. Another object of the invention is to provide a process in which waste streams are minimized.

[0011] BRIEF SUMMARY OF THE INVENTION

[0012] In accordance with the present invention there is provided a process for the production of a concentrated aqueous formic acid solution.

[0013] The process comprises the steps of: - providing a first aqueous solution comprising formate ions and one or more metal ions, - subjecting the first solution to bipolar membrane electrodialysis, thereby obtaining a second aqueous solution comprising formic acid, - extracting formic acid from the second solution using an organic solvent, thereby forming a formic acid poor aqueous phase and a formic acid rich organic phase, and - distilling the formic acid rich organic phase, thereby obtaining a concentrated aqueous formic acid solution.

[0014] The inventors have surprisingly found that by performing bipolar membrane electrodialysis followed by extraction using an organic solvent, a single extraction / distillation step is surprisingly enough to obtain a concentrated formic acid solution. Therefore, a concentrated formic acid solution can be obtained with relatively low energy usage. In addition, the inventors found that the efficiency of extraction / distillation can be impacted when other ionic compounds such as HC1 are present. Since BPM-ED does not rely on addition of extra compounds such as HC1 for acidification of formate, the combination of BPM-ED and extraction / distillation is surprisingly effective.

[0015] In addition, the aqueous formic acid poor aqueous phase can be easily recycled because the process does not rely on the addition of other chemicals to the aqueous phase in the formation of formic acid or concentration. The recycled aqueous phase can for instance be used as electrolyte for electrochemical production of formate, which also positively affects the energy usage of the entire process of formic acid production.

[0016] BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic representation of a process and / or system for the production of a concentrated aqueous formic acid solution.

[0018] Figures 2-5 show results for extraction of formic acid from an aqueous solution using a tertiary amine.

[0019] DETAILED DESCRIPTION OF THE INVENTION

[0020] According to the invention there is provided a process for the production of a concentrated aqueous formic acid solution. The process comprises a step of providing a first aqueous solution comprising formate ions and one or more metal ions. For instance, the solution may comprise sodium formate and / or potassium formate. In addition, the first aqueous solution may also comprise other compounds, for instance acidic and / or basic compounds such as CO2, bicarbonate, and / or their conjugated acids and / or bases.

[0021] In embodiments, the concentration of formate in the first aqueous solution is 0.1-3.0 M, preferably 0.5-2.0 M. These concentrations of formate can for instance be found in product streams coming from an electrolyzer cell in which carbon dioxide is electrochemically reduced into formate.

[0022] Negatively charged ions with a higher electronegativity than formate, for instance halide ions, may negatively influence the performance of the process. Therefore, the concentration of such ions in the first aqueous solution, if any, is preferably lower than the concentration of formate ions. For instance, the concentration of such ions is preferably 1.0 % by weight or less relative to the weight of entire first aqueous solution, more preferably 0.5 wt.% or less, such as 0.2 wt.% or less.

[0023] The first solution is subjected to bipolar membrane electrodialysis. The term electrodialysis, as used herein, refers to a process in which ions are transported through ion-exchange membranes under the influence of an applied electric field. In electrodialysis, anion and / or cationexchange membranes are used to create separate compartments between an electrode pair. When a potential difference is applied between the electrodes, the membranes selectively allow certain ions to permeate, thereby increasing the concentration of certain ions in some compartments, and decreasing the concentration of those ions in other compartments. Typically, a stack of alternation anion- and cation-exchange membranes is used, resulting in alternating compartments containing an increased concentration of ions (i.e., the concentrate) or containing a decreased concentration of ions (i.e., the diluate), respectively. Depending on the application, the diluate and / or the concentrate may be used for further process steps.

[0024] Bipolar membrane electrodialysis is a specific type of electrodialysis in which bipolar membranes are applied in the electrodialysis stack. Bipolar membranes comprise a cation-exchange layer and an anion-exchange layer, and can be used to split water into H+and OH? In this way, bipolar membrane electrodialysis can be used to produce an acidic concentrate, an alkaline concentrate and a diluate.

[0025] By subjecting the first solution to bipolar membrane electrodialysis, formate ions are acidified to form a second aqueous solution comprising formic acid (i.e., the acidic concentrate comprising from BPMED). Preferably, in the bipolar membrane electrodialysis step, the conditions are chosen such that the concentration of acidic concentrate stays below 2.5 M, more preferably below 2.0 M, even more preferably below 1.5 M, such as 0.5-2.0 M or 0.75-1.5 M. At higher concentrations, the current efficiency of the bipolar membrane electrodialysis step may be negatively affected due to unwanted diffusion of formic acid and leakage of OH- in the bipolar membrane electrodialysis stack.

[0026] Advantageously, bipolar membrane electrodialysis can produce an acidic concentrate comprising formic acid from solutions comprising formate, without the need for adding additional chemicals to convert formate into formic acid. This means that the acidic concentrate, alkaline concentrate and / or diluate can be used further without the need to apply additional separation steps in order to remove chemicals that are otherwise often used for acidification.

[0027] In order to prevent unwanted transport of water through the membranes in the bipolar membrane electrodialysis step which could negatively affect performance, ion-exchange membranes designed for low water flux are preferred. Preferably, ion-exchange membranes with a water permeability of 5.0 mL / (bar x m2x h) or lower, more preferably below 3.0 mL / (bar x m2x h), even more preferably 2.5 mL / (bar x m2x h) or lower, preferably measured at NaCl concentrations between 0.1-0.7 M, are used in the electrodialysis step. Suitably, water permeability of an ion-exchange membrane for a certain NaCl concentration can be measured by bringing a draw solution with that NaCl concentration in contact with a pure water solution through said membrane, and by measuring the rate of water permeation from the feed solution into the draw solution over time.

[0028] Preferably, the bipolar membrane electrodialysis step is performed at current densities of 200-1000 A / m2, more preferably 300-500 A / m2.

[0029] Preferably, the bipolar membrane electrodialysis step is operated continuously. By using a feed with constant concentration, resistance is kept low and current efficiency is high compared to batch processes.

[0030] The process further comprises a step of extracting formic acid from the second solution using an organic solvent, thereby forming a formic acid poor aqueous phase and a formic acid rich organic phase, and a step of separating the formic acid poor aqueous phase and the formic acid rich organic phase.

[0031] The solubility of formic acid in the organic solvent is preferably higher than the solubility of formic acid in water. Solubility of formic acid in the organic solvent can be the result of different types of chemical and / or physical interactions between formic acid and the organic solvent, such as the formation of a chemical bond, ionic interaction, any type of dipole interaction, and / or van der Waals interaction.

[0032] If the interaction between formic acid and the organic solvent is too weak, extraction of formic acid into the organic solvent is not efficient. However, if the interaction is too strong, recovery of the solvent in order to obtain the concentrated formic acid is energy intensive, which is unwanted. Therefore, the interaction between formic acid and the organic solvent preferably involves the formation of a chemical bond.

[0033] In embodiments, extraction of formic acid into the organic solvent results in an acid-base reaction between formic acid and the organic solvent. Therefore, the organic solvent preferably has basic functionality. In embodiments, the organic solvent has one or more basic moieties with a pKa higher than the pKa of formic acid (i.e. pKa 3.75). For instance, the one or more basic moieties may have a pKa of 4.0, or higher , preferably 5.0 or higher, more preferably 7.0 or higher, such as 5.0-14.0 or 8.0-12.0. Such basic moieties may react with the H+of formic acid, and upon protonation of the basic moiety, the solvent may form an adduct (e.g. a salt) with the conjugated base of formic acid, formate.

[0034] In embodiments, the organic solvent comprises one or more amine groups, preferably one or more tertiary amine groups. Tertiary amines may undergo acid-base reactions with formic acid in which the N-group gets protonated, and forms a salt by balancing the proton by formate (HCOO ). Without wishing to be bound by theory, the inventors believe that this type of interaction is less energy intensive to break when subsequently recovering the organic solvent compared to breaking a chemical bond, e.g. an amide bond that is formed upon interaction of a primary or secondary amine with a carboxylic acid. It was found that trioctylamine is particularly suitable as organic solvent for extraction of formic acid, but other (tertiary) amines are also suitable.

[0035] The organic solvent solubility in water is preferably low, in order to prevent mixing of the phases during extraction / separation. Preferably, the solubility of the organic solvent in water is 5 wt.% or lower, more preferably 1 wt.% or lower, or even 0.1 wt.% or lower or 0.01 wt.% or lower, at which point the organic solvent can considered to be insoluble in water. In case a co-solvent is used, this also applies to the co-solvent.

[0036] Preferably, the amount of organic solvent added is as low as possible for extraction of the formic acid. However, when the amount is too low, it may not be possible to extract enough formic acid. Preferably, the molar ratio of organic solvent to formic acid is in the range of 0.5-5.0, more preferably 0.6-3.0, such as 0.7-1.5. The extraction of formic acid towards the organic phase can be improved by adding a hydrophobic co-solvent. Addition of a co-solvent may increase the distribution coefficient while at the same time decreasing the water content in the concentrated formic acid solution.

[0037] It was found that the loading of formic acid in amine did not depend on the initial concentration of formic acid in the water. This means surprisingly that a single extraction step after acidification using BPM-ED was enough to obtain a concentrated formic acid stream with high concentration of formic acid.

[0038] As can be seen in example 1, it was also found that the distribution coefficient was higher at lower initial formic acid concentration. This means that the concentration final concentration of formic acid in the organic phase does not depend on initial formic acid concentration, and that a lower starting concentration of formic acid results in a lower end concentration of HCOOH in the water phase. Therefore, extraction is preferably performed continuously in countercurrent mode, in which the fresh amine solution is brought into contact with the lowest formic acid solution.

[0039] The process also comprises the step of distilling the formic acid rich organic phase, thereby obtaining a concentrated aqueous formic acid solution.

[0040] Preferably, in order to facilitate separation of the formic acid from the organic solvent by distillation and / or to prevent contamination of the concentrated formic acid solution, the boiling point of the organic solvent is 5 °C or more above the boiling point of formic acid, more preferably 10 °C or more, even more preferably 20 °C or more at the working pressure of the distillation column. By selecting an organic solvent with a sufficiently high boiling point compared to formic acid, the vapor pressure of the organic solvent will be low enough that an extra distillation step in order to remove organic solvent from the concentrated formic acid solution is not necessary. Preferably, if a co-solvent is used, the co-solvent does not interact strongly with formic acid, meaning that formic acid will not dissolve in the co-solvent. In addition, the co-solvent preferably has a lower vapor pressure and / or higher boiling point than the organic solvent, meaning that the cosolvent can remain in the residue together with the organic solvent during a subsequent distillation step, and is unlikely to contaminate the concentrated formic acid solution.

[0041] Vegetable oils (e.g. sunflower oil) are particularly suitable as hydrophobic co-solvent, because they are environmentally friendly and / or have a low vapor pressure compared to other hydrophobic solvents such as toluene. In addition, formic acid is not soluble in vegetable oil, and the low vapor pressure and / or high boiling point of vegetable oils mean that they can remain in the residue together with the organic solvent during the distillation step and are unlikely to contaminate the concentrated formic acid solution.

[0042] After distillation, the organic solvent may be recycled to the extraction step. If a co-solvent is used, the co-solvent may remain in the organic solvent during distillation and / or recycling of the organic solvent for extraction.

[0043] In order to lower the amount of energy needed for distillation, and / or in order to prevent degradation by applying high temperatures, the step of distilling the formic acid rich organic phase preferably comprises vacuum distillation. In embodiments, vacuum distillation is performed using a pressure of 500 mbar or lower as working pressure of the distillation unit preferably 200 mbar or lower, more preferably 100 mbar or lower.

[0044] Preferably, the concentrated formic acid solution has a formic acid concentration of 50 % or more by weight relative to the weight of the concentrated formic acid solution, more preferably 60 wt.% or more, even more preferably 70 wt.% or more, such as 80 wt.% or more.

[0045] Preferably, the concentrated aqueous formic acid solution obtained after distillation contains 5.0 % or less by weight of organic solvent used for the extraction relative to the weight of the concentrated aqueous formic acid solution, more preferably 1.0 wt.% or less, even more preferably 0.5 wt.% or less, such as 0.1 wt.% or less.

[0046] Preferably, the electrodialysis step, the extraction step and / or the separation step are performed continuously. Advantages of performing the BPM-ED in a continuous mode include providing a constant concentration of formate in the feed. This leads to a lower resistance and increased efficiency in the BPM-ED step.

[0047] Extraction and separation can be performed batch-wise, e.g. using a separation funnel, or continuously. Preferably, extracting formic acid from the second solution using an organic solvent is performed continuously, preferably in countercurrent stream.

[0048] The first aqueous solution comprising formate ions and one or more metal ions may be the result of electrochemically reducing carbon dioxide. Advantageously, the process of the present invention can be applied to the product stream from an electrolyzer. Therefore, the process may further comprise a step of electrochemically reducing carbon dioxide, thereby producing a first aqueous solution comprising formate ions and one or more metal ions. Such electrochemical reduction of carbon dioxide is for instance described in WO2017014635, which is incorporated herein in its entirety. This electrolysis product can be used directly as first aqueous solution for the bipolar membrane electrodialysis step. Alternatively or additionally, the electrolysis product can be concentrated before subjecting it to the bipolar membrane electrodialysis step. Concentration can for instance be done using reverse osmosis.

[0049] Because the BPM-ED process does not rely on addition of chemicals in order to acidify formate ions, and because the organic solvent and optionally the co-solvent can be easily separated from the concentrated stream, there is no need for extensive waste stream treatments, and streams can be readily recycled without needing extensive purification steps. In embodiments, the alkaline concentrate of the electrodialysis step is recycled, for instance as electrolyte in an optional step of electrochemically reducing carbon dioxide.

[0050] In embodiments, the formic acid poor aqueous phase obtained in the separation step and / or the diluate obtained in the electrodialysis step may be recycled, preferably in the electrodialysis step.

[0051] In such cases, the formic acid poor aqueous phase and / or diluate may be subjected to purification and / or concentration steps (e.g. selected from reverse osmosis, electrodialysis and freeze concentration) prior to being recycled in the electrodialysis step.

[0052] According to the invention, there is also provided a system suitable for the production of a concentrated aqueous formic acid solution, preferably using the process as described herein.

[0053] The system may comprise an electrolysis unit configured for electrochemical reduction of carbon dioxide.

[0054] The system comprises a bipolar membrane electrodialysis unit. The electrodialysis unit preferably comprises an inlet, which inlet is preferably configured to receive a product stream from the electrolysis unit, if present. The electrodialysis unit preferably also comprises at least an outlet for acidic concentrate.

[0055] The system also comprises a liquid-liquid extraction unit for extracting and separating formic acid from the acidic concentrate into an organic phase.

[0056] The system also comprises a distillation unit, preferably a vacuum distillation unit configured to operate at sub -atmospheric pressures such as 500 mbar or lower.

[0057] The system may also comprise means to recycle one or more intermediate streams, such as a diluate or the alkaline concentrate from the BPM-ED unit, a formic acid poor aqueous phase the liquid-liquid extraction unit, and / or one or more fractions or a residue from the distillation unit. The system may optionally also comprise one or more purification and / or concentration units, such as a reverse osmosis unit, for purifying and / or concentration one or more recycle streams.

[0058] Figure 1 is a schematic representation of a process and / or system for the production of a concentrated aqueous formic acid solution. First aqueous solution 10 comprising formate ions and one or more metal ions is subjected to bipolar membrane electrodialysis in electrodialysis unit 1. Second aqueous solution 11 comprising formic acid is extracted using organic solvent 17 and separated in liquid-liquid extraction unit 2 into formic acid poor aqueous phase 18 and formic acid rich organic phase 12. Formic acid rich organic phase 12 is distilled in distillation unit 3, thereby obtaining a concentrated aqueous formic acid solution 20. First aqueous solution 10 may be obtained from electrolyzer 5, in which carbon dioxide may electrochemically be reduced into formate. In addition to second aqueous solution 11, the electrodialysis step may also produce alkaline concentrate 13 which may be recycled as electrolyte to electrolyzer 5, and / or diluate 14, which may be recycled as feed for bipolar membrane electrodialysis. If diluate 14 is recycled for bipolar membrane electrodialysis, it may be concentrated in reverse osmosis unit 4, to make the concentration of formate ions in stream 15 suitable for being subjected to bipolar membrane electrodialysis again. Formic acid poor aqueous phase 18 may be recycled in the electrodialysis step (not shown). Bottom fraction or residue 19 of the distillation step may be recycled as organic solvent 17 (not shown).

[0059] EXAMPLES

[0060] Example 1 - extraction of formic acid using a tertiary amine Different mixtures of formic acid in water (total volume ca. 50 mb) were prepared, after which formic acid was extracted with trioctylamine (TOA). After extraction, the amine and water phase were separated using a separation funnel and the two phases were collected for analysis.

[0061] The concentration of formic acid in the water phase was determined by titration with a NaOH solution, using a Metrohm automated titration apparatus.

[0062] In addition, the distribution coefficient of the extract (KDE) is given as a function of the TOA / HCOOH ratio (mol TOA / mol HCOOH). The distribution coefficient is calculated based on concentration (in mol formic acid / liter). The distribution coefficient is defined by the following formula: in which KDE is the distribution coefficient, Co is the concentration of formic acid (in mol / L) at the start of the experiment, CE refers to the concentration of formic acid after the extraction, and mw and mwA are the amount of water (W) and amine (TO A) used in the experiment.

[0063] Example 1-1 - varying trioctylamine : formic acid ratio

[0064] In this experiment, extraction was carried out at different TOA / HCOOH ratios. Figure 2 shows the distribution coefficient for varying TOA / HCOOH ratios. Figure 3 shows the loading of HCOOH in the organic phase (circles, left y-axis) and the concentration of HCOOH in water (triangles, right y-axis) for varying TOA / HCOOH ratios. It can be seen that the distribution coefficient is constant and independent on the ratio between formic acid and tertiary amine. Therefore, higher ratio of tertiary amine to formic acid results in lower concentration of HCOOH in water phase after extraction. Example 1-2 - varying starting concentration of HCOOH

[0065] In this experiment, the starting concentration of formic acid in water was varied between 0.25 M and 2.0 M, and in all cases, a 1:1 molar ratio of TOA to HCOOH was used.

[0066] As can be seen in Figures 4 and 5 (closed circles), the distribution coefficient KDE shows a large dependency on the starting concentration, and the starting concentration of water does not influence the loading of HCOOH in the organic phase. This means that a lower starting concentration of formic acid results in a lower end concentration of HCOOH in the water phase after extraction.

[0067] Example 1-3 - presence of other salts than formate

[0068] Addition of KC1 results in a decrease of the distribution coefficient, as can be seen in figure 5 (open circles). This is caused by Cl being preferentially extracted using tertiary amine, thereby decreasing the effectivity of formic acid extraction.

[0069] Example 2 - production of a concentrated formic acid solution

[0070] A IM formic acid solution was prepared by adding 26.3 g (2.0 eq.) formic acid to 540.3 g demineralized water. Subsequently, 99.5 g (1.0 eq.) trioctylamine was added to the formic acid solution, resulting in 2 distinct layers. After stirring for 1.5 h at room temperature, the phases were separated using a separating funnel.

[0071] The organic phase was distilled using vacuum distillation at 50 mb ar and the results are shown in Table 1. Table 1

[0072] The obtained fractions as well as the residue were characterized usingXH-NMR. Titration was used to determine the concentration of formic acid in the aqueous phase. Fraction 1 contained mostly water and small amounts of formic acid. Fraction 2 was an aqueous solution of formic acid with a concentration of 66 mass%.XH-NMR analysis showed that the residue was trioctylamine with a purity according toXH-NMR of 100 mol%. The overall trioctylamine recovery was 96.9 mol%.

Claims

Claims1. Process for the production of a concentrated aqueous formic acid solution, comprising the steps of:- providing a first aqueous solution comprising formate ions and one or more metal ions,- subjecting the first solution to bipolar membrane electrodialysis, thereby obtaining a second aqueous solution comprising formic acid,- extracting formic acid from the second solution using an organic solvent, thereby forming a formic acid poor aqueous phase and a formic acid rich organic phase,- separating the formic acid poor aqueous phase and the formic acid rich organic phase,- distilling the formic acid rich organic phase, thereby obtaining a concentrated aqueous formic acid solution.

2. Process according to claim 1, wherein the organic solvent is reactive towards formic acid, preferably by acid-base reaction.

3. Process according to claim 1 or 2, wherein the organic solvent has one or more amine groups, preferably one or more tertiary amine groups.

4. Process according to any one of claims 1-3, wherein the concentration of formate in the first aqueous solution is 0.5-3.0 M.

5. Process according to any one of claims 1-4, wherein the molar ratio between organic solvent and formic acid in the extracting step is 0.5-2.0.

6. Process according to any one of claims 1-5, wherein extracting formic acid is performed in the presence of an organic co-solvent, preferablya vegetable oil.

7. Process according to claim 6, wherein the boiling point of the organic co-solvent is higher than the boiling point of the organic solvent.

8. Process according to any one of claims 1-7, wherein the concentrated formic acid solution has a formic acid concentration of 60 % or more by weight relative to the weight of the concentrated formic acid solution, preferably 80 wt.% or more.

9. Process according to any one of claims 1-8, wherein the step of distilling the formic acid rich organic phase comprises vacuum distillation, preferably at a pressure of 200 mbar or lower.

10. Process according to any one of claims 1-9, wherein the step of extracting formic acid from the second solution using an organic solvent is performed continuously from a electrolysis product stream comprising formate.

11. Process according to any one of claims 1-10, further comprising a step of electrochemically reducing carbon dioxide, thereby producing a first aqueous solution comprising formate ions and one or more metal ions.

12. Process according to any one of claims 1-11, further comprising a step of recycling an alkaline concentrate obtained in the electrodialysis step, preferably as electrolyte in the optional step of electrochemically reducing carbon dioxide.

13. Process according to any one of claims 1-12, further comprising a step of recycling a diluate obtained in the electrodialysis step and / or theformic acid poor aqueous phase, preferably in the electrodialysis step.

14. Process according to claim 12 or 13, wherein recycling comprises concentrating and / or purifying the alkaline concentrate, diluate and / or formic acid poor aqueous phase.

15. Process according to any one of claims 1-14, wherein one or more of the steps are performed continuously.

16. Process according to claim 15, wherein the steps of extracting and separating are performed continuously, and wherein the second aqueous solution is countercurrently contacted with the organic solvent.

17. System suitable for the production of a concentrated aqueous formic acid solution, preferably using the method according to any one of claims 1-16, the system comprising:- optionally, an electrolyzer;- a bipolar membrane electrodialysis unit;- a liquid-liquid extraction unit;- a distillation unit;- optionally, one or more reverse osmosis units.

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