Method for synthesizing 2,5-franzicarboxylic acid

Abstract

The present invention relates to a method for synthesizing 2,5-furandicarboxylic acid (FDCA), comprising the steps of: (1) oxidizing an aqueous solution of 5-hydroxymethylfurfural (HMF) at a temperature above 100°C in the presence of molecular oxygen, a heterogeneous catalyst containing ruthenium, and a strong base to obtain a reaction product comprising an FDCA acid salt in aqueous solution; (2) separating the heterogeneous catalyst from the reaction product in aqueous solution; and (3) reusing the heterogeneous catalyst in the oxidation reaction of step (1).

Description

[Technical Field]

[0001] This project, which led to the present invention, was funded by a public-private partnership in the bio-industry under the European Union Horizon 2020 Research and Innovation Programme (grant agreement number 745766).

[0002] The present invention relates to a method for synthesizing 2,5-franzicarboxylic acid (FDCA) by oxidation of 5-hydroxymethylfurfural (HMF).

[0003] 2,5-Franzicarboxylic acid is an oxidized derivative of 5-hydroxymethylfurfural and is useful as a monomer for the manufacture of plastics, especially polyesters. Furthermore, since HMF is obtained from sugars, it is a derivative that can be obtained from raw materials that are widely available in nature. [Background technology]

[0004] HMF oxidation processes that allow for the acquisition of 2,5-franzicarboxylic acid as the main product are known from the literature.

[0005] U.S. Patent No. 4,977,283 (Hoechst) describes a method for oxidizing HMF in an aqueous environment with a maximum pH of 8 in the presence of a platinum group metal catalyst. The patent indicates that the ratio of various products obtained by the oxidation reaction to by-products can be varied by adjusting the pH. As suggested in the patent, the pH can be adjusted using a base such as sodium hydroxide or potassium hydroxide, an acid, or a buffer solution, thereby usually maintaining the pH below 8. The oxidation reaction can be carried out at a temperature between 30°C and the boiling point of water, preferably 60 to 90°C, and although the reaction yield relative to the theoretically achievable yield is expressed in relation to the 2,5-franzicarboxylate disodium salt in the aqueous solution, the examples do not show that the product was recovered.

[0006] U.S. Patent Application No. 2008 / 0103318 (Battelle) describes a method for oxidizing HMF using a platinum-supported catalyst. Here again, the pH must be maintained below 7, but it is emphasized that the pH-dependent selectivity can be varied by using weak bases such as carbonates or bicarbonates. 2,5-Franzicarboxylic acid is one of the oxidation products described. The use of strong bases such as NaOH is not recommended because it may lead to secondary reactions such as disproportionation (Cannizzaro reaction).

[0007] However, the metal catalysts used in the HMF oxidation process described above become poisoned and consequently lose their catalytic activity. This means that catalyst replacement and regeneration are frequently required, which increases the already high cost of precious metals such as platinum.

[0008] Another FCDA manufacturing process using a platinum catalyst is described in European Patent No. 2 601 182, which states that the presence of a weak base allows for catalyst reuse, and the examples show a process carried out at a temperature of 100°C using NaHCO3 or magnesium carbonate hydroxide.

[0009] Patent application WO 2016 / 028488 A1 describes an oxidation process in which an aqueous solution containing at least 5% by mass of HMF is brought into contact with an oxygen source with a neutral or acidic pH in the presence of a ruthenium-based heterogeneous catalyst. However, this process has limited selectivity for FDCA, with its selectivity among the various products obtained by the confirmed oxidation reaction being at most 60 mol%. This maximum value is reached even at very high oxygen partial pressures (70 bar). Furthermore, these reaction products are solids and require complex operations to separate from the heterogeneous catalyst. Therefore, from an economic standpoint, challenges remain in achieving efficient industrial production, particularly in obtaining FDCA selectively in high yield and recovering the products through simple separation operations. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] U.S. Patent No. 4,977,283 [Patent Document 2] U.S. Patent Application No. 2008 / 0103318 [Patent Document 3] European Patent No. 2,601,182 [Patent Document 4] Patent Application WO 2016 / 028488 A1 [Patent Document 5] European Patent No. 2,994,458 [Patent Document 6] European Patent No. 3,207,032 [Patent Document 7] PCT / EP2019 / 068860 [Non-Patent Document]

[0011] [Non-Patent Document 1] S. Brunauer, P. H. Emmett and E. Teller, J Am. Chem. Soc., 1938, 60, 309 [Summary of the Invention] [Problems to be Solved by the Invention]

[0012] There is also a need to produce FDCA having properties suitable for use in polymerization processes. The low selectivity in known processes generally leads to the formation of many by-products such as oligomers and molecules having one functional group, salts, or conjugated organic substances, which color the product and can affect the polymerization process.

[0013] On the other hand, the method for synthesizing 2,5-furandicarboxylic acid according to the present invention has a significant advantage in that 2,5-furandicarboxylic acid can be obtained in a high yield by using a heterogeneous catalyst containing ruthenium. The catalyst can be separated by simple filtration and can be recycled several times while maintaining its catalytic activity. Furthermore, FDCA is obtained in a dissociated form in the reaction environment. Also, since FDCA has water solubility, it can be easily recovered from the catalyst without the use of an organic solvent and can be purified through solid-liquid separation.

Means for Solving the Problems

[0014] Therefore, according to a first aspect, the present invention relates to a method for synthesizing 2,5-furandicarboxylic acid by an oxidation reaction of an aqueous solution of 5-hydroxymethylfurfural, which is catalyzed by a heterogeneous catalyst containing ruthenium under adjusted pH conditions, preferably at a temperature above 100 °C, in the presence of oxygen molecules and a strong base.

[0015] Under such conditions, despite using a strong base, the heterogeneous catalyst containing ruthenium surprisingly not only selectively gives 2,5-furandicarboxylic acid even when air is present as an oxidizing agent, but also is less likely to have dirt adhere to the catalyst surface than known processes.

[0016] When the heterogeneous catalyst is separated from the reaction product present in a dissociated form in an aqueous solution, the catalyst can be recycled several times in the oxidation reaction while maintaining a high yield of FDCA, even if it is present in a smaller amount than the reagent HMF. Then, the aqueous solution containing the reaction product in a dissociated form undergoes one or more optional purification steps and is finally acidified to give solid FDCA.

[0017] Furthermore, the procedure according to the present invention facilitates obtaining monomers, particularly 2,5-franján carboxylic acid, which are especially suitable for use as monomers for polyester synthesis. In fact, monomers with a low yellowness index, indicating that oligomers that may inhibit polymerization have been removed, can be obtained by simple nanofiltration of the dissociated form of the 2,5-franján carboxylic acid salt.

[0018] Accordingly, according to another aspect, the present invention relates to a method for purifying FDCA, comprising the step of nanofiltration of an aqueous solution of FDCA in a dissociated form, preferably in the form of a sodium salt. The subsequent purification operation of solid FDCA is further facilitated because there are no oligomers present. This is because a simple wash with water is sufficient to obtain an FDCA composition of high purity, particularly containing only limited amounts of monofunctional impurities, and the purification method is particularly suitable for use as a monomer for polyester synthesis.

[0019] Accordingly, in a further embodiment, the present invention relates to a high-purity FDCA composition having a low content of inorganic salts and residual monocarboxylic acids. [Modes for carrying out the invention]

[0020] The present invention will be described in detail below.

[0021] The first object of the present invention is a method for synthesizing 2,5-franzicarboxylic acid (FDCA), 1) A step of oxidizing an aqueous solution of 5-hydroxymethylfurfural (HMF) at a temperature exceeding 100°C in the presence of an oxygen molecule, a heterogeneous catalyst containing ruthenium, and a strong base to obtain a reaction product containing an FDC acid salt in the aqueous solution. 2) A step of separating the heterogeneous catalyst from the reaction product in an aqueous solution. 3) A step of reusing the heterogeneous catalyst in the oxidation reaction of step 1). This is a synthesis method that includes [the specified element].

[0022] After one or more optional purification steps, it is desirable to neutralize the reaction product in the aqueous solution containing the FDCAs separated in step 2) above so that the resulting FDCAs can then be separated in solid form. This method is advantageous when the catalytic active phase is used in an amount of 0.5% to 10% by mass relative to the mass of HMF. Furthermore, this method allows for the catalyst to be recycled several times while maintaining a reaction yield of over 85%, preferably over 90%.

[0023] The starting material to be oxidized in step 1) of the method according to the present invention is an aqueous solution of 5-hydroxymethylfurfural (HMF).

[0024] HMF is obtained by dehydrating sugars, particularly hexoses such as fructose and glucose obtained by hydrolysis and possible isomerization reactions of polysaccharide-containing biomass. This dehydration reaction can be carried out by various techniques that generally use acid catalysts, and may or may not use aqueous and non-aqueous solvents. For example, HMF obtained by methods using quaternary ammonium salts described in European Patent No. 2994458, European Patent No. 3207032, or PCT / EP2019 / 068860 is suitable as a starting material.

[0025] The HMF used as a starting material in the method according to the present invention may include by-products of sugar treatment.

[0026] As the aqueous HMF solution, one with high purity can be advantageously used. For example, an aqueous solution obtained from an HMF composition having a purity of more than 98.5% is particularly suitable, and containing less than 0.25% by mass, preferably less than 0.1% by mass, of quaternary ammonium salt in terms of nitrogen atoms relative to the HMF. If an excess amount of quaternary ammonium salt is present, it may actually adversely affect the selectivity of the catalyst due to interaction with the catalytic active phase.

[0027] The purity of HMF can be measured, for example, by an externally calibrated HPLC / UV analysis method. For example, the HPLC / UV analysis method can be performed using a "Phenomenex Gemini NX-C18" column (150 mm × 3.0 mm × 5 μm, flow rate: 0.5 mL / min, column temperature: 30 °C) and 1% v / v HCOOH aqueous solution (A) and acetonitrile (B) as eluents, with the following gradient.

[0028] [Table 1]

[0029] Nitrogen content can be measured, for example, by elemental analysis or ion chromatography using a conductivity detector (CI-CD). The amount of nitrogen derived from quaternary ammonium salts can be measured stoichiometrically from quantitative analysis of ammonium cations using an external standard method by performing CI-CD chromatography analysis using a Metrosep C4-100 column (100 mm × 4.0 mm × 5 μm, flow rate: 1.0 mL / min, column temperature: 30°C) and a mixture of aqueous nitrate solution (7.5 mmol / L) and 20% v / v acetonitrile as the eluent.

[0030] The HMF composition is preferably one in which the total amount of one or more components selected from organic acids, compounds having at least one keto or aldehyde functional group (other than HMF), dimers, oligomers, and humic substances obtained as by-products of the dehydration reaction of the starting material saccharide is less than 4% by mass, preferably less than 3% by mass, and more preferably less than 1% by mass, relative to the mass of HMF. The HMF composition is also particularly preferably one in which the furfural content is less than 0.10% by mass, relative to the mass of HMF.

[0031] Preferably, the initial HMF composition contains fructose and / or sugar anomers in an amount of less than 3% by mass relative to the mass of HMF, preferably less than 0.5% by mass, and more preferably less than 0.1% by mass. The fructose content can be measured, for example, by IC-PAD analysis using a Metrosep Carb 2 column (250 mm × 4.0 mm × 5 μm, flow rate: 0.7 mL / min, column temperature: 30°C) and an aqueous NaOH solution as the constant composition eluent.

[0032] Examples of suitable compositions include those obtained by the method described in PCT / EP2019 / 068860.

[0033] In the method according to the present invention, the oxidation of HMF proceeds in an aqueous solution and does not require the use of an organic solvent. This is because the product obtained from the oxidation reaction, which exists in a dissociated form as indicated by the pH conditions, is readily soluble in water, just like HMF. The initial concentration of HMF in the aqueous solution is preferably 1.5% to 35% by mass, more preferably 2% to 20% by mass (corresponding to a mass ratio of HMF:H2O of 1:50), and more preferably 2% to 10% by mass.

[0034] In the method according to the present invention, the oxidizing substance responsible for the oxidation of HMF is an oxygen molecule or a compound containing an oxygen molecule, such as air, air with a high oxygen content, or an oxygen mixture containing an inert gas. The reaction can preferably be carried out in a sealed reactor under reduced pressure, or by circulating O2, air, or air containing a high amount of O2 into the reactor.

[0035] The method according to the present invention is preferably carried out using high-pressure oxygen, but is particularly advantageous in that it does not necessarily require it. In practice, it can be advantageously carried out even with air at a pressure higher than atmospheric pressure and 2 MPa (20 bar) or less, i.e., with an oxygen partial pressure of 0.5 MPa (5 bar) or less. This makes it possible to suppress the amount of CO2 generated during synthesis through combustion at high temperatures.

[0036] The oxidation step of the method according to the present invention is carried out in the presence of a heterogeneous catalyst containing ruthenium. This catalyst is preferably selected from the group consisting of supported metallic ruthenium, supported ruthenium oxide, unsupported ruthenium oxide, supported ruthenium hydroxide, unsupported ruthenium hydroxide, and mixtures thereof, and is preferably supported metallic ruthenium, or a mixture of supported ruthenium oxide and supported ruthenium hydroxide, preferably RuO2 and Ru(OH) x A mixture in the form of the above is particularly preferred, where x is preferably 2 to 4, preferably 2 or 4, and more preferably 4. The ruthenium oxide of the process catalyst according to the present invention may be in the form of a hydrate.

[0037] Optimal materials for forming the support for the catalyst include, for example, carbon, nonmetallic oxides (silica and graphene oxide, etc.), functionalized graphite which may be multilayered, and combinations thereof, but carbon is particularly preferred. The support material may be in a form having a nanostructure and / or a form having functional groups, and in order to ensure good dispersion of the stationary phase on the support surface, the catalytic active phase is preferably contained in an amount of 0.5% to 20% by mass, more preferably 1% to 10% by mass, relative to the catalyst.

[0038] In the present invention, a preferred catalyst, more specifically the catalyst support, having a microporous structure with a high specific surface area (i.e., having pores with a diameter not exceeding approximately 2.0 nm (20 Å) according to the IUPAC classification) is advantageous in that it can highly disperse the catalytically active phase and improve its overall activity and selectivity. Supermicroporous structures (pore diameter of 7 to 20 angstroms) and ultramicroporous structures (pore diameter of less than 7 angstroms) are particularly preferred. The specific surface area of ​​the catalyst according to the present invention is 600 to 1200 m². 2 / g is preferred, and 700-1100m 2 / g is more preferable, 800-1000m 2 / g is even more preferable.

[0039] Therefore, the supported catalyst according to the present invention is 800-1600 m 2It is preferable to prepare using a carrier having a specific surface area of / g as a starting material.

[0040] The specific surface area can be measured by measuring the gas adsorption amount on the material surface according to the BET method disclosed in S. Brunauer, P. H. Emmett and E. Teller, J Am. Chem. Soc., 1938, 60, 309.

[0041] Depending on the value of the specific surface area of the material, nitrogen or helium is used as the gas.

[0042] In this specification, the BET specific surface area (value is 50 - 400 m 2 / g) of the mesoporous material is measured by degassing the catalyst sample overnight in a vacuum of 100 °C, about 0.13 * 10 -3 Pa, measuring the nitrogen adsorption amount at 77 K and about 0.3 of P / P0, and assuming that the molecular cross-sectional area of nitrogen or argon is 16.2 Å 2 and measuring.

[0043] In this specification, after degassing the catalyst sample overnight in a vacuum of 100 °C, about 0.13 * 10 -3 Pa, measuring the helium adsorption amount at 4.2 K and P / P0 of about 0.3, assuming that the molecular cross-sectional area of helium is 1 Å 2 and measuring the BET specific surface area (value is 400 - 1000 m 2 / g) of the microporous material.

[0044] According to a preferred embodiment of the present invention, the cumulative pore volume value of the catalyst is preferably 0.25 - 0.8 cm 3 / g, more preferably 0.3 - 0.6 cm 3 / g, the specific surface area of the microporous body is preferably 900 - 1100 m 2 / g, and the pore diameter of the micropores is preferably 3.5 - 5 angstroms.

[0045] Ruthenium-based catalysts can be prepared by techniques known to those skilled in the art, regardless of whether the supported material is metallic ruthenium, ruthenium oxide, ruthenium hydroxide, or a mixture thereof.

[0046] For example, supported oxides and supported hydroxides can be produced by finely dispersing metal salts on a substrate by grafting, sol-gel formation, heat treatment, steam explosion, combustion, deposition, adsorption using a solution, coprecipitation, or impregnation, such as initial wet impregnation, or CVD (chemical vapor deposition).

[0047] The catalyst preparation step can be carried out separately from the oxidation step according to the present invention, or it may be carried out as a preliminary step in the oxidation step method.

[0048] According to one aspect of the present invention, the catalyst contains ruthenium as an active catalyst species, but may be combined with a structural promoter that can improve its performance. For example, metal oxides and mixed metal oxides may function as structural promoters.

[0049] The method according to the present invention may optionally be carried out in the presence of one or more catalysts other than ruthenium, selected from, for example, platinum, palladium, iron, manganese, copper, cobalt, and nickel. These metals can be used in the form of supported catalysts and in the form of mixed metals such as polyoxometalates.

[0050] According to a preferred embodiment of the method according to the present invention, the catalyst preferably contains Ru-supported carbon in an amount of 1% to 10% by mass, preferably in combination with a structural promoter such as sodium, cesium, barium, potassium, or bismuth (e.g., Na2O), or more preferably composed of these.

[0051] According to one aspect of the present invention, during the oxidation reaction, the presence of a dilute strong base such as NaOH causes Ru(OH) to be released from the ruthenium metal. x A mixture of ruthenium oxide and ruthenium hydroxide, such as +RuO2 / C, is formed in situ.

[0052] In another preferred embodiment of the method according to the present invention, the catalyst is Ru(OH) x It is more preferable that the material contains or is composed of supported carbon.

[0053] In another preferred embodiment of the method according to the present invention, the catalyst is preferably included in combination with ruthenium oxide, preferably sodium, cesium, barium, potassium, bismuth, or a structural promoter (e.g., Na2O), or more preferably composed of these.

[0054] The catalyst used in the method according to the present invention is used in a limited amount relative to the amount of reagent. Preferably, the amount of metal catalyst is less than 10% by mass, preferably less than 8% by mass, and more preferably less than 6% by mass, relative to the mass of HMF. It is desirable that the metal catalyst be present in an amount of more than 0.5% by mass, preferably more than 0.6% by mass, and even more preferably more than 0.7% by mass, relative to the mass of HMF.

[0055] The oxidation reaction of 5-hydroxymethylfurfural is carried out at a temperature above 100°C, preferably below 160°C, more preferably 150°C or lower, and most preferably 140°C or lower.

[0056] In the presence of a ruthenium-based catalyst, catalytic efficiency increases at oxidation temperatures of 110°C or higher; therefore, temperatures of 120°C or higher, and more preferably 130°C or higher, are preferred.

[0057] The strong base required to carry out step 1) of the present invention preferably has a solubility in water of 45 g / L or more at 25°C, more preferably 100 g / L or more, and even more preferably 200 g / L or more. Preferably, the strong base of the present invention is selected from the group consisting of sodium hydroxide, potassium hydroxide, ammonia, ammonium hydroxide, barium hydroxide, lithium hydroxide, cesium hydroxide, strontium hydroxide, rubidium hydroxide, trimethylamine, methylamine, and diethylamine. A soluble base having a hydroxyl group is preferred, but sodium hydroxide is particularly preferred because it facilitates subsequent purification operations.

[0058] These bases neutralize the pH of the initial reaction mixture and buffer the acid produced during FDCA formation. They are used in amounts necessary to maintain the pH of the reaction environment between 6.5 and 9.

[0059] These strong bases should preferably be added as gradually as possible throughout the reaction, depending on the reaction rate (and the resulting change in pH), to prevent excess amounts from being present in the reaction mixture due to the possibility of causing condensation reactions, and to prevent the formation of sodium oxides that inactivate the catalytically active phase.

[0060] Therefore, a pH of 7 or higher and 8.5 or lower is desirable, and 7.5 or higher and 8 or lower is preferable.

[0061] This catalyst has been demonstrated to maintain almost its catalytic activity under these conditions, and its reuse makes it possible to selectively produce FDCA by converting almost all of the HMF. This catalyst can be recycled several times while continuously maintaining an FDCA production yield of over 90%.

[0062] When a sparingly soluble base such as basic magnesium carbonate is introduced instead of sodium hydroxide to carry out the reaction, it tends to deposit on the surface of the catalyst, resulting in reduced activity compared to when NaOH is added gradually, thus limiting the possibility of recycling.

[0063] The strong base is added as a properly diluted aqueous solution, preferably at a concentration of 50 g / kg to 350 g / kg, more preferably 150 g / kg to 300 g / kg.

[0064] This oxidation step 1) can preferably be carried out in a reactor that can be stirred sufficiently vigorously, or in any case in a reactor that can ensure a wide gas-liquid-solid interface. Examples include reactors with internal or external recirculation functions, mechanical stirring or gas-injection type stirrers, or reactors with fixed beds, such as jet loop type or air-lift type reactors. The characteristics of this reactor allow for limiting the reaction time to typically 12 hours to 6-8 hours, and also provide a good effect on catalytic activity and selectivity.

[0065] At the endpoint of the oxidation reaction (step 1), the 2,5-franzicarboxylic acid obtained in this invention exists in a dissociated form in an aqueous solution.

[0066] In step 2) of the method according to the present invention, the heterogeneous catalyst is separated from the reaction product in an aqueous solution by known techniques.

[0067] According to one aspect of the method according to the present invention, the heterogeneous catalyst in step 2) is separated by filtration, decantation, centrifugation, and separation by at least one operation selected from the group consisting of separation by an electrochemical cell or electrostatic precipitator, a wet scrubbing tower or a liquid cyclone.

[0068] This separation process preferably involves performing one or more identical or different filtration operations, such as belt filters, rotary drum filters, filter presses, and candle filters, either sequentially or in parallel.

[0069] Of these filtration operations, microfiltration and ultrafiltration are preferred, and are carried out through a membrane of a suitable material or, for example, by tangential flow.

[0070] Tangential flow microfiltration (TFF) is preferably carried out using sintered steel or ceramic membranes and is particularly suitable for catalyst separation.

[0071] According to a preferred embodiment of the method of the present invention, the heterogeneous catalyst is separated from the reaction product of step 2) by at least one tangential flow microfiltration, and it is desirable that this microfiltration be carried out while washing the catalyst with water one or more times.

[0072] This filtration procedure should preferably be performed at a temperature above 40°C with a pH in the basic range to retain the FDCA salt in the solution.

[0073] The catalyst separated in step 2) can be reused in oxidation step 1) either as is or, preferably after being washed and / or regenerated, according to step 3) of the method of the present invention.

[0074] According to step 3), the catalyst separated in step 2) can be added to the oxidation reaction in step 1) either alone or, preferably, in addition to the amount of unused catalyst. This added material is preferably in the form of an aqueous slurry with a concentration of 95% by mass or less. Keeping the catalyst in a suspension is actually useful for maintaining appropriate catalytic activity.

[0075] These operations, which involve washing and / or regenerating the catalyst separated in step 2), should preferably be carried out using water at a temperature of 40-60°C to dissolve any reaction products and by-products that may be adsorbed on the catalyst surface and to suppress the adhesion of contaminants to the active phase.

[0076] Since the amount of water used varies depending on the quantity and properties of the reaction products and by-products present, it is desirable to repeat the washing operation several times.

[0077] In a preferred embodiment, the catalyst washing water is reused to dilute the reaction product in the subsequent operation of purifying the 2,5-franzicarboxylate. This operational configuration is particularly advantageous in that it can reduce the overall amount of water used while improving the recovery rate.

[0078] After the catalyst has been separated, FDCA can be obtained in solid form by neutralizing the reaction products in the aqueous solution. The FDCA thus obtained can be easily recovered by one or more separation operations selected from known techniques, such as filtration, decantation, and centrifugation. Alternatively, it can be obtained in solid form by crystallizing FDCA from an aqueous solution of FDCA existing as a salt and then filtering it.

[0079] The reaction product can be neutralized by adding an inorganic acid such as sulfuric acid, hydrochloric acid, nitric acid, or acetic acid, preferably at a concentration of 20% to 70%, more preferably 40% to 60%.

[0080] If the strong base used in the first step is caustic soda, it is preferable to use sulfuric acid.

[0081] Those skilled in the art can easily identify a precipitation method (e.g., the amount and method of adding acid) that optimizes the particle size of the resulting precipitate and its recovery rate, thereby suppressing the inclusion of inorganic salts formed within the precipitate itself and other possible organic by-products or intermediates. The particle size of the precipitate affects the recovery and final purification of the FDCA obtained in solid form. Solid FDCA is purified by known techniques. Purification is, for example, washing and subsequent solid-liquid separation before final drying, which can be carried out by crystallization or solid-liquid separation by extraction using organic solvents (e.g., acetone, methanol, ethanol).

[0082] For solid-liquid separation, filtration is preferred. Preferred examples include filtration using candle filters, belt filters, rotary filters (centrifugal rotary drums), and filter presses, with candle filters and belt filters being preferred. These operations are preferably carried out at high temperatures (50-60°C), but from the viewpoint of favoring condensation, it is advantageous that high temperatures are not necessary, and these operations can be easily carried out by diluting the reaction product with water. Furthermore, filtration can remove salts and partially oxidized HMF products (e.g., residual monocarboxylic acids) derived from the acidification operation, which are said to affect the properties of the final product. In addition, filtration allows for further washing of the solid FDCA.

[0083] In a particularly preferred embodiment, when separating solid FDCA by filtration, the neutralized reaction product can be suitably diluted using catalyst washing water.

[0084] According to a particularly preferred embodiment of the present invention, after step 2) and before the precipitation of FDCA, the method includes an (optional) step of purifying the 2,5-frangic carboxylate present in the reaction product by known techniques, such as one or more membrane separation operations (filtration), passing through a decolorizing ion exchange resin, or a hydrogenation reaction. This purification is preferably carried out by a filtration operation using at least one nanofiltration membrane. This operation effectively removes high molecular weight condensates (oligomers) from the 2,5-frangic carboxylate that may color the final product.

[0085] In fact, spectrophotometric colorimetric analysis of the solid FDCA obtained by this embodiment shows a yellowness index (YI) of less than 20, more preferably less than 15, and even more preferably 5 or less. While we do not wish to be bound by any theory, the presence of impurities that increase the yellowness index appears to adversely affect the polymerization reaction, particularly the degree of polymerization and viscosity (branching).

[0086] A person skilled in the art can select the type of membrane to be used, taking into account the membrane material, its electrochemical properties, and its porosity, according to the characteristics of the reaction products subjected to the filtration operation. Furthermore, based on the characteristics of the selected material, a person skilled in the art can easily evaluate whether it is advantageous to select the optimal pH conditions and operating pressure for each separation operation and whether one or more diafiltration steps (i.e., the steps of adding water to dilute the residue and repeating the separation operation) can be carried out favorably.

[0087] For example, filtration operations are generally carried out using a combination of naturally derived organic membranes (e.g., rubber, polysaccharides) or synthetic organic membranes (e.g., polymer membranes) and inorganic membranes such as ceramic, metal, or glass membranes.

[0088] Among organic membranes, polyamides, polyimides, polyalkylenes, polyetherimides, polyetherethers, poly(etherketones), polycarbonates, cellulose acetates, and their derivatives are preferred, and membranes made of polypiperazinamide, which have a low inhibitory rate against organic salts, are particularly preferred.

[0089] Specific examples of suitable organic membranes include polysulfone, aromatic polyamide, polypiperazineamide, polyethylene, polytetrafluoroethylene (PTFE), polypropylene, polyvinyl alcohol, polystyrene, polybenzimidazole (PBI), polyphenylene, polyphosphazene, polyvinylidene fluoride (PVDF), polyethersulfone (PES), polyacrylonitrile (PAN), and polyvinyl chloride (PVC).

[0090] Both isotropic (or symmetrical) and anisotropic (or asymmetrical) films, as well as composite films, are preferred, but the use of anisotropic films is preferred.

[0091] Dense membranes (with pore sizes less than 1 nm) are preferably used at any purification stage in this process. Porous membranes (i.e., those with pore sizes of 1 nm to 10 μm, for example, macroporous membranes with pore sizes greater than 50 nm, mesoporous membranes with pore sizes of 2 nm to 50 nm, or microporous membranes with pore sizes of 1 nm to 2 nm) can also be advantageously used, particularly in step 2) of separating the catalyst from the reaction product.

[0092] The membrane used in the purification process employing nanofiltration according to the present invention preferably has an average pore size of 5 nm or less, and more preferably has an average pore size corresponding to a molecular weight cutoff (MWCO) of approximately 700 to approximately 300 Da. These characteristics allow for particularly efficient separation of FDCA sodium salts.

[0093] The above-mentioned membrane may be formed in various configurations, such as planar, tubular, capillary, or hollow fiber forms. Planar membranes can be used as is in a filter press system or rotary system, or wrapped and placed in a spiral membrane module to improve surface area and occupied volume.

[0094] The membrane separation operation according to the present invention can be carried out in batches or continuously. Depending on the circumstances, normal flow filtration (vertical) or tangential flow filtration can be preferably used. Membrane separation operation by tangential flow is preferred.

[0095] In accordance with the present invention, the nanofiltration operation is preferably carried out using a membrane made of a material selected from the group consisting of polysulfone, polypiperazinamide, polyamide, and polyimide.

[0096] In a preferred embodiment, nanofiltration is carried out by tangential flow (TFF) using a polymer membrane having a helical structure.

[0097] Some nanofiltration operations are preferably carried out sequentially and may be performed by dilution and / or subsequent continuous diafiltration. The amount of water added can be varied depending on the amount and type of reaction products and by-products present.

[0098] According to one particularly preferred embodiment, catalyst washing water is used in the nanofiltration purification operation.

[0099] Those skilled in the art can easily identify appropriate operating conditions for maintaining the FDCA sodium salt in solution while preventing excessive dilution and minimizing contamination of the film.

[0100] To achieve this objective, it is also preferable to maintain the concentration of the reaction product passing through nanofiltration at less than 50 g / kg in order to suppress the precipitation of 2,5-FDCA salts, which tend to cause membrane fouling.

[0101] According to this embodiment of the present invention, it is desirable to concentrate the permeate to an appropriate concentration value using a known method such as evaporation in order to facilitate the recovery of FDCA in the solution.

[0102] This concentration is preferably carried out by osmosis, while paying attention to maintaining solubility, in order to prevent the precipitation of FDCA salts on the membrane surface.

[0103] Subsequently, FDCA is obtained in solid form as described above.

[0104] The resulting FDCA has a purity of preferably over 98.5%, more preferably over 99%, and even more preferably over 99.5%, with an inorganic salt (e.g., sulfate) content of less than 500 ppm relative to the mass of FDCA, and a residual monocarboxylic acid content of less than 1% by mass, preferably less than 0.5% by mass, making it particularly suitable for use as a monomer for polyester synthesis.

[0105] Accordingly, the second object of the present invention is an FDCA composition characterized in that the purity of 2,5-franchalic acid is greater than 99%, preferably greater than 99.5%, the content of inorganic salts is less than 500 ppm relative to the mass of FDCA, and the content of monocarboxylic acids is less than 1% by mass, preferably less than 0.5% by mass, and more preferably less than 0.1% by mass. Among these monocarboxylic acids, the FDCA composition of the present invention preferably contains 2-furanic acid in an amount of 0.1% by mass or less (preferably 0.05% or less) relative to the mass of FDCA, and / or preferably contains levulinic acid in an amount of 0.1% by mass or less (preferably 0.05% or less) relative to the mass of FDCA.

[0106] The purity and monocarboxylic acid content can be measured, for example, by externally calibrated HPLC / PDA analysis. For example, HPLC / PDA analysis can be performed using a Rezex column "ROA-Organic Acid H+ (8%)" 300 × 7.8 mm type, at a flow rate of 0.6 mL / min, a temperature of 60-65°C, and recording wavelengths of 254 nm and 285 nm, by fixed-composition elution with a 0.005NH2SO4 aqueous solution.

[0107] The content of inorganic salts, particularly inorganic anions, can be measured, for example, by ion chromatography equipped with a conductivity detector (CI-CD), using a "Metrosep A Supp 5" 250 mm × 4.0 mm × 5 μm column with a stationary phase based on polyvinyl alcohol having quaternary ammonium groups, by fixed-composition elution using an aqueous solution of 3.2 mM Na2CO3 + 1 mM NaHCO3 under conditions such as flow rate: 0.7 mL / min and column temperature: 30°C.

[0108] The present invention also relates to the use of this composition in polymerization reactions, particularly for the synthesis of polyesters.

[0109] The above composition can be advantageously obtained by subjecting an aqueous solution of dissociated FDCA to at least one nanofiltration step, followed by neutralization, precipitation, and purification by at least one rinse with water, and then solid-liquid separation.

[0110] Accordingly, a third object of the present invention is a method for purifying FDCA, comprising the steps of nanofiltration of an aqueous solution of FDCA in a dissociated form, followed by the step of precipitating FDCA, and washing the FDCA obtained in a solid state with water.

[0111] According to one embodiment of the above purification method, an aqueous solution of FDCA in its dissociated form is advantageously prepared according to the above-described method for synthesizing 2,5-franzicarboxylic acid, and is obtained, in particular, after step 2) of separation from the catalyst.

[0112] In another embodiment, the aqueous solution of FDCA in its dissociated form is preferably prepared by oxidizing an aqueous HMF solution in an aqueous solution where the pH is maintained in the range of greater than 7 and less than 12, preferably by adding a weak base or a strong base progressively, in the presence of an oxygen-containing gas and a supported catalyst containing a platinum group metal, preferably platinum. Examples of weak bases include sodium bicarbonate, potassium bicarbonate, sodium carbonate, potassium carbonate, calcium carbonate, magnesium carbonate, calcium hydroxide, magnesium hydroxide, dibasic and tribasic phosphate buffers and mixtures thereof. More advantageously, the aqueous solution of FDCA in its dissociated form is prepared according to the method for synthesizing 2,5-franzicarboxylic acid described in European Patent No. 2 601 182.

[0113] In both cases, the initial HMF solution can be advantageously prepared from an HMF composition obtained by the method described in PCT / EP2019 / 068860.

[0114] The method according to the present invention can be carried out in a batch or continuous manner and has the advantage of not requiring the use of organic solvents.

[0115] The method according to the present invention will be described in the following examples, but this does not limit the present invention. [Examples]

[0116] The catalyst used in the following examples is a RuCl3 aqueous solution (8.3 mM) and has a specific surface area of ​​1500 m². 2 The solution was prepared from activated carbon carriers at a concentration of / g. Approximately 286 mL of solution was used for about 10 g of carrier. After vigorous stirring for 15 minutes, the solid was separated, washed with deionized water, and dried overnight at 50°C.

[0117] The obtained powder was treated with NaOH (1.0 M, approximately 28 mL) while vigorously stirring for 24 hours. The solid was then dried at 140°C for another 24 hours to obtain a Ru(OH)3 / C catalyst containing approximately 5% ruthenium.

[0118] (Example 1) Process 1) 1 kg of a 2% aqueous solution of HMF (HMF 20 g / kg) and a supported ruthenium hydroxide catalyst (5% Ru(OH) prepared by the method described above) x The mixture (C, x=3) was placed in a 2L autoclave so that the mass ratio of Ru / HMF was 5%.

[0119] Air was introduced into the reactor to bring the pressure to 20 bar, and the reactor was heated to an internal temperature of 130°C.

[0120] The above reactor was supplied with an airflow of 150 NL / h for 16 hours, and a continuous supply of aqueous caustic soda solution (150 g / kg) was used to maintain a constant pH value of 7.5 to 8.

[0121] Process 2) The final aqueous solution containing the reaction products (FDCA salt and reaction intermediate) was filtered off the catalyst (through a 0.22 μm diameter millipoaseptum), and the PDA in the Rezex column was analyzed by liquid chromatography using a 0.005NH2SO4 eluent (flow rate = 0.6 mL / min; temperature = 60°C).

[0122] The synthesis yield was calculated as 88% by the ratio of the molar concentration of 2,5-FDCA salt in the synthesis solution obtained by chromatographic analysis to the molar concentration of 2,5-FDCA salt theoretically calculated based on the initial molar concentration of the HMF solution supplied during the process.

[0123] Process 3) The catalyst recovered by filtration in step 2) was reused under the same process conditions as in step 1) described above. Despite the catalyst recovery conditions in step 2) not being optimized, the synthesis yield of 2,5-FDCA, as calculated above, was 78%.

[0124] (Comparative Example 1) Process 1) 1 kg of a 2% aqueous solution of HMF (20 g / kg HMF) and a supported ruthenium hydroxide catalyst (5% Ru(OH)3 / C, the same as in Example 1) were placed in a 2 L autoclave so that the mass ratio of Ru / HMF was 5%. Magnesium hydroxide was then added to the reactor in a molar ratio of 1:2 to HMF.

[0125] Air was introduced into the reactor to bring the pressure to 20 bar, the internal temperature was heated to 130°C, and an airflow of 150 NL / h was supplied for 16 hours.

[0126] Process 2) The final aqueous solution containing the reaction products (FDCA salt and reaction intermediate) was separated from the catalyst by filtration (through a 0.22 μm diameter millipoaseptum), and analyzed for PDA in a Rezex column by liquid chromatography using a 0.005NH2SO4 eluent (flow rate = 0.6 mL / min; temperature = 60°C).

[0127] The synthesis yield was calculated as 83% by the ratio of the molar concentration of 2,5-FDCA salt in the synthesis solution obtained by chromatographic analysis to the molar concentration of 2,5-FDCA salt theoretically calculated based on the initial molar concentration of the HMF solution supplied during the process.

[0128] For the separated catalysts, the specific surface area, pore size distribution, and cumulative pore volume were quantified and compared with the values ​​of the unused catalyst and the catalyst recovered after Example 1 (catalyst recovered by filtration before reuse).

[0129] [Table 2]

[0130] In Comparative Example 1, where insoluble Mg(OH)2 was used as a relatively weak base, a dramatic decrease in specific surface area and accommodable pore volume was observed. In Example 1, where a soluble strong base was available as an alternative, the catalytic properties were maintained.

[0131] Surface contamination of the active surface can also be confirmed by the relative amount of magnesium, which limits the catalytic activity of ruthenium oxide / ruthenium hydroxide, on the ruthenium surface relative to sodium, as shown in the atomic composition profile obtained by X-ray photoelectron spectroscopy (XPS) (see table below).

[0132] [Table 3]

[0133] The XPS spectrum was obtained using an Escalab 200-C VG spectrometer equipped with a 5-channel tron ​​hemispherical analyzer and featuring an anode dual-source that separately transmits non-monochromatic X-rays corresponding to MgKα (energy = 1253.6 eV, linewidth = 0.7 eV) and AlKα (energy = 1486.6 eV, linewidth = 0.8 eV). The pressure inside the analysis chamber during measurement was approximately 5 × 10⁻¹⁰. -9 Data was collected as mbar. The analysis range was 3 mm. 2 That was the case.

[0134] Process 3) The catalyst recovered by filtration in step 2) was reused under the same process conditions as in step 1) described above. The synthesis yield of 2,5-FDCA, calculated as described above, was only 67%.

[0135] (Example 2) Process 1) 10 kg of a 10% aqueous solution of HMF (HMF 100 g / kg) and a supported ruthenium hydroxide catalyst (Ru(OH) x A mixture of RuO2 / C (5%, x=3) was added to a 10L jet-loop reactor so that the mass ratio of Ru / HMF was 0.75%.

[0136] Air was introduced into the reactor to bring the pressure to 20 bar, and the reactor was heated to an internal process temperature of 130°C.

[0137] The reactor was supplied with an airflow of 20 NL / min for 8 hours, and a caustic soda aqueous solution (250 g / kg) was continuously supplied at a variable flow rate directly controlled using a pH control device for the process, thereby maintaining the pH value at 7.5 to 8.

[0138] Process 2) The final aqueous solution containing the reaction products (FDCA salt and reaction intermediates) was separated from the catalyst by tangential filtration using a 2 μm sintered steel filter and analyzed by liquid chromatography as described in the above examples.

[0139] The synthesis yield of 2,5-FDCA was 95%, compared to the theoretically calculated synthesis yield of 2,5-FDCA based on the initial concentration of the HMF solution supplied to the process.

[0140] Process 3) The catalyst recovered in step 2) was washed with water at 50°C, filtered, and reused under the process conditions of step 1) described above. This reuse operation was repeated several times. The table below shows the yield results, calculated as the ratio of the concentration of 2,5-FDCA salt in the synthesis solution to the theoretically calculated concentration of 2,5-FDCA salt based on the initial concentration of the HMF solution supplied to the process.

[0141] [Table 4]

[0142] The 2,5-FDCA salt solution was appropriately diluted to a concentration of 10 g / kg. This solution was treated using a helical membrane nanofiltration system with tangential flow, using a polypiperazinamide membrane with a cutoff of 300-500 Da. This treatment was carried out at a rate of 10-15 L / h / m². 2 By operating under constant flow rate conditions, it is possible to achieve a 38% desalting of salts from monomers.

[0143] The resulting residue contained impurities (colored substances with YI=80) derived from the aldol condensation phenomenon.

[0144] Next, the permeate containing the aqueous solution of 2,5-FDCA sodium salt was concentrated by osmosis to a concentration not exceeding 50 g / kg. The total monomer recovery rate was 85% by mass (relative to the FDCA produced).

[0145] 2,5-FDCA was recovered as an acid by precipitation using 5M dilute sulfuric acid. The precipitated solid was recovered by filtering the resulting slurry using a candle filter, followed by washing and drying.

[0146] The obtained FDCA composition was analyzed by liquid chromatography, and the purity of the monomer itself was determined using the method described above.

[0147] The residual sulfuric acid content was evaluated by ion chromatography using a "Metrosep A Supp 5" column (250 mm × 4.0 mm × 5 μm) with polyvinyl alcohol containing quaternary ammonium groups as the stationary phase, and an electrical conductivity detector (Metrohm CI-CD) (fixed composition eluent: 3.2 mM Na2CO3 aqueous solution + 1 mM NaHCO3 aqueous solution, flow rate: 0.7 mL / min, column temperature: 30°C).

[0148] The sulfuric acid content was less than 200 ppm.

[0149] The obtained monomer had a purity of 99.5%, with a furophilic acid content of less than 0.05%, a furancarboxaldehyde content of 0.3%, and a formylfurophilic acid content of 0.02%.

Claims

1. A method for synthesizing 2,5-franzicarboxylic acid (FDCA), 1) A step of oxidizing an aqueous solution of 5-hydroxymethylfurfural (HMF) at a temperature exceeding 100°C in the presence of oxygen molecules, a heterogeneous catalyst containing ruthenium, and a strong base to obtain a reaction product containing an FDC acid salt in the aqueous solution. 2) A step of separating the heterogeneous catalyst from the reaction product in an aqueous solution. 3) A step of reusing the heterogeneous catalyst in the oxidation reaction of step 1). Includes, The heterogeneous catalyst containing ruthenium is selected from the group consisting of supported ruthenium, supported ruthenium oxide, supported ruthenium hydroxide, unsupported ruthenium hydroxide, and mixtures thereof. Here, the support for the supported catalyst is selected from the group consisting of carbon, nonmetallic oxides, functionalized graphite, and combinations thereof. The aforementioned strong base has a solubility in water of 45 g / L or more at 25°C. The strong base is selected from the group consisting of sodium hydroxide, potassium hydroxide, ammonia, ammonium hydroxide, barium hydroxide, lithium hydroxide, cesium hydroxide, strontium hydroxide, rubidium hydroxide, trimethylamine, methylamine, and diethylamine. A method for maintaining the pH between 6.5 and 9 during oxidation in step 1).

2. The method according to claim 1, wherein the strong base is selected from the group consisting of sodium hydroxide, potassium hydroxide, barium hydroxide, lithium hydroxide, cesium hydroxide, strontium hydroxide, and rubidium hydroxide.

3. The method according to claim 1 or 2, wherein the oxidation in step 1) is carried out at a temperature of less than 160°C.

4. The method according to any one of claims 1 to 3, wherein the separation of the heterogeneous catalyst in step 2) is carried out by at least one operation selected from the group consisting of filtration, decantation, centrifugation, and separation by an electrochemical cell, electrostatic precipitator, wet scrubbing tower, or liquid cyclone.

5. The method according to claim 4, wherein the separation of the heterogeneous catalyst in step 2) is carried out by at least one tangential flow microfiltration.

6. The method according to any one of claims 1 to 5, wherein the catalyst is cleaned and / or regenerated after step 2) and before reuse in step 3).

7. The method according to any one of claims 1 to 6, wherein, after step 2), the reaction product in the aqueous solution is purified by at least one nanofiltration operation.

8. The method according to claim 6 or 7, wherein the catalyst is washed with water and the resulting catalyst washing water is used in a purification operation by nanofiltration.

9. The method according to any one of claims 1 to 8, comprising neutralizing the reaction product in an aqueous solution and then separating the FDCA acid obtained therein in solid form.

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