Method for the oxidation of hydroxymethylfurfural

Abstract

The present invention relates to a method for producing 2,5-furandicarboxylic acid (FDCA) from hydroxymethylfurfural (HMF) by two-stage oxidation of HMF, and to a method for producing polyesters, polyamides or polyurethanes from the resulting FDCA.

Description

[Technical field]

[0001] The present invention relates to a method for producing 2,5-furandicarboxylic acid (FDCA) from hydroxymethylfurfural (HMF) by two-stage oxidation of HMF, and to a method for producing polyesters, polyamides or polyurethanes from the resulting FDCA. [Background technology]

[0002] 5-Hydroxymethylfurfural (HMF) is a polyfunctional molecule with an aromatic 5-ring system, aldehyde and alcohol groups. The many functional groups make this molecule a versatile platform chemical that can serve as the basis for many other compounds. Compounds that can be produced based on HMF include chemicals that are already produced on an industrial scale by petrochemical routes, such as caprolactam and adipic acid, but also compounds with great potential applications, such as 2,5-furandicarboxylic acid (FDCA), for which efficient industrial production is not yet available. FDCA can serve as a monomer for the production of polyethylene furanoate (PEF), which competes with polyethylene terephthalate (PET) as a sustainable raw material base with advantageous technical properties, such as an improved gas barrier effect. Other examples of plastic applications where FDCA can be used as a terephthalic acid replacement are polybutylene terephthalate (PBT) and polybutylene adipate terephthalate (PBAT). In principle, FDCA can be used in all polymer applications where diacids are used as monomers.

[0003] Formal oxidation of both the aldehyde and alcohol groups of 2,5-hydroxymethylfurfural (HMF) (CAS number 67-47-0) in aqueous solution gives 2,5-furandicarboxylic acid (FDCA) (CAS number 3238-40-2) via the intermediate products HFCA (hydroxymethyl-2-furancarboxylic acid) (CAS number 6388-41-6) and FFCA (5-formyl-2-furancarboxylic acid) (CAS number 13529-17-4).

[0004] Homogeneous and heterogeneous catalytic oxidation processes for the production of FDCA from HMF are known in the prior art. For example, processes are also known for the oxidation of HMF to FDCA using noble metal catalysts in a single step at basic pH values. Considering that a high pH value is required for the complete oxidation of the second aldehyde group of 5-formyl-2-furan carboxylic acid (FFCA), an intermediate product in the oxidation of HMF to FDCA, it is disadvantageous that HMF is sensitive to high pH values ​​due to its reactivity. Therefore, in the processes of the prior art, pH values ​​are often set that represent a compromise between the desired highest possible conversion to FDCA and the pH instability of HMF that should be avoided, but which are therefore not optimally designed for either requirement. Furthermore, the common processes for the oxidation of HMF to FDCA generally require long reaction times, which are economically disadvantageous. The processes are usually carried out in a single step, i.e. the adjustment and maintenance of the desired pH value required for the conversion of HMF under oxygen supply is carried out in one process step so that FDCA is formed in one process step without deliberately changing the set process parameters, in particular the pH value.

[0005] US 2012 / 0271060 discloses a one-step process for producing FDCA from HMF, in which the oxidation of HMF is carried out at a temperature above 140° C. Such a process is neither economical nor gentle due to the temperature used. EP 2601182 discloses a one-step process for producing FDCA from HMF, in which a weak alkaline solution is used. Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention overcomes the drawbacks of the prior art and is accordingly based on the technical problem of providing a process which allows, in particular, the economical oxidation of HMF to FDCA, in particular in short reaction times, with an increased FDCA yield and / or an improved carbon balance. [Means for solving the problem]

[0007] The present invention solves the underlying technical problem by providing the independent and dependent claims as well as the teachings of this specification. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The present invention relates in particular to a process for the preparation of 2,5-furandicarboxylic acid (FDCA) from hydroxymethylfurfural (HMF), in particular by a two-stage oxidation of HMF, comprising: a) providing an aqueous solution containing HMF having a pH value in the range of 7.0 to 10.0, at least one lye, and at least one precious metal catalyst; b) a process step of reacting an aqueous solution containing HMF in the presence of at least one noble metal catalyst provided according to process step a) under oxidative conditions and maintaining a constant pH value in the range of 7.0 to 10.0 by addition of 0.7 to 1.3 molar equivalents (eq) of at least one alkaline solution (relative to the amount of substance of HMF in the aqueous solution used) to obtain an intermediate product solution containing hydroxymethyl-2-furan carboxylic acid (HFCA) and / or 5-formyl-2-furan carboxylic acid (FFCA); c) reacting the intermediate product solution under oxidative conditions in the presence of at least one noble metal catalyst provided according to process step a) at a pH value range of 10.5 to 14.0 to obtain a solution containing 2,5-furandicarboxylic acid (FDCA); The present invention provides a method comprising:

[0009] In a preferred embodiment, the present invention relates to a process as described above, wherein process step c) is carried out whilst adjusting and maintaining a constant pH value by addition of at least one alkaline liquid, in particular a single and constant pH value in the range from 10.5 to 14.0.

[0010] The present invention relates in particular to a process for the preparation of 2,5-furandicarboxylic acid (FDCA) from hydroxymethylfurfural (HMF), in particular by a two-stage oxidation of HMF, comprising: a) providing an aqueous solution containing HMF having a pH value in the range of 7.0 to 10.0, at least one alkaline liquid, and at least one precious metal catalyst; b) a process step of reacting an aqueous solution containing HMF in the presence of at least one noble metal catalyst provided according to process step a) under oxidative conditions and maintaining a constant pH value in the range of 7.0 to 10.0 by addition of 0.7 to 1.3 molar equivalents (eq) of at least one alkaline solution (relative to the amount of substance of HMF in the aqueous solution used) to obtain an intermediate product solution containing hydroxymethyl-2-furan carboxylic acid (HFCA) and / or 5-formyl-2-furan carboxylic acid (FFCA); c) reacting the intermediate product solution in the presence of at least one noble metal catalyst provided according to process step a) under oxidative conditions and adjusting and maintaining a constant pH value in the range of 10.5 to 14.0 by addition of at least one alkaline solution to obtain a solution containing 2,5-furandicarboxylic acid (FDCA); The present invention provides a method comprising:

[0011] Accordingly, a method for producing FDCA from HMF, preferably by a two-stage process, is provided, comprising process steps (hereinafter also referred to as "steps" for short) a), b) and c). For this purpose, in process step a), the starting product HMF, at least one alkaline liquid and at least one noble metal catalyst are provided in an aqueous solution having a pH value in the range of 7.0 to 10.0.

[0012] In process step b), i.e. in the first stage, the HMF contained in an aqueous solution is then reacted, in particular oxidized, in the presence of a noble metal catalyst, under oxidizing conditions and by addition of 0.7 to 1.3 molar equivalents (eq) of at least one alkaline solution, while maintaining the pH value provided in process step a), i.e. at a constant pH value in the range of 7.0 to 10.0, to obtain hydroxymethyl-2-furan carboxylic acid (HFCA) and / or 5-formyl-2-furan carboxylic acid (FFCA), the molar equivalent being relative to the amount of substance of HMF in the aqueous solution. An intermediate product solution comprising hydroxymethyl-2-furan carboxylic acid (HFCA) and / or 5-formyl-2-furan carboxylic acid (FFCA) is obtained, having a pH value in the range of 7.0 to 10.0.

[0013] Preferably over the entire time course of process step b), a molar equivalent of at least one alkaline solution according to the invention is added continuously to the aqueous solution, which is necessary to keep the pH value constant.

[0014] Then, i.e. after the intermediate product solution containing HFCA and / or FFCA has been obtained, preferably after all the HMF has been reacted, in process step c), i.e. in the second stage, the intermediate product solution is further reacted in the presence of at least one noble metal catalyst under oxidizing conditions and by the addition of a further amount of at least one alkali liquid, while adjusting and maintaining a pH value in the range of 10.5 to 14.0, which is higher than the pH value used in the preceding process step b) according to the invention. Thus, in this process step c), the pH value of the intermediate product solution obtained in process step b) is raised to a pH value in the range of 10.5 to 14.0 and then kept constant by the addition of at least one further alkali liquid, during which HFCA and / or FFCA, in particular both, are converted, in particular oxidized, to FDCA. In process step c), HFCA and / or FFCA are converted to FDCA, and thus in this process step a solution containing FDCA is obtained.

[0015] In process step c), the addition of the at least one alkaline liquid can preferably be carried out in portions, i.e. first a portion of the at least one alkaline liquid is added to the aqueous intermediate product solution at the beginning of process step c) to raise the pH value and then a further portion is added continuously to the aqueous intermediate product solution in order to maintain a constant pH value over the entire time course of process step c).

[0016] In a preferred embodiment, the process according to the invention comprises after process step c) an additional process step d), in which the at least one noble metal catalyst is separated from the solution comprising FDCA, in particular by filtration.

[0017] In a particularly preferred embodiment, the present invention relates to a process according to the invention, in which in a process step a0), prior to process step a), the pH value of an aqueous solution comprising HMF having a pH value of 3.0 to 6.0 is increased, in particular under non-oxidizing conditions, in particular without the supply of air or oxygen, to a pH value in the range of 7.0 to 10.0.

[0018] In a particularly preferred embodiment of the present invention, in process step a0), the pH value can be increased by addition of at least one alkaline liquid.

[0019] In a preferred embodiment, an alkaline liquid is provided in process step a) which is used in both process steps b) and c), and in a particularly preferred embodiment also in process step a0).

[0020] In a preferred embodiment, a strong alkaline liquid is provided in process step a) which is used in both process steps b) and c), and in a particularly preferred embodiment also in process step a0).

[0021] In a particularly preferred embodiment, the at least one alkaline liquid is NaOH or KOH.

[0022] In a preferred embodiment, at least two different alkaline liquids are provided in process step a), which alkaline liquids are preferably each strong alkaline liquid.

[0023] In a preferred embodiment, at least two different alkaline liquids are provided in process step a), which are preferably a strong alkaline liquid and a weak alkaline liquid, respectively.

[0024] In a preferred embodiment, at least two different alkaline liquids are provided in process step a), a first alkaline liquid is used in process step b) and a second alkaline liquid is used in process step c).

[0025] In a preferred embodiment, at least two different alkaline liquids are provided in process step a), a first weak alkaline liquid is used in process step b) and a second strong alkaline liquid is used in process step c).

[0026] In a particularly preferred embodiment, the first weak alkaline liquid, in particular used in process step b), is selected from the group consisting of ammonia, carbonates, bicarbonates, formates and acetates.

[0027] In a particularly preferred embodiment, the second strong alkaline liquid used, in particular in process step c), is NaOH or KOH.

[0028] In a preferred embodiment, the at least one noble metal catalyst provided in process step a) comprises at least one noble metal selected in particular from the group consisting of copper, ruthenium, cobalt, iridium, rhodium, platinum, palladium, gold and silver.

[0029] In a preferred embodiment, the at least one noble metal catalyst provided in process step a) comprises at least one noble metal selected in particular from the group consisting of ruthenium, cobalt, iridium, rhodium, platinum, palladium, gold and silver.

[0030] In a particularly preferred embodiment, the noble metal catalyst comprises at least one noble metal, in particular selected from the group consisting of copper, ruthenium, cobalt, iridium, rhodium, platinum, palladium, gold and silver, and at least one dopant, in particular lead, tin, thallium, tellurium, cobalt or bismuth, in particular bismuth.

[0031] In a particularly preferred embodiment, the noble metal catalyst comprises at least one noble metal, in particular selected from the group consisting of ruthenium, cobalt, iridium, rhodium, platinum, palladium, gold and silver, and at least one dopant, in particular lead, tin, thallium, tellurium, cobalt or bismuth, in particular bismuth.

[0032] In a particularly preferred embodiment, the precious metal catalyst is a Pt-Bi precious metal catalyst.

[0033] In a particularly preferred embodiment, the noble metal catalyst used in process step b) is a gold catalyst and the noble metal catalyst used in process step c) is a Pt-Bi noble metal catalyst, both catalysts advantageously being supported.

[0034] In a particularly preferred embodiment, the precious metal catalyst is copper-free.

[0035] In a preferred embodiment, the noble metal catalyst provided in process step a) is in particular a metal oxide, in particular magnesium oxide, cerium oxide, zirconium oxide, hydroxyapatite, titanium dioxide, hydrotalcite (HAT), Al 2 O 3 and carbon (C).

[0036] In a particularly preferred embodiment, the amount of the noble metal catalyst provided in process step a) used is 0.1 to 25, in particular 1 to 25, in particular 2 to 20, in particular 5 to 15, in particular 7 to 14, in particular 5 g / l (based on the volume of the aqueous solution comprising HMF).

[0037] In a particularly preferred embodiment, the amount of HMF used provided in process step a) is 0.1 to 2.5, in particular 0.2 to 2.0, in particular 0.3 to 1.5, in particular 0.4 to 0.8, in particular 0.4 mol / l (relative to the volume of the aqueous solution containing HMF).

[0038] In a preferred embodiment, in process step b) 0.8 to 1.2, in particular 0.9 to 1.1 molar equivalents (eq) of at least one alkaline liquid are added (relative to the amount of substance of HMF in the aqueous solution used).

[0039] In a preferred embodiment, in process step c) 0.7 to 1.3, in particular 0.8 to 1.2, in particular 0.9 to 1.1 molar equivalents (eq) of at least one alkaline liquid are added (relative to the amount of substance of HMF in the aqueous solution used).

[0040] In a particularly preferred embodiment of the present invention, in process step c) the same at least one noble metal catalyst is used as in the preceding process step b), in particular in process step c) the at least one noble metal catalyst which was used in process step b).

[0041] In a particularly preferred embodiment of the present invention, the at least one noble metal catalyst used in process step b) is not separated from the intermediate product solution comprising hydroxymethyl-2-furancarboxylic acid (HFCA) and / or 5-formyl-2-furancarboxylic acid (FFCA) and is therefore also used in process step c).

[0042] In a particularly preferred embodiment of the present invention, a different noble metal catalyst is used in process step c) than in the preceding process step b).

[0043] In a preferred embodiment, two precious metal catalysts are provided in process step a), a first precious metal catalyst is used in process step b) and a second precious metal catalyst is used in process step c), wherein the first precious metal catalyst is not identical to the second precious metal catalyst.

[0044] In a preferred embodiment, two precious metal catalysts are provided in process step a), a first precious metal catalyst is used in process step b) and a second precious metal catalyst is used in process step c), the first precious metal catalyst comprising a different precious metal than the second precious metal catalyst.

[0045] In a preferred embodiment, two or more precious metal catalysts are provided in process step a), a first precious metal catalyst is used in process step b) and another precious metal catalyst is used in process step c), and the first precious metal catalyst is not identical to the other precious metal catalyst.

[0046] In a preferred embodiment, two or more precious metal catalysts are provided in process step a), a first precious metal catalyst is used in process step b) and another precious metal catalyst is used in process step c), the first precious metal catalyst comprising a different precious metal than the other precious metal catalyst.

[0047] In a particularly preferred embodiment, oxidizing conditions, in particular during process steps b) and / or c), are reaction conditions which result in the supply of oxygen or air to the aqueous solution, in particular by means of an air or oxygen gassing device, in particular a gassing stirrer or blower or / and a flow channel, in particular with simultaneous mechanical agitation of the solution, for example by means of a stirrer or a vortex-forming unit.

[0048] In a particularly preferred embodiment, in particular during process steps b) and / or c), in particular b) and c), oxidative conditions are the supply of oxygen to the solution by means of an air or oxygen gas treatment device, in particular at a flow rate of 10 to 5000, in particular 100 to 5000, in particular 400 to 2000, in particular 600 to 1500, in particular 1000 ml / min per litre reaction volume.

[0049] In a particularly preferred embodiment, in particular during process steps b) and / or c), in particular b) and c), oxidative conditions are the supply of air to the solution by means of an air or oxygen gas treatment device, in particular at a flow rate of 50 to 25 000, in particular 500 to 25 000, in particular 2000 to 10 000, in particular 3000 to 7500, in particular 5000 ml / min per litre of reaction volume.

[0050] In a particularly preferred embodiment, in particular during process steps b) and / or c), in particular b) and c), oxidative conditions are the supply of oxygen to the solution by means of an air or oxygen gas treatment unit, in particular at a flow rate of 10-5000, in particular 100-5000, in particular 400-2000, in particular 600-1500, in particular 1000 ml / min per litre reaction volume, and by mechanical agitation of the solution, for example by means of a stirrer or a vortex-forming unit.

[0051] In a particularly preferred embodiment, in particular oxidative conditions during process steps b) and / or c), in particular b) and c), are the supply of air to the solution by means of an air or oxygen gas treatment device, in particular at a flow rate of 50 to 25 000, in particular 500 to 25 000, in particular 2000 to 10 000, in particular 3000 to 7500, in particular 5000 ml / min of air per litre of reaction volume, and by mechanical agitation of the solution, for example by means of a stirrer or a vortex forming unit.

[0052] In a particularly preferred embodiment, the oxidative conditions in process steps b), c) or b) and c) are provided by a gassed stirrer.

[0053] The gassing stirrer preferably used in steps b) and c) according to the invention provides both the function of an air or oxygen gassing device and the function of an agitator.

[0054] In a preferred embodiment, process steps b) and / or c) are carried out under mechanical agitation, in particular stirring or vortexing, in particular using a gassed stirrer.

[0055] In a preferred embodiment, the aqueous solution is stirred in process step b) by means of a stirrer, in particular at a speed of 50 to 5000, in particular 200 to 1000, in particular 300 to 900, in particular 400 to 500 r / min (rotations of the stirring shaft per minute, also called rpm).

[0056] In a preferred embodiment, the aqueous solution is stirred in process step c) by means of a stirrer, in particular at a speed of 50 to 5000, in particular 200 to 1000, in particular 300 to 900, in particular 400 to 500 r / min (rotations of the stirrer shaft per minute).

[0057] In a preferred embodiment, the aqueous solution is stirred in process steps b) and c) by means of a stirrer, in particular at a speed of 50 to 5000, in particular 200 to 1000, in particular 300 to 900, in particular 400 to 500 r / min (rotations of the stirrer shaft per minute).

[0058] In a particularly preferred embodiment, the process steps a0), a), b) and c), in particular a), b) and c), in particular b) and c), are carried out at a pressure of from normal pressure to 20 bar, in particular from normal pressure to 10 bar, in particular from normal pressure to 5 bar.

[0059] In a particularly preferred embodiment, process steps a0), a), b) and c), in particular a), b) and c), in particular b) and c), are carried out at normal pressure.

[0060] In a preferred embodiment process step b) or c) or both process steps are carried out at a temperature of 40 to 100°C, in particular at a temperature of 50 to 90°C, in particular at a temperature of 55 to 80°C, in particular at a temperature of 55 to 65°C, in particular at 60°C.

[0061] In a preferred embodiment, the process according to the invention comprises, after process step c) or d), an additional process step f), in which the FDCA obtained in process step c), preferably as anion, i.e. as unprotonated FDCA, is protonated, this protonation being carried out in particular by adjusting the solution containing the FDCA to a pH value between 1.0 and 6.5 in order to precipitate the FDCA.

[0062] In a preferred embodiment, the method according to the invention comprises an additional process step f) after process step c) or d), in which the solution containing FDCA is adjusted to a pH value between 1.0 and 6.5 and the FDCA is precipitated to obtain protonated FDCA.

[0063] In a preferred embodiment, the method according to the invention comprises an additional process step e) after process step c) or d) and advantageously before process step f), in particular after process step d) and before process step f), in which process step e) the solution comprising FDCA is purified.

[0064] In a preferred embodiment, the method according to the invention comprises after process step c) or d) or f), in particular after d) or f), an additional process step g), in which the protonated FDCA (after process step f)) or the non-protonated FDCA (after process step c) or d)) is purified, preferably by washing, recrystallization, melting, adsorption or a combination thereof.

[0065] In a preferred embodiment, the method according to the invention comprises an additional process step g) after process step f), in which the protonated or non-protonated FDCA is purified, preferably by washing, recrystallization, melting, adsorption or a combination thereof.

[0066] In a preferred embodiment, process step g) results in isolated FDCA.

[0067] In a preferred embodiment, the method according to the invention comprises an additional process step h) after process step c), d), e), f) or g), in which process step h) the protonated or non-protonated FDCA is converted into a methyl ester, an ethyl ester or a dimethyl ester.

[0068] The present invention also relates to a process for the preparation of a polyester, polyamide or polyurethane, in particular polyethylene furanoate (PEF), which process comprises the process for the preparation of an FDCA according to the invention and then polymerization of the FDCA obtained from process step c), d), e), f) or g), advantageously obtained after process step d), e), f) or g).

[0069] In a preferred embodiment, the process for producing polyesters, polyamides or polyurethanes comprises purifying the FDCA obtained from process step c), d) or f), advantageously d) or f), prior to polymerization, in particular by process step g).

[0070] In a particularly preferred embodiment, the method according to the invention consists of process steps a), b) and c), in particular without further process steps being carried out between these process steps.

[0071] In a preferred embodiment, no further process steps are carried out between process steps b) and c).

[0072] In a preferred embodiment, no purification step is carried out between process steps b) and c).

[0073] In a preferred embodiment, the intermediate product solution comprising hydroxymethyl-2-furancarboxylic acid (HFCA) and / or 5-formyl-2-furancarboxylic acid (FFCA) obtained in process step b) is reacted in process step c) without further process steps, in particular purification and / or separation steps, in particular filtration steps.

[0074] In a preferred embodiment, the method comprises a process step b1) after process step b) and before process step c), in which the at least one noble metal catalyst is separated from the intermediate product solution comprising hydroxymethyl-2-furan carboxylic acid (HFCA) and / or 5-formyl-2-furan carboxylic acid (FFCA), in particular by filtration.

[0075] In a particularly preferred embodiment, the method comprises a process step b2) after process step b1) and before process step c), in which at least one noble metal catalyst, in particular at least one noble metal catalyst which is not identical to the at least one noble metal catalyst separated in process step b1), is added to the intermediate product solution comprising hydroxymethyl-2-furancarboxylic acid (HFCA) and / or 5-formyl-2-furancarboxylic acid (FFCA).

[0076] In the context of the present invention, "separation" or "separation step" is understood to mean the separation of at least one catalyst from a solution, in particular an intermediate product solution comprising hydroxymethyl-2-furan carboxylic acid (HFCA) and / or 5-formyl-2-furan carboxylic acid (FFCA) or a solution comprising 2,5-furan dicarboxylic acid (FDCA), while the composition of the solution, in particular the intermediate product solution comprising hydroxymethyl-2-furan carboxylic acid (HFCA) and / or 5-formyl-2-furan carboxylic acid (FFCA) or a solution comprising 2,5-furan dicarboxylic acid (FDCA), remains unchanged. Preferably, after the separation or separation step, the substances, in particular the reactants, products and by-products, contained in the solution, in particular the intermediate product solution comprising hydroxymethyl-2-furan carboxylic acid (HFCA) and / or 5-formyl-2-furan carboxylic acid (FFCA) or the solution comprising 2,5-furan dicarboxylic acid (FDCA), are present in the same ratios, in particular volume ratios and / or substance amount ratios, to one another as before the separation or separation step.

[0077] In the context of the present invention, the "separation" or "separation process" of at least one catalyst from a solution, in particular an intermediate product solution comprising hydroxymethyl-2-furancarboxylic acid (HFCA) and / or 5-formyl-2-furancarboxylic acid (FFCA), or a solution comprising 2,5-furandicarboxylic acid (FDCA), is not a purification or purification process of a substance, in particular an intermediate product or product, contained in the solution, in particular an intermediate product solution comprising hydroxymethyl-2-furancarboxylic acid (HFCA) and / or 5-formyl-2-furancarboxylic acid (FFCA), or a solution comprising 2,5-furandicarboxylic acid (FDCA), in particular hydroxymethyl-2-furancarboxylic acid (HFCA) and / or 5-formyl-2-furancarboxylic acid (FFCA) or 2,5-furandicarboxylic acid (FDCA).

[0078] In the context of the present invention, "purification" or "purification process" is understood to mean the removal of reactants and / or by-products from a mixture comprising products and reactants and / or by-products. Preferably, purification or a purification process is understood to mean the removal of reactants, in particular HMF, intermediate products, in particular hydroxymethyl-2-furan carboxylic acid (HFCA) and / or 5-formyl-2-furan carboxylic acid (FFCA) and / or 2,5-furan dicarboxylic acid (FDCA) by-products. Preferably, the purification or purification process is washing, recrystallization, melting, adsorption, extraction, distillation or a combination thereof.

[0079] In a particularly preferred embodiment of the invention, the method according to the invention comprises process steps a), b) and c), in which no further process steps are carried out between process steps a), b) and c), but optionally further process steps are carried out before carrying out process step a) and / or after carrying out process step c), in particular carrying out process step a0) before process step a) and at least one of process steps d) to g) after process step c).

[0080] According to the invention, the method comprises process steps a) to c), preferably a0) to c), in particular a) to d), preferably a0) to d), preferably a) to e), preferably a0) to e), in particular a) to f), preferably a0) to f), preferably a) to g), preferably a0) to g). Particularly preferred according to the invention, the method comprises process steps a0), a), b), c), d), e) and f). However, it can also be envisaged that the method comprises steps a), b), c), d), e) and f). Particularly preferred according to the invention, the method comprises process steps a0), a), b), c), d), e), f) and g). Particularly preferred according to the invention, the method comprises process steps a), b), c), d), e), f) and g).

[0081] In a particularly preferred embodiment the method comprises process steps a) to c), preferably a) to d), preferably a) to e), preferably a) to f), preferably a0) to c), in particular a0) to d), in particular a0) to e), in particular a0) to f), preferably a0) to g), preferably a) to g).

[0082] In a preferred embodiment, the method is carried out in the order of process steps a), b), c) and, if optionally provided, d), e) and f), in particular in the order of a0), a), b), c) and, if optionally provided, d), e), f) and g).

[0083] In one embodiment of the method for producing FDCA according to at least process steps a) to c), preferably according to the invention, the conversion of HMF to FDCA is carried out in a batch process, i.e. with batchwise feeding of the reactants and removal of the product, advantageously in a batch reactor system, in particular a reactor.

[0084] According to the present invention, in one embodiment of the process for the preparation of FDCA according to at least steps a) to c), the conversion of HMF to FDCA is carried out in a continuous mode, i.e. with a constant supply of reactants and removal of the product, advantageously in a continuous reactor system.

[0085] According to the invention, neither HMF nor the intermediate products nor FDCA are used, reacted or produced during the process in a solvent other than water, in particular in an organic solvent. Preferably, no organic solvents are used in the process according to the invention.

[0086] In a preferred embodiment, water is used as the only solvent in the process according to the invention.

[0087] The present invention therefore relates in particular to a process for the preparation of 2,5-furandicarboxylic acid (FDCA) from hydroxymethylfurfural (HMF), in particular by a two-stage oxidation of HMF, comprising: a) providing an aqueous solution containing HMF having a pH value in the range of 7.0 to 10.0, at least one alkaline liquid, and at least one precious metal catalyst; b) reacting an aqueous solution containing HMF in the presence of at least one noble metal catalyst under oxidative conditions and maintaining a constant pH value in the range of 7.0 to 10.0 by addition of 0.7 to 1.3 molar equivalents (eq) of at least one alkaline solution (relative to the amount of substance of HMF in the aqueous solution used) to obtain an intermediate product solution containing hydroxymethyl-2-furan carboxylic acid (HFCA) and / or 5-formyl-2-furan carboxylic acid (FFCA); c) reacting the intermediate product solution in the presence of at least one noble metal catalyst under oxidative conditions and adjusting and maintaining a constant pH value in the range of 10.5 to 14.0 by adding at least one alkaline solution to obtain a solution containing 2,5-furandicarboxylic acid (FDCA); The present invention provides a method comprising:

[0088] In the context of the present invention, normal pressure is understood to be the gas pressure which corresponds to the average atmospheric pressure at the earth's surface of 101325 Pa = 1.01325 bar.

[0089] In the context of the present invention, an "agitator" is understood to be a stirring device, i.e. a device having stirring elements arranged on at least one stirring shaft and designed to stir a solution.

[0090] In the context of the present invention, a "vortex forming unit" is understood to be a device designed to be able to induce a flow movement in a solution.

[0091] In the context of the present invention, a "weak alkaline solution" is understood to be an alkaline solution having a pKa between 10.4 and 3.75.

[0092] In the context of the present invention, a "strong alkali" is understood to be an alkali with a pKb of <3.

[0093] In the context of the present invention, the term "molar equivalent (eq)" is understood to be the amount of substance (mol) that corresponds to the amount of substance being referred to. For example, if there are 3 moles of substance A in a solution of volume 2 L (concentration of A 1.5 mol / L) to which 0.5 molar equivalents of substance B are added, this corresponds to 0.5 eq, i.e. 1.5 moles added to the solution (concentration of B 0.75 mol / L).

[0094] In the context of the present invention, "oxidative conditions" are understood in particular to be reaction conditions or reaction environments characterized by process parameters such as temperature, pH value, pressure and the presence of oxygen, such that oxidation of the starting materials, in particular HMF, or intermediate products, in particular HFCA and / or FFCA, is possible, in particular during process steps b) and / or c).In the context of the present invention, "oxidative conditions" are understood in particular to be reaction conditions characterized by the supply of oxygen or air to the aqueous solution, for example by means of an air or oxygen gassing device, for example a gassing stirrer or blower and / or a flow channel, in particular with simultaneous mechanical agitation of the solution, for example by means of a stirrer or a vortex-forming unit.

[0095] In the context of the present invention, "non-oxidizing conditions" are understood to be in particular reaction conditions or reaction environments characterized by process parameters such as temperature, pH value, pressure and the presence of oxygen such that oxidation of the starting materials, in particular HMF, or the intermediate products, in particular HFCA and / or FFCA, is not possible, in particular during process steps b) and / or c).In the context of the present invention, "non-oxidizing conditions" are understood to be in particular reaction conditions that are not characterized by the supply of oxygen or air to the aqueous solution.

[0096] In the context of the present invention, a "supply" of air or oxygen is understood to mean an inflow of air or oxygen in the aqueous solution beyond the pure diffusion process, i.e. a local concentration increase, which is brought about in a targeted manner by suitable process techniques, in particular by using an air or oxygen gassing device, in particular a gassing stirrer. This supply is advantageously a continuous supply. This supply serves to replenish the oxygen present in the aqueous solution consumed by the reaction, so that the oxygen in the aqueous solution is not depleted.

[0097] In the context of the present invention, "air" is understood to be a gas mixture having a volume fraction of oxygen of 20-22% by volume, in particular about 21% by volume, in particular 21% by volume (relative to the total volume of air).

[0098] In the context of the present invention, a "two-stage" or "two-stage" process is understood to be a process characterized by an initial state, in which at least one desired chemical reaction is initiated and initial reaction conditions are preferably set or set, and a final state, in which a desired, in particular maximum amount of starting materials has reacted, between the initial and final states, the reaction conditions, in particular the pH value, have been intentionally changed at least once by a human or artificial operator. In contrast, a one-stage process is characterized in that between the initial and final states, the pH value has not been intentionally changed by the operator, in particular the reaction conditions have not been changed at all.

[0099] In the context of the present invention, the term "constant" pH value or "maintaining a constant pH value" is understood to mean keeping the specific pH value mentioned in each case constant with a maximum deviation of ±0.2 pH value units, in particular keeping the specific pH value mentioned in each case constant with a maximum deviation of ±0.1 pH value units, in particular having exactly the specified pH value.

[0100] In the context of the present invention, the pH value is determined as follows.

[0101] For pH adjustment and control, for example a titration device with integrated pH measurement and alkaline metering, such as the Dulcometer PHD from Prominent, is used. As pH electrode, for example the pH electrode HA 405-DXK-S8 / 325 from Mettler Toledo or equivalent electrodes from other manufacturers are used. The pH electrode is calibrated before use with two buffer solutions (for example WTW technical buffer) at pH 7.00 and pH 10.01 at 25° C. As the reaction is carried out at temperatures higher than 25° C., a Pt-100 element is connected to the titration device for temperature compensation.

[0102] In the context of the present invention, "protonated FDCA" is understood to be 2,5-furandicarboxylic acid with CAS number 3238-40-2.

[0103] In the context of the present invention, "unprotonated FDCA" is understood to be the mono- or divalent anion of 2,5-furandicarboxylic acid.

[0104] In the context of the present invention, "FDCA" is understood to be 2,5-furandicarboxylic acid, CAS number 3238-40-2, which, when dissolved, can exist in protonated or unprotonated form depending on the pH value of the solution containing FDCA.

[0105] In the context of the present invention, the term "at least one" is understood to be a quantity data representing a number such as 1 or 2 or 3 or 4 or 5 or 6 or 7 or 8 or 9 or 10. In a particularly preferred embodiment, the term "at least one" can represent the number exactly 1. In a further preferred embodiment, the term "at least one" can also mean 2 or 3 or 4 or 5 or 6 or 7.

[0106] In the context of the present invention, the term "at least one precious metal catalyst" is understood to be a numerically defined number of precious metal catalysts, which number may be 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or more.

[0107] In the context of the present invention, where quantitative data, in particular percentages, of components of a product or composition are given, these, together with other explicit or technically obvious further components of the composition or product, amount to 100% of the composition and / or product, unless expressly stated otherwise or obvious in the art.

[0108] In the context of the present invention, when the "presence", "inclusion", "possession" or "containing" of an ingredient is stated or implied, this means that the respective ingredient is present in a specifically measurable amount.

[0109] The number of decimal places displayed corresponds to the precision of the respective measurement method used.

[0110] In the context of the present invention, if the one and two decimal places or the second decimal place is not indicated, it is set to zero.

[0111] In the context of the present invention, the term "and / or" is understood as disclosing all members of the group connected by this term "and / or" either alternatively or multiplexed with one another in any combination. This means that the expression "A, B and / or C" is understood to disclose: a) A or B or C, or b) (A and B), or c) (A and C), or d) (B and C), or e) (A and B and C).

[0112] In the context of the present invention, the terms "comprise" and "have" are understood to mean that in addition to the elements expressly included by these terms, further elements not expressly included may be added. In the context of the present invention, these terms are also understood to mean that only the elements expressly included are included, and that no further elements are present. In this particular embodiment, the meaning of the terms "comprise" and "have" is synonymous with the term "consisting of". Furthermore, the terms "comprise" and "have" also include compositions that, in addition to the elements expressly included, also include other elements that are not mentioned but have functional and qualitatively dependent properties. In this embodiment, the terms "comprise" and "have" are synonymous with the term "consisting essentially of". The term "consisting of" means that only the elements expressly included are present, and the presence of further elements is excluded.

[0113] Further embodiments of the invention are the subject matter of the dependent claims and other independent claims.

[0114] The invention will now be described in more detail with reference to the following examples and the associated figures. [Brief description of the drawings]

[0115] [Figure 1] FIG. 1 shows NaOH consumption curves as a function of the pH value adjusted in process step b) for tests 5a-f. [Diagram 2]FIG. 14 shows the C balance as a function of the adjusted pH value in process step b) for tests 5a-f. [Diagram 3] FIG. 1 shows NaOH consumption curves as a function of the pH value adjusted in process step c) for tests 6a-6d. [Figure 4] FIG. 1 shows the selectivity of intermediates and HMF as well as the C balance as a function of the adjusted pH value in process step c) for tests 6a-6d. [Diagram 5] FIG. 2 shows NaOH consumption curves for the process mode according to the invention with two different catalysts. EXAMPLES

[0116] (Example) Example 1

[0117] One-stage method (comparison method) The catalyst used was a platinum / bismuth catalyst supported on activated carbon (3.5% Pt / 1% Bi / C (=Norit SX UltraCat)). The oxidation of HMF was carried out under the following reaction conditions.

[0118] Reaction volume (batch) 500ml Catalyst amount 10.1g / l Base material initial concentration 0.4mol / l pH 9.0 Temperature 60℃ Pressure: Normal pressure O 2 Flow rate 0.5l / min Titrant NaOH (16% by weight dry matter (DM) based on total mass) Stirring speed 300 rpm (agitator).

[0119] The reaction time was sometimes 5.8 hours (Example 1a) and sometimes 23.1 hours (Example 1b), with otherwise identical reaction conditions. Example 2

[0120] The two-step process according to the present invention The catalyst used was the same as in Example 1 (3.5% Pt / 1% Bi / C (=Norit SX UltraCat)). The oxidation of HMF was carried out under the following reaction conditions.

[0121] Reaction volume 500ml Catalyst amount 9.5g / l Base material initial concentration 0.4mol / l pH 9.0 for steps a) and b) pH of step c) 12.0 Temperature 60℃ Pressure in steps b) and c) Normal pressure O in steps b) and c) 2 Flow rate 0.5l / min Titrant for steps b) and c) NaOH (16% by weight dry matter (DM) relative to the total mass) Stirring speed for steps b) and c) 300 rpm (stirrer).

[0122] In process step b), 1.13 equivalents of NaOH were added before switching to process step c), while keeping the pH value constant.

[0123] To adjust and maintain the pH value in process step c), 0.88 equivalents of NaOH were added.

[0124] The results obtained under the reaction conditions of Examples 1 and 2 are shown in Table 1. [Table 1]

[0125] It can be seen that the C balance in Example 2 according to the present invention is clearly better than that in Comparative Example 1. Furthermore, in Example 2, the same amount of FDCA can be produced in a much shorter time than in Example 2b, and the content of the resulting secondary components is lower. Example 3

[0126] Addition of 2 and 4 equivalents of alkaline solution at the start of the reaction (Comparative Example) The catalyst used was a hydrotalcite-supported Pt / bismuth catalyst (2.5% Pt / 1% Bi / HT). HMF oxidation was carried out under the following reaction conditions:

[0127] Reaction volume (batch) 500ml Catalyst amount 5.0g / l Base material initial concentration 0.4mol / l pH Unstable pH value, starting pH 13.2, ending pH 9.6 Temperature 60℃ Pressure: Normal pressure O 2 Flow rate 0.5l / min Titrant NaOH (16% by weight dry matter (DM) based on total mass) Stirring speed 300 rpm (agitator). Example 3a

[0128] The total required NaOH amount of 100 g (16 wt%), corresponding to 2 equivalents of NaOH per mole of HMF, was added directly at the start of the reaction. Example 3b

[0129] The total required NaOH amount of 200 g (16 wt%), corresponding to 4 equivalents of NaOH per mole of HMF, was added directly at the start of the reaction. Example 4

[0130] Method according to the invention The same catalyst was used as in Example 3. The oxidation of HMF was carried out under the following reaction conditions:

[0131] Reaction volume (batch) 500ml Catalyst amount 5.0g / l Base material initial concentration 0.4mol / l pH 9.0 for steps a) and b) pH of step c) 11.6 Temperature of steps b) and c) 60°C Pressure in steps b) and c) Normal pressure O in steps b) and c) 2 Flow rate 0.5l / min Titrant for steps b) and c) NaOH (16% by weight dry matter (DM) relative to the total mass) Stirring speed for steps b) and c) 300 rpm (stirrer).

[0132] In process step b), 0.8 equivalents of NaOH were added before switching to process step c), during which the pH value was kept constant. To adjust and maintain the pH value in process step c), 1.2 equivalents of NaOH were added. A total of 2 equivalents of NaOH were added.

[0133] The results for Examples 3a, 3b and 4 are shown in Table 2. [Table 2]

[0134] It can be seen that Example 4 according to the invention gives a clearly better C balance, more FDCA and less intermediate products than the two comparative examples 3a and 3b. Example 5

[0135] Change in pH value in process step b) The catalyst used was a hydrotalcite-supported platinum / Bi catalyst (2.5% Pt / 1% Bi / HT).

[0136] The oxidation of HMF was carried out in process steps a) and b) under the following reaction conditions:

[0137] Reaction volume (batch) 500ml Catalyst amount 5.0g / l Base material initial concentration 0.4mol / l Temperature 60℃ Pressure: Normal pressure O 2 Flow rate 0.5l / min Titrant NaOH 16 (16% by weight dry matter (DM) based on the total mass) Stirring speed 900 rpm (Büchi gassed stirrer).

[0138] The pH value of process step b) was selected as follows (Table 3) and kept constant by adding the corresponding amount of NaOH. Process step c) was not performed. [Table 3]

[0139] Figure 1 shows a comparison of titration curves.

[0140] It is clear that the reaction rate of process step b) depends on the pH value. The higher the pH value, the faster the reaction. Figure 2 shows the C balance at the end of process step b) (addition of 1 equivalent of NaOH (corresponding to 50 g of NaOH)).

[0141] Higher pH values ​​resulted in higher reaction rates and associated increased losses of products and / or intermediates. An acceptable C balance of ≥ 93% was only achieved for pH values ​​≤ pH 10. Example 6

[0142] Change in pH value in process step c) The catalyst used was a hydrotalcite-supported platinum / Bi catalyst (2.5% Pt / 1% Bi / HT).

[0143] The oxidation of HMF was carried out under the following reaction conditions:

[0144] Reaction volume (batch) 500ml Catalyst amount 5.0g / l Base material initial concentration 0.4mol / l pH value of steps a) and b) 9.0 Temperature of steps b) and c) 60°C Pressure in steps b) and c) Normal pressure O in steps b) and c) 2 Flow rate 0.5l / min Stirring speed for steps b) and c) 900 rpm (Büchi gassed stirrer).

[0145] In process step b), 0.8 equivalents of NaOH were added before switching to process step c).

[0146] The pH values ​​of process step c) were selected for the various examples as shown in Table 4 and were adjusted and kept constant by adding the corresponding amounts of NaOH. [Table 4]

[0147] FIG. 3 shows the titration curves for different pH values ​​of process step c).

[0148] Figure 4 shows the C balance, FDCA selectivity, and intermediate selectivity as a function of pH value.

[0149] At pH 10, the C balance is the highest at 98%, but the FDCA selectivity is also the lowest at 64%. The high intermediate selectivity (34%) indicates that the reaction is not yet complete. The highest FDCA selectivity is 97.5% at pH 12. Under these conditions, the intermediate selectivity is also the lowest at 0.44%. Example 7

[0150] Different catalysts used for the first and second steps First stage catalyst: 1% Au / Al 2 O 3 Second stage catalyst 2.5%Pt / 1.0%Bi / HAT (HT=hydrotalcite).

[0151] The reaction was carried out under the following reaction conditions:

[0152] Reaction volume 500ml Catalyst amount in the first stage: 12.5g / l Catalyst amount for the second stage: 5.0g / l Base material initial concentration 0.4mol / l First stage pH 9.0 Second stage pH 11.7 Temperature 60℃ Pressure: Normal pressure O2 Flow rate 500ml / min Stirring speed 900 rpm (Büchi gassed stirrer).

[0153] After addition of 0.8 equivalents of NaOH in process step b), the catalyst is separated by filtration and the filtered solution is used without further treatment in the second stage in process step c) with addition of 1.1 equivalents of NaOH.

[0154] FIG. 5 shows the NaOH consumption curves for the process mode according to the invention using two different catalysts.

[0155] The results are shown in Table 5. [Table 5]

[0156] Complete HMF conversion is achieved with acceptable C balance and high FDCA selectivity.

Claims

1. A method for producing 2,5-furandicarboxylic acid (FDCA) from hydroxymethylfurfural (HMF) by two-stage oxidation of the HMF, comprising: a) providing an aqueous solution containing HMF having a pH value in the range of 7.0 to 10.0, at least one alkaline liquid, and at least one noble metal catalyst; b) reacting the aqueous solution comprising HMF in the presence of at least one noble metal catalyst provided according to process step a) under oxidative conditions and maintaining a constant pH value in the range of 7.0 to 10.0 by adding 0.7 to 1.3 molar equivalents (eq) of the at least one alkaline solution (relative to the amount of substance of HMF in the aqueous solution used) to obtain an intermediate product solution comprising hydroxymethyl-2-furancarboxylic acid (HFCA) and / or 5-formyl-2-furancarboxylic acid (FFCA); c) reacting said intermediate product solution under oxidative conditions in the presence of at least one noble metal catalyst provided according to process step a) at a pH value ranging from 10.5 to 14.0 to obtain a solution containing 2,5-furandicarboxylic acid (FDCA); A method comprising:

2. 2. The method according to claim 1, wherein process step c) is carried out while adjusting and maintaining a constant pH value in the range of 10.5 to 14.0 by addition of said at least one alkaline liquid.

3. 2. The method according to claim 1, wherein in process step a0) prior to process step a), the pH value of the aqueous HMF solution having a pH value of 3.0 to 6.0 is increased, in particular under non-oxidizing conditions, in particular without the supply of air and oxygen, to a pH value in the range of 7.0 to 10.

0.

4. 2. The method according to claim 1, wherein in process step a) at least two different alkalis are provided, and in process step b) a first alkali, in particular a weak alkali, is used and in process step c) a second alkali, in particular a strong alkali, is used.

5. 2. The method according to claim 1, wherein the at least one alkaline solution, in particular a strong alkaline solution, is NaOH or KOH.

6. 2. The method according to claim 1, wherein in process step c) 0.7 to 1.3 molar equivalents (eq) of the at least one alkaline liquid are added (relative to the amount of HMF in the aqueous solution used).

7. 2. The method according to claim 1, wherein the oxidizing conditions, in particular during process steps b) and / or c), are reaction conditions that result in the supply of oxygen or air to the aqueous solution, in particular by means of an air or oxygen gassing device, in particular a gassing stirrer or blower and / or a channel, in particular with simultaneous mechanical agitation of the solution, for example by means of a stirrer or vortex-forming unit.

8. 2. The method according to claim 1, wherein process steps b) and c) are carried out with mechanical agitation, in particular agitation by means of a stirrer or a vortex-forming unit.

9. 10. The method of claim 1, wherein the at least one noble metal catalyst comprises at least one noble metal selected from the group consisting of copper, ruthenium, rhodium, cobalt, iridium, platinum, palladium, gold, and silver.

10. 2. The method according to claim 1, wherein the at least one noble metal catalyst comprises at least one noble metal and at least one dopant, in particular lead, tin, thallium, tellurium, cobalt or bismuth, and is in particular a Pt-Bi noble metal catalyst.

11. 10. The method of claim 1, wherein process steps b), c) or both are carried out at a temperature of 40 to 100°C.

12. 2. The method according to claim 1, wherein process step c) is followed in process step d) by separating the at least one noble metal catalyst from the FDCA-containing solution, in particular by filtration.

13. 2. The method according to claim 1, wherein process step c) or d) is followed in process step f) by protonating the FDCA obtained in process step c) or d), said protonation being carried out in particular by adjusting the pH of the solution containing the FDCA to a pH value of 1.0 to 6.5 to obtain protonated FDCA.

14. 2. The method of claim 1, wherein process step c) or d) is followed by process step e) in which the solution containing FDCA is purified.

15. 2. The method of claim 1, wherein, following process step c), d) or f), in process step g), the protonated or unprotonated FDCA is purified, preferably by washing, recrystallization, melting, adsorption or a combination thereof.

16. 2. The method of claim 1, wherein process step c), d), e), f), or g) is followed by process step h), in which the protonated or unprotonated FDCA is converted to a methyl ester, an ethyl ester, or a dimethyl ester.

17. 17. A method for producing a polyester, polyamide or polyurethane, in particular polyethylene furanoate (PEF), which comprises carrying out the method according to any one of claims 1 to 16, followed by polymerization of the FDCA obtained from process steps c), d), e), f) or g).

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