Process for preparing furan-2,5-dicarboxylic acid

Abstract

A process for preparing furan-2,5-dicarboxylic acid is disclosed. The process includes the following steps: preparing or providing a starting mixture including 5-(hydroxy-methyl)furfural (HMF), 5,5-[oxy-bis(methylene)]bis-2-furfural (di-HMF), and water; subjecting said starting mixture to oxidation conditions in the presence of an oxygen-containing gas and a catalytically effective amount of a heterogeneous catalyst including one or more noble metals on a support so that both HMF and di-HMF react to give furane-2,5-dicarboxylic acid in a product mixture also including water and oxidation by-products. The use of a catalyst is also disclosed, the catalyst including one or more noble metals on a support as an heterogeneous oxidation catalyst for catalyzing in an aqueous starting mixture the reaction of both HMF and di-HMF to furane-2,5-dicarboxylic acid.

Claims

1. Process for preparing furane-2,5-dicarboxylic acid comprising the following steps: (a) preparing or providing a starting mixture comprising 5-(hydroxymethyl)furfural (HMF), 5,5-[oxy-bis(methylene)]bis-2-furfural (di-HMF), and water, wherein a total amount of water in the starting mixture is at least 50 wt.-%, based on a total weight of the starting mixture and wherein a pH of the starting mixture is in a range of from 4.0 to 7.0, (b) subjecting said starting mixture to oxidation conditions in the presence of an oxygen-containing gas and a catalytically effective amount of a heterogeneous catalyst comprising one or more noble metals on a support so that both HMF and di-HMF react to give furane-2,5-dicarboxylic acid in a product mixture also comprising water.

2. The process according to claim 1, wherein the starting mixture has a molar ratio of HMF to di-HMF in the range of from 100 to 0.8, and/or a total weight of HMF and di-HMF in the starting mixture is in a range of from 0.1 to 50 wt.-%, based on the total weight of the starting mixture.

3. The process according to claim 1, wherein a pH of the product mixture is below 7.

4. The process according to claim 1, wherein said starting mixture at a temperature in a range of from 70 C. to 200 C., is subjected to said oxidation conditions in the presence of said oxygen-containing gas and said catalytically effective amount of a heterogeneous catalyst comprising one or more noble metals on a support, so that both HMF and di-HMF react to give furane-2,5-dicarboxylic acid in the product mixture also comprising water and oxidation by-products.

5. The process according to claim 1, wherein said starting mixture is subjected to said oxidation conditions in a pressurized reactor, wherein an oxygen partial pressure in the reactor at least temporarily is in a range of from 1 to 100 bar, during the reaction of both HMF and di-HMF to furane-2,5-dicarboxylic acid.

6. The process according to claim 1, wherein a total amount of acetate ions and acetic acid in said starting mixture is below 10 wt.-%, wherein a total amount of carboxylic acid ions and carboxylic acid in the starting mixture is below 10 wt.-%.

7. The process according to claim 1, wherein the step of preparing said starting mixture comprises (a1) preparing or providing a material mixture comprising one, two or more compounds selected from the group consisting of hexoses, oligosaccharides comprising hexose units, and polysaccharides comprising hexose units, and (a2) subjecting said material mixture to reaction conditions so that a mixture results comprising HMF, di-HMF, and water.

8. The process according to claim 1, wherein in said heterogeneous catalyst comprising one or more noble metals on a support (i) at least one of said noble metals is selected from the group consisting of gold, platinum, iridium, palladium, osmium, silver, rhodium and ruthenium, and/or (ii) said support is selected from the group consisting of carbon, metal oxides, metal halides, and metal carbides.

9. The process according to claim 1, wherein in said heterogeneous catalyst comprising one or more noble metals on a support at least one of said noble metals is selected from the group consisting of platinum, iridium, palladium, osmium, rhodium and ruthenium, and said support is carbon.

10. The process according to claim 1, wherein in said heterogeneous catalyst comprising one or more noble metals on a support said one or one of said more noble metals is platinum and said support is carbon, and a content of platinum on the support is in a range of from 0.1 to 20 wt.-%, based on a total weight of the heterogeneous catalyst comprising one or more noble metals on a support.

11. The process according to claim 1, wherein in said heterogeneous catalyst comprising one or more noble metals on a support a molar ratio of said one or one of said more noble metals to a total amount of HMF and di-HMF is in a range of from 1:1 000 000 to 1:10.

12. The process according to claim 1, wherein the product mixture obtained in step (b) comprises furan-2,5-di carboxylic acid in dissolved form.

13. A catalyst comprising one or more noble metals on a support as an heterogeneous oxidation catalyst for accelerating in an aqueous starting mixture a conversion of both HMF and di-HMF to furane-2,5-dicarboxylic acid, wherein a pH of the starting mixture is in a range of from 4.0 to 7.0.

14. The process according to claim 7, wherein the step of preparing said starting mixture further comprises (a3) subjecting the mixture resulting from step (a2) to additional treatment conditions, without adding a carboxylic acid and/or without adding an acidic solvent for dissolving HMF and di-HMF, so that said starting mixture results.

15. The process according to claim 3, wherein the pH of the product mixture is in a range of from 1 to 4.

16. The process according to claim 4, wherein said starting mixture is at a temperature in a range of from 100 C. to 135 C.

17. The process according to claim 5, wherein the oxygen partial pressure in the reactor at least temporarily is in a range of from 1 to 20 bar.

18. The process according to claim 9, wherein at least one of said noble metals is platinum.

19. The process according to claim 10, wherein in the content of platinum on the support is in a range of from 1 to 10 wt.-%.

20. The process according to claim 12, wherein the product mixture obtained in step (b) does not comprise furan-2,5-dicarboxylic acid in solid form.

Description

EXAMPLES

(1) Catalyst Screening Experiments:

(2) Catalyst screening was carried out in a series of single experiments designated Experiment 1 to Experiment 3. In each single experiment 1 to 3 the organic reactant compounds HMF and di-HMF were in parts catalytically converted by means of a heterogeneous platinum catalyst to FDCA. The general experimental procedure for each screening experiment of 1 to 3 was as follows:

(3) In a first step, by filling into a steel autoclave reactor (inner volume 90 ml) specific amounts of deuterated water (D.sub.2O, 99.9 atom %, Sigma Aldrich (151882)), HMF (99+%), and di-HMF (99+%) an aqueous starting material mixture was prepared having a composition similar to the composition of HMF feed-streams usually obtained in sugar dehydration). The amounts of the reactants and D.sub.2O are identified in table 1 below:

(4) TABLE-US-00001 TABLE 1 D.sub.2O 28.5 g total amount of reactants 1.5 g HMF and di-HMF HMF 1.0, 0.75 or 0.5 g di-HMF* 0.5, 0.75 or 1.0 g *di-HMF can, e.g., be synthesized according to WO 2013/033081, example 45.

(5) The starting concentration C.sub.0[HMF+di-HMF] of HMF+di-HMF in each aqueous reactant mixture was correspondingly 5% by weight, based on the total mass of the aqueous reactant mixture (total mass of deuterated water, HMF and di-HMF). The solid heterogeneous catalyst (0.928 g of 5 wt % Pt/C, 50 wt % H.sub.2O) was added to the respective aqueous reactant mixture and, thus, a reaction mixture comprising deuterated water, HMF, di-HMF, and the heterogeneous catalyst was obtained.

(6) In a second step, the filled reactor was tightly sealed and pressurized with synthetic air (total pressure 100 bar to obtain conditions so that both HMF and di-HMF react to give FDCA. The starting mixture in the reactor comprising HMF, di-HMF and deuterated water was heated to a temperature of 100 C. while stirring at 2000 rpm. After reaching 100 C., this temperature was maintained for 18 hours while continuing stirring the heated and pressurized reaction mixture during the reaction time. A product mixture comprising FDCA, oxidation by-products, deuterated water and the heterogeneous catalyst resulted.

(7) In a third step, after the temperature had been maintained for 18 hours, to give a cooled product mixture the steel autoclave reactor was (i) allowed to cool down to room temperature (approximately 22 C.), (ii) depressurized and (iii) opened.

(8) The product mixture obtained was in the form of a suspension.

(9) For the purpose of product analysis of the cooled product mixture, a solution of deuterated sodium hydroxide (NaOD, 40 wt.-% in D.sub.2O, 99.5 atom % D, Sigma Aldrich) was carefully added to the product mixture until a slightly alkaline product mixture having a pH in the range of from 9 to 10 was reached. The slightly alkaline product mixture comprised the disodium salt of FDCA in completely dissolved form, and the heterogeneous catalyst in solid form.

(10) In a fourth step, the heterogeneous catalyst in the slightly alkaline product mixture was separated from the solution by syringe filtration, and the filtrate (i.e. the remaining solution comprising the disodium salt of FDCA in completely dissolved form) was subsequently analyzed by .sup.1H-NMR spectroscopy. .sup.1H-NMR spectroscopy was used to determine the concentration of FDCA, FFCA, HMF and di-HMF.

(11) NMR Analysis:

(12) NMR sample preparation and NMR measurements:

(13) 3-(Trimethylsilyl)propionic-d.sub.4 acid sodium salt (Standard 1, 68.39 mg, corresponding to 0.397 mmol, 98+ atom % D, Alfa Aesar (A14489)) and Tetramethylammonium iodide (Me.sub.4N+I, Standard 2, 80.62 mg, corresponding to 0.397 mmol, 99%, Alfa Aesar (A12811)) were added as internal standards to 5.0 g of a slightly alkaline product mixture, exhibiting a pH value in the range of from 9 to 10. Finally, 0.7 ml of this prepared sample liquid were transferred into a NMR tube for .sup.1H NMR quantification experiments.

(14) NMR-spectra were recorded in D.sub.2O at 299 K using a Bruker-DRX 500 spectrometer with a 5 mm DUL 13-1H/19F Z-GRD Z564401/11 probe, measuring frequency 499.87 MHz. Recorded Data were processed with the software Topspin 2.1, Patchlevel 6 (Supplier: Bruker BioSpin GmbH, Silberstreifen 4, 76287 Rheinstetten, Germany).

(15) Interpretation of NMR spectra:

(16) Interpretation of NMR spectra is based on published reference data as indicated below.

(17) Disodium salt of FDCA (disodium salt of compound of formula (I)):

(18) .sup.1H NMR (500 MHz, D2O, 299 K): 6.97 ppm (2H, s, furan-H); 13C{1H} NMR: 166.1 ppm (COO), 150.0 ppm (furan C atoms), 115.8 ppm (furan C atoms).

(19) Reference: J. Ma, Y. Pang, M. Wang, J. Xu, H. Ma and X. Nie, J. Mater. Chem., 2012, 22, 3457-3461.

(20) Sodium salt of FFCA (sodium salt of compound of formula V):

(21) .sup.1H NMR (500 MHz, D2O, 299 K): 9.49 ppm (1H, s, CHO); 7.42 ppm (1H, d, 3J=3.67 Hz, furan-H); 7.03 ppm (1H, d, 3J=3.67 Hz, furan-H).

(22) Reference: A. J. Carpenter, D. J. Chadwick; Tetrahedron 1985, 41(18), 3803-3812.

(23) Screening Experiments:

(24) In each single experiment a cooled product mixture, and based thereon a slightly alkaline product mixture comprising the disodium salt of FDCA in completely dissolved form was obtained. As shown in Table 1, HMF conversion in mol % and yield in mol % are summarized.

(25) TABLE-US-00002 TABLE 1 Relevant parameters of catalyst screening experiments. HMF di-HMF Cat- di- Con- Con- alyst HMF HMF version version Y.sub.FDCA Y.sub.FFCA Exp. [g] [g] [g] [mol %] [mol %] [mol %] [mol %] 1 0.928 1.00 0.50 100 100 78.3 <1.0 2 0.928 0.75 0.75 100 100 63.4 1.4 3 0.928 0.50 1.00 100 100 48.2 3.3

(26) TABLE-US-00003 TABLE 2 Relevant parameters of catalyst screening experiments. HMF HMF di-HMF di-HMF ratio of FDCA Y.sub.FDCA Y.sub.FFCA C.sub.HMF+di-HMF Y.sub.min, di-HMF Exp. [g] [mmol] [g] [mmol] HMF:di-HMF [mmol] [mol %] [mol %] [mol %] [mol %] 1 1.00 7.93 0.50 2.13 3.72 9.58 78.3 <1.0 65.1 13.2 2 0.75 5.95 0.75 3.20 1.86 7.86 63.4 1.4 48.2 15.2 3 0.50 3.96 1.00 4.27 0.93 6.07 48.2 3.3 31.7 16.5

(27) HMF conversion in mol % was calculated as follows (di-HMF conversion was calculated accordingly):
HMF Conversion[mol %]=[1(C.sub.final[HMF]/C.sub.0[HMF])]*100,

(28) wherein C.sub.[HMF] is the concentration in % by weight measured in the slightly alkaline product mixture and C.sub.0[HMF] is the concentrations in % by weight measured based on the added amount of HMF and the volume of the starting mixture.

(29) Conversion [mol %] and yield [mol %] are average values calculated from a first value based on internal standard 1 and a second value based on internal standard 2 (general deviation is less than 5%).

(30) The yield definition (exemplified for FDCA):

(31) $Y_{\mathrm{FDCA}}=\frac{n_{\mathrm{FDCA}}}{n_{\mathrm{HMF}}+2.Math.n_{\mathrm{di}\text{-}\mathrm{HMF}}}$

(32) wherein
n.sub.[FDCA]=[mol FDCA (based on Standard 1)+mol FDCA (based on Standard 2)]/2
n.sub.[HMF]=m.sub.0[HMF]/M.sub.[HMF]
and
n.sub.[di-HMF]=M.sub.0[di-HMF]/M.sub.[di-HMF]

(33) wherein C.sub.[FDCA] is the concentration of FDCA in % by weight in the filtrate obtained in the fourth step, C.sub.0[HMF] is the HMF starting concentration in % by weight, C.sub.0[di-HMF] is the di-HMF starting concentration in % by weight, M.sub.FDCA, M.sub.HMF and M.sub.di-HMF are the respective molecular weights in g/mol.

(34) The yield [mol %] for FFCA was determined mutatis mutandis as for the yield of FDCA.

(35) The amount of converted HMF based on the amount of HMF and di-HMF (C.sub.HMF+di-HMF) was calculated by the following formula:

(36) $C_{\mathrm{HMF}+\mathrm{di}\text{-}\mathrm{HMF}}=\frac{n_{\mathrm{HMF}}}{n_{\mathrm{HMF}}+2.Math.n_{\mathrm{di}\text{-}\mathrm{HMF}}}$

(37) The minimum yield of di-HMF (Y.sub.min,di-HMF) was calculated by:
Y.sub.min,di-HMF=Y.sub.FDCAC.sub.HMF+di-HMF

(38) In table 1, the results of the three experiments described above are shown. In all three experiments the molar amount of FDCA obtained after oxidation is larger than the molar amount of HMF provided at the beginning of the corresponding experiment. Thus, di-HMF was successfully converted into FDCA, with a considerable yield.

(39) Moreover, table 1 shows that the yield of FDCA is increasing with increasing ratio n.sub.HMF/(h.sub.HMF+2n.sub.di-HMF).