PROCESS FOR THE SYNTHESIS OF 2,5-FURANDICARBOXYLIC ACID

Abstract

The present invention is directed to a process for the synthesis of 2,5-furandicarboxylic acid (FDCA) comprising the steps of: (1) oxidising an aqueous solution of 5 hydroxymethylfurfural (HMF) in the presence of molecular oxygen, of a heterogeneous catalyst comprising ruthenium and of a strong base at a temperature above 100° C., obtaining a reaction product in aqueous solution comprising a salt of FDCA acid; (2) separating said heterogeneous catalyst from said reaction product in aqueous solution, and (3) re-using said heterogeneous catalyst in the oxidation reaction in step (1).

Claims

1. A process for the synthesis of 2,5-furandicarboxylic acid (FDCA) comprising the steps of: 1) oxidising an aqueous solution of 5-hydroxymethylfurfural (HMF) in the presence of molecular oxygen, of a heterogeneous catalyst comprising ruthenium and of a strong base at a temperature above 100° C., obtaining a reaction product in aqueous solution comprising a salt of FDCA acid; 2) separating said heterogeneous catalyst from said reaction product in aqueous solution, 3) re-using said heterogeneous catalyst in the oxidation reaction in step 1), wherein said heterogeneous catalyst comprising ruthenium is selected from the group consisting of supported ruthenium, supported ruthenium oxides, supported ruthenium hydroxides, unsupported ruthenium hydroxides and mixtures thereof, wherein, for the supported catalysts, the support is selected from the group consisting of carbon, non-metal oxides, functionalised graphite and combinations thereof.

2. The process according to claim 1 in which the said strong base has a solubility in water at 25° C. of 45 g/l or higher.

3. The process according to claim 1 in which the pH is maintained from 6.5 to 9 during the oxidation in step 1).

4. The process according to claim 1 in which the oxidation in step 1) is carried out at a temperature below 160° C.

5. (canceled)

6. The process according to claim 1 in which said 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 electrochemical cells, electrostatic precipitators, wet scrubbers or hydrocyclones.

7. The process according to claim 6 in which said separation of the heterogeneous catalyst in step 2) is carried out through at least one tangential flow microfiltration.

8. The process according to claim 1 in which the catalyst is washed and/or regenerated after step 2) and before re-use in step 3).

9. The process according to claim 1 in which after step 2) the said reaction product in aqueous solution is purified by at least one nanofiltration operation.

10. The process according to claim 8 in which the catalyst is washed with water and the resulting catalyst washing water is used in the purification operation by nanofiltration.

11. The process according to claim 1 in which the reaction product in aqueous solution is subjected to neutralisation and subsequent separation of the FDCA acid thus obtained in solid form.

12. (canceled)

13. (canceled)

14. (canceled)

15. The process according to claim 2 in which the pH is maintained from 6.5 to 9 during the oxidation in step 1).

16. The process according to claim 2 in which the oxidation in step 1) is carried out at a temperature below 160° C.

17. The process according to claim 3 in which the oxidation in step 1) is carried out at a temperature below 160° C.

18. The process according to claim 15 in which the oxidation in step 1) is carried out at a temperature below 160° C.

19. The process according to claim 2 in which said 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 electrochemical cells, electrostatic precipitators, wet scrubbers or hydrocyclones.

20. The process according to claim 3 in which said 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 electrochemical cells, electrostatic precipitators, wet scrubbers or hydrocyclones.

21. The process according to claim 4 in which said 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 electrochemical cells, electrostatic precipitators, wet scrubbers or hydrocyclones.

22. The process according to claim 15 in which said 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 electrochemical cells, electrostatic precipitators, wet scrubbers or hydrocyclones.

23. The process according to claim 18 in which said 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 electrochemical cells, electrostatic precipitators, wet scrubbers or hydrocyclones.

Description

EXAMPLES

[0114] The catalyst used in the following examples was prepared from an aqueous solution of RuCl.sub.3 (8.3 mM) and an activated carbon support with a specific surface area of 1500 m.sup.2/g. Approximately 286 mL of solution was used for about 10 g of support. After 15 minutes of vigorous stirring the solid was separated, washed with demineralised water and dried overnight at 50° C.

[0115] The powder obtained was treated with NaOH (1.0 M, approximately 28 mL) with agitation for 24 h. The solid was then dried at 140° C. for another 24 hours, yielding a Ru(OH).sub.3/C catalyst containing about 5% of ruthenium.

Example 1

[0116] Step 1) 1kg of a 2% aqueous solution of HMF (HMF 20 g/kg) and a supported catalyst based on ruthenium hydroxide (Ru(OH.sub.)x/C 5% prepared as described above, x=3) were loaded into a 2 L autoclave in order to have a Ru/HMF ratio by weight of 5%.

[0117] The reactor was brought to a pressure of 20 bar with air and heated to an internal temperature of 130° C.

[0118] The reactor was fed with an air flow of 150 NL/h for 16 hours, continuously feeding an aqueous caustic soda solution (150 g/kg) to maintain a constant pH value between 7.5 and 8.

[0119] Step 2)

[0120] The final aqueous solution containing the reaction product (FDCA salts and reaction intermediates) was filtered from the catalyst (through a 0.22 μm diameter millipore septum) and analysed by liquid chromatography—PDA in a Rezex column with 0.005N H.sub.2SO.sub.4 eluent (Flow=0.6 mL/min; temperature=60° C.).

[0121] A synthesis yield of 88%, calculated as the ratio of the molar concentration of the salt of 2,5-FDCA in the synthesis solution obtained by chromatographic analysis to that calculated theoretically taking the initial molar concentration of the HMF solution fed to the process into account, was obtained.

[0122] Step 3)

[0123] The catalyst recovered by filtration in step 2) was reused as such under the process conditions reported for step 1). Although the conditions for the recovery of catalyst from step 2) had not been optimised, a synthesis yield of 2,5-FDCA of 78% was obtained, calculated as indicated above.

Comparative Example 1

[0124] Step 1)

[0125] 1 kg of a 2% aqueous solution of HMF (HMF 20 g/kg) and a supported catalyst based on ruthenium hydroxide (Ru(OH).sub.3/C 5% as in Example 1) were loaded into a 2 L autoclave in order to have a Ru/HMF ratio by weight of 5%. The reactor was charged with Magnesium hydroxide with molar ratio respect to HMF 1:2.

[0126] The reactor was brought to a pressure of 20 bar with air and heated to an internal temperature of 130° C., then fed with an air flow of 150 NL/h for 16 hours.

[0127] Step 2)

[0128] The final aqueous solution containing the reaction product (FDCA salts and reaction intermediates) was separated from the catalyst by filtration (through a 0.22 μm diameter millipore septum) and analysed by liquid chromatography—PDA in a Rezex column with 0.005N H.sub.2SO.sub.4 eluent (Flow=0.6 mL/min; temperature=60° C.).

[0129] A synthesis yield of 83%, calculated as the ratio of the molar concentration of the salt of 2,5-FDCA in the synthesis solution obtained by chromatographic analysis to that calculated theoretically taking the initial molar concentration of the HMF solution fed to the process into account, was obtained.

[0130] The separated catalyst has been characterized in terms of specific surface area, pore size distribution and cumulative volume pores and compared to those of the fresh catalyst and to those of the catalyst recovered after Example 1 (catalyst recovered by filtration before its reuse).

TABLE-US-00002 Micropores Specific surface area (measured Pore with He) volume Catalyst Base [m.sup.2/g] [cm.sup.3/g] fresh — 977 0.58 Comparative Mg(OH).sub.2 190 0.02 Example 1 (after 1st use) Example 1 NaOH 942 0.55 (after 1st use)

[0131] A drastic reduction of specific surface area and accessible pore volume can been observed in Comparative example 1 wherein an insoluble weaker base as Mg(OH).sub.2 has been used. The catalytic characteristics has been preserved instead in presence of a soluble strong base in Example 1.

[0132] The fouling of active surface is confirmed by also X-ray photoelectron spectroscopy (XPS) analysis of the atomic composition profile (see Table below), which demonstrates a relevant quantity of magnesium deposited on ruthenium respect to sodium limiting the catalytic activities of ruthenium oxide/hydroxide:

TABLE-US-00003 Ru Magnesium Sodium Catalyst Base [%] [%] [%] fresh — 1.1 — 1.3 Comparative Mg(OH).sub.2 0.1 15.1 1.2 Example 1 (after 1st use) Example 1 NaOH  1.05 — 1.8 (after 1st use)

[0133] The XPS spectra were collected using an Escalab 200-C VG spectrometer with a 5-channeltron hemispheric analyser, equipped with a double anode source that separately transmits non-monochromatic X radiation corresponding to Mg Kα line (energy=1253.6 eV, line width=0.7 eV) and to Al Kα line (energy=1486.6 eV, line width=0.8 eV) and a pressure in the analysis chamber during the measurement of about 5×10.sup.−9 mbar. The analyzed area was 3 mm.sup.2.

[0134] Step 3)

[0135] The catalyst recovered by filtration in step 2) was reused as such under the process conditions reported for step 1). A synthesis yield of 2,5-FDCA of merely 67% was obtained, calculated as indicated above.

Example 2

[0136] Step 1)

[0137] 10 kg of a 10% aqueous solution of HMF (HMF 100 g/kg) and a supported ruthenium hydroxide based catalyst (Ru(OH).sub.x+RuO.sub.2/C 5%), in which x=3 in order to have a Ru/HMF ratio by weight of 0.75%, were loaded into a 10 L Jet-loop reactor.

[0138] The reactor was brought to a pressure of 20 bar with air and heated to an internal process temperature of 130° C.

[0139] The reactor was fed with an air flow of 20 NL/min for 8 hours, continuously feeding an aqueous solution of caustic soda (250 g/kg) at a variable flow rate directly managed by a pH management and control apparatus for the process step to maintain a pH value between 7.5 and 8.

[0140] Step 2)

[0141] The final aqueous solution containing the reaction product (FDCA salts and reaction intermediates) was separated from the catalyst by tangential filtration on a 2 μm sintered steel filter and analysed by liquid chromatography as shown in the example above.

[0142] A synthesis yield of 2,5-FDCA of 95% in comparison with that theoretically calculated taking into account the initial concentration of the HMF solution fed to the process, was obtained.

[0143] Step 3)

[0144] The catalyst recovered through filtration during step 2) was washed with water at 50° C., filtered and reused under the process conditions reported for step 1). The re-use operation was repeated several times. The table shows the results for yield, calculated as the ratio of the concentration of the 2,5-FDCA salt in the synthesis solution to that theoretically calculated taking into account the initial concentration of HMF solution fed to the process:

TABLE-US-00004 Re-use Yield (%) I 98.2 II 90.8 III 91.9 IV 90.8

[0145] The 2,5-FDCA salt solution was appropriately diluted to a concentration of 10 g/kg. The solution was processed by a spirally wound membrane nanofiltration system with tangential flow using a membrane with a cut-off of 300-500 Da in polypiperazine amide. The process described in this way, operating at a constant flow condition of 10-15 L/h/m.sup.2 made it possible to achieve salt rejection of the salts from the monomer of 38%.

[0146] The retentate contained impurities deriving from aldol condensation phenomena (coloured substances YI=80).

[0147] The permeate containing the aqueous solution of the sodium salt of 2,5-FDCA was subsequently concentrated by osmotic processes up to a concentration not exceeding 50 g/kg. The total recovery yield for the monomer was 85% by weight (compared to the FDCA produced).

[0148] 2,5-FDCA was recovered in acid form by precipitation processes with 5M dilute sulfuric acid. The precipitated solid was recovered by candle filtration of the slurry obtained and then washed and dried.

[0149] The composition of FDCA obtained was analysed by liquid chromatography to assess the purity of the monomer itself as indicated above.

[0150] The residual sulfate content was evaluated by means of ion chromatography with a conductivity detector (Metrohm CI-CD) using a “Metrosep A Supp 5” column (250 mm×4.0 mm×5 um) with polyvinyl alcohol bearing quaternary ammonium groups as the stationary phase (isocratic elution of an aqueous solution of 3.2 mM Na.sub.2CO.sub.3+1 mM NaHCO.sub.3; flow: 0.7 mL/min; column temperature: 30° C.).

[0151] The sulfate content was less than 200 ppm.

[0152] The monomer obtained had a purity of 99.5%, a furoic acid content of less than 0.05%, a furancarboxyaldehyde content of 0.3% and a formyl furoic acid content of 0.02%.