Process for the preparation of an aromatic dicarboxylic acid

Abstract

An aromatic dicarboxylic acid of chemical formula HOOCAr.sup.1COOH is prepared in a process wherein a feedstock comprising at least an aromatic aldehyde compound of chemical formula (1): OHCAr.sup.1COOH, wherein Ar.sup.1 represents an arylene or heteroarylene moiety, and an aqueous electrolyte are provided; the feedstock and the aqueous electrolyte are introduced into an electrolytic cell comprising electrodes, wherein at least one of the electrodes comprises a non-noble metal and/or an oxide and/or a hydroxide thereof and/or carbon; and the aromatic aldehyde compound of formula (1) is oxidized electrochemically to yield the aromatic dicarboxylic acid.

Claims

1. A method for the preparation of an aromatic dicarboxylic acid of chemical formula HOOC-Ar.sup.1-COOH, comprising: providing an aqueous electrolyte and a feedstock wherein the feedstock comprises at least an aromatic aldehyde compound of chemical formula (1)
OHC-Ar.sup.1-COON(1), wherein Ar.sup.1 represents an arylene or heteroarylene moiety, and wherein the aqueous electrolyte contains an aromatic dicarboxylic acid represented by the chemical formula (2)
HOOC-Ar.sup.2-COOH(2), wherein Ar.sup.2 is the same or different from Ar.sup.1 and represents an arylene or heteroarylene moiety; introducing the feedstock and the aqueous electrolyte into an electrolytic cell comprising electrodes, wherein at least one of the electrodes comprises a non-noble metal and/or an oxide and/or a hydroxide thereof and/or carbon; and oxidizing the aromatic aldehyde compound of formula (1) electrochemically to yield the aromatic dicarboxylic acid.

2. The method according to claim 1, wherein Ar.sup.1 and Ar.sup.2 are the same or different and are independently selected from phenylene, furylene and pyridylene moieties.

3. The method according to claim 1, wherein Ar.sup.1 and Ar.sup.2 are the same.

4. The method according to claim 1, wherein the feedstock has been obtained by oxidation of Ar.sup.1-(R.sup.1).sub.2, wherein Ar.sup.1 has the meaning as defined in claim 1 and each R.sup.1 is independently selected from methyl, hydroxymethyl, alkoxymethyl, carbonyloxymethyl and formyl.

5. The method according to claim 4, wherein the oxidation of the Ar.sup.1-(R.sup.1).sub.2 has been carried out by an oxygen-containing gas in presence of a catalyst comprising cobalt, manganese and optionally bromine.

6. The method according to claim 5, wherein the oxidation of the Ar.sup.1-(R.sup.1).sub.2 has been conducted in a solvent comprising an aliphatic carboxylic acid or an aliphatic carboxylic anhydride.

7. The method according to claim 1, wherein the electrolytic cell is a divided cell.

8. The method according to claim 1, wherein the non-noble metal is nickel or copper.

9. The method according to claim 1, wherein the carbon is used as a cathode material in the at least one of the electrodes of the electrolytic cell.

10. The method according to claim 1, wherein the aqueous electrolyte further contains an alkaline solution.

11. The method according to claim 10, wherein the alkaline solution comprises an alkaline compound selected from an alkali metal hydroxide, alkali metal carbonate, alkali metal bicarbonate, ammonia, ammonium carbonate, ammonium bicarbonate, a trialkylamine and combinations thereof.

12. The method according to claim 1, wherein the aqueous electrolyte does not contain 2,2,6,6-tetramethylpiperidine 1-oxyl.

13. The method according to claim 1, wherein the potential difference between the electrodes in the electrolytic cell is at most 10 V.

14. The method according to claim 1, wherein the aromatic aldehyde compound of formula (1) is oxidized at a temperature in the range of 10 to 250 C. and at a pressure in the range of 0.5 to 20 bar.

15. The method according to claim 1, wherein the residence time of the feedstock in the electrolytic cell is in the range of 0.1 to 24 hours.

16. The method according to claim 1, wherein the method is conducted in a continuous mode.

17. The method according to claim 1, wherein the aromatic dicarboxylic acid obtained after the electrochemical oxidation of the aromatic aldehyde compound of formula (1) is recovered by acidizing the aqueous electrolyte and allowing the aromatic dicarboxylic acid to precipitate.

Description

EXAMPLE 1

(1) In 50 milliliters of 0.5 M NaOH in water FFCA was dissolved in a concentration of 50 mmol/liter. A divided electrolytic cell consisting of two compartments separated from each other by means of a porous glass frit, was used. The FFCA solution was placed in one compartment, i.e. the anode compartment, of the divided electrolytic cell. The anode compartment was further provided with an anode, i.e. a nickel plate. The other compartment, i.e., the cathode compartment, was provided with an aqueous solution of 0.5M NaOH and a cathode consisting of a nickel mesh. Both compartments were stirred. At room temperature, i.e. about 20 C., a current was applied on the electrodes. The current was 6.4 mA, corresponding with a current density of 0.8 mA/cm.sup.2. The voltage measured at the anode was 0.4-0.7 V versus reference Ag/AgCl electrode. The current was continued for 6.7 hours. At the anode the FFCA was oxidized to FDCA. At the cathode hydrogen evolved. After 6.7 hours the content of the solution in the anode compartment was analyzed. The conversion of FFCA was measured as molar percentage of aldehydes that have disappeared. Apart from FFCA and FDCA, only a trace of 5-hydroxymethyl-furan-2-carboxylic acid (HMFCA) was detected in the solution of the anode compartment. HMFCA is believed to be the product of the Cannizarro reaction that may have taken place in the anode compartment. Since only a trace of HMFCA was found, it is understood that any HMFCA that is formed is also further oxidized to FDCA at the anode. The aldehyde conversion is shown in Table 1 below.

(2) A similar experiment was conducted with a solution comprising 50 mM/L FFCA and 50 mM/L FDCA in 50 milliliters 0.5 M NaOH solution. This solution was also subjected to electrochemical oxidation. After 6.7 hrs the solution in the anode compartment was analyzed. The compounds found were FFCA and FDCA. The results are shown in Table 1.

(3) For comparison two experiments were conducted with 50 mM/L furfural in 0.5 M NaOH solution and 50 mM/L furfural and 50 mM/L furoic acid in 50 mL of 0.5 M NaOH. The reaction with furfural was continued for 5.0 hours; the reaction with furfural and furoic acid lasted 6.7 hours. The conversion of the aldehyde is shown in Table 1.

(4) TABLE-US-00001 TABLE 1 Experiment No. Reagent Aldehyde conversion, % 1 FFCA 89.3 2 FFCA + FDCA 90.0 3 Furfural 62.1 4 Furfural + furoic acid 71.9

(5) The experiments show that the electrochemical oxidation of an aromatic aldehyde that contains a carboxyl substituent proceeds faster and leads to a more complete conversion than the corresponding unsubstituted aromatic aldehyde.

EXAMPLE 2

(6) To show the influence of the total charge, reaction temperature, and the composition of the feedstock, a series of experiments were carried out in substantially the same way as described for the experiments in Example 1. The electrolyte was 0.5 M NaOH solution. The feedstock and the concentration thereof (in mmoles per liter NaOH solution) have been shown in Table 2. Table 2 also shows the reaction temperature as well as time of the feedstock in the electrolytic cell when the maximum conversion was obtained. The electrodes both consisted of nickel mesh. The current applied amounted to 22.4 mA, corresponding with a current density of 0.8 mA/cm.sup.2 and a potential at the anode of 0.4-0.8 V versus a reference Ag/AgCl electrode. In experiment No. 9 a feedstock was used that consisted of crude FDCA, obtained in the oxidation of methoxymethylfurfural with oxygen in acetic acid using a Co, Mn and Br-containing catalyst. The crude FDCA contained about 1% wt FFCA, based on the total crude FDCA, and minor amounts of color bodies. The Table also shows the conversion of the aromatic aldehyde compound.

(7) TABLE-US-00002 TABLE 2 Reaction Residence Aldehyde Exp. No. Feedstock temperature, C. time, hr conversion, % 5 50 mM FFCA 20 5.6 99.8 6 50 mM FFCA + 50 mM FDCA 20 5.6 99.8 7 50 mM FFCA + 50 mM FDCA 75 3.7 99.2 8 5 mM FFCA + 45 mM FDCA 20 1.7 100.0 9 50 mM crude FDCA 20 1.0 100.0

(8) Comparison between Experiment Nos. 1 and 2 of Table 1 with Experiment Nos. 5 and 6 of Table 2 shows that when the charge passed through the cell is increased, the conversion is further enhanced to virtual completion. Comparison between Experiment Nos. 6 and 7 shows that an increased reaction temperature increases the reaction rate. Experiments 8 and 9 show the suitability of the present process in the purification of mixtures of FDCA and FFCA. Since the oxidation of FFCA also converts any HMFCA that may be formed due to a Cannizarro reaction, the yield of FDCA is optimized. Whereas the feedstock of experiment No. 9 shows a brown/yellow color, the product after electrochemical oxidation is almost colorless, indicating that major color bodies have been removed.

EXAMPLE 3

(9) The use of an undivided electrolytic cell was also shown in Experiment Nos. 10-13. A glass vessel used as an undivided electrolytic cell was filled with 50 mL of a solution of feedstock as indicated in Table 4 having a concentration of the number of millimoles indicated per liter aqueous 0.5 M NaOH, an anode and a cathode. The material of the anode was a nickel mesh as indicated in Example 2, and the cathode was made of nickel mesh or carbon paper. A current of 22.4 mA was applied between the anode and cathode. The electrochemical oxidation was conducted at room temperature, i.e. 20 C., for a period as shown as the residence time in Table 3. The feedstock, cathode material and aldehyde conversion in the aqueous electrolyte after the residence time indicated are also shown in Table 3. The electrolyte was also varied by using 0.5 M NaOH in water or 0.5 M triethyl amine (TEA) in water. The feedstock in experiment Nos. 11-13 was crude FDCA, including 1% wt FFCA, based on the total crude FDCA and minor amounts of color bodies.

(10) TABLE-US-00003 TABLE 3 Exp. Cathode Residence Aldehyde No. Feedstock material Electrolyte time, hr conversion, % 10 50 mM FFCA + 50 mM FDCA Ni mesh NaOH 5.6 97.9 11 150 mM crude FDCA Ni mesh NaOH 5.6 98.4 12 50 mM crude FDCA Carbon paper NaOH 3.5 100.0 13 50 mM crude FDCA Carbon paper TEA 5.1 99.1
In addition to a virtually complete conversion of the aldehyde compound, the resulting product in experiment Nos. 10-13 also showed considerably less coloring, indicating that also color bodies were oxidized.

EXAMPLE 4

(11) To show that the present process can also be applied to aromatic aldehyde compounds other than FFCA, two further experiments were conducted on a feedstock comprising benzaldehyde and benzoic acid in one experiment and on 4-carboxybenzaldehyde (4-CBA) and terephthalic acid in the second experiment. The experiments were conducted in a way similar to the experiments in Example 2. The divided electrolytic cell was used. Both the anode and the cathode were nickel mesh electrodes. The electrolyte was 0.5M NaOH. The reaction temperature was 20 C. and the current was 22.4 mA. The electrochemical oxidation was continued for 5.6 hours.

(12) The concentration of the materials (number of millimoles per liter) and the results are shown in Table 5.

(13) TABLE-US-00004 TABLE 5 Experiment Aldehyde No. Feedstock conversion, % 14 5 mM benzaldehyde + 45 mM benzoic acid 71.4 15 50 mM 4-CBA + 50 mM terephthalic acid 81.6

(14) The results show that also when benzaldehyde is further substituted with a carboxyl group the electrochemical oxidation with a non-noble metal-containing electrode is facilitated.

EXAMPLE 5

(15) To show the suitability of non-noble metals other than nickel, four experiments were performed in substantially the same way as described for the experiments in Example 1. The electrolyte was 0.5 M NaOH solution. The feedstock was a solution of crude FDCA (containing 1% wt FFCA) with a concentration of 50 mM per liter 0.5 M aqueous NaOH. The anode was either a stainless steel plate (Exp. No. 16), a tin plate (Exp. No. 17), a copper mesh (Exp. No. 18) or carbon paper (Exp. No. 19). The cathode was a nickel mesh, as used in Exp. No. 2. The reaction temperature was 20 C. The current applied amounted to 22.4 mA.

(16) For comparison reasons the same electrochemical conditions were applied to a platinum mesh anode and a nickel mesh cathode (cf. Exp. No. 20). The total conversion after 5.6 hours was recorded for Exp. Nos. 16, 19 and 20, whereas the total conversion of aldehyde for Exp. No. 17 was reached after 3.2 hours and for Exp. No. 18 already after 0.4 hours. The results are summarized in Table 5

(17) TABLE-US-00005 TABLE 5 Residence Aldehyde Exp. No. Anode material time, hr conversion, % 16 Stainless steel 5.6 92.3 17 Tin plate 3.2 100 18 Copper mesh 0.4 100 19 Carbon paper 5.6 78.0 20 Platinum mesh 5.6 33.0

(18) The results show that non-noble metals that are used as anode material perform better than noble metals, even when the noble metal is present as anode with a larger surface area. The copper electrode is particularly effective. Also the carbon electrode is significantly more efficient than the platinum electrode.