METHOD OF PREPARING 2-HYDROXYADPIC ACID AND ADIPIC ACID

Abstract

A method of preparing 2-hydroxyadpic acid and adipic acid is provided. The method of preparing 2-hydroxyadpic acid and adipic acid comprises a step of the electrolysis of 2,5-furandicarboxylic acid using a metal electrode at a constant current in a sulfuric acid solution containing a quaternary ammonium salt. The metal electrode is a bismuth electrode or a lead electrode. The quaternary ammonium salt is represented by formula (I):

##STR00001## wherein R.sub.1 to R.sub.4 are independently a C.sub.2-5 hydrocarbon group, and X.sup. is ClO.sub.4.sup., H.sub.2PO.sub.4.sup., or Br.sup..

Claims

1. A method of preparing 2-hydroxyadpic acid and adipic acid, comprising a step of: electrolyzing 2 to 3 mM of 2,5-furandicarboxylic acid using a metal electrode at a constant current in a sulfuric acid solution containing a quaternary ammonium salt, wherein the metal electrode is a bismuth electrode or a lead electrode, and the quaternary ammonium salt is represented by formula (I): ##STR00004## wherein R.sub.1 to R.sub.4 are independently a C.sub.2-5 hydrocarbon group, and X.sup. is ClO.sub.4.sup., H.sub.2PO.sub.4.sup., or Br.sup..

2. The method of preparing 2-hydroxyadpic acid and adipic acid as claimed in claim 1, wherein the step of electrolyzing 2 to 3 mM of 2,5-furandicarboxylic acid is conducted at ambient temperature and pressure.

3. The method of preparing 2-hydroxyadpic acid and adipic acid as claimed in claim 1, wherein the quaternary ammonium salt is selected from the group consisting of tetrabutylammonium phosphate, tetrapentylammonium bromide, tetraethylammonium perchlorate, and tributylmethylammonium phosphate.

4. The method of preparing 2-hydroxyadpic acid and adipic acid as claimed in claim 1, wherein the bismuth electrode is selected from the group consisting of an electroplated bismuth thin film-modified carbon electrode, a bismuth nanosheets-modified carbon electrode, and a bismuth-modified copper electrode prepared by electroless deposition.

5. The method of preparing 2-hydroxyadpic acid and adipic acid as claimed in claim 1, wherein a current density of the constant current ranges from 5 mA/cm.sup.2 to 30 mA/cm.sup.2.

6. The method of preparing 2-hydroxyadpic acid and adipic acid as claimed in claim 1, wherein a concentration of the quaternary ammonium salt ranges from 10 mM to 50 mM.

7. The method of preparing 2-hydroxyadpic acid and adipic acid as claimed in claim 1, wherein a concentration of the sulfuric acid ranges from 0.05 M to 1 M.

8. A method of preparing 2-hydroxyadpic acid, comprising a step of: electrolyzing 2 to 3 mM of 2,5-furandicarboxylic acid using a bismuth electrode at a constant current in a 0.05 M to 1 M of sulfuric acid solution.

9. The method of preparing 2-hydroxyadpic acid as claimed in claim 8, wherein the bismuth electrode is an electroplated bismuth thin film-modified carbon electrode.

10. The method of preparing 2-hydroxyadpic acid as claimed in claim 8, wherein a current density of the constant current ranges from 5 mA/cm.sup.2 to 30 mA/cm.sup.2.

Description

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0029] In order to describe the technical solutions of the present disclosure more clearly, numerous specific details are provided in the following specific embodiments. Apparently, the present disclosure can be practiced without certain specific details.

[0030] A method of preparing 2-hydroxyadpic acid (HAA) and adipic acid (AA) according to one embodiment of the present disclosure comprises steps of electrolyzing 2 to 3 mM (e.g., 2 mM, 2.5 mM, 3 mM) 2,5-furandicarboxylic acid (FDCA) using a bismuth electrode at a constant current in a sulfuric acid solution containing a specific quaternary ammonium salt (QAS).

[0031] The QAS is represented by the following general formula (I), wherein R.sub.1 to R.sub.4 are independently a C.sub.2-5 hydrocarbon group, and X.sup. is ClO.sub.4.sup., H.sub.2PO.sub.4.sup., or Br.sup..

##STR00003##

[0032] Optionally, the QAS may be selected from the group consisting of tetrabutylammonium phosphate (TBAP), tetrapentylammonium bromide (TPAB), tetraethylammonium perchlorate (TEAP), and tributylmethylammonium phosphate (MBAP). The QAS concentration may range from 10 mM to 50 mM, such as 10 mM, 15 mM, 20 mM, 25 mM, 30 mM, 35 mM, 40 mM, 45 mM, and 50 mM. The bismuth electrode is selected from the group consisting of an electroplated bismuth thin film-modified carbon electrode (C|Bi), a bismuth nanosheets-modified carbon electrode (C|nanoBi), and a bismuth-modified copper electrode prepared by electroless deposition (Cu|Bi).

[0033] In the embodiment, the applied current density for the electrolysis may range from 5 mA/cm.sup.2 to 30 mA/cm.sup.2, such as 5 mA/cm.sup.2, 7 mA/cm.sup.2, 9 mA/cm.sup.2, 11 mA/cm.sup.2, 13 mA/cm.sup.2, 15 mA/cm.sup.2, 17 mA/cm.sup.2, 19 mA/cm.sup.2, 21 mA/cm.sup.2, 23 mA/cm.sup.2, 25 mA/cm.sup.2, 27 mA/cm.sup.2, and 30 mA/cm.sup.2. Optionally, a concentration of the sulfuric acid may range from 0.05 M to 1 M, such as 0.05 M, 0.1 M, 0.2 M, 0.3 M, 0.4 M, 0.5 M, 0.6 M, 0.7 M, 0.8 M, 0.9 M, and 1 M.

[0034] A method of preparing HAA and AA according to another embodiment of the present disclosure comprises a step of electrolyzing 2 to 3mM (e.g., 2 mM, 2.5 mM, 3 mM) of FDCA using a bismuth electrode at a constant current density in a 0.05 M to 1 M (e.g., 0.1 M, 0.2 M, 0.3 M, 0.4 M, 0.5 M, 0.6 M, 0.7 M, 0.8 M, 0.9 M, 1 M) of sulfuric acid solution. In the embodiment, a specific type of bismuth electrode (i.e., the C|Bi electrode) can be used for the electrolysis of FDCA without the addition of a QAS, which similarly enables the ring-opening of FDCA. Optionally, the applied current density for the electrolysis may range from 5 mA/cm.sup.2 to 30 mA/cm.sup.2, such as 5 mA/cm.sup.2, 7 mA/cm.sup.2, 9 mA/cm.sup.2, 11 mA/cm.sup.2, 13 mA/cm.sup.2, 15 mA/cm.sup.2, 17 mA/cm.sup.2, 19 mA/cm.sup.2, 21 mA/cm.sup.2, 23 mA/cm.sup.2, 25 mA/cm.sup.2, 27 mA/cm.sup.2, and 30 mA/cm.sup.2.

[0035] It is worth mentioning that the method of the present invention for preparing HAA and AA involves the electrolysis of FDCA at ambient temperature and pressure, without the need for precious metal catalysts or hydrogen gas. This process enables the ring-opening and hydrogenation of FDCA to synthesize HAA, AA, and other nylon monomers or their precursors.

[0036] As used herein and in the appended claims, singular articles such as a and an and the and similar referents in the context of describing the elements (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. As used herein and in the appended claims, the term or is to be construed to cover the term and/or, unless otherwise indicated herein or clearly contradicted by context.

Electrode Preparation Process

Synthesis of the C|nanoBi Electrode

[0037] Prior to the electrode preparation, the carbon paper (Toray carbon paper) was successively cleaned with nitric acid (65%) for 5 min, ethanol (95%) for 5 min, and deionized water for 10 min under sonication. After the cleaning process, the carbon paper was dried under nitrogen purge. Then, a BiOI plating solution (pH 1.75) containing potassium iodide (0.4 M), bismuth (III) nitrate (40 mM), and 1,4-benzoquinone (50 mM) was prepared under stirring.

Electroplating and Pretreatment of the BiOI Modified Carbon Electrode

[0038] The BiOI-modified carbon electrode was firstly prepared by the electrochemical deposition of BiOI on the cleaned carbon paper (exposed area: 1.5 cm.sup.2) at a constant potential of 0.1 V vs. Ag/AgCl for 4 minutes in the BiOI plating solution. Thereafter, the obtained BiOl-modified electrode was further subjected to the electrochemical reduction process in 0.1 M borate buffer (0.1 M, pH 9.2) at a constant potential of 1.2 V vs. RHE for 30 minutes. After the reduction reaction, the electrode was taken out, rinsed with deionized water, and dried under nitrogen purge. The obtained electrode was designated as the nanoBi electrode.

Synthesis of the C|Bi Electrode

[0039] The C|Bi electrode was prepared by the electrochemical deposition of bismuth film on the cleaned carbon paper (exposed area: 1.5 cm.sup.2) at a constant current density of 5 mA/cm.sup.2 for 5 minutes in the plating solution containing nitric acid (1 M) and bismuth nitrate (30 mM). After the electrochemical deposition, the electrode was taken out, rinsed with deionized water, and dried under nitrogen purge. The obtained electrode was designated as the C|Bi electrode.

Synthesis of the Cu|Bi Electrode

[0040] Prior to the electrode preparation, a copper foil was successively cleaned with acetone for 10 min and diluted HCl aqueous solution (1.9%) for 10 min under sonication before its usage. After the cleaning process, the copper foil was dried under nitrogen purge. A water-acetonitrile mixture (volume ratio: 1:1) containing nitric acid (1 M) and bismuth nitrate (30 mM) was prepared as reaction media for the electroless deposition. The Cu|Bi electrode was prepared by immersing the cleaned copper foil (exposed surface area: 1.5 cm.sup.2) in 10 mL of the prepared reaction media for 2 minutes, and brown bismuth metal was immediately formed on the surface. The obtained Cu|Bi electrode was slowly rinsed with deionized water and dried under nitrogen purge.

Preparation of Electrolyte Solution

[0041] The catholyte and anolyte used for electrolysis were different. The catholyte was the sulfuric acid solution (0.05 M1.0 M) containing FDCA (23 mM) and specific QAS (0 to 50 mM; QAS: tetrabutylammonium phosphate (TBAP), tetrapentylammonium bromide (TPAB), tetraethylammonium perchlorate (TEAP), or tributylmethylammonium phosphate (MBAP)), whereas the anolyte was the sulfuric acid solution (2 M).

Set-Up of the Electrochemical Cell

[0042] The electrochemical analyses were performed using an Iviumn-Stat workstation (Ivium Technologies B.V., Netherlands) connected with a well-sealed customized two-compartment H-cell. The anodic compartment and cathodic compartment of the H-cell were separated with a Nafion 117 film. The C|Bi, C|nanoBi, or Cu|Bi electrode was used as the working electrode and placed with a Ag/AgCl reference electrode in the cathodic compartment containing catholyte solution, whereas the tantalum-iridium-titanium mesh counter electrode was placed in the anodic compartment containing anolyte solution. After placements, the cathodic compartment was sealed to facilitate subsequent analysis of gas products. The electrolysis experiments were performed at a specific constant applied current density under magnetic stirring at 1000 rpm, and the corresponding potentials were 100% iR compensated and reported against the reversible hydrogen electrode (RHE) scale. All the electrolysis were repeated 3 times to ensure the reproducibility of the results.

The C|Bi Electrode

[0043] The electrochemical preparation of the C|Bi electrode was achieved via the electrochemical reduction of Bi.sup.3+ to Bi.sup.0 at an applied current density of +5 mA/cm.sup.2 for 5 minutes. The surface morphology of the of the prepared C|Bi electrode was characterized using a scanning electron microscope (SEM). The results, shown in FIG. 1a to FIG. 1d (scale bars being 20 m, 10 m, 5 m, and 2 m, respectively), indicate that the prepared C|Bi electrode has stepped surface.

The BiOI-Modified Carbon Electrode

[0044] SEM was used to analyze the surface morphology of the BiOI-modified carbon electrode. Refer to FIG. 2a to FIG. 2d (scale bars being 10 m, 5 m, 2 m, and 1 m, respectively). The results show hydrangea morphology formed by interlaced sheets.

The C|nanoBi Electrode

[0045] O and I elements of the BiOI-modified carbon electrode were completely removed by the electrochemical reduction process to obtain the C|nanoBi electrode. Raman spectrometer was used to analyze the physicochemical properties of the prepared electrodes. As revealed from FIG. 3a and FIG. 3b, the C|nanoBi electrode exhibited two characteristic peaks at 69.21 cm.sup.1 and 97 cm.sup.1 that are, respectively, responsible for the first-order E.sub.g and A.sub.1g stretching modes of BiBi bonds. In addition, the Raman features characteristic to BiI bonds and BiO bonds (e.g., peaks at 86.5 and 146 cm.sup.-1) were not observed, which suggests that the BiOI template was almost completely transformed into the metallic Bi after the electrochemical reduction process. SEM was used to analyze surface morphology of the C|nanoBi electrode. As revealed from FIG. 4a to FIG. 4d (with scale bars of 10 m, 5 m, 2 m, and 1 m, respectively), the C|nanoBi electrode has a hydrangea flower morphology similar to that of the BiOI-modified carbon electrode.

The Cu|Bi Electrode

[0046] SEM was used to analyze surface morphology of the Cu|Bi electrode. As revealed from FIG. 5a-FIG. 5d (scale bars being 5 m, 2 m, 1 m, and 0.5 m, respectively), the prepared Cu|Bi electrode is dendrite-structured.

Effects of TBAP Concentration on the Electrocatalytic Performance of the Different Bismuth Electrodes

[0047] The electrocatalytic performance of the above-mentioned C|Bi, C|nanoBi, and Cu|Bi electrodes towards the electrocatalytic reduction of FDCA was characterized by the 2-h electrolysis at a constant current of 10 mA/cm.sup.2 in the H.sub.2SO.sub.4 solution (0.1 M) containing FDCA (2.5 mM) and TBAP of various concentrations along with the product analyses.

[0048] As revealed from FIG. 6a-FIG. 6c (being the C|Bi electrode, the C|nanoBi electrode, and the Cu|Bi electrode, respectively), all the electrodes required a potential of 0.8 V vs. RHE to maintain an applied current density of 10 mA/cm.sup.2 in the absence of TBAP. In addition, the presence of TBAP increased the potential of all the electrodes to maintain an applied current density of 10 mA/cm.sup.2. Nevertheless, the increase in the potential didn't correlate with the concentration of TBAP.

[0049] As revealed from FIG. 6d-FIG. 6f, all the electrodes had minimal electrocatalytic performance towards the electrosynthesis of HAA via the electrochemical reduction of FDCA when the electrolysis experiments were performed in the absence of TBAP. In contrast, when the electrolysis experiments were performed in the presence of TBAP, the electrocatalytic performance of all the bismuth electrodes were significantly enhanced. Specifically, the HAA Faradaic efficiencies, HAA selectivity, and overall carbon balance of the C|Bi electrode increased from 7.24%, 42.7% and 9.08% to 30.67%, 86.56%, and 88.24%, respectively. The HAA faradaic efficiencies, HAA selectivity, and overall carbon balance of the C|nanoBi electrode increased from 0%, 0%, 0%, to 31.2%, 90.49%, and 92.26%, respectively. The HAA Faradaic efficiencies, HAA selectivity, and overall carbon balance of the Cu|Bi electrode increased from 0%, 0%, 0%, to 14.88%, 77.7%, and 80.69%, respectively. Furthermore, as revealed from TABLE 1 to TABLE 3, when the electrolysis experiments were performed in the absence of TBAP, all the bismuth electrodes showed no activity for the production of AA. However, when the electrolysis experiments were performed in the presence of TBAP (10 mM), the C|Bi electrode showed activity towards the generation of AA from the electrochemical reduction of FDCA. The C|nanoBi and Cu|Bi electrodes also showed activity towards the generation of AA from the electrochemical reduction of FDCA when the electrolysis experiments were performed in the presence of TBAP with concentration of 20 mM. These findings indicate that the inclusion of TBAP in the electrolyte for the electrolysis improves the electrocatalytic performance of the bismuth electrodes towards the electrosynthesis of HAA and AA. Note that the generation of other products, such 2-furoic acid (2-FA) and 6-hydroycaproic acid (HCA) was also observed when the electrolysis experiments were performed in the presence of TBAP (>10 mM). The formation of HCA in the presence of TBAP could be attributed to the further hydrogenation of AA at the bismuth electrodes.

TABLE-US-00001 TABLE 1 Summary of the products generated from the 2-h electrolysis at 10 mA/cm.sup.2 using the C|Bi electrode in H.sub.2SO.sub.4 solution (0.1M) containing FDCA (2.5 mM) and TBAP of various concentrations. TBAP Amount of concentration product FE.sub.Product Selectivity Yield (mM) Product (mole/cm.sup.2) (%) (%) (%) 0 HCA 0.00 0.00 0.00 0.00 2-FA 0.01 0.00 0.05 0.02 AA 0.00 0.00 0.00 0.00 10 HCA 0.18 0.24 0.41 0.31 2-FA 0.02 0.00 0.04 0.03 AA 0.01 0.02 0.03 0.02 20 HCA 0.31 0.42 0.65 0.52 2-FA 0.02 0.00 0.04 0.03 AA 0.03 0.03 0.06 0.05 30 HCA 0.60 0.80 1.42 1.02 2-FA 0.02 0.00 0.05 0.04 AA 0.06 0.06 0.13 0.10 50 HCA 0.65 0.87 1.28 1.10 2-FA 0.04 0.01 0.08 0.07 AA 0.05 0.06 0.10 0.09

TABLE-US-00002 TABLE 2 Summary of the products generated from the 2-h electrolysis at 10 mA/cm.sup.2 using the C|nanoBi electrode in H.sub.2SO.sub.4 solution (0.1M) containing FDCA (2.5 mM) and TBAP of various concentrations. TBAP Amount of concentration product FE.sub.Product Selectivity Yield (mM) Product (mole/cm.sup.2) (%) (%) (%) 0 HCA 0.00 0.00 0.00 0.00 2-FA 0.00 0.00 0.00 0.00 AA 0.00 0.00 0.00 0.00 10 HCA 0.11 0.15 0.26 0.18 2-FA 0.01 0.00 0.03 0.02 AA 0.00 0.00 0.00 0.00 20 HCA 0.17 0.23 0.34 0.28 2-FA 0.03 0.00 0.06 0.05 AA 0.05 0.06 0.10 0.08 30 HCA 0.22 0.30 0.46 0.37 2-FA 0.02 0.00 0.04 0.03 AA 0.07 0.07 0.14 0.11 50 HCA 0.55 0.74 1.12 0.94 2-FA 0.05 0.01 0.11 0.09 AA 0.07 0.07 0.13 0.11

TABLE-US-00003 TABLE 3 Summary of the products generated from the 2-h electrolysis at 10 mA/cm.sup.2 using the Cu|Bi electrode in H.sub.2SO.sub.4 solution (0.1M) containing FDCA (2.5 mM) and TBAP of various concentrations. TBAP Amount of concentration product FE.sub.Product Selectivity Yield (mM) Product (mole/cm.sup.2) (%) (%) (%) 0 HCA 0.00 0.00 0.00 0.00 2-FA 0.00 0.00 0.00 0.00 AA 0.00 0.00 0.00 0.00 10 HCA 0.02 0.02 0.06 0.03 2-FA 0.01 0.00 0.05 0.02 AA 0.00 0.00 0.00 0.00 20 HCA 0.20 0.26 0.51 0.32 2-FA 0.03 0.00 0.07 0.05 AA 0.04 0.04 0.10 0.06 30 HCA 0.06 0.08 0.18 0.10 2-FA 0.01 0.00 0.04 0.02 AA 0.04 0.04 0.12 0.07 50 HCA 0.01 0.02 0.03 0.02 2-FA 0.01 0.00 0.02 0.02 AA 0.08 0.09 0.22 0.14

[0050] Further, inductively coupled plasma optical emission spectrometry (ICP-OES) was used to measure contents of bismuth on the C|Bi electrode, the C|nanoBi electrode, and the Cu|Bi electrode. The results show that the contents of bismuth in the C|Bi electrode, the C|nanoBi electrode, and the Cu|Bi electrode are 3.157 mole/cm.sup.2, 1.359 mole/cm.sup.2, and 1.810 mole/cm.sup.2, respectively. The obtained bismuth contents were then used for calculating turnover frequency for the production of HAA (TOF.sub.HAA). As revealed in FIG. 6g, the TOF.sub.HAA, ranked from highest to lowest, are the C|nanoBi electrode, the Cu|Bi electrode, and the C|Bi electrode.

[0051] FIG. 6h-6j show the conversion of FDCA and the yields of main products obtained from the 2-h electrolysis at 10 mA/cm.sup.2 in H.sub.2SO.sub.4 solution (0.1 M) containing FDCA (2.5 mM) and TBAP of various concentrations using the C|Bi electrode, the C|nanoBi electrode, and the Cu|Bi electrode, respectively. It can be found that the inclusion of TBAP in the electrolyte solution for the electrolysis significantly improved the conversion of FDCA at all the bismuth electrodes. In addition, HAA was generated after the FDCA conversion reached a certain level.

[0052] In summary, the HAA faradaic efficiency, HAA selectivity, overall carbon balance, and TOF.sub.HAA gradually levelled off when the electrolysis experiments were performed in the presence of sufficient TBAP (20 mM). In addition, when the electrolysis experiments were performed in the presence of 30 mM TBAP, the C|nanoBi electrode exhibited the best electrocatalytic performance towards the electrosynthesis of HAA, in terms of TOF.sub.HAA (16.67 h.sup.), HAA selectivity (93.86%), HAA Faradaic efficiency (36.27%), HAA yield (75.48%), and the overall carbon balance (97.41%).

Effects of QAS on the Electrocatalytic Performance of the C|nanoBi Electrode Towards the Electrocatalytic Reduction of FDCA

[0053] The effects of QAS (QAS: TBAP, TPAB, MBAP and TEAB) on the electrocatalytic performance of the C|nanoBi electrode towards the electrocatalytic reduction of FDCA were investigated by a series of 2-h electrolysis experiments at 10 mA/cm.sup.2 in the H.sub.2SO.sub.4 solution (0.1 M) containing FDCA (2.5 mM) and QAS (30 mM). As revealed in FIG. 7a, the potentials for the C|nanoBi electrode to maintain a current density of 10 mA/cm.sup.2 in the presence of different QASs were sequentially ranked as TPAB, TBAP, MBAP, and TEAB. As revealed in FIG. 7b-7e, including TPAB, TBAP, MBAP or TEAB in the electrolyte solution for the electrolysis of FDCA facilitated the ring-opening reactions of FDCA to generate HAA as the main product. In addition, the electrocatalytic performance of the C|nanoBi electrode towards the electrosynthesis of HAA, in terms of HAA faradaic efficiency (FIG. 7b), HAA selectivity (FIG. 7c), HAA yield and FDCA conversion (FIG. 7d), and TOF.sub.HAA (FIG. 7e). in the presence of different QASs were sequentially ranked as TBAP, TPAB, MBAP, and TEAB. This difference in the electrocatalytic performance of the C|nanoBi electrode could be attributed to the difference in the length of the hydrocarbon chain and type of anion of QAS. Specifically, the electrolysis experiments were performed in the presence of QAS with hydrocarbon chain containing four or five carbons, the C|nanoBi electrode showed enhanced electrocatalytic performance towards the electrosynthesis of HAA via the electrocatalytic reduction of FDCA. In contrast, the C|nanoBi electrode showed poor electrocatalytic performance towards the electrosynthesis of HAA via the electrocatalytic reduction of FDCA when the electrolysis experiments were performed in the presence of QAS with hydrocarbon chain containing less than four carbons or with an asymmetric structure. In addition, halogen anions in the QAS were found to have the negative impacts on the electrocatalytic performance of the C|nanoBi electrode. It is important to note that the noticeable production of AA was only observed when the electrolysis experiments were performed in the presence of 30 mM TBAP (TABLE 4).

TABLE-US-00004 TABLE 4 Summary of the products generated from the 2-h electrolysis at 10 mA/cm.sup.2 using the C|nanoBi electrode in H.sub.2SO.sub.4 solution (0.1M) containing FDCA (2.5 mM) and QAS (30 mM) Amount of QAS product FE.sub.Product Selectivity Yield (30 mM) Product (mole/cm.sup.2) (%) (%) (%) TPAB HCA 0 0 0 0 2-FA 0.02 0 0.04 0.03 AA 0 0 0 0 TBAP HCA 0.22 0.3 0.46 0.37 2-FA 0.02 0 0.04 0.03 AA 0.07 0.07 0.14 0.11 MBAP HCA 0 0 0 0 2-FA 0.02 0 0.05 0.03 AA 0 0 0 0 TEAB HCA 0 0 0 0 2-FA 0.01 0 0.04 0.01 AA 0 0 0 0

Effects of H.SUB.2.SO.SUB.4 .Concentration on the Electrocatalytic Performance of the C|nanoBi Electrode Towards the Electrocatalytic Reduction of FDCA

[0054] The effects of H.sub.2SO.sub.4 concentration on the electrocatalytic performance of the nanoBi electrode towards the electrocatalytic reduction of FDCA were investigated by a series of 2-h electrolysis experiments at 10 mA/cm.sup.2 in the H.sub.2SO.sub.4 solution (0.05 M, 0.1 M, 0.5 M, and 1 M) containing FDCA (2.5 mM) and TBAP (30 mM). As revealed in FIG. 8a, the potentials for the C|nanoBi electrode to maintain a current density of 10 mA/cm.sup.2 increased with decreasing H.sub.2SO.sub.4 concentration of electrolyte solution used for the electrolysis. As revealed in FIG. 8b-8e, the H.sub.2SO.sub.4 concentration had a significant effect on the electrocatalytic performance towards the electrocatalytic reduction of FDCA. In addition, the C|nanoBi electrode exhibited the best electrocatalytic performance of towards the electrosynthesis of HAA, in terms of HAA faradaic efficiency (FIG. 8b), HAA selectivity (FIG. 8c), HAA yield and FDCA conversion (FIG. 8d), and TOF.sub.HAA (FIG. 8e), when the electrolysis experiments were performed in 0.1 M H.sub.2SO.sub.4 containing FDCA (2.5 mM) and TBAP (30 mM). It is important to note that when the concentrated H.sub.2SO.sub.4 solution (0.5 M or 1 M) was used for electrolysis, FDCA conversion remained at 70%, but the overall carbon balance decreased, indicating that the other side reactions, involving the consumption of FDCA, became pronounced in the presence of concentrated H.sub.2SO.sub.4. In addition, as revealed from TABLE 5, noticeable production of AA was also observed when the electrolysis experiments were performed in the H2SO4 solution with concentrations of 0.1 M and 0.5 M.

TABLE-US-00005 TABLE 5 Summary of the products generated from the 2-h electrolysis at 10 mA/cm.sup.2 using the C|nanoBi electrode in the H.sub.2SO.sub.4 solution of various concentration (0.05M, 0.1M, 0.5M, and 1M) containing FDCA (2.5 mM) and TBAP (30 mM). Amount of H.sub.2SO.sub.4 solution product FE.sub.Product Selectivity Yield (M) Product (mole/cm.sup.2) (%) (%) (%) 0.05 HCA 0 0 0 0 2-FA 0.02 0 0.05 0.03 AA 0 0 0 0 0.1 HCA 0.22 0.3 0.46 0.37 2-FA 0.02 0 0.04 0.03 AA 0.07 0.07 0.14 0.11 0.5 HCA 0 0 0 0 2-FA 0.01 0 0.02 0.01 AA 0.05 0.06 0.18 0.12 1.0 HCA 0 0 0 0 2-FA 0 0 0.01 0.01 AA 0 0 0 0

HAA Yield and Faradaic Efficiency of Products Generated From the 2-h Electrolysis of FDCA Using Different Electrode Materials

[0055] FIG. 9 shows the electrocatalytic performance, in terms of faradaic efficiency and HAA yield, of the various electrode materials obtained from the 2-h electrolysis at a constant current of 10 mA/cm.sup.2 in the sulfuric acid solution (0.1 M) containing FDCA (2.5 mM) and TBAP (30 mM). It was found that both lead plate and C|nanoBi electrode exhibited activity towards simultaneous ring-opening and hydrogenation of FDCA and produced HAA as the main products. Specifically, the lead plate showed a HAA faradaic efficiency of 10.19% and a HAA yield of 21.46%, whereas the C|nanoBi electrode exhibited a high HAA faradaic efficiency of 36.27% and a high HAA yield of 75.48%. However, electrolysis experiments using other electrodes, including carbon paper, copper foil, and bismuth-palladium electrodes, mainly generate hydrogen and didn't generate HAA and AA. These findings indicate that the electrode materials also play an important role in determining the product faradaic efficiency, product selectivity, and product yield from the electrocatalytic reduction of FDCA.

Effects of Applied Current Density for the Electrolysis on the Electrocatalytic Performance of the Nanobi Electrode Towards the Electrocatalytic Reduction of FDCA

[0056] The effects of applied current density for the electrolysis on the electrocatalytic performance of the C|nanoBi electrode towards the electrocatalytic reduction of FDCA were investigated by a series of electrolysis experiments at various applied current densities (5 mA/cm.sup.2, 10 mA/cm.sup.2, 20 mA/cm.sup.2, 30 mA/cm.sup.2) in the H.sub.2SO.sub.4 solution (0.1 M) containing FDCA (2.5 mM) and TBAP (30 mM). For the fair comparison, the total charge passage for each electrolysis experiment was fixed at 72 C/cm.sup.2. As revealed in FIG. 10a, the potentials for the C|nanoBi electrode to maintain the specific applied current density increased with increasing applied current densities used for the electrolysis experiments. As revealed in FIG. 10b-10e, the applied current used for the electrolysis had a significant effect on the electrocatalytic performance towards the electrocatalytic reduction of FDCA. In addition, the C|nanoBi electrode exhibited the best electrocatalytic performance of towards the electrosynthesis of HAA, in terms of HAA faradaic efficiency (FIG. 10b), HAA selectivity (FIG. 10c), HAA yield and FDCA conversion (FIG. 10d), and TOF.sub.HAA (FIG. 10e), when the electrolysis experiments were performed at an applied current density of 10 mA/cm.sup.2 in 0.1 M H.sub.2SO.sub.4 containing FDCA (2.5 mM) and TBAP (30 mM). It is important to note that electrolysis experiments performed at 5 mA/cm.sup.2 resulted in the highest FDCA conversion (83.2%), but lowest overall carbon balance (24%), indicating that the other side reactions, involving the consumption of FDCA, became pronounced at low applied current density (i.e., 5 mA/cm.sup.2). In addition, as revealed from TABLE 6, noticeable production of AA was also observed when the electrolysis experiments were performed at lower applied current densities (i.e., 5 mA/cm.sup.2, and 10 mA/cm.sup.2). Nevertheless, when the electrolysis experiments were performed at high applied current densities (i.e., 20 mA/cm.sup.2 and 30 mA/cm.sup.2), the hydrogen evolution reaction became significant, resulting in lower FDCA conversion, lower HAA faradaic efficiency, lower HAA selectivity, and lower TOF.sub.HAA.

TABLE-US-00006 TABLE 6 Summary of the products generated from the 2-h electrolysis at various applied current densities (5 mA/cm.sup.2, 10 mA/cm.sup.2, 20 mA/cm.sup.2, 30 mA/cm.sup.2) using the C|nanoBi electrode in the H.sub.2SO.sub.4 solution (0.1M) containing FDCA (2.5 mM) and TBAP (30 mM). The total charge passage for each electrolysis experiment was fixed at 72 C/cm.sup.2. Current Amount of density product FE.sub.Product Selectivity Yield (mA/cm.sup.2) Product (mole/cm.sup.2) (%) (%) (%) 5 HCA 0 0 0 0 2-FA 0.03 0 0.06 0.05 AA 0.09 0.09 0.18 0.15 10 HCA 0.22 0.3 0.46 0.22 2-FA 0.02 0 0.04 0.02 AA 0.07 0.07 0.14 0.07 20 HCA 0 0 0 0 2-FA 0.02 0 0.07 0.02 AA 0 0 0 0 30 HCA 0 0 0 0 2-FA 0.02 0 0.12 0.02 AA 0 0 0 0

Example 1

Method of Preparing 2-Hydroxyadipic Acid and Adipic Acid

[0057] 2.5 mM of 2,5-furandicarboxylic acid was electrolyzed in a 0.1 M of sulfuric acid solution containing 30 mM TBAP by using a bismuth nanosheets-modified carbon electrode at a constant current of 10 mA/cm.sup.2 for 2 hours.

Example 2

Method of Preparing 2-Hydroxyadipic Acid

[0058] 2.5 mM of 2,5-furandicarboxylic acid was electrolyzed in a 0.1 M of sulfuric acid solution by using an electroplated bismuth thin film-modified carbon electrode at a constant current of 10 mA/cm.sup.2 for 2 hours.

Example 3

Method of Preparing 2-Hydroxyadipic Acid and Adipic Acid

[0059] 2.5 mM of 2,5-furandicarboxylic acid was electrolyzed in a 0.05 M of sulfuric acid solution containing 30 mM TBAP by using a bismuth nanosheets-modified carbon electrode at a constant current of 10 mA/cm.sup.2 for 2 hours.

Example 4

Method of Preparing 2-Hydroxyadipic Acid

[0060] 2.5 mM of 2,5-furandicarboxylic acid was electrolyzed in a 0.1 M of sulfuric acid solution containing 30 mM of TPAB by using a bismuth nanosheets-modified carbon electrode at a constant current of 10 mA/cm.sup.2 for 2 hours.

Example 5

Method of preparing 2-Hydroxyadipic Acid and Adipic Acid

[0061] 2.5 mM of 2,5-furandicarboxylic acid was electrolyzed in a 0.1 M of sulfuric acid solution containing a 30 mM of TBAP by using a bismuth nanosheets-modified carbon electrode at a constant current of 5 mA/cm.sup.2 for 2 hours.

[0062] In summary, using FDCA as the reactant, a bismuth metal electrode with specific quaternary ammonium salts, or a bismuth metal electrode with a particular morphology without the addition of quaternary ammonium salts, enables simultaneous ring-opening and hydrogenation of 2,5-furandicarboxylic acid. This process does not require high temperatures, high pressure, precious metal catalysts, or other chemical agents. Additionally, using water as the hydrogen source eliminates the costs and energy consumption associated with hydrogen production, storage, and transport. It also avoids competition with green hydrogen production, making this method highly applicable in green, low-carbon chemical industrial production.

[0063] While the preferred embodiments of the present disclosure have been described above, it will be recognized and understood that various changes and modifications can be made, and the appended claims are intended to cover all such changes and modifications which may fall within the spirit and scope of the present disclosure.