Method and system for preparing FDCA through continuous oxidation of HMF and coupling hydrogen production through electrolysis of water

Abstract

The invention provides a method for preparing FDCA through continuous oxidation of HMF and coupling water electrolysis for hydrogen production, which comprises the following steps: taking a solution A dissolved with an auxiliary agent and alkali as an anolyte of an electrolytic bath, and taking a solution B dissolved with an electrolyte as a catholyte of the electrolytic bath; the auxiliary agent comprises at least one of ferrocyanide and ferricyanide; respectively conductively connecting the anode soaked in the anolyte and the cathode soaked in the catholyte with the positive electrode and the negative electrode of a power supply, and carrying out electrolytic treatment; in the electrolytic treatment process, a solution C containing HMF is continuously added into the anolyte, the HMF is oxidized into FDCA on the anode side, FDCA in the anolyte in the electrolytic process is continuously extracted and separated, and the anolyte after FDCA is separated and recycled is recycled; and the cathode is subjected to hydrogen evolution reaction, so that water is electrolyzed to produce hydrogen. The invention further provides a system for implementing the method. The method disclosed by the invention can be used for efficiently and highly selectively synthesizing FDCA at low potential, and is low in cost.

Description

Technical Field

[0001] The invention belongs to the field of preparing value-added products by oxidizing organic matter, and in particular to the field of HMF oxidation. Background Art

[0002] As society pursues sustainable development, people have begun to explore the use of cleaner energy and materials. In terms of energy, hydrogen energy, as a green and efficient secondary energy source, has the advantages of a wide range of raw materials, high calorific value, and clean and renewable. The development and utilization of hydrogen energy plays a strategic role in the sustainable development of the world. The use of renewable energy such as solar energy, wind energy, tidal energy, etc. to generate electricity and provide energy for water electrolysis to produce hydrogen is regarded as the development trend of hydrogen energy in the future. However, the oxygen evolution reaction at the anode of water electrolysis has the disadvantage of slow kinetics, which makes the oxygen evolution overpotential very high during the electrolysis process. The voltage of the electrolytic cell must be higher than 2V to achieve effective electrolysis. Therefore, it is often necessary to use electrochemical catalysts to achieve efficient water electrolysis to produce hydrogen at a lower potential. Moreover, the value of the oxygen produced by the anode oxygen evolution reaction is not high, so the value of the entire water electrolysis hydrogen production system is not high.

[0003] In terms of materials, 2,5-furandicarboxylic acid (FDCA) is listed as one of the "12 platform chemicals" by the U.S. Department of Energy. As a material that can replace terephthalic acid (TPA) to prepare biodegradable plastics, it has received widespread attention in recent years, and it is expected that low-cost large-scale production of FDCA can be achieved, and the application of biodegradable plastics can be popularized. The electrochemical oxidation of 5-hydroxymethylfurfural (HMF) to prepare FDCA is the mainstream trend in the current FDCA preparation industry. Researchers have prepared a large number of HMF oxidation (HMFOR) catalysts for this process, but these catalysts have the disadvantages of complicated preparation process and poor stability. After about 10 cycles, they will quickly lose their activity and their selectivity will be greatly reduced. Secondly, HMF will quickly generate humin in alkaline solution, resulting in the loss of raw materials. Therefore, the content of HMF in the electrolysis process is very low, only between 10mM-50mM, and rarely reaches more than 100mM, which also leads to lower preparation efficiency. In addition, the above production method is intermittent, which further reduces the efficiency of FDCA production. In addition, organic substances containing aldehyde and hydroxyl groups, such as methanol and formaldehyde, often have high economic value when oxidized to obtain carboxylic acid products. Summary of the invention

[0004] In view of the problems of poor oxidation efficiency and selectivity of existing HMF oxidation schemes at low potential, difficulty in achieving stable and continuous synthesis, and high cost, the present invention provides a method for preparing FDCA by continuous oxidation of HMF and coupling electrolysis of water to produce hydrogen, aiming to provide a method for preparing FDCA by continuous and highly selective oxidation at low potential.

[0005] A second object of the present invention is to provide a system for implementing the method.

[0006] A method for continuously oxidizing HMF to prepare FDCA and coupling water electrolysis to produce hydrogen, wherein a solution A containing an auxiliary agent and an alkali is used as an anolyte of an electrolytic cell, and a solution B containing an electrolyte is used as a catholyte of the electrolytic cell; the auxiliary agent comprises at least one of ferrocyanide and ferrocyanide; an anode immersed in the anolyte and a cathode immersed in the catholyte are respectively connected to a positive electrode and a negative electrode of a power source for electrolysis;

[0007] During the electrolysis process, a solution C containing HMF is continuously added to the anolyte to oxidize the HMF into FDCA on the anode side, and the FDCA in the anolyte during the electrolysis process is continuously extracted and separated, and the anolyte after the FDCA is separated and recovered is recycled;

[0008] The cathode undergoes a hydrogen evolution reaction, causing water to be electrolyzed to produce hydrogen.

[0009] The present invention innovatively provides a preparation idea of ​​HMF continuous oxidation and coupling with water electrolysis to produce hydrogen, which innovatively adds the auxiliary agent to the anolyte, and the oxidized component in the auxiliary agent directly or the reduced component loses electrons under the action of the electric field and then transforms into an oxidized state to assist in the oxidation of HMF. With the oxidation of HMF, the oxidized auxiliary agent regains electrons and transforms into a reduced state, and the reduced auxiliary agent continues to lose electrons under the action of the electric field and transforms into an oxidized state to continue to participate in the oxidation of HMF, so that the cyclic transformation of the oxidized state-reduced state of the auxiliary agent under the electric field can achieve the efficiency, high selectivity, and mild continuous oxidation of HMF. The method of the present invention can synthesize FDCA efficiently and selectively at low potential, and its cost is low.

[0010] In the present invention, the auxiliary agent includes at least one of potassium ferrocyanide, sodium ferrocyanide, potassium ferrocyanide and sodium ferrocyanide.

[0011] In the present invention, the alkali in the solution A includes at least one of sodium hydroxide, potassium hydroxide and lithium hydroxide.

[0012] In the present invention, in solution A, the concentration of the auxiliary agent is controlled at 1-2M, preferably 1.1-1.5M; more preferably 1.2-1.4M; the concentration of the base is controlled at 1-2M, preferably 1.1-1.5M; more preferably 1.2-1.4M.

[0013] Preferably, there is no particular requirement for the HMF concentration in solution C, for example, it is controlled within the range of 0.5 to 2M.

[0014] In the present invention, the electrolyte in solution B is an acidic electrolyte or an alkaline electrolyte, wherein the acidic electrolyte includes at least one of sulfuric acid and hydrochloric acid; the alkaline electrolyte includes at least one of lithium hydroxide, sodium hydroxide and potassium hydroxide;

[0015] Preferably, the concentration of the electrolyte in solution B is 0.5-4M.

[0016] In the present invention, the anode and cathode are carbon-based electrodes, preferably carbon cloth, carbon paper, carbon felt or graphite felt.

[0017] In the present invention, the temperature of the electrolysis stage is 30-90°C.

[0018] In the present invention, the potential in the electrolysis stage is 1.2-1.65V, and can further be 1.5-1.6V; the current is 0.2-1A; and can further be 300-500mA cm 2 .

[0019] In the present invention, during the electrolysis stage, the anolyte of the electrolysis stage is continuously taken out, and the FDCA therein is continuously separated and then used as the anolyte for continuous recycling.

[0020] The present invention also provides a system for implementing the method, comprising an electrolytic cell, and a separator for dividing the electrolytic cell chamber into an anode chamber and a cathode chamber;

[0021] The anode chamber is provided with an anode and an anode liquid for soaking the anode; the cathode chamber includes a cathode and a cathode liquid for soaking the cathode; the anode is conductively connected to the positive electrode of the power supply, and the cathode is conductively connected to the negative electrode of the power supply;

[0022] The system further comprises an anolyte storage tank, a solution C storage tank and an anolyte separation tank, wherein the outlet of the anolyte storage tank and the outlet of the solution C storage tank are respectively connected to the inlet of the anode chamber, the outlet of the anode chamber is connected to the inlet of the anolyte separation tank, the feed liquid outlet of the anolyte separation tank is connected to the inlet of the anolyte storage tank and / or the inlet of the anode chamber, and the anolyte separation tank is also provided with an FDCA production outlet;

[0023] The system further comprises a cathode liquid storage tank and a hydrogen storage tank, wherein the outlet of the cathode liquid storage tank is connected to the cathode chamber inlet, and the hydrogen outlet of the cathode chamber is connected to the hydrogen storage tank.

[0024] In the present invention, the separation layer is an ion exchange membrane, preferably a cation exchange membrane or an anion exchange membrane.

[0025] In the present invention, the steps of continuous preparation using the system are, for example: adding anolyte to the anode chamber, adding catholyte to the cathode chamber, inserting the anode and cathode into the anode liquid in the anode chamber and the cathode liquid in the cathode chamber respectively, and connecting the anode and cathode to the positive electrode and the negative electrode of the power supply respectively to conduct electrolysis; during the electrolysis process, continuously adding solution C to the anode chamber; and continuously extracting the reaction anode liquid in the anode chamber, separating the reaction anode liquid through the anode liquid separation tank to obtain FDCA, and directly circulating the anode liquid after separating FDCA to the anode chamber, or; circulating to the anode liquid storage tank and then continuously reused in the anode chamber.

[0026] Beneficial Effects

[0027] The present invention innovatively adds the auxiliary agent to the anolyte, so that the auxiliary agent and the electric field can be used for the continuous oxidation of HMF through synergistic coupling, so that FDCA can be synthesized efficiently and selectively at a low potential with low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The polarization curves of carbon felt electrode to various substances. It can be seen from the figure that when carbon felt is used as an electrode, other substances except potassium ferrocyanide will not be oxidized below 1.8V, which ensures that the system will not destroy the raw materials and products during the cycle, verifying the feasibility of the scheme.

[0029] Figure 2 The infrared spectrum of the product obtained in the example of oxidation of HMF of the present invention is compared with the infrared spectrum of FDCA, which proves that the scheme can obtain FDCA with higher purity. Specific implementation plan

[0030] The specific implementation methods of the present invention are described in detail and completely below. Obviously, the examples described here are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, other examples obtained by ordinary technicians in this field without creative work are all within the scope of protection of the present invention.

[0031] The present invention provides a system for continuously oxidizing HMF to prepare a value-added product FDCA, which comprises an electrolytic cell, and a separator for dividing a chamber of the electrolytic cell into an anode chamber and a cathode chamber;

[0032] The anode chamber is provided with an anode and an anode liquid for soaking the anode; the cathode chamber includes a cathode and a cathode liquid for soaking the cathode; the anode is conductively connected to the positive electrode of the power supply, and the cathode is conductively connected to the negative electrode of the power supply;

[0033] The system further comprises an anolyte storage tank and an anolyte separation tank, wherein the anolyte outlet is connected to the inlet of the anolyte separation tank, the feed liquid outlet of the anolyte separation tank is connected to the inlet of the anolyte storage tank, and the outlet of the anolyte storage tank is connected to the inlet of the anode chamber;

[0034] The system further comprises a cathode liquid storage tank and a hydrogen storage tank, wherein the outlet of the cathode liquid storage tank is connected to the cathode chamber inlet, and the hydrogen outlet of the cathode chamber is connected to the hydrogen storage tank.

[0035] In the present invention, the separation layer is an ion exchange membrane (diaphragm), preferably a cation exchange membrane or an anion exchange membrane.

[0036] Example 1: Oxidation of 5-hydroxymethylfurfural to prepare 2,5-furandicarboxylic acid

[0037] (1) Preparation of cathode and anode:

[0038] A: Anode: Use carbon felt with a thickness of 4 mm as the anode material, cut into a 4 cm × 4 cm square. Before use, the carbon felt needs to be ultrasonically cleaned in 1M hydrochloric acid, acetone, anhydrous ethanol and deionized water for 15 minutes, and then vacuum dried at 60°C.

[0039] B: Cathode: Pt / C is used as the cathode.

[0040] (2) Prepare a reaction solution: Add 0.14 mol potassium ferrocyanide and 0.14 mol potassium hydroxide into 100 mL of deionized water to obtain an anolyte.

[0041] (3) Preparation of 5-hydroxymethylfurfural aqueous solution (Solution C): Add 0.01 mol of 5-hydroxymethylfurfural into 20 mL of water and mix well.

[0042] (4) Preparation of cathode electrolyte: The cathode electrolyte is 1 M KOH solution (catholyte).

[0043] (5) Assembling the electrolytic cell:

[0044] Anolyte is added to the anode chamber, catholyte is added to the cathode chamber, the anode and cathode are respectively inserted into the anode liquid in the anode chamber and the cathode liquid in the cathode chamber, and the anode and cathode are respectively conductively connected to the positive electrode and the negative electrode of the power supply to perform electrolysis; during the electrolysis process, solution C is continuously added to the anode chamber; and the reaction anode liquid in the anode chamber is continuously sampled, and the reaction anode liquid is separated into FDCA in an anode liquid separation tank, and the anode liquid after the FDCA is separated is directly circulated to the anode chamber, or; after being circulated to the anode liquid storage tank, it is continuously reused in the anode chamber.

[0045] Constant current during electrolysis phase: 300-500mAcm-2 The measured potential was 1.2-1.65V.

[0046] In the present invention, during the electrolysis stage, the dissolved C is continuously dripped into the anode liquid of the electrolysis stage at a speed of 10-20 mL / h.

[0047] In the present invention, when FDCA in the anolyte of the electrolysis stage accumulates to a certain extent, the anolyte can be output to a separation tank, sulfuric acid is added thereto, the pH of the system is regulated to about 7, and the FDCA therein is separated; and the concentration of the anolyte of the separated FDCA is regulated by adjusting the concentration of the auxiliary agent and the alkali (same as the first concentration, mainly to adjust the concentration of the alkali) and then circulated to the anode chamber for the synthesis of the next batch of HMF. The synthesis is continuously cyclically performed in this way.

[0048] Figure 2 It is a comparison between the infrared curve of the FDCA produced by the present invention after extraction and the infrared curve of the standard FDCA.

[0049] Note: The standard sample and the product obtained by filtration were tested by infrared.

[0050] 3150cm -1 With 3124cm -1 =CH stretching vibration, 960, 840, 759 cm -1 The three peaks are the out-of-plane bending vibration of =CH; 1186, 1040cm -1 =CH in-plane bending vibration; 1570, 1522cm -1 is the stretching vibration of C=C, 1265, 1162cm -1 It is the asymmetric stretching vibration of CO. It can be judged that there is a furan ring. At the same time, 3300cm -1 There is free OH stretching vibration on the left and right, 1663cm -1 There is stretching vibration of C=O, 1417cm -1 CO stretching vibration, 1223cm -1 It is the in-plane bending vibration of OH, indicating the presence of carboxyl groups.

[0051] In the present invention, the anolyte produced by the first electrolysis was tested, showing that the yield of FDCA was 99.36%;

[0052] The yield of FDCA detected in the anolyte produced from the second electrolysis cycle was 99.12%;

[0053] The yield of FDCA detected in the anolyte produced from the third electrolysis cycle was 99.01%;

[0054] The yield of FDCA detected in the anolyte produced from the fourth electrolysis cycle was 98.90%;

[0055] The yield of FDCA detected in the anolyte produced from the fifth electrolysis cycle was 98.62%.

[0056] Studies have shown that by coupling the auxiliary agent and electrolysis described in the present invention, FDCA can be continuously synthesized from HMF at a low potential, and FDCA can be synthesized continuously, highly stably and highly selectively.

[0057] Example 2

[0058] Compared with Example 1, the only difference is that the concentrations of potassium ferricyanide and alkali in the anolyte are changed.

[0059] The concentrations of potassium ferrocyanide and alkaline solution in the anolyte were changed respectively. Other operations and parameters were the same as those in Example 1. The results of the first batch of electrolysis are shown in Table 1.

[0060] Table 1

[0061] Potassium ferrocyanide concentration / M Sodium hydroxide concentration / M HMF / mM Yield % 0.8 0.8 100 52.2293 1 0.8 100 55.41401 1.2 0.8 100 60.27389 1.4 0.8 100 68.10828 1.6 0.8 100 66.56051 1.4 1 100 85.98726 1.4 1.2 100 92.94268 1.4 1.4 100 99.36306

[0062] Comparative Example 1

[0063] Compared with Example 1, the only difference is that potassium ferrocyanate is not added to the anolyte, and other operations and parameters are the same as Example 1.

[0064] like Figure 1 As shown by the green line, a high potential of nearly 2V is required to obtain a current of 100mA, indicating that the ideal FDCA synthesis effect cannot be obtained at low potentials.

[0065] Comparative Example 2

[0066] Compared with Example 1, the only difference is that the anode and the cathode are not energized; the FDCA yield is only about 70%, and the effect of more than 97% cannot be achieved.

[0067] The present invention responds to the strategy of sustainable development, produces value-added products by oxidizing HMF with a circulated redox medium, and simultaneously produces hydrogen with high efficiency.

[0068] The applicant declares that the above examples are only specific implementations of the present invention, but the protection scope of the present invention is not limited to the above examples. Those skilled in the art should understand that any transformation and replacement that can be easily obtained by those skilled in the art within the technical scope disclosed by the present invention are within the protection scope of the present invention.

Claims

1. A method for preparing FDCA by continuous oxidation of HMF and coupling water electrolysis to produce hydrogen, characterized in that: A solution A containing an auxiliary agent and an alkali is used as the anolyte of the electrolytic cell, and a solution B containing an electrolyte is used as the catholyte of the electrolytic cell; the auxiliary agent comprises at least one of ferrocyanide and ferrocyanide; the anode immersed in the anolyte and the cathode immersed in the catholyte are respectively connected to the positive electrode and the negative electrode of the power supply for electrolytic treatment; During the electrolysis process, a solution C containing HMF is continuously added to the anolyte to oxidize the HMF into FDCA on the anode side, and the FDCA in the anolyte during the electrolysis process is continuously extracted and separated, and the anolyte after the FDCA is separated and recovered is recycled; The cathode undergoes a hydrogen evolution reaction, causing water to be electrolyzed to produce hydrogen.

2. The method for producing hydrogen by continuous oxidation of HMF and coupled water electrolysis according to claim 1, characterized in that: The auxiliary agent includes at least one of potassium ferrocyanide, sodium ferrocyanide, potassium ferrocyanide and sodium ferrocyanide; Preferably, the alkali in the solution A includes at least one of sodium hydroxide, potassium hydroxide and lithium hydroxide.

3. The method for producing hydrogen by continuous oxidation of HMF and coupled water electrolysis as claimed in claim 1, characterized in that: In solution A, the concentration of the auxiliary agent should be 1 to 2 M, preferably 1.1 to 1.5 M; more preferably 1.2 to 1.4 M; Preferably, the concentration of the base is controlled at 1 to 2 M, preferably 1.1 to 1.5 M; more preferably 1.2 to 1.4 M; Preferably, the HMF concentration in solution C is controlled at 0.5-2M.

4. The method for producing hydrogen by continuous oxidation of HMF and coupled water electrolysis according to claim 1, characterized in that: The electrolyte in solution B is an acidic electrolyte or an alkaline electrolyte, wherein the acidic electrolyte includes at least one of sulfuric acid and hydrochloric acid; the alkaline electrolyte includes at least one of lithium hydroxide, sodium hydroxide and potassium hydroxide; Preferably, the concentration of the electrolyte in solution B is 0.5-4M.

5. The method for producing hydrogen by continuous oxidation of HMF and coupled water electrolysis according to claim 1, characterized in that: The anode and cathode are carbon-based electrodes, preferably carbon cloth, carbon paper, carbon felt or graphite felt.

6. The method for producing hydrogen by continuous oxidation of HMF and coupled water electrolysis according to any one of claims 1 to 5, characterized in that: The temperature of the electrolysis stage is 30-90°C.

7. The method for producing hydrogen by continuous oxidation of HMF and coupled water electrolysis according to any one of claims 1 to 6, characterized in that: The potential during the electrolysis phase is 1.2-1.65 V; the current is 100-1000 mA cm -2 .

8. The method for producing hydrogen by continuous oxidation of HMF coupled with water electrolysis as claimed in any one of claims 1 to 7, wherein the anolyte is continuously output, and the FDCA therein is continuously separated and then used as the anolyte for continuous recycling.

9. A system for implementing the method according to any one of claims 1 to 8, characterized in that: The invention comprises an electrolytic cell and a separator for dividing a chamber of the electrolytic cell into an anode chamber and a cathode chamber; The anode chamber is provided with an anode and an anode liquid for soaking the anode; the cathode chamber includes a cathode and a cathode liquid for soaking the cathode; the anode is conductively connected to the positive electrode of the power supply, and the cathode is conductively connected to the negative electrode of the power supply; The system further comprises an anolyte storage tank, a solution C storage tank and an anolyte separation tank, wherein the outlet of the anolyte storage tank and the outlet of the solution C storage tank are respectively connected to the inlet of the anode chamber, the outlet of the anode chamber is connected to the inlet of the anolyte separation tank, the feed liquid outlet of the anolyte separation tank is connected to the inlet of the anolyte storage tank and / or the inlet of the anode chamber, and the anolyte separation tank is also provided with an FDCA production outlet; The system further comprises a cathode liquid storage tank and a hydrogen storage tank, wherein the outlet of the cathode liquid storage tank is connected to the cathode chamber inlet, and the hydrogen outlet of the cathode chamber is connected to the hydrogen storage tank.

10. The system according to claim 9, characterized in that The separation layer is an ion exchange membrane, preferably a cation exchange membrane or an anion exchange membrane.

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