A method of electrocatalyzing 5-hydroxymethylfurfural and its byproduct 2,5-furandicarboxylic acid

Abstract

The application discloses a method for electrocatalysis of 5-hydroxymethylfurfural and its by-products into 2,5-furan dicarboxylic acid. The method comprises the following steps: placing high-concentration 5-hydroxymethylfurfural and its by-products in a strong alkali electrolyte, adding a catalyst, and performing electrocatalysis reaction to directly convert into high-value 2,5-furan dicarboxylic acid. The production process is clean and pollution-free, and does not need a complicated separation and purification process. The production process is driven by renewable electricity, the reaction conditions of electrocatalysis of 5-hydroxymethylfurfural and its by-products are regulated, and the generation of humins and other wastes is reduced, so that high yield of 2,5-furan dicarboxylic acid is realized under an industrial-grade current density. The method provides a new idea for high-value conversion of organic solid wastes, pollution reduction and carbon reduction, and economic benefit improvement.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemical catalytic oxidation, and particularly relates to a method for improving conversion of a 5-hydroxymethylfurfural byproduct into 2,5-furan dicarboxylic acid. BACKGROUND

[0002] Polyester is the largest thermoplastic polymer material in China, and polyethylene terephthalate (PET) in particular exhibits excellent physical and mechanical properties, non-toxicity, no smell, no taste, etc., and becomes the main raw material for synthetic dacron and the preferred material for packaging. The waste generated by its large-scale use has become a resource and environmental problem of great concern to the whole society. Developing a biobased polymer polyethylene 2,5-furan dicarboxylate (PEF) that is non-toxic, renewable, controllably degradable, and 100% recyclable, and effectively replacing petroleum-based PET, is an effective way to achieve plastic industry pollution reduction and carbon reduction, and to build a circular economy for the polymer industry.

[0003] 2,5-furan dicarboxylic acid (FDCA) is a key raw material for synthesizing PEF and can be prepared by chemoselective oxidation of 5-hydroxymethylfurfural (HMF), which can be synthesized by hydrolysis of biomass organic solid waste raw materials such as agricultural and forestry waste. In the process of preparing HMF, due to its own chemical properties, it is easy to continue to undergo other side reactions in the reaction process, generating humins and other soluble polymers as byproducts, which are difficult to separate effectively. On the other hand, in recent years, electrochemical oxidation of HMF to prepare FDCA under alkaline conditions has attracted widespread attention as a green, pollution-free and low-cost way to synthesize high-value oxygen-containing chemicals. However, HMF is extremely easy to degrade in an alkaline environment, and Cannizzaro reaction occurs, producing humins and other byproducts. At the same time, the formation of humins will adhere to the surface of the catalyst, blocking the active sites and reducing the yield of the product. The existence of the above problems leads to the following problems in the process of preparing FDCA: complex separation steps, large amount of organic solvent, large amount of solid waste, low yield, low efficiency, high cost, etc., which seriously limits the large-scale application of biobased plastics.

[0004] Humins have complex chemical structures and their composition varies greatly depending on the type of raw material, the concentration of reactants, temperature, the nature of the solvent, and the process of separation and subsequent treatment. Through reaction conversion technology innovation, reaction process optimization and control, it is expected to realize the high value conversion of organic solid waste resources such as HMF preparation (including HMF and / or humins mixed raw materials) and alkaline oxidation process (HMF degradation waste liquid, Cannizzaro by-product) into FDCA. The literature Facile Production of 2,5-Furandicarboxylic Acid via Oxidation of Industrially Sourced Crude 5-Hydroxymethylfurfural, under optimized reaction conditions, with HMF and its corresponding by-products (20wt%) as raw materials, 60bar O2 / N2 and acetic acid solution, using Co / Mn / Br catalyst for uniform oxidation to prepare FDCA, the yield is 95%. This report proves that through high temperature and high pressure thermal catalytic method, the yield of FDCA can be successfully improved, which shows the possibility of improving the yield of FDCA by regulating the reaction conditions, but so far there is no method of driving with renewable power at normal temperature and pressure, by regulating the reaction conditions of electrocatalysis 5-hydroxymethylfurfural and its by-products, reducing the generation of humins, realizing high yield of FDCA at industrial current density. SUMMARY

[0005] In alkaline medium, HMF will be degraded into humins and Cannizzaro reaction will occur, resulting in Cannizzaro products dimethylol furan (DHMF) and 5-hydroxymethyl-2-furancarboxylic acid (HMFCA), both of which can be oxidized to FDCA under strong alkaline conditions (pH ~ 14). In the presence of high concentration of substrates, the conversion rate of DHMF and HMFCA is improved again. Although 5-hydroxymethylfurfural is unstable, the competition of humins and Cannizzaro reaction makes it possible to achieve high conversion rate of FDCA. The purpose of the present invention is to provide a method for reducing the generation of HMF by-products and humins waste, accelerating electrochemical oxidation, realizing industrial grade large current density and high FDCA yield, and expanding the industrial preparation potential of electrocatalytic HMF to FDCA.

[0006] A method for electrocatalyzing 5-hydroxymethylfurfural and its by-products to 2,5-furandicarboxylic acid, characterized in that it comprises the following steps:

[0007] The catalyst, the counter electrode, the reference electrode and the electrolyte solution containing 5-hydroxymethylfurfural and its by-products are assembled into an electrolytic cell, and a voltage is applied to carry out electrocatalytic reaction, and the 5-hydroxymethylfurfural and its by-products are oxidized to FDCA;

[0008] The catalyst is coated on 1*1 cm 2 Metal oxide on foam metal, foam nickel supported bimetallic hydroxide, preferably, the metal oxide is at least one of cobalt oxide, nickel oxide, scandium oxide, iron oxide, manganese oxide, and the bimetallic hydroxide is at least one of nickel-iron, nickel-cobalt, nickel-aluminum bimetallic hydroxide;

[0009] The counter electrode is a platinum electrode or a graphite electrode, and the reference electrode is a mercury / mercury oxide electrode or a silver / silver chloride electrode;

[0010] The loading amount of the metal oxide catalyst on the foam metal is 1-10 mg / cm 2 ;

[0011] Preferably, the loading amount of the catalyst is 2-5 mg / cm 2 ;

[0012] The preparation method of the metal oxide electrode comprises the following steps:

[0013] The silica hard template is immersed in a metal salt solution, stirred for 0.5-2 h, dried, placed in a crucible, calcined at 200-300 ℃ for 4 h to obtain a solid, the obtained solid is immersed in a metal salt solution, stirred for 0.5-2 h, dried, placed in a crucible, calcined at 500-600 ℃ for 6 h, and finally the silica hard template is leached with 2M NaOH aqueous solution to obtain a metal oxide;

[0014] The concentration of the metal salt solution is 0.1M-1M;

[0015] The metal salt is at least one of cobalt nitrate, scandium nitrate, nickel nitrate, iron nitrate, manganese nitrate, cobalt chloride, scandium chloride, nickel chloride, iron chloride, manganese chloride, cobalt sulfate, scandium sulfate, nickel sulfate, iron sulfate, and manganese sulfate;

[0016] Preferably, the concentration of the metal salt solution is 0.1M-0.5M;

[0017] Preferably, the stirring time is 0.5-1 h.

[0018] The foam metal is selected from at least one of foam nickel, foam iron, and foam copper, and preferably the foam metal is foam nickel;

[0019] The 5-hydroxymethylfurfural and its by-products refer to 5-hydroxymethylfurfural degradation waste liquid under alkaline conditions, 5-hydroxymethylfurfural Cannizzaro reaction waste liquid, and 5-hydroxymethylfurfural and biomass organic solid waste derived cellulose, hemicellulose, fructan, fructose, glucose, and / or sugar oligomers or other hydrolysis, degradation products to generate humins mixture by polymerization.

[0020] Specifically, 5-hydroxymethylfurfural and its by-products are 5-hydroxymethylfurfural in alkaline solution at room temperature for 5-30h to form a solution containing humins and Cannizzaro reaction products.

[0021] The alkaline electrolyte is a potassium hydroxide or sodium hydroxide solution with a concentration of 1-15M; preferably potassium hydroxide, and the concentration of the lye is 3-10M;

[0022] The concentration of 5-hydroxymethylfurfural and its by-products is 10-1500mM, and the proportion of by-products is 10-50wt.%;

[0023] More preferably, the concentration is 100-500mM, and the proportion of by-products is 10-30wt.%;

[0024] The voltage range of the applied voltage is 0.3-0.6V (vs. Hg / HgO).

[0025] The beneficial effects of the present application are as follows:

[0026] (1) The present application catalytically oxidizes 5-hydroxymethylfurfural and its by-products humins into FDCA by electrocatalytic method, reduces the generation of by-products, improves the electrocatalytic current density and the yield of FDCA, has greater economic benefits than other methods, and is more suitable for industrialization and large-scale promotion.

[0027] (2) The present application can be carried out at room temperature and normal pressure, has high selectivity and yield of products, does not require complex separation and purification process of products, reduces the accumulation and blockage of humins in pipes, bends and valves in actual industrial production process, and solves the urgent problems in production process.

[0028] (3) Humins waste has not been effectively utilized and is an important source of environmental pollution. The present application converts HMF and / or humins mixture into FDCA to the maximum extent, reduces the generation of waste, improves carbon balance, reduces greenhouse gas emissions, and maximally reduces the impact on the natural environment. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is the HMF degradation graph under different concentrations of HMF and KOH and temperature in the present application.

[0030] Figure 2 is the change of the oxidation reaction intermediate of 50mM HMF and its by-products in 1M KOH in the potentiostatic electrolysis process in Example 2 of the present application.

[0031] Figure 3is the linear scan voltammogram of the foam nickel supported nickel-iron bimetallic hydroxide electrocatalytic oxidation in Example 4 of the present application. DETAILED DESCRIPTION

[0032] The present application will be further described in details below with reference to the examples and the accompanying drawings, but the embodiments of the present application are not limited thereto.

[0033] Example 1

[0034] Preparation of mesoporous Co3O4 electrode material

[0035] 1. Dissolve 1.67 g of Co(NO3)2·6H2O in 6 mL of ethanol to make the impregnation stock solution. Place 500 mg of silica template (pore volume 1 cm3 / g) in a container A and put a magnetic stir bar in it. 3 / g) in container A, and put a magnetic stir bar in it.

[0036] 2. Inject about 3.7 mL of Co(NO3)2·6H2O stock solution into container A using a lab pipette.

[0037] 3. Close container A and place it on a stirring plate and stir to ensure that the silica and precursor solution are well mixed. A short (30 seconds) sonication before stirring will facilitate mixing.

[0038] 4. After stirring for 1 hour, open container A and place it in a 50 °C oven to dry for 12 h to obtain a dry sample.

[0039] 5. Grind the dried pink solid to a powder using a spatula. Then transfer the powder from container A to a crucible and keep it at 200 °C for 4 hours. In this step, Co(NO3)2·6H2O decomposes to black Co3O4.

[0040] 6. Transfer the product from step 5 to container B and inject the remaining stock solution. After closing container B and stirring for 1 hour, open container B and place it in a 50 °C oven until the ethanol is completely evaporated.

[0041] 7. Transfer the dried solid from step 6 to a crucible and calcine it at 500 °C for 6 hours. This step produces Co3O4.

[0042] 8. Transfer the product from step 7 to a polypropylene (PP) bottle body and seal it tightly. Leach the silica hard template with 2 M aqueous NaOH solution. Collect the black solid, i.e. ordered mesoporous Co3O4, by centrifugation.

[0043] Example 2

[0044] Electrochemical activity test of mesoporous Co3O4 as working electrode

[0045] (1) An initial concentration of 50 mM 5-hydroxymethylfurfural was left in 1 M KOH solution at room temperature for 5 h to form a solution containing 10 wt.% of by-products as electrolyte.

[0046] (2) A three-electrode system was used, in which 3 mg of Co3O4 catalyst was coated on 1 x 1 cm 2 of foam nickel as the working electrode, a platinum electrode as the counter electrode, a mercury / mercury oxide electrode as the reference electrode, and an electrolyte containing 5-hydroxymethylfurfural and its by-products were assembled into an electrolytic cell.

[0047] (3) The electrolysis was continuously stirred at a constant voltage of 0.47 V vs. Hg / HgO for 50 min. After the reaction was completed, the reaction products were detected at the anode by high-performance liquid chromatography, and the yield of FDCA was 93%.

[0048] Example 3

[0049] Preparation of foam nickel supported nickel-iron double metal hydroxide electrode material

[0050] 1. Foam nickel was cut into thin pieces (1 cm x 3 cm) and then cleaned using hydrochloric acid (3 M), acetone, ethanol, and ultrapure water by ultrasonic cleaning for 15 minutes, respectively.

[0051] 2. The cleaned foam nickel was immediately placed in a 50 mL beaker containing a mixture of FeCl3·6H2O (2.5 mmol) and 5% H2O2 (25 mL), which had been reacted for 5 minutes. After 1 minute of treatment, the solution was decanted and rinsed with deionized water.

[0052] 3. The modified foam was placed in a plastic petri dish and dried in an oven at 60°C for 24 hours.

[0053] Example 4

[0054] Electrochemical activity test of foam nickel supported nickel-iron double metal hydroxide as working electrode

[0055] (1) An initial concentration of 250 mM 5-hydroxymethylfurfural was left in 5 M KOH solution at room temperature for 25 h to form a solution containing 20 wt.% of by-products as electrolyte.

[0056] (2) A three-electrode system was used, in which foam nickel supported nickel-iron double metal hydroxide was used as the working electrode, a platinum electrode as the counter electrode, a mercury / mercury oxide electrode as the reference electrode, and an electrolyte containing 5-hydroxymethylfurfural and its by-products were assembled into an electrolytic cell.

[0057] (3) The electrolysis was continuously stirred at a constant voltage of 0.47 V vs. Hg / HgO for 50 min. After the reaction was completed, the reaction products were detected at the anode by high-performance liquid chromatography, and the yield of FDCA was 98%.

[0058] Example 5

[0059] Preparation of mesoporous Sc2O3 electrode materials

[0060] 1. Dissolve 2.57g of Sc(NO3)3·6H2O in 8mL of ethanol to prepare the impregnation stock solution. 500mg of silica template (pore volume 1cm³) 3 Place g) into container A and put a magnetic stir bar into it.

[0061] 2. Use a laboratory pipette to inject half of the Sc(NO3)3·6H2O stock solution into container A.

[0062] 3. Close container A and place it on a stirring tray, keeping it at room temperature. Stir to ensure thorough mixing of the silica and precursor solution. Perform a short (30 seconds) ultrasonic treatment before stirring to promote mixing.

[0063] 4. After stirring for 1 hour, open container A and place it in a 50℃ oven to dry for 12 hours to obtain a dried sample.

[0064] 5. Grind the dried solid into powder using a scraper. Then transfer the powder from container A to a crucible and maintain it at 300°C for 4 hours.

[0065] 6. Transfer the product from step 5 to container B, and add the remaining stock solution. Close container B and stir for 1 hour. Then open container B and place it in a 50°C oven until the ethanol has completely evaporated.

[0066] 7. Transfer the dried solid from step 6 to a crucible and calcine at 500°C for 6 hours. This step will produce highly crystalline Sc2O3.

[0067] 8. Transfer the product from step 7 to a polypropylene (PP) bottle and seal it tightly. Leach the silica hard template with a 2M NaOH aqueous solution. Collect the solid, i.e., mesoporous Sc2O3, by centrifugation.

[0068] Example 6

[0069] Electrochemical activity testing of mesoporous Sc2O3 electrode materials as working electrodes

[0070] (1) An electrolyte was prepared by placing 100 mM 5-hydroxymethylfurfural in 3 M KOH solution at room temperature for 30 h to form a solution containing 30 wt.% byproducts.

[0071] (2) Using a three-electrode system, 5 mg of SC2O3 catalyst was coated onto a 1×1 cm² substrate. 2a three-electrode system, 3 mg of nickel oxide catalyst was coated on 1 x 1 cm2foamed nickel as the working electrode, platinum electrode as the counter electrode, mercury / mercury oxide electrode as the reference electrode and electrolyte containing 5-hydroxymethylfurfural and its by-products were assembled into an electrolytic cell.

[0072] (3) The electrolysis was continuously stirred at a constant voltage of 0.47 V vs. Hg / HgO for 50 min. After the reaction, the reaction product was detected at the anode by high performance liquid chromatography, and the yield of FDCA was 96%.

[0073] Example 7

[0074] Preparation of nickel oxide electrode material

[0075] Except that the content of the first step nickel-based raw material was different from that of Example 1, the remaining steps were the same, specifically: 1.94 g of Ni(NO3)2·6H2O was dissolved in 7 mL of ethanol to prepare an impregnation stock solution.

[0076] Example 8

[0077] Electrochemical activity test of nickel oxide electrode material as working electrode

[0078] (1) The initial concentration of 5-hydroxymethylfurfural was 50 mM, and the solution containing 20 wt.% by-products was formed by placing it in 3 M KOH solution at room temperature for 20 h as the electrolyte.

[0079] (2) A three-electrode system was used, 3 mg of nickel oxide catalyst was coated on 1 x 1 cm2foamed nickel as the working electrode, platinum electrode as the counter electrode, mercury / mercury oxide electrode as the reference electrode and electrolyte containing 5-hydroxymethylfurfural and its by-products were assembled into an electrolytic cell. 2

[0080] (3) The electrolysis was continuously stirred at a constant voltage of 0.47 V vs. Hg / HgO for 50 min. After the reaction, the reaction product was detected at the anode by high performance liquid chromatography, and the yield of FDCA was 95%.

[0081] The above examples are the preferred embodiments of the present application, but the embodiments of the present application are not limited by the above examples, and any changes, modifications, substitutions, combinations, simplifications made without departing from the spirit and principles of the present application are equivalent replacement methods and are included in the protection scope of the present application.​

Claims

1. A method of electrocatalyzing 5-hydroxymethylfurfural and its byproduct 2,5-furan dicarboxylic acid, characterized in that, The method comprises the following steps: An electrolytic cell is assembled by a working electrode, a counter electrode, a reference electrode and an alkaline electrolyte containing 5-hydroxymethylfurfural and its by-products, and an electrocatalytic reaction is carried out by applying a voltage, wherein the 5-hydroxymethylfurfural and its by-products are oxidized into 2,5-furandicarboxylic acid; the voltage range of the applied voltage is 0.3-0.6 V; the 5-hydroxymethylfurfural and its by-products are a solution containing humins or Cannizzaro reaction products formed by 5-hydroxymethylfurfural in an alkaline solution at room temperature; The alkaline solution is a potassium hydroxide or sodium hydroxide solution with a concentration of 1-15 M; the concentration of the 5-hydroxymethylfurfural and its by-products is 10-1500 mM, and the proportion of the by-products is 10-50 wt.%. The working electrode is a foam metal with a size of 1*1 cm2, and the surface of the working electrode is coated with a metal oxide catalyst or loaded with a double-metal hydroxide catalyst; the metal oxide catalyst is at least one of cobalt oxide, nickel oxide, scandium oxide, iron oxide and manganese oxide, and the double-metal hydroxide catalyst is at least one of nickel-iron, nickel-cobalt and nickel-aluminum double-metal hydroxide.

2. The method of claim 1, wherein, The counter electrode is a platinum electrode or a graphite electrode, and the reference electrode is a mercury / mercury oxide electrode or a silver / silver chloride electrode.

3. The method of claim 1, wherein, The loading of the metal oxide catalyst or the double metal hydroxide catalyst on the foamed metal is 1 to 10 mg / cm 2 .

4. The method of claim 1, wherein, The preparation method of the metal oxide catalyst comprises the following steps: The silica hard template is immersed in a metal salt solution, stirred for 0.5-2 h, dried, placed in a crucible, calcined at 200-300 DEG C for 4 h to obtain a solid, the obtained solid is immersed in a metal salt solution, stirred for 0.5-2 h, dried, placed in a crucible, calcined at 500-600 DEG C for 6 h, and finally leached with a 2 M NaOH aqueous solution to remove the silica hard template to obtain the metal oxide; The concentration of the metal salt solution is 0.1 M-1 M; The metal salt is at least one of cobalt nitrate, scandium nitrate, nickel nitrate, iron nitrate, manganese nitrate, cobalt chloride, scandium chloride, nickel chloride, iron chloride, manganese chloride, cobalt sulfate, scandium sulfate, nickel sulfate, iron sulfate and manganese sulfate; The concentration of the metal salt solution is 0.1 M-0.5 M.

5. The method of claim 1, wherein, The foam metal is selected from at least one of foam nickel, foam iron and foam copper.

6. The method of claim 1, wherein The concentration of the alkaline solution is 3-10 M.

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