Process for the selective oxidation coupling of 5-hydroxymethylfurfural for the production of electrical energy

Abstract

The application discloses a method for producing electric energy by selective oxidation coupling of 5-hydroxymethylfurfural, which comprises the following steps: adding an anode electrolyte containing 5-hydroxymethylfurfural in an anode storage tank to an anode discharge chamber of a liquid flow fuel cell, and circulating back to the anode storage tank; adding a cathode electrolyte containing an oxidation-reduction electrolyte in a cathode storage tank to a cathode discharge chamber of the liquid flow fuel cell, and circulating back to the cathode storage tank; introducing air into the cathode discharge chamber and the cathode storage tank; connecting the cathode and the anode of the liquid flow fuel cell with an external load to form a loop, and generating electric energy while oxidizing 5-hydroxymethylfurfural. Thus, by performing the oxidation reaction of 5-hydroxymethylfurfural in the form of a fuel cell, 5-hydroxymethylfurfural oxidation products can be generated under mild conditions, the method can also regulate the product distribution, specifically, HMFCA or FDCA can be generated, and in addition, the co-production of electric energy can also be realized.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of biomass chemical engineering, and particularly relates to a method for selective oxidation coupling electric energy production of 5-hydroxymethylfurfural. BACKGROUND

[0002] 5-hydroxymethylfurfural (HMF) is an important platform compound derived from biomass, which has a furan ring, an aldehyde group and a hydroxyl group, and is a chemical intermediate with active chemical properties. HMF can generate various derivatives through oxidation, hydrogenation and other reactions, and is a promising fine chemical raw material. HMF can obtain various products through oxidation, for example, 5-hydroxymethyl-2-furancarboxylic acid (HMFCA), 2,5-furandicarboxaldehyde (DFF), 5-formyl-2-furancarboxylic acid (FFCA) and 2,5-furandicarboxylic acid (FDCA). These derivatives obtained from HMF have important economic value. DFF can be used to synthesize new polymer materials, pharmaceutical intermediates, fluorescent agents and macrocyclic ligands, and can also be used as bactericides, fluorescent materials and the like, and has high application value in the fields of medical treatment, industry and fine chemical industry; FDCA is listed as one of the 12 high-value-added compounds by the US Department of Energy, and can be derived into various important chemicals through different chemical conversions. FDCA can be used to produce 2,5-furandicarboxylic acid diol ester (PEF), which is a recyclable bio-based polyester and can replace petroleum-based plastic polyethylene terephthalate (PET) to produce bottles and outer packaging and other daily plastic products; HMFCA can be used as a precursor for the synthesis of various polyester materials, and can also be used to synthesize non-benzene ring bio-based plasticizers, and is reported to have certain anti-tumor activity and can be used as an interleukin inhibitor; FFCA is an intermediate for oxidation to FDCA, and has good application prospects in the fields of medicine and furan polyester. It can be seen that the oxidation products of HMF have wide applications, and therefore how to efficiently and greenly oxidize HMF has been a key problem in the utilization of biomass resources.

[0003] Currently, there are many studies on the oxidation of HMF to produce FDCA. As early as 2001, foreign scholars reported that in a homogeneous system, HMF was chemically oxidized with air as the oxidant, Co(OAc)2, Mn(OAc)2 and HBr as the catalyst at 125℃ and 70bar, and the yield of FDCA was 60.9%(Walt Partenheimer, Vladimir V. Grushin. Synthesis of 2,5-Diformylfuran and Furan-2,5-Dicarboxylic Acid by Catalytic Air-Oxidation of 5-Hydroxymethylfurfural. Unexpectedly Selective Aerobic Oxidation of Benzyl Alcohol to Benzaldehyde with Metal=Bromide Catalysts[J]. Advanced Synthesis & Catalysis, 2001, 343(1): 102-111.). Hansen et al. used copper salt and tetramethylpiperidine oxide (TEMPO) as catalyst, t-BuOOH as oxidant, and under the optimal conditions, the yield of FDCA was 45%(Hansen TS, Sádaba I, Garcia-Suarez EJ, Riisager A. Cu catalyzed oxidation of 5-hydroxymethylfurfural to 2,5-diformylfuran and 2,5-furandicarboxylic acid under benign reaction conditions[J]. Applied Catalysis A: General, 2013, 456: 44-50.).Origin Materials and Eastman Chemical Company jointly designed a commercial production route for FDCA in 2017, and subsequently applied for a patent, using Co / Mn / Br catalyst, at 132 °C, 8.96 bar of air, to obtain a FDCA yield of 89.4% (Janka M, Lange D, Morrow M, Bowers B, Parker K, Shaikh A, Partin L, Jenkins J, Moody P, Shanks T, Sumner C, US Pat, 20150011783A1, Eastman Chemical Company, Kingsport, TN (US), 2015.). Zhang Junhua et al. applied for a patent in 2018, using potassium ferrate as an oxidant, to directly catalyze the oxidation of HMF in an alkaline solution to prepare FDCA (Zhang Junhua, Xie Wenhxing, Liang Qidi. Preparation method of catalyst for catalytic oxidation of HMF to prepare FDCA and its application, CN108043409A[P]. 2018.). However, there are still great challenges in homogeneous catalytic system, not only the yield of FDCA product is very low, but also the product separation and catalyst recovery and regeneration are difficult. In order to solve these two problems, heterogeneous catalyst gradually becomes the main research direction at present.

[0004] In recent years, heterogeneous catalytic system for the oxidation of HMF to FDCA has been widely studied. Heterogeneous catalysts are easy to recover and regenerate, and even can use cheap and readily available oxygen and air as oxidants, which conforms to the mainstream trend of green and environmental protection. Due to the difficulty of activating oxygen molecules, high-activity noble metal catalysts such as platinum, gold, palladium, and rhodium are mainly used for the oxidation of HMF to FDCA. Air Rass et al. optimized Bi-Pt / C catalyst, which can obtain 98% yield of FDCA under 100 ℃, 40 bar air (Ait Rass H; Essayem N, Besson M. Selective aqueous phase oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid over Pt / C catalysts: influence of the base and effect of bismuth promotion [J]. Green Chemistry, 2013). In order to avoid the use of a large amount of base, some researchers coated MgO with carbon to prepare an alkaline carrier, and then loaded Pt by impregnation method. Under the optimal conditions (110 ℃, 1 MPa O2), the FDCA yield can reach 97% without base (Base-free aerobic oxidation of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid over a Pt / C–O–Mg catalyst [J]. Green Chemistry, 2015, 18.). With the in-depth study, researchers found that supported gold catalysts can exhibit excellent performance in the selective oxidation of HMF to FDCA. By loading gold on TiO2 and CeO2, more than 99% of FDCA yield can be achieved (Casanova O, Iborra S, Corma A. Biomass into chemicals: aerobic oxidation of 5-hydroxymethyl-2-furfural into 2,5-furandicarboxylic acid with gold nanoparticle catalysts [J]. Chemsuschem, 2010, 2(12): 1138-1144.).Villa et al. found that Au-Pd alloy catalysts have a synergistic effect, and Au8-Pd2 / AC catalyst obtained by optimizing the molar ratio of the two exhibits the highest catalytic activity. More than 99% of FDCA yield can be obtained at 60°C, 30 bar oxygen atmosphere, and reaction for 2h (Villa A, Schiavoni M, Campisi S, et al. Pd-modified Au on Carbon as an Effective and Durable Catalyst for the Direct Oxidation of HMF to 2,5-Furandicarboxylic Acid [J]. Chemsuschem, 2013, 6(4): 609-612.). The Netherlands Avantium company has built a 40t / year HMF oxidation synthesis FDCA commercial device, which has been officially put into production in 2011. Pt / C is selected as the catalyst for HMF oxidation synthesis of FDCA at 100°C, 100 bar air. NOVAMONT company also uses Pt / C as catalyst, and realizes HMF oxidation synthesis of FDCA in weak base sodium bicarbonate solution at 100°C, 5 bar oxygen pressure, and obtains 95% of FDCA yield (Sajid M, Zhao X, Liu D. Production of 2,5-furandicarboxylic acid (FDCA) from 5-hydroxymethylfurfural (HMF): recent progress focusing on the chemical-catalytic routes [J]. Green Chemistry, 2018, 20(24): 5427-5453.). Although the research of heterogeneous system has made outstanding progress, and has been applied to commercial production, there are still some obvious shortcomings. The most significant is that almost all the methods of chemical oxidation to synthesize FDCA need high temperature and high pressure conditions, and the supported noble metal catalysts used in the reaction process will gradually deactivate, which greatly increases the cost of catalyst.

[0005] In general, the oxidation of 5-hydroxymethylfurfural using the existing method requires relatively harsh reaction conditions, for example, the oxidation reaction needs to be carried out at high temperature and / or high pressure.

[0006] Therefore, it is necessary to improve the method for oxidizing 5-hydroxymethylfurfural. SUMMARY

[0007] The present application aims to at least partly improve at least one of the above technical problems.

[0008] To improve the above technical problems, the present application provides a method for selective oxidation coupling of 5-hydroxymethylfurfural to produce electric energy, which comprises: adding an anode electrolyte containing 5-hydroxymethylfurfural in an anode storage tank to an anode discharge chamber of a liquid flow fuel cell, and circulating back to the anode storage tank; adding a cathode electrolyte containing a redox electrolyte in a cathode storage tank to a cathode discharge chamber of a liquid flow fuel cell, and circulating back to the cathode storage tank; passing air into the cathode discharge chamber and the cathode storage tank; wherein the redox electrolyte comprises at least one of vanadyl sulfate, ferric chloride, ferric nitrate, ferric citrate, phosphomolybdic acid, phosphomolybdovanadic acid, copper chloride, potassium ferricyanide; connecting the cathode and the anode of the liquid flow fuel cell with an external load to form a loop, and oxidizing 5-hydroxymethylfurfural while generating electric energy. Thus, the oxidation reaction of 5-hydroxymethylfurfural is carried out in the form of a fuel cell, which can oxidize 5-hydroxymethylfurfural to generate the corresponding product under mild conditions. Specifically, the method of the present application can conveniently regulate the product distribution by adjusting the electron transfer rate, and can selectively oxidize 5-hydroxymethylfurfural to generate 5-hydroxymethylfurfuric acid (HMFCA) or 2,5-furan dicarboxylic acid (FDCA). In addition, the method of the present application can generate 5-hydroxymethylfurfural oxidation products while obtaining electric energy, and can realize the co-production of electric energy.

[0009] According to an embodiment of the present application, the method further comprises the step of assembling a liquid flow fuel cell, which comprises an anode storage tank, an anode discharge chamber, an anode, an anode graphite bipolar plate, an ion exchange membrane, a cathode graphite bipolar plate, a cathode, a cathode discharge chamber, an external load and a cathode storage tank; the ion exchange membrane is located between the anode graphite bipolar plate and the cathode graphite bipolar plate; the anode graphite bipolar plate is located on the side of the ion exchange membrane close to the anode discharge chamber, and the cathode graphite bipolar plate is located on the side of the ion exchange membrane close to the cathode discharge chamber; the anode graphite bipolar plate is provided with a first recess, and the anode is arranged in the first recess and located on the side of the anode graphite bipolar plate close to the anode discharge chamber; the cathode graphite bipolar plate is provided with a second recess, and the cathode is arranged in the second recess and located on the side of the cathode graphite bipolar plate close to the cathode discharge chamber; the anode storage tank is connected to the anode discharge chamber through a pipeline, and the cathode storage tank is connected to the cathode discharge chamber through a pipeline; the external load is arranged outside the liquid flow fuel cell, and the cathode and the anode are connected to the external load, respectively. Thus, 5-hydroxymethylfurfural in the anode discharge chamber can be selectively oxidized to generate target products, and in the cathode discharge chamber, oxygen molecules in the air can be reduced to generate water, while electric energy can be generated.

[0010] According to an embodiment of the present application, the anode is formed by loading an anode electron carrier on a first conductive substrate; the anode electron carrier is selected from at least one of silver oxide, copper oxide, nickel oxide, manganese dioxide, cobalt oxide, iron oxide, nickel phosphide, cobalt phosphide, nickel sulfide, cobalt sulfide, nickel boride, nickel nitride, tricobalt tetroxide, nickel hydroxide, cobalt hydroxide, nickel oxyhydroxide, and cobalt oxyhydroxide; the first conductive substrate is selected from one of copper foam, nickel foam, carbon felt, carbon paper, and carbon cloth; optionally, the loading amount of the anode electron carrier is 0.001-10 mg / cm 2 Thus, 5-hydroxymethylfurfural can be oxidized on the surface of the anode to generate oxidized products by losing electrons, specifically, FDCA or HMFCA can be generated.

[0011] According to an embodiment of the present application, the cathode is formed by loading a cathode electron carrier on a second conductive substrate; the cathode electron carrier is selected from one of metallic platinum, metallic ruthenium, carbon black, iron phthalocyanine, iron-nitrogen-carbon composite, cobalt-nitrogen-carbon composite, and graphene; the second conductive substrate is selected from one of copper foam, nickel foam, carbon felt, carbon paper, and carbon cloth; optionally, the loading amount of the cathode electron carrier is 0.001-10 mg / cm 2 Thus, oxygen in the air can be reduced on the surface of the cathode to generate water.

[0012] According to an embodiment of the present application, the ion exchange membrane is selected from an anion exchange membrane or a cation exchange membrane.

[0013] According to an embodiment of the present application, the method further comprises: controlling the temperature of the anode electrolyte in the anode storage tank and the temperature of the cathode electrolyte in the cathode storage tank to be 20-100°C by a heating device. Thus, the method of the present application can have a higher yield of 5-hydroxymethylfurfural oxidation products.

[0014] According to an embodiment of the present application, the concentration of 5-hydroxymethylfurfural is 0.001-5 mol / L. Thus, a higher concentration of 5-hydroxymethylfurfural oxidation products can be obtained.

[0015] According to an embodiment of the present application, the anode electrolyte contains a first supporting electrolyte; optionally, the first supporting electrolyte is an inorganic base; the concentration of the first supporting electrolyte is 0.01-6 mol / L. Thus, the conductivity of the solution can be improved, and the reaction rate can be accelerated.

[0016] According to an embodiment of the present application, the concentration of the redox electrolyte is 0.001-4 mol / L; thus, the conductivity of the cathode electrolyte can be increased, and the further transfer of electrons to oxygen in the air can be promoted.

[0017] According to an embodiment of the present application, the catholyte further comprises a second supporting electrolyte; the second supporting electrolyte comprises an inorganic acid or an inorganic base; the concentration of the second supporting electrolyte is 0.01-6 mol / L. In this way, the electrical conductivity can be improved, and the reaction rate can be improved.

[0018] According to an embodiment of the present application, the resistance of the external load is 0-2000 ohms, and the output voltage of the flow-type fuel cell is 0-1 V; optionally, the 5-hydroxymethylfurfural is added to the anode discharge chamber in a fed-batch manner. In this way, good electricity generation and HMF oxidation effects can be obtained. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 is a schematic diagram of the structure of a flow-type fuel cell in one embodiment of the present application.

[0020] BRIEF DESCRIPTION OF DRAWINGS

[0021] 1-anode liquid storage tank, 2-anode discharge chamber, 3-anode graphite bipolar plate, 4-ion exchange membrane, 5-cathode graphite bipolar plate, 6-cathode discharge chamber, 7-external load, 8-cathode liquid storage tank. DETAILED DESCRIPTION

[0022] Embodiments of the present application are described in detail below. The embodiments described below are exemplary only, and are intended to explain the present application, but are not to be understood as limiting the present application. In the embodiments, specific technologies or conditions not described are performed according to technologies or conditions described in the literature in the art or according to product instructions. The reagents used are not described by the manufacturer, and are all conventional products that can be obtained commercially.

[0023] The present application provides a novel method for selective oxidation coupling of 5-hydroxymethylfurfural to produce electric energy, which comprises: adding an anolyte containing 5-hydroxymethylfurfural in an anode liquid storage tank to an anode discharge chamber of a flow-type fuel cell, and circulating back to the anode liquid storage tank; adding a catholyte containing a redox electrolyte in a cathode liquid storage tank to a cathode discharge chamber of a flow-type fuel cell, and circulating back to the cathode liquid storage tank; introducing air into the cathode discharge chamber and the cathode liquid storage tank; wherein the redox electrolyte comprises at least one of vanadyl sulfate, ferric chloride, ferric nitrate, ferric citrate, phosphomolybdic acid, phosphomolybdovanadic acid, copper chloride, and potassium ferricyanide; connecting the cathode and the anode of the flow-type fuel cell with an external load to form a loop, and oxidizing 5-hydroxymethylfurfural while generating electric energy. In this way, the oxidation reaction of 5-hydroxymethylfurfural is carried out in the form of a fuel cell, and 5-hydroxymethylfurfural can be oxidized to generate the corresponding product under mild conditions, specifically, 5-hydroxymethylfurfuric acid (HMFCA) or 2,5-furan dicarboxylic acid (FDCA) can be generated, and the co-production of electric energy is realized at the same time.

[0024] For the sake of understanding, the principles of the present application are briefly explained below:

[0025] The oxidation reaction of 5-hydroxymethylfurfural (HMF) involves electron transfer, and the oxidation reaction can occur as long as the oxidation-reduction potential of the oxidant is higher than that of the aldehyde group and the hydroxyl group of HMF, i.e. the reaction is thermodynamically feasible. However, the speed of the reaction depends on the kinetics of electron transfer. To improve the electron transfer rate, an electron carrier can be used to construct an electron transfer chain to realize step-by-step electron transfer, thereby improving the kinetic rate of electron transfer. On the other hand, the directional movement of electrons can form an electric current, so the oxidation reaction of HMF mediated by the electron carrier can be carried out in the form of a fuel cell. Not only can the oxidation of HMF be realized, but also the oxidation driving force and electron transfer rate can be regulated by adjusting the cathode electron carrier and external load, thereby better regulating the oxidation process. In particular, by selecting the anode electron carrier and electrolyte, the cathode electron carrier and electrolyte, and the output voltage of the battery (by adjusting the external load), the oxidation driving force can be regulated, thereby realizing the selective oxidation of HMF, such as oxidizing the hydroxyl group, the aldehyde group, or both to carboxyl group, thereby obtaining different oxidation products. The oxidation rate of HMF can also be regulated in the above-mentioned manner, while co-producing electric energy.

[0026] According to an embodiment of the present application, the method further comprises the step of assembling a liquid flow fuel cell, referring to Figure 1 The liquid flow fuel cell comprises an anode liquid storage tank 1, an anode discharge chamber 2, an anode, an anode graphite bipolar plate 3, an ion exchange membrane 4, a cathode graphite bipolar plate 5, a cathode, a cathode discharge chamber 6, an external load 7, and a cathode liquid storage tank 8. The ion exchange membrane 4 is located between the anode graphite bipolar plate 3 and the cathode graphite bipolar plate 5. The anode graphite bipolar plate 3 is located on the side of the ion exchange membrane 4 close to the anode discharge chamber 2, and the cathode graphite bipolar plate 5 is located on the side of the ion exchange membrane 4 close to the cathode discharge chamber 6. The anode graphite bipolar plate 3 is provided with a first recess, and the anode is arranged in the first recess and located on the side of the anode graphite bipolar plate 3 close to the anode discharge chamber 2. The cathode graphite bipolar plate 5 is provided with a second recess, and the cathode is arranged in the second recess and located on the side of the cathode graphite bipolar plate 5 close to the cathode discharge chamber 6. The anode liquid storage tank 1 is connected to the anode discharge chamber 2 through a pipeline, and the cathode liquid storage tank 8 is connected to the cathode discharge chamber 6 through a pipeline. The external load 7 is arranged outside the liquid flow fuel cell, and the cathode and the anode are connected to the external load 7. Thus, the 5-hydroxymethylfurfural in the anode discharge chamber 2 can be selectively oxidized to generate target products, and in the cathode discharge chamber 6, oxygen molecules in the air undergo a reduction reaction to generate water, while generating electric energy.

[0027] According to an embodiment of the present application, the anode is formed by loading anode electron carriers on a first conductive substrate; thus, the anode electrolyte containing 5-hydroxymethylfurfural can be oxidized on the surface of the anode to generate oxidation products by losing electrons.

[0028] According to an embodiment of the present application, the anode electron carriers are selected from at least one of silver oxide, copper oxide, nickel oxide, manganese dioxide, cobalt oxide, iron oxide, nickel phosphide, cobalt phosphide, nickel sulfide, cobalt sulfide, nickel boride, nickel nitride, tricobalt tetraoxide, nickel hydroxide, cobalt hydroxide, nickel oxyhydroxide, and cobalt oxyhydroxide; thus, these compounds have certain redox potentials, can oxidize aldehyde groups and / or hydroxyl groups, and are hardly soluble in water, which can avoid the separation of products from catalysts. Specifically, in the anode discharge chamber of the liquid flow fuel cell, the high-valence anode electron carriers oxidize HMF to generate HMFCA or FDCA, are reduced themselves, and quickly transfer electrons to the oxidized cathode electron carriers in the cathode discharge chamber through an external circuit to generate electric energy, at which time the anode electron carriers restore the high-valence state and continue to participate in the catalytic cycle.

[0029] According to an embodiment of the present application, the first conductive substrate is selected from one of foamed copper, foamed nickel, carbon felt, carbon paper, and carbon cloth; thus, these substrate materials have good electrical conductivity and porosity, and can provide abundant reaction sites for the loading and reaction of the anode electron carriers. In addition, the selection of the first conductive substrate material also needs to consider the acidity and alkalinity of the electrolyte, and the use of the above-mentioned materials as the first conductive substrate can avoid the dissolution and corrosion of the first conductive substrate.

[0030] According to some embodiments of the present application, the loading amount of the anode electron carriers is 0.001-10 mg / cm 2 ; thus, the electron transfer rate can be ensured to be high, which is beneficial to the generation of HMF oxidation products. If the loading amount is too small, the electron transfer rate will be too slow, the current will be too low, which is not conducive to the oxidation of HMF and the production of electric energy; if the loading amount is too large, raw materials will be wasted, and obvious shedding will occur during long-term operation.

[0031] In the process of loading the anode electron carriers on the first conductive substrate to form the anode, the loading method is not limited in the present application, for example, it can be coating, electrodeposition, in-situ growth, etc.

[0032] According to the embodiment of the present application, the cathode is formed by loading the cathode electron carrier on the second conductive substrate; thus, the electrons are transmitted to the cathode through the external circuit and are received by the cathode electron carrier. The cathode discharge chamber and the cathode liquid storage tank are both continuously connected with air, so that the cathode electron carrier and the redox electrolyte are oxidized and regenerated. By screening the cathode electron carrier, the oxygen in the air can be reduced to water. By adjusting the size of the external load, the output voltage and power of the battery can be adjusted, so as to adjust the transmission rate of the electrons. Therefore, the method provided by the present application can selectively oxidize 5-hydroxymethylfurfural and convert chemical energy into electrical energy.

[0033] According to some embodiments of the present application, the cathode electron carrier is selected from at least one of metal platinum, metal ruthenium, carbon black, iron phthalocyanine, iron-nitrogen-carbon composite, cobalt-nitrogen-carbon composite, and graphene; these compounds can promote the electron transmission kinetics by changing the valence state of the active center, thereby catalyzing the four-electron reduction of oxygen to generate water. Specifically, the cathode electron carrier reduced in the cathode discharge chamber is oxidized by the redox electrolyte or the air introduced, and the electrolyte can also be further oxidized and regenerated by contacting with the introduced air in the cathode liquid storage tank. Therefore, oxygen is the final electron acceptor, and the overall reaction is the oxidation of 5-hydroxymethylfurfural by oxygen to generate the corresponding product. In order to obtain a faster reaction rate and a higher battery power density, the preferred cathode electron carrier and redox electrolyte can reduce oxygen to water by four electrons.

[0034] According to some embodiments of the present application, the second conductive substrate is selected from one of foamed copper, foamed nickel, carbon felt, carbon paper, and carbon cloth; these compounds have good electrical conductivity and porosity, and the use of the above-mentioned compounds as the second conductive substrate can provide abundant reaction sites for the loading of the catalyst and the reaction. Moreover, the selection of the conductive substrate material also needs to consider the acidity and alkalinity of the electrolyte, and the use of the above-mentioned compounds as the second conductive substrate can also avoid the dissolution and corrosion of the second conductive substrate.

[0035] According to some embodiments of the present application, the loading amount of the cathode electron carrier is 0.001-10 mg / cm 2 . Thus, a high electron transmission rate can be ensured, which is beneficial to the generation of 5-hydroxymethylfurfural oxidation products. If the loading amount is too small, the electron transmission rate will be too slow, the current will be too low, which is not conducive to the oxidation of 5-hydroxymethylfurfural and the production of electrical energy; if the loading amount is too large, raw materials will be wasted, and obvious shedding will occur during long-term operation.

[0036] In the process of loading the cathode electron carrier on the second conductive substrate to form the cathode, the loading method is not limited in the present application, for example, it can be coating, electrodeposition, in-situ growth, etc.

[0037] According to an embodiment of the present application, the ion exchange membrane is selected from an anion exchange membrane or a cation exchange membrane. The cation exchange membrane includes but is not limited to a perfluorosulfonic acid membrane, and the anion exchange membrane includes but is not limited to a hydroxide ion exchange membrane.

[0038] The type and ion permeability of the ion exchange membrane significantly affect the internal resistance of the battery, and thus affect the electrode reaction rate. The selection of the ion exchange membrane is also related to the cathode electrolyte and the anode electrolyte used, and a person skilled in the art can select an appropriate ion exchange membrane type according to the use requirements.

[0039] According to an embodiment of the present application, the method further comprises: controlling the temperature of the anode electrolyte in the anode storage tank and the temperature of the cathode electrolyte in the cathode storage tank to be 20-100℃ by the heating device, which can be 20℃, 25℃, 30℃, 40℃, 50℃, 60℃, 70℃, 80℃, 90℃, 100℃, and preferably, the temperature of the anode electrolyte and the temperature of the cathode electrolyte can be controlled to be 20-60℃. The electrode reaction is significantly affected by the temperature, and increasing the temperature is beneficial to increasing the reaction rate on the electrode surface, the diffusion rate of the active material, and thus the electron transfer rate. However, 5-hydroxymethylfurfural can undergo various side reactions under alkaline conditions, such as condensation and other reactions of 5-hydroxymethylfurfural under the catalysis of alkali, to generate humus and other substances, and the generation rate of humus significantly increases at a higher temperature. The inventors have found that when the temperature of the anode electrolyte and the temperature of the cathode electrolyte are controlled within the above temperature range, the electron transfer rate is higher, which is beneficial to the generation of 5-hydroxymethylfurfural oxidation products and has less by-products. If the temperature of the anode electrolyte and the temperature of the cathode electrolyte are too low, the electron transfer rate is too low, which is not conducive to the generation of 5-hydroxymethylfurfural oxidation products; if the temperature of the anode electrolyte and the temperature of the cathode electrolyte are too high, too many by-products are generated.

[0040] According to an embodiment of the present application, the concentration of 5-hydroxymethylfurfural is 0.001-5mol / L, which can be 0.001mol / L, 0.01mol / L, 0.05mol / L, 0.1mol / L, 0.15mol / L, 0.2mol / L, 1mol / L, 2mol / L, 3mol / L, 4mol / L, 5mol / L. Preferably, the concentration of 5-hydroxymethylfurfural is 0.001-2mol / L. Thus, when the concentration of 5-hydroxymethylfurfural is within the above range, a higher oxidation product concentration can be obtained while reducing the generation of humus and other by-products. If the concentration of 5-hydroxymethylfurfural is too low, the concentration of 5-hydroxymethylfurfural oxidation products is too low; if the concentration of 5-hydroxymethylfurfural is too high, the degree of condensation or degradation of 5-hydroxymethylfurfural to generate humus also increases, resulting in too many by-products.

[0041] According to an embodiment of the present application, the anolyte contains a first supporting electrolyte; thereby, on one hand, the conductivity of the solution can be improved, and on the other hand, the reaction environment for the oxidation of HMF can be provided, and the reaction rate can be accelerated.

[0042] According to some embodiments of the present application, the first supporting electrolyte is an inorganic base, which includes but is not limited to potassium hydroxide.

[0043] According to some embodiments of the present application, the concentration of the first supporting electrolyte is 0.01-6 mol / L, for example, it can be 0.01 mol / L, 0.1 mol / L, 0.5 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, or 6 mol / L. Preferably, the concentration of the first supporting electrolyte is 0.01-4 mol / L. Thereby, the charge conduction rate of the electrolyte can be ensured to be high, and the reaction rate can be fast. If the concentration of the first supporting electrolyte is too low, the charge conduction rate of the electrolyte will be too low, resulting in a large internal resistance of the battery; if the concentration of the first supporting electrolyte is too high, the side reaction will be intense, resulting in a small yield of the target product, in addition, the high concentration of the base will also increase the corrosion of the electrode and the aging of the ion exchange membrane, reducing the service life of the electrode and the ion exchange membrane.

[0044] According to an embodiment of the present application, the concentration of the redox electrolyte is 0.001-4 mol / L, for example, it can be 0.001 mol / L, 0.37 mol / L, 0.8 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, or 4 mol / L; thereby, on one hand, these electrolytes can increase the conductivity of the catholyte, and on the other hand, these electrolytes can also act as redox electron carriers to promote the further transfer of electrons to the oxygen in the air.

[0045] According to some embodiments of the present application, the catholyte further contains a second supporting electrolyte; the second supporting electrolyte includes an inorganic acid or an inorganic base, the inorganic acid includes but is not limited to sulfuric acid; the concentration of the second supporting electrolyte is 0.01-6 mol / L, for example, it can be 0.01 mol / L, 0.5 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, 5 mol / L, or 6 mol / L. Thereby, the conductivity can be improved, and an acidic or basic environment can be provided for the electrode reaction, and the reaction rate can be improved.

[0046] According to embodiments of the present application, the resistance of the external load is 0-2000 ohms, and the output voltage of the liquid flow fuel cell is 0-1 V; connecting the external load is a prerequisite for forming a circuit and realizing the transfer of electrons from 5-hydroxymethylfurfural to oxygen in the air, otherwise the oxidation of 5-hydroxymethylfurfural cannot proceed. The size of the external load directly determines the speed of electron transfer. When the external load is 0 ohms, i.e. the battery is discharged in the form of a short circuit, the electron transfer rate is the fastest. When the resistance of the external load increases, the ohmic resistance of the electron transfer increases, and the oxidation rate of 5-hydroxymethylfurfural on the anode decreases. When the external load is infinite, i.e. in an open circuit state, no current is generated, electrons cannot be transferred to oxygen, and the HMF oxidation reaction cannot proceed. According to some embodiments of the present application, the preferred external load is 0-2000 ohms, so that the output voltage of the liquid flow fuel cell is 0-1 V, at which a good power generation and HMF oxidation effect can be obtained.

[0047] According to some specific embodiments of the present application, the output voltage can be stabilized by an electrochemical workstation, and the external load is automatically adjusted to ensure that the output voltage of the battery is stable at a set value, such as 0.7 V.

[0048] In some embodiments of the present application, the 5-hydroxymethylfurfural is added to the anode discharge chamber in a fed-batch manner. The fed-batch is to supplement 5-hydroxymethylfurfural to the anode discharge chamber, and to supplement multiple batches at a time, i.e. to supplement HMF to the anode discharge chamber after a period of time, and to supplement the first supporting electrolyte if necessary. In this way, on the one hand, the rate of HMF generating humus can be reduced, and on the other hand, the product concentration can be increased, and the product separation and purification cost can be reduced.

[0049] The present application will be described below with reference to specific embodiments, and it should be noted that these embodiments are only descriptive and do not limit the present application in any way.

[0050] Example 1

[0051] Screening of anode electron carriers and comparison of their discharge characteristics in liquid flow fuel cells.

[0052] Nickel sulfide, cobalt sulfide, nickel phosphide, cobalt phosphide, nickel chloride, silver oxide were prepared by electrodeposition, high temperature sintering, co-precipitation and other methods, and were uniformly loaded on the nickel foam to prepare anodes. The anode electrolyte contains 1 mol / L of potassium hydroxide as the first supporting electrolyte, and contains 0.1 mol / L of HMF. The carbon felt loaded with carbon black is used as the cathode, and 0.37 mol / L of vanadyl sulfate (pentavalent), i.e. (VO2)2SO4, is used as the redox electrolyte of the cathode electrolyte, and 2 mol / L of sulfuric acid is used as the second supporting electrolyte. Nafion115 membrane is used as the ion exchange membrane. After the battery device is assembled, the anode electrolyte and the cathode electrolyte are continuously pumped into the anode discharge chamber and the cathode discharge chamber, respectively, and are circulated back to the anode storage tank and the cathode storage tank, respectively.

[0053] The discharge characteristics of different anode electron carriers, open-circuit voltage, maximum output power density and product yield are shown in Table 1. As can be seen from Table 1, for the synthesis of HMFCA, the nickel foam loaded with silver oxide as the anode has the highest maximum power density and product yield. For the synthesis of FDCA, the battery with the nickel foam loaded with nickel sulfide as the anode has the highest maximum power density and FDCA yield, and is significantly better than other electrodes. It is shown that the nickel foam loaded with silver oxide and nickel sulfide is an excellent anode material for selective oxidation of HMF, and silver oxide and nickel sulfide are excellent anode electron carriers for promoting selective oxidation of HMF. At the same time, by selecting a suitable anode electron carrier, selective oxidation of HMF can be realized.

[0054] Table 1 HMF oxidation and power generation characteristics of different anode electron carriers

[0055]

[0056] Example 2

[0057] Different cathode redox electrolytes are screened, and the power generation characteristics and FDCA yield in the flow battery during HMF oxidation and synthesis of FDCA are compared.

[0058] The experimental process is same as Example 1. The nickel sulfide-loaded nickel foam is used as an anode, the carbon felt loaded with carbon black is used as a cathode, vanadyl sulfate (pentavalent), iron chloride, hydrogen peroxide, potassium permanganate and potassium dichromate are selected as cathode redox electrolytes or oxidants respectively, and the discharge performance is compared. The composition of the iron chloride electrolyte solution is 0.8 mol / L of iron chloride, and 0.5 mol / L of sulfuric acid is contained as a second supporting electrolyte. The composition of the vanadyl sulfate (pentavalent) is 0.37 mol / L of vanadyl sulfate (pentavalent), and 2 mol / L of sulfuric acid is contained as a second supporting electrolyte. The composition of the hydrogen peroxide electrolyte solution is 10% of hydrogen peroxide by mass fraction. The composition of the potassium permanganate and potassium dichromate electrolyte solution is 50 mmol / L of electrolyte concentration, and 2 mol / L of sulfuric acid is added as a second supporting electrolyte.

[0059] The discharge characteristics, open-circuit voltage, maximum power density and FDCA yield of the batteries using different cathode redox electrolytes are shown in Table 2. As shown in Table 2, the battery using vanadyl sulfate (pentavalent) as the cathode redox electrolyte can achieve a maximum FDCA yield of 95%, although the power density is not the maximum; the power density and FDCA yield of hydrogen peroxide are almost 0, which cannot realize effective oxidation of HMF, due to the large overpotential and slow electron transfer rate; when potassium permanganate is selected as the cathode redox electrolyte, the maximum power density is as high as 77.6 mW / cm 2 , but the manganese dioxide solid generated by the reduction of potassium permanganate in the process of long-time discharge can block the flow channel, resulting in the decrease of the external circuit current, the deterioration of the catalytic effect, and the decrease of the product yield; iron chloride and potassium dichromate can both realize the oxidation of HMF, but the yield and power density are relatively low. The reaction system disclosed in the present application can conveniently realize the regulation of the product yield and power generation performance by screening the cathode redox electrolyte.

[0060] Table 2 Discharge characteristics and FDCA yield of the battery using different cathode redox electrolytes or oxidants

[0061]

[0062] Example 3

[0063] Different cathode redox electrolytes are screened, and the power generation performance and product yield of the liquid flow fuel cell in the oxidation of HMF to generate HMFCA are compared.

[0064] The experimental process is the same as that of Example 1. The silver oxide-loaded nickel foam is used as the anode, the carbon felt loaded with carbon black is used as the cathode, and vanadyl sulfate (pentavalent), iron chloride, hydrogen peroxide, potassium permanganate, and potassium dichromate are respectively selected as the cathode redox electrolyte or oxidant to compare the discharge performance. The composition of the iron chloride electrolyte solution is 0.8 mol / L of iron chloride, and 0.5 mol / L of sulfuric acid is added as the second supporting electrolyte. The composition of the vanadyl sulfate (pentavalent) is 0.37 mol / L of vanadyl sulfate (pentavalent), and 2 mol / L of sulfuric acid is added as the second supporting electrolyte. The composition of the hydrogen peroxide electrolyte solution is 10% by mass of hydrogen peroxide. The composition of the potassium permanganate and potassium dichromate electrolyte solution is 50 mmol / L of electrolyte concentration, and 2 mol / L of sulfuric acid is added as the second supporting electrolyte.

[0065] The discharge characteristics of the batteries using different cathode redox electrolytes or oxidants, the open-circuit voltage, the maximum power density, and the HMFCA yield are shown in Table 3. As can be seen from Table 3, several cathode redox electrolytes or oxidants can be used to prepare HMFCA from HMF, but the hydrogen peroxide has the lowest power density and HMFCA yield due to the limited electron transfer rate on the electrode surface. The other cathode redox electrolytes or oxidants can achieve an HMFCA yield of more than 90%. When vanadyl sulfate is used, a maximum power density of 172.0 mW / cm 2 and an HMFCA yield of 97% can be obtained. In addition, when iron chloride, potassium permanganate, and potassium dichromate are used as the cathode redox electrolyte, high power density can be obtained while selectively oxidizing HMF to generate HMFCA. The above results further show that the oxidation of HMF can be conveniently regulated by selecting the anode electron carrier and the cathode redox electrolyte.

[0066] Table 3 Discharge characteristics and HMFCA yield of the batteries using different cathode redox electrolytes and oxidants

[0067]

[0068] Example 4

[0069] Effect of reaction conditions on the discharge characteristics of the flow-type fuel cell using vanadyl sulfate (pentavalent) as the cathode redox electrolyte and the generation of FDCA.

[0070] The experimental process is the same as that in Example 1. The nickel sulfide-loaded nickel foam is used as the anode, the carbon felt loaded with carbon black is used as the cathode, 0.37 mol / L vanadyl sulfate (pentavalent) is used as the cathode redox electrolyte, 2 mol / L sulfuric acid is used as the second supporting electrolyte, the reaction conditions are changed, including the HMF concentration, the potassium hydroxide concentration, the temperature, and the type of ion exchange membrane, and the changes of the maximum power density of the battery and the product yield are explored. The influence of the related parameters is shown in Table 4.

[0071] As shown in Table 4, when the HMF oxidation synthesis of FDCA is taken as the target, the maximum power density of the battery gradually increases with the increase of the HMF concentration, but the increasing amplitude gradually becomes smaller, when the substrate concentration increases to a certain extent, the substrate diffusion is no longer the limiting step of the reaction, and the power density depends on the kinetics on the electrode surface; increasing the potassium hydroxide concentration can increase the maximum power density of the battery, but the FDCA yield increases first and then decreases with the increase of the alkali concentration, and the highest FDCA yield is obtained at 1 mol / L potassium hydroxide concentration; increasing the battery temperature can also increase the maximum power density of the battery, but the FDCA yield continuously decreases with the increase of the temperature, and long-time discharge test shows that the increase of the potassium hydroxide concentration and the battery temperature can promote the polymerization of HMF to generate a large amount of humus, thereby reducing the yield of FDCA, and the promoting effect of the temperature on the humus is more significant than that of the alkali concentration. The above results show that the reaction system of the application can conveniently regulate the power density of the battery and the product yield by changing the reaction conditions.

[0072] Table 4 Influence of different operating conditions on the HMF oxidation synthesis of FDCA coupled power generation

[0073]

[0074] Example 5

[0075] Influence of reaction conditions on the discharge characteristics of the vanadyl sulfate (pentavalent) as the cathode redox electrolyte of the flow-type fuel cell and the generation of HMFCA

[0076] The experimental process is the same as that in Example 1. The nickel sulfide-loaded nickel foam is used as the anode, the carbon felt loaded with carbon black is used as the cathode, 0.37 mol / L vanadyl sulfate (pentavalent) is used as the cathode redox electrolyte, 2 mol / L sulfuric acid is used as the second supporting electrolyte, the reaction conditions are changed, including the HMF concentration, the potassium hydroxide concentration, the temperature, and the type of ion exchange membrane, and the changes of the maximum power density of the battery and the product yield are explored. The influence of the related parameters is shown in Table 4.

[0077] As can be seen from the table, when HMF is oxidized to synthesize HMFCA as the target, with the increase of the external load, i.e. the increase of the external output voltage, the HMFCA yield is obviously increased, because through the external output voltage, the selective oxidation of the anode electron carrier to HMF can be adjusted, the selectivity to HMFCA is increased, and then the HMFCA yield is improved; the maximum power density of the battery gradually increases with the increase of the HMF concentration; with the increase of the potassium hydroxide concentration, the maximum power density of the battery first increases and then decreases, and the highest power density 172.0 mW / cm 2 The change trend of the HMFCA yield is consistent with that of the power density, and under the condition of 1 mol / L potassium hydroxide, the highest HMFCA yield of 97% can be realized. Long-time discharge test shows that appropriately increasing the alkali concentration can promote the reaction, but too high alkali concentration can promote the polymerization of HMF to generate a large amount of humus, thereby reducing the HMFCA yield. It can be seen that the reaction system of the application can conveniently control the battery power density and product yield by changing the reaction conditions.

[0078] Table 5 Influence of different operation conditions on HMF oxidation to generate HMFCA coupled power generation

[0079]

[0080] Example 6

[0081] Effect of fed-batch operation on HMF oxidation to generate FDCA

[0082] The experimental process is the same as that in Example 1. The load nickel sulfide foamed nickel is used as the anode, the carbon felt loaded with carbon black is used as the cathode, 0.37 mol / L vanadyl sulfate (pentavalent) is used as the cathode redox electrolyte, and 2 mol / L sulfuric acid is used as the second supporting electrolyte. Discharge is carried out under short circuit condition. The anode is supplemented with 0.1 mol / L HMF every 60 minutes. The FDCA yield and concentration in the anode electrolyte measured at different times are shown in the table. It can be seen that with the increase of the feeding times, the FDCA concentration increases. After 10 times of feeding, the concentration of FDCA is 925.5 mmol / L, and the mass concentration is 144.5 g / L. The FDCA yield is 95.7% during the whole fed-batch operation. The above results show that a high FDCA concentration can be obtained by fed-batch operation, and a high FDCA selectivity can be maintained.

[0083] Table 6 Anode FDCA yield and concentration change table in fed-batch operation

[0084]

[0085]

[0086] Example 7

[0087] Effect of fed-batch operation on HMF oxidation to HMFCA

[0088] The experiment was carried out as in Example 1. The silver oxide-loaded nickel foam was used as the anode, the carbon felt loaded with carbon black was used as the cathode, 0.37 mol / L vanadyl sulfate (pentavalent) was used as the cathode redox electrolyte, and 2 mol / L sulfuric acid was used as the second supporting electrolyte. Discharge was carried out at an output voltage of 0.7 V. The anode was supplemented with 0.15 mol / L HMF every 60 minutes. The HMFCA yield and concentration in the anode electrolyte at different times are shown in Table 7. It can be seen that the HMFCA concentration increases with the increase of the number of feedings. After 5 feedings, the HMFCA concentration is 636.8 mmol / L, and the mass concentration is 90.5 g / L. The HMFCA yield in the entire feeding operation is 84.9%. From the above results, it can be seen that a high HMFCA concentration can be obtained by fed-batch operation, and a high HMFCA selectivity can be maintained.

[0089] Table 7 HMFCA yield and concentration in the anode in fed-batch operation at different times

[0090] Time (h) HMFCA concentration (mmol / L) HMFCA yield (%) 1 142.7 94.6％ 2 251.1 83.6％ 3 400.5 88.9％ 4 521.7 86.8％ 5 636.8 84.9％

[0091] It should be noted that in the present specification, the terms "first", "second" are used only for the purpose of description, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features.

[0092] In the description of the present specification, the description referring to the terms "one embodiment", "some embodiments", "an example", "a specific example", or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments or examples. Furthermore, the person skilled in the art can combine and combine the different embodiments or examples described in the present specification and the features of the different embodiments or examples without contradiction.

[0093] Although the embodiments of the present application have been shown and described above, it should be understood that the above embodiments are exemplary and cannot be understood as limiting the present application, and the person skilled in the art can make changes, modifications, replacements and variations to the above embodiments within the scope of the present application.

Claims

1. A process for the selective oxidative coupling of 5-hydroxymethylfurfural to electrical energy production, characterized in that, The method comprises: adding an anode electrolyte containing 5-hydroxymethylfurfural in an anode storage tank to an anode discharge chamber of a flow fuel cell and circulating back to the anode storage tank; adding a cathode electrolyte containing a redox electrolyte in a cathode storage tank to a cathode discharge chamber of a flow fuel cell and circulating back to the cathode storage tank; and introducing air into the cathode discharge chamber and the cathode storage tank; wherein the redox electrolyte is vanadyl sulfate; connecting the cathode and the anode of the flow fuel cell with an external load to form a loop, oxidizing 5-hydroxymethylfurfural and generating electric energy at the same time, The anode is formed by loading an anode electron carrier on a first conductive substrate; The anode electron carrier is selected from at least one of silver oxide and nickel sulfide; The concentration of the redox electrolyte is 0.001-4 mol / L.

2. The method of claim 1, wherein, The method further comprises the step of assembling a flow fuel cell, which comprises an anode storage tank, an anode discharge chamber, an anode, an anode graphite bipolar plate, an ion exchange membrane, a cathode graphite bipolar plate, a cathode, a cathode discharge chamber, an external load and a cathode storage tank; The ion exchange membrane is located between the anode graphite bipolar plate and the cathode graphite bipolar plate; the anode graphite bipolar plate is located on the side of the ion exchange membrane close to the anode discharge chamber, and the cathode graphite bipolar plate is located on the side of the ion exchange membrane close to the cathode discharge chamber; The anode graphite bipolar plate is provided with a first recess, and the anode is arranged in the first recess, and the anode is located on the side of the anode graphite bipolar plate close to the anode discharge chamber; The cathode graphite bipolar plate is provided with a second recess, and the cathode is arranged in the second recess, and the cathode is located on the side of the cathode graphite bipolar plate close to the cathode discharge chamber; The anode storage tank is connected to the anode discharge chamber through a pipeline, and the cathode storage tank is connected to the cathode discharge chamber through a pipeline; The external load is arranged outside the flow fuel cell, and the cathode and the anode are connected with the external load respectively.

3. The method of claim 1, wherein, The first conductive substrate is selected from one of foamed copper, foamed nickel, carbon felt, carbon paper and carbon cloth; Optionally, the loading of the anodic electron carrier is 0.001-10 mg / cm 2 .

4. The method of claim 1, wherein, The cathode is formed by loading a cathode electron carrier on a second conductive substrate; The cathode electron carrier is selected from at least one of metal platinum, metal ruthenium, carbon black, iron phthalocyanine, iron-nitrogen-carbon composite, cobalt-nitrogen-carbon composite and graphene; The second conductive substrate is selected from one of foamed copper, foamed nickel, carbon felt, carbon paper and carbon cloth; Optionally, the cathode electron carrier has a loading of 0.001-10 mg / cm 2 .

5. The method of claim 2, wherein, The ion exchange membrane is selected from an anion exchange membrane or a cation exchange membrane.

6. The method of claim 1, wherein, The method further comprises: controlling the temperature of the anode electrolyte in the anode storage tank and the temperature of the cathode electrolyte in the cathode storage tank to be 20-100℃ by a heating device.

7. The method of claim 1, wherein, The concentration of 5-hydroxymethylfurfural is 0.001-5 mol / L.

8. The method of claim 1, wherein, The anode electrolyte contains a first supporting electrolyte; Optionally, the first supporting electrolyte is an inorganic base; The concentration of the first supporting electrolyte is 0.01-6 mol / L.

9. The method of claim 1, wherein, The cathode electrolyte further comprises a second supporting electrolyte; The second supporting electrolyte comprises an inorganic acid or an inorganic base; The concentration of the second supporting electrolyte is 0.01-6 mol / L.

10. The method of claim 1, wherein, The resistance of the external load is 0-2000 ohms, and the output voltage of the liquid flow fuel cell is 0-1V. Optionally, the 5-hydroxymethylfurfural is added to the anode discharge chamber in a fed-batch form.

Images