Photo-assisted biomass conversion method and application thereof in hydrogen production

Abstract

The invention discloses a photo-assisted biomass conversion method and application of the photo-assisted biomass conversion method in hydrogen production. Belongs to the technical field of solar photocatalysis. The conversion method comprises the following steps: mixing an aqueous dispersion with illumination; dispersomes of the mixed aqueous dispersion comprise heteropoly acid and biomass. According to the conversion method, protons in the biomass can be combined with heteropolyacid to form heteropolyblue on the premise that external heat energy is not applied and a noble metal catalyst is not added, the method is simple, energy is saved, the cost is low, and a basis can be provided for subsequent hydrogen production. The invention also provides a method for producing hydrogen from biomass, which is implemented by using the preparation method.

Description

Technical Field

[0001] The present invention relates to the field of solar energy photocatalysis technology, and in particular to a light-assisted biomass conversion method and an application thereof in hydrogen production. Background Art

[0002] Traditional biomass hydrogen production and biomass conversion technologies require high-heat and high-pressure energy input or oxygen-assisted conversion to obtain the target hydrogen production and highly selective generation of small-molecule carbon products. Even so, over-oxidation is still inevitable, and H2 is often produced along with by-products CO2 and CO, resulting in energy waste and affecting the purity of hydrogen. In the traditional biomass hydrogen production process, since H2 is further decomposed from small-molecule carbon products, in terms of the choice of target products, only one of hydrogen and small-molecule carbon products can be selected.

[0003] How to control the degree of oxidation so that biomass can be converted into small molecule compounds with high added value, and at the same time generate intermediate products that can further produce hydrogen, so as to improve the purity of hydrogen and enhance the value of biomass conversion, is an important research direction for researchers in this field. Summary of the invention

[0004] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention proposes a light-assisted biomass conversion method, which can combine protons and heteropoly acids in biomass to form heteropoly blue without applying external heat energy and adding precious metal catalysts, and simultaneously generate small molecule products with high added value; the method is simple, energy-saving, low-cost, and can provide a basis for subsequent hydrogen production.

[0005] The present invention also provides an application of the above conversion method, specifically a method for producing hydrogen from biomass.

[0006] According to an embodiment of the first aspect of the present invention, there is provided a light-assisted biomass conversion method, the conversion method comprising irradiating a mixed aqueous dispersion with light;

[0007] The dispersoid of the mixed aqueous dispersion includes heteropoly acid (HPA for short) and biomass.

[0008] The mechanism of the method is as follows:

[0009]

[0010] The further and more detailed mechanism is as follows:

[0011] Heteropolyacid absorbs light energy, undergoes photogenerated electron transitions, and combines with protons to generate heteropoly blue (HPB), which simultaneously oxidizes biomass and water and stores electrons. At the same time, water is oxidized to produce hydroxyl groups that further attack biomass, causing it to break down into small molecular products.

[0012] In the above formula, CH2O2 (formic acid) is illustrative and is the main small molecule product. In actual production, other small molecule products such as arabinose, glyceraldehyde, ethanolaldehyde, formaldehyde, etc. may also be generated; but no gaseous carbon-containing products are produced, that is, the small molecule products are not further oxidized.

[0013] The preparation method according to the embodiment of the present invention has at least the following beneficial effects:

[0014] Without applying external heat energy, high temperature and high pressure reaction conditions, and without adding additives such as heavy precious metal catalysts, the protons in the biomass are combined with the heteropoly acid to form heteropoly blue, and at the same time, formic acid with economic value is formed; the conversion method provided by the present invention has many advantages such as simple and mild conditions, energy saving, low cost, environmental friendliness, and high product value.

[0015] In addition, the present invention uses light-assisted biomass conversion, the limitation of light energy, and the use of HPA can significantly inhibit the continued oxidation of small molecule products, that is, biomass can only be converted into small molecule products with high added value, and will not continue to oxidize to generate gas products such as carbon dioxide.

[0016] Heteropoly blue is a stable, non-toxic, green and mobile hydrogen energy liquid carrier, which is convenient for long-term transportation and storage. That is, the conversion method provided by the present invention also provides a basis for subsequent hydrogen production.

[0017] According to some embodiments of the invention, the biomass comprises at least one of glucose, fructose, sucrose, starch, cellulose and lignin.

[0018] According to some embodiments of the present invention, in the mixed aqueous dispersion, the concentration of the biomass is 0.02-0.5 M. For example, it may be about 0.05 M, 0.1 M, 0.2 M, 0.3 M or about 0.4 M.

[0019] According to some embodiments of the present invention, the structure of the heteropolyacid is a Keggin structure or a Dawson structure.

[0020] According to some embodiments of the present invention, the heteropolyacid includes at least one of an unmodified tungsten-based heteropolyacid and a transition metal atom-doped tungsten-based heteropolyacid. The oxidizing energy of the heteropolyacid selected by the present invention is suitable, and it can obtain enough protons from the biomass, but at the same time it will not over-oxidize the biomass, so the potential required for the subsequent electrolysis of the generated heteropoly blue to generate hydrogen is lower, and the hydrogen purity is higher. If the heteropolyacid has a higher proton reserve, the potential required for the subsequent electrolysis of the heteropoly blue is lower, otherwise it is higher. Compared with other types of heteropolyacids, the transition metal atom-doped tungsten-based heteropolyacid has a higher oxidizability as a whole because the transition metal atom has a high oxidizability.

[0021] According to some embodiments of the present invention, the synthesis process of the transition metal atom-doped tungsten-based heteropoly acid comprises the following steps:

[0022] D1. reacting a tungsten precursor, a central atomic source and an acid to obtain a vacancy tungsten-based heteropoly acid;

[0023] D2. reacting the vacant tungsten-based heteropoly acid with a transition metal source.

[0024] D3. The mixture obtained in step D2 is mixed with potassium chloride to obtain a precipitate;

[0025] dissolving the obtained precipitate in water; and extracting the aqueous solution of the dissolved precipitate with ether under acidic conditions;

[0026] The obtained loaded organic phase was distilled under reduced pressure.

[0027] The above synthesis method utilizes vacancy guidance to synthesize a tungsten-based heteropoly acid embedded with a highly oxidizable transition metal atom, wherein the transition metal atom acts as a coordinating atom of the heteropoly acid and has the effect of enhancing the oxidizability of the heteropoly acid.

[0028] This synthesis method does not involve the use of precious metal elements.

[0029] In step D3, the process of obtaining the precipitate is essentially a process of providing the heteropolyacid anion with an anti-cation to precipitate it and separate it from the solution.

[0030] The process of ether extraction is actually a process of purifying the solid product and also a process of cation replacement, specifically replacing the potassium ions with corresponding hydrogen ions.

[0031] According to some embodiments of the present invention, in step D1, the tungsten precursor includes sodium tungstate.

[0032] According to some embodiments of the present invention, in step D1, the central atom source includes at least one of sodium silicate and phosphoric acid, and specifically, silicon or phosphorus is used as the central atom.

[0033] According to some embodiments of the present invention, in step D1, the molar ratio of the tungsten precursor to the central atom source is 5 to 12:1 (calculated as the molar ratio of tungsten atoms to central atoms), for example, about 6:1, 7:1, 8:1, 9:1, 10:1, 11:1 or about 12:1.

[0034] According to some embodiments of the present invention, in step D1, the acid includes at least one of hydrochloric acid and glacial acetic acid.

[0035] According to some embodiments of the present invention, in step D1, the concentration of the acid is 5 to 20 M. For example, it can be about 5.5 to 6.5 M hydrochloric acid aqueous solution; or it can be 15 to 20 M acetic acid (or glacial acetic acid).

[0036] According to some embodiments of the present invention, in step D1, the molar ratio of the tungsten precursor to the acid is 0.5 to 1.1:1, for example, about 0.6:1, 0.7:1, 0.8:1, 0.9:1 or about 1.0:1.

[0037] According to some embodiments of the present invention, in the mixed system of step D1, the feed concentration of the tungsten precursor is 0.5-1 g / mL. For example, it can be about 0.6 g / mL, 0.7 g / mL, 0.8 g / mL or about 0.9 g / mL. That is, in actual production, water is also added to the reaction to better disperse the tungsten precursor and the central atomic source.

[0038] According to some embodiments of the present invention, step D1 further includes solid separation and drying performed sequentially after the reaction.

[0039] According to some embodiments of the present invention, in step D2, the transition metal source includes at least one of sodium molybdate and sodium vanadate.

[0040] According to some embodiments of the present invention, in step D2, the mass ratio of the transition metal source to the vacant tungsten-based heteropoly acid is 1:2 to 80. For example, it can be about 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10, 1:20, 1:30, 1:40, 1:50, 1:60, 1:70 or about 1:75.

[0041] According to some embodiments of the present invention, step D2 is performed in an acidic solution. The acid acts as a pH regulator to maintain the pH of step D2 at 4 to 7; for example, it can be about 4.5, 5, 5.5, 6 or about 6.5. In actual production, if the acid is too strong, a certain amount of alkaline substances, such as sodium carbonate, can also be added to adjust the pH to the above range.

[0042] According to some embodiments of the present invention, in the reaction system of step D2, the feed concentration of the vacant tungsten-based heteropoly acid is 0.15 to 0.35 g / mL. For example, it can be about 0.18 g / mL, 0.2 g / mL, 0.23 g / mL, 0.25 g / mL, 0.28 g / mL, 0.3 g / mL or about 0.32 g / mL. Part of the liquid is provided by the acid, and the remaining liquid is supplemented by adding water.

[0043] According to some embodiments of the present invention, in step D3, the process of dissolving the obtained precipitate in water is not strictly limited to the solid-liquid ratio, as long as it can be fully dissolved and the concentration can be kept as high as possible. For example, water can be gradually added to obtain an aqueous solution with a concentration close to saturation.

[0044] According to some embodiments of the present invention, in step D3, during the ether extraction, the O / A ratio is 1:1 to 3. For example, it can be about 1:2.

[0045] According to some embodiments of the present invention, the acidic condition is created by adding hydrochloric acid. The concentration of the hydrochloric acid used is 11.5-12.5 mol / L. In step D3, the mass of the precipitate and the volume ratio of the acid added to create the acidic condition is 1 g: 3-7 mL. For example, it can be about 1 g: 4 mL, 1 g: 5 mL, 1 g: 6 mL or about 1 g: 6.5 mL.

[0046] According to some embodiments of the present invention, the heteropoly acid includes at least one of vanadium-doped silicotungstic acid, molybdenum ...phosphotungstic acid, vanadium-doped phosphotungstic acid, and vanadium-molybdenum co-doped silicotungstic acid.

[0047] According to some embodiments of the present invention, in the mixed aqueous dispersion, the concentration of the heteropoly acid is ≥ 0.1 M. In actual production, if the usage ratio of heteropoly acid to biomass is increased, the conversion efficiency of biomass raw materials can be improved to a certain extent.

[0048] According to some embodiments of the present invention, in the mixed aqueous dispersion, the concentration of the heteropoly acid is 0.1 to 0.3 M. For example, it may be about 0.15 M, 0.2 M or about 0.25 M. Within this concentration range, both economy and operability can be met. If the actual production equipment is upgraded or the conversion efficiency of biomass needs to be improved in a short period of time, exploration outside this range can also be carried out.

[0049] According to some embodiments of the present invention, the duration of the illumination is 16 to 36 hours. For example, it can be about 20 hours, 22 hours, 24 hours, 26 hours, 28 hours, 30 hours, 32 hours or about 36 hours. When the illumination intensity, biomass concentration, etc. remain unchanged, within this time range, as the illumination time increases, the conversion efficiency of biomass increases, but after more than 36 hours, the conversion efficiency remains almost unchanged.

[0050] According to some embodiments of the present invention, the light source used for the illumination includes light with a wavelength of ≤400nm. That is, the light that can actually assist the process of converting the biomass into small molecule compounds is ultraviolet light. In actual production, the conversion efficiency of the biomass can be adjusted by adjusting the intensity of the ultraviolet light in the light source.

[0051] According to some embodiments of the present invention, the light source used for the illumination includes full-spectrum sunlight or simulated sunlight. The simulated sunlight may be a full-spectrum xenon lamp. More specifically, the power of the full-spectrum xenon lamp is 250 to 350 W; for example, it may be about 300 W. The current of the full-spectrum xenon lamp is 15 to 25 A; for example, it may be about 20 A.

[0052] According to some embodiments of the present invention, in the conversion method, the conversion rate of the biomass into formic acid is ≥1.3%; for example, it can be about 1.5%, 2.0%, 2.5%, 3.0%, 3.5% or about 4.0% (the conversion rate here is the conversion rate of a single cycle). Specifically, when the biomass is glucose, and after 14 light cycles, the conversion rate of formic acid is ≥50%, for example, it can be about 55%, 56%, 57% or about 60%. It can be seen that the method provided by the present invention has the function of converting biomass into methanol in a targeted manner, and the conversion rate and selectivity are high.

[0053] According to some embodiments of the present invention, the conversion method is carried out in an atmosphere isolated from oxygen. That is, the conversion method does not require additional introduction of oxygen and sacrificial agents; the reaction conditions are simple and the cost is low.

[0054] According to some embodiments of the present invention, the conversion method comprises the following steps:

[0055] S1. Synthesis of transition metal atom-doped tungsten-based heteropolyacids;

[0056] S2. irradiating the mixed aqueous dispersion with light.

[0057] For the specific process of step S1, please refer to steps D1 to D3 of the synthesis process.

[0058] According to an embodiment of the second aspect of the present invention, a method for producing hydrogen from biomass is provided, the method comprising electrolyzing a mixture obtained by the conversion method described in the embodiment of the first aspect of the present invention.

[0059] The mechanism of the method is as follows:

[0060]

[0061] The generated heteropolyacid can be recycled and reused to participate in the conversion method and promote the conversion of the biomass into small molecule products.

[0062] The method according to the embodiment of the present invention has at least the following beneficial effects:

[0063] Objectively speaking, the method for producing hydrogen from biomass provided by the present invention is a process of using heteropolyacid as a catalyst to photocatalytically decompose biomass to generate formic acid (small molecule product) and hydrogen.

[0064] In traditional technology, biomass hydrogen production technology has the limitations of high energy consumption, low production capacity and excessive oxidation. The method provided by the present invention breaks the above limitations, uses solar energy instead of thermal energy, and uses heteropolyacids as photocatalytic hydrogen storage mediators to achieve the simultaneous conversion of biomass into hydrogen and small molecule carbon products. Heteropolyacids selectively convert biomass into high-value small molecule products, and at the same time, heteropolyacids are reduced to heteropoly blue to achieve the purpose of hydrogen storage. Heteropoly blue can extract hydrogen under the low bias generated by small solar PV panels, or under the spontaneous catalysis of platinum carbon catalysts. Regardless of the method, it has the characteristics of simplicity, low cost, mild conditions, and green environmental protection. The hydrogen produced is of high purity and is free of other impurity gas pollution. After hydrogen is extracted from heteropoly blue, it becomes heteropolyacid for the next round of recycling. The entire technology chain only inputs solar energy and biomass, and outputs high-value small molecule carbon products and pure green hydrogen. Small molecule carbon products can be used as biochemical raw materials or as organic hydrogen storage carriers.

[0065] The method provided by the present invention has high energy efficiency, good selectivity, mild conditions and is environmentally friendly. At the same time, it provides a new method and technology for solar photocatalytic biomass conversion hydrogen storage and production.

[0066] According to some embodiments of the invention, the electrolyzing comprises using the mixture as an anolyte.

[0067] According to some embodiments of the present invention, the electrolysis requires the cooperation of a cathode liquid. The cathode liquid is a phosphoric acid aqueous solution. The concentration of the phosphoric acid aqueous solution is 1 to 3 M. For example, it can be about 1.5 M, 2.0 M or about 2.5 M.

[0068] According to some embodiments of the present invention, during the electrolysis process, the current reaches 50 mA cm -1 When the working potential is ≤0.6 V vs. RHE, for example, it may be about 0.58 V vs. RHE.

[0069] According to some embodiments of the present invention, during the electrolysis process, the current reaches 100 mA cm -1 When the working potential is ≤0.65 V vs. RHE, for example, it may be about 0.62 V vs. RHE.

[0070] According to the above correspondence between voltage and current, it can be known that in the method provided by the present invention, the required voltage is relatively low, and while extracting hydrogen from heteropoly blue, the small molecular carbon products such as formic acid obtained by the conversion method can be avoided from being destroyed (generating gaseous by-products); thereby, higher purity hydrogen can be obtained; and the obtained hydrogen does not need to be subjected to additional purification treatment.

[0071] According to some embodiments of the present invention, the electrolysis is performed in an oxygen-free environment.

[0072] According to some embodiments of the present invention, in the method, the heteropoly acid can be reused, and the catalytic activity remains substantially unchanged within 300 hours of repeated use, that is, the heteropoly acid hardly deteriorates within the service life.

[0073] A system for producing hydrogen from biomass for implementing the method described in the second aspect of the present invention comprises a photocatalytic unit and an electrolytic unit;

[0074] The photocatalytic unit comprises a reaction pool which is airtight and light-transmissive;

[0075] The electrolysis unit comprises an electrolytic cell, a power source, an anode and a cathode; the power source is connected to the anode and the cathode respectively; the anode and the cathode are arranged in the electrolytic cell;

[0076] The electrolytic cell and the reaction cell are connected via a valve.

[0077] According to some embodiments of the present invention, the reaction pool is made of quartz glass.

[0078] According to some embodiments of the present invention, the power source comprises a PV panel (ie, a solar panel), thereby further utilizing solar energy without the need to input additional electrical energy.

[0079] According to some embodiments of the present invention, the anode is carbon felt, and the carbon felt is hydrophilic.

[0080] According to some embodiments of the present invention, the cathode includes a Pt electrode, a Pt / C electrode, or a counter electrode carrying a HER catalyst.

[0081] According to some embodiments of the present invention, the electrolytic cell comprises an anode cell and a cathode cell; the anode is arranged in the anode cell, and the cathode is arranged in the cathode cell. Furthermore, the reaction cell is connected to the anode cell in the electrolytic cell.

[0082] According to some embodiments of the present invention, the anode liquid is provided in the anode cell.

[0083] According to some embodiments of the present invention, a cathode liquid is provided in the cathode cell. The cathode liquid is a phosphoric acid aqueous solution. The concentration of the phosphoric acid aqueous solution is 1 to 3 M. For example, it can be about 1.0 M, 1.5 M, 2.0 M or about 2.5 M.

[0084] According to some embodiments of the present invention, the anode cell and the cathode cell are separated by a proton exchange membrane.

[0085] According to some embodiments of the present invention, the system further comprises a flow pump, thereby realizing the process of transferring the material in the reaction tank to the anode tank and transferring the mixed water dispersion to the reaction tank.

[0086] If there is no special explanation, the actual meaning of “about” in the present invention is that the error is allowed to be within the range of ±2%, for example, about 100 is actually 100±2%×100.

[0087] Unless otherwise specified, “between” in the present invention includes the number itself, for example, “between 2 and 3” includes the endpoint values ​​2 and 3.

[0088] Other features and advantages of the present invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0089] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0090] Figure 1 It is a schematic flow chart of the method for converting heteropoly blue and the method for producing hydrogen from biomass in the embodiments of the present invention.

[0091] Figure 2 It is the infrared spectrum of the sodium tungstate used in the embodiment of the present invention and the transition metal atom-doped tungsten-based heteropoly acid synthesized in embodiments 1 to 5.

[0092] Figure 3 This is the distribution diagram of glucose conversion products after 14 cycles in Example 5.

[0093] Figure 4 It is the current-voltage curve of electrolyzing heteropoly blue in step S3 of Example 1 and Comparative Examples 1-2. DETAILED DESCRIPTION

[0094] The following will be combined with the embodiments to clearly and completely describe the concept of the present invention and the technical effects produced, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0095] In the description of the present invention, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0096] Example 1

[0097] refer to Figure 1 This example provides a light-assisted biomass conversion method, and based on the conversion method, provides a method for producing hydrogen from biomass:

[0098] The steps of the light-assisted biomass conversion method are as follows:

[0099] S1. Synthesis of transition metal atom-doped tungsten-based heteropolyacid:

[0100] S1a. 182 g of sodium tungstate and 11 g of sodium silicate were dissolved in 200 mL of water; 130 mL of 6 M hydrochloric acid was added thereto; the resulting mixture was boiled for 1 h, filtered and dried to form a vacancy tungsten-based heteropoly acid.

[0101] S1b. Dissolve 1.9 g of sodium vanadate in 300 mL of water, add 145 g of the lacunatized tungsten-based heteropoly acid obtained in step S1a, and then add 185 mL of 6M sulfuric acid.

[0102] The resulting mixture was stirred for 45 min.

[0103] Then, solid potassium carbonate was added thereto to adjust the pH value to 6-7.

[0104] S1c. Add 80g of solid potassium chloride to the mixture obtained in step S1b to precipitate orange potassium salt (vanadium-doped potassium silicotungstate), dissolve the obtained solid in water, and finally extract the obtained aqueous solution with ether under acidic conditions; and obtain purified vanadium-doped silicotungstic acid (heteropolyacid) by vacuum distillation of the obtained organic phase. The O / A ratio of the extraction process is about 1:2; the acid added under acidic conditions is 12M hydrochloric acid, and the mass volume ratio of the added amount to the orange potassium salt is 1g:3.5mL.

[0105] S2. Light-assisted conversion of biomass to generate heteropoly blue and small molecule products:

[0106] S2a prepares a mixed aqueous solution, wherein the solute is 0.1M vanadium-doped tungsten-based heteropoly acid obtained in step S1, and 0.1M glucose;

[0107] S2b. Full spectrum illumination of the mixed aqueous solution obtained in step S2a for 16 hours. Before the reaction, an inert gas was introduced to exhaust the air and the reaction was sealed. The light source used for full spectrum illumination was a full spectrum xenon lamp with a current of 20A and a power of 300W.

[0108] In this process, part of the biomass is converted into formic acid products, and the heteropoly acid is reduced to heteropoly blue to store hydrogen.

[0109] The method for producing hydrogen from biomass comprises the following specific steps:

[0110] After step S2, the following step S3 is performed:

[0111] S3. The liquid mixture obtained in step S2 is transferred to an electrolytic cell as an anode liquid for electrolysis.

[0112] During the electrolysis process, carbon felt is used as the working electrode (anode), platinum sheet is used as the counter electrode (cathode), and 1M phosphoric acid is used as the cathode liquid. The weak bias voltage generated by a small PV solar panel can meet the reaction requirements, and formic acid is not consumed. After the hydrogen production reaction is completed, the heteropoly blue is converted back into heteropoly acid for the next round of photocatalytic cycle.

[0113] In this case, the system used for biomass hydrogen production includes a photocatalytic unit and an electrolytic unit;

[0114] The photocatalytic unit includes a sealed and light-transmissive reaction pool made of glass, in which the mixed aqueous solution obtained in step S1 is placed during use.

[0115] The electrolysis unit includes an electrolytic cell, a power source (PV solar panel), an anode (carbon felt) and a cathode (platinum sheet); the power source is connected to the anode and the cathode respectively;

[0116] The electrolytic cell comprises an anode cell and a cathode cell separated by a proton exchange membrane; wherein the anode cell contains an anode liquid, and the cathode cell contains cathode liquid; the anode cell and the reaction cell of the electrolytic cell are connected through a valve, wherein the liquid is transferred under the action of a flow pump.

[0117] Example 2

[0118] This example provides a method for preparing heteropoly blue, and based on the preparation method, provides a method for producing hydrogen from biomass:

[0119] The steps of the heteropoly blue hydrogen storage method are as follows:

[0120] S1. Synthesis of transition metal atom-doped tungsten-based heteropolyacid:

[0121] S1a. 182 g of sodium tungstate and 11 g of sodium silicate were dissolved in 200 mL of water; 130 mL of 6 M hydrochloric acid was added thereto; the resulting mixture was boiled for 1 h, filtered and dried to form a vacant tungsten-based heteropoly acid (vacant silicotungstic acid).

[0122] S1b. 8 g of sodium molybdate was dissolved in 70 mL of water, and 30 mL of 4 M HCl aqueous solution was added, and then 30 g of the vacant tungsten-based heteropoly acid obtained in step S1a was added thereto.

[0123] The resulting mixture was stirred for 45 min.

[0124] S1c. Add 14 g of solid potassium chloride to the mixture obtained in step S1b to precipitate an orange potassium salt (molybdenum-doped potassium silicotungstate), which is then redissolved and extracted (the dissolution and extraction operations are the same as in Example 1) to obtain a purified heteropolyacid (molybdenum-doped silicotungstic acid).

[0125] S2. Light-assisted conversion of biomass to produce heteropoly blue and small molecule products:

[0126] S2a prepares a mixed aqueous solution, wherein the solute is 0.1M molybdenum-doped tungsten-based heteropoly acid obtained in step S1, and 0.1M glucose;

[0127] S2b. Full spectrum illumination of the mixed aqueous solution obtained in step S2a for 16 hours. Before the reaction, inert gas was introduced to exhaust the air and the reaction was sealed. The light source used was the same as in Example 1.

[0128] In this process, part of the biomass is converted into formic acid products, and the heteropoly acid is reduced to heteropoly blue to store hydrogen.

[0129] The method for producing hydrogen from biomass comprises the following specific steps:

[0130] After step S2, the following step S3 is performed:

[0131] S3. The liquid mixture obtained in step S2 is transferred to an electrolytic cell as an anode liquid for electrolysis.

[0132] During the electrolysis process, carbon felt is used as the working electrode (anode), platinum sheet is used as the counter electrode (cathode), and 1M phosphoric acid is used as the cathode liquid. The weak bias voltage generated by a small PV solar panel can meet the reaction requirements, and formic acid is not consumed. After the hydrogen production reaction is completed, the heteropoly blue is converted back into heteropoly acid for the next round of photocatalytic cycle.

[0133] In this example, the system for producing hydrogen from biomass is the same as that in Example 1.

[0134] Example 3

[0135] This example provides a method for preparing heteropoly blue, and based on the preparation method, provides a method for producing hydrogen from biomass:

[0136] Wherein, the preparation method of heteropoly blue comprises the following steps:

[0137] S1. Synthesis of transition metal atom-doped tungsten-based heteropolyacid:

[0138] S1a. Dissolve 120g of sodium tungstate in 150mL of water; add 3mL of phosphoric acid (about 14.6M) and 22mL of glacial acetic acid (about 17.5M) thereto in sequence, stir (mix evenly) and filter to obtain the vacant tungsten-based heteropoly acid.

[0139] S1b. Mix 20 mL of 1M sodium molybdate aqueous solution and 16 mL of 1M hydrochloric acid aqueous solution, and add 11 g of vacant tungsten-based heteropoly acid thereto; add 12 mL of 1M hydrochloric acid dropwise to adjust the solution pH to 6 to 6.5.

[0140] S1c. Add 15 g of solid potassium chloride precipitate to the mixture obtained in step S1b, redissolve and extract (the specific operation is the same as in the embodiment) to obtain purified heteropolyacid (molybdenum-doped phosphotungstic acid).

[0141] S2. Light-assisted conversion of biomass to generate heteropoly blue and small molecule products:

[0142] S2a prepares a mixed aqueous solution, wherein the solute is 0.1M molybdenum-doped tungsten-based heteropoly acid obtained in step S1, and 0.1M glucose;

[0143] S2b. Full spectrum illumination of the mixed aqueous solution obtained in step S2a for 16 seconds. Before the reaction, an inert gas was introduced to exhaust the air and the reaction was sealed. The light source used was the same as in Example 1.

[0144] In this process, part of the biomass is converted into formic acid products, and the heteropoly acid is reduced to heteropoly blue to store hydrogen.

[0145] The method for producing hydrogen from biomass comprises the following specific steps:

[0146] After step S2, the following step S3 is performed:

[0147] S3. The liquid mixture obtained in step S2 is transferred to an electrolytic cell as an anode liquid for electrolysis.

[0148] During the electrolysis process, carbon felt is used as the working electrode (anode), platinum sheet is used as the counter electrode (cathode), and 1M phosphoric acid is used as the cathode liquid. The weak bias voltage generated by a small PV solar panel can meet the reaction requirements, and formic acid is not consumed. After the hydrogen production reaction is completed, the heteropoly blue is converted back into heteropoly acid for the next round of photocatalytic cycle.

[0149] In this example, the system for producing hydrogen from biomass is different from that in Example 1 in that:

[0150] The concentration of the catholyte was 2M.

[0151] Example 4

[0152] This example provides a method for preparing heteropoly blue, and based on the preparation method, provides a method for producing hydrogen from biomass:

[0153] Wherein, the preparation method of heteropoly blue comprises the following steps:

[0154] S1. Synthesis of transition metal atom-doped tungsten-based heteropolyacid:

[0155] S1a. Dissolve 120 g of sodium tungstate in 150 mL of water; add 3 mL of phosphoric acid and 22 mL of glacial acetic acid in turn, stir evenly, and then filter to obtain the vacant tungsten-based heteropoly acid.

[0156] S1b. Dissolve 8.2 g of sodium acetate in 100 mL of water, stir until all the solid is dissolved, add 6 mL of acetic acid until the pH is 4.8, add 3.05 g of sodium vanadate and 20 g of vacuous tungsten-based heteropoly acid, stir the solution at 25°C for 48 h, and filter the solution.

[0157] S1c. Add 15 g of solid potassium chloride precipitate to the filtrate obtained in step S1b, redissolve and extract (the operation is the same as in Example 1) to obtain purified heteropolyacid (vanadium-doped phosphotungstic acid).

[0158] S2. Light-assisted conversion of biomass to generate heteropoly blue and small molecule products:

[0159] S2a prepares a mixed aqueous solution, wherein the solute is 0.1M vanadium-doped tungsten-based heteropoly acid obtained in step S1, and 0.1M sucrose;

[0160] S2b. Full spectrum illumination of the mixed aqueous solution obtained in step S2a for 16 seconds. Before the reaction, an inert gas was introduced to exhaust the air and the reaction was sealed. The light source used was the same as in Example 1.

[0161] In this process, part of the biomass is converted into formic acid products, and the heteropoly acid is reduced to heteropoly blue to store hydrogen.

[0162] The method for producing hydrogen from biomass comprises the following specific steps:

[0163] After step S2, the following step S3 is performed:

[0164] S3. The liquid mixture obtained in step S2 is transferred to an electrolytic cell as an anode liquid for electrolysis.

[0165] During the electrolysis process, carbon felt is used as the working electrode (anode), platinum sheet is used as the counter electrode (cathode), and 1M phosphoric acid is used as the cathode liquid. The weak bias voltage generated by a small PV solar panel can meet the reaction requirements, and formic acid is not consumed. After the hydrogen production reaction is completed, the heteropoly blue is converted back into heteropoly acid for the next round of photocatalytic cycle.

[0166] In this example, the system for producing hydrogen from biomass is different from that in Example 1 in that:

[0167] The concentration of the catholyte was 1.5M.

[0168] Example 5

[0169] This example provides a method for preparing heteropoly blue, and based on the preparation method, provides a method for producing hydrogen from biomass:

[0170] Wherein, the preparation method of heteropoly blue comprises the following steps:

[0171] S1. Synthesis of transition metal atom-doped tungsten-based heteropolyacid:

[0172] Dissolve 4.8g of sodium vanadate in about 230mL of water. Acidify the solution with 4M 45mL of hydrochloric acid. Then slowly add 120g of the molybdenum-doped tungsten-based heteropoly acid synthesized in Example 2 and stir vigorously (dissolve). Add 15g of solid potassium chloride to precipitate vanadium and molybdenum co-doped potassium silicotungstate, redissolve and extract (operate the same as in Example 1) to obtain purified heteropoly acid (vanadium-molybdenum co-doped silicotungstic acid).

[0173] S2. Light-assisted conversion of biomass to produce heteropoly blue and small molecule products:

[0174] S2a prepares a mixed aqueous solution, wherein the solute is 0.1M vanadium, molybdenum doped tungsten heteropoly acid obtained in step S1, and 0.1M fructose;

[0175] S2b. Full spectrum illumination of the mixed aqueous solution obtained in step S2a for 16 seconds. Before the reaction, an inert gas was introduced to exhaust the air and the reaction was sealed. The light source used was the same as in Example 1.

[0176] In this process, part of the biomass is converted into formic acid products, and the heteropoly acid is reduced to heteropoly blue to store hydrogen.

[0177] The method for producing hydrogen from biomass comprises the following specific steps:

[0178] After step S2, the following step S3 is performed:

[0179] S3. The liquid mixture obtained in step S2 is transferred to an electrolytic cell as an anode liquid for electrolysis.

[0180] During the electrolysis process, carbon felt is used as the working electrode (anode), platinum sheet is used as the counter electrode (cathode), and 1M phosphoric acid is used as the cathode liquid. The weak bias voltage generated by a small PV solar panel can meet the reaction requirements, and formic acid is not consumed. After the hydrogen production reaction is completed, the heteropoly blue is converted back into heteropoly acid for the next round of photocatalytic cycle.

[0181] In this example, the system for producing hydrogen from biomass is different from that in Example 1 in that:

[0182] The concentration of the catholyte was 2M.

[0183] Example 6

[0184] This example provides a method for preparing heteropoly blue, and based on the preparation method, provides a method for producing hydrogen from biomass, which is different from Example 1 in that:

[0185] Step S1 is not included, and in step S2, an equal amount of silicotungstic acid is used to replace the heteropoly acid obtained in step S1 of Example 1.

[0186] Example 7

[0187] This example provides a method for preparing heteropoly blue, and based on the preparation method, provides a method for producing hydrogen from biomass, which is different from Example 1 in that:

[0188] Step S1 is not included, and in step S2, the heteropoly acid obtained in step S1 of Example 1 is replaced by an equal amount of phosphomolybdic acid.

[0189] Test Case

[0190] In the first aspect of this example, the infrared spectra of the raw material sodium tungstate used in the example and the transition metal atom-doped tungsten-based heteropoly acid obtained in Examples 1 to 5 were tested. The results showed that the central atoms of the heteropoly acids in Examples 1, 2, and 5 were the same and had similar peak positions, which were significantly different from the peak positions in Examples 3 and 4, indicating that different central atoms would change the overall stretching vibration energy of the heteropoly acid, and the doping of a small amount of transition metal would not significantly change the overall structural bond energy of the heteropoly acid. The specific results are as follows: Figure 2 shown.

[0191] The second aspect of this example tests the types and proportions of the products in step S2 of the embodiment, as well as the hydrogen production in step S3. The test method is: using liquid phase and time-of-flight quadrupole LC / MS to quantitatively and directional analyze the glucose conversion products, and gas chromatography to detect gas phase products. The test results show that no gas phase carbon products are generated. The types of products obtained in step S2 include arabinose, glyceraldehyde, ethanolaldehyde and formaldehyde, among which formic acid accounts for the largest proportion in the products; it can be clearly seen that there is a significant synergistic effect between the central atom Si, the transition metal atoms Mo and V in Example 5. The specific test results are shown in Table 1.

[0192] Table 1 Types and quantities of small molecule products obtained in step S2 of the embodiment

[0193] Examples Formic acid (μmol) Arabinose (μmol) Glyceraldehyde (μmol) Glycolaldehyde(μmol) Example 1 164.4 29.63527 17.64914 10.06271 Example 2 86.4 28.00272 6.2193 16.8907 Example 3 163 28.81252 16.27964 11.75884 Example 4 90 22.99171 16.33309 7.73945 Example 5 243.6 43.94597 38.55902 9.84892 Example 6 71.16 42.36201 18.37063 8.23831 Example 7 113.52 56.15444 44.43116 6.15735

[0194] The third aspect of this example tests the yield of the small molecule product in step S2 and the cumulative yield of formic acid therein during 14 cycles of Example 5. The test method is the same as the second aspect of this example, and the yield calculation formula of formic acid is:

[0195] Yield (%) = amount of substance (formic acid) / 6 × amount of substance (glucose);

[0196] The results show that after 14 cycles, the formic acid yield reaches 56%, indicating that the activity of the heteropolyacid has not decreased significantly after 14 cycles and that formic acid has not been consumed in the hydrogen production process. Figure 3And as shown in Table 2.

[0197] Table 2 Cumulative yield of small molecule products and cumulative yield of formic acid in 14 cycles of Example 5

[0198]

[0199]

[0200] In Table 2, for the first cycle, the actual running time is 32 h, that is, the heteropoly acid is reused once (twice in total); the other cycle times are similar.

[0201] The fourth aspect of this example tests the glucose conversion rate, formic acid yield, hydrogen production and corresponding potential and current values ​​during a single operation in different embodiments.

[0202] In Examples 1 to 2 and Example 7, the conditions are the same during the electrolysis of heteropoly blue to generate hydrogen. Comparison of the results shows that if the transition metal-doped tungsten-based heteropoly acid is replaced with the molybdenum-based heteropoly acid commonly used in the industry, the potential required for the electrolysis of heteropoly blue will be significantly increased.

[0203] In all embodiments, the conditions are the same during the light-assisted biomass conversion process. From the comparison of the results, it can be seen that if the transition metal-doped tungsten-based heteropoly acid is replaced with an undoped tungsten-based heteropoly acid, the yield of formic acid will be significantly reduced, that is, the types of small molecule products will be more mixed, and the ability to generate high value-added products in a targeted manner will be reduced.

[0204] Some test results are shown in Table 3 and Figure 4 As shown. Figure 4 Among them, tungsten-based heteropoly blue corresponds to Example 6, molybdenum-based heteropoly blue corresponds to Example 7, and transition metal-doped tungsten-based heteropoly blue corresponds to Example 1.

[0205] Table 3 The generation rate of formic acid, the conversion rate of glucose, the potential required for heteropoly blue to release hydrogen at different current densities and the amount of hydrogen produced in Examples 1 to 7.

[0206]

[0207]

[0208] In summary, the preparation method provided by the present invention can convert biomass into small molecule products represented by formic acid, and convert heteropoly acid into heteropoly blue without adding other reagents, only based on biomass as raw material and light as energy; and further, heteropoly blue is electrolyzed to release hydrogen; thereby, high-purity hydrogen without further purification and high-value-added small molecule products can be obtained; the whole process is mild, environmentally friendly and easy to implement.

[0209] The embodiments of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments. Various changes can be made within the knowledge of ordinary technicians in the relevant technical field without departing from the purpose of the present invention. In addition, the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

Claims

1. A light-assisted biomass conversion method, characterized in that: The conversion method comprises irradiating a mixed aqueous dispersion with light; The dispersoid of the mixed aqueous dispersion includes heteropolyacid and biomass.

2. The conversion method according to claim 1, characterized in that The biomass includes at least one of glucose, fructose, sucrose, starch, cellulose and lignin; and / or, in the mixed aqueous dispersion, the concentration of the biomass is 0.02-0.5M.

3. The conversion method according to claim 1, characterized in that In the mixed aqueous dispersion, the concentration of the heteropoly acid is ≥0.1M.

4. The conversion method according to claim 1, characterized in that The heteropoly acid includes at least one of an unmodified tungsten-based heteropoly acid and a transition metal atom-doped tungsten-based heteropoly acid; and / or the structure of the heteropoly acid is a Keggin structure or a Dawson structure.

5. The conversion method according to claim 4, characterized in that When the heteropoly acid is selected from the transition metal atom-doped tungsten-based heteropoly acid, the synthesis process of the transition metal atom-doped tungsten-based heteropoly acid comprises the following steps: D1. reacting a tungsten precursor, a central atomic source and an acid to obtain a vacancy tungsten-based heteropoly acid; D2. reacting the vacant tungsten-based heteropoly acid with a transition metal source; D3. The mixture obtained in step D2 is mixed with potassium chloride to obtain a precipitate; dissolving the obtained precipitate in water; and extracting the aqueous solution of the dissolved precipitate with ether under acidic conditions; The obtained loaded organic phase was distilled under reduced pressure.

6. The conversion method according to claim 5, characterized in that In step D1, the central atom source includes at least one of sodium silicate and phosphoric acid; and / or, in step D2, the transition metal source includes at least one of sodium molybdate and sodium vanadate.

7. The transformation method according to any one of claims 1 to 6, characterized in that The duration of the illumination is 16 to 36 hours; and / or the light source used for the illumination includes light with a wavelength of ≤400nm.

8. A method for producing hydrogen from biomass, characterized in that: The method comprises electrolyzing the mixture obtained by the conversion method according to any one of claims 1 to 7.

9. The method according to claim 8, characterized in that The electrolysis includes using the mixture as an anolyte.

10. The method according to claim 8, characterized in that During the electrolysis process, the current reached 50 mA cm -1 When the working potential is ≤0.6V vs.RHE; and / or, during the electrolysis process, the current reaches 100mA cm -1 When the working potential is ≤0.65Vvs.RHE.

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