Method for hydrogen production by biomass torrefaction-gasification chemical looping water cycle

Abstract

The present application relates to the field of functional materials, energy conversion and environmental protection technology, and more particularly to a biomass baking-gasification chemical chain water circulation hydrogen production method, which is used for biomass resource cascade utilization and hydrogen-rich syngas production. In the baking stage, the catalyst is mixed with biomass to absorb the moisture therein and release and utilize the moisture in the gasification process. The present application provides a new type of metal-support catalyst, the metal active phase of which mainly includes Ce-Mn, Ce-Zr, Mn-Zr and other bimetallic and multimetallic materials, and the support is CaO. The catalyst includes a CaO support and active metal particles dispersed on the support, the active metal particles are dispersed on the surface of the CaO support by embedding, the doping of the metal is conducive to the formation of oxygen vacancies, increases the electron cloud density, reduces the valence electron energy level, and makes the catalyst have excellent hydrogen production performance and stability in the cyclic adsorption of H2O and CO2. The abundant oxygen vacancies provide active sites for the adsorption and dissociation of H2O in biomass, and promote the hydrogen production from biomass gasification.

Description

Technical Field

[0001] This invention relates to the fields of functional materials, energy conversion and environmental protection, and in particular to a biomass roasting-gasification chemical loop water cycle hydrogen production method. Background Technology

[0002] Hydrogen energy, as a clean, efficient, and renewable energy source, is playing an increasingly important role in the global energy transition and in addressing climate change. With decreasing dependence on fossil fuels and increasing demand for sustainable energy, hydrogen energy is considered a key technology for achieving decarbonization in the industrial, transportation, and power sectors. The widespread application of hydrogen energy is expected to reduce greenhouse gas emissions, improve air quality, and promote economic growth and energy security.

[0003] Among various hydrogen production routes, biomass roasting-gasification hydrogen production technology has significant advantages. Biomass resources, such as agricultural waste, forestry residues, and organic waste, are abundant renewable carbon sources. The roasting process effectively removes moisture and unstable volatile components, thereby improving their quality as gasification feedstock. This pretreatment step not only reduces biomass particle size, enhancing its storage and transportation convenience, but also reduces or eliminates ash slagging and corrosion problems during thermal conversion. During roasting, the H / C and O / C ratios of biomass decrease, its mass and energy density increase, and its chemical composition becomes similar to coal, which helps improve the efficiency and calorific value of subsequent gasification reactions.

[0004] The gasification process utilizes oxygen-containing substances such as air, oxygen, and water vapor to convert roasted biomass into syngas under high-temperature conditions. The main components include hydrogen, carbon monoxide, carbon dioxide, and small amounts of hydrocarbons. Compared to traditional direct combustion or anaerobic digestion, gasification technology can extract energy from biomass more efficiently and reduce pollutant emissions. Furthermore, by optimizing gasification conditions and subsequent purification processes, high-purity hydrogen can be obtained, providing high-quality energy for fuel cells and other hydrogen energy applications.

[0005] Compared with two-stage pyrolysis-gasification, baking-gasification requires less heat than high-temperature pyrolysis, thus saving more energy. However, biomass baking-gasification hydrogen production technology also has the following bottlenecks that urgently need to be overcome: (1) Low hydrogen atom utilization rate. In the biomass baking process, water is the main condensable volatile, followed by a large amount of acetic acid, and a small amount of methane, furfural, and hydroxyacetone. The water in biomass is released in the form of evaporation, while the polymer undergoes dehydration and depolymerization reactions, and the hydroxyl groups form water which is released, resulting in water waste; (2) High gasification temperature. The high-temperature vaporization of alkali metal compounds in biomass ash causes problems such as equipment corrosion and slagging, and the heating energy consumption in the hydrogen production process is large; (3) Low syngas quality. Adsorption-enhanced biomass gasification technology can remove CO2 gas in situ and increase the concentration of hydrogen in the product, but the existing catalyst has poor stability.

[0006] Furthermore, numerous studies have reported on the application of calcium-based chemical looping technology in biomass gasification, enabling in-situ CO2 adsorption and tar cracking. However, most current research focuses on single roasting / gasification processes or combinations of roasting pretreatment and chemical looping gasification, failing to fully utilize the moisture in biomass, thus requiring further improvement in hydrogen production efficiency. Therefore, there is an urgent need to design novel, efficient, and stable catalysts, combined with new biomass roasting-gasification chemical looping water cycle hydrogen production methods, to jointly promote further improvements in the efficiency and quality of biomass chemical looping hydrogen production. Summary of the Invention

[0007] To address the shortcomings of existing biomass roasting-gasification hydrogen production technologies and further improve the yield and quality of hydrogen-rich syngas produced by biomass gasification, this invention proposes a metal-supported catalyst, its preparation method, and its application in biomass roasting-gasification chemical loop water cycle hydrogen production. The aim is to significantly improve the conversion rate of biomass, the hydrogen yield, and the quality of hydrogen in the product during the hydrogen production process through the use of the metal-supported catalyst.

[0008] Therefore, the first technical solution of this application discloses a biomass roasting-gasification chemical loop water cycle hydrogen production method, including the following steps:

[0009] (1) Biomass baking reaction: Biomass and metal-supported catalyst are mixed and baked to obtain solid product 1;

[0010] (2) Gasification and regeneration reaction: Solid product 1 is gasified to obtain hydrogen-rich synthesis gas and solid product 2. Solid product 2 is decarbonized to obtain a regenerated metal-supported catalyst, which is used in step (1) to realize the cycle of step (1)-(2).

[0011] The metal-supported catalyst is a CaO support and active metal particles dispersed on the support. The active metal particles include single-metal, bimetallic, or multi-metal particles composed of Ce, Mn, and Zr. The active metal particles are dispersed on the surface of the CaO support by embedding to form an embedded cellular structure.

[0012] Furthermore, in the metal-supported catalyst, the molar ratio of Ca element in the CaO support to the sum of metal elements in the active metal particles is 15-30:1.

[0013] Furthermore, the CaO support in the metal-supported catalyst has a size of 40-60 mm, and the active metal particles have a grain size of 10-30 nm.

[0014] Furthermore, the weight ratio of the biomass to the metal-supported catalyst is 1:0.5-1.

[0015] Furthermore, the baking reaction temperature is 220-280℃.

[0016] Furthermore, the heating rate of the baking reaction is 2-20℃ / min.

[0017] Furthermore, the baking reaction time is 20-60 minutes.

[0018] Furthermore, the gasification and regeneration reaction temperature is 680-720℃.

[0019] The beneficial effects of this invention are as follows:

[0020] 1. This invention applies a metal-supported catalyst with an embedded cellular structure to a biomass roasting-gasification chemical loop water cycle hydrogen production method. The catalyst includes a CaO support and active metal particles dispersed on the support. The active metal particles are dispersed on the surface of the CaO support by embedding, forming an embedded cellular structure and electronic state. The metal doping is conducive to the formation of oxygen vacancies, increases the electron cloud density, and reduces the valence electron energy level, resulting in excellent hydrogen production performance and stability of cyclic adsorption of H2O and CO2. It can provide active sites for the adsorption and dissociation of H2O in biomass and promote biomass gasification hydrogen production.

[0021] 2. This invention proposes a novel biomass roasting-gasification chemical loop water cycle hydrogen production scheme: During the low-temperature roasting process, a metal-supported catalyst adsorbs and stores the moisture in the biomass; during the high-temperature gasification process, some of the H2O adsorbed on the catalyst surface dissociates into OH-. – and H +This facilitates the formation of active OH groups at Lewis acid sites on the catalyst surface, promoting the biomass gasification reaction. Simultaneously, the catalyst activates H2O, enabling directional cracking for hydrogen production, thus improving gasification efficiency and hydrogen atom utilization to some extent. During the regeneration stage, calcium carbonate desorbs CO2 and reverts to its original phase, ensuring recycling. Attached Figure Description

[0022] Figure 1 Schematic diagram of a biomass roasting-gasification chemical chain water cycle scheme;

[0023] Figure 2 TEM image of the prepared metal-supported catalyst;

[0024] Figure 3 The effects of baking and catalysis on hydrogen atom utilization (HUE) of biomass gasification;

[0025] Figure 4 The effect of catalysts with different metal doping on the cycle stability of CO2 adsorption;

[0026] Figure 5 The effect of catalysts with different metal doping on the syngas yield of biomass gasification;

[0027] Figure 6 The effect of different baking temperatures on the syngas yield of biomass gasification;

[0028] Figure 7 Changes in cumulative syngas yield from biomass gasification with reaction time;

[0029] Figure 8 XRD pattern of catalyst in biomass roasting-gasification chemical loop water cycle process. Detailed Implementation

[0030] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0031] The first embodiment of this application discloses a biomass roasting-gasification chemical loop water cycle hydrogen production method, including the following steps:

[0032] (1) Biomass baking reaction: Biomass and metal-supported catalyst are mixed and baked to obtain solid product 1;

[0033] (2) Gasification and regeneration reaction: Solid product 1 is gasified to obtain hydrogen-rich synthesis gas and solid product 2. Solid product 2 is decarbonized to obtain a regenerated metal-supported catalyst, which is used in step (1) to realize the cycle of step (1)-(2).

[0034] The metal-supported catalyst comprises a CaO support and active metal particles dispersed on the support. The active metal particles include single-metal, bimetallic, or multi-metal particles composed of Ce, Mn, and Zr. These active metal particles are dispersed on the surface of the CaO support through an intercalation method, forming an embedded cellular structure. The CaO support in the metal-supported catalyst has a size of 40-60 mm. The active metal particles have a grain size of 10-30 nm.

[0035] In the metal-supported catalyst, the molar ratio of Ca element in the CaO support to the sum of metal elements in the active metal particles is 15-30:1. Therefore, the catalyst of this application is mainly CaO, which adsorbs water at low temperature and dissociates at high temperature, while simultaneously adsorbing CO2 in the syngas. At the same time, the active metal provides oxygen vacancies to help improve the CO2 adsorption effect. This method differs from the existing technology that simply produces hydrogen through the cracking of water by the active metal to increase the yield and concentration of hydrogen. The method of this application can avoid the waste of water.

[0036] In this embodiment, the specific preparation method of the metal-supported catalyst is as follows:

[0037] A mixture of soluble metal salts, containing at least a calcium metal salt, is mixed with citric acid and stirred in a water bath to obtain a gel-like solution.

[0038] A solid sample is obtained by foaming and drying the gel-like solution.

[0039] The solid sample was calcined to obtain a metal-supported catalyst.

[0040] In this embodiment, the soluble metal salt includes soluble salts of Ca, Ce, Mn, and Zr, such as metal chlorides, nitrates, and sulfates. It should be noted that the soluble metal salt mixture must include at least a Ca salt, which, after the reaction, generates calcium oxide as a support, allowing the metal-supported catalyst structure to be formed.

[0041] In this embodiment, the water bath temperature is 80-90℃, the foaming temperature is 180-190℃, and the calcination temperature is 850-950℃. It is understood that, for the next reaction to proceed more smoothly, after the foaming and calcination, the obtained sample needs to be crushed and ground. In this application, calcination is preferably carried out in a muffle furnace under an oxygen or air atmosphere. After calcination, the sample is crushed to a particle size ≤0.3mm and then ground to between 0.10-0.25mm, resulting in a CaO support size of 40-60mm and an active metal particle grain size of 10-30nm in the catalyst.

[0042] In the embodiments of this application, citric acid acts as a complexing agent, rapidly decomposing at temperatures above 175°C to provide hydroxyl and carboxyl functional groups, thereby promoting cross-linking and foaming of the metal salt solution, and efficiently forming a bulky and rapidly dispersed precursor. The preferred addition amount is 1-1.5 times the total molar amount of metal atoms in the soluble metal mixture, based on the molar ratio.

[0043] Furthermore, in the soluble metal salt mixture, the molar ratio of Ca to other metal elements is 30:1:1.

[0044] A preferred method for preparing a metal-supported catalyst and a TEM image of the metal-supported catalyst obtained by the method will be disclosed below.

[0045] Preparation of metal-supported catalysts

[0046] 1) Mix calcium nitrate, manganese nitrate, cerium nitrate and citric acid (in the material, the molar ratio of Ca, Mn and Ce elements is 30:1:1), and the molar amount of citric acid added is 1.3 times the total molar amount of all metal atoms;

[0047] 2) Add an appropriate amount of deionized water to prepare a solution;

[0048] 3) Stir the prepared solution at 80°C for 30 minutes;

[0049] 4) Place the solution obtained in step 3) in a drying oven, foam and dry it at a temperature range of 180°C for 5 hours, and then crush and grind the resulting solid sample.

[0050] 5) Place the sample ground in step 4) into a muffle furnace and calcine it at 850°C in air for 4 hours, with the heating rate maintained at 2.5°C / min. Grind the calcined solid powder until the particle size is less than 0.3 mm.

[0051] TEM image of the prepared embedded cellular structured metal-supported catalyst is shown below. Figure 2As shown, the obtained metal-supported catalyst exhibits an embedded cellular structure, with the active metal particles embedded on the surface of the support, and the two interacting strongly. Furthermore, the doping of the active metal particles facilitates the formation of oxygen vacancies, increases electron cloud density, and lowers the valence electron energy level, resulting in excellent hydrogen production performance and stable cyclic adsorption of H2O and CO2.

[0052] In a further embodiment, a schematic diagram of the biomass roasting-gasification chemical chain water cycle scheme of this application is disclosed, such as... Figure 1 As shown: This method first involves a biomass roasting reaction. As the temperature rises, moisture in the biomass evaporates. The metal-supported catalyst absorbs and stores the moisture from the biomass. The CaO stored on the support is converted into Ca(OH)2, i.e., solid product 1. The metal active substances and oxygen vacancies surrounding the support provide sites for water adsorption and dissociation, facilitating moisture absorption and allowing the moisture to be stored by the catalyst, avoiding waste. Then, solid product 1 undergoes a gasification and regeneration reaction. During this process, the temperature rises to 680-720℃. The moisture stored in solid product 1 dissociates at high temperature to generate CaCO3 (solid product 2), and H2O decomposes to produce H2 and active -OH groups, further promoting the biomass gasification reaction. This completes the preparation of hydrogen-rich syngas. Compared with existing technologies using a single roasting / gasification process, this method saves drying energy, strengthens the reaction process, and improves gasification efficiency. Simultaneously, solid product 2 undergoes further decarbonization to generate CaO, completing the regeneration of the metal-supported catalyst, which is then recycled for the roasting reaction. The XRD pattern of its evolution process is shown in the figure. Figure 8 As shown.

[0053] In this embodiment, the biomass is at least one of straw, wood, fruit shells, and bamboo, and the weight ratio of biomass to metal-supported catalyst is 1:0.5-1.

[0054] In this embodiment, the baking reaction temperature is 220-280℃, the heating rate is 2-20℃ / min (from room temperature to the baking reaction temperature), the reaction time is 20-60min, the reaction auxiliary atmosphere is N2, and the flow rate is 20-80mL / min.

[0055] In this embodiment, the gasification and regeneration reaction temperature is 680-720℃, the heating rate is 20-80℃ / min, the reaction time is 20-60min, the reaction auxiliary atmosphere is N2, and the flow rate is 20-80mL / min.

[0056] Example 1: Biomass roasting-gasification chemical loop water cycle hydrogen production method

[0057] (1) Biomass roasting reaction: 40 mL / min of N2 was introduced into a roasting reactor at a temperature of 250 °C. A mixture of 0.3 g of metal-supported catalyst prepared by the preferred method and 0.3 g of pine wood was used to carry out the roasting reaction to obtain Ca(OH)2.

[0058] (2) Gasification and regeneration reaction: Solid product 1 is fed into a gasification reactor at 680°C to carry out a gasification reaction to obtain syngas and CaCO3; CaCO3 is decarbonized and regenerated to obtain regenerated CaO, and the regenerated catalyst is sent back to the baking reactor for repeated cycles to achieve full utilization of water in biomass.

[0059] Example 2

[0060] Compared with Example 1, the only difference is that the temperature in the baking reactor is changed to 220°C, while other operations and parameters are the same as in Example 1.

[0061] Example 3

[0062] Compared with Example 1, the only difference is that the temperature in the baking reactor is changed to 280°C, while other operations and parameters are the same as in Example 1.

[0063] Example 4

[0064] Compared to Example 1, the only difference is that in step 1, Mn is doped only in the calcium-based catalyst, and calcium nitrate, manganese nitrate, and citric acid are mixed (the molar ratio of Ca to Mn in the material is 15:1). Other operations and parameters are the same as in Example 1.

[0065] Example 5

[0066] Compared to Example 1, the only difference is that in step 1, Ce is doped only in the calcium-based catalyst, and calcium nitrate, cerium nitrate, and citric acid are mixed (the molar ratio of Ca to Ce in the material is 15:1). Other operations and parameters are the same as in Example 1.

[0067] Example 6

[0068] Compared to Example 1, the only difference is that in step 1, no metal is added; only calcium nitrate is mixed with citric acid to obtain a catalyst containing only CaO. Other operations and parameters are the same as in Example 1.

[0069] Comparative Example 1

[0070] Compared to Example 1, the only difference is that no catalyst is added. All other operations and parameters are the same as in Example 1.

[0071] Comparative Example 2

[0072] Compared to Example 1, the only difference is that no baking process is performed. All other operations and parameters are the same as in Example 1.

[0073] Comparative Example 3

[0074] Compared to Example 1, the only difference is that no catalyst is added and no baking process is performed. All other operations and parameters are the same as in Example 1.

[0075] The performance of the gases obtained in Examples 1-6 and Comparative Examples 1-3, including hydrogen atom utilization rate, was compared. The results are shown in Table 1. Figures 3-7 . Figure 3 The comparison of hydrogen atom utilization rates under the operating conditions of Example 1 (catalyst + roasted biomass) and Comparative Examples 1 (roasted biomass), 2 (catalyst + raw biomass), and 3 (raw biomass) demonstrates the promoting effect of metal-supported catalyst and roasting process on biomass gasification hydrogen production process, and that the two can also synergistically improve hydrogen atom utilization rate. Figure 4 A comparison of the CO2 adsorption-desorption cycle capacity of four different metal-supported catalysts, including Ca 15 The Mn1 catalyst (Example 4) exhibited the strongest CO2 adsorption capacity, while Ca... 15 Ce1 (Example 5) and Ca 15 Ce 0.5 Mn 0.5 The catalyst (Example 1) showed good cycling stability, while the CaO catalyst (Example 6) experienced a significant performance decline due to agglomeration and sintering during the cycling process. Figure 5 Example 1 (Ca) 15 Ce 0.5 Mn 0.5 catalyst), 4(Ca 15 Mn1 catalyst), 5(Ca 15 The gasification syngas yield under Ce1) and 6 (CaO catalyst) conditions, where Ca... 15 The Mn1 catalyst (Example 4) showed the highest syngas yield, and the active component Ca2MnO4 could improve O2 production. 2- The high mobility is beneficial for CO2 adsorption; Figure 6 The following are the gasification syngas yields under the operating conditions of Examples 1 (250℃), 2 (220℃), and 3 (280℃). The lower the baking temperature, the greater the solid retention rate and the higher the syngas yield during the gasification stage. Figure 7 The cumulative syngas yield during the gasification stage under the operating conditions of Example 1 shows that H2, CO, CH4 and C2-C3 are generated rapidly in the first 10 minutes and then gradually stabilize, while the release rate of CO2 is relatively stable throughout the gasification process.

[0076] Table 1. Gasification test results of the steps in the examples and comparative examples.

[0077]

[0078] Compared to the condition without a catalyst and without a baking process (Comparative Example 3), the hydrogen atom utilization rate of the biomass baking-gasification chemical looping hydrogen production process (Example 1) using a Ce / Mn-doped metal-supported catalyst can be improved by 32.8%. The moisture generated during the biomass baking process is stored, released, and utilized through a calcium-based chemical looping water cycle. Ce doping (Example 5) helps the catalyst form a more porous structure. 4+ and Ce 3+ A rapid and reversible transition occurs between them, generating more oxygen vacancies, increasing oxygen storage capacity and oxygen transport capacity, and helping to improve CO2 adsorption stability. Mn doping (Example 4) helps prevent catalyst grain growth and agglomeration during gasification, maintaining excellent catalyst performance and thus improving gas production rate. Ce and Mn synergistically promote electron donation from Ca atoms to surface oxygen, which is beneficial for CO2 diffusion and O2 production. 2- The migration of CO2. In the later stage of gasification, the metal-supported catalyst can be decarbonized and regenerated. As shown in Examples 1 and 2, the lower the baking temperature, the higher the solid retention rate and the higher the syngas yield in the gasification stage. As shown in Examples 1, 4, and 5, for Ce and Mn, the bimetallic activation catalytic hydrogen production effect is not as good as that of single metal activation, but it is still significantly improved compared with the traditional baking-gasification performance. The CO2 yield decreased, which indicates that the synergistic interaction between Ce and Mn promotes the electron donation of Ca atoms to surface oxygen, which is beneficial to the diffusion of CO2 and O2. 2- The migration of electrons between Ce and Mn. Specifically, the presence of electron transfer between Ce and Mn promotes the generation of oxygen vacancies, i.e.

[0079] Ce 3+ +Mn 3+ →Ce 4+ +Mn 2+ Oxygen vacancies can reduce the gap between the highest occupied molecular orbital of CaO and the lowest unoccupied molecular orbital of CO2. Therefore, it becomes easier for CaO to donate electrons to CO2, leading to the breaking of old Ca-O bonds and the formation of new CO bonds.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A biomass roasting-gasification chemical loop water cycle hydrogen production method, characterized in that, Includes the following steps: (1) Biomass baking reaction: Biomass and metal-supported catalyst are mixed and baked to obtain solid product 1; (2) Gasification and regeneration reaction: Solid product 1 is gasified to obtain hydrogen-rich synthesis gas and solid product 2. Solid product 2 is decarbonized to obtain a regenerated metal-supported catalyst, which is used in step (1) to realize the cycle of step (1)-(2). The metal-supported catalyst is a CaO support and active metal particles dispersed on the support. The active metal particles include single-metal, bimetallic, or multi-metal particles composed of Ce and Mn. The active metal particles are dispersed on the surface of the CaO support by embedding to form an embedded cellular structure. The molar ratio of Ca element in the CaO carrier to the sum of metal elements in the active metal particles is 15-30:

1. The baking reaction temperature is 220-280℃.

2. The hydrogen production method according to claim 1, characterized in that, The CaO support in the metal-supported catalyst has a size of 40-60 mm, and the active metal particles have a grain size of 10-30 nm.

3. The hydrogen production method according to claim 1, characterized in that, The weight ratio of biomass to metal-supported catalyst is 1:0.5-1.

4. The hydrogen production method according to claim 1, characterized in that, The heating rate of the baking reaction is 2-20℃ / min.

5. The hydrogen production method according to claim 1, characterized in that, The baking reaction time is 20-60 minutes.

6. The hydrogen production method according to claim 1, characterized in that, The gasification and regeneration reaction temperature is 680-720℃.

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