Biomass baking-gasification chemical looping water circulation hydrogen production method

Abstract

The invention relates to the technical field of functional materials, energy conversion and environmental protection, in particular to a biomass baking-gasification chemical looping water circulation hydrogen production method which is used for gradient utilization of biomass resources and preparation of hydrogen-rich synthesis gas. The invention provides a novel metal-carrier catalyst and a preparation method thereof, in the gasification stage, the catalyst and biomass are mixed to absorb water # imgabs0 # in the biomass and release and utilize the water # imgabs0 # in the gasification process, in the novel metal-carrier catalyst provided by the invention, a metal active phase mainly comprises bimetallic and multi-metal materials such as Ce-Mn, Ce-Zr, Mn-Zr and the like, and a carrier is CaO. The catalyst comprises a CaO carrier and active metal particles dispersed on the carrier, the active metal particles are dispersed on the surface of the CaO carrier in an embedding manner, and doping of metal is beneficial to formation of oxygen vacancies, increase of electron cloud density and reduction of valence electron energy level, so that the catalyst has excellent hydrogen production performance and stability of cyclic adsorption of H2O and CO2. The rich oxygen vacancies provide active sites for adsorption and dissociation of H2O in biomass, and biomass gasification for hydrogen production is promoted.

Description

Technical Field

[0001] The present invention relates to the technical fields of functional materials, energy conversion and environmental protection, and in particular to a biomass baking-gasification chemical chain water cycle hydrogen production method. Background Art

[0002] As a clean, efficient and renewable energy carrier, hydrogen plays an increasingly important role in global energy transformation and climate change response. With the reduction of dependence on fossil fuels and the increase in demand for sustainable energy, hydrogen is regarded as one of the key technologies to achieve low carbonization in the industrial, transportation and power sectors. The widespread use of hydrogen is expected to reduce greenhouse gas emissions, improve air quality, and promote economic growth and energy security.

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

[0004] The gasification process uses oxygen-containing substances such as air, oxygen, and water vapor to convert the baked biomass into syngas under high temperature conditions. The main components include hydrogen, carbon monoxide, carbon dioxide, and a small amount of hydrocarbons. Compared with traditional direct combustion or anaerobic digestion, gasification technology can extract energy from biomass more efficiently and reduce pollutant emissions. In addition, 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, the heat required for baking-gasification is lower than that required for high-temperature pyrolysis, thus saving more energy. However, the biomass baking-gasification hydrogen production technology also has the following bottlenecks that need to be broken through: (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, a small amount of methane, furfural and hydroxyacetone. The water in the biomass is released in the form of evaporation, while the polymer undergoes dehydration and depolymerization reactions, and the hydroxyl groups form water and are released, resulting in a waste of water; (2) High gasification temperature. The high-temperature vaporization of alkali metal compounds in the biomass ash causes equipment corrosion and slagging, and the heating energy consumption in the hydrogen production process is high; (3) The quality of the synthesis gas is low. Adsorption-enhanced biomass gasification technology can remove CO2 gas in situ and increase the hydrogen concentration of the product, but the stability of existing catalysts is poor.

[0006] In addition, there have been many research reports on the use of calcium-based chemical chaining technology in biomass gasification, which can achieve in-situ CO2 adsorption and tar cracking. However, most of the current research focuses on a single roasting / gasification process or a combination of roasting pretreatment and chemical chaining gasification, and does not fully utilize the water in the biomass. The efficiency of hydrogen production still needs to be further improved. Therefore, it is urgent to design new, efficient, and stable catalysts, and combine them with new biomass roasting-gasification chemical chaining water cycle hydrogen production methods to jointly promote the further improvement of biomass chemical chaining hydrogen production efficiency and hydrogen quality. Summary of the invention

[0007] In order to make up for the shortcomings of the existing biomass torrefaction-gasification hydrogen production technology and further improve the yield and product quality of hydrogen-rich synthesis gas produced by biomass gasification, the present invention proposes a metal-carrier catalyst and a preparation method thereof and an application in biomass torrefaction-gasification chemical chain water cycle hydrogen production, aiming to significantly improve the biomass conversion rate, hydrogen yield and hydrogen quality in the hydrogen production process through the use of metal-carrier catalysts.

[0008] To this end, the first technical solution of the present application discloses a biomass roasting-gasification chemical chain water cycle hydrogen production method, comprising the following steps:

[0009] (1) Biomass roasting reaction: Biomass and metal-support catalyst are mixed and roasted to obtain a solid product 1;

[0010] (2) Gasification and regeneration reaction: solid product 1 is subjected to gasification reaction 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 steps (1)-(2);

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

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

[0013] Furthermore, the CaO carrier size in the metal-carrier catalyst is 40-60 mm, and the grain size of the active metal particles is 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°C.

[0016] Furthermore, the baking reaction temperature rise rate is 2-20°C / min.

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

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

[0019] The beneficial effects of the present invention are:

[0020] 1. The present invention applies a metal-support catalyst with an embedded butyl cell structure to a biomass roasting-gasification chemical chain 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 to form an embedded butyl cell structure and electronic state. The doping of the metal is conducive to the formation of oxygen vacancies, increases the electron cloud density, and reduces the valence electron energy level, so that it has excellent hydrogen production performance and cyclic adsorption stability of H2O and CO2, and can provide active sites for the adsorption and dissociation of H2O in biomass, thereby promoting biomass gasification hydrogen production.

[0021] 2. The present invention proposes a new scheme for hydrogen production by water cycle of biomass baking-gasification chemical chain: during the low-temperature baking process, the metal-carrier catalyst absorbs and stores the water in the biomass; during the high-temperature gasification process, part of the H2O adsorbed on the catalyst surface will dissociate into OH – and H +, which is conducive to the formation of active OH groups with Lewis acid sites on the catalyst surface, promoting the occurrence of biomass gasification reaction. At the same time, the catalyst catalyzes the activation of H2O and directional cracking to produce hydrogen, which improves the gasification efficiency and hydrogen atom utilization rate to a certain extent. In the regeneration stage, calcium carbonate desorbs CO2 and evolves back to the original phase to ensure circulation. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

[0024] Figure 3 Effects of torrefaction and catalysis on hydrogen utilization efficiency (HUE) of biomass gasification;

[0025] Figure 4 Effects of different metal-doped catalysts on the stability of CO2 adsorption cycles;

[0026] Figure 5 Effects of different metal-doped catalysts on syngas yield from biomass gasification;

[0027] Figure 6 Effect of different torrefaction temperatures on the syngas yield of biomass gasification;

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

[0029] Figure 8 XRD pattern of catalyst in biomass torrefaction-gasification chemical chain water cycle process. DETAILED DESCRIPTION

[0030] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

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

[0032] (1) Biomass roasting reaction: Biomass and metal-support catalyst are mixed and roasted to obtain a solid product 1;

[0033] (2) Gasification and regeneration reaction: solid product 1 is subjected to gasification reaction 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 steps (1)-(2);

[0034] The metal-carrier catalyst is a CaO carrier and active metal particles dispersed on the carrier, the active metal particles include single metal, bimetallic or multimetallic particles composed of Ce, Mn and Zr, the active metal particles are dispersed on the surface of the CaO carrier by embedding to form an embedded cellular structure; the size of the CaO carrier in the metal-carrier catalyst is 40-60 mm. The grain size of the active metal particles is 10-30 nm.

[0035] In the metal-carrier catalyst, the molar ratio of the Ca element in the CaO carrier to the sum of the metal elements in the active metal particles is 15 to 30:1; therefore, the catalyst of the present application is mainly CaO, and CaO adsorbs water at low temperatures, dissociates at high temperatures, and simultaneously adsorbs CO2 in the gasified synthesis gas; at the same time, the active metal provides oxygen vacancies to assist in improving the CO2 adsorption effect; thus, the method of the present application is different from the prior art method of simply producing hydrogen through the cracking effect of active metals on water to increase the yield and concentration of hydrogen, and the method of the present application can avoid wasting water.

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

[0037] Mixing a soluble metal salt mixture containing at least a metal calcium salt with citric acid and stirring in a water bath to obtain a gel solution;

[0038] The gel-like solution is foamed and dried to obtain a solid sample;

[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 elements, such as metal chlorides, nitrates, sulfates, etc. It should be noted that the soluble metal salt mixture needs to include at least Ca salt, which generates calcium oxide as a carrier after the reaction, so that the structure of the metal-carrier catalyst is formed.

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

[0042] In the embodiment of the present application, the role of citric acid is to act as a chelating agent. When the temperature is higher than 175°C, it quickly decomposes to provide hydroxyl and carboxyl functional groups, thereby promoting the cross-linking and foaming of the metal salt solution to efficiently form a precursor with loose volume and high-speed dispersion. The preferred amount of citric acid added is 1-1.5 times the total molar amount of metal atoms in the soluble metal mixture in terms of molar ratio.

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

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

[0045] Preparation of metal-supported catalysts

[0046] 1) Calcium nitrate, manganese nitrate, cerium nitrate and citric acid are mixed (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 appropriate amount of deionized water to prepare a solution;

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

[0049] 4) placing the solution obtained in step 3) in a drying oven, foaming and drying at a temperature range of 180° C. for 5 hours, and crushing and grinding the obtained solid sample;

[0050] 5) placing the sample ground in step 4) into a muffle furnace, calcining at 850° C. in an air atmosphere for 4 hours, with a heating rate of 2.5° C. / min, and grinding the calcined solid powder to a particle size of less than 0.3 mm;

[0051] The TEM image of the prepared embedded butyl cell structure metal-support catalyst is shown in Figure 2As shown; it can be seen that the obtained metal-support catalyst presents an embedded tricera structure, and the active metal particles are embedded in the surface of the support, and there is a strong interaction between the two. On the other hand, the doping of active metal particles is conducive to the formation of oxygen vacancies, increases the electron cloud density, reduces the valence electron energy level, and has excellent hydrogen production performance and cyclic adsorption stability of H2O and CO2.

[0052] In a further embodiment, a schematic diagram of the water cycle scheme of the biomass roasting-gasification chemical chain of the present application is disclosed, such as Figure 1 As shown: the method first performs a biomass baking reaction. As the temperature rises, the water in the biomass evaporates, the metal-carrier catalyst absorbs and stores the water in the biomass, and the carrier CaO stores and transforms into Ca(OH)2, i.e., solid product 1. The metal active substances and oxygen vacancies around the carrier provide sites for the adsorption and dissociation of water, which helps to absorb water, so that the water can be stored by the catalyst to avoid waste; then the solid product 1 is gasified and regenerated. In this process, the temperature rises to 680-720°C, and the water stored in the solid product 1 dissociates at high temperature to generate CaCO3 (solid product 2), and H2O is cracked to generate H2 and active -OH groups, which further promote the biomass gasification reaction, thereby completing the preparation of hydrogen-rich synthesis gas. Compared with the prior art using a single baking / gasification process, it saves drying energy consumption, strengthens the reaction process, and improves the gasification efficiency; at the same time, the solid product 2 is further decarbonized to generate CaO, completing the regeneration of the metal-carrier catalyst, and is recycled in the baking reaction. The XRD diagram of its evolution process is shown in Figure 8 shown.

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

[0054] In this embodiment, the baking reaction temperature is 220-280°C, the heating rate is 2-20°C / 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°C, the heating rate is 20-80°C / 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 chain water cycle hydrogen production method

[0057] (1) Biomass torrefaction reaction: 40 mL / min of N2 was introduced into a torrefaction reactor at a temperature of 250°C, and a mixture of 0.3 g of the metal-support catalyst prepared by the preferred preparation method and 0.3 g of pine wood was passed through a bed to perform a torrefaction reaction to obtain Ca(OH)2;

[0058] (2) Gasification and regeneration reaction: The solid product 1 is introduced into a gasification reactor at 680°C for gasification reaction to obtain synthesis gas and CaCO3; CaCO3 is decarbonized and regenerated to obtain regenerated CaO, and the regenerated catalyst is sent to the baking reactor again, and the cycle is repeated to fully utilize the water in the 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., and the other operations and parameters are the same as 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., and the other operations and parameters are the same as Example 1.

[0063] Example 4

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

[0067] Example 6

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

[0069] Comparative Example 1

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

[0071] Comparative Example 2

[0072] Compared with Example 1, the only difference is that the baking process is not performed. Other operations and parameters are the same as in Example 1.

[0073] Comparative Example 3

[0074] Compared with Example 1, the only difference is that no catalyst is added and no baking process is performed. 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, such as hydrogen atom utilization rate, was compared. The results are shown in Table 1 Figure 3-Figure 7 . Figure 3 The results show that the utilization rate of hydrogen atoms in Example 1 (catalyst + torrefied biomass) is compared with that in Comparative Examples 1 (toasted biomass), 2 (catalyst + original biomass), and 3 (original biomass), which proves the promoting effect of the metal-support catalyst and the torrefaction process on the biomass gasification hydrogen production process, and the two can also synergistically improve the utilization rate of hydrogen atoms. Figure 4 Comparison of CO2 adsorption and desorption cycle capabilities of four different metal-support catalysts, among which Ca 15 The Mn1 catalyst (Example 4) has the strongest CO2 adsorption capacity, while the Ca 15 Ce1 (Example 5) and Ca 15 Ce 0.5 Mn 0.5 The catalyst (Example 1) has good cycle stability, while the performance of the CaO catalyst (Example 6) is significantly reduced due to agglomeration and sintering during the cycle. Figure 5 For Example 1 (Ca 15 Ce 0.5 Mn 0.5 Catalyst), 4(Ca 15 Mn1 catalyst), 5(Ca 15 The yield of gasification synthesis gas under conditions of Ce1) and 6 (CaO catalyst) is shown in Figure 2. 15 The syngas yield of Mn1 catalyst (Example 4) is the highest, and the active component Ca2MnO4 can increase the O 2- The mobility is good for the adsorption of CO2; Figure 6 The gasification syngas yields under the working conditions of Examples 1 (250°C), 2 (220°C), and 3 (280°C) are shown. The lower the baking temperature, the greater the solid retention rate, and the higher the syngas yield in the gasification stage; Figure 7 The cumulative synthesis gas yield in the gasification stage under the working conditions of Example 1 shows that H2, CO, CH4 and C2-C3 are produced 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 of the embodiment and the comparative example

[0077]

[0078] Compared with the condition without adding catalyst and without baking process (Comparative Example 3), the hydrogen atom utilization rate of the biomass baking-gasification chemical chain gasification hydrogen production process (Example 1) using Ce / Mn doped metal-support catalyst can be increased by 32.8%. The water generated by biomass during baking can be stored, released and utilized through the calcium-based chemical chain water cycle. Ce doping (Example 5) helps the catalyst to form more porous structures. 4+ and Ce 3+ Rapid reversible transformation occurs between the two, generating more oxygen vacancies, increasing the oxygen storage capacity and oxygen transmission capacity, and helping to improve the CO2 adsorption stability. Mn doping (Example 4) is beneficial to prevent the grain growth and agglomeration of the catalyst during the gasification process, so that the catalyst maintains excellent performance, thereby improving the gasification process gasification rate. Ce and Mn synergistically promote the electron supply of Ca atoms to surface oxygen, which is beneficial to the diffusion of CO2 and O 2- Migration. In the later stage of gasification, the metal-supported catalyst can be decarbonized and regenerated. It can be seen from Examples 1 and 2 that the lower the baking temperature, the higher the solid retention rate and the higher the syngas yield in the gasification stage. It can be seen from Examples 1, 4 and 5 that for Ce and Mn, the effect of bimetallic activation on catalytic hydrogen production is not as good as that of single metal activation, but it is still greatly improved compared with traditional baking-gasification performance. The CO2 yield is reduced, which indicates that the synergistic interaction between Ce and Mn promotes the electron supply of Ca atoms to the surface oxygen, which is beneficial to the diffusion of CO2 and O 2- Specifically, the existence of electron transfer between Ce and Mn promotes the generation of oxygen vacancies, namely

[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, resulting in the breaking of the old Ca-O bond and the formation of a new CO bond.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A biomass roasting-gasification chemical chain water cycle hydrogen production method, characterized in that: The steps include: (1) Biomass roasting reaction: Biomass and metal-support catalyst are mixed and roasted to obtain a solid product 1; (2) Gasification and regeneration reaction: solid product 1 is subjected to gasification reaction 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 steps (1)-(2); Among them, the metal-carrier catalyst is a CaO carrier and active metal particles dispersed on the carrier, the active metal particles include single metal, bimetallic or multi-metallic particles composed of Ce, Mn and Zr, and the active metal particles are dispersed on the surface of the CaO carrier by embedding to form an embedded cellular structure.

2. The method for producing hydrogen according to claim 1, characterized in that: In the metal-carrier catalyst, the molar ratio of the Ca element in the CaO carrier to the sum of the metal elements in the active metal particles is 15 to 30:

1.

3. The method for producing hydrogen according to claim 1, characterized in that: The CaO carrier size in the metal-carrier catalyst is 40-60 mm, and the grain size of the active metal particles is 10-30 nm.

4. The method for producing hydrogen according to claim 1, characterized in that: The weight ratio of the biomass to the metal-supported catalyst is 1:0.5-1.

5. The method for producing hydrogen according to claim 1, characterized in that: The baking reaction temperature is 220-280°C.

6. The method for producing hydrogen according to claim 1, characterized in that: The baking reaction heating rate is 2-20°C / min.

7. The method for producing hydrogen according to claim 1, characterized in that: The baking reaction time is 20-60 minutes.

8. The method for producing hydrogen according to claim 1, characterized in that: The gasification and regeneration reaction temperature is 680-720°C.

Images