A method for preparing and applying a biochar semi-coke-based catalyst

Abstract

This invention discloses a method for preparing a biochar semi-coke-based catalyst, characterized by the following preparation steps: S1, preparing biomass semi-coke; S2, activating the prepared biomass semi-coke to obtain an activated biochar semi-coke-based catalyst. The biomass semi-coke in this invention contains natural Ca and Al species, which can synergistically interact with the biochar support. The porous biochar is used to crack macromolecules with three or more rings in the tar, while the metal species are used to crack small volatile fragments with two or fewer rings in the tar, thereby promoting tar reforming and increasing hydrogen yield.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of tar reforming, and particularly relates to a preparation method and application of a biochar semi-coke-based catalyst. BACKGROUND

[0002] Biomass waste is the largest and most abundant renewable resource on earth. Using pyrolysis gasification technology to convert biomass waste into clean fuel gas, and then preparing chemicals, fuels or energy is an important way to realize the development and utilization of biomass waste according to local conditions. However, tar and ash particles are the main by-products of the biomass waste pyrolysis gasification process. The production of tar and ash particles reduces the gasification efficiency and the quality of the produced gas. Ash particles and sticky tar can cause corrosion of equipment and blockage of pipelines, which damages the stable operation of the gasification system and is a bottleneck problem for the popularization and application of gasification technology. Purifying synthesis gas and developing various catalysts to achieve efficient tar reforming have become the current research focus. Biomass semi-coke has the characteristics of developed pore structure, low price and can be directly prepared "in situ" using biomass raw materials. Therefore, biomass semi-coke-based catalysts have gradually become an important application and research topic in the field of tar reforming.

[0003] Currently, the commonly used tar catalysts include natural catalysts (such as dolomite, olivine), inorganic salt catalysts (such as alkali metals, metal oxides), and synthetic catalysts (such as nickel-based, semi-coke-based metal catalysts), and molecular sieve catalysts, noble metal catalysts. Compared with the semi-coke-based catalyst, the semi-coke-based catalyst is cheap and easy to obtain, has a rich specific surface area, is rich in micropores and mesopores, and in the process of use, new micropores are generated in situ due to the reaction of carbon and tar volatile components, effectively avoiding the deactivation of the catalyst due to the accumulation of carbon. In the previous research, Tian et al. [1] found that the conversion rate of toluene reached 97% and 85.3% respectively when the Co-Ni and Co-Fe doped biochar catalysts were used at 700 ℃. G. Yang et al. [2] found that the biochar catalyst doped with Ca achieved a tar conversion rate of 70% at 800 ℃. In addition, Zhang et al. [3] found that when pine was gasified at 750 ℃, the tar conversion rate increased from 73.1% to 92.6% when using activated 10wt% Ni-loaded biochar catalyst compared with unactivated catalyst. In addition, patent CN 106590705A discloses a method for secondary catalytic reforming of tar using in-situ hot composite semi-coke prepared from low-quality high-alkali coal and biomass pyrolysis as a catalyst. After adding the composite semi-coke catalyst, the tar yield decreased by about 40%. Patent CN 109876788A relates to a method for preparing a biomass-activated semi-coke catalyst, which is simple, easy to operate, and low in cost. The obtained catalyst shows good catalytic activity (~80%) for naphthalene, a model compound of tar. The above-mentioned catalysts are prepared from coal or biomass, but do not involve directional regulation of the microstructure and active sites of carbon materials.

[0004] In recent years, more and more attention has been paid to the application of dual-function catalysts with calcium oxide and calcium aluminate as carriers in the reforming of biomass tar to produce hydrogen, which can not only absorb carbon dioxide produced in the hydrogen production process, but also have good catalytic effect. Patent CN 109621936A discloses a CaO-biochar deoxidation catalyst, which is prepared by mixing Ca salt with organic material and then rapidly pyrolyzing under inert gas atmosphere. The catalyst has a tar conversion rate of 70% at 550 ℃, a soybean oil WHSV of 2 h -1Under certain conditions, catalytic upgrading of oily compounds is carried out to collect high-quality liquid fuels. Patent CN 112473680A relates to a bifunctional calcium-based catalyst, which uses a calcination-hydration method to prepare a calcium aluminum stone catalyst support, and then uses a hydrothermal method to load the metal active component. This catalyst not only catalyzes hydrogen production but also absorbs CO2 gas, further promoting H2 generation. Furthermore, patent CN 116328772A discloses a Ni-Ca-Al catalyst for hydrogen production from coal tar reforming. This catalyst uses NiO as the active component and chemically activated Al2O3 as the support, containing abundant oxygen vacancies, providing active sites for NiO anchoring and increasing the synergistic effect between NiO and the Al2O3 support. Additionally, the addition of Ca further promotes the formation of oxygen vacancies, improves the dispersibility of NiO, and significantly enhances the activity and stability of the catalyst. Patent CN 115254126A proposes a highly efficient biochar-based Fe-Ni-Ca composite catalyst for treating alkali and alkaline earth metals (AAEM) in the volatiles of biomass pyrolysis. At the same time, the catalyst can also promote the cracking of biomass pyrolysis tar and maintain an activity similar to that of fresh catalysts.

[0005] [1] B. Tian, ​​S. Mao, F. Guo, J. Bai, R. Shu, L. Qian, Q. Liu, Monolithic biochar-supported cobalt-based catalysts with high-activity and superior-stability for biomass tar reforming, Energy, 242 (2022) 122970.

[0006] [2] G. Yang, Q. Hu, J. Hu, H. Yang, S. Yan, Y. Chen, X. Wang, H.Chen, Hydrogen-rich syngas production from biomass gasification using biochar-based nanocatalysts, Bioresour. Technol., (2023) 129005.

[0007] [3] Z. Miao, F. Guifang, L. Na, Y. Mingde, L. Xiaoxian, W. Yulong, Tar removal in pine pyrolysis catalyzed by bio-char supported nickelcatalyst, J. Anal. Appl. Pyrolysis, 169 (2023) 105843. Summary of the Invention

[0008] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing and applying a biochar semi-coke-based catalyst. The natural Ca and Al species contained in biomass semi-coke can synergistically interact with the biochar support, promoting tar reforming. Doping the activated carbon catalyst with Al species significantly enhances the decomposition of light compounds during tar reforming, with a marked decrease in the peak intensities of naphthalene, biphenyl, and acenaphthene after using the Al / activated carbon catalyst. Doping the activated carbon catalyst with Ca species significantly increases both the gas yield and the H2 / CO ratio during tar reforming.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] A method for preparing a biochar semi-coke-based catalyst includes the following preparation steps:

[0011] S1. Preparation of biomass semi-coke;

[0012] S2. The obtained biomass semi-coke is activated to obtain activated biochar semi-coke-based catalyst.

[0013] Preferably, in step S1, the specific preparation steps are as follows: placing the biomass raw material into a reactor and heating it in nitrogen to perform pyrolysis to obtain biomass semi-coke; the biomass raw material is corn cob or poplar wood with a diameter of 0.3~0.9 mm, the nitrogen flow rate is 50~500 mL / min, the heating rate is 10~50 ℃ / min, the temperature is raised to 450~550 ℃, and the pyrolysis time is 0.5~2h.

[0014] Preferably, in step S2, the activation treatment method uses steam activation, the steam heating rate is 5~15 ℃ / min, the temperature is heated to 750~850 ℃ and held for 0.5~2 h, the mass ratio of steam to biochar is 0~0.9, and the total flow rate of steam and N2 is 450~550 mL / min.

[0015] Application of a biochar semi-coke-based catalyst in tar reforming.

[0016] A method for improving the decomposition effect of light compounds in tar reforming involves using an Al-doped activated carbon catalyst for tar reforming, wherein the light compounds are one or more of naphthalene, biphenyl, or acenaphthene.

[0017] Preferably, the method for doping Al onto the aforementioned activated carbon catalyst is as follows: using an impregnation / hydrothermal synthesis method, the activated carbon catalyst and aluminum salt are added to deionized water, mixed and stirred, dried, and calcined under nitrogen to obtain an Al / activated carbon catalyst, wherein the aluminum salt is aluminum nitrate or aluminum acetate.

[0018] A method for improving the gas yield and H2 / CO ratio in tar reforming involves using a Ca-doped activated carbon catalyst for tar reforming.

[0019] Preferably, the method for doping Ca onto the aforementioned activated carbon catalyst is as follows: using an impregnation / hydrothermal synthesis method, the activated carbon catalyst and calcium salt are added to deionized water, mixed and stirred, dried, and calcined under nitrogen to obtain a Ca / activated carbon catalyst, wherein the calcium salt is calcium nitrate or calcium acetate.

[0020] A tar reforming method that simultaneously enhances the reforming and retention effects of tar and fixed particles utilizes a membrane reactor coupled with an activated biochar semi-coke-based catalyst for tar reforming. The membrane reactor is a tubular membrane reactor employing a SiC porous membrane, with the aforementioned catalyst filling the internal channels or outer walls.

[0021] When the diameter of the tar molecules mentioned above is 0.65-0.75 nm, the tubular membrane reactor uses a porous membrane with a pore size of 2.5-2.8 μm, and the catalyst has a pore size of 2.8-3.4 nm.

[0022] The advantages of this invention are:

[0023] (1) The natural Ca and Al species contained in the biomass semi-char in this invention can have a synergistic effect with the biochar carrier. The porous biochar is used to crack macromolecules with 3 rings or more in the tar, while the metal species are used to crack small volatile fragments with 2 rings or less in the tar, thereby promoting tar reforming and increasing hydrogen production.

[0024] (2) By doping Al species onto the activated carbon catalyst, the decomposition of light compounds in tar reforming can be significantly improved, and the peak intensities of naphthalene and biphenyl / acenaphthene are significantly reduced after using Al / activated carbon catalyst; by doping Ca species onto the activated carbon catalyst, the gas yield and H2 / CO ratio in tar reforming can be significantly increased.

[0025] (3) By coupling the membrane reactor with the tar reforming catalyst, the present invention can reform and retain tar and solid particles in situ in one step, and there is a strong synergistic effect between the catalyst and the membrane.

[0026] (4) This invention achieves the targeted and efficient removal of tar molecules of different molecular diameters by adjusting the mass ratio of activator and biomass semi-coke to directionally control ash content, specific surface area of ​​porous carbon and average pore size. Attached Figure Description

[0027] Figure 1 The following are diagrams of the SiC membrane-gasification system of the present invention: (a) a physical image of the SiC membrane, (b) a membrane-based quartz tube reactor, (c) a carbon-based catalyst placed inside or outside the membrane, and (d) a physical image of a metal filter liner.

[0028] Figure 2 Here are the XRD and XPS analysis images of different catalysts: (a) magnified XRD images of different catalysts, (b) overall XRD images of different catalysts, (c) XPS analysis of Ca in biochar, (d) XPS analysis of Ca in A-Biochar.

[0029] Figure 3 The following are the effects of catalysts on product distribution: (a) Effect on tar yield and tar removal rate, (b) Effect on syngas yield and H2 / CO, (c) Effect on solid particle yield and solid particle retention rate, (d) SEM image and particle size analysis of solid particles, (e) Effect of activated carbon-based catalysts on tar yield and tar removal rate, and (f) Effect of activated carbon-based catalysts on syngas yield and H2 / CO.

[0030] Figure 4 Here are the GC-MS analysis results: (a) catalyst-free and semi-coke-based catalysts, (b) activated carbon-based catalysts;

[0031] Figure 5 The TGA-MS results are as follows: phenol (m / z=94) (a-a'), indene (m / z=116) (b-b'), naphthalene (m / z=128) (c-c'), biphenyl / acenaphthene (m / z=154) (d-d'), fluorene (m / z=166) (e-e'), and anthracene / phenanthrene (m / z=178) (f-f');

[0032] Figure 6 The graphs are: (a) tar yield and tar conversion efficiency with and without catalyst under M2.6μm SiC membrane, and (b) particulate matter yield and particulate matter removal efficiency.

[0033] Figure 7 This is a graph showing the effect of the average pore size of the SiC membrane and catalyst, and the diameter of tar molecules on the tar removal rate. Detailed Implementation

[0034] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. Example

[0035] This embodiment uses corn cobs as raw material to prepare corn cob semi-coke through pyrolysis, and uses a physical activation method to prepare activated semi-coke-based catalysts, including the following specific preparation steps:

[0036] S1. Preparation of biomass semi-coke:

[0037] Biomass feedstock corn cobs or poplar wood (0.3-0.9 mm) were placed in a quartz tube reactor (inner diameter: 25 mm, length: 750 mm) and pyrolyzed for 1 h under an inert atmosphere of nitrogen (N2, flow rate 400 mL / min), at a temperature of 500 ℃ and a heating rate of 30 ℃ / min to obtain a biochar semi-coke catalyst.

[0038] S2, Activation Treatment:

[0039] Approximately 15 g of biomass semi-coke was loaded into the middle of a quartz tube reactor (750 mm in length and 25 mm in inner diameter), heated to 800 °C at a heating rate of 10 °C / min, and held at the terminal temperature for 1 h. The corresponding steam to biochar (S / B) mass ratio was 0.9, and the total flow rate of the gas mixture (steam / N2) was fixed at 500 mL / min, thus obtaining an activated biochar-based tar reforming catalyst.

[0040] Al single-metal catalysts were prepared using an impregnation / hydrothermal synthesis method with activated carbon catalyst as a support, including the following specific preparation steps:

[0041] Activated carbon catalyst and aluminum nitrate Al(NO3)3 (Al2O3: 10-15 wt%) were mixed and stirred in a beaker containing 50 mL of deionized water for 6 hours; dried at 80 °C for 12 h; and calcined at 800 °C for 1 h under an inert atmosphere or nitrogen (N2) to obtain an Al / activated carbon catalyst. Alternatively, activated carbon catalyst and aluminum nitrate Al(NO3)3 were mixed evenly in a beaker containing 50 mL of deionized water, placed in a reactor, and hydrothermally synthesized at 180 °C for 12 h, dried at 80 °C for 12 h, and calcined at 800 °C for 1 h under an inert atmosphere or nitrogen (N2) to obtain an Al / activated carbon catalyst.

[0042] Using activated carbon catalyst as a support, Ca single-metal catalysts were prepared by impregnation / hydrothermal synthesis, including the following specific preparation steps:

[0043] Activated carbon catalyst and calcium nitrate Ca(NO3)2 (10-15 wt%) were mixed and stirred for 6 hours in a beaker containing 50 mL of deionized water; dried at 80 °C for 12 hours; and calcined at 800 °C for 1 hour under an inert atmosphere or nitrogen (N2) to obtain a Ca / activated carbon catalyst. Alternatively, activated carbon catalyst and aluminum nitrate Al(NO3)3 were mixed evenly in a beaker containing 50 mL of deionized water, placed in a reactor, and hydrothermally synthesized at 180 °C for 12 hours, dried at 80 °C for 12 hours, and calcined at 800 °C for 1 hour under an inert atmosphere or nitrogen (N2) to obtain a Ca / activated carbon catalyst.

[0044] Performance testing

[0045] 1. Biochar-based catalyst gasification experiment

[0046] The gasification experiment was conducted in a membrane-based quartz tube reactor. Figure 1 (b) The membrane (100 mm in length, 36 mm in outer diameter, 24 mm in inner diameter, bottom-sealed) is connected to a stainless steel tube via a sealing flange with a graphite gasket to ensure that all volatiles are discharged through the membrane before or after interaction with the carbon-based catalyst (e.g., Figure 1 (as shown in (c)). For comparison, a porous stainless steel filter with a diameter of approximately 3 mm without solid particle filtration capability was used. Figure 1 (d) This can be considered a fixed-bed reactor. For each experiment, 3 g of biomass was added to the reactor after preheating it to the specified temperature (800 °C). Simultaneously, steam was injected into the reactor via a liquid injection pump and a steam generator, with a steam-to-biomass (S / B) mass ratio of 1.5. The carrier gas (N2) flow rate was 500 mL / min, corresponding to a volatile retention time of 29 s. During gasification, particulate matter (PMs) in the volatiles were retained by a silicon carbide (SiC) membrane, while tar volatiles were cracked / reformed by a carbon-based catalyst. The liquid product was collected through a sprayer filled with tetrahydrofuran (THF), and PMs and biotar were separated sequentially by filtration and rotary evaporation. Non-condensable gases were collected in a gas bag for subsequent analysis.

[0047] 2. Characterization of properties of activated biochar semi-coke-based catalysts

[0048] X-ray diffraction (XRD) analysis was performed on different catalysts, and the results are as follows: Figure 2 As shown in (a), the overall pattern is as follows: Figure 2(b) In the XRD patterns of Biochar, A-Biochar, ACcomm, and Ca / ACcomm catalysts, broad peaks at 2θ of 20–40° were observed, confirming the amorphous nature of the carbonaceous materials. Peaks at 2θ of 20.86°, 26.64°, 36.55°, 50.14°, and 59.96° were found in all catalysts, which can be classified as the (100), (011), (110), (112), and (211) crystal planes of SiO2 (PDF 79–1906).

[0049] In the A-Biochar and Ca / ACcomm catalysts, peaks at 2θ of 31.60°, 33.15°, 41.383°, and 44.161° were observed, corresponding to the (103), (112), (200), and (161) crystal planes of the Al4Ca (PDF 14-0428) species, which were absent in the Biochar and ACcomm catalysts. Furthermore, peaks at 31.23°, 31.65°, and 39.38° could be classified as the (111), (013), and (113) crystal planes of the SiCa (PDF 26-0324) species, which were observed in the A-Biochar and Ca / ACcomm catalysts but absent in the Biochar and ACcomm catalysts.

[0050] The Ca-containing peaks observed in A-Biochar catalysts indicate that, during activation, the metal active sites are better exposed on the carbonaceous matrix, which should facilitate the interaction between biovolatiles and the catalyst. This result was obtained using Biochar and A-Biochar catalysts (…). Figure 2 XPS surface analysis of (c)-(d) further supports this. Compared to Biochar, A-Biochar shows higher peak intensity in the Ca2p scanning mode, indicating higher Ca2p activity. 3 / 2 and Ca2p 1 / 2 The peaks are located at binding energies of approximately 346.8 eV and 250.4 eV, respectively.

[0051] The porosity analysis results of different catalysts are summarized in Table 1. As a reference catalyst, the ACcomm catalyst has a surface area of ​​approximately 672.6 m² / g and a micropore area of ​​491.1 m² / g, while the Biochar catalyst has a surface area of ​​208.7 m² / g. When the semi-coke is activated under a steam-to-semi-coke mass ratio of 0.5, the surface area increases to approximately 324.4 m² / g, and the pore size also increases, from 2.4 nm for Biochar to 3.1 nm for A-Biochar. Unless otherwise specified, all catalysts tested in this invention were obtained under a steam-to-semi-coke mass ratio of 0.5. In the catalytic gasification of biomass, larger volatile fractions can be broken down into smaller fractions within the mesoporous structure of the catalyst. These smaller fractions can be further broken down by micropores as they pass through the catalyst bed. This layered pore effect of the A-Biochar catalyst is beneficial for the reforming / cracking of biotar to produce clean syngas. During the activation process, the mass ratio of water vapor to semi-coke was 0.3, 0.5, and 0.7, respectively. The properties of the prepared catalysts are shown in Table 1.

[0052] Table 1 Properties of different catalysts

[0053]

[0054] in: a BET surface area, b t-Plot micropore area c The total pore volume of a single-point adsorption at p / p° = 1 for a pore with a diameter less than 808 nm. d t-Plot microwell volume e 4V / A by the BET method.

[0055] 3. Effect of catalyst on product distribution

[0056] like Figure 3 As shown in (a), in the SiC film ( Figure 1 In (c) using a Biochar catalyst, the tar conversion increased from approximately 48.9% without the catalyst to approximately 81.6%. These results were accompanied by an increase in syngas yield (approximately 66 mmol / g biomass). Figure 3 (b) and the improvement in PM removal efficiency (89%) Figure 3 (c) Biochar was steam-activated at 800 °C with a steam-to-semi-coke mass ratio of 0.3, reducing its surface area from 208.7 m². 2 / g increased to 333.5 m 2Further increasing the steam-to-biochar mass ratio to 0.5, 0.7, and 0.9 resulted in a slight decrease in surface area and a slight increase in total volume and average pore size (Table 1). At a steam-to-biochar mass ratio of 0.5, the highest tar conversion rate of approximately 86.1% (tar yield of 13.8 g / m³) was achieved. 3 Simultaneously, syngas yield and PM removal efficiency increased to 74 mmol / g biomass (H2 / CO ratio approximately 2.1) and 94.5%, respectively. Subsequently, the optimal A-Biochar activated at a steam-to-biochar mass ratio of 0.5 was used. Furthermore, Figure 4 GC-MS spectra in (a) and Figure 5 The TGA-MS model confirmed the advantages of activated semi-coke catalysts over unactivated semi-coke catalysts in tar cracking / reforming. This strong beneficial effect of catalyst activation on tar cracking / reforming reactions and syngas quality improvement is attributed to the higher ash-forming mineral content (48.2% A-Biochar vs. 22.3% Biochar, Table 2) and the higher specific surface area (324.4 m² A-Biochar). 2 / g, relative to Biochar 208.7m 2 / g), and better exposure to metallic species (especially Ca).

[0057] Table 2 Organic analysis, industrial analysis and ash composition of different catalysts

[0058]

[0059] in: a ad: dry base, b daf: Anhydrous and ash-free substrate. c Difference.

[0060] Since the position of the catalyst inside or outside the membrane can affect tar conversion efficiency by adjusting the secondary reactions of volatiles, an additional evaluation of the catalytic performance was conducted when an A-Biochar catalyst was loaded externally. The results showed that the tar conversion efficiency was significantly improved to approximately 96.4%, and the H2 / CO ratio increased to 2.4. Simultaneously, by loading the A-Biochar catalyst externally, the removal rate of inhalable particulate matter also increased to approximately 95.9%. This indicates that the catalyst facilitates the cracking of heavy volatiles and steam reforming reactions, thereby reducing the formation of coke deposits in inhalable particulate matter.

[0061] To elucidate the role of active metals in porous carbon matrices and biochar, four catalysts were prepared, including ACcomm (a commercial activated carbon catalyst) and ACcomm catalysts doped with the same amounts of Ca, Al, and Ca / Al as the A-Biochar catalyst. The ACcomm catalyst was used as a control catalyst, exhibiting a lower ash content (~13.4%) and a significantly larger specific surface area (672.6 m²). 2 The ACcomm catalyst exhibits a tar conversion efficiency of approximately 94.3% and a gas yield of 58 mmol / g biomass, respectively, which are lower than those of the A-Biochar catalyst. This indicates that metal species (most abundant Ca and Al) play a significant role in the A-Biochar catalyst. Furthermore, the ACcomm catalyst shows similar, or even slightly lower, efficiency for removing inhalable particulate matter compared to the A-Biochar catalyst. This suggests that the porous structure of the carbon matrix in both A-Biochar and ACcomm catalysts has a positive effect on the retention of inhalable particulate matter, attributed to the strong cracking effect of the porous structure on heavy volatile substances.

[0062] The pyrolysis effect of porous carbon matrix was demonstrated by the near-colorless tar obtained using A-Biochar and ACcomm series catalysts, as well as the GC-MS spectrum. Figure 4 The absence of heavy compound peaks in (b) and TGA-MS modes was further confirmed. The m / z signal of indene (116) was also observed. Figure 5 (b-b')), naphthalene (128) Figure 5 (c-c')) and biphenyl / acenaphthene (154) Figure 5 Compared to (d-d')), fluorene (166) using A-Biochar catalyst... Figure 5 (e-e') and anthracene / phenanthrene (178) Figure 5 The (f-f') signal was significantly reduced and even undetectable after using the ACcomm catalyst, suggesting the superior effect of porous matrices on the pyrolysis of heavy compounds.

[0063] Regarding the role of metal species, studies have found that doping ACcomm catalysts with Ca, Al, and Ca / Al species has little effect on the yield of PMs, and only slightly increases the tar conversion rate, from about 94% for ACcomm catalysts to 95%-96% for Al-doped, Ca-doped, and / or Ca / Al-doped catalysts. Figure 3(e)). However, the gas yield and H2 / CO ratio increased significantly, from 58 mmol / g biomass (H2 / CO approximately 1.50) for the ACcomm catalyst to approximately 70 mmol / g biomass (H2 / CO approximately 2.4) for the Al / ACcomm catalyst and approximately 79 mmol / g biomass (H2 / CO approximately 2.4) for the Ca / ACcomm catalyst. Figure 3 (f) Figure 4 (b) shows that after doping the ACcomm catalyst with Al species, the decomposition of light compounds (1-2 rings, such as naphthalene) is significant, while they are almost undetectable after doping with Ca species. TGA-MS analysis also revealed similar results. The peak intensities of naphthalene (m / z=128) and biphenyl / acenaphthene (m / z=154) were significantly reduced after using the ACcomm catalyst doped with Ca and Al species. Figure 5 (c') and (d')). These results indicate that Ca and Al in the A-Biochar catalyst should be the major active species in the gas generation reactions of relatively light tar fragments (e.g., compounds with 1-2 rings) cracking and reforming, and that the Ca species is slightly superior to the Al species in improving gas yield and H2 / CO ratio. Figure 3 (b) and 3 (f)). The superior effect of Ca is attributed to the higher alkalinity of Ca / ACcomm (1.67 mmol / g) compared to Al / ACcomm's 1.08 mmol / g, as confirmed by CO2-TPD test results.

[0064] The above results demonstrate that doping the ACcomm catalyst with Al species can effectively crack naphthalene, biphenyl, or acenaphthene. In addition, doping the ACcomm catalyst with Ca species can not only effectively crack naphthalene, biphenyl, or acenaphthene, but also significantly improve the tar reforming gas yield and H2 / CO ratio.

[0065] 4. Synergistic effect of catalyst and membrane reactor

[0066] During the experiment, the mass ratio of carbon-based catalyst to biomass was 1:1.5, and the packing method of the carbon-based catalyst was as follows. Figure 1 The membrane was filled as shown in (c) to ensure that all volatiles were discharged through the membrane before or after interacting with the carbon-based catalyst. Coupling the membrane reactor with the tar reforming catalyst allows for simultaneous in-situ reforming and retention of tar and solid particles, with a strong synergistic effect between the catalyst and the membrane. Tar reforming was performed using different catalysts coupled with membrane reactors. The reforming and retention effects of tar and solid particles, as well as the gas yield and H2 / CO ratio, were compared. Specific results are shown in Tables 3 and 4.

[0067] Table 3. Reforming and retention of tar and solid particles after coupling different catalysts with membrane reactors.

[0068]

[0069] According to Table 3 and Figure 6 As can be seen, taking a 2 μm silicon carbide membrane and an A-Biochar catalyst as an example, without the catalyst, the membrane's retention rates for tar and solids are only 48.94% and 56.16%, respectively. With only the catalyst present, the catalyst's reforming effects on tar and solid particles are only 71.23% and 9.59%, respectively. However, when the two are coupled, the reforming effect on tar reaches 96.36%, while the retention rate of solid particles reaches 95.89%. Therefore, coupling a membrane reactor with a tar reforming catalyst can simultaneously improve both in-situ reforming and retention of tar and solid particles.

[0070] Table 4. Tar reforming gas yield and H2 / CO ratio after coupling different catalysts with membrane reactors

[0071]

[0072] Table 4 shows that the H2 / CO ratio of the membrane in the tar reforming process is 1.06 in the absence of a catalyst, and 1.64 in the presence of only the A-Biochar catalyst. However, when the membrane is coupled with the A-Biochar catalyst, the H2 / CO ratio reaches 2.35, and the gas yields of CO2 and CH4 are also higher than in the cases with only the membrane or only the A-Biochar catalyst. This indicates that coupling the membrane with the A-Biochar catalyst is beneficial. Furthermore, when the membrane is coupled with the Ca / ACcomm catalyst, the H2 / CO ratio is the highest, reaching 2.43, and the gas yields of CO2 and CH4 also increase significantly. This demonstrates that doping the ACcomm catalyst with Ca species can significantly improve the gas yield and H2 / CO ratio in tar reforming.

[0073] In addition, such as Figure 7 As shown, by studying the influence of membrane pore size and catalyst average pore size on the tar removal rate of different molecular dynamic diameters, it can be seen that the smaller the SiC membrane pore size (2.6 μm-50 μm), the better the cracking effect on tar molecules with smaller molecular diameters. When the membrane pore size is 2.6 μm, the removal rate of tar molecules with a molecular diameter of 0.69 nm is the highest, approximately 70%. However, the influence of catalyst average pore size on the tar removal rate of different molecular diameters is more complex. When the catalyst average pore size is 3.1 nm, the tar removal effect is optimal, with a removal rate of approximately 96%.

[0074] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any way, and all technical solutions obtained by equivalent substitution or equivalent transformation fall within the protection scope of the present invention.

Claims

1. A method for improving the decomposition effect of light compounds in tar reforming, characterized by, The tar is reformed by using the activated carbon catalyst doped with Al, and the light compounds are one or more of naphthalene, biphenyl or acenaphthylene.

2. The method of improving the decomposition effect of light compounds of tar reforming according to claim 1, characterized in that, The preparation method of the activated carbon catalyst comprises the following preparation steps: S1, preparing biomass semi-coke; S2, activating the prepared biomass semi-coke to obtain the activated carbon catalyst.

3. The method of claim 2, wherein the tar reforming light compound decomposition effect is improved by adding the catalyst to the tar reforming catalyst. In the step S1, the specific preparation steps are as follows: the biomass raw material is put into a reactor, and pyrolysis is carried out by heating in nitrogen to prepare biomass semi-coke; the biomass raw material is corn cob or poplar, the diameter is 0.3-0.9 mm, the flow rate of nitrogen is 50-500 mL / min, the heating rate is 10-50 ℃ / min, the temperature is raised to 450-550 ℃, and the pyrolysis time is 0.5-2 h.

4. The method of claim 2, wherein the tar reforming light compound decomposition effect is improved. In the step S2, the activation method is steam activation, the heating rate of steam is 5-15 ℃ / min, the temperature is raised to 750-850 ℃, and the temperature is maintained for 0.5-2 h, the mass ratio of steam to biomass is 0-0.9, and the total flow rate of steam and N2 is 450-550 mL / min.

5. The method of claim 1, wherein the method is characterized by, The method for doping Al on the activated carbon catalyst is as follows: the activated carbon catalyst and an aluminum salt are mixed and stirred in deionized water, impregnated or hydrothermally synthesized, dried, and calcined under nitrogen to obtain an Al / activated carbon catalyst; the aluminum salt is aluminum nitrate or aluminum acetate.

6. The method of claim 2, wherein the tar reforming light compound decomposition effect is improved. The tar is reformed by using the activated carbon catalyst doped with Ca and Al to improve the tar reforming gas yield and the H2 / CO ratio.

7. The method of improving the decomposition effect of light compounds of tar reforming according to claim 6, characterized in that, The method for doping Ca on the activated carbon catalyst is as follows: the activated carbon catalyst and a calcium salt are mixed and stirred in deionized water, impregnated or hydrothermally synthesized, dried, and calcined under nitrogen; the calcium salt is calcium nitrate or calcium acetate.

8. The method of claim 2, wherein the tar reforming light compound decomposition effect is improved. The tar is reformed by using the activated carbon catalyst doped with Ca and Al to improve the tar reforming gas yield and the H2 / CO ratio.

9. The method of claim 8, wherein the tar reforming light compound decomposition effect is improved. The tar is reformed by using the activated carbon catalyst doped with Ca and Al to improve the tar reforming gas yield and the H2 / CO ratio. The tar is reformed by using the activated carbon catalyst doped with Ca and Al to improve the tar reforming gas yield and the H2 / CO ratio. When the diameter of the tar molecule is 0.65-0.75 nm, the SiC porous membrane with a pore size of 2.5-2.8 μm is used in the tubular membrane reactor, and the pore size of the catalyst is 2.8-3.4 nm.

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