Low rank coal gasification tar steam reforming monolithic catalyst and method of making same
By growing an Al2O3 coating in situ on a woody semi-coke support and loading NiMgAl-LDH-like hydrotalcite nanosheets, the problems of easy carbon deposition in Ni-based catalysts and loss during biomass wood block gasification were solved, achieving high efficiency in tar catalytic activity and stability, suitable for steam reforming of tar from low-rank coal gasification.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- TAIYUAN UNIVERSITY OF TECHNOLOGY
- Filing Date
- 2024-05-08
- Publication Date
- 2026-06-30
AI Technical Summary
Existing Ni-based catalysts are prone to carbon deposition and sintering during tar removal. Powdered catalysts suffer from problems such as large bed pressure drop and large temperature gradient. Traditional ceramic-based monolithic catalysts have low specific surface area and suffer serious losses during biomass wood block gasification, which affects their application performance.
NiMgAl-LDO metal oxide nanoparticles obtained by pyrolysis of NiMgAl-LDH-type hydrotalcite nanosheets were loaded onto a wood semi-coke support with an in-situ grown Al2O3 coating to resist gasification loss, forming an integral catalyst. An Al2O3 coating was grown in-situ on the wood semi-coke and NiMgAl-LDH-type hydrotalcite nanosheets were loaded thereon through hydrothermal synthesis.
It improves the catalyst's resistance to gasification loss and catalytic activity, enhances the contact between reactants and active components, and improves the catalyst's stability and activity, making it suitable for steam reforming of tar from low-rank coal gasification.
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of catalyst preparation technology, and relates to a catalyst for steam reforming of tar, and particularly to an integral catalyst for steam reforming of tar from low-rank coal gasification and its preparation method. Background Technology
[0002] my country has high reserves of low-rank coal, accounting for about 55% of the total coal reserves. The efficient utilization of low-rank coal is the prerequisite and necessary condition for its large-scale development.
[0003] Compared to other technologies, low-rank coal gasification technology can fully utilize its advantages of high volatile matter content and fast reaction speed to produce syngas. However, the high volatile matter content of low-rank coal inevitably leads to a significant tar problem. Therefore, effectively removing coal tar from the syngas produced by low-rank coal gasification is crucial for its subsequent use.
[0004] Steam catalytic reforming of tar can remove tar under relatively mild conditions and make full use of tar components to produce syngas, making it a promising method for tar removal.
[0005] Ni-based catalysts are widely used in tar removal research due to their excellent ability to break C-C and CH bonds and their low cost. However, their application is greatly limited by their tendency to coke and sinter during tar molecule cracking. In addition, powdered catalysts have significant drawbacks in industrial applications, such as large pressure drop in the catalyst bed and large temperature gradients at various points in the bed.
[0006] Monolithic catalysts effectively overcome the shortcomings of powdered catalysts, and their monolithic structure simplifies loading, unloading, and maintenance in reactors, reducing costs and operating expenses. However, traditional ceramic-based monolithic catalyst supports have a low specific surface area, resulting in poor dispersion of active components on the support surface.
[0007] Biomass wood blocks, as a monolithic matrix, not only have the advantage of low price but also possess a well-developed porous structure with long, internally permeable, and slightly curved mesoporous channels, which facilitates full contact between reactants and active components, improving activity and stability. However, carbonized wood blocks suffer from gasification loss, which has become a major limiting factor for their application.
[0008] CN 113426450A relates to a monolithic catalyst for biomass tar steam reforming and its preparation method. It employs a hydrothermal synthesis method to grow Ni-Fe-Ce hydrotalcite in situ on a woody semi-coke support, aiming to improve the dispersion of active metals and inhibit their aggregation. However, its shortcomings include not considering the gasification loss of biomass logs and insufficient consideration of the overall stability of the catalyst.
[0009] Wang et al. (Journal of Analytical and Applied Pyrolysis, 2021, 155, 105033.) reported a boron-doped Ni-based biomass semi-coke catalyst, using boron doping to improve the gasification loss problem of semi-coke. However, their experimental results clearly show that while the catalyst exhibits anti-gasification loss effects within 600℃ and 1 h, the problem of severe gasification loss persists as the reaction temperature and reaction time increase. Summary of the Invention
[0010] The purpose of this invention is to provide a monolithic catalyst for low-rank coal gasification tar steam reforming. This catalyst not only has high tar catalytic activity and stability, but also effectively improves the gasification loss resistance of monolithic wood-based semi-coke catalysts.
[0011] The present invention also aims to provide a method for preparing the monolithic catalyst for low-rank coal gasification tar steam reforming.
[0012] The present invention firstly provides a monolithic catalyst for low-rank coal gasification tar steam reforming, which consists of an active component and a support. The active component is NiMgAl-LDO metal oxide nanoparticles obtained by pyrolysis of NiMgAl-LDH-type hydrotalcite nanosheets, which are loaded on an in-situ grown Al2O3-coated anti-gasification loss woody semi-coke support by in-situ growth pyrolysis treatment.
[0013] The monolithic catalyst described above not only has a continuous and permeable pore structure, but also a stable structure with good resistance to gasification loss. Furthermore, the active component nanoparticles supported on the catalyst are uniformly dispersed, which can effectively improve the adsorption and activation performance of the reactants. It exhibits high activity and stability in catalytic low-rank coal gasification tar steam reforming.
[0014] In the monolithic catalyst of the present invention, the active component accounts for 5% to 10% of the total mass of the catalyst, the Al2O3 coating accounts for 10% to 20% of the total mass of the catalyst, and furthermore, the Ni component in the active component accounts for 5% to 20% of the total mass of the active component as elemental Ni.
[0015] Specifically, in the monolithic catalyst of the present invention, the NiMgAl-LDH type hydrotalcite nanosheets are obtained by hydrothermal synthesis of a mixed salt aqueous solution of nickel, aluminum and magnesium with added urea and ammonium fluoride as a precursor solution, and the NiMgAl-LDO metal oxide nanoparticles are obtained by high-temperature treatment of NiMgAl-LDH type hydrotalcite nanosheets under an inert atmosphere.
[0016] Specifically, in the monolithic catalyst of the present invention, the in-situ grown Al2O3 coating anti-gasification loss wood semi-coke is a modified wood semi-coke coated with Al2O3 obtained by hydrothermal synthesis treatment of wood semi-coke impregnated with urea and aluminum salt, followed by high-temperature treatment in an inert atmosphere.
[0017] The present invention further provides a method for preparing the aforementioned monolithic catalyst for low-rank coal gasification tar steam reforming, the method comprising the following steps:
[0018] 1) Wood semi-coke is impregnated with an aluminum salt aqueous solution containing urea, and hydrothermal synthesis is carried out at 90-180℃. Then, it is subjected to high-temperature treatment at 500-600℃ under an inert atmosphere to obtain wood semi-coke with an in-situ grown Al2O3 coating that is resistant to gasification loss.
[0019] 2) Urea and ammonium fluoride are added to a mixed salt solution of nickel, magnesium and aluminum salts to obtain a precursor mixed solution;
[0020] 3) A mixed solution of wood semi-coke impregnation precursors with in-situ grown Al2O3 coatings to resist gasification loss was hydrothermally synthesized at 90–180℃, and NiMgAl-LDH-type hydrotalcite nanosheets were loaded onto them. The mixture was then treated at 500–600℃ under an inert atmosphere to obtain an integral catalyst for low-rank coal gasification tar steam reforming of wood semi-coke coated with Al2O3 and loaded with NiMgAl-LDO metal oxide nanoparticles.
[0021] Specifically, the urea-containing aluminum salt aqueous solution in step 1) is a uniformly mixed solution obtained by adding urea and aluminum salt to water and stirring for 0.5 to 1 hour, wherein the preferred molar ratio of urea to aluminum salt is 1:3 to 6.
[0022] Specifically, in the precursor mixture solution of step 2), the molar ratio of nickel salt, magnesium salt, and aluminum salt should satisfy (Ni 2+ +Mg 2+ ) / Al 3+ =2~3∶1, and the preferred molar ratio of the mixed salt to urea and ammonium fluoride is 1∶3~6∶6~10.
[0023] Furthermore, in steps 1) and 3) of the present invention, the impregnation is preferably carried out by vacuum impregnation, in which the corresponding solution is impregnated with the corresponding carrier so that the solution can be completely impregnated into the carrier.
[0024] Furthermore, the hydrothermal synthesis treatment time described in this invention is preferably 6 to 24 hours, and the high-temperature treatment time is preferably 2 to 4 hours.
[0025] Furthermore, the present invention preferably involves drying the hydrothermal synthesis product before subjecting it to high-temperature treatment. Specifically, the drying process is preferably carried out at 100–120°C for 8–12 hours.
[0026] This invention does not specifically limit the raw material, wood semi-coke, and it can be wood semi-coke prepared by various conventional methods. Preferably, the wood semi-coke used in this invention is obtained by treating raw wood blocks that have been soaked and dried in water at a high temperature of 500-600°C.
[0027] More preferably, the raw wood blocks are soaked in water for 1 to 2 hours, dried at 100 to 120°C for 8 to 12 hours, and then treated at 500 to 600°C for 2 to 4 hours to obtain wood semi-char.
[0028] The method for preparing the monolithic catalyst for steam reforming of low-rank coal gasification tar of the present invention is relatively easy and convenient to implement. The prepared monolithic catalyst for steam reforming of low-rank coal gasification tar is suitable for application in the steam reforming process of low-rank coal gasification tar.
[0029] The monolithic catalyst for low-rank coal gasification tar steam reforming of the present invention uses modified monolithic wood semi-coke resistant to gasification loss as a carrier, and metal oxide particles obtained by pyrolysis of hydrotalcite-like nanosheets grown in situ on the monolithic wood semi-coke carrier as active components. Considering the improvement of the monolithic catalyst's resistance to gasification loss and catalytic activity, a multifunctional synergistic effect is achieved.
[0030] Among these methods, the in-situ growth of an Al2O3 coating within the long and permeable twisted channels of the monolithic wood semi-coke helps protect the wood semi-coke from oxidation under high-temperature hydrothermal conditions and reduces catalyst loss during steam reforming. Simultaneously, the in-situ growth of nano-flower-like hydrotalcite nanosheets with high specific surface area and uniform dispersion in the wood semi-coke microchannels via hydrothermal synthesis, followed by pyrolysis to obtain metal oxide nanoparticles, can greatly improve the contact and activation between the active components and reactants, enhance the dispersion of the active components, and improve the activity and stability of the catalyst, showing promising application prospects. Detailed Implementation
[0031] The specific embodiments of the present invention will be further described in detail below with reference to examples. These examples are only used to more clearly illustrate the technical solutions of the present invention, so that those skilled in the art can better understand and utilize the present invention, and are not intended to limit the scope of protection of the present invention.
[0032] Unless otherwise specified, the production processes, experimental methods, or testing methods involved in the embodiments of this invention are all conventional methods in the prior art, and their names and / or abbreviations are all conventional names in the field, which are very clear and distinct in the relevant application areas. Those skilled in the art can understand the conventional process steps based on the names and apply the corresponding equipment, and implement them according to conventional conditions or the conditions recommended by the manufacturer.
[0033] The various instruments, equipment, raw materials or reagents used in the embodiments of this invention are not subject to any special restrictions on their source. They are all conventional products that can be purchased through regular commercial channels and can be prepared according to conventional methods known to those skilled in the art. Example
[0034] Example 1
[0035] Take a cylindrical raw wood block with a specification of φ15mm×12mm, soak and wash it in deionized water for 1 hour, and then dry it in an oven at 110℃ for 12 hours to obtain a pretreated raw wood block.
[0036] Pretreated virgin wood blocks were placed in a tube furnace and heated to 600℃ at a rate of 5℃ / min for 4 hours to obtain unmodified wood semi-coke carrier.
[0037] Weigh 1.76g of urea and 2.20g of aluminum nitrate and dissolve them in deionized water. Stir for 0.5h to obtain a homogeneous solution. Immerse the unmodified wood semi-coke carrier in the solution and use vacuum impregnation to ensure that the solution completely wets the unmodified wood semi-coke carrier.
[0038] The impregnated unmodified wood semi-coke carrier was placed in a hydrothermal reactor, sealed, and then placed in an oven for hydrothermal reaction treatment at 120℃ for 6 hours. The reaction product was washed five times with deionized water to remove residual precipitates and impurities, and then placed in a tube furnace and treated at 600℃ for 4 hours under a nitrogen atmosphere at a rate of 2℃ / min to prepare the modified wood semi-coke carrier coated with Al2O3.
[0039] Weigh 2.40g urea, 3.10g ammonium fluoride, 0.44g nickel nitrate, 1.12g aluminum nitrate, and 1.12g magnesium nitrate, add them to 150ml deionized water, and stir thoroughly for 30min to obtain a precursor mixture solution. Add the modified woody semi-coke carrier to the precursor mixture solution and perform vacuum impregnation until the modified woody semi-coke carrier is completely impregnated.
[0040] The impregnated modified wood semi-coke carrier and the precursor mixture were placed together in a hydrothermal reactor, sealed, and then placed in an oven and heated to 120°C for 12 hours to grow nano-flower-like LDH on the modified wood semi-coke carrier. The reaction product was washed 5 times with deionized water and dried in an oven at 100°C for 12 hours.
[0041] The dried product was placed in a tube furnace and heated to 550℃ at a rate of 2℃ / min for 4 hours, followed by natural cooling to prepare the catalyst NiMgAl-LDO@Al2O3 for steam reforming of low-rank coal gasification tar.
[0042] Example 2
[0043] Take a cylindrical raw wood block with a specification of φ15mm×12mm, soak and wash it in deionized water for 1 hour, and then dry it in an oven at 110℃ for 12 hours to obtain a pretreated raw wood block.
[0044] Pretreated virgin wood blocks were placed in a tube furnace and heated to 600℃ at a rate of 5℃ / min for 4 hours to obtain unmodified wood semi-coke carrier.
[0045] The raw wood blocks were soaked and washed in deionized water for 1 hour, and then dried in an oven at 110°C for 12 hours to obtain pretreated raw wood blocks.
[0046] Pretreated raw wood blocks with dimensions of 15mm×15mm×12mm were placed in a tube furnace and heated to 600℃ at a rate of 5℃ / min for 4 hours to obtain unmodified wood semi-coke carriers.
[0047] Weigh 0.88g of urea and 1.10g of aluminum nitrate and dissolve them in deionized water. Stir for 0.5h to obtain a homogeneous solution. Immerse the unmodified wood semi-coke carrier in the solution and use vacuum impregnation to ensure that the solution completely wets the unmodified wood semi-coke carrier.
[0048] The impregnated unmodified wood semi-coke carrier was placed in a hydrothermal reactor, sealed, and then placed in an oven for hydrothermal reaction treatment at 120℃ for 6 hours. The reaction product was washed five times with deionized water to remove residual precipitates and impurities, and then placed in a tube furnace and treated at 600℃ for 4 hours under a nitrogen atmosphere at a rate of 2℃ / min to prepare the modified wood semi-coke carrier coated with Al2O3.
[0049] Weigh 2.40g urea, 3.10g ammonium fluoride, 0.44g nickel nitrate, 1.12g aluminum nitrate, and 1.12g magnesium nitrate, add them to 150ml deionized water, and stir thoroughly for 30min to obtain a precursor mixture solution. Add the modified woody semi-coke carrier to the precursor mixture solution and perform vacuum impregnation until the modified woody semi-coke carrier is completely impregnated.
[0050] The impregnated modified wood semi-coke carrier and the precursor mixture were placed together in a hydrothermal reactor, sealed, and then placed in an oven and heated to 120°C for 12 hours to grow nano-flower-like LDH on the modified wood semi-coke carrier. The reaction product was washed 5 times with deionized water and dried in an oven at 100°C for 12 hours.
[0051] The dried product was placed in a tube furnace and heated to 550℃ at a rate of 2℃ / min for 4 hours, followed by natural cooling to prepare the catalyst NiMgAl-LDO@Al2O3-1 / 2 for steam reforming of low-rank coal gasification tar.
[0052] Example 3
[0053] Except for changing the hydrothermal reaction temperature of the modified wood semi-coke support and precursor mixture solution to 90℃, the other preparation processes were exactly the same as in Example 1, and the catalyst NiMgAl-LDO@Al2O3-90℃ was prepared.
[0054] Example 4
[0055] Except for changing the hydrothermal reaction temperature of the modified wood semi-coke support and precursor mixture solution to 150℃, the other preparation processes were exactly the same as in Example 1, and the catalyst NiMgAl-LDO@Al2O3-150℃ was prepared.
[0056] Example 5
[0057] Except for changing the hydrothermal reaction time of the modified wood semi-coke support and precursor mixture solution to 6h, the other preparation process was exactly the same as in Example 1, and the catalyst NiMgAl-LDO@Al2O3-6h was prepared.
[0058] Example 6
[0059] Except for changing the hydrothermal reaction time of the modified wood semi-coke support and precursor mixture solution to 24h, the other preparation process was exactly the same as in Example 1, and the catalyst NiMgAl-LDO@Al2O3-24h was prepared.
[0060] Comparative Example 1
[0061] Take a cylindrical raw wood block with a specification of φ15mm×12mm, soak and wash it in deionized water for 1 hour, and then dry it in an oven at 110℃ for 12 hours to obtain a pretreated raw wood block.
[0062] Pretreated virgin wood blocks were placed in a tube furnace and heated to 600℃ at a rate of 5℃ / min for 4 hours to obtain unmodified wood semi-coke carrier.
[0063] Weigh 2.40g urea, 3.10g ammonium fluoride, 0.44g nickel nitrate, 1.12g aluminum nitrate, and 1.12g magnesium nitrate, add them to 150ml deionized water, and stir thoroughly for 30min to obtain a precursor mixture solution. Add the woody semi-coke support to the precursor mixture solution and vacuum impregnate until the woody semi-coke support is completely wetted.
[0064] The impregnated wood semi-coke carrier and the precursor mixture were placed together in a hydrothermal reactor, sealed, and then placed in an oven and heated to 120°C for 12 hours to grow nano-flower-like LDH on the wood semi-coke carrier. The reaction product was washed 5 times with deionized water and dried in an oven at 100°C for 12 hours.
[0065] The dried product was placed in a tube furnace and heated to 550℃ at a rate of 2℃ / min for 4 hours, followed by natural cooling to prepare NiMgAl-LDO catalyst for steam reforming of low-rank coal gasification tar.
[0066] The difference between this comparative example and Example 1 is that the woody semi-coke carrier was not modified by coating with Al2O3; otherwise, it is the same as Example 1.
[0067] Comparative Example 2
[0068] Take a cylindrical raw wood block with a specification of φ15mm×12mm, soak and wash it in deionized water for 1 hour, and then dry it in an oven at 110℃ for 12 hours to obtain a pretreated raw wood block.
[0069] Pretreated virgin wood blocks were placed in a tube furnace and heated to 600℃ at a rate of 5℃ / min for 4 hours to obtain unmodified wood semi-coke carrier.
[0070] Weigh 1.76g of urea and 2.20g of aluminum nitrate and dissolve them in deionized water. Stir for 0.5h to obtain a homogeneous solution. Immerse the unmodified wood semi-coke carrier in the solution and use vacuum impregnation to ensure that the solution completely wets the unmodified wood semi-coke carrier.
[0071] The impregnated unmodified wood semi-coke carrier was placed in a hydrothermal reactor, sealed, and then placed in an oven for hydrothermal reaction treatment at 120℃ for 6 hours. The reaction product was washed five times with deionized water to remove residual precipitates and impurities, and then placed in a tube furnace and treated at 600℃ for 4 hours under a nitrogen atmosphere at a rate of 2℃ / min to prepare the modified wood semi-coke carrier coated with Al2O3.
[0072] Weigh 0.44 g of nickel nitrate, 1.12 g of aluminum nitrate, and 1.12 g of magnesium nitrate, add them to 150 ml of deionized water, and stir thoroughly for 30 min to obtain a precursor mixture solution. Add the modified wood semi-coke support to the precursor mixture solution and vacuum impregnate until the modified wood semi-coke support is completely wetted. Repeat the impregnation 5 times, then remove and dry in an oven at 80 °C for 12 h.
[0073] The dried product was placed in a tube furnace and heated to 550℃ at a rate of 2℃ / min for 4 hours, followed by natural cooling to prepare the catalyst NiMgAlO@Al2O3 for steam reforming of low-rank coal gasification tar.
[0074] The difference between this comparative example and Example 1 is that the step of in-situ growth of hydrotalcite-like nanosheets on the surface of the modified wood semi-coke carrier was omitted. Ni, Mg, and Al ions were directly grown on the Al2O3 coating surface of the modified wood semi-coke carrier by impregnation. The rest of the preparation process was the same as in Example 1.
[0075] Comparative Example 3
[0076] Take a cylindrical raw wood block with a specification of φ15mm×12mm, soak and wash it in deionized water for 1 hour, and then dry it in an oven at 110℃ for 12 hours to obtain a pretreated raw wood block.
[0077] Pretreated virgin wood blocks were placed in a tube furnace and heated to 600℃ at a rate of 5℃ / min for 4 hours to obtain unmodified wood semi-coke carrier.
[0078] Weigh 6g of pseudoboehmite powder and add it to 100ml of deionized water. Heat to 65℃ and stir under reflux for 2 hours. Add 25% nitric acid solution dropwise to adjust the pH to 1.5. Maintain the temperature at 65℃ and stir under reflux until aluminum sol is formed.
[0079] Unmodified wood semi-coke carrier was immersed in aluminum sol and subjected to repeated vacuum treatment 5 times. After being taken out and washed 3 times, it was treated at a constant temperature of 80℃ in an oven for 12 hours. Then, it was placed in a tube furnace and heated to 600℃ at a rate of 2℃ / min under a nitrogen atmosphere for 4 hours to prepare modified wood semi-coke carrier coated with Al2O3.
[0080] Weigh 2.40g urea, 3.10g ammonium fluoride, 0.44g nickel nitrate, 1.12g aluminum nitrate, and 1.12g magnesium nitrate, add them to 150ml deionized water, and stir thoroughly for 30min to obtain a precursor mixture solution. Add the modified woody semi-coke carrier to the precursor mixture solution and perform vacuum impregnation until the modified woody semi-coke carrier is completely impregnated.
[0081] The impregnated modified wood semi-coke carrier and the precursor mixture were placed together in a hydrothermal reactor, sealed, and then placed in an oven and heated to 120°C for 12 hours to grow nano-flower-like LDH on the modified wood semi-coke carrier. The reaction product was washed 5 times with deionized water and dried in an oven at 100°C for 12 hours.
[0082] The dried product was placed in a tube furnace and heated to 550℃ at a rate of 2℃ / min for 4 hours, followed by natural cooling to prepare the catalyst NiMgAl-LDO@Al2O3(WI) for steam reforming of low-rank coal gasification tar.
[0083] The difference between this comparative example and Example 1 is that the unmodified wood semi-coke carrier is modified by sol-gel impregnation coating, while the rest is the same as Example 1.
[0084] Comparative Example 4
[0085] Take a cylindrical raw wood block with a specification of φ15mm×12mm, soak and wash it in deionized water for 1 hour, and then dry it in an oven at 110℃ for 12 hours to obtain a pretreated raw wood block.
[0086] Pretreated virgin wood blocks were placed in a tube furnace and heated to 600℃ at a rate of 5℃ / min for 4 hours to obtain unmodified wood semi-coke carrier.
[0087] Weigh 1.10g of aluminum nitrate and dissolve it in 100ml of deionized water. Add 100ml of 1.5mol / L ammonia solution dropwise to adjust the pH to 10. Stir for 1h to obtain a uniformly mixed Al(OH)3 precipitate.
[0088] Unmodified wood semi-coke carrier was immersed in Al(OH)3 precipitate solution and subjected to vacuum treatment five times. The precipitate was then injected into the pores of the unmodified wood semi-coke carrier. The carrier was then removed, washed three times, and treated at 80℃ in an oven for 12 hours. Finally, it was placed in a tube furnace and heated to 600℃ at a rate of 2℃ / min under a nitrogen atmosphere for 4 hours to prepare a modified wood semi-coke carrier coated with Al2O3.
[0089] Weigh 2.40g urea, 3.10g ammonium fluoride, 0.44g nickel nitrate, 1.12g aluminum nitrate, and 1.12g magnesium nitrate, add them to 150ml deionized water, and stir thoroughly for 30min to obtain a precursor mixture solution. Add the modified woody semi-coke carrier to the precursor mixture solution and perform vacuum impregnation until the modified woody semi-coke carrier is completely impregnated.
[0090] The impregnated modified wood semi-coke carrier and the precursor mixture were placed together in a hydrothermal reactor, sealed, and then placed in an oven and heated to 120°C for 12 hours to grow nano-flower-like LDH on the modified wood semi-coke carrier. The reaction product was washed 5 times with deionized water and dried in an oven at 100°C for 12 hours.
[0091] The dried product was placed in a tube furnace and heated to 550℃ at a rate of 2℃ / min for 4 hours, followed by natural cooling to prepare the catalyst NiMgAl-LDO@Al2O3(DP) for steam reforming of low-rank coal gasification tar.
[0092] The difference between this comparative example and Example 1 is that the unmodified wood semi-coke carrier is modified by deposition and precipitation coating treatment, while the rest is the same as Example 1.
[0093] Application Example 1: Evaluation of Catalytic Effect of Catalysts
[0094] In a quartz tube fixed-bed reactor with an inner diameter of 16 mm, toluene was used as a model compound for low-rank coal gasification tar, and steam reforming reactions were carried out using the catalysts for steam reforming of low-rank coal gasification tar prepared in Examples 1-6 and Comparative Examples 1-4, respectively.
[0095] A cylindrical monolithic low-rank coal gasification tar steam reforming catalyst with a diameter of 15 mm and a height of 12 mm was fixed in the constant temperature section of the fixed bed reactor and pretreated with pure H2 at 800℃ for 2 hours before the reaction.
[0096] The steam reforming reaction was set at a temperature of 550℃, a water-to-carbon ratio of 2, and a mass hourly space velocity of 5 h⁻¹. -1 The reaction time was 20 hours. The reaction products were sampled in real time, dried, and then analyzed online by chromatography to calculate the toluene conversion rate, hydrogen yield, CO selectivity, and CO2 selectivity.
[0097] The mass of the catalyst before and after the reaction was weighed to obtain the mass loss rate of the catalyst, so as to quantify the catalyst's ability to resist gasification loss.
[0098] The adhesion stability of the coating on the modified wood semi-coke carrier after ultrasonic vibration test was tested, and the catalyst mass before and after ultrasonic treatment was recorded to obtain the coating peeling rate.
[0099] The specific test results are listed in Table 1:
[0100]
[0101] As can be seen from the experimental results in Table 1, using monolithic wood-based semi-coke as a carrier, and modifying it with a coating and growing a hydrotalcite-like nanosheet structure in situ, the activity and stability of the catalyst can be improved in each embodiment. Furthermore, by adjusting the coating method, hydrothermal synthesis temperature and time, and the growth mode of the active components, the synergistic effect of the monolithic catalyst for steam reforming low-rank coal gasification tar can be achieved.
[0102] Compared with Comparative Example 1, the toluene conversion rate and catalyst mass loss rate clearly show that by introducing Al2O3 as a coating, the problem of easy gasification loss of wood semi-coke under high temperature and water vapor environment can be effectively alleviated. The toluene conversion rate and hydrogen yield are both increased. The results show that the Al2O3 coating with high specific surface area and the micro-torsional channels existing in the wood semi-coke itself enhance the diffusion and mass transfer of reactants during the catalytic reaction. The decrease in CO selectivity indicates that the catalyst improves the water vapor shift reaction activity and enhances the adsorption and activation of water during the reaction process.
[0103] Compared with Example 1, Example 2 demonstrates that by adjusting the Al2O3 coating preparation process, the properties of the coating can be optimized, further improving the catalyst's oxidation resistance and the coating's stability.
[0104] Comparing Examples 1 with Examples 3-6, it can be seen that by adjusting the hydrothermal synthesis conditions, the morphology of hydrotalcite-like nanosheets can be further improved, such as increasing the specific surface area, increasing the exposure of active sites, and improving the dispersion of active metals. Appropriate hydrothermal synthesis time and hydrothermal temperature help to modulate the controllable growth of hydrotalcite-like nanosheet structures.
[0105] Furthermore, a comparison between Example 1 and Comparative Example 2 shows that the in-situ grown hydrotalcite-like structure can improve the contact between reactants and active components compared to catalysts that directly impregnate the active components in an Al2O3 coating, thus significantly improving catalyst activity and stability.
[0106] Compared with Example 1, Comparative Examples 3 and 4 showed a decrease in toluene conversion and hydrogen yield, indicating that the coating method also affects the catalyst's reactivity. The coating obtained by in-situ hydrothermal synthesis is more stable and has better reactivity than that obtained by impregnation and deposition / precipitation methods.
[0107] Application example: Resistance to gasification loss of catalysts
[0108] To test the resistance to gasification loss of wood semi-coke at different temperatures, catalytic effects of the catalyst in Example 1 were tested at steam reforming reaction temperatures of 600℃ and 700℃ for 20 h, and at a reaction temperature of 700℃ for 50 h. The catalytic effects were compared with those of Comparative Example 1 and Comparative Example 2 catalysts at a reaction temperature of 700℃ for 50 h. The results are shown in Table 2.
[0109]
[0110] In Example 1, increasing the reaction temperature and time slightly increased the toluene conversion rate, but did not significantly reduce the catalyst mass loss. However, further comparison of Comparative Examples 1 and 2 showed that catalysts without coating or in-situ grown hydrotalcite exhibited varying degrees of decrease in activity and stability after increasing the reaction temperature and time. The decrease in resistance to gasification loss and activity was more pronounced in the uncoated catalyst of Comparative Example 1.
[0111] The above application examples show that in-situ growth of Al2O3 coating on monolithic wood semi-coke followed by in-situ growth of hydrotalcite-like nanosheets and pyrolysis to obtain metal oxide nanoparticles is of great significance for improving the antioxidant properties, structural stability, and catalytic activity of monolithic catalysts. It also shows good prospects for application in the steam reforming reaction of low-rank coal gasification tar.
[0112] The above embodiments of the present invention do not describe all details exhaustively, nor do they limit the present invention to the above embodiments. Various changes, modifications, substitutions, and variations made by those skilled in the art to the embodiments without departing from the principles and spirit of the present invention should be included within the scope of protection of the present invention.
Claims
1. A monolithic catalyst for low-rank coal gasification tar steam reforming, comprising: wood-based semi-coke with an in-situ grown Al2O3 coating as a support, supporting in-situ grown NiMgAl-LDH-type hydrotalcite nanosheets; and obtaining NiMgAl-LDO metal oxide nanoparticles as the active component via pyrolysis. The active component accounts for 5%–10% of the total mass of the catalyst, the Al2O3 coating accounts for 10%–20% of the total mass of the catalyst, and the Ni component in the active component, calculated as elemental Ni, accounts for 5%–20% of the total mass of the active component. in, NiMgAl-LDH-type hydrotalcite nanosheets were prepared by hydrothermal synthesis using a mixed salt solution of nickel, aluminum, and magnesium containing urea and ammonium fluoride as a precursor solution, and then NiMgAl-LDO metal oxide nanoparticles were obtained by high-temperature treatment under an inert atmosphere. Among them, the in-situ grown Al2O3 coating anti-gasification loss wood semi-coke is a modified wood semi-coke coated with Al2O3 obtained by hydrothermal synthesis treatment of wood semi-coke impregnated with urea and aluminum salt, followed by high-temperature treatment in an inert atmosphere.
2. A method for preparing a monolithic catalyst for low-rank coal gasification tar steam reforming, comprising the following steps: 1) Wood semi-coke is impregnated with an aluminum salt aqueous solution containing urea, and hydrothermal synthesis is carried out at 90-180℃. Then, it is subjected to high-temperature treatment at 500-600℃ under an inert atmosphere to obtain wood semi-coke with an in-situ grown Al2O3 coating that is resistant to gasification loss. 2) Urea and ammonium fluoride are added to a mixed salt solution of nickel, magnesium and aluminum salts to obtain a precursor mixed solution; 3) A mixed solution of wood semi-coke impregnation precursors with in-situ grown Al2O3 coatings to resist gasification loss was hydrothermally synthesized at 90–180℃, and NiMgAl-LDH-type hydrotalcite nanosheets were loaded onto them. The mixture was then treated at 500–600℃ under an inert atmosphere to obtain an integral catalyst for low-rank coal gasification tar steam reforming of wood semi-coke coated with Al2O3 and loaded with NiMgAl-LDO metal oxide nanoparticles.
3. The method for preparing the monolithic catalyst according to claim 2, characterized in that: The wood semi-char is obtained by treating raw wood blocks that have been soaked and dried in water at a high temperature of 500-600℃.
4. The method for preparing the monolithic catalyst according to claim 3, characterized in that: The raw wood blocks are soaked in water for 1-2 hours, dried at 100-120℃ for 8-12 hours, and then treated at 500-600℃ for 2-4 hours to obtain semi-charred wood.
5. The method for preparing the monolithic catalyst according to claim 2, characterized in that: In the urea-containing aluminum salt aqueous solution, the molar ratio of aluminum salt to urea is 1:3 to 6.
6. The method for preparing the monolithic catalyst according to claim 2, characterized in that: The molar ratio of nickel salt, magnesium salt, and aluminum salt in the precursor mixture solution satisfies (Ni 2+ +Mg 2+ ) / Al 3+ =2~3∶1, the molar ratio of mixed salt to urea and ammonium fluoride is 1∶3~6∶6~10.
7. The method for preparing the monolithic catalyst according to claim 2, characterized in that: The hydrothermal synthesis treatment time is 6–24 hours, and the high-temperature treatment time is 2–4 hours.
8. The application of the monolithic catalyst for low-rank coal gasification tar steam reforming as described in claim 1 in the steam reforming of low-rank coal gasification tar.