Solid waste-based calcium-iron composite catalyst, preparation method and application thereof

Abstract

The application discloses a solid waste-based calcium-iron composite catalyst and a preparation method and application thereof, and belongs to the technical field of hydrogen production catalysts. The preparation method provided by the application comprises the following steps: after red mud is ground and sieved, the red mud is sequentially subjected to acid pickling, alkali washing and water washing, and then is dried and calcined to obtain pretreated red mud; carbide slag is washed with water, dried, and then calcined to obtain pretreated carbide slag; the pretreated red mud and the pretreated carbide slag are mixed at a mass ratio of (20-25):(75-80), and then are dispersed in a citric acid aqueous solution, heated and stirred, dried, and then subjected to high-temperature reduction to obtain the calcium-iron composite catalyst. The raw materials are widely sourced and low in cost, the high-value utilization of solid waste can be realized, the catalyst obtained can efficiently catalyze the hydrogen production by methane cracking, can catalyze CO2 generated by carbon deposition in the process of steam gasification to generate CO in the process of catalyst regeneration, has high hydrogen production rate and carbon deposition removal effect, and the catalyst has good sintering resistance and excellent recycling performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of hydrogen production catalysts, in particular to a solid waste-based calcium-iron composite catalyst, a preparation method thereof and an application thereof. BACKGROUND

[0002] The information disclosed in the background of the present application is only intended to increase the understanding of the overall background of the present application and should not necessarily be regarded as acknowledging or implying in any form that the information constitutes prior art known to those skilled in the art.

[0003] Methane catalytic cracking for hydrogen production is a promising technology, which directly decomposes methane into H2 and solid carbon at high temperature through catalysts, avoiding CO2 emissions in traditional hydrogen production processes. The reaction equation is: The obtained H2 has high purity and is a high-efficiency and clean energy source, which is suitable for various application scenarios, including fuel cells, chemical industry raw materials, and energy storage media, etc. Compared with traditional methane steam reforming for hydrogen production, methane catalytic cracking for hydrogen production has lower energy consumption, with ΔH 298K 74.8 kJ / mol, and lower energy consumption, so methane catalytic cracking for hydrogen production as a clean H2 production method has received extensive attention.

[0004] The commonly used methane catalytic cracking catalysts for hydrogen production include Ni, Co, and Fe, etc. The synthesis process of the catalysts for methane catalytic cracking for hydrogen production is complicated, which further increases the cost of the catalysts. Bayer red mud is a solid waste produced by the aluminum industry, which contains a large amount of Fe2O3, Al2O3, SiO2, TiO2, etc. Fe2O3 is a raw material for preparing Fe-based catalysts for catalyzing methane cracking, so the Bayer red mud has good application prospect in the field of methane catalytic cracking. However, the original red mud has poor pore structure, and the contained Na and K elements accelerate the sintering of the catalyst. In addition, carbon produced in the process of methane catalytic cracking will deposit on the surface and pores of the catalyst, leading to the deactivation of the catalyst. In the process of methane catalytic cracking for hydrogen production, efficient catalysis of methane cracking and removal of carbon deposition to regenerate the deactivated catalyst are technical difficulties.

[0005] In the prior art, steam is used to react with the carbon deposition on the catalyst to effectively remove the carbon deposition and regenerate the catalyst, and hydrogen energy is also prepared. However, CO2 is produced in the gasification process. Therefore, how to provide a solid waste-based catalyst to realize efficient catalytic cracking of methane for hydrogen production while converting the CO2 produced in the carbon deposition gasification process into other energy substances to improve the economic benefit of the methane catalytic cracking for hydrogen production process is a problem to be solved. SUMMARY

[0006] Therefore, the application provides a solid waste-based calcium-iron composite catalyst, a preparation method and application thereof, solves the problems of low catalytic activity and easy sintering of the existing red mud-based solid waste catalyst, and the gasification process for removing accumulated carbon can effectively convert CO2 into CO.

[0007] In a first aspect, the application provides a preparation method of a solid waste-based calcium-iron composite catalyst, comprising the following steps:

[0008] The red mud is ground and sieved, then sequentially subjected to acid washing, alkali washing and water washing, dried, calcined to obtain pretreated red mud;

[0009] The carbide slag is washed with water, dried, and then calcined to obtain pretreated carbide slag;

[0010] The pretreated red mud and the pretreated carbide slag are mixed at a mass ratio of (20-25):(75-80), dispersed in a citric acid aqueous solution, heated and stirred, dried, and then reduced at high temperature to obtain the solid waste-based calcium-iron composite catalyst.

[0011] Preferably, the acid washing, alkali washing and water washing steps are specifically as follows: the ground and sieved red mud is added into a hydrochloric acid solution and stirred for 1-3 h, then ammonia water is added and stirred until the pH is 7.5-8.5, then the mixture is left to stand and filtered, and then washed with water until neutral.

[0012] Further, the amount of the red mud and the hydrochloric acid solution is 10 g:(400-600) mL, the concentration of the hydrochloric acid solution is 0.5-2 mol / L, and the concentration of the ammonia water is 20-30 wt%.

[0013] Preferably, in the step of drying and then calcining to obtain the pretreated red mud, the drying temperature is 100-130℃, and the drying time is 5-20 h; the calcining temperature is 500-700℃, and the calcining time is 1-3 h.

[0014] Preferably, in the step of washing and then drying the carbide slag, the water washing step is specifically as follows: the carbide slag is washed with water until the washing liquid is clear, the drying temperature is 100-130℃, and the drying time is 5-20 h.

[0015] Preferably, in the step of calcining to obtain the pretreated carbide slag, the calcining temperature is 700-900℃, and the calcining time is 1-3 h.

[0016] Preferably, the amount ratio of the total mass of the pretreated red mud and the pretreated carbide slag to the citric acid aqueous solution is 10 g:(200-300) mL, and the concentration of the citric acid aqueous solution is 10-20 wt%.

[0017] Preferably, in the heating-stirring and drying step, the temperature of the heating-stirring is 60-80 DEG C, the stirring time is 2-5 h; the temperature of the drying is 100-130 DEG C, and the drying time is 5-20 h.

[0018] Preferably, the temperature of the high-temperature reduction is 750-850 DEG C, the time of the high-temperature reduction is 1-2 h, and the reducing gas of the high-temperature reduction is selected from H2, CO or CH4.

[0019] In a second aspect, the present application provides a solid waste-based calcium-iron composite catalyst prepared by the above preparation method, wherein the active components of the solid waste-based calcium-iron composite catalyst include CaO, CaAl2Si2O8, CaTiO3 and Fe.

[0020] In a third aspect, the present application provides an application of the above solid waste-based calcium-iron composite catalyst in catalyzing methane cracking to produce hydrogen.

[0021] Compared with the prior art, the present application has the following beneficial effects:

[0022] (1) The present application uses solid waste red mud and carbide slag as main raw materials to prepare a composite catalyst, and the raw materials are widely available and low in cost, so that the high-value utilization of solid waste can be realized; in addition, the red mud and the carbide slag are pretreated before being mixed and calcined, so that the composite catalyst obtained by calcination has a good pore structure and high catalytic activity, which is conducive to improving the conversion rate of the methane cracking, and the methane conversion rate is as high as 80% or more.

[0023] (2) The solid waste-based calcium-iron composite catalyst prepared by the present application has active components including CaO, CaAl2Si2O8, CaTiO3 and Fe. Fe has high-efficiency catalytic performance in catalyzing methane cracking to produce hydrogen at 700-900 DEG C, and Fe from the red mud has the advantages of low cost, non-toxicity and high-temperature resistance; in the process of water vapor gasification carbon deposition, CaO from the carbide slag in-situ captures CO2 generated by water vapor gasification carbon deposition to generate CaCO3, and CaCO3 reacts with hydrogen generated by water vapor gasification carbon deposition to generate CaO and CO, realizing the conversion of CO2 to CO and the in-situ conversion of CaO-CaCO3-CaO (i.e. regeneration of the solid waste-based calcium-iron composite catalyst); therefore, the solid waste-based calcium-iron composite catalyst provided by the present application can not only efficiently catalyze methane cracking to produce hydrogen, but also catalyze CO2 generated by water vapor gasification carbon deposition to generate CO in the process of catalyst regeneration, and the CO can be further utilized as an energy material, and the hydrogen production rate and the carbon deposition removal effect are high.

[0024] (3) The CaTiO3 generated by the reaction of TiO2 in the red mud and CaO in the carbide slag is a perovskite type substance, which has abundant electron transfer channels and helps the methane cracking reaction to proceed, and the reaction of Al2O3 and SiO2 in the red mud with CaO generates CaAl2Si2O8 with high sintering resistance, which helps to maintain the stability of the solid waste-based calcium-iron composite catalyst and makes it have excellent recycling performance. BRIEF DESCRIPTION OF DRAWINGS

[0025] The drawings accompanying the specification of this application form a part thereof, serve to further provide a further understanding of the application, and together with the description of the exemplary embodiments of the application, explain the application, but do not limit the application in any way. Obviously, for those skilled in the art, other drawings can also be obtained from these drawings without any creative effort.

[0026] Figure 1 is a scanning electron microscope (SEM) image of the solid waste-based calcium-iron composite catalyst of Example 1 of the application;

[0027] Figure 2 is a transmission electron microscope (TEM) image of the solid waste-based calcium-iron composite catalyst of Example 1 of the application;

[0028] Figure 3 is a schematic diagram of the methane catalytic cracking hydrogen production system of Example 2 of the application;

[0029] Figure 4 is a curve of the conversion rate of methane cracking catalyzed by the red mud catalyst of Comparative Example 1 of the application;

[0030] Figure 5 is a gas composition diagram of the carbon deposition water vapor gasification of the red mud catalyst of Comparative Example 1 of the application;

[0031] Figure 6 is a curve of the conversion rate of methane cracking catalyzed by the modified red mud catalyst of Comparative Example 2 of the application;

[0032] Figure 7 is a gas composition diagram of the carbon deposition water vapor gasification of the modified red mud catalyst of Comparative Example 2 of the application;

[0033] Figure 8 is a curve of the conversion rate of methane cracking catalyzed by the solid waste-based calcium-iron composite catalyst of Example 1 of the application;

[0034] Figure 9 is a gas composition diagram of the carbon deposition water vapor gasification of the solid waste-based calcium-iron composite catalyst of Example 1 of the application;

[0035] Figure 10 is a graph of the average conversion rate of the solid waste-based calcium-iron composite catalyst of Example 1 of the application in multiple cycles of catalyzing methane cracking.

[0036] Figure 11 is a hydrogen yield graph of the carbon deposition in the multiple steam gasification process of the solid waste-based calcium-iron composite catalyst of the present application;

[0037] Figure 12 is an X-ray diffraction pattern of the catalysts of Example 1, Comparative Example 1 and Comparative Example 2 of the present application;

[0038] wherein, 1, a methane storage tank; 2, a solid waste-based calcium-iron composite catalyst storage tank; 3, a methane cracking furnace; 4, a hydrogen storage tank; 5, a CO storage tank; 6, a condenser; 7, a CO2 in-situ conversion furnace; 8, a gasification furnace; 9, a steam generator; 10, a water tank; 11, a deactivated solid waste-based calcium-iron composite catalyst storage bin; 12, a NaOH solution tank. DETAILED DESCRIPTION

[0039] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the present application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0040] The present application provides a preparation method of a solid waste-based calcium-iron composite catalyst, comprising the following steps:

[0041] The red mud is ground and sieved, and then sequentially subjected to acid washing, alkali washing and water washing, dried, and calcined to obtain pretreated red mud;

[0042] The carbide slag is washed with water, dried, and then calcined to obtain pretreated carbide slag;

[0043] The pretreated red mud and the pretreated carbide slag are mixed in a mass ratio of (20-25):(75-80), dispersed in a citric acid aqueous solution, heated and stirred, dried, and then reduced at high temperature to obtain the solid waste-based calcium-iron composite catalyst.

[0044] The present application finds that the red mud without acid washing treatment has low catalytic efficiency in the process of catalyzing methane cracking, and the conversion rate is continuously reduced as the reaction time is prolonged due to continuous carbon deposition. The red mud treated by acid washing has a good pore structure, which can improve the methane conversion rate. However, the red mud treated by acid washing and calcined and reduced as a catalyst will still have continuous carbon deposition in the process of catalytic reaction, the H2 yield in the gas produced by steam gasification is very low, and the carbon deposition removal effect is poor.

[0045] The present invention uses pretreated red mud and pretreated carbide slag as the main raw materials. The active ingredients of the solid waste-based calcium iron composite catalyst obtained after calcination and reduction include CaO, CaAl2Si2O8, CaTiO3, and Fe. The Fe in the red mud has the performance of efficiently catalyzing the catalytic cracking of methane to produce hydrogen at 800-900°C. During the process of steam gasification of carbon deposits, the CaO contained in the carbide slag in situ captures the CO2 generated by the steam gasification of carbon deposits to form CaCO3. The CaCO3 reacts with the hydrogen generated by the steam gasification of carbon deposits to form calcium oxide and CO, realizing the conversion of CO2 to CO and also achieving the in-situ conversion of CaO-CaCO3-CaO (regeneration of the solid waste-based calcium iron composite catalyst).

[0046] The specific reaction process includes:

[0047] CH4→2H2+C

[0048] C+H2O→CO+H2

[0049] CO+H2O→CO2+H2

[0050] CaO+CO2→CaCO3

[0051] CaCO3+H2→CaO+H2O+CO

[0052] The CaTiO3 generated by the reaction of TiO2 in the red mud of the present invention and CaO in the carbide slag is a perovskite-type material with abundant electron transfer channels, which helps to carry out the methane cracking reaction. The Al2O3 and SiO2 in the red mud react with CaO to generate CaAl2Si2O8 with high sintering resistance, which helps to maintain the stability of the solid waste-based calcium-iron composite catalyst. It can be seen that the present invention realizes efficient catalytic methane cracking and hydrogen production and catalyst regeneration through the synergistic effect between red mud and carbide slag. The present invention can realize the high-value utilization of solid waste red mud and carbide slag.

[0053] The present invention does not impose any particular restrictions on the source of red mud, and Bayer red mud is preferred. The present invention does not impose any particular restrictions on the source of carbide slag, and it can be obtained through channels well known to those skilled in the art.

[0054] In the present invention, the particle size of the red mud after grinding and screening is preferably 100-150 mesh. The red mud after grinding and screening has an increased specific surface area, which is beneficial for subsequent acid washing. The present invention does not impose any particular restrictions on the specific grinding and screening process, and grinding and screening methods commonly used by those skilled in the art can be used.

[0055] In the present invention, the acid washing, alkaline washing, and water washing steps are specifically as follows: the ground and sieved red mud is added to a hydrochloric acid solution and stirred for 1-3 hours, followed by the addition of aqueous ammonia and stirring until the pH reaches 7.5-8.5. The solution is allowed to stand, filtered, and then rinsed with water until the solution is neutral. Acid washing dissolves the metal elements in the red mud. Ammonia is added to promote the precipitation of metal ions such as Fe and to remove soluble elements such as Na and K by filtration, thereby enriching Fe.

[0056] In the present invention, the amount of the red mud and the hydrochloric acid solution is 10 g: (400-600) mL, the concentration of the hydrochloric acid solution is 0.5-2 mol / L, and the concentration of the ammonia water is 20-30 wt %. The present invention does not impose any particular limitation on the standing time in the post-standing filtration step, but preferably is 20-60 minutes.

[0057] In the present invention, in the step of drying and then calcining to obtain pretreated red mud, the drying temperature is 100-130°C and the drying time is 5-20 hours. The calcination temperature is 500-700°C and the calcination time is 1-3 hours. Calcination removes organic matter from the red mud and converts all of the Fe element in the red mud into oxides, providing a basis for the subsequent quantitative addition of pretreated red mud. The present invention does not impose any particular restrictions on the calcination process; equipment and methods commonly used in the art can be used. The calcination process of the present invention is preferably carried out in an air atmosphere.

[0058] In the present invention, the step of washing the carbide slag and then drying it comprises the following steps: rinsing the carbide slag with water until the washing liquid is clear; and removing soluble impurities from the carbide slag by water washing. The drying temperature is 100-130°C, and the drying time is 5-20 hours. The main component of the washed and dried carbide slag is Ca(OH)2.

[0059] In the present invention, in the step of calcining to obtain pretreated carbide slag, the calcination temperature is 700-900°C and the calcination time is 1-3 hours. The calcium element in the dried carbide slag is converted into CaO by calcination, providing a basis for the subsequent quantitative addition of the pretreated carbide slag.

[0060] After the step of calcining to obtain pretreated red mud and pretreated carbide slag, the present invention further comprises the step of grinding the pretreated red mud and pretreated carbide slag to increase the specific surface area and facilitate full mixing of the two.

[0061] In the present invention, the total mass of the pretreated red mud and pretreated carbide slag to the citric acid aqueous solution is 10g:(200-300)mL; the concentration of the citric acid aqueous solution is 10-20wt%. The coordination effect of citric acid can promote the dispersion of ions in the solution, thereby improving the performance of the synthetic material.

[0062] In the drying step after heating and stirring of the present invention, the heating and stirring temperature is 60-80° C., and the stirring time is 2-5 hours; the drying temperature is 100-130° C., and the drying time is 5-20 hours.

[0063] In the present invention, the high-temperature reduction temperature is 750-850°C, the high-temperature reduction time is 1-2 hours, and the reducing gas used in the high-temperature reduction is selected from H2, CO, or CH4. The present invention does not impose any particular limitations on the specific steps and equipment for the high-temperature reduction, and steps and commonly used equipment familiar to those skilled in the art can be employed. The high-temperature reduction step reduces the Fe2O3 in the material to Fe.

[0064] The present invention also provides a solid waste-based calcium-iron composite catalyst prepared by the above-mentioned preparation method. The active ingredients of the solid waste-based calcium-iron composite catalyst include CaO, CaAl2Si2O8, CaTiO3, and Fe. CaO is used to in-situ capture CO2 generated by water vapor gasification and carbon deposition to produce CaCO3; CaAl2Si2O8 has high sintering resistance, thereby alleviating sintering of the catalyst under high-temperature reactions; CaTiO3 is a perovskite-type material with abundant electron transfer channels, which facilitates the methane cracking reaction; and Fe has the performance of efficiently catalyzing the catalytic cracking of methane to produce hydrogen.

[0065] The present invention also provides the use of the above-mentioned solid waste-based calcium-iron composite catalyst in catalytic methane cracking to produce hydrogen. The solid waste-based calcium-iron composite catalyst of the present invention can achieve efficient catalytic methane cracking to produce hydrogen, with a methane conversion rate exceeding 80%. It also has excellent carbon deposit removal and hydrogen production effects during steam gasification reactions, with an H2 yield exceeding 80% in the steam gasification gas, and exhibits excellent cycle performance.

[0066] The technical solution of the present invention is further described below with reference to specific embodiments.

[0067] The red mud raw material in the following examples is Bayer red mud, whose main components are SiO2, Fe2O3, Al2O3, Na2O, TiO2 and K2O; the main components of the carbide slag raw material are Ca(OH)2, CaCO3, Al2O3, SiO2, MgO, Na2O.

[0068] Example 1

[0069] This embodiment provides a method for preparing a solid waste-based calcium-iron composite catalyst.

[0070] (1) Grinding the red mud raw material and screening it into red mud particles with a particle size of 100-120 mesh;

[0071] (2) Take 10 g of the red mud particles obtained by screening, add it to 500 mL of 1 mol / L hydrochloric acid, stir it in a 20 ° C water bath for 2 h to obtain a red suspension, add 25% concentration of ammonia water to the red suspension and continue stirring until the pH of the suspension is 8, let the obtained suspension stand for 0.5 h and then vacuum filter it, rinse the filter residue with deionized water until it is neutral, dry the obtained filter residue in a 120 ° C drying oven for 12 h, put it into a muffle furnace and calcine it at 600 ° C for 2 h, grind it to 100-120 mesh, and obtain pretreated red mud.

[0072] (3) Take 20g of original carbide slag and rinse it with deionized water until the washing liquid is clear. Then dry the obtained solid in a drying oven at 120℃ for 12h, put it into a muffle furnace and calcine it at 800℃ for 2h, and grind it to 100-120 mesh to obtain pretreated carbide slag.

[0073] (4) 2.5 g of pretreated red mud, 7.5 g of pretreated carbide slag, 30 g of citric acid and 200 mL of water were mixed, stirred in a 70 ° C water bath for 3 h, then dried in a 120 ° C drying oven for 12 h, and then placed in a muffle furnace and calcined at 800 ° C for 1 h to obtain a solid waste-based calcium iron catalyst precursor;

[0074] (5) The solid waste-based calcium iron catalyst precursor was reduced in a 50 mL / min H2 atmosphere at a reduction temperature of 800°C and a reduction time of 1.5 h to obtain a solid waste-based calcium iron composite catalyst.

[0075] Figure 1 This is a scanning electron microscope (SEM) image of the solid waste-based calcium iron composite catalyst of Example 1. It can be seen that the material particles are uniform in size and have a well-developed pore structure; Figure 2 This is the transmission electron microscope (TEM) image of the solid waste-based calcium-iron composite catalyst of Example 1. It can be seen that CaO, CaAl2Si2O8, CaTiO3 and Fe phases are distributed in the material, among which CaTiO3 and the edges of other phases form channels for electron transfer, which is conducive to the chemical reaction.

[0076] Example 2

[0077] This embodiment provides a methane catalytic cracking hydrogen production system and a catalytic cracking hydrogen production method thereof, which uses the solid waste-based calcium-iron composite catalyst of Example 1 as a catalyst for methane catalytic cracking hydrogen production.

[0078] like Figure 3As shown, the methane in the methane storage tank 1 and the solid waste-based calcium iron composite catalyst in the solid waste-based calcium iron composite catalyst storage tank 2 enter the methane cracking furnace 3, where the methane is catalytically cracked. The hydrogen generated by the reaction enters the hydrogen storage tank 4 for storage. The solid waste-based calcium iron composite catalyst that has completed the catalytic cracking of methane in the methane cracking furnace 3 enters the gasifier 8. The water in the water tank 10 enters the steam generator 9 to generate water vapor, which enters the gasifier 8. In the gasifier 8, the water vapor vaporizes the carbon deposits on the surface and in the pores of the solid waste-based calcium iron composite catalyst. The products of the water vapor gasification of the carbon deposits include CO2, CO, and hydrogen. The CaO in the solid waste-based calcium iron composite catalyst will adsorb CO2 and react to generate CaCO3. After the carbon deposits are post-treated, the solid waste-based calcium iron composite catalyst is regenerated (at this time, CaO has adsorbed CO2 to react and generate CaCO3) and enters the CO2 in-situ converter 7. The gas in the gasifier 8 enters the NaOH solution tank 12. The CO2 that is not adsorbed reacts with NaOH, while CO and hydrogen enter the CO2 in-situ converter 7. In the solid waste-based calcium iron composite catalyst, CaCO3 generated by the adsorption of CO2 will react with the hydrogen entering the CO2 in-situ converter 7 from the NaOH solution tank 12 to generate CaO, thereby achieving the regeneration of the solid waste-based calcium iron composite catalyst and generating CO at the same time, thereby achieving the in-situ conversion of CO2. The regenerated solid waste-based calcium iron composite catalyst enters the methane cracking furnace 3 to catalytically crack methane. The CO generated in the CO2 in-situ converter 7 and the CO entering the CO2 in-situ converter 7 from the NaOH solution tank 12 are cooled by the condenser 6 and then enter the CO storage tank 5 for storage. The condensed water enters the steam generator 9 and can be reused, thereby achieving water recycling. When the solid waste-based calcium iron composite catalyst is deactivated, the deactivated solid waste-based calcium iron composite catalyst enters the deactivated solid waste-based calcium iron composite catalyst storage bin 11. The deactivated solid waste-based calcium iron composite catalyst can be used as a raw material for the cement industry.

[0079] Comparative Example 1

[0080] This comparative example provides a method for preparing a red mud-based catalyst.

[0081] The red mud raw material was ground and sieved into red mud particles with a particle size of 100-120 mesh; the red mud particles were dried at 120°C, the dried sample was calcined at 600°C in a muffle furnace for 2h, ground to 100-120 mesh, and reduced in a H2 atmosphere of 50mL / min at a reduction temperature of 800°C and a reduction time of 1.5h to obtain a red mud-based catalyst.

[0082] Comparative Example 2

[0083] This comparative example provides a method for preparing a modified red mud-based catalyst.

[0084] (1) Grinding the red mud raw material and screening it into red mud particles with a particle size of 100-120 mesh;

[0085] (2) Take 10 g of the red mud particles obtained by screening, add it to 500 mL of 1 mol / L hydrochloric acid, stir it in a 20 ° C water bath for 2 h to obtain a red suspension, add 25% concentration of ammonia water to the red suspension and continue stirring until the pH of the suspension is 8, let the obtained suspension stand for 0.5 h and then vacuum filter it, rinse the filter residue with deionized water until it is neutral, dry the obtained filter residue in a 120 ° C drying oven for 12 h, put it into a muffle furnace and calcine it at 600 ° C for 2 h, grind it to 100-120 mesh, and reduce it in a H2 atmosphere of 50 mL / min, the reduction temperature is 800 ° C, and the reduction time is 1.5 h to obtain a modified red mud-based catalyst.

[0086] Application Examples

[0087] The catalytic methane cracking and enhanced carbon deposition gasification performances of the catalysts prepared in Example 1 and Comparative Examples 1 and 2 for hydrogen production were measured and compared in a vertical fixed-bed reactor.

[0088] The detection method is as follows: the catalysts prepared in Example 1 and Comparative Examples 1 and 2 are respectively placed in a vertical fixed-bed reactor for a catalytic methane cracking reaction at a temperature of 850°C, a time of 3 hours, and a weight space velocity of 2 L / (g·h). The reactor temperature is then lowered to 600°C, and the atmosphere is switched to 30% H2O / 70% N2 to initiate a carbon deposition gasification reaction for 20 minutes. After the gasification reaction is completed, the reactor is heated to 800°C and calcined in 100% N2 for 30 minutes to convert CaCO3 into CaO. After the calcination is completed, the reactor is heated to 850°C and the next cycle of the catalytic methane cracking reaction is initiated. The gas produced during the methane catalytic cracking and carbon deposition gasification process is condensed, dust-cleaned, and dried before entering a gas analyzer, where the volume fractions of H2, CO, CH4, and CO2 in the gas are measured in real time.

[0089] The formula for calculating the conversion rate of methane in the methane catalytic cracking process is:

[0090]

[0091] Where X CH4 is the conversion rate of methane, %; is the volume fraction of H2 in the product gas, volume %; is the volume fraction of CH4 in the product gas, volume %.

[0092] The average conversion rate of methane in each methane catalytic cracking cycle is calculated as follows:

[0093]

[0094] Where X Ave,CH4 represents the average conversion rate of CH4 during the catalytic cracking of methane, %. t is the reaction time of catalytic cracking of methane, 3h.

[0095] During the carbon deposition gasification process, the flow rate calculation formula for various gases such as H2, CO, CH4 or CO2 is:

[0096]

[0097] Where i represents the component of the gas produced by carbon deposition gasification, such as H2, CO, CH4 or CO2. i is the flow rate of H2, CO, CH4 or CO2 in the synthesis gas, mL / min. is the volume fraction of H2, CO, CH4 or CO2 in the produced gas, %.

[0098] The formula for calculating the yield of various gases during carbon deposition gasification within a certain period of time is:

[0099]

[0100] Where Y i is the volume fraction of H2, CO, CH4 or CO2 in the gas produced within a certain period of time, %. t1 is the carbon deposition gasification time, min.

[0101] The methane cracking conversion rate curve of the red mud catalyst of Comparative Example 1 is as follows: Figure 4 As shown in the figure, the gas composition of the carbon deposited water vapor gasification of the red mud catalyst in comparative example 1 is as follows Figure 5 As shown, it can be seen that the conversion rate of methane cracking catalyzed by the red mud catalyst of Comparative Example 1 is very low, with a maximum of only 42%, and due to continuous carbon deposition, the conversion rate continues to decrease with the extension of the reaction time. The H2 yield in the steam gasification gas produced by the carbon-deposited red mud catalyst is 36%, the CO yield is 30%, and the CO2 yield is 22%.

[0102] The methane cracking conversion rate curve of the modified red mud catalyst of Comparative Example 2 is as follows: Figure 6 As shown in the figure, the gas composition of the modified red mud catalyst carbon deposition water vapor gasification of comparative example 2 is as follows Figure 7 As shown in the figure, the maximum conversion rate of methane cracking catalyzed by the modified red mud catalyst after acid washing pretreatment is only 67%, which is improved compared with the red mud catalyst in Comparative Example 1. The H2 yield of the steam gasification gas produced by the carbon-deposited modified red mud catalyst is 32%, the CO yield is 33%, and the CO2 yield is 26%.

[0103] The methane cracking conversion rate curve of the solid waste-based calcium iron composite catalyst in Example 1 is as follows: Figure 8As shown in the figure, the gas composition of the carbon deposited water vapor gasification of the solid waste-based calcium iron composite catalyst in Example 1 is as follows Figure 9 As shown. It can be seen that the conversion rate of methane cracking catalyzed by the solid waste-based calcium iron composite catalyst can reach up to 86%, which is a significant improvement over the catalysts of Comparative Examples 1 and 2. The H2 yield in the steam gasification gas produced by the carbon-deposited solid waste-based calcium iron composite catalyst is 83%, the CO yield is 9%, and the CO2 yield is 7%. The hydrogen production is greatly improved. This is because the CaO component in the solid waste-based calcium iron composite catalyst absorbs the CO2 produced by the steam gasification of carbon deposits, thereby enhancing the carbon removal and hydrogen production effects.

[0104] Figure 10 This is a graph showing the average conversion rate of methane cracking catalyzed by multiple cycles of the solid waste-based calcium-iron composite catalyst in Example 1. Figure 11 The hydrogen yield diagram of the solid waste-based calcium iron composite catalyst during multiple steam gasification processes of carbon deposits. It can be seen that the solid waste-based calcium iron composite catalyst of Example 1 has efficient catalytic methane cracking hydrogen production performance and excellent cycle stability. The reason for this phenomenon is that the pore structure of the red mud is improved after acid washing, which enhances the catalytic activity of Fe. The CaTiO3 generated by the reaction of TiO2 in the red mud and CaO in the carbide slag is a perovskite-type substance with rich electron transfer channels, which is conducive to the methane cracking reaction. The Al2O3 and SiO2 in the red mud react with the CaO in the carbide slag to generate CaAl2Si2O8 with high sintering resistance. It has strong sintering resistance and can enable the solid waste-based calcium iron composite catalyst to maintain a stable microstructure during multiple catalytic methane cracking and carbon deposition gasification cycles. Figure 12 2 are X-ray diffraction patterns of the catalysts of Example 1, Comparative Example 1 and Comparative Example 2. It can be seen that the catalyst of Example 1 contains CaO, CaAl2Si2O8, CaTiO3 and Fe phases.

[0105] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A method for preparing a solid waste-based calcium iron composite catalyst, characterized in that: The steps include: The red mud is ground and sieved, and then sequentially washed with acid, alkali and water, dried and calcined to obtain pretreated red mud; washing the carbide slag with water, drying it, and then calcining it to obtain pretreated carbide slag; The pretreated red mud and pretreated carbide slag are mixed in a mass ratio of (20-25): (75-80) and dispersed in a citric acid aqueous solution, heated and stirred, dried, and then reduced at high temperature to obtain the product; The ratio of the total mass of the pretreated red mud and pretreated carbide slag to the citric acid aqueous solution is 10 g: (200-300) mL; the concentration of the citric acid aqueous solution is 10-20 wt %.

2. The preparation method according to claim 1, wherein The acid washing, alkali washing and water washing steps are specifically as follows: adding the ground and sieved red mud to a hydrochloric acid solution and stirring for 1 to 3 hours, then adding ammonia water and stirring until the pH value is 7.5 to 8.5, letting it stand and then filtering, and then washing with water until it is neutral.

3. The preparation method according to claim 2, wherein The amount of the red mud and the hydrochloric acid solution is 10 g: (400-600) mL, the concentration of the hydrochloric acid solution is 0.5-2 mol / L; the concentration of the ammonia water is 20-30 wt%.

4. The preparation method according to claim 1, wherein In the step of drying and then calcining to obtain pretreated red mud, the drying temperature is 100-130° C., and the drying time is 5-20 hours; the calcining temperature is 500-700° C., and the calcining time is 1-3 hours.

5. The preparation method according to claim 1, wherein In the step of washing the carbide slag with water and then drying it, the washing step specifically comprises: washing the carbide slag with water until the washing liquid is clear, the drying temperature is 100-130° C., and the drying time is 5-20 hours; In the step of calcining to obtain pretreated carbide slag, the calcination temperature is 700-900° C. and the calcination time is 1-3 hours.

6. The preparation method according to claim 1, wherein In the drying step after heating and stirring, the heating and stirring temperature is 60-80° C., and the stirring time is 2-5 hours; the drying temperature is 100-130° C., and the drying time is 5-20 hours.

7. The preparation method according to claim 1, wherein The temperature of the high-temperature reduction is 750-850° C., the time of the high-temperature reduction is 1-2 hours, and the reducing gas for the high-temperature reduction is selected from H 2 , CO or CH 4 .

8. The solid waste-based calcium iron composite catalyst prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The active components of the solid waste-based calcium-iron composite catalyst include CaO, CaAl2Si2O8, CaTiO3 and Fe.

9. Use of the solid waste-based calcium-iron composite catalyst as claimed in claim 8 in catalytic methane cracking to produce hydrogen.

Images