Preparation method and application of iron-based red mud catalyst

Abstract

The invention discloses a preparation method of an iron-based red mud catalyst. The preparation method comprises the following steps: (1) drying, crushing and sieving red mud for later use; (2) adding acid into the red mud powder, and stirring to completely dissolve alkali metal in the red mud powder; (3) adding water and alkali into the red mud powder, and stirring to dissolve Si in the red mud powder, (4) stirring and mixing the red mud powder and an adhesive, putting the mixture into a granulator, and granulating the red mud catalyst according to the length-diameter ratio of 3-5; and (5) granulating the red mud catalyst, drying, and heating to remove free water, acid, chemical crystal water and adhesive to obtain the iron-based red mud catalyst. The catalyst can prevent the iron-based catalyst from being oxidized and inactivated under the high-temperature condition of synthesis gas, and high-temperature biomass gasification and efficient hydrogen reforming are achieved.

Description

Technical Field

[0001] This invention relates to a catalyst for syngas reforming H2, specifically to a catalyst, its preparation method, and its application. Background Technology

[0002] The water-gas shift reaction (WGS) is a process that converts carbon monoxide and water vapor into carbon dioxide and hydrogen. The specific reaction equation is CO(g) + H₂O(g) ⇌ CO₂(g) + H₂(g). The water-gas shift reaction can not only reduce the CO concentration in syngas but also increase the H₂ content in reformed gas. However, the natural gas reforming process for hydrogen production contains a large amount of CO, which can easily lead to catalyst poisoning.

[0003] Currently, the most common catalysts are copper-based and iron-based catalysts. However, copper-based catalysts require careful temperature control during use to prevent high-temperature deactivation. Iron-based catalysts have attracted widespread attention due to their advantages such as low cost, low environmental pollution, easy availability, and wide distribution. However, ordinary iron-based catalysts are sensitive to reduction treatment, and their application under harsh reduction conditions often leads to catalyst deactivation. To achieve the hydrogen purity levels required for industrial applications, the development of advanced catalysts for water-gas shift reactions has never ceased.

[0004] Red mud is an industrial solid waste generated during alumina production. It is usually piled up and pollutes the environment, so there is a need to develop effective utilization methods. Red mud contains abundant Fe and Ca, which have catalytic effects on gasification. Using it as a coal gasification catalyst can achieve "waste treatment with waste". However, since syngas contains oxidizing components (such as H2O and CO2), these components will cause the iron in the red mud to oxidize and lose its activity when using traditional iron-based red mud as a catalyst, resulting in a significant decrease in the cracking catalytic effect. Therefore, it is necessary to improve the technology and optimize the function of iron-based red mud catalysts.

[0005] CN109201063A discloses a red mud-based semi-coke catalyst, its preparation method, and its uses. The preparation method includes the following steps: (1) pretreating red mud to obtain a solid precipitate; (2) physically mixing coal powder with the solid precipitate obtained in step (1), granulating, and obtaining solid particles; (3) pyrolyzing the solid particles obtained in step (2) to obtain the red mud-based semi-coke catalyst. This invention enables the comprehensive utilization of solid waste red mud. Through the catalytic reforming effect of the iron-based red mud catalyst, the CO content in the syngas can be significantly reduced, and the H2 content can be increased. Currently, there are no reports on red mud catalysts used to prevent the oxidation and deactivation of iron-based catalysts under high-temperature conditions of syngas, and to achieve efficient reforming of hydrogen from high-temperature biomass gasification. Summary of the Invention

[0006] Purpose of the invention: To address the shortcomings of existing technologies, this invention provides a method for preparing an iron-based red mud catalyst for efficient hydrogen reforming from syngas and its application, preventing the oxidation and deactivation of the iron-based catalyst under high-temperature conditions of syngas, and realizing high-temperature and efficient hydrogen reforming from biomass gasification syngas.

[0007] To address the aforementioned technical problems, this invention discloses a method for preparing an iron-based red mud catalyst for efficient H2 reforming from syngas, comprising the following steps: (1) Dry the red mud, crush it, and sieve it for later use; (2) Add acid to red mud powder and stir for 60-80 min to completely dissolve the alkali metals to obtain acid-washed red mud; (3) Add the acid-washed red mud into water, add alkali and stir for 60-80 min to dissolve the Si in it to obtain alkali-washed red mud; (4) Add the alkaline washed red mud to the binder and stir for 20-30 min, then put it into the granulator to granulate the red mud catalyst; (5) After the catalyst is granulated, dried and heated to remove free water, acid, chemical water of crystallization and binder, the iron-based red mud catalyst is obtained.

[0008] In step (1), the drying conditions are drying in an oven at 100-120 ℃ for 24-48 h, preferably drying in an oven at 110 ℃ for 24 h, and then grinding the brittle red mud obtained after drying into powder of 45-350 μm in a mortar.

[0009] In step (2), the acid is hydrochloric acid. The purpose of hydrochloric acid washing is to dissolve the alkali metal components in the minerals and prevent the catalyst from melting at high temperatures. The amount of acid used depends on the alkali metal content in the red mud. Typically, the amount of hydrochloric acid used reaches the molar amount required for complete dissolution of the alkali metal. Generally, based on the alkali metal mass content range of approximately 1-2% in the red mud, the amount of hydrochloric acid used is excessive. Only hydrochloric acid has been tested for dissolving alkali metals; the hydrochloric acid concentration was 1 mol / L, and the amount used was 3-5% relative to the volume percentage of the red mud. This ensures complete dissolution and release of the alkali metal, preventing the red mud catalyst from melting and clogging pores at high temperatures.

[0010] In step (3), the alkali is sodium hydroxide. The purpose of alkali washing is to dissolve the Si component in the red mud, preventing Si from reacting with the active components of the catalyst at high temperatures, which could lead to catalyst poisoning and reduced catalyst activity. Generally, based on the Si content in the red mud being approximately 9 wt%, the amount of sodium hydroxide used is 10-12%, which is an excess. The amount of alkali can be appropriately increased. The amount of sodium hydroxide used is a percentage relative to the volume of the red mud. Only the dissolution of Si with sodium hydroxide has been tested, and the concentration of sodium hydroxide was 1 mol / L.

[0011] In step (4), the adhesive is sodium carboxymethyl cellulose, the mass ratio of red mud powder to adhesive is 30~50:1, and the aspect ratio of red mud particles is 3-5.

[0012] In step (5), the obtained red mud particles are first air-dried for 12-24 hours; then dried at 95-115 °C for 6-12 hours, followed by drying at 180-220 °C for 2-4 hours; finally heated to 280-320 °C and held for 3-6 hours to obtain the red mud catalyst. Preferably, the obtained red mud particles are first air-dried for 12 hours; then dried at 105 °C for 6 hours, followed by drying at 200 °C for 2 hours; finally heated to 300 °C and held for 3 hours to obtain the iron-based red mud catalyst.

[0013] The iron-based red mud catalyst obtained by the above preparation method is also within the scope of protection of this application.

[0014] The present invention further provides a reduced iron-based red mud catalyst obtained by reducing the above-mentioned iron-based red mud catalyst at 750-830 °C for 8-12 h under a mixed composition of hydrogen and nitrogen.

[0015] This invention further proposes the application of the above-mentioned iron-based red mud catalyst or reduced iron-based red mud catalyst in high-temperature biomass gasification reforming H2.

[0016] In practical applications, the iron-based red mud catalyst is subjected to a red mud catalyst reduction reaction at 750-830 °C for 8-12 h under a mixed composition of hydrogen and nitrogen to form a reduced state iron-based red mud catalyst. This ensures that the iron-based components in the catalyst are reduced, which is used to inhibit the oxidation of iron-based components during tar cracking and to ensure the high-efficiency reforming performance of the red mud catalyst for H2. Then, it is used for high-temperature syngas catalytic reforming of H2 to achieve high-temperature and high-efficiency reforming of hydrogen from biomass gasification syngas.

[0017] This application utilizes the reduction of iron in red mud to form a reduced-state iron-based red mud catalyst, which inhibits the oxidative deactivation of iron-based red mud during the high-temperature catalytic cracking of gasified tar. The reduced-state iron-based red mud catalyst is then used to achieve high-efficiency high-temperature reforming of hydrogen from biomass gasification syngas. Through a mixed reduction reaction of hydrogen and nitrogen, the red mud catalyst contains 5-20% metallic iron (Fe), 20-50% ferrous oxide (FeO), 30-60% magnetite (Fe3O4), and only 0.1-3% iron oxide (Fe2O3), thus forming the iron element in the red mud catalyst used for high-temperature, high-efficiency hydrogen reforming.

[0018] Beneficial effects: Compared with existing technologies, this application uses industrial waste as an effective catalyst, utilizing a hydrogen-nitrogen mixture to reduce iron-based red mud, inhibiting the oxidative deactivation of the iron-based catalyst during syngas reforming, achieving efficient hydrogen reforming from biomass gasification syngas, realizing industrial application of waste-to-waste treatment, with low cost and extremely high cost-effectiveness; simultaneously, this application achieves an H2 / CO ratio of 5.97 in biomass gasification syngas. It achieves direct high-temperature reforming of syngas after biomass gasification, providing an important guarantee for the efficient utilization of downstream syngas. Attached Figure Description

[0019] Figure 1 XRD pattern analysis of iron-based red mud catalyst, where the blue line represents the observed intensity at each step; the red line represents the calculated pattern; the gray solid line represents the difference between the observed and calculated intensities; the vertical lines represent the positions of all Bragg reflections; and the colored lines are individual diffraction patterns for all phases. Figure 2 These are the experimental results for the third and fourth groups. Detailed Implementation

[0020] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0021] The composition of red mud varies depending on its source and the composition of bauxite itself, but it is always primarily composed of Fe2O3, Al2O3, and other alkali metal oxides. The red mud used in the following examples is a high-iron-content solid waste discharged during the extraction of alumina in the aluminum industry.

[0022] Example 1: Preparation of iron-based red mud catalyst for hydrogen reforming from syngas.

[0023] (1) Dry the red mud in an oven at 110 °C for 24 hours to dehydrate it, and grind the dried brittle red mud into 45-350 μm powder in a mortar.

[0024] (2) Add 40 g of ground red mud powder to 10 ml of distilled water and 3 ml of 1 mol hydrochloric acid and stir for 15-20 min to obtain acid-washed red mud.

[0025] (3) Add 10 ml of distilled water and 5 ml of 1 molar sodium hydroxide to the acid-washed red mud and stir for 15-20 min to obtain alkaline-washed red mud; (4) Mix the alkaline washed red mud with 1 g of sodium carboxymethyl cellulose binder, stir continuously until the powder is evenly mixed, put it into a granulator, and granulate the red mud catalyst with a length-to-diameter ratio of 3:5 to obtain red mud particles.

[0026] (5) The red mud particles were air-dried for 12 h, dried at 105 ℃ for 6 h to remove free water, dried at 200 ℃ for 2 h to remove chemically adsorbed water, and finally heated to 300 ℃ and held for 3 h to remove the binder, thus preparing iron-based red mud catalyst particles.

[0027] Table 1 and Figure 1 The composition of the prepared iron-based red mud catalyst is quantitatively analyzed and XRD results are shown.

[0028] Table 1. Quantitative analysis of compound components in iron-based red mud catalysts.

[0029]

[0030] Example 2: Application of red mud catalyst in high-temperature biomass gasification reforming of hydrogen.

[0031] The iron-based red mud catalyst prepared in Example 1 was dried and placed in a reactor. A reduction reaction of the red mud catalyst was carried out at 800 °C for 10 h under a mixed hydrogen and nitrogen atmosphere to form an elemental iron-based catalyst. The effect of syngas reforming H2 under different reaction temperatures was tested. The values ​​of hydrogen and carbon monoxide were directly measured by a calibrated GC. The initial ratio is the H2 / CO ratio without the iron-based red mud catalyst, while the reforming ratio is the H2 / CO ratio after using the iron-based red mud catalyst. The improvement rate was calculated as (reforming ratio - initial ratio) / initial ratio.

[0032] Table 2

[0033] As can be seen from the table above, in the first group of reaction tests at 673 ℃, the initial H2 / CO ratio increased from 0.81 to 5.97, an increase of 637.04%; in the second group of reaction tests at 694 ℃, the initial H2 / CO ratio increased from 0.85 to 3.18, an increase of 274.12%; in the third group of reaction tests at 732 ℃, the initial H2 / CO ratio increased from 1.02 to 4.53, an increase of 344.12%; and in the fourth group of reaction tests at 747 ℃, the initial H2 / CO ratio increased from 1.00 to 5.19, an increase of 419.00%.

[0034] In the initial stage of the reaction (Group 1), the addition of iron-based red mud catalyst significantly increased the proportion of H2 in the syngas while decreasing the proportion of CO, resulting in a significant increase in the H2 / CO ratio, with an increase rate as high as 637.04%. As the reaction proceeded and the temperature gradually increased, the H2 / CO ratio gradually increased. In the later stage of the reaction (Group 4), the H2 / CO ratio reached 5.19, demonstrating a significant reforming effect. Figure 2 This is a graph showing the changes in H2 and CO concentrations during the experiment.

[0035] Conventional biomass gasification H2 / CO ratios are 0.5 to 1. Compared to existing biomass gasification syngas reforming H2, this invention, using an iron-based red mud catalyst, significantly improves the H2 / CO ratio to a maximum of 5.97, stabilizing at around 5.00 in the later stages of the reaction, while also minimizing environmental pollution. Compared to existing precious metal nickel-based catalysts, although nickel-based catalysts have high catalytic efficiency, their operating costs are extremely high, with expensive catalyst consumption and regeneration. In contrast, the red mud catalyst used in this syngas reforming H2 / CO technology is a waste product from the aluminum production industry, incurring virtually no cost and achieving an industrial application of "waste-to-waste" treatment.

[0036] This invention provides a method and approach for preparing red mud catalysts. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A method for preparing an iron-based red mud catalyst, characterized in that, Includes the following steps: (1) Red mud particles are dried, crushed and sieved to obtain red mud powder for later use; (2) Add acid to the red mud powder obtained in step (1) and stir to completely dissolve the alkali metals in it to obtain acid-treated red mud; (3) The acid-washed red mud is put into water, and alkali is added to dissolve the Si in it to obtain alkali-washed red mud; (4) Mix the red mud after alkali washing with the binder evenly, put it into a granulator for granulation, and obtain catalyst granules. The red mud catalyst granulation is carried out with an aspect ratio of 3-5. (5) After granulating the catalyst, drying and heating are carried out to remove free water, acid, chemical water of crystallization and binder to obtain iron-based red mud catalyst.

2. The preparation method according to claim 1, characterized in that, In step (1), the red mud particles are dried in an oven at 100-120 ℃ for 24-48 h, and the resulting brittle red mud is ground into powder of 45-350 μm in a mortar.

3. The preparation method according to claim 1, characterized in that, In step (2), the acid is hydrochloric acid.

4. The preparation method according to claim 1, characterized in that, In step (3), the alkali is sodium hydroxide.

5. The preparation method according to claim 1, characterized in that, In step (4), the binder is sodium carboxymethyl cellulose, and the mass ratio of the red mud after alkali treatment to the binder is 30~50:

1.

6. The preparation method according to claim 1, characterized in that, In step (5), the obtained catalyst granules are first air-dried for 12-24 h; then dried at 95-115 ℃ for 6-12 h; then dried at 180-200 ℃ for 2-4 h; and finally heated to 280-320 ℃ and held for 3-6 h to obtain the iron-based red mud catalyst.

7. The iron-based red mud catalyst obtained by the preparation method according to any one of claims 1-6.

8. A reduced iron-based red mud catalyst, characterized in that, The iron-based red mud catalyst described in claim 7 is obtained by reducing it at 750-830 °C for 8-12 h under a mixture of hydrogen and nitrogen.

9. The application of the iron-based red mud catalyst of claim 7 or the reduced iron-based red mud catalyst of claim 8 in high-temperature biomass gasification reforming H2.

10. The application according to claim 9, characterized in that, The iron-based red mud catalyst is reduced at 750-830℃ for 8-12 h under a mixture of hydrogen and nitrogen to form a reduced iron-based red mud catalyst, which is used for high-temperature catalytic reforming of H2 in syngas to achieve high-temperature and efficient reforming of hydrogen from biomass gasification syngas.

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