Preparation method and application of composite red mud catalyst for synthesis gas tar cracking

Abstract

The invention discloses a preparation method of a composite red mud catalyst for synthesis gas tar cracking, which comprises the following steps: (1) drying red mud, grinding into powder, mixing the red mud powder obtained by grinding with an adhesive, and adding water and acid under a stirring condition to completely dissolve alkali metal in the red mud powder to obtain red mud particles; (2) grinding biomass pyrolysis semi-coke particles, and mixing the ground biomass pyrolysis semi-coke particles with the red mud particles obtained in the step (1) for 10-15 minutes to obtain red mud glue; (3) putting the red mud glue into a granulator, and carrying out red mud catalyst granulation according to the length-diameter ratio of 3 to 5, so as to obtain composite red mud particles; and (4) air-drying, drying and heating the composite red mud particles obtained in the step (3) to obtain the composite red mud catalyst. The catalyst can prevent the iron-based catalyst from being oxidized and inactivated under the high-temperature condition of the synthesis gas, and high-temperature biomass gasification tar catalytic cracking and efficient cleaning purification are achieved.

Description

Technical Field

[0001] The invention relates to a catalyst for catalytic cracking of biomass gasification synthesis gas tar, and in particular to a composite red mud catalyst and a preparation method and application thereof. Background Art

[0002] The reaction temperature during the gasification of agricultural and forestry biomass / urban waste is relatively low. In the fluidized bed gasifier, the biomass is converted into a gaseous mixture mainly containing H2, CO, CO2, CH4 and H2O. The synthesis gas also contains a certain amount of impurity components, including particulate matter, sulfur, chlorine, ammonia and alkali metals, which can cause catalyst poisoning and deactivation, pipeline blockage, reactor corrosion in the downstream synthesis gas process, resulting in impure products and low quality. Due to the relatively low gasification temperature and the short residence time of the synthesis gas in the gasifier, tar formation is the main problem faced by almost all types of fluidized bed gasifiers, which can cause serious problems in downstream pipelines and reactors (such as blockage, corrosion and scaling).

[0003] Existing technology usually uses a washing tower to cool and wash to remove tar, but this process creates environmental problems such as water pollution. Another efficient approach is to use a catalyst to catalytically crack tar gas at high temperature to convert tar components into effective synthesis gas components such as CO and H2. This is an efficient synthesis gas purification and tar cracking technology. The main catalysts currently used are precious metal catalysts such as nickel and cobalt, which have a high conversion rate and a fast reaction rate. However, precious metal resources are scarce and costly, and are not suitable for large-scale industrial applications in gasification tar cracking. There is an urgent need to develop new catalysts with low cost and high cracking efficiency.

[0004] Red mud is a waste generated during the industrial processing of aluminum ore. It is usually piled up and pollutes the environment, and effective utilization methods need to be developed. Red mud contains a large amount of iron elements, which can be used for catalytic cracking of hydrocarbons and is suitable for catalytic cracking of synthesis gas tar, realizing the application of "waste treatment with waste" technology. However, due to the presence of oxidizing atmosphere (H2O and CO2) in synthesis gas, the iron element in the single red mud catalyst will be oxidized and deactivated, and the cracking catalytic performance will deteriorate, so it is necessary to improve the red mud catalyst technology and optimize its functions.

[0005] At present, some catalysts based on red mud are also disclosed. For example, CN113042059A discloses a method for preparing a red mud-based catalyst for biomass pyrolysis, which comprises the following steps: (1) grinding red mud and alkali together to obtain uniformly mixed solid particles; (2) removing Fe from the solid particles obtained in step (1) by high-temperature roasting, crushing, adding water, magnetic stirring and vacuum filtration to obtain a solution containing only Si and Al; (3) roasting the Si and Al solution obtained in step (2) and vacuum filtration to obtain a solid red mud-based catalyst. The use of this catalyst can not only effectively utilize the solid waste generated by the aluminum industry, but also prepare high-quality catalysts for use in biomass. CN 109201063A discloses a red mud-based semi-coke catalyst and a preparation method and use thereof. The preparation method comprises the following steps: (1) pre-treating red mud to obtain a solid precipitate; (2) physically mixing coal powder with the solid precipitate obtained in step (1), granulating to obtain solid particles; (3) pyrolyzing the solid particles in step (2) to obtain a red mud-based semi-coke catalyst. The present invention can realize the comprehensive utilization of solid waste red mud, and can catalytically crack the heavy components in coal pyrolysis tar into light components through the catalytic quality improvement effect of the red mud-based semi-coke catalyst, thereby improving the quality of coal pyrolysis tar, making full use of biomass resources and generating high-quality oil and gas resources. CN117244551A discloses a method for preparing an iron-based catalyst, including the following contents: (1) drying, grinding and screening red mud raw materials and biochar raw materials respectively; (2) mixing the red mud particles obtained in step (1) with the biochar particles in a certain proportion; (3) loading the mixture in step (2) into a fixed bed reactor, passing a gas containing carbon dioxide into the reactor, and performing activation treatment; (4) cooling the reactor to room temperature, taking out the mixture after the reaction, washing and drying, and obtaining an iron-based catalyst. It treats two solid waste materials, red mud and biochar, together, expands and modifies the biochar at high temperature by red mud, and reduces and loads the iron on the modified biochar, which has low cost, simple preparation method, and can be mass-produced. At present, there is no report on a composite red mud catalyst for preventing oxidation deactivation of iron-based catalysts under high temperature conditions of synthesis gas, and realizing catalytic cracking and efficient clean purification of high-temperature biomass gasification tar. Summary of the invention

[0006] Purpose of the invention: In view of the shortcomings of the prior art, the present invention provides a method for preparing a composite red mud catalyst for synthesis gas tar cracking and its application, so as to prevent the oxidation deactivation of the iron-based catalyst under high temperature conditions of synthesis gas, and realize the catalytic cracking and efficient and clean purification of high-temperature biomass gasification tar.

[0007] In order to solve the above technical problems, the present invention discloses a method for preparing a composite red mud catalyst for syngas tar cracking, comprising the following steps:

[0008] (1) drying the red mud and grinding it into powder, mixing the ground red mud powder with a binder, adding water and an acid under stirring conditions to completely dissolve the alkali metal therein, and obtaining red mud particles;

[0009] (2) taking biomass pyrolysis semi-coke particles, grinding them, and mixing them with the red mud particles obtained in step (1) for 10-15 minutes to obtain red mud glue;

[0010] (3) placing the red mud gum into a granulator, granulating the red mud catalyst with an aspect ratio of 3-5 to obtain composite red mud particles;

[0011] (4) The composite red mud particles obtained in step (3) are air-dried, dried, and heated to remove free water, acid, chemical crystallization water, and binder to obtain a composite red mud catalyst.

[0012] Wherein, in step (1), the drying condition is drying in an oven at 90-120°C for 24-48 hours, preferably, drying in an oven at 110°C for 24 hours, and the brittle red mud obtained after drying is ground into a powder of 45-350 μm in a mortar.

[0013] Wherein, the binder is sodium carboxymethyl cellulose, and the mass ratio of red mud powder to the binder is 30 to 50:1.

[0014] The acid is hydrochloric acid, and the hydrochloric acid washing is used to dissolve the alkali metal components in the minerals to prevent the catalyst from melting at high temperatures. The amount of acid used depends on the alkali metal content in the red mud. Usually, the amount of hydrochloric acid used reaches the molar amount of the alkali metal completely dissolved. Generally, based on the alkali metal content in the red mud of about 1-2%, the amount of hydrochloric acid used is 3-5%, ensuring that the alkali metal is completely dissolved and precipitated to prevent the red mud catalyst from melting and blocking the pores at high temperatures.

[0015] In step (2), in step (2), the biomass pyrolysis semi-coke particles are ground to a particle size of 45-350 μm, and the biomass pyrolysis semi-coke particles account for 30-40% of the total mass of the biomass pyrolysis semi-coke particles and red mud particles.

[0016] In step (4), the obtained composite red mud particles are first naturally air-dried for 12-24 hours; then dried at 90-120°C for 6-12 hours, and then the sample is dried at 150-200°C for 2-4 hours; finally heated to 250-300°C and maintained for 3-6 hours to obtain a composite red mud catalyst. Preferably, the obtained composite red mud particles are first naturally air-dried for 12 hours; then dried at 105°C for 6 hours, and then the sample is dried at 200°C for 2 hours; finally heated to 300°C and maintained for 3 hours to obtain a composite red mud catalyst.

[0017] The composite red mud catalyst obtained by the above preparation method is also within the protection scope of the present application.

[0018] The present invention further provides an iron-based red mud catalyst obtained by subjecting the composite red mud catalyst to a reduction reaction at 750-830° C. for 8-12 hours under a nitrogen component.

[0019] The present invention further proposes the use of the composite red mud catalyst or the iron-based red mud catalyst in the catalytic cracking of high-temperature biomass gasification tar.

[0020] In specific applications, the composite red mud catalyst is subjected to a composite red mud catalyst reduction reaction at 750-830° C. for 8-12 hours under a nitrogen component to form a reduced iron-based red mud catalyst, ensuring that the iron base in the catalyst is reduced, while still containing a biomass semi-coke component, which is used to inhibit iron-based oxidation during tar cracking and ensure the efficient catalytic cracking performance of the red mud catalyst, and then used for high-temperature syngas tar catalytic cracking to achieve high-temperature clean purification of biomass gasification syngas.

[0021] The present application reduces the iron element in red mud by adding biomass semi-coke to form a reduced iron-based composite red mud catalyst, and again uses the bio-semi-coke to inhibit the oxidation and deactivation of the reduced iron-based red mud during the high-temperature catalytic cracking of gasified tar, and uses the reduced red mud catalyst to achieve efficient catalytic cracking and high-temperature purification of biomass gasification tar. After the biomass semi-coke reduction reaction, the bio-semi-coke is used again to inhibit the oxidation of the red mud catalyst during the gasification tar cracking process, so that the metallic iron (Fe) in the red mud catalyst accounts for 5-20% of the total iron content, ferrous oxide (FeO) accounts for 20-50% of the total iron content, ferrosoferric oxide (Fe3O4) accounts for 30-60% of the total iron content, and ferric oxide (Fe2O3) accounts for only 0.1-3% of the total iron content, thereby forming the iron element in the composite red mud catalyst during the high-temperature tar cracking process.

[0022] Beneficial effects: Compared with the prior art, this application uses industrial waste as an effective catalyst, utilizes biomass pyrolysis semi-coke, inhibits the oxidation deactivation of iron-based catalysts during the synthesis gas purification process, achieves efficient catalytic cracking of biomass gasification synthesis gas tar, realizes the industrial application of waste treatment, has low cost and extremely high cost performance; at the same time, this application achieves a biomass gasification synthesis gas tar content of less than 30g / Nm 3 Within the range, the tar removal rate reaches 82.8-97.7%. The direct high-temperature purification effect of the syngas after biomass gasification has been achieved, providing an important guarantee for the clean and efficient utilization of the downstream syngas. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1XRD pattern analysis of composite red mud catalyst, where the blue line is the observed intensity at each step; the red line is the calculated pattern; the gray solid line is the difference between the observed intensity and the calculated intensity; the vertical line is the position of all Bragg reflections) the colored lines are individual diffraction patterns of all phases;

[0024] Figure 2 These are the experimental results for the third and fourth groups. DETAILED DESCRIPTION

[0025] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments, and the above and / or other advantages of the present invention will become more clear.

[0026] The red mud varies with the source and composition of the bauxite, but is always mainly composed of Fe2O3 and Al2O3 and other alkali metal oxides. The red mud used in the following examples is a high-iron solid waste discharged when alumina is extracted in the aluminum industry.

[0027] Example 1 Preparation of composite red mud catalyst.

[0028] (1) Dry the red mud in an oven at 110° C. for 24 hours to dehydrate it, grind the dried brittle red mud into 45-350 μm powder in a mortar, mix 30 g of the ground red mud powder with 1 g of sodium carboxymethyl cellulose binder, add 10 ml of distilled water and 2 ml of 1 molar hydrochloric acid while continuously stirring the powder, and stir and mix to obtain red mud particles.

[0029] (2) taking biomass pyrolysis semi-coke particles, crushing and grinding them to a particle size of 45-350 μm, and uniformly mixing the ground biomass pyrolysis semi-coke particles with red mud particles in a mass ratio of 3:7 until a viscosity similar to that of glue is reached to obtain red mud glue;

[0030] (3) placing the red mud gum into a granulator, granulating the red mud catalyst with a diameter to length ratio of 1:5 to obtain composite red mud particles;

[0031] (4) The composite red mud particles were naturally air-dried for 12 h, dried at 105 °C for 6 h to remove free water, dried at 200 °C for 2 h to remove chemically adsorbed water, and finally heated to 300 °C for 3 h to remove the binder to prepare the composite red mud catalyst particles.

[0032] Table 1 and Figure 1 This is the quantitative analysis of the components and XRD results of the prepared composite red mud catalyst.

[0033] Table 1 Quantitative analysis of the components of composite red mud catalyst

[0034] Mineral Name Compound composition Composite red mud catalyst Anatase <![CDATA[TiO2]]> 5.2 Boehmite γAlO·OH 7.7 Calcite <![CDATA[CaCO3]]> 2.3 Three water stone <![CDATA[Al(OH)3]]> 1.8 Goethite <![CDATA[α-(Fe 3+ ,Al)O(OH)]]> 31.4 Hematite <![CDATA[α-Fe2O3]]> 32.2 Ilmenite <![CDATA[Fe 2+ TiO3]]> 1.2 Garnet <![CDATA[Ca3Al2(SiO4) 3-x (OH) 4x x=1.5-3]]> 1.8 quartz <![CDATA[SiO2]]> 1.6 Rutile <![CDATA[TiO2]]> 2.0 Sodalite <![CDATA[Na8Cl2Al6Si6O 24 ]]> 12.8 total 100.0

[0035] Example 2 Application of composite red mud catalyst in catalytic cracking of high-temperature biomass gasification tar.

[0036] The composite red mud catalyst prepared in Example 1 was dried and placed in a reactor, and a reduction reaction of the composite red mud catalyst was carried out at 800°C for 10 h under a nitrogen component to form a single iron-based composite catalyst. The cracking effects and tar removal rates of various gasification tars were tested under different reaction temperature conditions.

[0037] Table 2

[0038]

[0039] It can be seen from the above table that in the first group of reaction tests under 678°C conditions, the original tar content decreased from 7.9 to 1.4, and the tar removal rate was 82.8%; in the second group of reaction tests under 755°C conditions, the original tar content decreased from 5.1 to 0.8, and the tar removal rate was 84.2%; in the third group of reaction tests under 784°C conditions, the original tar content decreased from 27.7 to 0.7, and the tar removal rate was 97.7%; in the fourth group of reaction tests under 799°C conditions, the original tar content decreased from 19.4 to 0.7, and the tar removal rate was 96.5%.

[0040] For the first and second groups, at a relatively low temperature of 678-755°C, the tar removal rate was only 82.8-84.2%; as the temperature increased to 784-799°C, the tar removal rate increased significantly to 96.5-97.7%. Therefore, as the reaction temperature increased, the tar removal rate increased significantly. Figure 2 The graphs show the experimental results of the third group (Raw-2) and the fourth group (Raw-1).

[0041] Compared with the existing biomass gasification synthesis gas scrubber, the latter can remove 80-85% of tar, but the environmental water pollution is serious; compared with the existing precious metal nickel-based catalyst, although the nickel-based catalytic efficiency can also reach 80-90%, the use cost is extremely high, and the catalyst consumption and regeneration costs are expensive. The tar removal rate of the composite red mud catalyst used in this technology is 82.8-97.7%. This catalyst is an aluminum industry waste, with almost no cost, realizing the industrial application of "waste treatment with waste".

[0042] The present invention provides a preparation idea and method of a composite red mud catalyst. There are many methods and ways to implement the technical solution. The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, without departing from the principle of the present invention, several improvements and modifications can be made, and these improvements and modifications should also be regarded as the protection scope of the present invention. All components not specified in this embodiment can be implemented by existing technologies.

Claims

1. A method for preparing a composite red mud catalyst for synthesis gas tar cracking, characterized in that: The steps include: (1) drying the red mud and grinding it into powder, mixing the ground red mud powder with a binder, adding water and acid under stirring conditions to completely dissolve the alkali metal therein, and obtaining red mud particles; (2) taking biomass pyrolysis semi-coke particles, grinding them, and mixing them with the red mud particles obtained in step (1) for 10-15 minutes to obtain red mud glue; (3) placing the red mud gum into a granulator, granulating the red mud catalyst with an aspect ratio of 3-5 to obtain composite red mud particles; (4) The composite red mud particles obtained in step (3) are air-dried, dried, and heated to obtain a composite red mud catalyst.

2. The preparation method according to claim 1, characterized in that: In step (1), the drying condition is drying in an oven at 90-120° C. for 24-48 hours.

3. The preparation method according to claim 1, characterized in that: The binder is sodium carboxymethyl cellulose, and the mass ratio of red mud powder to the binder is 30-50:

1.

4. The preparation method according to claim 1, characterized in that: The acid is hydrochloric acid.

5. The preparation method according to claim 1, characterized in that: In step (2), the biomass pyrolysis semi-coke particles are ground to a particle size of 45-350 μm, and the biomass pyrolysis semi-coke particles account for 30-40% of the total mass of the biomass pyrolysis semi-coke particles and the red mud particles.

6. The preparation method according to claim 1, characterized in that: In step (4), the obtained composite red mud particles are first naturally air-dried for 12-24 hours; then dried at 90-120°C for 6-12 hours, and then the sample is dried at 150-200°C for 2-4 hours; finally, heated to 250-300°C and maintained for 3-6 hours to obtain a composite red mud catalyst.

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

8. An iron-based red mud catalyst, characterized in that: The composite red mud catalyst according to claim 7 is obtained by subjecting the composite red mud catalyst to a reduction reaction at 750-830° C. for 8-12 hours under a nitrogen component.

9. Use of the composite red mud catalyst according to claim 7 or the iron-based red mud catalyst according to claim 8 in catalytic cracking of high-temperature biomass gasification tar.

10. The use according to claim 9, characterized in that: The composite red mud catalyst is subjected to reduction reaction at 750-830° C. for 8-12 hours under nitrogen component to form a reduced iron-based red mud catalyst, which is used for catalytic cracking of high-temperature synthesis gas tar to achieve high-temperature clean purification of biomass gasification synthesis gas.

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