A method for preparing an iron-based catalyst

Abstract

The present invention discloses a method for preparing an iron-based catalyst, comprising the following steps: (1) drying, grinding, and screening a red mud raw material and a biochar raw material; (2) mixing the red mud particles obtained in step (1) with the biochar particles in a certain proportion; (3) charging the mixture in step (2) into a fixed bed reactor, introducing a gas containing carbon dioxide into the reactor, and performing an activation treatment; (4) cooling the reactor to room temperature, removing the mixture after the reaction, washing it with water, and drying it to obtain an iron-based catalyst. The present invention treats two solid waste materials, red mud and biochar, together, expands and modifies the biochar at high temperature using red mud, and reduces and loads iron onto the modified biochar. The method has low cost, a simple preparation method, and can be produced on a large scale.

Description

Technical Field

[0001] The present invention belongs to the field of waste gas treatment, and specifically relates to a method for preparing an iron-based catalyst by utilizing red mud and biochar. Background Art

[0002] Biochar, a byproduct of biomass conversion, contains a large amount of carbon and is a key factor affecting the overall biomass yield. The effective use of biochar is crucial for biomass utilization, and the general application model is to modify it into an adsorbent. However, the product has low value and can be replaced, and the processing process may cause secondary pollution. Red mud, as a waste material from the aluminum industry, is harmful to the environment and contains a large amount of alkaline substances, making it difficult to treat. The general treatment method is to sinter it into building materials. However, the problem is that its quality as a building material is low, its application occasions are limited, and its usage is limited.

[0003] CN202110294171.X discloses a preparation method and application of sludge-red mud composite biochar containing Fe-CON active sites. This method grinds and mixes sludge, red mud and urea, and then anneals them under inert gas to obtain active sites containing Fe-CON. CN202011142113.7 discloses a method for enhanced removal of difficult-to-degrade dyes in water using red mud biochar. Similarly, this method starts with biomass and mixes it with red mud to obtain biochar under a nitrogen atmosphere. CN202110351635.6 discloses a composite biochar and a preparation method thereof, in which hydrothermal carbon and red mud are formed into particles as the core, and hydrothermal carbon and alkali-formed particles are wrapped on the outside, and the composite particles are carbonized in an inert gas to obtain composite biochar. The above patents are all products for the purpose of preparing biochar. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention provides a method for preparing an iron-based catalyst. This method combines two solid waste materials, red mud and biochar, to process them together. The red mud then expands and modifies the biochar at high temperatures, and then reduces and loads the iron onto the modified biochar. This method is low-cost, simple to prepare, and suitable for large-scale production.

[0005] The preparation method of the iron-based catalyst of the present invention comprises the following steps: (1) drying, grinding and screening the red mud raw material and the biochar raw material respectively; (2) mixing the red mud particles obtained in step (1) with the biochar particles in a certain proportion; (3) charging the mixture in step (2) into a fixed bed reactor, introducing a gas containing carbon dioxide, and performing an activation treatment; (4) cooling the reactor to room temperature, taking out the mixture after the reaction, washing it with water, and drying it to obtain the iron-based catalyst.

[0006] In the method of the present invention, the red mud raw material in step (1) is generally derived from the aluminum industry. Based on the dry weight of the red mud raw material, the iron oxide content is 30% to 60%, silicon oxide is 3% to 20%, calcium oxide is 2% to 10%, aluminum oxide is 10% to 20%, sodium oxide is 0% to 10%, and titanium oxide is 0% to 10%.

[0007] In the method of the present invention, the biochar raw material in step (1) is generally a by-product of biomass cracking and gasification, has a certain initial pore structure, and a specific surface area of ​​2 to 20 m 2 / g.

[0008] In the method of the present invention, the drying conditions in step (1) are: a drying temperature of 90 to 110°C and a drying time of 8 to 24 hours. The purpose of drying is to remove moisture from the red mud raw material.

[0009] In the method of the present invention, after the grinding and screening in step (1), the particle size of the red mud particles is 5 to 50 microns, and the particle size of the biochar particles is 45 to 180 microns.

[0010] In the method of the present invention, the mass ratio of the red mud particles and the biochar particles mixed in step (2) is 0.1~1:1.

[0011] In the method of the present invention, the carbon dioxide content in the carbon dioxide-containing gas in step (3) is 10% to 80% by volume, and the remaining inert gas and / or nitrogen is used as the balance gas.

[0012] In the method of the present invention, the activation treatment conditions in step (3) are: temperature of 600-900°C and time of 1-6 hours.

[0013] In the method of the present invention, the washing process in step (4) is to rinse 2 to 4 times with water 5 to 10 times the volume of the mixture, and the drying process is to dry at 90 to 110° C. for 8 to 24 hours.

[0014] This method utilizes the alkaline functional groups and metals in red mud, combined with the introduced carbon dioxide to create and expand pores in the biochar, while using the generated carbon monoxide to reduce metal oxides such as iron oxide, and then load them onto the generated porous biochar to form a catalyst. Since the binding process between the active center of the catalyst and the carrier is a solid-phase process, most of the active centers will be loaded onto the outer surface of the carrier, so using the obtained catalyst powder as a precursor for a formed catalyst can most effectively utilize the loaded metal active centers. This method not only solves the pollution problem by integrating red mud and biochar solid waste, but also produces a catalyst with high application value.

[0015] The iron-based catalyst of the present invention can be used for selective hydrogenation, such as Fischer-Tropsch synthesis, etc.; it can also be used for selective oxidation reactions, such as alkane dehydrogenation and olefin epoxidation. At the same time, the catalyst can be used as a catalytic oxidation environmentally friendly catalyst for the purification of oily wastewater and indoor harmful gases. DETAILED DESCRIPTION

[0016] The preparation method and effects of the catalyst of the present invention are further illustrated below with reference to the examples.

[0017] Example 1

[0018] (1) Take 10g of red mud sample 1 (iron oxide 55%, silicon oxide 22%, calcium oxide 2%, aluminum oxide 15%, titanium oxide 3%, sodium oxide 3%) and 20g of biochar sample 1 (specific surface area 5m 2 / g) were dried at 110 °C for 12 h;

[0019] (2) Grind and sieve the dried red mud and biochar particles obtained in step 1 to ~10 μm and ~135 μm, respectively, to obtain 5 g of red mud sample and 12 g of biochar sample, and then evenly mix 5 g of red mud and 10 g of biochar in a ratio of 0.5:1;

[0020] (3) The mixture from step 2 was placed in a fixed bed reactor and nitrogen containing 30% carbon dioxide was introduced. The temperature was raised to 800°C, maintained for 2 hours, and then cooled to room temperature.

[0021] (4) The mixture after the reaction in step 3 was taken out, rinsed with 300 mL of water three times, and then dried at 110°C for 12 hours to obtain a catalyst. The properties are shown in Table 1.

[0022] Example 2

[0023] (1) Take 10g of red mud sample 2 (iron oxide 64%, silicon oxide 18%, calcium oxide 2%, aluminum oxide 15%, titanium oxide <1%, sodium oxide <1%) and 20g of biochar sample 2 (specific surface area 8m 2 / g) were dried at 110 °C for 12 h;

[0024] (2) After drying, the red mud and biochar particles were ground and sieved to ~10 μm and ~135 μm, respectively, to obtain 5 g of red mud sample and 13 g of biochar sample, and then 5 g of red mud and 5 g of biochar were evenly mixed in a ratio of 1:1;

[0025] (3) The mixture from step 2 was placed in a fixed bed reactor and nitrogen containing 20% ​​carbon dioxide was introduced. The temperature was raised to 800°C, maintained for 2 hours, and then cooled to room temperature.

[0026] (4) The mixture after the reaction in step 3 was taken out, rinsed with 300 mL of water three times, and then dried at 110°C for 12 hours to obtain a catalyst. The properties are shown in Table 1.

[0027] Example 3

[0028] (1) Take 10g of red mud sample 2 (iron oxide 64%, silicon oxide 18%, calcium oxide 2%, aluminum oxide 15%, titanium oxide <1%, sodium oxide <1%) and 30g of biochar sample 3 (specific surface area 10m 2 / g) were dried at 110 °C for 12 h;

[0029] (2) Grind and sieve the dried red mud and biochar particles obtained in step 1 to ~10 μm and ~135 μm, respectively, to obtain 5 g of red mud sample and 20 g of biochar sample, and then evenly mix 5 g of red mud and 15 g of biochar in a ratio of 1:3;

[0030] (3) The mixture from step 2 was placed in a fixed bed reactor and nitrogen containing 50% carbon dioxide was introduced. The temperature was raised to 800°C, maintained for 2 hours, and then cooled to room temperature.

[0031] (4) The mixture after the reaction in step 3 was taken out, rinsed with 300 mL of water three times, and then dried at 110°C for 12 hours to obtain a catalyst. The properties are shown in Table 1.

[0032] Comparative Example 1

[0033] The same method as Example 1 was used, except that pure nitrogen was used instead of nitrogen containing 30% carbon dioxide in step (3), to obtain a catalyst. The properties of the catalyst are shown in Table 1.

[0034] Comparative Example 2

[0035] The same method as Example 1 was used, except that the activation temperature in step (3) was 500°C. A catalyst was obtained, and its properties are shown in Table 1.

[0036] Comparative Example 3

[0037] The same method as Example 1 was used, except that in step (2), 5 g of red mud and 2.5 g of biochar were uniformly mixed in a ratio of 2:1 to obtain a catalyst. The properties of the catalyst are shown in Table 1.

[0038] Example 4

[0039] The catalyst powder obtained by the above method was applied to the Fischer-Tropsch synthesis reaction in a fixed-bed reactor of a micro-reactor evaluation device. The catalyst loading was 0.3 g, the syngas H2 / CO ratio was 2, the flow rate was 100 mL / min, the reaction temperature was 300°C, and the operating pressure was 5 MPa. Carbon monoxide concentrations were measured using an Agilent 7890A gas chromatograph. The conversion rates over reaction time are shown in Table 2.

[0040] Table 1 Physical properties of catalysts in Examples and Comparative Examples

[0041]

[0042] Table 2 Reaction conversion rates of Examples and Comparative Examples

[0043]

Claims

1. A method for preparing an iron-based catalyst, characterized in that The method comprises the following contents: (1) drying, grinding and screening red mud raw materials and biochar raw materials respectively to obtain red mud particles and biochar particles; (2) mixing the red mud particles obtained in step (1) with the biochar particles in a certain proportion to obtain a mixture; (3) charging the mixture in step (2) into a fixed bed reactor, introducing a gas containing carbon dioxide, and performing activation treatment; (4) cooling the reactor to room temperature, taking out the mixture after the reaction, washing it with water, and drying it to obtain an iron-based catalyst; the mass ratio of the red mud particles to the biochar particles in step (2) is 0.1-1:1; the activation treatment conditions in step (3) are: temperature of 600-900°C, and time of 1-6 hours.

2. The method according to claim 1, wherein: Based on the dry weight of the red mud raw material, the iron oxide content is 30%~60%, silicon oxide is 3%~20%, calcium oxide is 2%~10%, aluminum oxide is 10%~20%, sodium oxide is 0~10%, and titanium oxide is 0~10%.

3. The method according to claim 1, wherein: The biochar raw material in step (1) is a by-product of biomass cracking and gasification, has a certain initial pore structure, and a specific surface area of ​​2 to 20 m 2 / g.

4. The method according to claim 1, wherein: The drying conditions in step (1) are: drying temperature 90-110° C., and drying time 8-24 hours.

5. The method according to claim 1, wherein: After the grinding and screening in step (1), the particle size of the red mud particles is 5 to 50 microns, and the particle size of the biochar particles is 45 to 180 microns.

6. The method according to claim 1, wherein: In the carbon dioxide-containing gas in step (3), the carbon dioxide content is 10% to 80% by volume, and the remaining inert gas and / or nitrogen is used as the balance gas.

7. Use of the iron-based catalyst prepared by the method according to any one of claims 1 to 6 in selective hydrogenation and selective oxidation reactions.

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