CN105664957B - A kind of preparation method of methane self-heating recapitalization mixed catalyst for magnetically fluidized bed reactor - Google Patents

Abstract

A method for preparing a methane autothermal reforming mixed catalyst used in a magnetic fluidized bed reactor. The invention first prepares nickel-magnesium-aluminum gel with a lower nickel mass percentage content and cobalt cerium with a higher cobalt mass percentage content. The aluminum gel is uniformly mixed with nickel-magnesium-aluminum gel and cobalt-cerium-aluminum gel in a certain proportion by means of ultrasonic mixing and supercritical drying, and finally roasted in an air atmosphere to obtain a mixed catalyst. The present invention designs catalyst components with different catalytic properties and controls the combination degree of each part to ensure synergistic effects without chemical combination, maintain a high methane conversion rate and provide a reducing atmosphere to avoid cobalt-based components Oxidative deactivation; controlling the high content of active metals in the cobalt-based component ensures strong high-temperature magnetic properties. The present invention can be used in magnetic fluidized bed reactors and provide catalytic oxidation activity to eliminate carbon deposits generated during the reforming process, and the magnetic field strength can be reduced 45%, and the reaction efficiency increased by more than 10%.

Description

Preparation of a Mixed Catalyst for Autothermal Reforming of Methane in a Magnetic Fluidized Bed Reactor method

technical field

The invention relates to the field of natural gas catalysis, in particular to a method for preparing a methane autothermal reforming catalyst applied to a magnetic fluidized bed reactor.

Background technique

Syngas is a mixture of hydrogen and carbon monoxide and is an important chemical raw material. In the industry, synthesis gas is mainly produced by methane reforming, and the synthesis gas is further converted into chemical products such as methanol, ammonia, dimethyl ether, low-carbon alcohols or alkanes, which has the advantages of low cost and environmental friendliness. At present, methane reforming technologies mainly include steam reforming of methane, partial oxidation of methane and autothermal reforming of methane. Methane autothermal reforming is a combination of endothermic methane reforming reaction and exothermic methane combustion (or partial oxidation) reaction, which can not only directly supply the heat required for the reaction from inside the reactor more efficiently, but also can It is an energy-saving and efficient methane reforming technology that requires continuous regulation of the ratio of hydrogen and carbon monoxide in the reaction product synthesis gas.

The two biggest problems facing the industrialization of methane reforming technology are catalyst deactivation due to carbon deposition and low reaction efficiency. The high-efficiency mass transfer and heat transfer capabilities of the fluidized bed reactor are conducive to the coupling of endothermic and exothermic reactions in the autothermal reforming process of methane, improving reaction efficiency, reducing carbon deposition and energy consumption, and have greater energy efficiency than fixed bed reactors. Advantage. However, the reaction efficiency in a fluidized bed reactor is often affected by the fluidization quality of the particles therein. Especially for most nanocatalysts, phenomena such as channeling and throttling often occur in the fluidization process, which seriously affect the contact efficiency of gas-solid phase. The magnetic fluidized bed reactor is the product of the combination of fluidization technology and electromagnetic technology. When the solid particles are ferromagnetic substances, or a considerable amount of ferromagnetic substances are mixed in the solid particles, the formation and growth of air bubbles and particle agglomerations in the fluidized bed can be prevented by the action of an external magnetic field, and the fluidization quality can be improved, thereby Improve the mass transfer efficiency between gas and solid. The magnetic fluidized bed reactor has been successfully applied to the industrial production of caprolactam hydrogenation [X. Meng, et al., Catal. Today 79-80 (2003) 21-27]. But its application in the methane reforming industry is still in the research stage. The development of magnetic catalysts that can efficiently catalyze reactions is a necessary prerequisite for the application of magnetic fluidized bed reactors.

Nickel and cobalt are the most commonly used catalytic active metals for methane reforming reaction. They have the characteristics of high catalytic activity and low cost, and both nickel and cobalt are magnetic, so they can be used as magnetic media in magnetic fluidized bed reactors. The Curie temperature of nickel is only 358°C. Since the common temperature range of methane reforming reaction is 700°C-850°C, cobalt (Curie temperature 1150°C) must be used as the catalyst active metal to ensure the magnetism of the catalyst. Chinese patent [201110354252.0, 201510096945.2] reported a variety of synthesis methods of magnetic cobalt-based catalysts, but a single cobalt-based catalyst will be rapidly oxidatively deactivated under the conditions of autothermal reforming of methane in the presence of oxygen [V.R. Choudhary, et al ., Chem. Eng. J. 121 (2006) 73-77], resulting in neither methane reforming catalytic activity nor magnetic properties.

In order to solve this problem, researchers have incorporated other metals with better reducibility (such as platinum, palladium, rhodium, nickel, etc.) into cobalt-based catalysts by chemical synthesis to prepare dual-active metal catalysts to avoid their oxidation deactivation[ K. Nagaoka, et al., Appl. Catal. A 268 (2004) 151-158.]. However, the chemical combination of cobalt and other metals is not conducive to its high-temperature magnetism, especially the reforming of methane is a structure-sensitive reaction, and the particle size of the active metal is inversely proportional to the catalytic performance of the catalyst. Therefore, it is generally necessary to control the mass percentage of the active metal below 20. % to ensure a smaller metal particle size. The multi-active metal catalyst reduces the content of cobalt, which further makes the catalyst weak in magnetism, which requires an additional high-intensity magnetic field when it is applied to a magnetic fluidized bed reactor, which not only consumes a lot of energy, but also has a poor effect on improving the reaction efficiency. For example, when using a chemically synthesized cobalt-nickel bimetallic catalyst in a magnetic fluidized bed reactor, a magnetic field above 230Oe is required to improve the reaction efficiency [L. Chen et al., Int. J. Hydrogen Energy. 35 (2010) 8494 -8502.]. Therefore, bimetallic catalysts prepared by chemical synthesis methods are difficult to balance the high-temperature magnetic properties and catalytic properties of the catalysts, and cannot be efficiently used in magnetic fluidized bed reactors to catalyze the autothermal reforming reaction of methane.

Mixing the catalyst by physical doping can also change the performance of the catalyst. Compared with chemical doping, the physical mixing method is more convenient and different types of catalysts can be mixed. However, the activity of general physical mixed catalysts often follows the principle of mixing [B. Fidalgo, et al., Appl. Catal. A 390 (2010) 78-83.], and it is difficult to produce synergistic effects, resulting in the inability to effectively combine the characteristics of various types of catalysts . Therefore, there are no reports of physically mixed catalysts being used for methane autothermal reforming, especially there is no catalyst that can simultaneously have higher methane autothermal reforming activity and high-temperature magnetic requirements, so that the magnetic fluidized bed reactor can be used in methane autothermal reforming. It is difficult to apply in the whole reaction.

Contents of the invention

The object of the present invention is to provide a method for preparing a mixed catalyst for autothermal reforming of methane used in a magnetic fluidized bed reactor.

The technical scheme adopted in the present invention is: firstly, respectively prepare nickel-magnesium-aluminum gel with lower nickel mass percentage content and cobalt-cerium-aluminum gel with higher cobalt mass percentage content; The cobalt-cerium-aluminum gel is homogeneously mixed by means of ultrasonic mixing and supercritical drying, and finally roasted in an air atmosphere to obtain a mixed catalyst. The essence of the present invention is to design catalyst components with different catalytic properties, and use ultrasonic mixing and supercritical drying methods to control the degree of combination of each part, so as to ensure that it will not only produce synergistic effects during use, but also avoid chemical combination and loss Their respective characteristics meet the requirements of their high-efficiency application in catalytic methane autothermal reforming reactions in magnetic fluidized bed reactors. Among them, the active metal content of nickel-based components is controlled to be low to ensure that it has good methane reforming activity, which is used to maintain a high methane conversion rate and provide a reducing atmosphere to avoid oxidation and deactivation of cobalt-based components; on the other hand, control cobalt The active metal content of the base component is high to ensure that it has strong high-temperature magnetism, which is used to make the mixed catalyst efficiently applied to the magnetic fluidized bed reactor and provide catalytic oxidation activity to eliminate carbon deposits generated in the reforming process.

Concrete process of the present invention and parameter are as follows:

(1) Prepare a mixed aqueous solution of magnesium nitrate and aluminum nitrate, in which the mass ratio of magnesium nitrate to aluminum nitrate is 0.04-0.13:1, the total molar concentration of magnesium ions and aluminum ions is 0.5-1mol/L, drop under vigorous stirring conditions Add ammonia water with a mass percentage of 0.5-5% until the pH of the solution is 7-8, and continue stirring for 2-4 hours to obtain a magnesium-aluminum hydrogel;

(2) Prepare 0.1-0.3mol/L nickel nitrate aqueous solution, wherein the mass ratio of nickel nitrate to aluminum nitrate in step 1 is 0.06-0.09:1, and slowly drop the nickel nitrate aqueous solution to the vigorously stirred magnesium aluminum hydrogel , then dropwise add ammonia water with a mass percentage of 0.5-5% until the pH of the solution is 9.5-10.5, continue to stir for 2-4 hours, and use deionized water and absolute ethanol to filter and wash respectively to obtain nickel-magnesium-aluminum alcohol coagulation glue;

(3) Prepare a mixed aqueous solution of cerium nitrate and aluminum nitrate, in which the mass ratio of cerium nitrate to aluminum nitrate is 0.03-0.05:1, and the total molar concentration of cerium ions and aluminum ions is 0.5-1mol/L, drop under vigorous stirring conditions Add ammonia water with a mass percentage of 0.5-5% until the pH of the solution is 7-8, and continue stirring for 2-4 hours to obtain a cerium-aluminum hydrogel;

(4) Prepare 0.3-0.6mol/L cobalt nitrate aqueous solution, wherein the mass ratio of cobalt nitrate to aluminum nitrate in step 3 is 0.19-0.26:1mol/L, slowly add the cobalt nitrate aqueous solution to the vigorously stirred cerium aluminum water In the gel, add ammonia water with a mass percentage of 0.5-5% dropwise until the pH of the solution is 9.5-10.5, continue to stir for 2-4 hours, and use deionized water and absolute ethanol to filter and wash respectively to obtain cobalt-cerium-aluminum alcohol gel;

(5) Mix the nickel-magnesium-aluminum alcohol gel and the cobalt-cerium-aluminum alcohol gel in an ethanol solution at a mass ratio of 0.4-1:1 for 10-30 minutes, and then place them in an autoclave for supercritical drying to remove ethanol. Finally, it is calcined at 500-650° C. for 2-6 hours in an air atmosphere to obtain a mixed catalyst.

Compared with prior art, the catalyst that the present invention obtains has the following advantages:

(1) The catalyst obtained in the present invention can not only stably catalyze the autothermal reforming reaction of methane, but also can use a magnetic fluidized bed reactor to enhance the reaction efficiency, which solves the problem that the current catalyst cannot have both the activity of autothermal reforming of methane and high temperature magnetic problems;

(2) The combination degree of the nickel-based component and the cobalt-based component in the mixed catalyst is controlled by the method of gel ultrasonic mixing and supercritical drying, and there is a synergistic effect between the two components, and the catalyst activity is higher than that obtained by the ordinary physical mixing method. More than 24%, and has a good ability to resist carbon deposition;

(3) The composition of the cobalt-based component in the mixed catalyst and its mass ratio in the mixed catalyst ensure the high-temperature magnetic properties of the catalyst. When applied to a magnetic fluidized bed reactor, the required external magnetic field strength can be reduced to below 120Oe, which is better than that of bimetallic catalysts The required magnetic field strength is reduced by more than 45%, and the reaction efficiency is increased by more than 10%.

Description of drawings

Figure 1 is the X-ray diffraction pattern of different catalysts after methane autothermal reforming reaction.

Detailed ways

Example 1

Prepare a mixed solution of magnesium nitrate and aluminum nitrate, wherein the mass ratio of magnesium nitrate to aluminum nitrate is 0.09:1, the total molar concentration of magnesium ions and aluminum ions is 1mol/L, and the mass percentage is 0.5 under vigorous stirring. % ammonia water until the pH value of the solution was 7.5, and continued to stir for 2 hours to obtain a magnesium aluminum hydrogel. Prepare a 0.3mol/L nickel nitrate solution, wherein the mass ratio of nickel nitrate to aluminum nitrate in the previous step is 0.06:1, slowly add the nickel nitrate solution dropwise to the vigorously stirred magnesium aluminum hydrogel, and then add the mass Ammonia water with a percentage content of 2.5% until the pH of the solution is 9.5, and after continuing to stir for 2 hours, use deionized water and absolute ethanol to filter and wash, respectively, to obtain a nickel-magnesium-aluminum alcohol gel. Prepare a mixed aqueous solution of cerium nitrate and aluminum nitrate, wherein the mass ratio of cerium nitrate to aluminum nitrate is 0.05:1, the total molar concentration of cerium ions and aluminum ions is 1mol/L, and the mass percentage is added dropwise under vigorous stirring conditions. 0.5% ammonia water until the pH value of the solution was 7.5, and continued to stir for 2 hours to obtain a cerium-aluminum hydrogel. Prepare a 0.6mol/L cobalt nitrate aqueous solution, wherein the mass ratio of cobalt nitrate to aluminum nitrate in the previous step is 0.26:1, slowly add the cobalt nitrate aqueous solution to the vigorously stirred cerium aluminum hydrogel, and then drop the mass percent Ammonia water with a content of 3% was added until the pH of the solution was 10.5. After stirring for 4 hours, deionized water and absolute ethanol were used for suction filtration and washing respectively to obtain a cobalt-cerium-aluminum alcohol gel. Mix the nickel-magnesium-aluminum alcohol gel and the cobalt-cerium-aluminum alcohol gel in an ethanol solution at a mass ratio of 0.4:1 for 20 minutes, then place them in an autoclave for supercritical drying to remove ethanol, and then place them in an air atmosphere at 500 ° C Calcined for 5 hours to obtain a mixed catalyst.

The mixed catalyst was placed in a tubular reaction tube, and a hydrogen-nitrogen mixed gas was passed through to carry out pre-reduction at 850° C. for 1.5 hours. The volume percentage of hydrogen in the hydrogen-nitrogen mixed gas was 50%. Adjust the temperature of the reactor to 750°C, apply an axial magnetic field of 90Oe to the reactor, feed a mixed reaction gas of methane, carbon dioxide and oxygen to keep the catalyst fluidized, and carry out the autothermal reforming reaction of methane for 50 hours. The direction of the magnetic field Coaxial with the tubular reactor, the volume ratio of methane, carbon dioxide and oxygen in the mixed reaction gas is 1:0.6:0.2, the reaction space velocity is 210 L/(h g _cat ), and the methane conversion rate is 83%, compared with 11% higher than traditional fluidized bed reactor.

The X-ray diffraction pattern of the sample after the reaction is shown in Figure 1. Accompanying drawing 1 represents to use single nickel-based composition as the sample after catalyst reaction, produces obvious carbon deposition characteristic peak 1 on the catalyst after reaction; B represents to use single cobalt-based composition as the sample after catalyst reaction, and metal Cobalt is oxidized, and the metal characteristic peak 2 disappears; c represents the sample after using this embodiment as the catalyst reaction, the carbon deposition characteristic peak 1 does not appear on the sample after the reaction, and the metal characteristic peak 2 does not disappear, indicating that there is neither accumulation Carbon, active metals are also not oxidized.

Example 2

Prepare a mixed aqueous solution of magnesium nitrate and aluminum nitrate, wherein the mass ratio of magnesium nitrate to aluminum nitrate is 0.06:1, the total molar concentration of magnesium ions and aluminum ions is 0.5mol/L, and the mass percentage is added dropwise under vigorous stirring. 0.5% ammonia water until the pH value of the solution was 8, and continued to stir for 3 hours to obtain a magnesium aluminum hydrogel. Prepare a 0.1mol/L nickel nitrate aqueous solution, wherein the mass ratio of nickel nitrate to aluminum nitrate in the previous step is 0.09:1, slowly add the nickel nitrate solution dropwise to the vigorously stirred magnesium aluminum hydrogel, and then add the mass Add 1% ammonia water until the pH of the solution is 10, continue to stir for 4 hours, wash with deionized water and filter with absolute ethanol to obtain a nickel-magnesium-aluminum alcohol gel. Prepare a mixed aqueous solution of cerium nitrate and aluminum nitrate, wherein the mass ratio of cerium nitrate to aluminum nitrate is 0.03:1, the total molar concentration of cerium ions and aluminum ions is 0.5mol/L, and the mass percentage is added dropwise under vigorous stirring conditions 0.5% ammonia water until the pH value of the solution was 8, and continued to stir for 2 hours to obtain a cerium-aluminum hydrogel. Prepare 0.3mol/L cobalt nitrate solution, wherein the mass ratio of cobalt nitrate to aluminum nitrate in the previous step is 0.19:1, slowly add it dropwise to the vigorously stirred cerium aluminum gel, and then add dropwise ammonia water with a mass percentage of 2.5% After the pH of the solution was 10, the stirring was continued for 2 hours, and then washed with deionized water and suction-filtered with absolute ethanol to obtain a cobalt-cerium-aluminum alcohol gel. The nickel-magnesium-aluminum gel and the cobalt-cerium-aluminum gel were ultrasonically mixed in an ethanol solution at a mass ratio of 1:1 for 10 minutes, then placed in an autoclave for supercritical drying to remove ethanol, and then calcined at 650°C in an air atmosphere for 2 Hour, obtain mixed catalyst;

The mixed catalyst was placed in a tubular reaction tube, and a hydrogen-nitrogen mixed gas was passed through to carry out pre-reduction at 800° C. for 2 hours. The volume percentage of hydrogen in the hydrogen-nitrogen mixed gas was 80%. Adjust the temperature of the reactor to 700°C, apply an axial magnetic field of 110 Oe to the reactor, feed a mixed reaction gas of methane, carbon dioxide and oxygen to keep the catalyst fluidized, and carry out the methane autothermal reforming reaction for 10 hours. The magnetic field The direction is coaxial with the tubular reactor, the volume ratio of methane, carbon dioxide and oxygen in the mixed reaction gas is 1:0.4:0.3, the reaction space velocity is 180 L/(h g _cat ), and the conversion rate of methane is 79%. Compared with the traditional fluidized bed reactor, it is 10% higher.

Claims (1)

1. a preparation method for the methane autothermal reforming mixed catalyst of magnetic fluidized bed reactor, it is characterized in that comprising the following steps: (1) Prepare a mixed aqueous solution of magnesium nitrate and aluminum nitrate, in which the mass ratio of magnesium nitrate to aluminum nitrate is 0.04-0.13:1, the total molar concentration of magnesium ions and aluminum ions is 0.5-1mol/L, drop under vigorous stirring conditions Add ammonia water with a mass percentage of 0.5-5% until the pH of the solution is 7-8, and continue stirring for 2-4 hours to obtain a magnesium-aluminum hydrogel; (2) Prepare a 0.1-0.3mol/L nickel nitrate aqueous solution, wherein the mass ratio of nickel nitrate to aluminum nitrate in step (1) is 0.06-0.09:1, slowly add the nickel nitrate aqueous solution to the vigorously stirred magnesium aluminum water In the gel, add ammonia water with a mass percentage of 0.5-5% dropwise until the pH of the solution is 9.5-10.5, continue to stir for 2-4 hours, and use deionized water and absolute ethanol to filter and wash, respectively, to obtain nickel-magnesium-aluminum alcohol gel; (3) Prepare a mixed aqueous solution of cerium nitrate and aluminum nitrate, in which the mass ratio of cerium nitrate to aluminum nitrate is 0.03-0.05:1, and the total molar concentration of cerium ions and aluminum ions is 0.5-1mol/L, drop under vigorous stirring conditions Add ammonia water with a mass percentage of 0.5-5% until the pH of the solution is 7-8, and continue stirring for 2-4 hours to obtain a cerium-aluminum hydrogel; (4) Prepare 0.3-0.6mol/L cobalt nitrate aqueous solution, wherein the mass ratio of cobalt nitrate to aluminum nitrate in step (3) is 0.19-0.26:1, slowly add the cobalt nitrate aqueous solution to the vigorously stirred cerium aluminum water In the gel, add ammonia water with a mass percentage of 0.5-5% dropwise until the pH of the solution is 9.5-10.5, continue to stir for 2-4 hours, and use deionized water and absolute ethanol to filter and wash respectively to obtain cobalt-cerium-aluminum alcohol gel; (5) Mix the nickel-magnesium-aluminum alcohol gel and the cobalt-cerium-aluminum alcohol gel in an ethanol solution at a mass ratio of 0.4-1:1 for 10-30 minutes, and then place them in an autoclave for supercritical drying to remove ethanol. Finally, it is calcined at 500-650° C. for 2-6 hours in an air atmosphere to obtain a mixed catalyst.