Methane oxidative coupling catalyst as well as preparation method and application thereof

Abstract

The invention discloses a methane oxidative coupling catalyst as well as a preparation method and application thereof. The methane oxidative coupling catalyst is prepared by roasting a mixed material containing a nano-catalyst intermediate state and a flocculating agent in a protective atmosphere, and the methane oxidative coupling catalyst contains a sodium element. The intermediate state of the low-temperature OCM nano-catalyst is subjected to rapid solid-liquid separation by adopting a polymeric flocculant, and the result shows that the catalyst prepared by the separation method disclosed by the invention keeps higher reaction activity in the methane oxidative coupling reaction under the condition of not changing the composition of active components of the catalyst, and meanwhile, the reaction time of the catalyst is greatly shortened. The CO yield is further improved. Therefore, the method for rapidly separating the methane oxidative coupling catalyst can reduce the preparation cost of the catalyst and improve the preparation efficiency of the catalyst.

Description

Technical Field

[0001] This invention relates to the technical field of nanocatalyst preparation and separation, and more specifically, to methane oxidative coupling catalysts, their preparation methods, and applications. Background Technology

[0002] Ethylene is one of the world's largest-produced chemical products and plays an important role in the national economy. Currently, ethylene production mainly comes from petroleum.

[0003] To address the over-reliance on petroleum resources for ethylene production feedstock, direct natural gas (methane) to ethylene (OCM) technology has attracted widespread attention. Among these technologies, low-temperature nanocatalysts have garnered significant interest due to their high C2 hydrocarbon yield and economic viability.

[0004] However, the separation of methane oxidative coupling nanocatalysts currently mainly relies on laboratory methods such as centrifugation, which is costly and time-consuming, making it difficult to apply to catalyst scale-up and industrialization processes.

[0005] Therefore, how to achieve rapid separation of methane oxidative coupling catalysts is a technical problem that needs to be solved. Summary of the Invention

[0006] To address the problems in existing technologies, this invention proposes a methane oxidative coupling catalyst, its preparation method, and its applications. To overcome the aforementioned catalyst separation issues, this invention provides a method and application scheme for efficient solid-liquid separation in the preparation process of methane oxidative coupling catalysts. A polymeric flocculant is used to rapidly separate the intermediate state of the low-temperature OCM nanocatalyst into solid and liquid phases. Results show that the catalyst prepared by the separation method of this invention maintains high reactivity in the methane oxidative coupling reaction while further improving CO yield, without altering the composition of the active components. Therefore, the rapid separation method for methane oxidative coupling catalysts of this invention can reduce catalyst preparation costs and improve catalyst preparation efficiency.

[0007] One objective of this invention is to provide a methane oxidative coupling catalyst, which is obtained by calcining a mixture including a nano-catalyst intermediate and a flocculant in a protective atmosphere, and the methane oxidative coupling catalyst contains sodium.

[0008] In the methane oxidative coupling catalyst of the present invention, preferably,

[0009] The methane oxidative coupling catalyst is selected from lanthanide catalysts supported on sodium; preferably, the lanthanide catalyst is selected from lanthanum oxycarbonate catalysts; and / or,

[0010] The mass content of sodium in the methane oxidative coupling catalyst is 5%-20%; preferably 5%-15%; for example, 5%, 7%, 10%, 12%, 15%, 18%, or 20%.

[0011] In the methane oxidative coupling catalyst of the present invention, preferably,

[0012] The flocculant is selected from at least one of polyacrylamide, cellulose and its derivatives, lignin and its derivatives, and chitosan and its derivatives.

[0013] In the methane oxidative coupling catalyst of the present invention, preferably,

[0014] The polyacrylamide is selected from at least one of anionic polyacrylamide, cationic polyacrylamide, or nonionic polyacrylamide; and / or,

[0015] The cellulose is selected from sodium carboxymethyl cellulose; and / or,

[0016] The lignin is selected from alkali-degraded lignin.

[0017] In the technical solution of the present invention, the existing polyacrylamide preparation process uses an initiator containing sodium salt, which will result in sodium polyacrylamide. In the technical solution of the present invention, the flocculant is preferably selected from sodium-containing flocculants, that is, preferably selected from at least one of sodium-containing polyacrylamide, sodium-containing cellulose and its derivatives, or sodium-containing lignin and its derivatives.

[0018] A second objective of this invention is to provide a method for preparing a methane oxidative coupling catalyst, comprising the following steps:

[0019] A flocculant was added to a mixture containing intermediate nano-catalysts, followed by sedimentation and solid-liquid separation. The solid material was dried, ground, and then calcined in a protective atmosphere to obtain the methane oxidative coupling catalyst.

[0020] The methane oxidative coupling catalyst described in one of the objectives of this invention is preferably prepared using the method described above.

[0021] In the preparation method of the methane oxidative coupling catalyst of the present invention, more preferably, a flocculant is added to the mixture containing the intermediate state of the nano-catalyst, and the mixture is allowed to settle. Then, the solid-liquid separation mixture is filtered by vacuum filtration, and the filtered product is placed in an oven for drying to obtain a solid product. The solid product is then calcined in a protective atmosphere to obtain the methane oxidative coupling catalyst.

[0022] In the preparation method of the methane oxidative coupling catalyst of the present invention, preferably,

[0023] The mixture containing the intermediate state of the nanocatalyst includes the intermediate state of the nanocatalyst, sodium element, and solvent;

[0024] Preferably, the preparation of the mixture containing the intermediate state of the nanocatalyst includes the following steps: adding an alkaline solution containing sodium to a solution containing the nanocatalyst precursor, and after the reaction, obtaining the mixture containing the intermediate state of the nanocatalyst.

[0025] In the preparation method of the methane oxidative coupling catalyst of the present invention, preferably,

[0026] The nanocatalyst precursor is selected from soluble lanthanum salts; preferably from lanthanum nitrate; and / or,

[0027] In the solution containing the nanocatalyst precursor, the lanthanum concentration is 0.6 wt%-0.8 wt%; for example, 0.6 wt%, 0.65 wt%, 0.7 wt%, 0.75 wt%, 0.8 wt%; and / or,

[0028] The sodium-containing alkaline solution is a sodium hydroxide solution; preferably, an alkaline solution containing 0.1-0.2 g of sodium hydroxide is added dropwise per minute to each kilogram of solution containing the nano-catalyst precursor until the pH value is adjusted to 11.5-12, at which point the addition of alkaline solution is stopped; for example, an alkaline solution containing 0.1 g, 0.125 g, 0.15 g, 0.175 g, or 0.2 g of sodium hydroxide is added dropwise per minute to each kilogram of solution containing the nano-catalyst precursor until the pH value is adjusted to 11.5, 11.6, 11.7, 11.8, 11.9, or 12, at which point the addition of alkaline solution is stopped; and / or,

[0029] The solvent in the solution containing the nanocatalyst precursor and the sodium-containing alkaline solution is water, and / or...

[0030] The reaction is performed at room temperature; and / or,

[0031] The reaction time is 50-70 hours; for example: 50 hours, 55 hours, 60 hours, 65 hours, 70 hours; and / or,

[0032] The intermediate state of the nanocatalyst is selected from lanthanum hydroxide.

[0033] In the preparation method of the methane oxidative coupling catalyst of the present invention, preferably,

[0034] The mass-to-volume ratio of the flocculant to the mixture containing the intermediate state of the nano-catalyst is 0.01-5 g:1 L; preferably 1-5 g:1 L; more preferably 2-4 g:1 L; for example, 0.01 g / L:1 L, 0.1 g / L:1 L, 0.5 g / L:1 L, 1 g / L:1 L, 2 g / L:1 L, 3 g / L:1 L, 4 g / L:1 L, 5 g / L:1 L; and / or,

[0035] The settlement is static settlement; and / or,

[0036] The solid-liquid separation method is vacuum filtration; and / or,

[0037] The drying temperature is 80-200℃; for example: 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃; and / or,

[0038] The drying time is 10-18 hours; for example: 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours; and / or,

[0039] The grinding time is 20-40 minutes; for example: 20 minutes, 25 minutes, 30 minutes, 35 minutes, 40 minutes.

[0040] In the preparation method of the methane oxidative coupling catalyst of the present invention, preferably,

[0041] The roasting is carried out at 500-700℃ for 2-6 hours; preferably at 500-600℃ for 2-3 hours; for example, the roasting is carried out at 500℃, 525℃, 550℃, 575℃, 600℃, 625℃, 650℃, 675℃, or 700℃ for 2 hours, 3 hours, 4 hours, 5 hours, or 6 hours, respectively; more preferably, the heating rate of the roasting is 2-5℃ / min; for example, 2℃ / min, 3℃ / min, 4℃ / min, or 5℃ / min.

[0042] Flocculants are substances that enable rapid separation of solids and liquids in a solid-liquid mixture. Existing technologies typically apply flocculants primarily to wastewater treatment and other fields, with no reports on their use in the separation of methane oxidative coupling catalysts. Furthermore, the flocculant of this invention does not alter the active components of the catalyst, has no impact on the yield of C2 products catalyzed by the catalyst, and simultaneously improves the selectivity and yield of CO, demonstrating significant industrial value.

[0043] A third objective of this invention is to provide an application of a methane oxidative coupling catalyst as described in one objective of this invention, or a methane oxidative coupling catalyst prepared by the method described in another objective of this invention, in the reaction of methane oxidative coupling to ethylene.

[0044] The substances and parameters not limited in this invention can be selected according to existing technology, which is a conventional technical means in this field.

[0045] The endpoints and any values ​​of the ranges disclosed in this invention are not limited to the precise ranges or values; these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. In the following, various technical solutions can, in principle, be combined with each other to obtain new technical solutions, which should also be considered as specifically disclosed herein.

[0046] Compared with the prior art, the present invention has at least the following advantages:

[0047] This invention solves the problems of high cost and long time consumption in solid-liquid separation of existing nanocatalysts. Without affecting the catalytic effect of nanomethane oxidative coupling catalyst, it provides an industrial solid-liquid separation method of nanoparticles without changing the active components. Moreover, the flocculant of this invention has no effect on the yield of C2 products obtained by catalyst catalysis, while improving the selectivity and yield of CO, which has very good industrial value. Detailed Implementation

[0048] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0049] It should also be noted that the various specific technical features described in the following embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the various possible combinations will not be described separately in this invention.

[0050] Furthermore, various embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention. The resulting technical solutions are part of the original disclosure of this specification and also fall within the protection scope of the present invention.

[0051] Unless otherwise specified, the raw materials used in the examples and comparative examples are all disclosed in the prior art, such as those that can be directly purchased or prepared according to the preparation methods disclosed in the prior art.

[0052] Nonionic polyacrylamide was purchased from Beijing Inokai Technology Co., Ltd.; sodium carboxymethyl cellulose was purchased from Beijing Inokai Technology Co., Ltd.

[0053] Preparation Example 1

[0054] The preparation process of the mixture containing the intermediate state of the nanocatalyst is as follows:

[0055] Accurately weigh lanthanum nitrate hexahydrate and dissolve it in deionized water (lanthanum element concentration is 0.74 wt%). Stir until completely dissolved. At room temperature (~25℃), slowly add 25 wt% sodium hydroxide solution to the solution (0.15 g sodium hydroxide per minute per kilogram of solution). Adjust the final pH value to 12 and maintain this condition for 60 h to obtain a mixed solution containing the intermediate state of lanthanide nanocatalyst, wherein the intermediate state of nanocatalyst is lanthanum hydroxide.

[0056] Example 1

[0057] This embodiment illustrates an industrial-scale method for solid-liquid separation using the catalyst provided by the present invention, comprising the following steps:

[0058] Step 1. Add 3g of nonionic polyacrylamide to 1L of the solution containing the intermediate state of lanthanide nanocatalyst prepared in Preparation Example 1, stir and let stand. Within 5s, solid-liquid separation occurs (suspension to supernatant volume ratio 1:3). After circulating and filtration, dry at 120℃ for 12h to obtain mixed powder.

[0059] Step 2. The mixed powder is placed in a ball mill and ground at 400 rpm / min for 30 min. Then it is placed in a muffle furnace and heated to 500°C at a heating rate of 5°C / min under nitrogen protection. It is calcined for 2 h and then cooled to room temperature under nitrogen protection to obtain methane oxidative coupling catalyst a.

[0060] Example 2

[0061] This embodiment illustrates an industrial-scale method for solid-liquid separation using the catalyst provided by the present invention, comprising the following steps:

[0062] Step 1. Add 3g of sodium carboxymethyl cellulose to 1L of the intermediate state of lanthanide nanocatalyst prepared in Preparation Example 1, stir and let stand for 30min to achieve solid-liquid separation (suspension to supernatant volume ratio 1:3), circulate and filter, and dry at 120℃ for 12h to obtain mixed powder.

[0063] Step 2. The mixed powder is placed in a ball mill and ground at 400 rpm / min for 30 min. Then it is placed in a muffle furnace and heated to 500°C at a heating rate of 5°C / min under nitrogen protection. It is calcined for 2 h and then cooled to room temperature under nitrogen protection to obtain methane oxidative coupling catalyst b.

[0064] Example 3

[0065] This embodiment illustrates an industrial-scale method for solid-liquid separation using the catalyst provided by the present invention, comprising the following steps:

[0066] Step 1. Add 4g of nonionic polyacrylamide to 1L of the solution containing the intermediate state of lanthanide nanocatalyst prepared in Preparation Example 1, stir and let stand. Within 5s, solid-liquid separation occurs (suspension to supernatant volume ratio 1:3). After circulating and filtration, dry at 120℃ for 12h to obtain mixed powder.

[0067] Step 2. The mixed powder is placed in a ball mill and ground at 400 rpm / min for 30 min. Then it is placed in a muffle furnace and heated to 600°C at a heating rate of 5°C / min under nitrogen protection. It is calcined for 3 h and then cooled to room temperature under nitrogen protection to obtain methane oxidative coupling catalyst c.

[0068] Comparative Example 1

[0069] This comparative example illustrates an industrial-scale solid-liquid separation method using a reference methane oxidative coupling catalyst, comprising the following steps:

[0070] Catalyst d was prepared according to the method in Example 1, except that no flocculant was added during the solid-liquid separation process, and the standing time was extended to 40 min to achieve solid-liquid separation (suspension to supernatant volume ratio 1:3).

[0071] Comparative Example 2

[0072] This comparative example illustrates an industrial-scale solid-liquid separation method using a reference methane oxidative coupling catalyst, comprising the following steps:

[0073] Catalyst e was prepared according to the method in Example 1, except that no flocculant was added during the solid-liquid separation process. High-speed centrifugation was used to separate the methane oxidative coupling catalyst into solid and liquid phases. The centrifugation time was 8000 rpm / min for 10 minutes. The centrifuge could hold a total of 6 centrifuge tubes, and each tube could centrifuge approximately 80 mL of the solid-liquid mixture. The centrifuge could process 80 mL * 6 = 0.48 L at a time. Currently, 1 L takes about 1 hour in the laboratory. The centrifuged material was washed with deionized water, then alcohol-washed, and calcined to obtain the methane oxidative coupling catalyst e.

[0074] Comparative Example 3

[0075] This comparative example is used to illustrate the catalyst and its preparation method for incorporating other natural polymeric flocculants provided by the present invention.

[0076] Catalyst f was prepared according to the method in Example 1, except that starch was added as a flocculant during the solid-liquid separation process, and the standing time was extended to 30 min to achieve solid-liquid separation (suspension to supernatant volume ratio 1:3) to obtain methane oxidative coupling catalyst f.

[0077] Test Example 1

[0078] This test example is used to illustrate the catalytic performance of the catalyst of the present invention.

[0079] 0.1 g of catalyst a was loaded into a fixed-bed quartz tube reactor. Under normal pressure, the molar ratio of methane to oxygen was 3:1, the total space velocity of methane and oxygen was 40020 ml / gh, and the reaction temperature was 500℃. The methane conversion rate and ethylene-ethane selectivity are shown in Table 1.

[0080] Test Example 2-3

[0081] This test example is used to illustrate the catalytic performance of the catalyst of the present invention.

[0082] The method of test example 1 was followed for the oxidative coupling of methane to ethylene ethane, except that catalysts b and c were used respectively. The methane conversion and ethylene ethane selectivity of the methane oxidative coupling reaction are shown in Table 1.

[0083] Comparative Test Example 1

[0084] The oxidative coupling of methane to ethylene ethane was carried out according to the method of Test Example 1, except that catalyst d was used. The methane conversion and ethylene ethane selectivity of the methane oxidative coupling reaction are shown in Table 1.

[0085] Comparative test case 2-3

[0086] The method of test example 1 was followed for the oxidative coupling of methane to ethylene ethane, except that the catalyst e / f was used. The methane conversion and ethylene ethane selectivity of the methane oxidative coupling reaction are shown in Table 1.

[0087] The methane conversion and ethylene-ethane selectivity of the methane oxidative coupling catalysts prepared in the above examples and comparative examples are shown in Table 1, as detailed below:

[0088] Table 1

[0089]

[0090] Table 2 summarizes the solid-liquid separation time of the catalyst intermediate during the preparation of the above-described examples and comparative examples of methane oxidative coupling catalysts.

[0091] Table 2

[0092]

[0093] Table 2 shows that the present invention shortens the sedimentation and separation time of the methane oxidative coupling catalyst by adding flocculants. Example 1 can quickly separate and filter the catalyst emulsion, greatly shortening the catalyst separation time. Compared with the centrifugal separation equipment of Comparative Example 2, which has high requirements and the centrifugal operation is relatively time-consuming and labor-intensive compared with separation and filtration, the product filtration and separation of the present invention by adding flocculants is more convenient and efficient.

[0094] Table 3

[0095]

[0096] Table 1 shows that the experimental results in Examples 1, 2, and 3 indicate that adding flocculants did not reduce the catalytic activity of the methane oxidative coupling catalyst. Furthermore, the introduction of flocculants can increase the CO yield in the direct natural gas (methane) to ethylene (OCM) reaction with minimal impact on the C2 yield, suggesting this approach has good industrial application prospects. This invention hypothesizes that the flocculant may also encapsulate sodium elements during the flocculation of the catalyst's intermediate state, and that the flocculant itself contains a certain amount of sodium. These factors lead to an increase in the sodium content of the methane oxidative coupling catalyst, as shown in Table 3, thus having a certain beneficial impact on the overall performance of the methane oxidative coupling catalyst.

[0097] The present invention has been described in detail above with reference to specific embodiments and exemplary examples; however, these descriptions should not be construed as limiting the present invention. Those skilled in the art will understand that various equivalent substitutions, modifications, or improvements can be made to the technical solutions and embodiments of the present invention without departing from the spirit and scope of the invention, and all such modifications and improvements fall within the scope of the present invention. The scope of protection of the present invention is defined by the appended claims.

[0098] All publications, patent applications, patents, and other references mentioned in this specification are incorporated herein by reference. Unless otherwise defined, all technical and scientific terms used in this specification have the meanings commonly understood by those skilled in the art. In case of conflict, the definitions in this specification shall prevail.

[0099] When this specification uses the prefixes “known to those skilled in the art,” “prior art,” or similar terms to derive materials, substances, methods, steps, apparatus, or components, the objects derived from such prefixes cover those commonly used in the art at the time of this application, but also include those that are not currently commonly used but will become generally recognized in the art as suitable for similar purposes.

[0100] In the context of this specification, except where expressly stated otherwise, any matters or issues not mentioned shall apply directly to those known in the art without any modification.

Claims

1. A methane oxidative coupling catalyst, characterized in that: The methane oxidative coupling catalyst is obtained by calcining a mixture including a nano-catalyst intermediate and a flocculant in a protective atmosphere, and the methane oxidative coupling catalyst contains sodium.

2. The methane oxidative coupling catalyst according to claim 1, characterized in that: The methane oxidative coupling catalyst is selected from lanthanide catalysts supported on sodium; preferably, the lanthanide catalyst is selected from lanthanum oxycarbonate catalysts; and / or, The mass content of sodium in the methane oxidative coupling catalyst is 5%-20%; preferably 5%-15%.

3. The methane oxidative coupling catalyst according to claim 1, characterized in that: The flocculant is selected from at least one of polyacrylamide, cellulose and its derivatives, lignin and its derivatives, and chitosan and its derivatives.

4. The methane oxidative coupling catalyst according to claim 3, characterized in that: The polyacrylamide is selected from at least one of anionic polyacrylamide, cationic polyacrylamide, or nonionic polyacrylamide; and / or, The cellulose is selected from sodium carboxymethyl cellulose; and / or, The lignin is selected from alkali-degraded lignin.

5. A method for preparing a methane oxidative coupling catalyst, characterized in that, Includes the following steps: A flocculant was added to a mixture containing intermediate nano-catalysts, followed by sedimentation and solid-liquid separation. The solid material was dried, ground, and then calcined in a protective atmosphere to obtain the methane oxidative coupling catalyst. The methane oxidative coupling catalyst according to any one of claims 1-4 is preferably prepared by the method described above.

6. The method for preparing the methane oxidative coupling catalyst according to claim 5, characterized in that: The mixture containing the intermediate state of the nanocatalyst includes the intermediate state of the nanocatalyst, sodium element, and solvent; Preferably, the preparation of the mixture containing the intermediate state of the nanocatalyst includes the following steps: adding an alkaline solution containing sodium to a solution containing the nanocatalyst precursor, and after the reaction, obtaining the mixture containing the intermediate state of the nanocatalyst.

7. The method for preparing the methane oxidative coupling catalyst according to claim 6, characterized in that: The nanocatalyst precursor is selected from soluble lanthanum salts; preferably from lanthanum nitrate; and / or, In the solution containing the nanocatalyst precursor, the lanthanum concentration is 0.6 wt%-0.8 wt%; and / or, The sodium-containing alkaline solution is a sodium hydroxide solution; preferably, an alkaline solution containing 0.1-0.2 g of sodium hydroxide is added dropwise per minute to each kilogram of solution containing the nano-catalyst precursor, and the addition of the alkaline solution is stopped when the pH value is adjusted to 11.5-12; and / or, The solvent in the solution containing the nanocatalyst precursor and the sodium-containing alkaline solution is water, and / or... The reaction is performed at room temperature; and / or, The reaction time is 50-70 hours; and / or, The intermediate state of the nanocatalyst is selected from lanthanum hydroxide.

8. The method for preparing the methane oxidative coupling catalyst according to claim 5, characterized in that: The mass-to-volume ratio of the flocculant to the mixture containing the intermediate state of the nanocatalyst is 0.01-5 g:1 L; preferably 1-5 g:1 L; more preferably 2-4 g:1 L; and / or, The settlement is static settlement; and / or, The solid-liquid separation method is vacuum filtration; and / or, The drying temperature is 80-200℃; and / or, The drying time is 10-18 hours; and / or, The grinding time is 20-40 minutes.

9. The method for preparing the methane oxidative coupling catalyst according to claim 5, characterized in that: The calcination is carried out at 500-700℃ for 2-6 hours; preferably at 500-600℃ for 2-3 hours; and more preferably, the heating rate of the calcination is 2-5℃ / min.

10. The use of a methane oxidative coupling catalyst as described in any one of claims 1-4 or a methane oxidative coupling catalyst prepared by the method as described in any one of claims 5-9 in the reaction of methane oxidative coupling to ethylene.

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