Composite metal oxide catalyst for synthesizing alpha olefins, preparation method and application thereof

Abstract

The present invention discloses a composite metal oxide catalyst for synthesizing alpha-olefins, its preparation method, and application, belonging to the technical field of organic synthesis. The catalyst comprises a first metal oxide, a second metal oxide, and an additive. The first metal oxide comprises one or more of Al2O3, TiO2, or CeO2; the second metal oxide comprises MgO; and the additive comprises Y2O3. The preparation method comprises: mixing the first metal oxide and the second metal oxide and ball-milling them uniformly, calcining them, mixing them with alkaline solution, reacting them under high temperature and high pressure, and drying them to obtain an intermediate; soaking the intermediate in an organic solution of the additive, drying, and calcining them. The catalyst has a hydrophobic surface and acid-base active sites, which impart fatty alcohol dehydration activity to the catalyst and the ability to inhibit the formation of fatty ethers. The preparation process is simple, and the content of oxygen-containing compounds such as fatty alcohols and fatty ethers in the alpha-olefin synthesis process is less than 0.01%, which is beneficial for subsequent processing and utilization of downstream products.

Description

Technical Field

[0001] The present invention relates to the technical field of organic synthesis, in particular to a composite metal oxide catalyst for synthesizing alpha olefins.

[0002] The invention also relates to a preparation method and application of the catalyst. Background Art

[0003] Linear alpha-olefins are important industrial raw materials, primarily used in the synthesis of polyolefin comonomers, oilfield additives, and synthetic lubricants (PAOs). There are multiple methods for synthesizing alpha-olefins, including ethylene oligomerization, paraffin cracking, Fischer-Tropsch synthesis, and fatty alcohol dehydration. The paraffin cracking method suffers from complex reaction processes and high investment and operating costs. The Fischer-Tropsch synthesis produces a mixture of alkanes and olefins of varying carbon chains, making olefin separation difficult. Ethylene oligomerization, a component of the petrochemical industry, requires abundant ethylene feedstock and supporting industries.

[0004] Fatty alcohol dehydration is an effective way to convert biomass alcohols (typically C8-C22 alcohols) into linear alpha olefins. Fatty alcohols are obtained by hydrolysis and hydrogenation of natural oils and fats. Natural oils and fats such as cottonseed oil, palm oil, and coconut oil are abundant and offer the advantage of being a low-cost raw material source.

[0005] Downstream products of α-olefins, such as polyethylene comonomers and PAO, require very high oxygen-containing compound content in the α-olefin raw materials. Excessive oxygen-containing compounds will cause a significant decrease in the degree of polymerization and purity of the product. Therefore, reducing the amount of oxygen-containing compounds generated during the synthesis of α-olefins can simplify the subsequent processing of α-olefins and improve the quality indicators of downstream products. The dehydration reaction of fatty alcohols is as follows:

[0006]

[0007] Oxygenates primarily arise from two sources: incomplete conversion of fatty alcohols, resulting in residual fatty alcohols as oxygenates; and fatty ethers, a byproduct of fatty alcohol dehydration, as oxygenates. Existing technologies for dehydrating fatty alcohols to synthesize alpha olefins have yet to address controlling the oxygenate content through catalyst design and preparation. Summary of the Invention

[0008] The present invention provides a composite metal oxide catalyst for synthesizing alpha-olefins. The catalyst has a hydrophobic surface and acid-base active sites, resulting in fatty alcohol dehydration activity while also inhibiting fatty ether formation. The catalyst is simple to prepare, and the content of residual fatty alcohols, by-product fatty ethers, and other oxygenated compounds during alpha-olefin synthesis is less than 0.01%, facilitating subsequent processing and utilization in downstream products.

[0009] To achieve the above objectives, the present invention adopts the following specific technical solutions:

[0010] A composite metal oxide catalyst for synthesizing alpha olefins comprises a first metal oxide, a second metal oxide, and an additive. The first metal oxide comprises one or more of Al2O3, TiO2, or CeO2; the second metal oxide comprises MgO; and the additive comprises Y2O3.

[0011] Furthermore, the mass ratio of the first metal oxide, the second metal oxide and the auxiliary agent is (96.2-98.5):(1.35-3.26):(0.15-0.54).

[0012] Preferably, in the catalyst, the acidic site concentration is 0.13-0.29 mmol / g, and the basic site concentration is 0.15-0.42 mmol / g.

[0013] The dehydration reaction of fatty alcohols includes intramolecular dehydration and intermolecular dehydration. Intramolecular dehydration requires the construction of acid-base active sites. The O atoms on the alcohol molecules are chemically adsorbed on the acid sites on the catalyst surface. β The H atoms on the surface are adsorbed on the basic sites, and the CO bonds and the adjacent C β The -H bonds are simultaneously broken to produce alpha olefins (some alpha olefins are isomerized to internal olefins) and H2O molecules. Intermolecular dehydration reactions occur when an alcohol molecule adsorbed on an acidic site on the catalyst interacts with another alcohol molecule adsorbed on a nearby acidic site. The CO bond in one alcohol molecule and the OH bond in the other alcohol molecule are simultaneously broken, removing a water element. The two molecules then recombine to form an ether.

[0014] In the catalyst of the present invention, metal oxides such as Al2O3, TiO2, and CeO2 are doped with MgO to form acid-base active sites, effectively inhibiting the formation of fatty ethers. Y2O3 improves the dispersibility of active components such as the first and second metal oxides, promoting the rapid reaction of the raw fatty alcohols. It also creates a hydrophobic surface that facilitates the rapid desorption of generated water, thereby increasing the conversion rate of fatty alcohols and reducing the fatty alcohol content in the product.

[0015] Therefore, the catalyst of the present invention improves the conversion rate of fatty alcohols while also suppressing the generation of fatty ethers.

[0016] The present invention also provides a method for preparing the composite metal oxide catalyst for synthesizing α-olefins, comprising the following steps:

[0017] S1: mixing the first metal oxide and the second metal oxide, ball-milling them until uniform, and calcining them;

[0018] Furthermore, the mass ratio of the first metal oxide to the second metal oxide is (96.2-98.5):(1.35-3.26); and the mixing and ball milling time is about 8-12 hours.

[0019] Furthermore, the calcination is performed at 800-1000°C for 12-14 hours. This calcination allows the two metal oxides to be thoroughly mixed in a sub-molten state, thereby achieving a high degree of doping. If the calcination temperature is lower than 800°C or the calcination time is less than 12 hours, the doping level will be insufficient. If the calcination temperature is higher than 1000°C or the calcination time is longer than 14 hours, excessive melting will occur, causing sintering of the catalyst surface and a reduction in specific surface area.

[0020] S2: mixing the product obtained in step S1 with alkali solution, reacting under high temperature and high pressure, and drying to obtain an intermediate;

[0021] Preferably, the alkali solution may be sodium hydroxide.

[0022] Furthermore, the high-temperature, high-pressure reaction is carried out at 250-300°C and 3.0-4.0 MPa for 6-8 hours. The high-temperature alkaline solution treatment can etch the catalyst surface, disrupting the original lattice and causing lattice distortion, thereby introducing oxygen defects. When the reaction temperature is below 250°C or the reaction pressure is below 3.0 MPa, the degree of lattice distortion is low and insufficient to introduce oxygen defects. When the reaction temperature is above 300°C or the reaction pressure is above 4.0 MPa, the lattice distortion is excessive, causing the framework structure to collapse and the catalyst activity to decrease.

[0023] S3: dissolving the auxiliary agent precursor in an organic solvent to obtain an auxiliary agent solution, soaking the intermediate obtained in step S2 in the auxiliary agent solution, and then drying and calcining to obtain the catalyst;

[0024] Furthermore, the auxiliary agent precursor includes yttrium nitrate, and the organic solvent includes ethylene glycol and / or ethanol.

[0025] Preferably, the organic solvent comprises a mixed solution of ethylene glycol and ethanol; more preferably, the mass ratio of yttrium nitrate, ethylene glycol and ethanol is 1:(4.2-5.4):(93.6-94.8).

[0026] In the additive solution, the role of yttrium nitrate is mainly to provide a precursor for yttrium oxide; the role of ethanol is mainly to dissolve yttrium nitrate and ethylene glycol, so that the solvent can fully penetrate into the pore structure of the catalyst during catalyst immersion; the addition of ethylene glycol can make yttrium nitrate and its decomposition product yttrium oxide adhere to and be highly dispersed on the catalyst surface during high-temperature treatment.

[0027] Furthermore, the soaking time is 10-12 hours.

[0028] Furthermore, the calcination temperature is 500-600° C., and the calcination time is 4-6 hours.

[0029] The catalyst is subjected to high-temperature treatment in step S1 and sub-molten salt etching in step S2, so that the metal oxides are mutually doped and oxygen defects are formed, thereby having acid-base dual active sites; at the same time, the catalyst is treated by an auxiliary agent modification method so that the active components of the catalyst are highly dispersed and have a hydrophobic effect.

[0030] The present invention also provides an application of the composite metal oxide catalyst for synthesizing α-olefins, characterized in that the catalyst is placed in a fixed bed reactor and heated at a liquid space velocity of 0.1-1.0h -1 , under a pressure of 100-300KPa, the temperature is raised to 300-350℃ at a rate of 0.5-2.0℃ / min to carry out the reaction.

[0031] In a fixed-bed reactor, these reaction conditions effectively maximize the catalyst's performance, enabling the highly selective production of alpha-olefins. Compared to existing technologies, the present invention utilizes techniques such as high-temperature calcination, sub-molten salt curing, and etching the surface of composite metal oxides to intermix the metal oxides and form oxygen vacancies, resulting in uniformly distributed acid-base active sites. These acid-base active sites enable the catalyst to catalyze the highly selective synthesis of alpha-olefins from fatty alcohols, reducing the production of fatty ether byproducts. Furthermore, by introducing the hydrophobic additive metal oxide Y2O3, the present invention enhances the catalyst's hydrophobicity and fatty alcohol conversion rate, thereby reducing the fatty alcohol content in the product. The alpha-olefins synthesized using this method contain less than 0.01% oxygenates, facilitating the processing and utilization of downstream products. DETAILED DESCRIPTION

[0032] The embodiments of the present invention will be described in detail below with reference to specific examples, but those skilled in the art will appreciate that the following examples are intended only to illustrate the present invention and should not be construed as limiting the scope of the present invention. Where specific conditions are not specified in the examples, the methods were performed according to conventional conditions or the conditions recommended by the manufacturer. Where the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0033] In the present invention, if there is no particular limitation on the amount of each substance added, any ratio can be used.

[0034] Example 1

[0035] A method for preparing a composite metal oxide catalyst for synthesizing alpha olefins:

[0036] (1) 19.3 g Al2O3 and 0.5 g MgO were mixed and ball-milled for 8 h to obtain sample 1.

[0037] (2) Sample 1 was calcined at 1000°C for 13 h to obtain sample 2.

[0038] (3) Dissolve 20 g of sodium hydroxide in 100 ml of deionized water to obtain solution 1.

[0039] (4) Solution 1 was placed in an autoclave, and sample 2 was added to solution 1. The reaction was carried out at 260°C and 3.5 MPa for 6 h, and then dried at 80°C for 2 h to obtain sample 3.

[0040] (5) Yttrium nitrate, ethylene glycol, and ethanol were mixed in a mass ratio of 1:4.8:94.2 to prepare 100 ml of solution 2.

[0041] (6) Sample 3 was immersed in solution 2 for 11 h, dried at 80 °C for 2 h, and finally calcined at 500 °C for 6 h.

[0042] The resulting catalyst includes a first metal oxide, Al2O3; a second metal oxide, MgO; and an additive metal oxide, Y2O3. The mass ratio of Al2O3, MgO, and Y2O3 is 96.95:2.51:0.54. The catalyst has an acidic site concentration of 0.15 mmol / g and a basic site concentration of 0.28 mmol / g.

[0043] 2 mL of the above catalyst was loaded into a fixed bed tubular reactor, and the catalyst was heated to 300 °C at a rate of 1.0 °C / min under a pressure of 200 kPa and heated to 300 °C at a liquid space velocity of 0.3 h -1 The reaction results are listed in Table 1.

[0044] Example 2

[0045] A method for preparing a composite metal oxide catalyst for synthesizing alpha olefins:

[0046] (1) 18.9 g TiO2 and 0.26 g MgO were mixed and ball-milled for 8 h to obtain sample 1.

[0047] (2) Sample 1 was calcined at 800°C for 14 h to obtain sample 2.

[0048] (3) Dissolve 20 g of sodium hydroxide in 100 ml of deionized water to obtain solution 1.

[0049] (4) Solution 1 was placed in an autoclave, sample 2 was added to solution 1, reacted at 300°C and 3.2 MPa for 8 h, and dried at 80°C for 2 h to obtain sample 3.

[0050] (5) Yttrium nitrate, ethylene glycol, and ethanol were mixed in a mass ratio of 1:5.0:94.8 to prepare 100 ml of solution 2.

[0051] (6) Sample 3 was immersed in solution 2 for 12 h, dried at 80 °C for 2 h, and finally calcined at 600 °C for 4 h.

[0052] The resulting catalyst includes a first metal oxide, TiO2; a second metal oxide, MgO; and an auxiliary metal oxide, Y2O3. The mass ratio of TiO2, MgO, and Y2O3 is 98.35:1.35:0.3. The catalyst has an acidic site concentration of 0.25 mmol / g and a basic site concentration of 0.38 mmol / g.

[0053] 2 mL of the above catalyst was loaded into a fixed bed tubular reactor, and the catalyst was heated to 350°C at a rate of 1.5°C / min under a pressure of 300 kPa and a liquid space velocity of 0.5 h -1 The reaction results are listed in Table 1.

[0054] Example 3

[0055] A method for preparing a composite metal oxide catalyst for synthesizing alpha olefins:

[0056] (1) 19.1 g of CeO2 and 0.57 g of MgO were mixed and ball-milled for 8 h to obtain sample 1.

[0057] (2) Sample 1 was calcined at 900°C for 12 h to obtain sample 2.

[0058] (3) Dissolve 20 g of sodium hydroxide in 100 ml of deionized water to obtain solution 1.

[0059] (4) Solution 1 was placed in an autoclave, and sample 2 was added to solution 1. The reaction was carried out at 280°C and 3.0 MPa for 8 h, and then dried at 80°C for 2 h to obtain sample 3.

[0060] (5) Yttrium nitrate, ethylene glycol, and ethanol were mixed in a mass ratio of 1:4.2:93.7 to prepare 100 ml of solution 2.

[0061] (6) Sample 3 was immersed in solution 2 for 10 h, dried at 80 °C for 2 h, and finally calcined at 550 °C for 5 h.

[0062] The resulting catalyst includes a first metal oxide, CeO2; a second metal oxide, MgO; and an additive metal oxide, Y2O3. The mass ratio of CeO2, MgO, and Y2O3 is 96.95:2.9:0.15. The catalyst has an acidic site concentration of 0.18 mmol / g and a basic site concentration of 0.26 mmol / g.

[0063] 2 mL of the above catalyst was loaded into a fixed bed tubular reactor, and the catalyst was heated to 320°C at a rate of 1.0°C / min under a pressure of 200 kPa and a liquid space velocity of 1.0 h -1 The reaction results are listed in Table 1.

[0064] Example 4

[0065] A method for preparing a composite metal oxide catalyst for synthesizing alpha olefins:

[0066] (1) 19.3 g Al2O3 and 0.34 g MgO were mixed and ball-milled for 10 h to obtain sample 1.

[0067] (2) Sample 1 was calcined at 800°C for 12 h to obtain sample 2.

[0068] (3) Dissolve 20 g of sodium hydroxide in 100 ml of deionized water to obtain solution 1.

[0069] (4) Solution 1 was placed in an autoclave, sample 2 was added to solution 1, reacted at 300°C and 4.0 MPa for 8 h, and dried at 80°C for 2 h to obtain sample 3.

[0070] (5) Yttrium nitrate, ethylene glycol, and ethanol were mixed in a mass ratio of 1:4.8:94.7 to prepare 100 ml of solution 2.

[0071] (6) Sample 3 was immersed in solution 2 for 12 h, dried at 80 °C for 2 h, and finally calcined at 500 °C for 6 h.

[0072] The resulting catalyst included a first metal oxide, Al2O3; a second metal oxide, MgO; and an additive metal oxide, Y2O3. The mass ratio of Al2O3, MgO, and Y2O3 was 98.09:1.73:0.18. The catalyst had an acidic site concentration of 0.21 mmol / g and a basic site concentration of 0.31 mmol / g.

[0073] 2 mL of the above catalyst was loaded into a fixed bed tubular reactor, and the catalyst was heated to 350°C at a rate of 2.0°C / min under a pressure of 100 kPa and a liquid space velocity of 0.1 h -1 The reaction results are listed in Table 1.

[0074] Example 5

[0075] A method for preparing a composite metal oxide catalyst for synthesizing alpha olefins:

[0076] (1) 18.9 g Al2O3 and 0.34 g MgO were mixed and ball-milled for 8 h to obtain sample 1.

[0077] (2) Sample 1 was calcined at 900°C for 12 h to obtain sample 2.

[0078] (3) Dissolve 20 g of sodium hydroxide in 100 ml of deionized water to obtain solution 1.

[0079] (4) Solution 1 was placed in an autoclave, sample 2 was added to solution 1, reacted at 300°C and 3.5 MPa for 8 h, and dried at 80°C for 2 h to obtain sample 3.

[0080] (5) Yttrium nitrate, ethylene glycol, and ethanol were mixed in a mass ratio of 1:4.8:94.2 to prepare 100 ml of solution 2.

[0081] (6) Sample 3 was immersed in solution 2 for 10 h, dried at 80 °C for 2 h, and finally calcined at 550 °C for 5 h.

[0082] The resulting catalyst includes a first metal oxide, Al2O3; a second metal oxide, MgO; and an additive metal oxide, Y2O3. The mass ratio of Al2O3, MgO, and Y2O3 is 98.01:1.76:0.23. The catalyst has an acidic site concentration of 0.16 mmol / g and a basic site concentration of 0.23 mmol / g.

[0083] 2 mL of the above catalyst was loaded into a fixed bed tubular reactor and the catalyst was heated to 350°C at a rate of 1.0°C / min under a pressure of 300 kPa and a liquid space velocity of 0.2 h -1 The reaction results are listed in Table 1.

[0084] Comparative Example 1

[0085] A method for preparing a composite metal oxide catalyst for synthesizing alpha olefins:

[0086] (1) 19.3 g Al2O3 and 0.5 g MgO were mixed and ball-milled for 8 h to obtain sample 1.

[0087] (2) Sample 1 was calcined at 1000°C for 13 h to obtain sample 2.

[0088] (3) Yttrium nitrate was mixed with ethylene glycol and ethanol in a mass ratio of 1:4.8:94.2 to prepare a 100 ml solution.

[0089] (4) Sample 2 was immersed in the solution for 11 h, dried at 80 °C for 2 h, and finally calcined at 500 °C for 6 h.

[0090] The resulting catalyst includes a first metal oxide, Al2O3; a second metal oxide, MgO; and an additive metal oxide, Y2O3. The mass ratio of Al2O3, MgO, and Y2O3 is 96.95:2.51:0.54. The catalyst has an acidic site concentration of 0.08 mmol / g and a basic site concentration of 0.016 mmol / g.

[0091] 2 mL of the above catalyst was loaded into a fixed bed tubular reactor, and the catalyst was heated to 300 °C at a rate of 1.0 °C / min under a pressure of 200 kPa and heated to 300 °C at a liquid space velocity of 0.3 h -1 The reaction results are listed in Table 1.

[0092] Comparative Example 2

[0093] A method for preparing a composite metal oxide catalyst for synthesizing alpha olefins:

[0094] (1) 19.3 g Al2O3 and 0.5 g MgO were mixed and ball-milled for 8 h to obtain sample 1.

[0095] (2) Sample 1 was calcined at 1000°C for 13 h to obtain sample 2.

[0096] (3) Dissolve 20 g of sodium hydroxide in 100 ml of deionized water to obtain solution 1.

[0097] (4) Solution 1 was placed in an autoclave, sample 2 was added to solution 1, reacted at 260°C and 3.5 MPa for 6 h, and dried at 80°C for 2 h to obtain a catalyst.

[0098] The resulting catalyst included a first metal oxide, Al2O3, and a second metal oxide, MgO, with a mass ratio of Al2O3 to MgO of 97.47:2.53. The catalyst had an acidic site concentration of 0.06 mmol / g and a basic site concentration of 0.11 mmol / g.

[0099] 2 mL of the above catalyst was loaded into a fixed bed tubular reactor, and the catalyst was heated to 300 °C at a rate of 1.0 °C / min under a pressure of 200 kPa and heated to 300 °C at a liquid space velocity of 0.3 h -1 The reaction results are listed in Table 1.

[0100] Table 1 Test results of products of Examples 1-5 and Comparative Examples 1-2

[0101] Example α-olefins (%) Internal olefins (%) Fatty alcohol (%) Fatty ether (%) Example 1 93.052 6.939 0.009 0 Example 2 93.545 6.45 0.005 0 Example 3 93.24 6.754 0.006 0 Example 4 93.636 6.357 0.007 0 Example 5 93.544 6.45 0.006 0 Comparative Example 1 91.25 6.45 0.04 2.26 Comparative Example 2 90.948 7.162 1.25 0.64

[0102] As shown in Table 1, the total amount of oxygen-containing compounds in the products of Examples 1-5 is less than 0.01%. The results of Comparative Examples 1-2 show that the oxygen-containing compound content in the products is significantly increased due to the lack of sub-molten salt etching in Comparative Example 1 and the lack of the additive addition step in Comparative Example 2.

[0103] Finally, it should be noted that the above embodiments are intended only to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art will appreciate that the technical solutions described in the aforementioned embodiments may be modified, or some or all of the technical features therein may be replaced with equivalents. Such modifications or replacements do not deviate from the essence of the corresponding technical solutions within the scope of the technical solutions of the various embodiments of the present invention. Furthermore, those skilled in the art will appreciate that although some embodiments herein include certain features included in other embodiments but not others, the combination of features from different embodiments is intended to be within the scope of the present invention and to form different embodiments. For example, in the claims above, any of the claimed embodiments may be used in any combination. The information disclosed in this background section is intended solely to enhance understanding of the overall background technology of the present invention and should not be construed as an admission or any form of implication that such information constitutes prior art already known to those skilled in the art.

Claims

1. An application of a composite metal oxide catalyst for synthesizing α-olefins, characterized in that: The catalyst is placed in a fixed bed reactor at a liquid space velocity of 0.1-1.0h -1 , under a pressure of 100-300 kPa, heating to 300-350 ° C at a rate of 0.5-2.0 ° C / min to carry out the reaction; The composite metal oxide catalyst for synthesizing alpha olefins comprises a first metal oxide, a second metal oxide and an additive; The first metal oxide includes one or more of Al2O3, TiO2 or CeO2; the second metal oxide includes MgO; the auxiliary agent includes Y2O3; The mass ratio of the first metal oxide, the second metal oxide and the auxiliary agent is (96.2-98.5):(1.35-3.26):(0.15-0.54); In the catalyst, the acidic site concentration is 0.13-0.29 mmol / g, and the basic site concentration is 0.15-0.42 mmol / g; The preparation method of the composite metal oxide catalyst for synthesizing alpha olefins comprises the following steps: S1: mixing the first metal oxide and the second metal oxide, ball-milling them uniformly, and calcining them; the calcination is performed at 800-1000° C. for 12-14 hours; S2: mixing the product obtained in step S1 with alkali solution, reacting under high temperature and high pressure, and drying to obtain an intermediate; the high temperature and high pressure reaction is at 250-300°C and 3.0-4.0 MPa for 6-8 hours; S3: dissolving the auxiliary agent precursor in an organic solvent to obtain an auxiliary agent solution, soaking the intermediate obtained in step S2 in the auxiliary agent solution, and then drying and calcining to obtain the intermediate; The calcination temperature is 500-600° C., and the calcination time is 4-6 hours.

2. The use according to claim 1, characterized in that In step S1, the mixing and ball milling time is 8-12 hours.

3. The use according to claim 1, characterized in that In step S3, the auxiliary agent precursor includes yttrium nitrate, and the organic solvent includes ethylene glycol and / or ethanol.

4. The use according to claim 3, characterized in that The organic solvent includes a mixed solution of ethylene glycol and ethanol.

5. The use according to claim 4, characterized in that The mass ratio of the yttrium nitrate, ethylene glycol and ethanol is 1:(4.2-5.4):(93.6-94.8).

6. The use according to claim 1, characterized in that In step S3, the soaking time is 10-12 hours.

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