Preparation method and application of silicon-aluminum aerogel

Abstract

The invention belongs to the technical field of catalyst preparation, and particularly relates to a preparation method and application of silicon-aluminum aerogel. The preparation method comprises the following steps: (1) dissolving a silicon source in an alcoholic solution, and adding an acid solution for hydrolysis to obtain a silicon solution; (2) adding an aluminum source into the silicon solution obtained in the step (1), and uniformly stirring; (3) adjusting the pH value to 4-5 by using ammonia water, gelatinizing the solution at a constant temperature of 40-120 DEG C, and aging for 12-48 hours; and (4) carrying out hydrophobic treatment on the gel obtained in the step (3), and drying and roasting the gel to obtain the SiO2-Al2O3 aerogel. The preparation process is simple and controllable, meanwhile, equipment is simple, industrial amplification is easy, olefin isomerization can be achieved, and greenhouse gas carbon dioxide can be directly converted into high-added-value isoolefin.

Description

Technical Field

[0001] The invention belongs to the technical field of catalyst preparation, and specifically relates to a preparation method of silicon-aluminum aerogel and application thereof. Background Art

[0002] Isoolefins are important chemical raw materials and intermediates, such as isobutylene. Isobutylene can be used to prepare chemical products such as isobutyl alcohol and methyl tert-butyl ether, among which isobutyl alcohol is also a gasoline additive with excellent performance. Isobutylene is mainly obtained from the C4 fraction produced by the process of producing ethylene from naphtha steam cracking and the catalytic cracking process. However, my country's oil resources are tight. Up to now, olefin isomerization is mainly carried out through molecular sieve catalysts, but it is easy to have side reactions such as hydrogenation in a hydrogen-rich atmosphere. Research on catalytic hydrogenation of carbon dioxide is mainly focused on the preparation of linear olefins, alcohols and aromatic compounds, and there is no report on the preparation of isoolefins. Molecular sieves with strong acid sites have a certain hydrogenation effect. The linear olefins generated by carbon dioxide and hydrogen over metal oxide catalysts are easily hydrogenated to obtain alkanes or isoalkanes or benzene compounds. Therefore, it is very important to prepare appropriate acid catalysts that can effectively catalyze olefin isomerization and can prepare isoolefins from carbon dioxide hydrogenation in one step. At the same time, in the context of global carbon neutrality, the preparation of high value-added products by catalytic hydrogenation of carbon dioxide is of great significance. Summary of the invention

[0003] The present invention aims to provide a method for preparing a silicon-alumina aerogel, and can effectively catalyze the isomerization of olefins and catalyze the hydrogenation of carbon dioxide to prepare isoolefins.

[0004] In order to achieve the above object, the technical solution of the present invention is as follows:

[0005] The present invention provides a method for preparing a silicon-aluminum aerogel, wherein the silicon-aluminum aerogel is SiO 2 -Al 2 O 3 Aerogel, the molar ratio of Si to Al is 3-90:1; the preparation method comprises the following steps:

[0006] (1) dissolving a silicon source in an alcohol solution, adding an acid solution for hydrolysis, and obtaining a silicon solution;

[0007] (2) adding an aluminum source to the silicon solution obtained in step (1) and stirring evenly;

[0008] (3) adjusting the pH to 4-5 with aqueous ammonia, and subjecting the solution to constant temperature gelation at 40-120° C. and aging for 12-48 h;

[0009] (4) subjecting the gel obtained in step (3) to hydrophobic treatment to prevent the pore structure of the aerogel from collapsing after calcination, drying the gel, and calcining to obtain SiO 2 -Al 2 O 3 Aerogel.

[0010] In the above technical solution, further, the silicon source is at least one of tetraethyl orthosilicate, silicon dioxide, and sodium silicate.

[0011] In the above technical solution, further, the alcohol is at least one of ethanol, propanol, isopropanol and butanol.

[0012] In the above technical solution, further, the acid is at least one of hydrochloric acid, nitric acid and sulfuric acid; and the hydrolysis temperature is 30-60°C.

[0013] In the above technical solution, further, the aluminum source is at least one of boehmite, aluminum nitrate, aluminum sulfate, and aluminum chloride.

[0014] In the above technical solution, further, the hydrophobic treatment is: soaking in hexamethyldisilazane or hexadecyltrimethoxysilane for 60 hours;

[0015] The drying temperature is 80°C and the drying time is 12h;

[0016] The calcination temperature is 500° C. and the calcination time is 2 h.

[0017] Another aspect of the present invention provides an application of the silica-alumina aerogel prepared by the above preparation method in olefin isomerization, wherein the silica-alumina aerogel is used as a catalyst in a fixed bed reactor and a reaction gas is introduced to carry out olefin isomerization;

[0018] The olefin isomerization conditions are as follows: the reaction gas is olefin, olefin and N 2 or H 2 Any one of the mixed gases; reaction temperature 150-350°C, reaction pressure 1-5MPa, reaction gas flow rate 10-200mL / min.

[0019] The present invention also provides an application of the silicon-aluminum aerogel prepared by the above preparation method in the preparation of isoolefins by hydrogenation of carbon dioxide. In a fixed bed reactor, the reaction gas is a mixed gas of carbon dioxide and hydrogen. The silicon-aluminum aerogel is coupled with an iron-containing catalyst to achieve a one-step preparation of isoolefins by carbon dioxide and hydrogen.

[0020] The reaction conditions are: pressure 1-8MPa, reaction gas flow rate 10-200mL / min, reaction temperature 250-400°C for the iron catalyst bed and 150-340°C for the silicon-alumina aerogel bed.

[0021] In the above technical solution, further, the olefin is one of the olefins having a carbon number of 4-7.

[0022] In the above technical solution, further, the iron-containing catalyst is Fe 2 O 3 , Fe 4 O 3 , iron carbide or at least one of the following:

[0023] In the above technical solution, further, in the reaction gas, the volume ratio of carbon dioxide is 20-70%, and the balance is hydrogen.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) SiO prepared by the present invention 2 -Al 2 O 3 Aerogels have a large specific surface area and extremely weak Lewis acid sites.

[0026] (2) SiO 2 -Al 2 O 3 The aerogel preparation process is simple and controllable, and can be easily scaled up industrially.

[0027] (3) SiO 2 -Al 2 O 3 Aerogel is a catalyst that can efficiently catalyze olefin isomerization and reduce the occurrence of side reactions.

[0028] (4) SiO 2 -Al 2 O 3 Aerogel as a catalyst is coupled with an iron-containing catalyst to catalyze the hydrogenation of carbon dioxide to isomerized olefins in one step, which is of great significance for carbon neutrality and reduction of carbon dioxide emissions, and can save petroleum resources.

[0029] In summary, the SiO prepared by the present invention 2 -Al 2 O 3 Aerogel catalysts have good catalytic stability and good industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 The SiO prepared in Example 1 2 -Al 2 O 3 XRD pattern of aerogel. DETAILED DESCRIPTION

[0031] The following examples illustrate the SiO 2 -Al 2 O 3 The preparation method of aerogel and its application in olefin isomerization and carbon dioxide hydrogenation reaction are described in detail, but the present invention is not limited thereto. At the same time, the embodiments only provide some conditions for achieving this purpose, but do not mean that these conditions must be met to achieve this purpose.

[0032] Example 1

[0033] SiO with Si / Al ratio of 3 2 -Al 2 O 3 Aerogel preparation. Mix 12.48 g of tetraethyl orthosilicate and 14.38 g of isopropanol in a Teflon beaker, slowly drip 17.51 ​​g of hydrochloric acid into the solution, and hydrolyze the solution at 40°C for 2 hours; after the hydrolysis is complete, add 6 g of boehmite and stir for 30 minutes, adjust the pH to between 4-5 with ammonia water, gel the solution at 60°C and age for 48 hours; add 50 ml of hexamethyldisilazane and place it for 60 hours for hydrophobic treatment, wash the hydrophobic treated gel five times with 60 ml of isopropanol, dry at 80°C, and calcine at 500°C for 2 hours. Its XRD spectrum is shown in Figure 1 .

[0034] Example 2

[0035] SiO with Si / Al ratio of 15 2 -Al 2 O 3 Aerogel preparation. 37.55 g of tetraethyl orthosilicate and 14.38 g of isopropanol were mixed in a Teflon beaker, 17.51 ​​g of hydrochloric acid was slowly dripped into the solution, and the solution was hydrolyzed at 40°C for 2 h; after the hydrolysis was complete, 3 g of boehmite was added and stirred for 30 min, the pH was adjusted to between 4 and 5 with ammonia water, the solution was gelled at 60°C and aged for 48 h; 50 ml of hexamethyldisilazane was added and placed for 60 h for hydrophobic treatment, and the hydrophobic treated gel was washed five times with 60 ml of isopropanol, dried at 80°C, and calcined at 500°C for 2 h.

[0036] Example 3

[0037] SiO with Si / Al ratio of 30 2 -Al 2 O 3Aerogel preparation. Mix 75.10 g of tetraethyl orthosilicate and 14.38 g of isopropanol in a Teflon beaker, slowly drip 17.51 ​​g of hydrochloric acid into the solution, and hydrolyze the solution at 40°C for 2 h; after the hydrolysis is complete, add 3 g of boehmite and stir for 30 min, adjust the pH to between 4-5 with ammonia water, gel the solution at 60°C and age for 48 h; add 50 ml of hexamethyldisilazane and place it for 60 h for hydrophobic treatment, wash the hydrophobic treated gel five times with 60 ml of isopropanol, dry at 80°C, and calcine at 500°C for 2 h.

[0038] Example 4

[0039] SiO with Si / Al ratio of 90 2 -Al 2 O 3 Aerogel preparation. Mix 225.30 g of tetraethyl orthosilicate and 14.38 g of isopropanol in a Teflon beaker, slowly drip 17.51 ​​g of hydrochloric acid into the solution, and hydrolyze the solution at 40°C for 2 h; after the hydrolysis is complete, add 6 g of boehmite and stir for 30 min, adjust the pH to between 4-5 with ammonia water, gel the solution at 60°C and age for 48 h; add 50 ml of hexamethyldisilazane and place for 60 h for hydrophobic treatment, wash the hydrophobic treated gel five times with 60 ml of isopropanol, dry at 80°C, and calcine at 500°C for 2 h.

[0040] SiO prepared in Example 1-4 2 -Al 2 O 3 The specific surface area and pore volume of the aerogels are listed in Table 1.

[0041] Table 1SiO 2 -Al 2 O 3 Specific surface area and pore volume of aerogel

[0042]

[0043]

[0044] Example 5

[0045] Weigh 200 mg of SiO prepared in Example 1 2 -Al 2 O 3 The aerogel (Si / Al=3) was loaded into a quartz reaction tube, and pure hydrogen was introduced at about 20 mL / min at 400 °C for 2 h. The reaction temperature was lowered to 250 °C, butene and N 2The mixed gas was pressurized to 3MPa and the mixed gas flow rate was 20ml / min to start the reaction; after the reaction, it was heated to 175℃ by an incubator and a heating belt, and the reaction product was quantitatively analyzed by gas chromatography. The reaction time was 6-8h. The specific reaction performance is listed in Table 2.

[0046] Example 6

[0047] Weigh 200 mg of SiO prepared in Example 1 2 -Al 2 O 3 The aerogel (Si / Al=3) was loaded into a quartz reaction tube, and pure hydrogen was introduced at about 20 mL / min at 400 °C for 2 h. The reaction temperature was lowered to 250 °C, butene and H were introduced. 2 The mixed gas was pressurized to 3MPa and the mixed gas flow rate was 20ml / min to start the reaction; after the reaction, it was heated to 175℃ by an incubator and a heating belt, and the reaction product was quantitatively analyzed by gas chromatography. The reaction time was 6-8h. The specific reaction performance is listed in Table 2.

[0048] Comparative Example 1

[0049] Weigh 200 mg of MOR molecular sieve and put it into a quartz reaction tube. First, introduce pure hydrogen at about 20 mL / min and treat at 400 °C for 2 h. Then lower the reaction temperature to 250 °C and introduce butene and H 2 The mixed gas was pressurized to 3MPa and the mixed gas flow rate was 20ml / min to start the reaction; after the reaction, it was heated to 175℃ by an incubator and a heating belt, and the reaction product was quantitatively analyzed by gas chromatography. The reaction time was 6-8h. The specific reaction performance is listed in Table 2.

[0050] Comparative Example 2

[0051] Weigh 200 mg of SAPO-34 molecular sieve and put it into a quartz reaction tube. First, introduce pure hydrogen at about 20 mL / min and treat at 400 °C for 2 h. Then lower the reaction temperature to 250 °C and introduce butene and H 2 The mixed gas was pressurized to 3MPa and the mixed gas flow rate was 20ml / min to start the reaction; after the reaction, it was heated to 175℃ by an incubator and a heating belt, and the reaction product was quantitatively analyzed by gas chromatography. The reaction time was 6-8h. The specific reaction performance is listed in Table 2.

[0052] Table 2 Butene isomerization reaction results

[0053]

[0054] Example 7

[0055] Weigh 200 mg of SiO prepared in Example 1 2 -Al2 O 3 Aerogel (Si / Al=3) was loaded into the lower part of the quartz reaction tube, followed by quartz wool and quartz sand, and finally 100 mg 5K-Fe 3 O 4 Catalyst. After the quartz reaction tube is installed on the fixed bed reaction device, pure hydrogen is introduced at about 20mL / min, and the metal bed is reduced at 400℃ for 2h, then the temperature is lowered to 340℃ for the metal catalyst bed and 150℃ for the molecular sieve catalyst bed, the gas is switched to a mixture of carbon dioxide and hydrogen, the pressure is increased to 3MPa, and the reaction is started at a mixed gas flow rate of 20ml / min; after the reaction, it is heated to 175℃ by an insulated box and a heating belt, and the reaction product is quantitatively analyzed by gas chromatography, and the reaction time is 6-8h. The specific reaction performance is listed in Table 3.

[0056] Example 8

[0057] Weigh 200 mg of SiO prepared in Example 2 2 -Al 2 O 3 Aerogel (Si / Al=15) was loaded into the lower part of the quartz reaction tube, followed by quartz wool and quartz sand, and finally 100 mg 5K-Fe 3 O 4 Catalyst; After the quartz reaction tube is installed on the fixed bed reaction device, pure hydrogen is introduced at about 20mL / min, and the metal bed is reduced at 400℃ for 2h, then the temperature is lowered to 340℃ for the metal catalyst bed and 150℃ for the molecular sieve catalyst bed, the gas is switched to a mixture of carbon dioxide and hydrogen, the pressure is increased to 3MPa, and the reaction is started at a mixed gas flow rate of 20ml / min; after the reaction, it is heated to 175℃ by an insulated box and a heating belt, and the reaction product is quantitatively analyzed by gas chromatography, and the reaction time is 6-8h. The specific reaction performance is listed in Table 3.

[0058] Example 9

[0059] Weigh 200 mg of SiO prepared in Example 3 2 -Al 2 O 3 Aerogel (Si / Al=30) was loaded into the lower part of the quartz reaction tube, followed by quartz wool and quartz sand, and finally 100 mg 5K-Fe 3 O 4Catalyst; After the quartz reaction tube is installed on the fixed bed reaction device, pure hydrogen is introduced at about 20mL / min, and the metal bed is reduced at 400℃ for 2h, then the temperature is lowered to 340℃ for the metal catalyst bed and 150℃ for the molecular sieve catalyst bed, the gas is switched to a mixture of carbon dioxide and hydrogen, the pressure is increased to 3MPa, and the reaction is started at a mixed gas flow rate of 20ml / min; after the reaction, it is heated to 175℃ by an insulated box and a heating belt, and the reaction product is quantitatively analyzed by gas chromatography, and the reaction time is 6-8h. The specific reaction performance is listed in Table 3.

[0060] Example 10

[0061] Weigh 200 mg of SiO prepared in Example 4 2 -Al 2 O 3 Aerogel (Si / Al=90) was loaded into the lower part of the quartz reaction tube, followed by quartz wool and quartz sand, and finally 100 mg 5K-Fe 3 O 4 Catalyst; After the quartz reaction tube is installed on the fixed bed reaction device, pure hydrogen is introduced at about 20mL / min, and the metal bed is reduced at 400℃ for 2h, then the temperature is lowered to 340℃ for the metal catalyst bed and 150℃ for the molecular sieve catalyst bed, the gas is switched to a mixture of carbon dioxide and hydrogen, the pressure is increased to 3MPa, and the reaction is started at a mixed gas flow rate of 20ml / min; after the reaction, it is heated to 175℃ by an insulated box and a heating belt, and the reaction product is quantitatively analyzed by gas chromatography, and the reaction time is 6-8h. The specific reaction performance is listed in Table 3.

[0062] Table 3 Carbon dioxide hydrogenation reaction results

[0063]

[0064] The above results indicate that the present invention can exhibit excellent isoolefin preparation performance by rationally optimizing the reaction conditions and the ratio of the iron-containing catalyst to the molecular sieve catalyst.

[0065] The above is an explanation of the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a silicon-aluminum aerogel, characterized in that: The silicon-aluminum aerogel is SiO2-Al2O3 aerogel, and the molar ratio of Si to Al is 3-90:1; the preparation method comprises the following steps: (1) dissolving a silicon source in an alcohol solution, adding an acid solution for hydrolysis, and obtaining a silicon solution; (2) adding an aluminum source to the silicon solution obtained in step (1) and stirring evenly; (3) adjusting the pH to 4-5 with aqueous ammonia, and subjecting the solution to constant temperature gelation at 40-120° C. and aging for 12-48 h; (4) The gel obtained in step (3) is subjected to a hydrophobic treatment, and the gel is dried and calcined to obtain a SiO2-Al2O3 aerogel.

2. The method according to claim 1, characterized in that: The silicon source is at least one of tetraethyl orthosilicate, silicon dioxide, and sodium silicate; The alcohol is at least one of ethanol, propanol, isopropanol and butanol.

3. The method according to claim 1, characterized in that: In step (1), the acid is at least one of hydrochloric acid, nitric acid and sulfuric acid; and the hydrolysis temperature is 30-60°C.

4. The method according to claim 1, characterized in that: In step (2), the aluminum source is at least one of boehmite, aluminum nitrate, aluminum sulfate, and aluminum chloride.

5. The method according to claim 1, characterized in that: In step (4), the hydrophobic treatment is: soaking in hexamethyldisilazane or hexadecyltrimethoxysilane for 60 hours; The drying temperature is 80°C and the drying time is 12h; The calcination temperature is 500° C. and the calcination time is 2 h.

6. Use of the silica-alumina aerogel prepared by the preparation method according to any one of claims 1 to 5 in olefin isomerization, characterized in that: In a fixed bed reactor, olefin isomerization is carried out by introducing reaction gas using silica-alumina aerogel as catalyst; The olefin isomerization conditions are as follows: the reaction gas is any one of olefins, olefins and N2 or H2 mixed gas; the reaction temperature is 150-350°C, the reaction pressure is 1-5MPa, and the reaction gas flow rate is 10-200mL / min.

7. Use of the silicon-alumina aerogel prepared by the preparation method according to any one of claims 1 to 5 in the preparation of isoolefins by hydrogenation of carbon dioxide, characterized in that: In a fixed bed reactor, the reaction gas is a mixture of carbon dioxide and hydrogen, and the carbon dioxide and hydrogen are used to prepare isoolefins in one step by coupling the silica-alumina aerogel with an iron-containing catalyst. The reaction conditions are: pressure 1-8MPa, reaction gas flow rate 10-200mL / min, reaction temperature 250-400°C for the iron catalyst bed and 150-340°C for the silicon-alumina aerogel bed.

8. The use according to claim 6 or 7, characterized in that: The olefin is one of olefins having 4 to 7 carbon atoms.

9. The use according to claim 7, characterized in that: The iron-containing catalyst is at least one of Fe2O3, Fe4O3 and iron carbide.

10. The use according to claim 7, characterized in that: In the reaction gas, carbon dioxide accounts for 20-70% by volume, and the remainder is hydrogen.

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