Modified silica gel carrier and preparation method thereof

Abstract

The invention provides a modified silica gel carrier and a preparation method thereof, and the preparation method comprises the following steps: (1) adding an inorganic acid solution into a silicate aqueous solution, adjusting the pH value of the solution to 10-12, and reacting; (2) adding an aqueous solution of modified hydrotalcite for reaction; (3) adding carbonate or bicarbonate of alkaline earth metal; (4) adding an aqueous solution of inorganic acid, and adjusting the pH value of the solution to 9-10 for reaction; and (5) acidifying, washing, drying and activating to obtain the silica gel carrier. According to the prepared modified silica gel carrier, the specific surface area of silica gel is effectively increased, and the stability of the modified silica gel carrier is also improved.

Description

Technical Field

[0001] The invention relates to the technical field of silica gel carrier modification, and in particular to a modified silica gel carrier and a preparation method thereof. Background Art

[0002] As a catalyst carrier, silica gel can significantly improve the catalyst activity with a high specific surface area when it has appropriate pore volume, pore size and distribution. When preparing carrier silica gel (silica gel carrier) by traditional methods, in order to obtain a high specific surface area, the pore volume and pore size are sacrificed. Therefore, new methods must be used to meet the preparation process requirements of catalyst carrier silica gel (silica gel carrier).

[0003] Patent CN109835909B relates to a method for preparing a silica gel carrier, wherein the silica gel carrier is made of silicate and inorganic acid as raw materials, and the preparation process is as follows: using silicate solution as the base liquid, adding inorganic acid solution, adjusting the pH value of the solution; adding ethanol aqueous solution of slurry hydrotalcite; passing carbon dioxide gas, adding organic alcohol aqueous solution of inorganic acid, adjusting the pH value of the solution; obtaining a silica gel product after hydrothermal reaction, acidification, washing, drying, and activation. This process prepares a silica gel carrier by modifying hydrotalcite, thereby improving the pore volume and distribution of silica gel.

[0004] Patent CN102861613A discloses a modified silica gel carrier, which contains 1%-15% carbon nanofibers by weight. A method for preparing a modified silica gel carrier, which is carried out by cracking gaseous alkanes or olefins on a silica gel carrier; the cracking temperature is 600℃~800℃, the reaction time is 2h~10h, the gaseous alkanes include methane, ethane, propane and butane, etc., and the gaseous olefins include ethylene, propylene, butene, etc. Application of modified silica gel carrier in the preparation of slurry bed Fischer-Tropsch synthesis catalyst: the modified silica gel carrier is impregnated with a solution containing an active metal component Co salt, and a drying step and a calcination step may be included after impregnation. The modified silica gel carrier of the present invention has good wear resistance, strong collision resistance, low cost, and the catalyst prepared with the modified silica gel carrier has high activity stability, and is suitable for slurry bed or ebullating bed Fischer-Tropsch synthesis reaction.

[0005] However, with the advancement of science and technology and the increase in industrialization needs, traditional silica gel carriers have been unable to meet the requirements in certain specific application scenarios. Therefore, modifying silica gel carriers to improve their performance has become an important direction of current research. Based on this, the present invention provides a modified silica gel carrier and a preparation method thereof. Summary of the invention

[0006] The purpose of the present invention is to provide a modified silica gel carrier and a preparation method thereof, which effectively increases the specific surface area of ​​silica gel and also improves the stability of the modified silica gel carrier.

[0007] In one aspect, the present invention provides a method for preparing a modified silica gel carrier, the steps comprising: (1) Adding an inorganic acid solution to the silicate aqueous solution to adjust the pH value of the solution to 10-12 for reaction; (2) adding an aqueous solution of modified hydrotalcite to react; (3) Adding carbonate or bicarbonate of alkaline earth metal; (4) adding an aqueous solution of an inorganic acid and adjusting the pH value of the solution to 9 to 10 for reaction; (5) After acidification, cooling, filtration, washing, drying and activation, a silica gel carrier is obtained.

[0008] Furthermore, the silicate aqueous solution is a sodium silicate aqueous solution.

[0009] Furthermore, the inorganic acid includes any one of sulfuric acid, hydrochloric acid and nitric acid.

[0010] Furthermore, in step (1), the reaction temperature is 45-55° C., and the reaction time is 25-35 minutes.

[0011] Furthermore, the mass fraction of the aqueous solution of the modified hydrotalcite is 2% to 8%.

[0012] Furthermore, the weight ratio of the sodium silicate aqueous solution, the modified hydrotalcite aqueous solution, and the carbonate or bicarbonate of an alkaline earth metal is (180-220):(7-9):(13-17), wherein the concentration of the sodium silicate aqueous solution is 1-1.4 mol / L.

[0013] Furthermore, the preparation method of the modified hydrotalcite comprises: (1) dissolving NaOH and Na2CO3 in deionized water, stirring until dissolved, and then adding hydroxylated carbon nanotubes and stirring to obtain a mixed solution containing carbon nanotubes; (2) dissolving Ni(NO3)2·6H2O and Al(NO3)3·6H2O in deionized water to obtain a nitrate solution; (3) adding the nitrate solution to the mixed solution containing carbon nanotubes, stirring at 500-600 r / min for 35-45 min, then adding an anhydrous ethanol solution of a silane coupling agent, adjusting the temperature to 75-85°C, continuing to stir at a speed of 200-240 r / min for 20-24 h, cooling and centrifuging to wash until the pH is less than 7.0, and drying at a temperature of 55-60°C for 10-12 h.

[0014] Furthermore, in the step (1), the usage ratio of NaOH, Na2CO3, deionized water and hydroxylated carbon nanotubes is (2.8-3.6) g: (1.06-3.18) g: (45-55) mL: (0.05-0.15) g.

[0015] Furthermore, in the step (2), the usage ratio of Ni(NO3)2·6H2O, Al(NO3)3·6H2O and deionized water is (8.72-11.63) g: (3.75-7.5) g: (500-600) mL.

[0016] Furthermore, the silane coupling agent is γ-mercaptopropyltriethoxysilane.

[0017] Furthermore, the weight ratio of the silane coupling agent, anhydrous ethanol and hydroxylated carbon nanotubes is 1:(9-11):(16-20).

[0018] Furthermore, the carbonate or bicarbonate of the alkaline earth metal includes any one of lithium carbonate, lithium bicarbonate, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, cesium carbonate and cesium bicarbonate.

[0019] Furthermore, the reaction step in step (4) comprises: reacting at 45-55°C for 1.8-2.2 hours, and then reacting at 90-100°C for 3.5-4.5 hours.

[0020] Furthermore, in the step (5), the acidification step is to adjust the pH value to 4-6 using an inorganic acid aqueous solution.

[0021] Furthermore, the drying temperature in step (5) is 300-340°C.

[0022] Furthermore, the activation step in step (5) comprises activation at 550-650° C. for 3.5-4.5 h under inert gas protection.

[0023] In another aspect, the present invention provides a modified silica gel carrier prepared by the above method.

[0024] The beneficial effects of the present invention are: The present invention uses inorganic acid to adjust the pH of silicate to 10-12, and after a period of reaction, adds a modified hydrotalcite aqueous solution and continues the reaction under the same temperature condition, so that the generated silica gel particles can be more dispersed and less likely to agglomerate, promote the modification of the surface of the silica gel particles, increase the roughness and porosity thereof, and thus improve the specific surface area.

[0025] In the present invention, the introduction of modified hydrotalcite significantly improves the thermal stability and chemical stability of the silica gel carrier. Elements such as Ni and Al in the modified hydrotalcite form chemical bonds with the hydroxyl groups on the surface of the silica gel to construct a relatively stable structure. The hydrotalcite prepared from nickel nitrate and aluminum nitrate (nickel aluminum hydrotalcite) has a specific crystal structure, and its interlayer distance may be optimized due to the ionic radius and charge distribution of nickel and aluminum, which is conducive to the formation of a more open and regular pore structure. This structure helps to increase the roughness and number of pores on the surface of the silica gel, thereby increasing the specific surface area. In contrast, other combinations have small or irregular interlayer distances due to differences in ionic radius and charge, and the pore structure is relatively not open enough, and the effect of improving the specific surface area is limited. In addition, the combination of iron nitrate and aluminum nitrate may cause changes in the crystal structure due to the large ionic radius of iron, affecting the formation of the pore structure and the improvement of the specific surface area. In addition, the reaction activity of nickel nitrate and aluminum nitrate in aqueous solution is moderate, which is conducive to the formation of a uniform and dense precipitate. This precipitate can form more crystal nuclei during the crystallization process, thereby increasing the number of active sites and pores on the surface of the silica gel. Furthermore, in a high temperature environment, nickel-aluminum hydrotalcite can maintain the integrity of the structure, prevent thermal decomposition or thermal expansion of silica gel, and effectively improve stability.

[0026] In addition, the addition of carbon nanotubes enhances the mechanical strength of the silica gel carrier to a certain extent. When used in conjunction with the silane coupling agent γ-mercaptopropyltriethoxysilane, the hydrophobicity of the silica gel surface is further enhanced, thereby improving its stability in different media. One end of the silane coupling agent reacts with the hydroxyl group on the silica gel surface, while the other end forms a chemical bond with other materials (such as polymers, metals, etc.), thereby enhancing the bonding force between the silica gel carrier and these materials.

[0027] The present invention uses γ-mercaptopropyltriethoxysilane as a silane coupling agent when preparing modified hydrotalcite. The thiol (-SH) functional group can form a stronger hydrogen bond during the hydrolysis process, which is conducive to the condensation reaction with the hydroxyl (-OH) on the surface of the silica gel. This strong interaction allows γ-mercaptopropyltriethoxysilane to cover the surface of the silica gel more effectively, forming a dense coupling layer, thereby increasing the roughness and porosity of the silica gel surface and improving the specific surface area. The thiol functional group can also undergo a grafting reaction with other active sites on the surface of the silica gel, further increasing the number of active sites and pores on the surface of the silica gel. This grafting reaction helps to form a more complex and stable pore structure, thereby increasing the specific surface area.

[0028] The present invention also utilizes carbonates or bicarbonates of alkaline earth metals (such as lithium carbonate, sodium carbonate, etc.) to react with hydroxyl groups on the surface of silica gel to form new chemical bonds. The formation of these chemical bonds increases the active sites on the surface of silica gel and helps to form more micropores and mesopores, further increasing the specific surface area.

[0029] In the present invention, by optimizing the pH value and adjusting the reaction time, the pH value is adjusted to 9-11 by an inorganic acid aqueous solution, and the reaction is carried out at 45-55°C for 1.8-2.2 hours, and at 90-100°C for 3.5-4.5 hours, which can further promote the adjustment of the internal structure of the silica gel particles and the formation of pores. The optimization of these steps helps to form a more uniform and stable pore structure, thereby increasing the specific surface area.

[0030] Finally, the activation step in the present invention is to activate at 550-650°C for 3.5-4.5 hours under the protection of inert gas, which helps to remove residual impurities and moisture in the silica gel carrier and improve its purity. At the same time, high-temperature activation also promotes further adjustment of the internal structure of the silica gel particles and the opening of the pores, thereby enhancing the stability and service life of the silica gel carrier. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. The hydroxylated carbon nanotubes have a carbon content of >99.8% and are purchased from the Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences.

[0032] The invention provides a method for preparing a modified silica gel carrier. The method comprises the following steps: adjusting the pH value of a sodium silicate aqueous solution to 10-12 by using an inorganic acid aqueous solution, reacting at a temperature of 45-55°C for 25-35 minutes, subsequently adding an aqueous solution of modified hydrotalcite, reacting at a temperature of 45-55°C for 50-70 minutes, adding carbonate or bicarbonate of an alkaline earth metal, adjusting the pH value to 9-11 by using an inorganic acid aqueous solution, reacting at a temperature of 45-55°C for 1.8-2.2 hours, reacting at a temperature of 90-100°C for 3.5-4.5 hours, adjusting the pH value to 4-6 by using an inorganic acid aqueous solution, cooling to room temperature, suction filtering, washing, drying and activating to obtain the modified silica gel carrier.

[0033] Among them, the inorganic acid includes but is not limited to any one of sulfuric acid, hydrochloric acid and nitric acid; the carbonate or bicarbonate of the alkaline earth metal includes but is not limited to any one of lithium carbonate, lithium bicarbonate, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, cesium carbonate and cesium bicarbonate.

[0034] The weight ratio of the sodium silicate aqueous solution, the modified hydrotalcite aqueous solution, and the carbonate or bicarbonate of an alkaline earth metal is (180-220): (7-9): (13-17), wherein the concentration of the sodium silicate aqueous solution is 1-1.4 mol / L, and the mass fraction of the modified hydrotalcite aqueous solution is 3-5%; The preparation method of modified hydrotalcite comprises: (1) Dissolve NaOH and Na2CO3 in deionized water, stir until dissolved, then add hydroxylated carbon nanotubes and stir to obtain a mixed solution containing carbon nanotubes; the amount ratio of NaOH, Na2CO3, deionized water and hydroxylated carbon nanotubes is (2.8-3.6) g: (1.06-3.18) g: (45-55) mL: (0.05-0.15) g; (2) Dissolve Ni(NO3)2·6H2O and Al(NO3)3·6H2O in deionized water to obtain a nitrate solution; the dosage ratio of Ni(NO3)2·6H2O, Al(NO3)3·6H2O and deionized water is (8.72-11.63) g: (3.75-7.5) g: (500-600) mL; (3) Adding a nitrate solution to a mixed solution containing carbon nanotubes, stirring at 500-600 r / min for 35-45 min, then adding an anhydrous ethanol solution of a silane coupling agent, adjusting the temperature to 75-85°C, continuing stirring at a speed of 200-240 r / min for 20-24 h, cooling and centrifuging to a pH value less than 7.0, and drying at a temperature of 55-60°C for 10-12 h. The silane coupling agent is γ-mercaptopropyltriethoxysilane, and the weight ratio of the silane coupling agent, anhydrous ethanol and hydroxylated carbon nanotubes is 1:(9-11):(16-20). The drying temperature of the obtained modified silica gel carrier is 300-340°C. The activation step of the obtained modified silica gel carrier includes activating at 550-650°C for 3.5-4.5 h under inert gas protection.

[0035] The following is further described with examples.

[0036] Example 1 In the reaction kettle, add 200g of 1.2mol / L sodium silicate aqueous solution, heat to 50℃, add 1.0mol / L sulfuric acid aqueous solution, stop adding sulfuric acid when the pH value of the reaction solution is 11, react at 50℃ for 0.5h, then add 8g of 4% slurry modified hydrotalcite aqueous solution, react at 50℃ for 1.0h after the addition is completed; add 15g sodium carbonate; adjust the pH value to 10 with 1.0mol / L sulfuric acid aqueous solution, react at 50℃ for 2.0h; then react at 95℃ for 4.0h; adjust the pH value to 5 with 1.0mol / L sulfuric acid aqueous solution at 95℃; cool to room temperature, filter, wash with pure water three times, dry the solid at 320℃, and then activate at 600℃ for 4 hours under inert gas protection to obtain a modified silica gel carrier.

[0037] Wherein, the preparation method of the modified hydrotalcite comprises: (1) 3.2 g NaOH and 2.12 g Na2CO3 were dissolved in 50 mL deionized water, stirred until dissolved, and then 0.01 g hydroxylated carbon nanotubes were added and stirred to obtain a mixed solution containing carbon nanotubes; (2) 10.18 g Ni(NO3)2·6H2O and 5.63 g Al(NO3)3·9H2O were dissolved in 550 mL deionized water to obtain a nitrate solution; (3) The nitrate solution was added to the mixed solution containing carbon nanotubes, stirred at 550 r / min for 40 min, and then an anhydrous ethanol solution of silane coupling agent γ-mercaptopropyltriethoxysilane was added, and the weight ratio of silane coupling agent, anhydrous ethanol and hydroxylated carbon nanotubes was 1:10:18; the temperature was adjusted to 80°C, and stirring was continued at a speed of 220 r / min for 22 h. After cooling, the mixture was centrifuged and washed until the pH was less than 7.0, and dried at 60°C for 11 h.

[0038] Example 2 Referring to Example 1, 15 g of sodium carbonate was replaced with 15 g of sodium bicarbonate, and other conditions were the same as in Example 1.

[0039] Example 3 Refer to Example 1, except that 15 grams of sodium carbonate are replaced by 15 grams of lithium carbonate, and other conditions are the same as in Example 1.

[0040] Example 4 Refer to Example 1, except that 15 grams of sodium carbonate are replaced by 15 grams of lithium bicarbonate, and other conditions are the same as in Example 1.

[0041] Example 5 Refer to Example 1, except that 15 grams of sodium carbonate are replaced by 15 grams of potassium bicarbonate, and other conditions are the same as in Example 1.

[0042] Example 6 Refer to Example 1, except that 15 grams of sodium carbonate are replaced by 15 grams of cesium carbonate, and other conditions are the same as in Example 1.

[0043] Comparative Example 1 Refer to Example 1, except that 15 g of sodium carbonate is removed. Other conditions are the same as those in Example 1.

[0044] Comparative Example 2 Refer to Example 1, except that 15 g of sodium carbonate is replaced by 15 g of sodium hydroxide. Other conditions are the same as those in Example 1.

[0045] Comparative Example 3 Refer to Example 1, except that after adding 15 g of sodium carbonate, a 1.0 mol / L aqueous solution of n-butanol sulfate was used, the volume ratio of n-butanol to water was 1:15, and the pH value of the solution was adjusted to 10. Other conditions were the same as in Example 1.

[0046] Test Example: The properties of the modified silica gel carriers prepared in the above examples and comparative examples were tested; specific surface area: gas adsorption BET method test, GB / T19587-2004; pore volume: BJH (Barrett-Joyner-Halenda) method test, ISO 15901-2.

[0047] The experimental data are shown in the following table:

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the present invention and are not intended to limit the technical solutions described in the present invention. Those skilled in the art should understand that the present invention can still be modified or replaced by equivalents. All technical solutions and improvements that do not depart from the spirit and scope of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for preparing a modified silica gel carrier, characterized in that the steps include: (1) Adding an inorganic acid solution to the silicate aqueous solution to adjust the pH value of the solution to 10-12 for reaction; (2) adding an aqueous solution of modified hydrotalcite to react; (3) Adding carbonate or bicarbonate of alkaline earth metal; (4) adding an aqueous solution of an inorganic acid and adjusting the pH value of the solution to 9 to 10 to carry out the reaction; (5) Acidification, cooling, filtration, washing, drying and activation to obtain a silica gel carrier; The preparation method of the modified hydrotalcite comprises: (1) dissolving NaOH and Na2CO3 in deionized water, stirring until dissolved, and then adding hydroxylated carbon nanotubes and stirring to obtain a mixed solution containing carbon nanotubes; (2) dissolving Ni(NO3)2·6H2O and Al(NO3)3·6H2O in deionized water to obtain a nitrate solution; (3) adding the nitrate solution to the mixed solution containing carbon nanotubes, stirring at 500-600 r / min for 35-45 min, then adding an anhydrous ethanol solution of a silane coupling agent, adjusting the temperature to 75-85°C, continuing to stir at a speed of 200-240 r / min for 20-24 h, cooling and centrifuging to wash until the pH value is less than 7.0, and drying at a temperature of 55-60°C for 10-12 h to obtain the modified hydrotalcite.

2. The method for preparing a modified silica gel carrier according to claim 1, characterized in that: The inorganic acid includes any one of sulfuric acid, hydrochloric acid and nitric acid.

3. The method for preparing a modified silica gel carrier according to claim 1, characterized in that: In the step (1), the reaction temperature is 45-55° C. and the reaction time is 25-35 minutes.

4. The method for preparing a modified silica gel carrier according to claim 1, characterized in that: The mass fraction of the aqueous solution of the modified hydrotalcite is 2% to 8%.

5. The method for preparing a modified silica gel carrier according to claim 1, characterized in that: The carbonate or bicarbonate of the alkaline earth metal includes any one of lithium carbonate, lithium bicarbonate, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, cesium carbonate and cesium bicarbonate.

6. The method for preparing a modified silica gel carrier according to claim 1, characterized in that: The reaction step in step (4) comprises: reacting at 45-55°C for 1.8-2.2 hours, and then reacting at 90-100°C for 3.5-4.5 hours.

7. The method for preparing a modified silica gel carrier according to claim 1, characterized in that: The acidification step in step (5) is to adjust the pH value to 4-6 using an inorganic acid aqueous solution.

8. The method for preparing a modified silica gel carrier according to claim 1, characterized in that: The drying temperature in step (5) is 300-340° C.; the activation step in step (5) includes activation at 550-650° C. for 3.5-4.5 hours under inert gas protection.

9. A modified silica gel carrier prepared by the preparation method of a modified silica gel carrier according to any one of claims 1 to 8.

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