CN108046280B - Silica-alumina gel and preparation method thereof - Google Patents
Silica-alumina gel and preparation method thereof Download PDFInfo
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Abstract
The invention discloses a silica-alumina gel and a preparation method thereof, belonging to the field ofThe technical field of silica-alumina gel. In the silicon-aluminum adhesive of the invention, Al2O33-8% of SiO2The mass content of (A) is not lower than 82%; the specific surface area of the silica-alumina gel is 300-550m2The pore volume is 0.6-1.0mL/g, and the compressive strength is not lower than 50N; the invention also provides a preparation method of the silica-alumina gel, which is obtained by carrying out sol-gel, aging, exchanged acid treatment, water washing, ammonia treatment and drying on sodium silicate, aluminum salt and raw material acid. The silica-alumina ratio in the silica-alumina gel has wide adjusting range, large pore volume and specific surface area, high compressive strength, uniform framework structure and strength and stable product quality; the preparation process is simple, the operation is convenient, and the method can be widely applied to the fields of catalysts and catalyst carriers, adsorption separation, molecular sieve preparation and the like.
Description
Technical Field
The invention belongs to the technical field of silica-alumina gel, and particularly relates to silica-alumina gel and a preparation method thereof.
Background
The silica-alumina gel is silica gel containing alumina and has a chemical molecular formula of mSiO2·nAl2O3·xH2O, which is chemically stable, nonflammable, and insoluble in any solvent, is mainly used for catalysts and catalyst carriers in the petrochemical industry, and is also used for dryers, liquid adsorbents, gas separation, and the like in the industry.
In the prior art, the preparation methods of the silica-alumina gel mainly comprise three methods: 1) the sol-gel method adds aluminum salt, the silica-alumina chemical bond coordination bond in the silica-alumina gel obtained by the method is stable, the skeleton structure is stable, the product strength is high, the stable skeleton structure is beneficial to the adjustment of the pore structure and the loading of the catalyst, the solution control is not uniform in the sol and gel process, uniform solution can not be formed, mostly suspension or emulsion is adopted, and the uniformity of the product is influenced; 2) the template method is adopted to prepare the silica-alumina gel, a template removing process is required to be added, the process is complex, the problems of influencing the strength of a framework, the pore structure and the impurity content exist in the template removing process, and the template method also has the problems of difficult environmental protection treatment and high cost; 3) the carbonization method utilizes aluminum salt and a silicon-containing compound to react with carbon dioxide for gelation, a pH swing method is adopted in the gelation process, a silicon source is introduced in the swing process, the pore volume and the aperture of the silica-alumina gel obtained by the method are small, hole expansion is needed, and the strength and the specific surface area of a skeleton after hole expansion are reduced, so that the silica-alumina gel is limited in the application field to a certain extent.
US4758338 discloses a process for preparing silica-alumina gel by controlling pH at 2-10 by pH swing method to obtain alumina sol, and adding silicon source to obtain amorphous silica-alumina gel, which has complicated reaction process, difficult control, low product strength, low silica content of no more than 10%. Chinese CN106587085A discloses a preparation method of macroporous silica-alumina gel, which comprises the steps of pulping boehmite, adding silica sol, controlling the pH value to be 3-5, keeping the temperature, adding alkali to adjust the pH value of slurry to be 9-10 to obtain silica-alumina gel, and drying to obtain macroporous silica-alumina gel; the reaction process of the method is limited by the stirring uniformity, the pulping of the raw material boehmite and the uniformity of the pH value, uniform silicon-aluminum gel cannot be obtained in the reaction process, the content of silicon-aluminum chemical coordination bonds is low, and the strength of the obtained macroporous silicon-aluminum gel is low, so that the application field is limited. Chinese CN1765742A discloses a method for preparing amorphous silica-alumina gel by carbonization, which comprises mixing sodium aluminate solution and silicon-containing compound solution, introducing carbon dioxide gas, controlling pH value to gel, filtering, washing and drying to obtain the final product; the method has low preparation cost, the obtained amorphous silica-alumina gel has large specific surface area and pore volume, and can be used as a catalytic cracking hydrocracking catalyst carrier, although the silica-alumina sol obtained in the initial stage of the reaction process of the method is more uniform, the product uniformity is reduced along with the later gelation process, and the obtained product has low strength.
Disclosure of Invention
The invention provides silica-alumina gel and a preparation method thereof, and solves the problems that the silica content of the silica-alumina gel is low and the specific surface area, the pore volume and the strength cannot be considered simultaneously in the prior art.
The invention relates to a silica-alumina gel, which is mainly realized by the following technical scheme: in the silica-alumina gel, Al2O33-8% of SiO2The mass content of (A) is not lower than 82%; the specific surface area of the silica-alumina gel is 300-550m2The pore volume is 0.6-1.0mL/g, and the compressive strength is not less than 50N.
In the silica alumina gel of the invention, SiO2High content of Al2O3Adjustable content, wide silicon-aluminum ratio adjusting range, uniform framework structure and strength, large pore volume, large specific surface area, high compressive strength, stable framework structure and pore structure, good product quality, large pore volume, large specific surface area and high compressive strength, and can be widely usedThe method is applied to the fields of catalysts and catalyst carriers, adsorption separation, molecular sieve preparation and the like.
As a preferred embodiment, the silica alumina gel has a pore volume of 0.7-0.9mL/g and a pore size of 6-10 nm. The silica-alumina gel has large pore volume, uniform pore diameter, stable skeleton structure, stable product performance and wide application range, and can resist ammonia treatment.
The invention relates to a preparation method of silica-alumina gel, which is mainly realized by the following technical scheme: the method comprises the following steps: 1) mixing aluminum salt and raw material acid, and adding water to obtain aluminum salt acid solution with aluminum salt mass concentration of 1-20% and raw material acid mass concentration of 5-45%; taking sodium silicate, adding water to prepare a sodium silicate solution with the mass concentration of 5-25%; 2) adding the sodium silicate solution obtained in the step 1) into the acid solution obtained in the step 1), wherein the volume ratio of the sodium silicate solution to the acid solution is 15-18:5-7, carrying out sol-gel reaction at 15-45 ℃, the reaction pressure is 0.05-1.5MPa, and the pH value after the reaction is 2.5-8.5, so as to obtain gel; 3) aging the gel obtained in the step 1), performing exchange acid treatment, washing with water, performing ammonia treatment, and drying to obtain the silica-alumina gel.
The method takes sodium silicate as a silicon source, takes aluminum salt as an aluminum source, the aluminum salt can be aluminum chloride, aluminum nitrate, aluminum sulfate and the like, the aluminum salt is firstly dissolved in raw material acid, the aluminum salt is prepared in the raw material acid in the sol-gel reaction process, the aluminum salt can be completely mixed with the raw material acid and form uniform liquid, the aluminum salt can react with the sodium silicate to form uniform gel, the solution is transparent or semitransparent liquid, the framework and strength uniformity of the silica-alumina gel is ensured in the reaction process, the framework structure and pore structure of the silica-alumina gel are further stabilized under the action of aging and exchanged acid soaking, and micropores and pores with low adsorption and low activity are treated by washing with water and ammonia to obtain larger pore volume, large pore volume and high compressive strength; the preparation method is simple in preparation process, convenient to operate and easy to realize industrialization, and can be widely applied to methods in the fields of catalyst and catalyst carrier, adsorption separation, molecular sieve preparation and the like.
As a preferred embodiment, the gel obtained in step 1) has a spheronization distance of 1 to 3m and is buffered in a receiver, the pH of the water in the receiver being 6.0 to 9.0 and the temperature of the water in the receiver being 20 to 40 ℃. The raw material acid can be organic acid or inorganic acid, can be monoacid or polyacid, and is preferably sulfuric acid; the sol-gel reaction is carried out in a reactor and buffered using a receiver.
As a preferred embodiment, in the step 2), during the ammonia treatment, the ammonia is any one or more of ammonia water, ammonium chloride, ammonium sulfate, ammonium carbonate or ammonium bicarbonate, the treatment concentration is 0.05-1.5%, the treatment temperature is 20-90 ℃, and the treatment time is 1-12 h; preferably: the ammonia is ammonia water, the treatment concentration is 0.1-1%, the treatment temperature is 40-80 ℃, and the treatment time is 4-8 h. The purpose of the ammonia treatment is also to treat the low adsorption and low activity micropores and pores to obtain a larger pore volume, and at this time, the low adsorption and low activity micropores and pores which are not treated by the water washing are treated again to obtain a larger pore volume.
In a preferred embodiment, the concentration by mass of the sodium silicate is 10 to 20%, the concentration by mass of the aluminum salt is 5 to 15%, the concentration by mass of the raw material acid is 10 to 30%, and the pH value of the reaction is 3.5 to 7.5. Because the concentrations of the sodium silicate, the aluminum salt and the raw material acid can influence the uniformity of acid-base reaction, namely sol-gel reaction, the invention strictly controls the concentrations of the three raw materials to obtain uniform gel, fully ensures the framework uniformity and the strength uniformity of the silica-alumina gel in the reaction process and improves the comprehensive performance of the silica-alumina gel.
As a preferred embodiment, in the step 2), the aging is carried out at a temperature of 25-85 ℃ for 0.5-50 h; preferably: the temperature is 30-60 ℃ and the time is 2-35 h. The framework structure and the pore structure of the silica-alumina gel are further stabilized by controlling the aging temperature and the aging time, so that the quality stability of the silica-alumina gel is improved.
As a preferred embodiment, in the step 2), during the exchange acid treatment, the exchange acid is any one or more of hydrochloric acid, sulfuric acid, aluminum nitrate, nitric acid, aluminum sulfate, oxalic acid or citric acid, the mass concentration of the exchange acid is 0.05-10%, the treatment temperature is 30-100 ℃, and the treatment time is 1-12 h; preferably: the exchange acid is a mixed acid consisting of sulfuric acid, oxalic acid and aluminum sulfate, the mass concentration of the exchange acid is 0.1-5%, the treatment temperature is 30-60 ℃, and the treatment time is 2-6 h. The exchange acid is not a strict acid but a substance whose solution exhibits acidity, and includes hydrochloric acid, sulfuric acid, and also includes aluminum nitrate and aluminum sulfate; the aged gel is directly placed in exchange acid for soaking, so that the skeleton structure and the pore structure of the silica-alumina gel are further stabilized, and the quality stability of the silica-alumina gel is improved.
In a preferable embodiment, in the step 2), the temperature is 20 to 90 ℃ during water washing, the pH value of the end point of the water washing is 4.5 to 7.0, and the specific resistance of the gel after the water washing is not lower than 1000 Ω · cm; preferably: the temperature is 30-60 ℃, and the pH value of the washing end point is 5.0-6.5. The purpose of water washing is to process the micropores and small holes with low adsorption and low activity to obtain larger pore volume, and the water washing end point is judged according to the pH value, so that the judgment is easy and the control is convenient.
As a preferable embodiment, in the step 2), the drying is carried out at the temperature of 80-400 ℃ for 12-48 h; preferably: two times of drying process are adopted, the temperature of the first drying is 80-200 ℃, the time is 10-36h, the temperature of the second drying is 200-. The drying is to remove the moisture in the silica-alumina gel, so as to obtain dry particles; and after drying, screening and packaging to obtain the final product.
Compared with the prior art, the invention has the beneficial effects that: in the silica alumina gel of the invention, SiO2High content of Al2O3The content is adjustable, the silicon-aluminum ratio adjusting range is wide, the framework structure and the strength are uniform, the pore volume is large, the specific surface area is large, the compressive strength is high, the framework structure and the pore structure are stable, the product quality is good, the large pore volume, the specific surface area and the high compressive strength are considered, and the catalyst can be widely applied to the fields of catalyst and catalyst carriers, adsorption separation, molecular sieve preparation and the like; the preparation process is simple, convenient to operate and easy to realize industrialization.
Detailed Description
The technical solutions of the present invention will be described clearly and completely with reference to specific embodiments of the present invention, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention relates to a silicon-aluminum adhesive, wherein in the silicon-aluminum adhesive, Al is contained2O33-8% of SiO2The mass content of (A) is not lower than 82%; the specific surface area of the silica-alumina gel is 300-550m2The pore volume is 0.6-1.0mL/g, and the compressive strength is not less than 50N.
Preferably, the pore volume of the silica-alumina gel is 0.7-0.9mL/g, and the pore size is 6-10 nm.
The preparation method of the silica-alumina gel comprises the following steps: 1) mixing aluminum salt and raw material acid, and adding water to obtain aluminum salt acid solution with aluminum salt mass concentration of 1-20% and raw material acid mass concentration of 5-45%; taking sodium silicate, adding water to prepare a sodium silicate solution with the mass concentration of 5-25%; 2) adding the sodium silicate solution obtained in the step 1) into the acid solution obtained in the step 1), wherein the volume ratio of the sodium silicate solution to the acid solution is 15-18:5-7, carrying out sol-gel reaction at 15-45 ℃, the reaction pressure is 0.05-1.5MPa, and the pH value after the reaction is 2.5-8.5, so as to obtain gel; 3) aging the gel obtained in the step 1), performing exchange acid treatment, washing with water, performing ammonia treatment, and drying to obtain the silica-alumina gel.
Specifically, the gel obtained in the step 1) has a balling distance of 1-3m, and is buffered in a receiver, the pH value of water in the receiver is 6.0-9.0, and the temperature of the water in the receiver is 20-40 ℃.
Further, in the step 2), when ammonia is treated, the used ammonia is any one or more of ammonia water, ammonium chloride, ammonium sulfate, ammonium carbonate or ammonium bicarbonate, the treatment concentration is 0.05-1.5%, the treatment temperature is 20-90 ℃, and the treatment time is 1-12 hours; more preferably: the ammonia is ammonia water, the treatment concentration is 0.1-1%, the treatment temperature is 40-80 ℃, and the treatment time is 4-8 h.
Preferably, the mass concentration of the sodium silicate is 10-20%, the mass concentration of the aluminum salt is 5-15%, the mass concentration of the raw material acid is 10-30%, and the pH value of the reaction is 3.5-7.5.
Further, in the step 2), the temperature is 25-85 ℃ and the time is 0.5-50h during aging; more preferably: the temperature is 30-60 ℃ and the time is 2-35 h.
Preferably, in the step 2), when the exchange acid is treated, the exchange acid is any one or more of hydrochloric acid, sulfuric acid, aluminum nitrate, nitric acid, aluminum sulfate, oxalic acid or citric acid, the mass concentration of the exchange acid is 0.05-10%, the treatment temperature is 30-100 ℃, and the treatment time is 1-12 hours; more preferably: the exchange acid is a mixed acid consisting of sulfuric acid, oxalic acid and aluminum sulfate, the mass concentration of the exchange acid is 0.1-5%, the treatment temperature is 30-60 ℃, and the treatment time is 2-6 h.
More specifically, in the step 2), the temperature is 20-90 ℃ during water washing, the pH value of the end point of the water washing is 4.5-7.0, and the specific resistance of the gel after the water washing is not lower than 1000 omega cm; more preferably: the temperature is 30-60 ℃, and the pH value of the washing end point is 5.0-6.5.
Furthermore, in the step 2), the drying is carried out at the temperature of 80-400 ℃ for 12-48 h; more preferably: two times of drying process are adopted, the temperature of the first drying is 80-200 ℃, the time is 10-36h, the temperature of the second drying is 200-.
Example one
The preparation method of the silica-alumina gel comprises the following steps:
1) mixing aluminum salt and raw material acid, and adding water to prepare an aluminum salt acid solution, wherein the mass concentration of the aluminum salt is 8%, and the mass concentration of the raw material acid is 15%; taking sodium silicate, adding water to prepare a sodium silicate solution with the mass concentration of 10%;
2) adding the solution of the sodium silicate obtained in the step 1) into the acid solution obtained in the step 1), wherein the volume ratio of the solution of the sodium silicate to the acid solution is 15:5, placing the solution of the sodium silicate and the acid solution into a reactor, and carrying out sol-gel reaction at 35 ℃, the reaction pressure is 0.34Mpa, the pH value after the reaction is 6.5, so as to obtain gel, and the balling distance of the gel is 3 m;
3) aging the obtained gel at 35 deg.C for 2 h;
4) performing exchange acid treatment on the aged gel, wherein the mass concentration of the exchange acid is 0.6%, the treatment temperature is 30 ℃, and the treatment time is 3 hours, wherein the exchange acid is mixed acid consisting of sulfuric acid, oxalic acid and aluminum sulfate;
5) washing the gel after the exchange acid treatment with water at the temperature of 40 ℃ until the end point of the washing with water is pH 5.5, wherein the specific resistance of the gel after the washing with water is 1200 omega cm;
6) carrying out ammonia treatment on the washed gel, wherein all ammonia is ammonia water, the treatment concentration is 0.2%, the temperature is 40 ℃, and the treatment time is 4 h;
7) and (3) drying the gel subjected to ammonia treatment twice, wherein the primary drying temperature is 90 ℃, the drying time is 12 hours, the secondary drying temperature is 400 ℃, and the drying time is 4 hours, so as to obtain the silica-alumina gel.
Through detection, in the silica alumina gel obtained in the embodiment, Al is contained2O3Is 3.5% by mass of SiO2Has a mass content of 91.5%, a pore volume of 0.65mL/g, and a specific surface area of 510m2(iv)/g, compressive strength 106N.
Example two
The preparation method of the silica-alumina gel comprises the following steps:
1) mixing aluminum salt and sulfuric acid, and adding water to prepare an aluminum salt acid solution, wherein the mass concentration of the aluminum salt is 12% and the mass concentration of the sulfuric acid is 10.5%; taking sodium silicate, adding water to prepare the sodium silicate solution with the mass concentration of 14.5%;
2) adding the solution of the sodium silicate obtained in the step 1) into the acid solution obtained in the step 1), wherein the volume ratio of the solution of the sodium silicate to the solution of the acid is 18:7, placing the solution of the sodium silicate and the solution of the acid in a reactor, carrying out sol-gel reaction at 31 ℃, the reaction pressure is 0.36Mpa, the pH value after the reaction is 7.0, when the reaction is finished, the pH value of water in a receiver is 9.0, the temperature of the water is 40 ℃, obtaining gel, and the balling distance of the gel is 1 m;
3) aging the obtained gel at 45 deg.C for 4 hr;
4) performing exchange acid treatment on the aged gel, wherein the mass concentration of the exchange acid is 2.5%, the treatment temperature is 40 ℃, and the treatment time is 2 hours, wherein the exchange acid is aluminum sulfate;
5) washing the gel subjected to the exchange acid treatment with water at the temperature of 50 ℃, wherein the washing end point is the pH value of 6.0, and the specific resistance of the gel after washing is 1500 omega cm;
6) performing ammonia treatment on the gel after water washing, wherein all ammonia is ammonium bicarbonate, the treatment concentration is 0.4%, the temperature is 60 ℃, and the treatment time is 5 hours;
7) and (3) drying the gel subjected to ammonia treatment twice, wherein the primary drying temperature is 100 ℃, the drying time is 24 hours, the secondary drying temperature is 200 ℃, and the drying time is 12 hours, so as to obtain the silica-alumina gel.
Through detection, in the silica alumina gel obtained in the embodiment, Al is contained2O3Is 4.5% by mass of SiO2Has a mass content of 89.5%, a pore volume of 0.76mL/g, and a specific surface area of 488m2(ii)/g, compressive strength of 84N.
EXAMPLE III
The preparation method of the silica-alumina gel comprises the following steps:
1) mixing aluminum salt and sulfuric acid, and adding water to prepare an aluminum salt acid solution, wherein the mass concentration of the aluminum salt is 13% and the mass concentration of the sulfuric acid is 19%; taking sodium silicate, adding water to prepare the sodium silicate solution with the mass concentration of 18.5%;
2) adding the solution of the sodium silicate obtained in the step 1) into the acid solution obtained in the step 1), wherein the volume ratio of the solution of the sodium silicate to the solution of the acid is 16:6, placing the solution of the sodium silicate and the solution of the acid into a reactor, carrying out sol-gel reaction at 28 ℃, the reaction pressure is 0.36Mpa, the pH value after the reaction is 3.5, when the reaction is finished, the pH value of water in a receiver is 6.0, the temperature of the water is 20 ℃, obtaining gel, and the balling distance of the gel is 2 m;
3) aging the obtained gel at 35 deg.C for 24 hr;
4) performing exchange acid treatment on the aged gel, wherein the mass concentration of the exchange acid is 1.5%, the treatment temperature is 50 ℃, and the treatment time is 4 hours, wherein the exchange acid is oxalic acid;
5) washing the gel after the exchange acid treatment with water at the temperature of 60 ℃ until the pH value is 5.8, wherein the specific resistance of the gel after washing with water is 1000 omega cm;
6) performing ammonia treatment on the washed gel, wherein all ammonia is ammonium chloride, the treatment concentration is 0.8%, the temperature is 40 ℃, and the treatment time is 6 hours;
7) and (3) drying the gel subjected to ammonia treatment twice, wherein the primary drying temperature is 120 ℃, the drying time is 36 hours, the secondary drying temperature is 300 ℃, and the drying time is 2 hours, so as to obtain the silica-alumina gel.
Through detection, in the silica alumina gel obtained in the embodiment, Al is contained2O3Is 4.7% by mass of SiO2Has a mass content of 88.5%, a pore volume of 0.82mL/g, and a specific surface area of 458m2(iv)/g, compressive strength of 65N.
Compared with the prior art, the invention has the beneficial effects that: in the silica alumina gel of the invention, SiO2High content of Al2O3The content is adjustable, the silicon-aluminum ratio adjusting range is wide, the framework structure and the strength are uniform, the pore volume is large, the specific surface area is large, the compressive strength is high, the framework structure and the pore structure are stable, the product quality is good, the large pore volume, the specific surface area and the high compressive strength are considered, and the catalyst can be widely applied to the fields of catalyst and catalyst carriers, adsorption separation, molecular sieve preparation and the like; the preparation process is simple, convenient to operate and easy to realize industrialization.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (8)
1. A preparation method of silica-alumina gel is characterized by comprising the following steps:
in the silica-alumina gel, Al2O33-8% of SiO2The mass content of the silica-alumina gel is not less than 82 percent, and the specific surface area of the silica-alumina gel is 300-550m2Per g, pore volume of 0.7-0.9mL/g, poresThe diameter is 6-10nm, and the compressive strength is not lower than 50N;
the preparation method of the silica-alumina gel comprises the following steps:
1) mixing aluminum salt and raw material acid, and adding water to obtain aluminum salt acid solution with aluminum salt mass concentration of 1-20% and raw material acid mass concentration of 5-45%; taking sodium silicate, adding water to prepare a sodium silicate solution with the mass concentration of 5-25%;
2) adding the sodium silicate solution obtained in the step 1) into the acid solution obtained in the step 1), wherein the volume ratio of the sodium silicate solution to the acid solution is 15-18:5-7, carrying out sol-gel reaction at 15-45 ℃, the reaction pressure is 0.05-1.5MPa, and the pH value after the reaction is 2.5-8.5, so as to obtain gel;
the balling distance of the gel is 1-3m, buffering is carried out in a receiver after reaction, the pH value of water in the receiver is 6.0-9.0, and the temperature of the water in the receiver is 20-40 ℃;
3) aging the gel obtained in the step 1), performing exchange acid treatment, washing with water, performing ammonia treatment, and drying to obtain silica-alumina gel;
aging at 25-85 deg.C for 0.5-50 hr;
when the exchange acid is treated, the exchange acid is any one or more of hydrochloric acid, sulfuric acid, aluminum nitrate, nitric acid, aluminum sulfate, oxalic acid or citric acid, the mass concentration of the exchange acid is 0.05-10%, the treatment temperature is 30-100 ℃, and the treatment time is 1-12 hours;
when washing, the temperature is 20-90 ℃, the pH value of the washing end point is 4.5-7.0, and the specific resistance of the gel after washing is not lower than 1000 omega cm;
when ammonia is treated, the used ammonia is any one or more of ammonia water, ammonium chloride, ammonium sulfate, ammonium carbonate or ammonium bicarbonate, the treatment concentration is 0.05-1.5%, the treatment temperature is 20-90 ℃, and the treatment time is 1-12 h;
the drying is carried out at 80-400 ℃ for 12-48 h.
2. The preparation method of the silica-alumina gel according to claim 1, which is characterized in that:
in the step 3), ammonia is used in the ammonia treatment, the treatment concentration is 0.1-1%, the treatment temperature is 40-80 ℃, and the treatment time is 4-8 h.
3. The method for preparing the silica-alumina gel according to claim 1 or 2, which is characterized in that:
in the step 1), the mass concentration of the sodium silicate is 10-20%, the mass concentration of the aluminum salt is 5-15%, the mass concentration of the raw material acid is 10-30%, and the pH value after reaction is 3.5-7.5.
4. The preparation method of the silica-alumina gel according to claim 1, which is characterized in that:
in the step 3), the temperature is 30-60 ℃ during aging, and the time is 2-35 h.
5. The preparation method of the silica-alumina gel according to claim 1, which is characterized in that:
in the step 3), when the exchange acid is treated, the exchange acid is a mixed acid consisting of sulfuric acid, oxalic acid and aluminum sulfate, the mass concentration of the exchange acid is 0.1-5%, the treatment temperature is 30-60 ℃, and the treatment time is 2-6 h.
6. The preparation method of the silica-alumina gel according to claim 1, which is characterized in that:
in the step 3), the temperature is 30-60 ℃ during water washing, and the pH value at the end point of the water washing is 5.0-6.5.
7. The preparation method of the silica-alumina gel according to claim 1, which is characterized in that:
in the step 3), two drying processes are adopted during drying, wherein the temperature for the first drying is 80-200 ℃ and the time is 10-36h, and the temperature for the second drying is 200-400 ℃ and the time is 2-12 h.
8. The silica-alumina gel is characterized in that:
the silica-alumina gel is prepared by the preparation method of the silica-alumina gel according to any one of claims 1 to 7.
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