RU2801455C2 - Silica-alumina composition with improved stability and method for its production - Google Patents

Abstract

FIELD: alumina products.

SUBSTANCE: invention relates to a new method for producing silica-alumina and to silica-alumina obtained in accordance with the method of the invention. The method includes obtaining a suspension of alumina, adding a first source of silicon dioxide to a suspension of alumina, hydrothermal aging, drying and calcining the resulting suspension of silicon dioxide-alumina. Then, a solution containing a second source of silicon dioxide is added to the obtained silica-alumina intermediate. Moreover, the second source of silicon dioxide is chemically different from the first source of silicon dioxide. The resulting resuspended silica - alumina - is dried and calcined.

EFFECT: improved performance of the final silica-alumina product, in particular, a product having improved heat resistance and purity.

15 cl, 1 dwg, 1 tbl, 2 ex

Description

FIELD OF TECHNOLOGY TO WHICH THE INVENTION RELATES

The invention relates to a new process for producing silica-alumina (silica alumina), silica-alumina according to the method of the invention, and silica-alumina having improved characteristics.

BACKGROUND OF THE INVENTION

Silicon dioxide-alumina (silica alumina) is used in the field of catalyst carriers. Many prior art documents describe methods for producing silica-alumina, and the focus is on obtaining a uniform distribution of silica on alumina and/or obtaining matrices with high pore volume. This can be achieved by mixing boehmite with, for example, amorphous silica, such as sodium silicate, under certain conditions. Problems associated with making silica-alumina in this way include impurities such as SiO ₂ (quartz) in the final product, as well as problems associated with decreasing the surface area of the silica-alumina.

US 5,187,138 describes a hydroisomerization catalyst supported on an alumina or amorphous silica-alumina support (modified by adding silica as a surface modifier). The silica and alumina base materials used in the present invention may be soluble silicon-containing compounds such as alkali metal silicates, tetraalkoxysilane or orthosilicic esters, aluminum sulfates, nitrates or chlorides, alkali metal aluminates, or inorganic salts or alkoxides, or the like. The method includes precipitation and aging, followed by filtration, drying and calcination to obtain a carrier material. The support material is then impregnated with a suitable silicon-containing compound, for example ethylorthosilicate, in isopropanol. Other sources of silicon include silanes, colloidal silicon dioxide, silicon chlorides, or other inorganic silicon salts. US 5,187,138 explains that the silica used as a modifier is chemically similar to the silica in the bulk of the catalyst support. The use of silica as a surface modifying agent improves the activity and selectivity of the catalyst.

The method of the present invention aims to improve the performance of the final silica-alumina product, in particular a product having improved heat resistance and purity.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a process for producing a silica-alumina product comprising the following steps:

i) obtaining a slurry of alumina;

ii) adding a first source of silica to the alumina slurry to form a silica-alumina slurry;

iii) hydrothermally aging the silica-alumina slurry to form a hydrothermally aged silica-alumina slurry;

iv) drying the hydrothermally aged silica-alumina slurry to form a dried aged silica-alumina intermediate;

v) calcining the dried aged silica-alumina intermediate to form the calcined dried aged silica-alumina intermediate;

vi) adding the calcined dried aged silica-alumina intermediate from step v) to a solution comprising a second silica source, the second silica source being chemically different from the first silica source from step ii) to form resuspended silica silicon-alumina;

vii) drying the resuspended silica-alumina to form dried resuspended silica-alumina; And

viii) calcining the dried resuspended silica-alumina to form a silica-alumina product.

The alumina slurry includes alumina and at least water.

The alumina slurry preferably has a pH in the range of 8 to 10, and most preferably a pH of 9. Even more preferably, the alumina slurry may be a Ziegler process slurry having a pH in the range of 8-10, more specifically about 9.

The alumina is preferably boehmite. The alumina preferably includes particles having a crystallite size in the (120) plane from 40 Å to 60 Å, preferably a crystallite size in the (120) plane from 40 Å to 50 Å, more preferably a crystallite size in the (120) plane of about 45 Å.

The first silica source includes a silica sol, precipitated silica, or fumed silica. The first silica source may include a mixture of silica sol, precipitated silica, or fumed silica. The silica sol is preferably a colloidal silica sol.

When the first silica source is in the form of a silica sol, the silica sol preferably consists of silica particles having a particle size of about 40 Å to 50 Å. The silica sol preferably has a pH of 8 to 10, preferably 9.

The first silica source preferably comprises a stable aqueous dispersion of silica particles, for example a colloidal silica sol. The silica sol can be stabilized with a base, preferably a base including ammonia, eg ammonium hydroxide solution.

The pH of the silica-alumina slurry is in the range of 6 to 9, preferably 6 to 8, most preferably about 7.

The ratio of silica to alumina in the silica-alumina slurry is 1-7% by weight, preferably 5-7% by weight.

The hydrothermal aging of step iii) of the method according to the invention takes place at temperatures from 100°C to 150°C, preferably at temperatures from 120°C to 130°C, for a period of time from 3 to 6 hours. The temperature and time parameters are chosen independently.

The hydrothermally aged silica-alumina slurry is dried at a temperature of about 90°C to 130°C, preferably at a temperature of 100°C to 105°C, using conventional technology (for example, a spray dryer), to obtain dried aged silica - alumina intermediate. The dried aged silica-alumina is preferably a silica-boehmite intermediate with a crystallite size of 50 Å to 60 Å.

The calcination of the dried aged silica-alumina intermediate takes place at temperatures of 300-600°C for a period of 2 to 6 hours depending on the source of the alumina.

The second source of silicon dioxide includes SiO ₂ , silicon alkoxide, silicone esters, and aqueous silicon compounds. The invention provides mixtures of these silica sources. The solution comprising the second silica source in step vi) of the process of the invention may contain an alcoholic solvent such as 2-propanol.

The amount of the second source of silicon dioxide in solution at stage vi) of the invention is 1-5% of the mass. from the total solution. The amount of solvent in the solution in step vi) of the method of the invention is 95-99% of the total solution. The second silica source is chemically different from the first silica source.

Step vi) of the process of the invention may include an impregnation step in which the second silica source can be impregnated into the calcined dried aged silica-alumina intermediate. This impregnation step can be carried out in a solvent, eg water, or an alcoholic solvent, eg 2-propanol. This forms a resuspended silica-alumina.

The resuspended silica-alumina is then dried as in step vii) of the method of the invention. Drying takes place at temperatures above the boiling point of the solvent, i.e. if the solvent is water, a suitable drying temperature may be 90-120°C, preferably 100-110°C, to form dried resuspended silica-alumina. If the solvent is an alcohol, such as isopropyl alcohol, then a suitable drying temperature is about 30°C. Drying is carried out at atmospheric pressure or under a suitable vacuum, or both.

The dried resuspended silica-alumina is then calcined as in step viii) of the process of the invention. The calcination of the dried resuspended silica-alumina takes place at temperatures of 300-600°C for 2-6 hours, depending on the source of alumina. Time and temperature parameters are selected independently. Precipitation of the second source of silica is believed to act as an additive to stabilize the calcined dried aged silica-alumina intermediate, which in turn produces a silica-alumina product having improved surface retention with fewer impurities. This method also increases the acidity of the silica-alumina product.

According to a second aspect of the invention there is provided a silica-alumina product obtained in accordance with the method of the invention.

According to a third aspect of the invention, there is provided a silica-alumina product comprising at least one of the following, preferably more than one of the following, and most preferably all of the following:

i) BET specific surface after calcination at 550° C. for 6 hours less than 300 m ² /g, preferably less than 295 m ² /g;

ii) total acidity, measured with NH3-TPD, greater than 1.80 µmol/m ² ; preferably more than 2.00 µmol/m ² , and most preferably more than 2.50 µmol/m ² ;

iii) residual surface area after calcination in air at 1200° C. for 24 hours greater than 30 m ² /g, preferably greater than 50 m ² /g and most preferably greater than 60 m ² /g; And

iv) a pore volume greater than 0.7 ^cc /g.

The methods used to measure the various characteristics of a silica-alumina product are described below in the Analytical Methods section.

The present invention will now be described with reference to the following drawings and examples.

Figure 1 shows the data of X-ray diffraction analysis of silicon dioxide-alumina powders obtained in accordance with example 1.

ANALYTICAL METHODS

Product properties were determined using the following analytical methods:

The chemical composition was obtained using analysis method ICP-AES. Determination of the content of residual carbon in the materials was carried out by burning organic materials in the sample using a LECO analyzer. A sample of the powder was weighed into the crucible. The pure oxygen furnace device ensured complete combustion of the organic materials in the sample and gave the carbon content of the sample expressed in % wt.

The products were identified by phase X-ray diffraction analysis. Samples were placed over the diameter of an XRD plastic disc. Received XRD data. Alumina and silica, as well as other phases, were obtained by comparison with standards.

The surface area of the silica-alumina product and the pore volume were determined using the N _{2 adsorption isotherm and the N 2} desorption isotherm. Data were collected on heat-treated samples at 550° C. for 3 hours or after heating at 1200° C. for 24 hours (residual surface area or RSA). In this regard, the samples were degassed for 0.5 h in a stream of N ₂ at 300°C.

The BET specific surface area (m ² /g) was estimated using the BET equation.

The total pore volume was determined from the volume of nitrogen adsorbed at saturation (estimated at a relative pressure p/p ₀ equal to 0.992).

NH ₃ -TPD is a temperature programmed precipitation in which total acid sites are measured (µmol/m ² ). The sample was calcined at 550°C for 3 h before analysis. Then the sample was heated at 500°C under vacuum. Gaseous ammonia (NH ₃ ) was allowed to adsorb at room temperature. Acidity was calculated from total ammonia adsorbed per gram of materials (mmol/g) divided by BET surface area (m ² /g), the results were expressed in µmol/m ² after unit conversion.

EXAMPLES:

Example 1:

A weighed amount of a colloidal silica solution containing a weighed amount of ammonia, at pH 9 and a nominal size of 43 Å, was added to a suspension of boehmite with crystal sizes (120) 45 Å at a pH of about 9, diluted with deionized water (DI-water).

The resulting silica-boehmite suspension was subjected to hydrothermal aging at a temperature of 130°C for 4 hours. The aged silica-boehmite dioxide suspension had a pH of 7 at the end of the operation. a boehmite intermediate with a crystallite size of 57 Å. The dried aged silica-boehmite intermediate was then calcined at 550°C for 3 hours.

The calcined dried aged silica-boehmite product had a BET specific surface area of 291 m ² /g and a pore volume of 0.74 cm ³ /g. The total acidity measured with NH3-TPD was 1.8 µmol/m ² .

A dilute solution of TEOS in 2-propanol (0.7 ml in 10 ml) was prepared. Calcined dried aged silica-boehmite intermediate (10 g) was added to the solution and stirred for 6 hours at room temperature to form resuspended silica-alumina. The resuspended silica-alumina was then transferred to an open container to dry overnight, with a residual carbon content of 0.33%. The solvent was then further extracted under vacuum at 30° C. for 2 hours to give dried resuspended boehmite-silica with a residual carbon content of 0.11%. The dried resuspended silica-boehmite was then calcined at 550° C. for 6 hours to form the silica-boehmite product.

The silica-boehmite product had:

i) BET specific surface area 285 m ² /g;

ii) pore volume 0.73 ^cc /g;

iii) 9% wt. SiO ₂ / (SiO ₂ +Al ₂ O ₃ );

iv) total acidity, measured with NH3-TPD, equal to 2.8 µmol/m ² ; And

v) after calcination in air at 1200° C. for 24 hours, a residual surface area (RSA) of 71 m ² /g.

Comparative example 1:

A weighed amount of the colloidal silica solution of Example 1 was added to the boehmite suspension at pH 9, which was diluted in DI-water. The pH dropped slightly to 7. The slurry composition was hydrothermally aged at 110° C. for 4 hours. The slurry was then spray dried to give silica mixed with boehmite with a crystallite size of 49 Å. The powder was calcined at 550°С for 3 h.

The material received was:

i) BET specific surface area 333 m ² /g;

ii) 10% wt. SiO ₂ / (SiO ₂ +Al ₂ O ₃ );

iii) after calcination in air at 1200° C. for 24 hours, a residual surface area (RSA) of 26 m ² /g.

The results of Example 1 and Comparative Example 1 are summarized in Table 1:

Table 1:

Example 1 Comparative Example 1 Stage 1 Stage 2 SiO ₂ /(SiO ₂ +Al ₂ O ₃ ) (wt %) 6 9 10 BET surface area @ 550°C, 3 h ( ^m2 /g) 291 285 333 RSA BET @ 1200°C/24h ( ^m2 /g) 64 71 26

X-ray diffraction data on the powders in FIG. 1, obtained according to the procedure of Example 1, after adding the second source of silica, showed a reduction in crystalline impurities, indicating a stability effect of the second source of silica.

Claims (27)

1. A method for producing a silica-alumina (silica alumina) product, comprising the following steps: i) obtaining a slurry of alumina; ii) adding a first source of silica to the alumina slurry to form a silica-alumina slurry; iii) hydrothermally aging the silica-alumina slurry to form a hydrothermally aged silica-alumina slurry; iv) drying the hydrothermally aged silica-alumina slurry to form a dried aged silica-alumina intermediate; v) calcining the dried aged silica-alumina intermediate to form the calcined dried aged silica-alumina intermediate; vi) adding the calcined dried aged silica-alumina intermediate from step v) to a solution comprising a second silica source, the second silica source being chemically different from the first silica source from step ii) to form resuspended silica silicon-alumina; vii) drying the resuspended silica-alumina to form dried resuspended silica-alumina; And viii) calcining the dried resuspended silica-alumina to form a silica-alumina product. 2. The method of claim 1, wherein the alumina slurry comprises alumina and at least water. 3. The method according to claim 1 or 2, wherein the alumina is boehmite. 4. The method according to claim 3, in which the boehmite includes particles having a crystallite size in the (120) plane from 40 Å to 50 Å. 5. The method of claim 1, wherein the first silica source comprises a silica sol, precipitated silica, fumed silica, or a mixture thereof, preferably a silica sol, more preferably a colloidal silica sol. 6. The method of claim 5, wherein the silica sol consists of silica particles having a particle size of 40 Å to 50 Å. 7. The method according to any one of claims 1 to 6, in which the ratio of silicon dioxide to alumina in a suspension of silicon dioxide-alumina is 1-7% wt., preferably 5-7% wt. 8. The method according to claim 1, wherein the hydrothermal aging of step iii) takes place at temperatures from 100°C to 150°C for a period of 3 to 6 hours. 9. The process of claim 1 wherein the hydrothermally aged silica-alumina slurry is dried at 90° C. to 130° C. to form a dried aged silica-alumina intermediate. 10. The method of claim 1 wherein the second silica source comprises SiO ₂ , silicon alkoxide, silicone esters, aqueous silica compounds, or mixtures thereof. 11. The method according to claim 1 or 10, in which the amount of the second source of silicon dioxide in solution at stage vi) is 1-5% wt. from the total solution. 12. The method according to any one of claims 1, 10 or 11, wherein step vi) of the method of the invention comprises an impregnation step in which the second source of silica is impregnated into the calcined dried aged silica-alumina intermediate to form resuspended silica- aluminum oxide. 13. The method according to any one of claims 1-11, in which, the calcination occurs at temperatures of 300-600°C for 2-6 hours. 14. Silica-alumina product obtained by the method according to any one of claims 1 to 13. 15. A silica-alumina product having all of the following: i) a specific surface area measured by the BET method after calcination at 550° C. for 6 hours less than 300 m ² /g, preferably less than 295 m ² /g; ii) total acidity, measured with NH3-TPD, greater than 1.80 µmol/m ² ; preferably more than 2.00 µmol/m ² , and most preferably more than 2.50 µmol/m ² ; iii) a residual surface area after calcination in air at 1200° C. for 24 hours greater than 50 m ² /g and most preferably greater than 60 m ² /g; And iv) a pore volume greater than 0.7 ^cc /g.