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Silica Alumina Composition with Improved Stability and Method for Making Same

20210394158 · 2021-12-23

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    Abstract

    The invention relates to a novel method of making a silica alumina including the use of two silica sources, the first silica source differing chemically from the second silica source, to a silica alumina made according to the method of the invention and to a silica alumina having improved characteristics.

    Claims

    1. A method of making a silica alumina product including the following steps: i) providing an alumina slurry; 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 product; v) calcining the dried aged silica alumina intermediate product to form a calcined dried aged silica alumina intermediate product; vi) adding the calcined dried aged silica alumina intermediate product from step v) to a solution including a second source of silica, the second source of silica differing chemically from the first source of silica provided in step ii) to form a re-slurried silica alumina; vii) drying the re-slurried silica alumina to form a dried re-slurried silica alumina; and viii) calcining the dried re-slurried silica alumina to form the silica alumina product.

    2) The method of claim 1 wherein the alumina slurry includes alumina and at least water.

    3) The method of claim 1 or claim 2 wherein the alumina is boehmite.

    4) The method of claim 3 wherein the boehmite includes particles having a crystallite size on the (120) plane of between 40 Å and 50 Å.

    5) The method of claim 1 wherein the first source of silica includes a silica sol, a precipitated silica, a fumed silica or mixtures thereof.

    6) The method of claim 5 wherein the silica sol is made up of silica particles having a particle size of 40 Å to 50 Å.

    7) The method of claim 1 wherein the ratio of silica to alumina in the silica alumina slurry is between 1 and 7% by weight.

    8) The method of claim 1 wherein the hydrothermal aging step of step iii) occurs at temperatures between 100° C. and 150° C. for a period of 3 to 6 hours.

    9) The method of claim 1 wherein the hydrothermally aged silica alumina slurry is dried at a temperature of 90 to 130° C. to form a dried, aged silica alumina intermediate product.

    10) The method of claim 1 wherein the second source of silica includes SiO.sub.2, silicon alkoxide, silicon esters, aqueous silicon compounds or mixtures thereof.

    11) The method of claim 1 or claim 10 wherein the amount of the second source of silica in the solution of step vi) is between 1 and 5 wt. % of the total solution.

    12) The method of claim 1 wherein step vi) of the process of the invention includes an impregnation step whereby the second source of silica is impregnated into the calcined dried aged silica alumina intermediate product to form a re-slurried silica alumina.

    13) The method of claim 1 wherein calcination occurs at temperatures of between 300° C. and 600° C. for 2 to 6 hours.

    14) A silica alumina product produced according to the method of claim 1.

    15) A silica alumina product including at least one of the following characteristics: i) BET Surface area after calcination at 550° C. for 6 hours of below 300 m.sup.2/g; ii) total acidity measured by NH3-TPD of above 1.80 μmol/m.sup.2; iii) residual surface area after calcination in air at 1200° C. for 24 hours above 30 m.sup.2/g; and iv) a pore volume above 0.70 cc/g.

    Description

    [0037] The invention will now be described with reference to the following Figures and Examples.

    [0038] FIG. 1 is an X-ray diffraction analysis of the silica alumina powders obtained according to Example 1.

    ANALYTICAL TECHNIQUES

    [0039] The properties of the product are measured by the following analytical techniques:

    [0040] The chemical composition is obtained by means of ICP-AES analysis. The determination of residual carbon content on materials is carried out by means of combustion of the organic materials in the sample using a LECO analyzer apparatus. A sample of the powder is weighted in a crucible. A furnace system that operates with pure oxygen ensures complete combustion of the organic materials in the sample and gives the carbon content of the sample, expressed as % by weight.

    [0041] The products are identified using X-ray analyses for the phases. The samples are placed into an XRD diameter plastic disc. XRD data is acquired. The alumina and silica and other phases are obtained comparing with referenced standards.

    [0042] The silica alumina product surface area and pore volume data are both determined by N.sub.2 adsorption and desorption isotherm. Data is collected on heat treated samples at 550° C. for 3 hours or after 1200° C. for 24 hours (Residual Surface Area or RSA). The samples are therefore degassed for 0.5 hours under N.sub.2 flow at 300° C.

    [0043] The BET surface area (m.sup.2/g) is evaluated using the B.E.T. equation.

    [0044] The total pore volume is determined from the volume of nitrogen adsorbed at saturation (evaluated at relative pressure p/p.sub.0 equal to 0.992).

    [0045] NH.sub.3-TPD is temperature program deposition which measures the total amount of acid centres (μmol/m.sup.2). The sample is calcined at 550° C. for 3 hours before analysis. Then the sample is heated at 500° C. under vacuum. The gaseous ammonia (NH.sub.3) is allowed to adsorb at room temperature. The acidity is calculated from the total amount of adsorbed ammonia per gram of materials (mmol/g) divided by BET surface area (m.sup.2/g), the results are expressed as μmol/m.sup.2 after units of measurement conversion.

    EXAMPLES

    Example 1

    [0046] A weighted amount of colloidal silica solution containing a weighted amount of ammonia, at pH 9, and a nominal size of 43 Å was added to a boehmite slurry with crystal sizes (120) of 45 Å at pH of about 9 diluted with deionized water (DI water).

    [0047] The resulting silica boehmite slurry was hydrothermally aged at a temperature of 130° C. for 4 hours. The aged silica boehmite slurry at the end of the run had a pH of 7. The aged silica boehmite slurry was then dried resulting in a dried, aged silica boehmite intermediate product having a crystallite size of 57 Å. The dried, aged silica boehmite intermediate product was then calcined at 550° C. for 3 hours.

    [0048] The calcined dried aged silica boehmite product had a BET surface area of 291 m.sup.2/g and a pore volume of 0.74 cc/g. The total acidity measured by NH3-TPD resulted in 1.8 μmol/m.sup.2.

    [0049] A diluted solution of TEOS in 2-propanol (0.7 ml in 10 ml) was prepared. The calcined dried aged silica boehmite intermediate product (10 g) was added to the solution and stirred for 6 hours at room temperature to form a re-slurried silica alumina. The re-slurried silica alumina was then transferred to an open container to dry out over-night and had a residual carbon content of 0.33%. The solvent was then further extracted via vacuum at 30° C. for 2 hours to form a dried re-slurried boehmite silica with a residual carbon content of 0.11%. The dried re-slurried silica boehmite was then calcined at 550° C. for 6 hours to form a silica boehmite product.

    [0050] The silica boehmite product has: [0051] i) a BET surface area of 285 m.sup.2/g; [0052] ii) a pore volume of 0.73 cc/g; [0053] iii) 9% wt. SiO.sub.2/(SiO.sub.2+Al.sub.2O.sub.3); [0054] iv) total acidity measured by NH3-TPD of 2.8 μmol/m.sup.2; and [0055] v) after calcination in air at 1200° C. for 24 hours a residual surface area (RSA) of 71 m.sup.2/g.

    Comparative Example 1

    [0056] A weighted amount of colloidal silica solution of Example 1 was added to a boehmite slurry at a pH of 9 that was diluted in DI water. The pH slightly dropped to 7. The slurry composition was hydrothermally aged at a temperature of 110° C. for 4 hours. The slurry was then spray dried resulting in a silica mixed boehmite with a crystallite size of 49 Å. The powder was calcined at 550° C. for 3 hours.

    [0057] The resulting material has: [0058] i) BET surface area of 333 m.sup.2/g; [0059] ii) 10% wt. SiO.sub.2/(SiO.sub.2+Al.sub.2O.sub.3); [0060] iii) after calcination in air at 1200° C. for 24 hours the residual surface area (RSA) of 26 m.sup.2/g.

    [0061] The Results of Example 1 and Comparative Example 1 are summarized in Table 1:

    TABLE-US-00001 TABLE 1 Example 1 Comparative Step 1 Step 2 Example 1 SiO.sub.2/(SiO.sub.2 + Al.sub.2O.sub.3) % wt 6 9 10 BET SA @ 550° C./3 h m.sup.2/g 291 285 333 BET RSA@ 1200° C./24 h m.sup.2/g 64 71 26

    [0062] The X-ray diffraction analysis as per FIG. 1 on the powders obtained according to the procedure of Example 1 after the addition of the second silica source, showed suppressed crystalline impurities indicating that the stability effect of the second silica source.