Aluminas and Methods for Producing Same

Abstract

The present invention is directed to a method for producing a modified alumina by modifying a surface of an alumina with the addition of a phosphono group containing modifier. The invention is further directed to a modified alumina produced according to the method of the present invention and to a modified alumina having specific characteristics.

Claims

1. A method for producing a modified alumina including the steps of: i) providing an alumina, wherein the alumina is an aluminium oxyhydroxide; and ii) adding an phosphono group containing modifier to the alumina to produce a surface modified alumina.

2) The method of claim 1 including a further step of aging the alumina before the addition of the phosphono group containing modifier to form an aged alumina having a crystallite size of 35 to 450 Å (as measured on the 120 plane).

3) The method of claim 1 including a further step of aging the surface modified alumina to form an aged surface modified alumina.

4) The method of any one of claims 1 to 3 including the further steps of aging the alumina before the addition of the phosphono group containing modifier to form an aged alumina having a crystallite size of 35 to 450 Å (as measured on the 120 plane) and aging the surface modified alumina to form an aged surface modified alumina.

5) The method of any one of claims 1 to 4 including drying the surface modified alumina or the aged surface modified alumina.

6) The method of claim 1 wherein the phosphono containing modifier includes an organic phosphorous compound and at least one carboxyl (COOH) group bearing at least one phospono moiety.

7) The method of claim 6 wherein the phosphono moiety includes a primary phosphono-alkylcarboxylic acid, a secondary phosphono-alkylcarboxylic acids, a primary dicarboxylic acid, a secondary alkyl dicarboxylic acid, a primary phosphono-alkyl tricarboxylic acid, a phosphine alkane carboxylic acid or mixtures thereof.

8) The method of any one of claim 1, 6 or 7 wherein the phosphono group containing modifier is added in amounts of from less than 10 wt. % based on the alumina, preferably in amounts between 3 wt. % and 10 wt. % based on the alumina, more preferably in amounts of from less than 8 wt. % based on the alumina, and most preferably in amounts between 3 wt. % and 8 wt. % based on the alumina.

9) The method of any one of claim 1, 2 or 4 wherein the alumina is aged at a temperature of between 100° C. and 200° C. for a period of between 0.5 and 4 hours.

10) The method of any one of claims 1, 3 and 4 wherein the surface modified alumina is aged at a temperature of between 95° C. and 125° C. for a period of between 0.5 and 2 hours.

11) The method of claim 1 or 5 wherein drying takes place at a temperature of between 85° C. and 250° C.

12) A modified alumina produced according to the method of any one of claims 1 to 11.

13) A modified alumina including at least one of the following characteristics, preferably more than one of the following characteristics and most preferably all of the following characteristics after dispersion at a pH of 8 or above: i) an isoelectric point of at a pH of less than 4; ii) a dispersibility of greater than 90% when dispersed at a loading of 5, 10 or 20% into a basic solutions; iii) a particle size distribution having a D50 below 250 nm when dispersed at a loading of 5, 10 or 20% into a basic solutions; and/or, preferably and iv) a viscosity of less than 50 cP at 500 s.sup.−1.

Description

FIGURES

[0074] FIGS. 1-3 show results of time dependent viscosity of modified alumina materials as compared with other high pH dispersible materials.

ANALYTICAL METHODS

[0075] The properties of the products of the present invention are measured by the following analytical techniques.

[0076] The alumina is identified using X-ray analyses. The samples are placed into an XRD 2″ diameter plastic disc with a 1″ diameter opening. XRD data is acquired on a Bruker AXS D4-ENDEAVOR apparatus. Boehmite and pseudoboehmite, aluminum oxide, aluminum hydroxide, or mixtures are identified by X-ray diffraction as described in the A.S.T.M. X-ray Diffraction Index. The boehmite single particle crystallite sizes are obtained by XRD diffraction technique by X-ray diffraction peaks by using the Debye formula. Crystal sizes are expressed by the length obtained for diffraction peak, the 120 peak. Analysis of peak-width on X-ray powder diffraction peaks at 120 gives the values commonly reported for crystallites size.

[0077] Boehmite crystallite size by X-ray diffraction measured 120 crystal size is normal 90° to the 120 plane. This peak (crystal plane) is the most accessible in Boehmite's X-ray diffraction pattern and has been used for the characterization of the alumina.

[0078] The particle size of the dispersed alumina is determined using a Horiba instrument.

[0079] The surface area values are determined by N2 adsorption. Data is collected on heat treated samples at 550° C. for 3 hours. The samples are then degassed for 0.5 hours under flowing nitrogen at 300° C. Data is collected on a Quantachrome Apparatus. The surface area (m.sup.2/g) is evaluated using the B.E.T. equation.

[0080] The isoelectric point values are determined using a Malvern Zetasizer. A dispersion of the material is produced at ca. 1 wt. % solids and a pH of 10. An aliquot is injected into a capillary cell and a zetapotential measurement carried out on the instrument. The pH of the solution is titrated down 0.5 pH units at a time until a pH of 3 is reached. The isoelectric point is the pH at which the zetapotential crosses the X axis.

[0081] The dispersibility of an alumina dispersion is evaluated by producing a slurry at the indicated weight loading and pH (e.g. 5 wt. % at pH 10) and stirring for 30 minutes. The slurry is then centrifuged at 1600 rpm for 20 mins.

[0082] The viscosity of the dispersions is measured at the indicated concentrations, by transferring an aliquot of the dispersion into the concentric cylinder geometry of a TA instrument DHR 2 rheometer maintained at 25° C. A shear sweep is run from 0.1 to 3600 s.sup.−1.

[0083] To more fully illustrate the present invention, the following non-limiting examples are presented.

EXAMPLES

Example 1

[0084] Boehmite alumina slurry was aged for 2.5 hours at 140° C. under autogenous pressure to achieve the desired crystallite size of 114 Å. The slurry was discharged from the reactor and portioned to provide identical batches.

[0085] A phosphono group containing modifier, trade name, Cublen P50 was diluted to 10% active using deionized water and added to the alumina slurry whilst stirring at 5 wt. % on an Al.sub.2O.sub.3 basis. The slurry was stirred for 30 minutes and then dried on a Buchi 290 spray dryer.

Example 2

[0086] The alumina slurry prepared as in Example 1 was modified using 7 wt. % Cublen P50 and dried using a Buchi B290 dryer.

Example 3

[0087] The alumina slurry prepared as in Example 1 was modified using 5 wt. % Cublen P50 and recharged into the reactor where it was aged for 1 hours at 105° C. and dried on a Buchi B290 drier.

Comparative Example 1

[0088] The alumina slurry prepared as in Example 1 was modified using 5 wt. % citric acid on an Al.sub.2O.sub.3 basis, aged at 105° C. for 1 hour and spray dried.

Comparative Example 2

[0089] The alumina slurry prepared as in Example 1 was modified using 5 wt. % citric acid on an Al.sub.2O.sub.3 basis, aged at 105° C. for 1 hour and spray dried. Malonic acid was then added as per the prior art.

Comparative Example 3

[0090] The alumina slurry as prepared as in Example 1 was doped with 1.5 wt. % nitric acid on and Al.sub.2O.sub.3 basis and spray dried.

Comparative Example 4

[0091] Unmodified alumina was used as a control.

[0092] The dispersibility of modified alumina of the present invention and the comparative examples are shown in Table 1, with the viscosities shown in FIGS. 1-3.

TABLE-US-00001 TABLE 1 Dispersibilities of modified materials: wt. % % Viscosity of Crystal Modifier dispersibility 10% sol at pH Size A added pH 10 10 (Pa .Math. S) Example 1 114 3 93 1.32 × 10e−3 Example 2 114 7 90 1.36 × 10e−3 Example 3 114 5 96 1.85 × 10e−3 Comparative 114 5 96 0.027 Example 1 Comparative 114 5 95 0.010 Example 2 Comparative 114 1.5 Gelled 0.147 Example 3 Comparative 114 0  0 1.17 × 10e−3 Example 4* *Sample did not disperse, and fell out of suspension once agitation was removed.

[0093] As can be seen, the modified alumina(s) of the present invention is highly dispersible at a pH of 10 with moderately low loadings of the phosphono group containing modifier. The dispersibility of the modified alumina of the present invention is similar to that of the Citric acid modified materials, however the viscosity of the materials when dispersed at 5, 10 and 20 wt. % is substantially different (FIGS. 1-3). The unmodified and acid modifier materials are not as dispersible under high pH conditions and would not be effective.