RU2815078C2 - Aluminum oxides and methods for production thereof - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: group of inventions relates to a method of producing surface-modified aluminium oxide and surface-modified aluminium oxide. In the method, aluminium oxyhydroxide is provided, a modifier containing a phosphon group is added to aluminium oxyhydroxide to obtain surface-modified aluminium oxide and the surface-modified aluminium oxide is dried after adding a modifier containing a phosphono-group. Surface-modified aluminium oxide has more than one of the following characteristics after dispersion at pH = 8 or higher: isoelectric point at pH less than 4; dispersibility of more than 90% when dispersing with dosage of 5, 10 or 20% by weight in basic solutions; particle size distribution having D₅₀ below 250 nm, when dispersed at dosage of 5, 10 or 20% by weight in basic solutions; and/or viscosity less than 50 cP at 500 s^-1.

EFFECT: obtaining surface-modified aluminium oxide, which is dispersible at pH = 8 and higher and has low viscosity.

11 cl, 3 dwg, 1 tbl, 3 ex

Description

FIELD OF TECHNOLOGY TO WHICH THE INVENTION RELATES

The present invention relates to a method(s) for producing surface-modified alumina. In particular, the present invention relates to a method for producing surface-modified alumina that is dispersible at pH=8 and above and which has low viscosity at pH=8 and above. The present invention relates to a modified alumina obtained according to the method of the present invention, and to a modified alumina having specific characteristics.

BACKGROUND OF THE INVENTION

It is well known that alumina modified with citric acid produces modified alumina which is dispersible at pH=8 and above. However, a problem with such citric acid-modified aluminas is that at pH=8 and above, the viscosity of these materials rapidly increases to a point where processing of these materials becomes difficult.

To solve this problem, the use of a second carboxylic acid, such as malonic acid, is required. The addition of malonic acid reduces the viscosity of citric acid-modified alumina at pH=8 and above.

Although this solution is effective, it requires the use of a second modifier and significantly increases the amount of modifier added. This may be detrimental for some applications, such as ceramics, where the additional modifier may cause difficulties during the molding and firing production steps and may result in undesirable interactions with other components of the system.

The purpose of the present invention is to overcome the disadvantages known in the art.

The inventors have unexpectedly found a new method for modifying the surface of alumina to obtain a modified alumina that is dispersible at pH=8 and above and which has low viscosity at pH=8 and above, and also has a low modifier dosage.

SUMMARY OF THE INVENTION

According to one aspect of the invention, there is provided a method for producing modified alumina, comprising the steps of:

i) provide the presence of aluminum oxide; And

ii) adding a modifier containing a phosphono group to the alumina to obtain surface-modified alumina.

The present invention may include the additional step of drying the surface-modified alumina after adding the phosphono group-containing modifier.

The present invention may also include:

a) an additional step in which the alumina is aged before adding a phosphono group-containing modifier to form aged alumina having crystallites measuring 35-450 Å (as measured on a 120 plane); or

b) an additional step of aging the surface-modified alumina to form aged surface-modified alumina; or

c) steps a) and b) described above.

The present invention may include the aging step described in either a) or b)) above and a drying step, or both the aging steps described in c) above and the drying step.

Thus:

A first embodiment of the first aspect of the present invention is a method for producing modified alumina, comprising the steps of:

i) provide the presence of aluminum oxide;

ii) aging the alumina to form aged alumina by hydrothermal treatment until the alumina has crystallites measuring 35-450 Å (measured on a 120 plane);

iii) adding a phosphono group-containing modifier to the aged alumina to obtain a surface-modified alumina; And

iv) optionally, drying the surface modified alumina to obtain modified alumina.

A second embodiment of the first aspect of the present invention is a method for producing modified alumina, comprising the steps of:

i) provide the presence of aluminum oxide;

ii) adding a phosphono group-containing modifier to the alumina to produce surface-modified alumina;

iii) aging the surface-modified alumina by heat treating the surface-modified alumina (preferably at elevated temperature under autogenous pressure) to form aged surface-modified alumina; And

iv) optionally, drying the aged surface modified alumina to obtain modified alumina.

A third embodiment of the first aspect of the present invention is a method for producing modified alumina, comprising the steps of:

i) provide the presence of aluminum oxide;

ii) aging the alumina to form aged alumina by hydrothermal aging until the alumina has crystallites measuring 35-450 Å (measured on a 120 plane);

iii) adding a phosphono group-containing modifier to the alumina to produce surface-modified alumina;

iv) aging the surface-modified alumina by heat treating the surface-modified alumina (preferably at elevated temperature under autogenous pressure) to form aged surface-modified alumina; And

v) optionally, drying the aged surface modified alumina to obtain modified alumina.

It is preferable to include a drying step in all embodiments of the first aspect of the present invention.

According to a second aspect of the present invention, there is provided a modified alumina produced according to the method of the present invention.

According to a third aspect of the present invention, there is provided a modified alumina having at least one, preferably more than one, most preferably all of the following characteristics after dispersion at pH=8 or higher:

i) isoelectric point at pH less than 4;

ii) dispersibility greater than 90% when dispersing at a dosage of 5, 10 or 20% by weight in the main solution;

iii) a particle size distribution having a D ₅₀ below 250 nm when dispersed at 5, 10 or 20% by weight in stock solutions; and/or

iv) Viscosity less than 50 cP at 500 s ^-1 .

The isoelectric point is measured by measuring electrokinetic potentials starting at pH=10, titrating with acid.

Dispersibility is measured such that the pH of the resulting suspension is maintained above the isoelectric point (IEP) of the material.

Particle size distribution is measured using a light scattering meter including a Horiba 950 and proper dilution.

By basic solution for measuring dispersibility and particle size distribution we mean a solution with a pH of 9 or higher. The preferred stock solution is ammonium hydroxide solution.

Viscosity is measured by transferring an aliquot of the suspension into a concentric cylindrical geometry DHR 2 viscometer with TA means, maintained at 25°C. The shear scan is carried out from 0.1 to 3600 s ^-1 .

The characteristics of the modified alumina defined in the third aspect of the present invention are applicable to the modified alumina of the second aspect of the present invention.

DETAILED DESCRIPTION OF PREFERRED IMPLEMENTATION OPTIONS

The present invention is directed to a method for producing modified alumina by modifying the surface of alumina by adding a phosphono group-containing modifier. Optionally, the present invention is directed to a method for producing modified alumina by modifying the surface of alumina, or hydrothermally aged alumina by adding a phosphono group-containing modifier. The present invention may thus include one or more aging steps. The present invention preferably includes a drying step. Various embodiments of the first aspect of the present invention are described in embodiments of the first aspect of the present invention. The present invention is further directed to a modified alumina produced by the process of the present invention and a modified alumina having specific characteristics.

Elements of the present invention will be described below:

ALUMINIUM OXIDE

Aluminum oxide includes aluminum oxyhydroxide, aluminum oxide, aluminum hydroxide, or mixtures thereof. The aluminum oxide is preferably aluminum oxyhydroxide. The aluminum oxyhydroxide preferably includes boehmite or pseudoboehmite and is most preferably boehmite.

The alumina may be in the form of dry particles included in an aqueous suspension, an oxidized alumina composition, or mixtures thereof. In a preferred embodiment of the present invention, alumina is included in the aqueous suspension. An aqueous suspension is prepared by adding alumina, preferably boehmite, to at least water.

The aluminum oxide to be used in the present method has crystallites of controlled size.

In this regard, the alumina of the present invention may include particles having an average crystallite size of 30 to 500 Å, preferably 40 to 400 Å, most preferably 80 to 200 Å, measured by X-ray diffraction on a 120 plane. Crystallite size aluminum oxide can be modified by including an aging step (hydrothermal aging). This step involves heating the alumina at a temperature between 100 and 200°C for a period of 0.5 to 4 hours until the alumina crystallite size is between 40 and 450 Å.

Additionally, the alumina may have a BET surface area of 80 to 300 m ² /g, preferably a BET surface area of 120 to 250 m ² /g.

MODIFIER CONTAINING A PHOSPHONO GROUP

The phosphono group-containing modifier of the present invention includes an organic phosphorus compound, preferably a linear or branched alkyl group having from 1 to 20 carbon atoms. The phosphono group-containing modifier preferably also contains at least one carboxyl (COOH) group and carries at least one phosphono moiety. The phosphono moiety includes a primary phosphono-alkylcarboxylic acid, a secondary phosphono-alkylcarboxylic acid, a primary dicarboxylic acid, a secondary alkyl-dicarboxylic acid, a primary phosphono-alkyl-tricarboxylic acid, a phosphine-alkane-carboxylic acid, or mixtures thereof. The phosphono moiety is more preferably a primary alkylcarboxylic acid, a secondary phosphonoalkylcarboxylic acid, a primary dicarboxylic acid, a secondary alkyldicarboxylic acid, a primary phosphonoalkyltricarboxylic acid, or a mixture thereof. The most preferred phosphono group-containing modifier is 2-phosphonobutane-1,2,4-tricarboxylic acid.

A modifier containing a phosphono group is mixed with aluminum oxide to distribute it on the surface of the aluminum oxide.

The phosphono group-containing modifier is preferably added to the aqueous alumina slurry or to the aged aqueous alumina slurry.

The phosphono group-containing modifier is added in amounts of less than 10% by weight of alumina, preferably in amounts of between 3% by weight and 10% by weight of alumina, more preferably in amounts of less than 8% by weight of oxide aluminum, and most preferably in amounts between 3% by weight and 8% by weight based on alumina. The percentages are preferably based on alumina in hydrated powder form.

AGING

As is known in the art of the invention, aging refers to hydrothermal aging.

Hydrothermal aging of the alumina can occur before the addition of the phosphono group-containing modifier for a period of time between 0.5 and 4 hours at a temperature between 100 and 200°C.

Alternatively or additionally, aging can be carried out after adding the phosphono group-containing modifier for a period of time between 0.5 and 2 hours at a temperature between 95 and 125°C.

It is preferable to carry out aging after adding the phosphono group-containing modifier for a period of time between 0.5 and 2 hours at a temperature between 95 and 125°C.

DRYING STAGE

As is well known to those skilled in the art, typical processes for producing alumina include a drying step.

The drying step can be carried out through direct and indirect heating methods. These methods may include spray drying, contact drying, tank drying, or other drying technologies. In a preferred method, drying occurs in a spray dryer.

The drying process can take place in an inert atmosphere, for example nitrogen or air, and depending on which drying method is chosen, drying can take place at temperatures between 85°C and 250°C, preferably between 100°C and about 250° C, most preferably between 105°C and 120°C. Additionally, depending on the drying technology chosen, those skilled in the art will know what the drying duration should be, and thus this duration will vary between a few seconds and 2-6 hours.

For example, if drying is performed using a spray dryer, the drying step is performed with an outlet temperature preferably from about 100°C to about 120°C, and a residence time from several seconds to several minutes. If a contact drying device is used, the equipment may be externally heated by oil that circulates within the outer jacket to a target temperature, preferably in the range of 200° C. to 250° C., with a residence time of only a few minutes to several hours.

ILLUSTRATIVE METHODS OF THE INVENTION:

In a first embodiment of the present invention, the phosphono group-containing modifier of the present invention is mixed under moderate conditions of temperature and pressure with an aqueous slurry of alumina. A drying step may then follow.

Alternatively, the aqueous alumina slurry may first be hydrothermally aged to the desired crystallite size to form the aged alumina slurry, and then the phosphono group-containing modifier may be added to the aged alumina slurry. A drying step may then follow.

As an additional option, the alumina slurry may first be hydrothermally aged to the desired crystallite size to form the aged alumina slurry, and then the phosphono group-containing modifier may be added to the aged alumina slurry. Then, after adding the phosphono group-containing modifier, a further aging step follows, for example by heating at a temperature between 95 and 125°C in a closed reactor vessel under autogenous pressure (for example), for a sufficient time, preferably for a period of time between 1 and 4 o'clock. A drying step may then follow.

Drying occurs without the need for any intermediate filtration or washing steps to form modified alumina. Preferably, drying occurs.

The present invention will now be described by way of example with reference to the following examples and figures.

FIGURES:

Fig. 1-3 show the results of the time dependence of the viscosity of modified alumina materials compared to other high pH dispersible materials.

ANALYTICAL METHODS:

The properties of the products of the present invention were measured using the following analytical techniques.

Aluminum oxide was identified using X-ray analysis. Samples were placed in a 2-inch diameter plastic disk with a 1-inch diameter hole in the XRD. XRD data were acquired on a Bruker AXS D4-ENDEAVOR device. Boehmite and pseudoboehmite, alumina, aluminum hydroxide, or mixtures thereof were identified by X-ray diffraction as described in A.S.T.M. X-ray Diffraction Index. The crystallite sizes of individual boehmite particles were obtained by XRD diffraction technology through X-ray diffraction peaks using the Debye formula. Crystal sizes were expressed in terms of the length obtained for the diffraction peak, peak 120. Analysis of the peak widths of the X-ray powder diffraction peaks at 120 gives values typically reported as crystallite size.

The boehmite crystallite size at crystal size 120 measured by x-ray diffraction is perpendicular (90°) to the 120 plane. This peak (crystallographic plane) is the most accessible in the boehmite x-ray diffraction structure and has been used to characterize alumina.

The particle size of the dispersed alumina is determined using Horiba.

Surface area values were determined by N ₂ uptake. Data were collected on heat-treated samples at 550°C for 3 hours. The samples were then degassed for 0.5 hours under a nitrogen stream at 300°C. Data were collected on a Quantachrome device. Surface area ( ^m2 /g) was estimated using the BET equation

Isoelectric point values were determined using the Malvern Zetasizer. The material dispersion was formed at 1% by weight solids and pH=10. An aliquot of the sample was injected into the capillary cell, and an electrokinetic potential measurement was performed on the above-mentioned means. The pH of the solution was titrated down in 0.5 pH increments over time until the pH reached 3. The isoelectric point is the pH at which the electrokinetic potential crosses the X-axis.

The dispersibility of the alumina dispersion was assessed by preparing a suspension at the specified dosage by weight and pH (eg, 5% by weight at pH=10) and stirring for 30 minutes. The suspension was then centrifuged at 1600 vol. min. within 20 minutes.

The viscosity of the dispersions was measured at the indicated concentrations by transferring an aliquot of the dispersion into a concentric cylindrical geometry DHR 2 viscometer with TA, maintained at 25°C. The shear scan was carried out from 0.1 to 3600 s ^-1 .

To more fully illustrate the present invention, the following non-limiting examples are provided.

EXAMPLES:

Example 1

The boehmite-alumina suspension was aged for 2.5 hours at 140°C under autogenous pressure to achieve the required crystallite size of 114 Å. The suspension was poured from the reactor and divided into parts to provide identical portions.

A phosphono-containing modifier, trade name Cublen P50, was diluted to 10% active using deionized water and added to a stirred alumina slurry at 5% by weight based on Al ₂ O ₃ . The suspension was stirred for 30 minutes and then dried on a Buchi 290 spray dryer.

Example 2

The alumina slurry prepared as in Example 1 was modified using 7% by weight Cublen P50 and dried using a Buchi 290 dryer.

Example 3

The alumina slurry prepared as in Example 1 was modified with 5% by weight Cublen P50 and poured into a reactor where it was aged for 1 hour at 105°C and dried on a Buchi 290 dryer.

Comparative Example 1

The alumina slurry prepared as in Example 1 was modified with 5% by weight Al ₂ O ₃ -based citric acid, aged at 105° C. for 1 hour and spray dried.

Comparative Example 2

The alumina slurry prepared as in Example 1 was modified with 5% by weight Al ₂ O ₃ -based citric acid, aged at 105° C. for 1 hour and spray dried. Malonic acid was then added according to the prior art.

Comparative Example 3

To the alumina suspension prepared as in Example 1, 1.5% by weight Al ₂ O ₃ -based nitric acid was added and spray dried.

Comparative Example 4

Unmodified alumina was used as a control sample.

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

Table 1 - dispersibility of modified materials:

Crystal size, Å % by weight of added modifier % dispersibility,
pH 10 Viscosity of 10% sol at pH 10 (Pa*s) Example 1 114 3 93 1.32*10 ^-3 Example 2 114 7 90 1.36*10 ^-3 Example 3 114 5 96 1.85*10 ^-3 Comparative Example 1 114 5 96 0.027 Comparative Example 2 114 5 95 0.010 Comparative Example 3 114 1.5 Gel formation 0.147 Comparative Example 4* 114 0 0 1.17*10 ^-3

* The sample did not disperse and fell out of the suspension after stopping stirring

As can be seen, the modified aluminum oxide(s) of the present invention are highly dispersible at pH=10 with moderately low dosages of phosphono-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 these materials dispersible at 5, 10 and 20% by weight is significantly different (FIGS. 1-3). Unmodified and acid-modified material are not as dispersible under high pH conditions and are ineffective.

Claims (18)

1. A method for producing surface-modified aluminum oxide, including the steps of: i) provide the presence of aluminum oxyhydroxide; And ii) adding a modifier containing a phosphono group to the aluminum oxyhydroxide to obtain surface-modified aluminum oxide; And iii) drying the surface-modified alumina after adding a modifier containing a phosphono group. 2. The method of claim 1, including the additional step of aging the aluminum oxyhydroxide before adding a phosphono group-containing modifier to form aged aluminum oxyhydroxide having crystallites measuring 35-450 Å when measured on a 120 plane. 3. The method of claim 1, including the further step of aging the surface modified alumina to form an aged surface modified alumina, in which case the aged surface modified alumina is dried to form a surface modified oxide. aluminum 4. The method according to any of paragraphs 1-3, including the additional steps of aging the aluminum oxyhydroxide before adding a modifier containing a phosphono group to form an aged aluminum oxyhydroxide having crystallites measuring 35-450 Å when measured on a 120 plane, and aging surface modified alumina to form an aged surface modified alumina, in which case the aged surface modified alumina is dried to form a surface modified alumina. 5. The method of claim 1, wherein the phosphono group-containing modifier includes an organic phosphorus compound and at least one carboxyl group bearing at least one phosphono moiety. 6. The method according to claim 5, in which the phosphono-component includes a primary phosphono-alkylcarboxylic acid, a secondary phosphono-alkylcarboxylic acid, a primary dicarboxylic acid, a secondary alkyl-dicarboxylic acid, a primary phosphono-alkyl-tricarboxylic acid, a phosphine-alkane- carboxylic acid or mixtures thereof. 7. Method according to any one of paragraphs. 1, 5 or 6, wherein the phosphono group-containing modifier is added in amounts of less than 10% by weight based on aluminum oxyhydroxide, preferably in amounts between 3% by weight and 10% by weight based on aluminum oxyhydroxide, more preferably in amounts of less than 8% by weight based on aluminum oxyhydroxide, and most preferably in amounts between 3% by weight and 8% by weight based on aluminum oxyhydroxide. 8. Method according to any one of paragraphs. 1, 2 or 4, in which the aluminum oxyhydroxide is aged at a temperature between 100°C and 200°C for a period of time between 0.5 to 4 hours. 9. Method according to any one of paragraphs. 1, 3 or 4, in which the surface-modified alumina is aged at a temperature between 95°C and 125°C for a period of time between 0.5 and 2 hours. 10. Method according to claim 1, 3 or 4, in which drying occurs at a temperature between 85°C and 250°C. 11. Surface modified alumina having more than one of the following characteristics after dispersion at pH=8 or higher: i) isoelectric point at pH less than 4; ii) dispersibility greater than 90% when dispersing at 5, 10 or 20% by weight in stock solutions; iii) a particle size distribution having a D ₅₀ below 250 nm when dispersed at 5, 10 or 20% by weight in stock solutions; and/or iv) Viscosity less than 50 cP at 500 s ^-1 .

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