JPWO2020072607A5 - - Google Patents

Description

The present invention relates to method(s) of manufacturing surface modified alumina. In particular, the present invention relates to a method for producing surface-modified alumina that is dispersible at pH 8 or higher and has low viscosity at pH 8 or higher. The present invention also extends to modified aluminas produced according to the method of the present invention, and modified aluminas having unique characteristics.

Alumina modified with citric acid is well known to produce a dispersed modified alumina at a pH of 8 or higher. However, the problem with these citric acid modified aluminas is that at pH's above 8, the viscosity of these materials increases rapidly to the point that they become difficult to process.

To address this problem, a second carboxylic acid is required, such as malonic acid. The addition of malonic acid reduces the viscosity of citric acid-modified alumina at pHs above 8.

Although this solution is effective, it requires the use of a second modifier and substantially increases the amount of modifier added. This is the case, for example, in ceramics, where additional modifiers can create potential complications during the formation and burnout stages of manufacturing, and the potential to introduce undesirable interactions with other components of the system. May be harmful for some applications.

The aim of the invention is to overcome the disadvantages presented by what is known in the art.

The inventors have surprisingly been able to produce modified aluminas that are dispersible at pHs above 8 and have low viscosity at pHs above 8, as well as having low loadings of modifiers. We have discovered a new method to modify the surface of alumina.

According to one aspect of the invention;
A method of making a modified alumina is provided that includes the steps of: i) providing alumina; and ii) adding a phosphono group-containing modifier to the alumina to produce a surface-modified alumina.

The present invention can further include drying the surface-modified alumina after adding the phosphono group-containing modifier.

Further, the present invention:
a) a further step of aging the alumina prior to addition of the phosphono group-containing modifier to form a aged alumina having a crystallite size of 35 to 450 Å (measured in 120 planes); or b) a further step of aging the surface-modified alumina to form a mature surface-modified alumina; or c) a) and b) above.
can include.

The present invention can include a ripening step as in either (a) or b) above, and a drying step, or both a ripening step and a drying step as in c) above.

therefore:
The first option of the first aspect of the invention is:
i) preparing alumina;
ii) aging the alumina by hydrothermal treatment until the alumina has a crystallite size of 35 to 450 Å (measured on 120 planes) to form a aged alumina;
iii) adding a phosphono group-containing modifier to aged alumina to produce a surface-modified alumina; and iv) optionally drying the surface-modified alumina to produce a modified alumina;
This is a method for producing modified alumina that includes a process.

The second option of the first aspect of the invention is:
i) preparing alumina;
ii) adding a phosphono group-containing modifier to alumina to produce surface-modified alumina;
iii) aging the surface-modified alumina by heat treating the surface-modified alumina (preferably at elevated temperatures under autogenic pressure) to form a mature surface-modified alumina; and iv) optionally aging . Drying surface-modified alumina to produce modified alumina;
This is a method for producing modified alumina that includes a process.

A third option of the first aspect of the invention is:
i) preparing alumina;
ii) aging the alumina by hydrothermal aging until the alumina has a crystallite size of 35 to 450 Å (measured on 120 planes) to form a aged alumina;
iii) adding a phosphono group-containing modifier to alumina to produce surface-modified alumina;
iv) aging the surface-modified alumina by heat treating the surface-modified alumina (preferably at elevated temperatures under autogenous pressure) to form a mature surface-modified alumina; and v) optionally aging the surface-modified alumina. to produce modified alumina;
This is a method for producing modified alumina that includes a process.

All selections of the first aspect of the invention preferably include a drying step.

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

According to a third aspect of the present invention, there is provided a modified alumina comprising at least one, preferably more than one, and most preferably all of the following characteristics after dispersion at a pH of 8 or higher:
i) isoelectric point at pH below 4;
ii) dispersibility higher than 90% when dispersed in basic solutions at loadings of 5, 10 or 20% by weight;
iii) a particle size distribution with a D ₅₀ of less than 250 nm when dispersed in a basic solution at a loading of 5, 10 or 20% by weight; and or iv) a viscosity of less than 50 cP at 500 s ⁻¹ .

The isoelectric point is determined by zeta potential measurement starting at a pH of 10 and 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 measurement device including a Horiba 950 and appropriate dilution.

A basic solution for measuring dispersibility and particle size distribution means a solution with a pH of 9 or higher. A suitable basic solution is ammonium hydroxide solution.

Viscosity is measured by transferring an aliquot of the suspension to the concentric cylindrical geometry of a TA instrument DHR2 rheometer maintained at 25°C. The shear sweep operates from 0.1 to 3600 s ⁻¹ .

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

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is directed to a method of producing modified alumina by modifying the surface of the alumina by adding a phosphono group-containing modifier. Optionally, the present invention is directed to producing modified alumina by modifying the surface of alumina or hydrothermally aged alumina by adding a phosphono group-containing modifier. Accordingly, the present invention may include one or more ripening steps. The present invention preferably includes a drying step. Various options for the first aspect of the invention are outlined in Options for the first aspect of the invention. Further, the present invention is directed to modified alumina produced according to the method of the present invention, and to modified alumina having unique characteristics.

Elements of the invention are described below.

Alumina Alumina comprises aluminum oxyhydroxide, aluminum oxide, aluminum hydroxide, or mixtures thereof. The alumina is preferably aluminum oxyhydroxide. The aluminum oxyhydroxide preferably comprises boehmite or pseudoboehmite, and is most preferably boehmite.

The alumina may be in dry particle form, in an aqueous slurry, in an acidified alumina composition, or in a mixture thereof. In a preferred embodiment of the invention, the alumina is included in an aqueous slurry. The aqueous slurry is prepared by adding alumina, preferably boehmite, to at least water.

The alumina to be used by this method has a controlled crystallite size.

In this regard, the alumina of the present invention may comprise particles having an average crystallite size of 30 to 500 Å, preferably 40 to 400 Å, most preferably 80 to 200 Å, as measured by X-ray diffraction in the 120 plane. The crystallite size of alumina 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.

Furthermore, the alumina has a BET surface area of 80 to 300 m ² /g, preferably 120 to 250 m 2 /g.
It can have a BET surface area of m ² /g.

Phosphono Group-Containing Modifier The phosphono group-containing modifier of the present invention comprises an organophosphorus compound, preferably a straight chain or branched alkyl group having from 1 to 20 carbon atoms. The phosphono group-containing modifier also preferably contains at least one carboxyl (COOH) group and has at least one phosphono moiety. The phosphono moiety includes a first phosphono-alkyl carboxylic acid, a second phosphono-alkyl carboxylic acid, a first dicarboxylic acid, a second alkyl dicarboxylic acid, a first phosphono-alkyltricarboxylic acid, a phosphine alkane carboxylic acid, or a mixture 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 phosphono-alkyltricarboxylic acid, or a mixture thereof. The most preferred phosphono group-containing modifier is 2-phosphonobutane-1,2,4-tricarboxylic acid.

The phosphono group-containing modifier is mixed with the alumina so that it is distributed over the alumina surface.

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 present in an amount less than 10% by weight based on alumina, preferably in an amount between 3% and 10% by weight based on alumina, more preferably in an amount less than 8% by weight based on alumina. , and most preferably in an amount between 3% and 8% by weight based on alumina. This proportion is preferably based on alumina in hydrated powder form.

Aging As is well known in the field of the present invention, aging refers to hydrothermal ripening .

Hydrothermal aging of the alumina can be carried out at temperatures between 100 and 200° C. for a period between 0.5 and 4 hours before adding the phosphono group-containing modifier.

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

After addition of the phosphono group-containing modifier, it is preferred to carry out aging at a temperature between 95°C and 125°C for a period between 0.5 and 2 hours.

Drying Process As is well known to those skilled in the art, common methods of manufacturing alumina include a drying process.

The drying process can be by direct or indirect heating methods. These methods can include spray drying, contact drying, pan drying or other drying techniques. In a preferred method, drying is carried out in a spray dryer.

The drying step can be carried out in an inert atmosphere, for example nitrogen, or in air, and depending on which drying method is chosen, drying is carried out between 85°C and 250°C, preferably from 100°C. It can be carried out at a temperature of between about 250°C, most preferably between 105°C and 120°C. Further depending on the drying technique chosen, the person skilled in the art will know how long to dry, and thus the time will vary from a few seconds to 2 to 6 hours.

For example, if drying is carried out using a spray dryer, the drying step is carried out at an exit temperature, preferably from about 100°C to about 120°C, and a residence time of from a few seconds to a few minutes. If a contact dryer is used, the device is heated from the outside with oil circulating inside the housing to the desired temperature, preferably in the range 200°C to 250°C, for a residence time of only a few minutes to several hours. I can do it.

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

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

As a further option, the alumina slurry can first be hydrothermally aged to the desired crystallite size to form a mature alumina slurry, and then a phosphono group-containing modifier can be added to the mature alumina slurry. A further maturation step is then carried out, after the addition of the phosphono group-containing modifier, by heating for a sufficient period of time, preferably from 1 to 4 hours, at a temperature between 95 and 125° C., for example in a closed reaction vessel operated under autogenous pressure. Continued by doing. A drying step may follow.

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

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

drawing:
Figures 1-3 show time-dependent viscosity results for modified alumina materials compared to other high pH dispersive materials.

Analytical Methods The unique properties of the products of the invention were determined using the following analytical techniques.

Alumina is identified using X-ray analysis. The sample is placed in a 2" plastic disk for X-ray diffraction containing a 1" diameter aperture. XDR data are obtained using a Bruker AXS D4-ENDEAVOR instrument. Boehmite and pseudo-boehmite, aluminum oxide, aluminum hydroxide or mixtures are A. S. T. M. Identification is by X-ray diffraction as described in the X-ray diffraction index. The crystallite size of a single particle of boehmite is obtained by the X-ray diffraction technique using the Debye equation according to the X-ray diffraction peaks. The crystal size is expressed by the length obtained for the 120 diffraction peaks. Peak width analysis of the X-ray powder diffraction peaks at 120 gives commonly reported values for crystallite size.

The boehmite crystallite size measured by X-ray diffraction is 90° normal to the 120 plane. This peak (crystal plane) is most commonly obtained in the X-ray diffraction pattern of boehmite and has been used to characterize alumina.

The particle size of the dispersed alumina is measured using a Horiba instrument.

Surface area values are determined by N ₂ adsorption. Data is collected on samples heat treated at 550° C. for 3 hours. The sample is then degassed for 0.5 hour at 300° C. under a stream of nitrogen. Data is collected with Quantachrome Apparatus. The surface area (m ² /g) is B.
E. Evaluate using the T equation.

Isoelectric point values are measured using a Malverm Zetasizer. A dispersion of the material is made at approximately 1% solids by weight and a pH of 10. Aliquots are injected into the capillary cell and zeta potential measurements are taken with this device. The pH of the solution is titrated down by 0.5 pH at a time until a pH of 3 is reached. The isoelectric point is the pH at which the zeta potential intersects the X-axis.

The dispersibility of the alumina-forming dispersion is evaluated by making a slurry at the indicated loading weight and pH (eg, 5% by weight at pH 10) and stirring for 30 minutes. The slurry is then centrifuged at 1600 rpm for 20 minutes.

The viscosity of the dispersion is measured by transferring an aliquot of the dispersion, at the indicated concentration, to the concentric cylindrical geometry of a TA instrument DHR2 rheometer maintained at 25°C. The shear sweep operates from 0.1 to 3600 s ⁻¹ .

In order to more fully illustrate the invention, the following non-limiting examples are provided.

Example 1
The boehmite alumina was aged at 140° C. for 2.5 hours under autogenous pressure to the desired crystallite size of 114 Å. The slurry was removed from the reactor and divided to make identical batches.

A phosphono group-containing modifier, Cublen P50 trade name, was diluted to 10% active using deionized water and stirred at 5% by weight based on Al ₂ O ₃ while being added to the alumina slurry. The slurry was stirred for 30 minutes and dried in 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 B290 dryer.

Example 3
The alumina slurry prepared as in Example 1 was modified using 5% by weight Cublen P50 and put back into the reactor where it was aged for 1 hour at 105°C and
i Dry with B290 dryer.

Comparative example 1
An alumina slurry prepared as in Example 1 was modified using 5% by weight citric acid on Al ₂ O ₃ basis, aged at 105° C. for 1 hour, and spray dried.

Comparative example 2
An alumina slurry prepared as in Example 1 was modified using 5% by weight citric acid on Al ₂ O ₃ basis, aged at 105° C. for 1 hour, and spray dried. Malonic acid was then added as per conventional techniques.

Comparative example 3
An alumina slurry prepared as in Example 1 was doped with 1.5% by weight nitric acid based on Al ₂ O ₃ and spray dried.

Comparative example 4
Unmodified alumina was used as a control.

The dispersibility of the modified alumina of the present invention and the comparative example is shown in Table 1, and the viscosity is shown in Figures 1-3.

As can be seen, the modified alumina(s) of the present invention were highly dispersible at pH 10 with moderately low loadings of phosphono group-containing modifiers. Although the dispersibility of the modified alumina of the present invention is similar to that of the citric acid-modified material, the viscosities of the materials when dispersed at 5, 10, and 20% by weight are substantially different (Figure 1- 3). Unmodified and acid modifier materials are not dispersible or effective under high pH conditions.

Claims (10)

i) providing an alumina, wherein the alumina is aluminum oxyhydroxide; and
ii) Aging the alumina by hydrothermal treatment at a temperature between 100° C. and 200° C. for a period between 0.5 and 4 hours to produce aged alumina having a crystallite size of 35 to 450 Å measured in 120 planes. form, and
iii) A method for producing a modified alumina comprising adding a phosphono group-containing modifier to aged alumina in an amount of less than 10% by weight based on the aged alumina to produce a surface modified alumina. 2. The method of claim 1, further comprising aging the surface-modified alumina by hydrothermally treating the surface -modified alumina to form aged surface-modified alumina. 3. The method of claim 1 or 2, comprising drying the surface-modified alumina or aged surface-modified alumina. 2. The method of claim 1, wherein the phosphono-containing modifier comprises an organophosphorus compound and at least one phosphono moiety with at least one carboxyl (COOH) group. Claims wherein the phosphono moiety comprises a first phosphono-alkyl carboxylic acid, a second phosphono-alkyl carboxylic acid, a first dicarboxylic acid, a second alkyl dicarboxylic acid, a first phosphono-alkyltricarboxylic acid, a phosphine alkane carboxylic acid, or a mixture thereof. The method described in Section 4 . 6. A method according to any one of claims 1, 4 or 5 , wherein the phosphono group-containing modifier is added in an amount between 3% and 10% by weight based on the alumina . 7. The method of claim 6, wherein the phosphono group-containing modifier is added in an amount between 3% and 8% by weight based on alumina. 3. The method of claim 2 , wherein the surface-modified alumina is aged at a temperature between 95<0>C and 125<0>C for a period between 0.5 and 2 hours. 4. A method according to claim 3 , wherein the drying is carried out at a temperature between 85<0>C and 250<0>C. Alumina modified with a phosphono group-containing modifier, wherein the modified alumina, after dispersion at a pH of 8 or higher, has at least one of the following characteristics:
i) isoelectric point at pH below 4;
ii) dispersibility higher than 90% when dispersed in basic solutions at 5, 10 or 20% loading;
iii) a particle size distribution having a D50 of less than 250 nm when dispersed in a basic solution at a loading of 5, 10 or 20%; and/ or
iv) Alumina containing a viscosity of less than 50 cP at 500 s.