EP4669618A1

EP4669618A1 - Aluminum oxide powder and synthesis thereof

Info

Publication number: EP4669618A1
Application number: EP24704436.5A
Authority: EP
Inventors: Joachim Erz; Witold Katerinak; Franz Schmidt; Christian SCHULZE ISFORT
Original assignee: Evonik Operations GmbH
Current assignee: Evonik Operations GmbH
Priority date: 2023-02-21
Filing date: 2024-02-12
Publication date: 2025-12-31
Also published as: MX2025009548A; WO2024175388A1; IL322768A; KR20250153780A; TW202440466A; JP2026504537A; CN120731190A

Abstract

Aluminum oxide powder and method of making, the powder consisting of aggregates of primary particles, characterized in that it has an aggregate particle size distribution with a median aggregate particle size (D50) of 220 nm to 500 nm, preferably of 230 to 400 nm, and more preferably of 250 nm to 300 nm as determined by dynamic light scattering measurement, and it has a BET of 10 m²/g to 100 m²/g.

Description

Aluminum oxide powder and synthesis thereof

Field of the Invention

The invention relates generally to an aluminum oxide powder and a method for making the aluminum oxide.

Background of the Invention

Prior art

It is known to produce aluminum oxide powder by means of pyrogenic processes. Pyrogenic processes include flame hydrolysis, in which an aluminum halide, generally aluminum chloride, is hydrolyzed at high temperatures with the formation of aluminum oxide and hydrochloric acid.

Many possible uses of aluminum oxide powders are known, including applications in the paper industry, and, in particular, in ink-jet papers, as abrasives in dispersions for chemical mechanical polishing in the electronics industry, and as additive for lithium-ion batteries.

Generally, existing aluminum oxide powders with large primary particles are formed by high flame temperatures achieved by using large hydrogen excess in the reaction mixture. See, for example, US8197791B2, JP6147614B2, and DE10360087A1. These patent documents describe the synthesis of aluminum oxides using a pyrogenic process with hydrogen used in an excess of at least above 1.6 times the stoichiometrically required amount. The JP6147614B2 uses hydrogen in an excess of at least above 5. However, the high excess of hydrogen leads to small aggregate particle sizes and a low plant utilization (capacity).

Summary of the Invention

An object of the invention is to provide an aluminum oxide powder with an aggregate particle size distribution that is large. “Large” aggregate particle size distribution means an aggregate particle size distribution having a median particle size (D50) of 220 nm to 500 nm, preferably of 230 to 400 nm, and, more preferably of 250 to 300 nm as determined by dynamic light scattering measurement.

Another object of the invention is to provide an improved pyrogenic process for making the aluminum oxide powder that improves plant utilization and efficiency and reduces the overall carbon dioxide (CO2) footprint of the produced aluminum oxide.

It has been unexpectedly discovered that using a lower hydrogen (H2) excess over the stoichiometrically required amount during the pyrogenic synthesis results in an aluminum oxide powder that has a large aggregate particle size distribution. Specifically, it has been found, that by lowering the hydrogen excess in the reaction mixture during the pyrogenic synthesis, the produced aluminum oxide has significantly larger aggregate particle size distribution than an aluminum oxide produced with a larger hydrogen excess in the reaction mixture. This is rather unique for a pyrogenic aluminum oxide because it is independent from the BET specific surface area of the aluminum oxide. Typically, in existing pyrogenically produced aluminum oxide powders the aggregate particle size distribution shifts to smaller values with increasing BET specific surface area values and vice versa when the BET specific surface area values decrease, then the aggregate particle size distribution shifts to larger values.

Also, the lower hydrogen excess in the synthesis process results in higher plant efficiency and lower carbon dioxide (CO2) footprint of the final product.

Moreover, it has been found that the aluminum oxide obtained by the modified pyrogenic process shows significantly improved properties in coating formulations requiring low moisture and high air permeability.

According to an embodiment, an aluminum oxide powder is provided consisting of aggregates of primary particles. The aluminum oxide powder is characterized in that it has an aggregate particle size distribution with a median aggregate particle size (D50) of 220 nm to 500 nm, preferably of 230 to 400 nm, and more preferably of 250 nm to 300 nm as determined by dynamic light scattering measurement.

The aluminum oxide powder has a BET of 10 m²/g to 100 m²/g, preferably 10 m²/g to 55 m²/g.

The aluminum oxide powder may contain chlorine in an amount of 10 ppm to 3000 ppm.

The aluminum oxide powder is preferably of pyrogenic origin meaning that it is a pyrogenic aluminum oxide powder.

The aluminum oxide powder may be obtained in a pyrogenic process wherein hydrogen is fed in the reaction mixture in an excess of the stoichiometrically required amount for full reaction at a gamma ratio of less than 1.6. According to an embodiment, a process for the production of aluminum oxide powder is provided, the process comprising: feeding vaporized aluminum chloride, hydrogen and air to a mixing chamber; transferring the mixture of aluminum chloride, hydrogen and air into a reaction chamber; igniting the mixture and producing solid aluminum oxide; and separating the aluminum oxide powder, wherein the process is characterized in that the hydrogen is used at a gamma ratio of less than 1.6, preferably 1.0 to 1.3, and, more preferably 1.0 to 1.1.

In an embodiment, the hydrogen is used at a gamma ratio of 1.05, and the solid aluminum powder produced has a D50 of 250 nm to 300 nm and a BET of 10 m²/g to 55 m²/g.

In the process, the aluminum chloride may be first vaporized and the vapor may be transferred by means of a carrier gas to the mixing chamber, the hydrogen and air may be fed separately from the aluminum chloride to the mixing chamber, and the air may be optionally enriched with oxygen and/or optionally pre-heated. The reaction chamber may be a burner with a flame burning inside the reaction chamber. The aluminum oxide powder is separated from the gaseous substances, and then treated with steam and optionally with air.

The process may have a discharge rate of the reaction mixture from the mixing chamber into the reaction chamber of at least 10 m/s, and a lambda ratio from 1 to 5.

The process may further use a secondary gas consisting of air and/or nitrogen which is introduced into the reaction chamber, and preferably may employ a ratio of primary air/secondary gas from 10 to 0.5.

The invention further relates to the use of the aluminum oxide powder produced pyrogenically by the above process as an ink-absorbing substance in ink-jet media or in a dispersion composition for a lithium-ion battery separator coating, or as an additive in a lithium-ion battery anode or cathode active material.

These and other features and advantages of the invention will become apparent to those skilled in the art of the invention from the following detailed description and drawings. Brief Description of the Drawings

Fig. 1 illustrates the aggregate particle size distribution of aluminum oxide powder obtained by a pyrogenic process according to an embodiment of the invention and the aggregate particle size distribution of a conventional aluminum oxide powder.

Fig. 2 provides a simplified schematic diagram of a pyrogenic process for making aluminum oxide according to an embodiment of the invention.

Fig. 3 is a simplified schematic diagram of a lithium-ion battery with a separator coated on both sides thereof with an aluminum oxide coating according to an embodiment of the present invention.

Detailed Description

The aluminum oxide powder of the present invention is a pyrogenically prepared aluminum oxide, also referred to as fumed aluminum oxide powder, or fumed alumina powder. ‘Pyrogenically’ is here to be understood as meaning a powder obtainable by flame hydrolysis or flame oxidation. The powders so prepared consist of aggregates of sintered primary particles, which are formed first during the reaction. The aggregates of the sintered primary particles may also be referred to as secondary particles. A plurality of aggregates may subsequently form agglomerates. Owing to the reaction conditions, pyrogenically prepared powders exhibit only very low surface porosity and hydroxyl groups at the surface of up to 10 OH/nm .

In an embodiment, the aluminum oxide powder may be characterized by: a BET specific surface area of 10 to 100 m²/g and, preferably, 10 to 55 m²/g, and a D50 of 220 nm to 500 nm, preferably of 230 to 400 nm, and, more preferably, of 250 to 300 nm.

The aluminum oxide powder may have a chlorine content in an amount of greater than 10 ppm and less than 3000 ppm.

The aluminum oxide powder may further exhibit a monomodal distribution of the aggregate particle diameters, which means that only one single peak signal is obtained on analysis of the aggregate particle size (or diameter) distribution. The single peak of the monomodal distribution of the aggregate diameters may be between 220 nm to 500 nm, preferably between 230 nm to 400 nm, and, more preferably between 250 nm to 300 nm.

Referring now to figure 2, a pyrogenic process for the synthesis of the aluminum oxide powder is provided. The process comprises vaporizing aluminum chloride (AICI3) in evaporator 7 and feeding the vapors ‘a’ of the aluminum chloride into a mixing chamber 1. The vapors may be transferred into the mixing chamber via an inert gas. Separately from the vapors of the aluminum chloride, combustion gas comprising hydrogen ‘b’ and primary air ‘c’ are introduced into the mixing chamber 1. The air ‘c’ may optionally be enriched with oxygen. The air ‘c’ may optionally be pre-heated before supplied to the mixing chamber 1.

Aluminum oxide particles produced are in the form of aggregated primary particles, wherein the primary particles are free from pores and bear hydroxyl groups on their surface. Hydrochloric acid is formed as a byproduct in the conversion of the aluminum chloride most part of which is removed from the aluminum oxide particles via a steam treatment. Thus, only a very small amount of chlorine stays with the aluminum oxide particles.

Hydrogen b is preferably used in a small excess compared to the theoretical needed for the complete hydrolysis of the aluminum chloride following the equations:

2H₂ + O₂ 2H₂O

2AICI₃+ 3H₂O AI₂O₃ + 6HCI

The ratio of the hydrogen supplied over the stoichiometrically required hydrogen is referred to as a “gamma” ratio.

The ratio of the oxygen supplied over the stoichiometrically required oxygen is referred to as a “lambda” ratio.

The “gamma” and “lambda” ratio itself is commonly known to a person skilled in the art, e.g. as described in LIS8197791 B2.

The oxygen excess which is required for this reaction for full hydrolysis of the aluminum chloride, i.e., the lambda ratio is from greater than 1 to 5. The reaction mixture ‘d’ is fed in a central tube to a burner (inside reaction chamber 2) and ignited. The exit speed of the reaction mixture from the burner may range from 10 m/s to 100 m/s. The flame burns in a water-cooled reaction chamber 2. The reaction gases and solids from the reaction chamber are cooled down in the cooling coils 3 before entering a gas-solid separation unit 4, for example, a cyclone and/or filter.

The aluminum oxide powder that is formed is then separated from the gas in the downstream gas-solid separation unit 4, deposited at the bottom of the gas-solid separation unit 4 (e.g., a cyclone) and collected via a bottom outlet. The powder from 4 is transferred to the deacidification equipment 5 for removing the acid from the powder and the aluminum oxide powder is treated with air and steam which are fed in a counter-current direction inside the equipment 5 at an elevated temperature, for example, of about 700 °C. The temperature may not be limited to the 700 °C but may generally range from 400 °C to 900 °C. The purpose of the treating of the aluminum oxide powder with air and steam at the elevated temperature is to remove chlorine (e.g., HCL, chlorine gas) and adjust the pH value of the powder between a value of 2 to 7. Depending on the particular application intended for the aluminum powder, the powder pH can be adjusted to a particular value within the 2-7 range. The powder is collected in a silo 6 and can be further processed as may be needed, e.g., may be packed. The discharge rate of the reaction mixture from the mixing chamber into the reaction chamber may be at least 10 m/s.

The gamma ratio may be from 0.9 to less than 1.6, preferably from 1.0 to 1.3, and more preferably from 1.0 to 1 .1. A particularly preferred gamma ratio results in a slight excess of hydrogen and may range from greater than 1.0 to 1.1.

A range from 0.2 to 0.6 kg of AlCh/m³ of gas may be used.

In a particular embodiment of the process according to the invention, a secondary gas consisting of air and/or nitrogen can be introduced into the reaction chamber. The ratio primary air/secondary gas preferably has values of from 10 to 0.5. The introduction of a secondary gas can help to avoid caking in the reaction chamber.

The aluminum oxide powder according to the invention combines optimized relationship between aggregate size and BET and can be used in many applications including, for example, as a filler in cosmetic compositions, as an insulating material in electronics, as a catalytically active substance in various reactions, as an ink absorbing substance in ink-jet media, as a ceramic coating, or in lithium-ion battery anode or cathode active material compositions.

The aluminum oxide powder is particularly advantageous in the forming of a dispersion used for the coating of a polyolefin separator of a lithium-ion battery. Figure 3 illustrates a lithium-ion battery generally designated with numeral 300 including a separator made from a membrane 316 and coated with the coating layer 318. The coating layer 318 is formed on both sides of the membrane 316 by applying an aqueous dispersion of the aluminum oxide of the invention. The lithium-ion battery 300 can be used in electronic and electrical apparatuses 400 including, for example, mobile phones, computers (lap top computers, desk top computers, computer pads), electronic watches, key fabs, electric appliances, power tools, vacuum cleaners, electric lawn mowers and electric vehicles. The lithium-ion battery 300 further includes an active cathode material 312 on a cathode plate 310, and an anode active material 322 on an anode plate 320. An electrolyte 324 is placed around the separator and between the anode and cathode active materials 322 and 312.

A method for making a dispersion containing the aluminum oxide may comprise:

- placing in water an aggregated aluminum oxide powder, one amino alcohol having 1-6 carbon atoms, and at least one carboxylic acid from the group comprising dicarboxylic acids and/or hydroxy tricarboxylic acids having from 2 to 7 carbons,

- producing a pre-dispersion by introducing energy in an amount of less than the energy required for the formation of the dispersion (e.g., less than 1000 kJ/m³), and

- then, producing a dispersion by introducing the pre-dispersion in a high energy mill and grinding the pre-dispersion by means of the high-energy mill at a pressure of at least 500 bar.

For example, the pre-dispersion may be formed by introducing an energy into the aqueous slurry of less than 1000 kJ/m^{3 (}kilojoule per cubic meter). In an embodiment, the pre-dispersion may be formed by introducing an energy into the aqueous slurry of 200 kJ/m³ or less.

In an embodiment, the pre-dispersion may be divided into at least two part streams, and these part streams may be placed in a high energy mill under pressure of at least 500 bar, released via a nozzle and allowed to impinge on one another in a gas- or liquid-filled reaction chamber.

The aggregated aluminum oxide may have a BET specific surface area from 10 to 100 m²/g, and more preferably 10 to 55 m²/g.

The amino alcohol may be present in the dispersion in an amount of from 2.5 to 8.0 2 pmol/m ( .mol per square meter) of the aluminum oxide specific surface area. The

2 carboxylic acid may be present in an amount of from 1.0 to 4.0 pmol/m of the aluminum oxide specific surface area.

Introducing energy in the water slurry for producing the pre-dispersion can be effected by using mechanical means. Suitable mechanical means for producing a dispersion, such as e.g. a pre-dispersion as described herein, are generally known in the art and may include, as illustrative but non-limiting examples, stirring, agitating, shaking and/or milling. In particular, shear conditions may be applied for introducing energy in the water slurry.

Suitable devices for the preparation of the pre-dispersion may be, for example, rotor/stator machines or toothed discs.

In a preferred embodiment, the pressure during the high-energy grinding process may be at least 2000 bar. Also, it is noted that it may be advantageous to expose the dispersion to the high-energy grinding process several times.

The invention provides an aqueous dispersion obtainable by the above process. The dispersion may comprise AI2O3 particles in an amount of at least 20 wt% solid content in the total dispersion weight, preferably 40 to 60 wt% and, and more preferably 50 to 60 wt% solid content in the total dispersion with a low viscosity of less than 100 mPas, preferably 100 to 10 mPas and more preferably 60 to 15 mPas. The solid content as this term is used here is the weight percentage of aluminum oxide particles in the dispersion.

The dispersion of the aluminum oxide may preferably have a monomodal particle size distribution with a single peak between 220 nm and 500 nm.

For the application of the ceramic coating for the lithium-ion battery separator, the dispersion may preferably have a basic pH and be free of any components which are hygroscopic such as sodium dihydrogen phosphate or phosphonic acids which are used in some conventional metal oxide dispersions. It has been found that aluminum oxide dispersions with higher basic pH provide improved compatibility with the binder systems used in the coating slurry formulation.

Examples

Analysis

The aggregate particle size distribution is determined by DLS (dynamic light scattering). The BET specific surface area of the particles is determined in accordance with DIN 66131.

Gamma ratio = H2 supplied/stoichiometrically required H2 lambda ratio = O2 supplied/stoichiometrically required O2

Example 1 inventive:

Aluminum chloride (AICI3) is being vaporized and the vapors are transferred into a mixing chamber. Separately from the raw material, combustion gas including hydrogen and primary air are introduced into the mixing chamber. The combustion gas has an excess of 1.02 of hydrogen compared to the theoretical needed for the complete hydrolysis of the AICI3 following the equations: 2H₂ + O₂ 2H₂O 2AICI3+ 3H₂O AI2O3 + 6HCI

The oxygen excess for this reaction for obtaining full hydrolysis of AICI3 is 1.04. Hence, the gamma and lambda ratio values were 1.02 and 1.04 respectively.

The reaction mixture was fed in a central tube to a burner and ignited. The exit speed of the reaction mixture from the burner was 33.7 m/s. The flame burned in a water-cooled reaction chamber. The powder formed was deposited in a downstream cyclone and filter and then treated with air and steam in counter-current at approximately 700°C.

The obtained powder had a BET specific surface area of 45 m²/g. The aggregate particle size distribution obtained by dynamic light scattering is shown in figure 1 and had a D50 value of 260 nm.

Example 2 comparative:

Comparative example 1 was carried out according to the procedure described in example 1 except that the combustion gas had an excess of 2.21 hydrogen compared to the theoretical needed for the complete hydrolysis of the aluminum chloride following the equations:

2H₂ + O₂ 2H₂O

2AICI₃ + 3H₂O AI₂O₃ + 6HCI

The oxygen excess for this reaction for obtaining full hydrolysis of AICI3 was 0.95. The gamma and lambda ratio values for example 2 were 2.21 and 0.95 respectively.

The reaction mixture was fed in a central tube to a burner and ignited. The exit speed of the reaction mixture from the burner was 37.6 m/s. The flame burned in a water-cooled reaction chamber. The powder formed was deposited in a downstream cyclone and filter and then treated with air and steam in counter-current at 700°C.

The obtained powder had a BET specific surface area of 48 m²/g.

The aggregate particle size distribution obtained by dynamic light scattering is shown in figure 1 and had a D50 value of 206 nm.

Measurement of Aggregate size distribution:

Aggregate size distribution is determined via DLS measurement using a SYMPATEC NANOPHOX equipment. For analysis, 20 gr dispersion of 1 wt% aluminum oxide in water is prepared via ultrasound treatment using an ultrasound equipment (Hielscher UP400St, 50% amplitude) for 5 minutes. For accurate measurement using the NANOPHOX, a single scattered light ratio in the range of 20 to 80% is set by diluting between 100 to 500 mg of this as-produced dispersion with distilled water to 2.5 g total amount.

More examples were carried out analogously to example 1, with the key parameters of the reaction condition and the physicochemical values of the produced aluminum oxide powders included in Table 1. Examples 1 , and 3 are working examples according to the invention. Examples 2, and 4 are comparative examples. Table 1 : oxide powders In table 1 *VB is the exit speed from the burner. Also, the gamma and lambda values are based on the core gases of primary air, hydrogen, and inert gas. The concentration (“c”) of AI2O3 in the total gas volume based on the core gases which are all gases which go through the core tube (i.e. , the AICI3 (as gas phase) and the PH2; primary air). All other gases (MH2 and secondary air) are not considered for the concentration of the concentration of the AhCh core. The concentration of the AI2O3 (all) refers to the concentration of the AI2O3 based on the overall gas flows including the MH2 and secondary air. It is noted that the MH2 and secondary air are do not contribute to product changes; only the core gases contribute to the product changes.

Although the invention has been described in reference to only specific examples, it should be understood that the invention is not limited only to the described specific examples. The skilled person after reading the present disclosure would be able to envisage a number of variations of the described examples and other examples that fall within the scope of the invention as defined in the following claims. For example, an element described as employed either alone or in combination with other features in an example may also be used with another combination of features in another example without departing from the scope of the disclosed and claimed invention.

Claims

1. Aluminum oxide powder consisting of aggregates of primary particles, characterized in that it has an aggregate particle size distribution with a median aggregate particle size (D50) of 220 nm to 500 nm, preferably of 230 to 400 nm, and more preferably of 250 nm to 300 nm as determined by dynamic light scattering measurement, and it has a BET of 10 m²/g to 100 m²/g.

2. The aluminum oxide powder of claim 1, further characterized in that, it has a BET of 10 m²/g to 55 m²/g.

3. The aluminum oxide powder of any of the preceding claims, characterized in that it has D50 of 250 nm to 300 nm and BET of 10 m²/g to 55 m²/g.

4. The aluminum oxide powder of any of the preceding claims, further characterized in that it contains chlorine in an amount of greater than 10 ppm and less than 3000 ppm.

5. The aluminum oxide powder of any of the preceding claims, further characterized in that it is a pyrogenic aluminum oxide powder.

6. The aluminum oxide powder of claim 5, further characterized in that it is obtained by a pyrogenic process wherein hydrogen is fed in the reaction mixture in excess of the stoichiometrically required amount for full reaction at a gamma ratio of less than 1.6.

7. A process for the production of aluminum oxide powder according to claim 1, the process comprising: feeding vaporized aluminum chloride, hydrogen and air to a mixing chamber; transferring the mixture of aluminum chloride, hydrogen and air into a reaction chamber; igniting the mixture and producing solid aluminum oxide; and separating the aluminum oxide powder, wherein the process is characterized in that the hydrogen is used at a gamma ratio of less than 1.6, preferably 0.9 to 1.3, and more preferably 1.0 to 1.1.

8. The process of claim 7, characterized in that the hydrogen is used at a gamma ratio of 1.05, and the solid aluminum powder produced has a D50 of 250 nm to 300 nm and a BET of 10 m²/g to 55 m²/g.

9. The process of any of the preceding claims characterized in that the aluminum chloride is first vaporized and the vapor is transferred by means of a carrier gas to the mixing chamber, the hydrogen and air are fed separately from the aluminum chloride to the mixing chamber, the air is optionally enriched with oxygen and/or is optionally pre-heated, the reaction chamber is a burner and the flame burns into the reaction chamber, the aluminum oxide powder is separated from the gaseous substances, and then treated with steam and optionally with air.

10. The process of any of the preceding claims characterized in that the discharge rate of the reaction mixture from the mixing chamber into the reaction chamber is at least 10 m/s, and the lambda ratio is from 1 to 5.

11. The process according to any of the preceding claims, characterized in that a secondary gas consisting of air and/or nitrogen is introduced into the reaction chamber and preferably in that the ratio primary air/secondary gas is from 10 to 0.5.

12. Use of the aluminum oxide powder produced by flame hydrolysis according to any of the preceding claims as an ink-absorbing substance in ink-jet media or in a dispersion composition for a lithium-ion battery separator coating, or as an additive in a lithium-ion battery anode or cathode active material.