EP2702107A1

EP2702107A1 - Silicon dioxide powder having large pore length

Info

Publication number: EP2702107A1
Application number: EP12706802.1A
Authority: EP
Inventors: Frank Menzel; Michael Hagemann; Andreas Hille; Arkadi Maisels
Original assignee: Evonik Degussa GmbH
Current assignee: Evonik Operations GmbH
Priority date: 2011-04-27
Filing date: 2012-02-21
Publication date: 2014-03-05
Also published as: ES2693907T3; EP3156459A1; JP5823026B2; DE102011017587A1; CN104961136A; CN103476876A; US20140030525A1; WO2012146405A1; EP3156459B1; PL3156459T3; KR101544299B1; CN104961136B; CN103476876B; JP2014518833A; UA112439C2; KR20140006975A

Abstract

The invention relates to silicon dioxide powder in the form of aggregated primary particles, having a specific pore length L of 2.5 x 10⁵ to 4 x 10⁵ m/pg, wherein L is defined as the quotient from the square of the BET surface and the cumulative pore volume of 2 to 50 nm, which volume is determined by the BJH method, according to the formula L = (BET x BET)/BJH volume. The invention also relates to silanized silicon dioxide powder in the form of aggregated primary particles, having a specific pore length L of 2 x 10⁵ to 3.5 x 10⁵ m/pg, wherein the surface of the aggregates or parts thereof is/are coated with chemically bound silyl groups. The invention further relates to a thermal insulation material comprising the silicon dioxide powder and/or the silanized silicon dioxide powder.

Description

Silica powder with a large pore length

The invention relates to a silica powder and a silanized

Silica powder and its preparation. The invention further relates to a heat insulating material containing these silica powder. The flame hydrolysis for the production of silica is a long-known, industrially carried out process. In this method, a vaporized or gaseous hydrolyzable silicon halide is reacted with a flame formed by combustion of hydrogen and an oxygen-containing gas. The combustion flame thereby provides water for the hydrolysis of the silicon halide and sufficient heat for the hydrolysis reaction. A silica produced in this way is called fumed silica.

In this process, primary particles are initially formed, which are almost free of internal pores. These primary particles fuse during the process via so-called "sintering necks" into aggregates that are macroporous due to their three-dimensional, open structure.

Due to this structure, fumed silica powders are ideal thermal insulators because the aggregate structure provides sufficient mechanical stability, minimizes heat transfer through solid-state conductivity through the "sintered necks", and produces sufficiently high porosity Convection minimized.

The technical problem of the present invention was a

To provide silica powder, which can be expected due to its structure improved thermal insulation properties. Another object was to provide a method of making this

Silica powder. The invention relates to a silica powder in the form of aggregated primary particles, which has a specific pore length L of 2.5 × 10 ⁵ to

4 x 10 ⁵ m / pg, preferably 2.8 to 3.5 x 10 ⁵ m / pg, where L is defined as the quotient of the square of the BET surface area and the cumulative pore volume determined by the BJH method from 2 to 50 nm, according to the formula L = (BET x BET) / BJH volume.

The primary particles are largely spherical, their surface smooth and they have only a small number of micropores. They are fused over Sinterhälse firmly to aggregates. The aggregates form three-dimensional, open, the microporosity-determining structures.

Due to the feedstocks or the production process, the powder according to the invention may have small amounts of impurities. As a rule, the content of S 10 O 2 is at least 99% by weight, preferably at least

99.5% by weight. The BET surface area of the silica particles of the present invention is not limited. In general, the BET surface area is 200 m ² / g to 1000 m ² / g. In a particular embodiment, the BET surface area of the

Silica powder 400 to 600 m ² / g, more preferably, a BET surface area of 450 to 550 m ² / g.

Furthermore, it may be advantageous if by means of the BJH method

certain cumulative volumes of the pores from 2 to 50 nm of the

Silica powder has a value of 0.7 to 0.9 cm ³ / g, particularly preferably 0.80 to 0.85 cm ³ / g.

In a further embodiment of the invention, the silica powder has a micropore volume determined by means of t-plot of 0.030 to 0.1 cm ³ / g, preferably 0.035 to 0.070 cm ³ / g.

The mean pore size of the silica powder is preferably 6 to 9 nm. The median value of the number distribution of the primary particle diameter D ₅₀ is preferably 4 to 6 nm and the 90% range of the number distribution of the primary particle diameter 1, 5 to 15 nm.

Another object of the invention is a process for preparing the silica powder according to the invention, in which igniting a gas mixture containing an oxidizable and / or hydrolyzable silicon compound, hydrogen and an oxygen-containing gas 1, preferably air 1, in a burner and the flame in a reaction chamber burns into the reaction chamber in addition oxygen-containing gas 2, preferably air 2, are, then optionally treated the resulting solid with steam, separated from gaseous substances, with the proviso that

a) in the burner

the quotient I from the supplied amount of oxygen and stoichiometrically required amount of oxygen 2 to 4 and

the quotient II from supplied amount of hydrogen and

Stoichiometrically required amount of hydrogen 0.70 to 1.30 and the outflow velocity v of the gas mixture from the burner 10 to 100 ms ^"1 , preferably 30 to 60 ms ^{" 1}

b) in the reaction space,

the quotient III from a total amount of oxygen and stoichiometrically required amount of oxygen 2 to 4 and

the quotient III / quotient I is 1, 1 to 1, 5.

It is essential that the quantities of starting material defined by the quotients and their ratio, together with a high outflow rate, be maintained in order to obtain the silica powder according to the invention.

In a particular embodiment, the inventive method is carried out so that

Quotient I = 2.20 to 3.00, particularly preferably 2.30 to 2.80,

Quotient II = 0.80 to 0.95, particularly preferably 0.85 to 0.90, Quotient III = 2.50 to 3.80, more preferably 3.00 to 3.45, and

v = 30 to 60 ms ^"1 .

In a further embodiment

Quotient I = 2.20 to 3.00, particularly preferably 2.30 to 2.80,

Quotient II = 1, 00 to 1, 30, particularly preferably 1, 03 to 1, 20,

Quotient III = 2.50 to 3.80, more preferably 3.00 to 3.45, and

v = 30 to 60 ms ^"1 .

The stoichiometrically required amount of oxygen is defined as the

Amount of oxygen required to convert at least the silicon compounds into silicon dioxide and to react any remaining hydrogen.

The stoichiometrically required amount of hydrogen is defined as the

Amount of hydrogen required to be at least that in the

Silicon compounds to convert chlorine to hydrogen chloride. As the silicon compound, at least one selected from the group consisting of SiCl ₄ , CH ₃ SiCl ₃ , (CH ₃ ) ₂ SiCl ₂ , (CH ₃ ) ₃ SiCl, HSiCl ₃ , H ₂ SiCl ₂ H ₃ SiCl (CH ₃ ) ₂ HSiCl , CH ₃ C ₂ H ₅ SiCl _2, (nC ₃ H ₇₎ SiCl ₃ and (H ₃ C) _x Cl _3-x SiSi (CH ₃₎ _y Cl _3-y with R = CH ₃ and x + y = 2 to 6 are used. It is particularly preferable to use SiCl ₄ or a mixture of SiCl ₄ and CH ₃ SiCl ₃ . After separation of gaseous substances, the silica powder can be treated with steam. This treatment serves primarily to remove the chloride-containing groups possibly adhering to the surface of the particles when using chlorine-containing starting materials. At the same time, this treatment reduces the number of agglomerates. The process can be carried out continuously by treating the powder with water vapor, optionally together with air, in cocurrent or countercurrent. The temperature at which the steam treatment takes place is between 250 and 750 ° C, with values of 450 to 550 ° C being preferred. Another object of the invention is a silanized silica powder in the form of aggregated primary particles having a specific pore length L of 2 x 10 ⁵ to 3.5 x 10 ⁵ m / pg, preferably 2.5 to 3.2 x 10 ⁵ m / pg, wherein L is defined as the quotient of the square of the BET surface area and the cumulative pore volume determined by the BJH method of 2 to 50 nm, according to the formula L = (BET x BET) / BJH volume and in which the surface of the Aggregates or parts thereof with chemically bonded silyl groups, preferably with linear and / or branched alkylsilyl groups, particularly preferably with 1 to 20 carbon atoms, are occupied. The specific surface area of the silanized silica powder may preferably be more than 400 to 550 m ² / g. The carbon content is usually 0, 1 to 10 wt .-% and preferably 0.5 to 5 wt .-%, each based on the silanized silica powder.

Another object of the invention is a method for producing the silanized silica powder, wherein the inventive

Sprayed silica powder with one or more, optionally dissolved in an organic solvent silanization and then thermally treated the mixture, preferably at a temperature of 120 to 400 ° C over a period of 0.5 to 8 hours, optionally under inert gas. The surface modification agent is preferably selected from the group consisting of hexamethyldisilazane, dimethyldimethoxysilane, dimethyldiethoxysilane, trimethylmethoxysilane, methyltrimethoxysilane,

Butyltrimethoxysilane, dimethyldichlorosilane, trimethylchlorosilane and / or silicone oils selected. Another object of the invention is a thermal insulation material, which comprises the inventive silica powder and / or the silanized

Contains silica powder. Furthermore, the thermal insulation material

Contain opacifiers and / or binders. Furthermore, the use of the silica powder or the silanized silica powder as a filler in rubber, silicone rubber and

Plastics, for adjusting rheology in paints and varnishes, as a carrier for catalysts and as an ingredient in ink-receiving media

Subject of the invention.

Examples

Analytical determinations

The BET surface area is determined according to DIN ISO 9277. BJH methods and t-plot methods are described in DIN 66134 and DIN 66135. In the process, the layer thickness equation is used for the t-plot method

t = (26.6818 / (0.0124806-log (p / p ₀ ))) ⁰ ' ⁴ , with p = gas pressure and

Po = saturation vapor pressure of the adsorptive at the measurement temperature, both with the unit Pa.

The primary particle diameters are determined using a Zeiss particle size analyzer TGZ 3 from analysis of TEM images taken with a Hitachi (H 7500) and a CCD camera from the company SIS (MegaView II). The image magnification for evaluation is 30000: 1 with a pixel density of 3.2 nm. The number of particles evaluated is approximately 10000. The preparation is carried out in accordance with ASTM 3849-89. Example 1: 12 kg / h of silicon tetrachloride are vaporized and transferred by means of nitrogen into the mixing chamber of a burner. At the same time 35 Nm ³ / h of hydrogen and 190 Nm ³ / h of air 1 are added to the mixing chamber. The mixture is ignited and burned in a flame into a reaction chamber. The exit velocity from the burner is 53.0 ms ^-1 . In addition, 50 Nm ³ / h of air 2 are introduced into the reaction chamber

Reaction gases and the resulting silica are sucked by applying a negative pressure through a cooling system and thereby cooled to values between 100 and 160 ° C. In a filter or cyclone, the solid is separated from the exhaust gas stream and subsequently treated at a temperature of 560 ° C with steam. Example 2 is carried out analogously to Example 1, but 30.7 Nm ³ / h of hydrogen and 168 Nm ³ / h of air 1 are added to the mixing chamber. The

Exit velocity from the burner is 47.2 ms ^"1 .

Example 3 is carried out analogously to Example 1, but 26 Nm ³ / h of hydrogen and 170 Nm ³ / h of air are added to the mixing chamber. The

Exit velocity from the burner is 46.6 ms ^"1 .

Table 1 shows the starting materials and the quantities calculated therefrom. The physicochemical values of the obtained

Silica powders are shown in Table 2. As comparative examples, the silica powder AEROSIL ^® 300 commercially available are used (C1) and AEROSIL ^® 380 (C2), both Evonik Degussa; Cab-O-Sil EH5 ^® (C3), Cabot; REOLOSIL QS 30 (C4), and Tokuyama HDK ^® 40 (C5), Wacker.

The calculation of the quotients I-III shall be shown for example 1. The underlying reaction equation is:

SiCl ₄ + 2 H ₂ + O 2 -> SiO ₂ + 4 HCl.

So 2 moles of hydrogen and 1 mole of oxygen are needed per mole of SiCl ₄ . 1 12.0 kg (0.659 kmol) SiCl ₄ are burned with 35 Nm ^{3 of} hydrogen and 190 Nm ^{3 of} air, corresponding to 39.9 Nm ^{3 of} oxygen.

Accordingly, the stoichiometrically required hydrogen demand is 2 x 0.659 kmol = 1, 318 kmol = 29.54 Nm ³ hydrogen. Thus, quotient II is 35 / 29.54 = 1.18.

The stoichiometric oxygen demand is increasing

Fraction (a) needed to form the silica, and

Portion (b) needed to transfer excess hydrogen to water together. It is calculated as follows for the above example: fraction a): formation of SiO ₂ = 0.659 kmol = 14.77 Nm ³ O ₂

Part b): H ₂ O from the amount of hydrogen not reacted with SiCl ₄ : 35 Nm ³ H ₂ - 29.54 Nm ³ H ₂ = 5.46 Nm ³ H ₂ unreacted

According to H ₂ + 0.5 O ₂ -> H ₂ O, an amount of 5.46 / 2 = 2.23 Nm ³ O _{2 is} required. Stoichiometric oxygen demand = proportions (a + b) = (14.77 + 2.23) Nm ³ 0 ₂ = 17 Nm ³ 0 ₂ . This results in quotient I being used at (190 * 0.21) Nm ³ 0 ₂ /

17 Nm ³ 0 ₂ needed to 2,70.

In the method according to the invention is additionally air in the

Reaction chamber introduced. As a result, the stoichiometric oxygen demand does not change. The quotient III is calculated from the total amount of oxygen introduced, burner plus reaction space, from (190 + 50) * 0.21 Nm ³ 0 ₂ used / 17 Nm ³ 0 ₂ needed at 3.41 and the ratio lll / l to 1, 26th

FIG. 1 shows the pore length of the silica powders 1 to 3 according to the invention and the comparative examples C1 to C5. It can be seen the significantly larger pore length of the silica powder according to the invention.

Table 1: Starting materials and conditions of use

Example 1 2 3

SiCU kg / h 1 12.0 1 12.0 1 12.0

H ₂ Nm ³ / h 35.0 30.7 26.0

Air 1 Nm ³ / h 190.0 168.0 170.0

Air 2 Nm ³ / h 50.0 50.0 50.0

V ms ^"1 53.0 47.2 46.6

quotient

I 2,70 2,39 2,42

II 1, 18 1, 04 0.88

III 3.41 3, 10 3, 13 lll / l 1, 26 1, 30 1, 29 Table 2: Physicochemical properties

2-50 nm; & Number distribution; n.d. = not determined

Claims

claims

1 . Silica powder in the form of aggregated primary particles,

characterized in that it has a specific pore length L of 2.5 x 10 ⁵ to 4 x 10 ⁵ m / pg, where L is defined as the quotient of the square of the BET surface area and the cumulative one determined by the BJH method Pore volume from 2 to 50 nm, according to the formula L = (BET x BET) / BJH volume.

2. Silica powder according to claim 1, characterized in that the BET surface area is 400 to 600 m ² / g.

3. silica powder according to claims 1 or 2, characterized

characterized in that the cumulative volume of the pores of 2 to 50 nm determined by the BJH method is 0.7 to 0.9 cm ³ / g.

4. Silica powder according to claims 1 to 3, characterized

in that the micropore volume determined by means of t-plot is 0.030 to 0.10 cm ³ / g.

5. A method for producing the silica powder according to

Claims 1 to 4, characterized in that one comprises a gas mixture containing an oxidizable and / or hydrolyzable

Silicon compounds, hydrogen and an oxygen-containing gas 1 ignited in a burner and burns the flame into a reaction chamber in the reaction chamber additionally oxygen-containing gas 2, then optionally treated the resulting solid with steam, separated from gaseous substances, it being true that

a) in the burner

the quotient I from supplied amount of oxygen and

stoichiometrically required oxygen amount 2 to 4 and

the quotient II from supplied amount of hydrogen and

stoichiometrically required amount of hydrogen 0.70 to 1, 30 and the outflow velocity v of the gas mixture from the burner 10 to 100 ms ^"1 , preferably 30 to 60 ms ^{" 1} is

b) in the reaction space,

the quotient III from a total supplied amount of oxygen and stoichiometrically required oxygen amount 2 to 4 and

the quotient III / quotient I is 1, 1 to 1, 5.

6. The method according to claim 5, characterized in that the following applies:

Quotient I = 2.20 to 3.00, quotient II = 0.80 to 0.95, quotient III = 2.50 to 3.80, v = 30 to 60 ms ^"1 .

7. The method according to claim 5, characterized in that the following applies:

Quotient I = 2.20 to 3.00, quotient II = 1.00 to 1.30, quotient III = 2.50 to 3.80, v = 30 to 60 ms ^"1 .

8. The method according to claims 5 to 7, characterized in that at least one silicon compound selected from the group consisting of SiCl ₄ , CH ₃ SiCl ₃ , (CH ₃ ) ₂ SiCl ₂ , (CH ₃ ) ₃ SiCl, HSiCl ₃ , H ₂ SiCl ₂ H ₃ SiCl (CH ₃₎ ₂ HSiCl, CH ₃ C ₂ H ₅ SiCl _2, (nC ₃ H ₇₎ SiCl ₃ and (H ₃ C) _x Cl _3-x SiSi (CH ₃₎ _y Cl _3-y with R = CH ₃ and x + y = 2 to 6 is used.

9. Silanized silica powder in the form of aggregated primary particles, characterized in that it has a specific pore length L of

2 × 10 ⁵ to 3.5 × 10 ⁵ m / pg, where L is defined as the quotient of the square of the BET surface area and the cumulative pore volume of 2 to 50 nm determined by the BJH method, according to Formula L = (BET x BET) / BJH volume and in which the surface of the aggregates or parts thereof are coated with chemically bonded silyl groups.

10. A silica powder according to claim 9, characterized in that the BET surface area is 400 to 550 m ² / g.

1 1. Heat insulating material containing the silica powder according to

Claims 1 to 4 and / or the silanized silica powder according to claims 9 or 10.

12. Use of the silica powder according to claims 1 to 4 or the silanised silica powder according to claims 9 or 10 as

A filler in rubber, silicone rubber and plastics, for adjusting rheology in paints and varnishes, as a carrier for catalysts and as an ingredient in ink-receiving media.