EP1317513A1

EP1317513A1 - Method for producing an iron oxide nucleus containing aluminium

Info

Publication number: EP1317513A1
Application number: EP01971964A
Authority: EP
Inventors: Ulrich Meisen
Original assignee: Bayer AG
Current assignee: Lanxess Deutschland GmbH
Priority date: 2000-09-07
Filing date: 2001-08-27
Publication date: 2003-06-11
Also published as: AU2001291799A1; CA2421189A1; WO2002020673A1; DE10044097A1; US20020127176A1; US6508290B2

Abstract

The invention relates to a method for producing an iron oxide nucleus containing aluminium comprising a FeOOH crystal structure made of FeCl2. Said nucleus is suitable as a base material for producing iron oxide yellow and for use as a yellow coloured pigment.

Description

Process for producing an iron oxide seed containing aluminum

The present invention relates to a method for producing an aluminum-containing iron oxide nucleus with an α-FeOOH crystal structure from FeCl ₂ . This germ is suitable as a starting material for the production of iron oxide yellow and for use as a yellow color pigment.

Synthetic iron oxides are usually prepared by the method Laux-, the pen niman- method, the precipitation process, the neutralization process or the roasting process (Ullmann's Encyclopedia of Industrial Chemistry, 5 ^th edition, 1992, volume A20, page 297 ff). The iron oxides thus obtained are generally used as pigments.

Basically, two methods are known for producing fine-particle α-FeOOH (needle width between 5 and 30 nm):

- The so-called acid process

- The so-called alkaline process

In the acidic process, an iron (II) component, i.e. an iron salt dissolved in water, is initially introduced and an alkaline component, usually an alkali or alkaline earth metal compound or ammonia solution dissolved or suspended in water, is metered in with intensive mixing. The amount of alkaline component added is generally between 15% and 70% of the stoichiometrically required amount. After the addition of the alkaline component, the pH is in the weakly acidic range.

After the addition of the alkaline component has ended, an oxidizing agent, usually atmospheric oxygen, is used for the oxidation. The reaction is carried out at temperatures between 20 ° C and 50 ° C. At significantly higher temperatures the risk of undesirable magnetite formation. The end point of the reaction can be recognized by a sharp drop in the pH value and the redox potential. After the reaction has ended, the properties of the product obtained (generally called germ) are determined and, if suitable, this is further processed directly to give the α-FeOOH pigment.

The alkaline process differs from the acid process in the amount of the alkaline component added. In the alkaline process, this is at least 120% of the stoichiometrically required amount, but is generally significantly higher. The temperatures at which this reaction is carried out can be somewhat higher than the temperatures used in the acidic process, since the risk of magnetite formation is lower here.

In principle, the alkaline process gives relatively long-needle α-FeOOH crystallites with a length to width ratio of 10: 1 to 30: 1. Since these crystals are also very low in dendrites, this process is particularly suitable for the production of α-FeOOH as a starting product for magnetic tapes.

For the production of α-FeOOH pigments for use in paints and lacquers, the germs produced by the alkaline process cannot be used directly, or can only be used to a limited extent, since all of the coloring metals present in the Fe component are incorporated in this process. These metals (especially Mn, Cr, Cu, Ni) significantly impair the color properties and thus restrict the use of germs produced in this way as color pigments.

For the production of iron oxide yellow pigments, an α-FeOOH seed is preferably used and this is then coarsened (built up) in acid, which reduces the incorporation of the coloring metals. Furthermore, the build-up may only be carried out at pH values of less than approx. 4, since at higher pH values the coloring metals are incorporated to an increasing extent. Furthermore, the partial the shape of the α-FeOOH, the color properties, the viscosity of the lacquer and the need for binding agents.

In order to achieve a desired low viscosity in the lacquer and a low binder requirement, short-needle α-FeOOH particles are required. These can be produced from long-needle α-FeOOH particles by intensive grinding. A cheaper alternative is the direct production of short-needle α-FeOOH particles.

About the particle shape of the α-FeOOH germ and thus that of the one built up from it

To control pigments in the direction of low length to width ratio, modifying additives are required. The use of B, Al, Ga, Si, Ge, Sn or Pb as seed modifiers is known from US Pat. No. 4,620,879. This patent describes an iron oxide yellow with a particularly low silking index, which is achieved by a corresponding procedure for pigment build-up and by adding the modifiers listed above.

Although the use of FeCl ₂ is described in this patent, precise conditions for producing an α-FeOOH nucleus from FeCl are not mentioned. However, since FeCl ₂ , especially in the nucleation phase, differs significantly from

FeSO differs, the conditions under which a good pigment is obtained with FeSO cannot be transferred to FeCl.

The present invention was based on the object of a method for the simple and inexpensive production of a short-needle α-FeOOH germ after

To provide precipitation processes. In a further step, this c-FeOOH seed is built up to an α-FeOOH pigment.

This object is achieved by the method according to the invention: It is a method for producing aluminum-containing iron oxide nuclei with -

FeOOH crystal structure with an aspect ratio AV of 2100 to 3600 and one BET surface area from 50 to 150 m2 / g. In the present context, the aspect ratio is the product of the BET surface area and the average crystallite size, which was determined by X-ray analysis from the 110 reflex of the α-FeOOH. These very fine-particle 0! -FeOOH seeds can be produced using the following procedure using FeCl ₂ :

a.) To an iron-chloride solution with a total Fe content of 20 - 100 g / 1, preferably 40 - 65 g / 1 and an Fe-ffl content of 0.1 - 10 mol% Fe-DI ( based on total Fe), an AI component in amounts of 4 - 13 mol% based. Fe total given with stirring,

b.) this mixture is heated to a falling temperature between 30 ° C. and 60 ° C., preferably 35-50 degrees,

c.) a precipitant with an active substance content of 2-10

Equivalents per liter, preferably 4-8 equivalents per liter, and the molar ratio Fe + Al to precipitant is 20% - 80%, preferably 30% - 60% of the stoichiometry,

d.) the precipitated suspension is then oxidized with an oxidizing agent at such a rate that the oxidation rate is 2-50 mol% / h, preferably 10-35 mol% / h of the iron to be oxidized and

e.) the Al-containing α-FeOOH nucleus obtained after the oxidation are optionally isolated.

The Al-containing α-FeOOH nucleus obtained after the oxidation can optionally be used without further isolation, after testing the properties, for the production of iron oxide yellow pigments.

The preferred procedure is as follows: Starting chemicals:

FeCl ₂ solution with an Fe content of 55 g / 1 Fe, of which 1.5 mol% Fe-Lπ AlCl solution, NaOH solution with an NaOH content of 300 g / 1 = 7.5 equivalents of NaOH / 1

Al / Fe ratio: 12 - 13 ratio Fe + AI / precipitant: 35 - 40%

Reaction conditions:

Temperature: 44 ° C

Oxidation rate: 30 - 35 mol% Fe-II / h

A1C1 ₃ (as an aqueous solution) is preferably used as Al component. The use of Si or Ti as a seed modifier, in the form of their chlorides, is also possible, but requires a higher technical outlay in production.

NaOH, KOH, Na ₂ CO ₃ , K ₂ CO ₃ , Mg (OH) ₂ , MgO, MgCO ₃ ,

Ca (OH) ₂ , CaO, CaCO, NH or secondary or tertiary aliphatic amines can be used in aqueous solution or aqueous slurry.

Atmospheric oxygen, oxygen, ozone, H ₂ O ₂ , chlorine, nitrates of the alkali or alkaline earth metals or NH NO ₃ are used as oxidizing agents.

If the iron-chloride solution used contains larger amounts at pH values of less than 4 precipitable coloring metals, these can be precipitated by adding an alkaline component to the iron-II-chloride solution up to pH 4. The resulting solid can be separated from the supernatant clear, purified solution by sedimentation, filtration or centrifugation. In addition to the Desired coloring metals are also Fe-HI removed, which significantly undesirably influences the reaction to the α-FeOOH germ (formation of black magnetite).

The reaction is carried out in batch or continuous stirred tanks, in

Stirred tank cascades, loop reactors or stirrerless reactors with two-component nozzles as mixing elements.

After the α-FeOOH nuclei according to the invention have been produced, they are converted into a pigment, which is done by means of coarsening of the nuclei particles known per se (pigment build-up). However, since the α-FeOOH nuclei according to the invention are not used as such, it is necessary to describe the pigment structure to form an iron oxide yellow pigment.

The Al-containing seed produced by the process according to the invention is pumped to a solution of FeCl or FeSO ₄ or another Fe-H salt. 7 - 15 mol of Fe-11 salt as a solution with an Fe content of 30 - 100 g / 1 Fe are added to one mol of FeOOH in the nucleus. Adding higher amounts of Fe-II salt also leads to α-FeOOH yellow pigments, but the brightness decreases with increasing amount of Fe-II salts added, which is generally undesirable.

This suspension is then heated to the reaction temperature, which is between 50 ° C and 90 ° C. After the fall temperature has been reached, oxidation and precipitation are started at the same time. As a rule, atmospheric oxygen is added via a suitable gassing device and the pH of the suspension is regulated with an alkaline precipitant. The pH value is regulated in a range from 2.4 to 4.8. The oxidation rate should be between 0.5 and 8 mol% Fe-iπ / h.

After the reaction has ended (ie when all Fe-11 has been oxidized), the solid formed is separated off by filtration. It is washed salt-free and can then be dried. The yellow pigment produced by this process is characterized by high color purity, almost isometric particle shape, low oil number and high chemical purity. The sum of its properties makes it particularly suitable for:

- Application in the field of paints and varnishes

- Applications as raw material for catalysts

- Food coloring applications

- Applications in the area of paper coloring

- Applications in the field of polymer coloring - Applications as a UV stabilizer

- Applications in the field of high quality building materials (plasters etc.)

- Applications in the field of emulsion paints

This process is particularly economical due to the inexpensive raw materials and the high production rate in yellow pigment production. Due to the special reaction procedure and the use of a precisely specified germ, it is possible to safely produce particularly high-quality yellow pigments, which have application advantages compared to pigments produced by other processes. Environmentally relevant chemicals are not used in the production of the yellow pigments according to the invention.

In the preferred embodiment (use of FeCl ₂ , A1C1 ₃ , NaOH and air as starting materials), an almost closed material cycle is possible by electrolysis of the NaCl obtained as a by-product. The sodium hydroxide solution obtained in this way can be used directly in the process again. The products H ₂ and Cl ₂ formed during chlor-alkali electrolysis can be converted to HC1, which is then used again for pickling the steel sheets. This particularly environmentally friendly technology is currently not possible with FeSO ₄ , since the electrolysis of Na ₂ SO ₄ does not work satisfactorily. Description of the measurement methods used

1. Measurement of the BET surface

The BET surface area is determined according to the so-called 1-point method according to DIN 66131.

90% »He and 10% N ₂ are used as the gas mixture, it is measured at 77.4 K. Before the measurement, the sample is baked at 140 ° C for 60 minutes.

2. X-ray measurement of the crystallite size

The crystallite size is determined on the Phillips powder diffractometer. The 110 reflex is used to determine the crystallite size.

α-iron oxide hydroxide (M (FeOOH) = 88.9 g / mol

2.1 Area of application

Determination of the crystallite size in goethite in the range from 5 to 100 nm.

2.2 basis

The determination in goethite is carried out after X-ray diffractometric irradiation by reflection detection. The evaluation is carried out using silicon as an external standard.

2.3 reagent

Silicon standard for angle calibration (ICDD No. 27-1402), Philips PW 1062/20

2.4 devices 2.4.1 Diffractometer: Philips PW 1800 goniometer

Type: Theta - 2 theta

2.4.2 Sample feed: 21-fold sample changer

2.4.3 Detector: Xe proportional counter tube

2.4.4 Reflex evaluation: X-Pert Software Rev. 1.2 on HP Vectra VL

2.4.5 Agate grater and pestle

2.4.6 Sample holder: Philips PW 1811/00 and PW 1811/27

2.5 X-ray diffractometric conditions

2.5.1 X-ray tube: long fine focus, Cu anode, 60 kV, 2200 W

2.5.2 Radiation: CuKαj, λ = 0.154056 nm

2.5.3 Generator: 40 kV, 40 mA

2.5.4 Scan parameters:

2.5.4.1 Scan Type: Step Scan

2.5.4.2 Step size: 0.020 ° 2theta

2.5.4.3 Step measurement time: 2.00 s 2.5.5 Silicon standard:

2.5.5.1 Starting angle: 27.00 ° 2theta

2.5.5.2 End angle: 30.00 ° 2theta

2.5.6 Sample:

2.5.6.1 Starting angle: 18.50 ° 2theta

2.5.6.2 End angle: 23.50 ° 2theta

2.6 Execution

2.6.1 External standard:

2.6.1.1 Place the silicon standard (2.1) in the sample holder of the diffractometer and start the measurement program.

2.6.1.2 Determine the maximum and the half width of the silicon reflex with the Miller indices hkl = 111 in the 2 theta angle range 27.00 ° to 30.00 °. Print out the peak parameters (Tab. 1) and, if necessary, the diffractogram.

2.6.2 Determination in the sample:

2.6.2.1 Rub about 2 g of sample in the agate drip tray (4.5).

2.6.2.2 Place about 1 g sample in the sample holder (4.6) of the diffractometer and start the measurement program. 2.6.2.3 Determine the maximum and the integral width of the goethite reflex with the Miller indices hkl = 110 in the 2Theta angle range 18.50 ° to 23.50 °. Print out the peak parameters (Tab. 2) and, if necessary, the diffractogram.

2.7 calculations

2.7.1 In the crystallite size determination table (X'Pert

Software, Rev. 1.2, (Philips Analytical GmbH, Kassel, DE) Profile Widths) the integral width (Width of Broadened Profile), the maximum (Peak Position / ⁰ 2Theta) of the goethite reflex as well as the reflective half width (Width of Standard Profile / FWHM) of the silicon standard. Create and print out the evaluation report (Tab. 2).

2.7.2 The crystallite size in the X'Pert program is determined according to the Scherrer equation:

k - λ

^ (Crystallite)

W _S ize • COS0

^ (Crystallite size) crystallite size in nm k form factor of the crystallites = 0.9 (literature mean) λ wavelength in nm w _size integral width of the goethite reflex - reflex half width of the silicon standard cosö maximum of the goethite reflex in ° 2theta

Table 1

Table 2

Table 3

Crystallite size determination via X'Pert program; Scherrer equation Menu item: Additional functions in the X'Pert program section: X'Pert organizer

Anodes - material Cu (copper)

Radiation type Cu Kα

Wavelength (nm) 0.154184

K factor (form factor mean) 0.9000

Intensity ratio Cu Kαj / Cu K ₂ 0.5000

3. Measurement of the color values

The color values are measured as described in EP-A 0911 370. Examples

Example 1: Aluminum-containing germ from FeCl ₂ and AIC1 ₃

In a discontinuous stirred tank with a useful volume of 30 liters, equipped with a three-stage cross-bar stirrer and a gassing device (ring with holes below the stirrer), 14.095 1 FeCl ₂ solution with 55.07 g / 1 Fe and a Fe-rfl content of 1.5 mol were placed -% (based on total Fe). 914 g of AlCl ₃ solution with 5.06% by weight of Al and 3.95% by weight of HC1 were then added.

The FeCl ₂ amount corresponded to 13.9 mol Fe (Fe-fl and Fe-ITI), the AlCl ₃ amount 1.71 mol, the HCl amount 0.989 mol. The Al Fe total ratio accordingly corresponded to 12.3 mol% based on total Fe. This solution was heated to 44 ° C. with stirring and gassing with 300 Nl / h nitrogen. After this temperature had been reached, 1615 ml of sodium hydroxide solution containing 300 g of NaOH / 1 (corresponding to 7.5 equivalents per liter) were pumped in in 6 minutes using a gear pump. Accordingly, 33.8% of the metals Fe + Al were precipitated. Immediately after the precipitation had ended, the gassing was stopped with nitrogen and 97 Nl / h of air were gassed for the purpose of oxidation. 180 minutes after

When the oxidation started, the reaction was complete. The oxidation rate was accordingly 33.3 mol% Fe-II / h. (Only the 33.8% of the Fe precipitated by the NaOH were taken into account. The Fe-ITI content was calculated as Fe-II. It was further assumed that Fe and AI were precipitated equally).

The germ obtained had the following properties:

BET surface area: 100 m ² / g crystallite size: 27.0 nm

AV: 2700 (AV = BET surface area multiplied by crystallite size) Comparative Example 1: Aluminum-containing germ from FeCl ₂ and A1C1 ₃

In a discontinuous stirred tank with a useful volume of 30 liters, equipped with a three-stage cross-bar stirrer and a gassing device (ring with

Holes below the stirrer) are given 14.095 1 FeCl ₂ solution with 55.07 g / 1 Fe and an Fe-ITI content of 1.5 mol% (based on total Fe). 914 g of AlCl ₃ solution with 5.06% by weight of Al and 3.95% by weight of HC1 are then added.

The FeCl ₂ amount corresponds to 13.9 mol Fe (Fe-E and Fe-HI), the AlCl ₃ amount 1.71 mol, the HCl amount 0.989 mol. The ratio Al / Fe total therefore corresponds to 12.3 mol% based on total Fe. This solution is heated to 34 ° C. with stirring and gassing with 300 Nl / h nitrogen. After this temperature has been reached, 1615 ml of sodium hydroxide solution with a content of 300 g NaOH / 1 (corresponding to 7.5 equivalents per liter) are pumped in in 6 minutes using a gear pump. Accordingly, 33.8% of the Fe + AI metals are precipitated by NaOH. Immediately after the precipitation had ended, the gassing was stopped with nitrogen and gassed with 97 Nl / h of air. The reaction was complete 180 minutes after the start of the oxidation. The oxidation rate was accordingly 33.3 mol%> Fe-II / h. (Only the 33.8% of the Fe that was precipitated by the NaOH were taken into account.

Percentage was calculated as Fe-13. It was further assumed that Fe and AI are precipitated equally).

The germ had the following properties:

BET surface area: 173 m ₂ / g crystallite size: 17.5 nm

AV: 3027 Comparative Example 2: Aluminum-containing germ from FeCl ₂ and A1C1 ₃

11.58 l FeCl solution with 55.09 g / 1 Fe and a Fe-ILT content of 1.0 are placed in a discontinuous stirred tank with a useful volume of 30 liters, equipped with a three-stage cross-bar stirrer and a gas supply device (ring with holes below the stirrer) mol% (based on total Fe). 818 g of AlCl ₃ solution with 6.00% by weight of Al and 1.6% by weight of HC1 are then added.

The FeCl ₂ amount corresponds to 9.5 mol Fe (Fe-H and Fe-uT), the AlCl ₃ amount 1.82 mol, the HCl amount 0.36 mol. The ratio Al / Fe total corresponds accordingly

19.2 mol% based on total Fe. This solution is heated to 44 ° C. with stirring and gassing with 300 Nl / h nitrogen. After this temperature has been reached, 1061 ml of sodium hydroxide solution with a content of 300 g NaOH / 1 (corresponding to 7.5 equivalents per liter) are pumped in in 10 minutes using a gear pump. According to this, 32.1% of the metals Fe + AI are precipitated by NaOH. Immediately after the precipitation had ended, the gassing was stopped with nitrogen and gassed with 67 Nl / h of air. The reaction was complete 135 minutes after the start of the oxidation. The oxidation rate was therefore 44.5 mol% Fe-II / h. (Only the 32.1% of the Fe which was precipitated by the NaOH were taken into account. The Fe-IH content was calculated as Fe-U. It was further assumed that Fe and Al were precipitated uniformly).

The germ had the following properties:

BET surface area: 186 m ² / g

Crystallite size: 15.5 nm

AV: 2883 Example 4: Yellow pigment production

2 mol of yellow germ suspension from example 1 (calculated as mol of α-FeOOH) and 20 mol of FeCl with a

Fe content of 95.7 g / 1 Fe given. This suspension is heated to 60 ° C. with constant stirring. Once this temperature has been reached, a pH of 3.4 is maintained by continuously adding sodium hydroxide solution with 300 g / 1 NaOH. At the same time, 76 Nl / h of air are gassed. After a fumigation time of 1618 minutes, all Fe-U was oxidized, which corresponds to an oxidation rate of 3.7 mol% Fe / h.

The yellow pigment produced has the following properties:

BET surface area: 32.7 m ² / g crystallite size: 27 nm

Color strength (against Bayferrox ^® 915): 97% da *: 0.2 db *: -1.2 dL * (against Bayferrox ^® 915): -0.7 da *: 0.7 db *: -1.2

Example 5: Yellow pigment production

If, instead of the germ from example 1, the germ from example 2 is used and the amount of air is set to 76 Nl / h, the reaction conditions obtained are otherwise identical after 1618 minutes (oxidation rate 3.7 mol% / h)

Yellow pigment with the following properties:

BET surface area: 45.6 m ² / g

Crystallite size: 25 nm color strength (against Bayferrox ^® 915): 97% da *: 0.1 db *: -2.6 dL * (against Bayferrox ^® 915): -3.4 da *: 1.1 db *: -4.0

Example 6: Yellow pigment production

If the seed from Example 3 is used instead of the seed from Example 1, the following yellow pigment is obtained under the reaction conditions of Example 5:

BET surface area: 32.7 m ² / g crystallite size: 32 nm

Color strength (against Bayferrox ^® 915): 101% da *: -0.9 db *: -2.1 dL * (against Bayferrox ^® 915): -2.4 da *: -1.0 db *: -4.0 Only the pigment produced with a germ according to the invention is similar in color to the comparison type Bayferrox ^® 915 in order to be able to be used as a high-quality yellow pigment. The two yellow pigments produced from the germs of the comparative examples are clearly too dark (in the shade) and not yellow enough.

Claims

claims

1. A process for the production of aluminum-containing iron oxide nuclei with - FeOOH crystal structure with an aspect ratio of 2100 to 3600 and a BET surface area of 50 to 150 m2 / g using FeC12, characterized in that

a.) to an iron (II) chloride solution with a total Fe content of 20 - 100 g / 1, preferably 40 - 65 g / 1 and an Fe-IH content of 0.1 - 10 mol% Fe-fll ( based on total Fe) first an AI component in amounts of 4 -

13 mol%) Total Fe is added with stirring,

c.) a precipitant with an active ingredient content of 2-10 equivalents per liter, preferably 4-8 equivalents per liter is added to the mixture, and the molar ratio Fe + Al to precipitant 20% - 80%, preferably 30% - 60% the stoichiometry is

d.) the precipitated suspension is then oxidized with an oxidizing agent at such a rate that the oxidation rate is 2-50 mol% / h, preferably 10-35 mol% / h, of the iron to be oxidized.

2. The method according to claim 1, characterized in that aluminum chloride is used as Al component.

3. The method according to claims 1 and 2, characterized in that as precipitant NaOH, KOH, Na ₂ CO ₃ , K ₂ CO ₃ , Mg (OH) ₂ , MgO, MgCO ₃ , Ca (OH) ₂ , CaO, CaCO, NH ₃ or secondary or tertiary aliphatic amines can be used in aqueous solution or aqueous slurry.

4. Process according to claims 1 to 3, characterized in that atmospheric oxygen, oxygen, ozone, H ₂ O ₂ , chlorine, nitrates of the alkali or alkaline earth metals or NH ₄ NO ₃ are used as the oxidizing agent.

5. The method according to claims 1 to 4, characterized in that the reaction is carried out in discontinuous or continuous stirred tanks, in stirred tank cascades, loop reactors or stirrerless reactors with two-component nozzles as mixing elements.

6. Use of the α-FeOOH nuclei produced according to one of claims 1-5 for the production of yellow pigment.