Process for producing iron oxide pigments

Abstract

The present invention relates to a method for producing iron oxide pigments according to the Penniman process, characterized in that a two-stage nucleation step is not carried out, and to the use of such iron oxide pigments.

Description

[Technical field]

[0001] The present invention relates to a method for producing iron oxide pigments according to the Penniman process, characterized in that no separate nucleation step is carried out, and to the use of such iron oxide pigments. [Background technology]

[0002] Iron oxide color pigments, which are employed as environmentally friendly colorants in ceramics, building materials, plastics, paints, and paper, are essentially available in black, yellow, red, orange, and brown hues.

[0003] Iron oxide pigments are obtained by solid-state reactions of iron salts (red, brown and black pigments), precipitation methods and hydrolysis reactions (yellow, red, orange and black pigments) as described in (Non-Patent Document 1) and also by the oxidation of iron with aromatic nitro compounds in the presence of hydrolyzable polyvalent salts, the so-called Laux process, as disclosed, for example, in (Patent Document 1) and (Patent Document 2).

[0004] The solid-state reaction is carried out from a black precursor reaction product (calcination method) or from FeSO 4 It is primarily used to produce red iron oxide from the Copperas process.

[0005] a) Laux process The Laux process starts with nitrobenzene and Fe metal, and initially produces black or yellow iron oxide and aniline. To produce red iron oxide with this process, the black iron oxide thus obtained is calcined. The process is technically complex and not easy to control, since control chemicals must be used in various ratios to obtain the desired particle size. In addition, the required equipment is technically demanding and therefore expensive. The reaction also produces aniline as a secondary reaction product, which by its nature requires special occupational hygiene measures.

[0006] b) Sedimentation Process Yellow, orange, red, and black iron oxide pigments can be produced by precipitation processes (US Pat. No. 5,399,433; yellow iron oxide pigments, and US Pat. No. 5,499,433; red iron oxide by direct precipitation process).

[0007] Iron oxide pigments obtained by the precipitation process are produced from solutions of iron salts and alkaline compounds in the presence of air, but have the disadvantage that stoichiometric amounts of neutral salts are produced, which must be disposed of with the wastewater or processed in a time-consuming and costly manner. 2 O 3 It is technically difficult because only a narrow range is available and the reaction is not easy to control. Red iron oxide produced by the precipitation process has the disadvantage of a heavy salt load, which pollutes the wastewater and is therefore environmentally unfavorable.

[0008] c) Hydrothermal reaction process The hydrothermal reaction process is described, for example, in US Pat. No. 5,399,633. With the hydrothermal reaction process, it is possible to produce good red iron oxide pigments for high added value applications, such as paints and inks. However, in this case the high process costs required by the pressure technology are counterproductive. Therefore, this process is not suitable for simpler applications where a cheap product is required.

[0009] d) Penniman process According to the Penniman process (disclosed for example in US Pat. No. 5,399,623 and US Pat. No. 5,499,636), red iron oxide pigments are prepared by dissolving metallic iron and adding and oxidizing red iron oxide nuclei. For nucleation, nitric acid is usually used, so that nitrates or ammonia are present in the wastewater, which must be removed using high technical efforts. This leads to high production costs, as in the case of hydrothermal reaction and precipitation processes.

[0010] Furthermore, US Pat. No. 5,399,633 discloses the Penniman process, which requires two nucleation steps, in which the reaction of metallic iron, oxygen and nitric acid produces particles with sizes below 100 nm and particles with sizes below 40 nm. 2 / g~150m 2 The nuclei are formed separately in the form of a suspension of hematite nuclei having a BET specific surface area of ​​1000 nm / g, and then iron, an iron(II) nitrate solution and oxygen are combined to form the pigment.

[0011] However, the Penniman process uses metallic iron as a raw material, which is dissolved by the acid released during the process, reducing the amount of neutral salts formed during the precipitation step, and therefore provides an economical process for the direct production of iron oxide pigments.

[0012] An additional advantage of the Penniman process is that it produces pigments with advantageous hues while producing less neutral salts.

[0013] However, the disadvantage of the Penniman process is that it requires two process steps: 1) nucleation and 2) pigment build-up. Therefore, the manufacturing method is operationally cumbersome. During nucleation, toxic nitrous gas is generated and must be treated. It also produces residues that must be landfilled and wastewater containing heavy metals. To achieve the desired hue, the Penniman process is time consuming. To achieve a specific hue, constant and close monitoring of the manufacturing process by skilled personnel is also required. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] DE 4 63 773 A1 [Patent Document 2] DE 5 15 758 A1 [Patent Document 3] U.S. Patent No. 2,388,659A1 [Patent Document 4] U.S. Patent No. 5,421,878A1 [Patent Document 5] DE 19917786 A1 [Patent Document 6] U.S. Pat. No. 1,327,061 [Patent Document 7] U.S. Pat. No. 1,368,748 [Patent Document 8] International Publication No. 2016 / 038152A1 Brochure [Non-patent literature]

[0015] [Non-Patent Document 1] Ullmann's Encyclopedia of Industrial Chemistry, VCH, Weinheim, 1992, vol.A20, p.298ff Summary of the Invention [Problem to be solved by the invention]

[0016] It was therefore an object of the present invention to produce iron oxide pigments by means of a substantially simplified Penniman process. It was also an object of the present invention to minimize or avoid the disadvantages associated with the nucleation step, such as, for example, toxic nitrous gas, and residues that must be landfilled, and heavy metal-containing wastewater. [Means for solving the problem]

[0017] Surprisingly, this objective has been achieved by producing iron oxide pigments according to the Penniman process, which does not have a two-stage nucleation step.

[0018] In the context of the present invention, the phrase "two-stage nucleation step" is preferably defined as a situation where the nucleation step is carried out in such a way that the nuclei (typically in the form of a suspension) are present as reaction products, e.g. in a separate reactor or vessel, and are then incorporated simply as reactants in the pigment production process of the present invention. [Brief description of the drawings]

[0019] [Figure 1] FIG. I is a graph showing the CIELAB colorimetric values ​​of Examples 1-9. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Preferably, the iron oxide pigment is produced as follows: a) introducing a solution containing iron, iron(II) nitrate, and water; b) heating the solution; c) during and / or after heating, an oxygen-containing gas is bubbled through the solution to obtain a pigment suspension; and d) The pigment suspension is then filtered, washed and / or dried.

[0021] Based on the total volume of the solution, the proportion of iron is preferably 1 to 250 g / L, more preferably 40 to 85 g / L, and most preferably 50 to 75 g / L.

[0022] Based on the total volume of the solution, the ratio of iron (II) nitrate is preferably 1 to 250 g / L, more preferably 40 to 50 g / L, and most preferably 44 to 46 g / L. Based on the total volume of the solution, the ratio of iron (II) nitrate is particularly preferably 45 g / L.

[0023] The solution is preferably heated to 60-100° C., preferably 70-95° C., very preferably 84-86° C., at atmospheric pressure. It is particularly preferred if the solution is heated to 85° C. at atmospheric pressure.

[0024] In working under pressure, the solution is preferably heated to between 50 and 250°C, more preferably between 100 and 200°C.

[0025] The oxygen-containing gas is blown in at a rate of preferably 1 to 200 L / h per 1 L of solution, more preferably 10 to 40 L / h per 1 L of solution, extremely preferably 25 to 35 L / h per 1 L of solution, and particularly preferably 30 L / h per 1 L of solution.

[0026] Air is preferably used as the oxygen-containing gas. The oxygen-containing gas is blown in for a period of preferably 5 to 150 hours, more preferably 50 to 120 hours, and most preferably 65 to 75 hours.

[0027] This means that by judicious selection of initial and reaction conditions, not only can the desired color locus be better established than in the conventional Penniman process, but also the complex monitoring steps in the manufacturing process can be significantly reduced.

[0028] In addition, it is possible to open up the color space, which was previously unattainable with existing Penniman processes. Some of these colorimetric values ​​are shown in Figure I.

[0029] The iron oxide pigments obtained in this way can be suitably deagglomerated and / or ground and / or heat treated, and preferably contain additives which improve the processability of the pigments.

[0030] The invention further encompasses the use of the iron oxide pigments according to the invention for colouring lime- and / or cement-finished building materials, asphalt, paints, inks, coloured gels, paper, plastics, food colours and / or pharmaceuticals, preferably by mixing the iron oxide pigments with lime- and / or cement-finished building materials, asphalt, paints, inks, coloured gels, paper, plastics, food colours and / or pharmaceuticals.

[0031] The iron oxide pigments are also suitable for use as industrial oxides in the fields of catalysis, abrasives, etc.

[0032] The subject matter of the invention arises not only from the subject matter of the individual patent claims, but also from the individual patent claims taken in combination with one another. The same applies to all parameters disclosed in the specification and to any combination thereof.

[0033] The present invention will be described in more detail in the following examples, but is not to be construed as being limited in any way by them.

[0034] I. Description of the measurement methods used I.1 Equipment Heatable 9 litre steel kettle, bottom insert sieve, gas inlet ring, blade stirrer, combined pH electrode, thermocouple.

[0035] I.2 Work guidelines A solution containing iron, iron(II) nitrate, and water was introduced into a steel kettle. The solution was then heated. Air was bubbled into the heated solution for a period of time. Gassing of the solution was continued until the pigment suspension reached the desired color space. The pigment suspension thus obtained was then filtered, and the pigment filter cake thus obtained was washed with water, dried, and ground.

[0036] I.3 Colorimetric determination (pure color) The color evaluation of the pigments was carried out at a pigment volume concentration of 10% in Alkydal L64® thixotropic (uncured alkyd resin, Bayer AG). The remission values ​​and the CIELAB data (DIN 5033, Part 7) were measured using a measuring device equipped with an Ulbricht sphere (illumination condition d / 8″, standard illuminant CI2″) including surface reflection. The remission values ​​obtained were converted into the CIELAB color data system according to DIN 5033, Part 3.

[0037] Without the use of a gloss trap, a spectrophotometer ("colorimeter") was used with a measurement geometry of d / 8, as described in ISO 7724 / 2-1984(E) section 4.1.1, in DIN 5033 Part 7 (July 1983) section 3.2.4 and in DIN 53236 (January 1983) section 7.1.1.

[0038] A DATAFLASH® 2000 measuring device (manufactured by Datacolor International Corp., USA) was used. The colorimeter was calibrated against a white ceramic working standard as described in ISO 7724 / 2-1984(E)section 8.3. The reflectance data of the working standard against an ideal matt white body was imported into the colorimeter, so that after calibration with the white working standard, all color measurements are related to the ideal matt white body. Black point calibration was performed using a black hollow body provided by the colorimeter manufacturer.

[0039] The result of the color measurement is a reflectance spectrum. When calculating the colorimetric quantities, it does not matter with what light source the measurement was performed (exception: fluorescent samples). From the reflectance spectrum, any desired colorimetric quantities can be calculated. The colorimetric quantities used in this case are calculated according to DIN 6174 (CIELAB values). Among other measurements, the colorimetric value "b *" is calculated according to DIN 6174. The following applies to the color impression: negative b * The higher the value, the bluer the color pigment.

[0040] Any gloss traps present were removed. The temperature of the colorimeter and test specimens was approximately 25°C ± 5°C.

[0041] 1.4 Remaining iron The iron remaining after the reaction was determined by drying at 80° C. in an air circulating drying oven and reweighing the unused iron after rinsing by means of water.

[0042] I.5 Final Fe Analysis The determination of Fe was carried out by cerium titration under inert conditions. 3 (depends on solid content) sample, 3 of water and 20cm 3 After digestion in 100 ml of hydrochloric acid (37%), the solution of iron(II) and (III) chlorides thus obtained was poured into 10 cm 3 of sulfuric acid (about 48.5% by weight) and diluted with deionized water to 200 cm 3 Potentiometric titration was performed using an automatic titrator (Mettler Memotitrator DL70) with titer-stable cerium(IV) sulfate solution (c[Ce(SO4)2] = 0.25 mol / L), but the actual titration was performed in several steps controlled by the automatic titrator.

[0043] In the first step, iron(II) was oxidized to iron(III) using cerium(IV) sulfate solution. In the second step, reduction of iron(III) to iron(II) was carried out using a slight excess of 7% titanium(III) chloride solution (approximately 7% in 10% HCl). In the third step, total iron was determined in a two-stage titration using cerium(IV) sulfate solution, where first the excess titanium(III) produced by reduction was oxidized to titanium(IV) and then the iron(II) was reduced to iron(III). The results of these titrations were then determined from the raw data and the output of the automatic titrator.

[0044] [Table 1]

[0045] [Table 2]

[0046] [Table 3]

[0047] [Table 4]

[0048] [Table 5]

[0049] [Table 6]

[0050] [Table 7]

[0051] [Table 8]

[0052]

Table 9

[0053]

Table 10

[0054]

Table 11

[0055]

Table 12

Claims

1. A method for producing an iron oxide pigment according to the Penniman process, characterized in that the method does not include a two-stage nucleation step.

2. a) introducing a solution comprising iron, iron(II) nitrate, and water; b) heating the solution; c) during and / or after heating, an oxygen-containing gas is bubbled through the solution to obtain a pigment suspension; and d) The pigment suspension is then filtered, washed and / or dried.

2. The process according to claim 1 ,

3. 3. A process according to claim 1 or 2, characterized in that the proportion of iron is between 1 and 250 g / L, in particular between 40 and 85 g / L, based on the total volume of the solution.

4. The method according to claim 3, characterized in that the proportion of iron is 50-75 g / L, based on the total volume of the solution.

5. 5. The process according to claim 1, wherein the proportion of iron(II) nitrate is from 1 to 250 g / L, in particular from 40 to 50 g / L, based on the total volume of the solution.

6. 6. A process according to claim 5, characterised in that the proportion of iron(II) nitrate is 44 to 46 g / L, in particular 45 g / L, based on the total volume of the solution.

7. A process according to any one of claims 1 to 6, characterised in that the solution is heated to 60 to 100°C, in particular 70 to 95°C, under atmospheric pressure.

8. 8. The process according to claim 7, characterized in that the solution is heated to 84-86°C.

9. A process according to any one of claims 1 to 6, characterised in that the solution is heated under pressure to 50 to 250°C, in particular to 100 to 200°C.

10. 10. The process according to claim 1, characterized in that 1 to 200 L / h of oxygen-containing gas are blown in per liter of solution, in particular 10 to 40 L / h of oxygen-containing gas per liter of solution.

11. 11. The process according to claim 10, characterized in that 25 to 35 L / h of oxygen-containing gas is blown in per 1 L of solution.

12. 12. The process according to claim 1, wherein air is used as the oxygen-containing gas.

13. 13. The process according to claim 1, wherein the blowing in of the oxygen-containing gas is carried out for a period of from 5 to 150 hours, in particular for a period of from 50 to 120 hours.

14. 14. The process according to claim 13, characterized in that the blowing in of oxygen-containing gas is carried out for a period of 65 to 75 hours.

15. A process according to any one of the preceding claims, characterized in that the iron oxide pigments are deagglomerated or ground.

16. 16. The method according to claim 1, further comprising adding to the pigment an additive which improves its processability.

17. A process according to any one of the preceding claims, characterized in that the iron oxide pigment is heat treated.

18. 18. A method for colouring lime- and / or cement-finished building materials, asphalt, paints, inks, coloured gels, paper, plastics, food colours and / or medicines with the iron oxide pigments produced as claimed in any one of claims 1 to 17, characterized in that the iron oxide pigments are mixed with the lime- and / or cement-finished building materials, asphalt, paints, inks, coloured gels, paper, plastics, food colours and / or medicines.

19. Use of the iron oxide pigment produced as claimed in any one of claims 1 to 17, characterized in that the iron oxide pigment is used as an industrial oxide in the fields of catalysts, abrasives, etc.

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