LANXESS-Laux brochure english - BAYFERROX ... 4 The basic reaction in the Laux process, i.e. the reaction

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    Inorganic pigments

    using the Laux process

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    The LANXESS pigments business has been committed for many years to sustainable production processes as one of its core competencies. The Laux process in Krefeld-Uerdingen �������� � �� ����� ����������������������������������� ����- duction method for iron oxide pigments.

    The method is exemplary in that it fully exploits the heat pro- duced by the chemical reaction to generate steam and hot wa- ������������� ���������������� ������������ �������������������

    The Laux process is the key to the special properties of LANXESS’s yellow, black and red shades. Particularly with the reds, a very broad range of hues can be produced, from reds with a yellow to reds with a blue undertone. The red shades with a blue undertone are quite unique compared with other iron oxide reds available on the market because they display only a slight color shift even under intense milling conditions.

    ��� ��� ���� ��� � ��������� ��� ����� ������������ ��� ����������� ��� ��- trobenzene with metallic iron to aniline and iron oxides, was implemented on an industrial scale as far back as 1911 at the Krefeld-Uerdingen site. While the aniline was needed to

    manufacture dyestuffs, the iron oxide byprod- uct could not be put to ��������������� ��������������������� �� ��� ������� �� ��� 1914 to use the resulting iron oxide as a colorant, but the quality of the iron oxide was not adequate for pigment appli- cations. It took another eleven years before Dr. Laux, a chem- ist, succeeded in optimizing the process and obtaining iron � � ����� �������� ���� ���� ��������� ���!�� �� ��"� ����� #�� 1926, one year after its discovery, iron oxide production was launched in Krefeld.

    Since then, iron oxide production at the Krefeld plant has un- dergone remarkable development. After starting out with a ca- pacity of roughly 1,000 metric tons in 1926, production has steadily increased. At present, 280,000 metric tons of iron oxide pigment are produced at the plant, two-thirds of that by the Laux process. In other words, LANXESS operates the world’s largest production plant for synthetic iron oxide pig- ments in Krefeld.

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    Fig. 1: Basic patent on the Laux process

    In the Laux process, nitrobenzene is reacted with cast iron borings. Depending on the reaction conditions and the control chemicals, a suspension of black or yellow iron oxide results, which subsequently is washed, concentrated and dried. Red

    � ���� ��

    pigments cannot be obtained directly by these means; they are produced by subsequent calcining of the black paste un- der oxidative conditions.

    Nitrobenzene Cast iron

    Reaction Aniline

    Fe3O4 Black

    FeO(OH) Yellow


    Fe2O3 Red

    Mixture Brown

    2 Fe + C6H5 - NO2 + 2 H2O

    2 FeO(OH) + C6H5 - NH2


    9 Fe + 4 C6H5 - NO2 + 4 H2O

    3 Fe3O4 + 4 C6H5 - NH2


    2 Fe3O4 + 0,5 O2

    3 Fe2O3


    Fig. 2: Diagram of the Laux process

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    The basic reaction in the Laux process, i.e. the reaction of ni- trobenzene with cast iron, is extremely exothermic. After vari- ous process and plant optimizations, LANXESS has succeed- ed in exploiting virtually all the heat of reaction to produce hot water and steam for use in downstream processing steps. This

    reduces primary energy demand by 28 % and cooling water output by as much as 56 %, making the Laux process one of the most ecologically compatible and resource-conserving processes for the production of iron oxide pigments.

    One raw material in the Laux process is nitrobenzene, ob- tained by the nitration of benzene with nitric acid. The second raw material, cast iron borings, is a byproduct from the ma- chining of cast iron parts in various industries, such as auto- motive manufacturing.

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    Pigment properties

    �������!��� In the Laux process, all three basic iron oxide colors - red, yel- low and black - are available in a relatively broad color spec- trum. Due to the scattering power of iron oxides, the particle size has a direct influence on the shade.

    Red When it comes to red, the smaller the particles, the more pro- nounced the yellow undertone, while larger particles produce more of a blue undertone. The difference in prevailing particle size spans a rather wide range, from 0.09 μm for Bayferrox® 105 M to 0.7 μm for Bayferrox® 180 M.

    One unique advantage of the Laux process is its ability to produce red shades with a blue undertone. Significant differ- ences exist in this area between the Laux process and others, because the other manufacturing processes have difficulty ob- taining the required particle sizes.

    Black In the case of black, the shade of the pigment likewise depends on the size of the primary particles, ranging from the bluish Bayferrox® 306 to the high-tinting-strength Bayferrox® 330. $�� �� �� � �� ���� � ���� �� ���� ���� ��� ��&����� � "�� ��� ����� size. The larger the primary particles, the bluer the undertone of the shade. However, this effect is obtained at the cost of tinting � ���� ���������������������������� ���� ���������� ������

    Fig. 3: The Laux process produces red pigments with a bluish undertone that set it apart from other processes.

    Bayferrox® 110 M Bayferrox® 140 M Bayferrox® 180 M

    Bayferrox® 318 Bayferrox® 306

    Particle size Increasing Tinting strength Decreasing Shade Brownish Bluish

    Fig. 4: Particle size affects the shade.

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    Yellow With yellow, the range of shades achieved in pigments manu- factured by the Laux process is narrower. By selecting the right raw materials, the Laux process also can produce yel- low pigments that nearly rival precipitated pigments. Bayfer- rox® 3420 is the micronized version of Bayferrox® 420 and frequently selected as an alternative to precipitated yellow in paint and coating applications. The yellow grade, Bayferrox 415, is mainly used to color building materials on account of its darker, bluer shade.

    ��" ��� ���� Iron oxide pigments are lightfast thanks to their chemical and physical properties. In practical pigment applications, however, the interface between pigment and binder is a critical factor, this being particularly evident in coloring laminates yellow. A distinct difference in color shift can be observed when using a yellow iron oxide pigment produced by the precipitation process (Bay- ferrox® 920), one by the Laux process (Bayferrox® 420) and a post-treated yellow pigment (Colortherm® Yellow 10).

    UV radiation at the interface of the pigment/binder matrix pre- sumably leads to partial reduction of the resin, expressed by a green shift. This may be attributable to catalytic effects. In the

    case of Colortherm® Yellow 10, the inorganic post-treatment ��������� ����� ���� ��������� ������� ��������� ���������� ����- ening catalytic degradation and greatly reducing color shift.

    Fig. 5: Differences in lightfastness








    Bayferrox® 920 Std‘03 Bayferrox® 420 Std‘99 Colortherm® Yellow 10


    Lightfastness of Bayferrox® 920, 420 and Colortherm® 10 (Blue Wool Scale, level 8)

    Test conditions: Xenotest 150 S/ca. 160 h until wool sample 8 fades

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    200 °C 220 °C 240 °C 260 °C 280 °C 300 °C 320 °C

    # $

    %� �

    Limit to DIN-EN 12877 Part 2

    Colortherm® Red 110M Precipitated Red

    ��� �� ����� �����&������� �������� ��!�"��� ������'�$ (to DIN-EN 12877-2 Method B)

    (��!��� �������)�

    Laminates increasingly are used in outdoor applications, a trend that tightens quality requirements on the lightfastness of the decorative papers.

    (��!��� ����� ����� � In terms of temperature stability, Laux pigments again offer dis- tinct advantages over precipitated iron oxide pigments.

    Although red as hematite (Fe 2 O

    3 ) is heat-stable thanks to its

    chemical structure, the various iron oxide reds nevertheless display remarkable differences attributable to the production process.

    The red iron oxide pigments produced by the Laux process are heated to as high as 800 °C during calcining and therefore