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 Anthraquinone Process for Production of Hydrogen Peroxide
  • Anthraquinone Process for Production of Hydrogen Peroxide
  • The anthraquinone process is based on the following processes: oxidation of a 2-alkyl-anthrahydroquinone with air to the corresponding 2-alkyl-anthraquinone and hydrogen peroxide and catalytic (back)-reduction of the 2-alkyl-anthraquinone to the 2-alkyl-anthrahydroquinone with hydrogen.

    In this cyclic process hydrogen peroxide is formed from hydrogen and oxygen:

    The alkyl-group substituent R on the anthraquinone differs from manufacturer to manufacturer. In addition to 2-ethyl-(mainly used), 2-tert-butyl-, 2-tert-amyl- and 2-sec-amyl-anthraquinones are also utilized. Mixtures of different alkyl anthraquinones can also be used.

    The solvent mixture has to fulfill a number of requirements: low solubility in water, low volatility, good dissolving properties, chemical stability under the reaction conditions used, low viscosity etc.

    In the first step of the process the anthraquinone is hydrogenated to the hydroquinone with palladium as the preferred catalyst: on carriers, such as gauze, or in suspension. The reaction is carried out at about 40,°C and at pressures up to ca. 5 bar with cooling and only to ca. 50% hydrogenation to suppress side reactions (see below).

    The subsequent oxidation proceeds with air at 30 to 80 °C and pressures up to 5 bar, if necessary after catalyst separation and a precautionary filtration. It can be carried out in co- or countercurrent mode, in a single step or multistep process. The hydrogen peroxide formed during the oxidation is extracted from the reaction mixture with water e.g. in pulsating packed towers. The extraction yield is ca. 98 %. The hydrogen peroxide solutions obtained are 15 to 35 % by weight and must be freed from residual  organic compounds before they can be concentrated by distillation.

    Commercial hydrogen peroxide solutions always contain stabilizers, such as diphosphates, organic complexing agents or tin compounds, to prevent their decomposition to oxygen and water.

    After separating off the hydrogen peroxide, the working solution has to be dried and freed of byproducts e.g. with active aluminum oxide. This occurs in a bypass.

    In practice, the anthraquinone process is much more complicated than has been described above, in that byproducts such as 1,2,3,4-tetrahydroanthraquinone are formed, particularly in the hydrogenation step. These behave similarly to anthrahydroquinones, but their further hydrogenation leads to octahydroanthrahydroquinones which are unusable in this process. Other byproducts such as oxanthrones and anthrones can only be partially regenerated. These unusable byproducts have to be removed from the process.

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