Deacon process

As the Deacon process, the production of chlorine by oxidation of hydrogen chloride with oxygen is known. The case was registered by the English chemist Henry Deacon (1822-1876) in 1868 for a patent.

History

Above all, the 1792 introduced Leblanc process for soda production and the subsequent strong development of the chemical industry led to massive accumulation of hydrogen chloride, which was delivered either dissolved directly into the air or in water as hydrochloric acid in the wastewater. In the sixties of the 18th century, therefore, occurred several laws in force where the untargeted delivery of hydrogen chloride gas or hydrochloric acid was severely restricted. Henry Deacon succeeded with his invention of a breakthrough in a double sense, on the one hand the environmental problem was solved with hydrogen chloride and the other a valuable material was obtained, which could be sold, for example, chloride of lime as well.

Chemistry

The classical ( one-tier) Deacon process is the reaction of HCl gas in accordance with oxygen ( air or pure oxygen) with the following equation:

The reaction is exothermic with a reaction enthalpy of -114.8 kJ / mol and is an equilibrium reaction, that the reaction does not proceed completely.

The reaction is carried out at temperatures of about 400-450 ° C at a fixed ( " heterogeneous " ) catalysts based on CuCl2 or CuSO4. In the following picture of the equilibrium conversion of 4 moles of HCl with one mole of O2 is shown as a function of temperature ( at atmospheric pressure):

To achieve a high conversion of hydrogen chloride is a lower reaction temperature would be more convenient, but is here used in the catalysts based on copper, the reaction rate is too low. The equilibrium conversion of HCl can be increased still by increasing the pressure and increasing the oxygen excess, a complete or almost complete conversion is not achieved at 400-450 ° C reaction temperature thereby.

Technical implementation

The chemical reaction seems simple, but the technical realization is connected with such massive problems that this process until today could not prevail on a large scale production of chlorine or for recycling of hydrogen chloride. When technical problems occur mainly corrosion and the handling of the catalyst in a reactor to:

  • Corrosion occurs especially in the cooling of the gas mixture leaving the reactor (HCl, O2, Cl2, H 2 O ) to the metal surfaces.
  • The catalyst based on copper is converted during the reaction intermediate also to CuCl, CuO and CuO2 or consistent with these compounds in equilibrium. Especially CuCl, with its low melting point of about 430 ° C and its sublimation property, that is, to evaporate from the solid phase, provides for bonding of the catalyst in the reactor and the discharge of the catalyst with the reaction gases from the reactor.

Formally, the one -step reaction in two separate sub- steps, in which first of CuO is reacted with HCl to give CuCl 2, and water, which is then oxidized in a second reaction to form chlorine and CuO:

This separation of the reaction has made it possible to carry out the technical process in two separate reactors, the reaction temperature may now select optimal for each individual reaction. Also this two-step reaction is not more equilibrium reaction, so that the problem of the gas separation of the product gases and corrosion in the product work-up is reduced. Theoretically, the first reactor operates only with the gases HCl, and H2O in the reaction, and the second with O2 (or air ) and chlorine.

However, no technical breakthrough is hereby been achieved because of the mechanical transport of the catalyst from one reactor to another and back again is anything but trivial. Also, the reactions do not completely separate from each other, so that the real problem is reduced but not completely eliminated.

Technical developments

In the following years, until the recent past, research has been conducted on this method, both for the development of improved catalyst systems as well as for better technical realization. This resulted in several variants or further developments of the Deacon process, which were partially realized on a large scale:

  • Shell - Chlor process from Shell
  • MT- chlorine process the Mitsui Toatsu Chemicals, today Mitsui Chemicals (Japan)
  • KEL chlorine process of the M. W. Kellogg and DuPont
  • Carrier Catalyst Process USC ( University of Southern California)
  • Sumitomo - Chlor process of Sumitomo Chemicals ( Japan)
Henry Deacon (industrialist) Exothermic reaction Chemical equilibrium Chemical kinetics KBR (company)
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