Eka Nobel Ab

Akzo Nobel Chemicals International B.v.

Anders Dahl

Roy Hammer-Olsen

Philip Byrne

Maria Norell

Ursula Soderberg

The invention relates to a process of producing chlorine dioxide comprising the steps of reducing chlorate ions in an acid reaction medium maintained in a reaction zone of a chlorine dioxide generator, which reaction medium contains alkali metal ions and sulfate ions, so to form chlorine dioxide and a solid salt of acidic alkali metal sulfate. The process further comprises the steps of separating said solid acidic alkali metal sulfate from the reaction medium, contacting said solid acidic alkali metal sulfate with an aqueous medium in a mixing tank to effect at least partial conversion to neutral solid alkali metal sulfate, separating the at least partially neutralized solid alkali metal sulfate from the aqueous medium on a rotary drum filter operating with vacuum inside and with part of the drum submerged in a slurry of the at least partially neutralized solid alkali metal sulfate and the aqueous medium, and forming an acid filtrate.

Method of producing chlorine dioxide

The invention relates to a process of producing chlorine dioxide comprising the steps of reducing chlorate ions in an acid reaction medium maintained in a reaction zone of a chlorine dioxide generator, which reaction medium contains alkali metal ions and sulfate ions, so to form chlorine dioxide and a solid salt of acidic alkali metal sulfate. The process further comprises the steps of separating said solid acidic alkali metal sulfate from the reaction medium, contacting said solid acidic alkali metal sulfate with an acid aqueous medium in a mixing tank to effect at least partial conversion to neutral solid alkali metal sulfate, separating the at least partially neutralized solid alkali metal sulfate from the acid aqueous medium on a filter and forming an acid filtrate, feeding at least a portion of said acid filtrate to the mixing tank, and transferring an acid aqueous medium to the reaction zone of the chlorine dioxide generator, which acid aqueous medium is a portion of the acid filtrate or acid aqueous medium from the mixing tank or a mixture thereof.

The present invention relates to a process for production of chlorine dioxide by reacting in a reaction vessel an alkali metal chlorate, sulfuric acid and methanol as a reducing agent. A reaction medium is maintained at a temperature from about 50.degree. C. to about 100.degree. C. and is subjected to a subatmospheric pressure sufficient to effect evaporation of water whereby a mixture of chlorine dioxide and water vapor is withdrawn from an evaporation region in the reaction vessel and alkali metal sulfate is precipitated in a crystallization region in the reaction vessel. Raw methanol purified by separation and adsorption is used as reducing agent. The raw methanol is purified by dilution with water whereby an unpolar phase is separated and and the remaining methanol-water phase is contacted by an adsorbing agent. The adsorbing agents used can be zeolites, active carbon or polymer adsorbing agents.

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Saltsjö-Boo, Sweden

Anders Dahl