Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B1/00—Electrolytic production of inorganic compounds or non-metals
  • C25B1/01—Products
  • C25B1/34—Simultaneous production of alkali metal hydroxides and chlorine, oxyacids or salts of chlorine, e.g. by chlor-alkali electrolysis
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B15/00—Operating or servicing cells
  • C25B15/08—Supplying or removing reactants or electrolytes; Regeneration of electrolytes
  • C25B15/087—Recycling of electrolyte to electrochemical cell

Definitions

• the present invention relates in particular to processes for the electrolytic production of chlorine and sodium hydroxide solution from sulfate-containing salt, in which the brine is circulated.
• the impurities in the salt are enriched in the brine circuit if they are not removed by continuous cleaning operations except for residual levels that are tolerable during electrolysis. After passing through the electrolysis cell, the brine is acidified and dechlorinated. In the further course of the brine cycle, there are process and plant-related variants. The majority of large-scale plants are still amalgam plants, most of them have open salt dissolving stations. In this case, an alkalization of the brine is necessary before the re-saturation in order to safely avoid emissions of residual chlorine. Usually, the necessary excess of sodium hydroxide solution is added at the time of re-saturation, so that the hydroxides of magnesium and iron also precipitate out during the dissolving process.
• Calcium carbonate and barium sulfate are then precipitated by adding barium compounds and soda. Soda and caustic soda are used in excess in order to achieve the most complete precipitation possible. Barium compounds are added in the deficit so that they are fully implemented.
• a certain sulfate content in the brine is tolerable. In the membrane process, the tolerable limit of a few g / 1 is determined by the membranes currently available. It is expected that sulfate-resistant membranes will also be available in the future. In the case of the amalgam process with graphite anodes, the graphite burnup, which increases with the sulfate content, determines the upper limit. When using titanium anodes, relatively high sulfate contents of up to 30 g sulfate / l can be controlled with the amalgam process.
• An object of the present invention is to provide a process which does not require the relatively expensive barium compounds for sulfate precipitation. Furthermore, it is an object of the present invention Carry out sulfate precipitation without the use of precipitation chemicals, whereby sulfate compounds that can be used directly should be obtained.
• the sulfate can be removed from the circulating brine under certain additional conditions as a Glauber's salt by cooling crystallization without adversely affecting the electrolysis process.
• the volumetric flow of the first partial flow is preferably approximately half to twice the volumetric flow of hydrochloric acid. 15 to 25%, more preferably about 20%, hydrochloric acid is preferably used.
• Hydrochloric acid diluted in this way is still sufficient to bring about chlorate decomposition. With more concentrated hydrochloric acid, solid sodium chloride can precipitate.
• condensate from the chlorine cooling is expediently branched off, which is returned to the brine anyway for environmental reasons.
• the partial brine flow in which the chlorate removal takes place is, for example, approximately 0.5 to 2% of the main brine flow.
• Glauber's salt precipitation can be carried out according to known laws without any problems. It is known that the solubility of Glauber's salt in concentrated brine is never strongly dependent on temperature. For example, the solubility of Glauber salt, reported in g SO 4/1, at 5 ° C and about 15 at 0 ° C for about 10 degrees.
• the parameters determining the Glauber's salt cooling crystallization precipitation can be specified in a simple manner for the other parameters present in a technical electrolysis cell.
• a sodium chloride salt with 0.5% sulfate content is also used to strengthen a brine that has been depleted in the electrolysis cell by 40 g / 1, so a partial flow of 2% of the brine flow to 5 ° C to cool so that the sulfate introduced when 40 g of salt are dissolved per 1 brine is removed. With more cooling, the partial flow for the cooling crystallization can be kept smaller.
• the brine in this second partial stream is preferably cooled to temperatures between -5 and 10 ° C., particularly preferably to temperatures between 0 and 5 ° C.
• the present invention accordingly also relates to the particularly preferred combination of Glauber's salt cooling crystallization precipitation, chlorate removal and the last-described precipitation of the further impurities.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Life Sciences & Earth Sciences (AREA)
• Sustainable Development (AREA)
• Inorganic Chemistry (AREA)
• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)

Applications Claiming Priority (2)

Publications (3)

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ID=6162527

Family Applications (1)

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Cited By (3)

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Family Cites Families (4)

• 1982
  • 1982-05-03 DE DE19823216418 patent/DE3216418A1/de not_active Withdrawn
• 1983
  • 1983-04-20 EP EP83103829A patent/EP0093319B1/fr not_active Expired
  • 1983-04-20 DE DE8383103829T patent/DE3364877D1/de not_active Expired
  • 1983-04-27 JP JP58073104A patent/JPS58199882A/ja active Pending

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