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
  • C25B1/24—Halogens or compounds thereof
  • C25B1/26—Chlorine; Compounds thereof

Definitions

• Aqueous hydrochloric acid is electrolyzed in a di aphragm cell to recover chlorine and hydrogen therefrom.
• the acid to be electrolyzed should have a concentration of from 18 to 28% by weight of HCl and should be degraded by not more than 2% by weight during its passage through the cell.
• the mean temperature in the cell is kept at from 75 to 90 C.
• This object may be achieved for example by appropriate choice of the diaphragm which prevents mixing of the gases formed on the cathode and anode sides but does not impede the flow of current.
• Another possibility is to decrease the resistance in the electrolyte by carrying out the electrolysis in the region of maximum conductivity of hydrochloric acid, or to decrease the hydrogen overvltage at the graphite cathodes generally used.
• the hydrogen overvoltage may be lowered for example in known manner by adding certain metals to the electrolyte, the added metal cations being deposited in the course of the electrolysis on the cathodes and the electrolytic decomposition takes place at the layers of the electrodes thus activated with a decrease in the overvoltage.
• Metals of the platinum group, copper, nickel, antimony, silver, molybdenum and cobalt are preferred as metals and they may be added to the electrolytes either batchwise or continuously.
• acids having an HCl concentration of more than 20% up to about 26% by weight are used.
• the rate of flow of the acid is controlled so that a concentration gradient between the acid introduced into the electrolyzer and the acid withdrawn of more than 3% by weight, for example of 5% by weight, is maintained. Since there is no freedoin as regards the temperature of the acid leaving the cell because of its HCl partial pressure (generally a temperature of the effluent acid of C. should not be exceeded) it is necessary to cool the acid strongly before it enters the cell. In this way the mean temperature in the cell is kept fairly low.
• the temperature range used is therefore one in which the hydrochloric acid has a low conductivity 30 that an increased amount of energy has to be used.
• the acid being electrolyzed is preferably degraded by from 0.5 to 1.6% by weight.
• the low degradation of the hydrochloric acid is achieved by passing the acid to be electrolyzed at an increased rate of flow through the cathode and anode chambers at the known and conventional current densities of from 2000 to 5000 amperes per square meter. In this way it is possible to eliminate the resistance produced by the gas bubbles forming at the electrodes, as the bubbles are rapidly detached from the cathode and anode and entrained. A considerable decrease in the cell potential is thus achieved by simple means.
• Another advantage of the method in accordance with the invention is that it is possible to use a higher mean cell temperature. Because of the increased throughput of acid it is possible to allow the acid to enter at a relatively high temperature and a further gain of potential is achieved because of the higher conductivity of hydrochloric acid at increasing temperatures.
• EXAMPLE A 25% by weight hydrochloric acid is passed through a diaphragm cell (having an anode area of 2.32 m. and consisting of thirty successive individual cells) at such a rate that the concentration of the degraded acid leaving the cell is 21.5%. At a current of 9400 amperes a cell potentail of 2.25 volts is measured. The mean temperature of the acid is 65 C.
• a process as claimed in claim 1 wherein said aqueous hydrochloric acid being electrolyzed is substantially free of metal additives which lower the hydrogen overvoltage at the cathodes of the cell.

Landscapes

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

Applications Claiming Priority (1)

Publications (1)

Family

ID=5776115

Family Applications (1)

Country Status (5)

Cited By (11)

• 1970
  • 1970-07-08 DE DE19702033802 patent/DE2033802A1/de active Pending
• 1971
  • 1971-06-28 US US00157766A patent/US3756930A/en not_active Expired - Lifetime
  • 1971-06-29 FR FR7123739A patent/FR2098096A5/fr not_active Expired
  • 1971-07-07 BE BE769632A patent/BE769632A/xx unknown
  • 1971-07-07 GB GB3185871A patent/GB1346656A/en not_active Expired

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