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
• • 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
  • C25B1/14—Alkali metal compounds
  • C25B1/16—Hydroxides

Definitions

• the present invention relates to a process for the production of alkali hydroxide and nitrogen monoxide from alkali nitrites by electrolysis of aqueous solutions.
• High-proof nitrogen monoxide can be produced by burning ammonia with oxygen on platinum catalysts in the presence of steam as a protective gas, the N0 2 which is formed at the same time subsequently being separated off (DE-AS 10 85 142).
• NO is used for the production of hydroxylamine and its derivatives.
• a process has now been found for the simultaneous production of alkali metal hydroxide and nitrogen monoxide from alkali metal nitrite, which is characterized in that an aqueous solution containing alkali metal nitrite is electrolyzed in the anode compartment of a cation-exchange membrane cell.
• a membrane cell is to be understood as a cell divided into an anode and a cathode space by an ion exchange membrane. Both half-spaces have separate electrodes and can be filled with different solutions.
• Polymers which are as inert as possible and which carry acidic groups can be used as material for the cation exchange membrane, in particular perfluorinated polymers which carry sulfonic acid or carboxylic acid groups.
• Such cation exchange membranes are commercially available, for example under the trademark Nafion.
• Various types are available, e.g. simple foils or composite systems with embedded support fabric. The skilled worker is familiar with these developments from the technology of chloralkali electrolysis. The same applies to electrode material and electrode shapes.
• Steel is generally used for the cathodes, but other metals and alloys or conductive compounds that are stable in alkaline solution and that are particularly characterized by a low hydrogen overvoltage, such as e.g. Nickel, cobalt or precious metals such as platinum and ruthenium.
• Sodium and potassium nitrite are preferably used as alkali nitrite.
• the nitrite solution need not be pure; it can e.g. derive from the absorption of nitrous or nitrous gases in lye.
• Such solutions then contain alkali nitrite, alkali nitrate and possibly other inorganic salts in small amounts.
• halides should be absent, because otherwise anodic formation of free halogen can occur.
• concentration of nitrite is not critical. However, the concentration in the starting solution should be chosen so that a sufficiently high conductivity occurs, since otherwise a high resistance of the solution must be overcome with heating and loss of energy.
• concentration of nitrite and nitrate can briefly exceed the saturation limit; however, this procedure is not preferred, since the salt crystals which precipitate make insertion or pumping around very difficult. It is therefore preferred to work in practice with concentrations just below the respective saturation limit.
• the ano.lyt concentration is at temperatures above 50 ° C., preferably between 8 and 40% by weight NaNO 2 . At room temperature, the preferred concentration range is 8 to 35% by weight NaNO 2 .
• the reaction 2 NO 2 ⁇ NO 3 - + NO + e should take place in the anode compartment.
• a pH range of 3 to 6 should be maintained in the anode compartment.
• the hydroxide ions are initially discharged, while at pH values below 3.5 the nitrite solutions decompose to form nitrous gases.
• An optimal pH range for the anolyte is 4-5. No measures to maintain the pH are required during electrolysis. However, if the electrolysis is continued after the nitrite has been consumed, the pH may drop below 3.5.
• the anolyte containing only nitrate can then advantageously be processed on fertilizers.
• Electrolysis at normal pressure and temperatures between 20 and 100 ° C. is preferred. Higher or lower temperatures are possible, but technically or energetically less favorable.
• a cell voltage of less than 1. volt can be estimated from the reversible electrode potentials for the electrolysis of nitrite. Taking into account the current density, the temperature, the composition of the electrolyst, the membrane resistance, the electrode overvoltages and the geometry of the cell, cell voltages above 1 volt, in particular above 2 volts, will result in the practical case.
• a membrane cell whose anode and cathode compartments were 70 ml each, was connected to two circuits for catholyte and anolyte (each consisting of anode compartment or cathode compartment, hose connections, reservoir for electrolyte and pump) for better mixing of the electrolyte and to enlarge the mixture.
• catholyte and anolyte each consisting of anode compartment or cathode compartment, hose connections, reservoir for electrolyte and pump
• 1.6 l of a 40% sodium nitrite solution with 846 g of NaNO 2 and 56 g of NaNO 3
• 0.6 l of sodium hydroxide solution (246 g / 1 NaOH
• the membrane is a .RTM.Nafion 315 membrane
• the cathode is a steel plate with 10 cm 2 surface and as the anode, a titanium sheet (surface 10 cm2), the Ru0 2 (70:30 wt .-% activated with Ti0 2 /.
• the Electrode spacing was 6 mm and electrolysis was carried out at 80 ° C. with a current density of 5 k A / m 2 and a cell voltage of around 4.8 V. Water was continuously added to the catholyte so that the NaOH concentration remained constant same extent formed during the electrolysis liquor H 2 SO 4 was removed via an overflow from the catholyte and determined by titrimetry.
• Example 2 In a similar electrolysis cell with the same membrane as in Example 1, in which an iron mesh was installed as the cathode and a platinum mesh as the anode, 750 ml of NaOH (10%, density 1.11) and 900 ml of NaNO 2 - were used in the cathode compartment. Solution (40.5%, density 1.34 g / cm 3 ) filled.

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• 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 (2)

Publications (1)

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ID=6076229

Family Applications (1)

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Cited By (1)

Citations (1)

• 1979
  • 1979-07-20 DE DE19792929357 patent/DE2929357A1/de not_active Withdrawn
• 1980
  • 1980-07-11 EP EP80103997A patent/EP0029083A1/fr not_active Withdrawn

Patent Citations (1)

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