Chemistry: electrical and wave energy – Processes and products – Electrostatic field or electrical discharge
Patent
1990-01-29
1992-06-09
Tung, T.
Chemistry: electrical and wave energy
Processes and products
Electrostatic field or electrical discharge
204103, 204129, C25B 100
Patent
active
051204088
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method for the electrochemical generation of N.sub.2 O.sub.5.
It has been reported (German Patent No: 231,546; J Zawadski et al, Rocz.Chem., 1948, 22, 233) that N.sub.2 O.sub.5 can be produced by electrolysing a solution of N.sub.2 O.sub.4 in anhydrous nitric acid. The processes described in these reports are advantageous because they require no chemical dehydrating agents, such as poly-phosphoric acid. However, neither report suggested any advantage in controlling the reaction conditions during electrolysis.
J E Harrar et al, J Electrochem. Soc., 1983, 130, 108 described a modification of these early processes, which used controlled potential techniques. By maintaining a constant potential between the HNO.sub.3 /N.sub.2 O.sub.4 anolyte solution and the anode, the authors were able to improve current efficiency and thereby lower the cost of the electrochemical method. The authors have also described this modification in later U.S. Pat. Nos. 4,432,902 and 4,525,252.
The work of these authors, for the purpose of dehydrating HNO.sub.3, was predated by UK Patent No: 18603 (H Pauling), which also described electrolysis as a means of dehydrating HNO.sub.3.
The process described by Harrar et al, however, requires a sophisticated potentiostatic (constant anode potential) control and necessitates the use of a reference electrode.
It is one object of the present invention to provide a method for the electrosynthesis of N.sub.2 O.sub.5 that avoids the need for potentiostatic control and a reference electrode.
Further objects and advantages of the present invention will become apparent from the following detailed description thereof.
According to the present invention there is provided a method for the electrochemical generation of N.sub.2 O.sub.5 comprising
providing an electrochemical cell having an anode plate situated in an anode compartment and a cathode plate situated in a cathode compartment, the anode plate and the cathode plate being in substantially parallel relationship,
continuously passing a solution of N.sub.2 O.sub.4 in HNO.sub.3 through the anode compartment,
continuously passing a solution of N.sub.2 O.sub.4 in HNO.sub.3 through the cathode compartment,
whilst the N.sub.2 O.sub.4 in the HNO.sub.3 is passing through the anode and the cathode compartments, applying a potential difference between the anode and the cathode whereby electrical current is passed through the cell, and N.sub.2 O.sub.5 is formed in the anode compartment,
wherein the solution of N.sub.2 O.sub.4 in HNO.sub.3 is passed repeatedly through the anode compartment and either the potential difference between the anode and the cathode or the electrical current passing through the cell is maintained at a constant level.
By performing the present method at either a constant cell voltage (using a constant voltage generator) or a constant cell current (using a constant current generator), the need for potentiostatic control and a reference electrode is avoided.
The present process may be operated in either a continuous or a semi-continuous manner. In the former case the anolyte passed into the anode compartment contains, at all times, sufficient N.sub.2 O.sub.4 to allow the use of a cell current high enough to maintain a high production rate and low power consumption. The retention of the N.sub.2 O.sub.4 concentration at these levels may be effected, for example, by replacing the N.sub.2 O.sub.4 electrolysed to N.sub.2 O.sub.5 in the anode compartment.
By contrast, in a semi-continuous process there is no replacement of electrolysed N.sub.2 O.sub.4 in the anolyte. This means that, as the N.sub.2 O.sub.4 in the anolyte is converted to N.sub.2 O.sub.5, the anolyte concentration of N.sub.2 O.sub.4 will, if the electrolysis proceeds for long enough, fall to zero. In one embodiment of the semi-continuous process, the anolyte is repeatedly passed into and out of the anode compartment of the cell until all, or substantially all, of the N.sub.2 O.sub.4 in the anolyte is converted to N.sub.2 O.sub.5.
In continuous o
REFERENCES:
patent: 4432902 (1984-02-01), McGuire et al.
patent: 4443308 (1984-04-01), Coon et al.
patent: 4525252 (1985-06-01), McGuire et al.
Bagg Greville E. G.
Marshall Rodney J.
Schiffrin David J.
Walsh Francis C.
Ryser David G.
The Secretary of State for Defence in Her Britannic Majesty's Go
Tung T.
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