Process for preparing dinitrogen pentoxide

Details Process for preparing dinitrogen pentoxide Process for preparing dinitrogen pentoxide

1992-04-17

1994-06-07

Langel, Wayne

Chemistry of inorganic compounds

Nitrogen or compound thereof

Oxygen containing

C01B 220

Patent

active

053187636

DESCRIPTION:

BRIEF SUMMARY
This invention relates to the preparation of dinitrogen pentoxide (N.sub.2 O.sub.5) by the reaction between dinitrogen pentoxide (N.sub.2 O.sub.4) and ozone.
N.sub.2 O.sub.5 is a powerful and selective nitrating agent, especially when dissolved in inert organic solvents. Hitherto, its use as a nitrating agent has been limited because of its relatively high cost and lower thermal stability.
One process of N.sub.2 O.sub.5 preparation which is capable of producing a high purity product with a relatively long shelf life is the reaction of gaseous N.sub.2 O.sub.4 with ozone. Ozone is produced at a maximum concentration of about 4 wt% in oxygen within a silent electrical discharge ozoniser, and is immediately reacted with a stoichiometric amount of N.sub.2 O.sub.4 vapour in an inert gas carrier to give N.sub.2 O.sub.5. The inert gas stream containing the N.sub.2 O.sub.5 product is then brought into contact with a cold surface maintained at a low temperature of typically -70.degree. C. to condense out the product as a solid, whilst at the same time minimizing losses.
There are several disadvantages with this process. These are: the volume of carrier gas is high in comparison with the volume of gaseous N.sub.2 O.sub.5 product. The potential for product losses in the carrier gas is therefore high, which is one reason for employing a very low recovery temperature. a detrimental effect in the thermally unstable N.sub.2 O.sub.5 product. and use. be used, which leads to high operating costs especially since the high volume of carrier gas must also be cooled to the same temperature. falls as the thickness of product builds up. is difficult to achieve, especially when these reagents are present in such low concentrations. A slight excess of ozone is lost in the carrier gas which adds to operating costs, whereas a slight excess of N.sub.2 O.sub.4 leads to N.sub.2 O.sub.4 contamination in the condensed product. produces nitric acid contamination in the product by reaction with N.sub.2 O.sub.5.
It is an object of the present invention in a first aspect to provide a process for generating N.sub.2 O.sub.5 by reaction between ozone and N.sub.2 O.sub.4 whereby the aforementioned disadvantages are overcome or at least mitigated in part.
Accordingly, a process for preparing N.sub.2 O.sub.5 comprises the steps of
(a) providing a solution of N.sub.2 O.sub.4 in a first body of a volatile inert organic solvent,
(b) contacting the solution with a carrier gas containing ozone at a temperature sufficient to promote formation of N.sub.2 O.sub.5 in, and evaporation of solvent into, the carrier gas,
(c) contacting the N.sub.2 O.sub.5 -laden carrier gas with a second body of inert organic solvent at a temperature below that of step (b) to condense the N.sub.2 O.sub.5 therein, and
(d) recovering the condensed N.sub.2 O.sub.5 within the solvent from step (c).
FIG. 1 of the Drawing represents an apparatus for carrying out the process according to the present invention.
The principal advantage of the gas/liquid interaction in step (b) is that the heat generated during the exothermic reaction between ozone and N.sub.2 O.sub.4 in step (b) is both absorbed by intimate contact with liquid solvent of relatively high specific heat capacity and counteracted by the latent heat of vaporization of the solvent and N.sub.2 O.sub.4. In this way, large temperature increases are suppressed and thermal decomposition of the N.sub.2 O.sub.5 avoided. Although this means that the carrier gas becomes contaminated with solvent vapour, step (c) provides an effective means of recovering this solvent by low temperature condensation into the second body of solvent whilst at the same time directly converting the N.sub.2 O.sub.5 into readily storable, transportable and usable form without an intermediate solids handling stage.
The chemical identity of the first and second bodies of solvent are preferably the same to avoid the problem of one solvent contaminating the other. Preferably, this solvent comprises C.sub.1 or C.sub.2 chloroalkane, especially dichloromethane, or a

REFERENCES:
patent: 4432902 (1984-02-01), McGuire et al.
patent: 5128001 (1992-07-01), Bagg et al.

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