Chemistry: electrical and wave energy – Processes and products – Electrostatic field or electrical discharge
Patent
1995-07-14
1998-01-27
Gorgos, Kathryn L.
Chemistry: electrical and wave energy
Processes and products
Electrostatic field or electrical discharge
204178, C01B 2100
Patent
active
057118590
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The field of the present invention is that of the treatment and the upgrading of nitrous oxide N.sub.2 O (laughing gas) and, more particularly, of its conversion into a product of the type NO.sub.x where x=1 or 2, as well as into derivatives such as, for example, nitric acid HNO.sub.3.
The present invention relates to a process for the plasma-chemical oxidation of dinitrogen monoxide.
DESCRIPTION OF THE PRIOR ART
Out of a volume of 100 of N.sub.2 O discharged into the atmosphere, it is generally accepted that 70% is derived from metabolism in the plant kingdom, 10% from combustions of all types, 10% from internal combustion engines of motor vehicles and the remaining 10% are industrial gaseous effluents. 2% of these effluents originate from the production of nitric acid and 8% from the production of adipic acid (one of the basic components of polyamide 6,6). (Cf. 5th International Workshop on nitrous
In recent times, considerable research means and efforts have been devoted to nitrous oxide N.sub.2 O, since it is suggested that its accumulation in the atmosphere may constitute an environmental risk. In particular, N.sub.2 O is suspected to be involved in the greenhouse effect phenomenon.
The lifetime of N.sub.2 O in the atmosphere is of the order of 170 years. It is a stable gas at room temperature which virtually does not combine with molecular oxygen and which is quite resistant to the action of standard oxidizing agents.
The three main usual routes of treatment or of upgrading of N.sub.2 O are:
1--thermal destruction by incineration,
2--catalytic decomposition into gaseous nitrogen and oxygen N.sub.2 and O.sub.2,
3--and thermal conversion into NO.sub.x where x=1 or 2 and into derivatives thereof.
The third route is particularly advantageous since the compounds NO.sub.x are recyclable, for example into nitric acid HNO.sub.3. The upgrading of N.sub.2 O into HNO.sub.3 is of the greatest interest, especially for adipic acid producers, given that nitric acid is used to convert cyclohexanol and/or cyclohexanone, by oxidation, into adipic acid, this reaction furthermore producing approximately one mole of N.sub.2 O per mole of final adipic acid. (Nylon Production: an Unknown Source of Atmospheric Nitrous Oxide--N. H. Thiemens, W. C. Trogler, Science, February 1991).
In order for this recycling to be viable, it is essential that the conversion of N.sub.2 O into NO.sub.x should be performed in an economically profitable manner, that is to say with reduced amounts of energy, of reactants and of catalysts.
However, it is found that the N.sub.2 O reaction giving NO+1/2 N.sub.2 is in competition with the N.sub.2 O reaction giving N.sub.2 +1/2 O.sub.2.
The conversion of N.sub.2 O into NO.sub.x is thus very intricate to carry out, as is illustrated by the patent JP 61 25 79 40 which relates to a process for the preparation of dicarboxylic acids in which recycling of nitric acid is carried out. According to this process, the gaseous side products of the oxidation, using nitric acid, of cyclohexanol and/or cyclohexanone into adipic acid are subjected to continuous thermal decomposition without a catalyst for converting N.sub.2 O into NO.sub.x. The latter compound is then converted into nitric acid by oxidation and absorption into water, according to the following reaction scheme:
2 NO+O.sub.2 .fwdarw.2 NO.sub.2
3 NO.sub.2 +H.sub.2 O.fwdarw.2 HNO.sub.3 +NO
The HNO.sub.3 is then recycled into the reaction for the synthesis of adipic acid.
According to this Japanese patent, the gaseous side products NO+NO.sub.2, which are factors limiting the conversion of N.sub.2 O into NO.sub.x, should be removed as fully as possible.
The starting NO.sub.x should be at a content below 10% and preferably below 5%.
The reaction temperature is between 1000.degree. and 1300.degree. C., and is preferably 1000.degree. to 1200.degree. C., and the residence time is from 10.sup.-2 to 100 seconds, and preferably from 10.sup.-1 to 10 seconds. The gas to be treated is preheated using a hot air heating appliance of the
REFERENCES:
patent: 1035684 (1912-08-01), Bunet et al.
"Diagnostics and Modeling of N.sub.2 O RF Glow Discharges," Todd A. Cleland et al., 1997 INIST CNRS., pp. 3103-3111, Jul. 1992.
C.R. Acad. Sc. Paris, t. 272, Jean Mahenc et al., Jan. 25, 1971, pp. 345-346.
"Decomposition of N.sub.2 O in a Glow Discharge,"J.M. Austin et al., J. Phys. D: Appl. Phys., pp. 2236-2241, vol. 6, 1973 (no month available).
Caplus 1971; 104,395. no month available.
Caplus 1974: 43,602. no month available.
Caplus 1989: 645,952. no month available.
Caramel Andre
Czernichowski Albin
Gorius Andre
Gorgos Kathryn L.
Mayekar Kishor
Rhone-Poulenc Chimie
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