Chemistry: electrical and wave energy – Processes and products – Processes of treating materials by wave energy
Patent
1992-02-13
1994-05-24
Walsh, Donald P.
Chemistry: electrical and wave energy
Processes and products
Processes of treating materials by wave energy
423 2, B01D 500
Patent
active
053145925
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method for separation and enrichment of oxygen 18 with a laser, and more particularly to a method for enrichment of oxygen 18 utilizing infrared multiple-photon decomposition of a saturated aliphatic ether other than dimethyl ether or a saturated cyclic ether with a TEA--CO.sub.2 laser.
DESCRIPTION OF THE PRIOR ART
There exist naturally three isotopes of oxygen, oxygen 16, oxygen 17 and oxygen 18, which account for 99.8%, 0.037% and 0.204% of the Earth's oxygen, respectively. Enriched oxygen 18 isotope is widely used as a tracer and is in strong demand. Therefore, an economical method of enrichment of oxygen 18 capable of supplying large amounts of oxygen 18 would profit a society and promote scientific progress.
Methods for enrichment of oxygen 18 able to produce more than 1 g/day that have been studied up to now include the distillation method, the electrolytic method and the chemical exchange method. Actual enrichment of oxygen 18 is currently being conducted using the NO low temperature distillation method at a production rate of 3 kg/year of oxygen 18 having at least 90% purity. However, the enrichment factor (.alpha..sub.18) of .sup.18 O (1.037) is low, the operatrion temperature is low (-151.8.degree. C.), and too large plant systems (a low enrichment distillation column (42 m) and a high distillation column (90 m)) are required. The inventors therefore studied the laser isotope enrichment method for its potential to enable reduction of plant size, highly selective single-step enrichment, and shortening of the processing time.
When a gaseous substance is irradiated with strong pulsed infrared laser light, it dissociates after absorption of several tens of infrared photons per single molecule. This is known as infrared multiple-photon decomposition. By properly selecting the starting materials and irradiation conditions, it is possible to dissociate isotopes with high selectivity. Thus, the infrared multiple-photon decomposition can be applied for enrichment and separation of isotopes.
Laser isotope separation and enrichment with a TEA--CO.sub.2 laser, which posesses relatively high laser power and is one of the easiest to operate among commercially available pulsed infrared lasers, has been studied in detail.
Chemical compounds already studied for enrichment of oxygen 18 utilizing oxygen 18 selective infrared multiple-photon decomposition with a TEA--CO.sub.2 laser include dimethyl ether 1 [V. V. Vizhn, Y. N. Molin, A. K. Petrov, and A. R. Sorokin, Appl. Phys., 17, 385 (1978)], 2 ]K. O. Kutschke, C. Willis, P. A. Hackett, J. Photochem., 21, 207 (1983)], 3 [Tetsuro. Majima, Takashi. Igarashi, and Shigeyoshi. Arai, Nippon Kagaku kaishi, 1490 (1984) ], perfluoroacetone [P. A. Hackett, C. Willis, and M. Gauthier, J. Chem. Phys., 71, 2682 (1982)], and UO.sub.2 (hexafluoroacethyl acetone), (tetrahydorofuran) [D. M. Cox, R. B. Hall, J. A. Horsley, G. M. Kremer, P. Rabinowitz, and A. Kaldor, Science, 205, 390 (1979)].
One object of laser isotope separation and enrichment is to enable high selectivity and to increase decomposition and product yields. Generally, higher decomposition and product yields decrease selectivity. Laser isotope separation and enrichment are generally optimized by optimum selection of starting materials and irradiation conditions. In the laser enrichment of oxygen 18, ethers whose C--O bonds dissociate initially are some of the most suitable raw materials.
Dimethyl ether absorbs infrared energy by the inverse symmetric stretching vibration of C--O--C bond and fluoro-substituted carbonyl compounds absorb infrared energy by the stretching vibration of C--F bond in the oscillation region of a TEA--CO.sub.2 laser. The selective laser multiple-photon decomposition of oxygen 18 can be initiated by irradiation with TEA--CO.sub.2 laser light on the lower wavenumber side of the absorption.
The enrichment of oxygen 18 by the prior art methods using dimethyl ether as a raw material generally involves the use of relatively expensive ra
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Chemical Abstracts, vol. 111, No. 16, p. 559, Oct. 9, 1989, No. 142702q, V. B. Laptev, et al, "Laser Separation of Oxygen Isotopes By IR Multiphoton Dissociation of Dimethyl Ether".
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Arai Shigeyoshi
Majima Tetsuro
Sugita Kyoko
Mai Ngoclan T.
Rikagaku Kenkyusho
Walsh Donald P.
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