Springer Online Journal Archives 1860-2000
Abstract The laboratory scale-up of a two-stage laser enrichment process for carbon isotopes, involving infrared multiphoton dissociation of freon-22, is described. Unmodified commercial equipment and materials were used. An initial study of the effect of fluence, laser frequency, freon-22 pressure and pressure of argon, nitrogen and trifluoromethyl chloride was made in short irradiation cells (constant fluence) in order to define optimum process parameters. The process was then scaled to higher throughput in longer cells (1–5 m) in which compensation for beam-energy depletion by absorption was made by reduction in the beam area by focussing. From the scale-up experiments, measurements of yield and enrichment of the tetrafluoroethylene product gave demonstrated production rates. These, coupled with measurements of the absorption, allowed extrapolation to production rates assuming total utilization of the available output energy. Using a 100 W TEA CO2 laser (10 J, 10 Hz) we have demonstrated production rates of 0.20 g h−1 carbon-12 at 99.99% carbon-12, 11 mg h−1 carbon-13 at 72% carbon-13 and 2 kg per annum carbon-13 at 50%. Energy absorption measurements imply a capability to produce 3 kg per annum carbon-13 at over 95% carbon-13 in a two-stage process. The apparatus was used to produce gram quantities of carbon-13 depleted freon-22 (99.99% carbon-12). A comparison of the infrared multiphoton dissociation of this material with that of natural freon-22 (1.11% carbon-13) showed that under the conditions required to give selective dissociation of13CF2HCl that12CF2HCl was excited as a result of a dominantly radiative interaction and that collisional transfer from13CF2HCl molecules played a minor role.
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