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  • Author or Editor: D. Axente x
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Abstract  

Enrichment of 13C by chemical exchange between CO2 and amine carbamate in nonaqueous solvents has been mathematically modelled in two ways. The height equivalent to a theoretical plate and steady-state separation, based on the two models, have been obtained. If only the isotopic exchange between CO2 gas and amine carbamate is considered, the model can estimate the process performance for pressures close to the atmospheric one and room temperature. For process analysis at pressures higher than the atmospheric one and lower temperatures, a two-step model has been used. Using the two models the effects of pressure have been studied.

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Abstract  

Starting with an accurate mathematical model a theoretical study for the analysis of the separation of uranium isotopes by chemical exchange has been presented. The experimental data used in this study were obtained by reverse breakthrough technique and the numerical algorithm developed for simulation in previous studies was adapted and found to be suitable for this kind of processes. The model parameters were identified from experimental data and simulations were carried out for different experimental conditions.

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Abstract  

The rate of nitrogen isotope exchange between NO and HNO3 has been measured as a function of nitric oxide pressure 0.1–0.4 MPa for 1 and 2 M·1–1 HNO3. It is concluded that15N/14N exchange rate in NO–HNO3 system has a linear dependence of NO pressure as indicated by rate measurements at different NO partial pressure and constant overall pressure, by adding helium in reactor. Using the rate law:R=k[HNO3]2[N2O3] the15N/14N exchange rates for nitric acid concentrations 1.5–10 M·1–1 were calculated.

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Abstract  

The rate of nitrogen isotope exchange between NO and HNO3 has been measured as a function of nitric acid concentration of 1.5–4M·1–1. The exchange rate law is shown to beR=k[HNO3]2[N2O3] and the measured activation energy isE=67.78kJ ·M–1 (16.2 kcal·M–1). It is concluded that N2O3 participates in15N/14N exchange between NO and HNO3 at nitric acid concentrations higher than 1.5M·1–1.

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Abstract  

Thermal decomposition of uranium double fluoride in a screw reactor in the temperature range of 250–500 °C is presented. Using integral reactor relation, kinetic parameters are discussed in terms of the shrinking core grain model. Arrhenius global activation energy is also determined.

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Abstract  

The basic isotopic exchange reaction is responsible for the separation of15N in the Nitrox system that between gaseous nitrogen oxides and aqueous nitric acid with a single stage separation factor α=1.055 for 10M nitric acid, at 25°C and atmospheric pressure takes place. In order to know what happens in15N separation at higher pressure, when the isotopic transport between two phases is improved, a stainless steel laboratory experimental plant with a 1000 mm long × 18 mm i.d. column, packed with triangular wire springs 1.8×1.8×0.2 mm2, was utilised. At 1.5 atm (absolute), and 2.36 ml·cm−2·min−1 flow rate HETP was 7% smaller than at atmospheric pressure and 1.5 times smaller flow rate. HETP at 3.14 ml·cm−2·min−1 flow rate and 1.8 atm is practically equal with that obtained at atmospheric pressure and 2 times smaller flow rate. The operation of the15N separation plant at 1.8 atm (absolute), instead of atmospheric pressure, will permit doubling of the 10M nitric acid flow rate and of15N production of the given column.

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Abstract  

The rate of the15N/14N isotopic exchange between NO−HNO3 at high nitric acid concentration (2–10M) have been measured. The experimental data were obtained by contacting nitric oxide at atmospheric pressure with nitric acid solution labelled with15N, in a glass contactor.

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