Evaluation of Critical Parameters of Neon Isotopes for Comparative Analysis of Various Methods for Separating Them

Abstract

Several tasks related to the use of xenon (Xe) and neon (Ne) isotopes were formulated at the end of the 20th century [1]. Xe has nine stable isotopes ( 124 Xe, 126 Xe, 128 Xe, 129 Xe, 130 Xe, 131 Xe, 132 Xe, 134 Xe, 136 Xe); Ne, three ( 20 Ne, 21 Ne, 22 Ne) [1, 2].The separation coeffi cient can be used to evaluate technical and economic factors of the process for separating a binary gas mixture [1, 3] and is approximated for diffusion separation of a mixture (through a porous diaphragm) as [1,4] (1)where M h and M l are the molecular masses of the heavy and light components, respectively.Equation (1) is valid for Knudsen fl ow through a porous diaphragm. The separation coeffi cients for the binary mixtures 20 Ne-21 Ne, 20 Ne-22 Ne, and 21 Ne-22 Ne are k s 20-21 ≅ 1.0247, k s 20-22 ≅ 1.0488, k s 21-22 ≅ 1.0235, respectively. The separation in one stage is miniscule; however, it can be increased by combining diffusion cells [5]. The mole ratio 20 Ne: 22 Ne ≈ 9.8:1.0 or y 22 Ne ≈ 0.092 is used for estimating the number of diffusion cells (number of contact stages) for separating the 20 Ne-22 Ne mixture. The separation coeffi cient of the mixture is set to k s 20-22 ≅ 1.0488 = const whereas k s 20-22 ≅ 1.0200 for comparison. Figure 1 shows the required number of diffusion cells (calculated by the literature method [6]). Stable Xe isotopes are produced in Russia mainly by centrifuge technology [1]. The separation coeffi cient for a binary mixture of ideal gases by centrifuge technology (at constant temperature) is [1](2) where ϖ is the angular velocity; a, the rotor radius; T, the temperature; and R, the gas constant.

Comparative Analysis of Various Adsorbents for Low-Temperature Separation of a 20Ne–22Ne Isotopic Mixture

“…A 20 Ne-22 Ne separation coefficient k s ≈ 1.003 over NaX zeolite at 78 K was reported [1]. Figure 1 shows the number of contact stages as a function of 22 Ne mole fraction in the product where the Lewis assumption is valid [3,4].…”

“…Adsorption isotherms of Ne isotopes were evaluated in previous work [3]. Adsorption of natural Ne on various ACs and zeolites at liquid N 2 temperature was studied at normal pressure and near the triple point [5][6][7].…”

“…Previous results were considered in selecting the adsorbents [1, 2, 5-7]. The Ne isotope adsorption isotherms were calculated approximately using the Dubinin equation (theory of bulk fi lling of micropores, TBFM) and the published critical parameters of the isotopes [3].…”

“…(5), the last functions z((τ 2 π) -1 ) T=77 were calculated as (11) (the 20 Ne and 22 Ne critical parameters in Eqs. (6)- (11) were taken from the literature [3]). Then, adsorption of the Ne isotopes at the given pressure was evaluated using Eq.…”

“…This result was expected if Eq. (3) was adequate for the examined systems because the critical temperatures differed by only ΔT ≈ 1.1 K [3]; the molar masses, by ΔM ≈ 0.182 g/mol [1]. The adsorption isotherms of natural Ne and 22 Ne differed more signifi cantly with ΔT ≈ 6.3 K [3] and ΔM ≈ 1.820 g/mol [1].…”