A. Ikeda

J. Miyazaki

K. Fukuda

K. Kotoh

K. Yamada

S. Fukada

T. Kawano

T. Nishida

T. Uda

Y. Asakura

National Institute for Fusion Science (NIFS-Repository)

§3. Experimental Analysis of Hydrogen Adsorption for Isotope Separation/ Purification by Pressure Swing Adsorption Kotoh, K., Fukada, S. (Kyushu Univ. Eng.), Nishida, T., Ikeda, A., Fukuda, K. (Kinki Univ. Eng. Kyushu), Asakura, Y., Uda, T., Kawano, T., Yamada, K., Miyazaki, J. The hydrogen isotope separation process is necessary for the environmental safety management of exhausted gas from LHD deuterium experiments. Several methods are available for the isotope separation. The method of pressure swing adsorption (PSA), operating rapid desorption in a short period, has become applied to medium-massive separation of air-components. In this study, aiming at applying the PSA to the isotope separation process, we examine the multi-component adsorption behavior of hydrogen isotopes on an adsorbent. In this work, we investigate the adsorption isotherms for H2 and D2 on synthetic zeolite 5A-type at the liquid nitrogen temperature 77.4 K and the isotope separation factors in Hz-D2 or Hz-HD-D2 systems, using a volumetric adsorption apparatus. Isotherms are necessary for theoretical prediction of the multi-component adsorption behavior. Figure 1 shows experimental isotherms for H2 and D2 on the zeolite in a wide range of equilibrium pressure from 10-2 to 105 Pa, which can be closely approximated by an error-functional expression with respect to adsorption potential, proposed here: R=_I_ r C exp{- (£_£)2 }d£ Qs a& lr» 2a2 ' (1) £-£ = RTln(P / P) (2) where Q is the amount adsorbed on a basis of evacuated adsorbent, and Qs the amount adsorbed in saturation. The adsorption potential is expressed by Eq.(2), where P is the equilibrium pressure, and P the representative pressure corresponding to the mean potential £ . The isotope separation factor in an adsorption system is defined as SF = (x heavy / XZight) ads a~ / ' (Yheavy YZight) gas (3) where x is the mole fraction of a heavy or light component in the adsorbed phase, and Y the mole fraction in the gas phase. Figure 2 shows hydrogen isotope separation factors with respect to the amount of each isotopic mixture adsorbed in a wide range roughly between 0.002 and 4 mol/kg, where experimental values are plotted. A solid line represents the values of SFD21H2 estimated from the ideal adsorbed solution (lAS) theory using the isotherms for H2 and D2. This solid line curve simulating the plot lineup of SFD2/H2 suggests that the behavior of hydrogen isotopes on the zeolite can be interpreted by the lAS theory. Broken lines empirically approximate the experimental SFD2/HD and SFDHlH2 · The experimental values of SFD2/HD' SFDHlH2 and SFD21H2 in each of H2-HD-D2 mixtures are consistent with accuracy of a 0.4-2.30/0 error in the relationship of SFD IH = SFD IHDSFDHIH . ( 4) 2 2 2 2 Figure 2 demonstrates that SFD21H2 values from about 2 to more than 3, SFD2/HD values from about 1.6 near to 2, and SFDHlH2 values from about 1.3 to around 1.6 are expectable in the cryo-sorption system of hydrogen on the zeolite 5A-type at 77.4 K. In prediction of the adsorption behavior of hydrogen isotopes including tritium, it is inferable from the zero-point-energy mass-effect that the separation factors SFT2/H2 and SFDTIH2 are larger than SFD21H2 while the factor SFHTIH2 is near but less than SFD IH . 2 2 The fundamental characteristics of adsorption, important in the consideration of the isotope separation process using the PSA method, are revealed in this work. bil 10° S Q .§. 10-1 "C ~ .Q Experimental .. 10-2 Q .: D2 til "C 0: H2 ~ .. 10-3 C = -: Error-functional curves Q ~ for approximation 10-5 10-2 101 102 103 104 105 Pressure [Pa] Fig. 1 Isotherms for H2 and D2 on zeolite 5A-type at 77.4 K 4 .......,..,......--.-......1 ~erlmental • o : (D2/112)0/(D2/112)I In Dz..H2 ~ : (D2/H2)0/(D2/H2)I In D z..HD-H 2 V : (D2/HD) a/(D2/HD) 1 In H2-HD-D 2 :: ::::~::::;:::::: :~:> 1--=-= : Estimation based on lAS theory .1kppiuzimatiuD o -3 -2 -1 1 10 10 10 10 10 AmOWlt of mixture adsorbed [mollkg] Fig. 2 Separation factors of hydrogen isotopes on zeolite 5A-type at 77.4 K 277 

Experimental Analysis of Hydrogen Adsorption for Isotope Separation/ Purification by Pressure Swing Adsorption

Experimental Analysis of Hydrogen Adsorption for Isotope Separation/ Purification by Pressure Swing Adsorption

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