Cryogenic Adsorption Behavior Of Hydrogen Isotopes On Carbonaceous Adsorbents

Some of the best-known theories of cryogenic adsorption of hydrogen isotopes on solid Adsorbents are briefly reviewed in the first chapter. Many research works with respect to hydrogen isotopes cryogenic adsorption, focusing on its applications to fusion fuel process technology, are summarized. Comments are given on some of the application examples and a few aspects needed to study in the near future are also presented.In the second chapter, adsorption isotherms of H2 and D2 on Activated Carbon (AC), Carbon Molecular Sieve (601) and Carbon Nano-fibers (CNF), are investigated at liquid nitrogen temperature by using a method of differential pressure. Surface modification tests of three kinds of carbonaceous absorbents are carried out to demonstrate the feasibility of increasing their adsorption amount of hydrogen isotopes. Kinetics of adsorption process is studied through the on-line pressure monitoring and adsorption rate is measured by monitoring pressure change over the factor of time in the adsorption process. The method of direct reduction of Pd2+ in alkaline aqueous solution is adopted to deposit Pd on porous surface of carbonaceous adsorbents. Results indicate that Pd nano-crystallites are produced and these Pd nano-crystallites have a high catalytic activity to hydrogen isotope exchange reactions.In the third chapter, the possibility of recovering low concentration hydrogen isotopes from a helium gas stream is tested by analyzing a series of break-through curves at the different levels of hydrogen concentration in helium gas. Results show that 601 and AC are good candidate adsorbents and cryogenic adsorption of hydrogen isotopes on these porous adsorbents at liquid nitrogen temperature is an attractive way to recover low concentration hydrogen gas from a helium stream.The last chapter involves theoretical calculations with respect to isotherms and kinetics of the cryogenic adsorption of hydrogen isotopeson various carbonaceous adsorbents. Two kinds of Langmuir isotherm models, the one type of active adsorption sites and the two types of active adsorption sites, are used to calculate an adsorption isotherm respectively. Isotherm calculation results indicate that the hydrogen isotope gas molecules are adsorbed on the surfaces of carbonaceous adsorbents according to the model of multiple types of active sites. Accordingly, a localized Langmuir monolayer is anticipated to achieve if hydrogen isotope molecules occupy all kinds of the active sites. According to the theoretical calculation of kinetic process, it is concluded that the adsorption rate of hydrogen isotope gas is related not only to the gas pressure gradient, but also to the cover rate of adsorbate molecules on the surface of an adsorbent.