Study On The Hydrogen Purification And Recovery Abilities Of Zr-based Metal Hydrides

For its react readily ability with impurity gas, metal hydride can be used as purifier to absorb impurity gas among hydrogen. As reversible hydrogen storage materials, metal hydride can be used as recovery to take in hydrogen from mixed gas. The structure and morphology of materials were characterized by XRD and SEM, The hydrogen sorption thermodynamic properties and kinetic properties of materials were measured by manometric sorption measurement system, concentration of impurity gas was measured by gas chromatography, surface condition of materials was detected by XPS.Firstly, hydrogen absorption PCT and absorption kinetics of Zr-based metal hydrides were measured. Enthalpy, entropy and activation energy of hydrogen absorption were obtained.Absorption process of N2, O2 and CH4, CO2 for Zr-based metal hydrides were investigated, including absorption efficiency, absorption capacity and absorption products. Absorption efficiencies of N2 and O2 were measured at various temperatures. Results show that concentration of N2 and O2 were lower than 0.500 ppm. N2 and O2 absorption capacities of material were obtained, by measuring the N2 and O2 absorption breakthrough curves. It was found that H2O emerged before concentration of O2 arising when purify H2 contains O2. By analyzing the surface of materials using XPS, it was found that N2 absorption products of materials were ZrN and TiN, N2 absorption products of materials were oxides and hydroxides of Ti and Zr.CH4 and CO2 absorption efficiencies were influenced by temperature, and absorption efficiency decreased as temperature decreasing. It is notable that CO2 would react with H and produce CH4. As for CH4 and CO2 absorption, lower temperature decreasing C atoms diffusion rate, accumulating C atoms on the surface of materials. Accumulated C atoms on the surface would react with H and produce CH4, increasing concentration of CH4 and decreasing absorption capacity. CH4 and CO2 absorption capacities of material were obtained, by measuring the CH4 and CO2 absorption breakthrough curves. By analyzing the surface of materials using XPS, it was found that CO2 absorption products of materials was TiC.The influence of N2 and O2 on hydrogen absorption were investigated for Zr-based metal hydrides, based on the study of N2, O2, CH4 and CO2 absorption process. Fitting hydrogen absorption curves with kinetic model, it was found that rate-limited step of hydrogen absorption was hydride formation. As for H2 contains N2, rate-limited step of hydrogen absorption was chemical absorption and Elovich formal fit absorption kinetic curves quiet well. As for H2 contains O2, hydrogen absorption process could divided into faster absorption period and slow absorption period. In faster absorption period, rate-limited step of hydrogen absorption was hydride formation. In slow absorption period, rate-limited step of hydrogen absorption was chemical absorption and kinetic curves could be fitted by oxidation model. As for H2 contains both N2 and O2, hydrogen absorption kinetic curves could by fitted by oxidation model.N2 and O2 alter hydrogen absorption process, result in materials poisoning. Materials was modified by electroless plating to improve anti-poisoning ability. Then the absorption kinetic curves was measured among H2 contains both N2 and O2, it was found that Pd coating could improve anti-poisoning ability of materials. Another surface modification method was selected, which was pre-treating materials before electroless plating. It was found that absorption kinetic of pre-treated materials was excellent. According to the kinetic curves analysis, rate-limited step was transferred from chemical absorption into two diffusion by Pd coating. And Pd is a permselective membrane which separate H from mixed gas.