(718d) Tailoring the Electric Resistivity of a Molecular Sieve Adsorbent for Electrothermal Regeneration

Electrothermal regeneration is an adsorbent regeneration technique whereby electric current is passed through a material with sufficiently low resistivity (typically, 0.1 â?? 10 Ω.m) and heat is generated by the Joule effect. This allows for rapid adsorbent regeneration that is decoupled from the purge gas flow. Molecular sieves are effective adsorbents because they have tailored and structured pore size distributions. Unlike carbonaceous materials, however, molecular sieves have high electrical resistivity that prevents their electrothermal regeneration. In this study, carbon nano tube (CNT) was added to zeolite Y (high resistivity, >E+7 Ω.m) to decrease its resistivity. CNT was added by CH₄ decomposition on cobalt impregnated zeolite Y. The effect of CNT growth condition on the properties of zeolite Y was investigated to find the optimum condition to improve its electrical conductivity without compromising its adsorption properties. Specifically, the effect of calcination temperature and duration, cobalt cations reduction, and methane decomposition were studied. Modified samples were characterized using bulk elemental analysis, scanning electron microscopy (SEM), X-ray diffraction, and resistivity measurements. The results indicated that reduction temperature has the most significant effect on the size and amount of CNT deposited on the surface of zeolite Y during each step. The reduction temperature could significantly alter properties of prepared sample, as its CNT content decreased from 37 to 9 %C and its conductivity decreased from 6.25 to 0.71 S/m, once the temperature decreased from 500 to 400 ºC. SEM images revealed smaller CNT for samples prepared at lower reduction temperature. Although reducing the temperature resulted in less CNT on the zeolite, it led to less change in zeolite adsorption properties while providing suitable conductivity for electrothermal regeneration. The developed low-temperature procedure could be applied to tailor the electric resistivity of other adsorbents.