(661f) Tailoring Resistivity of Engelhard Titanosilicate (ETS-10) Molecular Sieve By Carbon Addition
Resistive heating is a technique for regenerating adsorbents whereby electric current is passed through a material with sufficiently low resistivity (typically, 0.1 – 10 Ω.m) and heat is generated by the Joule effect. This allows for rapid and low-cost adsorbent regeneration that is decoupled from the purge gas flow. Molecular sieves are effective adsorbents because they have tailored and highly structured pore size distributions. Unlike carbonaceous materials, however, molecular sieves have high electrical resistivity that prevents their regeneration by resistive heating. In this study, different methods were investigated for adding carbon (low resistivity) to Engelhard Titanosilicate (ETS-10) molecular sieve (high resistivity, ~5E+6 Ω.m) in order to decrease its resistivity without compromising its unique physical structure. Carbon was added to ETS-10 using chemical vapor deposition (CVD) of ethanol, thermal degradation of polyvinyl alcohol (PVA), and mixing with powdered carbon. Modified samples were characterized using micropore surface analysis, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning electron microscopy (SEM), and resistivity measurements. XPS, SEM, and a color change from white to grey confirmed the addition of carbon onto ETS-10 using all tested methods. Results from resistivity measurements showed decreases in ETS-10 resistivity, by up to 6 orders of magnitude, for the modified samples. The BET surface area of samples prepared by CVD was between 55 and 99% lower than untreated ETS-10, suggesting that the carbon coating caused pore blockage. Conversely, using PVA degradation, decreases in BET surface area were less significant, especially at 400 °C (5% decrease). Mixing of ETS-10 with carbon significantly decreased the resistivity, but the resulting mixtures required large amounts of binder to maintain uniformity and mechanical stability, drastically decreasing the ETS-10 weight ratio. For samples with the lowest resistivity (e.g., mixed with carbon), heating rates were measured during resistive heating and compared with more traditional heating methods, with results suggesting that faster and more energy efficient heating is possible.