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OPTIMIZING SYNTHESIS CONDITIONS AND SUPPORT TYPE FOR STRUCTURED PSA ADSORBENTS Alessandra Mosca and Jonas Hedlund Division of Chemical Technology, Luleå University of Technology, SE-97187, Luleå, Sweden Tel. +46 920 491293, Fax +46 920 491199, E-mail: Alessandra.Mosca@ltu.se SUMMARY Thin faujasite films were grown on porous and dense cordierite monoliths by hydrothermal treatment using a gel or a clear solution. Well defined FAU films with a thickness of 2 m and 1 m could be grown by using the gel on the dense and porous supports, respectively. However, a relatively high weight gain after synthesis was recorded for the porous monolith due to zeolite crystallization in the pores, which may be undesirable for PSA applications. The films grown in the clear solution consisted of both FAU and sodalite crystals. The thickness of the FAU films was about 2 or 0.7 m, depending on support type. A 5 times lower weight gain was observed and much less zeolite grew in the pores of the porous substrate, which may be an advantage for PSA applications. By using the clear solution and a multiple-step synthesis on the porous support a 1.5 m FAU film with no sodalite crystals was grown. The adsorption properties of the samples are currently under investigation. INTRODUCTION Structured adsorbents in the form of supported thin zeolite films may have superior properties compared to traditionally used zeolite adsorbents in the form of beads [1, 2], which may have mass - and heat - transfer limitations in PSA applications. Structured adsorbents may thus result in improved performance in PSA applications. FAU zeolite is a suitable adsorbent for CO2 separation from flue gas or O2 enrichment from air by PSA. EXPERIMENTAL Porous (400 cpsi, Corning) and dense (100 cpsi, Rauschert) cordierite monoliths were used as structured supports. The supports were seeded with 60 nm faujasite crystals, as described elsewhere [3]. A gel with molar composition of 14Na2O:1Al2O3:10SiO2:797H2O or a clear synthesis solution with molar composition of 80Na2O:1Al2O3:9SiO2:500H2O was used for film growth. Hydrothermal treatment was performed in an oil bath under reflux at 100 C. The samples were characterized by SEM, XRD, and weight gain after synthesis was recorded. RESULTS AND DISCUSSION Figures 1 (a, d) show SEM images of a faujasite film grown for 6 hours and 40 minutes on a porous cordierite monolith using the clear solution. The FAU film is uneven and relatively large sodalite crystals are embedded. The FAU film thickness is about 700 nm and the sodalite crystals vary from 1 to about 2 m in size. A faujasite film grown using the clear solution on a dense cordierite support is more even and with a film thickness of about 2 m and smaller sodalite crystals are observed, as shown in Figures 1 (b, e). These results showPDF Image | Structured Zeolite Adsorbents for PSA Applications
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