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1.5. Scope of the present work 11 1.4.2 Monolith supports Monoliths are structured supports with parallel channels, available with various cell den- sities and geometries [34, 40]. Low pressure drop, uniform flow distribution, thermal stability and easy scale-up are some of the advantages with these materials. The mineral cordierite, (Fe, Mg)2Al4Si5O18 is often used for monoliths, since it has a low coefficient of thermal expansion and a tailorable macrostructure. Monoliths are widely used in cat- alytic converters for cars since the 1960s [34, 41] rather than in adsorption processes. Further, they may also be employed as diesel particulate filters to purify the exhaust gases from diesel engines. 1.4.3 Coated monoliths The monolith supports may be coated with an active material (adsorbent or catalytic material) using different techniques, such as wash-coating, dip-coating, slip-coating, or slurry-coating. Due to the difficulties in washcoating the monolith with pure zeolite, a binder material is needed. However, the binder causes a reduction in the accessible surface area of the zeolite coating and increases the diffusion resistance of the adsorbing species. Further, due to surface tension effects during manufacturing, more material is deposited in the corners of the monolith channels, consequently increasing the diffusion path [37]. Alternatively, a zeolite film may be grown on the monolith as explored by our group [42]. Thin ZSM-5 zeolite films without binder material were grown on 400 cpsi cordierite monoliths by first depositing a monolayer of colloidal zeolite seed crystals on the monoliths and then growing the crystals to thin films. The catalytic activity of the films was subsequently evaluated by p-xylene isomerisation, and the effect of film thickness on mass transfer was clearly demonstrated. As opposed to washcoated monoliths, these films had an even thickness, i.e. no effects of surface tension leading to thicker films in the corners. 1.5 Scope of the present work In this work, very thin zeolite films were grown on the walls of ceramic cordierite mono- liths to arrive at adsorbents with desirable adsorption and mass transfer properties. The goal was to develop a competitive alternative to traditionally used adsorbents in the form of beads or extrudates. In order to reach this goal, the scope of the present work was: • To study the effect of different synthesis routes on the growth of zeolite films on cordierite monoliths • To study the effect of different ceramic cordierite monoliths on zeolite film growth • To investigate the CO2 and NOx adsorption properties of the structured adsorbentsPDF Image | Structured Zeolite Adsorbents for PSA Applications
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