Structured zeolite adsorbents

Sammanfattning: Zeolites are microporous crystalline aluminosilicates with unique properties, and therefore used in adsorption processes, for membrane separation, in catalysis, and in sensor technologies. Pressure swing adsorption (PSA) is a commonly used technology for purifying gases and is based on the ability of materials like zeolites, to selectively adsorb and desorb particular gas molecules as the gas pressure is increased and reduced, respectively. Adsorbents in form of beads and extrudates are traditionally used in PSA processes. When using materials in this form, there is a trade-off between pressure drop and heat- and mass-transfer limitations. Novel structured adsorbents with low pressure drop and reduced heat- and mass-transfer limitations may represent a competitive alternative to traditionally used adsorbents. Thin zeolite films grown on monolith substrates may be particularly suitable for the purpose. In this work, thin NaX and MFI zeolite films were grown on ceramic cordierite monoliths and the adsorption ofCO2 and NOx was measured. NaX zeolite films with controllable thickness were grown on cordierite monoliths with different cell density. In this study, suitable synthesis conditions for the growth of supported NaX films were identified. The CO2 adsorption capacity and the pressure drop for the supported films were compared to those of a packed NaX bed. Although the adsorption capacity per gram sample was 25 times lower, the pressure drop of the structured adsorbent was 100 times lower than the NaX packed bed, indicating the potential advantage of structured adsorbents in PSA processes. NOx adsorption on supported MFI films with varying Si/Al and Na/Al ratio was also studied. An increase of Al and Na content in the films results in a higher amount of physisorbed NO2 at low temperature, due to an increase in the number of weak adsorption sites. At higher temperature, the amount of NO2 adsorbed was nearly independent of aluminum and sodium concentration for all MFI film samples. The results from this work indicate that novel structured adsorbents based on supported thin NaX and MFI zeolite films represent a competitive alternative to traditional adsorbents and can be used as selective adsorbents for CO2 and NOx adsorption.