Laminated Adsorbents with Very Rapid CO₂ Uptake by Freeze-Casting of Zeolites

Abstract

Structured zeolite 13X monoliths with a laminated structure and hierarchical macro-/microporosity were prepared by freeze-casting aqueous suspensions of zeolite 13X powder, bentonite, and polyethylene glycol. Colloidally stable suspensions with a low viscosity at both room temperature and near freezing could be prepared at alkaline conditions where both the zeolite 13X powder and bentonite carry a negative surface charge. Slow directional freezing of the suspensions led to the formation of well-defined and thin lamellar pores and pore walls while fast freezing resulted in more cylindrical pores. The wall thickness, which varied between 8 and 35 μm, increased with increasing solids loading of the suspension. Thermal treatment at 1053 K of the freeze-cast bodies containing between 9 and 17 wt % bentonite resulted in mechanically stable zeolite 13X monoliths. The monoliths displayed a carbon dioxide uptake capacity of 4-5 mmol/g and an uptake kinetics characterized by a very fast initial uptake where more than 50% of the maximum uptake was reached within 15 s. Freeze-cast laminated zeolite monoliths could be used to improve the volumetric efficiency and reduce the cycle time, of importance in, for example, biogas upgrading and CO2 separation from flue gas.

Hierarchy concepts: classification and preparation strategies for zeolite containing materials with hierarchical porosity

“…During cooling, the dispersant freezes and thus segregates from the particle-rich domains 166 and acts as a macroporogen, which is finally removed by sublimation. Next to aqueous suspensions, freeze casting based on organic dispersants, such as tert-butylalcohol, [167][168][169] camphene 170 or 1,4-dioxane 171 has been reported in the literature.…”

“…The cooling is realised by e.g. liquid nitrogen 166 or an appropriate coolant set to a temperature suitable for the dispersant used (e.g. ethanol at À100 1C for freezing of tert-butyl alcohol (TBA) 168 or +20 1C water bath for the freezing of camphene 170 ).…”

“…In addition, for a controlled freezing, the mould -and in particular the cooling part of it -has to be designed in accordance with the desired temperature profile. Therefore, such monolithic materials mostly are freeze casted in the shape of cylinders 166,175 and tubes. 168 Once frozen, the ice-template has to be removed by sublimation which usually is performed via freeze drying in vacuum.…”

“…For the preparation of cylindrical zeolite A (LTA) 175 and zeolite 13X (FAU) monoliths, 166 Ojuva et al used bentonite and polyethylene glycol (PEG) as inorganic binder and intermittent binder, respectively (see also Fig. 18b).…”

Effect of titania addition on the properties of freeze-cast alumina samples

“…This behavior can provide to these materials an enhanced fluid permeability and chemical stability [12,13]. Freeze-cast materials have been used in a range of applications, including biomaterials [14,15], sensors [16,17], drug delivery systems [18,19], photocatalysis [20,21], and gas purification [22][23][24]. 4 The addition of titania into alumina has been widely investigated for a variety of applications, including catalysts and mechanically reliable ceramics [25][26][27][28].…”