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Gebald C.,ETH Zurich | Gebald C.,Climeworks LLC | Wurzbacher J.A.,ETH Zurich | Wurzbacher J.A.,Climeworks LLC | And 3 more authors.
Environmental Science and Technology | Year: 2013

The stability of amine-functionalized nanofibrilated cellulose sorbent for direct air capture of CO2 is investigated during temperature-vacuum- swing (TVS) cycling. The presence of O2 at 90 C degrades the sorbent, reducing its CO2 adsorption capacity by 30% after 15 h of treatment in moist air with a dew point of 22 C. In contrast, exposure to moist CO 2 at 90 C with a dew point of 22 C does not deteriorate its CO 2 adsorption capacity after 15 h. Performing 100 TVS consecutive cycles, with CO2 adsorption from ambient air containing 400-530 ppm CO2 at 30 C and 60% relative humidity and with CO2 desorption at 90 C and 30 mbar, resulted in a reduction of the equilibrium CO2 adsorption capacity by maximum 5%. The average CO2 adsorption capacity during TVS cyclic operation is 0.90 mmol CO2/g. © 2013 American Chemical Society. Source

Gebald C.,ETH Zurich | Gebald C.,Climeworks LLC | Wurzbacher J.A.,ETH Zurich | Wurzbacher J.A.,Climeworks LLC | And 4 more authors.
Environmental Science and Technology | Year: 2014

A fundamental analysis of single-component and binary CO2 and H2O adsorption of amine-functionalized nanofibrillated cellulose is carried out in the temperature range of 283-353 K and at CO2 partial pressures in the range of 0.02-105 kPa, where the ultralow partial pressure range is relevant for the direct capture of CO2 from atmospheric air. Single-component CO2 and H2O adsorption experimental data are fitted to the Toth and Guggenheim-Anderson-de Boer models, respectively. Corresponding heats of adsorption, derived from explicit solutions of the van't Hoff equation, are -50 kJ/mol CO2 and -48.8 kJ/mol H2O. Binary CO2/H2O adsorption measurements for humid air reveal that the presence of H2O at 2.55 kPa enhances CO2 adsorption, while the presence of CO2 at 0.045 kPa does not influence H2O adsorption. The energy demand of the temperature-vacuum-swing adsorption/desorption cycle for delivering pure CO2 from air increases significantly with H2O adsorption and indicates the need to reduce the hygroscopicity of the adsorbent. © 2014 American Chemical Society. Source

Cruz R.T.,Federal University of Rio Grande do Sul | Braganca S.R.,Federal University of Rio Grande do Sul | Bergmann C.P.,Federal University of Rio Grande do Sul | Graule T.,Empa Material Science and Technology | Clemens F.,Empa Material Science and Technology
Ceramics International | Year: 2014

This work presents the effects of processing on the shape stability of different ceramic-polymer compounds (feedstocks) to obtain, by extrusion, thin tubular Ba0.5Sr0.5Co0.8Fe0.2O 3-δ (BSCF) perovskite membranes with a diameter of 10 mm and wall thickness of <300 μm. The influence on the polymer degradation during compounding and the processability to achieve geometrically stable thin wall tubes after debinding were analyzed. The ceramic-polymer composite was evaluated with a torque rheometer and capillary rheometer using Arrhenius plots (temperature-viscosity relationship) to investigate the activation energy of viscous flow (Ef). The shape stability, e.g. roundness and straightness, of the extruded tubes before and after the debinding step was investigated for the different binder systems. The feedstock based on 52 vol% BSCF powder and a polymeric mixture of 80 wt% polystyrene (PS) and 20 wt% polyethylene glycol (PEG) demonstrated reproducible processing behavior and sufficient shape stability after debinding. The tubes fabricated with this feedstock showed good longitudinal shrinkage (2.86%) and roundness (ΔDmax-min/Dmax<1.62%), absence of defects, suitable straightness and a homogeneous microstructure. © 2013 Elsevier Ltd and Techna Group S.r.l.All rights reserved. Source

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