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CO2 adsorption on a yellow tuff has been studied, by performing dynamic breakthrough experiments in fixed bed, focusing on the thermodynamics and kinetics of the process. The effect of both temperature (25 - 150 °C) and CO2 partial pressure (0.01 - 0.20 atm) has been assessed. The CO2 adsorption isotherms in the low pressure region typical of combustion flue gases are more accurately described by the Freundlich equation than by the Langmuir one, thus indicating a multilayer and heterogeneous surface binding. The obtained values of the main thermodynamic parameters suggested that the adsorption process is spontaneous, exothermic and physical in nature. The pseudo-first order kinetic model better fitted the experimental data at all the investigated adsorption temperatures than the pseudo-second order does. Based on the thermodynamic properties, some insights into the process strategy for post-combustion capture (i.e. pressure vs vacuum swing) are derived.

Even though the performances of CO2 adsorbent materials for temperature swing adsorption (TSA) are typically assessed based on the equilibrium adsorption capacity, the actual feasibility of a sorbent in real applications cannot be reliably inferred from only this parameter. Indeed, more than the maximum CO2 uptake achievable at equilibrium, it is necessary to know the actual amount of CO2 that can be captured in a full adsorption/desorption cycle, namely the difference between the amount of CO2 adsorbed under adsorption and desorption conditions, which is defined as the CO2 working capacity. In this work, dynamic breakthrough and regeneration tests have been performed using a commercial activated carbon in a lab-scale TSA sound-assisted fluidized bed apparatus in order to experimentally evaluate the CO2 working capacity. In particular, the effect of adsorption/desorption temperatures (18 - 150 °C) and CO2 partial pressure (0.05 - 0.20 atm) has been evaluated.

The aim of the present work is to compare the adsorption performances of different materials (two activated carbons, four zeolites and a metal organic framework) under sound-assisted fluidization conditions (140 dB-80 Hz) in order to maximize the gas-solid contact efficiency and, in turn, minimize the limitations to the intrinsic adsorption capacity of the sorbents. All the tests were performed at ambient temperature and pressure with values of CO2 concentration typical of flue gases (5-10 vol.%). The different behaviors exhibited by the materials were explained on the basis of their textural properties. In particular, the microporosity falling in the range of 8.3-12 Å strongly affects the CO2 adsorption performances under the investigated operating conditions.

A large decrease in CO2 emissions through capturing and separation will be required to keep greenhouse gases at tolerable levels (1). Though several CO2 capture technologies have been proposed, temperature swing adsorption (TSA), consisting in adsorbing the CO2 on a solid material and, then, inducing the sorbent regeneration and CO2 recovery by a temperature increase and gas purge, has the potential to become one of the leading techniques by complementing or replacing the current absorption technology due to its low energy requirement (2). With reference to the sorbent, great attention is focused on fine powders (3). Indeed, sorbent in the form of fine powders can be the substrate to realize new highly specific materials whose properties can be tuned at a molecular level and, besides that, most of the commercial adsorbent materials are generally available in the form of fine powders (3). In this respect, sound assisted fluidization is considered to be one of the best technological alternatives to handle and process large amounts of fine powders (4). Moreover, it has already been proved to promote and remarkably enhance the CO2 capture on fine sorbents, due to large gas-solid contact efficiency, high rate of mass/heat transfer and low pressure drops (5,6). This work is focused on the CO2 desorption process by TSA in a sound-assisted fluidized bed (40mm ID) of fine activated carbon (Sauter mean diameter = 0.39m). In particular, desorption tests have been performed under ordinary and sound assisted fluidization conditions (140dB - 80Hz) in order to assess the capability of the sound in promoting and enhancing the desorption process efficiency in terms of CO2 recovery and purity and desorption time (td). The results obtained show that the application of the sound results in higher desorption rates, CO2 recovery and purity. Very regular and stable desorption profiles can be obtained under sound assisted fluidization conditions (Fig. 1). This stability makes it possible to successfully realize a cyclic adsorption/desorption process. Then, the effect of desorption temperature (Tdes) (25 - 150°C) and N2 purge flowrate (45.2 - 90.4Nl h-1) on the regeneration efficiency has also been assessed (Fig. 2a and b). An increase of both of them positively affect the desorption process in terms of enhanced desorption kinetics. Increasing temperatures also yield higher CO2 purities, whereas, no remarkable dilution effect has been observed when increasing the N2 flow rate. Finally, the activated carbon keeps its performances over 16 adsorption/desorption cycles, in terms of amount of CO2 adsorbed (nads), breakthrough time (tb) and fraction of bed used at tb (W), due to the stability of the regeneration process under sound-assisted fluidization conditions (Fig. 3c).

Metal foams are an interesting class of materials with very low specific weight and unusual physical, mechanical and acoustic properties due to the porous structure (1). These materials are currently manufactured by means of several conventional processes (2), limited by the impossibility to produce foams with complex geometry. This paper deals with the study of an innovative method to produce complex shaped precursors for aluminum foams through cold gas dynamic spray deposition process (CGDS), aluminum alloy (AlSi12) and titanium-hydride (TiH2) being the metal and the blowing agent, respectively. However, the success of this approach strongly depends on the achievement of a homogenous and deep mixing between AlSi12 and TiH2 fine powders, belonging to group C of Geldart's classification. Classical mixing methods (such as tumbling mixers, convective mixers, high-shear mixers, etc.) are suitable for large non-cohesive particles (> 30?m) but not for micronic particles (3), agglomerated due to strong interparticle forces. Alternatively, new wet and dry mixing techniques have been proposed for fine particles (4), suffering from different disadvantages: additional steps of filtration/drying are needed for wet methods, whereas, dry methods generally involves the reduction of the granulometry and the damaging or contamination of the original powders. The sound assisted fluidization technology (140dB-80Hz) has been adopted in this work to overcome the technical issues of mixing cohesive powders (5), thus obtaining a mixing to the scale of the primary particles in a simple, economic, not intrusive and not destructive way (the properties and morphology of the original particles were preserved). Therefore, the mixed powders were then sprayed by means of the proposed CGDS process on a stainless steel sheet to obtain the precursor. This was then heated up in a furnace at 600°C for 10 minutes to obtain the foam. In particular, two different types of mixtures with 1 wt% and 2.5 wt% of TiH2 were investigated; moreover, air compressed as well as helium were used as CGDS carrier gas in order to ensure a higher impact velocity and a better compacting of the powders. A very efficient mixing of powders has been achieved as confirmed by SEM/EDS analysis performed on samples taken from the sound assisted fluidized bed (Fig.1a) and by the time-dependence of the mixing degree (Fig.1b). Macrographs of created porous structures (Fig.2) showed that the coupling of sound assisted fluidization and CGDS process under optimal conditions is a promising and effective technique in manufacturing aluminum precursors for metal foams.