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Item Type: Tesi di dottorato
Resource language: English
Raganati, Federicafederica.raganati@unina.it
Date: 2014
Number of Pages: 165
Institution: Università degli Studi di Napoli Federico II
Department: Ingegneria Chimica, dei Materiali e della Produzione Industriale
Scuola di dottorato: Ingegneria industriale
Dottorato: Ingegneria chimica
Ciclo di dottorato: 26
Coordinatore del Corso di dottorato:
D'Anna, Andreaanddanna@unina.it
Salatino, PieroUNSPECIFIED
Date: 2014
Number of Pages: 165
Keywords: CO2 Capture, Sound-assisted Fluidization, Temperature Swing Adsorption
Settori scientifico-disciplinari del MIUR: Area 09 - Ingegneria industriale e dell'informazione > ING-IND/25 - Impianti chimici
Date Deposited: 10 Apr 2014 10:21
Last Modified: 15 Jul 2015 01:01
URI: http://www.fedoa.unina.it/id/eprint/9652

Collection description

Adsorption using solid sorbents is recognized to be attractive to complement or replace the current absorption technology for CO2 capture due to its low energy requirement. However, the development of new highly specific CO2 adsorbent is necessary: a solution is represented by fine materials, whose properties can be tuned at a molecular level by means of functionalization processes to tailor their CO2 capture performance. Another point to be addressed is the adoption of an adequate reactor configuration, which can, on one hand, fully exploit the potential and properties of these new-concept adsorbent materials by maximizing the contact between the CO2 molecules and the adsorbent particles, and, on the other hand, improve the heat transfer. In this respect, a fluidized bed could be a good solution, due to larger gas-solid contact efficiency, higher rate of mass and heat transfer and lower pressure drops. In particular, a more suitable reactor configuration is a sound assisted fluidized bed, namely provided with a system for the generation of acoustic vibrations to overcome the high interparticles forces characterizing fine powders. On these bases, the present PhD thesis focuses on the CO2 capture process by temperature swing adsorption on fine porous materials in a sound assisted fluidized bed. In order to perform adsorption/desorption tests, a laboratory scale sound assisted fluidized bed experimental rig has been set up. It is equipped with a system for the sound generation and with a continuous analyzer for the CO2 concentration measurement in the effluent gas stream. For the regeneration tests the reactor is externally heated by an ad-hoc designed heating jacket, provided with a window to allow the fluidization quality to be visually assessed. Both common adsorbent materials, two activated carbons, zeolite HZSM-5 and zeolite 13X, and a highly specific adsorbent material, a metal organic framework HKUST-1, were used. The experimental results show that the application of the sound can improve the fluidization quality as well as the adsorption efficiency (by maximizing the gas-solid contact) of all the selected adsorbent materials in terms of remarkably higher breakthrough time, adsorption capacity, fraction of bed utilized until breakthrough and adsorption rate. The experimental campaign has been also carried out, at ambient temperature and atmospheric pressure, in order to highlight the effect of some operating variables on the adsorption performances, i.e. sound intensity (120-140dB) and frequency (20-300Hz), CO2 partial pressure (0.05-0.15atm) and fluidization velocity (0.1-4.5cm/s). In particular, increasing sound intensities yield better adsorption performances, whereas, sound frequency has a not monotone effect on the fluidization quality and adsorption efficiency. The CO2 capture capacity increases with CO2 partial pressure, coherently with the partial pressure being the thermodynamic driving force of the adsorption process. Finally, the dependence of the breakthrough time on the contact time is linear for the tests performed in ordinary conditions, whereas, it is not monotone for the sound assisted tests. At the end of the experimental campaign, all the investigated adsorbent materials have been compared and their different adsorption behaviours explained on the basis of their textural properties. In particular, it has been found that there is a specific pore size range, 8-12 Å, which is the key factor affecting the adsorption capacity of the studied materials under the investigated operating conditions. Desorption tests have been performed on the materials characterized by the best adsorption performances, the HKUST-1 and one activated carbon at atmospheric pressure. In particular, an extra-situ regeneration strategy (150°C under a vacuum of 50mbar) has been developed to study the stability of HKUST-1 to cyclic adsorption/desorption operations, since HKUST-1 presents problems of thermal stability, limiting the desorption temperature to be used in a temperature swing adsorption process. The results show that HKUST-1 is very stable, keeping its adsorption performances over 10 adsorption/desorption cycles. As regards the activated carbon, two strategy of temperature swing adsorption have been tested in the sound assisted fluidized bed. The first regeneration strategy is an isothermal purge consisting in combining the effect of increasing temperature and decreasing CO2 partial pressure. The second regeneration strategy, heating and purge, consists in separating the thermal effect from the purging one. The application of the sound makes it possible, from one hand, to remarkably increase the desorption rate and, on the other, to significantly enrich the recovered CO2 stream. CO2 recovery and purity have opposing trends: higher desorption times yield a higher CO2 recovery, but lead to a lower CO2 purity of the desorbing stream. The desorption rate is positively affected by both desorption temperature (25-150°C) and N2 purge flow rate (45.2-90.4Nl h-1). The purity of the recovered CO2 stream is increased by increasing desorption temperatures, whereas, it is not affected by change of the N2 purge flow rate since dilution does not depend on the purge flow rate but only on the purge volume. The results obtained show that heating is very effective since 80% of the captured CO2 can be can be recovered with a 100% purity at a bland desorption temperature of 130°C. It is worth noting that for each desorption temperature the heating and purge strategy always makes it possible to enrich the stream of CO2 recovered with respect to the standard purge strategy, the CO2 recovery level being the same. The possibility to use the activated carbon in a cyclic operation has been also assessed: it is very stable, keeping its adsorption performances over 16 adsorption/desorption cycle. Finally, considerations about the energy cost and scale-up of the proposed technology for CO2 capture by temperature swing adsorption have also been reported.


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