CO2 chemical absorption is a post-combustion process that separates CO2 from the other components of the flue gases. Its main advantage is the high removal rate even for low CO2 partial pressures and it is practically carried out even for partial pressures below 140 mbar. Its main drawback is the cost of the solvent regeneration, which is high with traditional amine solvents. In order to overcome this problem several new kinds of solvents are being investigated. One of the new solvent families is the so called: Thermomorphic Lipophilic Biphasic System. In this case the limited solubility of the Lipophilic amines in water offers a new degree of freedom while optimizing the global process: it is in fact possible to perform the absorption with an initial biphasic solvent (organic, aqueous) which transforms into a mono-phasic one when a certain amount of CO2 is absorbed. Upon heating to a particular temperature value, again a biphasic system is formed. The organic formed phase acts as an auto-extractive agent pushing the equilibrium towards the regeneration direction. In this way three main advantages rise: (i) it is possible to send to the regeneration section of the plant only the aqueous phase, reducing the volumetric flow rate, hence the regeneration cost; (ii) the previously mentioned auto-extractive behavior increases the loading in terms of mol-CO2 absorbed /mol-Amine; (iii) choosing a proper solvent the regeneration can be performed at lower temperatures with respect to the conventional ones. This work aims assessing experimentally the CO2 absorption kinetic into a Lipophilic amine based solvent, namely 3M 1:3 DPA (dipropylamine) - DMCA (dimetylcyclohexylamine) in water using a Lewis Cell type reactor. Lastly an optimization procedure based on Genetic Algorithm is described and proposed in the last chapter. The optimization will evaluate the kinetic constants for the considered reaction mechanism. The results show the potential of the selected solvent in terms of activation energy, which is lower than more conventional solvents such as aqueous MEA and MDEA. The optimization procedure seems to well fit the problem. In order to obtain more precise results, a more complex reaction mechanism should be considered.
L’assorbimento chimico della CO2 é un processo in post-combustione che separa la CO2 dal resto dei gas combusti. Il vantaggio principale é l’alto tasso di rimozione ottenibile per basse pressioni parziali dell’anidride carbonica. Nella pratica viene eseguito anche con pressioni parziali minori di 140 mbar. D’altro canto lo svantaggio principale é il costo della rigenerazione dei solventi convenzionali. Per superare questo problema, nuove tipologie di solventi sono argomento di ricerca attuale. Uno di questi viene denominato: Thermomorphic Lipophilic Biphasic System. In questo caso la limitata solubilità delle ammine lipofiliche in acqua offre un nuovo grado di libertà per ottimizzare il processo globale: é possibile operare l’assorbimento con un solvente inizialmente bifasico che diventa monofasico dopo un certo quantitativo di CO2 assorbita. Riscaldando il solvente, una volta raggiunta una certa temperatura il sistema ritorna bifasico. La fase organica funge da agente autoestrattivo e spinge l’equilibrio verso il senso della rigenerazione. È possibile riconoscere tre vantaggi principali : (i) é possibile rigenerare solo la fase acquosa, riducendo la portata volumetrica da rigenerare e quindi il costo; (ii) il comportamento autoestrattivo aumenta il “loading” in termini di moli di CO2 assorbita per mole di Amine; (iii) selezionando un opportuno solvente, la rigenerazione può essere operata a temperature più basse rispetto ai solventi convenzionali. L’obiettivo di questo studio é valutare sperimentalmente la cinetica di assorbimento della CO2 in un solvente lipofilico: una soluzione acquosa 3M 1:3 DPA (dipropylamine) - DMCA (dimetylcyclohexylamine). La procedura sperimentale prevede l’uso di un reattore di tipo “Lewis Cell”. In fine una procedura di ottimizzazione volta a valutare le costanti cinetiche di un determinato sistema di reazioni considerato viene proposta. I valori ottenuti sperimentalmente dimostrano il potenziale del solvente selezionato in termini di energia di attivazione, la quale risulta minore rispetto ad altri solventi più convenzionali come soluzioni acquose di MEA e MDEA. La procedura di ottimizzazione ben descrive il problema e potrebbe migliorare i risultati considerando un meccanismo reazionale più complesso.
Experimental kinetic study of CO2 chemical absorption into a thermomorphic lipophilic biphasic solvent
TRISTANO, DANIELE PARTEMIO
2015/2016
Abstract
CO2 chemical absorption is a post-combustion process that separates CO2 from the other components of the flue gases. Its main advantage is the high removal rate even for low CO2 partial pressures and it is practically carried out even for partial pressures below 140 mbar. Its main drawback is the cost of the solvent regeneration, which is high with traditional amine solvents. In order to overcome this problem several new kinds of solvents are being investigated. One of the new solvent families is the so called: Thermomorphic Lipophilic Biphasic System. In this case the limited solubility of the Lipophilic amines in water offers a new degree of freedom while optimizing the global process: it is in fact possible to perform the absorption with an initial biphasic solvent (organic, aqueous) which transforms into a mono-phasic one when a certain amount of CO2 is absorbed. Upon heating to a particular temperature value, again a biphasic system is formed. The organic formed phase acts as an auto-extractive agent pushing the equilibrium towards the regeneration direction. In this way three main advantages rise: (i) it is possible to send to the regeneration section of the plant only the aqueous phase, reducing the volumetric flow rate, hence the regeneration cost; (ii) the previously mentioned auto-extractive behavior increases the loading in terms of mol-CO2 absorbed /mol-Amine; (iii) choosing a proper solvent the regeneration can be performed at lower temperatures with respect to the conventional ones. This work aims assessing experimentally the CO2 absorption kinetic into a Lipophilic amine based solvent, namely 3M 1:3 DPA (dipropylamine) - DMCA (dimetylcyclohexylamine) in water using a Lewis Cell type reactor. Lastly an optimization procedure based on Genetic Algorithm is described and proposed in the last chapter. The optimization will evaluate the kinetic constants for the considered reaction mechanism. The results show the potential of the selected solvent in terms of activation energy, which is lower than more conventional solvents such as aqueous MEA and MDEA. The optimization procedure seems to well fit the problem. In order to obtain more precise results, a more complex reaction mechanism should be considered.File | Dimensione | Formato | |
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https://hdl.handle.net/10589/133941