Browsing by Author "Freitas, Francisco A. da Silva"
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- Effect of cation exchange in the sorption of CO2, CH4 AND N2 and mixtures on binder-free faujasite zeolite YPublication . Aly, Ezzeldin; Zafanelli, Lucas F.A.S.; Freitas, Francisco A. da Silva; Silva, José A.C.Ion-exchange was performed on commercial binder-free NaY zeolite with alkali metal and alkaline earth metal cations to produce binder-free beads containing 23, 58 and 95% of potassium, as well as 56 and 71% of calcium exchanged from the bare samples. These cation-exchanged faujasites were studied by adsorption of carbon dioxide (CO2), methane (CH4), and nitrogen (N2) through single, binary, and ternary fixed bed breakthrough experiments, covering the temperature range between 308 and 348 K and pressure up to 350 kPa. The single and multi-component breakthrough apparatus that was used to study the fixed bed adsorption of CO2, CH4, and N2 and their binary/ternary mixture, is illustrated in Figure 1. The dynamic equilibrium loading is calculated by integrating the molar flow profiles of the breakthrough curves, as explained in previous works. The adsorption equilibrium data was then modelled by the extended dual-site Langmuir model, and the breakthrough curves were numerically simulated using Aspen Adsorption v10. Adsorption equilibrium measurements of CO2 on each of the studied material can reveal different behaviours and trends based on the modification of the intracrystalline environment through ion-exchange. Factors such as cation size, surface basicity, number and location of exchangeable cations, and strength of electric field can all have a great impact on the performance of the adsorbent. Figure 2 shows a comparison of the CO2 isotherms between NaY, K(23)Y, K(58)Y, K(95)Y, Ca(56)Y, and Ca(71)Y, collected at 308 K. A trend in the order of adsorption at low pressure (between 0 and 50 kPa) is observed: Ca(71)Y < Ca(56)Y < NaY < K(23)Y < K(58) < K(95)Y. As the exchange rate from Na+ to K+ increases, the CO2 adsorption capacity increases; the opposite is observed (decrease of adsorption uptake) when the rate changes from Na+ to Ca2+. At 25 kPa, the loading of binder-free Na(100)Y is equal to 4.05 mol/kg, compared to 4.29 for K(23)Y, 4.57 for K(58)Y, 4.97 for K(95)Y, 2.63 for Ca(56)Y and only 2.02 mol/kg for Ca(71)Y. This indicates a good response between the acidic CO2 to the basic properties of the zeolites containing larger monovalent cations at low pressure. Bigger cations such as K+ exhibit strong interaction with CO2, since they are both preferentially exchanged in the supercages; while smaller cations such as Na+ have less molecular interaction with the adsorbate molecules, since they are spread around the zeolite framework accessing narrow locations such as the sodalite cages, where CO2 cannot reach due to its size. Moreover, the CO2 loading of Ca(71)Y is significantly lower than all the rest (around half of that of NaY), which is due to the decrease of the amount of exchangeable cations between the divalent Ca2+ cations and the adsorbate molecules. For partial pressures above 200 kPa, K(23)Y and NaY are characterized with the highest adsorption capacity followed by K(95)Y and K(58)Y, then Ca(56) and finally Ca(71)Y, as shown in Figure 2. These trends are explained by the reduction of the basic strength and the electropositivity of exchangeable cations in larger ions, since they accept less charge transfer from the neighboring lattice oxygen atoms when compared to smaller cations. This leads to the weakening of the electric field induced by the exchangeable cations and so the adsorption capacity is reduced. It is also explained by the volume occupied by the large cations, which reduces the space available for adsorption of CO2 when the pores are reaching saturation. The studied binary experiments consist of 15% CO2 / 85% N2 (vol.%) mixture, representing a typical post-combustion stream. Figure 3a shows the adsorption breakthrough curves in binder-free K(95)Y for the binary mixture at 313 K. Figure 3b displays the breakthrough curves for ternary mixtures feeds of CO2 /CH4/ N2 (20/20/20 vol.% balanced with He) on binder-free zeolite KY, under conditions in the range used for biogas upgrading regarding the removal of CO2. As can be seen in Figure 3c, the binary experiment show a selectivity of CO2 over N2 around 105 at 313 K; the ternary system resulted in a selectivity of CO2 over CH4 and over N2 of around 14 and 32 at 313 K, respectively. These results indicate that binder-free K(95)Y works best in the low-pressure region and therefore, is a promising adsorbent for the recovery of CO2 from post-combustion streams. Numerical simulations were performed with a model implemented in Aspen Adsorption simulator, allowing to predict accurate breakthrough curves for dynamic experiments carried out in a fixed bed adsorption system, as shown in Figure 3. Briefly, most of the studied ion-exchanged materials show a lot of potential for the capture of CO2 from CO2/N2 and CO2/CH4/N2 mixtures. Nevertheless, each adsorbent differs from one another and can only reach its full potential under specific conditions. Therefore, it is possible to tune the adsorptive properties of zeolites by ion exchange, to optimize the most suitable material that enriches substantially the CO2 adsorption for a specific process.
- Post-combustion capture of CO2 in potassium-exchanged binder-free beads of Y zeolitePublication . Aly, Ezzeldin; Zafanelli, Lucas F.A.S.; Henrique, Adriano; Freitas, Francisco A. da Silva; Rodrigues, Alírio; Silva, José A.C.The generation of carbon dioxide is inherent in the combustion of fossil fuels, and the efficient capture of CO2 from industrial operations is regarded as an important strategy to achieve a significant reduction in atmospheric CO2 levels. Adsorption processes are promising capture technologies as they can use specific adsorbents by acting in the limit as molecular sieves to separate CO2 from other flue gas constituents. Experimental and theoretical studies concerning the adsorption of CO2 and N2 and their mixtures in potassium-exchanged Y zeolite (KY) are lacking information in the literature. Accordingly, this work aims to investigate by a series of fixed-bed adsorption breakthrough experiments the adsorption of single and binary mixtures (under compositions typical of post-combustion) of CO2/N2 in binder-free beads of KY zeolite, at 313, 373, and 423 K and total pressures up to 350 K. The single and multi-component breakthrough apparatus used in this work is shown in Figure 1. The dynamic equilibrium loading is calculated by integrating the molar flow profiles of the breakthrough curves, as explained in previous works [1]. The adsorption equilibrium data was then modelled by the extended dual-site Langmuir model, and the breakthrough curves were numerically simulated using ASPEN ADSORPTION. At 313 K and 350 kPa, the single-component data obtained showed that the amount adsorbed of CO2, and N2 is around 6.42 and 0.671 mol.kg-1, respectively. The binary experiments CO2/N2 carried out under typical post-combustion conditions, show a selectivity of CO2 over N2 around 104. Overall the numerical simulations performed on ASPEN ASDSORPTION provided results with decent accuracy and the model can predict the systematic behaviour of the breakthrough experiments as well as the dynamics of the fixed bed adsorption system. The results shown in the present work proves that potassium-exchanged binder-free beads of Y zeolite is a promising adsorbent that can efficiently separate CO2 from post-combustion streams by fixed bed adsorption.
- Post-combustion CO2 capture using Ion-exchanged binder-free NaY beadsPublication . Aly, Ezzeldin; Zafanelli, Lucas F.A.S.; Henrique, Adriano; Freitas, Francisco A. da Silva; Rodrigues, Alírio; Silva, José A.C.on-exchange processes on zeolites hold promise for improving adsorption mechanisms critical for post-combustion CO2 capture (PCC). Zeolites offer advantages such as favourable CO2 adsorption isotherms, rapid kinetics, non-toxicity, and cost-effectiveness, making them attractive candidates for carbon capture applications. In this study, we focus on exploring the impact of ion-exchange (K+ and Ca2+) on bare NaY zeolite for PCC. Fixed-bed breakthrough experiments were conducted on various ion-exchanged zeolites, including K(23)Y, K(58)Y, K(95)Y, Ca(56)Y, and Ca(71)Y, within a temperature range of 306 K to 344 K and pressures reaching up to 350 kPa. The objective of these experiments is to investigate the equilibrium, kinetics, and dynamic characteristics of the sorption process, covering both single and binary mixtures of CO2 and N2. Performance parameters such as selectivity and working capacity were evaluated based on the experimental outcomes. Following data collection, a mathematical model was calibrated utilizing Aspen Adsorption v10 software to simulate fixed-bed performance under standard PCC conditions.
- Separation of CO2/N2 in Ion-Exchange binder-free beads of zeolite NaY for Post-Combustion CO2 capturePublication . Aly, Ezzeldin; Zafanelli, Lucas F.A.S.; Henrique, Adriano; Gleichmann, Kristin; Rodrigues, Alírio; Freitas, Francisco A. da Silva; Silva, José A.C.Ion-exchange on bare commercial zeolites can offer improved adsorption processes. In the context of CO2/N2 separation for post-combustion CO2 capture (PCC), here, we report, the effect of ion-exchange on commercial binder-free NaY zeolite with alkali (K+) and alkaline earth (Ca2+) metal cations, achieving exchange levels of 23 %, 58 %, and 95 % for K+ and 56 % and 71 % for Ca2+. Adsorption isotherms of CO2 and N2 were measured over a temperature range of 306–344 K and pressures up to 350 kPa. At low pressures, the CO2 adsorption capacity increases as Na+ ions are exchanged to a higher level of K+, while a reverse trend is observed for Ca2+ exchange. At 25 kPa and 306 K, the CO2 loading (mol∙kg−1) follows the order 2.01-Ca(71)Y < 2.63-Ca(56)Y < 4.05-NaY < 4.29-K(23)Y < 4.59-K(58)Y < 4.72-K(95)Y. The selectivities of CO2 (15 %)/N2 (85 %) at 306 K and 101.3 kPa range from 52 for Ca(71)Y to 101 for K(23)Y, compared to 89 in the bare NaY zeolite. The working capacities for the most promising exchanged sample (K(23)Y) exhibit superior values of 4.51, 2.98, and 2.41 mol∙kg−1 considering regeneration pressures of 3, 10, and 15 kPa, relative to a feed pressure of 101.3 kPa, respectively. Dynamic simulations were conducted using the Aspen Adsorption package to accurately predict both single- and binary-component breakthrough curves.
- Single- and multi-component fixed-bed adsorption of CO2, CH4, and N2 on ion-exchanged binder-free NaY zeolitesPublication . Aly, Ezzeldin; Zafanelli, Lucas F.A.S.; Henrique, Adriano; Freitas, Francisco A. da Silva; Rodrigues, Alírio; Silva, José A.C.Ion-exchange was performed on bare commercial binder-free NaY zeolite with alkali (K+) and alkaline earth (Ca2+) metal cations in the range 23, 58, and 95% exchange for K+, and 56 and 71% for Ca2+, to be used as candidates regarding CO2 post-combustion capture (PCC) and biogas upgrading by adsorption processes. Adsorption equilibrium isotherms of CO2, CH4 and N2 were measured on all these cation-exchanged samples using a chromatographic technique between 308 and 348 K and pressures up to 350 kPa and modelled by the dual-site Langmuir isotherm. The CO2 adsorption capacity increases as Na+ is exchanged further by K+ and the reverse for the Ca2+ exchange. The single- and binary-component breakthrough curves were numerically simulated and accurately predicted using the Aspen Adsorption package. This work discloses the importance of ion-exchange on binder-free beads of NaY zeolite to improve its performance in PCC and biogas upgrading applications
- Vacuum pressure swing adsorption process using binder-free K(23)Y zeolite for post-combustion CO2 capturePublication . Aly, Ezzeldin; Zafanelli, Lucas F.A.S.; Henrique, Adriano; Gleichmann, Kristin; Rodrigues, Alírio; Freitas, Francisco A. da Silva; Silva, José A.C.This study presents the development of a Vacuum Pressure Swing Adsorption (VPSA) process utilizing binder- free K(23)Y zeolite for post-combustion CO2 capture. The ion-exchanged K(23)Y zeolite, characterized by a high CO2 selectivity of 97 over N2 at 10 kPa and an adsorption capacity exceeding 7 mol⋅kg− 1 350 kPa at 306 K, was evaluated under various operational conditions to optimize the VPSA process. Experimental and simulated breakthrough analyses provided essential data for adsorption equilibrium and sorption kinetics, which were modelled using Aspen Adsorption software. Optimization of key cycle steps, including pressurization, adsorption, blowdown, and evacuation, revealed that Light Product Pressurization significantly enhances process performance. Parametric studies demonstrated that reducing intermediate pressure from 0.2 bar to 0.07 bar increased CO2 purity from 84 % to 93 %, though it decreased recovery from around 99 % to 78 %, revealing a key trade-off. Similarly, extending adsorption time beyond 86 s enabled CO2 purity to exceed 90 %, though recovery decreased slightly. Under optimal conditions, the VPSA process achieved a CO2 purity and recovery of ~90 % and productivity of 0.367 molCO2⋅m− 3ads⋅s− 1 , with specific energy consumption of 144 kWh per ton of CO2 captured. The study demonstrates the viability of a simple 4-step VPSA configuration with binder-free K(23)Y, offering competitive performance and low energy consumption.