Atomistic Simulations of CO₂ and N₂ Adsorption in Silica Zeolites:  The Impact of Pore Size and Shape

Abstract

Adsorption of CO 2 and N 2 , both as single components and as binary mixtures, in three zeolites with identical chemical composition but differing pore structures (silicalite, ITQ-3, and ITQ-7) was studied using atomistic simulations. These three zeolites preferentially adsorb CO 2 over N 2 during both single-component and mixture adsorption. The CO 2 /N 2 selectivities observed in the three siliceous zeolites vary strongly as the adsorbent's crystal structure changes, with the selectivity in ITQ-3 being the largest. Our studies indicate that the different electric fields present inside zeolites with different crystal structures but identical chemical composition play an important role in the observed adsorption capacities and selectivities. The accuracy of the ideal absorbed solution theory in predicting the behavior of CO 2 /N 2 mixtures in silica zeolites based on single component adsorption data was also tested; this theory performs quite accurately for these adsorbed mixtures.

Modeling of the fixed - bed adsorption of carbon dioxide and a carbon dioxide - nitrogen mixture on zeolite 13X

“…The simulation results show that the zeolite 13X capacity for CO 2 adsorption is not affected by the presence of N 2 . These results are in line with the observations reported by Goj et al (2002) obtained by molecular simulation and by Harlick and Tezel (2003). The observations showed mixture isotherms in which the amount of CO 2 adsorption is almost unchanged from the analogous single component isotherm.…”

DL_MONTE: a general purpose program for parallel Monte Carlo simulation

“…The adsorption and separation of CO 2 from gas streams is an important area of research, and there are many published works, both experimental and computational, on adsorption and diffusion in bulk zeolite structures [28][29][30][31][32][33][34][35][36][37][38][39][40] using a variety of potential models. [41][42][43][44] Surface effects are very important for adsorption and much less work has been carried out on the adsorption and transport of CO 2 at zeolite surfaces, so this is where we chose to focus our work.…”

Advances in principal factors influencing carbon dioxide adsorption on zeolites

“…The quadrupole moment of certain gas varies as following: CO 2 > CO > N 2 > H 2 > CH 4 ≈ Ar ≈ Kr [28]. Goj et al [51] have effectively showed that the zeolites ITQ-3 and ITQ-7 adsorb preferentially the CO 2 to detriment of N 2 . This selectivity has been attributed to a strengthening of Coulombic interactions between the CO 2 molecules versus N 2 and the electric field of zeolites, which might be caused by the quadrupole moment of CO 2 (−1.43 × 10 13 cm 2 ) that is three times greater than that of N 2 .…”

“…Nevertheless, according to Calleja et al [10] and Katoh et al [19] the selectivity of zeolites M-ZSM-5 (M = Li + , Na + , K + , Rb + , Cs + ) might be due to fact that all the CO 2 molecules are adsorbed on the cations sites while N 2 might interact with the wall of ZSM-5. It has also been observed that the zeolites 13X, M-ZSM-5 (M = Li + , Na + , K + , Rb + , Cs + ), ZSM-5, KY, 4A, Na-4A, 5A, clinoptilolite and Na-mordenite, adsorb selectively the CO 2 in the presence of N 2 , O 2 , He, CH 4 , H 2 , C 2 H 4 , C 2 H 6 , SF 6 and Ar [16,18,19,[51][52][53][54][55][56].…”