Adsorption of CO₂over univalent cation-exchanged ZSM-5 zeolites

Abstract

Isotherms and IR spectra were measured for CO2-MZSM-5 (M = Li +, Na +, K +, Rb +, Cs +) adsorption systems. The observed adsorption characteristics were well approximated by a physical adsorption where the van der Waals force and an electrostatic interaction force are operating: the degree of irreversible adsorption (chemisorption) was less than 10% of the total adsorption. Although the adsorbed CO2 molecule interacts with both the cation and the pore wall, only the CO2-cation interaction can convert the IR inactive u1 vibration into an IR active state. The adsorption model proposed enables us to calculate the initial heat of adsorption as well as the molecular orientation angle of CO2 against the cation site.

Advances in principal factors influencing carbon dioxide adsorption on zeolites

“…Hence, the zeolites such as ZSM-5 and M-ZSM-5 (M = Li + , Na + , K + , Rb + , Cs + ) which have small cations might penetrate more easily within channels, are able to interact more strongly with the CO 2 [19,33]. This is in agreement with the results from a study performed by Yamazaki et al [21]. They showed that energy of the interaction between the CO 2 and the cations sites of zeolites M-ZSM-5 (M = Li + , Na + , K + , Rb + , Cs + ) decreases with the increase of the size of these cations sites.…”

“…Zeolites have a high potential for CO 2 capture, reaching an adsorption efficiency of 5.5 mmol of CO 2 /g of zeolite, combined with a degree of irreversible adsorption inferior to 10% (tables 1-3) [9][10][11][12][13][14][15][16][17][18][19][20][21]. The CO 2 adsorption is influenced by diverse structural characteristics of zeolites including size, polarizing power, distribution and the number of exchangeable cations in their cavities, the size of the pores and the Si/Al ratio.…”

“…This high affinity of zeolite NaA allows a better selectivity for CO 2 in the presence of N 2 and O 2 than NaX and NaY. Moreover, since the CO 2 can also interact with the pore wall of zeolites, the CO 2 adsorption might be limited by the size of zeolites pores at high pressures because the CO 2 -CO 2 interactions might prevent the adsorption of new molecules of CO 2 into the pore wall sites that are thus occupied by other molecules of CO 2 [12,19,21]. The shape of pores also seems to be important for the selective adsorption of CO 2 .…”

“…The degree of irreversible adsorption of CO 2 on zeolites M-ZSM-5 (M = Li + , Na + , K + , Rb + , Cs + ) which has been evaluated under a pressure inferior to 6.7 × 10 −2 MPa, was less than 10% of the total adsorption [21]. The adsorption capacity of zeolites depends on several factors including the size, polarizing power, distribution and the number of cations in their porous structure, Si/Al ratio, size, the form of their pores, the polarity and size of adsorbed molecules, the presence of water and other gas and presence of carbonates at their surface.…”

DL_MONTE: a general purpose program for parallel Monte Carlo simulation

“…The new CO 2 -zeolite interaction mixed the CLAYFF zeolite with CLAYFF parameters for the oxygen of CO 2 and EPM2 with a slightly modified r (Lennard-Jones size parameter) value for C. Figure 11 shows isotherms for CO 2 in silicalite (MFI) using this modified potential, which can be seen to reproduce the experimental isotherms of Yamazaki et al [54] very well. Using these isotherms, we calculate the heat of adsorption to be 17 kJ/mol which is slightly lower than the value published by Yamazaki et al of 23.4 kJ/mol; however, their calculation was over the temperature range 273-473 K, while our calculation was between 263 and 283 K, which may account for the different values.…”