Monte Carlo Simulation Strategies for Predicting CO₂/CH₄ Adsorption onto Activated Carbons from Pure Gas Isotherms

Abstract

ABSTRACT:The problem of predicting the adsorptive properties of activated carbon (AC) towards a mixture of gases from the simple knowledge of the adsorption properties of the pure components is addressed, with special reference to the CO 2 /CH 4 mixture. The adsorption process for the pure gases and their mixtures was simulated using the Grand Canonical Monte Carlo (GCMC) method and the calculations were then used to analyze experimental isotherms for the pure gases and for mixtures with different molar fractions in the gaseous phase. It was shown that the pore-size distributions (PSDs) "sensed" by each of the pure probe gases was different one from the other and also from the PSDs "seen" by the mixture. A mixing rule for combining the PSDs corresponding to the pure gases is proposed for obtaining predictions regarding the adsorption of the corresponding mixtures, which are then compared with those arising from the classical IAST approximation. For this purpose, selectivity curves for CO 2 relative to CH 4 have been calculated and compared with experimental values. It was concluded that, for the adsorbate/adsorbent system under study, the proposed GCMC mixed model was capable of predicting the binary adsorption equilibrium, and especially the selectivity, more accurately than the IAST.

CO2 and H2S Removal from CH4-Rich Streams by Adsorption on Activated Carbons Modified with K2CO3, NaOH, or Fe2O3

“…The selectivity of each sample for CO 2 toward CH 4 was calculated according to eq , considering the mole fractions in the gas and adsorbed phase where x and y are the molar fractions in the adsorbed and gas phases, respectively, which are obtained from the predictions with the extended SIPS model (eq ).…”

Strategies to Improve Pore-Size Distribution Characterization of Activated Carbons Using CO2and N2Isotherms: Volume Regularization and Etched Slit Models

“…Some strategies for this purpose are reported in the literature. Oliveira et al (2011b), for example, proposed a mixed model of PSD to predict the adsorptive behaviour of mixtures, using a weighted average of the distributions obtained from monocomponent isotherms. Those weights are the mole fractions of components in the gas phase, which can be interpreted as volume fractions.…”

“…Similarly, in the case of a supercritical gas adsorption, the PSD of CH 4 has good resolution for micropores; however, there is also a peak at 8.9 Å. The 26-Å pore was overestimated due to the reliability window, which leads the existing mesoporosity to be concentrated on that last PSD pore diameter (Oliveira et al 2011b).…”

“…The small number of pores in the kernels was chosen on purpose to make this effect more pronounced. For CH 4 , one has to take into account the window of reliability, that is to say, for pore sizes larger than 20 Å, the simulated isotherms become linearly dependent on each other, creating inconsistencies in the PSD (Gusev et al 1997;Oliveira et al 2011b).…”