Ternary Adsorption of Methane, Water, and Carbon Dioxide in Zeolite Na-ZSM-5 Studied Using in Situ ATR-FTIR Spectroscopy

Lindsay Ohlin,Allan Holmgren,Jonas Hedlund,Amirfarrokh Farzaneh,Mattias Grahn

doi:10.1021/acs.jpcc.7b04405

Lindsay Ohlin, Allan Holmgren + Show 3 more

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https://doi.org/10.1021/acs.jpcc.7b04405

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Abstract

The main component in biogas and natural gas is methane, but these gases also contain water and carbon dioxide that often have to be removed in order to increase the calorific value of the gas. Membrane and adsorbent-based technologies using zeolites are interesting alternatives for efficient separation of these components. To develop efficient processes, it is essential to know the adsorption properties of the zeolite. In the present work, adsorption of methane, carbon dioxide, and water from ternary mixtures in high silica zeolite Na-ZSM-5 was studied using in situ ATR (attenuated total reflection)–FTIR (Fourier transform infrared) spectroscopy. Adsorbed concentrations were extracted from the infrared spectra, and the obtained loadings were compared to values predicted by the ideal adsorbed solution theory (IAST). The IAST could not fully capture the adsorption behavior of this ternary mixture, indicating that the adsorbed phase is not behaving as an ideal mixture. The CO2/CH4 adsorption selectivities d...

Highlights

Natural gas is a fossil fuel containing methane as the main component (80−95%) together with various amounts of carbon dioxide, water, and other contaminants.[1,2] Even though natural gas is a fossil fuel, it is one of the most abundant assets in the world,[3] and it is considered as a better afuel alternative than coal and oil because of its favorable hydrogen-to-carbon ratio
The broad band is associated with hydrogen-bonded water, indicating the formation of water clusters and only a very small amount of water interacts with the defect-free parts of the pores, which is in agreement with the work of Jentys et al.[14]
This was expected since water has a much higher affinity for the zeolite compared to both carbon dioxide and methane at lower temperatures

Summary

Introduction

Natural gas is a fossil fuel containing methane as the main component (80−95%) together with various amounts of carbon dioxide, water, and other contaminants.[1,2] Even though natural gas is a fossil fuel, it is one of the most abundant assets in the world,[3] and it is considered as a better afuel alternative than coal and oil because of its favorable hydrogen-to-carbon ratio. Because of this convenient link, together with the fact that for many systems it works well, it has gained popularity as a simple means for predicting multicomponent adsorption in zeolites.[18−21,24,26] In this work, the IAST was used to predict the adsorbed concentrations of water, methane, and carbon dioxide for adsorption from ternary mixtures for various compositions of the gas phase, and the predicted values were compared to the adsorbed concentrations determined experimentally.

Results

Conclusion