(333c) Adsorption Separation of Methane and Carbon Dioxide from Landfill Gas

Landfill gas (LFG) is a multi-component mixture containing mainly methane and carbon dioxide and can be treated as an important resource for available methane gas as an energy source, as well as one of the main sources of methane and carbon dioxide emissions into the atmosphere. These reasons, together with a tighter control in emissions to meet Kyoto Protocol targets, put LFG into consideration for energy production.

In this work, adsorption separation of methane and carbon dioxide using silicalite was studied by using volumetric and concentration pulse chromatographic techniques. Adsorption isotherms of the pure methane and carbon dioxide systems were determined by the volumetric method in the pressure range between 0 and 5 atm. for temperatures 40, 70 and 100 °C. The applicability of different isotherm models, Langmuir, Freundlich, Sips, Flory-Huggins, Toth, Multisite-Langmuir, and Dualsite-Langmuir, temperature dependence Toth and temperature dependence Sips were discussed. Ideal separation factors were determined from the isotherms of the pure systems.

On the other hand, mixture adsorption isotherms for the binary system of methane and carbon dioxide at temperatures 40, 70 and 100 °C at 1 atmosphere total pressure were determined by using three binary concentration pulse methods:

1) HT - CPM (Harlick and Tezel - Concentration Pulse Method),

2) MTT - CPM (Modified Triebe and Tezel- Concentration Pulse Method)

3) MVV? CPM (Modified Van der Vlist and Van der Meijden- Concentration Pulse Method)

The applicability of these methods was discussed for determining the binary isotherms from concentration pulse chromatographic data. According to the results obtained, HT ? CPM is the best one among the three models studied for the CH₄-CO₂ system. The corresponding separation factors for the separation of the landfill gas were obtained. Finally, the applicability of the Extended Langmuir, Extended Dualsite Langmuir, Ideal Adsorbed Solution Theory, and Statistical Model were discussed.