(567b) Mixture Adsorption Equilibria of Carbon Dioxide and Nitrogen on Activated Carbon

The primary source of greenhouse gas emissions is CO₂ and the majority of these emissions result from the combustion of fossil fuels. Major components of the resulting flue gas are N₂ and CO₂. Adsorption is an attractive method for separating these two gases because it can be done at moderate temperatures and pressures.

This study focuses on CO₂-N₂ mixture adsorption equilibria on activated carbon at different temperatures and total pressures. While binary isotherms can be predicted from pure component isotherms using models, experimental binary isotherms are of interest because there may be non-idealities that cannot be predicted.

Single component isotherms were determined gravimetrically to predict the binary adsorption isotherms using the Extended Langmuir Model (ELM) and the Ideal Adsorbed Solution Theory (IAST). Experimental binary gas adsorption isotherms were determined using concentration pulse chromatography, where the mean retention times were used to calculate the adsorption capacities of the mixture.

As an example, when experimental binary isotherm data for a CO₂-N₂ mixture on OLC activated carbon collected at 30°C and 1 atm total pressure are compared to the predictions from ELM and IAST, it was observed that the experimental adsorption capacities of CO₂ were lower than those predicted, while the experimental adsorption capacities of N₂ were similar to those predicted. These results showed that experimental determination of binary isotherms is important for the observation of mixture adsorption behaviour for the design of gas separation systems by adsorption.