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Pure and Binary Gas Adsorption Equilibrium for CO2–N2 on Oxygen Enriched Nanostructured Carbon Adsorbents

Goel, Chitrakshi, Tiwari, Deepak, Bhunia, Haripada, Bajpai, Pramod K.
Energy & fuels 2017 v.31 no.12 pp. 13991-13998
Gibbs free energy, adsorbents, adsorption, carbon, carbon dioxide, fuels, heat, models, nitrogen, oxygen, prediction, sorption isotherms, temperature
Pure component (CO₂ and N₂) adsorption isotherms of oxygen enriched nanostructured carbon (RF-700) were evaluated using a static volumetric analyzer at four different adsorption temperatures ranging from 30 to 100 °C. Langmuir, Sips, and dual-site Langmuir (DSL) models were used to correlate pure component adsorption isotherms and it was found that Sips and DSL isotherm model fitted well with the experimental data, indicating the heterogeneous nature of the adsorbent surface. Fixed-bed column was used to obtain dynamic breakthrough data for binary system CO₂–N₂ at different adsorption temperatures (30–100 °C) and CO₂ feed concentrations (5–12.5% by volume). Extended Sips, extended DSL, and IAST (ideal adsorbed solution theory) models using pure component adsorption isotherm data were used for the prediction of adsorption of binary system (CO₂–N₂). Predicted equilibria data was compared with experimental breakthrough curve data, and it was found that extended forms of the isotherm models (Sips and DSL) underpredicted CO₂ adsorption equilibria because of the difference in adsorptive strengths of CO₂ and N₂ molecules. Ideal adsorbed solution theory failed to describe the mixed-gas adsorption equilibria. Asymmetric x–y diagrams showed positive deviation from Raoult’s law. The feasibility of the adsorption process was suggested by the negative value of molar Gibbs free energy change. The formation of more ordered configuration of CO₂ molecules on the adsorbent surface was seen as a higher heat of adsorption was exhibited for CO₂ as compared to N₂.