(400f) Adsorption of Methane and Nitrogen On Activated Carbons: Numerical Derivation of Nitrogen Adsorption Affinity Coefficient

In this paper, experimental investigations were carried out to determine the methane and nitrogen adsorption capacity of various activated carbons at the temperature range of 10 to 56 °C and pressure up to 50 bars. A temperature dependent isotherm equation, Toth equation, is used to model the experimental data of methane and nitrogen adsorption on an activated carbon labeled as AC5. The optimized parameters from Toth equation are used to calculate isosteric heat of adsorption.

Dubinin-Astakhov (D-A) equation is used to model the adsorption characteristic curve for methane adsorption. The derived micropore volume of 0.456 cm³/g for AC5 from the optimized D-A equation matches the experimental value of 0.452 cm³/g from nitrogen adsorption at 77 K. Heterogeneity parameter value of 1.250 indicates a broad micro-pore size distribution of AC5.

Using methane as the reference adsorbate, nitrogen affinity coefficient is calculated by numerically optimizing the D-A model for nitrogen adsorption data at 10 and 21 °C. The calculated nitrogen adsorption affinity coefficient is 0.857. Using this value in the D-A equation, the model predicts the nitrogen adsorption at 38 and 56 °C with an average relative error (ARE) of 6.67% and overall ARE for all the nitrogen adsorption data at 10, 21, 38 and 56 °C is 4.99%. This validates the nitrogen adsorption affinity coefficient calculated.