Determination of Effective Diffusion Coefficient of Methane Adsorption on Activated Carbon

Experimental data of methane adsorption on two types of activated carbon have been carried out at pressures up to 35 bar and at ambient temperature. Adsorption equilibrium and kinetics data at high pressure were measured using a volumetric method. A theoretical model has been presented to calculate the amount of adsorbed gas on adsorbents in a cylindrical tank. In the model, gas enters the bed axial direction. The continuity and diffusion equations of adsorbent particles have been solved simultaneously. The models have been used to simulate methane adsorption on activated carbon using in adsorbed natural gas technology (ANG). Longmuir relation and Peng-Robinson equation have been used to evaluate the equilibrium amount of adsorbed gas and compressibility factor. By successful fitting of the gas-solid equilibrium data in the Longmuir relation the corresponding model parameters have been derived and effective diffusivity has been extracted with a new simple method. The storage capacity of activated carbon with high micropore volume is found to be higher but the diffusion coefficient and adsorption rate is lower than carbons with low micropore volume. Importance of the diffusion in micro pores of particles has been investigated. Comparison of experimental results and uptake data of calculation without and with diffusion equation has been confirmed that significant difference exists between these two cases and diffusion resistance cannot be neglected.