Equilibrium adsorption and kinetic diffusion mechanism of CH₄/N₂ on coconut shell-based activated carbon

In order to clarify the equilibrium adsorption,thermodynamic and kinetic diffusion mechanism of CH₄/N₂ on the adsorbent,using activated carbon prepared in the lab as adsorbent,the adsorption isotherms of CH₄/N₂ on the activated carbon were measured by volumetric method at 298~338 K and 0~0.1 MPa. The model parameters,thermodynamic parameters and average relative deviation were obtained by using classical Langmuir and Sips model fitting equilibrium adsorption data. Adsorption isotherms of single component and CH₄-N₂ binary component with different proportions were measured based on the gravimetric method respectively. The separation performance and competitive adsorption mechanism were evaluated. The dynamic adsorption rate curves were measured by electronic balance,WM internal diffusion model,Lagergren quasi-first-order kinetic model and Makay second-order kinetic model were used to fit the dynamic adsorption data,the influence mechanism of temperature and pressure on the adsorption of methane and nitrogen was studied from the perspective of dynamics,and the diffusion control steps of methane and nitrogen in the adsorption process of activated carbon were discussed. The results show that the two equilibrium adsorption models match well while Sips model has the better fitting effect since Sips model takes the surface heterogeneity of activated carbon into consideration. It was found that the adsorption process of CH₄/N₂ on the activated carbon is a physical adsorption process and the adsorption heat of methane is greater than that of nitrogen by calculating. There exists a competitive adsorption of binary mixed gas,and CH₄ adsorption plays a dominant role,the adsorption capacity of the mixture gas is between the adsorption capacity of methane and that of nitrogen. The equilibrium separation coefficient is up to 4.21. The kinetic adsorption process of CH₄ and N₂ on the surface of activated carbon is mainly controlled by external diffusion,followed by surface adsorption process,and internal diffusion is not the main control step. The decrease of temperature and increase of pressure are favorable to internal diffusion,but unfavorable to external diffusion.Increasing temperature and pressure have different effects on diffusion and adsorption control.