A procedure to find thermodynamic equilibrium constants for CO₂ and CH₄ adsorption on activated carbon

Abstract

Thermodynamic equilibrium for adsorption means that the chemical potential of gas and adsorbed phase are equal. A precise knowledge of the chemical potential is, however, often lacking, because the activity coefficient of the adsorbate is not known. Adsorption isotherms are therefore commonly fitted to ideal models such as the Langmuir, Sips or Henry models. We propose here a new procedure to find the activity coefficient and the equilibrium constant for adsorption which uses the thermodynamic factor. Instead of fitting the data to a model, we calculate the thermodynamic factor and use this to find first the activity coefficient. We show, using published molecular simulation data, how this procedure gives the thermodynamic equilibrium constant and enthalpies of adsorption for CO 2 (g) on graphite. We also use published experimental data to find similar thermodynamic properties of CO 2 (g) and of CH 4 (g) adsorbed on activated carbon. The procedure gives a higher accuracy in the determination of enthalpies of adsorption than ideal models do.

Novel Porous Carbons Derived from Coal Tar Rejects: Assessment of the Role of Pore Texture in CO2 Capture under Realistic Postcombustion Operating Temperatures

“…The enthalpies of CO 2 adsorption on the materials MSP-20X, XiPPO_3, XPPO_1, and CWPO_1 are respectively equal to 20.2, 20.1, 24.5, and 23.9 kJ/mol. These values are in the typical range of CO 2 adsorption on activated carbons. , The decrease in heat of adsorption (opposite of the enthalpy of adsorption) as the average micropore size increases (Figure a) is due to the decrease of the adsorption potential.…”

“…Indeed, the higher the specific area and total pore volume the higher the density (per mass unit of and 23.9 kJ/mol. These values are in the typical range of CO 2 adsorption on activated carbons 59,60 . The decrease in heat of adsorption (opposite of the enthalpy of adsorption) as the average micropore size increases (Figure 5a) is due to the decrease of the adsorption potential.…”

“…These values are in the typical range of CO 2 adsorption on activated carbons. 53,54 The decrease in heat of adsorption (opposite of the enthalpy of adsorption) as the average micropore size increases (Figure 5a) is due to the decrease of the adsorption potential.…”

Adsorption Equilibrium and Diffusion of CH4, CO2, and N2 in Coal-Based Activated Carbon

“…In addition, Wang from China prepared nitrogen-doped activated carbon with high adsorption capacity for CO 2 . With the development of activated carbon preparation technologies, there are also some reports on the production of porous carbon materials using biomass waste. , It is noteworthy that though new-type zeolite molecular sieves have great potential in separating CH 4 , CO 2 , and N 2 mixtures, , activated carbon has elicited extensive research interest due to the capabilities for application in flue gas treatment, methane purification, adsorption and recovery of volatile organic compounds, prevention and control of air pollution, and so forth. − Among numerous studies, considerable attention has been paid to the effects of pore structure of activated carbon on CH 4 or CO 2 concentration . The adsorption and diffusion of CH 4 , CO 2 , and N 2 in the micropore structure of activated carbon are thus worthy of further study and discussion.…”

Characterizing Polymer Hydration Shell Compressibilities with the Small-System Method

“…Recently, Trinh et al [ 20 , 21 ] have extended the SSM to study the thermodynamic properties of adsorbed CO and CH layers on graphite and activated carbon surfaces. Motivated by these studies, we herein extend the SSM to investigate the compressibility of polymer hydration shells.…”