Adsorption of Supercritical Fluids on Graphitised Thermal Carbon Black:  Molecular Layer Structure Theory versus Grand Canonical Monte Carlo Simulation

Abstract

This paper presents a detailed analysis of adsorption of supercritical fluids on nonporous graphitized thermal carbon black. Two methods are employed in the analysis. One is the molecular layer structure theory (MLST), proposed recently by our group, and the other is the grand canonical Monte Carlo (GCMC) simulation. They were applied to describe the adsorption of argon, krypton, methane, ethylene, and sulfur hexafluoride on graphitized thermal carbon black. It was found that the MLST describes all the experimental data at various temperatures well. Results from GCMC simulations describe well the data at low pressure but show some deviations at higher pressures for all the adsorbates tested. The question of negative surface excess is also discussed in this paper.

Adsorption of argon from sub- to supercritical conditions on graphitized thermal carbon black and in graphitic slit pores: A grand canonical Monte Carlo simulation study

“…For very weak surfaces, the average density of the adsorbed phase can become less than the bulk gas density at high pressure, and it is only then that the surface excess becomes negative. Do et al 74 applied the molecular layer structure theory and have shown that it is the case for hypothetical weak surfaces, for example, in the case of graphite surface we have shown that the well depth of solid carbon atom has to be reduced by a factor of 8 before a negative surface excess can be observed. On the other hand, in the case of a slit pore the adsorbed phase volume is taken to be the pore volume, the average excess pore density is defined as…”

Grand Canonical Monte Carlo Simulation Study of Methane Adsorption at an Open Graphite Surface and in Slitlike Carbon Pores at 273 K

“…Theory and computation may be used not only for interpretation of experimental results but also to provide better insight into the adsorption mechanism. , Proper models of the adsorption system provide a basis for understanding the adsorption behavior and for predicting the type of materials and conditions of efficient adsorption storage. The theoretical treatment of the supercritical or the near-critical region is still not fully understood compared to the subcritical one. , As a result, there are many key questions that have not been resolved so far. However, several features of supercritical adsorption are well-known from many extensive theoretical studies.…”

“…However, several features of supercritical adsorption are well-known from many extensive theoretical studies. At first, under the supercritical conditions the fluids are characterized by weaker adsorption caused by thermal motion and relatively weak fluid−fluid interaction of molecules, for this reason the term “adsorption” under supercritical condition is more appropriately replaced by “densification”. − In fact, adsorption of supercritical fluids is generally monomolecular (it also can occur beyond the first layer if pressure is high enough), and the condensed phase never surrounds the porous medium. Consequently, it is impossible to obtain reliable information about the pore size distribution (PSD) in the range of mesopores, whereas, the analysis of the micropore region should be effective as a result of the lack of disturbances caused by polymolecular adsorption or capillary condensation .…”

“…Consequently, it is impossible to obtain reliable information about the pore size distribution (PSD) in the range of mesopores, whereas, the analysis of the micropore region should be effective as a result of the lack of disturbances caused by polymolecular adsorption or capillary condensation . Second, adsorption of supercritical fluids when plotted as surface excess of adsorption versus pressure for temperature close to the critical temperature exhibits a maximum at a pressure close to the critical pressure, and especially when the temperature is slightly greater than the critical temperature, the maximum behaves like a very sharp spike. ,− ,− It is well documented that the potential energies generated by pore walls, temperature, dimension, and shape of the pore impact on the position and shape of the surface excess maximum. , However, generally we can suspect that, as the pore size increases, the position of the maxima are shifted to higher bulk densities (i.e., pressures) . Next, for the fixed temperature the flattering of the excess adsorption isotherms is expected with increasing pore size .…”

Influence of H2O on Adsorbed CH4 on Coal Displaced by CO2 Injection: Implication for CO2 Sequestration in Coal Seam with Enhanced CH4 Recovery (CO2-ECBM)

“…In this measurement, the bulk phase refers to the free phase of CO 2 in the sample cell. Since the aggregation state of the adsorbate in the adsorbed phase is always regarded as a pseudo-liquid state, , the liquid density of CO 2 , that is, 1227 kg/m 3 , at the boiling point and the atmospheric pressure was given to ρ ads,CO 2 .…”