Adsorption capillary condensation

Wanless E J and Christenson H K 1994 Interaction between surfaces in ethanol adsorption, capillary condensation, and solvation forces J. Chem. Rhys. 101 4260-7... 

The first stage in the interpretation of a physisorption isotherm is to identify the isotherm type and hence the nature of the adsorption process(es) monolayer-multilayer adsorption, capillary condensation or micropore filling. If the isotherm exhibits low-pressure hysteresis (i.e. at p/p° < 0 4, with nitrogen at 77 K) the technique should be checked to establish the degree of accuracy and reproducibility of the measurements. In certain cases it is possible to relate the hysteresis loop to the morphology of the adsorbent (e.g. a Type B loop can be associated with slit-shaped pores or platey particles). 

Fluids in narrow pores adsorption, capillary condensation and critical points,... 

As progressively higher pressures are used during N2 adsorption, capillary condensation will occur in pores that are increasingly larger. The Kelvin equation illustrates that the equilibrium vapor pressure is lowered over a concave meniscus of liquid, which is why N2 is able to condense in catalyst pores at pressures lower than the saturahon pressure ... 

The most used methods for the characterization of flow and species transport inside a porous body include the identification of the characteristics of the pores of the porous structure and the particularisation of classic transport equations to this case. These equations are generally associated with equations describing the solid-fluid interaction, adsorption, capillary condensation and flow due to the capillary forces etc. Concerning the species displacement (flow) problem inside a porous structure, we can consider the following classification ... 

In terms of catalysis, important equilibrium processes include low-temperature gas adsorption (capillary condensation) and nonwetting fluid invasion, both of which are routinely used to characterize pore size distribution. Static diffusion in a Wicke-Kallenbach cell characterizes effective diffusivity. The simultaneous rate processes of diffusion and reaction determine catalyst effectiveness, which is the single most significant measure of practical catalytic reactor performance. 

Transfer mechanisms involved in SC CO2 permeation through such porous membranes can be convection (Poiseuille law), diffusion (Knudsen flow), and surface membrane interaction by adsorption, capillary condensation, etc. [11]. Mechanisms have been specifically investigated for nanofiltration and zeolite membranes. With a nanofilter presenting a pore diameter of about 1 nm, Sarrade [11] mentioned a Poiseuille flow associated with an irreversible CO2 adsorption on the micropore wall. Transfer... 

The flow of a condensable vapor through a mesoporous membrane is a phenomenon of great complexity [18,14]. As the membrane is exposed to a certain vapor pressure gradient, adsorption, capillary condensation and surface flow phenomena occur at the same time, during the initial stages of the experiment [15]. As the system reaches a steady state, a film of adsorbate has been formed on the pore walls, while at the same time capillary condensation occurs in the subcritical pores according to the modified for the case of adsorption, Kelvin equation (eq. 3). 

Many compounds and salts are sensitive to the presence of water vapour or moisture. When compounds interact with moisture, they retain the water by either bulk or surface adsorption, capillary condensation, chemical reaction and, in extreme cases, a solution (deliquescence). Deliquescence is where a solid dissolves and saturates a thin film of water on its surface. It has been shown that when moisture is absorbed to the extent that deliquescence takes place at a certain critical relative humidity, the liquid film surrounding the solid is saturated. This process is dictated by vapour diffusion and heat transport rates (Kontny et al. 1987). 

Evans, R., U.M.B. Marconi, and P. Tarazona. 1986. Fluids in narrow pores Adsorption, capillary condensation, and critical points. J. Chem. Phys, 84 2376-2399. 

Brunauer, Emmet, Teller (BED P. 1, C-lp, f(d-a) Dr/ p homogeneous surfaee, multilayer adsorption, capillary condensation... 

These sizes can be determined from the aspect of N, adsorption at 77 K, and hence N2 molecules are adsorbed by different mechanisms -multilayer adsorption, capillary condensation, and micropore filling for macropores, mesopores, and micropores, respectively. The critical widths of 50 and 2 nm are chosen from empirical and physical reasons. The pore width of 50 nm corresponds to the relative pressure of 0.96 for the adsorption isotherm. Adsorption experiments above that are considerably difficult and applicability of the capillary condensation theory is not sufficiently examined. The smaller critical width of 2 nm corresponds to the relative pressure of 0.39 through the Kelvin equation, where an unstable... 

Grand canonical Monte Carlo simulations performed for natural gas adsorbed on carbon have demonstrated that the optimum pore size is 0.76 nm, as mentioned earlier (methane adsorption (capillary condensation) does not takes place at room temperature) thus, a further increase of the slit width would lower the particle density without a significant increase in amounts adsorbed. These calculations predict that the theoretical maximum methane storage capacity of carbon at 3.5 MPa is 209 VA for a monolithic carbon that fills the vessel and contains a minimum amount of macropore volume and no external... 

Nitrogen adsorption is not, however, a sequential phenomena since pores of all sizes are accessible to nitrogen vapour from the onset of adsorption. Capillary condensation occurs from small to large pores and thus has a different mechanism of pore filling to mercury intrusion. Although the final pore distributions obtained from either adsorption or mercury porosimetry may be similar in certain size ranges and networks, the process of pore filling is not directly comparable. 

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