Average pore width

The table convincingly demonstrates how the unsuspected presence of micropores can lead to an erroneous value of the specific surface calculated from a Type II isotherm by application of the standard BET procedure. According to the foregoing analysis, the external specific surface of the solid is 114m g" the micropore volume (from the vertical separation of isotherms A and E) is 105 mm g but since the average pore width is not precisely known, the area of the micropore walls cannot be calculated. Thus the BET figure of 360m g calculated from isotherm E represents merely an apparent and not a true surface area. 

Characteristic Energies and Average Pore Width Calculated from the Adsorption Data of N2 at 77 K and C02 at 273 K... 

Comparable results were obtained when an IL (ethyl-methylimmidazolium-bis(trifluoro-methane-sulfonyl)imide EMI-TFSI) was tested using a series of nanoporous carbons with average pore width in the range of 0.65-1.1 nm [18], The ion sizes, calculated as 0.79 and 0.76 nm in the longest dimension for TFSI and EMI ions, respectively, are within the range of carbons pore size. Figure 8.8 points out that, when the average pore size decreases from 1.1 to 0.7 nm, the normalized capacitance increases below 0.7 nm, the normalized capacitance decreases. Since the maximum at 0.7 nm is... 

Fig. 1 shows the evolution of Woi and W02 with the extent of activation. It can be observed that both Woi and W02 increase with B.O., but that initially there is only the formation of small micropores, W02 being negligible up to about 30 % B.O.. Further activation leads to the formation of new micropores, but also to the enlargement of the micropores formed initially, as shown by the increase in Wo2- In addition, as the micropore volume increases, so does the average pore width. 

N2 adsorption isotherms in internal and ineterstitial nanopores of single wall carbon nanohorn (SWNH) were calculated by GCMC simulation and is compared with experimental one. Fitting of the GCMC-simulated isotherm to experimental one in internal nanopores gave the average pore width w = 2.9 nm. The N2 adsorption isotherm in the interstitial nanopores of the bundled SWNH particles well coincided with the observed one. 

TTie TWR used is a double pipe reactor, about 0.95 m in length, with an outer pressure bearing tube made of stainless steel (1.4989, o.d. 140 mm, i.d. 80 mm) and in inner porous tube of sintered stainless steel (1.4404, o.d. 66 mm, i.d. 60 mm, average pore width 35 pm). 

The Nj adsorption isotherms at 77 K were of Type I. The adsorption isotherms of Nj were analyzed by the SPE method using the high resolution a, -plots, as shown in Figure 1. The adsorption isotherm of N, on nonporous carbon black (Mitsubishi Chemical Co. 32B) was used as the standard isotherm. The features of the a -plots were similar to that published in the preceding paper." We can determine the micropore volume W , total surface area a , and the external surface area from the a -plots. The average pore width w can be evaluated from both the surface area and pore volume of slit-shaped micropores. Table 1 summarizes these pore parameters. 

Table 2.- Characteristic energies and average pore width calculated from N2 and CO2 adsorption data at 77 K and 273 K, respectively.

A threefold decrease in area and pore volume is thus represented with no change in average pore width. In other words, pores that disappear are lost completely, and pores that remain retain their initial structure. This also implies an overall shrinkage of the apparent volume and such has been observed in a number of cases. 

Thus, if the complete accessibility curve is divided into a series of increments the surface area of each increment may be calculated in the same way, where w is now the average pore width within each increment. 

The textural effects were found to be important up to an average pore width of 1.2 nm (sample Cq in Figure 6.1) for larger pores sizes, the surface chemistry controls the catalyst performance. 

Ikble 4.2. Observed and calculated adsorbed densities of selected adsorbates adsorbed on activated carbon fibers P5 (surface area 790 average pore width of 0.7 nm) and P20 (surface area 1430average pore width of 1.1 nm) (Ohkubo and Kaneko, 2001). 

Following this equation, the relation between the product nd the microporous surface area will not be always the same, but depends on the average pore width L. Thus, for a highly microporous activated carbon, or any other adsorbent with slit-shaped pores with a low external surface area, the enthalpy of immersion is proportional to the product EqWq but not to the microporous surface area 5. Anyway, Eq can be estimated from Equation (4.15) for a given liquid, this allowing for the calculation of micropore size distributions by using liquids with different molecular sizes, Stoeckli et al. (1990). 

In recent papers [19-21], a correlation between LFER parameters and stationary phase properties such as average pore width, alkyl chain length, bonding density, polar modification, etc., has been described. Such interrelations should extend the knowledge on retention mechanisms in liquid chromatography and hence serve to create alternative strategies for the design of new improved stationary phases. 

Average pore width (L) can be determined from the adsorption of water vapor on active carbons using an equation developed by Tsunoda [112,113] ... 

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