Nitrogen surface area

Another standard industry method for surface area is based on the adsorption of cetyltrimethylammonium bromide (CTAB) from aqueous solution. This is ASTM method D3765-85 (2). This method measures the specific surface area of carbon black exclusive of the internal area contained in micropores that are too small to admit the large CTAB molecules. Eor mbber-grade nonporous blacks the CTAB method gives excellent agreement with nitrogen surface areas. 

Porous polymers with large 77 K nitrogen surface areas also have infenor methane uptakes. For example Dow XV 43546, a porous polystyrene with a 77 K nitrogen BET area of 1600 mVg has a methane uptake of 67 mg/g at 25°C, 3.4 MPa, whereas Takcda HGK 971 carbon of similai" 77 K nitrogen surface area has an uptake of 116 mg methane per g. Rohm and Haas Amberlite porous polymers give similarly lower than expected methane uptakes. 

All catalysts are either it-in. cylinder or sphere. Catalyst B has a bimodal pore size distribution. The average pore diameter is defined as 40,000 x pore volume (ml/g) divided by nitrogen surface area (m2/g). 

Cobalt molybdate, Girdler No. G35A, received as pellets, then crushed and sieved to 35 to 65 mesh. 1.3% Co + 6.1% Mo on alumina BET nitrogen surface area 241 sq. meters per gram stabilized with thiophene in a flow reaction at 400° C. before use. Weight of catalyst used is noted with each set of results. 

Surfactant demand curves for three different grades with Brunauer, Emmett and Teller Test Method (BET) nitrogen surface areas of 9 and 15m2/g are shown in Figure 10.6. 

An early normalizing procedure, proposed by Kiselev (1957) to compare adsorption isotherms of hydrocarbons, water vapour, etc. on a series of different adsorbents, was simply to plot the surface excess concentration F (=n/A), obtained from a knowledge of the BET-nitrogen surface area, A (BET), versus p/p°. It is also possible to plot, instead of f, the reduced adsorption , n/nm, which still relies on the BET method to determine the monolayer capacity nm but does not require knowledge of the molecular cross-sectional area a. 

Figure 10.18. Development of the BET-nitrogen surface area during the dehydration of a fine gibbsite, versus % of mass loss. Same conditions as for Figure 1.17 (Rouquerol et al., 1979a).

It is important to realize that useful zeolites have large internal surfaces, that is, a reminder of the sponge analogy, and it is these surfaces that control their observable surface properties. Normally, surface areas of inorganic materials are quantified by standard gas sorption techniques, for example, N2 uptake analyzed by Brunauer, Emmett, and Teller (BET) isotherm plots, and zeolites have nitrogen surface areas in the approximate region 100-1000m g. These estimates should be considered with caution because ... 

Important physical characteristics for rubber blacks are, in addition to the average particle size, the DPB (dibutyl phthalate) absorption, which increases with increasing structure (agglomeration of primary particles), and the specific (nitrogen) surface area, which increases with decreasing particle size and increasing porosity of the primary particles, (see Table 5.7-7). 

It has to be stressed that the monolayer surface phase capacity is assumed to be constant over the whole bulk concentration region, i.e., n = const., for x (0,1). Under this assumption we can assess the specific surface areas of the solid adsorbents if the cross - sectional areas of adsorbed molecules are known. However, the following question arises here what molar areas to assign to the different kinds of molecules This problem is similar in the case of gas - solid adsorption and it may be sufficient to refer to the compilation by McLellan and Harnsberger [13]. It has been found that cross - sectional molar areas calculated by means of the molar volumes of the pure components are mostly in agreement with nitrogen surface area values [14]. 

Table XIV. The Partitioning of Phenanthrenea Between Silica Gel and Distilled Water as a Function of Nitrogen Surface Area ...

Mo V Nb Te molar ratio Catalyst (calcined in air) Surface area (m g) Catalyst (calcined in nitrogen) Surface area (mVg)... 

Particle density Total porosity Macropore porosity Micropore porosity Average macropore diameter Mesopore surface area Micropore volume Nitrogen surface area ... 

Nitrogen surface area Measure of total particle surface area, due to nitrogen gas being able to cover the full surface including pores without interface from surface organic functional groups. 

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