Nitrogen adsorption saturated vapor pressure

Krypton Sorption. Volumetric adsorption using gases with low saturated vapor pressure has been found to be an effective technique to gain detailed structural information for small quantities of porous materials, especially using krypton (Kr).27 The substitution of nitrogen by Kr reduces significantly the amount of unadsorbed molecules in the dead volume, allows for the characterization of small surface areas, and is thus ideal for mesoporous... 

Type 1 isotherms exhibit prominent adsorption at low relative pressures p/po (the relative pressure p/po is defined as the equilibrium v or pressure divided by the saturation vapor pressure) and then level off. Type 1 isotherm is usually considered to be indicative of adsorption in micropores (e.g., adsorption of benzene on microporous active carbon) or monolayer adsorption due to the stror adsorbent-adsorbate interactions (which may be the case for chemisorption, which involves chemical bonding between adsorbate and the adsorbent surface, e.g., adsorption of hydrogen on iron). In the case of nonpolar gases commonly used for charactmzation of porous solids (nitrogen, argon) [10, 12, 13, 17, 56], chemisorption is unlikely and therefore e I reflects usually adsorption on microporous solids. However, type I isotherms may also be observed for mesoporous materials with pore size close to the micropore range. In particular, in the case of adsorption of N2 at 77 K or Ar at both 77 K and 87 K in cylindrical pores, a type I isotherm would have to level off below the relative pressure of about 0.1 for the material to be exclusively microporous, as inferred fi-om tile results of recent studies of siliceous and carbonaceous ordered mesoporous materials (OMM) [57-59]. Consequently, when a type 1 isotherm does not level off below the relative... 

Sing (8) has presented an exceptionally clear and concise description of adsorption isotherms and methods for their interpretation in terms of pore size distribution. As shown in Figure 5.7, an adsorbate vapor such as nitrogen or water is adsorbed in a porous gel or powder in increasing amounts as the relative vapor pressure, / /po, is increased, p, being the saturated vapor pressure of the liquid. 

The adsorption-desorption method is a popular and commonly used method for characterization of surface and structural properties of porous materials, allowing the determination of their surface area, pore-size distribution, pore volume and adsorption energy distribution. Nitrogen is often used for the adsorbent gas but other adsorbent gases such as argon can also be used. According to this method, adsorption-isotherm (amount of adsorbed gas versus relative pressure [pressure/saturation vapor pressure of the adsorbent]) is drawn and the data are analyzed by assuming capillary condensation. 

The carbons used, for these two studies, were prepared from polyvinylidene chloride (PVDC) by carbonizing to 850 °C in nitrogen and activating in carbon dioxide at 850 °C to 24, 41, 70 and 85wt% bum-off. A commercial charcoal (Sutcliffe Speakman Co. Limited, No, 112 (UVD/20) prepared for adsorption from the liquid phase) was also used. Characterizations were made by adsorptions of nitrogen at 77 K and of carbon dioxide at 273 and 195 K, using the Brunauer-Emmett-Teller (BET) and Dubinin-Radushkevich (DR) equations of adsorption. The saturation vapor pressures of CO2 at 273 and 195 K are taken as 3.44 and 0.186 MPa, respectively. The carbons are described in Table 8.1. Thus, a... 

Essentially the static, volumetric gas adsorption equipment available commercially is for determining the amount of gas physically or chemically adsorbed on a powder surface. It is available for either single point or multipoint techniques and may be manual or automatic. Surface areas down to 1 m2 can be determined to 0.1 m2 using nitrogen adsorption provided care is taken. With coarser powders the dead space errors makes nitrogen unsuitable. Since the amount of gas in the dead space is proportional to the absolute pressure it is preferable to use gases with low saturation vapor pressures. Krypton with a... 

X-ray diffraction powder patterns were recorded on a CGR Theta 60 instrument, using monochromated CuKa radiation. The adsorption capacities for several adsorbates were measured at room temperature by gravimetry, using a Cahn RH microbalance as proposed by Vaughan and Lussier (3 ). The samples were first treated in air for 5 hours at 480°C. The experiment was performed by passing, over the sample, a stream of nitrogen saturated by the vapor pressure of the sorbate at room temperature, the relative pressure P/Po was then equal to 1. 

The hydrogen stream is water scrubbed to remove solids, ammonia and hydrogen chloride and to saturate it with water vapor. The CO converts to H2 via the shift reaction, and the Rectisol process selectively removes the sour gases (H2S and CO2). Pressure Swing Adsorption (PSA) removes residual impurities (CO, nitrogen, etc.) to produce H2 with a purity of 99.85%. 

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