Adsorption area

Work in the area of simultaneous heat and mass transfer has centered on the solution of equations such as 1—18 for cases where the stmcture and properties of a soHd phase must also be considered, as in drying (qv) or adsorption (qv), or where a chemical reaction takes place. Drying simulation (45—47) and drying of foods (48,49) have been particularly active subjects. In the adsorption area the separation of multicomponent fluid mixtures is influenced by comparative rates of diffusion and by interface temperatures (50,51). In the area of reactor studies there has been much interest in monolithic and honeycomb catalytic reactions (52,53) (see Exhaust control, industrial). Eor these kinds of appHcations psychrometric charts for systems other than air—water would be useful. The constmction of such has been considered (54). 

Synthetic zeolites and other molecular sieves are important products to a number of companies in the catalysis and adsorption areas and numerous applications, both emerging and well-established, are encouraging the industrial synthesis of the materials. There are currently no more than a few dozen crystalline microporous structures that are widely manufactured for commercial use, in comparison to the hundreds of structures that have been made in the laboratory. See Chapter 2 for details on zeolite structures. The highest volume zeolites manufactured are two of the earliest-discovered materials zeolite A (used extensively as ion exchangers in powdered laundry detergents) and zeolite Y (used in catalytic cracking of gas oil). 

Similarly to SPE, for the SPME technique CNTs with high porosity and large adsorption area seems to be a good candidate for SPME coating. In addition, the more thermal and physical resistance of carbon nanotubes in comparison with commercial SPME coatings, are the other important characteristics from the practical point of view. However, this technique has been just applied in environmental analysis till now. 

This phenomenon is known as surface denaturation. Adsorption area and, consequently, the extent of denaturation are decreased with an increasing specific adsorption of the anion. The dependence of the molecular weight versus adsorption area shows that the proteins of large molecular weight (above 15 kD) behave differently from the smaller proteins [94], as they possibly do not denaturate and spread on mercury to the same extent as... 

XAD-2 resin is a styrene-divinylbenzene copolymer that has a highly aromatic structure. It has a surface area of about 300 m2/g, an average pore diameter of 90 A, and a maximum pore diameter of 290 A. XAD-8 resin is a methyl methacrylate copolymer and has a slightly more hydrophilic surface than XAD-2. It has a surface area of about 140 m2/g, an average pore diameter of 250 A, and a maximum pore diameter of 375-840 A. Each exhibits different adsorption characteristics because of structural and surface chemistry differences. Both XAD resins have a significant number of micropores <25 A in diameter. The adsorption area is distributed biomodally in XAD-8 and has maximums at 22.5 A or less and at 375 A. XAD-2 has a maximum at 22.5 A or less and a slight increase at 240 A (11). This result indicates that XAD-2 adsorption is initially more diffusion-limited than XAD-8. 

The following data refer to the adsorption of dodecanol from solution in toluene by a sample of carbon black, the BET nitrogen adsorption area of which is 105 m2 g-1 ... 

In this equation 5° is the adsorption energy of the solute on a standard adsorbent. At is the adsorption area of the solute molecule. e° is the adsorption energy of the solvent per unit area on the same standard adsorbent, usually referred to as the solvent strength or eluotropic strength, a is the activity of the adsorbent and Va is the volume of the adsorbed solvent per gram of stationary phase. Hence, Va can be seen as a compensation factor for the dimensions of Ka i. Ka i/ Va is a dimensionless quantity. 

Surface characteristics (adsorption, area, surface energy, solubility)... 

Adsorbate Gas. For physical adsorption, any pure gas that does not react with the solid adsorbent can be used. However, for quantitative area measurements, a molecule of known adsorption area is required. Nitrogen gas is a very common choice and will be used in this experiment. 

The assumption of the significance of emulsifier adsorption capability to the kinetics of emulsion polymerization was suggested in our paper (6), for polar monomers, and by Roe (7) and Robb (8 for styrene. Paxton (2) demonstrated that the adsorption area occupied by a molecule of a given emulsifier (Ha-dodecyl benzyl sulphooate) on the surface of polymethylmethac-rylate latex particles, is 1.31 (nm), and so exceeds by a factor of 2.3 a similar area on the surface of polystyrene latex, equal to 0.33(n>n). ... 

Figure 13 Hydrophobicity of solid acids evaluated from the adsorptions of benzene and water CS2.5H0.5 PW12O40 (o), Cs3 PW12O40 ( ), H-ZSM-5 (Si/Al = 628) (A), H-ZSM-5 (Si/Al = 40) (0), AI2O3 ( ), and Si02-Al203 (A). Scene and Sh20 are adsorption areas of benzene and water, respectively...

The high porosity that results from activation increases the area for adsorption. One gram of char can produce about 1000 m of adsorption area. After activation, the char is further processed into three types of finished product powdered form called powdered activated carbon (PAC), the granular form called granular activated carbon (GAC), and activated carbon fiber (ACF). PAC is normally less than 200 mesh GAC is normally greater than 0.1 mm in diameter. ACF is a fibrous form of activated carbon. Figure 8.7 shows a schematic of the transformation of raw carbon to activated carbon, indicating the increase in surface area. 

Wolfram (1966) calculated the packing density of surfactant molecules on the polymer surface from the adsorption value at the CMC and showed that it varies with polymer polarity. Thus, the adsorption area of a SDDS molecule on various surfaces takes the following values (nm ) paraffin 0.41,... 

Several investigations have determined tbe absorption behavior of surfactant adsorption on particles of aqueous polymer dispersions by adsorption titration. The results have been similar to those observed by Wolfram for adsorption on a planar polymer surface determined from the wettipg angle. Thus, Paxton (1969) established that the area occupied by a sodium dodecylbenzylsulfonate molecule in a saturated adsorption layer (ylsiim) the surface of PMMA latex particles is 1.31 nm, whereas on the surface of polystyrene latex particles it is only 0.53 nm. The author considers that previous studies of adsorption of this emulsifier, which gave adsorption area Msitm) were carried out on interfaces with similar adsotption... 

In order to establish the correlation between the value of x and emulsifier adsorption characteristics in the givoi reaction system in latexes prepared according to the same redpes, as was used in determination of reaction order, the adsorption areas of emulsifier molecules in the saturated... 

As calculated value of the area occupied by emulsifier molecule on the particle surface of resultant latex assuming that all the emulsifier is adsorbed AsiiB adsorption area of emulsifier molecule at saturation of the adsorption layer Cf emulsifier concentration... 

Measurements have been made of tracer or intrinsic diffusion coefficients of water in a number of zeolites. Most refer to crystals nearly saturated with zeolitic water, while smoothed rather than adsorption areas were used in calculating the coefficients. From the temperature dependence of Da or Da, the activation energy, E, may be found using the Arrhenius equations Da = Do exp — E/RT or Da = Do exp — E/RT. Some results for tracer diffusion are summarized in Table VI. (iS). These shed considerable light upon certain aspects of intracrystalline diffusion for small polar molecules ... 

In the dry cleaning business or in vapor degreasing plants, losses of hydrocarbon or chlorinated hydrocarbon vapors occur from the use and recovery of solvents. These losses can be prevented by the use of activated adsorbent systems to capture the organic vapors from the vents or hoods of these devices. Activated carbon is one of the best adsorbents for this purpose because of its selectivity for organic vapors, and can provide up to 1000 m /g (ca. 8 acres/oz) of adsorption area. Solvent present in high concentrations in air may also be recovered by cooling the air to liquid nitrogen temperatures to condense the solvent. 

Iron-oxide-coated sand is another recently introduced arsenic adsorbent that has been shown to have promise for arsenic removal (8,9). However, because the effective adsorption area is only on the surface of the particle, minimal capacity should be expected compared with adsorbents that are pure hydrated iron oxide and are truly porous. An example of the latter type of adsorbent is granular ferric hydroxide (5). 

---