Packings specific surface area

Ul = liquid superficial velocity, m/s ap = packing specific surface area, m2/m3 g = acceleration due to gravity, m/s Pi, = liquid viscosity, kg/(m-s)... 

Packing Specific Surface Area (m /g) Packing Specific Surface Area (m /g)... 

Large active exposed surface area the specific surface area, e.g., the exposed surface area of the packing per cubic foot of packed volume, is important since larger specific area means a larger area available for contact between the liquid and the gas, resulting in more efficient scrubber operation. 

Comparing trays at 24-in. tray spacing with a state-of-the-art 2-2.5-in. (nominal) random packing, and with a state-of-the-art structured packing of 67 ft /ft specific surface area, all optimally designed, we found that ... 

Figure 9-62. Flooding data for structured packings as reported by Billet [109]. Numbers following packing type indicate specific surface area in m /m. Reproduced by pennis-sion of the American Institute of Chemical Engineers, Fair, J. R. and Bravo, J. L., Chemical Engineering Progress, V. 86, No. 1 (1990) p. 19 all rights reserved. Note, Uq = vapor velocity, meters/sec.

Brown et al. [494] developed a method for the production of hydrated niobium or tantalum pentoxide from fluoride-containing solutions. The essence of the method is that the fluorotantalic or oxyfluoroniobic acid solution is mixed in stages with aqueous ammonia at controlled pH, temperature, and precipitation time. The above conditions enable to produce tantalum or niobium hydroxides with a narrow particle size distribution. The precipitated hydroxides are calcinated at temperatures above 790°C, yielding tantalum oxide powder that is characterized by a pack density of approximately 3 g/cm3. Niobium oxide is obtained by thermal treatment of niobium hydroxide at temperatures above 650°C. The product obtained has a pack density of approximately 1.8 g/cm3. The specific surface area of tantalum oxide and niobium oxide is nominally about 3 or 2 m2/g, respectively. 

After it is washed, dried, and granulated, this silica gel has a very high specific surface area (about 700 m2-g 1) and is useful as a drying agent, a support for catalysts, a packing for chromatography columns, and a thermal insulator. 

Figvire 4.12 Suwaary of the various volume elements for a 25 cm x 4.6 mm I. D. column packed with Zorbax (5 micrometer particle diameter and 330 m /g specific surface area) and methanol-water (1 4) as mobile phase. 

Traditional methods of assessing the capacity of tower packings, which involve the use of the specific surface area S and the voidage e, developed from the fact that these... 

The secondary structure, the mesopores, is similar to the internal structure of standard HPLC particles. This secondary structure provides the surface for retention. The standard pore size is in the order of 13 nm, resulting in a specific surface area of about 300 mVg. Due to the lower ratio of retentive structure to interstitial space, the retentivity of monoliths and the preparative loadability tends to be significantly lower than the retentivity and loadability of packed beds of 10-nm particles. Since the monolithic columns described here are made from silica, they can be derivatized in the same way and with the same technology as silica-based particles. Also, the useful pH range is the same as for silica-based particles. 

Coupled columns packed with different stationary phases can be used to optimize the analysis time (71, 75). In this approach the different columns are connected in a series or in parallel. liie sample mixture is first fractioned on a relatively short column. Subsequently the fractions of the partially separated mixture are separated on other columns containing the same or other stationary phases in order to obtain the individual components. Columns differing in length (number of theoretical plates), adsorptive strength or phase ratio (magnitude of specific surface area), and selectivity (nature of the stationary phase) can be employed, whereas, the eluent composition remains unchanged. Identification of the individual sample components via coupled column technique requires a careful optimization of each column and precise control of each switching step. 

This results in almost the same specific surface area as found in capillary packed with macroporous silica beads. Next, the heparin was covalently immobilized on the surface of an etched capillary through a spacer using silane chemistry. 

The physical properties of silica are determined by its specific surface area, pore volume, average pore diameter, porosity, and the particle diameter and shape [8]. The latter two are responsible for the efficiency, the physical stability and the pressure drop of the packed columns and do not contribute to retention and selectivity. 

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