Interfacial transmission technique

The light transmission technique [3] is based on the fact that the fraction of light transmitted through a gas - liquid dispersion is related to the interfacial area and the length of the light pass, irrespective of bubble size. 

Estimate the volume of bubble-free slurry required to obtain a conversion of 30% for a hydrogen feed rate of 100 ft /min (at 60°F and 1 atm). By a light-transmission technique, Calderbank measured gas-liquid interfacial areas of 0.94 to 2.09 cm /cm for bubble sizes likely to be encountered in this system. Suppose for this illustration Mg = 1.0 cm-/cm of bubble-free slurry. The Henry s law constant for hydrogen in toluene at 50°C is 9.4 (g mole/cm )/(g moles/cm ), and its diffusivity is 1.1 x 10 " cm /sec. The density and viscosity of toluene at 50°C are 0.85 g/cm and 0.45 centi-poises, respectively. Equimolal feed rates of ethylene and hydrogen will be used. 

Vibrational spectroscopy is also widely used for the analysis of filled elastomers [87-89] in order to describe the polymer-filler interaction [87,89], interfacial region [89], sulfur and cross-linking chemistry of elastomers and bonding of BHT fragments to the EPDM matrix [88]. In the rubber industry the FTIR transmission technique is generally accepted... 

Auxiliary data are the sizes of bubbles and droplets. These data and the holdups of the two phases are measured by a variety of standard techniques. Interfacial area measurements utihze techniques of transmission or reflection of light. Data on and methods for finding sohi-bihties of gases or the relation between partial pressure and concentration in hquid are also well estabhshecT... 

Interfacial area measurement. Knowledge of the interfacial area is indispensable in modeling two-phase flow (Dejesus and Kawaji, 1990), which determines the interphase transfer of mass, momentum, and energy in steady and transient flow. Ultrasonic techniques are used for such measurements. Since there is no direct relationship between the measurement of ultrasonic transmission and the volumetric interfacial area in bubbly flow, some estimate of the average bubble size is necessary to permit access to the volumetric interfacial area (Delhaye, 1986). In bubbly flows with bubbles several millimeters in diameter and with high void fractions, Stravs and von Stocker (1985) were apparently the first, in 1981, to propose the use of pulsed, 1- to 10-MHz ultrasound for measuring interfacial area. Independently, Amblard et al. (1983) used the same technique but at frequencies lower than 1 MHz. The volumetric interfacial area, T, is defined by (Delhaye, 1986)... 

To calculate the gas absorption rate qL for Eq. (9.7), we need to know the gas-liquid interfacial area, which can be measured employing several techniques such as photography, light transmission, and laser optics. 

The fast isomerization of the spiropyran to the merocyanine provides a possibility of generating an interfacial shock wave. The methods used so far in studying the transmission of waves in mono-layers and the adjacent bulk phases require mechanical (16) or electrocapillary (17) excitation of the interface which involves the displacement of the aqueous bulk phase. In addition, the range of frequencies accessible to the investigation of interfacial waves by the conventional techniques is very limited. The fast photochemical generation of an interfacial shock wave is strictly occurring in the monolayer and provides a larger spectrum of frequencies which can be fully explored only after the development of appropriate detection methods. 

Photochemical processes in monolayers at the air-water interface can be controlled externally by variation of the various parameters like matrix composition, subphase composition, temperature and surface pressure. When the product of the reactions has a different area per molecule, the surface pressure may change at constant monolayer area. An interfacial shock wave has been generated in this way. This technique permits the investigation of the kinetics of reorganization processes and the transmission of mechanical signals in monolayers. 

There are several major areas of interfacial phenomena to which infrared spectroscopy has been applied that are not treated extensively in this volume. Most of these areas have established bodies of literature of their own. In many of these areas, the replacement of dispersive spectrometers by FT instruments has resulted in continued improvement in sensitivity, and in the interpretation of phenomena at the molecular level. Among these areas are the characterization of polymer surfaces with ATR (127-129) and diffuse reflectance (130) sampling techniques transmission IR studies of the surfaces of powdered samples with adsorbed gases (131-136) alumina(137.138). silica (139). and catalyst (140) surfaces diffuse reflectance studies of organo- modified mineral and glass fiber surfaces (141-143) metal overlayer enhanced ATR (144) and spectroelectrochemistry (145-149). 

Some of this theoretical thinking may be utilized in reactor analysis and design. Illustrations of gas-liquid reactors are shown in Fig. 19-26. Unfortunately, some of the parameter values required to undertake a rigorous analysis often are not available. As discussed in Sec. 7, the intrinsic rate constant kc for a liquid-phase reaction without the complications of diffusional resistances may be estimated from properly designed laboratory experiments. Gas- and liquid-phase holdups may be estimated from correlations or measured. The interfacial area per unit reactor volume a may be estimated from correlations or measurements that utilize techniques of transmission or reflection of light, though these are limited to small diameters. The combined volumetric mass-transfer coefficient kLa, can be also directly measured in reactive or nonreactive systems (see, e.g., Char-pentier, Advances in Chemical Engineering, vol. 11, Academic Press, 1981, pp. 2-135). Mass-transfer coefficients, interfacial areas, and liquid holdup typical for various gas-liquid reactors are provided in Tables 19-10 and 19-11. 

The local interfacial contact area may be determined directly by either light transmission or reflection techniques, In the former, a parallel beam of light is... 

To understand the importance of nanostructures in microsieving membranes, the basic structure of nanophased ceramics must be briefly described. Because the particles are extremely small, one to a few tens of nanometers, an important fraction of the atoms is found in or very near the interface between grains, as reported in Table 2 [32]. Figure 11 is a schematic representation of a nanophase material. One can see that individual grains in the 5 nm range induce a biphasic material with an interfacial phase between the grains and a residual nanoporosity, evidenced by positron lifetime spectroscopy [33]. Transmission electron microscopy is also a well-adapted technique for nanoscale structure characterization, as illustrated later. 

Transmission electron microscopy (TEM) This technique is used when the MPCM is in nanometer size range. The specimen must have a low density, allowing the electrons to travel through the sample. There are different ways to prepare the material it can be cut in very thin slices either by fixing it in plastic or working with it as frozen material. Pan et al. studied nanostructures that were prepared through the methodology in-situ interfacial polycondensation. 

The local interfacial contact area is determined directly by the light transmission and reflection techniques. 

Phase identification may be accomplished via XRD. FTIR is recommended as a complementary technique because it allows identification of phase amounts and structures not readily detectable with XRD (Ducheyne, 1990). Grain sizes may be determined through either optical microscopy, SEM, or transmission electron microscopy (TEM), depending on the order of the grain size. Additionally, TEM is useful to characterize second phases, crystal structure, and lattice imperfections. Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) may also be utilized to determine surface and interfacial compositions. Chemical stability and surface activity may be analyzed via XPS and measurements of ionic fluxes and zeta potentials. It is assumed that two different pathways of activity exist solution and cell-mediated (Jarcho, 1981). 

The morphology characterization of hybrid membranes is very important to identify the possible interfacial morphology and particle dispersion in the final membrane matrix. Electron microscopy is typically used to investigate the filler dispersion and the hybrid membrane morphology. Scanning electron microscopy is the most frequently used technique, and it allows the characterization of the sample surface. The sample s cross-sections can be examined to analyze the inner morphology. Transmission electron microscopy is also a very useful technique because it allows a direct evaluation of the inner morphology of the sample. 

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