Absorption separation system

Absorption refrigeration systems (ARS), 21 550-552 advantages of, 21 551 industrial and domestic use of, 21 552 Absorption separation systems, design of, 20 751... 

Ordinary diffusion involves molecular mixing caused by the random motion of molecules. It is much more pronounced in gases and Hquids than in soHds. The effects of diffusion in fluids are also greatly affected by convection or turbulence. These phenomena are involved in mass-transfer processes, and therefore in separation processes (see Mass transfer Separation systems synthesis). In chemical engineering, the term diffusional unit operations normally refers to the separation processes in which mass is transferred from one phase to another, often across a fluid interface, and in which diffusion is considered to be the rate-controlling mechanism. Thus, the standard unit operations such as distillation (qv), drying (qv), and the sorption processes, as well as the less conventional separation processes, are usually classified under this heading (see Absorption Adsorption Adsorption, gas separation Adsorption, liquid separation). 

Photochemical response of these liposomes is different from each other. With progression of trans - cis photoisomerization of azobenzene, ICD at the absorption band of the trans isomer decreases. As shown in Figure 4, depression in ICD is almost proportional to the amount of photoisomerization for the phase separated system. Photoisomerization in the domain of azobenzene aggregate proceeds independently from the rest of DPPC aggregate so that the depression in ICD corresponds to the concentration of remaining transazobenzene. When the two components are molecularly mixed, change of... 

The absorption of ozone into water and the processes for the wafer (cleaning, photoresist removal etc.) are often two separate systems with distances between them of up to 40 m. Therefore the decay rate of ozone or at least the liquid ozone concentration near the point of use should be measured to insure reproducibility of the process. 

The reactor system may consist of a number of reactors which can be continuous stirred tank reactors, plug flow reactors, or any representation between the two above extremes, and they may operate isothermally, adiabatically or nonisothermally. The separation system depending on the reactor system effluent may involve only liquid separation, only vapor separation or both liquid and vapor separation schemes. The liquid separation scheme may include flash units, distillation columns or trains of distillation columns, extraction units, or crystallization units. If distillation is employed, then we may have simple sharp columns, nonsharp columns, or even single complex distillation columns and complex column sequences. Also, depending on the reactor effluent characteristics, extractive distillation, azeotropic distillation, or reactive distillation may be employed. The vapor separation scheme may involve absorption columns, adsorption units,... 

Absorption Optical System. During an ultracentrifuge experiment the solute, if denser than the solvent, sediments toward the bottom of the cell, thereby generating a concentration gradient. (There are many types of experiments the two most common types will be described later.) The instrument is constructed with two separate optical systems that record the concentration gradient during an experiment. One of these, the absorption optical system, is especially useful in biochemistry for the study of proteins and nucleic acids which have chromophores which absorb visible or uv light. 

Weinberger and Lurie (1991) first applied HPCE to an analysis of illicit drug substances. These authors used a micellar electrokinetic chromatography (MEKC, discussed in Chapter 3, Section 3.7.2) separation system in 50 pirn i.d. bare silica capillaries (length 25-200 cm) the buffer consisted of 8.5 mM phosphate and 8.5 mM borate at pH 8.5 and contained 85 mM sodium dodecyl sulfate (SDS) and 15% acetonitrile. The applied voltage was 25 to 30 kV, and detection was by UV absorption at 210 nm. 

Although substantially true, this misunderstanding arises from the fact that the spectroscopist views the chromatograph as just another sampling device and not as a separation system. The point of interfacing a liquid chromatograph with an absorption spectrometer is to achieve a separation before detection. Consequently, the important dispersion characteristics are not those that take place in the column, but those that occurs in the interface between the chromatograph and the spectrometer and in the spectrometer itself... 

Most absorption separations of this type are carried out at pressures near atmospheric where the deviation of the vapor phase from perfect gas behavior is negligible. For such systems, Eqs. (13-23) and (13-29) may be combined to give... 

The phase-split block can be a single flash, a series of flashes, or a combination of flash and absorption/stripping columns. Flash temperature and pressure are design variable that may be optimised to fulfil a separation objective, as sharp gas/liquid split or recovery of some components. For water-driven condensers the recommended condensation temperature is of about 35 °C. Vapour components can be condensed and sent to the liquid separation system. The supercritical components carried in the liquid phase can be recovered in a stabiliser column (see later in this section). Further, these can be sent to the gas separation system, used as fuel, or purged. 

Peak identification is based on the comparison of normalized spectra representative for the peak with spectra of one or several standard compounds run in the same separation system and stored in a spectral library [107,116]. This approach is less powerful than for mass or infrared spectral searches due to the rather broad and featureless bands that typify absorption spectra. Absorption spectra of similar compounds and compounds with a chromophore well separated from the variation in molecular structure are often virtually identical. Also, spectral changes dependent on the experimental conditions (pH, mobile phase composition, temperature, etc.) occur frequently. For this reason user prepared local libraries tend to predominate over general libraries, in contrast to common practices in infrared and mass spectral searches. A favorable spectral match for an absorption spectrum by itself is not acceptable for absolute identification. 

Atomic absorption spectrometry is commonly used to measure a wide range of elements as shown in Table 2. Such techniques as flame, graphite furnace, hydride generation, and cold vapor are employed. Measurements are made separately for each element of interest in turn to achieve a complete analysis these techniques are relatively slow to use. More sensitive, but also more expensive, multielement analytical techniques such as inductively coupled plasma-atomic emission spectrometry and inductively coupled plasma-mass spectrometry can be used if lower (pgl and below) detection limits are required. These detectors can also be coupled with separation systems if speciation data, e.g., Cr(III) and Cr(VI), are needed. 

---