Two-step absorption

Production of hypochlorite takes place in a two-step absorption unit in which 23% caustic solution is fed counter-currently to the chlorine feed-stream. In the first step -the liquid jet-loop reactor - about 90% of the chlorine is converted to hypochlorite. In step two - a packed column - a very efficient absorption [1-3] is carried out in which the chlorine concentration in the off-gas is reduced to <1 ppm. The operating window of this apparatus with respect to chlorine load is quite large and varies from 100 to 6000 kg h-1 of chlorine. This high capacity is necessary for the consumption of peak loads from the electrolysis plant during short time periods. During start-up or shutdown of one electrolyser the total chlorine peak load can vary from 100 to 300 kg in just a few minutes. 

If an ion possesses two excited states with approximately same energy separation, energy transfer can occm between two ions in the first excited state (Figme 4c). One ion returns uomadiatively to the ground state while the second is promoted to the second excited state, then decays with emission of a photon whose energy is about twice that of incident photons. There are other upconversion processes two-step absorption, cooperative sensitization, cooperative luminescence. Upconversion by energy transfer is the most efficient process. 

The higher order grating signal after the photoexcitation of all-trans-f -carotene (Fig. 21) was interpreted by a two-step absorption model [117], By simultaneous fitting of the first- and second-order diffraction intensity versus the excitation intensity, the quantum yield of the photoisomerization (iso) and the kinetic parameters were determined. The results showed distinct solvent dependence. In hexane, the effect of 0iso was very small and the upper limit was obtained as 7 x 10-4. The nonlinear absorption in this case was caused by the excited absorption. In chloroform, saturation was observed in the absorption and it was attributed to formation of a trap state, most likely a photoisomer. By the fitting, (f>iso was obtained as 0.026 and the kinetic parameter and cross section of subsequent photoisomer absorption were determined. 

A second example, mentioned already, is microwave spectroscopy of Rydberg levels that have been excited by resonant two-step absorption of two dye lasers (Fig. 5.41b). The high accuracy of microwave spectroscopy allows the precise determination of finer details, such as field-induced energy shifts of Rydberg levels, broadening of Rydberg transitions by blackbody radiation, or other effects that might not be resolvable with optical spectroscopy. 

FIGURE 14 Schematic of two-step absorption isotherms tor surfactants on hydrophobic surfaces (dashed line, right verticai scale) and on hydrophilic surfaces (solid line, left vertical scale). The absorption models are inferred from the measured amounts of surfactant absorbed per unit surface area. 

ESA and the APTE effect. The probability for Excited State Absorption (ESA) in a two-step absorption (fVu), connecting a state ) to 3 by the intermediate state E2, is just given by the product of the probabilities for each step... 

The new process scheme is shown in Figure 9-39. The diagram depicts much of the existing plant equipment used for the operation of the Stretford process prior to the LO-CAT conversion. The revamped process was based on the conventional LO-CAT two-step absorption cycle with a venturi scrubber followed by an absorber column. The sullur separation method took advantage of the available equipment and followed the standard Stretford technique of skimming off the sulfur froth in the second oxidizer tank. The sulfur slurry from the fioth tank, containing about 20%. solids, was pumped to a vacuum belt filter where most of the solution was reclaimed through a wash process. The solid sulfur (80% solids content) was then sent to waste disposal. 

The above stm study also discovered a facile transport of surface gold atoms in the presence of the Hquid phase, suggesting that the two-step mechanism does not provide a complete picture of the surface reactions, and that adsorption/desorption processes may have an important role in the formation of the final equiHbrium stmcture of the monolayer. Support for the importance of a desorption process comes from atomic absorption studies showing the existence of gold in the alkanethiol solution. The stm studies suggest that this gold comes from terraces, where single-a tomic deep pits are formed (281—283). 

The reaction occurs in two steps ammonium carbamate is formed first, followed by a decomposition step of the carbamate to urea and water. The first reaction is exothermic, and the equilibrium is favored at lower temperatures and higher pressures. Higher operating pressures are also desirable for the separation absorption step that results in a higher carbamate solution concentration. A higher ammonia ratio than stoichiometric is used to compensate for the ammonia that dissolves in the melt. The reactor temperature ranges between 170-220°C at a pressure of about 200 atmospheres. 

We wish to show that no points to the leftbb of 2 on the isotherm 62 are accessible from point 1 via any adiabatic path, reversible or irreversible. Suppose we assume that some adiabatic path does exist between 1 and 2. We represent this path as a dotted curve in Figure 2.11a. We then consider the cycle I —>2 —> 1 — 1. The net heat associated with this cycle would be that arising from the last step 1 — 1, since the other two steps are defined to be adiabatic. We have defined the direction 1 — 1 to correspond to an absorption of heat, which we will call qy. From the first law, the net work vv done in the cycle, is given by w = —q, since AU for the cycle is zero. Thus, for this process, iv is negative (and therefore performed by the system), since qy is positive, having been absorbed from the reservoir. The net effect of this cycle, then, is to completely convert heat absorbed at a high temperature reservoir into work. This is a phenomenon forbidden by the Kelvin-Planck statement of the Second Law. Hence, points to the left of 2 cannot be reached from point 1 by way of any adiabatic path. 

The experimental Pjpp data have been used to build predictive models. However, since PAMPA is already a model, an in silica model based on this is a model of a model. The predictability for in vivo permeability or absorption of such in silica PAMPA model can be queshoned (see Eq. 11), since it is two steps from reality ... 

Itoh, M. Adachi, T. Transient absorption and two-step laser excitation fluorescence studies of the excited-state proton transfer and relaxation in the methanol solution of 7-hydroxyflavone. J. Am. Chem. Soc. 1984, 106, 4320 -324. 

Fig. 5.2. Two-step process for evaluation of intestinal drug absorption. The first step represents the prediction of intestinal permeability (e.g., over Caco-2 monolayers) from in-silico models or from physico-chemical...

The formation of hydrated electrons by the photolysis of halide ions in solution may be envisaged in two steps. The first step is the CTTS absorption leading to (X -). The second step is a slow, thermal process releasing the electron in competition with degradation and recapture. In the presence of acid and alcohol, photolysis of halide solutions generates H2 with a yield that increases both with acid and alcohol concentrations (seejortner et al., 1962, 1963, 1964). At 25°, the limiting quantum yields are 0.98 for Cl- at 185 nm, 0.6 and 0.5 for Brat 185 and 229 nm, respectively, and 0.3 and 0.25 for I- at 254 and 229 nm, respectively. Since most of these yields are less than 1, the direct reaction of HsO and (Xaq-) is ruled out. Instead, it is proposed that eh is produced from the... 

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