Quench, of reaction

The reaction can occur from the excited singlet and the triplet state as evidenced from the quenching of reaction in 2-pentanone and 2-hexa-none with piperylene. Piperylene can quench the reaction only partially, suggesting singlet state reaction mechanism for the unquenched fraction. Photoenolization resembles Type II process in that a y-hydrogen migrates to the carbonyl oxygen. 

Primary step I The relative efficiencies of biacetyl and butene-2 in the quenching of reaction I were found to be not far from unity in the case of the ketones studied consequently, primary process I occurred from the high vibrational levels of the triplet state, possessing sufficient energy to induce efficiently the isomerization of butene-2. The efficiency of energy transfer to cw-butene-2 compared with that to biacetyl, measured in terms of reaction I, was found to be in the following order 2-pentanone > 2-butanone > acetone. It is possible that this order reflects the facility with which the vibrational energy of the donors may be made available to... 

Single-turnover kinetic experiments provided evidence for a transient species with an absorption maximum at 312 nm. The intensity of that transient was increased by a S41A mutation. Rapid quenching of reaction... 

The compound could be isolated after rapid quenching of reaction mixtures.The C NMR spectrum was similar, but not identical with that of Compound Moreover, the compound (designate Q() produced by the M. jannaschii enzyme could serve as substrate for the archaeal enzyme by which it had been produced, but not for eubacterial riboflavin synthase. Vice versa. Compound ( produced by eubacterial riboflavin synthase could serve as a kinetically competent substrate for the eubacterial enzyme (see above) but could not be used by the enzyme from M. jannaschii. 

Submerged flames of H2, CO, H2S, and C2H2 with the flame gases in direct contact with liquid O2 or liquid air permit, in principle, the quenching of reaction intermediates from the flame as well as chemical reaction between these species and the cryogen itself O3, NO, N2O5, SO2, etc., have been recovered from the warmed filtrates and residues from such processes. 

If indirect heat transfer is used with a large temperature difference to promote high rates of cooling, then the cooling fluid (e.g., boiling water) is fixed by process requirements. In this case, the heat of reaction is not available at the temperature of the reactor effluent. Rather, the heat of reaction becomes available at the temperature of the quench fluid. Thus the feed stream to the reactor is a cold stream, the quench fluid is a hot stream, and the reactor effluent after the quench is also a hot stream. 

It turned out that the dodecylsulfate surfactants Co(DS)i Ni(DS)2, Cu(DS)2 and Zn(DS)2 containing catalytically active counterions are extremely potent catalysts for the Diels-Alder reaction between 5.1 and 5.2 (see Scheme 5.1). The physical properties of these micelles have been described in the literature and a small number of catalytic studies have been reported. The influence of Cu(DS)2 micelles on the kinetics of quenching of a photoexcited species has been investigated. Interestingly, Kobayashi recently employed surfactants in scandium triflate catalysed aldol reactions". Robinson et al. have demonshuted that the interaction between metal ions and ligand at the surface of dodecylsulfate micelles can be extremely efficient. ... 

Electron-transfer reactions producing triplet excited states can be diagnosed by a substantial increase in luminescence intensity produced by a magnetic field (170). The intensity increases because the magnetic field reduces quenching of the triplet by radical ions (157). 

Although o2one can be formed in certain chemical reactions, eg, F2 + H2O and P + O2, and by rapid quenching of plasma-heated oxygen (>3000° C) with Hquid oxygen, these methods have no commercial importance. 

A typical reactor operates at 600—900°C with no catalyst and a residence time of 10—12 s. It produces a 92—93% yield of carbon tetrachloride and tetrachloroethylene, based on the chlorine input. The principal steps in the process include (/) chlorination of the hydrocarbon (2) quenching of reactor effluents 3) separation of hydrogen chloride and chlorine (4) recycling of chlorine to the reactor and (i) distillation to separate reaction products from the hydrogen chloride by-product. Advantages of this process include the use of cheap raw materials, flexibiUty of the ratios of carbon tetrachloride and tetrachloroethylene produced, and utilization of waste chlorinated residues that are used as a feedstock to the reactor. The hydrogen chloride by-product can be recycled to an oxychlorination unit (30) or sold as anhydrous or aqueous hydrogen chloride. 

Another important concept in the discussion of photochromic systems is fatigue. Fatigue is defined as a loss in photochromic activity as a result of the presence of side reactions that deplete the concentration of A and/or B, or lead to the formation of products that inhibit the photochemical formation of B. The inhibition can result from quenching of the excited state of A or screening of active light. Fatigue, therefore, is caused by the absence of total reversibihty within the photochromic reaction (eq. 2). 

The preceding equation assumes the reaction is completely quenched immediately after the relief point is reached. This behavior is closely approximated if the reaction stops in the quench pool and the reactor empties quickly and thoroughly. If the reaction continues in the quench pool, the temperature Tr should be increased to the maximum adiabatic exotherm temperature. An equation is presented by CCPS (AIChE-CCPS, 1997) that includes the heat of reaction. In some cases, an experiment is necessary to confirm that the reaction indeed stops in the quench pool. 

The reaction section consists of the high pressure reactors filled with catalyst, and means to take away or dissipate the high heat of reaction (300-500 Btu/lb of olefin polymerized). In the tubular reactors, the catalyst is inside a multiplicity of tubes which are cooled by a steam-water condensate jacket. Thus, the heat of reaction is utilized to generate high pressure steam. In the chamber process, the catalyst is held in several beds in a drum-type reactor with feed or recycled product introduced as a quench between the individual beds. 

Chemical methods involve removing a portion of the reacting system, quenching of the reaction, inhibition of the reaction that occurs within the sample, and direct determination of concentration using standard analytical techniques—a spectroscopic metliod. These methods provide absolute values of the concentration of the various species that are present in the reaction mixture. However, it is difficult to automate chemical mediods, as the sampling procedure does not provide a continuous record of tlie reaction progress. They are also not applicable to very fast reaction techniques. 

Fig. 6.3. The VIR Model of Horie considers the chemical reaction process in terms of three components void, inert, and reactants. The influence of the inerts is critical as that component causes thermal quenching of incipient reactions.

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