Concurrent transfer time

An extremely interesting feature of these mechanisms is the fact that superoxide and the alkene radical cation are both formed in the reduction (Fig. 20) and also in the Frei oxidation (Fig. 19). In the Frei photo-oxidation, however, they are formed concurrently in a tight ion pair and collapse to product more rapidly than their diffusive separation. In the reduction (Fig. 20), the formation of the radical cation and superoxide occur in independent spatially separated events allowing the unimpeded diffusion of superoxide which precludes back-electron transfer (BET) and formation of oxidized products. The nongeminate formation of these two reactive species provides the time necessary for the radical cation to abstract a hydrogen atom from the solvent on its way to the reduced product. 

The extraction may be carried out in a countercurrent or concurrent extraction column. If there is sufficient mixing of the two phases, a very short contact time even for long chain olefins is adequate to ensure complete transfer of the catalyst from the aqueous phase into the olefin. 

When a new product is handed over from development to production, the handover is usually accompanied by a development transfer report. Unfortunately, many times the cleaning procedure is not included in the report and production must develop the procedure concurrently with producing the first few batches. This is a major oversight and the author suggests that production not accept such a report until the recommended cleaning procedures are included in the report. 

In concurrent downward-flow trickle beds of 1 meter in height and with diameters of respectively 5, 10 and 20 cm, filled with different types of packing material, gas-continuous as well as pulsing flow was realized. Residence time distribution measurements gave information about the liquid holdup, its two composing parts the dynamic and stagnant holdup and the mass transfer rate between the two. 

Under a nitrogen atmosphere, cobalt carbonyl probably experiences disproportionation by base (Scheme 5) to give Co(CO)4. One of the disproportionation by-products is the Co(II) ion which gives a blue color in aqueous NaOH due to the presence of small amounts of the Co(OH)42-ion. The subsequent reaction of the cobalt tetracarbonyl anion with 14 is probably a displacement (path a), giving the cr-allyl complex 16. However, the possibility of an electron-transfer pathway (path b), either as an alternative to, or concurrent with, the displacement pathway cannot be dismissed at this time. 

We have seen that the 180° 13C pulse reordered the 13C populations, but transfer of proton polarization to the 13C system occurred only when the and 13C 90° pulses were applied at time 4. We chose to use a matrix that represented the concurrent application of both pulses. However, these are independent, their Hamiltonians commute, and we could have considered instead the application of the two pulses separately—in either order. Here we examine the effect of applying the H pulse. 

The important point is that cyclic oligomers are not formed concurrently with linear polymer, chain transfer to polymer is slow as compared to propagation and its contribution is becoming noticeable only after keeping the reaction mixture unterminated for a prolonged period of time. Thus, within a time scale required to complete the polymerization, the contribution of chain transfer to polymer can be neglected. 

The flow of the combustion gases in direct-fired systems may be concurrent (i.e., the gases flow in the same direction as the feedstock) or countercurrent (i.e., the gases flow opposite to the movement of the feedstock). The benefits of a concurrent system are higher treatment temperatures, longer residence times, and treatment of fines. Countercurrent systems offer more efficient heat transfer, and lower volumes and temperatures of off-gas. ° In large part due to the beneficial aspects of the off-gas and consequent simplified APC system, countercurrent systems are used more commonly in rotary kilns. 

---