Phase contacting conditions

Phase Contacting Conditions Contacting of a gas stream and a liquid... 

Parallel flow. The direction of gas flow is parallel to the surface of the sohds phase. Contacting is primarily at the interface between phases, with possibly some penetration of gas into the voids among the solids near the surface. The solids bed is usually in a static-condition (Fig. 12-30). 

Amides are very weak nucleophiles, far too weak to attack alkyl halides, so they must first be converted to their conjugate bases. By this method, unsubstituted amides can be converted to N-substituted, or N-substituted to N,N-disubstituted, amides. Esters of sulfuric or sulfonic acids can also be substrates. Tertiary substrates give elimination. O-Alkylation is at times a side reaction. Both amides and sulfonamides have been alkylated under phase-transfer conditions. Lactams can be alkylated using similar procedures. Ethyl pyroglutamate (5-carboethoxy 2-pyrrolidinone) and related lactams were converted to N-alkyl derivatives via treatment with NaH (short contact time) followed by addition of the halide. 2-Pyrrolidinone derivatives can be alkylated using a similar procedure. Lactams can be reductively alkylated using aldehydes under catalytic hydrogenation... 

Favourable phase inversion conditions, as monitored by conductivity, were established for all surfactant blends in contact with alkanes. 

As described in Section 7.2.2, the phase-coexistence conditions are expressed in terms of the required matching variations of chemical potential in the two phases. Geometrically, this means that the Giiq(x) and Gsol(x) curves must have a common tangent line, which contacts the Guq curve at xliq and the Gsoi curve at xsoi. Figure 7.15 illustrates this... 

Although it is clear from Figure 3 that ortAo-hydroxyoximes are able to extract nickel under mildly acidic conditions (a pH value of 4 to 5), the attainment of equilibrium is slow, at least 1 h of phase contacting being required at moderate stirring speeds. The extraction rate shows an inverse first-order dependence on the hydrogen ion concentration,165 however, hence much shorter mixing times are adequate under the ammoniacal conditions used in commercial processes. 

For chemical reactions involving charged species in multiple (but contacting) phases, the condition for equilibrium is, in analogy to Eq. (30) of Chapter 7,... 

Because of interference from the radioactive decay of other nuclides (which are typically formed with much higher yields), extraction systems with relatively high decontamination factors from actinides, Bi, and Po must be chosen, and the transactinide activity can only be measured in the selectively extracting organic phase. For this reason, measurement of distribution coefficients is somewhat difficult. By comparing the Rf or Db detection rate under a certain set of chemical conditions to the rate observed under chemical control conditions known to give near 100% yield, distribution coefficients between about 0.2 and 5 can be determined. If the control experiments are performed nearly concurrently, many systematic errors, such as gas-jet efficiency and experimenter technique, are cancelled out. Additionally, extraction systems which come to equilibrium in the 5-10 second phase contact time must be chosen. 

Out of the parameters appearing in the Young equation, Eq. (1), only the surface tension of the liquid can be simply and accurately measured. However, the measured value of a/ can be used in the Young equation only under a certain condition, as discussed in the following. Gibbs was the first to note that the Young equation may need to be modified, even for an ideal solid surface. This is so because the three interfacial tensions may be influenced by each other at the three-phase contact line, due to the effect that one phase may... 

We conclude this section by giving a topical example of the utility of conditional averages in considering molecularly complex systems (Ashbaugh et al, 2004). We considered the RPLC system discussed above (p. 5), but without methanol n-Ci8 alkyl chains, tethered to a planar support, with water as the mobile phase. The backside of the liquid water phase contacts a dilute water vapor truncated by a repulsive wall see Fig. 1.2, p. 7. Thus, it is appropriate to characterize the system as consistent with aqueous liquid-vapor coexistence at low pressure. A standard CHARMM force-field model (MacKerell Jr. et al, 1998) is used, as are standard molecular dynamics procedures - including periodic boimdary conditions - to acquire the data considered here. Our interest is in the interface between the stationary alkyl and the mobile liquid water phases at 300 K. 

Aside from the requirement of a sharp residence time distribution, the ideal fixed-bed reactor should also allow all parts of the catalyst bed to fully participate in the overall conversion, i.e., all catalyst particles must be contacted by the reactant fluid. With a single fluid phase, this condition is generally met when the plug flow criterion is obeyed since in this case there is a uniform flow through the bed. However, in two... 

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