Selectivity defined

Extraction and Extractive Distillation. The choice of an extraction or extractive distillation solvent depends upon its boiling point, polarity, thermal stabiUty, selectivity, aromatics capacity, and upon the feed aromatic content (see Extraction). Capacity, defined as the quantity of material that is extracted from the feed by a given quantity of solvent, must be balanced against selectivity, defined as the degree to which the solvent extracts the aromatics in the feed in preference to paraffins and other materials. Most high capacity solvents have low selectivity. The ultimate choice of solvent is deterrnined by economics. The most important extraction processes use either sulfolane or glycols as the polar extraction solvent. 

Effect of Pressure The results are listed in Table IV. The effect of pressure on conversions and selectivities are shown in Figure 1. The CO conversion increased from 63% at 13.6 atm (200psig) to 90% at 75 atm (llOOpsig). The hydrocarbon selectivity, defined as (total carbon converted - total carbon in CO ) f total carbon converted, remained steady at 97%. the rest of 3% being converted to CO. The selectivity of Cc increased with increasing pressure while the aromatics in decreased. The C -KL make was substantially reduced by higher pressure, for example, from 59% at 13.6 atm to 29% at 74 atm. 

Study the effects of the parameters of the cooling water ramp function (TIMEhoia and Kramp) on the selectivity defined in the program as... 

We seek a shape-selective adsorbent, or a molecular sieve, that would discriminate among these four Cs aromatic compounds, and would preferentially adsorb /7-xylene. A measure of the goodness of the adsorbent is the selectivity, defined to be... 

Figure 1. Selectivities (defined in equations 6 and 7), fractional conversion of CH4, and product gas temperatures for CH4 oxidation over a 7 mm long, 12 wt.% Pt, 50 ppi foam monolith (circles) and a 10 mm long, 9.83 wt.% Rh, 80 ppi foam monolith (squares) with 4 slpm of feed gases and 2 different feed gas temperatures (open symbols = 25°C and filled symbols = 460°C).

If the alkyne is adsorbed as a di-jr-complex (structure L), the product olefin will be formed as an adsorbed species, which must, therefore, undergo desorption before appearing in the gas phase (see Fig. 4). Consequently, the selectivity defined as... 

All the above examples share high stereofacial selectivity defined by the configuration of the stereogenic center that connects the enone chromophore with the alkenyl side chain. However, chiral induction at the enone and/or the alkenyl tethered must be introduced to achieve stereofacial selectivity in the more general systems in which the alkene is connected at the a-carbon or /1-carbon of the enone. One of the successful early examples is found in Pirrung s120 synthesis of ( )-isocomene 263. Irradiation of 261 afforded the single product 262, which was transformed to isocomene in a two-step sequence. 

There is, however, a fundamental difference that makes optical selectivity based on ex far more important than the electrochemical selectivity derived from the applied potential. In electrochemistry, at a given applied potential, all electrochemical reactions that have equal or lower energy will take place. This means that the selectivity defined by the choice of the electrode potential only is very limited. In contrast, optical transitions are resonant and fall off on both sides of the absorption maximum. If not enough energy is applied, or if too much energy is applied, the transition (and therefore the interaction) is forbidden that is, its probability is low. 

The surface part of the sulfur cycle is connected with the functioning of the atmosphere-vegetation-soil system. Plants adsorb sulfur from the atmosphere in the form of S02 (fluxes C7 and C22) and assimilate sulfur from the soil in the form of SO4 (flux C15). In the hierarchy of soil processes, two levels can be selected defining the sulfur reservoirs as dead organics and S04 in soil . The transitions between them are described by flux C16 = b2STL, where the coefficient b2 = b2, b2 2 reflects the rate b2 of transition of sulfur contained in dead organics into the form assimilated by vegetation The coefficient b2>2 indicates the content of sulfur in dead plants. 

In the first case, when n = n2, the point selectivity, defined according to eq 131, becomes independent of the reactant concentration. Thus, the overall selectivity, obtained by integration of eq 131 over a range of conversions, will be identical to the point selectivity ... 

Using the data in Example 3.5.4 calculate the selectivity defined as the ratio of the moles of EO produced per mole of ethylene consumed times 100 percent, and plot the selectivity versus conversion. 

Under conditions optimized for limited power dissipation, effective mobilities and selectivities (defined as effective mobility ratios) are independent of the applied voltage. 

The best way to proceed is to choose a molecule reacting along two parallel paths and measure the selectivity defined as the ratio of rate of the two parallel reactions. If the two products come from different adsorbed states requiring different surface structures, a change of selectivity with dispersion or mode of preparation of the metal may be found. The most unequivocal case is when the specific activity for one of the parallel reactions changes from one catalyst to the next, while the specific activity for the other remains unchanged. 

The performance of platinum supported in LTL zeolite catalyst is well illustrated by data of Lane et al. [23] for conversion of -hexane in the presence of excess H2 at 330-440°C and atmospheric pressure (Table 4) Primary products were observed to form both from one-six and one-five ring closure, giving benzene and methylcyclohexane, respectively. The catalyst is remarkable for its high benzene selectivity, which increases with increasing conversion of n-hexane because some of the primary products are further converted into benzene For example, ultimate benzene selectivities (defined as the hexanes converted to benzene divided by the hexanes converted to benzene and light, C1-C5, hydrocarbons) as high as 93% were observed at 420°C. 

The unique behavior of cellulose acetate was supported recently by Koros (42). He found that of all glassy polymers Investigated, cellulose acetate had the highest solubility selectivity, defined as the ratio of the solubilities of two gases C0 and CH. Its extremely high solubility value of 8.9 measured at 35°C and 20 atm exceeds the values of the other polymers listed below by factors of... 

Per-pass conversion of ethylene is typically 30%. Selectivity, defined as the ratio of ethylene converted to ethylene oxide to ethylene reacted, is between 70 and 80%. A variety of reactor systems are used. 

Within the past decade, diastereosolective radical reactions have become feasible and the factors contolling selectivity defined. Chiral auxiliaries for radical reactions have been recently developed in analogy to those developed for carban-ion chemistry in the 1970s and 1980s. The first example of stoichiometric use of a chiral ligand for enantioselective radical additions was recently reported by Porter and coworkers [59,60,61]. Reaction of the amide 14 with allyltrimethyl-silane at -78 °C, initiated by triethylborane, in the presence of 1 equiv. each of zinc triflate and the chiral bidentate ligand 15, provided the allylated product in a yield up to 88% and ee of 90%, Eq. (18). The presumed intermediate is the a-keto radical complexed to the chiral Lewis acid. 

Saggio, 1., Gloaguen, 1., Poiana, G., Laufer, R., 1995. CNTF variants with increased biological potency and receptor selectivity define a functional site of receptor interaction. EMBO J. 14 (13), 3045-3054. 

The tie lines in the LL region in figure 3.31c are nearly parallel to the A-B axis of the diagram. When the tie lines are parallel to the A-B binary axis, the selectivity, defined as iyAlx/f)l y lx ), can approach values much greater than 1.0 this indicates that a very good separation of A from B is realized at this condition. 

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