Excess B Case

NEAT OPERATION VERSUS USING EXCESS REACTANT 

TABLE 4.1 Effect of Number of Trays in Recovery Column for 20% Excess of B 

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Table 4.2 lists equipment and economic results for the 10% excess case for different numbers of trays Nj-i in the recovery column. The minimum cost configuration has 20 trays. Table 4.3 compares the 10 and 20% excess B cases. 

Composition profiles in the reactive column are shown in Figure 4.13. The concentrations of A in the upper part of the column are higher than in the neat case (Fig. 4.2), and the concentrations of A in the lower part of the column are much higher than in the 20% excess B case (Fig. 4.13). 

Equation (5.40) also applies to the case when some of the excess B groups present are in the form of monofunctional reagents. In this latter situation the definition of r is modified somewhat (and labeled with a prime) to allow for the fact that some of the B groups are in the BB-type monomers (unprimed) and some are in the monofunctional (primed) molecules ... 

Thirdly, the multicomponent model was applied to the case of crystallization of a random A-B copolymer by Helfand and Lauritzen [127]. Their main result is that the composition of, 4 s and B s in the crystal is determined by kinetic, rather than equilibrium considerations the inclusion of excess B increases with growth rate. 

On the contrary, at x > x[f, there is a deficit of the B atoms because the reactivity of the A surface exceeds the flux of these atoms across the ApBq layer. Therefore, on reaching interface 1, each B atom is combined at this interface into the ApBq compound. In this case, there are no excessive B atoms for the formation of other compounds enriched in component A. Thus, none of compound layers located between A and ApBq can grow at the expense of diffusion of component B. This almost obvious result following in a natural way from the proposed physicochemical considerations is crucial for understanding the mechanism of formation of multiple compound layers. Perhaps, just its evident character is the main reason, firstly, why many researchers in the field have overlooked it and, secondly,... 

It is easy to notice that during the same nine seconds three B atoms could have displaced from substance B across the AB layer to interface 1, if the chemical transformations at interface 1 (including also external diffusion of the B atoms to phase A through interface 1) would occur instantaneously or if the excessive B atoms (there are two such atoms in the case under consideration) would be used in the formation of the layers of other compounds of the same binary system. In the examined case of a single compound, this possibility of diffusion of excessive B atoms from interface 2 to interface 1 is not realised because the diffusion path is closed up until the full completion of chemical transformations at interface 1. However, the existence of such a possibility must be borne in mind when analysing the multiple layer growth. 

Fig. 6.27 - Dimensionless plots for determining rate constants from redox catalysis experiments (a) Case 1 systems where ki may be determined, (b) Case 2 systems where k may be estimated. The numbers on the curves indicated the excess factor y = c lcp. The figure is drawn from tables supplied by J. M. Saveant.

The kinetic derivations look very similar to the A-B case in the preceding, with one very large difference. Unless the two monomers are in exact 1 1 stoichiometric ratio, the excess monomer will limit the molecular weight development. Once polymerization has begun, there are three species present in the reaction (in addition to the by-product, W, which is removed to prevent depolymerization). The structures of these three species and the symbols to be used for them are as follows ... 

Chemical kinetics the absolute values of kRi and kR2. The magnitude of the rate constant, kRi, will determine how much A can be converted during the time required to achieve molecular mixing. The extent of the conversion will determine the amount of R that is subject to excess B concentration and hence overreaction to S as determined by kR2. In some cases the kinetics can be determined by use of a stopped-flow reactor or similar device. For... 

This should be compared with losses of 0.63 mol/s in the single neat column case and 0.126 mol/s in the 20% excess case. The conversion of A to products C and D increases as more excess B is used. 

Figure 4.16 compares the reactive column composition profiles in the two excess reactant cases with those for base case neat operation. The concentrations of A are lower than the base case when an excess of B is used and larger when an excess of A is used. The opposite is true for the concentrations of B. The concentration of C at the top of the column is lower when an excess of A used. The concentration of D at the bottom of the column is lower when an excess of B used. 

If, on the other hand, the thermometer has previously been used at some temperature below the freezing-point of benzene, when the bulb is originally placed in the beaker of water at 7-8 C., the mercury will rise in the capillary and ultimately collect in the upper part of the reservoir at a. When the expansion is complete, again tap the thermometer sharply at R so that this excess of mercury drops down into b, and then as before check the success of the setting by placing the thermometer m some partly frozen benzene. In either case, if the adjustment is not complete, repeat the operations, making a further small adjustment, until a satisfactory result is obtained. 

Figure 9.8b shows a titration curve for a mixture consisting of two weak acids HA and HB. Again, there are two equivalence points. In this case, however, the equivalence points do not require the same volume of titrant because the concentration of HA is greater than that for HB. Since HA is the stronger of the two weak acids, it reacts first thus, the pH before the first equivalence point is controlled by the HA/A buffer. Between the two equivalence points the pH reflects the titration of HB and is determined by the HB/B buffer. Finally, after the second equivalence point, the excess strong base titrant is responsible for the pH. 

What we seek next is a quantitative relationship between the extent of the polymerization reaction, the composition of the monomer mixture, and the point of gelation. We shall base our discussion on the system described by reaction (5.U) other cases are derived by similar methods. To further specify the system we assume that A groups limit the reaction and that B groups are present in excess. Two parameters are necessary to characterize the reaction mixture ... 

Boron and carbon form one compound, boron carbide [12069-32-8] B C, although excess boron may dissolve ia boron carbide, and a small amount of boron may dissolve ia graphite (5). Usually excess carbon appears as graphite, except for the special case of boron diffused iato diamonds at high pressures and temperatures, eg, 5 GPa (50 kbar) and 1500°C, where boron may occupy both iaterstitial and substitutional positions ia the diamond lattice, a property utilized ia synthetic diamonds (see Carbon, diamond, synthetic). 

Figure 14-10 illustrates the gas-film and liquid-film concentration profiles one might find in an extremely fast (gas-phase mass-transfer limited) second-order irreversible reaction system. The solid curve for reagent B represents the case in which there is a large excess of bulk-liquid reagent B. The dashed curve in Fig. 14-10 represents the case in which the bulk concentration B is not sufficiently large to prevent the depletion of B near the liquid interface and for which the equation ( ) = I -t- B /vCj is applicable. 

The shunt capacitors can be provided on the LT or the HT side, whichever is more convenient. In the above case, since it is large, the HT side of the load-end transformer will be more convenient. The receiving-end transformer, however, will now be operating under more stringent conditions that must be taken in account or the capacitors may be provided on the LT side to relieve this transformer also from excessive currents. In Figure 23.18(b) we have considered them on the LT side. 

Fig. 9.2 shows how a simple open circuit gas turbine can be used as a cogeneration plant (a) with a waste heat recuperator (WHR) and (b) with a waste heat boiler (WHB). Since the products from combustion have excess air, supplementary fuel may be burnt downstream of the turbine in the second case. In these illustrations, the overall efficiency of the gas turbine is taken to be quite low ((tjo)cg = ccJf ca 0.25), where the subscript CG indicates that the gas turbine is used as a recuperative cogeneration plant. 

The obvious method of reducing corrosion in fused salts is to choose a system in which either the metal can come to equilibrium with the melt, or else truly protective passivity can be attained. In most cases in industry neither of these alternatives is used. In fact, fused salt baths are usually operated in air atmosphere, and the problem is the prevention of excessive corrosion. This can be done in two ways, (a) by reducing rates of ingress of oxidising species (mainly O2 and H2O) from the atmosphere, and rates of their diffusion in the melts, and (b) by keeping the oxidising power (redox potential) of the melt low by making periodic additions to the bath. 

At any point in the area above the curve, the sugar solution is supersaturated. This is the case at point B (300 g sugar per 100 g water at 20°C). Such a solution could be formed by carefully cooling a saturated solution at 60°C to 20°C, where a saturated solution contains 204 g sugar per 100 g water. The excess sugar stays in solution until a small seed crystal of sugar is added, whereupon crystallization quickly takes place. At that point the excess sugar... 

B. Back-titration. Many metals cannot, for various reasons, be titrated directly thus they may precipitate from the solution in the pH range necessary for the titration, or they may form inert complexes, or a suitable metal indicator is not available. In such cases an excess of standard EDTA solution is added, the resulting solution is buffered to the desired pH, and the excess of the EDTA is back-titrated with a standard metal ion solution a solution of zinc chloride or sulphate or of magnesium chloride or sulphate is often used for this purpose. The end point is detected with the aid of the metal indicator which responds to the zinc or magnesium ions introduced in the back-tit ration. 

Method B Standardisation with sodium oxalate. Standardisation may also be carried out with sodium oxalate in this case, an indirect procedure must be used as the redox indicators are themselves oxidised at the elevated temperatures which are necessary. The procedure, therefore, is to add an excess of the cerium(IV) solution, and then, after cooling, the excess is determined by... 

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