The Effect of Conversion

To obtain accurate quantitative information about the chain-length dependence of kt, several experimental parameters must first be tested. So far, only the results for experiments in which 20 pulses were applied have been shown. However, if the results might be (highly) dependent upon the amount of conversion, then a quantitative expression for the chain-length dependence of h has to include a conversion parameter. 

To vary the conversion in the experiments, the total number of laser pulses was varied between 20 and 130. As long as no inhibition and/or significant monomer and initiator consumption takes place, the conversion should increase linearly with the number of applied laser pulses. Experimental measurements, as shown in figure 4.28 for all three monomers, confirm that this was indeed the case. For MA, the lowest pulse number applied, 20, corresponds to a final conversion of approximately 0.6%, while the highest pulse number, 130, resulted in a conversion close to 3%. For BA, conversions as high as 6 % were reached. 

Fortunately, a simple explanation is at hand for the apparent increase in the slope of the oligomer data. As more polymer is present in the system, the system becomes increasingly viscous, meaning the rates of diffusion of oligomers and 1-mers are reduced. 

It should be noted though that this data is based upon measurements at polymer concentrations above C. At concentrations below C, a condition that applies to the experiments presented here, a somewhat stronger dependence upon conversion seems to exist [44]. 

Finally, as briefly noted before, the slopes of the graphs are only influenced by the effect of increasing conversion to the same extent as scatter is present in the results. 

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The effect of conversion is mostly an economic indicator. Additionally, a strong slowdown can indicate a reversible reaction. If this possibility is excluded by thermodynamic estimates, a strong inhibition of the rate is... 

The effect of conversion on the structure of an asphaltene molecule has been reported to depend on the operating conditions and on the presence or not of a catalyst. The effect of thermal processing reaction of a vacuum residue resulted in the selective cracking of the aliphatic or naphthenic side chains of the molecule, leaving the highly condensed aromatic core structure almost intact (see Fig. 16) [116]. 

As an opposite extreme, cases of fully reversible chain transfer (Ca° = C) were simulated. The effect of conversion on MJMn is plotted in Fig. 4 as a function of Ca with Aeq = 50. Early in the reaction, or low Xp the A1JMn quickly plunges below 2.0, followed by a steady convergence back to 2.0 at higher Xf. Faster reversible chain... 

In the previous section, we showed that resid feed takes more advantages of HCO recycling. In this section, we look at the effect of the boiling point range of recycle stream on the cracking yields. In Section 1.3.4, the effect of conversion level will be discussed. The data presented in these two sections are from resid feed. 

Table 12. The effect of conversion on the molecular weight of poly(4-methyl-l-pentene)...

The scheme (Figure 3.5) of the transformation of this P - acetic acid mixture over HMFI at 553 K was established from the effect of conversion (or of contact time) on product distribution.[69] At short contact times (i.e. at low conversions), PA was practically the only reaction product. However, there was also formation of a very small amount of o-HAP (Figure 3.6). This means that O acetylation is much faster than C acetylation (ca. 20 times) and that the latter reaction leads to the ortho isomer only. Because of the high rate of O acetylation, thermodynamic equilibrium between P, acetic acid and PA was established at relatively short contact times. At high conversions, the formation of o-HAP involved the participation of PA as demonstrated by the decrease in PA yield and the apparent secondary mode of o-HAP formation (Figure 3.6). This mode of o-HAP formation from PA is mainly intermolecular involving the acetylation of P by PA. The intramolecular transformation of PA into o-HAP is much slower as shown by comparing the transformations of pure PA and of an equimolar mixture of PA and P.[69] The formation of small amounts of p-HAP would result mainly from the hydrolysis of... 

FIGURE 7.1 The effects of conversion and stoichiometric imbalance on the number average degree of polymerization. 

In some cases it is possible to perform experiments at conversions low enough to allow neglect of the effect of conversion on the rate. In other words the rate is constant throughout the plug flow reactor. Equation (7.159) can then be integrated to ... 

Gulumian M, Bhoolia DJ, Du Toit RS, et al. 1993. Activation of UICC crocidolite The effect of conversion of some ferric ions to ferrous ions. Environ Res 60(2) 193-206. 

In some systems, the effect of conversion on the heterogeneous reaction rate is significant. For example, substituting n th order type kinetics [i.e., [Pg.125]

The effect of conversion level on product yields and quality is illustrated in Table XVII. Increased conversion results in higher yields of gas, butanes, and carbon. Gasoline yield also increases, up to a certain point, but its ratio to yields of coke and gaseous products becomes less favorable. This effect is apparent from Table XVII and is further illustrated by... 

Gardiner DS, Watson MA, Junor BJ, Briggs JD, More lA, Eindop GB.The effect of conversion from cyclosporin to azathioprine on renin-containing cells in renal allograft biopsies. Nephrol Dial Transplant 1991 6 363-367. 

From previous studies and the qualitative nature of the rate data a likely combination appeared to be a controlling surface reaction between adsorbed atomic oxygen and unadsorbed sulfur dioxide. In order to determine ail the constants in the rate equation for this mechanism, it is necessary to vary each partial pressure independently in the experimental work. Thus measuring the rate of reaction at different total pressures but at constant composition is not sufficient to determine all the adsorption equilibrium constants. Similarly, if the data are obtained at constant composition of initial reactants but varying conversions, the partial pressures of the individual components do not vary independently. However, in these cases it is possible to verify the validity of the rate equation even though values of the separate adsorption equilibrium constants cannot be ascertained. Olson and Schuler studied the effect of conversion alone and obtained the data in Table 9-1 at 480°C. 

Figure 3.33 shows the effect of conversion of epoxy (i.e. increasing viscosity) on the wavelength of the maximum emission for excitation at 475 nm and the ratio of emission intensity at 588 and 564nm. There is a sharp increase in emission intensity but no spectral shift at the conversion corresponding to the Tg at the cure temperature, indicating that the probe is sensitive to both conversion and vitrification. 

The results for CVD-16 represent the effect of conversion layer. It is obvious from these results that within the present experimental condition longer conversion time is preferable and comparison with other data should be done on the base of the conversion time 3hrs. 

To ascertain the effect of conversion on polymerization rate, it is useful to determine the ratio Rp / [m] instead of percent conversion as it takes into account the changes in monomer and initiator concentrations with time (or conversion). A plot of Rp / [m] versus conversion (Fig. 6.11) show that three stages can be distinguished in some polymerizations. Stage... 

Studies of the effect of conversion on degradation indicate that the extent of degradability increases with increased conversions. 

TABLE XI The Effect of Conversion on the Intrinsic Viscosity of PoIy(vinyl butyrate) [84]°... 

As is true for many industrial situations, the question of diffusional effects on multiple reaction selectivity is equally as important as the effectiveness of conversion considerations. The basic concepts were provided by Wheeler [133], through consideration of three categories of situations. 

Let us first ignore contributions from monomer partitioning and examine the effects of conversion upon copolymer composition. In most cases, thCTe will be a difference in monomer reactivities (Le. reactivity ratios 1) and a consequent drift in copolymer composition with conversion as the more reactive monomer is consumed preferentially (see Section 1.6.3). Since the total quantity of each monomer is added at the beginning of a batch emulsion polymerization, there is no control over this drift in copolymer composition. Hence, copolymors formed using batch processes can have quite broad composition distributions, the breadth of the distribution for each particular system depending upon the monomer reactivity ratios, the initial comonom composition and monomer partitioning (which is dealt with in Section 7.3.2.2). 

Table 15.5 shows the results of Mochel [22] for the effect of conversion upon the gel content of polychloroprene rubbers prepared by emulsion polymerization at 40 °C. In section (a) of this table are shown results for polymers produced in the absence of added sulfur section (b) shows results for polymers produced with the addition of 0.6 parts of sulfur per 100 parts by mass of chloroprene, before chemical peptization of the polymer. In both types of reaction system, polymer gel begins to form quite early in the reaction. However, these results indicate that sulfur has a slight tendency to act as a modifier during the polymerization, in that the onset of gel-formation is delayed when sulfur is present. Also delayed is the pdnt at which the polymer is virtually entirely gel. Mochel et al. [23] have reported results for the molar mass distribution of a thiuiam-modified polychloroprene rubber produced by emulsion polymerization at 40 °C,... 

Let us construct a reactor model that will predict the effects of conversion, current density, and electrolyte circulation rate on the chemical yield and run time of a cell for the production of -anisidine (see Clark et al., 1988 for details). The electrolytic cell used will be assumed to be of the narrow gap filter press type with total recirculation of... 

As seen in Figure 8.3. the effect of conversion on reactor volume for the adiabatic case is very different from the isothermal case in Figure 8.2. At all conversions, the reactor volume is less for the adiabatic case. Furthermore, the difference in reactor volumes widens as the conversion is increased. For example, at a 50% conversion, the isothermal reactor volume is 2.25 times that of the adiabatic reactor. At a 99% conversion, the ratio becomes 8. The adiabatic case benefits by the increase in... 

THE PROBLEM Construct a reactor model that will predict the effect of conversion, current density, and electrolyte recirculation rate on the chemical yield and run-time of a pilot plant cell producing p-anisidine. 

Complete optimization would embrace all the variables, but with the effect of conversion alone we can illustrate that optimization procedures which ignore interactive behavior can lead to wrong conclusions. Figure 6.16 shows the variation of capital and production costs with conversion X, again for a current density i of 2000 A/m, a ratio B2/A2 of 0.1, and optimum values for >15. 

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