Styrene reaction rate data

Continuous Polymerizations As previously mentioned, fifteen continuous polymerizations in the tubular reactor were performed at different flow rates (i.e. (Nj g) ) with twelve runs using identical formulations and three runs having different emulsifier and initiator concentrations. A summary of the experimental runs is presented in Table IV and the styrene conversion vs reaction time data are presented graphically in Figures 7 to 9. It is important to note that the measurements of pressure and temperature profiles, flow rate and the latex properties indicated that steady state operation was reached after a period corresponding to twice the residence time in the tubular reactor. This agrees with Ghosh s results ). 

Table II shows the experimental data as well as the maximum overall reaction rates of the monomers studied. All figures are average values of at least two preparations—i.e., four dilatometric measurements. The last column gives the reaction rate relative to that of a comparable styrene emulsion under the same conditions of temperature and dose rate whose reaction rate was accepted as unity.

Which is better for isothermal chemical reactions, pressure driven flow or drag flow between flat plates Assume laminar flow with first-order chemical reaction and compare systems with the same values for the slit width (2Y=H), length, mean velocity, and reaction rate constant. Free-radical polymerizations tend to be highly exothermic. The following data are representative of the thermal (i.e., spontaneous) polymerization of styrene ... 

Important applications of chemical reaction engineering (CRE) of all kinds can be found both inside and outside the chemical process industries (CPI). In this text, examples from the chemical process industries include the manufacture of ethylene oxide, phthaiic anhydride, ethylene glycol, metexylene, styrene, sul fur trioxide, propylene glycol, ketene, and i-fautane just to name a few. Also, plant safety in the CPI is addressed in both example problems and homework problems. These are real industrial reactions with aaua data and reaction rate law parameters. 

In the examples described above, the transition is shown from ideal (n = /2) to nonideal (n > /2) behavior. There are, however, systems for which ideal emulsion polymerization practically cannot be achieved. It is nevertheless possible to describe the kinetics of such systems quantitatively. Recently, Gerrens has obtained values of the propagation and termination rate constants at diflFerent temperatures for vinyltoluene and vinylxylene (28). The termination rate of polymer radicals of these monomers is so low that even at small rates of initiation in small particles, n is larger than /2. From measurements of the reaction rate before and after injection of additional initiator in the polymerizing system it was possible to calculate n both at the original and at the boosted initiation rate with the aid of Equation 5. Consistent results were obtained when the additional amount of initiator was varied. From these rate data, the termination rate constant was found to be 10 and 17 liters mole- sec. at 45° C. for vinyltoluene and vinylxylene, respectively. These values are to be compared with 10 for styrene (Table IV). 

The pulsed reactor consists of a fixed bed of catalyst pellets through which the reacting fluid moves in pulsating flow. Mass-transfer coefficients are increased because of the pulsating velocity superimposed on the steady flow. For viscous liquids, or any fluid-solid reaction system which has a high extemal-mass-transfer resistance, pulsation may be a practical way to increase the global reaction rate. Biskis and Smith measured mass-transfer coefficients for hydrogen in a-methyl styrene in pulsed flow and found increases up to 80% over steady values. Bradford" found similar results based on data for the dissolution of beds of j9-naphthoI particles in water. 

A detailed laser flash photolysis study of the reactions of the 4-methoxystyrene radical cation and its P-methyl and p.p-di-methyl analogs with amines and pyridines in acetonitrile and aqueous acetonitrile has been carried out. " Representative kinetic data are summarized in Table 6 and cover approximately 4 orders of magnitude in time scale. A combination of transient spectra, product studies, and redox potentials has been used to establish which of the three possible reactions contributes to the measured rate constant for any given radical cation/amine pair. For example, transient spectra obtained after quenching of the radical cations with either DABCO or aniline clearly show the formation of the amine radical cation, consistent with the fact that both of these amines have substantially lower oxidation potentials than any of the three styrenes. Reaction with primary amines occurs by addition, as evidenced by the formation of a transient in the 300-nm region that is assigned to the substituted benzyl radical. These results are consistent with the high oxi-... 

The combined data in Tables 7-9 for the additions of styrene radical cations to their neutral precursors (dimerizations) and to other alkenes lead to a potentially important conclusion with respect to the design of cross-addition reactions. These data indicate that dimerization rate constants are frequently several orders of magnitude greater than the rate constants for cross addition. The absolute rate constants for the two reactions can be used to adjust the concentrations of the neutral styrene that leads to the radical cation and the alkene in order to maximize the yield of the cross-addition product. The kinetic and mechanistic data obtained for these reactions thus provides the basis for the development of synthetic strategies that utilize radical cation chemistry. 

Rate data for the ozonolysis of a series of substituted styrenes in CCI4 at 25°C are summarized in Table 6.14. Do the data show a linear Hammett correlation with either tr, cr, or meta substituents in all three correlations.) If so, what is the value of p at 25°C What do these results suggest about the reaction mechanism Specifically, does the addition of ozone appear to be electrophilic or nucleophilic in nature ... 

Empirical rate equations have been reported for the mastication degradation of many polymers, for example, polyethylene [29], poly(methyl methacrylate) [30], styrene rubbers [31, 32], polychloroprene [33], and EPDM [34]. Reaction rate generally depends on [35]. Experiments on degradation rate have been performed also on the molten state [15, 16, 35]. Pohl and co-workers [15, 16] reported their data as the fraction of bonds broken (Eq. 2.17) as a function of capillary residence time. They found that the average rate of bond breaking b depends on shear rate y and absolute temperature T by the following equation for polyisobutylene ... 

FIGURE 12.14 Continuous UV data at 305 nm from ACOMP foUow the evolution of the TTC during 2-(dimethylamino)ethyl acrylate (DMAEA)/styrene (sty) copolymerization reactions by RAFT with different initial composition and indicate that the degradation process is slower for higher amount of styrene. Shown in the inset to figure are the plotted TTC decomposition rate constants versus styrene %. The rates were from exponential fits used as first-order approximations. Reprinted from Li Z, Serelis AK, Reed WF, Alb AM. Online monitoring of the copolymerization of 2-(dimethylamino(ethyl acrylate with styrene by RAFT deviations from reaction control. Polymer 2010 51 4726-4734. 2010 with permission from Elsevier. 

The structure and reactivity of anionic complexes [M(CO)2l2] (M = Rh, Ir) supported on ion exchange resins based on quaternized poly(4-vinylpyridine-co-styrene-co-divinylbenzene) have been investigated using a variety of techniques. The reactivity toward Mel of [M(CO)2l2l supported on thin polymer films was probed directly in situ by IR spectroscopy. For M = Ir oxidative addition gave a stable Me complex, [Ir(CO)2l3Me] , as observed in solution chemistry. The kinetic measurements represent a rare example of quantitative rate data for fundamental reaction steps of a heterogenized transition metal catalyst. ... 

Absolute rate constants for addition reactions of cyanoalkyl radicals are significantly lower than for unsubstituted alkyl radicals falling in the range 103-104 M V1.341 The relative reactivity data demonstrate that they possess some electrophilic character. The more electron-rich VAc is very much less reactive than the electron-deficient AN or MA. The relative reactivity of styrene and acrylonitrile towards cyanoisopropyl radicals would seem to show a remarkable temperature dependence that must, from the data shown (Table 3.6), be attributed to a variation in the reactivity of acrylonitrile with temperature and/or other conditions. 

Kochi (1956a, 1956b) and Dickerman et al. (1958, 1959) studied the kinetics of the Meerwein reaction of arenediazonium salts with acrylonitrile, styrene, and other alkenes, based on initial studies on the Sandmeyer reaction. The reactions were found to be first-order in diazonium ion and in cuprous ion. The relative rates of the addition to four alkenes (acrylonitrile, styrene, methyl acrylate, and methyl methacrylate) vary by a factor of only 1.55 (Dickerman et al., 1959). This result indicates that the aryl radical has a low selectivity. The kinetic data are consistent with the mechanism of Schemes 10-52 to 10-56, 10-58 and 10-59. This mechanism was strongly corroborated by Galli s work on the Sandmeyer reaction more than twenty years later (1981-89). 

Equation (1.20) is frequently used to correlate data from complex reactions. Complex reactions can give rise to rate expressions that have the form of Equation (1.20), but with fractional or even negative exponents. Complex reactions with observed orders of 1/2 or 3/2 can be explained theoretically based on mechanisms discussed in Chapter 2. Negative orders arise when a compound retards a reaction—say, by competing for active sites in a heterogeneously catalyzed reaction—or when the reaction is reversible. Observed reaction orders above 3 are occasionally reported. An example is the reaction of styrene with nitric acid, where an overall order of 4 has been observed. The likely explanation is that the acid serves both as a catalyst and as a reactant. The reaction is far from elementary. 

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