Propylene concentration profiles

Figure 10, Propylene concentration profiles in the multigrain model as a function of radius and time for a high-activity catalyst.

It can be seen from a typical, practically isothermal concentration profile (Figure 1) that at t = 0 all products exhibit a non-zero slope. This implies that all of them must be formed directly from the reactants propylene and oxygen, which eliminates the reaction schemes I and IV (Table III ). Therefore the following stoichiometric equations were used in the analysis ... 

The model describes, within the limits of measuring error, the experimental temperature and concentration profiles quite well over a wide temperature range (more than 100 C) and propylene conversion range (Table I), (Figures 2 - 4). But the reaction orders for propylene and oxygen have only a limited reliability since especially the oxygen concentration along the reactor varied only within narrow limits. Additionally, pressure and flow rate were, for the most part, held constant (Table I). 

Concentration profile of nitroxyl radicals resulted from thermo-oxidative destruction of other polymer - ethylene copolymer with propylene is presented in Figure 9b. In this case maximum concentration of nitroxyl radicals is observed not on the borders but in the center of sample the process of thermo-oxidative destruction proceeds mainly in sample depth [49],... 

Figure 3. Concentration profiles for different membranes giving an element concentration (in arbitrary units) across the thickness a and b, Cu concentration after exchange. The membranes have been obtained from a low density polyethylene after irradiation grafting with styrene followed by sulfonation. c, Cu concentration after exchange. The membrane has been obtained from a copolymer of tetra-fluororethylene and fluorinated propylene after irradiation grafting with styrene followed by sulfonation. d, Cl concentration after chlorhydratation of dimethyl annio ethyl methacrylate grafted on polyvinylidene fluoride.

Figure 2.34 simulates the copolymerization of ethylene and propylene in the presence of hydrogen. Ethylene, being the faster comonomer, has a much steeper radial concentration profile than propylene. In the same way, hydrogen reacts much more slowly and also diffuses rather fast and therefore has a flat radial concentration profile. The effect of these profiles on the CLD and CCD is clear polymer made near the surface of the particle will have higher molecular weight and ethylene fraction than the polymer made near the center of the particle. This modeling approach was first proposed by Soares and Hamielec for a version of the PFM [70]. 

Figure 31 shows the model analysis of the effects of radial gas dispersion coefficient on radial profiles of propylene concentration. The radial mass transfer has a significant effect on the conversion and yield. When the radial Peclet number decreases from 1400 to 200, the conversion of propylene increases by over 10%, and the yield of acrylonitrile increases by about 7%. Since the reaction is first order with respect to propylene, risers are operated under dilute conditions at Pe = 200, so the radial concentration distribution of propylene is uniform and radial mass transfer is not... 

Figure 31 Effects of radial Peclet number on radial profiles of propylene concentration in a high-density riser. (From Wei et al., 2000a.)...

Figure 6.12.7 Pilot plant reactor for propylene oxidation with H2O2 according to the Evonik-Uhde process. The (j,-reactor characteristics are realized in one dimension to improve heat and concentration profiles. Picture courtesy of Evonik.

Evonik and Uhde have also developed a HPPO process, which was commercialized in 2008 in Ulsan, South Korea (100 000 t a ). The indirect oxidation takes place at increased pressure and temperatures below 100 °C with the solvent methanol. The reaction is catalyzed by a titanium-silicate catalyst in a solid-bed reactor that is special due to its p,-reactor characteristic in one dimension. Using this new reactor type it is possible to improve isothermicity and to avoid disadvantageous concentration profiles. Figure 6.12.7 shows the pilot plant reactor of this new propylene oxidation process. Yields of 95% (relating to propylene) and 90% (relating to H2O2) are obtained in the Evonik/Uhde process. 

FIGURE 2 3 Typical concentration-time profiles for irradiation of a propylene-NO, mixture in a smog chamber. Reprinted with permission from Niki et ai. 

To simplify the analysis, we make use of a single adiabatic reactor. The sizing elements given before ensure the desired production rate. Figure 6.6 displays concentration and temperature profiles for an inlet temperature of 170 °C and a benzene /propylene ratio of 7. The above kinetic model gives per-pass selectivity... 

Figure 6.16 displays the temperature profile and liquid-phase molar fractions for cumene and DIPB. It may be observed that the temperature is practically constant over the reactive sections with a first plateau at 200 °C and a second one at 210 °C. The top temperature is at 198 °C while the bottom temperature climbs to 242 °C. The explanation may be found in the variation of concentrations for cumene and DIPB in the liquid phase. The maximum reaction rate takes place on the stages where propylene is injected. The cumene concentration increases rapidly and reaches a flat trend corresponding to the exhaustion of the propylene in liquid phase. It may be seen that the amount of DIPB increases considerably in the second reaction zone. This variation is very different from that with a cocurrent PFR. The above variations suggest that the productivity could be improved by providing several side-stream injections and/or optimizing the distribution of catalyst activity. 

Figure 5.20 shows concentration-time profiles for the decomposition of hydrocortisone butyrate at 60°C in a buffered aqueous propylene glycol (50 w/w%, pH 7.6). Consecutive, irreversible, first-order kinetic models [i.e., Equation (5.119a), Equation (5.119b), and Equation (5.119c)] fit reasonably well with the experimental... 

This allowed a profiling of the sensitivity of the trap to gas inlet temperature. The concept of creating a local exotherm in the washcoat to effect NOx desorption was tested via the introduction of propylene at a variety of concentrations and inlet temperatures. Aging was carried out as indicated in the Results and Discussion Section. 

Goh and Gollahalli [20] measured temperature profiles in piloted and nonpiloted propane and propylene flames in crossflow at R = 32-97. The profiles are generally characterized by off-axis single peak structure for all flames. The nonpiloted flames produced higher peak temperatures signifying increased oxidation of O2 under the same flow conditions. Tsue, Kadota, and Kono [71] measured the structure of propane diffusion flame in crossflow, including the flame temperature, velocity and concentration fields. Further, Tsue, Kadota, and... 

Fourier transform infrared step-scan photoacoustic spectroscopy was developed to study the composition of thermoplastic olefin films, as a function of depth below the surface. Infrared bands associated with talc, polypropylene (PP), and ethylene-propylene mbber (EPR) were used as depth-profiling probes to identify photoacoustic signals. Experiments were done at various modulation frequencies, enabling a stratification model to be developed. The uppermost layer (0-3 micrometre) showed large changes in talc and PP concentration, whilst the layer below showed a significant decrease in both the phases. In the third layer (6-9 micrometre), all three phases showed the maximum values. In the fourth layer (9-12 micrometre), the talc concentration reduced, whilst concentrations of EPR and PP were observed, decreasing with depth. 32 refs. 

Figure 5. (a) The ( A, SO,) anion symmetric streching mode of poly(propylene glycol)- LiCF,SO, for 0 M ratios of 2000 1 and 6 1. Solid symbols represent experimental data after subtraction of the spectrum corre-ponding to the pure polymer. Solid curves represent a three-component fit. Broken curves represent the individual fitted components, (b) Relative Raman intensities of the fitted profiles for the (A, SO,) anion mode for this system, plotted against square root of the salt concentration , solvated ions , ion pairs , triple ions, (c) The molar conductivity of the same system at 293 K. Adapted from A. Ferry, P. Jacobsson, L. M. Torell, Electrochim. Acta 1995,40, 2369 and F. M. Gray, Solid State Ionics 1990, 40/41, 637. 

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