Phase behavior reactor

Example 3.4 Find the mean residence time in an isothermal, gas-phase tubular reactor. Assume that the reactor has a circular cross section of constant radius. Assume ideal gas behavior and ignore any change in the number of moles upon reaction. 

Three-phase slurry reactors are commonly used in fine-chemical industries for the catalytic hydrogenation of organic substrates to a variety of products and intermediates (1-2). The most common types of catalysts are precious metals such as Pt and Pd supported on powdered carbon supports (3). The behavior of the gas-liquid-sluny reactors is affected by a complex interplay of multiple variables including the temperature, pressure, stirring rates, feed composition, etc. (1-2,4). Often these types of reactors are operated away from the optimal conditions due to the difficulty in identifying and optimizing the critical variables involved in the process. This not only leads to lost productivity but also increases the cost of down stream processing (purification), and pollution control (undesired by-products). 

An advantage of this approach to model large-scale fluidized bed reactors is that the behavior of bubbles in fluidized beds can be readily incorporated in the force balance of the bubbles. In this respect, one can think of the rise velocity, and the tendency of rising bubbles to be drawn towards the center of the bed, from the mutual interaction of bubbles and from wall effects (Kobayashi et al., 2000). In Fig. 34, two preliminary calculations are shown for an industrial-scale gas-phase polymerization reactor, using the discrete bubble model. The geometry of the fluidized bed was 1.0 x 3.0 x 1.0 m (w x h x d). The emulsion phase has a density of 400kg/m3, and the apparent viscosity was set to 1.0 Pa s. The density of the bubble phase was 25 g/m3. The bubbles were injected via 49 nozzles positioned equally distributed in a square in the middle of the column. 

As discussed in previous chapters, the phase behavior with changing temperature and pressure may be strongly influenced by small concentration gradients in multi-component systems already. Therefore, experimental control should take this into account. It is a common practice to use reactors with glass or sapphire windows. The transition of an inhomogeneous multiphase system to a homogeneous one can be observed visually as cloud point (Sect. 2.2, with the pressure and temperature values being monitored. 

The regioselective course of the Diels-Alder reaction in supercritical carbon dioxide was investigated. The analysis failed to confirm the previously reported dramatic effect of reaction conditions on Diels-Alder regiochemistry. The results highlighted the importance of verifying phase behavior when sampling CO2 reaction mixtures and the utility of a view-cell reactor that allows direct monitoring of phase behavior (Ren-slo et al., 1997). 

Civilian applications are numerous, but most funding of SCWO technology has stemmed from the military s need to find a safe and effective alternative to incineration of their wastes, as well as the need to clean up mixed wastes (radioactive and hazardous organic materials) at DOE weapons facilities. For better utilization of SCWO for its application to a wide range of waste types, a better fundamental understanding of reaction media, including reaction rates, reaction mechanisms, and phase behavior of multicomponent systems is required. Such an understanding would help optimize the process conditions to minimize reactor corrosion and salt... 

On the basis of the arguments regarding the cause of the non-minimum-phase behavior of the reactor-external-heat-exchanger process, the term... 

More complex fluid phase behavior can be accommodated by axial and radial dispersion features, among which radial dispersion ones are again the more important — and those only for a non-adiabatic reactor. 

Scaling up three-phase monolith reactors from pilot plant to industrial size is easy in some areas and more difficult in others. Since there is no interaction between the channels, the behavior within the monolith channels is independent of scale. Adding more parallel channels will not affect the flow, the mass and heat transfer, or reactions in each channel, as long as the flow distribution is uniform. Also, both the pilot plant reactors and the industrial reactors are adiabatic due to the absence of radial mixing. 

Complex reaction kinetics and phase behavior In many polymerization processes, the reaction mixture undergoes a significant phase change that affects the polymerization rate, polymer properties, and reactor operations (e.g., viscosity increase, particle formation, precipitation, etc.). 

Figure 12(e) shows the much more complex phase behavior observed when water is mixed with low volatility salts, in this case the sodium chloride-water system at 250 Ivir. " Due to the high critical temperature of sodium chloride, estimated at 3900K and 260 bar, this system is subcritical at SCWO reactor conditions. Figure 12(e) shows an operating line for 10 wt% NaCl at 250 bar. As this brine is heated from ambient temperature, a split into vapor and liquid phases occurs in the vicinity of 400°C, As temperature increases to 450 C. NaCl... 

The performance of three-phase microchannel reactors was found to exceed the performance of conventional multiphase reactors such as trickle beds or stirred tank suspension reactors [95,111]. The superior behavior was explained by the high specific interfacial area and the high mass transfer coefficient [112],... 

A brief discussion of the rate-controlling step in coal oxydesulfurization is given on the basis of the shrinking core model. A diree-phase slurry reactor is designed by including die nonideal behavior of die solid phase. 

The phase behavior of the feed and the reacting mixture at the reactor operating conditions was observed experimentally using a well-mixed fixed volume view cell equipped with sapphire windows (20 cm, 400 bar MAWP) as described earlier (9). The temperature and pressure at which a homogenous mixture was formed was determined. Based on these experimental measurements, we chose to operate the reactor at 70 °C and 138 bar for cyclohexene hydrogenation, and at 60 °C and 138 bar for the selective hydrogenation of toluene. 

Chemical kinetic information was obtained using an integral-reactor and the experimental results were interpreted with an homogeneous model. Preliminary observations of phase behavior may be useful for reactor optimization purposes before any information about kinetic phenomena becomes available. The phase boimdaries for the system C-H2-CO2 are shown in Fig. 13.7. 

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