Gas-phase packing efficiency

Failing to identify the limiting reactant can lead to failure in the scale-up of trickle-bed reactors (Dudukovic, 1999). Gas-limited reactions occur when the gaseous reactant is slightly soluble in the liquid and at moderate operating pressures. For liquid-limited reactions, concurrent upflow is preferred (packed bubble columns) as it provides for complete catalyst wetting and thus enhances the mass transfer from the liquid phase to the catalyst. On the other hand, for gas reactions, concurrent downflow operation (trickle-bed reactors), especially at partially wetted conditions, is preferred as it facilitates the mass transfer from the gas phase to the catalyst. The differences between upflow and downflow conditions disappear by the addition of fines (see Section 3.7.3, Wetting efficiency in trickle-bed reactors). 

Biphenyl. Since Z = 2, an inversion center is present in the middle of the bridging C-C bond between the two C6H5 rings. This means that both phenyl rings are coplanar. The planar conformation of biphenyl in the crystalline state, which differs from its non-planar conformation in the solution and gas phases, is attributable to efficient molecular packing stabilized by intermolecular interactions between the phenyl rings. 

The monoglycerides of the raffinate (the bottom product) is shown in Figure 9 as a function of the superficial velocity of the gas phase at a phase ratio of 19. At an superficial velocity of 10 mm/s the raffinate obtained with different packings is nearly the same except for the Sulzer Packing SMV. At lower superficial velocities the wire mesh packings (Sulzer CY) provide the best yields. The experiments are made at conditions where a falling film disintegrates into drops. Therefore, it seems understandable that the efficiency of the spray column and that of the collector-distributor installations do not much differ. 

Figure 13.44. Vapor or gas phase parameters for the Bolles/Fair correlation for random packing efficiency.

Spray contactors ate particularly important for the absorption of imparities from large volumes of Hue gas where tow pressure drop is of key importance. They are used where materials in the liquid phase (e.g., particles of limestone) or in the gas phase (e.g., droplets of tar) may cause plugging of packing or trays. Other important applications of spray contactors (which are outside the scope of this discussion) include particulate removal and hot gas quenching. When used for absorption, spray devices are not applicable to difficult separations and geueratty are limited to about Four transfer units even with countercurrent spray column designs. The tow efficiency of spray columns is believed to be due to entrainment of droplets in the gas and beckmixing of the gas induced by the sprays. 

One of the drawbacks of the monolith is the heat and mass transfer resistance between the bulk gas phase and the wash-coat. This resistance can be lessened when using a fixed oed packed with cmshed catalyst. Figure 3 illustrates the LO curves when the heat and mass transfer processes are not the rate determining steps. Two cases are considered depending on the efficiency of heat removal from the catalytic bed. Either the efficiency is low and the bed is close to adiabatic condition, or the efficiency is high and all the phases are at the temperature of the inlet gas. 

Supercritical Fluid Chromatography. The origin of SFC with packed columns goes back over two decades (17-26). The recent interest in SFC has been due in large part to the limitations in both chromatographic efficiency and detection methods with HPLC. The introduction of fused silica capillary columns with nonextractable stationary phases for SFC (O and the potential compatibility with gas phase detection methods (13) has served to further increase the attention given these methods. 

As discussed above, there have been major improvements in catalyst efficiency and selectivity. The amount of atactic polymer has been reduced, and the number of pounds of polymer produced per pound of catalyst has been increased from five- to tenfold and more. Polymerization in the gas phase has been improved [73] in order that resin with low atactic content can be produced without solvent removal or polymer washing. The new processes [74] have reduced and, in some cases, eliminated the purification and solvent recovery steps, thereby simplifying the polymerization process and reducing the cost of a polymer plant. In addition, the new processes yield polymers with reduced catalyst residues and fewer gels, resulting in better filterability and improved pack life during fiber melt spinning. 

Wet scrubbers countercurrent wet packing dust diameter 0.2 to 3 pm feed concentration < 0.1 g/m temperature < 100 °C gas phase Ap = 1.25 to 6 kPa. Turbulent bed contactor [see also Section 4.8 absorber] temperature < 100 °C OK for heavy sticky particles allows high gas and liquid flowrates with high mass transfer efficiencies for gas absorption 1 to 2 pm 2.5 to 20 kW s/m. ... 

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