Effect of Recycle Ratio

Pirjamali et al (1972) developed a correction procedure for interparticle gradients in recycle reactors. Their study involved recycle ratios n from 36 to 1000 (as defined in this book) that relates to their recycle ratio P 

The most important conclusions of their work were that the inter-particle effects are reasonably small for the particular recycle reactor design, and that kinetic constants determined in the recycle reactor were trustworthy. 

Georgakopoulos and Broucek (1987) investigated the effect of recycle ratio on non-ideality, both mathematically and experimentally. They investigated two cases from which the bypass case b was completely uninteresting, because total bypass of the catalyst bed could be avoided by feeding the makeup directly to the location of highest sheerfield, at the tip of the impeller blade. For their case a they showed on their Fig. 3. that from a recycle ratio of about 10 = 32 there was no observable falsification effect. This matched well the conclusion of Pirjamali et al. 

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The effect of recycle ratio on coke production is analogous to the effect of pressure. As the recycle ratio is decreased, the production of liquid products is increased. Reduction of recycle also lowers the fuel usage in the furnace because of lowered throughput. Recycle is often reduced to the minimum rate which still produces acceptable product qualities. 

The improved product distribution obtainable by recycling is illustrated by Figure 51. The upper half shows a comparison of gasoline yields from once-through and partial-recycle operations in a fixed-bed unit the lower half illustrates the effect of recycle ratio on gasoline yield in a... 

Figure 13. Effect of Recycle Ratio on the Projected Countercurrent...

Figure E9.5.1 Effect of recycle ratio—isothermal operation.

Figure E9.5.2 Effect of recycle ratio—adiabatic operation.

Figure E9.5.3 Effect of recycle ratio on outlet temperature—adiabatic operation.

FIGURE 60.18 Effect of recycle ratio on exhaust air humidity and specific energy consumption. 

Figure 1.9 shows the effect of recycle ratio R on the conversion. 

Fig. 1.9 Improving effect of recycle ratio R on the conversion and fraction of B to be removed in the membrane module at a fixed flow rate of B in the permeate stream...

Figure 6.20 shows the effect of bleeding ratio on the cell productivity for the Monod model. As j3 is reduced from 1 (no recycling) to 0.5, the cell productivity is doubled. 

In addition to the co-current flow mode shown in Figure U. 12 are other situations where the sweep/permeatc stream flows in the opposite direction to the feed stream (countercurrent flow mode). The effect of recycle on the preferred flow mode has been studied for those reactions oA bB - cC where the permeability of the reactant lies between those of the two products [Mohan and Govind, 1988a]. It has been found that at low values of the recycle ratio (i.e., the fraction of the product stream recycled), the countercurrent flow gives higher conversions than the co-current flow as a result of lower reactant losses and greater separation of the products. As the recycle ratio increases, the... 

Figure 6.38. Effect of recycling biomass concentration x. on a CSTR in a diagram of effluent substrate concentration versus mean residence time F(r = recycling ratio). (Adapted from Andrews, 1972.)...

In the Monsanto/Lummus Crest process (Figure 10-3), fresh ethylbenzene with recycled unconverted ethylbenzene are mixed with superheated steam. The steam acts as a heating medium and as a diluent. The endothermic reaction is carried out in multiple radial bed reactors filled with proprietary catalysts. Radial beds minimize pressure drops across the reactor. A simulation and optimization of styrene plant based on the Lummus Monsanto process has been done by Sundaram et al. Yields could be predicted, and with the help of an optimizer, the best operating conditions can be found. Figure 10-4 shows the effect of steam-to-EB ratio, temperature, and pressure on the equilibrium conversion of ethylbenzene. Alternative routes for producing styrene have been sought. One approach is to dimerize butadiene to 4-vinyl-1-cyclohexene, followed by catalytic dehydrogenation to styrene ... 

Effects of Cold Gas Recycle and Approach to Equilibrium. Product gases resulting from various CGR ratios were analyzed (Table XI). For the experiments tabulated, a decrease in the cold recycle ratio resulted consistently in increases in the product gas concentrations of water vapor, hydrogen, and carbon dioxide and a decrease in methane concentration. These trends may be noted in experiment HGR-12 as the CGR ratio decreased from 8.7 1 to 1.2 1, in experiment HGR-13 as it increased from 1.0 1 to 9.1 1, and in experiment HGR-14 as it decreased from 3.0 1 to 1.0 1. These trends indicate that the water-gas shift reaction (CO + H20 —> C02 + H2) was sustained to some degree. Except for the 462-hr period in experiment HGR-14, the apparent mass action constants for the water-gas shift reaction (based on the product gas compositions in Table XI) remained fairly constant at 0.57-1.6. These values are much lower than the value of 11.7 for equilibrium conversion at 400°C. In... 

Fig.4. Effect of Pe in a dispersed PFR and recycle ratio in a PFR with recycle stream at 26QX1 and 500 psig.

For reducing the recycle ratio, the acid content had to be increased. Although this was detrimental in terms of selectivity, this effect was more than counterbalanced by the reduction of loop passages [64]. 

The effects of tin/palladium ratio, temperatnre, pressnre, and recycling were studied and correlated with catalyst characterization. The catalysts were characterized by chemisorption titrations, in situ X-Ray Diffraction (XRD), and Electron Spectroscopy for Chemical Analysis (ESCA). Chemisorption studies with hydrogen sulfide show lack of adsorption at higher Sn/Pd ratios. Carbon monoxide chemisorption indicates an increase in adsorption with increasing palladium concentration. One form of palladium is transformed to a new phase at 140°C by measurement of in situ variable temperature XRD. ESCA studies of the catalysts show that the presence of tin concentration increases the surface palladium concentration. ESCA data also indicates that recycled catalysts show no palladium sulfide formation at the surface but palladium cyanide is present. 

The thiol was obtained in >98% yield with trace amounts of the disulfide at 175°C and 700 psig H2 reactor pressnre in 1.5 honrs at a 900 1 substrate catalyst molar ratio. As discussed above, it is known that palladinm and other groups 8 to 10 metal catalysts are poisoned by the prodnct thiol, traces of hydrogen sulfide byproduct, and hydrogen cyanide coprodnct (6), bnt it is surprising that this catalyst is so robnst The effects of solvents, temperature, pressure, catalyst, and recycle will be discnssed. The characterization of the catalyst by various techniques will help to explain some of these observations. 

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