Constant velocity feed

An initially clean activated carbon Led at 320 K is fed a vapor of benzene in nitrogen at a total pressure of 1 MPa. The concentration of benzene in the feed is 6 mol/m. After the Led is uniformly saturated with feed, it is regenerated using benzene-free nitrogen at 400 K and 1 MPa. Solve for Loth steps. For sim-phcity, neglect fluid-phase acciimiilation terms and assume constant mean heat capacities for stationary and fluid phases and a constant velocity. The system is described by... 

Selectivity is another catalyst attribute that is often considered when ranking catalysts. Selectivity may be defined as the ratio of the molar amount of key reactant converted to the desired product to the total molar amount of the key reactant converted. As such, selectivity is a measure of the efficiency of the catalyst in promoting the formation of the desired product as compared to other products. Since selectivity is a function of the relative rates of reaction with a given reaction system, selectivity will be a function of reaction temperature, space velocity, feed composition, reactor geometry, and degree of conversion. Comparing selec-tivities of different catalysts is therefore only meaningful when all the latter parameters are constant. 

Diffusion is the macroscopic result of the sum of all molecular motions involved in the sample studied. Molecular motions are described by the general equation of dynamics. However, because of the enormous difference in the orders of magnitude of the masses, sizes, and forces that characterize molecules and macroscopic solids, it can be shown [1] that, when a force field (e.g., an electric field to an ionic solution) is applied to a chemical system, the acceleration of the molecules or ions is nearly instantaneous, molecules drift at a constant velocity, and, in the absence of an external field and of internal forces acting on the feed components, which is the case in chromatography, the diffusional flux, /, of a chemical species i in a gradient of chemical potential is given by... 

These effects were studied running two new continuous assays. In continuous run 2, the system was operated with a total volume of 314 ml (110, 104, and 100 ml, for reactors 1, 2, and 3, respectively), keeping constant the feed flow rate, 55 ml/h, with and without recycle in the first reactor. Only one recycle flow rate was tested, 67.2 ml/h. In continuous run 3, only the first reactor was operated, changing the feed and recycle flow rates. Table 5 shows operational conditions and respective average values of ethanol, TRS, and glucose concentrations obtained for related steady states, in the two new tests. Figure 4 shows ethanol production vs residence time for operational conditions operated without recycle, with superficial velocities up to 3.1 x 10 cm/s and above 3.7x lO" cm/s. 

To visualize what this looks like, we will start with a packed column that is initially clean (c = 0). At time to, we start adding a feed with a concentration c p at a known interstitial velocity. Equation fl8-15al can be used to calculate the solute velocity u (the numerical calculation procedure is illustrated in Exanple 18-21. In Figure 18-4A the solute movement or characteristic diagram for this process is plotted. Solute starts at z = 0 at time to, and moves upward at velocity u, which is the slope of the characteristic line shown in the figure. The procedure will probably be easiest to understand after you study Example 18-2. The concentrations in the column are shown at four times in Figures 18-4 B, , D, and E. The solute moves upward in a wave at a constant velocity u. If adsorption is strong the wave... 

In the case of OPLC the eluent can be forced through the sorbent bed by means of a pump system using a chosen flow rate (20). Feeding the eluent by constant velocity, the speed of the front depends on the cross-sectional area of the sorbent layer in the direction of the development. Only linear developments are able to result in constant linear velocity other geometric shapes of sorbent layers (circular, triangular) are not. 

Every species i is moving in the z-direction at a different velocity, v. If we now introduce a constant velocity in a perpendicular direction, we can create a separate trajectory for each species (exactly as in Figure 7.3.1) provided we introduce the feed solution over a small area at z = 0. 

The specific cake resistance is the most troublesome parameter ideally constant, its value is needed to calculate the resistance to flow when the amount of cake deposited on the filter is known. In practice, it depends on the approach velocity of the suspension, the degree of flow consoHdation that the cake undergoes with time, the feed soHds concentration, and, most importantly, the appHed pressure drop Ap. This changes due to the compressibiHty of most cakes in practice. often decreases with the velocity and the feed concentration. It may sometimes go through a maximum when it is plotted against soHds concentration. The strongest effect on is due to pressure, conventionally expressed as ... 

Analysis of a method of maximizing the usefiilness of smaH pilot units in achieving similitude is described in Reference 67. The pilot unit should be designed to produce fully developed large bubbles or slugs as rapidly as possible above the inlet. UsuaHy, the basic reaction conditions of feed composition, temperature, pressure, and catalyst activity are kept constant. Constant catalyst activity usuaHy requires use of the same particle size distribution and therefore constant minimum fluidization velocity which is usuaHy much less than the superficial gas velocity. Mass transport from the bubble by diffusion may be less than by convective exchange between the bubble and the surrounding emulsion phase. 

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