Concentration profile packed column

Nonisothermal Gas Absorption. The computation of nonisothermal gas absorption processes is difficult because of all the interactions involved as described for packed columns. A computer is normally required for the enormous number of plate calculations necessary to estabUsh the correct concentration and temperature profiles through the tower. Suitable algorithms have been developed (46,105) and nonisothermal gas absorption in plate columns has been studied experimentally and the measured profiles compared to the calculated results (47,106). Figure 27 shows a typical Hquid temperature profile observed in an adiabatic bubble plate absorber (107). The close agreement between the calculated and observed profiles was obtained without adjusting parameters. The plate efficiencies required for the calculations were measured independendy on a single exact copy of the bubble cap plates installed in the five-tray absorber. 

Fig. 1.27 shows a differential type of contactor as in, say a countercurrent flow packed gas absorption column, together with the resulting approximate continuous concentration profiles. 

Equation 12.18 allows us to predict the concentration profile through a packed column operating at total reflux conditions. The resulting profile is known as a residue curve, since they were first developed by considering the batch vaporization of a mixture through time8,9. Such... 

Mass transfer in both the stationary and mobile phases are not instantaneous and, consequently, complete equilibrium is not established under normal separation conditions [2]. The result is that the solute concentration profile in the stationary phase is always displaced slightly behind the equilibrium position and the mobile-phase profile is slightly in advance of the equilibrium position [2]. A high degree of displacement will lead to wider peaks and reduced resolution. In fact, the largest problem associated with mass transport in the packed column revolves around moving the solute from the stationary phase to the mobile phase. 

The material balance from (1.228) is once again the starting point for investigating the concentration profile in a packed column being used to rectify a gaseous mixture. In this case the mole fractions will be used instead of the mole ratios. The amount transferred from the gas to the liquid phase is —NGdy, wherein NG is now the molar flow rate of the gas mixture rather than that of the carrier gas as in (1.228). Equation (1.228) is therefore replaced by... 

Prediction of Elution Profiles (Linear Equilibrium). For the case of local linear equilibrium (infinite rate of mass transfer), Lapidus and Amundson (25) derived equations for computing concentration distributions in a packed column. With concentrations at the inlet of the column, and initial conditions throughout the column known, concentration profiles at a specific distance from the column inlet can be computed. The derivation was based on a semi-infinite column, which differs mathematically from a finite column, in that effects of the mobile phase leaving the stationary phase are not modeled. Nonetheless, the solution obtained is useful for giving a qualitative picture of important parameters in column performance. The equation is ... 

Gel permeability Rate constant, fth-order heterogeneous reaction Bubble lubrication film length Mean free path, lattice spacing, or distance between particle collisions Pan length Characteristic length Gel or resin packed bed column length Development length for concentration profile in channel... 

The practical importance of this Taylor diffusion analysis lies in the justification of the effective transport models to take into account complicated velocity and concentration profiles in a simple manner, as well as providing a theoretical framework for the dispersion coefficient, D . Similar results have been worked out for turbulent flow, packed columns, and other situations. For correlations of the axial dispersion coefficients, see Himmelblau and Bischoff [4] and Wen and Fan [2]. 

Figure 10.10 demonstrates the simulated and measured concentration profiles for the pilot column with the reactive section filled with catalytically active rings. In the simulations, four components, namely, methanol, isobutene, MTBE and 1-butene, were chosen to represent the chemical system under consideration. Here, segment 1 corresponds to the reboiler. A satisfactory agreement between calculated and measured values can be clearly observed. In Fig. 10.11, the simulation results for the column packed with MULTIPAK are shown. Here, 16 components are considered, and, again, the liquid bulk composition profiles agree well with the experimental data. 

A 100.0 cm long column is packed with activated alumina. The column is initially totally saturated at c = 0.011 mol/L anthracene in cyclohexane solvent. It is then eluted with pure cyclohexane solvent (c = 0) at a superficial velocity of 30.0 cm/min. Predict and plot the oudet concentration profile using solute movement theory. 

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