Distillation temperature profile

FIG. 13-80 Reactive extracting distillation for methyl acetate production, (a) Composition profile, (b) Temperature profile. 

Why not put new lyrics to an old tune This is an excellent idea, and many have done this very thing. Rice" started w ith the Smith-Brinkley raethod" used to calculate distillation, absorption, extraction, etc., overhead and bottoms compositions, and developed distillation equations for determining the liquid composition on any tray. This together with bubble point calculations yield a column temperature profile useful for column analysis. 

The method starts with an assumption of the column temperature and flow profiles. The stage equations are then solved to determine the stage component compositions and the results used to revise the temperature profiles for subsequent trial calculations. Efficient convergence procedures have been developed for the Thiele-Geddes method. The so-called theta method , described by Lyster et al. (1959) and Holland (1963), is recommended. The Thiele-Geddes method can be used for the solution of complex distillation problems,... 

Thermodynamics and mass transfer. Operating pressure, number of plates and reflux ratio in the distillation column temperature profile in the column equilibrium conditions in the reactor... 

The composition and temperature profiles in the RDC are shown in Figure 7. The ester product with traces of methanol is the bottom product, whereas a mixture of water and fatty acid is the top product. This mixture is then separated in the additional distillation column and the acid is refluxed back to the RDC. The ester is further purified in a small evaporator and methanol is recycled back to the RDC. 

At first sight, adsorption and reaction are well-matched functionalities for integrated chemical processes. Their compatibility extends over a wide temperature range, and their respective kinetics are usually rapid enough so as not to constrain either process, whereas the permeation rate in membrane reactors commonly lags behind that of the catalytic reaction [9]. The phase slippage observed in extractive processes [10], for example, is absent and the choice of the adsorbent offers a powerful degree of freedom in the selective manipulation of concentration profiles that lies at the heart of all multifunctional reactor operation [11]. Furthermore, in contrast to reactive distillation, the effective independence of concentration and temperature profiles... 

The mathematical model comprises a set of partial differential equations of convective diffusion and heat conduction as well as the Navier-Stokes equations written for each phase separately. For the description of reactive separation processes (e.g. reactive absorption, reactive distillation), the reaction terms are introduced either as source terms in the convective diffusion and heat conduction equations or in the boundary condition at the channel wall, depending on whether the reaction is homogeneous or heterogeneous. The solution yields local concentration and temperature fields, which are used for calculation of the concentration and temperature profiles along the column. 

Figure 1. Extractive distillation column and its temperature profile...

In the case of temperature-sensitive separations the column temperature profile is constrained. Appropriate methods are stripping, liquid-liquid extraction, adsorption and crystallization, as well as vacuum distillation. 

The initial total flow rate and temperature profiles can make the difference between success and failure of a rigorous method. Usually for distillation columns, the condenser and reboiler temperatures are estimated and a calculation that assumes constant molal overflow Sec. 2.2.2) is used to initialize tbe internal vapor and liquid flow... 

Figure 2.17 Temperature profile in multicomponent distillation, Example 2,4. (From C. d.. King, Separation Processes, 2d ed, Copyright by McGraw-Hill, Inc. Reprinted by permission.)...

Fig. 2 presents the reactor temperature profile correlated with the sulpher content and the 360 ° C distillate inHVGO. 

Another phenomenon of highly nonlinear systems is parametric sensitivity. We illustrated this behavior for the temperature profile in the plug-flow reactor. Nonideal distillation systems can also show this sensitivity. For example, in Fig. 6.5 a small change in the feed composition or organic reflux flow can dramatically change the composition ( and t emperature) profile in the column. Instead of a vinyl acetate-rich profile in the top section, a water-rich profile can be present. 

Figure 6.12 illustrates this effect. As more LLK component comes in with the feed stream, more depression occurs in the rectifying section temperature profile. If we control a tray temperature near the top and the amount of LLK in the feed increases, the temperature on this tray will start to go down. We will increase heat input to drive it back to its setpoint value, and this will push more HK component out the top. Therefore holding a constant temperature on a tray near the top of the column w ould result in significant variations in the amount of heavy key component in the distillate product. All of the LLK components must go out the top of the column, and there is nothing we can do about it once these components enter the column. Action must be taken in the upstream column to keep LLK components out of this column. Similar effects occur in the stripping section and near the base when variations occur in the amount of HHK components in the feed. Now temperatures rise as more heavy components enter the column, and we drop more LK component into the bottoms product if we hold a constant temperature on a tray near the base of the column. 

Step 5. The final isobutane product is the distillate from the DIB column, and we want to keep the composition of the nC4 impurity at 2 mol %. Nothing can be done about the propane impurity. Whatever propane is in the fresh feed must leave in the product stream. Because the separation involves two isomers, the temperature profile is flat in the DIB column. Use of an overhead composition analyzer is necessary. 

Tables 11.5 to 11.7 contain process stream data. These data come from the TMODS dynamic simulation and not from a commercial steady-state simulation package. The corresponding stream numbers are shown on the flowsheet in Fig. 11.1. Tables 11.8 to 11.10 list the process equipment and vessel data. In the simulation, all gas is removed in a component separator prior to the distillation column. This involves the liquid from the separator and the absorber. The gas is sent back and combines with the vapor product from the separator to form the vapor feed to the absorber. Figure 11.2a shows the temperature profile in the azeotropic distillation column.

Figure 11.2 Temperature profiles, (at Azeotropic distillation column (b) reactor.

FIG. 13-56 Composition, flow, and temperature profiles in nonideal distillation process. 

The liquid composition, flow, and temperature profiles are shown in Fig. 13-56. In this particular system the vapor and liquid temperatures estimated by the rate-based model are quite close (as often is the case in distillation operations). 

Figure 4. Temperature profile in extractive distillation of aqueous ethanol...

In the Smuda process the pyrolysis reactor temperature is 350°C and the operating pressure is 4-5 psi. The pyrolysis gases from the pyrolysis vessel are sent directly to a distillation column. The distillation column has a typical temperature profile as follows top 140°C, Sulzer 250Y middle 322°C, Sulzer 350Y and bottom 331°C. 

The data in Table II pertaining to pyrolysis conditions shows that all four feedstocks were pyrolyzed under substantially similar conditions, namely steam-to-hydrocarbon weight ratios of 0.9 0.1, residence times of 0.3 sec, reactor exit pressures of 2.0 bar absolute, and reactor exit temperatures of 835°C. Care also was taken to maintain identical axial temperature profiles in the reactor for each of these runs. No unambiguous measure of substrate conversion during pyrolysis is possible for distillate feedstocks of the type used in the present experiments in terms of the empirical kinetic severity function of Zdonik et al. (5), all of the present experiments were conducted at a severity of about 2. 

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