Column train

The Tokuyama Soda single-step catalyst consists of a zirconium phosphate catalyst loaded with 0.1—0.5 wt % paHadium (93—97). Pilot-plant data report (93) that at 140°C, 3 MPa, and a H2 acetone mole ratio of 0.2, the MIBK selectivity is 95% at an acetone conversion of 30%. The reactor product does not contain light methyl substituted methyl pentanes, and allows MIBK recovery in a three-column train with a phase separator between the first and second columns. 

Prior to 1974, when fuel costs were low, distillation column trains used a strategy involving the substantial consumption of utilities such as steam and cooling water in order to maximize separation (i.e., product purity) for a given tower. However, the operation of any one tower involves certain limitations or constraints on the process, such as the condenser duty, tower tray flooding, or reboiler duty. 

Develop a mathematical model for the three-column train of distillation columns sketched below. The feed to the first column is 400 kg mol/h and contains four components (1, 2, 3, and 4), each at 25 mol %. Most of the lightest component is removed in the distillate of the first column, most of the next lightest in the second column distillate and the final column separates the final two heavy components. Assume constant relative volatilities throughout the system ai, CI2, and a3. The condensers are total condensers and the reboilers are partial. Trays, column bases, and reflux drums are perfectly mixed. Distillate flow rates are set by reflux drum... 

Figure 17.2 Concentration profiles along the column train of a TMB unit. Reproduced with permission from G. Zhongand G. Guiochon, Chem. Eng. Set, 51(1996) 4307 (Fig. 2).

Figure 17.3 illustrates the concentration profiles in the column train at the time immediately before the moment when the columns are switched. is positive, so the concentrations of both components in the columns III and IV are lower than the feed concentrations, as shown in Eq. 17.17. This results from the dilution of the feed, at the feed node, by the mobile phase stream entering into column III. From the raffinate node mass balance equation (Eq. 17.7g), we know that the concentration of the first component in the raffinate stream is exactly the same as its concentration at the inlet of column IV. At this stage, a stream of raffinate begins to be collected, at the end of this period. By contrast, the second component does not appear at the extract node during this first cycle and the fraction collected there is pure mobile phase. 

The analytical solution obtained for this model is not trivial as it is in the case of the elution and breakthrough problems. Accordingly, it is most useful for the investigation of separation carried out rmder linear or quasi-linear conditions. In such cases, it provides a useful starting point for further studies. Figure 17.9 shows a comparison between the experimental and the calculated concentration profiles along the column train of an SMB unit. It shows that the condition of ideality can be relaxed (see later. Section 17.4) and that the solution of the ideal... 

Lines for recycling top andlor bottom product to the feed tank These are useful for minimizing the amount of off-spec material produced. They are often essential when starting up a column train which is started one column at a time. 

Some factors that can mitigate disturbance amplification in a column train are... 

Feed forward control loops can often be used to dampen fluctuations in a column train, particularly if the disturbances occur stepwise rather than as a continuous fluctuation. 

Figure 19.13 Disturbance amplification in a column train, (a) No heat interaction (6) with heat interaction, poor control (c) with heat interaction, good control. (Parts b and c based on Dak E. Lupfer, Proc. 53rd Ann. Convention of the Gas Processors Assoc., March 25-27,1974. Reproduced courtesy of the Gas Processors Association.)...

Feed surge. Buckley et al. (68) recommend installing a separate feed surge upstream of a column in a column train when... 

In LGC, a single long capillary column is typically used in a temperature-programmed mode to perform the separation. Although this same separation scheme can be used in PGC, the major drawback is the speed of analysis. The solution is to use multiple column trains and column-switching techniques. This allows the chromatograph to be operated in an isothermal mode. 

Trap-bypass involves momentarily trapping part of the sample in a lights column and allowing heavier components to bypass this column. It is typically used to analyze a component matrix with a wide boiling-point range using a single column train. This operation is of less importance today with the advent... 

Finally, column selection allows multiple column trains to be merged alternately together while maintaining a constant carrier gas flow. The side that is selected at any moment in time is transferred downstream for detection, while the other stream is sent to vent. This configuration prevents the two column trains from interfering with each other. This is also of less importance due to the use of parallel chromatography. 

A sample of no more than 1 g of the EtOH-soluble portion of a detergent mixture is added to the column train as 100 mL of an EtOH solution. EtOH is added to the columns until all nonionic material is eluted from the last column, as indicated by measuring residue from evaporation of the eluate. The columns are then separated. The cation exchange column is treated with 400 mL 90 10 MeOH/12 M HCl to elute cations. The first anion exchange column is treated with 400 mL 90 10 MeOH/12 M HCl to elute strongly acidic surfactacts. The second anion exchange column is treated with 100 mL 80 20 MeOH/H20,... 

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