Absorbers Azeotropic distillation columns

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.

Step 1. For this process we must be able to set the production rate of vinyl acetate while minimizing yield losses to carbon dioxide. During the lifetime of the catalyst charge, catalyst activity decreases and the control system must operate under these different conditions. To maintain safe operating conditions, the oxygen concentration in the gas loop must remain outside the explosivity region for ethylene. The azeotropic distillation column must produce an overhead product with essentially no acetic acid and a bottoms product with no vinyl acetate. The absorber must recover essentially all of the vinyl acetate, water, and acetic acid from the gas recycle loop to prevent yield losses in the CCf removal system and purge,... 

The RadFrac block can be used for the ordinary distillation column and also for the extractive distillation column as shown in the example in Section 3.1. It can also be used as strippers (with a reboiler but no condenser), rectifiers (with a condenser but no reboiler), absorbers (with neither), and more complex columns with side pmnp-around. In the following, several columns other than the ordinary distillation will be outlined. The RadFrac can also be used as a heterogeneous azeotropic distillation column with decanter replacing the reflux drum at top of this column. The vapor-liquid-liquid calculation can be performed inside the column if needed. 

The concentration of the bottom fraction B is as high as 31 wt%. Most of 51 is fed via a heat exchange into distillation column C-2 to be separated into pure HCl (overhead fraction) and an azeotropic mixture (bottom fraction B2). Fraction B2 is recycled into the absorption column C-1. Hence, the operating line of the absorber has a sharp bend at a concentration of 22 wt%. 

In typical processes, the gaseous effluent from the second-stage oxidation is cooled and fed to an absorber to isolate the MAA as a 20—40% aqueous solution. The MAA may then be concentrated by extraction into a suitable organic solvent such as butyl acetate, toluene, or dibutyl ketone. Azeotropic dehydration and solvent recovery, followed by fractional distillation, is used to obtain the pure product. Water, solvent, and low boiling by-products are removed in a first-stage column. The column bottoms are then fed to a second column where MAA is taken overhead. Esterification to MMA or other esters is readily achieved using acid catalysis. 

Any higher alcohols that may have formed in the process from traces of higher olefins present in the propylene feed are absorbed from the azeotrope into mineral oil, in which isopropanol is insoluble. Pure isopropanol is obtained by ternary distillation of the cleaned water azeotrope with the appropriate proportion of added di-isopropyl ether. The ternary azeotrope (Table 19.2) is the top product from the column, and pure isopropanol is removed from the bottom (see Section 16.4 for related information). 

Following the scrubbing of the inert carrier gas the absorbent and absorbate are collected as a solution at the base of the column. A secondary process, desorption, is then required to achieve separation and liberate the absorbate. This separation is usually achieved by atmospheric pressure or vacuum distillation. Therefore the choice of absorbent is critical to ensure the materials have significant differences in boiling point and do not form an azeotrope. 

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