X

Pure

Dichloroethane

Heavy Ends

Reactor

FIG. 3.8.8 The direct chlorination step of the vinyl chloride process using a boiling reactor. This design eliminates the washing and neutralization steps and the resulting effluents. (Reprinted, with permission, from Smith and Patela, 1992.)

drum. A slight excess of ethylene ensures essentially 100% conversion of the chlorine.

As shown in Figure 3.8.8, the vapor from the reactor flows into the bottom of a distillation column, and high-purity dichloroethane is withdrawn as a sidestream, several trays from the column top. The design shown in Figure 3.8.8 is elegant in that the reaction heat is conserved to run the separation, and no washing of the reactor products is required. This design eliminates two aqueous streams which inevitably carry organics with them, require treatment, and cause loss of materials.

With improved heat recovery, using the energy system inherent in the process can often drive the separation system and operate at little or no increase in operating costs.

Figure 3.8.9 is a schematic for the recovery of acetone in a liquid waste containing hydrofluoric acid. This stream originates in the manufacture of an antibiotic precursor. It is pumped to a holding tank. Next, the hydrofluoric acid is neutralized with calcium hydroxide in a stirred reactor. The calcium fluorides that precipitate are difficult to filter. A totally enclosed, high-press filter press was tested. The filter cake had to be washed, generating large quan

Acetone-Rich Waste

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