FIG. 3.8.2 Flowsheet for the production of isopropyl alcohol by direct hydration of propylene. (Reprinted, with permission, from R. Smith and Eric Patela, 1992, Waste minimization in the process industries, Part 3: Separation and recycle systems, The Chemical Engineer [13 February].)
Waste water leaves the process from the bottom of the second column (C2) and the decanter of the azeotropic distillation column (C3). These streams contain small quantities of organics which must be treated before the final discharge. The chemical engineer can avoid this treatment by recycling the wastewater to the reactor inlet and substituting it for part of the fresh water feed (dotted line in Figure 3.8.2).
Sometimes waste streams can be recycled directly but between different processes. The waste streams from one process may become the feedstock for another.
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