I have a question about azeotropy
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During the production of epoxy resin, it is necessary to remove epichlorohydrin (boiling point 118°C) and water. In terms of the manufacturing process, the temperature is increased under negative pressure to 120°C in order to remove water and epichlorohydrin, after which separation is carried out using a condenser and a phase separator. But the boiling point of the azeotrope of water and epichlorohydrin is 88°C; why then raise the temperature to such a high level and waste energy? Wouldn’t 88°C be sufficient in theory?
Azeotropy has a specific composition; after removing the azeotrope, epichlorohydrin still needs to be removed as well
In an azeotrope, aren’t the composition ratios of the liquid phase and the vaporized gas phase exactly the same? Logically, it should be steamed away at the same time, right? Is it my understanding that’s wrong? For example, if the ratio of epichlorohydrin to water is 80% and 20%, then the vapor distilled during azeotropic distillation will also be 80% and 20% respectively; so they should be distilled together, right?
Oh, why not give it a try and see what happens?:)
Could it be that the liquid phase composition happens to be exactly equal to the azeotropic composition? It’s hardly possible to be this lucky! For example, in the initial liquid phase, the proportions of epichlorohydrin and water are 80% and 20%, respectively ； Their azeotropic compositions are 70% and 30%, and the azeotropic composition is an inherent property of the system, remaining unchanged regardless of the initial liquid phase composition.
Even at the azeotrope temperature, vaporization still requires heat absorption; therefore, the vaporization rate at 88°C must be very slow. In practice, an increase in temperature is needed to boost this rate. The water content in the raw material mixture is likely low, and as water evaporates, the azeotropic composition is disrupted, resulting in higher boiling points for the remaining components, which requires a higher temperature
Firstly, the amount of epichlorohydrin in the epichlorohydrin wastewater is significantly excessive. For an azeotrope, the composition remains constant; therefore, during the distillation of this wastewater, there will be an epichlorohydrin azeotrope phase and an epichlorohydrin pure phase. Since the boiling point of epichlorohydrin is 118°C, the operating temperature of the distillation tower must be relatively high.
I’m studying*, and I’ve also encountered an azeotrope problem recently
Check what the composition levels of water and epichlorohydrin are