Two issues that remain unclear in the ethyl acetate solvent recovery process
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The ethyl acetate solvent used in a certain process, which contains small amounts of toluene, dichloromethane, and water (all at levels of less than 10%), is recovered through distillation. The process steps are as follows: The ethyl acetate feed is pumped into the distillation column for separation; once a certain liquid level is reached in the bottom of the column, a reboiler is installed there to heat the liquid at the bottom. The vapor rises to the condenser at the top of the column, after which the feed is again pumped to the top of the column for further separation. The condensed liquid phase enters the oil-water separation tank; the entire water phase is removed, while the oil phase is pumped back using a reflux pump. After the reflux ratio is controlled, part of this oil phase is refluxed to the top of the tower and another part is removed, cooled in a cooler, and collected as an aqueous dichloromethane fraction, which is then placed in a fraction collection tank. I would like to ask: 1. In a distillation column, feed is first added at the bottom of the column and then at the top – what is the reason for this? I haven’t figured it out yet~ 2. Toluene is highly insoluble in water, dichloromethane is slightly soluble in water, while ethyl acetate is soluble in water but to a limited extent. Among these, dichloromethane has the lowest boiling point; therefore, after all the water phase has been removed, part of it returns to the top of the reflux tower, and the other part can be cooled down so that dichloromethane can be collected first? Additionally, can ethyl acetate and dichloromethane form an azeotrope, given that the difference in their boiling points is 37°C?
During distillation, the substances with lower boiling points must be separated first; otherwise, the system cannot reach equilibrium. Your case is definitely bottom feeding. Ethyl acetate and dichloromethane are definitely a new azeotrope; the water separation can only be carried out after the azeotropy between dichloromethane and ethyl acetate has been reached
1. In a distillation column, feeding is first done at the bottom of the column and then switched to feeding at the top – why? I haven’t figured it out yet~ The purpose of this operation is to remove water from the feed, and heterogeneous azeotropic distillation is used for that; the aqueous phase resulting from condensation and phase separation is taken as the product at the top of the tower, while ethyl ester along with trace amounts of toluene are obtained at the bottom of the tower. Initially, feeding at the bottom of the tower was intended to vaporize the light components of dichloromethane first, before proceeding with heterogeneous azeotropic distillation. 2. Toluene is highly insoluble in water, dichloromethane is slightly soluble in water, and ethyl acetate is soluble in water but to a limited extent. Among these, dichloromethane has the lowest boiling point; therefore, after all the water phase has been removed, part of it returns to the top of the reflux tower while another part is cooled, allowing dichloromethane to be collected first Additionally, can ethyl acetate and dichloromethane form an azeotrope, given that the difference in their boiling points is 37°C? If the amount of dichloromethane is small, even in the presence of an azeotrope, it is possible to choose direct evaporation since its quantity is low; there will just be a slight loss of ethyl ester