Distillation column separation problem
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Distillation of multi-component materials, where the light components are primarily water and ethylenediamine; these two substances have an azeotrope. The boiling point of the heavy components at the bottom of the tower is above 145 degrees. The process is carried out using steam at 0.8 Mpa pressure and under a negative pressure of 50 kpa. The current problem is that the water content in the residue at the bottom of the tower cannot be completely removed. Increasing the temperature at the bottom of the tower results in some of the components from the bottom of the tower reaching the top, yet water remains present in the residue. At the bottom is the product material, and water-free conditions are required in the design. I ask the expert to help diagnose the problem.
Both the azeotrope temperature and the boiling point difference of the Reorganization component are 40 degrees; separation should be good at atmospheric pressure. Why consider negative pressure? Based on your current process, the general approach remains the same: appropriately increase the reactor temperature and the reflux ratio, but the exact values required need to be determined through testing.
At first, normal-pressure distillation should be used; once not much water remains in the tank, a slight vacuum should be applied to direct the water into the collectors located before and after the vacuum pump. At this point, the reflux rate should be increased. This method of distillation is relatively inefficient
If the material does not form a salt with hydrochloric acid (does the material dissolve in water as you said? If the material is soluble in water, add alkali to adjust the pH to ≥13; ethylenediamine separates from the alkaline solution, and the upper layer containing ethylenediamine is removed. After that, the aqueous layer and the material are separated. The simplest approach is to use a Roots pump to concentrate the solution and remove the water; there are other methods as well, but they are not listed for now ； If the material is insoluble in water, hydrochloric acid is added first; ethylenediamine reacts with hydrochloric acid to form ethylenediamine hydrochloride, which is soluble in water, and after separation the material can be obtained
Increase the reflux ratio to raise the bottom temperature of the tower. The water content of the feed, the distribution of azeotropic components, and so on all have an impact
We have handled some similar cases before; I’ll check them for you later
You can first refer to the water level of the previous tower; if it falls within the acceptable range, then it’s due to this tower. If the temperature at the reboiler is sufficient and there are also light components, then the feed location needs to be considered; it is possible to raise the feed location slightly to lengthen the stripping section, allowing the light components to evaporate in that section. It is also possible to increase the temperature of the reboiler appropriately; of course, when raising the temperature, reflux must be increased accordingly. When increasing reflux, it is important to monitor the temperature changes on the sensitive plate, so as to allow the light components to evaporate while preventing the liquid in the reboiler from rising too much
The azeotrope temperature should be lower than both of those temperatures