Distillation separation problems of ethyl glycolate
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This post was last written by hu_Edited by di on 2009-10-29 21:04 I am doing my graduation thesis, and the research topic is the synthesis of ethyl glycolate. The content of ethyl glycolate in the product I synthesized has reached 75%. According to the information, use vacuum distillation to separate the target product, and collect the fractions at 68 C/25mmHg or 77~78C/42mmHg. The boiling point of ethyl glycolate is known to be 158-159 C. The raw material liquid contains the target product, ethanol, and catalyst p-toluenesulfonic acid. The difficulty of the subject is actually the distillation and separation section. The problem is as follows: The problem now is that when the temperature rises to 80 C and the vacuum degree is 0.02MPa, the distillation speed is very slow and can only reach 1 drop/2 minutes. The viscosity of the material gradually increases and finally polymerizes into a white paste. It is suspected that the acidic catalyst has not been neutralized. The hydroxyl group of glycolic acid or glycolic acid ester is very active and easy to react. Please lend a helping hand, help me, and guide the separation experiment. If I can't do it, the instructor won't graduate me, and now I'm stumped by this problem!
Make a suggestion: 1) Whether p-toluenesulfonic acid can precipitate p-toluenesulfonate by adding a suitable base. Filter and remove before separation.
suggestion: 1. Esters themselves are unstable when heated under acid and alkali conditions, so they must be removed. * * Sulfonic acid, since the target product is a small molecule with hydroxyl groups and has a certain solubility in water, you can consider using concentrated ammonia to neutralize it, and then filter it with suction to remove the catalyst. ； 2. The substance polymerizes or carbonizes at high temperatures. You can consider lowering the temperature, such as steam distillation, and then removing the water, or using an oil pump to increase the pumping rate, which can significantly lower the boiling point.