DMF distillation
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For DMF distillation, the recovery concentration must be controlled at over 99.2%. The raw material has a concentration of 94%, with water and other impurities present. After initial equilibrium at the desired temperature, water is distilled; once all the water has been distilled, DMF distillation begins, with a reflux to extraction ratio of 7:1, and the product concentration is 99.2% ； Subsequently, the recovery ratio was gradually increased to 6:1, 5:1, 4:1, 2:1, 1:1; in the later stages, the product concentration ranged from a maximum of 98.5 to a minimum of 89. The vacuum level remains at -0.89 MPa. What is the problem? Is the reflux ratio not appropriate? Please give me some advice!
It’s impossible to determine without all the information; distilled water and DMF are likely processed in separate columns, as DMF decomposes into formic acid at high temperatures
For one tower, remove the water first. Redistill DMF under high vacuum!
There’s a problem with your approach. First, water is distilled off, and then DMF. If you try to obtain more of DMF at this stage, using a low reflux ratio may result in an increase in impurity levels. You need to pay close attention to the temperature at the top of the tower; especially the temperature when the material is discharged at a ratio of 7:1, as it indicates the composition of the material. If you want to increase the yield, you can lower the temperature of the reactor bottom at this time, and control the temperature of the output material so that it reaches the desired level. That will do; if the temperature of the reactor bottom isn’t lowered, impurities will still be carried over in large quantities
Two batches have been produced so far; a small amount of water is removed first, and once the temperature at the top of the tower stabilizes and the concentration is found to be satisfactory, the reflux ratio is adjusted to reach an equilibrium state. Currently, the moisture content of the finished products ranges from a maximum of 0.8% to a minimum of 0.1%, with an average moisture content of 0.4%.
First, it is necessary to determine whether the impurity is heavier than DMF. If so, there is something wrong with your approach. For intermittent distillation, a purer DMF is required at the bottom of the tower; the reflux ratio should be increased gradually, rather than using the method you employed.