What should I do if the high boiling matter in the monomer exceeds the standard?
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Nowadays, the quality requirements for monomers are high, but high-boiling substances often appear to be unqualified during operation. How to control high-boiling substances in monomers? Thank you!
To control the content of high-boiling substances, it is mainly necessary to control the operation of the high-boiling tower, such as the temperature of the tower kettle, the reflux ratio, and the residual liquid at the bottom of the high-boiling tower. In addition, the molecular ratio and reaction temperature of the reaction should also be well controlled.
1. After exceeding the standard, the only way to adjust the fractionation control parameters is to reduce the temperature of the high tower kettle, appropriately increase the tower top pressure, and increase the reflux ratio.； 2. If possible, re-distillate the unqualified monomers ； 3. Reduce the polymerization reaction control temperature according to the amount of high boiling matter contained in the monomer.
If the monomer contains high boiling water just after starting the machine, it is normal. It usually takes a few days. If it is always like this, first, drain the residual liquid in time. Second, pay attention to the conversion ratio to see if there is excessive hydrogen chloride. The conversion temperature should not be too high.
The presence of lower content of high boilers can eliminate the double bonds of PVC long chain end groups, which has certain benefits for the thermal stability of the resin.； However, if a large amount exceeds the standard, chain transfer and polymerization inhibition will occur. ； Generally, when the content is high, the reaction temperature can be lowered.
Generally, the reasons for high boiling content are as follows:: (1) The content of high boiling matter in crude vinyl chloride is relatively high. A. There is too much hydrogen chloride in the ratio of hydrogen chloride to acetylene, resulting in more high boiling matter. B. The synthesis reaction temperature is too high, and the content of high boiling matter in the synthesis gas increases. (2) The temperature of the condenser at the top of the high tower is too high, and the reflux flow is small (severe space-time tower). (3) The temperature of the high tower kettle is too high (severe space-time tower), and high boiling matter cannot be fully condensed. (4) The residual liquid in the high tower was not treated in time, and the content of high boiling matter was high. (5) The high tower feeds too fast.