The issue of high pH value of VCM monomer
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The pH value of the VCM monomer is on the high side, around 12-14. I’m not sure what causes this. Could it be due to too fast a flow rate of the monomer, or might the presence of alkali in the solid-alkali dryer be responsible? Are there any other possible reasons? How can this issue be resolved? This post was last edited by redondo5 on 2007-12-29 at 18:30
I suspect the reasons are: 1) The temperature in your caustic scrubber is high, resulting in high moisture content in the crude VCM, which makes it alkaline. ~~~~~~~ Increase the water washing volume and reduce the alkali washing temperature. 2) The cooling and dehydration effect before the crude VCM enters the compressor is poor. ~~~~~~~~ Increase the amount of cooling water before the compressor to lower the temperature of the crude VC. 3) That could be the reason you mentioned, but if that’s indeed the case, the moisture content in the monomer must be quite high. In addition to the above tasks, increase the drainage rate of the water separator behind the full condenser. I’m not sure if the above is correct; please feel free to correct me, experts. This post was last edited by zhx-sdu on 2007-12-30 00:56.]
The main issue is the presence of water in the monomer, as well as the alkaline substances present in the solid-alkali dryer. Our monomer used to be acidic; by increasing the amount of alkaline cleaning agent used, the monomer became alkaline.
Is the alkali washing time too short? Is the concentration too low? I suspect that
A pH of 12 corresponds to an alkalinity of 400, right?
The pH value is also too high. I agree with what the person on floor 5 said – could it be that your solid alkali dryer isn’t draining water in a timely manner?
Personally, I think as long as the alkaline scrubber effectively removes all HCl, and the temperatures of the monomer before and after the machine are low enough, the alkaline tank behind the machine is not necessary. It is recommended to increase the cooling water volume and then drain the water from the alkali tank. This post was last edited by clq20040107 on 2008-1-4 22:19.]
I agree very much with what was said on the 3rd floor. If the moisture content in solid alkali drying is high, alkali loss is likely to occur. This is different from the CaO drying tower.
Measure the pH at the pre-cooler; see what the value is. If it’s not high, it’s definitely due to the loss of alkali in the solid alkali dryer. High saltwater temperatures in the total condenser and the final product condenser, as well as delayed drainage from the steam-water separator, can all lead to high moisture content in the monomer. This problem also occurs when solid alkali drying is used.
That is, just do more measurements and make comparisons, and you’ll know. Monomers with high basicity tend to cause self-polymerization easily.
Test in segments; the likelihood of improper operation of the solid-alkali dryer is high