Does vinyl chloride have an azeotrope with water?
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During the distillation of recycled vinyl chloride monomer, high-boiling substances such as dichloroethane and formaldehyde can be effectively removed, but water (which is also a high-boiling substance) cannot be removed; its level remains almost unchanged before and after distillation (around 500 ppm). Do vinyl chloride and water form an azeotrope that cannot be separated? In the PVC industry, vinyl chloride dehydration is generally achieved through solid alkali drying, molecular sieve drying, or agglomerator dehydration. Aside from preventing self-polymerization in tall towers, is distillation not capable of removing water at all?
This post was last edited by qugd on 2022-1-30 09:59. In the case of a two-component azeotrope, the proportion of each component is generally not so extreme; moreover, the boiling point of vinyl chloride is around -14 degrees, so it is unlikely that it can form an azeotrope with water. There must be some issue with the water removal and drying steps in your manufacturing process. In the process of removing water from organic substances, distillation is sometimes used for this purpose, but it seems not to work well for vinyl chloride. Among the hydrocarbons I’ve seen, water removal is most commonly achieved by treating reforming feedstock, and distillation can reduce the water content to below 10 ppm.
Thank you for your reply. The New Year is coming tomorrow; wish you a happy New Year! Everything goes well! Perhaps my post wasn’t clear enough; my question is this: For example, when using a high-boiling tower (tray tower) to distill dichloroethane, it’s possible to achieve a concentration of ~300 ppm in the feed material, with the concentration falling to ≤5 ppm after distillation ； The water content in the feed to the tower is around 500 ppm; after distillation, it remains almost unchanged at around 500 ppm as well. We did not carry out any water removal treatment before distilling the monomer. The volatility differences between water and vinyl chloride are also quite significant; then why can’t the water content be reduced through distillation?
For the drying and water removal of vinyl chloride, the reliable methods at present are the solid alkali method and pressure swing adsorption. Some patents for other methods either represent improvements to pressure swing adsorption or involve the use of additional agents that work in conjunction with solid alkali to remove water. There are no mature reports on the use of distillation for water removal.