Two questions regarding evaporation and catalysts in the polyoxymethylene production process
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This post was last edited by *nht1 on 2024-12-16 at 13:24. Hello everyone, I have been researching the production process of polyoxymethylene recently, and there are a few points I don’t quite understand. One of them is the process of concentrating formaldehyde – specifically, concentrating 40% formaldehyde to 70%. This is done through vacuum evaporation, during which water is vaporized and only formaldehyde remains in the liquid phase. However, since formaldehyde has a very low boiling point, it should be the one to evaporate first. So why is it that water is vaporized while formaldehyde gets concentrated? The other point is that in the production of triomethylenetetrahydrofuran, concentrated formaldehyde requires sulfuric acid as a catalyst. Sulfuric acid, being used as a catalyst, is a consumable material – but where does it go? There is also no step to remove sulfuric acid later on. Thank you!
Hello, regarding your two questions: 1. The boiling point of formaldehyde is indeed lower than that of water (around -19°C), but during vacuum evaporation, it is easier to evaporate water rather than formaldehyde by adjusting the pressure and temperature. This process is mainly because formaldehyde usually exists in the form of an aqueous solution; when the water is removed, the concentration of formaldehyde in the remaining liquid increases. 2. Regarding the use of sulfuric acid as a catalyst, it plays a role in accelerating the reaction during the production of trioxane, but it does not end up being part of the final product. Under normal circumstances, sulfuric acid is not completely consumed; most of it can be recovered through post-treatment processes such as neutralization and distillation. If the step for removing sulfuric acid is not explicitly stated, it may be because this process is omitted in the detailed process flow or integrated into other steps. I hope these explanations are helpful to you! .
Thank you for your reply; it seems you have a good understanding of the polyoxymethylene manufacturing process. I hope to have the opportunity to ask you more questions!
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The concentration process primarily relies on vacuum to lower the boiling point, allowing most of the water to be removed through flash evaporation; some formaldehyde is also removed during this process, but in relatively smaller quantities compared to the water
Theoretically, sulfuric acid is not a consumable, but in actual production, there is an acid discharge process during which the hydrogen ions are eventually neutralized by an alkaline solution. It was finally discharged
Positive pressure means that the phase with a lower boiling point is the gas phase, while negative pressure is the opposite. Therefore, there are two methods for concentrating formaldehyde solution: pressurization and depressurization