Benzyl alcohol distillation problem – seeking help from experts

First, consider the thermal insulation performance of the tower. Secondly, are there any improvements in the process operations? I encountered similar problems when producing m-diphenyl ether in my production facility before; chlorobenzene could be separated easily, but m-cresol was difficult to separate, resulting in a large amount of m-diphenyl ether being carried over. Later, a condenser (similar to a reboiler) was added to the upper part of the tower to allow intermittent water inlet and outlet, and the problem was solved; however, the operation was rather cumbersome.

Dude, is your cooler installed at the top of the tower or near it? Does it use cold water circulation to force the heavy components to stay below the top of the tower?

It is located near the top of the tower, and cold water circulation is used to force the heavier components to not rise to the top of the tower.

So what you mean is that there is no pipeline for removing the light components from the top of the pressure reduction tower; therefore, those light components must be removed earlier in the process. Even with a high reflux ratio, benzyl alcohol still contains dibenzyl ether, which indicates that too much benzyl alcohol was extracted. Based on material balance calculations, we can figure out how many tons need to be extracted; with some fine-tuning, it should be possible to gradually achieve the desired purity level. Regarding what you said – that \"keeping the temperature at the top of the tower below 80–100°C (the boiling points of benzaldehyde or benzyl chloride at -0.09 MPa) will basically prevent backflow\" – I think you’re confusing temperature with backflow. If backflow isn’t caused by non-condensable gases, then there’s no gas rising in the tower, and it makes little sense to keep the temperature below 80–100°C. Therefore, it’s necessary to increase the amount of vapor used for reboiling in order to establish backflow, and then reduce the draw rate; this should suffice to achieve the desired results. I hope this helps!

Thank you; it’s indeed a good plan

Is there any difference from reflux? ? ? ? ? ? ? ? ? Isn’t that just the same as increasing the backflow?

Yes, our distillation column does not have side streams; it is not a continuous distillation process. Temperature control at various stages is used, with the light components as well as the product coming out from the top of the column. Currently, in the initial distillation stage, I want to extract light components such as benzaldehyde, but benzyl alcohol will also rise to the top. Dibenzyl ether, on the other hand, will not reach the top, as the total amount of light components in the initial distillation stage accounts for only 3% of the crude product. If a large amount of reflux is needed, it is likely due to benzyl alcohol. The temperature at the top of the column still needs to reach the boiling point of benzyl alcohol

But this reflux does not pass through the top of the tower; it is equivalent to internal reflux within the tower, with the heavier components not passing through the tower top

Once the tower equilibrium is established, the heavy components also do not pass through the top of the tower

In the removal of the light fraction, my product benzyl alcohol is the heavier component; however, the amount of this light fraction is very small. If reflux is to occur, benzyl alcohol still needs to pass through the top of the tower. Do you mean that once equilibrium is established, it is the lighter components that are recycled?