May I ask which expert designed the toluene dehydration process?
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This post was last edited by jianzhen on 2022-1-10 at 15:03. As the title suggests, can the dehydration of toluene be achieved through simple distillation? Require reduction from 5000 ppm to 20 ppm
The toluene dehydration process utilizes the principle of azeotropic distillation; the toluene/water azeotrope is vaporized at the top of the tower, condensed in a condenser, and then sent to a decanter for separation. The toluene phase is recycled, while the water phase is discharged to the wastewater treatment system. The toluene content in the vapor from the top of the control tower can be kept appropriately higher than that of the azeotrope composition, allowing the requirement to reduce the water content in the tower feed from 5000 ppm to 20 ppm to be met.
I was wondering what criteria the expert used to determine that this is achievable; I did some manual calculations, and it seems that around 30 theoretical plates would be sufficient
Judging from the difference of over 26 degrees between the azeotrope point of toluene/water and the normal boiling point of toluene, separation should be relatively easy.
The level at the bottom needs to reach 200 ppm; I’m not sure if that can be achieved
Pure toluene is easy to handle; it becomes more difficult when there are impurities in the amount of a few parts per thousand. Osmotic vaporization could be considered; molecular sieve membranes can reduce toluene levels to 20PPM. The advantage is slight energy savings, while the disadvantage is that the equipment is somewhat expensive. .
Molecular sieves can also be used; they are relatively inexpensive
At room temperature, the solubility of water in toluene is 500–800 wtppm; if there are also small amounts of free water droplets present, the water content can reach several thousand wtppm. If the material processing rate exceeds several tons per hour, the investment in molecular sieve adsorption for dehydration along with the costs associated with its regeneration are too high; in such cases, azeotropic distillation for dehydration is a more economical option. It should be relatively easy to achieve a dehydration level of 50 wtppm, while reaching 30 wtppm requires stable operating conditions. Approximately 30 theoretical plates should be sufficient, and the required reflux ratio (the ratio of the reflux flow to the feed flow) is also low, typically ranging from 0.1 to 0.2. If the moisture content is required to be reduced to trace levels of 20 wtppm, a combined approach of azeotropic distillation dehydration and molecular sieve adsorption dehydration can be employed.
It is recommended to use distillation to remove most of the water, and then employ molecular sieves to reduce the water content to below 20PPM; this way, the operating costs for molecular sieve dehydration will be very low.
Master, does the reflux ratio need to be relatively high?
I have carried out the dehydration of butyl acetate, reducing the concentration from 5000 ppm to 1000 ppm, as that is all required for the final product. Full reflux water cutting will do. If you want it even lower, you can cut off a part of the material first and then finish the product.