Problems with vacuum distillation

This question is not very professional. What do you mean by \"can primary vacuum distillation separate two substances with a boiling point of only around 9 degrees\"? Separation is certainly possible, provided that there are enough theoretical plates and the column is tall enough (a temperature difference of 9 degrees is definitely sufficient for separation). However, detailed process calculations are necessary; it’s not certain what level of vacuum should be used. If the properties of the material are stable, then normal-pressure distillation can also be used. The main purpose of vacuum distillation is to reduce the temperature in the reactor (this is done because the material has a high boiling point under normal pressure or because it is a heat-sensitive substance that decomposes easily when heated). So your question is a bit confusing; without knowing the specific details, it’s impossible to address your issue!

Agree with what was said above. Generally, separation requirements are theoretically achievable; it also depends on economic viability and feasibility. With a boiling point difference of nine degrees, does it belong to thermosensitive substances? Are they homologs? Vacuum distillation has two advantages: one is that it allows the relative volatility to be increased appropriately ； Secondly, it can reduce the operating temperature of the tower bottom, thereby lowering the requirements for the quality of the heat transfer medium. Therefore, a specific analysis must be conducted for each particular system.

Characteristics of vacuum distillation: 1. Under reduced pressure, the relative volatility of the mixture decreases； 2. Under reduced pressure, the volume of the gas increases, resulting in a decrease in the processing capacity per unit of tower ； 3. Under reduced pressure, the bubble point of a substance decreases, making it easier to carry out production using low-pressure steam ； 4. As mentioned above, reduce thermal decomposition. This post was last edited by yzhms on 2008-1-19 21:02.]

The poster is referring to ordinary chemical experiments

The effects of reduced pressure are not necessarily good or bad. It depends on the equilibrium relationships of the specific separated system.

Reasons for using reduced pressure: First, materials are prone to deterioration at high temperatures, such as polymerization, decomposition, carbonization, and so on； II. Energy consumption: Reducing pressure can lower the boiling point of materials, thereby saving energy ； However, decompression itself also requires considerable energy; it is necessary to compare the energy consumption associated with high temperatures and that associated with decompression ； III. For some materials, reducing pressure can achieve a better separation effect. As for whether a temperature difference of only 9 degrees is sufficient for separation, as #2 said, as long as the tower is tall enough, separation is definitely possible; this has nothing to do with pressure.

Theoretically, a boiling point difference of a few degrees is more than sufficient for separation; this can be achieved by increasing the number of theoretical stages and raising the reflux ratio. I have also been in contact with molecular distillation (also known as short-path distillation), and I find that this type of equipment is capable of rapidly separating streams at low vacuum levels (with a absolute pressure of just a few Pa). It is suitable for handling heat-sensitive materials; you might want to take a look at it

Agreed. A temperature difference of nine degrees is definitely sufficient to separate them. I think the temperature difference between the separated substances here is even smaller

Agree with the opinion from the second floor; specific situations need to be analyzed on a case-by-case basis

Is it possible for an azeotrope to form? If there is light-induced pressure reduction, then it’s not possible

Some chemical engineering software can be used for testing, such as ASPEN

Reasons for using reduced pressure: First, under reduced pressure, the equilibrium temperature decreases, and a will increase, which is beneficial for separation； Second, a more important reason is that lowering the temperature can reduce degradation or polymerization losses. As for the issue of whether separation is possible with only a 9-degree temperature difference, as long as the tower is tall enough, separation is definitely achievable. This has something to do with pressure, but not much.

Distillation becomes more difficult after pressure reduction. Tianjin Beiyang Tongchuang Distillation Equipment Company has extensive experience in distillation towers; you can contact them for their advice