Intermittent distillation constraints

Intermittent distillation is a combination of multiple continuous distillations; its setup involves parameters related to the separation purity and reflux ratio typical of continuous distillation, as well as limits on the amount of vaporization. It also includes specifications regarding the sequence in which materials are extracted and the timing of these extractions, which are unique to intermittent distillation. This makes its setup more complex and requires higher standards, necessitating a thorough understanding of the composition of the components and the order in which they should be separated. I don’t have in-depth knowledge of intermittent distillation; please ask a teacher who has done simulations in this area to explain it in detail.

Thank you, LTY~ What I need to separate are isomers with a boiling point difference of just over two degrees; I’m not sure how to set it up, as it seems impossible to separate them. Please help, experts!

Then your problem is not one of batch distillation versus continuous distillation, but rather the relative volatility of the two components. It is recommended to try operating under low pressure or in a vacuum; if that doesn’t work, then extraction distillation or other methods should be considered.

Personally, I think crystallization separation or extraction methods should be considered; distillation is unlikely to be effective

Based on your description of the problem, it seems to be an issue with simulation. However, I would like to ask a question first: in reality, what method is used to separate these two isomers? As LTY said, things like extractive distillation or low-pressure distillation. The simulation calculations we carry out are based on reality; this reality does not have to be something that you have implemented yourself – it can be the results of experiments conducted by others, or a viable solution derived from theoretical analysis – and then software is used to conduct the simulation calculations. Returning to your question, since the difference in energy is very small, separating isomers is indeed a difficult task. Separation through extraction or other methods is a viable option; you can look up literature to see if there are any experiences from others that can be used as a reference, and then use software for simulation studies. If there really is none, why don’t you analyze the situation and come up with a feasible solution? That would solve the big problem then~ Hehe, good luck!

Thank you all for your advice^_^ Small factories use batch distillation for separation, but of course the yield is relatively low. The boiling points of the two components differ by 3.5 degrees; I made a mistake last time. I have looked into some literature; low-temperature crystallization separation is mainly used. I’ve tried to calculate continuous distillation, and it seems there are no issues with separation; my problem is that I don’t understand the calculations for batch distillation. Hehe, it seems I need to study this more thoroughly*.

Intermittent distillation is a distillation method that lacks a stripping section; the desired distillation result can be achieved by adjusting the reflux ratio over time

Intermittent distillation is a combination of multiple continuous distillations; its setup involves parameters related to the separation purity and reflux ratio typical of continuous distillation, as well as limits on the amount of vaporization. It also includes specifications regarding the sequence in which materials are extracted and the timing of these extractions, which are unique to intermittent distillation. This makes its setup more complex and requires higher standards, necessitating a thorough understanding of the composition of the components and the order in which they should be separated.

Is the guy a parrot or a myna? Looking at the posts on floor 2, they don’t even correct spelling mistakes. Intermittent distillation is a combination of multiple continuous distillations; its setup involves parameters related to the separation purity and reflux ratio typical of continuous distillation, as well as limits on the amount of vaporization. It also includes specifications regarding the sequence in which materials are extracted and the timing of these extractions, which are unique to intermittent distillation. This makes its setup more complex and requires higher standards, necessitating a thorough understanding of the composition of the components and the order in which they should be separated. I don’t have in-depth knowledge of intermittent distillation; please ask a teacher who has done simulations in this area to explain it in detail.

Compared to continuous distillation, the main characteristics of batch distillation are: 1. Unsteady state. The operating conditions are constantly changing, and the liquid level in the tower must be taken into account; for each batch of distillation, various materials such as the early boiling fraction, late boiling fraction, and the product must be collected. 2. There is no stripping section; due to this feature, it is difficult to obtain high-purity high-boiling compounds when the relative volatility is not particularly high on the high-boiling side. In terms of control strategies for batch distillation, there are the full reflux strategy (where the material collected from above serves as the reflux stream buffer), operation with a constant reflux ratio, and operation with a constant top composition (which is quite difficult to control). Intermittent distillation is less efficient and more energy-intensive compared to continuous distillation; its main advantage is that a single column can be used for the separation of multiple components, and it is easier to operate (though this mainly refers to the fact that initial fluctuations have little impact on the product at the top of the column – in reality, it’s quite troublesome). PRO/II’s batch distillation module is quite useful, but the data obtained through careful calculations have limited practical value. Firstly, it’s difficult to accurately account for factors such as the liquid holdup, and Secondly, frequent adjustments are hard to implement in practice.

It seems, as the teacher above mentioned, that batch distillation is more complicated to operate, but it is also more flexible; it isn’t as restricted by time and flow rates as continuous distillation. It appears that batch distillation requires more experience.