science

Reactive distillation

Reactive distillation is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Reactive distillation rather than just read about it. In short: Reactive distillation is a process where the chemical reactor is also the still. Separation of the product from the reaction mixture does not need a separate distillation step which saves energy (for heating) and materials.

Key takeaways

Reactive distillation belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Reactive distillation to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Reactive distillation from memory before moving on to harder problems.

Reference excerpt

Reactive distillation is a process where the chemical reactor is also the still. Separation of the product from the reaction mixture does not need a separate distillation step which saves energy (for heating) and materials. This technique can be useful for equilibrium-limited reactions such as esterification and ester hydrolysis reactions. Conversion can be increased beyond what is expected by the equilibrium due to the continuous removal of reaction products from the reactive zone. This approach can also reduce capital and investment costs. The conditions in the reactive column are suboptimal both as a chemical reactor and as a distillation column, since the reactive column combines these. The introduction of an in situ separation process in the reaction zone or vice versa leads to complex interactions between vapor–liquid equilibrium, mass transfer rates, diffusion and chemical kinetics, which poses a great challenge for design and synthesis of these systems. Side reactors, where a separate column feeds a reactor and vice versa, are better for some reactions, if the optimal conditions of distillation and reaction differ too much.

Applicable processes Reactive distillation can be used with a wide variety of chemistries, including the following:

Acetylation Aldol condensation Alkylation Amination Dehydration Esterification Etherification Hydrolysis Isomerization Neutralization Oligomerization Transesterification Hydrodesulfurization of light oil fractions

Examples The esterification of acetic acid with alcohols including methanol, n-butanol, ethanol, isobutanol, and amyl alcohol. Another interesting feature of this system is that it is associated with the formation of a minimum boiling ternary azeotrope of ester, alcohol and water, which is heterogeneous in nature. Hence, in a typical reactive distillation column that consists of both reactive and non-reactive zones, the heterogeneous azeotrope or a composition close to the azeotrope can be obtained as the distillate product. Moreover, the aqueous phase that forms after the condensation of the vapor is almost pure water. Depending on the requirement either of the phases can be withdrawn as a product and the other phase can be recycled back as reflux. The pure ester i.e. butyl acetate, being the least volatile component in the system, is realized as a bottom product. Removing organic acids from aqueous alcohol (ethanol, isopropanol) in dewatering columns is a simple example. An aqueous base (NaOH, KOH) is added to the top of the column, acid-base reactions occur in the column, and the resulting organic salts and excess base exit the bottom of the column with the separated water.

References

Worked examples

Example 1 — a first encounter with Reactive distillation

Start with the simplest possible case. Write down what Reactive distillation claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Reactive distillation before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Reactive distillation ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Reactive distillation

In research: Reactive distillation appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Reactive distillation in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Reactive distillation is common in secondary-school and first-year university syllabi. It links to neighbouring topics Distillation, so understanding it makes those chapters shorter.
In everyday life: Look for Reactive distillation outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Reactive distillation in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Reactive distillation means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Reactive distillation out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Reactive distillation in simple terms?

Why does Reactive distillation matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Reactive distillation?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Reactive distillation.