Batch vs. Continuous Distillation (Explained!)

Distillation is one of the most useful processes in chemistry. It can separate mixtures into their components, concentrating a product from what was once a reaction mixture. In this post, we’ll be looking at the difference between batch distillation and continuous distillation.

What Is Distillation?

Distillation is the process of separating parts of a (liquid) mixture by boiling the mixture and then condensing the vapor into a separate container. This process is repeated until all that remains is a concentrated version (typically high alcohol content) of the original liquid.

Distillation has many industrial and commercial uses, including the production of alcoholic beverages and perfume. It’s also used in chemistry to separate liquids such as water from more volatile solvents (e.g., essential oils). In geology, it’s used to extract minerals from ores, and in medicine, to produce sterile water or herbal remedies. 

The equipment used to distill is called a still.

What Is Batch Distillation (And How Does It Work?)

The distillation process can be performed in batch or continuous mode. Batch mode refers to the entire process carried out in a single vessel. The process of batch distillation gives the final product a high level of purity. 

How Batch Distillation Works

The following points outline how batch distillation works.

• The wash is poured into a pot still, and the pot is heated.
• As the wash begins to boil, ethanol vapors move up the neck of the still.
• The vapors continue moving through the neck into the lyne arm and the condenser. 
• When vapors cool in the condenser, they turn to liquid form.
• After moving into the condenser, they are distilled in a spirit still.
• After the distillation process in the spirit still, the product is sent to a “spirit safe” vessel where the distiller makes the cuts.

What Is Continuous Distillation (And How Does It Work?)

Continuous distillation is a process that allows you to produce ethanol from a fermented mash of grains and water. The mash is boiled, producing a vapor that’s condensed into ethanol. This can be done repeatedly, so the ethanol concentration increases until it reaches the desired strength. 

The continuous distillation process uses two columns, one called the rectifying column, and the other called the stripping column. The rectifying column contains packing material, also known as trays or plates. Any solids (grains) added with the wash are left on the plates and the vapor moves up the trays. These trays are designed to create small pockets of space for vapor to condense and flow down toward the bottom of the tray. 

A condenser cools down the vapors and turns them back into liquid to be collected in another container.

What’s The Difference Between Batch Distillation And Continuous Distillation?

 Batch distillation and continuous distillation are two methods of separating liquids that use the same basic principles. Both techniques involve boiling a solution, collecting the heads and tails of the resulting vapors, and then returning the vapors to the still for more distillation.

Batch Distillation	Continuous Distillation
Separate components of a mixture in batches.	Separates components of a mixture using a continuous process.
The still is stopped after each process to collect the product.	A product is constantly being produced without interruption.
The batch being distilled can be separated using a single distillation column.	It uses several columns for distilling.
Ideal for small amounts of mixtures that need distilling.	Suitable for large amounts of mixtures that require distilling.

Batch Distillation Column Design

The design of batch distillation columns can be simple or complex depending on factors such as pressure requirements and product purity levels. The following points outline the design.

• The wash is added to a vessel called the batch kettle. This is where the wash gets heated, and it’s often connected to a reboiler.
• The batch column is connected to the batch kettle and collects vapor from the kettle. Sometimes, the column can be connected to the kettle with pipes, and vapor passes through the pipes.
• The reboiler is used to heat the batch kettle. Reboiler tubes are often placed in the liquid to control the heat while providing a consistent supply of heat to the kettle.
• The condenser cools down the vapors and allows them to turn to liquid to be collected in a collecting jar.
• A reflux vessel collects any excess liquids flowing from the condenser. It’s also called a secondary condenser or overhead condenser.
• The section where cuts (heads, tails, and hearts) are made is called the precut, intercut, and pure cut collection vessel. 

Continuous Distillation Column Design

A computer program is often used to monitor the temperature and pressure of the wash at different stages of the process. Here’s an explanation of the continuous column design.

• The feed is introduced at the top of a column, and distillate is withdrawn from the bottom.
• The reboiler provides heat to the top section of the column to vaporize the incoming feed. 
• The vaporized stream then moves down through the packed bed, where it contacts a counter flow of reflux liquid. 
• Vapors are withdrawn from various stages in the column.
• The most common type of continuous distillation column used in industrial processes is packed-column towers with trays or plates as heat exchangers for heating and cooling streams.

Frequently asked questions

Conclusion

Whether you’re just starting or have already put in many years of hard work distilling your spirits, try a few batch experiments to get the hang of it. Then consider the costs and benefits of investing in a continuous still for larger batches. By doing so, you’ll be better able to make an informed decision about finding the best balance between consistency and cost.

Sources:

• Science Direct: Distillation Column-An Overview
• Sciencing: What’s the difference between Reflux and Distillation
• The Scotch Malt Whiskey Society: Battle Royale-Batch Vs Continuous Distillation
• Chemengghelp: Batch Distillation Column Operation and Controls
• Piping Mantra: What is a distillation column?
• Alexander Tsetskhladze: Continuous Distillation Overview