What Is a Reflux Condenser?

Vasanth S.
Vasanth S.
Some reflux condensers use a dry ice and acetone mixture.
Some reflux condensers use a dry ice and acetone mixture.

A reflux condenser is a laboratory glassware that is used to cool vapors. It consists of a glass tube encased in a glass cylinder. The tube connects the fractioning column with a flask and carries hot vapors produced from heating. Water is contained the glass cylinder; the water is pumped in and out of the cylinder through its side arms. The water cools the vapor within the tube and condenses it. The are two kinds of reflux condensers.

As the vapor condenses, it flows back into the reaction flask. This reduces the amount of solvent that is lost during the reaction. In addition, the reaction can be carried out over an extended period of time since the solvent is recycled back into the reaction flask.

The condenser is mainly used in the distillation process. A distillation is the separation of two liquids by heating. The liquid with the lower boiling point will vaporize first. It is converted back into a liquid inside the condenser. If the condenser deposits the liquid back in the reaction flask, it is called a reflux condenser.

There are two types of reflux condensers: air cooled and water cooled. The common air cooled reflux condensers include the air condenser and the Vigreux condenser. A Liebig condenser is the simplest water cooled reflux condenser. The Dimroth condenser and the Graham condenser are two other water cooled reflux condensers.

The air cooled reflux condenser only has one glass tube, and the vapors condense on the glass as they are cooled by the air. Some air cooled reflux condensers are filled with glass beads to aid in the condensation process. The Vigreux condenser features a series of indentations designed to increase the amount of surface area available for the vapor to condense on.

A water cooled reflux condenser has two glass tubes. The inner tube carries the hot vapor, while the outer tube carries the water. Water is used to cool the vapor. The Liebig condenser features a straight inner tube, while the Graham condenser has a spiral inner tube. There is a double spiral tube within the Dimroth condenser.

Generally, water is used to cool the vapor in water cooled reflux condensers, but there are other solvents which can be used to cool the vapor. These include ethanol and a dry ice and acetone mixture. These solvents are typically used when the reaction involves liquids which boil at a temperature that is below 32° F (0° C).

Why Is a Reflux Condenser Used?

Before exploring the broader purposes of reflux condensers, a quick review of the vaporization process may be useful. Applying heat to a liquid eventually changes it into a gaseous form. This happens at a specific boiling point temperature. For instance, water boils at 212° Fahrenheit at sea level with around 1,000 millibars of atmospheric pressure. Heat causes liquid molecules to vibrate faster and escape into the air.

As mentioned earlier, a reflux condenser helps return vapors back into liquid form. You may also see the term "knockback condenser" because that's essentially what they do — knock vapors back into liquid. Otherwise, vapor molecules can stay in the local atmosphere. In the case of water, this may impact humidity levels. On a broader scale, evaporated water comprises clouds that later release precipitation as part of our planet's water cycle.

Reflux Condenser Applications

Chemists and engineers use reflux condensers when they need to speed up specific thermal reactions. Reflux condensers allow them to continue thermal reactions without losing more solvent than necessary. They can maintain constant controlled high temperatures during those thermal reactions for longer periods of time. This is imperative in laboratory and industrial settings during organic synthesis, the intentional creation of organic compounds.

Organic synthesis plays an important role in creating new products. Pharmaceuticals and polymers are just a couple of examples. Organic synthesis is a major component of product and technology developments in many fields: manufacturing, scientific and academic research, electronics and agriculture, just to name a few. It's also key in food and drink production, especially in distilling alcoholic beverages such as vodka and gin. Without reflux condensers, creating these products would be inefficient or even impossible.

How To Use a Reflux Condenser

At its essence, using a reflux condenser is easy. However, successful usage begins with a proper setup. Your unique setup will depend on your production environment, but you can take the basic principles and apply them as you see fit. A typical reflux condenser assembly consists of some key components:

  • Heating mantle or apparatus
  • Container for the reactants
  • Condenser chamber or tube
  • Cooling apparatus around condenser

You can think of a reflux condenser somewhat like putting a lid on a pot of boiling water. The water never exceeds its boiling point temperature while in liquid form, but gaseous water can become far hotter than 212° F. The pot lid's temperature is lower than that of the steam, so it cools down the water vapor enough to change it back into a liquid state. With proper reflux condenser setup, that's exactly what will happen to any solvent that initially evaporates while being heated.

When connecting your reflux condenser, you'll also need to include solid connections. These will prevent solvent vapor from escaping, in turn reducing any loss of volume. Depending on the setting, these connectors will typically include some sort of tubing or piping. Secure connectors also include any metal joints, fittings and wiring needed to stop leaks or tubing that unexpectedly unlinks or bursts during the extended reaction time.

What Is the Advantage of a Reflux Condenser?

Reflux condensers permit extended heating times during organic synthesis. While this process has a huge range of applications, we can look at beverage distilling to understand its basic advantages. While brewing alcohol at home is usually illegal, we can see the process to understand how reflux condensers aid in the process. Commercial distilling uses similar principles.

The Science of Brewing

Reflux stills use the same process as a laboratory reflux condenser. But before the real brewing begins, you must first have a mash. It's a mixture of ingredients that includes grains along with other foods with high starch content — potatoes, molasses or corn, for example. The primary grain in the mixture is a malt, which contains enzymes that can deconstruct starches in the mash into sugars.

The first stage in creating a brew begins with heating the mash. Consistent heat over long periods of time causes the mash to undergo chemical reactions, producing a sugary liquid called wort. Distillers combine brewer's yeast with wort, resulting in a fermented mixture.

Once fermentation is complete, the strained mixture is placed into the kettle of the reflux still and heated to a constant temperature. Vapor rising through the condenser is cooled, with the liquid dripping back down. This process repeats until only the compound with the lowest boiling point remains. That compound drips out as liquid alcohol. The first bits of liquid are discarded to avoid toxic compounds. The rest is filtered as needed to produce the final product.

Discussion Comments

megh

I have an essential oil distiller with a graham water-cooled condenser. I've got aquarium tubing hooked up to it but I can't seem to find an attachment to hook up to a water supply (e.g. my sink). Any help would appreciated!

lluviaporos

@irontoenail - I didn't think of myself as a mad scientist so much as a general adventurer, like McGyver or something.

The experiment we did was using the reflux condenser to purify salt water, you see, and I could easily imagine doing that on a deserted island or something.

The only problem I could see was that we had to use water in order to cool down and condense the vapors, which didn't seem very efficient.

But then I realized that I was being an idiot and you could just as easily use cold salt water for that. You don't need to use tap water.

Of course, in reality I'm not likely to be able to whip out a reflux condenser if I ever got stuck on a desert island.

I'd have to make one out of coconuts and bamboo!

irontoenail

@Mor - Actually, distillation was interesting to me because it was one of the few things we did in chemistry that I could directly relate to real life. In lots of different ways, too, although since I was a bit of a capitalist when I was a student, my mind was dancing with different schemes after we did it, like distilling the roses in my mother's garden to get rose oil to sell.

Of course, when I found out it takes something like 10,000 pounds of roses to make one ounce of rose oil, I gave up on the idea.

Even if I had managed to get together all the equipment needed for the distillation, my mother's garden would have barely given me a drop.

It's too bad, because I really fancied myself as a mad scientist as well. And a reflux condenser does seem to be a vital piece of equipment for such a profession.

Mor

I always found distillation kind of exciting in chemistry classes at high school. I guess I really liked the idea of setting up what seemed like a fair amount of equipment (to me, as a high school student anyway) to do something that seemed like it was out of a genuine mad scientist movie.

Boiling a liquid, allowing it to separate and drip down into another container... it was interesting. And even better if you ended up with something of a different color at the end of it.

I guess I was thinking about the aesthetics of the act rather than what we were actually doing, but that's better than hating chemistry I suppose.

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    • Some reflux condensers use a dry ice and acetone mixture.
      By: Jane Doe
      Some reflux condensers use a dry ice and acetone mixture.