Distillation is a process of separating the component substances from a liquid mixture by selective evaporation and condensation. A large variety of equipment is utilized to perform distillations in a laboratory setting. In older times, distillation apparatus was connected with rubber stoppers and glass tubes; however, in modern practice, ground glass joints are far more common due to their versatility and ease of use.
- 1 Types of Distillation
- 2 Flasks
- 3 Condensers
- 4 Columns
- 5 Adapters
- 6 Heating devices
- 7 Stirring devices
- 8 Miscellaneous
Types of Distillation
Simple distillation is a process in which vapors from the boiling flask are directly fed into the condenser. This process is primarily used to separate mixtures of liquids with significantly different boiling points.
In fractional distillation, the vapors are fed through a fractionating column before entering the condenser. Cycles of vaporization and condensation within the column improves separation and allows liquids of much closer boiling points to be separated.
A vacuum distillation is any distillation conducted under reduced pressure. Reducing the pressure lowers the boiling points of the liquids in the mixture, allowing high-boiling mixtures to be easier to separate.
Flasks are commonly used for both the boiling vessel and receiver. Several types of flasks are listed below:
The Erlenmeyer flask has a conical shape and flat bottom. It has the advantage of being able to stand freely without needing a clamp and ring stand.
Round-bottom flasks are globe-shaped; they require a ring stand and clamp to stay upright. Multi-neck variations are common.
Wurtz, Engler and Claisen flasks
Round-bottom flasks with side arms, used with old condensers with no ground glass joints. The side arm is connected with the condenser through a rubber bung. These flasks are essentially their own still heads. The Claisen flask has an extra neck, from which the side arm branches.
These flasks also have a globular shape, but the bottom is flat. Subsequently, they can be freestanding without a clamp and ring stand.
Used in rotary evaporators and other special applications.
Flasks may have more than one neck. This allows for the attachment of additional apparatus to make a more complex system.
This ancient flask is notable for being its own condenser, its own still head and generally its own entire kit and kaboodle. A retort does not need any additional condensers and other parts, only a receiving flask. It provides crude simple distillation and cannot be used for fractional distillation, but it is useful as a low-cost all-glass apparatus for distilling aggressive liquids such as nitric acid.
This is a flask, usually pear-shaped, which is its own fractionating column (its neck functions as an air condenser and is indented like a Snyder column). The Favorsky flask is also usually its own still head, with a side arm (modern specimens have ground-glass side arms).
Condensers are used to convert gaseous vapor into liquid in a process called condensation.
The Liebig condenser is the simplest type of water cooled condenser. It consists of a straight tube as the vapor path which is surrounded by an outer jacket for the coolant path.
The Graham condenser is a very highly efficient distillation condenser. The vapor path is a tightly coiled tube surrounded by a water jacket, so it acts like a very long Liebig condenser.
The Friedrichs condenser is a complex type of condenser that is very efficient and can be used for both reflux and distillation. It consists of an internal cold finger that is filled with coolant that has a spiral path shaped into it which the vapor phase flows onto. Condensate flows down this spiral path.
Columns are used in fractional distillation to aid in the separation of mixtures of liquids with closer boiling points. They can also function as air-cooled condensers; such use is recommended with very high-boiling liquids, such as sulfuric acid, which can induce thermal cracking in water-cooled condensers.
A Vigreux column is a glass tube lined with many indentations pointing towards the center. The indentations serve to increase internal surface area, resulting in more efficient vaporization/condensation cycles. This leads to better separations of liquids with closer boiling points.
Similar to the Vigreux column, the Snyder column differs in shape: it has indentations in form of inverted teardrops.
Various distillation adapters are used to connect together the rest of the apparatus.
A still head is a three-way glass adapter. Usually, one tube of the adapter is set pointing downwards at a 75 degree angle relative to vertical. It connects the boiling flask to the condenser, and the third tube is generally used in conjunction with a thermometer to measure the temperature of the vapor.
This is an adapter containing a drip tube and hose barb. It is used to evacuate the apparatus when a vacuum distillation is performed. It can also be used in combination with a length of hose to lead vapors from the setup to a safer location for disposal. Alternately, it can divert vapors to a scrubber. There are two varieties of this adapter: some are straight and others have a 105 degree bend.
This adapter has two upper joints connected to one lower joint. This allows the attachment of additional apparatus to the system.
This adapter allows a thermometer to reach into the system while still maintaining an airtight seal.
This device consists of a heating element incorporated into a ceramic or metallic plate. It is often coupled with a magnetic stirrer. Hot plates are often used with a water or oil bath to provide even heating to the boiling flask.
Open flame heating devices
Spirit lamps and Bunsen burners are useful for distilling non-flammable liquids. They do not require electricity, but the Bunsen burner requires a gas main.
A thermometer is used to measure the temperature of the vapor passing into the condenser.