Vacuum distillation

We can clean liquids in a special way.

We use less air to make things boil. This helps us save time and energy. It also keeps liquids safe.

Lower air pressure makes things boil at lower heat. This is helpful for liquids that break when they get too hot.

Big factories use this to clean oil. They use tall towers to do this work. Some towers are 50 meters high.

This process can also make fresh water. It takes salt out of ocean water.

It is a very useful way to clean many things.

Distillation is a way to clean liquids. It works by using different boiling points. Boiling point is the heat needed to turn a liquid into gas.

Sometimes, heat can break a liquid. This is called decomposition. To stop this, we use vacuum distillation. This means we use less air pressure. Lower pressure makes liquids boil at lower temperatures. This saves time and power.

Big factories use this to clean crude oil. They use tall towers to do this work. Some towers are 50 meters high. These towers can be 14 meters wide. They can process a lot of oil every day.

This method also helps make fresh water. It is called desalination. We use it to take salt out of ocean water. The water boils at a low heat. Then, the steam turns back into clean water. This way, we can get fresh water to drink.

Vacuum distillation is a special way to clean and separate liquids. It works by using less air pressure than we have around us. This lower pressure makes it easier for liquids to boil. When things boil at lower temperatures, it can save a lot of time and energy. This method is very helpful for substances that might break if they get too hot. This breaking is called decomposition. By using a vacuum, we can purify these sensitive materials safely.

This process works by changing the boiling point of a liquid. Every liquid has a certain temperature where it turns into a gas. In a vacuum, that temperature goes down. You can even calculate this change using a tool called a nomograph. For example, a liquid might boil at 189 °C under normal air pressure. But inside a vacuum apparatus, that same liquid might boil at only 70 °C. This step-by-step change allows scientists to separate different parts of a mixture.

In big oil refineries, vacuum distillation is used on a huge scale. After crude oil is first processed, the leftover oil goes into vacuum columns. These columns are massive structures used to refine petroleum. Some towers are about 50 meters high. They can also be up to 14 meters wide. These giant machines can process 25,400 cubic meters of oil every single day. This helps keep the oil from turning into a thick, sticky substance called coke.

Scientists and engineers have studied these methods for a long time. Researchers like Karl Kolmetz and Andrew W. Sloley have written about designing these columns. They explain how to make them work well for oil and gas. Other people use smaller tools like a rotary evaporator in laboratories. This tool helps concentrate a substance by evaporating the liquid part. Even small businesses, like Empirical Spirits in Copenhagen, use these ideas to make flavored spirits. They use special ingredients like Koji and yeast to create their drinks.

Vacuum distillation is also used to solve a big problem: making fresh water. This process is called desalination. It is used in large plants to take salt out of ocean water. The salt water is put under a vacuum so it boils at a lower heat. The steam from the water is then caught and turned back into clean liquid. This clean water can be used for drinking. This way, we can turn salty ocean water into something useful for everyone.

Vacuum distillation is a specialized method used to separate and purify liquid compounds. It is also known as distillation under reduced pressure. This technique works by lowering the ambient pressure around a substance. This reduction in pressure causes the boiling point of the liquid to drop. Scientists use this method when a compound is difficult to distill at normal pressures. It is also vital when high heat would cause a substance to decompose. Decomposition happens when a chemical structure breaks down due to extreme temperatures.

The mechanism of vacuum distillation relies on the relationship between pressure and temperature. Every liquid has a specific boiling point at standard atmospheric pressure. When you reduce the pressure using a vacuum, the molecules can escape into a gas state more easily. This change can be calculated using a tool called a temperature-pressure nomograph. This tool uses the Clausius–Clapeyron relation to predict how much the boiling point will fall. For example, dimethyl sulfoxide boils at 189 °C at normal pressure. However, inside a vacuum apparatus, it can distill at only 70 °C.

In laboratory settings, different tools are used depending on the substance. Compounds that boil below 150 °C are usually distilled at ambient pressure. For substances with higher boiling points, scientists often use short-path distillation apparatus. Another common tool is the rotary evaporator, or "rotovap." This device helps concentrate or isolate a compound from a solution. It works by evaporating volatile solvents. Even less volatile solvents can be removed if a high vacuum and heat are applied. Environmental agencies even use rotary evaporation to measure solvents in paints and inks.

Industrial-scale vacuum distillation is much larger and serves different purposes. In oil refineries, it is used to process the heavy leftovers from atmospheric distillation. Petroleum crude oil is a complex mixture of hundreds of different hydrocarbons. These molecules can have between 3 and 60 carbon atoms. If crude oil is heated above 370 to 380 °C, it undergoes thermal cracking. This process forms petroleum coke, a thick substance that can plug furnace tubes and pipes. To prevent this, refineries use vacuum distillation to keep operating temperatures below 380 °C.

These industrial vacuum columns are massive engineering feats. They can reach heights of about 50 meters. Their diameters can be as large as 14 to 15 meters. These towers can process feed rates of up to 25,400 cubic meters per day. This is roughly equivalent to 160,000 barrels per day. Because the low pressure increases the volume of the vapor, these columns must be very wide. To maintain a low pressure drop from the top to the bottom, engineers use packing material. This material can be structured sheet metal or random shapes like Raschig rings.

Vacuum distillation is also used for desalination, which is the removal of salt from ocean water. In large plants, ocean water is placed under a vacuum to lower its boiling point. A heat source is applied so the fresh water boils off and is then condensed. This condensation prevents the vacuum chamber from filling with vapor. This allows the process to run continuously without losing vacuum pressure. Some systems use a heat sink to remove heat from the vapor. They often use the incoming cold ocean water as a coolant to preheat the feed.

There are even more specialized versions of this process. Molecular distillation is a form of vacuum distillation performed below 0.01 torr. At this extremely low pressure, the process enters the free molecular flow regime. In this state, the rate of evaporation no longer depends on pressure. Instead, mass transport is governed by molecular dynamics rather than fluid dynamics. This requires a very short path between the hot surface and the cold surface. This highly precise method is used industrially to purify various oils.