Understanding Vacuum Distillation

It is possible to purify compounds that are difficult to distill at ambient pressures using vacuum distillation, as well as to save time and energy by performing the distillation under reduced pressure. The boiling point difference between two compounds is used to separate them using this technique. It is used when the boiling point of the desired compound is difficult to achieve or when the compound will decompose if the boiling point is not achieved. Reduced pressures cause the boiling point of compounds to drop significantly. With the help of a temperature-pressure nomograph and the Clausius–Clapeyron relationship, it is possible to calculate the reduction in boiling point.

The following are some ways that vacuum distillation can improve a separation:

• Product degradation or polymer formation is prevented as a result of reduced pressure resulting in lower tower bottom temperatures.
• Product degradation or polymer formation is reduced as a result of a shorter mean residence time, which is especially true in columns rather than trays.
• Capacity, yield, and purity are all being improved.

Another advantage of vacuum distillation is that it has a lower initial capital cost, although it has a slightly higher operating cost. The use of vacuum distillation can reduce the height and diameter of a distillation column, as well as the overall capital cost of the column.

Vacuum Distillation in Petroleum Refining

A complex mixture of hundreds of different hydrocarbon compounds, petroleum crude oil has a carbon atom count ranging from 3 to 60 carbon atoms per molecule on average, although there may be small amounts of hydrocarbons outside of that range. The process of refining crude oil begins with the distillation of the incoming crude oil in an atmospheric distillation column, which operates at pressures slightly above atmospheric pressure to remove impurities.

vacuum distillation is also known as “low-temperature distillation” or “low-pressure distillation.”

It is critical not to subject the crude oil to temperatures above 370 to 380 degrees Celsius during the distillation process because high molecular weight elements in the crude oil will initiate thermal cracking and form petroleum coke at temperatures higher than that. The formation of coke would result in the plugging of the tubes in the furnace that heats the feed stream to the crude oil distillation column, which would cause the column to fail. Along with the distillation column itself, plugging would also occur in piping leading from the furnace to the column.

In order to achieve good vapour–liquid contact, the internals of a vacuum distillation column must maintain a very low pressure increase from the top of the column to the bottom of the vessel. Therefore, only products that are withdrawn from the side of the vacuum column are distilled using distillation trays in a vacuum column (referred to as side draws). The majority of the column’s packing material is used for the vapour–liquid contacting because packing material has a lower pressure drop than distillation trays, which results in a lower pressure drop. This packing material can be either organised sheet metal or randomly dumped packing, such as Raschig rings, depending on the application.

The use of multiple stages of steam jet ejectors to achieve an absolute pressure in the vacuum column ranging from 10 to 40 mmHg is the most common method of achieving this pressure.

Large Scale Water Purification

Vacuum distillation is commonly used in large industrial plants to remove salt from ocean water in order to produce fresh water. It is an efficient method of removing salt from ocean water. Desalination is the term used to describe this process. After being placed under a vacuum to lower its boiling point, and having a heat source applied, the ocean water boils off and condenses, releasing the fresh water. When water vapour condenses, it keeps it from filling the vacuum chamber, allowing for the effect to run indefinitely without a loss of vacuum pressure. The heat generated by the condensation of water vapour is removed by a heat sink, which uses the incoming ocean water as a coolant, thereby preheating the ocean water that is fed into the system. Some types of distillation do not use condensers, but instead compress the vapour mechanically with a pump, which is referred to as vacuum distillation. Essentially, this serves as a heat pump, drawing in heat from the vapour and allowing it to be returned to and reused by the incoming untreated water source after being concentrated. Many different types of vacuum distillation of water are used today, with the most commonly used being numerous distillation, vapor-compression desalination, and multi-stage flash distillation being the most common.

Conclusion

It is the process of lowering the pressure in a column above an organic solvent to a level lower than the vapour pressure of the mixture, creating a vacuum, and causing the elements with lower vapour pressures to evaporate away from the mixture. The advantage of vacuum distillation is that it has a lower initial capital cost, although it has a slightly higher operating cost. The use of vacuum distillation can reduce the height and diameter of a distillation column, as well as the overall capital cost of the column.

Vacuum distillation is also known as “low-temperature distillation” or “low-pressure distillation.” The process of refining crude oil begins with the distillation of the incoming crude oil in an atmospheric distillation column, which operates at pressures slightly above atmospheric pressure to remove impurities.

Vacuum distillation is commonly used in large industrial plants to remove salt from ocean water in order to produce fresh water. It is an efficient method of removing salt from ocean water.