Distillation Basics

We’ve previously written about Choosing Tower Internals for LNG and thought we would continue on the subject of distillation. Distillation is a critical process for columns and is often used for liquid, vapor, or both. Below we will show you distillation basics to help you better understand process towers.

What is Distillation?

In industrial terms, distillation is the separation of components in a solution based on the chemical’s vapor pressure. Liquid and vapor combine in a counterflow arrangement inside a vertical column in order to achieve distillation. Separated compounds are characterized by volatility, including different boiling temperature with different pressure. For example, we know water boils at 100 degrees Celsius, 212 degrees Fahrenheit, at 1 atmosphere of pressure. Raise the pressure, and the water will boil at a lower temperature. The same goes for many other chemicals put into towers such as LNG, Ethanol, etc.

Distillation Basics in Towers

Volatility and activity coefficients are the main considerations used in the design of a distillation column. The number of equations needed to factor are considerable given most distillation systems contain multiple components. There are even several types of distillation to consider:

  1. Simple distillation – This process may be used when the boiling points of the column’s liquids are significantly different from each other. It may also be used to separate liquids from nonvolatile components or solids. Simple distillation uses a mixture heated to change the most volatile component from a liquid to vapor. This vapor rises and often passes into a condenser where it is cooled by cold water or another method. These methods are designed to condense the vapor and allow it to be collected.
  2. Steam distillation – This process is used to separate chemicals that are heat-sensitive. Steam is added to the column to cause vaporization. The vapor is then cooled and condensed into two separate liquids. Sometimes they are collected separately. Other times the difference in their density allows them to separate naturally.
  3. Vacuum distillation – Vacuum distillation separates components with high boiling points. The column often has its pressure lowered to also lower the chemical’s boiling points. This method is preferable when normal boiling points are higher than the chemical’s decomposition temperature.
  4. Fractional distillation – This process is often used when boiling points of the components are close to each other using Raoult’s law. A fractionating column is used for separation with a series of distillations called rectification. Fractional distillation also uses a heated mixture that allows vapor to rise and enter the column. The vapor then cools and condenses on the column’s packing material. The rising vapor’s heat causes the liquid to again vaporize and move, which yields a higher purity sample.

The AMACS engineers are experts in the latest distillation techniques, as well as replacement-in-kind trays, packing, and parts for your columns. We are a reliable source for the expertise you need when purchasing internals for your distillation towers, and AMACS equipment is installed in process towers, worldwide. Our team offers consistent, quick delivery for tower internals in many common stocked alloys and diameters. Call us today to learn how we can partner with you to keep your process operating efficiently and cost effectively.