The key difference between steam distillation and hydrodistillation is that steam distillation uses steam for extraction, whereas hydrodistillation uses water, steam or a combination of water and steam for extraction.
Distillation is an industrial process which involves the heating of a liquid to create vapour that is collected when cooled separately from the original liquid. The process of distillation mainly uses the differences in boiling points or volatility of different components in a mixture.
CONTENTS
1. Overview and Key Difference
2. What is Steam Distillation
3. What is Hydrodistillation
4. Side by Side Comparison – Steam Distillation vs Hydrodistillation in Tabular Form
5. Summary
What is Steam Distillation?
Steam distillation is an industrial process that includes the separation of components in a heat-sensitive mixture via adding water to the distillation flask. This technique is very useful in industrial-scale applications as a purification technique to remove impurities in a compound. The components of the mixture should be volatile in order to successfully carry this process.
In steam distillation, we can separate the components in the mixture by vaporizing them at a boiling point that is lower than their actual boiling point. If this principle is not followed, some components may decompose before reaching the boiling point. If this happens, then we cannot separate them accurately.
Figure 01: Steam Distillation Apparatus
The process of steam distillation includes the addition of water to the distillation flask, where the mixture to be separated is placed. The water is added in order to drop down the boiling points of the components. Thereafter, we can heat the mixture while agitating it. As a result of this step, the components tend to vaporize quickly. Then the vapour pressure of the distillation flask increases. When this vapour pressure exceeds the atmospheric pressure, the mixture starts to boil. Since the mixture boils at low pressure (lower than the atmospheric pressure), the boiling point of the components also drops down.
What is Hydrodistillation?
Hydrodistillation is an industrial process which can be done using water or steam. The name “hydrodistillation” is used due to the use of water in either the liquid form or vapour form. This technique has long been used for the extraction of essential oils and compounds from plant materials. There are three ways of doing this extraction: water distillation, water and steam distillation, and direct steam distillation.
The method of distillation in water distillation is hydro-diffusion; method of distillation in water plus steam distillation is hydrolysis, while the method of distillation in direct steam distillation is decomposition by heat. When we are using a plant matrix in the process of hydrodistillation, water and steam act as the main media for free bioactive compounds. Generally, the oils and other bioactive compounds obtained through this method are dried over anhydrous sodium sulfate. Often, hydrodistillation is conducted at temperatures above the boiling point of water. Due to this reason, some volatile components and natural pigments can be lost from the plant matrix.
What is the Difference Between Steam Distillation and Hydrodistillation?
Steam distillation is a type of hydrodistillation. The key difference between steam distillation and hydrodistillation is that steam distillation uses steam for the extraction whereas hydrodistillation uses water, steam or a combination of water and steam for the extraction.
The following table summarizes the difference between steam distillation and hydrodistillation.
Summary – Steam Distillation vs Hydrodistillation
Steam distillation is a type of hydrodistillation. The key difference between steam distillation and hydrodistillation is that steam distillation uses steam for the extraction whereas hydrodistillation uses water, steam or a combination of water and steam for the extraction.
Reference:
1. Ryder, Edward J. “Lesser Salad Vegetables.” Leafy Salad Vegetables, 1979, pp. 229–257., doi:10.1007/978-94-011-9699-4_7.
Image Courtesy:
1. “Steam distillation” By Lazar.zenit – Own work (CC BY-SA 4.0) via Commons Wikimedia