Overview of Steam Distillation
Steam Distillation is a method of separating temperature-dependent substances. It's a particular type of distillation. Explaining in other terms, this is to separate the miscible liquid base according to its volatilities. For example, aromatic compounds. It plays a vital role in certain industrial regions. There is no chemical reaction taking place here. It's a physical process.
At a very high sustained temperature level, few organic compounds can decompose. Often, it is used to separate volatile essential oils from the plant materials.
Earlier, steam distillation was one of the popular laboratory methods used for the purification of organic compounds. But now, it has been replaced in many such uses by supercritical fluid extraction and vaccum distillation. However, it is more economical and straightforward than those alternatives and remains vital in specific industrial sectors.
Process of Extraction of Essential Oils by Steam Distillation
In general, we use steam distillation to extract the essential oil. Steam distillation applies low-pressure steam to replace the volatile compounds from intact plant material. Besides, steam distillation allows us for temperature control and the amount of steam applied to the plant material.
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Steam distillation is a method by which we can remove oil from plant matter. In the apparatus, a chamber with holes in the bottom is present to enable steam to flow through either fresh or dried herbs.
It consists of a lid that prevents the oil from diffusing into the air when steam is applied. Then, we can collect the water and oil droplets that have undergone consideration. Therefore, the separation of water and oil happens by passing through the filter.
How Does Steam Distillation Work?
Let us discuss the steam distillation working briefly. The majority of the complex organic compounds do not dissolve in water. Alternatively, they create a mixture that can be separated if it is allowed to settle when the water settles down, and the organic compounds float to the top.
The principle of the steam distillation method is that, when the heating of a mixture of two or more immiscible liquids happens, the vapour pressure exerted by the system will be increased. This happens because the sum of the vapor pressures of all the components of the mixture is now combined. This enables elements with high boiling points to evaporate at even lower temperatures by merely allowing them to form a mixture with water.
Steam Distillation Extraction Procedure
Let us discuss the working of steam distillation. In the extraction procedure, steam flows through the organic matter that comprises the separating compounds. The steam is condensed and produces a mixture of both steam and matter.
The mixture is then heated by passing additional steam, which proceeds to flow over the matter, evaporating the mixture. Due to reduced vapour pressure, the necessary organic compounds evaporate as part of the mixture. Moreover, the extraction of the mixture takes place from organic matter.
Principle of Steam Distillation
When a mixture of two liquids that are immiscible (e.g., water and organics) is heated and disturbed, each liquid's surface exerts its own vapour pressure as though another component of the mixture was absent. Here, the specific constituent independently extracts the vapour pressure on its own, and the vapour pressure of the system consequently increases.
The two immiscible liquids tend to boil when the vapour pressure of these liquids exceeds the atmospheric pressure. Most of the organic compounds are insoluble in water. At an absolute temperature, we can purify it because that is below the point at which such compounds decompose.
Advantages of Steam Distillation
Few of the advantages of using Steam Distillation are:
This process generates organic solvent-free products
There is no need for subsequent steps after the steam distillation process
It possesses a large capacity at the industrial scale for processing of oils.
The equipment is quite inexpensive
In the steam distillation of essential oils process from steam boiler, it requires very less amount of fuel
Majorly, this method is used for oil production on an industrial scale
Participates in extracting materials from the body of plants such as stem and roots
It is used as an oil steam distillation that possess high boiling points
Extraction of essential oils by steam distillation can be done easily
Applications of Steam Distillation
The steam distillation process is used to separate organic compounds that are temperature-sensitive like aromatic substances. It also helps to extract oils from natural products like citrus oil, eucalyptus oil, and more natural substances that are derived from the organic matter. Due to this reason, the steam distillation method is widely used in producing perfumes and cologne, and in the production of a few cooking materials.
Majorly, this method is used for extracting the orange oil on a big range in industries. In addition, the steam distillation application can also be found in the production of petroleum and food product industries used to separate fatty acids from the mixtures.
Steam distillation’s partial modification technique is used for the isolation of dairy flavours from the dairy products.
Crude oil contains a broad range of components where every component is isolated in a stepwise manner in oil refineries using the steam distillation process.
Essential Oils and Steam Distillation
For the production of essential oils, the most common and reliable method used is the method of steam distillation in which the aromatic hydrocarbons (essential oils) are extracted from a plant. In the procedure, the steam is made to move through the crushed or grinded plant material and then the hot steam with a bit of pressure can make the oils to be released from their protective sacs
Some Solved Problems on the Concept of Steam Distillation
Q1. In the procedure of steam distillation, the liquid mixture starts to boil when the sum of vapour pressure due to the water and also the organic compound becomes
a) Greater than the atmospheric pressure
b) Lesser than that of the atmospheric pressure
c) Equals to the atmospheric pressure
d) None of the mentioned above
Answer: For this situation, the correct option will be “option c”. During the processes of steam distillation, a mixture of the organic compounds (like aromatic compounds and oils) and water boils at a temperature when the sum of the vapour pressures of the organic compound and water becomes equal to the atmospheric pressure. And due to high vapour pressure of water at its boiling point, and thus the organic matter will begin to vaporise at a temperature, which is below its normal boiling point.
FAQs on Steam Distillation
1. What is the basic principle behind steam distillation?
The principle of steam distillation is based on Dalton's Law of Partial Pressures. It is used to separate substances that are immiscible with water and are volatile in steam. According to this principle, when two immiscible liquids are heated together, the total vapour pressure above the mixture is the sum of their individual vapour pressures. The mixture will boil when this total vapour pressure equals the atmospheric pressure. This allows the organic compound to vaporise and distil at a temperature much lower than its actual boiling point, preventing decomposition.
2. How does steam distillation differ from simple distillation?
Steam distillation and simple distillation differ in several key ways:
- Miscibility: Simple distillation is used for separating miscible liquids with different boiling points. Steam distillation is specifically for separating substances that are immiscible with water.
- Boiling Point: In simple distillation, the liquid with the lower boiling point vaporises first. In steam distillation, the mixture boils at a temperature lower than the boiling points of both water and the organic compound.
- Application: Simple distillation is suitable for stable liquids with significant boiling point differences. Steam distillation is ideal for purifying heat-sensitive compounds (like essential oils or aniline) that would decompose at their high boiling points.
3. What are the key steps involved in the steam distillation process?
The steam distillation process generally involves three main steps:
- Steam Generation and Introduction: Steam is generated in a separate flask (the steam generator) and is passed through the distillation flask containing the impure organic compound.
- Co-distillation: The mixture of the organic compound and water heats up. The compound, though having a high boiling point, becomes volatile in the presence of steam. The vapours of both water and the organic compound are carried over into a condenser.
- Condensation and Separation: The vapour mixture is cooled in a condenser, turning back into a liquid. Since the organic compound and water are immiscible, they form two distinct layers in the receiving flask and can be easily separated using a separating funnel.
4. What are some common examples of substances purified by steam distillation?
Steam distillation is widely used in industry and laboratories. Some common examples include:
- Extraction of essential oils from plant materials like cloves, eucalyptus, and citrus peels.
- Purification of aniline from a mixture containing non-volatile impurities.
- Separation of ortho-nitrophenol and para-nitrophenol, as o-nitrophenol is steam volatile while p-nitrophenol is not due to intermolecular hydrogen bonding.
- Extraction of fragrances used in perfumes and flavourings.
5. Why is steam distillation the preferred method for purifying temperature-sensitive organic compounds?
Steam distillation is preferred for temperature-sensitive compounds because it allows for purification at a temperature significantly below the compound's actual boiling point. Many organic substances, such as essential oils and certain aromatic compounds, decompose or denature when heated to their high boiling points. By introducing steam, the mixture boils when the sum of the partial pressures of water and the organic compound equals atmospheric pressure, which occurs below 100°C. This gentle process effectively prevents thermal decomposition, ensuring the integrity of the purified substance.
6. How does steam distillation allow a compound with a high boiling point (e.g., >150°C) to vaporise below 100°C?
The compound does not actually boil at 100°C; rather, the entire *mixture* boils below 100°C. In a mixture of two immiscible liquids like oil and water, each liquid exerts its own vapour pressure independently of the other. The total vapour pressure of the system is the sum of their individual partial pressures (P_total = P_water + P_oil). The mixture starts to boil when P_total equals the external atmospheric pressure. Since P_water contributes significantly to the total pressure, the system reaches the atmospheric pressure at a temperature lower than 100°C, carrying the high-boiling-point compound along with the steam.
7. What are the main limitations of the steam distillation technique?
While very useful, steam distillation has some limitations:
- It is only applicable to substances that are volatile in steam and immiscible with water.
- The compound to be purified should not react with or be decomposed by steam or hot water.
- The process can be energy-intensive due to the need to produce a large amount of steam.
- It can be inefficient if the vapour pressure of the organic compound is very low at 100°C, as a large volume of water would be required to distil a small amount of the product.
- The collected distillate is an aqueous mixture, requiring a subsequent separation step.
8. Describe the typical laboratory setup or apparatus for steam distillation.
A standard laboratory setup for steam distillation consists of three main parts:
- Steam Generator: A flask containing water that is heated to produce a continuous supply of steam. It is usually fitted with a long safety tube to prevent pressure buildup.
- Distillation Flask: This flask contains the impure organic compound. It has two openings: one for the steam to enter from the generator and another leading to the condenser.
- Condenser and Receiver: The mixture of steam and organic vapour passes into a water-cooled condenser, where it condenses back into a liquid. The resulting liquid (distillate) is collected in a receiving flask, often forming two immiscible layers.
9. How is Dalton's Law of Partial Pressures fundamental to the process of steam distillation?
Dalton's Law is the scientific principle that makes steam distillation work. The law states that for a mixture of non-reacting gases, the total pressure is the sum of the partial pressures of the individual components. In steam distillation, the two immiscible liquids behave like independent entities, and the total vapour pressure (P_total) above the liquid is the sum of the vapour pressure of water (P_water) and the vapour pressure of the organic compound (P_organic). Boiling occurs when P_total = P_atmospheric. Because P_water contributes to the total pressure, P_organic does not need to reach atmospheric pressure on its own. This allows the mixture to boil at a lower temperature, which is the core advantage of this technique.
