Extraction (chemistry)
Separation process based on solute distribution between two phases.
In chemistry, extraction is a separation technique used to isolate a substance from a surrounding material. The way a dissolved substance distributes itself between two different phases is governed by partition theory, which describes how the analyte transfers from its original solvent into the extraction solvent. The process is sometimes called washing when the goal is to remove unwanted impurities from a solvent that holds the target compound.
Various extraction methods exist, including liquid–liquid extraction, acid-base extraction, supercritical fluid extraction, solid-liquid extraction, solid-phase extraction, maceration (grinding), ultrasound-assisted extraction, microwave-assisted extraction, heat reflux extraction, instant controlled pressure drop extraction, pressurized liquid extraction, and perstraction.
In a laboratory, liquid–liquid extraction typically uses a separatory funnel. Two immiscible liquids are combined so that a solute moves from one phase into the other, depending on its relative solubility in each. This often involves pulling organic compounds out of water into an organic solvent, but it can also mean removing water-soluble impurities from an organic phase into water. Common extractants can be ranked by polarity using the Hildebrand solubility parameter, from least to most polar: ethyl acetate, acetone, ethanol, methanol, acetone:water (7:3), ethanol:water (8:2), methanol:water (8:2), and water.
For solid-liquid extraction on a lab scale, a Soxhlet extractor is often used. A solid sample containing the desired compound and impurities is placed in a thimble. An extracting solvent is chosen so that impurities do not dissolve, but the target compound has at least some solubility. The solvent is heated and refluxed; condensed solvent drips into the thimble, dissolves the desired compound, and then passes back through the filter into the flask. Once extraction is finished, the solvent is removed to collect the product.
In everyday life, boiling tea leaves in water extracts tannins, theobromine, and caffeine from the leaves into the water—a simple solid-liquid extraction. Many Americans use a microwave-assisted method for this. Coffee brewing often employs more advanced solid-liquid techniques, such as pressurized fluid in an espresso machine or heat reflux in a coffee percolator. Chefs use oil, both cold and hot, to pull aroma-bearing compounds from herbs and spices. Decaffeination of tea and coffee is another extraction process, where caffeine is removed from leaves or beans, often using supercritical fluid extraction with carbon dioxide or standard solid-liquid methods.
- field
- Chemistry
- known_for
- Separation process of substances from a matrix
- types
- Liquid–liquid, acid-base, supercritical fluid, solid-liquid, solid-phase, maceration, ultrasound-assisted, microwave-assisted, heat reflux, instant controlled pressure drop, pressurized liquid, perstr
- laboratory_applications
- Separatory funnel for liquid-liquid extraction; Soxhlet extractor for solid-liquid extraction
- everyday_applications
- Boiling tea leaves, brewing coffee, oil extraction of aromas, decaffeination of tea and coffee
Lore & Background
Extraction in chemistry is defined as a separation process that isolates a substance from a matrix. The equilibrium condition governing the distribution of a solute between two phases is described by partition theory, which depends on how the analyte moves from the initial solvent into the extracting solvent. The term 'washing' may also be used when impurities are extracted from the solvent containing the desired compound. Various types of extraction exist, including liquid–liquid extraction, acid-base extraction, supercritical fluid extraction, solid-liquid extraction, solid-phase extraction, maceration (grinding), ultrasound-assisted extraction, microwave-assisted extraction, heat reflux extraction, instant controlled pressure drop extraction, pressurized liquid extraction, and perstraction.
Reader's Guide
In laboratory applications, liquid-liquid extractions typically use a separatory funnel, where two immiscible phases are combined to separate a solute from one phase into the other based on relative solubility. Common extractants can be arranged in increasing order of polarity according to the Hildebrand solubility parameter, from ethyl acetate to water. Solid-liquid extractions at laboratory scales can use Soxhlet extractors, where a solid sample is placed in a thimble and an extracting solvent is refluxed to dissolve the desired compound, which then passes through a filter into the flask. Everyday examples include boiling tea leaves in water to extract tannins, theobromine, and caffeine, as well as brewing coffee using pressurized fluid (espresso machine) or heat reflux (coffee percolator). Chefs use oil to extract aroma-bearing compounds from herbs and spices. Decaffeination of tea and coffee removes caffeine molecules, often using supercritical fluid extraction with CO2 or standard solid-liquid extraction techniques.
Did You Know?
- The distribution of a solute between two phases is an equilibrium condition described by partition theory.
- Common extractants can be arranged in increasing order of polarity according to the Hildebrand solubility parameter.
- Boiling tea leaves in water extracts tannins, theobromine, and caffeine as an example of solid-liquid extraction.
- Decaffeination of tea and coffee often utilizes supercritical fluid extraction with CO2.
More in Chemical Reactors And Processes 1-24
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