Theory, Evolution, and Methods of Extraction Thimble
The transfer of a substance from one solvent to another by taking advantage of the difference in the solubility or the distribution coefficient of a substance in two insoluble (or slightly soluble) solvents. After repeated extraction, most of the compounds were extracted.
The solvent extraction process generally consists of extraction, washing, and reverse extraction. Generally, the process of extracting the solute from the organic phase is called extraction, the process of removing other solutes or contents from the loaded organic phase is called scrubbing, and the process of the water phase parsing the solute from the organic phase is called stripping.
The distribution law is the main basis of the extraction method theory. At the same time, when a certain soluble substance is added to two kinds of insoluble solvents, it can be dissolved in two kinds of solvents respectively. The experiment proves that, at a certain temperature, when the compound and the two kinds of solvents do not have a decomposition, electrolysis, association, and solvation, the ratio of the compound in the two liquid layers is a constant value. This is true regardless of the amount of material added.
Organic compounds are generally more soluble in organic solvents than in water. Extracting compounds dissolved in water with organic solvents is a typical example of extraction. During extraction, if a certain amount of electrolyte (such as sodium chloride) is added to the aqueous solution, the extraction effect can be improved by using the “salting-out effect” to reduce the solubility of organic matter and extraction solvent in the aqueous solution.
To extract the required solute completely from the solution, one extraction is usually not enough and must be repeated several times. The residual amount of the compound after extraction can be calculated by using the relation of the distribution law.
When you use a certain amount of solvent, you want to have as little left in the water as possible. In other words, it is better to divide the solvent several times and do multiple extractions than to do one extraction with the whole amount of solvent. But it should be noted that the above formula applies to solvents that are almost insoluble in water, such as benzene, carbon tetrachloride, etc. And water with a small amount of mutual solvent ether, the above formula is only approximate. But you can still qualitatively point to the expected outcome.
Instrument: dispensing funnel
Common extractants: toluene, dichloromethane, trichloromethane, gasoline, ether, straight-run gasoline, n-butanol, and carbon tetrachloride.
Requirements: the extraction agent and the original solvent are immiscible.
The extractant and the solute do not react with each other.
The solubility of the solute in the extractant is much higher than that in the original solvent.
Correlation law: organic solvent is soluble in the organic solvent, the polar solvent is soluble in the polar solvent, and vice versa.
In 1842 e. – m. Perillo studied the extraction of uranyl nitrate from nitric acid solution by ethyl ether. In 1903 l. editing used liquid sulfur dioxide to extract aromatic hydrocarbons from kerosene, the first industrial use of extraction.
In the late 1940s, the need to produce nuclear fuel spurred extraction research and development.
Today extraction is used in the petroleum refining industry and is widely used in the chemical, metallurgical, food, and atomic industries. For example, extraction has been used in the separation and refining of petroleum fractions, the extraction and purification of uranium, thorium, plutonium, the extraction and separation of non-ferrous metals, rare metals, precious metals, antibiotics, organic acids, alkaloids, and wastewater treatment.
Two co-existing liquid phases are formed by adding an extractant that is insoluble (at most partially soluble) with the solution to be separated. The dissolubility of each component (including the dissolution after chemical reaction) of the original solvent and the extractant is used to make them not equally distributed in the two liquid phases. For example, an aqueous solution of iodine is extracted with carbon tetrachloride. Almost all iodine is moved into carbon tetrachloride, and iodine is separated from a large amount of water.
The most basic operation is single-stage extraction. It is to make the material liquid and extraction agent contact closely in the mixing process, so that the extracted components through the interphase interface into the extraction agent until the components in the two-phase distribution is basically balanced. After that, the liquid was separated into two layers, that is, the extraction liquid changed from the extraction agent and the raffinate changed from the material liquid. When the single-stage extraction reaches the phase equilibrium, the phase equilibrium ratio of the extracted component B is called the distribution coefficient K.
The extraction rate (the ratio between the amount of extracted components in the extraction solution and the initial amount in the raw material solution) that can be achieved by single-stage extraction for a given component is relatively low, which often fails to meet the technical requirements.
In order to improve the extraction rate, a variety of methods can be adopted:
(1) multi-stage cross-flow extraction.
(2) multistage countercurrent extraction. Continuous countercurrent extraction. In the differential contact extraction tower (see extraction equipment), the material liquid and extraction agent contact mass transfer in the process of reverse flow, is also a common industrial extraction method.
The material liquid and extraction agent, the density is called a heavy phase, the density is called the light phase. The light phase enters from the bottom of the tower and overflows from the top. The heavy phase is added from the top of the tower and exported from the bottom of the tower. When the extraction column is operated, a liquid phase filled with the whole column is called the continuous phase. The other liquid phase is usually dispersed in the form of droplets and is called the dispersed phase. The dispersed phase liquid disperses when it enters the tower, and then condenses and stratifies before leaving the tower.