Extraction and drying _ Solvent
Original title Extraction and drying Extraction bra tape measure Extraction also known as solvent extraction or liquid-liquid extraction (to distinguish it from solid-liquid extraction that is leaching) also known as extraction (commonly used in the petroleum refining industry) is a mass transfer separation process in which a liquid extractant is used to treat an immiscible two-component or multi-component solution to achieve component separation and is a widely used unit operation Based on the principle of similar compatibility there are two ways of extraction 1 Liquid-liquid extraction which uses a selected solvent to separate a certain component in the liquid mixture The solvent must be immiscible with the extracted mixture liquid have selective solubility and must have good thermal and chemical stability and have low toxicity and corrosiveness For example benzene is used to separate phenols from coal tar; organic solvents are used to separate olefins from petroleum fractions; Br2 In CCl4 extraction water Two Solid-liquid extraction also known as leaching uses solvents to separate components from solid mixtures such as water to extract sugars from beets alcohol to extract soybean oil from soybeans to increase oil production and water to extract active ingredients from traditional Chinese medicines to make fluid extracts which is called “leaching” or “leaching” Although extraction is often used in chemical experiments its operation does not result in a change (or chemical reaction) in the chemical composition of the material being extracted so the extraction operation is a physical process Extraction is one of the means used in organic chemistry laboratories to purify and purify compounds The desired compound can be extracted from a solid or liquid mixture by extraction Liquid-liquid extraction which is commonly used in organic synthesis is introduced here Liquid-liquid extraction is a method of extracting a solute from a solution composed of one solvent and another solvent by using the different solubility of the solute in immiscible solvents Principle A compound is transferred from one solvent to another by using the difference of solubility or distribution coefficient of the compound in two immiscible (or slightly soluble) solvents After repeated extraction most of the compounds are extracted The partition law is the main basis of the theory of extraction method Substances have different solubility to different solvents At the same time in two immiscible solvents when a soluble substance is added it can be dissolved in the two solvents respectively Experiments show that at a certain temperature when the compound does not decompose electrolyze associate and solvate with the two solvents the ratio of the compound in the two liquid layers is a constant value This is true regardless of the amount of substance added It is a physical change Expressed by the formula CA/CB=K CA and CB respectively represent the amount and concentration of a compound in two immiscible solvents K is a constant called the “partition coefficient” Organic compounds are generally more soluble in organic solvents than in water Extraction of a compound dissolved in water with an organic solvent 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 “salting-out effect” can be used to reduce the solubility of organic matter and extraction solvent in the aqueous solution and the extraction effect can often be improved In order to completely extract the desired compound from the solution it is usually not enough to extract once and the extraction must be repeated several times The remaining amount of the compound after extraction can be calculated by using the relationship of the partition law Let V be the volume of the original solution Wo is the total amount of the compound before extraction W1 is the remaining amount of the compound after one extraction W2 is the residual amount of the compound after the second extraction W3 is the remaining amount of the compound after n times of extraction S is the volume of the extraction solution Expand the full text After one extraction the concentration of the compound in the original solution is w1/V while the concentration of the compound in the extraction solvent is (w0-w1)/S and the ratio of the two is equal to K After simplification the following formula is obtained w1= [KV/(KV+S)]w0 Similarly after the second extraction there is w2= [KV/(KV+S)]w1 Therefore after n extractions wn=w0[KV/(KV+S)]n When a certain amount of solvent is used it is desirable that the remaining amount in the water is as small as possible The above formula KV/ (KV + S) is always less than 1 so the larger n is the smaller wn is
That is to say it is better to divide the solvent into several times for multiple extractions than to use the whole amount of solvent for one extraction It should be noted however that the above formula applies to solvents that are nearly immiscible with water such as benzene carbon tetrachloride and the like The above formula is only approximate for solvents such as ether which have a small amount of mutual solubility with water However the expected results can be qualitatively indicated Application Compared with other methods for separating solution components the extraction method has the advantages of normal temperature operation energy saving no solid or gas involved and convenient operation Extraction is generally advantageous in the following cases 1 the boiling points of the components of the feed liquid are similar and even an azeotrope is formed which is not easy to work for rectification such as the separation of alkanes and aromatics in petroleum fractions and the dephenolization of coal tar; 2 For the separation of low-concentration high-boiling components the energy consumption of rectification is very high such as the dehydration of dilute acetic acid; for the separation of various ions such as the separation and purification of mineral leaching solution if chemicals are added for fractional precipitation not only the separation quality is poor but also the filtration operation is needed and the loss is also large; 3 Separation of unstable substances (such as heat-sensitive substances) such as the preparation of penicillin from fermentation broth The application of nutsche filter dryer extraction is still under development Most of the elements in the periodic table can be extracted and separated by extraction The selection and development of extractants the determination of process and operating conditions and the design and calculation of flowsheets and equipment are all subjects for the development of extraction operations Precautions for extraction 1 The single extraction solvent is not miscible with water Low solubility or insolubility in water; cannot be extracted separately with methanol ethanol THF etc; cannot be extracted with high boiling point solvent; [THF and saturated salt water are immiscible and can be used for extraction under special circumstances; Similarly for some substances with good water solubility you can try to saturate the aqueous solution with sodium chloride first and then extract it with acetonitrile The disadvantage of this method is that acetonitrile will extract some sodium chloride 2 Fully know the specific gravity of the extraction solvent Know which layer is the organic phase; the specific gravity of carbon tetrachloride chloroform and dichloromethane > water > toluene benzene petroleum ether diethyl ether methyl tert-butyl ether and ethyl acetate Do not throw away the product Neither the aqueous phase nor the organic phase can be discarded until the product is determined to be available; 3 If there is a large amount of solid precipitation during post-treatment It is better to filter first and then extract in layers; 4 When the product is emulsified in an aqueous phase Saturated aqueous sodium chloride solution is usually added and allowed to stand to promote layering; sometimes diatomite filtration can also demulsify; or centrifugal pump separation on the emulsion layer 5 A small number of times when extracting However the ratio of extraction solvent to aqueous solution should not be too small usually controlled between 02 and 1; 6 Remember to deflate when extracting Avoid flushing; 7 For substances that are highly soluble in water In general mixed solvent such as DCM/MeOH (10/1) ethyl acetate and methanol is used for extraction (Or other small molecular alcohol) or THF; CHCl3/i-Proh (3/1) In addition n-butanol is a good choice N-butanol itself is insoluble in water and has the common characteristics of small molecular alcohols and large molecular alcohols Method for drying substances 50l rotovap The process of removing small amounts of water and organic solvents from solids liquids or gases is called drying Many chemical experiments must be carried out under anhydrous conditions which requires that the raw materials solvents and instruments used should be dried and the moisture in the air should be prevented from entering the reactor during the experiment otherwise the quality and yield of the product will be affected Organic compounds must be dried before distillation to prevent heat from hydrolyzing certain compounds or forming azeotropic mixtures with water To determine the physical constants of compounds to carry out qualitative and quantitative analysis of compounds and to analyze and determine the structures of compounds by using chromatography ultraviolet spectroscopy infrared spectroscopy nuclear magnetic resonance spectroscopy mass spectrometry and other methods the compounds must be completely in a dry state in order to obtain the correct results Basic principles Drying methods are divided into physical methods and chemical methods Physical methods include natural drying drying vacuum drying fractionation azeotropic distillation and adsorption In addition ion exchange resins and molecular sieves are also commonly used for dehydration drying
