EXTRACTION

From Big Medical Encyclopedia

EXTRACTION (lat. extrahere to take, extend; synonym extraction) — separation process of mix of liquid or solid matters by extraction from it individual connections with the help of the selective solvents — extragents. Transition of the extracted (extracted) substance from one phase (liquid or firm) in other phase (a phase of liquid extragent) is result of extraction.

AA. use in laboratory and industrial conditions for extraction from biol. material and unmixing of proteins (see), including enzymes (see), and also fats (see), vitamins (see), hormones (see) and other biologically active compounds. Processes E. are important in modern pharmacy, especially for extraction of natural organic compounds from the dried-up or fresh vegetable raw materials. By E. receive a basic group of galenovy and neogalenical medicines, extracts and tinctures, drugs from raw materials of animal origin, alkaloids (see), antibiotics (see), etc. Extraction is widely applied in chemical, pharmaceutical, food, oil processing, metallurgical and other industries. Extraction is used in analytical chemistry and radiochemistry for division of chemical elements (see), and also for division, concoction and purification of radioisotopes (see).

AA. allows to remove selectively substances from initial solution, to increase concentration of the extracted substances, to divide the substances which are contained in initial solution and to receive them in pure form. To advantages E. low working temperatures, profitability of extraction of substances from dilute solutions (see), a possibility of division of connections with a close boiling point and constant boiling mixtures (see), compatibility treat with other technological processes, simplicity and a possibility of automation of process.

AA. consists of three stages: 1) mixing of a starting material with extragent; 2) mechanical division (stratifying) of two phases, at Krom turns out extract (solution of the extracted substance in extragent) and the rest of initial solution (raffinate) or hard material; 3) removal of extragent from extract and regeneration of extragent for re-using. Extract is separated by filtering (see), by centrifuging (see) or upholding; from extract with simultaneous regeneration of extragent for re-using apply distillation, evaporation, salting-out, crystallization, winterizing and other ways to release of individual substance.

AA. submits to Fick's laws (see) and equilibrium distribution (see Distributions the law). Kinetics E. k × Δc × F × t where M — amount of the extracted substance, k — a mass-transfer coefficient, Δc — a difference of concentration of extractive in both phases, F — the size of a contact surface of phases, t — time is described by the general equation of a mass exchange of M =. For acceleration and increase in completeness E. reach great values of M by increase in value to as a result of hashing, increase in a contact surface of the interacting phases (F) by means of crushing of materials or dispersion of one of liquid phases on small drops, increases up to optimum values of such parameters as time, temperature and amount of extragent. For the characteristic of distribution of substance between an aqueous phase and the organic phase which is not mixing up with it use such size as a distribution coefficient of D, to-ry represents the relation of concentration of substance in an organic phase and in an aqueous phase. Extent of extraction of E is expressed as a percentage:

where V vodn and V org — volumes of water and organic phases respectively.

Classification of processes E. it is based on various signs: mechanism E., a structure and properties of the received connections, properties of extragents, forms of finding of the extracted substance in solution, etc. Distinguish physical division (E. covalent bonding) and AA., happening to change of a chemical form of substances (the cation-exchange, anion-exchange extraction, AA. ionic associates and intra complex salts). Depending on type of the used extragent allocate extraction with neutral solvents and extraction by reagents of acid and main character.

Extragent shall have selectivity (well to dissolve the taken connection and it is bad to dissolve the accompanying connections), it is good to diffuse, have small viscosity, whenever possible to extract substance without its essential chemical transformations, it is easy to be regenerated, be non-toxic, available and rather cheap. At the choice of extragent it is also necessary to consider degree of miscibility of phases, relative ud. the weight (weight) and a tendency to formation of emulsions (see). Depending on properties of a starting material, requirements to an end product and other indicators as extragents apply water (E. water sometimes call lixiviation), alcohol, ether, glycerin, oils, chloroform, etc. Sometimes E. carry out by several solvents consistently or to mixes (e.g., at division of components with close solubility in initial solvent). At single E. extent of extraction of substance from initial solution is rather small therefore the interacting phases most often repeatedly mix and allow them to be stratified; most effectively from the point of view of extraction of the necessary substance oncoming traffic of initial solution and extragent.

Distinguish liquid E. — full or partial extraction of one or several components from homogeneous liquid mixture by processing by its solvent liquid, and also AA. in system a solid — liquid. Two main ways liquid E are known. from a homogeneous liquid phase — step and continuous. At step E. the cycle of mixing of original stock with extragent and the subsequent upholding of phases in separate devices is repeated. Used for step E. devices can be periodically acting (in the industry they have limited use owing to a low performance) and continuously acting (including devices with mechanical hashing). Apply return of a part of extragent from extract to fuller extraction of the necessary substance and a part of raffinate in the device towards to the leaving flows (multistage counterflow E. with return). Example continuous E. can serve often used in the industry continuous counterflow E. in columns with a nozzle, in hollow columns with the sprayer, etc. In differential and contact extractors process of change of structure of phases approaches continuous. During the carrying out continuous E. from a solid phase solvent evaporates in a special vessel, its couples are condensed in the refrigerator from where solvent flows down on the extracted material, passes through py, and extract flows down in a vessel again, from to-rogo there is an evaporation of solvent. The cycle is repeated before full extraction of the necessary substance. In vitro for E. from a solid phase use the Soxhlet apparatus used by hl. obr. for E. fats and other lipids (see). Vapors of the warmed-up solvent (hl. obr. ether) come to the refrigerator, from it solvent gets on the crushed material which is in a sleeve from the filter paper placed in a middle cylindrical part of the device. Ether impregnates material, dissolves the lipids which are contained in it and merges in a flask from where vapors of ether come to the refrigerator again, and extract collects in a flask.

The devices used in the industry for E. in system a solid — liquid is distinguished also on a duty (periodic, a floor at periodic, continuous), in the mutual direction of the movement of extragent and solid particles (direct-flow and counterflow, with process in the fixed, moving and «boiling» bed), by the form by circulation (with single passing of extragent, with recirculation of extragent), but to pressure in an extractor (atmospheric, vacuum and working under pressure), on properties of particles of a solid phase (coarse-grained, fine-grained, finely dispersed, pasty, fibrous substances), etc.

Bibliography: Akselrud G. A. and Lysyansky V. M. Extraction, System a solid — liquid, L., 1974; Birchbark A. M. and Beloglazov I. N. Liquid extractors, L., 1982; Zolotov Yu. A. and Kuzmin N. M. Extraction concoction, M., 1971; Morrison J. and Of Fraser. Extraction in analytical chemistry, the lane with English, M., 1960; I. A. Tekhnologiya's Ants of drugs, t. 1, M., 1980; Treybal R. Liquid-liquid extraction, the lane with English, M., 1966.

N. V. Gulyaeva.

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