Organic liquids are usually dried with solid inorganic desiccants, and a small amount of the latter should be used to avoid losses from adsorption of the substance by the desiccant. First, shake the organic liquid with a small amount of drying agent (up to 3% by weight of the solution), after some time a small layer of aqueous solution of the drying agent is released if substances that form hydrates with water (calcium chloride, sodium sulfate, caustic soda, sulfate) were taken for drying. magnesium). The liquid is drained, a fresh portion of the desiccant is added again, and this is repeated until the desiccant stops absorbing water, for example, calcium chloride does not blur, phosphorus anhydride does not stick together, etc. After this treatment, the organic liquid is placed in a flask, which close with a stopper with a calcium chloride tube and leave to stand overnight with a new portion of desiccant. Before distillation, the dried organic liquid is filtered or, most often, decanted.

2.5.3. Drying solids

Air dry at normal temperature

Many substances, both inorganic and organic, can be dried in the open air. Drying occurs due to the natural evaporation of the moisture contained in the substance until the pressure of water vapor in the air and above the body reaches a state of equilibrium.

The substance to be dried, for example, wet crystals, is poured onto a sheet of clean filter paper, spreading them in a layer no more than 3 - 5 mm thick. In this case, you should not crush the salt, since the looser the layer, the faster and better the drying will be. To protect from dust or contamination, cover the dried substance on top with another sheet of clean filter paper and leave for several hours. Then the dried substance is mixed with a spatula so that the wetter lower layers are on top; The mass should remain loose. The product is again covered with a sheet of filter paper and left to dry for another 12 hours. Sometimes the substance has to be mixed several times, especially if the layer thickness was significant. Place the dried salt into a jar with a spatula and close it tightly. If, when standing in a tightly closed jar, drops of water appear on its walls, this means that the substance has not been dried completely enough and the drying should be repeated.

Air drying is a rather lengthy operation and is used only when the substance being dried decomposes when heated or when they want to obtain the substance in the form of a loose, free-flowing powder without lumps. In this way, you can dry substances that are not hygroscopic, that is, they do not absorb moisture from the surrounding air.

Drying at reduced pressure (vacuum drying)

For drying substances that easily decompose or change when heated, even at normal pressure; drying is used at reduced pressure (under vacuum).

For this purpose, so-called electrically heated vacuum drying cabinets are used. Their maximum heating temperature is 200 °C:

Drying in a desiccator

It is convenient to dry highly hygroscopic substances that dissolve in air without heating in ordinary and vacuum desiccators. The latter have a hole into which a tube with a tap is inserted on a rubber stopper. This makes it possible to connect the desiccator with a vault jet pump, between which a pressure gauge and a safety bottle are placed.

Sometimes desiccators explode under vacuum, so you need to wrap them in a towel before turning on the pump. When opening the vacuum desiccator, to avoid spraying the dried substance with air, you should turn the tap very carefully and slowly. Only after the pressure has been equalized can the ground-in lid of the vacuum desiccator be opened.

A drying agent, a substance that vigorously absorbs moisture, is placed in the desiccator. The substance to be dried is placed in a bottle or cup, placed open on the porcelain insert of the desiccator and left in the latter for a day or more.

The drying agent is selected depending on the chemical properties of the substance being dried. Most often, calcium chloride, soda lime, caustic soda, caustic potassium, phosphoric anhydride, and concentrated sulfuric acid are used as desiccants for desiccators. It must be remembered that sulfuric acid cannot be used for drying in a vacuum; it is used only in ordinary desiccators to absorb moisture, residues of alcohol, ether, acetone, aniline, pyridine. For the adsorption of hydrocarbons, especially hexane, ligroin, benzene and its homologues, paraffin is used as a filler for the desiccator; To remove acidic substances, use caustic soda or caustic potassium. Water and alcohols are well absorbed by phosphoric anhydride and soda lime.

Basic dehumidifiers

Anhydrous sodium chloride is a cheap, widely used desiccant with high drying capacity. However, it dries slowly and is unsuitable for drying alcohols, phenols, amines, amino acids, amides, nitriles of acids, esters, some ketones and aldehydes, since it forms compounds with them. In addition, calcium chloride contains lime as an impurity, therefore, it cannot be used for drying acidic substances. It is used for preliminary drying of saturated, ethylene hydrocarbons, acetone, ethers and other compounds from water.

Anhydrous magnesium sulfate is one of the best neutral drying agents, having a high water absorption rate and good absorption capacity; used for drying the largest number of compounds.

Anhydrous sodium sulfate is a cheap neutral desiccant that is used to pre-remove large quantities of water, but it is slow and does not bind all the water. It cannot be used for drying benzene, toluene, chloroform.

Caustic soda and caustic potassium are good and quick drying agents, but they find only very limited use, exclusively for amines and ethers. Absorbent cotton, previously dried in an oven at 100 ° C, is an excellent drying agent and is used in calcium chloride tubes.

Table - Drying agents for organic compounds

Drying with heat and normal atmospheric pressure

The most widely used method is drying using heat and normal atmospheric pressure. The following methods of drying by heating are distinguished: 1) in the open air; 2) in drying cabinets.

The choice of drying method depends on the properties of the substance and conditions.

When drying in the open air, the dried substance is placed in a frying pan or in a porcelain cup and heated in some kind of bath (sand, oil, water) or on an electric stove. In this case, the substance is mixed with a glass rod or spatula, preventing a crust from forming. In this way, many substances, mainly inorganic, that can withstand heat can be dried.

The disadvantage of this drying method is that it is almost impossible to regulate the drying temperature and therefore overheating is possible, sometimes accompanied by melting of the substance being dried.

It is more convenient to dry the substance in drying cabinets. In laboratories you can find several types of drying cabinets for drying at normal atmospheric pressure: with electric, gas or other heating. They can be asbestos or metal (most often copper).

The duration of drying depends on the amount of the substance being dried, the thickness of its layer, the drying temperature and the humidity of the substance.

Drying rules

1. The substance to be dried must first be squeezed out of excess water.

2. The layer of substance when drying both in air and when heated should not exceed 10 mm.

3. The dried layer needs to be mixed and leveled again from time to time,

4. When drying in simple drying cabinets, overheating should be avoided. In most cases, the drying temperature should not exceed 105 – 110 °C.

5. It is dangerous to dry solids containing organic solvents in an electrically heated oven.

6. When using concentrated sulfuric acid as a drying agent, pour it into absorption flasks so much that liquid transfer does not occur.

6.Physical disinfectants

Sunlight. Direct sunlight has a detrimental effect on microbes, especially in open steppe areas. To use the disinfecting effect of the sun's rays, windows and doors of premises are kept open, and harnesses, blankets, carts and other items of household equipment and transport are exposed to the sun, especially in the middle of the day. However, it should be borne in mind that sunlight disinfects only the surface of objects, without penetrating into them. Diffused sunlight has a weaker effect, and in the shade microbes live for a long time. Artificial light sources. In veterinary practice, so-called bactericidal (i.e., bacteria-killing) lamps are used mainly for disinfecting the air of veterinary institutions, wall surfaces and livestock products in refrigeration chambers, as well as incubators. Typically, various mercury-quartz lamps emitting ultraviolet rays are used for this purpose. Drying. Non-spore forms of microbes die very quickly from drying out. Only microbes that have a fatty-wax shell are preserved, which protects them from drying out (for example, tuberculosis bacilli and erysipelas bacilli). Taking into account the effect of drying on pathogenic microbes, contaminated premises are thoroughly ventilated, drainage ditches are arranged around them, and in the premises where animals are located, abundant, moisture-absorbing (hygroscopic) bedding in the form of peat, sawdust, etc. is created. This creates conditions unfavorable for development of microorganisms, especially for microbes that do not have protective shells. That is why all premises during the summer need to be thoroughly ventilated, dried and prepared for housing animals for the autumn-winter period. Drying wet pastures is also of great sanitary importance. Sunlight and drying throughout the year (spring, summer, autumn) reliably disinfect pastures, meadows and water bodies contaminated with non-spore forms of microbes and filterable viruses. Spore forms of microbes (spores of anthrax, tetanus, etc.) and microbes that have a fatty-wax coating are more resistant; When pastures become infected with these microbes, a long time is required for natural disinfection of their surface.

Thermal agents.

Fire. Fire is the most reliable means of destroying pathogens of infectious diseases, but its use is limited. The corpses of animals with certain diseases, leftover food and garbage contaminated with spore microbes are burned in the fire. Flambing (firing). This is one way to use fire as a disinfectant. On a fire or with a blowtorch, burn the surface of equipment contaminated with microbes (shovels, pitchforks, buckets, etc.) that were in contact with infectiously sick animals, as well as personal care items (scrubbers, chain chamburs, buckets for watering animals, etc. .). Wooden parts (handles of shovels, forks, etc.) are fired until slightly browned (slightly brown), metal parts - until well heated. This method of disinfection is often used in poultry houses, especially in those departments where hatchery chickens are housed in the first days of life, as well as in rabbitries, since chemical disinfectants, in particular those with a smell (creolin, carbolic acid, etc.), have a harmful effect on the health of chickens and especially rabbits. Dry heat. This is no less reliable than fire. In hotly heated bathhouses, they hang infected clothes, dressing gowns, blankets and other fabric items that have been in contact with infectious animals on stretched ropes, and warm them there for several hours, maintaining a high temperature (80-90°) continuously in the bathhouse all the time furnace firebox. Such heating reliably kills all non-spore forms of microbes and filterable viruses. The air temperature of the bath is measured with a thermometer hung near the window inside the bath (viewing window). The effect of dry heat can be enhanced by water vapor, as is usually done in any bathhouse, by pouring water over the hot stones of a specially made oven in a furnace or a folded hearth with an installed water boiler. Ironing Using a well-heated iron on the surface of infected fabrics (clothing, dressing gowns, towels, etc.), especially when lightly moistening them (spraying), also completely kills all non-spore forms of microbes and filterable viruses, without causing damage to the ironed fabrics. Boiling water destroys all pathogens of infectious diseases. To disinfect objects contaminated with non-spore pathogens, it is enough to boil them in water for 30 minutes; if infected with spore microbes, boil for 1.5 hours. To enhance the disinfectant effect, add 2-3% soda, potash, green soap to boiling water, or make a saturated ash lye. Infected gowns, dressings, bags, blankets, bristles and wool are disinfected by boiling. Surgical instruments and syringes are boiled in a 1-2% soda solution. Woolen and cotton fabrics, as well as sweat sweaters, when infected with spore-forming pathogens, are also disinfected by boiling. When boiling, make sure that the things to be disinfected are completely immersed in boiling water; during boiling, they must be turned (stirred) all the time for better disinfection and to avoid damage (possible burning). Water vapor Woolen fabrics, cloth items, felt, brushes for cleaning horses when boiled can lose their strength, color and become unusable prematurely; to avoid this, they are disinfected with flowing water steam, using steam chambers for this purpose. Water vapor is more bactericidal than dry heat. The simplest steam disinfection chamber consists of a small cast-iron boiler mounted on a tagan or stove, and a wooden barrel attached to it, in the bottom of which several holes are drilled. Water is poured into the cauldron, things are hung in the barrel on crossbars or hooks, and then it is closed with a lid into which a thermometer is embedded. When the water in the boiler boils, steam penetrates through the holey bottom into the barrel and leaves it through a hole in the loosely closed lid. The beginning of disinfection is considered to be the moment when the temperature on the thermometer inside the chamber reaches the boiling point (about 100°). For soil spore infections, water vapor for disinfection is used only under high pressure, using autoclaves.

Biothermal method. Disinfection methods based on the use of the disinfecting effect of high temperature also include the biothermal method of disinfection. It is used for the disinfection of manure contaminated with non-spore forms of microbes or viruses. Manure contaminated with spore-forming microbes (anthrax, emphysematous carbuncle, tetanus, etc.) is burned.

The essence of the biothermal method is that in the manure, as a result of the vital activity of rapidly multiplying microbes in it, a high temperature develops, which has a detrimental effect on the causative agents of infectious diseases and helminth embryos found in the manure. For biothermal disinfection of manure, choose a site on level ground away from roads, ponds and premises where animals are located. In a designated area, a 0.5 m depression is dug, the bottom of which is compacted with clay mixed with building rubble. The width of such a recess is from 1.5 to 2 m, the length is arbitrary, depending on the amount of manure intended for disinfection. A layer (15-20 cm) of uninfected manure or straw is placed at the bottom of the recess. Then all the infected manure is placed in a cone-shaped stack. The height of such a stack is from 1.5 to 2 m. Manure stacked is covered on top and sides with a layer of 10-15 cm of straw or uncontaminated manure, and then covered with the same layer of sand or earth. For air access, holes are left into which wooden pipes or sheaves of reeds and reeds are placed. Dry manure is moistened with slurry during stacking. If the manure is very wet (from cattle), then dry horse manure is added to it.

In such cases, manure from calves suffering from paratyphoid fever, diplococcal infection, as well as from ringworm, paratyphoid abortion of mares is kept for 2 months;

manure obtained from horses suspected of being infected with infectious anemia is kept for 3 months;

from horses that gave a positive reaction to mallein - 2 months;

for contagious pleuropneumonia - 2 months;

for paratuberculosis - 6 months;

for tuberculosis - 4 months.

After this, it can be taken out for fertilization.

In organic chemistry, many reactions can only be carried out in the absence of moisture, so the starting substances are pre-dried.

Drying is the process of freeing a substance (regardless of its state of aggregation) from liquid impurities. When drying, water or residual organic solvents are most often removed. This process is often the final step in the purification of an individual chemical.

Drying can be carried out using physical methods of separation and purification of organic substances (freezing, salting out, sublimation, extraction, evaporation, azeotropic, fractional distillation, etc.), and using drying reagents. The choice of drying method is determined by the nature of the substance, its state of aggregation, the amount of liquid impurity and the required degree of drying (see Table 1.3). Drying is never absolute and depends on the temperature and the drying agent.

Table 1.3 The most common dehumidifiers and their applications

End of table. 1.3

Among chemical drying reagents, according to the methods of binding liquid impurities, three main groups of substances are distinguished:

1) substances that bind liquid impurities as a result of a chemical reaction: some metals (sodium, calcium), oxides (phosphorus (V), calcium, barium), hydrides (calcium, methylaluminum);

2) hygroscopic substances that form hydrates: anhydrous salts (calcium chloride, potassium carbonate, magnesium, sodium, potassium sulfates) and lower hydrates, which transform upon contact with liquid impurities into stable higher hydrates (magnesium perchlorate, the so-called anhydrone), concentrated sulfuric acid , sodium and potassium hydroxides;

3) substances that absorb liquid impurities due to physical adsorption: zeolites, active aluminum oxide, silica gel.

The drying agents used should not dissolve in organic solvents, but act quickly with sufficient drying capacity and be inert towards the substance being dried.

Drying gases. Gaseous substances are dried using chemicals and freezing. Low-boiling gases are frozen out (cooled to a low temperature) in a refrigeration trap (Fig. 1.45), which is connected to a vacuum line with an oil pump. The gas passes through a tube, the end of which almost reaches the bottom of the vessel, placed in a cooling bath with a mixture of dry ice and methanol or liquid nitrogen. Freezing allows you to achieve a high degree of drying, avoiding the reaction of the desiccant with the gas and its contamination.

To dry gases with solid chemical reagents, absorption devices (Fig. 1.46) and vessels for solid washers (Fig. 1.47) are used. Glass wool swabs are placed in these vessels where gases enter and exit to prevent the desiccant particles from being carried away with the gas. To dry gases with liquid reagents, various types of washing vessels are used, which are filled no more than 1/3 with a desiccant (Fig. 1.48). The most effective drying is carried out in flasks with a glass porous plate (Fig. 1.49).

1 - trap; 2 Dewar flask

a - drainage tube; b, d - calcium chloride tubes; c - duck for drying phosphorus gas (V) oxide

a - with a spray nozzle; b - with a curved gas scrubber 1, 2 - tubes for gas injection; 3 - nozzle; 4 - tube

By selecting the height of the irrigation layer and adjusting the gas transmission rate, good contact of the gas with the dryer is ensured. When using concentrated sulfuric acid, be sure to install safety flasks equipped with special devices that additionally secure the gas tubes.

Drying liquids. Liquids containing relatively large amounts of moisture are initially dried by physical methods and then using adsorbents or chemical drying reagents.

Liquids whose boiling points differ significantly from the boiling point of water and do not form azeotropic mixtures with it are dried by fractional distillation on an efficient column.

Azeotropic distillation is used to dry liquids that form double or triple azeotropic mixtures with water with a boiling point below the boiling point of the individual components. This physical method is often used for drying in combination with extraction. To separate the aqueous layer, an organic solvent that is immiscible with water is added to the liquid to be dried. The remaining water from the organic layer is removed by azeotropic distillation.

Most liquid organic substances are isolated from aqueous solutions using salting out. To do this, an electrolyte is added to the mixture, which does not dissolve in organic matter, but dissolves in water. The electrolyte is added in the form of solid

1 - flask with the substance to be dried; 2 - air intake valve; 3 - cooled trap for water vapor; 4 - Dewar vessel; 5 - chemical absorber; 6 - outlet to high vacuum

This substance or concentrated solution forms an aqueous phase, which is removed by decantation. The organic layer is dried and purified by distillation. For example, salting out using a concentrated solution of sodium chloride can remove some of the water from an aqueous solution of diethyl ether.

More often, drying of organic liquids is carried out in their direct contact with drying substances. To reduce the loss of substance due to adsorption, the desiccant is added in small portions (1-3% by weight of the solution). The vessel with the liquid to be dried is closed with a stopper, which, in the event of gaseous substances being released, is equipped with a calcium chloride tube. The contents of the vessel are shaken periodically. The resulting aqueous solution of the drying reagent is separated in a separatory funnel. If necessary, the operation is repeated. Sometimes the liquid with the drying agent is heated in a flask under reflux. The drying operation may

last from several hours to several days. The dried liquid is filtered or decanted and distilled.

Solutions of unknown substances are dried with indifferent desiccants (magnesium sulfate). Aqueous solutions of thermally unstable substances are subjected to freeze drying (Fig. 1.50). To do this, the solution is frozen in a thin layer and kept in a vacuum (1.33-2.66 Pa (0.01-2 mm Hg)). Due to the rapid evaporation of water due to sublimation, the frozen layer is cooled. Adsorbents trap released water vapor. The resulting fine-crystalline product retains

1 - container with the liquid to be dried; 2 - column with zeolite; 3 - a receiver for dry liquid its biological activity, its solubility increases, it is protected from the oxidative effects of air oxygen.

Organic liquids can be dried by passing through a column filled with molecular sieves (dynamic method) (Fig. 1.51) or by keeping them over an adsorbent (static method).

Drying crystalline substances. When drying crystalline substances, the liquid is first removed mechanically (by centrifugation, filtration, pressing, etc.).

Volatile impurities from crystalline non-hygroscopic substances are removed by distributing the substance in a thin (1-2 cm) layer on glass, filter-ceramic plates in the open air at room temperature. The dried substance is covered with filter paper to protect it from mechanical contamination.

Drying efficiency increases sharply with increasing temperature. Thermally stable crystalline substances can be dried in ovens at temperatures that must be well below the melting point of the substance. It is not recommended to remove volatile substances in this way (for example, residues of organic solvents), since the mixture of their vapors with air may explode upon contact with the heater wire spiral!

Fine-crystalline substances form a crust on the surface during drying, so for faster drying they are mixed repeatedly.

To dry substances that are unstable when heated, vacuum cabinets are used that regulate the temperature by changing the pressure.

Crystalline substances can be effectively dried using desiccators, in which the air is dried with chemical reagents. Vacuum desiccators are used to speed up drying. The vacuum in them is maintained using a water jet pump (Fig. 1.52). A thick-walled vessel under a vacuum can explode, so before working it should be wrapped in a towel or thick cloth.

Rice. 1.52. Connection diagram of a vacuum desiccator with a vacuum pump 1 - vacuum desiccator; 2 - pressure gauge; 3 - safety bottle

The drying reagent for desiccators is selected depending on the chemical properties of the substance being dried (see Table 1.3). Hydrocarbon solvents (benzene, petroleum ether) are removed using paraffin shavings or paraffin-impregnated paper.

Concentrated sulfuric acid is used to dry the residues of diethyl ether, ethanol, and basic substances (aniline, pyridine). When using it, to reduce splashing and increase the contacting surface, the lower part of the desiccator is filled with glass or ceramic Raschig rings; A Wulf safety bottle is installed between the desiccator and the water jet pump. Concentrated sulfuric acid is not used at elevated temperatures and for drying in vacuum (medium and high).

In vacuum desiccators, air is supplied and removed through a capillary tube bent upward or fenced off with a piece of cardboard, which protects the substance being dried and the desiccant from splashing.

A drying gun (Fisher) (Fig. 1.53) is used to dry relatively small quantities of substances at elevated temperatures in a vacuum. Liquid is poured into the flask up to half the volume at 30 °C below the boiling point of the substance being dried. Typically, non-flammable liquids are used (chloroform, water, carbon tetrachloride, etc.). Liquid vapors heat the dryer body, inside of which there is a drying boat.

Vessel; 2 - reflux condenser; 3 - flask; 4 - retort; 5 - porcelain boat

Rice. 1.54. Rotary

1 - water bath; 2 - rotating flask for evaporation; 3 - motor and seal; 4 - water refrigerator; 5 - distillate receiver; 6 - outlet to the vacuum pump; 7 - water inlet and outlet; 8 - supply of evaporated liquid

the substance in question. In a retort-shaped flask, the adsorbent traps the released volatile impurities. Drying continues for 1 hour.

Thermally unstable substances are dried at low temperatures (freeze drying). Sometimes azeotropic distillation is used to dry solids, so the water of crystallization from oxalic acid is distilled off with carbon tetrachloride.

Crystalline substances can also be dehydrated by extraction with solvents (acetone, methanol, ethanol, etc.), which are miscible with water and in which solids are insoluble. To quickly dry crystalline precipitates, a solvent is poured into a conical flask so that a layer of liquid forms above the level of the solid substance. The contents of the flask are shaken for about 1 minute, left for 15-20 minutes, and the liquid is drained; The operation is repeated with new portions of solvent 3-4 times. The solution is filtered, the crystals are dried on a ceramic porous tile under traction or in a vacuum desiccator, vacuum drying cabinet (hygroscopic substances).

Evaporation is the partial or complete removal of a solvent from a dissolved substance. Solutions of non-volatile solids are evaporated by boiling in an evaporation dish or beaker. The process is accelerated by passing a current of heated air over the surface of the liquid or removing vapors using adsorbents. To lower the temperature of the process and reduce the likelihood of air contamination with moisture, evaporation is carried out in a vacuum.

The process occurs most efficiently and quickly in rotary (film) evaporators, which make it possible to avoid overheating and boiling of the liquid (Fig. 1.54). In rotary evaporators, when using a water-jet pump, the evaporation rate from a 1-liter flask reaches 500 ml/h.

CONTROL QUESTIONS

Widely used in the chemical and food industries, in halogen-pharmacological production, in the processing of medicinal plant raw materials, and so on. Drying is used when carrying out various kinds of biochemical analyses, when preserving blood plasma and its individual fractions, tissues for transplantation, and for morphological or histochemical studies tissues, when obtaining preparations for electron microscopy, etc. V. is used as an aid in disinfection. Some types of microbes (influenza bacillus, meningococcus, gonococcus, dysenteric amoeba cysts and others) quickly die when dried. The causative agents of typhoid and paratyphoid fever, brucellosis, tuberculosis, diphtheria, smallpox and others can withstand drying for a long time. Microbial spores remain viable and virulent in a dried state for many years.

Existing drying methods are based on chemical binding, or sorption, of the liquid being removed, evaporating it at low, high temperatures or in a vacuum when heated or frozen - freeze drying.

In laboratories, gases are dried by passing them through concentrated sulfuric acid, located in Tishchenko, Drexel or Wulff flasks, through solid absorbers, for example, calcined calcium chloride, phosphoric anhydride and others, with which absorption columns or special vessels are filled.

Dehydration of liquids is carried out by introducing hygroscopic substances into them - pieces of fused calcium chloride or caustic potassium, calcined copper sulfate or calcium oxide and others. In this case, the desiccant should not chemically interact with the liquid being dried. The final dehydration of many organic liquids is carried out using sodium metal.

Solids are dried by heating them in porcelain cups, in open air braziers or in drying ovens, by keeping them in a desiccator over hygroscopic substances, usually over concentrated sulfuric acid, calcined calcium chloride, sodium hydroxide, phosphoric anhydride when removing water, over calcium chloride when removing alcohol, over paraffin when removing ether, heating in vacuum desiccators or vacuum drying ovens, heating using infrared rays.

Drying leads to a noticeable change in the physicochemical properties of substances, for example boiling and melting points, electrical conductivity, reactivity and others. Drying of substances that undergo denaturation and other irreversible changes even with moderate heating in a wet or dissolved state is carried out by lyophilization. The choice of drying method and conditions depends on the properties of the material being dried and its subsequent purpose.