Drying is a chemical operation performed to remove moisture. Solids are dried by heating, for example, in drying cabinets or storage in closed glass vessels, desiccators, over substances that absorb water vapor ( sulphuric acid, calcium chloride and phosphorus pentoxide). In both cases, the process is accelerated if the drying is carried out under reduced pressure or in a vacuum. Liquids are dried by prolonged storage or boiling over substances that absorb or destroy water. For drying liquids, in addition to the already mentioned CaCl 2 and H 2 O 5, fused sodium sulfate, metallic sodium and potassium, quicklime and others are used. Drying of gases is achieved by passing them over one of the same substances, as well as cooling to the temperature of liquid air, and water vapor condenses.

Soil drying

Soil drying is a method of influencing the soil, with the aim of mobilizing the stock of nutrients contained in it (mainly phosphoric acid), which at the same time turn into soluble forms available for plant nutrition. Until now, this method has been developed only in laboratory conditions. A number of experiments carried out in different time with different soils, it is definitely found that drying the soil increases the subsequent yield of plants. Drying the soil not only directly changes chemical (decomposition of unstable organic compounds) and physico-chemical (change

Read more about the disease in children.

Also during therapy, the possibility of sharing personal hygiene products, bedding, towels, hats, hairpins and hair ties should be minimized. During the treatment period, compliance with these rules is mandatory.

Pediculosis does not choose social status. Infection can occur in the cleanest family members.

Everyone should know not only how to quickly remove lice at home, but also how to prevent the possibility of re-infection. Drug use and therapy should be considered folk remedies. Medicines that can be purchased at pharmacies are available in the following forms:

• lotion;
• shampoo;
• spray;
• spray can;
• ointment;
• emulsion concentrate.

In addition to head lice, there are pubic and clothing insects. Adults have to deal with these forms of the disease. It is necessary to treat sexual partners at the same time. The entire course of therapy requires a daily change of bedding and underwear, processing them using a high temperature regime (washing and ironing).

Pharmacy anti-pediculosis agents

Consider the question of how to get rid of lice and nits in 1 day at home using traditional medicines purchased at a pharmacy.

Refers to a group of drugs that act after a single application. The tool is detrimental to both adults and their larvae and nits. With the treatment of the patient's head, it is simultaneously used to prevent pediculosis in other family members. Application rules:

How to get rid of lice and how to remove nits with this tool:

1. Cover your shoulders with a towel.
2. Briefly press the sprayer to treat the entire surface of the hair.
3. Leave for half an hour, you do not need to cover your head.
4. Wash hair thoroughly with normal soap, rinse well with water.
5. Dead lice, like nits, require long combing with a comb.

A drug based on permethrin. Active against head and pubic lice. Destroys pathogens after a single use. The application method is similar to Nittifor.

It can be used for prevention in a team environment where re-infection is possible. To do this, "Veda-2" is applied to the hair after shampooing and is not washed off after drying. The drug is active for 2 weeks, preventing insects from multiplying if they re-enter the hair.

Pedilin

Use the product with caution. Contact with mucous membranes or eyes requires immediate rinsing with plenty of water.

The drug is available in several forms. With a severe form of lice, an emulsion and Pedilin shampoo are used at the same time.

Means based on permethrin. It is considered one of the most effective drugs. Approved for use from the age of five. It is produced in the form of a concentrate, from which, immediately before the treatment of the infected area, a working solution of the emulsion is made (0.5 ml of concentrate is added for every 50 ml of water). The finished solution is active for 8 hours.

ethnoscience

Let us dwell on the question of how to remove nits and adults with folk remedies.

pharmachologic effect

Shows activity of the following protozoa:

• intestinal Giardia (Giardia intestinalis or Giardia Lamblia, Giardia duodenalis);
• vaginal Trichomonas (Trichomonas vaginalis);
• dysentery amoeba (Entamoeba histolytica).

The drug destroys strains of pathogens of severe anaerobic infectious processes in the intestine, including:

• gram-negative bacteroids (Bacteroides spp.), including Bacteroides fragilis, which produce enterotoxins and pyogenic bacteria B. melaninogenicus;
• gram-positive clostridia (Clostridium spp.);
• peptococci Peptococcus spp.;
• eubacteria (Eubacterium spp.);
• peptostreptococcus (Peptostreptococcus spp.);
• fusobacteria (Fusobacterium).

Description of Tinidazole from worms

How does Tinidazole work?

Passing through the processes of biotransformation in the liver, the active compound partially decomposes, forming pharmacologically active complexes that can inhibit the growth and vital activity of microorganisms, enhancing the effect of the drug.

Dosage form

The product is available in round convex tablets with a white or beige film coating. Two layers (white and yellowish-gray) are visible on the transverse fracture. One tablet contains 500 mg of the active ingredient.

What diseases are prescribed

The drug is also used in the combined treatment of gastrointestinal pathologies, the development of which provokes Helicobacter pylori, and in the treatment of aerobic-anaerobic infections (in combination with antibiotics).

How is it excreted from the body

The drug is completely and very actively absorbed into the mucous membrane of the stomach and intestines. Due to the similarity of the structure of tinidazole with fats, it exhibits almost 100% bioavailability (ability to be absorbed). The active substance quickly penetrates into the tissues of the body. Residues of the drug are found in the blood 72 hours after the last dose, the maximum concentration of the active ingredient in the blood is observed 2 hours after taking the tablets.

The drug passes through the placenta into the blood of the fetus during pregnancy. Excreted with human milk breastfeeding within 3 days.

The main amount, almost 50%, is excreted from the body mainly with bile, about 25% is excreted through the kidneys with urine, and 12% with feces.

Instructions for use

Tinidazole is considered by experts as an effective antihelminthic agent for giardiasis.

Giardiasis - what is it?

The ways of infection with Giardia are unwashed hands, water from the tap or reservoirs, which they drink without boiling. Often, Giardia enters the intestines from dirty fruits, berries, vegetables, and items infected with cysts (spore form), including bedding and underwear, toys, and dishes.

Giardiasis leads to biliary dyskinesia, atopic dermatitis, neurological disorders, damage to intestinal tissue, chronic inflammation v gallbladder and liver, allergic reactions with severe itching, chronic intoxication (poisoning) of the whole organism.

At the same time, the patient is observed: nausea, constipation or frequent defecation (up to 5-6 times a day) with copious frothy greenish-yellow stools with a pungent odor, as well as symptoms of poisoning with Giardia toxins and their metabolic products (headaches, allergic manifestations, loss of strength, irritability, neuroses).

The course of allergic reactions in giardiasis is protracted, with exacerbations.

How to take tinidazole with giardiasis

Patients of any age group take Tinidazole tablets once a day after meals or with food. This mode of using the drug is prescribed precisely for the invasion (introduction into the body) of lamblia.

For adults

Adult patients take 2 grams or 4 tablets with a dosage of 500 mg at a time.

For kids

The drug is approved for the treatment of giardiasis in childhood starting at the age of 12. Studies on the effect of the drug on patients younger than this age have not been conducted.

With giardiasis, children and adolescents from 12 years of age Tinidazole is prescribed in a single daily dose, which is calculated taking into account the weight of the child. The norm is 50 - 75 mg per kilogram of body weight.

For example: the weight of a child is 35 kg, we calculate the smallest daily dose using the formula 50 mg * 35 = 1,750 mg or 3.5 tablets.

However, the total dose per day for a child cannot be more than 2 grams.

Is it possible for pregnant and lactating mothers?

During pregnancy, the drug is absolutely contraindicated in the first three months of gestation, since various deviations in the intrauterine development of the embryo are possible.

The use of the drug after the first trimester is possible only:

• with the permission of the gynecologist in case of severe giardiasis, if there is no alternative medication in the treatment of a pregnant woman;
• in the event that the degree of possible benefit for the pregnant woman is higher than the likely negative impact of the product on the fetus.

Since the medicinal substance is easily absorbed into women's milk, breastfeeding of the baby is stopped for 72 hours after the mother takes the pills - the time during which the active substance is stored in milk.

Application features

1. In the treatment of giardiasis, joint treatment of persons in close contact (families, children's groups) is recommended.
2. If undesirable neurological side reactions appear, treatment is stopped.
3. Alcohol when using tablets is completely unacceptable, including 2 days before and after treatment, since when it is used together with the drug, there is an excessive accumulation of acetaldehyde, resulting in severe self-poisoning. At the same time, there is a high probability of developing a so-called disulfiram-like reaction with severe symptoms of intoxication (uncontrollable vomiting, tachycardia, cough, suffocation, drop in blood pressure, panic).
4. During the period of use of the drug, urine may turn dark.
5. During the use of the drug, you should not engage in activities that require an increased concentration of attention and high speed mental and motor responses.
6. If after therapy, after 7-10 days, Giardia is found in the feces or contents of the small intestine, which confirms the ineffectiveness of the treatment, a second course is prescribed using the same dosages.

Side effects

Sometimes during treatment side effect drug, which is expressed in the following disorders:

• dryness of the oral mucosa, taste of metal in the mouth, tongue coated with a white-yellow coating, glossitis (inflammation of the tissues and mucous membrane of the tongue), stomatitis, nausea, bouts of vomiting, diarrhea;
• neurological disorders, including headache, severe weakness;
• sudden hyperemia (reddening of the skin) due to vasodilation, dizziness;
• in rare cases, convulsive muscle contractions, ataxia (motor coordination disorder), decreased skin sensitivity and muscle strength, muscle atrophy during long-term treatment.

If such manifestations occur, be sure to stop using the pills and consult a doctor.

May be observed:

• changes in the blood picture (a temporary decrease in leukocytes - transient leukopenia);
• mycosis (fungal infection) of the urinary tract;
• slight fever, feeling tired.

Rarely, hypersensitivity reactions (allergic) can develop in the form of rashes, itching, blisters like urticaria, angioedema of the eyelids, face, tongue and larynx, preventing normal breathing. When such symptoms appear, it is necessary to urgently call an ambulance team and consult a doctor.

If undesirable manifestations do not disappear, but on the contrary, they increase, or any other negative side effects suddenly appear, it is necessary to consult a doctor.

Contraindications

The tool is prohibited for use:

• if the patient has a special sensitivity of an allergic nature to any of the ingredients in the medicine;
• with neurological disorders and organic lesions of the nervous system;
• if a violation of the functions of the hematopoietic organs with deviations in laboratory studies of the blood picture is detected;
• after severe injuries suffered within six months;
• in the first three months of pregnancy;
• during breastfeeding.

Interaction with other drugs

Tinidazole enhances the effect of indirect anticoagulants - warfarin, fraxiparine, therefore, to prevent the risk of hemorrhage, the dosage should be reduced by 50%.

In combination with ethanol (alcohol), it can give severe Antabuse-like reactions.
Ethionamide weakens the effect of the drug.

Normally tolerated with the parallel use of sulfonamides, antibiotics, including cephalosporins, aminoglycosides, rifampicin, erythromycin.

Analogues

Among the synonyms of the drug (drugs with the same active substance), Tinidazole-Acri is distinguished.

Analogues - pharmacological preparations with a different composition, but a similar therapeutic effect: Fazizhin, Metronidazole, Tiniba, Metrogyl, Clomezol.

Application of Tinidazole

In addition, most antihelminthic drugs have similar or similar negative effects, including allergic and neurological reactions of the body to the drug.

Organic liquids are usually dried with solid inorganic desiccants, and a small amount of the latter should be taken to avoid losses from adsorption of the substance by the desiccant. First, the organic liquid is shaken with a small amount of a drying agent (up to 3% by weight of the solution), after a while a small layer of an aqueous solution of the drying agent is released if substances that form hydrates with water (calcium chloride, sodium sulfate, sodium hydroxide, sodium 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, phosphoric anhydride does not stick together, etc. After such treatment, the organic liquid is placed in a flask, which stopper with a calcium chloride tube and leave to stand overnight with a new portion of the desiccant. Before distillation, the dried organic liquid is filtered off or, most commonly, decanted.

2.5.3. Drying solids

Drying outdoors 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 water vapor pressure in the air and above the body comes into equilibrium.

The substance to be dried, for example, wet crystals, is poured onto a sheet of clean filter paper, distributing them in a layer no more than 3-5 mm thick. In this case, salt should not be crushed, since the looser the layer, the sooner and better the drying will take place. To protect against dust or contamination, the substance to be dried is covered on top with another sheet of clean filter paper and left for several hours. Then the substance to be dried is mixed with a spatula so that the more moist lower layers are on top; the mass must 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 stirred several times, especially if the layer thickness was significant. The dried salt is folded with a spatula into a jar and tightly closed. If, when standing in a tightly closed jar, drops of water appear on its walls, this means that the substance was not dried completely enough and drying should be repeated.

Drying in air is a rather lengthy operation and is resorted to only when the substance to be dried decomposes when heated or when it is desired to obtain a substance in the form of a loose, free-flowing powder without lumps. In this way, it is possible to dry non-hygroscopic substances, i.e., not absorbing moisture from the surrounding air.

Drying under reduced pressure (vacuum drying)

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

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

Drying in a desiccator

It is convenient to dry highly hygroscopic substances deliquescent 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 jet pump, between which a manometer and a safety bottle are placed.

Sometimes desiccators explode under vacuum, so they must be wrapped in a towel before turning on the pump. When opening the vacuum desiccator, in order to avoid spraying the dried substance with air, turn the tap very carefully and slowly. Only after the pressure has been equalized can the lapped lid of the vacuum desiccator be opened.

A drying agent is placed in the desiccator, a substance that vigorously absorbs moisture. 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 to be dried. Most often, calcium chloride, soda lime, caustic soda, caustic potash, phosphoric anhydride, concentrated sulfuric acid are used as desiccants for desiccators. At the same time, 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, alcohol, ether, acetone, aniline, and pyridine residues. For the adsorption of hydrocarbons, especially hexane, naphtha, benzene and its homologues, paraffin is used as a filler for the desiccator; to remove acidic substances, caustic soda or caustic potash is used. Water and alcohols are well absorbed by phosphoric anhydride, soda lime.

Basic dryers

Anhydrous sodium chloride is a cheap and widely used desiccant with a high drying capacity. However, it dries slowly and is unsuitable for drying alcohols, phenols, amines, amino acids, amides, acid nitriles, esters, some ketones and aldehydes, as 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 sulphate is one of the best drying neutral agents, with high water absorption rate and good absorption capacity; used to dry the largest number of compounds.

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

Caustic soda and caustic potash are good and fast 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 pipes.

Table - Dryers for organic compounds

organic compounds	Dehumidifiers
hydrocarbons	CaS1 2 , CaSQ 4 , P 2 O 5 , Na
Halogen derivatives	CaC1 2, Na 2 SO 4, MgSO 4 P 2 O 5
	MgSO 4 , CaSO 4 , K 2 CO 3 , CaO
	CaC1 2, CaSO 4, Na
Aldehydes	CaC1 2, MgSO 4, Na 2 SO 4
	MgSO 4 , Na 2 SO 4 , K 2 CO 3
organic acids	MgSO 4 , Na 2 SO 4 j CaSO 4
	KOH, NaOH, K 2 CO 3 , CaO
Nitro compounds	CaC1 2, Na 2 SO 4

Drying with heat and normal atmospheric pressure

Drying at heating and normal atmospheric pressure is the most widespread. There are the following methods of drying when heated: 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 substance to be dried is placed in a frying pan or in a porcelain cup and heated in a bath (sand, oil, water) or on an electric stove. In this case, the substance is stirred with a glass rod or spatula, preventing the formation of a crust. In this way it is possible to dry many substances, mostly inorganic, which can withstand heat.

The disadvantage of this drying method is that it is almost impossible to control the drying temperature and therefore overheating is possible, sometimes accompanied by the melting of the substance to be 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 are asbestos or metal (most often copper).

The duration of drying depends on the amount of the substance to be dried, the thickness of its layer, the drying temperature and the moisture content of the substance.

Drying rules

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

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

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

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

5. Solids containing organic solvents are dangerous to dry in an electrically heated oven.

6. When using concentrated sulfuric acid as a drying agent, it should be poured into absorbing flasks so much that there is no transfer of liquid.

Drying (desiccation) is usually understood as the removal of water or solvent residues from a liquid, solid or gaseous substance.

Drying can be carried out by physical methods commonly used for separation and purification of substances (evaporation, freezing, extraction, azeotropic distillation, distillation, sublimation, etc.), as well as with the help of drying reagents.

When choosing a drying method, one should take into account the state of aggregation of the substance, its chemical properties, the content of water or other substance that must be removed during drying, and the required degree of drying.

Desiccant

Chemical drying agents can be divided into three main groups according to the way they bind water.

1. Substances that form hydrates with water. These are anhydrous salts (CaCl2, K2CO3) or lower hydrates, which, upon contact with water, turn into stable higher hydrates (Mg(ClO4)2-2H2O).

2. Substances that absorb water as a result of a chemical reaction, for example, some metals (Na, Ca) and oxides (P4O10, CaO).

3. Substances that absorb water by physical adsorption, such as active alumina, silica gel, zeolites.

Substances that form hydrates

Calcium chloride CaCl2 is most commonly used as a filler in drying tubes and columns for drying gases, as an absorbing agent in desiccators, and for the direct drying of many organic liquids.

Calcium chloride is used in powdered or calcined form. Powdered anhydrous CaCl2 contains, as a rule, a small amount of the basic salt Ca(OH)Cl. Calcium chloride is a medium efficiency desiccant. It is not very effective for drying HCl, HBr, HI, Br2, SO3 and is completely unsuitable for drying ammonia and amines, with which it forms complex compounds. Calcium chloride can be used repeatedly if it is regenerated by calcination after each use.

Concentrated sulfuric acid H2SO4 is an effective agent for drying gases with which H2SO4 does not react (H2, O2, N2, Cl2, CH4, C2H6, CO, HCl, N2O, etc.). Do not use sulfuric acid in vacuum desiccators as a water absorbent.

Conc. H2SO4 is a fairly strong oxidizing agent, especially when heated. It oxidizes HI and partially HBr (but not HCl) to free halogens. Therefore, it cannot be used to dry these substances, as well as H2S, РН3, AsH3, HCN, unsaturated hydrocarbons, ammonia, amines. The drying efficiency of H2SO4 decreases sharply as it is gradually diluted with water. Thus, 95.1% acid is already significantly less effective than 98.3% acid. Conc. H2SO4 sometimes contains SO2. Therefore, before drying the gases, it is necessary to heat the acid until smoke appears, while SO2 is completely removed.

Magnesium perchlorate (anhydrone) Mg(ClO4)2 is a highly efficient drying agent that can be used to dry most gases.

Anhydrone is used to absorb water vapor in the elemental analysis of organic substances when determining the hydrogen content, as well as to determine the absolute humidity of the air. In terms of drying efficiency, anhydrone is not inferior to phosphorus (V) oxide, differing favorably from the latter in that it is used in the form of grains, does not sinter upon absorption of water vapor, and does not form channels in the column.

Magnesium perchlorate also goes on sale in the form of Mg(ClO4)2-3H2O trihydrate, which is comparable in drying effect to conc. H2SO4.

When using perchlorates, it should be borne in mind that strong mineral acids and acidic oxides decompose them with the release of free perchloric acid, which can explode when interacting with the dried gas. Therefore, it is impossible to connect in series an absorption vessel with Mg(СlO4)2 and a washer with conc. H2SO4.

Anhydrous potassium carbonate (fused potash) K2CO3 is used to dry liquids and solutions of substances in organic solvents, when you can not be afraid of the alkalinity of the reagent (drying organic bases, alcohols, etc.), In laboratory conditions, the desiccant is prepared by briefly heating commercial potassium carbonate on a metal frying pan.

Sodium sulfate anhydrous Na2SO4 is a relatively ineffective desiccant. It is used for drying solutions of organic substances in non-polar solvents (benzene, diethyl ether, etc.). Obtained by calcining Na2SO4-10H2O in a metal pan.

Magnesium sulfate anhydrous MgSO4 is a more effective and capacious desiccant than anhydrous Na2SO4. Obtained by calcining MgSO4-7H2O at 210-250 °C.

Calcium sulfate anhydrous Ca2SO4 is similar in drying efficiency to conc. H2SO4. They are used for drying gases and liquids, as well as for filling desiccators.

Sodium and potassium hydroxides NaOH and KOH are used for filling absorption tubes, columns (drying gases) and desiccators, as well as for direct drying of some organic liquids. Fused NaOH is just as effective for drying gases as granulated CaCl2. Fused KOH is many times more efficient than NaOH.

Alkali metal hydroxides are often used to simultaneously absorb H2O and CO2.

Substances that bind water as a result of a chemical reaction

Phosphorus (V) oxide P4O10 is an extremely effective drying agent, but very difficult to handle. Under the action of water vapor, the P4O10 powder turns into a viscous sticky mass covered with an impermeable viscous film, which creates a great resistance to gas flow. Therefore, P4O10 is usually applied to glass or asbestos wool, glass beads or pieces of calcined pumice. Pumice stone is heated in a porcelain cup to 100°C and then moistened with conc. H3PO4. Phosphorus oxide is then spread on the pumice stone with stirring. The result is easy-to-handle reagent granules.

With halogens (with the exception of fluorine), phosphorus oxide does not react. With dry HF, HCl and HBr forms oxyhalides and metaphosphoric acid:

Sodium is a very effective reagent for drying hydrocarbons, ethers, etc. The surface of the metal is quickly covered with a layer of hydroxide, and further drying slows down. Therefore, they tend to introduce metal with the largest possible specific surface area, for example, in the form of a thin wire. Sodium can be used to dry liquids containing only a small amount of water.

Calcium hydride CaH2 is a very effective drying agent. Its reaction with water proceeds irreversibly over a wide temperature range.

Lithium-aluminum hydride LiAlH4 is one of the most effective drying agents. It is used only for the complete removal of traces of moisture from organic liquids.

Substances that bind water as a result of adsorption

The advantage of sorbents is that they are available, mostly chemically inert with respect to the drying gas, do not create significant resistance to the gas flow (when used in granular form), and are easily regenerated by heating in a flow of dry air.

Coarse-grained active alumina (alumina gel) is a more effective drying agent than silica gel.

In terms of drying activity, zeolites are much superior to alumogel and silica gel. Zeolites of some brands intensively absorb water vapor even at 100°C, and ammonia at 250-300°C, when silica gel completely loses activity. For example, zeolite grade KA adsorbs predominantly water molecules at normal temperature. At 70°С, 1 cm3 of KA zeolite tablet retains 62–85 mg H2O.

Drying solids

Drying process solids mostly based on the evaporation of moisture, which can be carried out at room temperature or by heating. Moisture evaporates when the pressure of water vapor above the surface of the solid being dried exceeds the partial pressure of water vapor in the surrounding gas phase. The water vapor pressure in the dried substance increases sharply with increasing temperature. Therefore, they try to carry out drying at an elevated temperature. The partial pressure of water vapor in the gas phase can be reduced by applying a vacuum or by drying with substances that effectively absorb moisture from the gas phase.

Many solid non-hygroscopic substances can be dried in the open air at ordinary temperatures. Moisture from the surface of the substance will evaporate until an equilibrium is established between the water vapor pressure in the test substance and in the air. To speed up the process, if possible, drying is carried out with the movement of air or mixing of the material. The thickness of the dried material layer should not exceed 1-2 cm. As a result of drying in air, an air-dry product with a very uneven residual moisture content is obtained. Air drying often precedes drying by other methods. Drying of solids in air is best done on filter-ceramic plates; when dried on filter paper, the product becomes contaminated with its fibers.

It is advisable to cover the substance dried in air with filter paper in order to protect it from dust and mechanical impurities. In addition, the photochemical effect of lighting on the product must be taken into account. Thus, many bromides, when dried in air, turn yellow under the action of light.

Thermally stable solids can be dried in ovens. Volatile substances, such as residues of volatile organic solvents, must not be removed in drying cabinets, since the mixture of solvent vapors with air can explode on contact with the wire coil of the heater, and low-melting substances must not be dried.

When drying fine-crystalline substances, a dense crust can form on their surface, which significantly reduces the rate of drying. In these cases, the substance to be dried during the drying process should be repeatedly mixed. Substances that easily decompose or change when heated to 100°C should be dried in vacuum ovens.

V Lately In laboratory practice, dryers began to be used, in which infrared lamps are used as a heat source. Infrared rays with a wavelength of 1000-3000 nm have sufficient penetrating power and do not cause chemical changes in the dried substance. Drying occurs at a lower temperature and faster than with conventional heating of substances. Devices for drying materials by infrared radiation are commercially available. The power consumption of the lamp is 500 W. Drying time for a sample of 3 g is from 5 to 10 minutes. First, a lamp is turned on, and a thermometer reservoir is placed in the center of the illuminated circle. By adjusting the height of the reflector, the required temperature is created to dry the substance. After that, a vessel with the substance to be dried is placed in the center of the illuminated circle for a set time.

Drying of solids with air dried by chemical reagents is carried out in laboratory conditions in desiccators. The drying agent is selected depending on chemical properties dried substance. Most often, anhydrous CaCl2, Mg(ClO4)2, P4O10, fused KOH, silica gel, and zeolites are placed at the bottom of the desiccator. To remove residual hydrocarbon solvents, paraffin shavings or filter paper strips impregnated with molten paraffin are used as a filler for the desiccator.

In a desiccator, water vapor moves due to diffusion or convection currents and therefore drying is slower than in an air current. Vacuum desiccators are used to speed up the process at room temperature. The vacuum is usually created by a water jet pump. In those cases where small amounts of a substance must be dried in a vacuum at an elevated temperature, an apparatus called a "drying gun" is used (Fig. 127). A moisture absorber (P4O10, CaCl2, adsorbents) is placed in retort 4. Liquid with a certain boiling point is poured into flask 3 up to half the volume and several “boiling stones” are added. The substance to be dried is introduced into vessel 1 in porcelain boat 5. The retort tap is connected to a vacuum pump. The liquid in flask 3 is heated to a boil. Hot vapors wash vessel 1, condense in the refrigerator and again flow into flask 3. After some time, the temperature in vessel 1 is equal to the temperature of the vapors of the liquid used.

Non-flammable liquids are usually used as a heat carrier: chloroform (tbp = 61 °C), trichlorethylene (tbp = 86 °C), water (tbp = 100 °C), tetrachlorethylene (tbp = 120 °C), trichloroethane (tbp = 146 °C). WITH).

The solid (precipitate) can be dehydrated by extraction with a solvent that is miscible with water but in which the precipitate is insoluble or very poorly soluble. For example, acetone, methyl or ethyl alcohol, and ether are used to quickly dry precipitates. Drying of wet crystalline precipitates can be carried out in one of the following ways.

1. The substance to be dried is placed in a conical flask with a ground glass stopper, where the appropriate solvent is added in such an amount that there is a solvent layer of several centimeters above the precipitate. The flask is closed and shaken vigorously for about 1 min, after which it is allowed to stand for 15–20 min. The solvent is then carefully drained off and replaced with a fresh portion. The solvent is changed 3-4 times, after which the precipitate is transferred to a funnel with a porous bottom (Buchner funnel), filtered under vacuum and, if the substance to be dried is non-hygroscopic, poured onto a ceramic porous tile, covered with a sheet of filter paper and left in air (or under draft) until the solvent has completely evaporated. Hygroscopic substances are dried in a vacuum desiccator or in a vacuum drying cabinet.

2. The substance to be dried is placed on a funnel with a porous glass bottom and gradually poured over with a drying liquid (solvent). The funnel is then attached to the suction unit and the solvent is filtered off. After disconnecting the unit from the vacuum source, loosen the precipitate on the filter with a glass rod or a porcelain spatula, add the solvent again, allow the precipitate to stand under the solvent layer for 10-15 minutes, after which the unit is reconnected to the vacuum source. Filter until the smell of the solvent is no longer felt. When this is achieved, turn off the vacuum, and the dehydrated precipitate is placed in a jar.

Drying of liquids and solutions

Some organic liquids containing water can be dried beforehand by salting out - by adding to them an electrolyte that does not dissolve in an organic solvent, but dissolves in water. The liquid is separated into two layers. The aqueous layer can be separated and the organic layer dried and purified by distillation. The substance to be salted out may be added in solid form or as a concentrated aqueous solution; for example, NaCl can remove most of the water from an aqueous solution of methyl ethyl ketone.

Liquids that do not form separately boiling (azeotropic) mixtures with water can often be dried by fractional distillation on an efficient column. The condition for successful drying is a sufficiently large difference in the boiling points of the liquid being dried and water. By this method, for example, it is possible to obtain almost dry methyl alcohol, the additional drying of which is achieved with the help of chemical drying agents (calcium metal, aluminum amalgam) and on KA zeolite.

If the dried substance dissolves water very poorly, but forms double or triple azeotropic mixtures with it, then it can be dried by distilling a small part of it together with water. As long as the binary mixture is distilled off, the distillate remains cloudy.

In combination with azeotropic distillation, drying can be carried out by extraction. To the liquid to be dried, an amount of a water-immiscible organic solvent is added to separate the aqueous layer, after which the remaining water from the organic solvent solution is removed by azeotropic distillation.

Drying of organic liquids is most often carried out by direct contact with a drying agent. The drying agent, which forms concentrated solutions with water (CaCl2, K2CO3, KOH), is added to the dried substance in parts, and the resulting solution of the drying agent in water is separated in a separating funnel. After drying, the liquid is separated from the solid drying agent by filtration.

In the case of aqueous solutions of thermally unstable substances, freeze drying is used. The principle of freeze drying is very simple. The aqueous solution is completely frozen in a thin layer and maintained in a vacuum of 1.33-266 Pa (0.01-2 mmHg). At this pressure, the water quickly evaporates (sublimates) and the frozen solution gradually cools. Removed water vapor is captured in cold traps or with the help of adsorbents. Freeze drying is not accompanied by foaming, leads to the formation of a finely crystalline product of increased solubility, protects the product from the oxidative action of atmospheric oxygen and preserves the biological activity of the dried substances.

Adsorbents such as aluminum gel and zeolites are widely used for drying organic liquids. Along with water, adsorbents absorb many other contaminants. For example, CaA zeolite can be used for selective absorption of polar substances (H2O, H2S, etc.) from non-polar liquids. NaA zeolite is used for deep drying of various oil fractions and many products of petrochemical synthesis.

Dehumidification of gases

Gases are dried with chemical reagents and freezing. At a high gas velocity, the equilibrium of saturated water vapor over the dryer, as a rule, does not have time to be established. The degree of drying of the gas depends on the properties of the dryer, the thickness of the layer and the size of the surface of the dryer in contact with the gas. Drying of gases with solid reagents is usually carried out in absorption devices (absorbers) shown in fig. 128, and in vessels for solid washers - Tishchenko's flask (Fig. 129, a). When filling absorption devices, it is necessary to ensure that the reagent is evenly distributed so that channels do not form in it. In order to strengthen the desiccant layer and prevent entrainment of its particles with the gas, small swabs of glass wool are placed in the absorption devices at the points of gas inlet and outlet. After filling the absorption devices, you should make sure that they do not create too much resistance to the current of the dried gas. If this is the case, then the filling is repeated with large pieces of drying agent, or the drying agent is mixed with pieces of pumice or porous phosphorus.

For drying gases conc. H2SO4 use vessels for liquid washer (Fig. 129). In this case, it is necessary to ensure good contact of the gas with the drying agent and to ensure that droplets of the agent are not carried away by the gas flow. This is achieved by selecting the height of the drying layer and the gas velocity. Vessels for liquid washers can be switched on two in series.

Efficient gas scrubbing devices are absorber columns with irrigated packing made from scraps of glass tubes, glass rings or balls. The advantage of refluxed packed columns is that no appreciable overpressure has to be created for the gas to pass through.

On fig. 130 shows a self-refreshing absorption column for gas purification. Gas passes into tube 1. An additional gas flow enters tube 2. Entraining liquid droplets in the tee, the gas drives them in a chain along tube 4 upwards. Coming out of a narrow hole above the nozzle 3, the gas bubbles burst and spray the liquid over the nozzle. The flowing liquid is separated from the gas in the receiver and returned to the cycle again. Tube 4, in which the chain of bubbles rises, is made narrow, otherwise the chain will break.

For drying gases (vapours) highest value have adsorbents (alumina, silica gel, zeolites). Anhydrous silica gel containing some cobalt chloride is blue in color and turns pink when saturated with moisture. Thus, according to appearance the sorbent in the drying column can be judged on its suitability for further drying.

A high degree of drying of gases can be achieved by freezing, i.e., by cooling them to a low temperature. During freezing, the gas is passed through a tube immersed almost to the bottom of the vessel, which is placed in a cooling bath.

Drying The process of removing residual water from a substance is called. There are a lot of methods for drying substances in the laboratory, the most commonly used are the absorption of water vapor by hygroscopic substances, the evaporation of water when heated, and drying in the open air at ordinary temperature.

Drying by absorption of water vapor by hygroscopic substances. The method is based on the ability of certain substances to absorb water or its vapor, forming crystallization compounds with it. Such substances include sulfuric acid, calcium chloride, calcium oxide, phosphorus (V) oxide, etc. If a substance to be dried is placed over a hygroscopic substance in a closed vessel (most often in a desiccator), it will begin to absorb water from the substance to be dried.

Drying outdoors at normal temperature. Many substances can be dried outdoors. To do this, the substance is placed on a clean sheet of filter paper and spread on it in a loose layer no more than 3-5 mm thick, covered with another sheet of filter paper on top to protect it from dust, and left for 12 hours. After 12 hours, the substance is stirred so that the lower layers are on top. After another 12 hours, the substance, as a rule, dries up, it is collected with a clean spatula in a jar and closed. Drying in air is a rather lengthy operation, used only if the substance is non-hygroscopic and decomposes when heated.

Heat drying. Drying at elevated temperatures in an oven is very widely used. The maximum temperature to which the drying cabinet is heated is 300 o C. The substance to be dried is placed on the shelf of the cabinet in an evaporating cup or on paper. The temperature inside the cabinet for removing water vapor should be 100-105 o C. The temperature should be increased gradually to avoid the formation of a dense "crust" on the surface of the substance. The duration of drying depends on the amount of substance, the thickness of its layer and the heating temperature.