Getting oxygen - Knowledge Hypermarket. Chemical and physical properties, applications and production of oxygen Methods for producing oxygen reactions

PROPERTIES OF OXYGEN AND METHODS OF ITS OBTAINING

Oxygen O2 is the most abundant element on earth. It is found in large quantities in the form of chemical compounds with various substances in the earth's crust (up to 50% wt.), in combination with hydrogen in water (about 86% wt.) and in a free state in atmospheric air in a mixture mainly with nitrogen in amount 20.93% vol. (23.15% wt.).

Oxygen is of great importance in the national economy. It is widely used in metallurgy; chemical industry; for gas-flame processing of metals, fire drilling of hard rocks, underground gasification of coals; in medicine and various breathing apparatus, for example for high-altitude flights, and in other areas.

Under normal conditions, oxygen is a colorless, odorless, and tasteless gas that is not flammable, but actively supports combustion. At very low temperatures, oxygen turns into a liquid and even a solid.

The most important physical constants of oxygen are as follows:

Oxygen is highly chemically active and forms compounds with all chemical elements except rare gases. Reactions of oxygen with organic substances have a pronounced exothermic character. Thus, when compressed oxygen interacts with fatty or finely dispersed solid combustible substances, their instant oxidation occurs and the heat generated contributes to the spontaneous combustion of these substances, which can cause a fire or explosion. This property must be especially taken into account when handling oxygen equipment.

One of the important properties of oxygen is its ability to form explosive mixtures with flammable gases and liquid flammable vapors over a wide range, which can also lead to explosions in the presence of an open flame or even a spark. Mixtures of air with gas or vapor fuels are also explosive.

Oxygen can be obtained: 1) by chemical methods; 2) electrolysis of water; 3) physically from the air.

Chemical methods involving the production of oxygen from various substances are ineffective and currently have only laboratory significance.

Electrolysis of water, i.e. its decomposition into its components - hydrogen and oxygen, is carried out in devices called electrolyzers. A direct current is passed through water, to which caustic soda NaOH is added to increase electrical conductivity; oxygen collects at the anode and hydrogen at the cathode. The disadvantage of this method is the high energy consumption: 12-15 kW are consumed per 1 m 3 0 2 (in addition, 2 m 3 N 2 is obtained). h. This method is rational in the presence of cheap electricity, as well as in the production of electrolytic hydrogen, when oxygen is a waste product.

The physical method is to separate the air into its components using deep cooling. This method makes it possible to obtain oxygen in almost unlimited quantities and is of major industrial importance. Electricity consumption per 1 m 3 O 2 is 0.4-1.6 kW. h, depending on the type of installation.

OBTAINING OXYGEN FROM THE AIR

Atmospheric air is mainly a mechanical mixture of three gases with the following volumetric content: nitrogen - 78.09%, oxygen - 20.93%, argon - 0.93%. In addition, it contains about 0.03% carbon dioxide and small amounts of rare gases, hydrogen, nitrous oxide, etc.

The main task in obtaining oxygen from air is to separate the air into oxygen and nitrogen. Along the way, argon is separated, the use of which in special welding methods is constantly increasing, as well as rare gases, which play an important role in a number of industries. Nitrogen has some uses in welding as a shielding gas, in medicine and other fields.

The essence of the method is deep cooling of the air, turning it into a liquid state, which at normal atmospheric pressure can be achieved in the temperature range from -191.8 ° C (beginning of liquefaction) to -193.7 ° C (end of liquefaction).

The separation of liquid into oxygen and nitrogen is carried out by using the difference in their boiling temperatures, namely: T bp. o2 = -182.97° C; Boiling temperature N2 = -195.8° C (at 760 mm Hg).

With the gradual evaporation of a liquid, nitrogen, which has a lower boiling point, will first pass into the gaseous phase, and as it is released, the liquid will be enriched with oxygen. Repeating this process many times makes it possible to obtain oxygen and nitrogen of the required purity. This method of separating liquids into their component parts is called rectification.

To produce oxygen from the air, there are specialized enterprises equipped with high-performance units. In addition, large metalworking enterprises have their own oxygen stations.

The low temperatures required to liquefy air are obtained using so-called refrigeration cycles. The main refrigeration cycles used in modern installations are briefly discussed below.

The refrigeration cycle with air throttling is based on the Joule-Thomson effect, i.e. a sharp decrease in gas temperature during its free expansion. The cycle diagram is shown in Fig. 2.

The air is compressed in a multi-stage compressor 1 to 200 kgf/cm2 and then passes through a refrigerator 2 with running water. Deep cooling of the air occurs in the heat exchanger 3 by the reverse flow of cold gas from the liquid collector (liquefier) ​​4. As a result of the expansion of the air in the throttle valve 5, it is additionally cooled and partially liquefied.

The pressure in collector 4 is regulated within 1-2 kgf/cm 2 . The liquid is periodically drained from the collection into special containers through valve 6. The non-liquefied part of the air is discharged through a heat exchanger, cooling new portions of incoming air.

Cooling of the air to liquefaction temperature occurs gradually; When the installation is turned on, there is a start-up period during which no air liquefaction is observed, but only cooling of the installation occurs. This period takes several hours.

The advantage of the cycle is its simplicity, but the disadvantage is the relatively high power consumption - up to 4.1 kW. h per 1 kg of liquefied air at a compressor pressure of 200 kgf/cm 2; at lower pressure, the specific energy consumption increases sharply. This cycle is used in low- and medium-capacity installations to produce oxygen gas.

The cycle with throttling and pre-cooling of air with ammonia is somewhat more complex.

The medium-pressure refrigeration cycle with expansion in an expander is based on a decrease in gas temperature during expansion with the return of external work. In addition, the Joule-Thomson effect is also used. The cycle diagram is shown in Fig. 3.

The air is compressed in compressor 1 to 20-40 kgf/cm 2, passes through refrigerator 2 and then through heat exchangers 3 and 4. After heat exchanger 3, most of the air (70-80%) is sent to the piston expansion machine-expander 6, and a smaller part air (20-30%) goes for free expansion into the throttle valve 5 and then into the collection 7, which has a valve 8 for draining the liquid. In expander 6

the air, already cooled in the first heat exchanger, does work - it pushes the piston of the machine, its pressure drops to 1 kgf/cm 2, due to which the temperature drops sharply. From the expander, cold air, having a temperature of about -100 ° C, is discharged outside through heat exchangers 4 and 3, cooling the incoming air. Thus, the expander provides very effective cooling of the installation at a relatively low pressure in the compressor. The work of the expander is used usefully and this partially compensates for the energy spent on air compression in the compressor.

The advantages of the cycle are: relatively low compression pressure, which simplifies the design of the compressor, and increased cooling capacity (thanks to the expander), which ensures stable operation of the installation when oxygen is taken in liquid form.

Low-pressure refrigeration cycle with expansion in a turboexpander, developed by Acad. P. L. Kapitsa, is based on the use of low pressure air with the production of cold only through the expansion of this air in an air turbine (turboexpander) with the production of external work. The cycle diagram is shown in Fig. 4.

The air is compressed by turbocompressor 1 to 6-7 kgf/cm2, cooled with water in refrigerator 2 and supplied to regenerators 3 (heat exchangers), where it is cooled by a reverse flow of cold air. Up to 95% of the air after the regenerators is sent to the turboexpander 4, expands to an absolute pressure of 1 kgf/cm 2 with external work performed and is sharply cooled, after which it is supplied to the pipe space of the condenser 5 and condenses the rest of the compressed air (5%), entering the annulus. From the condenser 5, the main air flow is directed to the regenerators and cools the incoming air, and the liquid air is passed through the throttle valve 6 into the collection 7, from which it is drained through valve 8. The diagram shows one regenerator, but in reality there are several of them and they are turned on one by one.

The advantages of a low-pressure cycle with a turboexpander are: higher efficiency of turbomachines compared to piston-type machines, simplification of the technological scheme, increased reliability and explosion safety of the installation. The cycle is used in high-capacity installations.

The separation of liquid air into components is carried out through the process of rectification, the essence of which is that the vaporous mixture of nitrogen and oxygen formed during the evaporation of liquid air is passed through a liquid with a lower oxygen content. Since there is less oxygen in the liquid and more nitrogen, it has a lower temperature than the steam passing through it, and this causes the condensation of oxygen from the steam and its enrichment of the liquid with the simultaneous evaporation of nitrogen from the liquid, i.e., its enrichment of the vapor above the liquid .

An idea of ​​the essence of the rectification process can be given by the figure shown in Fig. 5 is a simplified diagram of the process of repeated evaporation and condensation of liquid air.

We assume that air consists only of nitrogen and oxygen. Let's imagine that there are several vessels (I-V) connected to each other; the top one contains liquid air containing 21% oxygen. Thanks to the stepped arrangement of the vessels, the liquid will flow down and at the same time gradually become enriched with oxygen, and its temperature will increase.

Let us assume that in vessel II there is a liquid containing 30% 0 2, in vessel III - 40%, in vessel IV - 50% and in vessel V - 60% oxygen.

To determine the oxygen content in the vapor phase, we will use a special graph - Fig. 6, the curves of which indicate the oxygen content in liquid and vapor at various pressures.

Let's start evaporating the liquid in vessel V at an absolute pressure of 1 kgf/cm2. As can be seen from Fig. 6, above the liquid in this vessel, consisting of 60% 0 2 and 40% N 2, there may be an equilibrium vapor composition containing 26.5% 0 2 and 73.5% N 2, having the same temperature as the liquid . We feed this steam into vessel IV, where the liquid contains only 50% 0 2 and 50% N 2 and will therefore be colder. From Fig. 6 shows that the vapor above this liquid can contain only 19% 0 2 and 81% N 2, and only in this case its temperature will be equal to the temperature of the liquid in this vessel.

Consequently, the steam supplied to vessel IV from vessel V, containing 26.5% O 2, has a higher temperature than the liquid in vessel IV; therefore, the oxygen of the vapor condenses in the liquid of vessel IV, and part of the nitrogen from it will evaporate. As a result, the liquid in vessel IV will be enriched with oxygen, and the vapor above it will be enriched with nitrogen.

A similar process will occur in other vessels and, thus, when draining from the upper vessels into the lower ones, the liquid is enriched with oxygen, condensing it from the rising vapors and giving them its nitrogen.

Continuing the process upward, you can get steam consisting of almost pure nitrogen, and in the lower part - pure liquid oxygen. In reality, the rectification process that occurs in distillation columns of oxygen plants is much more complicated than described, but its fundamental content is the same.

Regardless of the technological scheme of the installation and the type of refrigeration cycle, the process of producing oxygen from air includes the following stages:

1) cleaning the air from dust, water vapor and carbon dioxide. CO 2 binding is achieved by passing air through an aqueous NaOH solution;

2) air compression in a compressor followed by cooling in refrigerators;

3) cooling of compressed air in heat exchangers;

4) expansion of compressed air in a throttle valve or expander to cool and liquefy it;

5) liquefaction and rectification of air to produce oxygen and nitrogen;

6) draining liquid oxygen into stationary tanks and discharging gaseous oxygen into gas tanks;

7) quality control of the oxygen produced;

8) filling transport tanks with liquid oxygen and filling cylinders with gaseous oxygen.

The quality of gaseous and liquid oxygen is regulated by relevant GOSTs.

According to GOST 5583-58, gaseous technical oxygen is produced in three grades: highest - with a content of no less than 99.5% O 2, 1st - no less than 99.2% O 2 and 2nd - no less than 98.5% O 2 , the rest is argon and nitrogen (0.5-1.5%). The moisture content should not exceed 0.07 g/f 3 . Oxygen obtained by electrolysis of water should not contain more than 0.7% hydrogen by volume.

According to GOST 6331-52, liquid oxygen is produced in two grades: grade A with a content of at least 99.2% O 2 and grade B with a content of at least 98.5% O 2 . The acetylene content in liquid oxygen should not exceed 0.3 cm 3 /l.

Process oxygen used to intensify various processes at metallurgical, chemical and other industries contains 90-98% O 2 .

Quality control of gaseous and also liquid oxygen is carried out directly during the production process using special instruments.

Administration Overall rating of the article: Published: 2012.06.01

Oxygen occupies 21% of atmospheric air. Most of it is found in the earth's crust, fresh water and living microorganisms. It is used in many areas of industry and is used for economic and medical needs. The demand for the substance is due to its chemical and physical properties.

How oxygen is produced in industry. 3 methods

Oxygen production in industry is carried out by dividing atmospheric air. The following methods are used for this:

The production of oxygen on an industrial scale is of great importance. Great care must be taken in the selection of technology and appropriate equipment. Mistakes made can negatively affect the technological process and lead to increased slaughter costs.

Technical features of equipment for oxygen production in industry

Industrial-type generators “OXIMAT” help to establish the process of obtaining oxygen in a gaseous state. Their technical characteristics and design features are aimed at obtaining this substance in industry of the required purity and required quantity throughout the day (without interruption). It should be noted that the equipment can operate in any mode, both with and without stops. The unit operates under pressure. At the inlet there should be dried air in a compressed state, free of moisture. Small, medium and large capacity models are available.

Air is an inexhaustible source of oxygen. To obtain oxygen from it, this gas must be separated from nitrogen and other gases. The industrial method of producing oxygen is based on this idea. It is implemented using special, rather cumbersome equipment. First, the air is greatly cooled until it turns into a liquid. Then the temperature of the liquefied air is gradually increased. Nitrogen gas begins to be released from it first (the boiling point of liquid nitrogen is -196 ° C), and the liquid is enriched with oxygen.

Obtaining oxygen in the laboratory. Laboratory methods for producing oxygen are based on chemical reactions.

J. Priestley obtained this gas from a compound called mercury(II) oxide. The scientist used a glass lens with which he focused sunlight on the substance.

In a modern version, this experiment is depicted in Figure 54. When heated, mercury (||) oxide (yellow powder) turns into mercury and oxygen. Mercury is released in a gaseous state and condenses on the walls of the test tube in the form of silvery drops. Oxygen is collected above the water in the second test tube.

Priestley's method is no longer used because mercury vapor is toxic. Oxygen is produced using other reactions similar to the one discussed. They usually occur when heated.

Reactions in which several others are formed from one substance are called decomposition reactions.

To obtain oxygen in the laboratory, the following oxygen-containing compounds are used:

Potassium permanganate KMnO4 (common name potassium permanganate; the substance is a common disinfectant)

Potassium chlorate KClO3 (trivial name - Berthollet's salt, in honor of the French chemist of the late 18th - early 19th centuries C.-L. Berthollet)

A small amount of a catalyst - manganese (IV) oxide MnO2 - is added to potassium chlorate so that the decomposition of the compound occurs with the release of oxygen1.

Structure of molecules of chalcogen hydrides H2E can be analyzed using the molecular orbital (MO) method. As an example, consider the diagram of molecular orbitals of a water molecule (Fig. 3)

For construction (For more details, see G. Gray "Electrons and Chemical Bonding", M., publishing house "Mir", 1967, pp. 155-62 and G. L. Miessier, D. A. Tarr, "Inorganic Chemistry", Prantice Hall Int. Inc ., 1991, p.153-57) diagram of the MO of the H2O molecule, we will combine the origin of coordinates with the oxygen atom, and place the hydrogen atoms in the xz plane (Fig. 3). The overlap of 2s- and 2p-AOs of oxygen with 1s-AOs of hydrogen is shown in Fig. 4. AOs of hydrogen and oxygen, which have the same symmetry and similar energies, take part in the formation of MOs. However, the contribution of AO to the formation of MO is different, which is reflected in different values ​​of the coefficients in the corresponding linear combinations of AO. The interaction (overlap) of 1s-AO of hydrogen and 2s- and 2pz-AO of oxygen leads to the formation of 2a1-bonding and 4a1-antibonding MOs.

Hello.. Today I will tell you about oxygen and how to obtain it. Let me remind you that if you have questions for me, you can write them in the comments to the article. If you need any help in chemistry, . I will be glad to help you.

Oxygen is distributed in nature in the form of isotopes 16 O, 17 O, 18 O, which have the following percentages on Earth - 99.76%, 0.048%, 0.192%, respectively.

In the free state, oxygen exists in the form of three allotropic modifications : atomic oxygen - O o, dioxygen - O 2 and ozone - O 3. Moreover, atomic oxygen can be obtained as follows:

KClO 3 = KCl + 3O 0

KNO 3 = KNO 2 + O 0

Oxygen is part of more than 1,400 different minerals and organic substances; in the atmosphere its content is 21% by volume. And the human body contains up to 65% oxygen. Oxygen is a colorless and odorless gas, slightly soluble in water (3 volumes of oxygen dissolve in 100 volumes of water at 20 o C).

In the laboratory, oxygen is obtained by moderately heating certain substances:

1) When decomposing manganese compounds (+7) and (+4):

2KMnO 4 → K 2 MnO 4 + MnO 2 + O 2
permanganate manganate
potassium potassium

2MnO 2 → 2MnO + O 2

2) When decomposing perchlorates:

2KClO 4 → KClO 2 + KCl + 3O 2
perchlorate
potassium

3) During the decomposition of berthollet salt (potassium chlorate).
In this case, atomic oxygen is formed:

2KClO 3 → 2 KCl + 6O 0
chlorate
potassium

4) During the decomposition of hypochlorous acid salts in the light- hypochlorites:

2NaClO → 2NaCl + O 2

Ca(ClO) 2 → CaCl 2 + O 2

5) When heating nitrates.
In this case, atomic oxygen is formed. Depending on the position in the activity series of the nitrate metal, various reaction products are formed:

2NaNO 3 → 2NaNO 2 + O 2

Ca(NO 3) 2 → CaO + 2NO 2 + O 2

2AgNO3 → 2Ag + 2NO2 + O2

6) During the decomposition of peroxides:

2H 2 O 2 ↔ 2H 2 O + O 2

7) When heating oxides of inactive metals:

2Аg 2 O ↔ 4Аg + O 2

This process is relevant in everyday life. The fact is that dishes made of copper or silver, having a natural layer of oxide film, form active oxygen when heated, which is an antibacterial effect. The dissolution of salts of inactive metals, especially nitrates, also leads to the formation of oxygen. For example, the overall process of dissolving silver nitrate can be represented in stages:

AgNO 3 + H 2 O → AgOH + HNO 3

2AgOH → Ag 2 O + O 2

2Ag 2 O → 4Ag + O 2

or in summary form:

4AgNO 3 + 2H 2 O → 4Ag + 4HNO 3 + 7O 2

8) When heating chromium salts of the highest oxidation state:

4K 2 Cr 2 O 7 → 4K 2 CrO 4 + 2Cr 2 O 3 + 3 O 2
bichromate chromate
potassium potassium

In industry, oxygen is obtained:

1) Electrolytic decomposition of water:

2H 2 O → 2H 2 + O 2

2) The interaction of carbon dioxide with peroxides:

CO 2 + K 2 O 2 →K 2 CO 3 + O 2

This method is an indispensable technical solution to the problem of breathing in isolated systems: submarines, mines, spacecraft.

3) When ozone interacts with reducing agents:

O 3 + 2KJ + H 2 O → J 2 + 2KOH + O 2

Of particular importance is the production of oxygen during the process of photosynthesis. occurring in plants. All life on Earth fundamentally depends on this process. Photosynthesis is a complex multi-step process. Light gives it its beginning. Photosynthesis itself consists of two phases: light and dark. During the light phase, the chlorophyll pigment contained in plant leaves forms a so-called “light-absorbing” complex,” which takes electrons from water, and thereby splits it into hydrogen ions and oxygen:

2H 2 O = 4e + 4H + O 2

Accumulated protons contribute to the synthesis of ATP:

ADP + P = ATP

During the dark phase, carbon dioxide and water are converted into glucose. And oxygen is released as a by-product:

6CO 2 + 6H 2 O = C 6 H 12 O 6 + O 2

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Oxygen appeared in the earth's atmosphere with the emergence of green plants and photosynthetic bacteria. Thanks to oxygen, aerobic organisms carry out respiration or oxidation. It is important to obtain oxygen in industry - it is used in metallurgy, medicine, aviation, national economy and other industries.

Properties

Oxygen is the eighth element of the periodic table. It is a gas that supports combustion and oxidizes substances.

Rice. 1. Oxygen in the periodic table.

Oxygen was officially discovered in 1774. English chemist Joseph Priestley isolated the element from mercuric oxide:

2HgO → 2Hg + O 2 .

However, Priestley did not know that oxygen is part of air. The properties and presence of oxygen in the atmosphere were later determined by Priestley’s colleague, the French chemist Antoine Lavoisier.

General characteristics of oxygen:

• colorless gas;
• has no smell or taste;
• heavier than air;
• the molecule consists of two oxygen atoms (O 2);
• in a liquid state it has a pale blue color;
• poorly soluble in water;
• is a strong oxidizing agent.

Rice. 2. Liquid oxygen.

The presence of oxygen can be easily checked by lowering a smoldering splinter into a vessel containing gas. In the presence of oxygen, the torch bursts into flames.

How do you get it?

There are several known methods for producing oxygen from various compounds in industrial and laboratory conditions. In industry, oxygen is obtained from air by liquefying it under pressure and at a temperature of -183°C. Liquid air is subjected to evaporation, i.e. gradually heat up. At -196°C, nitrogen begins to evaporate, and oxygen remains liquid.

In the laboratory, oxygen is formed from salts, hydrogen peroxide and as a result of electrolysis. The decomposition of salts occurs when heated. For example, potassium chlorate or bertholite salt is heated to 500°C, and potassium permanganate or potassium permanganate is heated to 240°C:

• 2KClO 3 → 2KCl + 3O 2;
• 2KMnO 4 → K 2 MnO 4 + MnO 2 + O 2 .

Rice. 3. Heating Berthollet salt.

You can also get oxygen by heating nitrate or potassium nitrate:

2KNO 3 → 2KNO 2 + O 2 .

When decomposing hydrogen peroxide, manganese (IV) oxide - MnO 2, carbon or iron powder is used as a catalyst. The general equation looks like this:

2H 2 O 2 → 2H 2 O + O 2.

A sodium hydroxide solution undergoes electrolysis. As a result, water and oxygen are formed:

4NaOH → (electrolysis) 4Na + 2H 2 O + O 2.

Oxygen is also separated from water using electrolysis, decomposing it into hydrogen and oxygen:

2H 2 O → 2H 2 + O 2.

On nuclear submarines, oxygen was obtained from sodium peroxide - 2Na 2 O 2 + 2CO 2 → 2Na 2 CO 3 + O 2. The method is interesting because carbon dioxide is absorbed along with the release of oxygen.

How to use

Collection and recognition are necessary to release pure oxygen, which is used in industry to oxidize substances, as well as to maintain breathing in space, under water, and in smoky rooms (oxygen is necessary for firefighters). In medicine, oxygen cylinders help patients with breathing difficulties breathe. Oxygen is also used to treat respiratory diseases.

Oxygen is used to burn fuels - coal, oil, natural gas. Oxygen is widely used in metallurgy and mechanical engineering, for example, for melting, cutting and welding metal.

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