The use of carbon dioxide in the food industry. What is carbon dioxide. Getting low temperatures

Carbon dioxide is a colorless gas with a slightly sour odor and taste, registered in the international classification of food additives under the code E290. It is used as a preservative, propellant, antioxidant and acidity regulator.

General characteristics of carbon dioxide

Carbon dioxide is a heavy, odorless, colorless gas known as carbon dioxide. A special feature of carbon dioxide is its ability, at atmospheric pressure, to pass from a solid state immediately to a gaseous state, bypassing the liquid stage (calorizator). In its liquid state, carbon dioxide is stored under elevated pressure. Solid state of carbon dioxide - crystals white - known as dry ice.

The formation of carbon dioxide occurs in the process of combustion and decay of organic substances, it is emitted during respiration by plants and animals, in nature it is in the air and mineral springs.

Benefits and harms of carbon dioxide

Carbon dioxide is not a toxic substance, therefore it is considered harmless to the human body. But, being an accelerator of the process of absorption of substances into the gastric mucosa, it provokes, for example, a rapid intoxication when drinking carbonated alcoholic beverages. It is not recommended to get carried away with the use of soda for everyone who has any problems with the gastrointestinal tract, because the most harmless negative manifestations of the action of E290 are bloating and belching.

Application of E290

The main application of Carbon Dioxide is its use as an E290 preservative in the production of carbonated drinks. It is often used in the fermentation process of grape raw materials to control fermentation. Е290 is a part of preservatives for storage in packages of meat and dairy products, bakery products, vegetables and fruits. Dry ice is used as a freezing and cooling agent to preserve ice cream as well as fresh fish and seafood. How the E290 baking powder "works" in the process of baking bread and baking.

On sale you can find E290 Carbon dioxide in cylinders or in the form of blocks of "dry ice" in special sealed packages.

E290 use of carbon dioxide in Russia

In the territory Russian Federation allowed to use food additive E290 in the food industry as a preservative and baking powder.

Carbon dioxide, a colorless gas with a barely perceptible odor, is not poisonous, heavier than air. Carbon dioxide is widespread in nature. It dissolves in water, forming carbonic acid H 2 CO 3, gives it a sour taste. The air contains about 0.03% carbon dioxide. The density is 1.524 times the density of air and is equal to 0.001976 g / cm 3 (at zero temperature and pressure of 101.3 kPa). Ionization potential 14.3V. Chemical formula - CO 2.

In welding, the term is used "carbon dioxide" cm. . In the "Rules for the Construction and Safe Operation of Pressure Vessels" the term "carbon dioxide", and in - term Carbon dioxide.

There are many ways to obtain carbon dioxide, the main of which are discussed in the article.

The density of carbon dioxide depends on the pressure, temperature and state of aggregation in which it is located. At atmospheric pressure and a temperature of -78.5 ° C, carbon dioxide, bypassing the liquid state, turns into a white snow-like mass "dry ice".

Under a pressure of 528 kPa and at a temperature of -56.6 ° C, carbon dioxide can be in all three states (the so-called triple point).

Carbon dioxide is thermally stable, dissociates into carbon monoxide and only at temperatures above 2000 ° C.

Carbon dioxide is the first gas to be described as a discrete substance... In the seventeenth century, Flemish chemist Jan Baptist van Helmont (Jan Baptist van Helmont) noticed that after burning coal in a closed vessel, the mass of the ash was much less than the mass of the burned coal. He explained this by the fact that coal is transformed into an invisible mass, which he called "gas."

The properties of carbon dioxide were studied much later in 1750. Scottish physicist Joseph Black (Joseph Black).

He found that limestone (calcium carbonate CaCO 3), when heated or interacted with acids, gives off a gas, which he called "bound air." It turned out that "bound air" is denser than air and does not support combustion.

CaCO 3 + 2HCl \u003d CO 2 + CaCl 2 + H 2 O

By passing "bound air" i.e. carbon dioxide CO 2 through an aqueous solution of lime Ca (OH) 2, calcium carbonate CaCO 3 is deposited on the bottom. Joseph Black used this experience to prove that carbon dioxide is produced by the respiration of animals.

CaO + H 2 O \u003d Ca (OH) 2

Ca (OH) 2 + CO 2 \u003d CaCO 3 + H 2 O

Liquid carbon dioxide is a colorless, odorless liquid, the density of which varies greatly with temperature. It exists at room temperature only at a pressure of more than 5.85 MPa. The density of liquid carbon dioxide is 0.771 g / cm 3 (20 ° C). At temperatures below + 11 ° C, it is heavier than water, and above + 11 ° C, it is lighter.

The specific gravity of liquid carbon dioxide varies significantly with temperature, therefore, the amount of carbon dioxide is determined and sold by weight. The solubility of water in liquid carbon dioxide in the temperature range 5.8-22.9 ° C is not more than 0.05%.

Liquid carbon dioxide is converted to gas when heat is supplied to it. Under normal conditions (20 ° C and 101.3 kPa) when 1 kg of liquid carbon dioxide evaporates, 509 liters of carbon dioxide are formed... With an excessively fast gas extraction, a decrease in pressure in the cylinder and insufficient heat supply, carbon dioxide cools, its evaporation rate decreases and when the “triple point” is reached, it turns into dry ice, which clogs the hole in the reduction gearbox, and further gas extraction stops. When heated, dry ice is directly converted into carbon dioxide, bypassing the liquid state. For the evaporation of dry ice, it is necessary to supply much more heat than for the evaporation of liquid carbon dioxide - therefore, if dry ice forms in the cylinder, it evaporates slowly.

For the first time liquid carbon dioxide was obtained in 1823. Humphrey Davy (Humphry Davy) and Michael Faraday (Michael Faraday).

Solid carbon dioxide, "dry ice", resembles snow and ice in appearance. The content of carbon dioxide obtained from dry ice briquette is high - 99.93-99.99%. Moisture content in the range of 0.06-0.13%. Dry ice, being in the open air, evaporates intensively, therefore containers are used for its storage and transportation. The production of carbon dioxide from dry ice is carried out in special evaporators. Solid carbon dioxide (dry ice) supplied in accordance with GOST 12162.

Carbon dioxide is most commonly used:

• to create a protective environment for metals;
• in the production of carbonated drinks;
• refrigeration, freezing and storage of food;
• for fire extinguishing systems;
• for cleaning surfaces with dry ice.

The density of carbon dioxide is high enough, which makes it possible to protect the reaction space of the arc from contact with air gases and prevents nitriding at relatively low consumption of carbon dioxide in the jet. Carbon dioxide is, during the welding process it interacts with the weld metal and has an oxidizing and carburizing effect on the weld pool metal.

Previously obstacles to the use of carbon dioxide as a protective medium were at the seams. The pores were caused by the boiling of the solidifying metal of the weld pool from the release of carbon monoxide (CO) due to its insufficient deoxidation.

At high temperatures, carbon dioxide dissociates to form a very active free, monoatomic oxygen:

Oxidation of the weld metal by free carbon dioxide liberated during welding is neutralized by the content of an additional amount of alloying elements with a high affinity for oxygen, most often silicon and manganese (in excess of the amount required to alloy the weld metal) or fluxes introduced into the welding zone (welding).

Both carbon dioxide and carbon monoxide are practically insoluble in solid and molten metal. The free active oxidizes the elements present in the weld pool, depending on their affinity for oxygen and concentration according to the equation:

Me + O \u003d MeO

where Me is a metal (manganese, aluminum, etc.).

In addition, carbon dioxide itself reacts with these elements.

As a result of these reactions, when welding in carbon dioxide, there is a significant burnout of aluminum, titanium and zirconium, and less intense - silicon, manganese, chromium, vanadium, etc.

The oxidation of impurities is especially vigorous when. This is due to the fact that, in consumable electrode welding, the interaction of the molten metal with gas occurs when a drop is at the end of the electrode and in the weld pool, and in non-consumable electrode welding, only in the pool. As is known, the interaction of gas with metal in the arc gap occurs much more intensively due to the high temperature and the larger surface of contact between the metal and gas.

Due to the chemical activity of carbon dioxide in relation to tungsten, welding in this gas is carried out only with a consumable electrode.

Carbon dioxide is non-toxic and non-explosive. At concentrations of more than 5% (92 g / m 3), carbon dioxide has a harmful effect on human health, since it is heavier than air and can accumulate in poorly ventilated rooms near the floor. At the same time, the volume fraction of oxygen in the air decreases, which can cause the phenomenon of oxygen deficiency and suffocation. Premises where welding is performed using carbon dioxide must be equipped with general exchange supply and exhaust ventilation. The maximum permissible concentration of carbon dioxide in the air of the working area is 9.2 g / m 3 (0.5%).

Carbon dioxide is supplied by. To obtain high-quality seams, gaseous and liquefied carbon dioxide of the highest and first grades is used.

Carbon dioxide is transported and stored in steel cylinders or large-capacity tanks in a liquid state, followed by gasification at the plant, with centralized supply of welding stations through ramps. In a standard one with a water capacity of 40 liters, 25 kg of liquid carbon dioxide is poured, which at normal pressure occupies 67.5% of the volume of the cylinder and gives 12.5 m 3 of carbon dioxide upon evaporation. In the upper part of the cylinder, air accumulates together with gaseous carbon dioxide. Water, which is heavier than liquid carbon dioxide, collects at the bottom of the cylinder.

To reduce the moisture content of carbon dioxide, it is recommended to install the cylinder with the valve down and, after settling for 10 ... 15 minutes, carefully open the valve and release the moisture from the cylinder. Before welding, it is necessary to release a small amount of gas from a normally installed cylinder to remove air trapped in the cylinder. Part of the moisture is retained in carbon dioxide in the form of water vapor, worsening during seam welding.

When gas is released from the cylinder, due to the throttling effect and heat absorption during the evaporation of liquid carbon dioxide, the gas is significantly cooled. With intensive gas extraction, the reducer may become clogged with frozen moisture contained in carbon dioxide, as well as dry ice. To avoid this, a gas heater is installed in front of the reducer when taking off carbon dioxide. The final removal of moisture after the reducer is carried out with a special desiccant filled with glass wool and calcium chloride, silica, copper sulfate or other moisture absorbers

The carbon dioxide cylinder is painted black, with the inscription in yellow letters "CARBON ACID".

Structural formula

True, empirical, or gross formula: CO 2

Chemical composition Carbon dioxide

Molecular mass: 44.009

Carbon dioxide (carbon dioxide, carbon dioxide, carbon (IV) oxide, carbonic anhydride) is a colorless gas (under normal conditions), odorless, with chemical formula CO 2... Density under normal conditions 1.98 kg / m³ (heavier than air). At atmospheric pressure, carbon dioxide does not exist in a liquid state, passing directly from a solid to a gaseous state. Solid carbon dioxide is called dry ice. At elevated pressures and normal temperatures, carbon dioxide turns into a liquid, which is used for its storage. The concentration of carbon dioxide in the Earth's atmosphere is 0.04% on average. Carbon dioxide readily transmits ultraviolet rays and rays of the visible part of the spectrum, which come to the Earth from the Sun and heat it. At the same time, it absorbs infrared rays emitted by the Earth and is one of the greenhouse gases, as a result of which it takes part in the process of global warming. A constant rise in the level of this gas in the atmosphere has been observed since the beginning of the industrial era.

Carbon monoxide (IV) - carbon dioxide, odorless and colorless gas, heavier than air, with strong cooling crystallizes in the form of a white snow-like mass - "dry ice". At atmospheric pressure, it does not melt, but evaporates, the sublimation temperature is -78 ° C. Carbon dioxide is formed when organic matter decays and burns. Contained in the air and mineral springs, it is released during the respiration of animals and plants. Let's dissolve in water (1 volume of carbon dioxide in one volume of water at 15 ° С).

By chemical properties carbon dioxide is an acidic oxide. When dissolved in water, forms carbonic acid. Reacts with alkalis to form carbonates and bicarbonates. It enters into reactions of electrophilic substitution (for example, with phenol) and nucleophilic addition (for example, with organomagnesium compounds). Carbon monoxide (IV) does not support combustion. Only some active metals burn in it. Interacts with active metal oxides. When dissolved in water, forms carbonic acid. Reacts with alkalis to form carbonates and bicarbonates.

The human body releases approximately 1 kg (2.3 lb) of carbon dioxide per day. This carbon dioxide is carried from the tissues, where it is formed as one of the end products of metabolism, through the venous system and then excreted through the exhaled air through the lungs. Thus, the content of carbon dioxide in the blood is high in the venous system, and decreases in the capillary network of the lungs, and little in the arterial blood. The carbon dioxide content of a blood sample is often expressed in terms of the partial pressure, that is, the pressure that the carbon dioxide contained in the blood sample would have if only it occupied the entire volume of the blood sample. Carbon dioxide ( CO 2) is transported in the blood by three different ways (the exact ratio of each of these three modes of transport depends on whether the blood is arterial or venous).

• Most of the carbon dioxide (70% to 80%) is converted by the enzyme carbonic anhydrase of erythrocytes into bicarbonate ions.
• About 5% - 10% of carbon dioxide is dissolved in blood plasma.
• About 5% - 10% of carbon dioxide is associated with hemoglobin in the form of carbamino compounds (carbohemoglobin).

Hemoglobin, the main oxygen-transporting protein in red blood cells, is capable of transporting both oxygen and carbon dioxide. However, carbon dioxide binds to hemoglobin in a different place than oxygen. It binds to the N-terminal ends of the globin chains and not to the heme. However, due to allosteric effects, which lead to a change in the configuration of the hemoglobin molecule upon binding, the binding of carbon dioxide reduces the ability of oxygen to bind with it, at a given oxygen partial pressure, and vice versa - the binding of oxygen to hemoglobin reduces the ability of carbon dioxide to bind with it. at a given partial pressure of carbon dioxide. In addition, the ability of hemoglobin to preferentially bind to oxygen or carbon dioxide also depends on the pH of the medium. These features are very important for the successful capture and transport of oxygen from the lungs to the tissues and its successful release in the tissues, as well as for the successful capture and transport of carbon dioxide from the tissues to the lungs and its release there. Carbon dioxide is one of the most important mediators of blood flow autoregulation. It is a powerful vasodilator. Accordingly, if the level of carbon dioxide in the tissue or in the blood rises (for example, due to intensive metabolism - caused, say, by physical activity, inflammation, tissue damage, or due to obstructed blood flow, tissue ischemia), then the capillaries expand, which leads to an increase in blood flow and accordingly, to an increase in the delivery of oxygen to the tissues and the transport of accumulated carbon dioxide from the tissues. In addition, carbon dioxide in certain concentrations (increased, but not yet reaching toxic values) has a positive inotropic and chronotropic effect on the myocardium and increases its sensitivity to adrenaline, which leads to an increase in the strength and frequency of heart contractions, the value of cardiac output and, as a consequence , stroke and minute blood volume. It also contributes to the correction of tissue hypoxia and hypercapnia (increased levels of carbon dioxide). Bicarbonate ions are very important for regulating blood pH and maintaining normal acid-base balance. Respiration rate affects the carbon dioxide content in the blood. Poor or slow breathing causes respiratory acidosis, while rapid and excessively deep breathing leads to hyperventilation and the development of respiratory alkalosis. Moreover, carbon dioxide is also important in the regulation of breathing. Although our body requires oxygen to ensure metabolism, low oxygen levels in the blood or tissues usually do not stimulate respiration (or rather, the stimulating effect of lack of oxygen on respiration is too weak and "turns on" late, with very low oxygen levels in the blood, at which a person often is already losing consciousness). Breathing is normally stimulated by an increase in the level of carbon dioxide in the blood. The respiratory center is much more sensitive to increased levels of carbon dioxide than to lack of oxygen. As a consequence, breathing in highly rarefied air (with a low partial pressure of oxygen) or a gas mixture that does not contain oxygen at all (for example, 100% nitrogen or 100% nitrous oxide) can quickly lead to unconsciousness without feeling short of breath (since the level of carbon dioxide in the blood does not rise, because nothing prevents its exhalation). This is especially dangerous for pilots of military aircraft flying at high altitudes (if an enemy missile hits the cockpit and the cockpit is depressurized, the pilots can quickly lose consciousness). This feature of the respiratory regulation system is also the reason why in aircraft flight attendants instruct passengers in the event of a depressurization of the aircraft cabin, first of all, put on an oxygen mask themselves, before trying to help someone else - doing this, helping the person to quickly lose consciousness himself, and even without feeling until the last moment any discomfort and need for oxygen. The human respiratory center tries to maintain a partial pressure of carbon dioxide in arterial blood no higher than 40 mm Hg. With conscious hyperventilation, the carbon dioxide content in the arterial blood can decrease to 10-20 mm Hg, while the oxygen content in the blood will hardly change or increase slightly, and the need to take another breath will decrease as a result of a decrease in the stimulating effect of carbon dioxide on the activity of the respiratory center. This is the reason why, after a period of conscious hyperventilation, it is easier to hold the breath for a long time than without prior hyperventilation. Such deliberate hyperventilation, followed by holding the breath, can lead to loss of consciousness before the person feels the need to breathe. In a safe environment, such a loss of consciousness does not threaten anything special (having lost consciousness, a person will also lose control over himself, stop holding his breath and take a breath, breathing, and with it, the supply of oxygen to the brain will be restored, and then consciousness will also be restored). However, in other situations, for example, before diving, it can be dangerous (loss of consciousness and the need to breathe will come at a depth, and in the absence of conscious control, water will enter the respiratory tract, which can lead to drowning). This is why hyperventilating before diving is dangerous and not recommended.

In industrial quantities, carbon dioxide is released from flue gases, or as a by-product of chemical processes, for example, during the decomposition of natural carbonates (limestone, dolomite) or in the production of alcohol (alcoholic fermentation). The mixture of the resulting gases is washed with a solution of potassium carbonate, which absorb carbon dioxide, turning into bicarbonate. The bicarbonate solution decomposes when heated or under reduced pressure, releasing carbon dioxide. In modern installations for the production of carbon dioxide, instead of bicarbonate, an aqueous solution of monoethanolamine is often used, which, under certain conditions, is capable of absorbing CO 2contained in the flue gas, and give it away when heated; in this way the finished product is separated from other substances. Also, carbon dioxide is produced in air separation plants as a by-product of obtaining pure oxygen, nitrogen and argon. Under laboratory conditions, small amounts are obtained by reacting carbonates and hydrocarbonates with acids, such as marble, chalk or soda with hydrochloric acid, using, for example, a Kipp apparatus. Using the reaction of sulfuric acid with chalk or marble results in the formation of poorly soluble calcium sulfate, which interferes with the reaction, and which is removed by a significant excess of acid. The reaction can be used to prepare drinks baking soda with citric acid or sour lemon juice. It was in this form that the first carbonated drinks appeared. Pharmacists were engaged in their manufacture and sale.

In the food industry, carbon dioxide is used as a preservative and baking powder; it is indicated on the packaging with the E290 code. Liquid carbon dioxide is widely used in fire extinguishing systems and fire extinguishers. Automatic carbon dioxide fire extinguishing systems are distinguished by their starting systems, which are pneumatic, mechanical or electrical. The device for supplying carbon dioxide to the aquarium may include a tank of gas. The simplest and most common method for producing carbon dioxide is based on a design for making alcoholic beverage mash. During fermentation, the carbon dioxide released may well provide feeding of aquarium plants. Carbon dioxide is used to carbonate lemonade and soda water. Carbon dioxide is also used as a protective medium for wire welding, but at high temperatures it dissociates with the release of oxygen. The liberated oxygen oxidizes the metal. In this regard, it is necessary to introduce deoxidizers, such as manganese and silicon, into the welding wire. Another consequence of the influence of oxygen, also associated with oxidation, is a sharp decrease in surface tension, which leads, among other things, to more intense metal spatter than when welding in an inert atmosphere. Carbon dioxide in cans is used in pneumatic weapons (in gas-cylinder pneumatics) and as a source of energy for engines in aircraft modeling. Storage of carbon dioxide in a steel cylinder in a liquefied state is more profitable than in the form of gas. Carbon dioxide has a relatively low critical temperature of + 31 ° C. About 30 kg of liquefied carbon dioxide is poured into a standard 40-liter cylinder, and at room temperature there will be a liquid phase in the cylinder, and the pressure will be about 6 MPa (60 kgf / cm²). If the temperature is above + 31 ° C, then carbon dioxide will go into a supercritical state with a pressure above 7.36 MPa. The standard working pressure for a conventional 40-liter cylinder is 15 MPa (150 kgf / cm²), but it must safely withstand a pressure 1.5 times higher, that is, 22.5 MPa - thus, working with such cylinders can be considered quite safe. Solid carbon dioxide - "dry ice" - is used as a refrigerant in laboratory research, in retail, when repairing equipment (for example: cooling one of the mating parts when landing in tension), etc. Carbon dioxide installations are used to liquefy carbon dioxide and obtain dry ice.

Measurement of the partial pressure of carbon dioxide is required in technological processes, in medical applications - the analysis of breathing mixtures during artificial ventilation of the lungs and in closed life support systems. Concentration analysis CO 2 in the atmosphere is used for environmental and scientific research, to study the greenhouse effect. Carbon dioxide is recorded using gas analyzers based on the principle of infrared spectroscopy and other gas measuring systems. A medical gas analyzer for recording the carbon dioxide content in exhaled air is called a capnograph. For measuring low concentrations CO 2 (as well as CO) in process gases or in atmospheric air, you can use the gas chromatography method with a methanator and registration on a flame ionization detector.

Annual fluctuations in the concentration of atmospheric carbon dioxide on the planet are determined mainly by the vegetation of the middle (40-70 °) latitudes of the Northern Hemisphere. Vegetation in the tropics is practically independent of the season, the dry desert belt of 20-30 ° (both hemispheres) makes a small contribution to the carbon dioxide cycle, and the land strips most covered with vegetation are asymmetrically located on Earth (there is an ocean in the southern hemisphere in the middle latitudes). Therefore, from March to September, due to photosynthesis, the content CO 2 falls in the atmosphere, and increases from October to February. Both wood oxidation (heterotrophic plant respiration, rotting, humus decomposition, forest fires) and the burning of fossil fuels (coal, oil, gas), which significantly increases in the winter season, contribute to the winter growth. Large amounts of carbon dioxide are dissolved in the ocean. Carbon dioxide makes up a significant portion of the atmospheres of some planets Solar system: Venus, Mars.

Carbon dioxide is non-toxic, but due to the effect of its increased concentrations in the air on air-breathing living organisms, it is classified as asphyxiant (English) Russian .. Slight increases in concentration up to 2-4% indoors lead to the development of drowsiness and weakness in people. Hazardous concentrations are considered levels of about 7-10%, at which suffocation develops, manifesting itself in headache, dizziness, hearing impairment and loss of consciousness (symptoms similar to those of altitude sickness), depending on the concentration, over a period of several minutes up to one hour. When air with high concentrations of gas is inhaled, death occurs very quickly from suffocation. Although, in fact, even a concentration of 5-7% CO2 is not fatal, even at a concentration of 0.1% (such a content of carbon dioxide is observed in the air of megacities) people begin to feel weak and sleepy. This shows that even at high oxygen levels, high CO2 concentrations have a strong effect on well-being. Inhalation of air with an increased concentration of this gas does not lead to long-term health problems, and after removal of the victim from the gas-polluted atmosphere, complete recovery of health occurs quickly.

It is +4), called carbon dioxide (other names: carbon dioxide, carbonic anhydride, carbon dioxide). It is customary to write this substance with the molecular formula CO2. Molar mass it is equal to 44.01 g / mol. In appearance, under normal conditions, carbonic anhydride is a colorless gas. At low concentrations, it is odorless; at higher concentrations, it acquires a pungent, sour odor.

For this chemical three aggregate states are possible, which are characterized by different meanings density:

• solid (dry ice); at a pressure of 1 atm. and a temperature of -78.5 ° C - 1562 kg / m³;
• liquid (carbon dioxide); at a pressure of 56 atm. and a temperature of +20 ° C - 770 kg / m³;
• gaseous; at a pressure of 1 atm. and a temperature of 0 ° C - 1,977 kg / m³.

The melting point of carbon dioxide is -78 ° C, the boiling point is -57 ° C. The substance is soluble in water: at 25 ° C and a pressure of 100 kPa, its solubility is 1.45 g / l.

Carbon dioxide is a naturally occurring chemical compound in which oxygen atoms are linked to a carbon atom by a covalent bond. The carbon dioxide molecule is linear and centrosymmetric. Both bonds between carbon and two oxygen atoms are equivalent (in fact, they are double). The molecule is symmetrical about its center, so it has no electrical dipole moment.

Carbon dioxide was one of the first gaseous chemical compounds to be identified with air. In the seventeenth century, the Flemish chemist Jan Baptista van Helmont noticed that when he burned coal in a closed vessel, the mass of the resulting ash was much less than ordinary. The properties of carbon dioxide were studied more thoroughly in 1750 by the Scottish physician Joseph Black.

Carbon dioxide at standard pressure and temperature is in the Earth's atmosphere in an amount of about 0.04% by volume. In the carbon cycle known as photosynthesis, carbon dioxide is absorbed by plants, algae, and cyanobacteria. As a result, water and carbohydrates are formed, but this process occurs only under the influence of light. Carbon dioxide is also produced when coal or hydrocarbons are burned, when liquids are fermented, and when people and animals breathe out air. In addition, it is emitted from volcanoes, hot springs, geysers.

In carbon dioxide plays an important role (absorbs and emits radiation in the thermal infrared range). Also, this chemical compound is one of the main sources of lowering the pH of the ocean: dissolving in water, it forms a weak carbonic acid: CO2 + H2O ↔ H2CO3, which is unable to completely dissociate into ions.

Carbon dioxide does not support combustion and respiration. The lit torch in its atmosphere is extinguished. Animals and humans are suffocated by high CO2 concentrations. At a 3% concentration in the air, breathing quickens, at a 10% concentration, loss of consciousness and rapid death occurs, and a 20% concentration causes instant paralysis.

Carbon dioxide is an anhydride of carbonic acid and therefore has the properties of an acidic oxide. Under laboratory conditions, it is obtained by the interaction of chalk with hydrochloric acid in CaCO3 + 2HCl → CaCl2 + CO2 + H2O. In industry, it is produced by thermal decomposition of limestone or chalk (less often magnesite or dolomite): CaCO3 → CaO + CO2. The production of carbon dioxide is a side process of the low-temperature separation of air into nitrogen and oxygen. Nowadays, special generators are produced for obtaining carbon dioxide from the air. These generators are used to supply CO2 to greenhouses in order to create a favorable environment for plants.

Carbon dioxide is widely used in chemical industries. It is used to make soda, to synthesize organic acids, and to make soft drinks. used as a refrigerant, for example, in winemaking. Carbon dioxide atmosphere is created to prevent rotting food products, the same grapes after harvest and before the start of wine production.

The production of carbon dioxide or liquefied carbon dioxide is carried out to fill it with which is used to extinguish fires. However, they cannot extinguish a person, as a significant part of the jet of liquid CO2 evaporates, while the temperature drops sharply (which can cause frostbite) and the CO2 turns into dry ice. Carbon dioxide is usually used to extinguish electrical wiring. The mechanism consists in stopping the supply of air oxygen to the fire site.

, carbon dioxide, properties of carbon dioxide, obtaining carbon dioxide

It is not fit to sustain life. However, this is what plants "feed" on, turning it into organic matter. Besides, it is a kind of "blanket" of the Earth. If this gas suddenly disappears from the atmosphere, the Earth will become much cooler, and the rains will practically disappear.

"Blanket of the Earth"

(carbon dioxide, carbon dioxide, CO 2) is formed when two elements combine: carbon and oxygen. It is formed during the combustion of coal or hydrocarbon compounds, during the fermentation of liquids, and also as a product of the breath of humans and animals. It is also found in small quantities in the atmosphere, from where it is assimilated by plants, which, in turn, produce oxygen.

Carbon dioxide is colorless and heavier than air. Freezes at -78.5 ° C to form snow, composed of carbon dioxide. In the form of an aqueous solution, it forms carbonic acid, but it is not stable enough to be easily isolated.

Carbon dioxide is the “blanket” of the Earth. It easily transmits ultraviolet rays that heat our planet, and reflects infrared emitted from its surface into outer space. And if suddenly carbon dioxide disappears from the atmosphere, it will primarily affect the climate. It will become much cooler on Earth, rain will fall very rarely. Where this will ultimately lead is not difficult to guess.

True, such a catastrophe does not threaten us yet. Rather, the opposite is true. Burning organic matter: oil, coal, natural gas, wood - gradually increases the carbon dioxide content in the atmosphere. This means that over time it is necessary to wait for a significant warming and humidification of the earth's climate. By the way, the old-timers believe that it is already noticeably warmer than it was during their youth ...

Carbon dioxide is released liquid low temperature, high pressure liquid and gaseous... It is obtained from waste gases from ammonia and alcohols production, as well as on the basis of special fuel combustion and other industries. Gaseous carbon dioxide is a colorless and odorless gas at a temperature of 20 ° C and a pressure of 101.3 kPa (760 mm Hg), density - 1.839 kg / m 3. Liquid carbon dioxide is simply a colorless, odorless liquid.

Non-toxic and non-explosive. At concentrations of more than 5% (92 g / m 3), carbon dioxide has a harmful effect on human health - it is heavier than air and can accumulate in poorly ventilated rooms near the floor. At the same time, the volume fraction of oxygen in the air decreases, which can cause the phenomenon of oxygen deficiency and suffocation.

Obtaining carbon dioxide

In industry, carbon dioxide is obtained from furnace gases, from decomposition products of natural carbonates (limestone, dolomite). The gas mixture is washed with a solution of potassium carbonate, which absorbs carbon dioxide, turning into bicarbonate. A solution of bicarbonate decomposes when heated, releasing carbon dioxide. When industrial production gas is pumped into cylinders.

In laboratory conditions, small quantities are obtained the interaction of carbonates and bicarbonates with acids, for example marble with hydrochloric acid.

"Dry ice" and other beneficial properties of carbon dioxide

In everyday practice, carbon dioxide is widely used. For instance, sparkling water with the addition of aromatic essences - a wonderful refreshing drink. AT food Industry carbon dioxide is also used as a preservative - it is indicated on the packaging under the code E290and also as a baking powder.

Carbon dioxide fire extinguishers used in fires. Biochemists have found that fertilization ... of air with carbon dioxidevery effective remedy to increase the productivity of various crops. Perhaps, such a fertilizer has a single, but significant drawback: it can only be used in greenhouses. In plants producing carbon dioxide, liquefied gas is filled into steel cylinders and sent to consumers. If you open the valve, then ... snow escapes from the hole with a hiss. What a miracle?

Everything is explained simply. The work expended in compressing the gas turns out to be much less than that required to expand it. And in order to somehow compensate for the arising deficit, carbon dioxide is sharply cooled, turning into "dry ice"... It is widely used for food preservation and before regular ice has significant advantages: first, its "cooling capacity" is twice as high per unit weight; secondly, it evaporates without residue.

Carbon dioxide is used as an active medium for wire welding, since at the temperature of the arc, carbon dioxide decomposes into carbon monoxide CO and oxygen, which, in turn, interacts with the liquid metal, oxidizing it.

Carbon dioxide in cans is used in pneumatic weapon and as energy source for motors in aeromodelling.