Carbon dioxide. Properties, production, application

Liquid

Carbon dioxide (carbon dioxide, CO 2) in all its states is widely used in almost all sectors of industry and the agro-industrial complex.

CO 2 accounts for 10% of the total market technical gases, which puts this product on par with the main air separation products.

Carbon monoxide (carbon dioxide, carbon dioxide, carbon dioxide, carbonic anhydride, carbon dioxide) - CO 2, a colorless gas, odorless, with a slightly sour taste.

The concentration of carbon dioxide in the Earth's atmosphere averages 0.038%

Physical

Density under normal conditions is 1.97 kg/m³. At atmospheric pressure, carbon dioxide does not exist in a liquid state, changing directly from a solid to a gaseous state. Solid carbon dioxide is called dry ice. At elevated pressure and normal temperatures, carbon dioxide turns into liquid, which is used for its storage.

Carbon dioxide easily passes through ultra-violet rays and rays of the visible part of the spectrum that come to the Earth from the Sun and heat it. At the same time, it absorbs the earth's emitted infrared rays and is one of greenhouse gases, as a result of which it takes part in the process global warming. A constant increase in the level of this gas in the atmosphere has been observed since the beginning of the industrial era.

Chemical

According to its chemical properties, carbon dioxide is classified as an acidic oxide. When dissolved in water, it forms carbonic acid. Reacts with alkalis to form carbonates and bicarbonates. It undergoes electrophilic substitution reactions (for example, with phenol - the Kolbe reaction) and nucleophilic addition (for example, with organomagnesium compounds).

Biological

Carbon dioxide plays one of the main roles in living nature, participating in many metabolic processes of a living cell. Carbon dioxide is produced as a result of many oxidative reactions in animals, and is released into the atmosphere through respiration. Atmospheric carbon dioxide is the main source of carbon for plants. However, it would be a mistake to say that animals only emit carbon dioxide, and plants only absorb it. Plants absorb carbon dioxide through photosynthesis, and without light they also release it.

Carbon dioxide is non-toxic but does not support respiration. High concentrations in the air cause suffocation (see Hypercapnia). Lack of carbon dioxide is also dangerous (see Hypocapnia)

Carbon dioxide also has physiological significance in animal organisms, for example, it is involved in the regulation of vascular tone (see Arterioles).

Receipt

In industry it is obtained from furnace gases, from decomposition products of natural carbonates (limestone, dolomite). The mixture of gases is washed with a solution of potassium carbonate, which absorbs carbon dioxide, turning into bicarbonate. A solution of bicarbonate decomposes when heated or under reduced pressure, releasing carbon dioxide. The gas produced during alcoholic fermentation is used for food purposes. After pre-treatment, the gas is pumped into cylinders.

Carbon dioxide is also produced at air separation plants, such as by-product obtaining pure oxygen, nitrogen and argon.

IN laboratory conditions small quantities are obtained by reacting carbonates and bicarbonates with acids, for example marble, chalk or soda with hydrochloric acid. Using sulfuric acid to react with chalk or marble results in the formation of slightly 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 with sour lemon juice. It was in this form that the first carbonated drinks appeared. Pharmacists were engaged in their production and sale.

Application

IN Food Industry carbon dioxide is used as a preservative and is indicated on the packaging under the code E290, and also as a dough leavening agent.

Liquid carbon dioxide (liquid food carbon dioxide) is liquefied carbon dioxide stored under high pressure (~ 65-70 Atm). Colorless liquid. Upon release liquid carbon dioxide from the balloon into the atmosphere, part of it evaporates, and the other part forms dry ice flakes.

Liquid carbon dioxide cylinders are widely used as fire extinguishers and for the production of carbonated water and lemonade.

Carbon dioxide is used as a protective medium in wire welding, but at high temperatures it dissociates and releases oxygen. The released oxygen oxidizes the metal. In this regard, it is necessary to introduce deoxidizing agents 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 spattering than when welding in argon or helium.

Carbon dioxide in cans is used in air guns and as a source of energy for engines in aircraft modeling.

Solid carbon dioxide - dry ice - is used in glaciers. Liquid carbon dioxide is used as a refrigerant and working fluid in thermal power plants (refrigerators, freezers, solar power generators, etc.).

Registration Methods

Carbon dioxide partial pressure measurement is required in technological processes, in medical applications - analysis of respiratory mixtures during artificial ventilation lungs and closed systems life support. Analysis of CO 2 concentration 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.

Carbon dioxide in the atmosphere

Changes in atmospheric carbon dioxide concentration (Keeling curve). Measurements at the Mauna Loa Observatory.

Annual fluctuations in the concentration of atmospheric carbon dioxide on the planet are determined mainly by the vegetation of the middle latitudes (40-70°) of the Northern Hemisphere.

Vegetation in the tropics is practically independent of the season, the dry desert belt of 20-30° (in both hemispheres) makes a small contribution to the carbon dioxide cycle, and the strips of land most covered with vegetation are located asymmetrically on Earth (in the Southern Hemisphere there is an ocean in the middle latitudes).
Therefore, from March to September, due to photosynthesis, the CO 2 content in the atmosphere decreases, and from October to February it increases. Contributions to winter growth come from both the oxidation of wood (heterotrophic respiration of plants, rotting, decomposition of humus, forest fires) and the combustion of fossil fuels (coal, oil, gas), which increases noticeably in the winter season.

The use of carbon dioxide in the welding field is very common. This is one of the main options that are used for various types metal connections. Physical properties carbon dioxide is defined as a universal substance for gas welding, gas and electric arc welding, and so on. This is a relatively inexpensive raw material that has been used here for many years. There are more effective options, but it is carbon dioxide that is most often used. It finds application both for training and for performing the most simple procedures.

Carbon dioxide is also called carbon dioxide. The substance is odorless and colorless in its normal state. At normal atmospheric pressure, carbon dioxide is not in a liquid state and immediately changes from solid to gaseous.

Applications of carbon dioxide

The chemical is used for more than just welding. The physical properties of carbon dioxide make it possible to use it as a leavening agent or preservative in the food industry. In many fire extinguishing systems, in particular in hand-held fire extinguishers. It is used to provide nutrition aquarium plants. Almost all carbonated drinks contain carbon dioxide.

In the welding industry, the use of pure carbon dioxide is not entirely safe for the metal. The point is that when exposed to high temperature it breaks down and oxygen is released from it. In turn, oxygen is dangerous for weld pool and to eliminate it negative impact, use a variety of deoxidizers, such as silicon and manganese.

The use of carbon dioxide is also found in cylinders for air pistols and rifles. As in welding cylinders, carbon dioxide is stored here in a liquefied state under pressure.

Chemical formula

Chemical properties carbon dioxide, as well as its other characteristics, directly depend on the elements that are part of the formula. The formula of carbon dioxide in chemistry is CO 2. This means that carbon dioxide contains one carbon atom and two oxygen atoms.

Chemical and physical properties

Having considered how it is designated chemical gas in chemistry, it is worth taking a closer look at its properties. The physical properties of carbon dioxide are manifested in various parameters. The density of carbon dioxide under standard atmospheric conditions is 1.98 kg/m3. This makes it 1.5 times heavier than atmospheric air. Carbon dioxide is odorless and colorless. If it is subjected to strong cooling, it begins to crystallize into so-called “dry ice.” The sublimation temperature reaches -78 degrees Celsius.

The chemical properties of carbon dioxide make it an acidic oxide, since it can form carbonic acid when dissolved in water. When interacting with alkalis, the substance begins to form bicarbonates and carbonates. With some substances, such as phenol, carbon dioxide undergoes an electrophilic substitution reaction. The substance enters into a nucleophilic addition reaction with organomagnesium substances. The use of carbon dioxide in fire extinguishers is due to the fact that it does not support the combustion process. Use in welding is due to the fact that some active metals burn in the substance.

Advantages

  • The use of carbon dioxide is relatively inexpensive, since the price of this substance is quite low when compared with other gases;
  • This is a very common substance that can be found in many places;
  • Carbon dioxide is easy to store and does not require complex safety measures;
  • Gas copes well with the duties for which it is intended.

Flaws

  • During use, oxides may form on the metal, which are released by the substance during heating;
  • For normal operation it is necessary to use additional consumables that would help eliminate the negative effects of oxides;
  • There are more efficient gases used in the welding industry.

Use of carbon dioxide in welding

This substance is used in the field of welding metal products as . It applies to both automatic and . Often it is not used in its pure form, but together with argon or oxygen in a gas mixture. IN production sector There are several options for supplying posts. Among them are the following methods:

  • Delivery from a cylinder. This is very convenient when we are talking about relatively small volumes of a substance. This ensures mobility, since it is not always possible to create a pipeline to the post.
  • Transport container for carbon dioxide. it's the same great option for consumption of the substance in small cylinders. It supplies more gas than in cylinders, but is less convenient to transport.
  • Stationary storage vessel. It is used for those who use carbon dioxide in large volumes. They are used when there is no autonomous station at the enterprise.
  • Autonomous station. This is the widest delivery method in terms of volume, as it can serve a post for almost any procedure, regardless of volume. Thus, the post receives the substance directly from the place of its production.

An autonomous station is a special workshop at an enterprise where carbon dioxide is produced. It can work either exclusively for its own needs or for supply to other workshops and organizations. To ensure the operating points of the enterprise, gas is supplied through pipelines. At times when the enterprise needs to store carbon dioxide, it is moved to special storage tanks.

Security measures

Storage and use of the substance is relatively safe. But in order to eliminate the possibility of accidents, you should adhere to the basic rules:

  • Despite the fact that carbon dioxide is not explosive or toxic, if its concentration is above 5%, a person will feel suffocation and oxygen deficiency. Do not allow any leakage or store anything in a closed, unventilated area.
  • If you lower the pressure, liquid carbon dioxide turns into a gaseous state. At this time, its temperature can be -78 degrees Celsius. This is harmful to the mucous membranes of the body. It also leads to frostbite of the skin
  • Inspection of large carbon dioxide storage tanks should be carried out using a hose gas mask. The tank must be heated to a temperature environment and be well ventilated.

Conclusion

Physical properties are not the only indicator by which gas for welding is selected. The combination of all parameters provides this substance with a confident position in modern market Supplies. Among the simplest procedures, this is an indispensable gas that almost every professional and novice welder has encountered.

One of the most commonly used technical gases is carbon dioxide. This gas is also called carbon dioxide, carbon dioxide, carbon dioxide and carbonic anhydride - CO2. The gas is colorless and tastes sour. It is used in most industrial processes, also in medicine, food and gas welding industries. It is also used in fire extinguishers and air gun cans. On a large scale, carbon dioxide for industry is produced by the interaction of dolomite or limestone and a solution of potassium carbonate. For sparkling water and bakery products carbon dioxide is produced by alcoholic fermentation.

Carbon dioxide is not toxic, but in strong concentrations it is dangerous to humans. Carbon dioxide in its liquid state upon contact with oxygen turns partly into “dry ice” and partly evaporates. During industrial production, technical gas is pumped into cylinders. Carbon dioxide in a liquid state is stored under high pressure of about 65-70 atmospheres.

Carbon dioxide has also found its use as an inert medium in wire welding. For better efficiency welding work usually other technical gases are used, especially when it is necessary to weld thick metal parts. But these gases cannot cover the simplified use of carbon dioxide cylinders with a welding installation, the ease of production and the low cost of the gas itself.

Taking into account all the advantages, carbon dioxide is the optimal gas for welding. For small volumes of carbon dioxide use, cylinders are used for welding work. 25 kg of liquid carbon dioxide is poured into a 40 liter cylinder, as a result of the evaporation of which about 12,500 liters of gas are released.

Carbon dioxide is stored in cylinders under a pressure of 5-6 MPa. The cylinder must be equipped with a reducer, heater and gas dryer. When carbon dioxide leaves the cylinder, it cools down greatly, which can lead to freezing of the water vapor that is in the gas and subsequent blockage of the reducer. Therefore, a special gas heater must be installed between the reducer and the cylinder valve. Passing through the tube, the gas is heated by an electric element, which is connected to a network with a voltage of 24 or 36 V. Moisture is removed from carbon dioxide using a desiccant, which consists of a container filled with compounds that perfectly absorb water. Dehumidifiers are divided into two types: high pressure(they are installed before the gearbox) and low pressure, installed after the gearbox.

Carbon dioxide for welding is of the highest, first and second grade, according to GOST 8050-85. However, the use of the second grade must be carried out strictly with a gas dryer. It should be noted that when welding parts using carbon dioxide, you can visually control the quality of the seam, position the cylinders at any angle, which gives an accurate result.

At the Engineering and Technical Center " Hellios» We have all types of carbon dioxide for welding work. Our specialists will advise you in more detail on all issues and present the relevant quality documents. We supply enterprises and individuals for many years and are ready for long-term cooperation with each new client.

Soda, volcano, Venus, refrigerator - what do they have in common? Carbon dioxide. We have collected for you the most interesting information about one of the most important chemical compounds on Earth.

What is carbon dioxide

Carbon dioxide is known mainly in its gaseous state, i.e. as carbon dioxide with simple chemical formula CO2. In this form, it exists under normal conditions - at atmospheric pressure and “ordinary” temperatures. But at increased pressure, over 5,850 kPa (such as, for example, the pressure at deep sea about 600 m), this gas turns into liquid. And when strongly cooled (minus 78.5°C), it crystallizes and becomes so-called dry ice, which is widely used in trade for storing frozen foods in refrigerators.

Liquid carbon dioxide and dry ice are produced and used in human activity, but these forms are unstable and easily disintegrate.

But carbon dioxide gas is distributed everywhere: it is released during the respiration of animals and plants and is an important component of chemical composition atmosphere and ocean.

Properties of carbon dioxide

Carbon dioxide CO2 is colorless and odorless. Under normal conditions it has no taste. However, if you inhale high concentrations of carbon dioxide, you may experience a sour taste in your mouth, caused by the carbon dioxide dissolving on mucous membranes and in saliva, forming a weak solution of carbonic acid.

By the way, it is the ability of carbon dioxide to dissolve in water that is used to make carbonated water. Lemonade bubbles are the same carbon dioxide. The first apparatus for saturating water with CO2 was invented back in 1770, and already in 1783 the enterprising Swiss Jacob Schwepp began industrial production soda ( trademark Schweppes still exists).

Carbon dioxide is 1.5 times heavier than air, so it tends to “settle” in its lower layers if the room is poorly ventilated. The “dog cave” effect is known, where CO2 is released directly from the ground and accumulates at a height of about half a meter. An adult, entering such a cave, at the height of his growth does not feel the excess of carbon dioxide, but dogs find themselves directly in a thick layer of carbon dioxide and are poisoned.

CO2 does not support combustion, which is why it is used in fire extinguishers and fire suppression systems. The trick of extinguishing a burning candle with the contents of a supposedly empty glass (but in fact carbon dioxide) is based precisely on this property of carbon dioxide.

Carbon dioxide in nature: natural sources

Carbon dioxide is formed in nature from various sources:

  • Respiration of animals and plants.
    Every schoolchild knows that plants absorb carbon dioxide CO2 from the air and use it in the processes of photosynthesis. Some housewives try to indoor plants make up for shortcomings. However, plants not only absorb, but also release carbon dioxide in the absence of light - this is part of the respiration process. Therefore, a jungle in a poorly ventilated bedroom is not very good idea: CO2 levels will rise even more at night.
  • Volcanic activity.
    Carbon dioxide is part of volcanic gases. In areas with high volcanic activity, CO2 can be released directly from the ground - from cracks and fissures called mofets. The concentration of carbon dioxide in valleys with mofets is so high that many small animals die when they get there.
  • Decomposition of organic matter.
    Carbon dioxide is formed during the combustion and decay of organic matter. Large natural emissions of carbon dioxide accompany forest fires.

Carbon dioxide is “stored” in nature in the form of carbon compounds in minerals: coal, oil, peat, limestone. Huge reserves of CO2 are found in dissolved form in the world's oceans.

The release of carbon dioxide from an open reservoir can lead to a limnological disaster, as happened, for example, in 1984 and 1986. in lakes Manoun and Nyos in Cameroon. Both lakes were formed on the site of volcanic craters - now they are extinct, but in the depths the volcanic magma still releases carbon dioxide, which rises to the waters of the lakes and dissolves in them. As a result of a number of climatic and geological processes, the concentration of carbon dioxide in waters exceeded a critical value. Was released into the atmosphere great amount carbon dioxide, which descended like an avalanche down the mountain slopes. About 1,800 people became victims of limnological disasters on Cameroonian lakes.

Artificial sources of carbon dioxide

The main anthropogenic sources of carbon dioxide are:

  • industrial emissions associated with combustion processes;
  • automobile transport.

Despite the fact that the share of environmentally friendly transport in the world is growing, the vast majority of the world's population will not soon have the opportunity (or desire) to switch to new cars.

Active deforestation for industrial purposes also leads to an increase in the concentration of carbon dioxide CO2 in the air.

CO2 is one of the end products of metabolism (the breakdown of glucose and fats). It is secreted in the tissues and transported by hemoglobin to the lungs, through which it is exhaled. The air exhaled by a person contains about 4.5% carbon dioxide (45,000 ppm) - 60-110 times more than in the air inhaled.

Carbon dioxide plays a large role in regulating blood flow and respiration. An increase in CO2 levels in the blood causes the capillaries to dilate, allowing more blood to pass through, which delivers oxygen to the tissues and removes carbon dioxide.

Respiratory system is also stimulated by an increase in carbon dioxide content, and not by a lack of oxygen, as it might seem. In reality, the lack of oxygen is not felt by the body for a long time and it is quite possible that in rarefied air a person will lose consciousness before he feels the lack of air. The stimulating property of CO2 is used in artificial respiration devices: where carbon dioxide is mixed with oxygen to “start” the respiratory system.

Carbon dioxide and us: why CO2 is dangerous

Carbon dioxide is needed to the human body just like oxygen. But just like with oxygen, an excess of carbon dioxide harms our well-being.

A high concentration of CO2 in the air leads to intoxication of the body and causes a state of hypercapnia. With hypercapnia, a person experiences difficulty breathing, nausea, headache and may even lose consciousness. If the carbon dioxide content does not decrease, then oxygen starvation occurs. The fact is that both carbon dioxide and oxygen move throughout the body on the same “transport” - hemoglobin. Normally, they “travel” together, attaching to different places on the hemoglobin molecule. However, increased concentrations of carbon dioxide in the blood reduce the ability of oxygen to bind to hemoglobin. The amount of oxygen in the blood decreases and hypoxia occurs.

Such unhealthy consequences for the body occur when inhaling air with a CO2 content of more than 5,000 ppm (this can be the air in mines, for example). To be fair, in ordinary life we practically never encounter such air. However, a much lower concentration of carbon dioxide does not have the best effect on health.

According to some findings, even 1,000 ppm CO2 causes fatigue and headaches in half of the subjects. Many people begin to feel stuffiness and discomfort even earlier. With a further increase in carbon dioxide concentration to 1,500 – 2,500 ppm critically, the brain is “lazy” to take the initiative, process information and make decisions.

And if a level of 5,000 ppm is almost impossible in Everyday life, then 1,000 and even 2,500 ppm can easily be part of reality modern man. Ours showed that in rarely ventilated school classrooms, CO2 levels significant part time it stays above 1,500 ppm, and sometimes jumps above 2,000 ppm. There is every reason to believe that the situation is similar in many offices and even apartments.

Physiologists consider 800 ppm to be a safe level of carbon dioxide for human well-being.

Another study found a link between CO2 levels and oxidative stress: the higher the carbon dioxide level, the more we suffer from oxidative stress, which damages our body's cells.

Carbon dioxide in the Earth's atmosphere

There is only about 0.04% CO2 in the atmosphere of our planet (this is approximately 400 ppm), and more recently it was even less: carbon dioxide crossed the 400 ppm mark only in the fall of 2016. Scientists attribute the rise in CO2 levels in the atmosphere to industrialization: in the mid-18th century, on the eve of the Industrial Revolution, it was only about 270 ppm.

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Application of carbon dioxide for storage food products based on its relatively low toxicity at low concentrations. Carbon dioxide limits the vital activity of harmful microorganisms, destroying them only in conditions of high concentration. Of the 37 forms of putrefactive bacteria, only 5 are not affected by carbon dioxide.

The use of carbon dioxide for plant nutrition is based on the process of photosynthesis. Plant leaves, with the help of chlorophyll, absorb carbon dioxide from the air and, together with water, process it into nutrients. organic matter necessary for their development and growth. This process is accompanied by the release of oxygen, that is, gas exchange occurs based on plant respiration. For enhanced building of organic nutrients plants must receive more water and carbon dioxide.

The use of carbon dioxide in electric welding is based on the principle of protecting molten metal from the harmful effects of atmospheric air. Active gases contained in the air - oxygen, hydrogen and nitrogen - enter into various chemical compounds with molten metal: they oxidize it, release moisture or dissolve in the metal, resulting in welds that are porous and leaky. Carbon dioxide pushes back atmospheric air from molten metal, thereby ensuring normal quality of welded joints.

The use of carbon dioxide increases the productivity of machine tools and reduces time lost on regrinding.

The use of carbon dioxide for blasting is based on its rapid transition under the influence of heating from a liquid to a gaseous state, followed by an explosion without the formation of a flame.

The use of carbon dioxide with radioactive carbon, and the study of metabolic products showed that carbon CO2 passes into the carboxyl group formed in this case succinic acid. Obviously, carbon dioxide can be assimilated by microbes for synthetic reactions. The possibility of significant enrichment of the soil layer due to reactions of a similar nature, which have not yet been completely studied, cannot be excluded.

The scope of application of carbon dioxide consumed for food and various technical needs is continuously expanding. Its development, especially in summer period, does not cover the demand. In the RSFSR, carbon dioxide is produced only in 30 regions, territories and autonomous republics, which causes significant interregional transport. Rail transportation of carbon dioxide, as an explosive cargo, is regulated by special rules.

An assessment of the use of carbon dioxide in the pilot area of ​​the Aleksandrovskaya area of ​​the Tuymazinsky field, carried out by BashNIPI - Oil, allowed us to state that the injection of CO2 into the area produced using conventional waterflooding led to an increase in oil production rates of wells by 2 times.


The advantages of using carbon dioxide for blowing include the possibility of absorbing it from acetylene into carbide sludge.

Grinding using carbon dioxide reduces abrasive consumption and machine time. In this case, thermal stresses are reduced, which helps to avoid cracks on the treated surface.

The use of carbon dioxide as a means to improve the weather on foggy days is interesting and promising.

One of large regions Application of carbon dioxide is the production of carbonated water. Carbonation is produced by dissolving carbon dioxide in water - Saturation of water with carbon dioxide is carried out with preliminary cooling and under pressure in commercial saturators.

These technological schemes are carried out using carbon dioxide or its mixture with a surfactant.

According to research data, oil recovery when using carbon dioxide increases when creating a rim of up to 10% of the pore volume of the formation.