Co2 description. Carbon dioxide, also known as carbon dioxide, also known as carbon dioxide... Producing carbon dioxide
In recent years, the prospects of CO 2 as a refrigerant have increased significantly. Carbon dioxide is one of the few refrigerants for refrigeration systems that is relevant in terms of efficiency and environmental safety. The use of traditional refrigerants is limited by various regulations, and there is a trend towards tightening them all over the world. In this regard, natural refrigerants are increasingly used. We are starting a column dedicated to the use of CO 2 refrigerant in the field of artificial refrigeration.
CO 2 refrigerant belongs to the group of so-called natural refrigerants (ammonia, propane, butane, water, etc.) which has zero ozone depletion potential (ODP=0) and is the reference unit for calculating global warming potential (GWP=1). Each of the natural refrigerants has its disadvantages, for example, ammonia is toxic, propane is flammable, and water has a limited range of applications. In contrast, CO 2 is not toxic or flammable, although its impact on the environment is not clear. On the one hand, CO 2 is contained in the air around us and is necessary for the flow of life processes. On the other hand, it is believed that a high concentration of carbon dioxide in the air is one of the causes of global warming.
The initiative to return to the use of CO 2 in refrigeration technology comes from the Scandinavian countries, where laws significantly limit the use of HFC and HCFC refrigerants. Ammonia is traditionally used as a refrigerant for industrial installations, but its quantity in the system is limited. This is not a problem for installations operating at high and medium temperatures (up to -15/-25°C), where the amount of ammonia is reduced by using a secondary coolant. For lower temperatures, the use of a secondary coolant is ineffective due to large losses due to temperature differences; in this case, CO 2 is used.
The figure above shows the phase diagram of CO 2. The curved lines that divide the diagram into separate sections define the limiting values of pressure and temperature for various phases: liquid, solid, vapor or supercritical. The points on these curves determine the pressures and corresponding temperatures at which two phases are in equilibrium, for example, solid and vapor, liquid and vapor, solid and liquid.
At atmospheric pressure, CO 2 exists in solid or vapor phases. At this pressure the liquid phase does not exist. At temperatures below –78.4°C, carbon dioxide is in the solid phase (“dry ice”). As the temperature rises, CO 2 sublimates into the vapor phase. At a pressure of 5.2 bar and a temperature of –56.6°C, the refrigerant reaches the so-called triple point. At this point, all three phases exist in an equilibrium state. At a temperature of +31.1°C CO 2 reaches its critical point, where its densities in the liquid and vapor phases are the same (figure above). Consequently, the difference between the two phases disappears and CO 2 exists in a supercritical state.
Carbon dioxide can be used as a refrigerant in various types of refrigeration systems, both subcritical and transcritical. When using CO 2 as a refrigerant, both the triple point and the critical point must be taken into account for all types of refrigeration systems. In the subcritical CO 2 cycle (figure above), the entire range of operating temperatures and pressures lies between the critical and triple points. Single-stage CO 2 refrigeration cycles are similar to other refrigerants, but have some disadvantages, primarily related to temperature and pressure limitations.
Transcritical CO 2 refrigeration systems are currently used in small and commercial refrigeration applications, such as mobile air conditioning systems, small heat pumps and supermarket refrigeration systems. Transcritical systems are practically not used in industrial refrigeration units. The operating pressure in the subcritical cycle is typically in the range of 5.7 to 35 bar with a corresponding temperature of -55 to 0°C. When the evaporator is defrosted with hot gas, the operating pressure increases by approximately 10 bar.
CO 2 is most widely used in cascade systems of industrial refrigeration units. This is due to the fact that the operating pressure range allows the use of standard equipment (compressors, regulators and valves).
There are different types of CO 2 cascade refrigeration systems: direct boiling systems, pump circulation systems, CO 2 systems with a secondary brine circuit, or combinations of these systems.
Application of carbonic acid (carbon dioxide)
Currently, carbon dioxide in all its states is widely used in all sectors of industry and the agro-industrial complex.
In gaseous state (carbon dioxide)
In the food industry
1. To create an inert bacteriostatic and fungistatic atmosphere (at concentrations above 20%):
· when processing plant and animal products;
· when packaging food products and medicines to significantly increase their shelf life;
· when dispensing beer, wine and juices as a displacing gas.
2. In the production of soft drinks and mineral waters (saturation).
3. In brewing and production of champagne and sparkling wines (carbonation).
4. Preparation of carbonated water and drinks using siphons and saturators, for personnel in hot shops and in the summer.
5. Use in vending machines for the sale of bottled gas and water and for the manual sale of beer and kvass, carbonated water and drinks.
6. In the production of carbonated milk drinks and carbonated fruit and berry juices (“sparkling products”).
7. In the production of sugar (defecation - saturation).
8. For long-term preservation of fruit and vegetable juices while preserving the smell and taste of a freshly squeezed product by saturating with CO2 and storing under high pressure.
9. To intensify the processes of precipitation and removal of tartaric acid salts from wines and juices (detartation).
10. For the preparation of drinking desalinated water using the filtration method. To saturate salt-free drinking water with calcium and magnesium ions.
In the production, storage and processing of agricultural products
11. To increase the shelf life of food products, vegetables and fruits in a controlled atmosphere (2-5 times).
12. Storing cut flowers for 20 days or more in a carbon dioxide atmosphere.
13. Storing cereals, pasta, grains, dried fruits and other food products in a carbon dioxide atmosphere to protect them from damage by insects and rodents.
14. For treating fruits and berries before storing, which prevents the development of fungal and bacterial rot.
15. For high-pressure saturation of cut or whole vegetables, which enhances flavor notes (“sparkling products”) and improves their shelf life.
16. To improve growth and increase productivity of plants in protected soil.
Today, in vegetable and flower growing farms in Russia, the issue of fertilizing plants in protected soil with carbon dioxide is an urgent issue. CO2 deficiency is a more serious problem than deficiency of mineral nutrients. On average, a plant synthesizes 94% of its dry matter mass from water and carbon dioxide; the plant receives the remaining 6% from mineral fertilizers! Low carbon dioxide content is now a factor limiting yield (primarily in small-volume crops). The air in a 1-hectare greenhouse contains about 20 kg of CO2. At maximum lighting levels in the spring and summer months, CO2 consumption by cucumber plants during photosynthesis can approach 50 kg h/ha (i.e., up to 700 kg/ha CO2 per daylight hours). The resulting deficit is only partially covered by the influx of atmospheric air through the transoms and the leakage of the enclosing structures, as well as by the night respiration of plants. In ground greenhouses, an additional source of carbon dioxide is soil filled with manure, peat, straw or sawdust. The effect of enriching greenhouse air with carbon dioxide depends on the amount and type of these organic substances that undergo microbiological decomposition. For example, when adding sawdust moistened with mineral fertilizers, the level of carbon dioxide at first can reach high values at night, and during the day when the transoms are closed. However, in general, this effect is not great enough and satisfies only part of the plants’ needs. The main disadvantage of biological sources is the short duration of increasing the concentration of carbon dioxide to the desired level, as well as the impossibility of regulating the feeding process. Often in ground greenhouses on sunny days with insufficient air exchange, the CO2 content as a result of intensive absorption by plants can fall below 0.01% and photosynthesis practically stops! Lack of CO2 becomes the main factor limiting the assimilation of carbohydrates and, accordingly, the growth and development of plants. It is possible to completely cover the deficit only through the use of technical sources of carbon dioxide.
17. Production of microalgae for livestock. When water is saturated with carbon dioxide in installations for autonomous algae cultivation, the algae growth rate increases significantly (4-6 times).
18. To improve the quality of silage. When ensiling succulent feed, the artificial introduction of CO2 into the plant mass prevents the penetration of oxygen from the air, which contributes to the formation of a high-quality product with a favorable ratio of organic acids, a high content of carotene and digestible protein.
19. For safe disinfestation of food and non-food products. An atmosphere containing more than 60% carbon dioxide within 1-10 days (depending on temperature) destroys not only adult insects, but their larvae and eggs. This technology is applicable to products with bound water content up to 20%, such as grain, rice, mushrooms, dried fruits, nuts and cocoa, animal feed and much more.
20. For the total destruction of mouse-like rodents by briefly filling burrows, storage facilities, and chambers with gas (a sufficient concentration of 30% carbon dioxide).
21. For anaerobic pasteurization of animal feed, mixed with water vapor at a temperature not exceeding 83 degrees C - as a replacement for granulation and extrusion, which does not require large energy costs.
22. For euthanizing poultry and small animals (pigs, calves, sheep) before slaughter. For anesthesia of fish during transportation.
23. For anesthesia of queen bees and bumblebees in order to accelerate the onset of oviposition.
24. To saturate drinking water for chickens, which significantly reduces the negative impact of elevated summer temperatures on poultry, helps thicken egg shells and strengthen the bones.
25. To saturate working solutions of fungicides and herbicides for better action of the preparations. This method allows you to reduce solution consumption by 20-30%.
In medicine
26. a) mixed with oxygen as a respiratory stimulant (at a concentration of 5%);
b) for dry carbonated baths (at a concentration of 15-30%) in order to lower blood pressure and improve blood flow.
27. Cryotherapy in dermatology, dry and water carbon dioxide baths in balneotherapy, breathing mixtures in surgery.
In the chemical and paper industries
28. For the production of soda, ammonium carbon salts (used as fertilizers in crop production, additives in ruminant animal feed, instead of yeast in baked goods and flour confectionery), white lead, urea, hydroxycarboxylic acids. For the catalytic synthesis of methanol and formaldehyde.
29. For neutralization of alkaline wastewater. Due to the self-buffering effect of the solution, precise pH regulation avoids corrosion of equipment and waste pipes, and there is no formation of toxic by-products.
30. In the production of paper for processing pulp after alkaline bleaching (increases the efficiency of the process by 15%).
31. To increase the yield and improve the physical and mechanical properties and bleachability of cellulose during oxygen-soda cooking of wood.
32. To clean heat exchangers from scale and prevent its formation (a combination of hydrodynamic and chemical methods).
In construction and other industries
33. For rapid chemical hardening of molds for steel and cast iron castings. The supply of carbon dioxide to casting molds accelerates their hardening 20-25 times compared to thermal drying.
34. As a foaming gas in the production of porous plastics.
35. For strengthening refractory bricks.
36. For semi-automatic welding machines for repairing bodies of passenger and passenger cars, repairing cabins of trucks and tractors and for electric welding of thin-sheet steel products.
37. In the manufacture of welded structures with automatic and semi-automatic electric welding in an environment of carbon dioxide as a protective gas. Compared to welding with a stick electrode, the convenience of work increases, productivity increases by 2-4 times, the cost of 1 kg of deposited metal in a CO2 environment is more than two times lower compared to manual arc welding.
38. As a protective medium in mixtures with inert and noble gases during automated welding and metal cutting, thanks to which very high quality seams are obtained.
39. Charging and recharging of fire extinguishers, for fire-fighting equipment. In fire extinguishing systems, for filling fire extinguishers.
40. Charging cans for gas weapons and siphons.
41. As a nebulizer gas in aerosol cans.
42. For filling sports equipment (balls, balls, etc.).
43. As an active medium in medical and industrial lasers.
44. For precise calibration of instruments.
In the mining industry
45. For softening of the coal rock mass during the mining of hard coal in rock-prone formations.
46. For carrying out blasting operations without creating a flame.
47. Increasing the efficiency of oil production by adding carbon dioxide to oil reservoirs.
In liquid state (low temperature carbon dioxide)
In the food industry
1. For quick freezing, to a temperature of -18 degrees C and below, of food products in contact freezers. Along with liquid nitrogen, liquid carbon dioxide is most suitable for direct contact freezing of various types of products. As a contact refrigerant, it is attractive due to its low cost, chemical passivity and thermal stability, does not corrode metal components, is not flammable, and is not dangerous to personnel. Liquid carbon dioxide is supplied to the product moving on the conveyor belt from the nozzles in certain portions, which at atmospheric pressure instantly turns into a mixture of dry snow and cold carbon dioxide, while fans constantly mix the gas mixture inside the apparatus, which, in principle, is capable of cooling the product from +20 degrees. C to -78.5 degrees C in a few minutes. The use of contact quick freezers has a number of fundamental advantages compared to traditional freezing technology:
Freezing time is reduced to 5-30 minutes; enzymatic activity in the product quickly ceases;
· the structure of tissues and cells of the product is well preserved, since ice crystals are formed of much smaller sizes and almost simultaneously in the cells and in the intercellular space of tissues;
· with slow freezing, traces of bacterial activity appear in the product, while with shock freezing they simply do not have time to develop;
· product weight loss as a result of shrinkage is only 0.3-1% (versus 3-6%);
· Easily volatile valuable aromatic substances will be preserved in much larger quantities. Compared to freezing with liquid nitrogen, freezing with carbon dioxide:
· cracking of the product is not observed due to too large a temperature difference between the surface and the core of the frozen product
· during the freezing process, CO2 penetrates into the product and during defrosting it protects it from oxidation and the development of microorganisms. Fruits and vegetables subjected to quick freezing and packaging on site most fully retain their taste and nutritional value, all vitamins and biologically active substances, which makes it possible to widely use them for the production of products for children's and dietary nutrition. It is important that non-standard fruit and vegetable products can be successfully used to prepare expensive frozen mixtures. Quick-freezers using liquid carbon dioxide are compact, simple in design and inexpensive to operate (if there is a nearby source of cheap liquid carbon dioxide). The devices exist in mobile and stationary versions, spiral, tunnel and cabinet types, which are of interest to agricultural producers and product processors. They are especially convenient when production requires freezing of various food products and raw materials at different temperature conditions (-10...-70 degrees C). Quick-frozen foods can be dried under high vacuum conditions - freeze drying. Products dried using this method are of high quality: they retain all nutrients, have increased restorative capacity, have minimal shrinkage and porous structure, and retain their natural color. Freeze-dried products are 10 times lighter than the original ones due to the removal of water from them, they are stored for a very long time in sealed bags (especially when the bags are filled with carbon dioxide) and can be cheaply delivered to the most remote areas.
2. For rapid cooling of fresh food products, packaged and unpackaged, to +2…+6 degrees C. Using installations whose operation is similar to the operation of quick-freezers: when liquid carbon dioxide is injected, tiny dry snow is formed, with which the product is processed for a certain time. Dry snow is an effective means of quickly reducing temperature, which does not lead to drying out of the product, like air cooling, and does not increase its moisture content, as happens when cooling with water ice. Dry snow cooling provides the required temperature reduction in just a few minutes, rather than the hours required with conventional cooling. The natural color of the product is preserved and even improved due to the slight diffusion of CO2 inside. At the same time, the shelf life of products increases significantly, since CO2 suppresses the development of both aerobic and anaerobic bacteria and mold fungi. It is convenient and profitable to refrigerate poultry meat (cut or in carcasses), portioned meat, sausages and semi-finished products. The units are also used where the technology requires rapid cooling of the product during or before molding, pressing, extruding, grinding or slicing. Devices of this type are also very convenient for use in poultry farms for in-line ultra-fast cooling from 42.7 degrees C to 4.4-7.2 degrees C of freshly laid chicken eggs.
3. To remove the skin from berries using the freezing method.
4. For cryopreservation of sperm and embryos of cattle and pigs.
In the refrigeration industry
5. For use as an alternative refrigerant in refrigeration systems. Carbon dioxide can serve as an effective refrigerant because it has a low critical temperature (31.1 degrees C), a relatively high triple point temperature (-56 degrees C), a high triple point pressure (0.5 mPa) and a high critical pressure ( 7.39 mPa). As a refrigerant it has the following advantages:
· very low price compared to other refrigerants;
· non-toxic, non-flammable and non-explosive;
· compatible with all electrical insulating and structural materials;
· does not destroy the ozone layer;
· makes a moderate contribution to the increase in the greenhouse effect compared to modern halogenated refrigerants. A high critical pressure has the positive aspect of a low compression ratio, resulting in significant compressor efficiency, allowing for compact and low-cost refrigeration designs. At the same time, additional cooling of the condenser electric motor is required, and the metal consumption of the refrigeration unit increases due to the increase in the thickness of the pipes and walls. It is promising to use CO2 in low-temperature two-stage installations for industrial and semi-industrial applications, and especially in air conditioning systems for cars and trains.
6. For high-performance frozen grinding of soft, thermoplastic and elastic products and substances. In cryogenic mills, those products and substances that cannot be ground in their usual form, for example gelatin, rubber, any polymers, tires, are ground quickly and with low energy consumption in frozen form. Cold grinding in a dry, inert atmosphere is necessary for all herbs and spices, cocoa beans and coffee beans.
7. For testing technical systems at low temperatures.
In metallurgy
8. For cooling difficult-to-cut alloys when processed on lathes.
9. To form a protective environment for smoke suppression in copper, nickel, zinc and lead smelting or bottling processes.
10. When annealing solid copper wire for cable products.
In the mining industry
11. As a low-blasting explosive in coal mining, which does not lead to the ignition of methane and coal dust during an explosion, and does not produce toxic gases.
12. Prevention of fires and explosions by displacing air from containers and mines containing explosive vapors and gases with carbon dioxide.
Supercritical
In extraction processes
1. Capturing aromatic substances from fruit and berry juices, obtaining plant extracts and medicinal herbs using liquid carbon dioxide. In traditional methods of extraction of plant and animal raw materials, various types of organic solvents are used, which are highly specific and rarely ensure the extraction of the full complex of biologically active compounds from raw materials. Moreover, the problem of separating solvent residues from the extract always arises, and the technological parameters of this process can lead to partial or even complete destruction of some components of the extract, which causes a change not only in the composition, but also in the properties of the isolated extract. Compared to traditional methods, extraction processes (as well as fractionation and impregnation) using supercritical carbon dioxide have a number of advantages:
· energy-saving nature of the process;
· high mass transfer characteristics of the process due to low viscosity and high penetrating ability of the solvent;
· high degree of extraction of relevant components and high quality of the resulting product;
· virtual absence of CO2 in finished products;
· an inert dissolving medium is used at a temperature that does not threaten thermal degradation of materials;
· the process does not produce waste water and waste solvents; after decompression, CO2 can be collected and reused;
· the unique microbiological purity of the resulting products is ensured;
· lack of complex equipment and multi-stage process;
· A cheap, non-toxic and non-flammable solvent is used. The selective and extraction properties of carbon dioxide can vary widely with changes in temperature and pressure, which makes it possible to extract most of the spectrum of currently known biologically active compounds from plant materials at low temperatures.
2. To obtain valuable natural products - CO2 extracts of spices, essential oils and biologically active substances. The extract practically copies the original plant material; as for the concentration of its constituent substances, we can state that there are no analogues among classical extracts. Chromatographic analysis data show that the content of valuable substances exceeds classical extracts tens of times. Production on an industrial scale has been mastered:
· extracts from spices and medicinal herbs;
· fruit aromas;
· extracts and acids from hops;
· antioxidants, carotenoids and lycopenes (including from tomato raw materials);
· natural coloring substances (from red pepper fruits and others);
lanolin from wool;
· natural plant waxes;
· sea buckthorn oils.
3. For the extraction of highly purified essential oils, in particular from citrus fruits. When extracting essential oils with supercritical CO2, highly volatile fractions are also successfully extracted, which give these oils fixing properties, as well as a more complete aroma.
4. To remove caffeine from tea and coffee, nicotine from tobacco.
5. To remove cholesterol from food (meat, dairy products and eggs).
6. For the production of low-fat potato chips and soy products;
7. For the production of high-quality tobacco with specified technological properties.
8. For dry cleaning of clothes.
9. To remove uranium compounds and transuranium elements from radioactively contaminated soils and from the surfaces of metal bodies. At the same time, the volume of water waste is reduced hundreds of times, and there is no need to use aggressive organic solvents.
10. For environmentally friendly PCB etching technology for microelectronics, without generating toxic liquid waste.
In fractionation processes
The separation of a liquid substance from a solution, or the separation of a mixture of liquid substances is called fractionation. These processes are continuous and therefore much more efficient than the separation of substances from solid substrates.
11. For refining and deodorizing oils and fats. To obtain commercial oil, it is necessary to carry out a whole range of measures, such as removing lecithin, mucus, acid, bleaching, deodorization and others. When extracting with supercritical CO2, these processes are carried out during one technological cycle, and the quality of the oil obtained in this case is much better, since the process takes place at relatively low temperatures.
12. To reduce the alcohol content in drinks. The production of non-alcoholic traditional drinks (wine, beer, cider) is in increasing demand for ethical, religious or dietary reasons. Even if these low-alcohol drinks are often of lower quality, their market is significant and growing rapidly, so improving such technology is a very attractive issue.
13. For energy-saving production of high-purity glycerin.
14. For energy-saving production of lecithin from soybean oil (with a phosphatidyl choline content of about 95%).
15. For flow-through purification of industrial wastewater from hydrocarbon pollutants.
In impregnation processes
The process of impregnation - the introduction of new substances, is essentially the reverse process of extraction. The required substance is dissolved in supercritical CO2, then the solution penetrates into the solid substrate, when the pressure is released, the carbon dioxide instantly evaporates, and the substance remains in the substrate.
16. For environmentally friendly dyeing technology for fibers, fabrics and textile accessories. Painting is a special case of impregnation. Dyes are usually dissolved in a toxic organic solvent, so dyed materials must be thoroughly washed, causing the solvent to either evaporate into the atmosphere or end up in wastewater. In supercritical dyeing, water and solvents are not used; the dye is dissolved in supercritical CO2. This method provides an interesting opportunity to dye different types of synthetic materials at the same time, such as plastic teeth and the fabric lining of a zipper.
17. For environmentally friendly technology, paint application. The dry dye dissolves in a stream of supercritical CO2, and along with it flies out of the nozzle of a special gun. Carbon dioxide immediately evaporates, and the paint settles on the surface. This technology is especially promising for painting cars and large equipment.
18. For homogenized impregnation of polymer structures with drugs, thereby ensuring a constant and prolonged release of the drug in the body. This technology is based on the ability of supercritical CO2 to easily penetrate many polymers, saturate them, causing micropores to open and swell.
In technological processes
19. Replacing high-temperature water vapor with supercritical CO2 in extrusion processes, when processing grain-like raw materials, allows the use of relatively low temperatures, the introduction of dairy ingredients and any heat-sensitive additives into the recipe. Supercritical fluid extrusion allows the creation of new products with an ultra-porous internal structure and a smooth, dense surface.
20. For the production of polymer and fat powders. A stream of supercritical CO2 with some polymers or fats dissolved in it is injected into a chamber with lower pressure, where they are “condensed” in the form of a completely homogeneous finely dispersed powder, the finest fibers or films.
21. To prepare for drying greens and fruits by removing the cuticular wax layer with a jet of supercritical CO2.
In chemical reaction processes
22. A promising area of application of supercritical CO2 is its use as an inert medium during chemical reactions of polymerization and synthesis. In a supercritical environment, synthesis can occur a thousand times faster than the synthesis of the same substances in traditional reactors. It is very important for industry that such a significant acceleration of the reaction rate, due to high concentrations of reagents in a supercritical medium with its low viscosity and high diffusivity, makes it possible to correspondingly reduce the contact time of the reagents. In technological terms, this makes it possible to replace static closed reactors with flow reactors that are fundamentally smaller, cheaper and safer.
In thermal processes
23. As a working fluid for modern power plants.
24. As a working fluid of gas heat pumps producing high-temperature heat for hot water supply systems.
In solid state (dry ice and snow)
In the food industry
1. For contact freezing of meat and fish.
2. For contact quick freezing of berries (red and black currants, gooseberries, raspberries, chokeberries and others).
3. Sales of ice cream and soft drinks in places remote from the power grid, cooled with dry ice.
4. When storing, transporting and selling frozen and chilled food products. The production of briquetted and granulated dry ice for buyers and sellers of perishable products is being developed. Dry ice is very convenient for transportation and for selling meat, fish, and ice cream in hot weather - the products remain frozen for a very long time. Since dry ice only evaporates (sublimates), there is no melted liquid, and transport containers always remain clean. Autorefrigerators can be equipped with a small-sized dry-ice cooling system, which is characterized by extreme simplicity of the device and high operational reliability; its cost is many times lower than the cost of any classical refrigeration unit. When transporting over short distances, such a cooling system is the most economical.
5. To pre-cool containers before loading products. Blowing dry snow in cold carbon dioxide is one of the most effective ways to pre-cool any containers.
6. For air transportation as a primary refrigerant in isothermal containers with an autonomous two-stage refrigeration system (granulated dry ice - freon).
During surface cleaning work
8. Cleaning of parts and components, engines from contaminants using treatment plants using dry ice granules in a gas flow. To clean the surfaces of components and parts from operational contaminants. Recently, there has been a great demand for non-abrasive express cleaning of materials, dry and wet surfaces with a jet of finely granulated dry ice (blasting). Without disassembling the units, you can successfully carry out:
· cleaning of welding lines;
· removal of old paint;
· cleaning of foundry molds;
· cleaning of printing machine units;
· cleaning of equipment for the food industry;
· cleaning of molds for the production of polyurethane foam products.
· cleaning of molds for the production of car tires and other rubber products;
· cleaning of molds for the production of plastic products, including cleaning of molds for the production of PET bottles; When dry ice pellets hit a surface, they instantly evaporate, creating a micro-explosion that removes contaminants from the surface. When removing brittle material such as paint, the process creates a pressure wave between the coating and the substrate. This wave is strong enough to remove the coating, lifting it from the inside. When removing sticky or sticky materials such as oil or dirt, the cleaning process is similar to a strong jet of water.
7. For cleaning stamped rubber and plastic products from burrs (tumbling).
During construction work
9. In the process of manufacturing porous building materials with the same size of carbon dioxide bubbles, evenly distributed throughout the entire volume of the material.
10. For freezing soils during construction.
11. Installation of ice plugs in pipes with water (by freezing them from the outside with dry ice), during repair work on pipelines without draining the water.
12. For cleaning artesian wells.
13. When removing asphalt surfaces in hot weather.
In other industries
14. Receiving low temperatures down to minus 100 degrees (when mixing dry ice with ether) for testing product quality, for laboratory work.
15. For cold fitting of parts in mechanical engineering.
16. In the production of ductile grades of alloy and stainless steels, annealed aluminum alloys.
17. When crushing, grinding and preserving calcium carbide.
18. To create artificial rain and obtain additional precipitation.
19. Artificial dispersal of clouds and fog, combating hail.
20. To generate harmless smoke during performances and concerts. Obtaining a smoke effect on pop stages during artist performances using dry ice.
In medicine
21. For the treatment of certain skin diseases (cryotherapy).
The most common processes for the formation of this compound are the rotting of animal and plant remains, the combustion of various types of fuel, and the respiration of animals and plants. For example, one person emits about a kilogram of carbon dioxide into the atmosphere per day. Carbon monoxide and dioxide can also be formed in inanimate nature. Carbon dioxide is released during volcanic activity and can also be produced from mineral water sources. Carbon dioxide is found in small quantities in the Earth's atmosphere.
The peculiarities of the chemical structure of this compound allow it to participate in many chemical reactions, the basis for which is carbon dioxide.
Formula
In the compound of this substance, the tetravalent carbon atom forms a linear bond with two oxygen molecules. The appearance of such a molecule can be represented as follows:
The hybridization theory explains the structure of the carbon dioxide molecule as follows: the two existing sigma bonds are formed between the sp orbitals of carbon atoms and the two 2p orbitals of oxygen; The p-orbitals of carbon, which do not take part in hybridization, are bonded in conjunction with similar orbitals of oxygen. In chemical reactions, carbon dioxide is written as: CO 2.
Physical properties
Under normal conditions, carbon dioxide is a colorless, odorless gas. It is heavier than air, which is why carbon dioxide can behave like a liquid. For example, it can be poured from one container to another. This substance is slightly soluble in water - about 0.88 liters of CO 2 dissolve in one liter of water at 20 ⁰C. A slight decrease in temperature radically changes the situation - 1.7 liters of CO 2 can dissolve in the same liter of water at 17⁰C. With strong cooling, this substance precipitates in the form of snow flakes - the so-called “dry ice” is formed. This name comes from the fact that at normal pressure the substance, bypassing the liquid phase, immediately turns into a gas. Liquid carbon dioxide is formed at a pressure just above 0.6 MPa and at room temperature.
Chemical properties
When interacting with strong oxidizing agents, 4-carbon dioxide exhibits oxidizing properties. The typical reaction of this interaction is:
C + CO 2 = 2CO.
Thus, with the help of coal, carbon dioxide is reduced to its divalent modification - carbon monoxide.
Under normal conditions, carbon dioxide is inert. But some active metals can burn in it, removing oxygen from the compound and releasing carbon gas. A typical reaction is the combustion of magnesium:
2Mg + CO 2 = 2MgO + C.
During the reaction, magnesium oxide and free carbon are formed.
In chemical compounds, CO 2 often exhibits the properties of a typical acid oxide. For example, it reacts with bases and basic oxides. The result of the reaction is carbonic acid salts.
For example, the reaction of a compound of sodium oxide with carbon dioxide can be represented as follows:
Na 2 O + CO 2 = Na 2 CO 3;
2NaOH + CO 2 = Na 2 CO 3 + H 2 O;
NaOH + CO 2 = NaHCO 3.
Carbonic acid and CO 2 solution
Carbon dioxide in water forms a solution with a small degree of dissociation. This solution of carbon dioxide is called carbonic acid. It is colorless, weakly expressed and has a sour taste.
Recording a chemical reaction:
CO 2 + H 2 O ↔ H 2 CO 3.
The equilibrium is shifted quite strongly to the left - only about 1% of the initial carbon dioxide is converted into carbonic acid. The higher the temperature, the fewer carbonic acid molecules in the solution. When the compound boils, it disappears completely, and the solution disintegrates into carbon dioxide and water. The structural formula of carbonic acid is presented below.
Properties of carbonic acid
Carbonic acid is very weak. In solutions, it breaks down into hydrogen ions H + and compounds HCO 3 -. CO 3 - ions are formed in very small quantities.
Carbonic acid is dibasic, so the salts formed by it can be medium and acidic. In the Russian chemical tradition, medium salts are called carbonates, and strong salts are called bicarbonates.
Qualitative reaction
One possible way to detect carbon dioxide gas is to change the clarity of the lime mortar.
Ca(OH) 2 + CO 2 = CaCO 3 ↓ + H 2 O.
This experience is known from a school chemistry course. At the beginning of the reaction, a small amount of white precipitate is formed, which subsequently disappears when carbon dioxide is passed through water. The change in transparency occurs because during the interaction process, an insoluble compound - calcium carbonate - is converted into a soluble substance - calcium bicarbonate. The reaction proceeds along this path:
CaCO 3 + H 2 O + CO 2 = Ca(HCO 3) 2.
Production of carbon dioxide
If you need to get a small amount of CO2, you can start the reaction of hydrochloric acid with calcium carbonate (marble). The chemical notation for this interaction looks like this:
CaCO 3 + HCl = CaCl 2 + H 2 O + CO 2.
Also for this purpose, combustion reactions of carbon-containing substances, for example acetylene, are used:
CH 4 + 2O 2 → 2H 2 O + CO 2 -.
A Kipp apparatus is used to collect and store the resulting gaseous substance.
For the needs of industry and agriculture, the scale of carbon dioxide production must be large. A popular method for this large-scale reaction is to burn limestone, which produces carbon dioxide. The reaction formula is given below:
CaCO 3 = CaO + CO 2.
Applications of carbon dioxide
The food industry, after large-scale production of “dry ice,” switched to a fundamentally new method of storing food. It is indispensable in the production of carbonated drinks and mineral water. The CO 2 content in drinks gives them freshness and significantly increases their shelf life. And carbidization of mineral waters allows you to avoid mustiness and unpleasant taste.
In cooking, the method of extinguishing citric acid with vinegar is often used. The carbon dioxide released during this process imparts fluffiness and lightness to confectionery products.
This compound is often used as a food additive to increase the shelf life of food products. According to international standards for the classification of chemical additives contained in products, it is coded E 290,
Powdered carbon dioxide is one of the most popular substances included in fire extinguishing mixtures. This substance is also found in fire extinguisher foam.
It is best to transport and store carbon dioxide in metal cylinders. At temperatures above 31⁰C, the pressure in the cylinder can reach critical and liquid CO 2 will go into a supercritical state with a sharp rise in operating pressure to 7.35 MPa. The metal cylinder can withstand internal pressure up to 22 MPa, so the pressure range at temperatures above thirty degrees is considered safe.
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 the simple chemical formula CO2. In this form, it exists under normal conditions - at atmospheric pressure and “ordinary” temperatures. But at increased pressure, above 5,850 kPa (such as, for example, the pressure at a sea depth of 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 activities, but these forms are unstable and easily disintegrate.
But carbon dioxide gas is ubiquitous: it is released during the respiration of animals and plants and is an important part of the chemical composition of the 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 Schweppes began industrial production of soda (the Schweppes brand 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 make up for shortcomings with an abundance of indoor plants. 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 a 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 catastrophe, 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. A huge amount of carbon dioxide was released into the atmosphere, which went down the mountain slopes like an avalanche. 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.
The respiratory system is also stimulated by an increase in carbon dioxide, 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 necessary for 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 the reality of modern man. Ours showed that in rarely ventilated school classrooms, CO2 levels remain above 1,500 ppm much of the time, and sometimes jump 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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