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Carbon dioxide. Carbon dioxide

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

The concentration of carbon dioxide in the Earth's atmosphere is on average 0.0395%.

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

Receipt

In industrial quantities, carbon dioxide is emitted 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. The mixture of gases obtained is washed with a solution of potassium carbonate, which absorb carbon dioxide, turning into hydrocarbonate. A solution of bicarbonate, when heated or under reduced pressure, decomposes, releasing carbon dioxide. In modern carbon dioxide production plants, instead of bicarbonate, an aqueous solution of monoethanolamine is more often used, which, under certain conditions, is able to absorb CO₂ contained in the flue gas, and release it when heated, thus separating the finished product from other substances.

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

In laboratory conditions, small amounts are obtained by reacting carbonates and bicarbonates with acids, such as marble, chalk, or soda with hydrochloric acid. Using the reaction of sulfuric acid with chalk or marble results in the formation of insoluble calcium sulfate, which interferes with the reaction and is removed by a significant excess of acid.

Beverages can be prepared by reacting baking soda with citric acid or acidic lemon juice. It was in this form that the first carbonated drinks appeared. Pharmacists were engaged in their manufacture and sale.

Application

IN Food Industry carbon dioxide is used as a preservative and baking powder, indicated on the packaging by the code E290.

Liquid carbon dioxide is widely used in fire extinguishing systems, in fire extinguishers, and in the production of carbonated water and lemonade.

Carbon dioxide is used as a protective medium in wire welding, but at high temperatures it dissociates with the release of oxygen. The released 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 argon or helium.

When carbon dioxide is used in the gas phase, it is used for storage under pressure, as a liquefied gas, in the form of a liquid phase. Storing carbon dioxide in a cylinder in a liquefied state is much more profitable than in the form of a gas. Carbon dioxide has a relatively low critical temperature of 31°C. When 30 kg of liquefied carbon dioxide is poured into a 40-liter cylinder with a normal pressure of 100 kgf / cm², then at a temperature of 31 ° C there will be only a liquid phase in the cylinder with a pressure of 100 kgf / cm². If the temperature is higher, then reduce the filling of the cylinder or use cylinders with a higher working pressure. If carbon dioxide is cooled, then at a temperature of 21 ° C, with normal filling, a gas phase will appear in the cylinder.

Solid carbon dioxide - "dry ice" - is used as a refrigerant in laboratory research, retail, etc.

Registration Methods

The measurement of the partial pressure of carbon dioxide is required in technological processes, in medical applications - the analysis of respiratory mixtures during artificial ventilation of the lungs and in closed life support systems. The 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 content of carbon dioxide in exhaled air is called a capnograph.

carbon dioxide in nature

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.

A large amount of carbon dioxide is dissolved in the ocean.

Carbon dioxide makes up a significant portion of some planets' atmospheres. solar system: Venus, Mars.

Toxicity

Carbon dioxide is heavy compared to air, a colorless and odorless gas. The impact of its elevated concentrations on living organisms classifies it as an asphyxiant gas. (English) Russian . Slight increases in concentration up to 2-4% in unventilated rooms lead to the development of drowsiness and weakness. Dangerous concentrations are considered levels of 7-10%, at which suffocation develops, manifesting itself in headache, dizziness, hearing loss and loss of consciousness over a period of several minutes to one hour. Poisoning with this gas does not lead to long-term consequences and after its completion there is a complete recovery of the body.

see also

Notes

Literature

  • Vukalovich M.P., Altunin V.V., Thermophysical properties of carbon dioxide, Atomizdat, Moscow, 1965. 456 p.
  • Tezikov A.D., Production and use of dry ice, Gostorgizdat, Moscow, 1960. 86 p.
  • Grodnik M.G., Velichansky A.Ya., Design and operation of coal plants, ″Food Industry″, Moscow, 1966. 275 p.
  • Talyanker Yu.E., Features of storage of liquefied gas cylinders, Welding Production Magazine, No. 11, 1972, Moscow.

Links

  • International Chemical Safety Card 0021
  • CID 280 from PubChem website
  • CO 2 Carbon dioxide, properties, applications (English)
  • Phase diagram (pressure-temperature) for carbon dioxide
  • Molview from bluerhinos.co.uk Carbon dioxide in 3D
  • Dry Ice information

, carbon dioxide , properties of carbon dioxide , production of carbon dioxide

It is not suitable for life support. However, plants “feed” on it, turning it into organic matter. In addition, 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 by combining two elements: 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 respiration of people and animals. In small quantities, it is also found 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 does not have sufficient stability to be easily isolated.

Carbon dioxide is the "blanket" of the Earth. It easily transmits ultraviolet rays that heat our planet, and reflects infrared rays 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, it will rain very rarely. What this will eventually lead to is not difficult to guess.

True, such a catastrophe does not yet threaten us. Rather, on the contrary. Burning organic matter: oil, coal, natural gas, wood - gradually increases the content of carbon dioxide in the atmosphere. This means that over time it is necessary to wait for a significant warming and moistening 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, liquid high pressure And gaseous. It is obtained from waste gases from the production of ammonia, alcohols, 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. This reduces the volume fraction of oxygen in the air, which can cause the phenomenon of oxygen deficiency and suffocation.

Getting carbon dioxide

In industry, carbon dioxide is produced 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 hydrogen carbonate. Hydrocarbonate solution decomposes when heated, releasing carbon dioxide. At industrial production gas is pumped into cylinders.

Under laboratory conditions, small amounts are obtained interaction of carbonates and bicarbonates with acids, such as marble with hydrochloric acid.

"Dry ice" and other beneficial properties of carbon dioxide

Carbon dioxide is widely used in everyday practice. For example, sparkling water with the addition of aromatic essences - a wonderful refreshing drink. IN Food Industry carbon dioxide is also used as a preservative - it is indicated on the packaging under the code E290 and also as a baking powder.

Carbon dioxide fire extinguishers used in fires. Biochemists have found that fertilizer ... air with carbon dioxide very effective tool for increasing the yield of various crops. Perhaps, such a fertilizer has a single, but significant drawback: it can only be used in greenhouses. At plants that produce carbon dioxide, liquefied gas is packaged in steel cylinders and sent to consumers. If you open the valve, then ... snow bursts out of the hole with a hiss. What a miracle

Everything is explained simply. The work expended on compressing the gas is much less than that required to expand it. And in order to somehow compensate for the resulting deficit, carbon dioxide cools sharply, turning into "dry ice". It is widely used to save food products and before ordinary ice has significant advantages: firstly, its “cooling capacity” is twice as high per unit weight; secondly, it evaporates without residue.

Carbon dioxide is used as the active medium in 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 canisters is used in air gun and as power source for engines in aeromodelling.

Carbon dioxide, carbon monoxide, carbon dioxide are all names for the same substance we know as carbon dioxide. So what are the properties of this gas, and what are its applications?

Carbon dioxide and its physical properties

Carbon dioxide is made up of carbon and oxygen. The formula for carbon dioxide is CO₂. In nature, it is formed during the combustion or decay of organic matter. In the air and mineral springs, the gas content is also quite high. in addition, humans and animals also release carbon dioxide when they exhale.

Rice. 1. Molecule of carbon dioxide.

Carbon dioxide is a completely colorless gas and cannot be seen. It also has no odor. However, with its high concentration, a person may develop hypercapnia, that is, suffocation. Lack of carbon dioxide can also cause health problems. As a result of a lack of this gas, the reverse state of suffocation can develop - hypocapnia.

If carbon dioxide is placed in conditions of low temperature, then at -72 degrees it crystallizes and becomes like snow. Therefore, carbon dioxide in the solid state is called "dry snow".

Rice. 2. Dry snow is carbon dioxide.

Carbon dioxide is 1.5 times denser than air. Its density is 1.98 kg/m³ chemical bond in a carbon dioxide molecule, covalent polar. It is polar because oxygen has a higher electronegativity value.

An important concept in the study of substances is the molecular and molar mass. The molar mass of carbon dioxide is 44. This number is formed from the sum of the relative atomic masses of the atoms that make up the molecule. The values ​​of relative atomic masses are taken from the table of D.I. Mendeleev and rounded up to whole numbers. Accordingly, the molar mass of CO₂ = 12+2*16.

To calculate the mass fractions of elements in carbon dioxide, you must follow the formula for calculating the mass fractions of each chemical element in substance.

n is the number of atoms or molecules.
A r is the relative atomic mass of a chemical element.
Mr is the relative molecular weight of the substance.
Calculate the relative molecular weight of carbon dioxide.

Mr(CO₂) = 14 + 16 * 2 = 44 w(C) = 1 * 12 / 44 = 0.27 or 27% Since carbon dioxide contains two oxygen atoms, n = 2 w(O) = 2 * 16 / 44 = 0.73 or 73%

Answer: w(C) = 0.27 or 27%; w(O) = 0.73 or 73%

Chemical and biological properties of carbon dioxide

Carbon dioxide has acidic properties, as it is an acidic oxide, and when dissolved in water forms carbonic acid:

CO₂+H₂O=H₂CO₃

It reacts with alkalis, resulting in the formation of carbonates and bicarbonates. This gas is non-flammable. It only burns some active metals such as magnesium.

When heated, carbon dioxide breaks down into carbon monoxide and oxygen:

2CO₃=2CO+O₃.

Like other acidic oxides, this gas easily reacts with other oxides:

СaO+Co₃=CaCO₃.

Carbon dioxide is a constituent of all organic substances. The circulation of this gas in nature is carried out with the help of producers, consumers and decomposers. In the process of life, a person produces about 1 kg of carbon dioxide per day. When we inhale, we get oxygen, but at this moment carbon dioxide is formed in the alveoli. At this point, an exchange occurs: oxygen enters the blood, and carbon dioxide goes out.

Carbon dioxide is produced during the production of alcohol. Also, this gas is a by-product in the production of nitrogen, oxygen and argon. The use of carbon dioxide is necessary in the food industry, where carbon dioxide acts as a preservative, and carbon dioxide in the form of a liquid is contained in fire extinguishers.

Substance with chemical formula CO2 and molecular weight 44.011 g / mol, which can exist in four phase states - gaseous, liquid, solid and supercritical.

The gaseous state of CO2 is commonly known as carbon dioxide. At atmospheric pressure it is a colorless gas without color and odor, at a temperature of +20? With a density of 1.839 kg/m? (1.52 times heavier than air), dissolves well in water (0.88 volume in 1 volume of water), partially interacting in it with the formation of carbonic acid. Included in the atmosphere on average 0.035% by volume. With a sharp cooling due to expansion (expanding), CO2 is able to desublimate - go immediately into a solid state, bypassing the liquid phase.

Gaseous carbon dioxide was previously often stored in stationary gas holders. Currently, this method of storage is not used; carbon dioxide in required quantity are obtained directly on site - by evaporating liquid carbon dioxide in a gasifier. Further, the gas can be easily pumped through any gas pipeline at a pressure of 2-6 atmospheres.

The liquid state of CO2 is technically called "liquid carbon dioxide" or simply "carbonic acid". It is a colorless, odorless liquid medium density 771 kg / m3, which exists only under a pressure of 3,482 ... 519 kPa at a temperature of 0 ... -56.5 degrees C ("low-temperature carbon dioxide"), or under a pressure of 3,482 ... 7,383 kPa at a temperature of 0 ... +31.0 deg.С ("high-pressure carbon dioxide"). High-pressure carbon dioxide is most often obtained by compressing carbon dioxide to a condensation pressure, while cooling it with water. Low-temperature carbon dioxide, which is the main form of carbon dioxide for industrial consumption, is most often produced in a high-pressure cycle by three-stage cooling and throttling in special plants.

With a small and medium consumption of carbon dioxide (high pressure), tons, a variety of steel cylinders are used for its storage and transportation (from cans for household siphons to containers with a capacity of 55 liters). The most common is a 40 l cylinder with a working pressure of 15,000 kPa, containing 24 kg of carbon dioxide. Steel cylinders do not require additional care, carbon dioxide is stored without loss for a long time. High pressure carbon dioxide cylinders are painted black.

With significant consumption, for storage and transportation of low-temperature liquid carbon dioxide, isothermal tanks of the most diverse capacity, equipped with service refrigeration units, are used. There are accumulative (stationary) vertical and horizontal tanks with a capacity of 3 to 250 tons, transportable tanks with a capacity of 3 to 18 tons. Vertical tanks require the construction of a foundation and are used mainly in conditions of limited space for placement. The use of horizontal tanks makes it possible to reduce the cost of foundations, especially if there is a common frame with a carbon dioxide plant. The tanks consist of an internal welded vessel made of low-temperature steel and having polyurethane foam or vacuum thermal insulation; outer casing made of plastic, galvanized or stainless steel; pipelines, fittings and control devices. The inner and outer surfaces of the welded vessel are subjected to special treatment, due to which the probability of surface corrosion of the metal is reduced to the level. In expensive imported models, the outer sealed casing is made of aluminum. The use of tanks provides filling and discharge of liquid carbon dioxide; storage and transportation without loss of the product; visual control of weight and operating pressure during filling, storage and dispensing. All types of tanks are equipped with a multi-level security system. Safety valves allow inspection and repair without stopping and emptying the tank.

With an instantaneous decrease in pressure to atmospheric pressure, which occurs during injection into a special expansion chamber (throttling), liquid carbon dioxide instantly turns into gas and the thinnest snow-like mass, which is pressed and carbon dioxide is obtained in a solid state, which is commonly called "dry ice". At atmospheric pressure, it is a white vitreous mass with a density of 1,562 kg / m?, with a temperature of -78.5 ° C, which sublimates in the open air - gradually evaporates, bypassing the liquid state. Dry ice can also be obtained directly at high-pressure plants used to produce low-temperature carbon dioxide from gas mixtures containing CO2 in an amount of at least 75-80%. The volumetric cooling capacity of dry ice is almost 3 times greater than that of water ice and is 573.6 kJ/kg.

Solid carbon dioxide is usually produced in briquettes with a size of 200 × 100 × 20-70 mm, in granules with a diameter of 3, 6, 10, 12 and 16 mm, rarely in the form of the finest powder (“dry snow”). Briquettes, pellets and snow are stored for no more than 1-2 days in stationary underground mine-type storages, divided into small compartments; transported in special isothermal containers with a safety valve. Containers from different manufacturers with a capacity of 40 to 300 kg or more are used. Sublimation losses are, depending on the ambient temperature, 4-6% or more per day.

At pressures above 7.39 kPa and temperatures above 31.6 degrees C, carbon dioxide is in the so-called supercritical state, in which its density is like that of a liquid, and its viscosity and surface tension are like that of a gas. This unusual physical substance (fluid) is an excellent non-polar solvent. Supercritical CO2 is able to fully or selectively extract any non-polar constituents with a molecular weight of less than 2,000 daltons: terpene compounds, waxes, pigments, high molecular weight saturated and unsaturated fatty acids, alkaloids, fat-soluble vitamins and phytosterols. Insoluble substances for supercritical CO2 are cellulose, starch, high molecular weight organic and inorganic polymers, sugars, glycosidic substances, proteins, metals and many metal salts. Having similar properties, supercritical carbon dioxide is increasingly used in the processes of extraction, fractionation and impregnation of organic and inorganic substances. It is also a promising working fluid for modern heat engines.

  • Specific gravity. The specific gravity of carbon dioxide depends on the pressure, temperature and state of aggregation in which it is located.
  • The critical temperature of carbon dioxide is +31 degrees. The specific gravity of carbon dioxide at 0 degrees and a pressure of 760 mm Hg. is equal to 1.9769 kg/m3.
  • The molecular weight of carbon dioxide is 44.0. The relative weight of carbon dioxide compared to air is 1.529.
  • Liquid carbon dioxide at temperatures above 0 deg. much lighter than water and can only be stored under pressure.
  • The specific gravity of solid carbon dioxide depends on the method of its production. Liquid carbon dioxide, when frozen, turns into dry ice, which is a transparent, glassy solid. In this case, solid carbon dioxide has the highest density (at normal pressure in a vessel cooled to minus 79 degrees, the density is 1.56). Industrial solid carbon dioxide is white, close to chalk in hardness,
  • its specific gravity varies depending on the method of obtaining within 1.3 - 1.6.
  • State equation. The relationship between the volume, temperature, and pressure of carbon dioxide is expressed by the equation
  • V= R T/p - A, where
  • V - volume, m3/kg;
  • R - gas constant 848/44 = 19.273;
  • T - temperature, K degrees;
  • p pressure, kg/m2;
  • A is an additional term characterizing the deviation from the equation of state for an ideal gas. It is expressed by the dependence A \u003d (0.0825 + (1.225) 10-7 p) / (T / 100) 10 / 3.
  • Triple point of carbon dioxide. The triple point is characterized by a pressure of 5.28 ata (kg/cm2) and a temperature of minus 56.6 degrees.
  • Carbon dioxide can be in all three states (solid, liquid and gaseous) only at the triple point. At pressures below 5.28 ata (kg/cm2) (or at temperatures below minus 56.6 degrees), carbon dioxide can exist only in solid and gaseous states.
  • In the vapor-liquid region, i.e. above the triple point, the following relations hold
  • i "x + i" "y \u003d i,
  • x + y = 1, where,
  • x and y - the proportion of the substance in liquid and vapor form;
  • i" is the enthalpy of the liquid;
  • i"" - steam enthalpy;
  • i is the enthalpy of the mixture.
  • From these values ​​it is easy to determine the values ​​of x and y. Accordingly, for the region below the triple point, the following equations will be valid:
  • i"" y + i"" z \u003d i,
  • y + z = 1, where,
  • i"" - enthalpy of solid carbon dioxide;
  • z is the proportion of the substance in the solid state.
  • At the triple point for three phases, there are also only two equations
  • i"x + i""y + i"""z = i,
  • x + y + z = 1.
  • Knowing the values ​​of i," i"," i""" for the triple point and using the above equations, you can determine the enthalpy of the mixture for any point.
  • Heat capacity. The heat capacity of carbon dioxide at a temperature of 20 degrees. and 1 ata is
  • Ср = 0.202 and Сv = 0.156 kcal/kg*deg. Adiabatic exponent k = 1.30.
  • The heat capacity of liquid carbon dioxide in the temperature range from -50 to +20 deg. characterized by the following values, kcal / kg * deg. :
  • Deg.С -50 -40 -30 -20 -10 0 10 20
  • Wed, 0.47 0.49 0.515 0.514 0.517 0.6 0.64 0.68
  • Melting point. The melting of solid carbon dioxide occurs at temperatures and pressures corresponding to the triple point (t = -56.6 degrees and p = 5.28 atm) or above it.
  • Below the triple point, solid carbon dioxide sublimates. The sublimation temperature is a function of pressure: at normal pressure it is -78.5 degrees, in vacuum it can be -100 degrees. and below.
  • Enthalpy. The enthalpy of carbon dioxide vapor in a wide range of temperatures and pressures is determined by the Planck and Kupriyanov equation.
  • i = 169.34 + (0.1955 + 0.000115t)t - 8.3724p(1 + 0.007424p)/0.01T(10/3), where
  • I - kcal / kg, p - kg / cm2, T - deg. K, t - deg. C.
  • The enthalpy of liquid carbon dioxide at any point can be easily determined by subtracting the latent heat of vaporization from the enthalpy of saturated steam. Similarly, by subtracting the latent heat of sublimation, one can determine the enthalpy of solid carbon dioxide.
  • Thermal conductivity. Thermal conductivity of carbon dioxide at 0 deg. is 0.012 kcal / m * hour * deg. C, and at a temperature of -78 deg. it drops to 0.008 kcal/m*hour*deg.C.
  • Data on the thermal conductivity of carbon dioxide in 10 4 tbsp. kcal/m*h*deg.С at above-zero temperatures are given in the table.
  • Pressure, kg/cm2 10 deg. 20 deg. 30 deg. 40 deg.
  • gaseous carbon dioxide
  • 1 130 136 142 148
  • 20 - 147 152 157
  • 40 - 173 174 175
  • 60 - - 228 213
  • 80 - - - 325
  • liquid carbonic acid
  • 50 848 - - -
  • 60 870 753 - -
  • 70 888 776 - -
  • 80 906 795 670
    The thermal conductivity of solid carbon dioxide can be calculated by the formula:
    236.5 / T1.216 st., kcal / m * hour * deg. C.
  • Thermal expansion coefficient. The volumetric expansion coefficient a of solid carbon dioxide is calculated depending on the change specific gravity and temperature. The linear expansion coefficient is determined by the expression b = a/3. In the temperature range from -56 to -80 degrees. the coefficients have the following values: a * 10 * 5st. \u003d 185.5-117.0, b * 10 * 5 st. = 61.8-39.0.
  • Viscosity. Viscosity of carbon dioxide 10 * 6st. depending on pressure and temperature (kg*sec/m2)
  • Pressure, ata -15 degrees. 0 deg. 20 deg. 40 deg.
  • 5 1,38 1,42 1,49 1,60
  • 30 12,04 1,63 1,61 1,72
  • 75 13,13 12,01 8,32 2,30
  • Dielectric constant. The dielectric constant of liquid carbon dioxide at 50 - 125 ati is in the range of 1.6016 - 1.6425.
  • Dielectric constant of carbon dioxide at 15 deg. and pressure 9.4 - 39 atm 1.009 - 1.060.
  • Moisture content of carbon dioxide. The content of water vapor in moist carbon dioxide is determined using the equation,
  • X = 18/44 * p'/p - p' = 0.41 p'/p - p' kg/kg, where
  • p' - partial pressure of water vapor at 100% saturation;
  • p is the total pressure of the vapor-gas mixture.
  • Solubility of carbon dioxide in water. The solubility of gases is measured by volumes of gas reduced to normal conditions (0 degrees, C and 760 mm Hg) per volume of solvent.
  • The solubility of carbon dioxide in water at moderate temperatures and pressures up to 4 - 5 atm obeys Henry's law, which is expressed by the equation
  • P \u003d H X, where
  • P is the partial pressure of the gas above the liquid;
  • X is the amount of gas in moles;
  • H is Henry's coefficient.
  • Liquid carbon dioxide as a solvent. The solubility of lubricating oil in liquid carbon dioxide at a temperature of -20 deg. up to +25 deg. is 0.388 g in 100 CO2,
  • and increases to 0.718 g in 100 g of CO2 at a temperature of +25 degrees. WITH.
  • The solubility of water in liquid carbon dioxide in the temperature range from -5.8 to +22.9 degrees. is not more than 0.05% by weight.

Safety

According to the degree of impact on the human body, gaseous carbon dioxide belongs to the 4th hazard class according to GOST 12.1.007-76 " Harmful substances. Classification and general safety requirements”. The maximum permissible concentration in the air of the working area has not been established; when assessing this concentration, one should be guided by the standards for coal and ozocerite mines, set within 0.5%.

When using dry ice, when using vessels with liquid low-temperature carbon dioxide, safety measures must be observed to prevent frostbite of the hands and other parts of the worker's body.

In industry, the main methods for the production of carbon dioxide CO2 are its production as a by-product of the reaction of converting methane CH4 into hydrogen H2, combustion (oxidation) of hydrocarbons, the reaction of decomposition of limestone CaCO3 into lime CaO and water H20.

CO2 as a by-product of the steam reforming of CH4 and other hydrocarbons into hydrogen H2

Hydrogen H2 is required by industry primarily for its use in the production of ammonia NH3 (Haber process, catalytic reaction of hydrogen and nitrogen); ammonia is needed for the production of mineral fertilizers and nitric acid. Hydrogen can be produced in various ways, including water electrolysis, which is beloved by ecologists - however, unfortunately, at present, all methods of hydrogen production, except for hydrocarbon reforming, are absolutely economically unjustified on the scale of large-scale production - unless there is an excess of "free" electricity. Therefore, the main method of hydrogen production, during which carbon dioxide is also released, is methane steam reforming: at a temperature of about 700 ... 1100 ° C and a pressure of 3 ... 25 bar, in the presence of a catalyst, steam H2O reacts with methane CH4 with the release of synthesis gas (the process is endothermic, that is, it goes with the absorption of heat):
CH4 + H2O (+ heat) → CO + 3H2

Propane can be steam reformed in the same way:
C3H8 + 3H2O (+ heat) → 2CO + 7H2

As well as ethanol (ethyl alcohol):
C2H5OH + H2O (+ heat) → 2CO + 4H2

Even gasoline can be steam reformed. There are more than 100 different chemical compounds in gasoline, the steam reforming reactions of isooctane and toluene are shown below:
C8H18 + 8H2O (+ heat) → 8CO + 17H2
C7H8 + 7H2O (+ heat) → 7CO + 11H2

So, in the process of steam reforming of one or another hydrocarbon fuel, hydrogen and carbon monoxide CO (carbon monoxide) were obtained. At the next stage of the hydrogen production process, carbon monoxide in the presence of a catalyst undergoes the reaction of moving an oxygen atom O from water to gas = CO is oxidized to CO2, and hydrogen H2 is released in free form. The reaction is exothermic, it releases about 40.4 kJ / mol of heat:
CO + H2O → CO2 + H2 (+ heat)

In industrial environments, the carbon dioxide CO2 released during the steam reforming of hydrocarbons is easy to isolate and collect. However, CO2 in this case is an undesirable by-product, simply releasing it freely into the atmosphere, although now the prevailing way of getting rid of CO2, is undesirable from an environmental point of view, and some enterprises practice more "advanced" methods, such as injection CO2 into declining debit oil fields or pumping it into the ocean.

Obtaining CO2 from the complete combustion of hydrocarbon fuels

When hydrocarbons such as methane, propane, gasoline, kerosene, diesel fuel, etc. are burned, that is, oxidized with a sufficient amount of oxygen, carbon dioxide and, usually, water are formed. For example, the combustion reaction of methane CH4 looks like this:
CH 4 + 2O 2 → CO 2 + 2H 2 O

CO2 as a by-product of H2 production by partial oxidation of fuel

About 95% of the industrially produced hydrogen in the world is produced by the above-described steam reforming of hydrocarbon fuels, primarily methane CH4 contained in natural gas. In addition to steam reforming, hydrogen can be obtained from hydrocarbon fuel with a fairly high efficiency by the partial oxidation method, when methane and other hydrocarbons react with an amount of oxygen insufficient for complete combustion of the fuel (recall that in the process of complete combustion of the fuel, briefly described above, carbon dioxide is obtained CO2 gas and H20 water). When a less than stoichiometric amount of oxygen is supplied, the reaction products are predominantly hydrogen H2 and carbon monoxide, also known as carbon monoxide CO; in small quantities, carbon dioxide CO2 and some other substances are obtained. Since, in practice, this process is usually carried out not with purified oxygen, but with air, there is nitrogen at the inlet and outlet of the process, which does not participate in the reaction.

Partial oxidation is an exothermic process, that is, heat is released as a result of the reaction. Partial oxidation is generally much faster than steam reforming and requires a smaller reactor. As seen in the reactions below, initially partial oxidation produces less hydrogen per unit of fuel than steam reforming does.

Reaction of partial oxidation of methane CH4:
CH 4 + ½O 2 → CO + H 2 (+ heat)

Propane C3H8:
C 3 H 8 + 1½O 2 → 3CO + 4H 2 (+ heat)

Ethyl alcohol C2H5OH:
C 2 H 5 OH + ½O 2 → 2CO + 3H 2 (+ heat)

Partial oxidation of gasoline using the example of isooctane and toluene, from more than a hundred chemical compounds present in gasoline:
C 8 H 18 + 4O 2 → 8CO + 9H 2 (+ heat)
C 7 H 18 + 3½O 2 → 7CO + 4H 2 (+ heat)

To convert CO into carbon dioxide and produce additional hydrogen, the water → gas oxygen shift reaction already mentioned in the description of the steam reforming process is used:
CO + H 2 O → CO 2 + H 2 (+ small amount of heat)

CO2 in sugar fermentation

In the production of alcoholic beverages and bakery products from yeast dough, the process of fermentation of sugars - glucose, fructose, sucrose, etc., is used, with the formation of ethyl alcohol C2H5OH and carbon dioxide CO2. For example, the glucose fermentation reaction C6H12O6 is:
C 6 H 12 O 6 → 2C 2 H 5 OH + 2CO 2

And the fermentation of fructose C12H22O11 looks like this:
C 12 H 22 O 11 + H 2 O → 4C 2 H 5 OH + 4CO 2

Wittemann CO2 production equipment

In the production of alcoholic beverages, the resulting alcohol is a desirable and, one might even say, a necessary product of the fermentation reaction. Carbon dioxide is sometimes released into the atmosphere, and sometimes left in the drink to carbonate it. In baking bread, the opposite is true: CO2 is needed to create bubbles that cause the dough to rise, and ethyl alcohol is almost completely evaporated during baking.

Many enterprises, primarily distilleries, for which CO 2 is a completely unnecessary by-product, have set up its collection and sale. The gas from the fermentation tanks is fed through alcohol traps to the carbon dioxide plant, where CO2 is purified, liquefied and bottled. In fact, it is the distilleries that are the main suppliers of carbon dioxide in many regions - and for many of them, the sale of carbon dioxide is by no means the last source of income.

There is a whole industry of production of equipment for the release of pure carbon dioxide in breweries and distilleries (Huppmann / GEA Brewery, Wittemann, etc.), as well as its direct production from hydrocarbon fuels. Gas suppliers such as Air Products and Air Liquide are also installing CO 2 recovery and purification stations, liquefaction and cylindering.

CO2 in quicklime production CaO from CaCO3

The production process for the widely used quicklime CaO also has carbon dioxide as a reaction by-product. The decomposition reaction of limestone CaCO3 is endothermic, needs a temperature of the order of +850°C and looks like this:
CaCO3 → CaO + CO2

If limestone (or other metal carbonate) reacts with acid, then carbon dioxide H2CO3 is released as one of the reaction products. For example, hydrochloric acid HCl reacts with limestone (calcium carbonate) CaCO3 as follows:
2HCl + CaCO 3 → CaCl 2 + H 2 CO 3

Carbonic acid is very unstable, and under atmospheric conditions quickly decomposes into CO2 and water H2O.