All names for carbon dioxide. Carbon dioxide (carbon dioxide)
Sooner or later, every serious aquarist faces the question of supplying the aquarium with CO2. And for good reason. Why do aquarium plants need it?
So, CO2 - what is it? We all know that they feed primarily on carbon dioxide dissolved in water. This is CO2. In nature, plants get it from the reservoir in which they grow. Since the volume of water in natural reservoirs is very large, its concentration in them is usually constant. But the same cannot be said about aquariums.
Plants quickly use up all the CO2 gas from the aquarium water, and by itself the recovery of its concentration will not occur, because the aquarium is a closed system. Even the fish contained in it will not be able to make up for the lack of CO2, as they exhale such a meager proportion that it will never be enough for plants. And as a result, aquarium plants stop growing.
In addition to the fact that plants stop growing due to a lack of CO2, water in which its content is low has an increased hardness (pH), which is detrimental to them. Even inexperienced aquarists have probably noticed that after adding plants, tap water becomes harder than it was in an empty aquarium. This is due to the fact that it contributes to the appearance of carbonic acid in the water, and it lowers the hardness. That is, it is important to understand: the less CO2 in the water, the higher its pH.
How to help
There are several ways to solve the problem of supplying plants with CO2. You can install a special cylinder and appropriate equipment, or you can go the other way and try to do everything you need with your own hands. Many people prefer this way. And it is clear why - after all, it is much more interesting and pleasant to solve the problem on your own, without resorting to the help of purchased equipment.
The only thing worth paying attention to is the result. Not knowing how everything works in the aquarium, you should not go there and change and redo something, so as not to be upset later. The important thing here is not participation, but understanding what you are doing.
Nowadays, more and more aquarists are engaged in breeding aquatic plants and independently solve problems with a lack of carbon dioxide in the water. To some extent, such a scale may well negate all the results of the fight against harmful emissions enterprises and cars, because homemade aquarium devices have become necessary and very fashionable, and their volumes are sometimes quite large. Of course, this is a figurative comparison, but there is some truth in these fears.
So, CO2 gas - what is it? How to deal with carbon dioxide in our aquarium and how to produce it inexpensively and in sufficient quantities? But it is quite realistic to make such a system ourselves and refill it 5-7 times a year.
What do aquarium plants need?
Once again, let's recall what CO2 is and why plants need it in an aquarium. CO2 for an aquarium is a source of carbon that plants need, like food for humans. Plants consume it in the light, but in the dark they need oxygen no less. This is the first problem that beginner aquarists face.
If you forget about this, then at night the aquarium will begin to freeze. Even if there is no obvious death of the flora, the plants will simply stop growing normally, and this will make all our efforts meaningless.
In other words, there must always be diffusion (aeration) in the aquarium. And oxygen should be enough for the dark half of the day. Usually there is a lot of it at the beginning of the day, but plants, like fish breathing it, “choose” it pretty quickly. In such a situation, CO2 will not only not be able to help, but will easily exacerbate the problem.
Something else is no less common. Beginners in the aquarium business, seeing how their seemingly unpretentious Vallisneria or easy-to-care Riccia with hygrophila completely refuse to grow, begin to play tricks with CO2 and experiment in the hope of improvement. And the point is not at all an insufficient amount of carbon dioxide or light. These easy-to-keep plants thrive in less light and less carbonated water. It turns out that simply, either the plants were bought “on the verge of death”, or the soil is too poor or the water is new, not yet settled.
What is more important - light, fertilizers or CO2?
Success is simple: CO2 for the aquarium, nutrients and light. And you need to treat it not fictitiously, but with all respect, because all its components are equally important for plant life. If you "disperse" the system in the direction of one of them, without taking into account the other two, then quite quickly and inevitably you will encounter the manifestation of Liebig's law instead of admiring the strong and healthy flora in your artificial reservoir. This is the so-called swing effect. Moreover, the more the system is overclocked, the more intervention will be required, and in the meantime, the plants "get tired and yearn."
As a result, instead of vigorous greenery in the aquarium, everything gradually fades, and then some of the plantings die altogether. Or the water will begin to fill with algae if the plants cannot “digest” our “broth”.
Factors affecting the composition of water in an aquarium
Interestingly, when thinking about CO2, oxygen, light, and nutrients, temperature is often overlooked. And it is the main regulator of aquarium photosynthesis. Not light and not CO2, as it might seem. Botanists are well aware of this, but "aquarium researchers" forget this fact quite often.
The regulatory role of waves such as infrared reflects precisely this function. Perhaps this is due to the fact that in the technologies used for manufacturing light sources used for aquariums, remembering the temperature is unprofitable. So they pretend it doesn't matter.
What can an aquarium do without?
An aquarium can do without fashionable and glamorous excesses. And not only can, but also safely manages. The main thing is to balance knowledge and cause-and-effect relationships obtained through research in the system. If the system is already in equilibrium, then it no longer needs to be touched! And do not try to fix something that is already working properly.
And yet, if the aquarium tank is too densely planted with plants, then even with good lighting, they may have enough CO2. This is especially true for slightly alkaline hard water. If both species that can absorb only unoccupied carbon dioxide are combined (these are all types of mosses, many grasses that grow only in acidic and soft water, lobelia), and eurion and stenoion species that are able to extract carbon from carbonates (and this is Vallisneria , elodea, echinodorus, etc.), then the concentration of CO2 will be especially low.
It is not at all difficult to cure this, since it is enough just to populate more fish in the aquarium. In those aquariums in which everything is normal with the ecology, and with a dense population of living creatures, plants do not lack carbon dioxide even with fairly powerful light. But in any case, an additional dose of CO2 will not be superfluous for such a reservoir.
We have considered in detail the role of CO2. What it is, now, too, is probably clear. It remains to learn how to make it at home.
The gentle method of supplying the aquarium with carbon dioxide
To enrich the aquarium with carbon dioxide, the easiest way is to use ordinary mash. However, she wanders unsteadily. Initially, there will be an excess of gas that will escape, create a greenhouse effect, or create an excess concentration of CO2 in the water. Then the rate of its production will drop sharply.
Disadvantages of the mash method
There are only two of them:
- The need for too frequent recharges (1.5-3 weeks).
- The complexity of monitoring the operation of the system during the day.
However, this does not mean that CO2 supply to the aquarium is not available to you, as these disadvantages are easily solved by using a tank system. True, it has a rather high price, and besides the purchase, it still needs to be professionally configured.
Consider one of the recipes for using such a mash. Its advantage is that fermentation takes place very smoothly and for a long time (3-4 months). Of course, there is nothing new in science, more gas will not come out of the same amount of matter, but the aquarium receives the required amount of CO2 evenly and slowly. For those who need a large amount of carbon dioxide, this recipe will by no means work, they definitely need a CO2 tank. In principle, no mash is suitable for stable high concentrations. But it copes quite satisfactorily with the task of supplying carbon dioxide to an average aquarium with a dense "population", nutrient soil and good illumination, if euryion and stenoion species coexist in its hard water.
How to make a CO2 production system for an aquarium with your own hands
We use a polyethylene container with a volume of 1.5 and 2 liters. In each case, the size of the containers may vary, depending on the volume of the aquarium and the amount of carbon dioxide required.
1. Pour the components into the container: 5-6 tablespoons (with a slide) of sugar, one tablespoon of soda and 2-3 tablespoons of starch (also with a slide).
2. Pour 1.5-2 cups of water, as seen in the photo.
3. We send everything to a water bath.
Important: there should be water in the pan almost to the level of the liquid in the bottles, otherwise the composition at the bottom will not become thick, but will remain liquid on top.
4. Cook until the consistency of thick jelly, that is, until ready. You need to get a very thick mixture. If you knock over the bottle, then it should almost not drain.
4. Cool the resulting mixtures.
While the bottles are cooling down, we are engaged in the manufacture of tight and reliable caps with neat pipe fittings. After all, CO2 is a gas, which means that sealing must be very thorough. It is convenient to use fittings for the VAZ brake system (about 12 rubles / pair in auto parts stores). We will need two such fittings, gaskets and washers for 8 (about 40 rubles / a pair of sets in OBI), as well as a pair of nuts for 8.
With a knife and a heated nail, you need to make a hole, then drive the fitting into it with a thread down (thread inside the bottle). Above through the washer, and below according to the scheme: gasket / washer / nut.
It makes no sense to use various adhesives for sealing, since they will not provide the required protection. But the cover made according to the described scheme will securely hold the tube, while the entire CO2 supply system will turn out to be quite resistant to manipulation and recharging.
After the bottles have cooled down, you need to add a teaspoon of yeast (can be dry) to our jelly, before thoroughly mixing them in water. For example, in a glass or a glass.
We put the bottles prepared in this way in place, carefully connect them and do not touch them for 3-4 months. Carbon dioxide is released evenly and slowly, and if low-flow "bell" type reactors are used, then the whole process will be easily controlled visually. When the level in the bottles drops below the middle, it's time to recharge them.
Reloading is easy. The fermented mixture turns into a liquid again and pours out, a new one is laid in its place, and you again get CO2 for the aquarium. A do-it-yourself device based on plastic bottles will easily survive many such recharges without losing its qualities. Gas is supplied round the clock.
Types of reactors for aquariums
- "Bell"- this is any reactor made on the principle of an inverted glass. It is not recommended to dissolve the mash with other types of reactors, since the process of carbon dioxide release will become uncontrollable, and the density of CO2 will become uneven.
- The simplest reactor of this type is disposable syringe attached to the wall of the aquarium on a suction cup. Converted bird drinkers also look quite aesthetically pleasing, and besides, they are inexpensive. There are many options: from a plastic cup turned upside down to complex designs.
The efficiency of any reactor directly depends on the "contact spot" - the size of the area of contact between water and gas. Laffart advises for every 100 liters of water (hardness 10 grams) to make a dissolution area of 30 square meters. cm. This is not so much - only 5x6 cm.
So, there is a dilemma - to manufacture a large reactor, or a small one, in which the dissolution process will be much better than in a large one.
Such an effect can be obtained by directing part of the water through a thin tube from the filter under the "flute" to obtain a "fountain" inside the reactor. If such a flow is organized, for example, in a reactor from a syringe (20 cubic meters), then the dissolution will improve several times, and the CO2 concentration will be uniform. And this is tantamount to the use of a bell-type reactor, which has more bulky dimensions.
Balloon method of CO2 enrichment
For large aquariums, the optimal method for enriching water with carbon dioxide is the balloon installation method. Such a system consists of a cylinder and a control system, that is, a gearbox, a valve, fittings, a coil with connectors, an air throttle and a power supply. It is not difficult to assemble such an installation yourself, but it is easier to buy a ready-made one in a store, however, it will cost several times more.
Advantages and disadvantages of the balloon method
Advantages:
- Stability of CO2 production.
- Large amount of gas produced.
- Profitability.
- If you connect a pH controller and a CO2 gas analyzer, you can fully automate the process.
Flaws:
- High price.
- The complexity of self-assembly.
- High pressure cylinder required.
Finally
Returning to the choice of CO2 generator, we should also mention another type - chemical. Unlike a mash-powered generator, a chemical one uses the reaction of an acid with carbonates. Like the Braga method, these are suitable for small aquariums - up to 100 liters in size. In addition to everything mentioned in this article, it is possible to purchase a CO2 gas analyzer in a store and use it to constantly monitor the state of water in your artificial reservoir.
Substance with the 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, this colorless gas colorless and odorless, 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 - immediately go 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 the required amount is obtained directly on site - by evaporating liquid carbon dioxide in the 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 with an average density of 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 ... at a temperature of 0 ... + 31.0 degrees C ("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, thereby reducing the likelihood of surface corrosion of the metal. 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 a gas and a thin 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 is outdoors sublimated - gradually evaporates, bypassing 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 200 × 100 × 20-70 mm in size, 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 storages of the mine type, 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 a pressure of over 7.39 kPa and a temperature of more than 31.6 degrees C, carbon dioxide is in the so-called supercritical state, in which its density is like that of a liquid, and the 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. With 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 has White color, 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 exist 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 volume expansion coefficient a of solid carbon dioxide is calculated depending on the change in 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. FROM.
- 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 requirements security." 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.
You already know that when you exhale, carbon dioxide leaves the lungs. What do you know about this substance? Probably a little. Today I will answer all questions related to carbon dioxide.
Definition
This substance under normal conditions is a colorless gas. In many sources, it can be called differently: carbon monoxide (IV), and carbonic anhydride, and carbon dioxide, and carbon dioxide.
Properties
Carbon dioxide (CO 2 formula) is a colorless gas that has an acidic smell and taste, and is soluble in water. If it is properly cooled, it forms a snow-like mass called dry ice (photo below), which sublimates at a temperature of -78 o C.
It is one of the products of decay or combustion of any organic matter. It dissolves in water only at a temperature of 15 ° C and only if the ratio of water: carbon dioxide is 1: 1. The density of carbon dioxide can be different, but under standard conditions it is 1.976 kg / m 3. This is if it is in gaseous form, and in other states (liquid / gaseous), the density values \u200b\u200bwill also be different. This substance is an acidic oxide, its addition to water leads to the production of carbonic acid. If you combine carbon dioxide with any alkali, then as a result of the subsequent reaction, carbonates and hydrocarbonates are formed. This oxide cannot sustain combustion, with a few exceptions. These are active metals, and in this kind of reaction, they take oxygen from him.
Receipt
Carbon dioxide and some other gases are released in large quantities when alcohol is produced or natural carbonates decompose. The resulting gases are then washed with dissolved potassium carbonate. This is followed by the absorption of carbon dioxide by them, the product of this reaction is hydrocarbonate, by heating the solution of which the desired oxide is obtained.
But now it is successfully replaced by ethanolamine dissolved in water, which absorbs the carbon monoxide contained in the flue gas and releases it when heated. Also, this gas is a by-product of those reactions in which pure nitrogen, oxygen and argon are obtained. In the laboratory, some carbon dioxide is produced when carbonates and bicarbonates react with acids. It is also formed when baking soda and lemon juice or the same sodium bicarbonate and vinegar react (photo).
Application
The food industry cannot do without the use of carbon dioxide, where it is known as a preservative and leavening agent, having the code E290. Any fire extinguisher contains it in the form of a liquid.
Also, tetravalent carbon monoxide, which is released during the fermentation process, serves as a good top dressing for aquarium plants. It is also found in the well-known soda, which many people often buy at the grocery store. Wire welding takes place in a carbon dioxide environment, but if the temperature this process is very high, then it is accompanied by the dissociation of carbon dioxide, in which oxygen is released, which oxidizes the metal. Then welding is not complete without deoxidizers (manganese or silicon). Bicycle wheels are pumped with carbon dioxide, it is also present in canisters of pneumatic weapons (this kind of it is called gas-balloon). Also, this oxide in the solid state, called dry ice, is needed as a refrigerant in trade, scientific research and when repairing some equipment.
ConclusionThat's how useful carbon dioxide is for humans. And not only in industry, it also plays an important biological role: without it, gas exchange, regulation of vascular tone, photosynthesis and many others cannot occur natural processes. But its excess or shortage in the air for some time can adversely affect physical state all living organisms.
Loss of strength, weakness, headache, depression - is this condition familiar? Most often this happens in autumn and winter, and poor health is attributed to a shortage sunlight. But it's not about him, but about the excess carbon dioxide in the air you breathe. The situation with the level of CO₂ in residential premises and transport in our country is truly catastrophic. Stuffiness, high humidity and mold are also the result of a lack of ventilation. Sealed plastic windows and air conditioners only exacerbate the situation. Do you know that with a twofold excess (relative to the street background) of the level of carbon dioxide in the air, brain activity decreases by 2 times? By the way, yawning students at lectures are an indicator of high CO₂ content in the classroom. And very often there is no ventilation in office buildings. What productivity can we talk about if a person simply does not have brains?
So let's start with the basics. A person breathes in oxygen and releases carbon dioxide. Carbon dioxide is also released when hydrocarbons are burned. The average level of CO₂ on our planet is currently about 400 PPM (Parts per million - parts per million, or 0.04%) and is constantly growing due to the constant growth in the consumption of petroleum products. At the same time, it is worth knowing that trees absorb carbon dioxide and this is precisely their main function (and not, as it is mistakenly believed that they only produce oxygen).
As long as a person is outdoors, there are no problems, but they begin when he is indoors. If a person is locked in a sealed room without fresh air, then he will die not from a lack of oxygen, as most people mistakenly believe, but from a multiple excess of carbon dioxide, which this person himself developed in his lungs. Let's set aside the problems of ventilation of public transport (I will write about this separately) and turn our attention to city apartments / country houses, in which there is a massive lack of ventilation.
At the same time, a person spends at least a third of his life in his house / apartment, but in reality half - you cannot save on your own health!
2. The problem of high CO₂ content in the air is especially relevant in the cold season, because In the summer, almost all windows are constantly open. And with the onset of cold weather, the windows are opened less and less, ultimately reducing to episodic ventilation. And, what a coincidence, it is in the cold season that depression, drowsiness and loss of strength appear.
3. Previously, there was even such a tradition - to seal the cracks on the windows before the cold weather. Often, together with window vents, they completely excluded the flow of fresh air into the house. I once again emphasize that fresh air is needed not because it contains the oxygen necessary for breathing, but in order to reduce the excess carbon dioxide content by replacing the air in the room.
4. Many people think that they also have an exhaust hood (in apartments, at least in the kitchen and in the bathroom), and the room will be ventilated through it. Yeah, in addition, installing plastic windows that are completely airtight. But how will the air go into the exhaust if you do not have an inflow in the form of either slots in the frames or an open window? And with good traction, it usually pulls air from the entrance.
5. It's worse just to put the air conditioner in the form of a split system and use it with the windows closed. Remember, when the air conditioner is running, DO NOT close the windows! Here is a modern hermetic country house, which has no gaps in the building envelope. And do not be led by stories that wood or aerated concrete "breathe" and therefore you can not give a damn about ventilation. Remember, this term refers to the high vapor permeability of the material, and not the ability to supply fresh outdoor air into the house.
6. Most are limited to a fan on the hood from the bathroom and kitchen. Okay, turn on the fan, all windows and doors are closed in the house. What will be the result? That's right, there will be a rarefaction in the house, because the new air has nowhere to come from. In order for natural ventilation to work, fresh air must enter the house.
7. For measuring the level of carbon dioxide in the air, relatively affordable sensors with an NDIR sensor have now appeared. The non-dispersive infrared method (NDIR) is based on the change in the intensity of infrared radiation before and after absorption in an infrared detector with selective sensitivity. Initially, I was going to buy such a sensor on aliexpress last year (then it cost about $ 100), but the increased price due to the growth of the dollar made me think and look for alternative options. Unexpectedly, this sensor was found in Russia under the Russian brand for the same $ 100 at last year's exchange rate. In total, I found the best offer on Yandex.Market and purchased the sensor at a price of 3,500 rubles. The model is called MT8057. Of course, the sensor has an error, but it is not important when we are talking that it is important for us to measure the concentration of carbon dioxide several times higher than the norm.
8. Closed plastic windows, air conditioners - all this is nonsense compared to the gas stove in the apartment (for the photo, I lit the gas burner, because it had to be washed to shoot the stove).
9. So, all attention is on the chart. Kitchen 9 square meters, ceilings 3 meters high, opened door to the kitchen (!), a closed window, there is a hood with a natural impulse (draft is weak in summer), one person. The sensor is placed at a height of 1 meter from the floor, on the dining table. The "normal" level of CO₂ in a room without people is about 600 PPM. One person comes - the level of CO₂ instantly rises. Leaves - falls. Comes again - rises again. And after that it turns on one (!) gas burner. The level of CO₂ almost instantly rises above 2000 PPM. Anxiety! We open the porthole. We observe how the concentration of carbon dioxide in the air slowly decreases. And add 1-2 more people here. Even if you do not turn on the gas stove, then 3 adults without performing heavy physical work raise the CO₂ level in the room to critical point in 30 minutes.
Cooking on a gas stove? Be sure to open the window and turn on the hood (do both at the same time).
Did you turn on the air conditioner? Be sure to open the window.
Are you just in the room? Be sure to open the hatch. And if there are a lot of people in the room, open the window.
And at night, during sleep, the window must be kept open.
In short, you either need to have a supply air duct or a permanently open window.
10. As for trees and how they can be useful. Their most important function during growth is the absorption of carbon dioxide. Few people think about why firewood burns and where there is so much energy in them. So this energy in the form of carbon accumulates in the trunk of a tree as a result of the absorption of carbon dioxide. Trees produce oxygen as a byproduct of photosynthesis.
11. Opening a window in the warm season is not difficult and in general the problem is not so urgent in summer (except when using air conditioners with closed windows). Problems begin in winter, because no one keeps the window open all the time, this is a huge uncontrolled loss of heat and it will be corny cold. It is precisely at this moment that it is worth raising the alarm. Health is priceless.
The problem is very serious and has a global character. For example, until the autumn of last year, I didn’t think at all about the importance of ventilation for health: in an apartment, in a country house. If you look into the past, then it was regular autumn depressions, drowsiness and bad mood during the cold season in a city apartment that prompted you to think in the direction of leaving the city and building, so to speak, because. in autumn-winter I had a headache and there was a general weakness of the body when I was in the city. But as soon as I went out into nature, the problem disappeared. I didn't write it off as a lack of sunlight, but that wasn't the point. In winter, I stopped keeping the window open (it’s cold) and I got a multiple excess of CO₂ in the apartment.
The simplest and most affordable solution to the problem is to keep the window open all the time, or to ventilate, focusing on the readings from the CO₂ sensor. A normal level of CO₂ in a room can be considered a concentration of up to 1000 PPM, if it is higher, it is urgent to ventilate. Humidity can be considered an indirect indicator of the high concentration of carbon dioxide in the air. If without objective reasons As the room temperature drops, the humidity starts to rise, which means that the CO₂ level also rises.
The danger of high concentrations of carbon dioxide in the air is that human body reacts with a very long delay. By the time you felt that it was stuffy in the room and you needed to ventilate it, you had already been in a room with a high content of CO₂ in the air for at least half an hour.
In the next post I will talk about what problems there are with ventilation in public transport(buses, trains, planes). I will also show you how to properly organize ventilation in a country house, which for some reason everyone forgets about.
To be continued.
Articles on the topic, for self-study.
Carbon dioxide CO 2(carbon dioxide, carbon dioxide, carbon dioxide, carbonic anhydride), depending on pressure and temperature, it can be in a gaseous, liquid or solid state.
In its gaseous state, carbon dioxide is a colorless gas with a slightly sour taste and smell. The Earth's atmosphere contains about 0.04% carbon dioxide. Under normal conditions, its density is 1.98 g / l - about 1.5 times more density air.
Diagram. Phase equilibrium of carbon dioxide
Liquid carbon dioxide (carbonic acid) represents colorless liquid without smell. At room temperature, it exists only at pressures above 5850 kPa. The density of liquid carbon dioxide is highly dependent on temperature. For example, at temperatures below +11°C liquid carbon dioxide is heavier than water, at temperatures above +11°C it is lighter. As a result of evaporation of 1 kg of liquid carbon dioxide, under normal conditions, approximately 509 liters of gas are formed.
At a temperature of about -56.6 ° C and a pressure of about 519 kPa, liquid carbon dioxide turns into a solid - "dry ice".
In industry, the most common 3 ways to produce carbon dioxide:
- from waste gases of chemical industries, primarily synthetic ammonia and methanol; the exhaust gas contains approximately 90% carbon dioxide;
- from flue gases of industrial boilers burning natural gas, coal and other fuels; flue gas contains 12-20% carbon dioxide;
- from exhaust gases generated during fermentation in the process of obtaining beer, alcohol, during the breakdown of fats; the exhaust gas is almost pure carbon dioxide.
According to GOST 8050-85, gaseous and liquid carbon dioxide is supplied in three types: premium, first and second grades. For welding, it is recommended to use carbon dioxide of the highest and first grade. The use of carbon dioxide of the second grade for welding is allowed, however, the presence of gas dryers is desirable. The allowable content of carbon dioxide and some impurities in various grades of carbon dioxide is shown in the table below.
Table. Characteristics of carbon dioxide grades
Safety precautions when working with carbon dioxide:
- Carbon dioxide is non-toxic and non-explosive, however, at its concentration in the air above 5% (92 g/m3), the proportion of oxygen decreases, which can lead to oxygen deficiency and suffocation. Therefore, you should be wary of its accumulation in poorly ventilated areas. To register the concentration of carbon dioxide in the air of industrial premises, gas analyzers are used - stationary automatic or portable.
- When the pressure decreases to atmospheric, liquid carbon dioxide turns into gas and snow with a temperature of -78.5 ° C and can lead to damage to the mucous membrane of the eyes and frostbite of the skin. Therefore, when taking samples of liquid carbon dioxide, it is necessary to use goggles and gloves.
- Inspection of the internal capacity of a previously operated tank for storing and transporting liquid carbon dioxide must be carried out in a gas mask. The tank must be heated to a temperature environment, and blow out the inner container with air or ventilate. The gas mask may not be used until the volume fraction of carbon dioxide inside the equipment is below 0.5%.
The use of carbon dioxide in welding
Carbon dioxide is used as an active protective gas in arc welding(usually in semi-automatic welding) with a consumable electrode (wire), including as part of a gas mixture (with oxygen, argon).
The supply of welding stations with carbon dioxide can be carried out in the following ways:
- directly from an autonomous station for the production of carbon dioxide;
- from a stationary storage vessel - with significant volumes of carbon dioxide consumption and the enterprise does not have its own autonomous station;
- from transport carbon dioxide capacity - with smaller volumes of carbon dioxide consumption;
- from cylinders - with small amounts of carbon dioxide or the impossibility of laying pipelines to the welding station.
An autonomous station for the production of carbon dioxide is a separate specialized workshop of an enterprise that produces carbon dioxide for its own needs and supplies to other organizations. Carbon dioxide is supplied to the welding stations through gas pipelines laid in the welding shops.
With large volumes of carbon dioxide consumption and the absence of an autonomous station at the enterprise, carbon dioxide is stored in stationary storage vessels into which it comes from transport tanks (see the figure below).
Picture. Scheme of supplying welding stations with carbon dioxide from a stationary storage vessel
With smaller volumes of consumption, the supply of carbon dioxide through pipelines can be carried out directly from the transport tank. The characteristics of some stationary and transport containers are shown in the table below.
Table. Characteristics of tanks for storage and transportation of carbon dioxide (carbon dioxide)
Brand | Mass of carbon dioxide, kg | Purpose | Storage time of carbon dioxide, days | Gasifier brand |
TsZhU-3.0-2.0 | 2 950 | Transport automobile ZIL-130 | 6-20 | EGU-100 |
NZHU-4-1.6 | 4 050 | Stationary storage | 6-20 | EGU-100 |
TsZhU-9.0-1.8 | 9 000 | Transport automobile MAZ 5245 | 6-20 | GU-400 |
NZHU-12.5-1.6 | 12 800 | Stationary storage | 6-20 | GU-400 |
UDKh-12.5 | 12 300 | Stationary storage | UGM-200M | |
TsZhU-40-2 | 39 350 | Transport railway | 40 | GU-400 |
RDKh-25-2 | 25 500 | Stationary storage | Unlimited, equipped with a refrigeration unit | GU-400 |
NZHU-50D | 50 000 | Stationary storage | Unlimited, equipped with a refrigeration unit | GU-400 |
With small volumes of carbon dioxide consumption or the impossibility of laying pipelines to welding stations, cylinders are used to supply carbon dioxide. A standard black cylinder with a capacity of 40 liters is filled with 25 kg of liquid carbon dioxide, which is usually stored at a pressure of 5-6 MPa. As a result of the evaporation of 25 kg of liquid carbon dioxide, approximately 12,600 liters of gas are formed. The scheme of carbon dioxide storage in a cylinder is shown in the figure below.
Picture. Scheme of storage of carbon dioxide (carbon dioxide) in a cylinder
To extract gas from a cylinder, it must be equipped with a reducer, a gas heater and a gas dryer. When carbon dioxide leaves the cylinder, as a result of its expansion, adiabatic cooling of the gas occurs. At a high gas flow rate (more than 18 l/min), this can lead to freezing of the water vapor contained in the gas and clogging of the reducer. In this regard, it is desirable to place a gas heater between the reducer and the cylinder valve. When gas passes through the coil, it is heated by an electric heating element connected to the network with a voltage of 24 or 36V.
A gas dryer is used to extract moisture from carbon dioxide. It is a body filled with a material (usually silica gel, blue vitriol or aluminum gel), absorbing moisture well. Dehumidifiers are of high pressure, installed before the reducer, and low pressure, installed after the reducer.
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