Chlorine and its compounds. Structure of the chlorine atom Atomic number of chlorine
In nature, chlorine occurs in a gaseous state and only in the form of compounds with other gases. Under conditions close to normal, it is a greenish, poisonous, caustic gas. It has more weight than air. Has a sweet smell. The chlorine molecule contains two atoms. In a calm state does not burn, but when high temperatures enters into interaction with hydrogen, after which an explosion is possible. As a result, phosgene gas is released. Very poisonous. So, even at a low concentration in the air (0.001 mg per 1 dm 3) it can cause death. chlorine says that it is heavier than air, therefore, it will always be near the floor in the form of a yellowish-green haze.
Historical facts
For the first time in practice, this substance was obtained by K. Schelee in 1774 by combining hydrochloric acid and pyrolusite. However, only in 1810, P. Davy was able to characterize chlorine and establish that it is a separate chemical element.
It is worth noting that in 1772 he was able to obtain hydrogen chloride - a compound of chlorine with hydrogen, but the chemist could not separate these two elements.
Chemical characterization of chlorine
Chlorine is a chemical element of the main subgroup of group VII of the periodic table. It is in the third period and has atomic number 17 (17 protons in the atomic nucleus). Reactive nonmetal. It is denoted by the letters Cl.
Is a typical representative gases that do not have a color, but have a sharp pungent odor. Usually toxic. All halogens are highly soluble in water. Upon contact with moist air, they begin to smoke.
The external electronic configuration of the Cl atom is 3s23p5. Therefore, in compounds, the chemical element exhibits oxidation levels of -1, +1, +3, +4, +5, +6 and +7. The covalent radius of the atom is 0.96 Å, the ionic radius of Cl is 1.83 Å, the affinity of the atom to the electron is 3.65 eV, the ionization level is 12.87 eV.
As mentioned above, chlorine is a fairly active non-metal, which allows you to create compounds with almost any metal (in some cases, by heating or with the help of moisture, while displacing bromine) and non-metals. In powder form, it reacts with metals only under the influence of high temperatures.
The maximum combustion temperature is 2250 °C. With oxygen, it can form oxides, hypochlorites, chlorites and chlorates. All compounds containing oxygen become explosive when interacting with oxidizing substances. It is worth noting that they can explode randomly, while chlorates explode only when exposed to any initiators.
Characteristics of chlorine by position in the periodic system:
Simple substance;
. element of the seventeenth group of the periodic table;
. the third period of the third row;
. the seventh group of the main subgroup;
. atomic number 17;
. denoted by the symbol Cl;
. reactive non-metal;
. is in the halogen group;
. under conditions close to normal, it is a yellowish-green poisonous gas with a pungent odor;
. the chlorine molecule has 2 atoms (formula Cl 2).
Physical properties of chlorine:
Boiling point: -34.04 °C;
. melting point: -101.5 °C;
. density in the gaseous state - 3.214 g/l;
. the density of liquid chlorine (during the boiling period) - 1.537 g / cm 3;
. density of solid chlorine - 1.9 g/cm 3 ;
. specific volume - 1.745 x 10 -3 l / g.
Chlorine: characteristics of temperature changes
In the gaseous state, it tends to liquefy easily. At a pressure of 8 atmospheres and a temperature of 20 ° C, it looks like a greenish-yellow liquid. It has very high corrosion properties. As practice shows, this chemical element can maintain a liquid state up to a critical temperature (143 ° C), subject to an increase in pressure.
If it is cooled to a temperature of -32 ° C, it will change to liquid, regardless of atmospheric pressure. With a further decrease in temperature, crystallization occurs (at -101 ° C).
Chlorine in nature
The earth's crust contains only 0.017% chlorine. The bulk is in volcanic gases. As indicated above, the substance has a high chemical activity, as a result of which it occurs in nature in compounds with other elements. However, many minerals contain chlorine. The characteristic of the element allows the formation of about a hundred different minerals. As a rule, these are metal chlorides.
Also, a large amount of it is in the oceans - almost 2%. This is due to the fact that chlorides are very actively dissolved and carried by rivers and seas. The reverse process is also possible. Chlorine is washed back to the shore, and then the wind carries it around. That is why its highest concentration is observed in coastal zones. In the arid regions of the planet, the gas we are considering is formed by the evaporation of water, as a result of which salt marshes appear. About 100 million tons are mined annually in the world given substance. Which, however, is not surprising, because there are many deposits containing chlorine. Its characteristics, however, largely depend on its geographical location.
Methods for obtaining chlorine
Today, there are a number of methods for obtaining chlorine, of which the following are the most common:
1. Aperture. It is the simplest and least expensive. Salt solution in diaphragm electrolysis enters the anode space. Further on the steel cathode grid flows into the diaphragm. It contains a small amount of polymer fibers. An important feature this device is countercurrent. It is directed from the anode to the cathode space, which makes it possible to obtain chlorine and lye separately.
2. Membrane. The most energy efficient, but difficult to implement in an organization. Similar to diaphragm. The difference is that the anode and cathode spaces are completely separated by a membrane. Therefore, the output is two separate streams.
It should be noted that the characteristics of the chem. element (chlorine) obtained by these methods will be different. More "clean" is considered to be the membrane method.
3. Mercury method with liquid cathode. Compared to other technologies, this option allows you to get the purest chlorine.
The basic scheme of the installation consists of an electrolyser and interconnected pump and amalgam decomposer. The mercury pumped by the pump together with a solution of common salt serves as the cathode, and carbon or graphite electrodes serve as the anode. The principle of operation of the installation is as follows: chlorine is released from the electrolyte, which is removed from the electrolyzer together with the anolyte. Impurities and chlorine residues are removed from the latter, saturated with halite and returned to electrolysis again.
The requirements of industrial safety and the unprofitability of production led to the replacement of the liquid cathode with a solid one.
The use of chlorine for industrial purposes
The properties of chlorine allow it to be actively used in industry. With the help of this chemical element, various (vinyl chloride, chloro-rubber, etc.) medications, disinfectants. But the biggest niche occupied in the industry is the production of hydrochloric acid and lime.
Methods for purifying drinking water are widely used. Today, they are trying to move away from this method, replacing it with ozonation, since the substance we are considering negatively affects the human body, besides, chlorinated water destroys pipelines. This is due to the fact that in the free state Cl adversely affects pipes made from polyolefins. However, most countries prefer the chlorination method.
Chlorine is also used in metallurgy. With its help, a number of rare metals (niobium, tantalum, titanium) are obtained. In the chemical industry, various organochlorine compounds are actively used for weed control and for other agricultural purposes, the element is also used as a bleach.
Due to its chemical structure, chlorine destroys most organic and inorganic dyes. This is achieved by completely discoloring them. Such a result is possible only if water is present, because the bleaching process occurs due to which it is formed after the breakdown of chlorine: Cl 2 + H 2 O → HCl + HClO → 2HCl + O. This method was used a couple of centuries ago and is still popular today.
The use of this substance for the production of organochlorine insecticides is very popular. These agricultural preparations kill harmful organisms, leaving plants intact. A significant part of all chlorine produced on the planet goes to agricultural needs.
It is also used in the production of plastic compounds and rubber. With their help, wire insulation, stationery, equipment, shells are made. household appliances etc. There is an opinion that rubbers obtained in this way are harmful to humans, but this has not been confirmed by science.
It is worth noting that chlorine (the characteristics of the substance were disclosed in detail by us earlier) and its derivatives, such as mustard gas and phosgene, are also used for military purposes to obtain chemical warfare agents.
Chlorine as a bright representative of non-metals
Non-metals are simple substances that include gases and liquids. In most cases, they conduct electric current worse than metals, and have significant differences in physical and mechanical characteristics. With the help of a high level of ionization, they are able to form covalent chemical compounds. Below, a characteristic of a non-metal will be given using the example of chlorine.
As mentioned above, this chemical element is a gas. Under normal conditions, it completely lacks properties similar to those of metals. Without outside help cannot interact with oxygen, nitrogen, carbon, etc. It exhibits its oxidizing properties in bonds with simple substances and some complex ones. Refers to halogens, which is clearly reflected in its chemical characteristics. In compounds with other representatives of halogens (bromine, astatine, iodine), it displaces them. In the gaseous state, chlorine (its characteristic is a direct confirmation of this) dissolves well. It is an excellent disinfectant. Kills only living organisms, which makes it indispensable in agriculture and medicine.
Use as a poison
The characteristic of the chlorine atom allows it to be used as a poisonous agent. For the first time, gas was used by Germany on April 22, 1915, during the First World War, as a result of which about 15 thousand people died. At the moment it does not apply.
Let us give a brief description of the chemical element as a suffocating agent. Affects the human body through suffocation. First, it irritates the upper respiratory tract and mucous membranes of the eyes. A strong cough begins with attacks of suffocation. Further, penetrating into the lungs, the gas corrodes the lung tissue, which leads to edema. Important! Chlorine is a fast acting substance.
Depending on the concentration in the air, the symptoms are different. With a low content in a person, redness of the mucous membrane of the eyes, slight shortness of breath is observed. The content in the atmosphere of 1.5-2 g / m 3 causes heaviness and thrills in the chest, sharp pain in the upper respiratory tract. Also, the condition may be accompanied by severe lacrimation. After 10-15 minutes of being in a room with such a concentration of chlorine, a severe burn of the lungs and death occurs. At denser concentrations, death is possible within a minute from paralysis of the upper respiratory tract.
Chlorine in the life of organisms and plants
Chlorine is found in almost all living organisms. The peculiarity is that it is present not in its pure form, but in the form of compounds.
In organisms of animals and humans, chloride ions maintain osmotic equality. This is due to the fact that they have the most suitable radius for penetration into membrane cells. Along with potassium ions, Cl regulates the water-salt balance. In the intestine, chloride ions create a favorable environment for the action of proteolytic enzymes of gastric juice. Chlorine channels are provided in many cells of our body. Through them, intercellular fluid exchange occurs and the pH of the cell is maintained. About 85% of the total volume of this element in the body resides in the intercellular space. It is excreted from the body through the urethra. Produced by the female body during breastfeeding.
At this stage of development, it is difficult to say unequivocally which diseases are provoked by chlorine and its compounds. This is due to the lack of research in this area.
Chlorine ions are also present in plant cells. He actively takes part in the energy exchange. Without this element, the process of photosynthesis is impossible. With its help, the roots actively absorb the necessary substances. But a high concentration of chlorine in plants can have a detrimental effect (slowing down the process of photosynthesis, stopping development and growth).
However, there are such representatives of the flora who were able to "make friends" or at least get along with this element. The characteristic of a non-metal (chlorine) contains such an item as the ability of a substance to oxidize soils. In the process of evolution, the plants mentioned above, called halophytes, occupied empty salt marshes, which were empty due to an overabundance of this element. They absorb chloride ions, and then get rid of them with the help of leaf fall.
Transportation and storage of chlorine
There are several ways to move and store chlorine. The characteristic of the element implies the need for special cylinders with high pressure. Such containers have an identification marking - a vertical green line. Cylinders must be thoroughly rinsed monthly. With prolonged storage of chlorine, a very explosive precipitate is formed in them - nitrogen trichloride. If all safety rules are not observed, spontaneous ignition and explosion are possible.
The study of chlorine
Future chemists should know the characteristics of chlorine. According to the plan, 9th graders can even make laboratory experiments with this substance based on basic knowledge of the discipline. Naturally, the teacher is obliged to conduct a safety briefing.
The order of work is as follows: you need to take a flask with chlorine and pour small metal shavings into it. In flight, the chips will flare up with bright bright sparks and at the same time a light white smoke of SbCl 3 will form. When tin foil is immersed in a vessel with chlorine, it will also spontaneously ignite, and fiery snowflakes will slowly fall to the bottom of the flask. During this reaction, a smoky liquid, SnCl 4 , is formed. When iron shavings are placed in the vessel, red “drops” are formed and red smoke of FeCl 3 will appear.
Along with practical work the theory is repeated. In particular, such a question as the characterization of chlorine by position in the periodic system (described at the beginning of the article).
As a result of the experiments, it turns out that the element actively reacts to organic compounds. If you place cotton wool soaked in turpentine in a jar of chlorine, it will instantly ignite, and soot will fall sharply from the flask. Sodium effectively smolders with a yellowish flame, and salt crystals appear on the walls of chemical dishes. Students will be interested to know that, while still a young chemist, N. N. Semenov (later Nobel Prize winner), after conducting such an experiment, collected salt from the walls of the flask and, sprinkling bread with it, ate it. Chemistry turned out to be right and did not let the scientist down. As a result of the experiment carried out by the chemist, ordinary table salt really turned out!
The main industrial method for obtaining chlorine is the electrolysis of a concentrated solution of NaCl (Fig. 96). In this case, chlorine is released at the anode (2Сl' - 2e– = Сl 2), and hydrogen is released in the cathode space (2Н + 2e - = H 2) and forms NaOH.
In the laboratory production of chlorine, the action of MnO 2 or KMnO 4 on hydrochloric acid is usually used:
MnO 2 + 4HCl = MnCl 2 + Cl 2 + 2H 2 O
2KMnO 4 + 16HCl = 2KSl + 2MnCl 2 + 5Cl 2 + 8H 2 O
In its characteristic chemical function, chlorine is similar to fluorine - it is also an active monovalent metalloid. However, its activity is less than that of fluorine. Therefore, the latter is able to displace chlorine from compounds.
The interaction of chlorine with hydrogen according to the reaction H 2 + Cl 2 \u003d 2HCl + 44 kcal
under normal conditions, it proceeds extremely slowly, but when the mixture of gases is heated or it is strongly illuminated (direct sunlight, burning magnesium, etc.), the reaction is accompanied by an explosion.
NaCl + H 2 SO 4 \u003d NaHSO 4 + HCl
NaCl + NaHSO 4 = Na 2 SO 4 + HCl
The first of them partly proceeds already at normal conditions and almost completely - with low heating; the second is carried out only at higher temperatures. For carrying out the process, mechanical furnaces of high productivity are used.
Cl 2 + H 2 O \u003d Hcl + HOCl
Being an unstable compound, HOCl decomposes slowly even in such a dilute solution. Salts of hypochlorous acid are called hypochlorous acid, or hypochlorites. HOCl itself and its salts are very strong oxidizing agents.
The easiest way to achieve this is by adding alkali to the reaction mixture. Since, as they form, H ions will bind OH ions "into undissociated water molecules, the equilibrium will shift to the right. Using, for example, NaOH, we have:
Cl 2 + H 2 O<–––>HOCl + HCl
HOCl + HCl + 2NaOH –––> NaOCl + NaCl + 2H 2 O
or in general:
Cl 2 + 2NaOH –––> NaOCl + NaCl + H 2 O
As a result of the interaction of chlorine with an alkali solution, therefore, a mixture of salts of hypochlorous and hydrochloric acids is obtained. The resulting solution (“javel water”) has strong oxidizing properties and is widely used for bleaching fabrics and paper.
1) HOCl \u003d HCl + O
2) 2HOCl \u003d H 2 O + Cl 2 O
3) 3HOCl \u003d 2HCl + HClO 3
All these processes are able to proceed simultaneously, but their relative rates strongly depend on the existing conditions. By changing the latter, it is possible to ensure that the transformation goes almost entirely along any one direction.
Under the action of direct sunlight, the decomposition of hypochlorous acid proceeds according to the first of them. It also proceeds in the presence of substances that can easily add oxygen, and some catalysts (for example, cobalt salts).
In the second type of decomposition, chlorine oxide (Cl 2 O) is obtained. This reaction takes place in the presence of water-removing substances (for example, CaCl 2). Chlorine oxide is an explosive brownish-yellow gas (m.p. -121 ° C, bp. +2 ° C) with an odor similar to the smell of chlorine. Under the action of Cl 2 O on water, HOCl is formed, i.e. chlorine oxide is anhydride of hypochlorous acid.
The decomposition of HOCl according to the third type proceeds especially easily when heated. Therefore, the effect of chlorine on a hot alkali solution is expressed by the overall equation:
ZCl 2 + 6KOH \u003d KClO 3 + 5KCl + 3H 2 O
2KSlO 3 + H 2 C 2 O 4 \u003d K 2 CO 3 + CO 2 + H 2 O + 2ClO 2
greenish-yellow chlorine dioxide is formed (g. pl. - 59 ° C, bp. + 10 ° C). Free ClO 2 is unstable and can decompose with
Ministry of Education and Science of the RUSSIAN FEDERATION
Federal STATE EDUCATIONAL INSTITUTION OF HIGHER PROFESSIONAL EDUCATION
IVANOVSK STATE CHEMICAL AND TECHNOLOGICAL UNIVERSITY
Department of TP and MET
Essay
Chlorine: properties, application, production
Head: Efremov A.M.
Ivanovo 2015
Introduction
General information for chlorine
Application of chlorine
Chemical methods for producing chlorine
Electrolysis. The concept and essence of the process
Industrial production of chlorine
Safety in chlorine production and environmental protection
Conclusion
Introduction
chlorine chemical element electrolysis
Due to the scale of the use of chlorine in various fields of science, industry, medicine and everyday life, the demand for it has recently increased dramatically. There are many methods for obtaining chlorine by laboratory and industrial methods, but they all have more disadvantages than advantages. The production of chlorine, for example, from hydrochloric acid, which is a by-product and waste of many chemical and other industries, or table salt mined in salt deposits, is a rather energy-intensive process, environmentally harmful and very dangerous to life and health.
At present, the problem of developing a technology for the production of chlorine, which would eliminate all the above disadvantages, and also have a high yield of chlorine, is very urgent.
.General information on chlorine
Chlorine was obtained for the first time in 1774 by K. Scheele by the interaction of hydrochloric acid with pyrolusite MnO2. However, only in 1810, G. Davy established that chlorine is an element and named it chlorine (from the Greek chloros - yellow-green). In 1813, J. L. Gay-Lussac proposed the name "Chlorine" for this element.
Chlorine is an element of group VII periodic system elements of D. I. Mendeleev. Molecular weight 70.906, atomic weight 35.453, atomic number 17, belongs to the halogen family. Under normal conditions, free chlorine, consisting of diatomic molecules, is a greenish-yellow non-flammable gas with a characteristic pungent and irritating odor. It is poisonous and causes suffocation. Compressed chlorine gas at atmospheric pressure turns into an amber liquid at -34.05 ° C, solidifies at -101.6 ° C and a pressure of 1 atm. Typically chlorine is a mixture of 75.53% 35Cl and 24.47% 37Cl. Under normal conditions, the density of chlorine gas is 3.214 kg/m3, which is about 2.5 times heavier than air.
Chemically, chlorine is very active, it combines directly with almost all metals (with some only in the presence of moisture or when heated) and with non-metals (except carbon, nitrogen, oxygen, inert gases), forming the corresponding chlorides, reacts with many compounds, replaces hydrogen in saturated hydrocarbons and joins unsaturated compounds. This is due to the wide variety of its application. Chlorine displaces bromine and iodine from their compounds with hydrogen and metals. Alkali metals in the presence of traces of moisture interact with chlorine with ignition, most metals react with dry chlorine only when heated. Steel, as well as some metals, is resistant to dry chlorine at low temperatures, so they are used for the manufacture of equipment and storage for dry chlorine. Phosphorus ignites in an atmosphere of chlorine, forming РCl3, and upon further chlorination - РCl5. Sulfur with chlorine, when heated, gives S2Cl2, SCl2 and other SnClm. Arsenic, antimony, bismuth, strontium, tellurium interact vigorously with chlorine. A mixture of chlorine and hydrogen burns with a colorless or yellow-green flame to form hydrogen chloride (this is a chain reaction). The maximum temperature of the hydrogen-chlorine flame is 2200°C. Mixtures of chlorine with hydrogen, containing from 5.8 to 88.5% H2, are explosive and can explode from the action of light, an electric spark, heating, from the presence of certain substances, such as iron oxides.
With oxygen, chlorine forms oxides: Cl2O, ClO2, Cl2O6, Cl2O7, Cl2O8, as well as hypochlorites (salts of hypochlorous acid), chlorites, chlorates and perchlorates. All oxygen compounds of chlorine form explosive mixtures with easily oxidized substances. Chlorine oxides are unstable and can explode spontaneously, hypochlorites decompose slowly during storage, chlorates and perchlorates can explode under the influence of initiators. Chlorine in water is hydrolyzed, forming hypochlorous and hydrochloric acids: Cl2 + H2O? HClO + HCl. The resulting yellowish solution is often referred to as chlorine water. When chlorinating aqueous solutions of alkalis in the cold, hypochlorites and chlorides are formed: 2NaOH + Cl2 \u003d NaClO + NaCl + H2O, and when heated - chlorates. By chlorination of dry calcium hydroxide, bleach is obtained. When ammonia reacts with chlorine, nitrogen trichloride is formed. During chlorination of organic compounds, chlorine either replaces hydrogen or adds via multiple bonds, forming various chlorine-containing organic compounds. Chlorine forms interhalogen compounds with other halogens. Chlorine fluorides ClF, ClF3, ClF3 are very reactive; for example, in a ClF3 atmosphere, glass wool ignites spontaneously. Chlorine compounds with oxygen and fluorine are known - chlorine oxyfluorides: ClO3F, ClO2F3, ClOF, ClOF3 and fluorine perchlorate FClO4.
Chlorine occurs in nature only in the form of compounds. Its average content in the earth's crust is 1.7 10-2% by weight. Water migration plays a major role in the history of chlorine in the earth's crust. In the form of the Cl- ion, it is found in the World Ocean (1.93%), underground brines and salt lakes. The number of own minerals (mainly natural chlorides) is 97, the main one being halite NaCl (Rock salt). There are also large deposits of potassium and magnesium chlorides and mixed chlorides: sylvin KCl, sylvinite (Na,K)Cl, carnalite KCl MgCl2 6H2O, kainite KCl MgSO4 3H2O, bischofite MgCl2 6H2O. In the history of the Earth, the supply of HCl contained in volcanic gases to the upper parts of the earth's crust was of great importance.
Chlorine quality standards
Index name GOST 6718-93High gradeFirst gradeVolume fraction of chlorine, not less than, %99.899.6Mass fraction of water, not more than, %0.010.04Mass fraction of nitrogen trichloride, not more than, %0.0020.004Mass fraction of non-volatile residue, not more,%0 .0150.10
Storage and transportation of chlorine
Chlorine produced by various methods is stored in special "tanks" or pumped into steel cylindrical (volume 10-250 m3) and spherical (volume 600-2000 m3) cylinders under pressure of own vapors of 18 kgf/cm2. The maximum storage volumes are 150 tons. Cylinders with liquid chlorine under pressure have a special color - protective color. In the event of a depressurization of a chlorine cylinder, a sharp release of gas occurs with a concentration several times higher than the lethal one. It should be noted that chlorine cylinders tend to accumulate highly explosive nitrogen trichloride over long periods of time and therefore chlorine cylinders must be routinely flushed and purged of nitrogen chloride from time to time. Chlorine is transported in containers, railway tanks, cylinders, which are its temporary storage.
2.Application of chlorine
Chlorine is consumed primarily by the chemical industry for the production of various organic chlorine derivatives used to obtain plastics, synthetic rubbers, chemical fibers, solvents, insecticides, etc. Currently, over 60% of the world's chlorine production is used for organic synthesis. In addition, chlorine is used to produce hydrochloric acid, bleach, chlorates and other products. Significant amounts of chlorine are used in metallurgy for chlorination during the processing of polymetallic ores, the extraction of gold from ores, and it is also used in the oil refining industry, agriculture, medicine and sanitation, for the neutralization of drinking and waste water, in pyrotechnics and a number of other areas of the national economy . As a result of the development of chlorine uses, mainly due to the success of organic synthesis, the world production of chlorine is more than 20 million tons / year.
The main examples of the application and use of chlorine in various branches of science, industry and household needs:
1.in the production of polyvinyl chloride, plastic compounds, synthetic rubber, from which they are made: insulation for wires, window profile, packaging materials, clothing and footwear, linoleum and gramophone records, varnishes, equipment and foam plastics, toys, instrument parts, Construction Materials. Polyvinyl chloride is produced by the polymerization of vinyl chloride, which today is most commonly prepared from ethylene in a chlorine-balanced process through an intermediate 1,2-dichloroethane.
CH2=CH2+Cl2=>CH2Cl-CH2ClCl-CH2Cl=> CH2=CHCl+HCl
1)as a bleaching agent (although not chlorine itself “bleaches”, but atomic oxygen, which is formed during the decomposition of hypochlorous acid according to the reaction: Cl2 + H2O ? HCl + HClO ? 2HCl + O*).
2)in the production of organochlorine insecticides - substances that kill insects harmful to crops, but are safe for plants (aldrin, DDT, hexachloran). One of the most important insecticides is hexachlorocyclohexane (C6H6Cl6).
)used as a chemical warfare agent, as well as for the production of other chemical warfare agents: mustard gas (C4H8Cl2S), phosgene (CCl2O).
)for water disinfection - "chlorination". The most common method of drinking water disinfection is based on the ability of free chlorine and its compounds to inhibit the enzyme systems of microorganisms that catalyze redox processes. For the disinfection of drinking water, chlorine (Cl2), chlorine dioxide (ClO2), chloramine (NH2Cl) and bleach (Ca(Cl)OCl) are used.
)registered in the food industry as food additive E925.
)in the chemical production of caustic soda (NaOH) (used in the production of rayon, in the soap industry), hydrochloric acid (HCl), bleach, chlorine chloride (KClO3), metal chlorides, poisons, drugs, fertilizers.
)in metallurgy for the production of pure metals: titanium, tin, tantalum, niobium.
TiO2 + 2C + 2Cl2 => TiCl4 + 2CO;
TiCl4 + 2Mg => 2MgCl2 + Ti (at Т=850°С)
)as an indicator of solar neutrinos in chlorine-argon detectors (The idea of a "chlorine detector" for detecting solar neutrinos was proposed by the famous Soviet physicist Academician B. Pontecorvo and implemented by the American physicist R. Davis and his colleagues. Having caught the neutrino nucleus of the chlorine isotope with an atomic weight of 37, turns into a nucleus of the argon-37 isotope, with the formation of one electron that can be registered.).
Many developed countries are striving to limit the use of chlorine in everyday life, including because the burning of chlorine-containing garbage produces a significant amount of dioxins (global ecotoxicants with powerful mutagenic
3. Chemical methods for producing chlorine
Previously, the production of chlorine by chemical means according to the methods of Weldon and Deacon was widespread. In these processes, chlorine was produced by the oxidation of hydrogen chloride formed as a by-product in the production of sodium sulfate from sodium chloride by the action of sulfuric acid.
the reaction proceeding when using the Weldon method:
4HCl + MnO2 => MnCl2 + 2H2O + Cl2
the reaction proceeding when using the Deacon method:
HCl + O2 => 2H2O + 2Cl2
In the Deacon process, copper chloride was used as a catalyst, a 50% solution of which (sometimes with the addition of NaCl) was impregnated into a porous ceramic support. The optimum reaction temperature on such a catalyst was usually in the range of 430490°. This catalyst is easily poisoned by arsenic compounds, with which it forms inactive copper arsenate, as well as by sulfur dioxide and trioxide. The presence of even small amounts of sulfuric acid vapor in the gas causes a sharp decrease in the yield of chlorine as a result of successive reactions:
H2SO4 => SO2 + 1/2O2 + H2O+ С12 + 2Н2O => 2НCl + H2SO4
С12 + Н2O => 1/2O2 + 2НCl
Thus, sulfuric acid is a catalyst that promotes the reverse conversion of Cl2 to HCl. Therefore, before oxidation on a copper catalyst, hydrochloric gas must be thoroughly purified from impurities that reduce the yield of chlorine.
Deacon's installation consisted of a gas heater, a gas filter, and a contact apparatus of a steel cylindrical casing, inside of which there were two concentrically arranged ceramic cylinders with holes; the annular space between them is filled with a catalyst. Hydrogen chloride was oxidized with air, so chlorine was diluted. A mixture containing 25 vol.% HCl and 75 vol.% air (~16% O2) was fed into the contact apparatus, and the gas leaving the apparatus contained about 8% C12, 9% HCl, 8% water vapor and 75% air . Such a gas, after washing out of it with HCl and drying with sulfuric acid, was usually used to obtain bleach.
Restoration of the Deacon process is currently based on the oxidation of hydrogen chloride not with air, but with oxygen, which makes it possible to obtain concentrated chlorine using highly active catalysts. The resulting chloro-oxygen mixture is washed from the residuals of HC1 successively with 36% and 20% hydrochloric acid and dried with sulfuric acid. The chlorine is then liquefied and oxygen is returned to the process. The separation of chlorine from oxygen is also carried out by absorbing chlorine under a pressure of 8 atm with sulfur chloride, which is then regenerated to obtain 100% chlorine:
Сl2 + S2CI2
Low-temperature catalysts are used, for example, copper dichloride activated with salts of rare earth metals, which makes it possible to carry out the process even at 100°C and, therefore, to sharply increase the degree of conversion of HCl to Cl2. On a chromium oxide catalyst, the combustion of HCl in oxygen is carried out at 340480°C. The use of a catalyst from a mixture of V2O5 with alkali metal pyrosulfates and activators on silica gel is described. The mechanism and kinetics of this process have been studied and the optimal conditions for its implementation, in particular, in a fluidized bed, have been established.
The oxidation of hydrogen chloride with oxygen is also carried out using a molten mixture of FeCl3 + KCl in two stages, carried out in separate reactors. In the first reactor, ferric chloride is oxidized to form chlorine:
2FeCl3 + 1
In the second reactor, ferric chloride is regenerated from iron oxide with hydrogen chloride:
O3 + 6HCI = 2FeCl3 + 3H20
To reduce the vapor pressure of ferric chloride, potassium chloride is added. This process is also proposed to be carried out in one apparatus, in which the contact mass, consisting of Fe2O3, KC1 and copper, cobalt or nickel chloride deposited on an inert carrier, moves from top to bottom of the apparatus. At the top of the apparatus, it passes a hot zone of chlorination, where Fe2Oz is converted into FeCl3, interacting with HCl, which is in the flow of gas going from bottom to top. Then the contact mass descends into the cooling zone, where elemental chlorine is formed under the action of oxygen, and FeCl3 passes into Fe2O3. The oxidized contact mass returns to the chlorination zone again.
A similar indirect oxidation of HCl to Cl2 is carried out according to the scheme:
2HC1 + MgO = MgCl2 + H2O
It is proposed to simultaneously obtain chlorine and sulfuric acid by passing a gas containing HCl, O2 and a large excess of SO2 through a vanadium catalyst at 400-600°C. Then H2SO4 and HSO3Cl are condensed from the gas and SO3 is absorbed by sulfuric acid; chlorine remains in the gas phase. HSO3Cl is hydrolyzed and the released HC1 is returned to the process.
Even more efficient oxidation is carried out by such oxidizing agents as PbO2, KMnO4, KClO3, K2Cr2O7:
2KMnO4 + 16HCl => 2KCl + 2MnCl2 + 5Cl2^ +8H2O
Chlorine can also be obtained by the oxidation of chlorides. For example, when NaCl and SO3 interact, reactions occur:
NaCl + 2SO3 = 2NaSO3Cl
NaSO3Cl = Cl2 + SO2 + Na2SO4
The decomposition of NaSO3Cl occurs at 275°C. A mixture of SO2 and C12 gases can be separated by absorbing chlorine SO2Cl2 or CCl4 or subjecting it to rectification, which results in an azeotropic mixture containing 88 mol. % Cl2 and 12 mol. %SO2. The azeotropic mixture can be further separated by converting SO2 to SO2C12 and separating excess chlorine, and decomposing SO2Cl2 at 200° into SO2 and Cl2, which are added to the mixture sent for rectification.
Chlorine can be obtained by oxidizing chloride or hydrogen chloride with nitric acid, as well as nitrogen dioxide:
ZHCl + HNO3 => Сl2 + NOCl + 2Н2O
Another way to obtain chlorine is the decomposition of nitrosyl chloride, which can be achieved by its oxidation:
NOCl + O2 = 2NO2 + Сl2
Also, to obtain chlorine, it is proposed, for example, to oxidize NOCl with 75% nitric acid:
2NOCl + 4HNO3 = Сl2 + 6NO2 + 2Н2O
A mixture of chlorine and nitrogen dioxide is separated by converting NO2 into weak nitric acid, which is then used to oxidize HCl in the first stage of the process to form Cl2 and NOCl. The main difficulty in the implementation of this process on an industrial scale is the elimination of corrosion. Ceramics, glass, lead, nickel, and plastics are used as materials for equipment. According to this method in the USA in 1952-1953. the plant was operating with a capacity of 75 tons of chlorine per day.
A cyclic method has been developed for the production of chlorine by the oxidation of hydrogen chloride with nitric acid without the formation of nitrosyl chloride according to the reaction:
2НCl + 2HNO3 = Сl2 + 2NO2 + 2Н2O
The process takes place in the liquid phase at 80°C, the chlorine yield reaches 100%, NO2 is obtained in liquid form.
Subsequently, these methods were completely replaced by electrochemical ones, but at present chemical methods chlorine production is being revived on a new technical basis. All of them are based on the direct or indirect oxidation of HCl (or chlorides), with the most common oxidizing agent being atmospheric oxygen.
Electrolysis. The concept and essence of the process
Electrolysis is a set of electrochemical redox processes that occur on electrodes during the passage of a constant electric current through a melt or solution with electrodes immersed in it.
Rice. 4.1. Processes occurring during electrolysis. Scheme of the electrolysis bath: 1 - bath, 2 - electrolyte, 3 - anode, 4 - cathode, 5 - power supply
Electrodes can be any materials that conduct electricity. Metals and alloys are mainly used, from non-metals, for example, graphite rods (or carbon) can serve as electrodes. Less commonly, liquids are used as an electrode. A positively charged electrode is an anode. The negatively charged electrode is the cathode. During electrolysis, the anode is oxidized (it dissolves) and the cathode is reduced. That is why the anode should be taken in such a way that its dissolution does not affect the chemical process occurring in the solution or melt. Such an anode is called an inert electrode. As an inert anode, you can take graphite (carbon) or platinum. As a cathode, you can take a metal plate (it will not dissolve). Suitable copper, brass, carbon (or graphite), zinc, iron, aluminum, stainless steel.
Examples of electrolysis of melts:
Examples of electrolysis of salt solutions:
(Cl? anions are oxidized at the anode, and not oxygen O? II of water molecules, since the electronegativity of chlorine is less than that of oxygen, and therefore, chlorine gives off electrons more easily than oxygen)
The electrolysis of water is always carried out in the presence of an inert electrolyte (to increase the electrical conductivity of a very weak electrolyte - water):
Depending on the inert electrolyte, electrolysis is carried out in a neutral, acidic or alkaline environment. When choosing an inert electrolyte, it is necessary to take into account that metal cations that are typical reducing agents (for example, Li +, Cs +, K +, Ca2 +, Na +, Mg2 +, Al3 +) are never reduced at the cathode in an aqueous solution and oxygen O? II of oxo acid anions is never oxidized at the anode with an element in the highest oxidation state (for example, ClO4?, SO42?, NO3?, PO43?, CO32?, SiO44?, MnO4?), water is oxidized instead.
Electrolysis includes two processes: the migration of reacting particles under the action of an electric field to the surface of the electrode and the transfer of charge from a particle to an electrode or from an electrode to a particle. The migration of ions is determined by their mobility and transfer numbers. The process of transfer of several electric charges is carried out, as a rule, in the form of a sequence of one-electron reactions, that is, in stages, with the formation of intermediate particles (ions or radicals), which sometimes exist for some time on the electrode in an adsorbed state.
The rates of electrode reactions depend on:
electrolyte composition
electrolyte concentration
electrode material
electrode potential
temperature
hydrodynamic conditions.
The measure of the reaction rate is the current density. This is a vector physical, the modulus of which is determined by the ratio of the current strength (the number of transferred electric charges per unit time) in the conductor to the cross-sectional area.
Faraday's laws of electrolysis are quantitative relationships based on electrochemical studies and help determine the mass of products formed during electrolysis. In the most general view laws are formulated as follows:
)Faraday's first law of electrolysis: The mass of a substance deposited on an electrode during electrolysis is directly proportional to the amount of electricity transferred to that electrode. The amount of electricity refers to the electric charge, usually measured in coulombs.
2)Faraday's Second Law of Electrolysis: For a given amount of electricity (electric charge), the mass of a chemical element deposited on an electrode is directly proportional to the equivalent mass of the element. The equivalent mass of a substance is its molar mass divided by an integer, depending on the chemical reaction in which the substance participates.
In mathematical form, Faraday's laws can be represented as follows:
where m is the mass of the substance deposited on the electrode in grams, is the total electric charge that has passed through the substance, = 96 485.33 (83) C mol? 1 is the Faraday constant, is the molar mass of the substance (For example, the molar mass of water H2O = 18 g / mol), - the valence number of ions of a substance (the number of electrons per ion).
Note that M/z is the equivalent mass of the deposited matter.
For Faraday's first law, M, F, and z are constants, so the larger the Q value, the larger the m value.
For Faraday's second law, Q, F, and z are constants, so the larger the value of M/z (equivalent mass), the greater the value of m.
In the simplest case direct current electrolysis leads to:
In a more complex case of alternating electric current, the total charge Q of the current I( ?) is summed over time ? :
where t is the total electrolysis time.
In industry, the electrolysis process is carried out in special devices - electrolyzers.
Industrial production of chlorine
Currently, chlorine is mainly produced by electrolysis of aqueous solutions, namely one of
The raw materials for the electrolytic production of chlorine are mainly NaCl solutions obtained by dissolving solid salt, or natural brines. There are three types of salt deposits: fossil salt (about 99% of the reserves); salt lakes with bottom sediments of self-saddle salt (0.77%); the rest is underground splits. Salt solutions, regardless of the way they are obtained, contain impurities that worsen the electrolysis process. Calcium cations Ca2+, Mg2+ and SO42- anions have a particularly unfavorable effect during electrolysis with a solid cathode, and impurities of compounds containing heavy metals, such as chromium, vanadium, germanium and molybdenum, have an effect during electrolysis with a liquid cathode.
Crystalline salt for chlorine electrolysis should have the following composition (%): sodium chloride not less than 97.5; Mg2+ not more than 0.05; insoluble sediment not more than 0.5; Ca2+ not more than 0.4; K+ not more than 0.02; SO42 - no more than 0.84; humidity not more than 5; admixture heavy metals(determined by amalgam test cm3 H2) no more than 0.3. Cleaning of brines is carried out with a solution of soda (Na2CO3) and milk of lime (suspension of a suspension of Ca (OH) 2 in water). In addition to chemical purification, solutions are freed from mechanical impurities by sedimentation and filtration.
Electrolysis of common salt solutions is carried out in baths with a solid iron (or steel) cathode and with diaphragms and membranes, in baths with a liquid mercury cathode. Industrial electrolyzers used for the equipment of modern large chlorine plants must have high productivity, simple design, be compact, operate reliably and stably.
Electrolysis proceeds according to the scheme:
MeCl + H2O => MeOH + Cl2 + H2,
where Me is an alkali metal.
During the electrochemical decomposition of table salt in electrolyzers with solid electrodes, the following main, reversible and irreversible ionic reactions occur:
dissociation of salt and water molecules (goes in the electrolyte)
NaCl-Na++Cl-
Chlorine ion oxidation (at the anode)
C1- - 2e- => C12
reduction of hydrogen ion and water molecules (at the cathode)
H+ - 2e- => H2
H2O - 2e - \u003d\u003e H2 + 2OH-
Association of ions into a sodium hydroxide molecule (in electrolyte)
Na+ + OH- - NaOH
Useful products are sodium hydroxide, chlorine and hydrogen. All of them are removed from the electrolyzer separately.
Rice. 5.1. Scheme of a diaphragm electrolyzer
The cavity of the cell with a solid cathode (Fig. 3) is divided by a porous
The first industrial electrolyzers operated in batch mode. The electrolysis products in them were separated by a cement diaphragm. Subsequently, electrolyzers were created, in which bell-shaped partitions served to separate the electrolysis products. At the next stage, electrolyzers with a flow diaphragm appeared. In them, the principle of counterflow was combined with the use of a separating diaphragm, which was made from asbestos cardboard. Further, a method was discovered for obtaining a diaphragm from asbestos pulp, borrowed from the technology of the paper industry. This method made it possible to develop designs of electrolyzers for a large current load with a non-separable compact finger cathode. To increase the service life of an asbestos diaphragm, it is proposed to introduce some synthetic materials into its composition as a coating or bond. It has also been suggested that diaphragms be entirely manufactured from new synthetic materials. There is evidence that such combined asbestos-synthetic or specially manufactured synthetic diaphragms have a service life of up to 500 days. Special ion-exchange diaphragms are also being developed, which make it possible to obtain pure caustic soda with a very low content of sodium chloride. The action of such diaphragms is based on the use of their selective properties for the passage of various ions.
The places of contacts of current leads to graphite anodes in early designs were taken out of the cell cavity. Later, methods were developed to protect the contact parts of the anodes immersed in the electrolyte. With the use of these techniques industrial electrolyzers with a lower current supply were created, in which the anode contacts are located in the cavity of the electrolyzer. They are used everywhere at the present time for the production of chlorine and caustic on a solid cathode.
A stream of saturated sodium chloride solution (purified brine) continuously enters the anode space of the diaphragm cell. As a result of the electrochemical process, chlorine is released at the anode due to the decomposition of common salt, and hydrogen is released at the cathode due to the decomposition of water. Chlorine and hydrogen are removed from the electrolyzer, without mixing, separately. In this case, the near-cathode zone is enriched with sodium hydroxide. The solution from the cathode zone, called electrolytic liquor, containing undecomposed table salt (approximately half of the amount supplied with brine) and sodium hydroxide, is continuously removed from the electrolyzer. At the next stage, the electrolytic liquor is evaporated and the content of NaOH in it is adjusted to 42-50% in accordance with the standard. Table salt and sodium sulfate precipitate with increasing concentration of sodium hydroxide.
The NaOH solution is decanted from the crystals and transferred as a finished product to a warehouse or caustic smelting stage to obtain a solid product. Crystalline table salt (reverse salt) is returned to electrolysis, preparing from it the so-called reverse brine. From it, in order to avoid the accumulation of sulfate in solutions, sulfate is extracted before preparing the return brine. The loss of table salt is compensated by the addition of fresh brine obtained by underground leaching of salt layers or by dissolving solid table salt. Before mixing it with the reverse brine, fresh brine is cleaned of mechanical suspensions and a significant part of calcium and magnesium ions. The resulting chlorine is separated from water vapor, compressed and transferred either directly to consumers or to liquefy chlorine. Hydrogen is separated from water, compressed and transferred to consumers.
The same chemical reactions take place in a membrane electrolyzer as in a diaphragm electrolyzer. Instead of a porous diaphragm, a cationic membrane is used (Fig. 5).
Rice. 5.2. Scheme of a membrane electrolyzer
The membrane prevents the penetration of chlorine ions into the catholyte (electrolyte in the cathode space), due to which caustic soda can be obtained directly in the electrolyzer almost without salt, with a concentration of 30 to 35%. Because there is no need to separate the salt, evaporation makes it much easier to produce 50% commercial caustic soda at a lower investment and energy cost. Since the concentration of caustic soda in the membrane process is much higher, expensive nickel is used as a cathode.
Rice. 5.3. Scheme of a mercury electrolyzer
The total decomposition reaction of common salt in mercury electrolyzers is the same as in diaphragm cells:
NaCl + H2O => NaOH + 1/2Cl2 + 1/2H2
However, here it takes place in two stages, each in a separate apparatus: an electrolyzer and a decomposer. They are structurally interconnected and are called an electrolytic bath, and sometimes a mercury electrolyzer.
At the first stage of the process - in the electrolyzer - the electrolytic decomposition of table salt takes place (its saturated solution is fed into the electrolyzer) with the production of chlorine at the anode, and sodium amalgam at the mercury cathode, according to the following reaction:
NaCl + nHg => l/2Cl2 + NaHgn
In the decomposer, the second stage of the process takes place, in which, under the action of water, sodium amalgam passes into sodium hydroxide and mercury:
NaHgn + H2O => NaOH + 1/2H2 + nHg
Of all the salt supplied to the electrolyzer with brine, only 15-20% of the supplied amount enters into reaction (2), and the rest of the salt, together with water, leaves the electrolyzer in the form of a chloranolyte - a solution of table salt in water containing 250-270 kg / m3 NaCl saturated with chlorine. The “strong amalgam” leaving the electrolyzer and water are supplied to the decomposer.
The electrolyser in all available designs is made in the form of a long and relatively narrow, slightly inclined steel trough, along the bottom of which a thin layer of amalgam, which is the cathode, flows by gravity, and anolyte on top. Brine and weak amalgam are fed from the upper raised edge of the cell through the "inlet pocket".
The strong amalgam flows out from the lower end of the cell through the "outlet pocket". Chlorine and chloranolyte jointly exit through a branch pipe, also located at the lower end of the cell. Anodes are suspended above the entire amalgam flow mirror or cathode at a distance of 3–5 mm from the cathode. The top of the cell is covered with a lid.
Two types of decomposers are common: horizontal and vertical. The former are made in the form of a steel inclined chute of the same length as the electrolytic cell. An amalgam stream flows along the bottom of the decomposer, which is installed at a slight inclination. A decomposer made of graphite is immersed in this flow. Water moves in the opposite direction. As a result of the decomposition of the amalgam, the water is saturated with caustic. The caustic solution, together with hydrogen, exits the decomposer through a branch pipe in the bottom, and the poor amalgam or mercury is pumped into the cell pocket.
In addition to the electrolyzer, decomposer, pockets and overflow pipelines, the set of the electrolysis bath includes a mercury pump. Two types of pumps are used. In cases where the baths are equipped with a vertical decomposer or where the decomposer is installed below the electrolytic cell, submersible centrifugal pumps of the conventional type are used, lowered into the decomposer. In baths where the decomposer is installed next to the electrolyser, the amalgam is pumped over by a cone rotary pump of the original type.
All steel parts of the electrolyzer that come into contact with chlorine or chloranolyte are protected by a coating of special grade vulcanized rubber (gumming). The protective layer of rubber is not absolutely resistant. Over time, it chlorinates, becomes brittle and cracks from the action of temperature. Periodically, the protective layer is renewed. All other parts of the electrolysis bath: decomposer, pump, overflows - are made of unprotected steel, since neither hydrogen nor a caustic solution corrode it.
Currently, graphite anodes are the most common in a mercury cell. However, they are being replaced by ORTA.
6.Safety in chlorine production
and environmental protection
The danger to personnel in the production of chlorine is determined by the high toxicity of chlorine and mercury, the possibility of the formation of explosive gas mixtures of chlorine and hydrogen, hydrogen and air in the equipment, as well as solutions of nitrogen trichloride in liquid chlorine, the use in the production of electrolyzers - devices that are under an increased electrical potential relative to earth, the properties of caustic alkali produced in this production.
Inhalation of air containing 0.1 mg/l of chlorine for 30-60 minutes is life threatening. Inhalation of air containing more than 0.001 mg/l of chlorine irritates the respiratory tract. Maximum allowable concentration (MAC) of chlorine in the air of settlements: average daily 0.03 mg/m3, maximum single 0.1 mg/m3, in air working area industrial premises is 1 mg/m3, the odor perception threshold is 2 mg/m3. At a concentration of 3-6 mg/m3, a distinct smell is felt, irritation (redness) of the eyes and mucous membranes of the nose occurs, at 15 mg/m3 - irritation of the nasopharynx, at 90 mg/m3 - intense coughing attacks. Exposure to 120 - 180 mg/m3 for 30-60 minutes is life-threatening, at 300 mg/m3 a lethal outcome is possible, a concentration of 2500 mg/m3 leads to death within 5 minutes, at a concentration of 3000 mg/m3 a lethal outcome occurs after several breaths . The maximum allowable concentration of chlorine for filtering industrial and civil gas masks is 2500 mg/m3.
The presence of chlorine in the air is determined by chemical reconnaissance devices: VPKhR, PPKhR, PKhR-MV using indicator tubes IT-44 (pink color, sensitivity threshold 5 mg / m3), IT-45 (orange color), aspirators AM-5, AM- 0055, AM-0059, NP-3M with indicator tubes for chlorine, universal gas analyzer UG-2 with a measurement range of 0-80 mg/m3, gas detector "Kolion-701" in the range of 0-20 mg/m3. In open space - with SIP "KORSAR-X" devices. Indoors - with SIP "VEGA-M" devices. To protect against chlorine in case of malfunctions or emergencies, all people in the workshops must have and use gas masks of grades “V” or “BKF” in a timely manner (except for mercury electrolysis workshops), as well as protective clothing: cloth or rubberized suits, rubber boots and mittens. Gas mask boxes against chlorine must be painted yellow.
Mercury is more poisonous than chlorine. The maximum permissible concentration of its vapors in the air is 0.00001 mg/l. It affects the human body when inhaled and when it comes into contact with the skin, as well as in contact with amalgamated objects. Its vapors and splashes are adsorbed (absorbed) by clothes, skin, teeth. At the same time, mercury easily evaporates at a temperature; available in the electrolysis shop, and the concentration of its vapors in the air is much higher than the maximum allowable. Therefore, electrolysis shops with a liquid cathode are equipped with powerful ventilation, which during normal operation ensures an acceptable level of mercury vapor concentration in the shop atmosphere. However, this is not enough for safe operation. It is also necessary to observe the so-called mercury discipline: follow the rules for handling mercury. Following them, the personnel, before starting work, passes through the sanitary inspection room, in the clean section of which they leave home clothes and puts on freshly laundered linen, which is overalls. At the end of the shift, overalls and dirty linen are left in the dirty section of the sanitary checkpoint, while the workers take a shower, brush their teeth and put on household items in the clean section of the sanitary checkpoint.
In workshops that work with chlorine and mercury, you should use a gas mask of brand "G" (the gas mask box is painted black and yellow colors) and rubber gloves., The rules of "mercury discipline" stipulate that work with mercury and amalgamated surfaces should be carried out only under a layer of water; spilled mercury should immediately be flushed down the drain, where there are mercury traps.
Emissions of chlorine and mercury vapor into the atmosphere, discharges into wastewater mercury salts and mercury droplets, compounds containing active chlorine, and soil poisoning with mercury sludge. Chlorine enters the atmosphere during accidents, with ventilation emissions and exhaust gases from various devices. Mercury vapor is carried out with air from ventilation systems. The norm of chlorine content in the air when released into the atmosphere is 0.03 mg/m3. This concentration can be achieved if an alkaline multi-stage off-gas washing is used. The norm of mercury content in the air when emitted into the atmosphere is 0.0003 mg/m3, and in wastewater when discharged into water bodies is 4 mg/m3.
Neutralize chlorine with the following solutions:
milk of lime, for which 1 weight part of slaked lime is poured into 3 parts of water, mixed thoroughly, then the lime mortar is drained from above (for example, 10 kg of slaked lime + 30 liters of water);
5% aqueous solution of soda ash, for which 2 weight parts of soda ash are dissolved with stirring with 18 parts of water (for example, 5 kg of soda ash + 95 liters of water);
5% aqueous solution of caustic soda, for which 2 parts by weight of caustic soda are dissolved with stirring with 18 parts of water (for example, 5 kg of caustic soda + 95 liters of water).
When chlorine gas leaks, water is sprayed to extinguish the vapors. The rate of water consumption is not standardized.
When liquid chlorine is spilled, the spill site is fenced with an earthen rampart, filled with milk of lime, a solution of soda ash, caustic soda, or water. To neutralize 1 ton of liquid chlorine, 0.6-0.9 tons of water or 0.5-0.8 tons of solutions are needed. To neutralize 1 ton of liquid chlorine, 22-25 tons of solutions or 333-500 tons of water are needed.
To spray water or solutions, watering and fire trucks, auto-bottling stations (AC, PM-130, ARS-14, ARS-15), as well as hydrants and special systems available at chemically hazardous facilities are used.
Conclusion
Since the volumes of chlorine produced by laboratory methods are negligible in comparison with the ever-increasing demand for this product, it is necessary to carry out comparative analysis doesn't make sense.
Of the electrochemical production methods, liquid (mercury) cathode electrolysis is the easiest and most convenient, but this method is not without drawbacks. It causes significant environmental damage through evaporation and leakage of metallic mercury and chlorine gas.
Electrolyzers with a solid cathode eliminate the risk of environmental pollution by mercury. When choosing between diaphragm and membrane electrolyzers for new production facilities, the latter are preferred as they are more economical and provide a higher quality end product.
Bibliography
1.Zaretsky S. A., Suchkov V. N., Zhivotinsky P. B. Electrochemical technology of inorganic substances and chemical current sources: A textbook for students of technical schools. M ..: Higher. School, 1980. 423 p.
2.Mazanko A. F., Kamaryan G. M., Romashin O. P. Industrial membrane electrolysis. M.: publishing house "Chemistry", 1989. 240 p.
.Pozin M.E. Technology of mineral salts (fertilizers, pesticides, industrial salts, oxides and acids), part 1, ed. 4th, rev. L., Publishing House "Chemistry", 1974. 792 p.
.Fioshin M. Ya., Pavlov VN Electrolysis in inorganic chemistry. M.: publishing house "Nauka", 1976. 106 p.
.Yakimenko L. M. Production of chlorine, caustic soda and inorganic chlorine products. M.: publishing house "Chemistry", 1974. 600 p.
Internet sources
6.Safety rules for the production, storage, transportation and use of chlorine // URL: #"justify">7. Hazardous Substances // URL: #"justify">. Chlorine: application // URL: #"justify">.
Kuzbass State Technical University
BJD subject
Characterization of chlorine as an emergency chemically hazardous substance
Kemerovo-2009
Introduction
1. Characteristics of AHOV (according to the issued task)
2. Ways to prevent an accident, protection from hazardous chemicals
3. Task
4. Calculation of the chemical situation (according to the issued task)
Conclusion
Literature
Introduction
In total, 3,300 economic facilities operate in Russia, which have significant reserves of hazardous chemical substances. More than 35% of them have choir stocks.
Chlorine (lat. Chlorum), Cl - a chemical element of the VII group of the periodic system of Mendeleev, atomic number 17, atomic mass 35.453; belongs to the halogen family.
Chlorine is also used for chlorination some oto ryh ores with the purpose and attraction of titanium, niobium, zirconium and others.
poisoning chlorine are possible in the chemical, pulp and paper, textile, pharmaceutical industries. Chlorine irritates the mucous membranes of the eyes and respiratory tract. Secondary infection usually joins the primary inflammatory changes. Acute poisoning develops almost immediately. When inhaling medium and low concentrations of chlorine, chest tightness and pain, dry cough, rapid breathing, pain in the eyes, lacrimation, increased levels of leukocytes in the blood, body temperature, etc. are noted. Bronchopneumonia, toxic pulmonary edema, depression, convulsions are possible. . In mild cases, recovery occurs in 3-7 days. As long-term consequences, catarrhs of the upper respiratory tract, recurrent bronchitis, pneumosclerosis are observed; possible activation of pulmonary tuberculosis. With prolonged inhalation of small concentrations of chlorine, similar, but slowly developing forms of the disease are observed. Prevention of poisoning, sealing of production facilities, equipment, effective ventilation, if necessary, the use of a gas mask. The maximum permissible concentration of chlorine in the air of production, premises is 1 mg/m 3 . The production of chlorine, bleach and other chlorine-containing compounds refers to industries with harmful working conditions.
Element VII of the subgroup of the Periodic Table of D.I. Mendeleev. At the external level - 7 electrons, therefore, when interacting with reducing agents, chlorine shows its oxidizing properties, attracting a metal electron to itself.
Physical properties of chlorine.
Chlorine is a yellow gas. Has a pungent odor.
Chemical properties of chlorine.
Free chlorine very active. It reacts with all simple substances except oxygen, nitrogen and noble gases:
Si + 2 Cl 2 = SiCl 4 + Q.
When interacting with hydrogen at room temperature, there is practically no reaction, but as soon as illumination acts as an external influence, a chain reaction occurs, which has found its application in organic chemistry.
When heated, chlorine is able to displace iodine or bromine from their acids:
Cl 2 + 2 HBr = 2 HCl + Br 2 .
Chlorine reacts with water, partially dissolving in it. This mixture is called chlorine water.
Reacts with alkalis:
Cl 2 + 2NaOH \u003d NaCl + NaClO + H 2 O (cold),
Cl 2 + 6KOH = 5KCl + KClO 3 + 3 H 2 O (heat).
Getting chlorine.
1. Electrolysis of sodium chloride melt, which proceeds according to the following scheme:
2. Laboratory method for obtaining chlorine:
MnO 2 + 4HCl \u003d MnCl 2 + Cl 2 + 2H 2 O.
