Characteristics of elements of group VII of the main subgroup, using chlorine as an example
general characteristics subgroups
Table 1. Nomenclature of elements of subgroup VIIA
P-elements, typical, non-metals (astatine is a semi-metal), halogens.
Electron diagram of the element Hal (Hal ≠ F):
The elements of subgroup VIIA are characterized by the following valences:
Table 2. Valency
3. The elements of subgroup VIIA are characterized by the following oxidation states:
Table 3. Oxidation states of elements
Characteristics of a chemical element
Chlorine is an element of group VII A. Serial number 17
Relative atomic mass: 35.4527 a. e.m. (g/mol)
Number of protons, neutrons, electrons: 17,18,17
Atomic structure:
Electronic formula:
Typical oxidation states: -1, 0, +1, +3, +4, +5, +7
Ionization energy: 1254.9(13.01) kJ/mol (eV)
Electron affinity: 349 (kJ/mol)
Electronegativity according to Pauling: 3.20
Characteristics of a simple substance
Bond type: covalent non-polar
Diatomic molecule
Isotopes: 35 Cl (75.78%) and 37 Cl (24.22%)
Crystal lattice type: molecular
Thermodynamic parameters
Table 4
Physical properties
Table 5
An aqueous solution of chlorine is highly dismutated (“chlorine water”)
Stage 1: Cl 2 + H 2 O = HCl + HOCl
Stage 2: HOCl = HCl + [O] – atomic oxygen
The oxidizing capacity in the subgroup decreases from fluorine to iodine = ˃
Chlorine is a strong oxidizing agent:
1. Interaction with simple substances
a) with hydrogen:
Cl 2 + H 2 = 2HCl
b) with metals:
Cl 2 + 2Na = 2NaCl
3Cl 2 + 2Fe = 2FeCl 3
c) with some less electronegative nonmetals:
3Cl 2 + 2P = 2PCl 3
Cl 2 + S = SCl 2
With oxygen, carbon and nitrogen, chlorine directly does not react!
2. Interaction with complex substances
a) with water: see above
b) with acids: does not react!
c) with alkali solutions:
in the cold: Cl 2 +2 NaOH = NaCl + NaClO + H 2 O
when heated: 3Cl 2 + 6 KOH = 5KCl + KClO 3 + 3H 2 O
e) with many organic substances:
Cl 2 + CH 4 = CH 3 Cl + HCl
C 6 H 6 + Cl 2 = C 6 H 5 Cl + HCl
The most important chlorine compounds
Hydrogen chloride, hydrogen chloride(HCl) is a colorless, thermally stable gas (under normal conditions) with a pungent odor, fumes in moist air, easily dissolves in water (up to 500 volumes of gas per volume of water) to form hydrochloric (hydrochloric) acid. At −114.22 °C, HCl turns into a solid state. In the solid state, hydrogen chloride exists in the form of two crystalline modifications: orthorhombic, stable below, and cubic.
An aqueous solution of hydrogen chloride is called hydrochloric acid. When dissolved in water, the following processes occur:
HCl g + H 2 O l = H 3 O + l + Cl − l
The dissolution process is highly exothermic. With water, HCl forms an azeotropic mixture. It is a strong monoprotic acid. Interacts energetically with all metals in the voltage series to the left of hydrogen, with basic and amphoteric oxides, bases and salts, forming salts - chlorides:
Mg + 2 HCl → MgCl 2 + H 2
FeO + 2 HCl → FeCl 2 + H 2 O
When exposed to strong oxidizing agents or during electrolysis, hydrogen chloride exhibits reducing properties:
MnO 2 + 4 HCl → MnCl 2 + Cl 2 + 2 H 2 O
When heated, hydrogen chloride is oxidized by oxygen (catalyst - copper(II) chloride CuCl 2):
4 HCl + O 2 → 2 H 2 O +2 Cl 2
However, concentrated hydrochloric acid reacts with copper to form a monovalent copper complex:
2 Cu + 4 HCl → 2 H + H 2
A mixture of 3 parts by volume of concentrated hydrochloric acid and 1 part by volume of concentrated nitric acid is called “aqua regia”. Aqua regia can even dissolve gold and platinum. The high oxidative activity of aqua regia is due to the presence of nitrosyl chloride and chlorine in it, which are in equilibrium with the starting substances:
4 H 3 O + + 3 Cl − + NO 3 − = NOCl + Cl 2 + 6 H 2 O
Due to the high concentration of chloride ions in the solution, the metal binds into a chloride complex, which promotes its dissolution:
3 Pt + 4 HNO 3 + 18 HCl → 3 H 2 + 4 NO + 8 H 2 O
Hydrogen chloride is also characterized by addition reactions to multiple bonds (electrophilic addition):
R-CH=CH 2 + HCl → R-CHCl-CH 3
R-C≡CH + 2 HCl → R-CCl 2 -CH 3
Chlorine oxides- inorganic chemical compounds of chlorine and oxygen, with the general formula: Cl x O y.
Chlorine forms the following oxides: Cl 2 O, Cl 2 O 3, ClO 2, Cl 2 O 4, Cl 2 O 6, Cl 2 O 7. In addition, the following are known: the short-lived radical ClO, the chlorine peroxide radical ClOO and the chlorine tetroxide radical ClO 4 .
The table below shows the properties of stable chlorine oxides:
Table 6
| Property | Cl2O | ClO2 | ClOClO 3 | Cl 2 O 6 (l)↔2ClO 3 (g) | Cl2O7 |
| Color and condition at room. temperature | Yellow-brown gas | Yellow-green gas | Light yellow liquid | Dark red liquid | Colorless liquid |
| Chlorine oxidation state | (+1) | (+4) | (+1), (+7) | (+6) | (+7) |
| T. pl., °C | −120,6 | −59 | −117 | 3,5 | −91,5 |
| Boil temperature, °C | 2,0 | 44,5 | |||
| d(f, 0°C), g*cm -3 | - | 1,64 | 1,806 | - | 2,02 |
| ΔH° sample (gas, 298 K), kJ*mol -1 | 80,3 | 102,6 | ~180 | (155) | |
| ΔG° sample (gas, 298 K), kJ*mol -1 | 97,9 | 120,6 | - | - | - |
| S° sample (gas, 298 K), J*K -1 *mol -1 | 265,9 | 256,7 | 327,2 | - | - |
| Dipole moment μ, D | 0.78 ± 0.08 | 1.78 ± 0.01 | - | - | 0.72 ± 0.02 |
Chlorine oxide (I), Dichlor oxide, hypochlorous acid anhydride - a compound of chlorine in the oxidation state +1 with oxygen.
Under normal conditions, it is a brownish-yellow gas with a characteristic odor reminiscent of chlorine. At temperatures below 2 °C the liquid is golden-red in color. Poisonous: affects Airways. Spontaneously slowly decomposes:
Explosive at high concentrations. Density under normal conditions is 3.22 kg/m³. Dissolves in carbon tetrachloride. Soluble in water to form weak hypochlorous acid:
Reacts quickly with alkalis:
Cl 2 O + 2NaOH (dil.) = 2NaClO + H 2 O
Chlorine dioxide- acid oxide. When dissolved in water, chlorous and perchloric acids are formed (disproportionation reaction). Dilute solutions are stable in the dark and decompose slowly in the light:
Chlorine dioxide- chlorine oxide ( IV), a compound of chlorine and oxygen, formula: ClO 2.
Under normal conditions, ClO 2 is a reddish-yellow gas with a characteristic odor. At temperatures below 10 °C ClO 2 is a red-brown liquid. Low stability, explodes in light, on contact with oxidizing agents and when heated. Let's dissolve well in water. Due to its explosive hazard, chlorine dioxide cannot be stored as a liquid.
Acidic oxide. When dissolved in water, chlorous and perchloric acids are formed (disproportionation reaction). Dilute solutions are stable in the dark and decompose slowly in the light:
The resulting chlorous acid is very unstable and decomposes:
Exhibits redox properties.
2ClO 2 + 5H 2 SO 4 (diluted) + 10FeSO 4 = 5Fe 2 (SO 4) 3 + 2HCl + 4H 2 O
ClO 2 + 2NaOH cold. = NaClO 2 + NaClO 3 + H 2 O
ClO 2 + O 3 = ClO 3 + O 2
ClO 2 reacts with many organic compounds and acts as a medium-strength oxidizing agent.
Hypochlorous acid- HClO, a very weak monoprotic acid in which chlorine has an oxidation state of +1. Exists only in solutions.
In aqueous solutions, hypochlorous acid partially decomposes into a proton and the hypochlorite anion ClO − :
Unstable. Hypochlorous acid and its salts - hypochlorites- strong oxidizing agents. Reacts with hydrochloric acid HCl, forming molecular chlorine:
HClO + NaOH (diluted) = NaClO + H 2 O 
Chlorous acid- HClO 2, a monobasic acid of medium strength.
Chlorous acid HClO 2 in its free form is unstable; even in a dilute aqueous solution it quickly decomposes:
Neutralized by alkalis.
HClO 2 + NaOH (dil. cold) = NaClO 2 + H 2 O
The anhydride of this acid is unknown.
An acid solution is prepared from its salts - chlorites formed as a result of the interaction of ClO 2 with alkali:
Exhibits redox properties.
5HClO2 + 3H2SO4 (diluted) + 2KMnO4 = 5HClO3 + 2MnSO4 + K2SO4 + 3H2O
Chloric acid- HClO 3, a strong monobasic acid in which chlorine has an oxidation state of +5. Not received in free form; in aqueous solutions at concentrations below 30% in the cold it is quite stable; in more concentrated solutions it decomposes:
Hypochlorous acid is a strong oxidizing agent; oxidizing capacity increases with increasing concentration and temperature. HClO 3 is easily reduced to hydrochloric acid:
HClO 3 + 5HCl (conc.) = 3Cl 2 + 3H 2 O
HClO 3 + NaOH (diluted) = NaClO 3 + H 2 O
When a mixture of SO 2 and air is passed through a strongly acidic solution, chlorine dioxide is formed:
In 40% perchloric acid, filter paper, for example, ignites.
8. Being in nature:
In the earth's crust, chlorine is the most common halogen. Since chlorine is very active, it occurs in nature only in the form of compounds in minerals.
Table 7. Finding in nature
Table 7. Mineral forms
The largest reserves of chlorine are contained in the salts of the waters of the seas and oceans.
Receipt
Chemical methods for producing chlorine are ineffective and expensive. Today they have mainly historical significance. Can be obtained by reacting potassium permanganate with hydrochloric acid:
Scheele method
Initially, the industrial method for producing chlorine was based on the Scheele method, that is, the reaction of pyrolusite with hydrochloric acid:
Deacon Method
Method for producing chlorine by catalytic oxidation of hydrogen chloride with atmospheric oxygen.
Electrochemical methods
Today, chlorine is produced on an industrial scale together with sodium hydroxide and hydrogen by electrolysis of a solution of table salt, the main processes of which can be represented by the summary formula:
Application
· Window profile made from chlorine-containing polymers
· The main component of bleaches is Labarraco water (sodium hypochlorite)
· In the production of polyvinyl chloride, plastic compounds, synthetic rubber.
· Production of organochlorines. A significant portion of the chlorine produced is consumed to obtain plant protection products. One of the most important insecticides is hexachlorocyclohexane (often called hexachlorane).
· Used as a chemical warfare agent, as well as for the production of other chemical warfare agents: mustard gas, phosgene.
· For water disinfection - “chlorination”.
· Registered in the food industry as food additives E925.
· In the chemical production of hydrochloric acid, bleach, berthollet salt, metal chlorides, poisons, drugs, fertilizers.
· In metallurgy for the production of pure metals: titanium, tin, tantalum, niobium.
· As an indicator of solar neutrinos in chlorine-argon detectors.
Many developed countries are striving to limit the use of chlorine in everyday life, including because the combustion of chlorine-containing waste produces a significant amount of dioxins.
Chlorine was probably obtained by alchemists, but its discovery and first research is inextricably linked with the name of the famous Swedish chemist Carl Wilhelm Scheele. Scheele opened five chemical elements- barium and manganese (together with Johan Hahn), molybdenum, tungsten, chlorine, and independently of other chemists (albeit later) - three more: oxygen, hydrogen and nitrogen. This achievement could not be repeated by any chemist subsequently. At the same time, Scheele, already elected as a member of the Royal Swedish Academy of Sciences, was a simple pharmacist in Köping, although he could have taken a more honorable and prestigious position. Frederick II the Great himself, the Prussian king, offered him the post of professor of chemistry at the University of Berlin. Refusing such tempting offers, Scheele said: “I cannot eat more than I need, and what I earn here in Köping is enough for me to eat.”
Numerous chlorine compounds were known, of course, long before Scheele. This element is part of many salts, including the most famous - table salt. In 1774, Scheele isolated chlorine in free form by heating the black mineral pyrolusite with concentrated hydrochloric acid: MnO 2 + 4HCl ® Cl 2 + MnCl 2 + 2H 2 O.
At first, chemists considered chlorine not as an element, but as a chemical compound of the unknown element muria (from the Latin muria - brine) with oxygen. It was believed that hydrochloric acid (it was called muric acid) contains chemically bound oxygen. This was “testified”, in particular, by the following fact: when a chlorine solution stood in the light, oxygen was released from it, and hydrochloric acid remained in the solution. However, numerous attempts to “tear” oxygen from chlorine led nowhere. Thus, no one has been able to obtain carbon dioxide by heating chlorine with coal (which, at high temperatures, “takes away” oxygen from many compounds containing it). As a result of similar experiments carried out by Humphry Davy, Joseph Louis Gay-Lussac and Louis Jacques Thenard, it became clear that chlorine does not contain oxygen and is a simple substance. The experiments of Gay-Lussac, who analyzed the quantitative ratio of gases in the reaction of chlorine with hydrogen, led to the same conclusion.
In 1811, Davy proposed the name “chlorin” for the new element - from the Greek. "chloros" - yellow-green. This is exactly the color of chlorine. The same root is in the word “chlorophyll” (from the Greek “chloros” and “phyllon” - leaf). A year later, Gay-Lussac “shortened” the name to “chlorine.” But still the British (and Americans) call this element “chlorine”, while the French call it chlore. The Germans, the “legislators” of chemistry throughout almost the entire 19th century, also adopted the abbreviated name. (in German chlorine is Chlor). In 1811, the German physicist Johann Schweiger proposed the name “halogen” for chlorine (from the Greek “hals” - salt, and “gennao” - give birth). Subsequently, this term was assigned not only to chlorine, but also to all its analogues in the seventh group - fluorine, bromine, iodine, astatine.
The demonstration of hydrogen combustion in a chlorine atmosphere is interesting: sometimes during the experiment an unusual phenomenon occurs by-effect: There is a buzzing sound. Most often, the flame hums when a thin tube through which hydrogen is supplied is lowered into a cone-shaped vessel filled with chlorine; the same is true for spherical flasks, but in cylinders the flame usually does not hum. This phenomenon was called the “singing flame.”
In an aqueous solution, chlorine reacts partially and rather slowly with water; at 25° C, equilibrium: Cl 2 + H 2 O HClO + HCl is established within two days. Hypochlorous acid decomposes in light: HClO ® HCl + O. It is atomic oxygen that is credited with the bleaching effect (absolutely dry chlorine does not have this ability).
Chlorine in its compounds can exhibit all oxidation states - from –1 to +7. With oxygen, chlorine forms a number of oxides, all of them in their pure form are unstable and explosive: Cl 2 O - yellow-orange gas, ClO 2 - yellow gas (below 9.7 o C - bright red liquid), chlorine perchlorate Cl 2 O 4 (ClO –ClO 3, light yellow liquid), Cl 2 O 6 (O 2 Cl–O–ClO 3, bright red liquid), Cl 2 O 7 – colorless, very explosive liquid. At low temperatures, unstable oxides Cl 2 O 3 and ClO 3 were obtained. ClO 2 oxide is produced on an industrial scale and is used instead of chlorine to bleach pulp and disinfect drinking water and wastewater. With other halogens, chlorine forms a number of so-called interhalogen compounds, for example, ClF, ClF 3, ClF 5, BrCl, ICl, ICl 3.
Chlorine and its compounds with a positive oxidation state are strong oxidizing agents. In 1822, the German chemist Leopold Gmelin obtained red salt from yellow blood salt by oxidation with chlorine: 2K 4 + Cl 2 ® K 3 + 2KCl. Chlorine easily oxidizes bromides and chlorides, releasing bromine and iodine in free form.
Chlorine in different oxidation states forms a number of acids: HCl - hydrochloric (hydrochloric, salts - chlorides), HClO - hypochlorous (salts - hypochlorites), HClO 2 - chlorous (salts - chlorites), HClO 3 - hypochlorous (salts - chlorates), HClO 4 – chlorine (salts – perchlorates). Of the oxygen acids, only perchloric acid is stable in its pure form. Of the salts of oxygen acids, hypochlorites are used in practice, sodium chlorite NaClO 2 - for bleaching fabrics, for the manufacture of compact pyrotechnic sources of oxygen (“oxygen candles”), potassium chlorates (Bertholometa salt), calcium and magnesium (for controlling agricultural pests, as components of pyrotechnic compositions and explosives, in the production of matches), perchlorates - components of explosives and pyrotechnic compositions; Ammonium perchlorate is a component of solid rocket fuels.
Chlorine reacts with many organic compounds. It quickly attaches to unsaturated compounds with double and triple carbon-carbon bonds (the reaction with acetylene proceeds explosively), and in the light to benzene. Under certain conditions, chlorine can replace hydrogen atoms in organic compounds: R–H + Cl 2 ® RCl + HCl. This reaction played a significant role in the history of organic chemistry. In the 1840s, French chemist Jean Baptiste Dumas discovered that the action of chlorine on acetic acid the reaction occurs with amazing ease
CH 3 COOH + Cl 2 ® CH 2 ClCOOH + HCl. With an excess of chlorine, trichloroacetic acid CCl 3 COOH is formed. However, many chemists were distrustful of Dumas' work. Indeed, according to the then generally accepted theory of Berzelius, positively charged hydrogen atoms could not be replaced by negatively charged chlorine atoms. This opinion was held at that time by many outstanding chemists, among whom were Friedrich Wöhler, Justus Liebig and, of course, Berzelius himself.
To ridicule Dumas, Wöhler handed over to his friend Liebig an article on behalf of a certain S. Windler (Schwindler - in German a fraudster) about a new successful application of the reaction allegedly discovered by Dumas. In the article, Wöhler wrote with obvious mockery about how in manganese acetate Mn(CH 3 COO) 2 it was possible to replace all the elements, according to their valence, with chlorine, resulting in a yellow crystalline substance consisting of only chlorine. It was further said that in England, by successively replacing all atoms in organic compounds with chlorine atoms, ordinary fabrics are converted into chlorine ones, and that at the same time things retain their appearance. In a footnote it was stated that London shops were selling a brisk trade in material consisting of chlorine alone, as this material was very good for nightcaps and warm underpants.
The reaction of chlorine with organic compounds leads to the formation of many organochlorine products, among which are the widely used solvents methylene chloride CH 2 Cl 2, chloroform CHCl 3, carbon tetrachloride CCl 4, trichlorethylene CHCl=CCl 2, tetrachlorethylene C 2 Cl 4. In the presence of moisture, chlorine discolors the green leaves of plants and many dyes. This was used back in the 18th century. for bleaching fabrics.
Chlorine as a poisonous gas.
Scheele, who received chlorine, noted a very unpleasant strong odor, difficulty breathing and coughing. As we later found out, a person smells chlorine even if one liter of air contains only 0.005 mg of this gas, and at the same time it already has an irritating effect on the respiratory tract, destroying the cells of the mucous membrane of the respiratory tract and lungs. A concentration of 0.012 mg/l is difficult to tolerate; if the concentration of chlorine exceeds 0.1 mg/l, it becomes life-threatening: breathing quickens, becomes convulsive, and then becomes increasingly rare, and after 5–25 minutes breathing stops. The maximum permissible concentration in the air of industrial enterprises is 0.001 mg/l, and in the air of residential areas - 0.00003 mg/l.
St. Petersburg academician Toviy Egorovich Lovitz, repeating Scheele's experiment in 1790, accidentally released a significant amount of chlorine into the air. After inhaling it, he lost consciousness and fell, then suffered excruciating chest pain for eight days. Fortunately, he recovered. The famous English chemist Davy almost died from chlorine poisoning. Experiments with even small amounts of chlorine are dangerous, as they can cause severe lung damage. They say that the German chemist Egon Wiberg began one of his lectures on chlorine with the words: “Chlorine is a poisonous gas. If I get poisoned during the next demonstration, please take me out into the fresh air. But, unfortunately, the lecture will have to be interrupted.” If you release a lot of chlorine into the air, it becomes a real disaster. This was experienced by the Anglo-French troops during the First World War. On the morning of April 22, 1915, the German command decided to carry out the first gas attack in the history of wars: when the wind blew towards the enemy, on a small six-kilometer section of the front near the Belgian town of Ypres, the valves of 5,730 cylinders were simultaneously opened, each containing 30 kg of liquid chlorine. Within 5 minutes, a huge yellow-green cloud formed, which slowly moved away from the German trenches towards the Allies. The English and French soldiers were completely defenseless. The gas penetrated through the cracks into all the shelters; there was no escape from it: after all, the gas mask had not yet been invented. As a result, 15 thousand people were poisoned, 5 thousand of them to death. A month later, on May 31, the Germans repeated the gas attack on the eastern front - against Russian troops. This happened in Poland near the city of Bolimova. At the 12 km front, 264 tons of a mixture of chlorine and much more toxic phosgene (carbonic acid chloride COCl 2) were released from 12 thousand cylinders. The tsarist command knew about what happened at Ypres, and yet the Russian soldiers had no means of defense! As a result of the gas attack, the losses amounted to 9,146 people, of which only 108 were as a result of rifle and artillery shelling, the rest were poisoned. At the same time, 1,183 people died almost immediately.
Soon, chemists showed how to escape from chlorine: you need to breathe through a gauze bandage soaked in a solution of sodium thiosulfate (this substance is used in photography, it is often called hyposulfite). Chlorine reacts very quickly with a thiosulfate solution, oxidizing it:
Na 2 S 2 O 3 + 4Cl 2 + 5H 2 O ® 2H 2 SO 4 + 2NaCl + 6HCl. Of course, sulfuric acid is also not a harmless substance, but its diluted aqueous solution is much less dangerous than poisonous chlorine. Therefore, in those years, thiosulfate had another name - “antichlor”, but the first thiosulfate gas masks were not very effective.
In 1916, the Russian chemist and future academician Nikolai Dmitrievich Zelinsky invented a truly effective gas mask, in which toxic substances were retained by a layer of activated carbon. Such coal with a very developed surface could retain significantly more chlorine than gauze soaked in hyposulfite. Fortunately, the “chlorine attacks” remained only a tragic episode in history. After the World War, chlorine had only peaceful professions left.
Use of chlorine.
Every year, huge amounts of chlorine are produced worldwide – tens of millions of tons. Only in the USA by the end of the 20th century. About 12 million tons of chlorine were produced annually by electrolysis (10th place among chemical production). The bulk of it (up to 50%) is spent on the chlorination of organic compounds - to produce solvents, synthetic rubber, polyvinyl chloride and other plastics, chloroprene rubber, pesticides, medicines, and many other necessary and useful products. The rest is consumed for the synthesis of inorganic chlorides, in the pulp and paper industry for bleaching wood pulp, and for water purification. Chlorine is used in relatively small quantities in the metallurgical industry. With its help, very pure metals are obtained - titanium, tin, tantalum, niobium. By burning hydrogen in chlorine, hydrogen chloride is obtained, and from it hydrochloric acid is obtained. Chlorine is also used for the production of bleaching agents (hypochlorites, bleach) and water disinfection by chlorination.
Ilya Leenson
Ministry of Education and Science of the RUSSIAN FEDERATION
Federal State Budgetary Educational Institution of Higher Professional Education
IVANOVSK STATE CHEMICAL-TECHNOLOGICAL UNIVERSITY
Department of TP and MET
Essay
Chlorine: properties, application, production
Head: Efremov A.M.
Ivanovo 2015
Introduction
General information for chlorine
Use of chlorine
Chemical methods for producing chlorine
Electrolysis. Concept and essence of the process
Industrial production of chlorine
Safety precautions in chlorine production and environmental protection
Conclusion
Introduction
chlorine chemical element electrolysis
Due to the large-scale use of chlorine in various fields of science, industry, medicine and in everyday life, the demand for it has recently increased catastrophically. There are many methods for producing chlorine using laboratory and industrial methods, but they all have more disadvantages than advantages. Obtaining 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-consuming process, harmful from an environmental point of view and very dangerous to life and health.
Currently, the problem of developing a technology for producing chlorine that would eliminate all of 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 reacting 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 of the periodic table of 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, that is, it is approximately 2.5 times heavier than air.
Chemically, chlorine is very active, directly combines 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 applications. Chlorine displaces bromine and iodine from their compounds with hydrogen and metals. Alkali metals, in the presence of traces of moisture, react with chlorine with ignition; most metals react with dry chlorine only when heated. Steel, as well as some metals, are resistant to an atmosphere of dry chlorine at low temperatures, so they are used for the manufacture of equipment and storage facilities for dry chlorine. Phosphorus ignites in a chlorine atmosphere, forming PCl3, and with further chlorination - PCl5. Sulfur with chlorine when heated gives S2Cl2, SCl2 and other SnClm. Arsenic, antimony, bismuth, strontium, tellurium react 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 light, an electric spark, heat, or 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 spontaneously explode; hypochlorites slowly decompose during storage; chlorates and perchlorates can explode under the influence of initiators. Chlorine in water hydrolyzes, forming hypochlorous and hydrochloric acids: Cl2 + H2O? HClO + HCl. The resulting yellowish solution is often called chlorine water. When aqueous solutions of alkalis are chlorinated in the cold, hypochlorites and chlorides are formed: 2NaOH + Cl2 = NaClO + NaCl + H2O, and when heated, chlorates are formed. Chlorination of dry calcium hydroxide produces bleach. When ammonia reacts with chlorine, nitrogen trichloride is formed. When chlorinating organic compounds, chlorine either replaces hydrogen or joins 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 spontaneously ignites. Known compounds of chlorine with oxygen and fluorine are 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 mass. Water migration plays a major role in the history of chlorine in the earth's crust. It is found in the form of Cl- ion in the World Ocean (1.93%), underground brines and salt lakes. The number of its own minerals (mainly natural chlorides) is 97, the main one being halite NaCl (Rock salt). Large deposits of potassium and magnesium chlorides and mixed chlorides are also known: sylvinite 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
Name of indicator GOST 6718-93 Highest grade First grade Volume fraction of chlorine, no less than, % 99.899.6 Mass fraction of water, no more than % 0.010.04 Mass fraction of nitrogen trichloride, no more than % 0.0020.004 Mass fraction of non-volatile residue, no more than %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 its own vapor pressure of 18 kgf/cm2. Maximum storage volumes are 150 tons. Cylinders with liquid chlorine under pressure have a special color - a protective color. If a chlorine cylinder depressurizes, a sudden release of gas occurs with a concentration several times higher than the lethal one. It should be noted that when chlorine cylinders are used for a long time, extremely explosive nitrogen trichloride accumulates in them, and therefore, from time to time, chlorine cylinders must undergo routine washing and cleaning of nitrogen chloride. Chlorine is transported in containers, railway tanks, and cylinders, which serve as temporary storage.
2.Use of chlorine
Chlorine is consumed primarily by the chemical industry for the production of various organic chlorine derivatives used to produce plastics, synthetic rubbers, chemical fibers, solvents, insecticides, etc. Currently, more than 60% of global 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, extraction of gold from ores, and it is also used in the oil refining industry, in agriculture, in 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 areas for the use of chlorine, mainly due to the success of organic synthesis, world production of chlorine is more than 20 million tons/year.
Main examples of the application and use of chlorine in various branches of science, industry and domestic needs:
1.in the production of polyvinyl chloride, plastic compounds, synthetic rubber, from which they make: wire insulation, window profiles, packaging materials, clothing and shoes, linoleum and gramophone records, varnishes, equipment and foam plastics, toys, instrument parts, Construction Materials. Polyvinyl chloride is produced by polymerization of vinyl chloride, which today is most often produced from ethylene by the chlorine-balanced method via the intermediate 1,2-dichloroethane.
CH2=CH2+Cl2=>CH2Cl-CH2ClCl-CH2Cl=> CH2=CHCl+HCl
1)as a bleaching agent (although it is not chlorine itself that “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, hexachlorane). 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 disinfecting drinking water is based on the ability of free chlorine and its compounds to inhibit the enzyme systems of microorganisms that catalyze redox processes. To disinfect drinking water, the following are used: chlorine (Cl2), chlorine dioxide (ClO2), chloramine (NH2Cl) and bleach (Ca(Cl)OCl).
)in the food industry it is registered as a 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, bertholite salt (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 T=850°C)
)as an indicator of solar neutrinos in chlorine-argon detectors (The idea of a “chlorine detector” for registering solar neutrinos was proposed by the famous Soviet physicist Academician B. Pontecorvo and implemented by the American physicist R. Davis and his collaborators. Having caught the neutrino nucleus of the chlorine isotope with an atomic weight of 37, transforms into the nucleus of the isotope argon-37, which produces one electron that can be registered.).
Many developed countries seek to limit the use of chlorine in everyday life, including because the combustion of chlorine-containing waste produces a significant amount of dioxins (global ecotoxicants with powerful mutagenic properties).
3.Chemical methods for producing chlorine
Previously, the production of chlorine by chemical means using the Weldon and Deacon methods 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 table salt by the action of sulfuric acid.
reaction occurring using the Weldon method:
4HCl + MnO2 =>MnCl2+ 2H2O + Cl2
reaction that occurs using Deacon's method:
HCl + O2 =>2H2O + 2Cl2
In the Dikonovsky process, copper chloride was used as a catalyst, a 50% solution of which (sometimes with the addition of NaCl) was impregnated with a porous ceramic carrier. The optimal reaction temperature on such a catalyst was usually within the range of 430-490°. This catalyst is easily poisoned by arsenic compounds, with which it forms inactive copper arsenate, as well as sulfur dioxide and sulfur 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 sequential reactions:
H2SO4 => SO2 + 1/2O2 + H2O+ C12 + 2H2O => 2НCl + H2SO4
C12 + H2O => 1/2O2 + 2HCl
Thus, sulfuric acid is a catalyst that promotes the reverse conversion of Cl2 to HCl. Therefore, before oxidation on a copper catalyst, hydrochloride 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 located ceramic cylinders with holes; the annular space between them is filled with a catalyst. Hydrogen chloride was oxidized with air, so the 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 it with HCl and drying it with sulfuric acid, was usually used to produce bleach.
The 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 chlorine-oxygen mixture is washed from HC1 residues successively with 36 and 20% hydrochloric acid and dried with sulfuric acid. The chlorine is then liquefied and the oxygen is returned to the process. Chlorine is also separated from oxygen by absorbing chlorine under a pressure of 8 atm with sulfur chloride, which is then regenerated to produce 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 sharply increase the degree of conversion of HCl to Cl2. On a chromium oxide catalyst, HCl is burned in oxygen at 340-480°C. The use of a catalyst from a mixture of V2O5 with alkali metal pyrosulfates and activators on silica gel at 250–20°C is described. The mechanism and kinetics of this process have been studied and the optimal conditions for its implementation have been established, in particular in a fluidized bed.
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 ferric oxide with hydrogen chloride:
O3 + 6HCI = 2FeCl3 + 3H20
To reduce the vapor pressure of ferric chloride, potassium chloride is added. It is also proposed to carry out this process in one apparatus, in which a 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 through a hot chlorination zone, where Fe2O3 is converted into FeCl3, interacting with HCl located in the gas flow going from bottom to top. Then the contact mass is lowered into the cooling zone, where, under the influence of oxygen, elemental chlorine is formed, and FeCl3 transforms into Fe2O3. The oxidized contact mass is returned to the chlorination zone.
A similar indirect oxidation of HCl to Cl2 is carried out according to the following scheme:
2HC1 + MgO = MgCl2 + H2O
It is proposed to simultaneously produce chlorine and sulfuric acid by passing a gas containing HCl, O2 and a large excess of SO2 through a vanadium catalyst at 400600°C. Then H2SO4 and HSO3Cl are condensed from the gas and SO3 is absorbed with sulfuric acid; chlorine remains in the gas phase. HSO3Cl is hydrolyzed and the released HC1 is returned to the process.
Oxidation is carried out even more efficiently by such oxidizing agents as PbO2, KMnO4, KClO3, K2Cr2O7:
2KMnO4 + 16HCl => 2KCl + 2MnCl2 + 5Cl2^ +8H2O
Chlorine can also be obtained by oxidation of chlorides. For example, when NaCl and SO3 interact, the following reactions occur:
NaCl + 2SO3 = 2NaSO3Cl
NaSO3Cl = Cl2 + SO2 + Na2SO4
NaSO3Cl decomposes 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 into SO2C12 and separating excess chlorine, and SO2Cl2 decomposing at 200° into SO2 and Cl2, which are added to the mixture sent for rectification.
Chlorine can be obtained by oxidation of 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 + Cl2
It is also proposed, for example, to oxidize NOCl with 75% nitric acid to obtain chlorine:
2NOCl + 4HNO3 = Cl2 + 6NO2 + 2H2O
The mixture of chlorine and nitrogen dioxide is separated, 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 carrying out this process on an industrial scale is the elimination of corrosion. Ceramics, glass, lead, nickel, and plastics are used as materials for equipment. Using this method in the USA in 1952-1953. The installation 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:
2HCl + 2HNO3 = Cl2 + 2NO2 + 2H2O
The process occurs in the liquid phase at 80°C, the yield of chlorine reaches 100%, NO2 is obtained in liquid form.
Subsequently, these methods were completely replaced by electrochemical ones, but currently chemical methods for producing chlorine are being revived again 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. Concept and essence of the process
Electrolysis is a set of electrochemical redox processes that occur on the electrodes during the passage of a direct electric current through a melt or solution with electrodes immersed in it.
Rice. 4.1. Processes occurring during electrolysis. Electrolysis bath diagram: 1 - bath, 2 - electrolyte, 3 - anode, 4 - cathode, 5 - power source
Electrodes can be any materials that conduct electric current. Metals and alloys are mainly used; non-metal electrodes can be, for example, graphite rods (or carbon). Less commonly, liquids are used as an electrode. A positively charged electrode is the anode. An electrode charged negatively is a 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. You can use graphite (carbon) or platinum as an inert anode. You can use a metal plate as a cathode (it will not dissolve). Copper, brass, carbon (or graphite), zinc, iron, aluminum, stainless steel are suitable.
Examples of electrolysis of melts:
Examples of electrolysis of salt solutions:
(Cl? anions are oxidized at the anode, and not oxygen O? II water molecules, since the electronegativity of chlorine is less than oxygen, and therefore chlorine gives up electrons more easily than oxygen)
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, which 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 anions of oxoacids are never oxidized at the anode with an element in the highest degree of oxidation (for example, ClO4?, SO42?, NO3?, PO43?, CO32?, SiO44?, MnO4?), water is oxidized instead.
Electrolysis involves two processes: the migration of reacting particles under the influence of an electric field to the surface of the electrode and the transfer of charge from particle to electrode or from electrode to particle. The migration of ions is determined by their mobility and transport 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 current density is a measure of the rate of reactions. This is a vector physical, the module of which is determined by the ratio of the current strength (the number of transferred electrical 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 their most general form, the 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 this electrode. By quantity of electricity we mean 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 the 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 passing through the substance = 96,485.33(83) C mol?1 is Faraday’s constant, is the molar mass of the substance (For example, the molar mass of water H2O = 18 g/mol), is 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 substance.
For Faraday's first law, M, F and z are constants, so the larger the value of Q, the larger the value of m will be.
For Faraday's second law, Q, F and z are constants, so the larger the M/z value (equivalent mass), the larger the m value will be.
In the simplest case, direct current electrolysis leads to:
In the more complex case of alternating electric current, the total charge Q of the current I( ?) is summed up 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 solutions of table salt NaCl, obtained by dissolving solid salt, or natural brines. There are three types of salt deposits: fossil salt (about 99% of reserves); salt lakes with bottom sediments of self-sedimented salt (0.77%); the rest are underground splits. Solutions of table salt, regardless of the route of their preparation, contain impurities that impair the electrolysis process. During electrolysis with a solid cathode, calcium cations Ca2+, Mg2+ and SO42- anions have a particularly adverse effect, and during electrolysis with a liquid cathode - impurities of compounds containing heavy metals, such as chromium, vanadium, germanium and molybdenum.
Crystalline salt for chlorine electrolysis must have the following composition (%): sodium chloride not less than 97.5; Mg2+ no more than 0.05; insoluble sediment no more than 0.5; Ca2+ no more than 0.4; K+ no more than 0.02; SO42 - no more than 0.84; humidity no more than 5; admixture of heavy metals (determined by amalgam test cm3 H2) no more than 0.3. Brine purification is carried out with a solution of soda (Na2CO3) and lime milk (a suspension of Ca(OH)2 in water). In addition to chemical purification, solutions are freed from mechanical impurities by settling and filtration.
Electrolysis of table 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 electrolysers used to equip modern large chlorine shops must have high performance, a simple design, be compact, operate reliably and steadily.
Electrolysis proceeds according to the following 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 basic, reversible and irreversible ionic reactions occur:
dissociation of molecules of table salt and water (occurs in the electrolyte)
NaCl-Na++Cl-
Oxidation of chlorine ion (at the anode)
C1- - 2e- => C12
reduction of hydrogen ion and water molecules (at the cathode)
Н+ - 2е- => Н2
Н2O - 2е - => Н2 + 2ОН-
Association of ions into a sodium hydroxide molecule (in an 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 electrolyzer 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 were used to separate the electrolysis products. At the next stage, electrolyzers with a flow diaphragm appeared. They combined the counterflow principle with the use of a separating diaphragm, which was made of asbestos cardboard. Next, a method was discovered for producing a diaphragm from asbestos pulp, borrowed from the technology of the paper industry. This method made it possible to develop designs for electrolysers for high current loads with a non-removable compact finger cathode. To increase the service life of the asbestos diaphragm, it is proposed to introduce some synthetic materials into its composition as a coating or bond. It is also proposed to make the diaphragms entirely 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 that make it possible to obtain pure caustic soda with a very low sodium chloride content. The action of such diaphragms is based on the use of their selective properties for the passage of various ions.
In early designs, the contact points of the current leads to the graphite anodes were removed from the electrolyzer cavity to the outside. Subsequently, methods were developed to protect the contact parts of anodes immersed in the electrolyte. Using these techniques, industrial electrolyzers with bottom current supply were created, in which the anode contacts are located in the cavity of the electrolyzer. They are used everywhere today for the production of chlorine and caustic soda on a solid cathode.
A stream of saturated solution of table salt (purified brine) continuously flows into the anode space of the diaphragm electrolyzer. As a result of the electrochemical process, chlorine is released at the anode due to the decomposition of table 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. A solution from the near-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 NaOH content in it is adjusted to 42-50% in accordance with the standard. Table salt and sodium sulfate precipitate when the concentration of sodium hydroxide increases.
The NaOH solution is decanted from the crystals and transferred as a finished product to a warehouse or caustic melting stage to obtain a solid product. Crystalline table salt (reverse salt) is returned to electrolysis, preparing the so-called reverse brine. To avoid the accumulation of sulfate in solutions, sulfate is removed from it before preparing the reverse brine. The loss of table salt is compensated by adding fresh brine obtained by underground leaching of salt layers or by dissolving solid table salt. Before mixing it with return 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 for chlorine liquefaction. Hydrogen is separated from water, compressed and transferred to consumers.
The same chemical reactions occur in a membrane electrolyzer as in a diaphragm electrolyzer. Instead of a porous diaphragm, a cationic membrane is used (Fig. 5).
Rice. 5.2. Diagram 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%. Since there is no need to separate the salt, evaporation makes it possible to produce 50% commercial caustic soda much more easily and at lower capital and energy costs. Since caustic soda in the membrane process is of much higher concentration, expensive nickel is used as the cathode.
Rice. 5.3. Schematic of a mercury electrolyzer
The total reaction of decomposition of table salt in mercury electrolyzers is the same as in diaphragm electrolyzers:
NaCl+H2O => NaOH + 1/2Сl2+ 1/2Н2
However, here it takes place in two stages, each in a separate apparatus: an electrolyzer and a decomposer. They are structurally combined with each other 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 supplied to the electrolyzer) to produce chlorine at the anode, and sodium amalgam at the mercury cathode, according to the following reaction:
NaCl + nHg => l/2Cl2 + NaHgn
The decomposer undergoes the second stage of the process, in which, under the influence of water, sodium amalgam is converted into sodium hydroxide and mercury:
NaHgn + H2O => NaOH +1/2H2+nHg
Of all the salt fed into the electrolyzer with brine, only 15-20% of the supplied amount enters into reaction (2), and the rest of the salt, along with water, leaves the electrolyzer in the form of chloranolyte - a solution of table salt in water containing 250-270 kg/ m3 NaCl saturated with chlorine. The “strong amalgam” coming out of the electrolyzer and water are fed into the decomposer.
The electrolyzer in all available designs is made in the form of a long and relatively narrow, slightly inclined steel trench, along the bottom of which a thin layer of amalgam flows by gravity, which is the cathode, and anolyte flows on top. Brine and weak amalgam are fed from the top raised edge of the electrolyser through the "inlet pocket".
Strong amalgam flows from the lower end of the electrolyser through the "outlet pocket". Chlorine and chloranolyte come out together through a pipe, also located at the lower end of the electrolyzer. 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 electrolyzer is covered with a lid.
Two types of decomposers are common: horizontal and vertical. The first are made in the form of a steel inclined chute of the same length as the electrolyser. A stream of amalgam flows along the bottom of the decomposer, which is installed at a slight angle. A decomposer nozzle made of graphite is immersed in this flow. Water moves in countercurrent. As a result of the decomposition of the amalgam, the water is saturated with caustic. The caustic solution along with hydrogen leaves the decomposer through a pipe in the bottom, and the poor amalgam or mercury is pumped into the cell pocket.
In addition to the electrolyzer, decomposer, pockets and transfer pipelines, the electrolysis bath kit includes a mercury pump. Two types of pumps are used. In cases where the baths are equipped with a vertical digester or where the digester is installed under the electrolyser, conventional submersible centrifugal pumps lowered into the digester are used. For baths in which the decomposer is installed next to the electrolyser, the amalgam is pumped with a conical rotary pump of the original type.
All steel parts of the electrolyser that come into contact with chlorine or chloranolyte are protected with a special grade of vulcanized rubber coating (gumming). The protective rubber layer is not completely resistant. Over time, it becomes chlorinated and becomes brittle and cracks due to 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 caustic solution corrodes it.
Currently, graphite anodes are the most common in mercury electrolyzers. However, they are being replaced by ORTA.
6.Safety precautions 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 formation in the equipment of explosive gas mixtures of chlorine and hydrogen, hydrogen and air, as well as solutions of nitrogen trichloride in liquid chlorine, the use in the production of electrolyzers - devices that are at an increased electrical potential relative to earth, the properties of the caustic alkali produced in this production.
Inhaling 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 permissible concentration (MPC) of chlorine in the air of populated areas: average daily 0.03 mg/m3, maximum one-time 0.1 mg/m3, in the air of the working area of industrial premises is 1 mg/m3, odor perception threshold 2 mg/m3. At a concentration of 3-6 mg/m3, a distinct odor is felt, irritation (redness) of the eyes and nasal mucous membranes 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 death is possible, a concentration of 2500 mg/m3 leads to death within 5 minutes, at a concentration of 3000 mg/m3 death occurs after a few breaths . The maximum permissible 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 emergency situations, all people in the workshops must have and promptly use gas masks of the “B” or “BKF” brands (except for mercury electrolysis workshops), as well as protective clothing: cloth or rubberized suits, rubber boots and mittens. Boxes of anti-chlorine gas masks should 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 through inhalation and contact with the skin, as well as through contact with amalgamated objects. Its vapors and splashes are adsorbed (absorbed) by clothing, skin, and teeth. At the same time, mercury easily evaporates at temperature; available in the electrolysis workshop, and the concentration of its vapors in the air far exceeds the maximum permissible. Therefore, liquid cathode electrolysis shops are equipped with powerful ventilation, which, during normal operation, provides permissible level mercury vapor concentrations. 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, before starting work, the staff goes through a sanitary checkpoint, in a clean section of which they leave their home clothes and put on freshly washed linen, which is special clothing. At the end of the shift, outer clothing and dirty linen are left in the dirty section of the sanitary inspection room, and workers take a shower, brush their teeth and put on household items in the clean department of the sanitary inspection room.
In workshops where they work with chlorine and mercury, you should use a gas mask of the “G” brand (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 be immediately washed down the drain where there are mercury traps.
The environment is threatened by emissions of chlorine and mercury vapor into the atmosphere, discharges of mercury salts and droplets of mercury, compounds containing active chlorine into wastewater, and soil poisoning by mercury sludge. Chlorine enters the atmosphere during accidents, with ventilation emissions and exhaust gases from various devices. Mercury vapor is carried out with the air from ventilation systems. The norm for chlorine content in the air when released into the atmosphere is 0.03 mg/m3. This concentration can be achieved if alkaline multi-stage exhaust gas washing is used. The norm for mercury content in the air when released 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 part by weight of slaked lime is poured into 3 parts of water, mixed thoroughly, then the lime solution is poured on top (for example, 10 kg of slaked lime + 30 liters of water);
5% aqueous solution of soda ash, for which 2 parts by weight of soda ash are dissolved with mixing with 18 parts of water (for example, 5 kg of soda ash + 95 liters of water);
A 5% aqueous solution of caustic soda, for which 2 parts by weight of caustic soda are dissolved with mixing with 18 parts of water (for example, 5 kg of caustic soda + 95 liters of water).
If chlorine gas leaks, water is sprayed to extinguish the vapor. The water consumption rate is not standardized.
When liquid chlorine spills, the spill site is fenced off with an earthen rampart and filled with lime milk, 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 required.
To spray water or solutions, watering and fire trucks, auto-filling stations (ATs, 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 obtained by laboratory methods are negligible in comparison with the constantly growing demand for this product, it makes no sense to conduct a comparative analysis on them.
Of the electrochemical production methods, the easiest and most convenient is electrolysis with a liquid (mercury) cathode, 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 with mercury. When choosing between diaphragm and membrane electrolysers for new production facilities, it is preferable to use the latter, since they are more economical and provide the opportunity to obtain a higher quality final product.
Bibliography
1.Zaretsky S. A., Suchkov V. N., Zhivotinsky P. B. Electrochemical technology of inorganic substances and chemical current sources: A textbook for technical school students. 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 V. N. 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
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Chlorine (χλωρός - green) - an element of the main subgroup of the seventh group, the third period of the periodic system of chemical elements of D.I. Mendeleev, with atomic number 17. Denoted by the symbol Cl (lat. Chlorum). Chemically active non-metal. It is part of the group of halogens (originally the name “halogen” was used by the German chemist Schweiger for chlorine [literally, “halogen” is translated as salt), but it did not catch on, and subsequently became common to group VII of elements, which includes chlorine).
The simple substance chlorine (CAS number: 7782-50-5) under normal conditions is a poisonous gas of yellowish-green color, with a pungent odor. Diatomic chlorine molecule (formula Cl2).
Chlorine atom diagram
Chlorine was first obtained in 1772 by Scheele, who described its release during the interaction of pyrolusite with hydrochloric acid in his treatise on pyrolusite:
4HCl + MnO2 = Cl2 + MnCl2 + 2H2O
Scheele noted the odor of chlorine, similar to that of aqua regia, its ability to react with gold and cinnabar, and its bleaching properties.
However, Scheele, in accordance with the phlogiston theory that was dominant in chemistry at that time, suggested that chlorine is dephlogisticated hydrochloric acid, that is, the oxide of hydrochloric acid. Berthollet and Lavoisier suggested that chlorine is an oxide of the element muria, but attempts to isolate it remained unsuccessful until the work of Davy, who managed to decompose table salt into sodium and chlorine by electrolysis.
Distribution in nature
There are two isotopes of chlorine found in nature: 35 Cl and 37 Cl. In the earth's crust, chlorine is the most common halogen. Chlorine is very active - it directly combines with almost all elements of the periodic table. Therefore, in nature it is found only in the form of compounds in the minerals: halite NaCl, sylvite KCl, sylvinite KCl NaCl, bischofite MgCl 2 6H2O, carnallite KCl MgCl 2 6H 2 O, kainite KCl MgSO 4 3H 2 O. The largest reserves of chlorine are contained in the salts of the waters of the seas and oceans.
Chlorine accounts for 0.025% of the total number of atoms in the earth's crust, the clarke number of chlorine is 0.19%, and human body contains 0.25% chlorine ions by weight. In the human and animal bodies, chlorine is found mainly in intercellular fluids (including blood) and plays an important role in the regulation of osmotic processes, as well as in processes associated with the functioning of nerve cells.
Isotopic composition
There are 2 stable isotopes of chlorine found in nature: with a mass number of 35 and 37. The proportions of their content are respectively 75.78% and 24.22%.
| Isotope | Relative mass, a.m.u. | Half life | Type of decay | Nuclear spin |
|---|---|---|---|---|
| 35Cl | 34.968852721 | Stable | — | 3/2 |
| 36Cl | 35.9683069 | 301000 years | β decay in 36 Ar | 0 |
| 37Cl | 36.96590262 | Stable | — | 3/2 |
| 38Cl | 37.9680106 | 37.2 minutes | β decay in 38 Ar | 2 |
| 39Cl | 38.968009 | 55.6 minutes | β decay to 39 Ar | 3/2 |
| 40Cl | 39.97042 | 1.38 minutes | β decay in 40 Ar | 2 |
| 41Cl | 40.9707 | 34 s | β decay in 41 Ar | |
| 42Cl | 41.9732 | 46.8 s | β decay in 42 Ar | |
| 43Cl | 42.9742 | 3.3 s | β-decay in 43 Ar |
Physical and physico-chemical properties
Under normal conditions, chlorine is a yellow-green gas with a suffocating odor. Some of its physical properties are presented in the table.
Some physical properties of chlorine
| Property | Meaning |
|---|---|
| Boiling temperature | −34 °C |
| Melting temperature | −101 °C |
| Decomposition temperature (dissociations into atoms) |
~1400°С |
| Density (gas, n.s.) | 3.214 g/l |
| Electron affinity of an atom | 3.65 eV |
| First ionization energy | 12.97 eV |
| Heat capacity (298 K, gas) | 34.94 (J/mol K) |
| Critical temperature | 144 °C |
| Critical pressure | 76 atm |
| Standard enthalpy of formation (298 K, gas) | 0 (kJ/mol) |
| Standard entropy of formation (298 K, gas) | 222.9 (J/mol K) |
| Melting enthalpy | 6.406 (kJ/mol) |
| Enthalpy of boiling | 20.41 (kJ/mol) |
When cooled, chlorine turns into a liquid at a temperature of about 239 K, and then below 113 K it crystallizes into an orthorhombic lattice with space group Cmca and parameters a=6.29 b=4.50, c=8.21. Below 100 K, the orthorhombic modification of crystalline chlorine becomes tetragonal, having a space group P4 2/ncm and lattice parameters a=8.56 and c=6.12.
Solubility
| Solvent | Solubility g/100 g |
|---|---|
| Benzene | Let's dissolve |
| Water (0 °C) | 1,48 |
| Water (20 °C) | 0,96 |
| Water (25 °C) | 0,65 |
| Water (40 °C) | 0,46 |
| Water (60°C) | 0,38 |
| Water (80 °C) | 0,22 |
| Carbon tetrachloride (0 °C) | 31,4 |
| Carbon tetrachloride (19 °C) | 17,61 |
| Carbon tetrachloride (40 °C) | 11 |
| Chloroform | Well soluble |
| TiCl 4, SiCl 4, SnCl 4 | Let's dissolve |
In the light or when heated, it reacts actively (sometimes with explosion) with hydrogen according to a radical mechanism. Mixtures of chlorine with hydrogen, containing from 5.8 to 88.3% hydrogen, explode upon irradiation to form hydrogen chloride. A mixture of chlorine and hydrogen in small concentrations burns with a colorless or yellow-green flame. Maximum temperature of hydrogen-chlorine flame 2200 °C:
Cl 2 + H 2 → 2HCl 5Cl 2 + 2P → 2PCl 5 2S + Cl 2 → S 2 Cl 2 Cl 2 + 3F 2 (ex.) → 2ClF 3
Other properties
Cl 2 + CO → COCl 2When dissolved in water or alkalis, chlorine dismutates, forming hypochlorous (and when heated, perchloric) and hydrochloric acids, or their salts:
Cl 2 + H 2 O → HCl + HClO 3Cl 2 + 6NaOH → 5NaCl + NaClO 3 + 3H 2 O Cl 2 + Ca(OH) 2 → CaCl(OCl) + H 2 O 4NH 3 + 3Cl 2 → NCl 3 + 3NH 4 Cl
Oxidizing properties of chlorine
Cl 2 + H 2 S → 2HCl + SReactions with organic substances
CH 3 -CH 3 + Cl 2 → C 2 H 6-x Cl x + HClAttaches to unsaturated compounds via multiple bonds:
CH 2 =CH 2 + Cl 2 → Cl-CH 2 -CH 2 -Cl
Aromatic compounds replace a hydrogen atom with chlorine in the presence of catalysts (for example, AlCl 3 or FeCl 3):
C 6 H 6 + Cl 2 → C 6 H 5 Cl + HCl
Chlorine methods for producing chlorine
Industrial methods
Initially, the industrial method for producing chlorine was based on the Scheele method, that is, the reaction of pyrolusite with hydrochloric acid:
MnO 2 + 4HCl → MnCl 2 + Cl 2 + 2H 2 O 2NaCl + 2H 2 O → H 2 + Cl 2 + 2NaOH Anode: 2Cl - - 2е - → Cl 2 0 Cathode: 2H 2 O + 2e - → H 2 + 2OH-
Since the electrolysis of water occurs parallel to the electrolysis of sodium chloride, the overall equation can be expressed as follows:
1.80 NaCl + 0.50 H 2 O → 1.00 Cl 2 + 1.10 NaOH + 0.03 H 2
Three variants of the electrochemical method for producing chlorine are used. Two of them are electrolysis with a solid cathode: diaphragm and membrane methods, the third is electrolysis with a liquid cathode (mercury production method). Among the electrochemical production methods, the easiest and most convenient method is electrolysis with a mercury cathode, but this method causes significant harm to the environment as a result of evaporation and leakage of metallic mercury.
Diaphragm method with solid cathode
The electrolyzer cavity is divided by a porous asbestos partition - a diaphragm - into cathode and anode spaces, where the cathode and anode of the electrolyzer are respectively located. Therefore, such an electrolyzer is often called diaphragm, and the production method is diaphragm electrolysis. A flow of saturated anolyte (NaCl solution) continuously flows into the anode space of the diaphragm electrolyzer. As a result of the electrochemical process, chlorine is released at the anode due to the decomposition of halite, and hydrogen is released at the cathode due to the decomposition of water. In this case, the near-cathode zone is enriched with sodium hydroxide.
Membrane method with solid cathode
The membrane method is essentially similar to the diaphragm method, but the anode and cathode spaces are separated by a cation-exchange polymer membrane. The membrane production method is more efficient than the diaphragm method, but more difficult to use.
Mercury method with liquid cathode
The process is carried out in an electrolytic bath, which consists of an electrolyzer, a decomposer and a mercury pump, interconnected by communications. In the electrolytic bath, mercury circulates under the action of a mercury pump, passing through an electrolyzer and a decomposer. The cathode of the electrolyzer is a flow of mercury. Anodes - graphite or low-wear. Together with mercury, a stream of anolyte - a solution of sodium chloride - continuously flows through the electrolyzer. As a result of the electrochemical decomposition of chloride, chlorine molecules are formed at the anode, and at the cathode, the released sodium dissolves in mercury forming an amalgam.
Laboratory methods
In laboratories, to produce chlorine, processes based on the oxidation of hydrogen chloride with strong oxidizing agents (for example, manganese (IV) oxide, potassium permanganate, potassium dichromate) are usually used:
2KMnO 4 + 16HCl → 2KCl + 2MnCl 2 + 5Cl 2 +8H 2 O K 2 Cr 2 O 7 + 14HCl → 3Cl 2 + 2KCl + 2CrCl 3 + 7H 2 O
Chlorine storage
The chlorine produced is stored in special “tanks” or pumped into steel cylinders high pressure. Cylinders with liquid chlorine under pressure have a special color - swamp color. It should be noted that during prolonged use of chlorine cylinders, extremely explosive nitrogen trichloride accumulates in them, and therefore, from time to time, chlorine cylinders must undergo routine washing and cleaning of nitrogen chloride.
Chlorine Quality Standards
According to GOST 6718-93 “Liquid chlorine. Technical specifications" the following grades of chlorine are produced
Application
Chlorine is used in many industries, science and household needs:
- In the production of polyvinyl chloride, plastic compounds, synthetic rubber, from which they make: wire insulation, window profiles, packaging materials, clothing and shoes, linoleum and records, varnishes, equipment and foam plastics, toys, instrument parts, building materials. Polyvinyl chloride is produced by the polymerization of vinyl chloride, which today is most often produced from ethylene by the chlorine-balanced method through the intermediate 1,2-dichloroethane.
- The bleaching properties of chlorine have been known for a long time, although it is not chlorine itself that “bleaches,” but atomic oxygen, which is formed during the breakdown of hypochlorous acid: Cl 2 + H 2 O → HCl + HClO → 2HCl + O.. This method of bleaching fabrics, paper, cardboard has been used for several centuries.
- Production of organochlorine insecticides - substances that kill insects harmful to crops, but are safe for plants. A significant portion of the chlorine produced is consumed to obtain plant protection products. One of the most important insecticides is hexachlorocyclohexane (often called hexachlorane). This substance was first synthesized back in 1825 by Faraday, but it found practical application only more than 100 years later - in the 30s of our century.
- It was used as a chemical warfare agent, as well as for the production of other chemical warfare agents: mustard gas, phosgene.
- To disinfect water - “chlorination”. The most common method of disinfecting drinking water; is based on the ability of free chlorine and its compounds to inhibit the enzyme systems of microorganisms that catalyze redox processes. To disinfect drinking water, the following are used: chlorine, chlorine dioxide, chloramine and bleach. SanPiN 2.1.4.1074-01 establishes the following limits (corridor) of the permissible content of free residual chlorine in drinking water of centralized water supply 0.3 - 0.5 mg/l. A number of scientists and even politicians in Russia criticize the very concept of chlorination of tap water, but cannot offer an alternative to the disinfecting aftereffect of chlorine compounds. The materials from which water pipes are made interact differently with chlorinated tap water. Free chlorine in tap water significantly reduces the service life of polyolefin-based pipelines: various types of polyethylene pipes, including cross-linked polyethylene, large ones known as PEX (PE-X). In the USA, to control the admission of pipelines made of polymer materials for use in water supply systems with chlorinated water, they were forced to adopt 3 standards: ASTM F2023 in relation to pipes, membranes and skeletal muscles. These channels perform important functions in regulating fluid volume, transepithelial ion transport and stabilizing membrane potentials, and are involved in maintaining cell pH. Chlorine accumulates in visceral tissue, skin and skeletal muscles. Chlorine is absorbed mainly in the large intestine. The absorption and excretion of chlorine are closely related to sodium ions and bicarbonates, and to a lesser extent to mineralocorticoids and Na + /K + -ATPase activity. 10-15% of all chlorine accumulates in cells, of which 1/3 to 1/2 is in red blood cells. About 85% of chlorine is found in the extracellular space. Chlorine is excreted from the body mainly through urine (90-95%), feces (4-8%) and through the skin (up to 2%). The excretion of chlorine is associated with sodium and potassium ions, and reciprocally with HCO 3 - (acid-base balance).
A person consumes 5-10 g of NaCl per day. The minimum human need for chlorine is about 800 mg per day. The baby receives the required amount of chlorine through mother's milk, which contains 11 mmol/l of chlorine. NaCl is necessary for the production of hydrochloric acid in the stomach, which promotes digestion and destroys pathogenic bacteria. Currently, the involvement of chlorine in the occurrence of certain diseases in humans is not well studied, mainly due to the small number of studies. Suffice it to say that even recommendations on the daily intake of chlorine have not been developed. Human muscle tissue contains 0.20-0.52% chlorine, bone tissue - 0.09%; in the blood - 2.89 g/l. The average person's body (body weight 70 kg) contains 95 g of chlorine. Every day a person receives 3-6 g of chlorine from food, which more than covers the need for this element.
Chlorine ions are vital for plants. Chlorine is involved in energy metabolism in plants by activating oxidative phosphorylation. It is necessary for the formation of oxygen during photosynthesis by isolated chloroplasts, and stimulates auxiliary processes of photosynthesis, primarily those associated with energy accumulation. Chlorine has a positive effect on the absorption of oxygen, potassium, calcium, and magnesium compounds by roots. Excessive concentration of chlorine ions in plants can also have a negative side, for example, reduce the chlorophyll content, reduce the activity of photosynthesis, retard the growth and development of plants Baskunchak chlorine). Chlorine was one of the first chemical agents used
— Using analytical laboratory equipment, laboratory and industrial electrodes, in particular: ESR-10101 reference electrodes that analyze the content of Cl- and K+.
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The physical properties of chlorine are considered: the density of chlorine, its thermal conductivity, specific heat and dynamic viscosity at various temperatures. The physical properties of Cl 2 are presented in the form of tables for the liquid, solid and gaseous states of this halogen.
Basic physical properties of chlorine
Chlorine is included in group VII of the third period of the periodic table of elements at number 17. It belongs to the subgroup of halogens, has relative atomic and molecular masses of 35.453 and 70.906, respectively. At temperatures above -30°C, chlorine is a greenish-yellow gas with a characteristic strong, irritating odor. It liquefies easily under normal pressure (1.013·10 5 Pa) when cooled to -34°C, and forms a clear amber liquid that solidifies at -101°C.
Due to its high chemical activity, free chlorine does not occur in nature, but exists only in the form of compounds. It is found mainly in the mineral halite (), and is also part of such minerals as sylvite (KCl), carnallite (KCl MgCl 2 6H 2 O) and sylvinite (KCl NaCl). The chlorine content in the earth's crust approaches 0.02% of the total number of atoms of the earth's crust, where it is found in the form of two isotopes 35 Cl and 37 Cl in a percentage ratio of 75.77% 35 Cl and 24.23% 37 Cl.
| Property | Meaning |
|---|---|
| Melting point, °C | -100,5 |
| Boiling point, °C | -30,04 |
| Critical temperature, °C | 144 |
| Critical pressure, Pa | 77.1 10 5 |
| Critical density, kg/m 3 | 573 |
| Gas density (at 0°C and 1.013 10 5 Pa), kg/m 3 | 3,214 |
| Saturated steam density (at 0°C and 3.664 10 5 Pa), kg/m 3 | 12,08 |
| Density of liquid chlorine (at 0°C and 3.664 10 5 Pa), kg/m 3 | 1468 |
| Density of liquid chlorine (at 15.6°C and 6.08 10 5 Pa), kg/m 3 | 1422 |
| Density of solid chlorine (at -102°C), kg/m 3 | 1900 |
| Relative density of gas in air (at 0°C and 1.013 10 5 Pa) | 2,482 |
| Relative density of saturated steam in air (at 0°C and 3.664 10 5 Pa) | 9,337 |
| Relative density of liquid chlorine at 0°C (relative to water at 4°C) | 1,468 |
| Specific volume of gas (at 0°C and 1.013 10 5 Pa), m 3 /kg | 0,3116 |
| Specific volume of saturated steam (at 0°C and 3.664 10 5 Pa), m 3 /kg | 0,0828 |
| Specific volume of liquid chlorine (at 0°C and 3.664 10 5 Pa), m 3 /kg | 0,00068 |
| Chlorine vapor pressure at 0°C, Pa | 3.664 10 5 |
| Dynamic viscosity of gas at 20°C, 10 -3 Pa s | 0,013 |
| Dynamic viscosity of liquid chlorine at 20°C, 10 -3 Pa s | 0,345 |
| Heat of fusion of solid chlorine (at melting point), kJ/kg | 90,3 |
| Heat of vaporization (at boiling point), kJ/kg | 288 |
| Heat of sublimation (at melting point), kJ/mol | 29,16 |
| Molar heat capacity C p of gas (at -73…5727°C), J/(mol K) | 31,7…40,6 |
| Molar heat capacity C p of liquid chlorine (at -101…-34°C), J/(mol K) | 67,1…65,7 |
| Gas thermal conductivity coefficient at 0°C, W/(m K) | 0,008 |
| Thermal conductivity coefficient of liquid chlorine at 30°C, W/(m K) | 0,62 |
| Gas enthalpy, kJ/kg | 1,377 |
| Enthalpy of saturated steam, kJ/kg | 1,306 |
| Enthalpy of liquid chlorine, kJ/kg | 0,879 |
| Refractive index at 14°C | 1,367 |
| Specific electrical conductivity at -70°С, S/m | 10 -18 |
| Electron affinity, kJ/mol | 357 |
| Ionization energy, kJ/mol | 1260 |
Chlorine Density
Under normal conditions, chlorine is a heavy gas with a density approximately 2.5 times higher. Density of gaseous and liquid chlorine under normal conditions (at 0°C) is equal to 3.214 and 1468 kg/m3, respectively. When liquid or gaseous chlorine is heated, its density decreases due to an increase in volume due to thermal expansion.
Density of chlorine gas
The table shows the density of chlorine in the gaseous state at various temperatures (ranging from -30 to 140°C) and normal atmospheric pressure (1.013·10 5 Pa). The density of chlorine changes with temperature - it decreases when heated. For example, at 20°C the density of chlorine is 2.985 kg/m3, and when the temperature of this gas increases to 100°C, the density value decreases to a value of 2.328 kg/m 3.
| t, °С | ρ, kg/m 3 | t, °С | ρ, kg/m 3 |
|---|---|---|---|
| -30 | 3,722 | 60 | 2,616 |
| -20 | 3,502 | 70 | 2,538 |
| -10 | 3,347 | 80 | 2,464 |
| 0 | 3,214 | 90 | 2,394 |
| 10 | 3,095 | 100 | 2,328 |
| 20 | 2,985 | 110 | 2,266 |
| 30 | 2,884 | 120 | 2,207 |
| 40 | 2,789 | 130 | 2,15 |
| 50 | 2,7 | 140 | 2,097 |
As pressure increases, the density of chlorine increases. The tables below show the density of chlorine gas in the temperature range from -40 to 140°C and pressure from 26.6·10 5 to 213·10 5 Pa. With increasing pressure, the density of chlorine in the gaseous state increases proportionally. For example, an increase in chlorine pressure from 53.2·10 5 to 106.4·10 5 Pa at a temperature of 10°C leads to a twofold increase in the density of this gas.
| ↓ t, °С | P, kPa → | 26,6 | 53,2 | 79,8 | 101,3 |
|---|---|---|---|---|
| -40 | 0,9819 | 1,996 | — | — |
| -30 | 0,9402 | 1,896 | 2,885 | 3,722 |
| -20 | 0,9024 | 1,815 | 2,743 | 3,502 |
| -10 | 0,8678 | 1,743 | 2,629 | 3,347 |
| 0 | 0,8358 | 1,678 | 2,528 | 3,214 |
| 10 | 0,8061 | 1,618 | 2,435 | 3,095 |
| 20 | 0,7783 | 1,563 | 2,35 | 2,985 |
| 30 | 0,7524 | 1,509 | 2,271 | 2,884 |
| 40 | 0,7282 | 1,46 | 2,197 | 2,789 |
| 50 | 0,7055 | 1,415 | 2,127 | 2,7 |
| 60 | 0,6842 | 1,371 | 2,062 | 2,616 |
| 70 | 0,6641 | 1,331 | 2 | 2,538 |
| 80 | 0,6451 | 1,292 | 1,942 | 2,464 |
| 90 | 0,6272 | 1,256 | 1,888 | 2,394 |
| 100 | 0,6103 | 1,222 | 1,836 | 2,328 |
| 110 | 0,5943 | 1,19 | 1,787 | 2,266 |
| 120 | 0,579 | 1,159 | 1,741 | 2,207 |
| 130 | 0,5646 | 1,13 | 1,697 | 2,15 |
| 140 | 0,5508 | 1,102 | 1,655 | 2,097 |
| ↓ t, °С | P, kPa → | 133 | 160 | 186 | 213 |
|---|---|---|---|---|
| -20 | 4,695 | 5,768 | — | — |
| -10 | 4,446 | 5,389 | 6,366 | 7,389 |
| 0 | 4,255 | 5,138 | 6,036 | 6,954 |
| 10 | 4,092 | 4,933 | 5,783 | 6,645 |
| 20 | 3,945 | 4,751 | 5,565 | 6,385 |
| 30 | 3,809 | 4,585 | 5,367 | 6,154 |
| 40 | 3,682 | 4,431 | 5,184 | 5,942 |
| 50 | 3,563 | 4,287 | 5,014 | 5,745 |
| 60 | 3,452 | 4,151 | 4,855 | 5,561 |
| 70 | 3,347 | 4,025 | 4,705 | 5,388 |
| 80 | 3,248 | 3,905 | 4,564 | 5,225 |
| 90 | 3,156 | 3,793 | 4,432 | 5,073 |
| 100 | 3,068 | 3,687 | 4,307 | 4,929 |
| 110 | 2,985 | 3,587 | 4,189 | 4,793 |
| 120 | 2,907 | 3,492 | 4,078 | 4,665 |
| 130 | 2,832 | 3,397 | 3,972 | 4,543 |
| 140 | 2,761 | 3,319 | 3,87 | 4,426 |
Density of liquid chlorine
Liquid chlorine can exist in a relatively narrow temperature range, the boundaries of which lie from minus 100.5 to plus 144 ° C (that is, from the melting point to the critical temperature). Above a temperature of 144°C, chlorine will not turn into a liquid state under any pressure. The density of liquid chlorine in this temperature range varies from 1717 to 573 kg/m3.
| t, °С | ρ, kg/m 3 | t, °С | ρ, kg/m 3 |
|---|---|---|---|
| -100 | 1717 | 30 | 1377 |
| -90 | 1694 | 40 | 1344 |
| -80 | 1673 | 50 | 1310 |
| -70 | 1646 | 60 | 1275 |
| -60 | 1622 | 70 | 1240 |
| -50 | 1598 | 80 | 1199 |
| -40 | 1574 | 90 | 1156 |
| -30 | 1550 | 100 | 1109 |
| -20 | 1524 | 110 | 1059 |
| -10 | 1496 | 120 | 998 |
| 0 | 1468 | 130 | 920 |
| 10 | 1438 | 140 | 750 |
| 20 | 1408 | 144 | 573 |
Specific heat capacity of chlorine
The specific heat capacity of chlorine gas C p in kJ/(kg K) in the temperature range from 0 to 1200°C and normal atmospheric pressure can be calculated using the formula:
where T is the absolute temperature of chlorine in degrees Kelvin.
It should be noted that under normal conditions the specific heat capacity of chlorine is 471 J/(kg K) and increases when heated. The increase in heat capacity at temperatures above 500°C becomes insignificant, and at high temperatures the specific heat of chlorine remains virtually unchanged.
The table shows the results of calculating the specific heat of chlorine using the above formula (the calculation error is about 1%).
| t, °С | C p , J/(kg K) | t, °С | C p , J/(kg K) |
|---|---|---|---|
| 0 | 471 | 250 | 506 |
| 10 | 474 | 300 | 508 |
| 20 | 477 | 350 | 510 |
| 30 | 480 | 400 | 511 |
| 40 | 482 | 450 | 512 |
| 50 | 485 | 500 | 513 |
| 60 | 487 | 550 | 514 |
| 70 | 488 | 600 | 514 |
| 80 | 490 | 650 | 515 |
| 90 | 492 | 700 | 515 |
| 100 | 493 | 750 | 515 |
| 110 | 494 | 800 | 516 |
| 120 | 496 | 850 | 516 |
| 130 | 497 | 900 | 516 |
| 140 | 498 | 950 | 516 |
| 150 | 499 | 1000 | 517 |
| 200 | 503 | 1100 | 517 |
At temperatures close to absolute zero, chlorine is in a solid state and has a low specific heat capacity (19 J/(kg K)). As the temperature of solid Cl 2 increases, its heat capacity increases and reaches a value of 720 J/(kg K) at minus 143°C.
Liquid chlorine has a specific heat capacity of 918...949 J/(kg K) in the range from 0 to -90 degrees Celsius. According to the table, it can be seen that the specific heat capacity of liquid chlorine is higher than that of gaseous chlorine and decreases with increasing temperature.
Thermal conductivity of chlorine
The table shows the values of the thermal conductivity coefficients of chlorine gas at normal atmospheric pressure in the temperature range from -70 to 400°C.
The thermal conductivity coefficient of chlorine under normal conditions is 0.0079 W/(m deg), which is 3 times less than at the same temperature and pressure. Heating chlorine leads to an increase in its thermal conductivity. Thus, at a temperature of 100°C, the value of this physical property of chlorine increases to 0.0114 W/(m deg).
| t, °С | λ, W/(m deg) | t, °С | λ, W/(m deg) |
|---|---|---|---|
| -70 | 0,0054 | 50 | 0,0096 |
| -60 | 0,0058 | 60 | 0,01 |
| -50 | 0,0062 | 70 | 0,0104 |
| -40 | 0,0065 | 80 | 0,0107 |
| -30 | 0,0068 | 90 | 0,0111 |
| -20 | 0,0072 | 100 | 0,0114 |
| -10 | 0,0076 | 150 | 0,0133 |
| 0 | 0,0079 | 200 | 0,0149 |
| 10 | 0,0082 | 250 | 0,0165 |
| 20 | 0,0086 | 300 | 0,018 |
| 30 | 0,009 | 350 | 0,0195 |
| 40 | 0,0093 | 400 | 0,0207 |
Chlorine viscosity
The coefficient of dynamic viscosity of gaseous chlorine in the temperature range 20...500°C can be approximately calculated using the formula:
where η T is the coefficient of dynamic viscosity of chlorine at a given temperature T, K;
η T 0 - coefficient of dynamic viscosity of chlorine at temperature T 0 = 273 K (at normal conditions);
C is the Sutherland constant (for chlorine C = 351).
Under normal conditions, the dynamic viscosity of chlorine is 0.0123·10 -3 Pa·s. When heated, the physical property of chlorine, such as viscosity, takes on higher values.
Liquid chlorine has a viscosity an order of magnitude higher than gaseous chlorine. For example, at a temperature of 20°C, the dynamic viscosity of liquid chlorine has a value of 0.345·10 -3 Pa·s and decreases with increasing temperature.
Sources:
- Barkov S. A. Halogens and the manganese subgroup. Elements of group VII of the periodic table of D. I. Mendeleev. A manual for students. M.: Education, 1976 - 112 p.
- Tables of physical quantities. Directory. Ed. acad. I. K. Kikoina. M.: Atomizdat, 1976 - 1008 p.
- Yakimenko L. M., Pasmanik M. I. Handbook on the production of chlorine, caustic soda and basic chlorine products. Ed. 2nd, per. and others. M.: Chemistry, 1976 - 440 p.