Where is chlorine used? Chlorine gas, the physical properties of chlorine, the chemical properties of chlorine. Chlorine chlorine production methods
Characterization of elements of group VII of the main subgroup, for example, chlorine
General characteristics of the subgroup
Table 1. The nomenclature of the elements of subgroup VIIA
P-elements, typical, non-metals (astatine - semimetal), halogens.
Electronic diagram of the Hal element (Hal ≠ F):
The elements of subgroup VIIA are characterized by the following valencies:
Table 2. Valency
3. The elements of subgroup VIIA are characterized by the following oxidation states:
Table 3. The degree of oxidation of the elements
Characterization 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)
The number of protons, neutrons, electrons: 17,18,17
Atom 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)
Pauling Electronegativity: 3.20
Characterization of a simple substance
Type of connection: covalent non-polar
Diatomic molecule
Isotopes: 35 Cl (75.78%) and 37 Cl (24.22%)
Type of crystal lattice: molecular
Thermodynamic parameters
Table 4
Physical properties
Table 5
Chemical properties
An aqueous solution of chlorine is subject to a large degree of dismutation ("chlorine water")
Stage 1: Cl 2 + H 2 O \u003d HCl + HOCl
Stage 2: HOCl \u003d HCl + [O] - atomic oxygen
The oxidizing ability in the subgroup decreases from fluorine to iodine \u003d ˃
Chlorine is a strong oxidizing agent:
1. Interaction with simple substances
a) with hydrogen:
Cl 2 + H 2 \u003d 2HCl
b) with metals:
Cl 2 + 2Na \u003d 2NaCl
3Cl 2 + 2Fe \u003d 2FeCl 3
c) with some less electronegative non-metals:
3Cl 2 + 2P \u003d 2PCl 3
Cl 2 + S \u003d 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 \u003d NaCl + NaClO + H 2 O
when heated: 3Cl 2 + 6 KOH \u003d 5KCl + KClO 3 + 3H 2 O
e) with many organic substances:
Cl 2 + CH 4 \u003d CH 3 Cl + HCl
C 6 H 6 + Cl 2 \u003d C 6 H 5 Cl + HCl
Essential Chlorine Compounds
Hydrogen chloride, hydrogen chloride(HCl) - a colorless, thermally stable gas (under normal conditions) with a pungent odor that fumes in moist air, easily dissolves in water (up to 500 volumes of gas per volume of water) with the formation of hydrochloric (hydrochloric) acid. At −114.22 ° C, HCl transforms into a solid state. In the solid state, hydrogen chloride exists in the form of two crystalline modifications: rhombic, 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 W \u003d H 3 O + W + Cl - W
The dissolution process is highly exothermic. HCl forms an azeotropic mixture with water. It is a strong monobasic acid. Vigorously interacts with all metals in a series of stresses 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
Under the action of 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 with oxygen (the catalyst is copper (II) chloride CuCl 2):
4 HCl + O 2 → 2 H 2 O +2 Cl 2
However, concentrated hydrochloric acid reacts with copper, and a complex of monovalent copper is formed:
2 Cu + 4 HCl → 2 H + H 2
A mixture of 3 parts by volume of concentrated hydrochloric and 1 parts by volume of concentrated nitric acid is called “aqua regia”. Imperial vodka can dissolve even 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 materials:
4 H 3 O + + 3 Cl - + NO 3 - \u003d NOCl + Cl 2 + 6 H 2 O
Due to the high concentration of chloride ions in the solution, the metal binds to the chloride complex, which contributes to its dissolution:
3 Pt + 4 HNO 3 + 18 HCl → 3 H 2 + 4 NO + 8 H 2 O
Hydrogen chloride is also characterized by reactions of addition to multiple bonds (electrophilic addition):
R-CH \u003d 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, 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 well-known: short-lived ClO radical, chlorine peroxide radical ClOO and chlorine tetraoxide radical ClO 4.
The table below presents the properties of stable chlorine oxides:
Table 6
| Property | Cl 2 O | Clo 2 | ClOClO 3 | Cl 2 O 6 (g) ↔2ClO 3 (g) | Cl 2 O 7 |
| Color and condition at room temperature | Tan 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 |
| T. boiling. ° C | 2,0 | 44,5 | |||
| d (w, 0 ° C), g * cm -3 | - | 1,64 | 1,806 | - | 2,02 |
| ΔH ° arr (gas, 298 K), kJ * mol -1 | 80,3 | 102,6 | ~180 | (155) | |
| ΔG ° arr (gas, 298 K), kJ * mol -1 | 97,9 | 120,6 | - | - | - |
| S ° arr (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), dichloride 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 resembling the smell of chlorine. At temperatures below 2 ° C, the liquid is golden red. Toxic: affects the respiratory tract. Spontaneously slowly decomposes:
At high concentrations, explosive. Density under normal conditions is 3.22 kg / m³. It is soluble in carbon tetrachloride. It is soluble in water with the formation of weak hypochlorous acid:
Quickly reacts with alkalis:
Cl 2 O + 2NaOH (decomp.) \u003d 2NaClO + H 2 O
Chlorine dioxide - acid oxide. When dissolved in water, chloride and chloric acid are formed (disproportionation reaction). Diluted solutions are stable in the dark, slowly decompose in the light:
Chlorine dioxide - chlorine oxide ( IV), a compound of chlorine and oxygen, the 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 reddish brown liquid. It is unstable, explodes in the light, in contact with oxidizing agents and when heated. It is soluble in water. Due to the explosion hazard, chlorine dioxide cannot be stored in liquid form.
Acid oxide. When dissolved in water, chloride and chloric acid are formed (disproportionation reaction). Diluted solutions are stable in the dark, slowly decompose in the light:
The resulting chloride is very unstable and decomposes:
It exhibits redox properties.
2ClO 2 + 5H 2 SO 4 (decomp.) + 10FeSO 4 \u003d 5Fe 2 (SO 4) 3 + 2HCl + 4H 2 O
ClO 2 + 2NaOH chol. \u003d NaClO 2 + NaClO 3 + H 2 O
ClO 2 + O 3 \u003d ClO 3 + O 2
ClO 2 reacts with many with organic compounds and acts as an oxidizing agent of medium strength.
Hypochlorous acid - HClO, a very weak monobasic 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 hypochlorite anion ClO -:
Unstable. Hypochlorous acid and its salts - hypochlorites - strong oxidizing agents. Reacts with hydrochloric acid HCl to produce molecular chlorine:
HClO + NaOH (decomp.) \u003d NaClO + H 2 O 
Chlorous acid - HClO 2, a monobasic acid of medium strength.
Chloric acid HClO 2 in its free form is unstable, even in a dilute aqueous solution it quickly decomposes:
It is neutralized by alkalis.
HClO 2 + NaOH (decomp. Cold) \u003d NaClO 2 + H 2 O
The anhydride of this acid is unknown.
An acid solution is obtained from its salts - chloritesresulting from the interaction of ClO 2 with alkali:
It exhibits redox properties.
5HClO 2 + 3H 2 SO 4 (decomp.) + 2KMnO 4 \u003d 5HClO 3 + 2MnSO 4 + K 2 SO 4 + 3H 2 O
Chloric acid - HClO 3, a strong monobasic acid in which chlorine has an oxidation state of +5. In free form not received; in aqueous solutions at a concentration below 30% in the cold it is quite stable; in more concentrated solutions it decomposes:
Chloric acid is a strong oxidizing agent; oxidative ability increases with increasing concentration and temperature. HClO 3 is easily reduced to hydrochloric acid:
HClO 3 + 5HCl (conc.) \u003d 3Cl 2 + 3H 2 O
HClO 3 + NaOH (decomp.) \u003d NaClO 3 + H 2 O
When passing a mixture of SO 2 and air through a strongly acidic solution, chlorine dioxide is formed:
In 40% perchloric acid, for example, filter paper ignites.
8. Being in nature:
In the earth's crust, chlorine is the most common halogen. Since chlorine is very active, in nature it is found only in the form of compounds in minerals.
Table 7. Being in nature
Table 7. Mineral forms
The largest chlorine reserves are contained in the salts of the waters of the seas and oceans.
Getting
Chemical methods for producing chlorine are ineffective and costly. Today they are mainly of historical importance. It can be obtained by the interaction of potassium permanganate with hydrochloric acid:
Scheele Method
Initially, the industrial method of producing chlorine was based on the Scheele method, that is, the reaction of pyrolusite with hydrochloric acid:
Deacon Method
The method of producing chlorine by catalytic oxidation of hydrogen chloride by atmospheric oxygen.
Electrochemical methods
Today, chlorine is produced on an industrial scale together with sodium hydroxide and hydrogen by electrolysis of a solution of sodium chloride, the main processes of which can be represented by the total formula:
Application
· Window profile made of chlorinated polymers
· The main component of bleaches is Labarrakova water (sodium hypochlorite)
· In the production of polyvinyl chloride, plastic compounds, synthetic rubber.
· Production of organochlorine. A significant part of the produced chlorine is consumed in obtaining 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”.
· In the food industry is registered as a food additive E925.
· In the chemical production of hydrochloric acid, bleach, bertholeta 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 strive to limit the use of chlorine in everyday life, including because a significant amount of dioxins is formed during the burning of chlorine-containing garbage.
Physical properties Under ordinary conditions, chlorine is a yellow-green gas with a pungent odor and is poisonous. It is 2.5 times heavier than air. In 1 volume of water at 20 degrees. C dissolves about 2 volumes of chlorine. This solution is called chlorine water.
At atmospheric pressure, chlorine at -34 degrees. C goes into a liquid state, and at -101 deg. C hardens. At room temperature, it transforms into a liquid state only at a pressure of 600 kPa (6 atm). Chlorine is highly soluble in many organic solvents, especially carbon tetrachloride, with which it does not interact.
Chemical properties. At the external electronic level of the chlorine atom there are 7 electrons (s 2 p 5), so it easily attaches an electron, forming the Cl - anion. Due to the presence of an unfilled d-level, 1, 3, 5, and 7 unpaired electrons can appear in the chlorine atom; therefore, in oxygen-containing compounds it can have an oxidation state of +1, +3, +5, and +7.
In the absence of moisture, chlorine is quite inert, but in the presence of even traces of moisture, its activity increases sharply. It interacts well with metals:
2 Fe + 3 Cl 2 \u003d 2 FeCl 3 (iron (III) chloride);
Cu + Cl 2 \u003d CuCl 2 (copper (II) chloride)
and many non-metals:
H 2 + Cl 2 \u003d 2 Hcl (hydrogen chloride);
2 S + Cl 2 \u003d S 2 Cl 2 (sulfur chloride (1));
Si + 2 Cl 2 \u003d SiCl 4 (silicon chloride. (IV));
2 P + 5 Cl 2 \u003d 2 PCl 5 (phosphorus (V) chloride).
Chlorine does not directly interact with oxygen, carbon, and nitrogen.
When chlorine dissolves in water, 2 acids are formed: hydrochloric, or hydrochloric, and hypochlorous:
Cl 2 + H 2 O \u003d Hcl + HClO.
When chlorine interacts with cold alkali solutions, the corresponding salts of these acids are formed:
Cl 2 + 2 NaOH \u003d NaCl + NaClO + H 2 O.
The resulting solutions are called javelin water, which, like chlorine water, has strong oxidizing properties due to the presence of ClO - and is used to bleach fabrics and paper. With hot alkali solutions, chlorine forms the corresponding salts of hydrochloric and perchloric acids:
3 Cl 2 + 6 NaOH \u003d 5 NaCl + NaCl 3 + 3 H 2 O;
3 Cl 2 + 6 KOH \u003d 5 KCl + KCl 3 + 3 H 2 O.
The resulting potassium chlorate is called the Bertholite salt.
When heated, chlorine easily interacts with many organic substances. In saturated and aromatic hydrocarbons, it replaces hydrogen, forming an organochlorine compound and hydrogen chloride, and attached to unsaturated hydrocarbons in place of a double or triple bond.
At very high temperatures, chlorine completely removes hydrogen from carbon. In this case, hydrogen chloride and soot are formed. Therefore, high-temperature chlorination of hydrocarbons is always accompanied by soot formation.
Chlorine is a strong oxidizing agent, therefore, it easily interacts with complex substances, which include elements that can oxidize to a higher valence state:
2 FeCl 2 + Cl 2 \u003d 2 FeCl 3;
H 2 SO 3 + Cl 2 + H 2 O \u003d H 2 SO 4 + 2 Hcl.
Chlorine (from the Greek. χλωρ? ς - "green") - an element of the main subgroup of the seventh group, the third period of the periodic system of chemical elements D. I. Mendeleev, with atomic number 17. It is designated by the symbol Cl (lat. Chlorum) Reactive non-metal. It is part of the halogen group (originally the German chemist Schweiger used the name “halogen” for chlorine [literally, “halogen” is translated as malt], but it did not take root, and subsequently became common to the VII group of elements, which includes chlorine).
The simple substance is chlorine (CAS number: 7782-50-5) under normal conditions - a poisonous gas of yellowish-green color, with a pungent odor. Diatomic chlorine molecule (Cl 2 formula).
History of the discovery of chlorine
The first gaseous anhydrous hydrogen chloride was collected by J. Prisley in 1772. (over liquid mercury). Chlorine was first obtained in 1774 by Scheele, who described its evolution during the interaction of pyrolusite with hydrochloric acid in his treatise on pyrolysite:
4HCl + MnO 2 \u003d Cl 2 + MnCl 2 + 2H 2 O
Scheele noted the smell of chlorine, similar to the smell of aqua regia, its ability to interact with gold and cinnabar, as well as its whitening properties.
However, Scheele, in accordance with the phlogiston theory that prevailed in chemistry at that time, suggested that chlorine is a de-log of hydrochloric acid, i.e., hydrochloric acid oxide. Bertollet and Lavoisier suggested that chlorine is an oxide of the element muriaHowever, attempts to isolate it were unsuccessful until the work of Davy, who was able to decompose sodium chloride and sodium chloride by electrolysis.
Spread in nature
In nature, there are two isotopes of chlorine 35 Cl and 37 Cl. In the earth's crust, chlorine is the most common halogen. Chlorine is very active - it directly connects with almost all elements of the periodic system. Therefore, in nature it occurs only in the form of compounds in the minerals: halite NaCI, sylvin KCl, sylvinite KCl · NaCl, bischofite MgCl 2 · 6H2O, carnallite KCl · MgCl 2 · 6H 2 O, kainite KCl · MgSO 4 · 3H 2 O. The largest chlorine reserves are contained in the salts of the waters of the seas and oceans (content in sea water 19 g / l). Chlorine accounts for 0.025% of the total number of atoms in the earth's crust, the clarke number of chlorine is 0.017%, and the human body contains 0.25% by weight of chlorine ions. In humans and animals, 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 work of nerve cells.
Physical and physico-chemical properties
Under normal conditions, chlorine is a yellow-green gas with a choking odor. Some of its physical properties are presented in the table.
Some physical properties of chlorine
| Property |
Value |
|---|---|
| Color (gas) | Yellow green |
| Boiling temperature | −34 ° C |
| The melting temperature | −100 ° C |
| Decomposition temperature (dissociation into atoms) |
~ 1400 ° C |
| Density (gas, n.o.) | 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 / molK) |
| 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) |
| Enthalpy of melting | 6.406 (kJ / mol) |
| Enthalpy of boiling | 20.41 (kJ / mol) |
| The energy of homolytic bond cleavage XX | 243 (kJ / mol) |
| Heterolytic bond cleavage energy XX | 1150 (kJ / mol) |
| Ionization energy | 1255 (kJ / mol) |
| Electron affinity energy | 349 (kJ / mol) |
| Atomic radius | 0.073 (nm) |
| Pauling Electronegativity | 3,20 |
| Allred-Rohov Electronegativity | 2,83 |
| Steady oxidation states | -1, 0, +1, +3, (+4), +5, (+6), +7 |
Chlorine gas is relatively easily liquefied. Starting from a pressure of 0.8 MPa (8 atmospheres), chlorine will be liquid even at room temperature. When cooled to a temperature of −34 ° C, chlorine also becomes liquid at normal atmospheric pressure. Liquid chlorine is a yellow-green liquid with a very high corrosive effect (due to the high concentration of molecules). By increasing the pressure, it is possible to achieve the existence of liquid chlorine up to a temperature of +144 ° C (critical temperature) at a critical pressure of 7.6 MPa.
At temperatures below −101 ° C, liquid chlorine crystallizes into an orthorhombic lattice with a space group Cmca and parameters a \u003d 6.29 Å b \u003d 4.50 Å, c \u003d 8.21 Å. Below 100 K, the orthorhombic modification of crystalline chlorine transforms into a tetragonal, having a spatial group P4 2 / ncm and the lattice parameters a \u003d 8.56 Å and c \u003d 6.12 Å.
Solubility
The degree of dissociation of the chlorine molecule Cl 2 → 2Cl. At 1000 K, it is 2.07 × 10 −4%, and at 2500 K it is 0.909%.
The odor threshold in air is 0.003 (mg / L).
In terms of electrical conductivity, liquid chlorine ranks among the most powerful insulators: it conducts current almost a billion times worse than distilled water, and 10 to 22 times worse than silver. The speed of sound in chlorine is about one and a half times less than in air.
Chemical properties
The structure of the electronic shell
At the valence level of the chlorine atom there is 1 unpaired electron: 1s 2 2s 2 2p 6 3s 2 3p 5, so the valency of 1 for the chlorine atom is very stable. Due to the presence of an unoccupied d-sublevel in the chlorine atom, the chlorine atom can also exhibit other valencies. Scheme of the formation of excited states of an atom:
Chlorine compounds are also known in which the chlorine atom formally exhibits valencies 4 and 6, for example, ClO 2 and Cl 2 O 6. However, these compounds are radicals, that is, they have one unpaired electron.
Metal interaction
Chlorine directly reacts with almost all metals (with some only in the presence of moisture or when heated):
Cl 2 + 2Na → 2NaCl 3Cl 2 + 2Sb → 2SbCl 3 3Cl 2 + 2Fe → 2FeCl 3
Interaction with non-metals
With non-metals (except carbon, nitrogen, oxygen and inert gases), forms the corresponding chlorides.
In light or when heated, it reacts actively (sometimes with an explosion) with hydrogen by a radical mechanism. Mixtures of chlorine with hydrogen containing from 5.8 to 88.3% hydrogen explode upon irradiation with the formation of hydrogen chloride. A mixture of chlorine with hydrogen in small concentrations burns with a colorless or yellow-green flame. The maximum temperature of the hydrogen-chlorine flame is 2200 ° C .:
Cl 2 + H 2 → 2HCl 5Cl 2 + 2P → 2PCl 5 2S + Cl 2 → S 2 Cl 2
Chlorine forms oxides with oxygen in which it exhibits an oxidation state of +1 to +7: Cl 2 O, ClO 2, Cl 2 O 6, Cl 2 O 7. They have a pungent odor, are thermally and photochemically unstable, prone to explosive decay.
When reacting with fluorine, not chloride is formed, but fluoride:
Cl 2 + 3F 2 (g) → 2ClF 3
Other properties
Chlorine displaces bromine and iodine from their compounds with hydrogen and metals:
Cl 2 + 2HBr → Br 2 + 2HCl Cl 2 + 2NaI → I 2 + 2NaCl
When reacting with carbon monoxide, phosgene is formed:
Cl 2 + CO → COCl 2
When dissolved in water or alkalis, chlorine dismutes, 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
Chlorination of dry calcium hydroxide gives bleach:
Cl 2 + Ca (OH) 2 → CaCl (OCl) + H 2 O
The action of chlorine on ammonia can produce nitrogen trichloride:
4NH 3 + 3Cl 2 → NCl 3 + 3NH 4 Cl
Oxidizing properties of chlorine
Chlorine is a very strong oxidizing agent.
Cl 2 + H 2 S → 2HCl + S
Reactions with Organic Substances
With saturated compounds:
CH 3 -CH 3 + Cl 2 → C 2 H 5 Cl + HCl
Joins unsaturated compounds by multiple bonds:
CH 2 \u003d CH 2 + Cl 2 → Cl-CH 2 -CH 2 -Cl
Aromatic compounds replace the 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
Production methods
Industrial methods
Initially, the industrial method of 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
In 1867, Deacon developed a method for producing chlorine by catalytic oxidation of hydrogen chloride with atmospheric oxygen. The Deacon process is currently used in the recovery of chlorine from hydrogen chloride, a by-product of the industrial chlorination of organic compounds.
4HCl + O 2 → 2H 2 O + 2Cl 2
Today, chlorine is produced on an industrial scale together with sodium hydroxide and hydrogen by electrolysis of a solution of sodium chloride:
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 process of electrolysis of water is parallel to the electrolysis of sodium chloride, the total 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 versions of the electrochemical method for producing chlorine are used. Two of them are solid-cathode electrolysis: diaphragm and membrane methods, the third is electrolysis with a liquid mercury cathode (mercury production method). Among the electrochemical methods of production, the easiest and most convenient way 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.
Solid cathode diaphragm method
The cell cavity is divided by a porous asbestos baffle — the diaphragm — into the cathode and anode spaces, where the cathode and anode of the cell are respectively located. Therefore, such an electrolyzer is often called diaphragm, and the production method is called diaphragm electrolysis. A stream of saturated anolyte (NaCl solution) continuously enters 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 at the cathode due to the decomposition of water. In this case, the cathode zone is enriched with sodium hydroxide.
Solid cathode membrane method
The membrane method is essentially similar to the diaphragm method, but the anodic and cathodic spaces are separated by a cation exchange polymer membrane. The membrane production method is more effective than the diaphragm, 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 an 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 stream of mercury. Anodes - graphite or low wear. Together with mercury, an anolyte stream - a sodium chloride solution - continuously flows through the electrolyzer. As a result of the electrochemical decomposition of chloride, chlorine molecules are formed at the anode, and sodium released at the cathode dissolves in mercury to form an amalgam.
Laboratory methods
In laboratories, processes based on the oxidation of hydrogen chloride by strong oxidizing agents (e.g., manganese (IV) oxide, potassium permanganate, and potassium dichromate) are usually used in laboratories to produce chlorine:
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 produced chlorine is stored in special “tanks” or pumped into high-pressure steel cylinders. Cylinders with liquid chlorine under pressure have a special color - swamp color. It should be noted that during long-term operation of chlorine cylinders, extremely explosive trichloride nitrogen accumulates in them, and therefore, from time to time, chlorine cylinders must undergo a scheduled washing and purification of nitrogen chloride.
Chlorine Quality Standards
According to GOST 6718-93 “Liquid chlorine. Specifications "the following grades of chlorine are produced
Application
Chlorine is used in many industries, science and domestic needs:
- In the production of polyvinyl chloride, plastic compounds, synthetic rubber, of which they make: insulation for wires, window profiles, packaging materials, clothes and shoes, linoleum and gramophone records, varnishes, equipment and polystyrene, toys, instrument parts, building materials. Polyvinyl chloride is produced by polymerization of vinyl chloride, which today is most often obtained from ethylene by a chlorine-balanced method through intermediate 1,2-dichloroethane.
- The bleaching properties of chlorine have been known since ancient times, although chlorine itself does not “bleach”, but atomic oxygen, which is formed during the decomposition 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 safe for plants. A significant part of the produced chlorine is consumed in obtaining 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 found practical application only after more than 100 years - in the 30s of the twentieth century.
- It was used as a chemical warfare agent, as well as for the production of other chemical warfare agents: mustard gas, phosgene.
- For water disinfection - “chlorination”. The most common way to disinfect drinking water; based on the ability of free chlorine and its compounds to inhibit the enzyme systems of microorganisms catalyzing redox processes. For the disinfection of drinking water, chlorine, chlorine dioxide, chloramine and bleach are used. SanPiN 2.1.4.1074-01 sets 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 they cannot offer alternatives to the disinfecting effect of chlorine compounds. The materials from which the water pipes are made interact differently with chlorinated tap water. Free chlorine in tap water significantly reduces the service life of pipelines based on polyolefins: various types of polyethylene pipes, including cross-linked polyethylene, large known as PEX (PEX, PE-X). In the USA, in order to control the admission of pipelines made of polymeric materials for use in chlorinated water pipelines, they had to adopt 3 standards: ASTM F2023 for cross-linked polyethylene (PEX) pipes and hot chlorinated water, ASTM F2263 for all polyethylene pipes and chlorinated water and ASTM F2330 in relation to multilayer (metal-polymer) pipes and hot chlorinated water. In terms of durability, when interacting with chlorinated water, copper water pipes show positive results.
- In the food industry is registered as a food additive E925.
- In the chemical production of hydrochloric acid, bleach, bertholite, 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 strive to limit the use of chlorine in everyday life, including because a significant amount of dioxins is formed during the burning of chlorine-containing garbage.
Biological role
Chlorine is one of the most important nutrient elements and is part of all living organisms.
In animals and humans, chlorine ions are involved in maintaining osmotic equilibrium; the chloride ion has an optimal radius for penetration through the cell membrane. This explains his joint participation with sodium and potassium ions in creating a constant osmotic pressure and regulation of water-salt metabolism. Under the influence of GABA (neurotransmitter), chlorine ions have a inhibitory effect on neurons by reducing the action potential. In the stomach, chlorine ions create a favorable environment for the action of proteolytic enzymes of gastric juice. Chlorine channels are present in many types of cells, mitochondrial membranes, and skeletal muscle. These channels perform important functions in the regulation of fluid volume, transepithelial transport of ions and stabilization of membrane potentials, and are involved in maintaining the pH of cells. Chlorine accumulates in the visceral tissue, skin, and skeletal muscle. Chlorine is absorbed mainly in the large intestine. The absorption and excretion of chlorine are closely associated with sodium ions and bicarbonates, to a lesser extent with mineralocorticoids and the activity of Na + / K + - ATPase. 10-15% of all chlorine is accumulated in the cells, of this amount from 1/3 to 1/2 - in red blood cells. About 85% of chlorine is in the extracellular space. Chlorine is excreted mainly with urine (90-95%), feces (4-8%) and through the skin (up to 2%). Chlorine excretion 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 the 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 the destruction of pathogenic bacteria. Currently, the participation of chlorine in the occurrence of certain diseases in humans has not been studied well enough, mainly due to the small number of studies. Suffice it to say that even recommendations on the rate of daily consumption of chlorine have not been developed. Human muscle tissue contains 0.20-0.52% chlorine, bone - 0.09%; in the blood - 2.89 g / l. In the body of an average person (body weight 70 kg) 95 g of chlorine. Every day, with food, a person receives 3-6 g of chlorine, which in excess covers the need for this element.
Chlorine ions are vital to plants. Chlorine is involved in energy metabolism in plants, activating oxidative phosphorylation. It is necessary for the formation of oxygen in the process of photosynthesis by isolated chloroplasts, stimulates the auxiliary processes of photosynthesis, especially those associated with the accumulation of energy. Chlorine has a positive effect on the absorption of oxygen, potassium, calcium, and magnesium compounds by the roots. Excessive concentration of chlorine ions in plants can have a negative side, for example, reduce the content of chlorophyll, reduce the activity of photosynthesis, delay the growth and development of plants.
But there are plants that, in the course of evolution, either adapted to salinization of soils, or in the struggle for space, empty salt marshes on which there is no competition took over. Plants growing on saline soils are called halophytes, they accumulate chlorides during the growing season, and then get rid of excess through leaf fall or release chlorides on the surface of leaves and branches and get double benefit by shading the surface from sunlight.
Among microorganisms, halophiles - halobacteria - which live in highly saline waters or soils, are also known.
Work Features and Precautions
Chlorine is a toxic suffocating gas; if it enters the lungs, it causes burns to the lung tissue, asphyxiation. It causes irritation to the respiratory tract when the concentration in the air is about 0.006 mg / l (i.e. two times higher than the chlorine odor perception threshold). Chlorine was one of the first chemical poisons used by Germany in the First World War. When working with chlorine, protective clothing, a gas mask, and gloves should be used. For a short time, respiratory organs can be protected from the ingress of chlorine by a rag dressing moistened with a solution of sodium sulfite Na 2 SO 3 or sodium thiosulfate Na 2 S 2 O 3.
The maximum permissible concentration of chlorine in atmospheric air is as follows: daily average - 0.03 mg / m³; maximum single - 0.1 mg / m³; in the working rooms of an industrial enterprise - 1 mg / m³.
Chlorine was first obtained in 1772 by Scheele, who described its evolution during the interaction of pyrolyusite with hydrochloric acid in his treatise on pyrolyusite: 4HCl + MnO 2 \u003d Cl 2 + MnCl 2 + 2H 2 O
Scheele noted the smell of chlorine, similar to the smell of aqua regia, its ability to interact with gold and cinnabar, as well as its whitening properties. However, Scheele, in accordance with the phlogiston theory that prevailed in chemistry at that time, suggested that chlorine is a de-log of hydrochloric acid, i.e., hydrochloric acid oxide.
Bertollet and Lavoisier suggested that chlorine is an oxide of the element of muria, however, attempts to isolate it were unsuccessful until the work of Davy, who was able to decompose sodium chloride and sodium chloride by electrolysis.
The name of the element comes from Greek clwroz - "green."
Being in nature, receiving:
Natural chlorine is a mixture of two isotopes of 35 Cl and 37 Cl. In the earth's crust, chlorine is the most common halogen. Since chlorine is very active, it is found in nature only in the form of minerals: halite NaCl, sylvin KCl, sylvinite KCl · NaCl, bischofite MgCl 2 · 6H 2 O, carnallite KCl · MgCl 2 · 6Н 2 O, kainite KCl · MgSO 4 · 3H 2 O. The largest chlorine reserves are contained in the salts of the waters of the seas and oceans.
On an industrial scale, chlorine is obtained together with sodium hydroxide and hydrogen during the electrolysis of sodium chloride solution:
2NaCl + 2H 2 O \u003d\u003e H 2 + Cl 2 + 2NaOH
For the recovery of chlorine from hydrogen chloride, which is a by-product of the industrial chlorination of organic compounds, the Deacon process (catalytic oxidation of hydrogen chloride by atmospheric oxygen) is used:
4HCl + O 2 \u003d 2H 2 O + 2Cl 2
In laboratories, they usually use processes based on the oxidation of hydrogen chloride by strong oxidizing agents (for example, manganese (IV) oxide, potassium permanganate, potassium dichromate):
2KMnO 4 + 16HCl \u003d 5Cl 2 + 2MnCl 2 + 2KCl + 8H 2 O
K 2 Cr 2 O 7 + 14HCl \u003d 3Cl 2 + 2CrCl 3 + 2KCl + 7H 2 O
Physical properties:
Under normal conditions, chlorine is a yellow-green gas with a choking odor. Chlorine is noticeably soluble in water ("chlorine water"). At 20 ° C, 2.3 volumes of chlorine dissolve in one volume of water. Boiling point \u003d -34 ° C; melting point \u003d -101 ° C, density (gas, n.o.) \u003d 3.214 g / l.
Chemical properties:
Chlorine is very active - it directly connects with almost all elements of the periodic system, metals and non-metals (except carbon, nitrogen, oxygen and inert gases). Chlorine is a very strong oxidizing agent, displaces less active non-metals (bromine, iodine) from their compounds with hydrogen and metals:
Cl 2 + 2HBr \u003d Br 2 + 2HCl; Cl 2 + 2NaI \u003d I 2 + 2NaCl
When dissolved in water or alkalis, chlorine dismutes, forming hypochlorous (and, when heated, perchloric) and hydrochloric acids, or their salts.
Cl 2 + H 2 O HClO + HCl;
Chlorine interacts with many organic compounds, entering into substitution or addition reactions:
CH 3 -CH 3 + xCl 2 \u003d\u003e C 2 H 6-x Cl x + xHCl
CH 2 \u003d CH 2 + Cl 2 \u003d\u003e Cl-CH 2 -CH 2 -Cl
C 6 H 6 + Cl 2 \u003d\u003e C 6 H 6 Cl + HCl
Chlorine has seven oxidation states: -1, 0, +1, +3, +4, +5, +7.
The most important compounds:
Hydrogen Chloride HCl - colorless gas, smoke in air due to the formation of mist with water vapor. It has a pungent odor and irritates the respiratory tract. Contained in volcanic gases and waters, in gastric juice. Chemical properties depend on the state in which it is (may be in a gaseous, liquid state or in solution). HCl solution is called hydrochloric (hydrochloric) acid. This is a strong acid, displaces weaker acids from their salts. Salts - chlorides - solid crystalline substances with high melting points.
Covalent Chlorides - compounds of chlorine with non-metals, gases, liquids or fusible solids having characteristic acidic properties, usually easily hydrolyzed with water to form hydrochloric acid:
PCl 5 + 4H 2 O \u003d H 3 PO 4 + 5HCl;
Chlorine Oxide (I) Cl 2 O., gas is brownish yellow with a pungent odor. It affects the respiratory organs. Easily soluble in water, forming hypochlorous acid.
Hypochlorous acid HClO. Exists only in solutions. It is a weak and unstable acid. Easily decomposes into hydrochloric acid and oxygen. Strong oxidizing agent. Formed by the dissolution of chlorine in water. Salts - hypochlorites, unstable (NaClO * H 2 O decomposes with explosion at 70 ° C), strong oxidizing agents. Widely used for bleaching and disinfection bleaching powdermixed salt Ca (Cl) OCl
Chloric acid HClO 2, in its free form is unstable, even in a dilute aqueous solution it quickly decomposes. Acid of medium strength, salt - chlorites, as a rule, are colorless and well soluble in water. Unlike hypochlorites, chlorites exhibit pronounced oxidative properties only in an acidic environment. The greatest application (for bleaching fabrics and paper pulp) has sodium chlorite NaClO 2.
Chlorine (IV) oxide ClO 2, - a greenish-yellow gas with an unpleasant (pungent) smell, ...
Chloric acid, HClO 3 - in free form is unstable: disproportionates to ClO 2 and HClO 4. Salts - chlorates; Of these, sodium, potassium, calcium and magnesium chlorates are of the greatest importance. These are strong oxidizing agents, in a mixture with reducing agents explosive. Potassium chlorate ( bertoletova salt) - KClO 3, was used to produce oxygen in the laboratory, but because of the high danger it was no longer used. Potassium chlorate solutions were used as a weak antiseptic, an external medicine for gargling.
Perchloric acid HClO 4, in aqueous solutions, perchloric acid is the most stable of all oxygen-containing acids of chlorine. Anhydrous perchloric acid, which is obtained using concentrated sulfuric acid from 72% HClO 4 is not very stable. This is the strongest monobasic acid (in aqueous solution). Salts - perchloratesare used as oxidizing agents (solid propellant rocket engines).
Application:
Chlorine is used in many industries, science and domestic needs:
- In the production of polyvinyl chloride, plastic compounds, synthetic rubber;
- For bleaching fabrics and paper;
- Production of organochlorine insecticides - substances that kill insects harmful to crops, but safe for plants;
- For water disinfection - "chlorination";
- In the food industry is registered as a food additive E925;
- In the chemical production of hydrochloric acid, bleach, barletole salt, metal chlorides, poisons, drugs, fertilizers;
- In metallurgy for the production of pure metals: titanium, tin, tantalum, niobium.
Biological role and toxicity:
Chlorine is one of the most important nutrient elements and is part of all living organisms. In animals and humans, chlorine ions are involved in maintaining osmotic balance, the chloride ion has an optimal radius for penetration through the cell membrane. Chlorine ions are vital for plants, participating in energy metabolism in plants, activating oxidative phosphorylation.
Chlorine in the form of a simple substance is poisonous; if it enters the lungs, it causes burns to lung tissue, asphyxiation. It causes irritation to the respiratory tract when the concentration in the air is about 0.006 mg / l (i.e. two times higher than the chlorine odor perception threshold). Chlorine was one of the first chemical poisons used by Germany in World War I.
Korotkova Yu., Shvetsova I.
HF Tyumen State University, 571 group.
Sources: Wikipedia: http://ru.wikipedia.org/wiki/Cl et al.,
Website RCTU them. D.I. Mendeleev:
Ministry of Education and Science of the RUSSIAN FEDERATION
Federal State Budgetary Educational Institution of Higher Vocational Education
IVANOVO STATE CHEMICAL-TECHNOLOGICAL UNIVERSITY
Department of TP and MET
abstract
Chlorine: properties, application, preparation
Head: Efremov A.M.
Ivanovo 2015
Introduction
Chlorine General
Chlorine use
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 large-scale use of chlorine in various fields of science, industry, medicine and in everyday life, the demand for it has dramatically increased recently. There are many methods for producing chlorine by laboratory and industrial methods, but all of them 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 produced in salt fields, is a fairly energy-intensive process, harmful from an environmental point of view and very dangerous for life and health.
At present, the problem of developing a technology for producing chlorine is very urgent, which would eliminate all the above disadvantages, and also have a high yield of chlorine.
.Chlorine General
Chlorine was first obtained in 1774 by C. 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 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 system of elements of D. I. Mendeleev. Molecular mass of 70.906, atomic mass of 35.453, atomic number - 17, belongs to the halogen family. Under normal conditions, free chlorine, consisting of diatomic molecules, is a greenish yellow non-combustible gas with a characteristic pungent and irritating odor. It is toxic and causes choking. Compressed chlorine gas at atmospheric pressure turns into an amber-colored 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 gaseous chlorine is 3.214 kg / m3, i.e. it is about 2.5 times heavier than air.
Chemically, chlorine is very active, directly binds to almost all metals (with some only in the presence of moisture or when heated) and non-metals (except carbon, nitrogen, oxygen, inert gases), forms 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 interact with chlorine with ignition, most metals react with dry chlorine only when heated. Steel, as well as some metals are resistant in the atmosphere of 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 PCl3, and with further chlorination - PCl5. Sulfur with chlorine when heated gives S2Cl2, SCl2 and other SnClm. Arsenic, antimony, bismuth, strontium, tellurium interact vigorously with chlorine. A mixture of chlorine with 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, electric sparks, heating, from the presence of certain substances, such as iron oxides.
Chlorine forms oxides with oxygen: Cl2O, ClO2, Cl2O6, Cl2O7, Cl2O8, as well as hypochlorites (hypochlorous acid salts), chlorites, chlorates and perchlorates. All oxygen compounds of chlorine form explosive mixtures with easily oxidized substances. Chlorine oxides are weak and can spontaneously explode, 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 called chlorine water. When chlorinating aqueous solutions of alkalis in the cold, hypochlorites and chlorides are formed: 2NaOH + Cl2 \u003d NaClO + NaCl + Н2О, and when heated, chlorates. Chlorination of dry calcium hydroxide gives bleach. When ammonia reacts with chlorine, nitrogen trichloride is formed. In the chlorination of organic compounds, chlorine either replaces hydrogen, or joins in multiple bonds, forming various chlorine-containing organic compounds. With other halogens, chlorine forms interhalogen compounds. Chlorine fluorides ClF, ClF3, ClF3 are very reactive; for example, in a ClF3 atmosphere, glass wool spontaneously ignites. Compounds of chlorine with oxygen and fluorine are known - chlorine oxyfluorides: ClO3F, ClO2F3, ClOF, ClOF3 and fluorine perchlorate FClO4.
Chlorine is found in nature only in the form of compounds. Its average content in the earth's crust is 1.7 · 10-2% by weight. The main role in the history of chlorine in the earth's crust is played by water migration. It is found in the form of the Cl– ion in the World Ocean (1.93%), underground brines, and salt lakes. The number of own minerals (mainly natural chlorides) is 97, the main of which is halite NaCl (Rock salt). Large deposits of potassium and magnesium chlorides and mixed chlorides are also known: sylvin KCl, sylvinite (Na, K) Cl, carnalite KCl · MgCl2 · 6H2O, cainite KCl · MgSO4 · 3H2O, bischofite MgCl2 · 6H2O. In the history of the Earth, the influx of HCl contained in volcanic gases into the upper parts of the earth's crust was of great importance.
Chlorine Quality Standards
Name of indicator GOST 6718-93 Top grade First grade Volume fraction of chlorine, not less than,% 99,899.6 Mass fraction of water, not more than,% 0,010,04 Mass fraction of nitrogen trichloride, not more than,% 0,0020,004 Mass fraction of non-volatile residue, not 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 (with a volume of 10-250 m3) and ball (with a volume of 600-2000 m3) cylinders under a vapor pressure of 18 kgf / cm2. The maximum storage volumes are 150 tons. Cylinders with liquid chlorine under pressure have a special color - a protective color. In case of depressurization of a chlorine cylinder, a sharp gas emission occurs with a concentration several times higher than the lethal one. It should be noted that during long-term operation of chlorine cylinders, extremely explosive trichloride nitrogen accumulates in them, and therefore, from time to time, chlorine cylinders must undergo a scheduled washing and purification of nitrogen chloride. Chlorine is transported in containers, railway tanks, cylinders, which are its temporary storage.
2.Chlorine use
Chlorine is consumed primarily by the chemical industry for the production of various organic chlorine derivatives, which are 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 for the production of hydrochloric acid, bleach, chlorates and other products. Significant amounts of chlorine go to metallurgy for chlorination in the processing of polymetallic ores, for 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 wastewater, in pyrotechnics and some other areas of the national economy . As a result of the development of the areas of use of chlorine, mainly due to the success of organic synthesis, the global chlorine production is more than 20 million tons / year.
The main examples of the application and use of chlorine in various fields of science, industry and domestic needs:
1.in the production of polyvinyl chloride, plastic compounds, synthetic rubber, of which they make: insulation for wires, window profiles, packaging materials, clothes and shoes, linoleum and gramophone records, varnishes, equipment and polystyrene, toys, instrument parts, building materials. Polyvinyl chloride is produced by polymerization of vinyl chloride, which today is most often obtained from ethylene by a chlorine-balanced method through intermediate 1,2-dichloroethane.
CH2 \u003d CH2 + Cl2 \u003d\u003e CH2Cl-CH2ClCl-CH2Cl \u003d\u003e CH2 \u003d CHCl + HCl
1)as a bleaching agent (although not chlorine itself “bleaches”, but atomic oxygen, which is formed during the decomposition of hypochlorous acid by the reaction: Cl2 + H2O? HCl + HClO? 2HCl + O *).
2)in the production of organochlorine insecticides - substances that kill insects harmful to crops, but 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 disinfecting 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. For disinfection of drinking water, chlorine (Cl2), chlorine dioxide (ClO2), chloramine (NH2Cl) and bleach (Ca (Cl) OCl) are used.
)in the food industry is registered as a food additive E925.
)in the chemical production of caustic soda (NaOH) (used in the manufacture of artificial silk, in the soap industry), hydrochloric acid (HCl), perchloric lime, bertholite salt (KClO3), metal chlorides, poisons, drugs, fertilizers.
)in metallurgy for the production of pure metals: titanium, tin, tantalum, niobium.
TiO2 + 2C + 2Cl2 \u003d\u003e TiCl4 + 2CO;
TiCl4 + 2Mg \u003d\u003e 2MgCl2 + Ti (at Т \u003d 850 ° С)
)as an indicator of solar neutrinos in chlorine-argon detectors (The idea of \u200b\u200ba “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 collaborators. Having caught the neutrino, the nucleus of a chlorine isotope with atomic weight 37, turns into the nucleus of the argon-37 isotope, with the formation of one electron that can be registered.).
Many developed countries seek 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
Chemical production of chlorine was previously common using the methods of Veldon and Deacon. In these processes, chlorine was obtained by oxidation of hydrogen chloride, which is formed as a by-product in the production of sodium sulfate from sodium chloride by the action of sulfuric acid.
the reaction proceeding using the Veldon method:
4НСl + МnO2 \u003d\u003e МnСl2 + 2Н2O + Сl2
the reaction proceeding using the Deacon method:
НСl + O2 \u003d\u003e 2Н2O + 2Сl2
In the Dikon process, chlorine copper was used as a catalyst, a porous ceramic support was impregnated with a 50% solution (sometimes with the addition of NaCl). The optimum reaction temperature on such a catalyst was usually in 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 trioxide. The presence in the gas of even small amounts of sulfuric acid vapor causes a sharp decrease in the yield of chlorine as a result of successive reactions:
H2SO4 \u003d\u003e SO2 + 1 / 2O2 + H2O + С12 + 2Н2O \u003d\u003e 2НCl + H2SO4
С12 + Н2O \u003d\u003e 1 / 2O2 + 2НСl
Thus, sulfuric acid is a catalyst that promotes the reverse conversion of Cl2 to Hcl. Therefore, hydrochloric gas must be thoroughly cleaned of impurities that reduce the yield of chlorine before oxidation on a copper catalyst.
The Deacon installation consisted of a gas heater, a gas filter, and a contact apparatus of a steel cylindrical casing, inside of which 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 obtained diluted. A mixture containing 25 vol.% HCl and 75 vol.% Air (~ 16% O2) was supplied to 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 with HCl and drying 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 by air, but by oxygen, which makes it possible to obtain concentrated chlorine using highly active catalysts. The resulting chlorine-oxygen mixture is washed from HC1 residues sequentially with 36% and 20% hydrochloric acid and dried with sulfuric acid. Then chlorine is 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:
Cl2 + S2CI2
Use low-temperature catalysts, for example, copper dichloride, activated by rare earth salts, which makes it possible to carry out the process even at 100 ° C and therefore dramatically increase the degree of conversion of Hcl to Cl2. On an oxide-chromium catalyst, the burning of HCl in oxygen is carried out at 340,480 ° C. The use of a catalyst from a mixture of V2O5 with alkali metal pyrosulfates and silica gel activators at 250-420 ° C is described. The mechanism and kinetics of this process are studied and the optimal conditions for its implementation are established, in particular in the fluidized bed.
Hydrogen chloride oxidation 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, the oxidation of ferric chloride with the formation of chlorine occurs:
2FeCl3 + 1
In the second reactor, ferric chloride is regenerated from iron oxide with hydrogen chloride:
O3 + 6HCI \u003d 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 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 through the hot chlorination zone, where Fe2O3 is converted to FeCl3, interacting with HCl in the gas flowing from the bottom up. Then the contact mass falls into the cooling zone, where under the influence of oxygen elemental chlorine is formed, and FeCl3 passes into Fe2O3. The oxidized contact mass returns to the chlorination zone again.
A similar indirect oxidation of Hcl in Cl2 is carried out according to the scheme:
2НС1 + MgО \u003d MgCl2 + Н2O
It was 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 by 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 oxidizing agents such as PbO2, KMnO4, KClO3, K2Cr2O7:
2KMnO4 + 16HCl \u003d\u003e 2KCl + 2MnCl2 + 5Cl2 ^ + 8H2O
Chlorine can also be obtained by the oxidation of chlorides. For example, in the interaction of NaCl and SO3 there are reactions:
NaCl + 2SO3 \u003d 2NaSO3Cl
NaSO3Cl \u003d Cl2 + SO2 + Na2SO4
The decomposition of NaSO3Cl occurs at 275 ° C. The gas mixture SO2 and C12 can be separated by absorbing chlorine SO2Cl2 or CCl4 or by rectifying it, resulting 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, while decomposing SO2Cl2 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:
ZNSl + HNO3 \u003d\u003e Сl2 + NOCl + 2Н2O
Another way to obtain chlorine is the decomposition of nitrosyl chloride, which can be achieved by its oxidation:
NOCl + O2 \u003d 2NO2 + Cl2
To produce chlorine, it is also proposed, for example, to oxidize NOCl with 75% nitric acid:
2NOCl + 4HNO3 \u003d Cl2 + 6NO2 + 2H2O
The mixture of chlorine and nitrogen dioxide is separated, processing NO2 into weak nitric acid, which is then used to oxidize Hcl in the first stage of the process with the formation of Cl2 and NOCl. The main difficulty in implementing this process on an industrial scale is the elimination of corrosion. As materials for the equipment used ceramics, glass, lead, nickel, plastics. By this method in the USA in 19521953. a plant with a capacity of 75 tons of chlorine per day worked.
A cyclic method for the production of chlorine by oxidation of hydrogen chloride with nitric acid without the formation of nitrosyl chloride by the reaction was developed:
2НСl + 2HNO3 \u003d Сl2 + 2NO2 + 2Н2O
The process proceeds 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 currently the chemical methods for producing chlorine are again being revived on a new technical basis. All of them are based on the direct or indirect oxidation of HCl (or chlorides), and the most common oxidizing agent is atmospheric oxygen.
Electrolysis. The concept and essence of the process
Electrolysis - a set of electrochemical redox processes that occur on the electrodes during the passage of a constant electric current through a melt or solution with electrodes immersed in it.
Fig. 4.1. Processes that occur during electrolysis. Electrolysis bath circuit: 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; of 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 the anode. A negatively charged electrode is a cathode. During electrolysis, the anode is oxidized (it dissolves) and the cathode is restored. That is why the anode should be taken so that its dissolution does not affect the chemical process 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). 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 on the anode, and not O? II oxygen of water molecules, since the electronegativity of chlorine is less than oxygen, and therefore, chlorine gives off electrons more easily than oxygen)
Water electrolysis is always carried out in the presence of an inert electrolyte (to increase the conductivity of a very weak electrolyte - water):
Depending on the inert electrolyte, electrolysis is carried out in a neutral, acid 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 +) and never oxygen at the anode of O? II anoxo acids are never reduced at the cathode in an aqueous solution with a highly oxidized element (e.g., 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 transferring 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.
A measure of the reaction rate is the current density. This is a physical vector, the module 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.
The laws of Faraday electrolysis are quantitative ratios based on electrochemical studies and help determine the mass of products formed during electrolysis. In the most general form, laws are formulated as follows:
)The first law of Faraday electrolysis: the mass of the substance deposited on the electrode during electrolysis is directly proportional to the amount of electricity transferred to this electrode. By the amount of electricity is meant an electric charge, measured, as a rule, in pendants.
2)The second law of Faraday 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 is involved.
In mathematical form, the laws of Faraday 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, \u003d 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 \u003d 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 precipitated substance.
For the first Faraday law, M, F and z are constants, so the larger the value of Q, the greater the value of m.
For the second Faraday 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 current I ( ?) sums 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 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 sediment 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 Ca2 +, Mg2 + and SO42- anions have a particularly unfavorable effect during solid-cathode electrolysis, while impurities of compounds containing heavy metals, such as chromium, vanadium, germanium, and molybdenum, have an electrolysis with a liquid cathode.
The crystalline salt for chlorine electrolysis should have the following composition (%): sodium chloride at least 97.5; Mg2 + not more than 0.05; insoluble siege not more than 0.5; Ca2 + not more than 0.4; K + not more than 0.02; SO42 - not more than 0.84; humidity no more than 5; admixture of heavy metals (determined by amalgam breakdown cm3 H2) not more than 0.3. Brine cleaning 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 cleaning, solutions are freed from solids by sedimentation and filtration.
The electrolysis of sodium chloride 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 workshops should have high performance, simple design, be compact, operate reliably and steadily.
Electrolysis proceeds according to the scheme:
MeCl + H2O \u003d\u003e MeOH + Cl2 + H2,
where Me is an alkali metal.
During electrochemical decomposition of sodium chloride in electrolyzers with solid electrodes, the following main, reversible and irreversible ionic reactions occur:
dissociation of molecules of salt and water (goes in the electrolyte)
NaCl-Na ++ Cl-
Oxidation of chlorine ion (at the anode)
C1- - 2- \u003d\u003e C12
reduction of a hydrogen ion and water molecules (at the cathode)
H + - 2- \u003d\u003e H2
Н2O - 2е - \u003d\u003e Н2 + 2ОН-
Association of ions in a molecule of sodium hydroxide (in an electrolyte)
Na + + OH- - NaOH
Useful foods are sodium hydroxide, chlorine, and hydrogen. All of them are removed from the cell separately.
Fig. 5.1. Diaphragm electrolyzer circuit
The cavity of the electrolyzer with a solid cathode (Fig. 3) is divided by a porous
The first industrial electrolyzers worked in batch mode. The electrolysis products in them were separated by a cement diaphragm. Later, electrolyzers were created in which baffles in the form of a bell were used to separate the electrolysis products. At the next stage, electrolyzers with a flowing diaphragm appeared. In them, the principle of counterflow was combined using a separation diaphragm, which was made of asbestos cardboard. Next was discovered a method of producing 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 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 asbosynthetic or specially made 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 the early structures were carried out of the cell cavity. Subsequently, methods were developed for protecting the contact parts of anodes immersed in an electrolyte. Using 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 present for the production of chlorine and caustic on a solid cathode.
A stream of a saturated solution of sodium chloride (purified brine) continuously enters 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 sodium chloride, and hydrogen at the cathode due to the decomposition of water. Chlorine and hydrogen are removed from the electrolyzer without mixing, separately. In this case, the cathode zone is enriched with sodium hydroxide. A solution from the cathode zone, called electrolytic liquor, containing undecomposed sodium chloride (approximately half of the amount supplied with brine) and sodium hydroxide, is continuously removed from the electrolyzer. In 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 with increasing concentration of sodium hydroxide.
The NaOH solution is decanted from the crystals and transferred as a finished product to the warehouse or to the 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. Sulphate is extracted from it in order to avoid the accumulation of sulfate in solutions before preparing the reverse 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. Fresh brine before mixing it with reverse 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 the water, compressed and transferred to consumers.
In the membrane electrolyzer, the same chemical reactions occur as in the diaphragm electrolyzer. Instead of a porous diaphragm, a cationic membrane is used (Fig. 5).
Fig. 5.2. Diagram of a membrane cell
The membrane prevents the penetration of chlorine ions into the catholyte (an electrolyte in the cathode space), due to which caustic soda with almost no salt can be obtained directly in the electrolyzer, with a concentration of 30 to 35%. Since the need to separate the salt disappears, evaporation makes it possible to obtain 50% commercial caustic soda much easier and with less investment and energy costs. Since caustic soda in the membrane process is much higher concentration, expensive nickel is used as a cathode.
Fig. 5.3. Scheme of a mercury cell
The total decomposition reaction of sodium chloride in mercury electrolyzers is the same as in diaphragm ones:
NaCl + H2O \u003d\u003e NaOH + 1 / 2Cl2 + 1 / 2H2
However, here it passes in two stages and 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 - electrolytic decomposition of sodium chloride takes place (its saturated solution is supplied to the electrolyzer) to produce chlorine at the anode, and sodium amalgams at the mercury cathode, according to the following reaction:
NaCl + nHg \u003d\u003e l / 2Cl2 + NaHgn
The second stage of the process takes place in the decomposer, in which, under the influence of water, sodium amalgam passes into sodium hydroxide and mercury:
NaHgn + H2O \u003d\u003e NaOH + 1 / 2H2 + nHg
Of all the salt supplied to the electrolyzer with brine, only 15-20% of the supplied quantity enters into reaction (2), and the rest of the salt, together with water, leaves the electrolyzer in the form of chloranolite - a solution of sodium chloride in water containing 250-270 kg / m3 of NaCl saturated with chlorine. A “strong amalgam” leaving 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 trough, along the bottom of which a thin layer of amalgam, which is the cathode, flows by gravity, and the anolyte is on top. The brine and weak amalgam are fed from the upper raised edge of the cell through the "input pocket".
A strong amalgam flows from the lower end of the cell through the “output pocket”. Chlorine and chloranolite together exit through a 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 first are made in the form of a steel inclined gutter of the same length as the electrolyzer. An amalgam stream flows along the bottom of the decomposer, installed with a slight slope. A degrader nozzle made of graphite is immersed in this stream. Water moves countercurrently. As a result of the decomposition of the amalgam, water is saturated with caustic. The caustic solution together with hydrogen leaves the decomposer through the pipe in the bottom, and the poor amalgam or mercury is pumped into the cell of the cell.
In addition to the electrolyzer, decomposer, pockets and transfer pipelines, a mercury pump is included in the electrolysis bath kit. Two types of pumps are used. In cases where the bathtubs are equipped with a vertical decomposer or when the decomposer is installed under the electrolyzer, conventional submersible centrifugal pumps are used, lowered into the decomposer. In bathtubs in which the decomposer is installed next to the electrolyzer, the amalgam is pumped with an original type cone rotary pump.
All steel parts of the electrolyzer in contact with chlorine or chloranolite are protected by a coating of vulcanized rubber of a special brand (gumming). The protective layer of rubber is not completely resistant. Over time, it is chlorinated, from the action of temperature it becomes brittle and crack. 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 corrode it.
Currently, graphite anodes are the most common in a mercury cell. However, ORTA comes to replace them.
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 in the apparatus 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 - apparatuses with increased electric potential relative to land, 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 airways. The maximum permissible concentration (MPC) of chlorine in the air of settlements: daily average 0.03 mg / m3, maximum one-time 0.1 mg / m3, in the air of the working area of \u200b\u200bindustrial 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, death is possible at 300 mg / m3, concentration of 2500 mg / m3 leads to death within 5 minutes, at a concentration of 3000 mg / m3, death occurs after several breaths . The maximum permissible concentration of chlorine for filtering industrial and civilian gas masks is 2500 mg / m3.
The presence of chlorine in the air is determined by chemical reconnaissance devices: VPHR, PPHR, 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, a universal gas analyzer UG-2 with a measuring range of 0-80 mg / m3, gas detector "Kolion-701" in the range of 0-20 mg / m3. In the open space - KIPSAR-X SIW devices. Indoors - VIPA VEGA-M devices. To protect against chlorine in the event of malfunctions or emergencies, all people in the workshops should carry and use gas masks of brands “B” or “BKF” (except for mercury electrolysis shops), as well as protective clothing: cloth or rubber suits, rubber boots and mittens. Boxes of gas masks against chlorine should be painted yellow.
Mercury is more toxic than chlorine. The maximum permissible concentration of its vapor in the air is 0.00001 mg / l. It affects the human body by inhalation and in contact with skin, as well as in contact with amalgamated objects. Vapors and sprays of it 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 air far exceeds the maximum permissible. Therefore, liquid cathode electrolysis shops are equipped with powerful ventilation, which during normal operation provides an acceptable level of mercury vapor concentration in the workshop atmosphere. However, this is not enough for safe operation. It is also necessary to observe the so-called mercury discipline: comply with the rules for handling mercury. Following them, the staff before starting work passes through the sanitary inspection room, in the clean section of which leaves home clothes and puts on freshly washed linen, which is overalls. At the end of the shift, overalls and dirty laundry are left in the dirty section of the sanitary inspection room, while workers take a shower, brush their teeth and put on household items in the clean section of the sanitary inspection room.
In workshops where chlorine and mercury are used, a “G” gas mask (gas mask is painted black and yellow) and rubber gloves should be used. The rules of “mercury discipline” stipulate that work with mercury and amalgamated surfaces should only be carried out under a layer of water; Spilled mercury should immediately be flushed to the sewers where there are mercury traps.
For the environment, emissions of chlorine and mercury vapor into the atmosphere, discharges of mercury salts and droplet mercury, compounds containing active chlorine, and poisoning of the soil with mercury sludge are dangerous. Chlorine enters the atmosphere during accidents, with ventilation emissions and gases from various devices. Mercury vapors are carried with air from ventilation systems. The norm of the chlorine content in the air when released into the atmosphere is 0.03 mg / m3. This concentration can be achieved by using alkaline multi-stage washing of gases. The norm of mercury content in the air when emitted into the atmosphere is 0.0003 mg / m3, and in the effluent when discharged into water bodies 4 mg / m3.
Neutralize chlorine with the following solutions:
milk of lime, for which 1 weight part of slaked lime is poured with 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 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 weight parts of caustic soda are dissolved with stirring with 18 parts of water (for example, 5 kg. Caustic soda + 95 liters of water).
When chlorine gas leaks, water is sprayed to extinguish the vapor. The rate of water consumption is not standardized.
When spilling liquid chlorine, the spill site is enclosed with an earthen rampart, poured 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.
For spraying water or solutions, water-washing and fire engines, autofilling 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 obtained by laboratory methods are negligible in comparison with the constantly growing demand for this product, it makes no sense to carry out a comparative analysis on them.
Of the electrochemical methods of production, the easiest and most convenient is electrolysis with a liquid (mercury) cathode, but this method is not without drawbacks. It causes significant environmental damage due to evaporation and leakage of metallic mercury and gaseous chlorine.
Solid cathode electrolyzers eliminate the risk of mercury pollution. Choosing between diaphragm and membrane electrolyzers for new production capacities, it is preferable to use the latter, since they are more economical and make it possible to obtain a final product of higher quality.
Bibliography
1.Zaretsky S. A., Suchkov V. N., Zhivinsky P. B. Electrochemical technology of inorganic substances and chemical current sources: Textbook for students of technical schools. M ..: Higher. School, 1980.423 s.
2.Mazanko A.F., Kamaryan G.M., Romashin O.P. Industrial membrane electrolysis. M .: publishing house "Chemistry", 1989.240 s.
.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 "Science", 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"\u003e 7. Emergency Chemically Hazardous Substances // URL: # "justify"\u003e. Chlorine: use // URL: # "justify"\u003e.
