Vinyl chloride is one of the simplest derivatives of acetylene obtained by the addition of hydrogen chloride. The main type of chemical reactions in which this substance is involved is the polymerization process. The final product - PVC - is widely used in all spheres of human activity. The manufacturing process of the compound and its derivatives is accompanied by the release of volatile substances that have a strong toxic effect on the human body.
general description
Vinyl chloride (vinyl chloride) is one of the most widely used chemical compounds, as it is a raw material for the production of PVC. This substance was first obtained by Liebig in 1830 in Germany from dichloroethane and potassium alcohol. After 42 years, another German chemist, Eugen Baumann, noticed that when stored in the light, flakes begin to precipitate from vinyl chloride. This scientist is considered the discoverer of polyvinyl chloride.
At first, this compound did not cause any interest among merchants and manufacturers of chemical products. Its production on an industrial scale began in the 30s. XX century
The empirical formula of vinyl chloride is: C 2 H 3 Cl. The structural formula is shown in the figure below.
Under normal conditions, vinyl chloride is a colorless gas, but since its boiling point is -13 ° C, it is usually worked with it in a liquid state.
Chemical properties of vinyl chloride
The main reactions inherent in this substance are:
- Polymerization.
- Substitution on the bond of carbon-chlorine. This process allows you to get alcoholates and vinyl esters. The chlorine atom is replaced in the presence of catalysts: halides, palladium and salts of other metals. If alcohol is used as solvent, esters are synthesized.
- Oxidation in the gas phase. The products of this reaction are formyl chloride, carbon monoxide, hydrochloric and formic acid. Complete oxidation is observed with the participation of a cobalt chromite catalyst or in an aqueous solution using potassium permanganate. The reaction with ozone in the liquid and gaseous state of vinyl chloride leads to the formation of formyl chloride and formic acid. During spontaneous combustion, carbon monoxide, hydrochloric acid and toxic phosgene (in small quantities) are released.
- Addition reactions. To obtain trichloroethane, which is used as a solvent, a chlorine addition reaction is carried out: by the ionic mechanism (in the liquid phase, in the absence of light, using a catalyst based on transition metals) or by radical reaction (at elevated temperature). Useful vinyl chloride products are also synthesized by acid catalysis and hydrogenation.
- Photodissociation Under the action of light with a wavelength of 193 nm, the HCl and Cl groups are cleaved from the vinyl chloride molecule.
- Pyrolysis. Vinyl chloride is a more stable thermal decomposition compound than other haloalkanes of this type. Pyrolysis begins at a temperature of 550 ° C. At 680 ° C, the yield of acetylene, hydrochloric acid, chloroprene, and vinylacetylene is about 35%. In the presence of water, vinyl chloride corrodes iron, steel, and aluminum due to the release of HCl.
Polymerization reaction
Vinyl chloride monomer can exist for a long time under normal conditions. The appearance of radicals as a result of photo- or thermochemical reactions leads to the activation of polymerization.
This process proceeds in 3 stages and is presented in the figure below.
physical characteristics
The main physical properties of the compound under normal conditions are as follows:
- molecular weight 62.499;
- melting point - 119 K;
- boiling point - 259 K;
- heat capacity in the liquid state - 84 J / (mol ∙ K);
- vapor pressure at 0 ° - 175 kPa;
- viscosity at -20 ° - 0.272 MPa ∙ s;
- lower explosive limit - 8.6% (by volume);
- autoignition temperature - 745 K.
The substance has good solubility in hydrocarbons, oil, alcohols, organic liquids; practically does not mix with water.
Getting
There are several industrial ways to get vinyl chloride:
- as a result of the reaction of hydrochloric acid with acetylene;
- from ethylene and chlorine (direct chlorination of ethylene, production of ethylene dichloride, its pyrolysis to vinyl chloride);
- oxychlorination of ethylene;
- in a combined way (direct chlorination, ethylene dichloride pyrolysis, oxychlorination) - an equilibrium process of ethylene and chlorine without the formation or consumption of hydrochloric acid.
Currently, the latter option is the most common and economically viable. The amount of vinyl chloride obtained by this technology is more than 95% of total world production. The chemistry of the reactions is shown in the figure below.
The entire volume of acid that is obtained by pyrolysis of ethylene dichloride is used as a raw material in the next stage of production (oxychlorination). The resulting product is purified by distillation, by-products are used in the production of solvents or re-utilized.
Production in Russia
In Russia, the production of vinyl chloride from acetylene is carried out at the following enterprises:
- AK "Nitrogen", (Novomoskovsk, Tula region).
- Plastcard OJSC (Volgograd).
- Khimprom OJSC (Volgograd).
- Usolyekhimprom OJSC, (Usolye-Sibirsky, Irkutsk Oblast).
Ethylene-based synthesis of substances is carried out in organizations such as:
- OJSC “Sayanskkhimplast” (Sayansk).
- Sibur-Neftekhim OJSC (Caprolactam, Dzerzhinsk).
- CJSC "Caustic" (Sterlitamak).
Acetylene synthesis is considered obsolete technology. The use of ethylene as a starting material has the following advantages:
- cheaper and affordable raw materials;
- high yield of the finished product;
- low energy and water consumption;
- the possibility of building production lines of high power.
This method has been used by leading global manufacturers for over 40 years. The main promising directions for the development of industrial production of vinyl chloride in Russia are the introduction of new capacities, the transition to ethane raw materials, the spread of oxygen oxychlorination technology and the development of related industries for the sale of caustic soda, which is formed as a by-product.
Application
The vast majority of vinyl chloride produced is used to make polyvinyl chloride (PVC). According to statistics, more than 50% of the production of this polymer is in Asia.
Polyvinyl chloride is the most diverse material of all polymers. Rigid building structures (pipes, external wall cladding, profiles) and elastic products (wires, cables, roofing materials) can be made from it. Unlike other polymeric materials, polyvinyl chloride, under the influence of ultraviolet rays, oxidation and liquid hydrocarbons, not only decays, but also partially crosslinks the polymer chains. This property is due to the presence of chlorine atoms in the structure of the compound. The high competitiveness of polyvinyl chloride is also due to its low price.
PVC is used for the manufacture of the following types of products (in decreasing order of production volume):
- pipes and their connecting parts;
- siding;
- windows, doors;
- profiles (including fences and flooring);
- floor coverings;
- roofing materials;
- consumer products;
- packaging;
- cables and wires (sheath, insulation);
- medical supplies;
- coatings, adhesives.
Other areas of use
A small fraction of vinyl chloride (about 1%) is used to produce copolymers, of which combinations with vinyl acetate, vinylidene chloride, acrylic monomers and alpha-olefins are of practical importance. The first type of copolymers received the greatest distribution. These materials bear the following trade names:
- Westolite;
- hostalite;
- winnol;
- hobbled;
- Corvik
- jeon;
- Sycron and others.
They are used for the manufacture of products such as:
- linoleum and other floor coverings;
- window frames;
- facing tiles;
- artificial leather;
- film;
- varnishes;
- nonwoven materials.
Toxicity
Vinyl chloride is a highly hazardous compound that leads to serious impairment in the human body. The substance is volatile and the main route of entry is inhalation. The source is the production of vinyl chloride, PVC and products from it.
Vinyl chloride causes disorders in the following organs and systems:
- CNS depression (dizziness, loss of orientation, toxic coma);
- damage to connective tissue and blood vessels;
- impaired reproductive function;
- carcinogenic effect (most often detected angiosarcoma of the liver, tumors and other localizations develop);
- digestive system - hepatitis, cholecystitis, cholangitis, gastritis, peptic ulcer;
- circulatory and hematopoietic system - hypertension, coronary heart disease, eosinophilia, thrombocytopenia;
- violation of cholesterol and general metabolism;
- mutagenic effect, the formation of chromosomal aberrations;
- inhibition of antimicrobial protection, a decrease in immune forces.
With prolonged exposure (from six months to 3 years) of toxic doses of this substance, "vinyl chloride disease" occurs. Its development passes through 3 stages, for which the following symptoms are characteristic:
- Weakness, migraine, nausea, anemia, soreness of the nail phalanges of the limbs, as well as the destruction of their bones. Upon termination of the harmful effects, the changes are reversible.
- Inflammation of the peripheral nerves, expressed in loss of sensitivity; arrhythmia, pain in the heart, violation of thermoregulation.
- Memory impairment, hallucinations, involuntary eye fluctuations, image splitting, sleep disturbance, decreased working capacity, pain in the stomach, nausea, vomiting, and an increase in bone pathologies.