Natural rubber has many analogues, and isoprene rubber is considered one of the most tonnage. The industry produces the most diverse types of these products, which differ in properties and in the type of catalysts that were used - lithium, complex and the like.
How is rubber
Isoprene rubber is synthetic, it is stereoregular, and it is obtained by polymerization of isoprene placed in an inert solvent with a complex catalyst. This is done, for example, SKI-3. The polymerization of isoprene in the solution must be continuous, for this there are batteries of four to six polymerizers, which are cooled by brine.
The monomer in the charge is concentrated to twelve to fifteen percent, then the degree of conversion will reach ninety-five percent, and the duration will be two to three hours at temperatures from zero to ten degrees Celsius. If it is necessary to obtain high molecular weight isoprene rubber, the purity of the reagents used in the polymerization is very high.
Stabilization and drying
In order to protect the polymer from oxidation, it is necessary to stabilize it with a mixture of phenylenediamine and neozone, which must be introduced into the polymerizate as a solution or aqueous suspension. To isolate isoprene rubber from the polymerizate as crumbs, the polymerizate must be mixed with steam and water, then additives that prevent agglomeration (clumping) should be introduced. After this, it is necessary to drive off the solvent. Now it is necessary to carry out the processes of degassing, separation of crumbs from water and drying in worm machines and belt dryers. At the end of this process, the production of isoprene rubber can be considered complete.
Now it will be briquetting in automatic installations under the press. SKI-3 brand is a synthetic isoprene rubber, which is produced in briquettes of thirty kilograms each. The briquette is wrapped in plastic film and placed in a four-layer paper bag. This film is quite well processed at the same time as the contents of isoprene rubber, its properties with a mixing temperature allow polyethylene to be softened and mixed with the bulk in a rubber mixer.
Structure
Each rubber, which is produced by industry, has its own characteristic and properties inherent only to this variety. Some rubbers have good mechanical strength, others have chemical resistance or gas impermeability, while others have no fear of temperature changes, and so on. The properties of individual synthetic rubbers are superior to natural in many ways and many times. So far, it has not yet been possible to surpass the elasticity of natural rubber, and this is the most important property for products such as aviation or automobile tires.
During operation, they always experience enormous deformation - both tension and compression, which causes intermolecular friction, heating and loss of quality. That is, the higher the elasticity of the rubber, the more durable the product. It is for this reason that natural rubber has not yet gone out of use, and it is used for the production of tires for high-speed and heavy aircraft and automobiles. Natural rubber is an isoprene polymer, which is why scientists have worked so hard to make isoprene rubber an analog to the natural one.
Formula
Natural rubber production resources are very limited. The usual rubber obtained in nature has the formula C 5 H 8 , as it turned out, it is absolutely identical to the molecular formula of isoprene, which is formed when the rubber is heated, in the products of its decomposition. The challenge is to find a reasonably affordable way. And isoprene rubber is obtained during the polymerization reaction, and here it is important to properly build the course of this reaction. The polymerization proceeds as follows: nCH 2 = C (CH 3 ) - CH = CH 2 ----> (-CH 2 - C (CH 3 ) = CH - CH 2 ) n.
The most promising method so far is the method of catalytic dehydrogenation of isopentane, which is released from oil gases. Pentane: CH 3 —CH 2 —CH 2 —CH 2 —CH 3 can also be the starting material for the production of isoprene, because when heated with catalysts, it also turns into isopentane. There is also a method of polymerization, in which the reaction of obtaining isoprene rubber is arranged so that rubber is obtained, very similar in structure to natural and, therefore, possessing the same excellent properties.
Isoprene
Isoprene is an unsaturated hydrocarbon belonging to the diene series. It is a volatile colorless liquid. The smell is very characteristic. Isoprene rubber is a natural monomer, since the remainder of its molecule has entered many other natural compounds - isoprenoids, terpenoids, and the like. It dissolves in organic solvents . Ethyl alcohol, for example, can be mixed in any ratio. But it dissolves poorly in water.
But it easily forms a structural unit of isoprene rubber during polymerization, due to which isoprene gutta-percha and rubbers are obtained. Isoprene can also enter into different reactions during copolymerization. In industry, it is indispensable, since with its help there is a synthesis of rubbers, medicines and even some fragrances. In our country, the production of synthetic isoprene rubber has been developing for a long time, and makes up about twenty-four percent of world production.
History
The first isoprene was obtained in 1860 by the method of pyrolysis from natural rubber. pyrolysis is the thermal (at high temperatures) decomposition of many inorganic and organic compounds under conditions of oxygen deficiency. Later, an isoprene lamp was invented - an electric lamp with a heated spiral, with which turpentine oil was thermally decomposed in laboratories.
The Second World War brought a huge need for isoprene rubbers, and therefore they learned to extract isoprene on an industrial scale through the pyrolysis of limonene. Still, isoprene was too expensive for the mass production of synthetic rubbers. The situation changed when a way was found to get it from oil. Then the isoprene polymerization technologies began to develop rapidly.
Role in the economy
The most important thing in planning the production of such a product as isoprene rubber is the correct choice of location, because you will have to deliver C 5 separation fractions to the destination from several cracking enterprises at once. In second place in importance - consideration in the plans for the disposal of the remaining hydrocarbons from the C 5 fraction.
By the beginning of the nineties of the twentieth century, Western Europe produced about eighty-five thousand tons of C 5 dienes, of which forty-four thousand tons were dimerized cyclopentadiene and twenty-three thousand tons were isoprene. The rest - about fifteen thousand tons - were piperylene. Ten years later, the global production of isoprene increased to eight hundred and fifty thousand tons per year.
The properties
Under standard conditions, isoprene, as already mentioned, is a volatile colorless liquid, almost insoluble in water, but miscible in any ratio with diethyl alcohol, standard, benzene, acetone. Isoprene is able to form azeotropic mixtures with a variety of different organic solvents. When considering the data of spectroscopic studies, it is clear that already at fifty degrees Celsius most of the isoprene molecules accept a stable s-trans conformation, only fifteen percent of the molecules are in s-cis conformation. Between these states, the energy difference is 6.3 kJ.
The chemical properties of isoprene represent it as a typical conjugated diene, which enters into the reactions of substitution, addition, complexation, cyclization, telomerization. Active in reaction with electrophiles and dienophiles.
Application
The main part of isoprene, which is currently being produced, is used in the synthesis of isoprene rubber, similar in structure and properties to natural rubber. It is especially used for tire production. There is another product of isoprene polymerization - polyisoprene, which is used much less because it has the properties of gutta-percha. For example, insulation for wires and golf balls are made from it. Isoprene rubber is used for the manufacture of all kinds of rubber products, where natural and other synthetic rubbers are combined.
For example, to reduce stickiness, butadiene-methylstyrene rubbers are added, and fatigue endurance is also increased if deformations are repeated. Nitrites add ozone resistance and resistance to thermal aging. Thus, observing a set of technical properties, isoprene rubbers perfectly manifest themselves when using conveyor belts, suction or pressure hoses, when lining machine shafts, in the manufacture of footwear, medical and other products.
Environmental hazard
Isoprene explodes easily and ignites. In high concentrations in the body, it can lead to paralysis and death. This mainly occurs at atmospheric saturation, and therefore metabolism occurs in the respiratory system when isoprene is converted into epoxides and diols.
Forty milligrams per cubic meter is considered a high concentration - this is the maximum dose. Small concentrations of isoprene in the air can have a narcotic effect on a person, cause irritation of the eyes, skin, respiratory tract and mucous membranes.
Biology
Modern scientists have found that isoprene vapor releases almost all plants into the atmosphere. The global volume of phytogenic isoprene is approximately estimated at (180-450) . 10 12 grams of carbon per year. This process is accelerated if the air temperature approaches thirty degrees Celsius, and also if the intensity of solar radiation is high while photosynthesis is already fully saturated. Isoprene biosynthesis is inhibited by fosmidomycin and compounds of a number of statins. Why plants do this is not fully understood. Perhaps isoprene gives them extra resistance to overheating. In addition, he is a trap of radicals, which means that he can protect plants from reactive oxygen species and from the effects of ozone.
Scientists also suggest that the synthesis of isoprene forces to constantly expend the molecules of NADPH and ATP, which the plant produces during photosynthesis. This means that the release of isoprene protects against photo-oxidative degradation and re-reduction if the lighting is excessive. There may be one drawback to this protection mechanism: carbon, which is so hard to produce during photosynthesis, is spent on the release of isoprene. Scientists did not stop at the plants and found out that the human body also knows how to produce diene hydrocarbons, and isoprene is most common among them.