Polymerization of propylene: scheme, equation, formula

What is the polymerization of propylene? What are the characteristics of the course of this chemical reaction? Let's try to find detailed answers to these questions.

Characteristics of compounds

The reaction schemes for the polymerization of ethylene and propylene demonstrate the typical chemical properties that all members of the olefin class possess. This unusual name was given to this class from the old name of the oil used in chemical production. In the 18th century, ethylene chloride was obtained, which was an oily liquid substance.

Among the features of all representatives of the class of unsaturated aliphatic hydrocarbons, we note the presence in them of one double bond.

The radical polymerization of propylene is explained precisely by the presence of a double bond in the structure of the substance.

The general formula

For all representatives of the homologous series of alkenes, the general formula has the form C _n H _2n . The lack of hydrogen in the structure explains the peculiarity of the chemical properties of these hydrocarbons.

The equation for the polymerization reaction of propylene is a direct confirmation of the possibility of a rupture in such a bond by using an elevated temperature and a catalyst.

An unsaturated radical is called allyl or propenyl-2. Why is polymerization of propylene? The product of this interaction is used for the synthesis of synthetic rubber, which, in turn, is in demand in the modern chemical industry.

Physical properties

The polymerization equation for propylene confirms not only the chemical but also the physical properties of the substance. Propylene is a gaseous substance with low boiling and melting points. This representative of the alkene class has insignificant water solubility.

Chemical properties

The equations for the polymerization reaction of propylene and isobutylene show that the processes proceed through a double bond. Alkenes act as monomers, and the final products of this interaction are polypropylene and polyisobutylene. It is the carbon-carbon bond in this interaction that will decay, and eventually the corresponding structures will be formed.

By the double bond, the formation of new simple bonds occurs. How does polymerization of propylene proceed? The mechanism of this process is analogous to the process occurring in all other representatives of this class of unsaturated hydrocarbons.

The polymerization reaction of propylene involves several variants of percolation. In the first case, the process is carried out in the gas phase. In the second variant, the reaction proceeds in the liquid phase.

In addition, the polymerization of propylene also proceeds through some obsolete processes, which involve the use of a saturated liquid hydrocarbon as the reaction medium.

Modern technology

The polymerization of propylene in mass according to Spheripol technology is the combination of a slurry reactor for making homopolymers. The process involves the use of a gas-phase reactor with a pseudo-liquid layer to create block copolymers. In such a case, the polymerization reaction of propylene involves the addition of additional compatible catalysts to the device, as well as pre-polymerization.

Process Features

The technology involves mixing components in a special device designed for pre-transformation. This mixture is then added to the loop polymerization reactors, where both hydrogen and spent propylene are fed.

The reactors operate at a temperature range of 65 to 80 degrees Celsius. The pressure in the system does not exceed 40 bar. Reactors, which are located in series, are used in factories designed for large volumes of polymer production.

A polymer solution is removed from the second reactor. Polymerization of propylene involves the transfer of the solution to a degasser of increased pressure. Here, the powder homopolymer is removed from the liquid monomer.

Manufacture of block copolymers

The polymerization equation for propylene CH2 = CH - CH3 in this situation has a standard flow mechanism, there are differences only in the conditions of the process. Together with propylene and ethylene, the powder from the degasser goes to a gas phase reactor operating at a temperature of about 70 degrees Celsius and a pressure of not more than 15 bar.

Block copolymers, after being withdrawn from the reactor, enter a special evacuation system from the monomer of the powdered polymer.

Polymerization of propylene and butadienes of an impact-resistant type allows the use of a second gas-phase reactor. It allows to increase the level of propylene in the polymer. In addition, it is possible to add additives to the finished product, the use of granulation, helps to improve the quality of the product obtained.

Specificity of polymerization of alkenes

There are some differences between the manufacture of polyethylene and polypropylene. The polymerization equation for propylene allows us to understand that a different temperature regime is assumed. In addition, some differences exist in the final stage of the process chain, as well as in the areas of use of end products.

Peroxide is used for resins that have excellent rheological properties. They have an increased level of fluidity of melts, similar physical properties with those materials that have a low yield index.

Resins having excellent rheological properties are used in the process of injection molding, as well as in the case of making fibers.

To increase the transparency and strength of polymeric materials, producers try to add special crystallizing additives to the reaction mixture. Some of the polypropylene transparent materials are gradually replaced with other materials in the area of blow molding and casting.

Peculiarities of polymerization

The polymerization of propylene in the presence of activated carbon proceeds more rapidly. At present, a catalytic complex of carbon with a transition metal based on the adsorption capacity of carbon is used. As a result of polymerization, a product having excellent performance characteristics is obtained.

The main parameters of the polymerization process are the reaction rate, as well as the molecular weight and stereoisomeric composition of the polymer. The physical and chemical nature of the catalyst, the polymerization medium, and the degree of purity of the constituents of the reaction system are also important.

A linear polymer is obtained both in the homogeneous and in the heterogeneous phase, when talking about ethylene. The reason is that the given substance does not have spatial isomers. To obtain isotactic polypropylene, try to use solid titanium chlorides, as well as organoaluminum compounds.

When a complex adsorbed on crystalline titanium chloride (3) is used, it is possible to obtain a product with predetermined characteristics. The regularity of the carrier lattice is not a sufficient factor for the catalyst to acquire high stereospecificity. For example, in the case of selecting titanium iodide (3), a greater amount of atactic polymer is observed.

The catalytic components considered are of the Lewis type, and therefore are related to the selection of the medium. The most beneficial environment is the use of inert hydrocarbons. Since titanium chloride (5) is an active adsorbent, aliphatic hydrocarbons are generally selected. How does polymerization of propylene proceed? The product formula has the form (-CH ₂ -CH ₂ -CH ₂ -) n. The algorithm of the reaction itself is analogous to the course of the reaction in the remaining representatives of a given homologous series.

Chemical interaction

Let's analyze the main options for interaction for propylene. Considering that in its structure there is a double bond, the main reactions proceed precisely with its destruction.

Halogenation proceeds at ordinary temperature. At the place of disruption of complex communication, unhindered attachment of halogen occurs. As a result of this interaction, a dihalogen compound is formed. The hardest thing is iodination. Bromination and chlorination takes place without additional conditions and energy costs. The fluorination of propylene proceeds with an explosion.

The hydrogenation reaction involves the use of an additional accelerator. The catalyst is platinum, nickel. As a result of chemical interaction of propylene with hydrogen, propane is formed - a representative of the class of limiting hydrocarbons.

Hydration (water addition) is carried out according to VV Markovnikov's rule. Its essence consists in attaching a double bond of the hydrogen atom to that of propylene carbon, which has its maximum amount. In this case, the halogen will be attached to the volume C, which has a minimum number of hydrogen.

Propylene is characterized by burning in oxygen in the air. As a result of this interaction, two main products will be obtained: carbon dioxide, water vapor.

When strong oxidizing agents, such as potassium permanganate, act on this chemical, its discoloration is observed. Among the products of the chemical reaction is a dihydric alcohol (glycol).

Preparation of propylene

All methods can be divided into two main groups: laboratory, industrial. Under laboratory conditions, it is possible to obtain propylene when hydrogen halide is split off from the starting haloalkyl when an alcohol solution of sodium hydroxide is exposed to them.

Propylene is formed during the catalytic hydrogenation of propyne. In the laboratory, this substance can be obtained by dehydration of propanol-1. In this chemical reaction, phosphoric or sulfuric acid, alumina, is used as catalysts.

How is propylene produced in large volumes? Due to the fact that this chemical is rarely found in nature, industrial options for its preparation have been developed. The most common is the isolation of alkene from refined products.

For example, cracking of crude oil in a special fluidized bed is carried out. Propylene is produced by pyrolysis of the gasoline fraction. At present, alkene is extracted from the associated gas, the gaseous products of coal coking.

There are a variety of pyrolysis options for propylene:

• In tubular furnaces;
• In a reactor using a quartz coolant;
• The Lavrovsky process;
• Autothermal pyrolysis according to the Bartlom method.

Among the exhausted industrial technologies, it is necessary to note the catalytic dehydrogenation of saturated hydrocarbons.

Application

Propylene has a variety of applications, and therefore is produced on a large scale in the industry. The appearance of this unsaturated hydrocarbon is due to the work of Natta. In the middle of the twentieth century, using the Ziegler catalytic system, he developed polymerization technology.

Natta managed to obtain a stereoregular product, which he called isotactic, because in the structure, methyl groups were located on one side of the chain. Due to this "packaging" of polymer molecules, the resulting polymeric material has excellent mechanical characteristics. Polypropylene is used for the production of synthetic fiber, is in demand as a plastic mass.

Approximately ten percent of petroleum propylene is consumed to produce its oxide. Until the middle of the last century, this organic substance was obtained by chlorohydrin method. The reaction proceeded through the formation of an intermediate product of propylene chlorohydrin. This technology has certain drawbacks, which are associated with the use of expensive chlorine and hydrated lime.

In our time, this technology has been replaced by the halkon process. It is based on the chemical interaction of propene with hydroperoxides. Propylene oxide is used in the synthesis of propylene glycols, which is used to manufacture polyurethane foams. They are considered to be excellent cushioning materials, so they are going to create packages, rugs, furniture, heat insulation materials, sorbing liquids and filter materials.

In addition, among the main applications of propylene, mention should be made of the synthesis of acetone and isopropyl alcohol. Isopropyl alcohol, being an excellent solvent, is considered a valuable chemical product. In the early twentieth century, this organic product was produced by the sulfuric acid method.

In addition, the technology of direct hydration of propene has been developed with introduction of acid catalysts into the reaction mixture. About half of all propanol produced goes to the synthesis of acetone. This reaction involves the elimination of hydrogen, carried out at 380 degrees Celsius. Catalysts in this process are zinc and copper.

Among the important applications of propylene, hydroformylation plays a special role. Propene goes to the production of aldehydes. Oxinsynthesis in our country began to be used since the middle of the last century. At present, this reaction occupies an important place in the petrochemical industry. The chemical reaction of propylene with synthesis gas (a mixture of carbon monoxide and hydrogen) at a temperature of 180 degrees, a cobalt oxide catalyst and a pressure of 250 atmospheres, two aldehydes are formed. One has a normal structure, the second has a curved carbon chain.

Immediately after the discovery of this technological process, it was this reaction that became the object of research for many scientists. They sought ways to mitigate the conditions of its course, tried to reduce the percentage in the resulting mixture of aldehyde branched structure.

For this purpose, economical processes were invented, involving the use of other catalysts. It was possible to reduce the temperature, pressure, increase the yield of aldehyde linear structure.

Acrylic acid esters, which are also associated with the polymerization of propylene, are used as copolymers. About 15 percent of petrochemical propene is used as a starting material to create acryonitrile. This organic component is necessary for the production of valuable chemical fiber - nitron, the creation of plastics, the production of rubbers.

Conclusion

Polypropylene is now considered the largest petrochemical production. Demand for this quality and inexpensive polymer is growing, so it gradually displaces polyethylene. It is indispensable for the creation of rigid packaging, plates, films, automotive parts, synthetic paper, ropes, carpet parts, as well as for the creation of a variety of household equipment. At the beginning of the twenty-first century, polypropylene production was the second largest in the polymer industry. Given the requests of various industries, we can conclude: in the near future, the trend of large-scale production of propylene and ethylene will continue.