What is the polymerization of propylene? What are the characteristics of this chemical reaction? Let's try to find detailed answers to these questions.
Characteristics of connections
Ethylene and propylene polymerization reaction schemes demonstrate the typical chemical properties that all members of the olefin class have. This class received such an unusual name 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 of one double bond in them.
The radical polymerization of propylene is explained precisely by the presence of a double bond in the structure of the substance.
General formula
For all representatives of the homologous series of alkenes, the general formula has the form СpН2p. The insufficient amount of hydrogens in the structure explains the peculiarity of the chemical properties of these hydrocarbons.
Propylene polymerization reaction equationis a direct confirmation of the possibility of a break in such a connection when using elevated temperature and a catalyst.
The unsaturated radical is called allyl or propenyl-2. Why polymerize propylene? The product of this interaction is used to synthesize synthetic rubber, which, in turn, is in demand in the modern chemical industry.
Physical properties
The propylene polymerization equation confirms not only the chemical, but also the physical properties of this substance. Propylene is a gaseous substance with low boiling and melting points. This representative of the alkene class has a slight solubility in water.
Chemical properties
The reaction equations for the polymerization of propylene and isobutylene show that the processes proceed through a double bond. Alkenes act as monomers, and the end products of such an interaction will be polypropylene and polyisobutylene. It is the carbon-carbon bond that will be destroyed during such an interaction, and eventually the corresponding structures will be formed.
At the double bond, new simple bonds are formed. How does the polymerization of propylene proceed? The mechanism of this process is similar to the process occurring in all other representatives of this class of unsaturated hydrocarbons.
Propylene polymerization reaction involves several optionsleaks. In the first case, the process is carried out in the gas phase. According to the second option, the reaction takes place in the liquid phase.
In addition, the polymerization of propylene also proceeds according to some outdated processes involving the use of a saturated liquid hydrocarbon as the reaction medium.
Modern technology
Polymerization of propylene in bulk using Spheripol technology is a combination of a slurry reactor for the production of homopolymers. The process involves the use of a gas-phase reactor with a pseudo-liquid bed to create block copolymers. In this case, the propylene polymerization reaction involves the addition of additional compatible catalysts to the device, as well as pre-polymerization.
Process Features
The technology involves mixing the components in a special device designed for preliminary transformation. Further, this mixture is added to the loop polymerization reactors, where both hydrogen and spent propylene enter.
Reactors operate at temperatures ranging from 65 to 80 degrees Celsius. The pressure in the system does not exceed 40 bar. The reactors, which are arranged in series, are used in plants designed for high-volume production of polymer products.
The polymer solution is removed from the second reactor. The polymerization of propylene involves transferring the solution to a pressurized degasser. Here, the removal of the powder homopolymer from the liquid monomer is carried out.
Production of block copolymers
Propylene polymerization equation CH2 =CH - CH3 in this situation has a standard flow mechanism, there are differences only in the process conditions. Together with propylene and ethene, the powder from the degasser goes to a gas-phase reactor operating at a temperature of about 70 degrees Celsius and a pressure of no more than 15 bar.
The block copolymers, after being removed from the reactor, enter a special system for removing the polymer powder from the monomer.
Polymerization of propylene and impact-resistant butadienes allows the use of a second gas-phase reactor. It allows you 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, which improves the quality of the resulting product.
Specificity of polymerization of alkenes
There are some differences between the manufacture of polyethylene and polypropylene. The propylene polymerization equation makes it clear that a different temperature regime is intended. In addition, some differences exist in the final stage of the technological 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 melt flow, similar physical properties to those materials that have a low flow rate.
Resin,having excellent rheological properties, are used in the injection molding process, as well as in the case of the manufacture of fibers.
To increase the transparency and strength of polymeric materials, manufacturers are trying to add special crystallizing additives to the reaction mixture. Part of the polypropylene transparent materials are gradually being replaced by other materials in the field of blow molding and casting.
Features of polymerization
Polymerization of propylene in the presence of activated carbon proceeds faster. At present, a carbon-transition metal catalytic complex based on the adsorption capacity of carbon is used. The result of polymerization is a product with excellent performance.
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, the degree of purity of the components of the reaction system are also important.
A linear polymer is obtained both in a homogeneous and in a heterogeneous phase, when it comes to ethylene. The reason is the absence of spatial isomers in this substance. To obtain isotactic polypropylene, they try to use solid titanium chlorides, as well as organoaluminum compounds.
When using a complex adsorbed on crystalline titanium chloride (3), it is possible to obtain a product with desired characteristics. The regularity of the support lattice is not a sufficient factor forthe acquisition of high stereospecificity by the catalyst. For example, if titanium iodide (3) is chosen, more atactic polymer is obtained.
The considered catalytic components have a Lewis character, therefore, they are associated with the selection of the medium. The most advantageous medium is the use of inert hydrocarbons. Since titanium (5) chloride is an active adsorbent, aliphatic hydrocarbons are generally chosen. How does the polymerization of propylene proceed? The product formula is (-CH2-CH2-CH2-)p. The reaction algorithm itself is similar to the course of the reaction in other representatives of this homologous series.
Chemical interaction
Let's analyze the main interaction options for propylene. Considering that there is a double bond in its structure, the main reactions proceed precisely with its destruction.
Halogenation proceeds at normal temperature. At the site of the rupture of the complex bond, the unhindered addition of the halogen occurs. As a result of this interaction, a dihalogenated compound is formed. The hardest part is iodization. Bromination and chlorination proceeds without additional conditions and energy costs. Propylene fluorination is explosive.
The hydrogenation reaction involves the use of an additional accelerator. Platinum and nickel act as a catalyst. As a result of the chemical interaction of propylene with hydrogen, propane is formed - a representative of the class of saturated hydrocarbons.
Hydration (water addition)carried out according to the rule of V. V. Markovnikov. Its essence is to attach a hydrogen atom to the double bond of propylene, which has its maximum amount. In this case, the halogen will attach to that C, which has the minimum number of hydrogen.
Propylene is characterized by combustion in atmospheric oxygen. As a result of this interaction, two main products will be obtained: carbon dioxide, water vapor.
When this chemical is exposed to strong oxidizing agents, such as potassium permanganate, its discoloration is observed. Among the products of the chemical reaction will be a dihydric alcohol (glycol).
Propylene production
All methods can be divided into two main groups: laboratory, industrial. Under laboratory conditions, propylene can be obtained by splitting off hydrogen halide from the original haloalkyl by exposing them to an alcoholic solution of sodium hydroxide.
Propylene is formed by the catalytic hydrogenation of propyne. Under laboratory conditions, this substance can be obtained by dehydration of propanol-1. In this chemical reaction, phosphoric or sulfuric acid, aluminum oxide are used as catalysts.
How is propylene produced in large volumes? Due to the fact that this chemical is rare in nature, industrial options for its production have been developed. The most common is the isolation of alkene from petroleum products.
For example, crude oil is cracked in a special fluidized bed. Propylene is obtained by pyrolysis of the gasoline fraction. ATat present, alkene is also isolated from associated gas, gaseous products of coal coking.
There are various options for propylene pyrolysis:
- in tube furnaces;
- in a reactor using a quartz coolant;
- Lavrovsky process;
- autothermal pyrolysis according to the Barthlome method.
Among the proven industrial technologies, catalytic dehydrogenation of saturated hydrocarbons should also be noted.
Application
Propylene has a variety of applications, and therefore is produced on a large scale in industry. This unsaturated hydrocarbon owes its appearance to the work of Natta. In the middle of the twentieth century, he developed polymerization technology using the Ziegler catalytic system.
Natta was able to obtain a stereoregular product, which he called isotactic, since in the structure the methyl groups were located on one side of the chain. Due to this type of "packaging" of polymer molecules, the resulting polymer substance has excellent mechanical characteristics. Polypropylene is used to make synthetic fibers, and 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 the chlorohydrin method. The reaction proceeded through the formation of the intermediate product propylene chlorohydrin. This technology has certain disadvantages, which are associated with the use of expensive chlorine and slaked lime.
In our time, this technology has been replaced by the chalcone process. It is based on the chemical interaction of propene with hydroperoxides. Propylene oxide is used in the synthesis of propylene glycol, which is used in the manufacture of polyurethane foams. Considered to be excellent cushioning materials, they are used to make packaging, rugs, furniture, thermal insulation materials, absorbent liquids and filter materials.
In addition, among the main applications of propylene, it is necessary to mention the synthesis of acetone and isopropyl alcohol. Isopropyl alcohol, being an excellent solvent, is considered a valuable chemical product. At the beginning of the twentieth century, this organic product was obtained by the sulfuric acid method.
In addition, the technology of propene direct hydration with the introduction of acid catalysts into the reaction mixture has been developed. About half of all propanol produced is spent on the synthesis of acetone. This reaction involves the elimination of hydrogen, is carried out at 380 degrees Celsius. The catalysts in this process are zinc and copper.
Among the important uses of propylene, hydroformylation occupies a special place. Propene is used to produce aldehydes. Oxysynthesis has been used in our country since the middle of the last century. At present, this reaction occupies an important place in petrochemistry. The chemical interaction of propylene with synthesis gas (a mixture of carbon monoxide and hydrogen) at a temperature of 180 degrees, a cob alt oxide catalyst and a pressure of 250 atmospheres, the formation of two aldehydes is observed. One has a normal structure, the second has a curvedcarbon chain.
Immediately after the discovery of this technological process, it was this reaction that became the object of research for many scientists. They were looking for ways to soften the conditions of its flow, tried to reduce the percentage of branched aldehyde in the resulting mixture.
For this, economical processes were invented that involve the use of other catalysts. It was possible to reduce the temperature, pressure, increase the yield of linear aldehyde.
Esters of acrylic acid, which are also associated with the polymerization of propylene, are used as copolymers. About 15 percent of the petrochemical propene is used as a starting material to create acrionitrile. This organic component is necessary for the manufacture of a valuable chemical fiber - nitron, the creation of plastics, the production of rubber.
Conclusion
Polypropylene is currently considered the largest petrochemical industry. The demand for this high-quality and inexpensive polymer is growing, so it is gradually replacing polyethylene. It is indispensable in 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, the production of polypropylene ranked second in the polymer industry. Taking into account the demands of various industries, we can conclude that the trend of large-scale production of propylene and ethylene will continue in the near future.
