What is propylene polymerization? What are the features of this chemical reaction? Let's try to find detailed answers to these questions.
Compound Characterization
Polymerization reactions of ethylene and propylene demonstrate the typical chemical properties that all members of the olefin class possess. This unusual name this class received 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 C n H 2n . The insufficient amount of hydrogen in the structure explains the chemical properties of these hydrocarbons.
The equation for the propylene polymerization reaction is a direct confirmation of the possibility of a break in such a bond when using an elevated temperature and a catalyst.
The unsaturated radical is called allyl or propenyl-2. Why is propylene polymerized? 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 propylene polymerization equation 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 class of alkenes has a slight solubility in water.
Chemical properties
The equations of the polymerization of propylene and isobutylene show that the processes proceed in a double bond. Alkenes act as monomers, and the final products of this interaction are polypropylene and polyisobutylene. It is the carbon-carbon bond during such an interaction that will be destroyed, and eventually the corresponding structures will form.
By a double bond, new simple bonds are formed. How does 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.
The propylene polymerization reaction involves several flow options. In the first case, the process is carried out in the gas phase. In the second embodiment, the reaction proceeds in the liquid phase.
In addition, the polymerization of propylene proceeds according to some outdated processes involving the use of a saturated liquid hydrocarbon as a reaction medium.
Modern technology
The bulk polymerization of propylene using Spheripol technology is a combination of a slurry reactor for the manufacture of 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 propylene polymerization reaction involves the addition of additional compatible catalysts to the device, as well as the preliminary polymerization.
Process features
The technology involves mixing the components in a special device designed for pre-conversion. Then this mixture is added to loop polymerization reactors, both hydrogen and spent propylene enter there.
Reactors operate at temperatures ranging from 65 to 80 degrees Celsius. System pressure does not exceed 40 bar. Reactors that are arranged in series are used in factories designed for large volumes of polymer production.
The polymer solution is removed from the second reactor. Polymerization of propylene involves the transfer of the solution to a pressure degasser. Here the powder homopolymer is removed from the liquid monomer.
Block copolymer production
Polymerization equation for propylene CH2 = CH - CH3 in this situation has a standard flow mechanism, there are differences only in the process. 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 removal from the reactor enter a special system of removal from the monomer of the powdered polymer.
The polymerization of propylene and butadiene impact-resistant type 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, helps to improve the quality of the resulting product.
Specificity of Alkenes Polymerization
There are some differences between the manufacture of polyethylene and polypropylene. The equation for the polymerization of propylene allows us to understand that it is supposed to use a different temperature regime. In addition, some differences exist in the final stage of the technological chain, as well as in the areas of use of the final products.
Peroxide is used for resins that have excellent rheological properties. They have an increased level of fluidity of the melts, similar physical properties to those materials that have a low yield index.
Resins 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. A part of the transparent polypropylene materials is gradually replaced by other materials in the field of blow molding and casting.
Features of polymerization
The polymerization of propylene in the presence of activated carbon proceeds faster. Currently, a catalytic complex of carbon with a transition metal is used, based on the adsorption capacity of carbon. Polymerization results in a product having 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, and the degree of purity of the components of the reaction system are also of importance.
A linear polymer is obtained in both a homogeneous and a heterogeneous phase, when it comes to ethylene. The reason is the absence of spatial isomers of 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 carrier lattice is not a sufficient factor for the acquisition of high stereospecificity by the catalyst. For example, in the case of the choice of titanium iodide (3), a larger amount of atactic polymer is observed.
The considered catalytic components are of a Lewis nature, therefore, are associated with the selection of the medium. The most beneficial medium is the use of inert hydrocarbons. Since titanium chloride (5) is an active adsorbent, aliphatic hydrocarbons are mainly chosen. How does polymerization of propylene proceed? The formula of the product has the form (-CH 2 -CH 2 -CH 2 -) p. The reaction algorithm itself is similar to the reaction in the remaining representatives of this homologous series.
Chemical interaction
Let us analyze the main interaction variants for propylene. Given that there is a double bond in its structure, the main reactions proceed precisely with its destruction.
Halogenation proceeds at ordinary temperature. At the place of breaking the complex connection, halogen unhindered joins. As a result of this interaction, a dihalogenated compound is formed. The most difficult is iodization. Bromination and chlorination proceeds without additional conditions and energy costs. 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 the chemical interaction of propylene with hydrogen, propane is formed - a representative of the class of saturated hydrocarbons.
Hydration (water addition) is carried out according to the rule of V.V. Markovnikov. Its essence is the addition of a hydrogen atom to the carbon of propylene, which has its maximum amount, via a double bond. In this case, the halogen will be attached to the C, which has a 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 strong oxidizing agents, for example, potassium permanganate, act on a given chemical substance, its discoloration is observed. Among the products of the chemical reaction will be dihydric alcohol (glycol).
Propylene production
All methods can be divided into two main groups: laboratory, industrial. Under laboratory conditions, propylene can be obtained by cleavage of hydrogen halide from the original halogenated by exposure to an alcohol solution of sodium hydroxide.
Propylene is formed by the catalytic hydrogenation of propine. In 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 to get propylene in large volumes? Due to the fact that this chemical is rare in nature, industrial options have been developed for its preparation. The most common is the allocation of alkene from refined products.
For example, crude oil is cracked in a special fluidized bed. Propylene is obtained by pyrolysis of a gasoline fraction. At present, alkene is also isolated from associated gas; gaseous products of coal coking are gaseous.
There are a variety of propylene pyrolysis options:
- in tube furnaces;
- in a reactor using quartz coolant;
- Lavrovsky process;
- autothermal pyrolysis according to the Bartlome method.
Among the proven industrial technologies, catalytic dehydrogenation of saturated hydrocarbons should be noted.
Application
Propylene has various fields of application; therefore, it is produced on a large scale in industry. This unsaturated hydrocarbon owes its appearance to the work of Natta. In the mid-twentieth century, using the Ziegler catalytic system, he developed the polymerization technology.
Natta managed to obtain a stereoregular product, which he called isotactic, since in the structure methyl groups were located on one side of the chain. Thanks to this option of “packing” polymer molecules, the resulting polymer substance has excellent mechanical characteristics. Polypropylene is used for the manufacture of synthetic fiber, it is in demand as a plastic mass.
About 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 an intermediate product of propylene chlorohydrin. This technology has certain disadvantages that are associated with the use of expensive chlorine and slaked lime.
Nowadays, this technology has been replaced by the chalcon 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 to make polyurethane foams. They are considered excellent cushioning materials, so they go to the creation of packages, rugs, furniture, heat-insulating materials, sorbing liquids and filter materials.
In addition, the synthesis of acetone and isopropyl alcohol should be mentioned among the main applications of propylene. 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 direct hydration of propene with the introduction of acidic catalysts into the reaction mixture was developed. About half of all propanol produced goes to acetone synthesis. This reaction involves the removal of hydrogen, carried out at 380 degrees Celsius. The catalysts in this process are zinc and copper.
Among the important applications of propylene, hydroformylation occupies a special place. Propene goes to the production of aldehydes. Oxysynthesis in our country began to be used from the middle of the last century. Currently, this reaction occupies an important place in the petrochemical industry. The chemical interaction 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, the formation of two aldehydes is observed. 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 looked for ways to soften the conditions of its course, tried to reduce the percentage in the resulting mixture of branched aldehyde.
For this, economical processes were invented, involving 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 starting material to create acryonitrile. This organic component is necessary for the manufacture of valuable chemical fiber - nitron, the creation of plastics, the production of rubbers.
Conclusion
Polypropylene is currently considered the largest petrochemical industry. Demand for this high-quality and inexpensive polymer is growing, so it is gradually replacing polyethylene. It is indispensable for creating rigid packaging, plates, films, automotive parts, synthetic paper, ropes, carpet parts, as well as for creating a variety of household equipment. At the beginning of the twenty-first century, polypropylene production ranked second in the polymer industry. Given the demands of various industries, we can conclude: in the near future, the trend of large-scale production of propylene and ethylene will continue.