Sokolov I.V., Ryabova Т.А., Tarlakovskaya E.A.
DESCRIPTION OF THE INDUSTRIAL PROCESS OF PROPYLENE OXIDE BY THE CHLORHYDRINE METHOD *
Аннотация:
the paper describes the process of obtaining propylene oxide by chlorohydrin method. There has been revealed the method peculiarity consisting in the rapid addition of chlorohydric acid to propylene, which allows increasing the rate of interaction by several times. The main component in this method is propylene and elemental chlorine. The main applications of propylene oxide from the production of synthetic polymers to medical devices and accessories are established. Moreover, the main physical properties and storage and transportation conditions of propylene oxide are described
Ключевые слова:
propylene, propylene oxide, production, catalytic oxidation, process flow diagram, chlorohydrin method
УДК 661.716.2.32
Sokolov I.V.
А first-year master's student,
Chemical Technology Department
Dzerzhinsky Polytechnic Institute
(Russia, Nizhny Novgorod)
Ryabova Т.А.
PhD in Chemistry, Associate Professor,
Department of Chemical and Food Technologies
Dzerzhinsky Polytechnic Institute
(Russia, Nizhny Novgorod)
Tarlakovskaya E.A.
PhD in Education, Assistant Professor,
Department of Economics and Humanities
Dzerzhinsky Polytechnic Institute
(Russia, Nizhny Novgorod)
DESCRIPTION OF THE INDUSTRIAL
PROCESS OF PROPYLENE OXIDE BY
THE CHLORHYDRINE METHOD
Abstract: the paper describes the process of obtaining propylene oxide by chlorohydrin method. There has been revealed the method peculiarity consisting in the rapid addition of chlorohydric acid to propylene, which allows increasing the rate of interaction by several times. The main component in this method is propylene and elemental chlorine. The main applications of propylene oxide from the production of synthetic polymers to medical devices and accessories are established. Moreover, the main physical properties and storage and transportation conditions of propylene oxide are described.
The paper substantiates the production of propylene oxide in several stages with a description of the technological scheme. The relevance of the chlorohydride method for producing propylene oxide on an industrial scale has been confirmed.
Keywords: propylene, propylene oxide, production, catalytic oxidation, process flow diagram, chlorohydrin method, chemical process parameters, chemical activity, propylene oxide application.
Nowadays the pyrolysis mechanism of hydrocarbon sources has been the basis of global propylene production. The use of light fuel feedstock for pyrolysis leads to a decrease in plant capacity. It can be increased by changing the focus to pyrolysis capacity with metathesis designs and conversion of ethylene to propylene through a single stage. This combination of production technologies helps to ensure smooth adjustment of the ratio of monomers produced, which helps to navigate in the market economy of their consumption. It is planned to increase capacity of catalytic cracking of heavy oil and gas fractions, main and by-product hydrocarbons. With the observation and monitoring of high selectivity of propylene production, as well as the versatility of resource provision, this very process will be likely accepted as a fundamental one for industrial organic synthesis and refining [5].
The raw material, which is produced in large quantities, to create basic products of the oil and chemical industry is propylene oxide, for example, glycol, polyurethane, cosmetics and pharmaceuticals. Elastic polyurethane foam, which is produced on the basis of propylene oxide through the interaction of polyatomic alcohols with propylene glycol, is effectively used worldwide in the design, furniture manufacturing, transportation, shoe industry. The use of polyurethane foams as a sealant allows to close the problem of energy saving. Calculations have been made, from which it follows that the number of polyurethane consumed by the population is a parameter of its financial and economic sustainability. 1, 2-epoxypropane or propylene oxide is often used as a fumigant to sterilize food products that are packaged in the material. In addition, propylene oxide is commonly isolated as the main raw material for the synthesis of polyoxypropylene polyols, propylene carbonate, polypropylene oxide, propylene sulfide, isopropanolamines, propylene oxide rubbers and surfactants. Propylene oxide is a transition product in the production of propylene glycol esters, epichlorohydrin rubbers, polyurethanes and polyester resins [7].
Propylene oxide is used in the production of a whole list of synthetic polymers used in various areas of human life. The main application of the studied material is the production of insecticides, synthesis of lubricants, solvents and hydraulic fluids. The resulting polymer is used in the synthesis of artificial rubbers and various types of polyurethanes.
In the medical field, namely medical devices and materials are decontaminated with propylene oxide. It is also most commonly used in the manufacture of engineering emulsifiers and synthetic detergents. Propylene oxide is used as a raw material for the synthesis of isopropanolamines, propylene glycol, propylene carbonate, polyoxypropylene polyols and propylene sulfide. Propylene oxide is often used to produce polypropylene oxide and its copolymers – propylene oxide rubbers. It is also common as a material for obtaining propylene glycol esters, and as a transition substance in obtaining polyurethanes, polyester resins. Polypropylene glycol (molecular weight range 400 - 2000), which is obtained by polymerizing propylene oxide in an alkaline or acidic environment, is a transition product for the production of polyurethane foams, alkyd resins, emulsifiers, fuel and lubricants and brake substances. Dipropylene glycol alone and together with diethylene glycol is used in the production of printing dyes, and it also acts as a hydrodynamic fluid with low solidification temperature. It has a negligible toxicity compared to ethylene glycol, which allows it to be used in the manufacture of medicines, perfumes and foodstuffs. Mixture of polyethylene with polypropylene glycol has property of initial substance for reception of nonionic detergents and special combustible and lubricating oils [4].
Propylene oxide is a poison. Propylene oxide degree of impact on the body belongs to the second class of danger according to GOST 12.1.007-76. The maximum permissible concentration (MPC) of vapors in the air of the working area is 1 mg/m. It is worth noting that a person smells from 0.36 mg/dm.
Propylene oxide has the property of self-ignition, where the flash point is -37 °C and the self-ignition temperature is from 2.1% to 37%. This substance is characterized by the PV category as mixture group T2, according to electrical equipment rules [2].
According to GOST 12.1.044-89 propylene oxide does not have the ability to burn and explode when interacting with oxygen, water and various components.
When working with propylene oxide it is necessary to use personal protective equipment. At high concentrations, which exceed MPC, you should work in a gas mask FGP-13A and FGP-130BKF according to GOST 12.4.121-83. [3]
If the concentrations exceed the maximum permissible concentration by 100 times, the use of isolating gas masks becomes mandatory. Process buildings must be equipped with general supply and exhaust ventilation.
Combustible propylene oxide when extinguishing a fire, the fire-extinguishing powder composition "Pyranite A" is used with a feed rate of 0.75 kg/m.. In the fire protection system of propylene oxide production fire extinguishing installations of UPAP type are used. In the case of propylene oxide spillage, the method of dilution with water is used for neutralization, and afterwards the place of the spillage is sprinkled with sand. Environmental protection in the production, transportation and storage of engineering propylene oxide is guaranteed by the tightness of equipment and containers. In accordance with this, gas emissions – are not allowed [10].
Propylene oxide (methyloxyran, 1, 2-propylene oxide, 1, 2-epoxypropane, propylene oxide technical, propyleneoxide, 2-epoxypropane, methyloxirane, 1, 2-propyleneoxide).
C3H6O is a colourless, flammable liquid with a characteristic odour. This type of substance is slightly soluble in water and in most organic solvents, and when reacted with water, propylene glycol is formed. Reaction with water leads to formation of propylene glycol:
(1),
Propylene oxide is chemically similar to ethylene oxide, with characteristic reactions of addition occurring with cycle breaking.
When interacting with alcohols and phenols, propylene oxide forms glycol ethers, namely, in the presence of alkalis – primary ether, and in the presence of acids – a mixture of primary and secondary ethers in equal ratio:
In the presence of SiO2, Al2O3 catalysts and at 240-500°C, isomerization of propylene oxide leads to a mixture of propane aldehyde, acetone and allyl alcohol. In the presence of Lewis acid, propylene oxide reacts with polymerization to form polypropylene oxide. Copolymers of propylene oxide with ethylene oxide, propylene glycol are of industrial importance.
Nowadays specific industrial methods for obtaining propylene oxide are known:
- сhlorohydrin (from propylene through propylenechlorohydrin with subsequent dehydrochlorination);
- peroxide process (chalcone process, oxidation of propylene by peroxides and hydroperoxides of isobutane and ethylbenzene);
- cumene (epoxidation of propylene by hydroperoxide-propylbenzene);
- joint production of propylene oxide and styrene.
At present, the main method for obtaining propylene oxide in industry is the chlorohydrin method (from propylene through propylenechlorohydrin with subsequent dehydrochlorination), which is discussed in this paper.
Elemental chlorine reacts with propylene and chlorohydrin to produce dichloropropane and dichloroisopropyl ether as side products:
CH2ClCH(OH)CH3 + Cl2→ CH2ClCH(OCl)CH3 (4),
CH2ClCH(OCl)CH3+CH2=CHCH3→CH2ClCH(CH3)–O–CH(CH3)CH2Cl (5),
CH2=CHCH3 + Cl2 → CH2ClCHClCH3 (6),
In terms of reactivity chlorine reunion is faster than addition of chlorovate acid, therefore it is necessary to suppress reactivity of chlorine with propene. For this purpose chlorine synthesis with water should be performed in a separate column. The actual chlorhydrogenation takes place in a second column. For higher yield a two-chamber unit with good contact between liquid phase and hydrocarbon is used [1].
The undissociated acid always joins at the double bond. In the presence of borate buffer (pH = 10) chlorohydrin does not actually join, and in an acidic environment (pH = 4, 7) chlorohydrination occurs. An increase in dissociation is tantamount to a decrease in the yield of chlorohydrin. The degree of dissociation of weak acids increases in proportion to temperature, then chlorohydrination at elevated temperatures decreases.
The dissociation constant of NOSL at 25°С is 1.05-10'7. If the dissociation constant at 65°С is calculated using thermodynamic characteristics, a change of only one tenth of a degree can be established, which is so small as to be of no practical importance.
The theoretical basis of the reaction is that 1 mol of chlorohydrin per 1 mol of hydrochloric acid is produced. In spite of this, many studies prove that HCl is taken in excess.
The ratio of propylenechlorohydrin to hydrochloric acid depends on the propylene ratio, the temperature and the concentration of the chlorohydrin. As the temperature increases, the excess amount of hydrochloric acid increases and can reach a high temperature. For example, at 75-80 °C the yield can be 50%, while at 40 °C and a propylene chlorohydrin concentration of 50 g/l the excess varies from 6% to 10%. Saponification of propylene chlorohydrin is similar to that of ethylene chlorohydrin, but it is about 20 times faster.
The occurrence of secondary reactions is explained by a decrease in the values of the exchange reaction rate. It has been experimentally proved that propylene oxide reacts with the formation of an intermediate compound, which is slowly saponified. In industrial production this feature must be taken into account, and propylene oxide must be removed from the reaction solution. In industrial plants the process is carried out in a double-chamber reactor, which is used to convert ethylene chlorohydrin. Under working conditions the yield in a reactor with double chamber is 87.5% propylene chlorohydrin with simultaneous formation of 11.0% propylene dichloride and 1.5% dichlorodisopropyl ether. And in a single-compartment reactor the yield is only 69.2% of the product, while 21.6% of the reacted propylene precipitated as propylene dichloride, and 9.2% goes to dichlorodiazopropyl ether. We can say that the two-chamber system is undoubtedly excellent for conversion of propylene to chlorohydrin. In the first chamber of the presented setup chlorine is dissolved using fresh water in circulating diluted in water propylene chlorohydrin. After loading the chlorine, the reaction mixture enters the second chamber, where it is poured into the propylene stream and the reaction is completed.
The propylene chlorohydrogenation reaction cannot avoid the formation of by-products, since the chlorohydrin solution contains free HCl, HC1 and C12. The reaction of chlorine and propylene results in the formation of 1.2 - dichloropropane, which further reacts with propylene chloride to form dichloroisopropyl ether [8].
The recommended operating temperature for suppressing side reactions is below 50-60 °C as with ethylene chlorohydrin. Under these conditions, ethylene dichloride is largely removed from the top of the column by the gas flow and prevents the formation of a second phase in the reactor. The reaction produces a heavy dichloride, which interferes with the pure propylene. But it can be driven off during the exchange reaction at 50-60°C using a hydrocarbon stream containing more than 45% propylene. During initial contact with the propylene stream, the aqueous phase should contain no more than 0.5 g/l of chlorine. The unreacted gas contains inert gases such as methane, ethane, propane or nitrogen.
The concentration of the chlorohydrin solution must not increase, but when side reactions occur. Therefore, it is difficult to bring the concentration of the substance to an economic value for a single passage through the apparatus, and one has to use the circulating system described above. At the outlet of the reactor the concentration of propylene chlorohydrin affects the final result to a greater extent than in the ethylene exchange reaction. Consequently, at a temperature of 45°C and chlorine concentration of 0.15 g/l in the case of propylene the yield of the quality product is 97%.
At a total concentration of propylene chlorohydrin below 5 g/l. the yield of the target product decreases to 89.5%. Reducing the temperature to 35°C leads to an increase in the yield of the product. And a further decrease in temperature does not increase the yield, but at a temperature of 15°C, there are losses of the product due to the difficult specifics of the apparatus and installation.
The process of saponification of propylene chlorohydrin into propylene oxide occurs similarly with the formation of ethylene oxide. Only lime milk containing no more than 1% MgO is used for the saponification process, otherwise propanal formation will predominate.
The rate of formation of propylene oxide is much lower than in the production of ethylene oxide. But to increase the reaction rate it is necessary to isolate the product as quickly as possible from the reaction system as it is formed [2].
The process of obtaining propylene oxide by chlorohydrogenation is shown in Scheme 1. In column 3, namely in the lower part, chlorine gas is injected to produce chlorinous acid. It is worth noting that the column is made of acid-resistant cladding. Excess of circulating gas is mixed with propylene gas and directed to the other part of column 3. Part of the reaction solution from column 3 is pumped to degassing column 4 for further processing. Circulation of masses is carried out through a bypass device. Fresh water enters the upper part of bypass tube in such quantity that chlorohydrin concentration in the column does not exceed 40 g/l and free chlorine content does not exceed 0.3 g/l.
Scheme 1 - Basic process flow diagram of propylene oxide production unit
1 - washing column with soda solution; 2 - compressor; 3 - column for chloropicrin; 4 - degassing column; 5 - hydrolyser; 6 - deflagmator; 7 - condenser for crude propylene oxide; 8 - tank for crude propylene oxide; 9 - pan column; 10 - condenser for pure propylene oxide.
In column 3 the temperature regime is maintained within 40-45 °С. Unreacted propylene and propane as well as hydrogen chloride leaving the top of column 3 and degassing column 4 mix with dichloropropane and enter under low vacuum into the cube of washing column 1, which is filled with Raschig rings. For neutralization of the reaction mixture and absorption of dichloropropane a soda solution is used fed to the top of the wash column. Neutralized mixture returns to column 3 through compressor 2.
In the same way a constant gas discharge is carried out to prevent accumulation of inert gases before feeding the circulating gas mixture into the reaction. In the case when, the optimal result can be considered when the propylene content in the gas entering the column 3 does not exceed 40 vol.%.
Through the bypass device the reaction mixture enters the hydrolyzer 5 from degassing column 4, where milk of lime with mass fraction of 10-20 % is added. Hydrolyzer is a steel tank of horizontal shape, which is equipped with partitions. Each cell (partition) is fed with steam to heat the reaction mixture to 60-80 °C. At the same time propylene hydrin is instantly transformed into propylene oxide, which evaporates together with the water vapor. Part of the water vapor and dichloropropane enters dephlegmator 6, where the water vapor condenses and returns to the cycle. The distillate of dichloropropane enters refrigerator 7, where it is cooled and then sent for storage to intermediate tank 8.
Crude propylene oxide is fractionated in distillation column 9 with 50 theoretical plates. At 34°С 98 % propylene oxide comes out of the upper part and water, dichloropropane and impurities of dichloroisopropyl ether, propionic aldehyde as well as propylene glycol remain in the cube of the column. Dichloropropane is periodically removed from the column cube for drying with calcium chloride. The output of propylene oxide is approximately 80% of the original chlorine. Despite the small size of the apparatuses, the operating plant runs continuously and shows high productivity [2].
In this paper, the basic methods for obtaining propylene oxide have been displayed, as well as the main physical and chemical properties have been studied. Its practical application has been determined.
The technological scheme of the industrial method for obtaining propylene oxide, namely the chlorohydrin method, is discussed. This method is currently in production as the main way to obtain propylene oxide from propylene through propylenechlorohydrin with subsequent dehydrochlorination. In terms of reactivity, chlorine reunification is faster than addition of chlorovate acid, so it is necessary to inhibit reactivity of chlorine with propene.
The paper explains that propylene oxide is a large-tonnage raw material for the production of a number of important petrochemical products, such as polyurethanes, glycols, cosmetics, medical products and many other products.
REFERENCES:
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Ссылка для цитирования:
Sokolov I.V., Ryabova Т.А., Tarlakovskaya E.A. DESCRIPTION OF THE INDUSTRIAL PROCESS OF PROPYLENE OXIDE BY THE CHLORHYDRINE METHOD // Вестник науки №6 (63) том 4. С. 922 - 932. 2023 г. ISSN 2712-8849 // Электронный ресурс: https://www.вестник-науки.рф/article/9294 (дата обращения: 19.05.2024 г.)
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