Propylene oxide is one of the products of organic synthesis. The consumption of this compound is constantly growing, as it is the raw material for valuable chemical products. There are several technologies for industrial synthesis of this substance.
General information
Propylene oxide, or propylene oxide, under normal conditions, is a clear liquid with a characteristic ethereal odor. It is characterized by addition reactions, which is associated with the ease of opening the three-membered epoxy ring in its structure. Due to this property, this compound reacts with many substances and is one of the most important products, which is subsequently used to obtain many other materials.
The empirical formula of propylene oxide is C 3 H 6 O. The synonyms for this compound are methyloxyran; 1,2 - propylene oxide; 1,2 - epoxypropane.
Physical properties
The main physical characteristics of this substance are:
- density (under normal conditions) - 859 kg / m 3 ;
- boiling point - 34.5 ° C;
- heat capacity - 1.97 J / (kg ∙ K);
- refractive index - 1,366;
- dynamic viscosity (at 25 ° C) - 0.28;
- lower concentration ignition limit - 2-21% (by volume).
Toxicity
The substance belongs to the second hazard class, MPC in water - 0.01 mg / l. In contact with propylene oxide, the following disorders may occur:
- irritation of the skin and mucous membranes;
- impaired coordination of movements;
- circulatory disturbance;
- depression of the central nervous system;
- corneal burn of the eye;
- numbness
- coma.
This compound also has a carcinogenic, mutagenic and cytotoxic effect.
Chemical properties
The chemical properties of propylene oxide include:
- solubility - good in most organic solvents and in water;
- when reacting with water, propylene glycol is formed;
- in reactions with alcohols and phenols glycol ethers are obtained;
- interaction with acids containing carboxyl groups gives esters (in the presence of alkali metals);
- polymerization with the participation of catalysts (alkalis, alcohols, phenols and others) leads to the formation of polypropylene oxide with a high molecular weight.
In the chemical industry, copolymers with ethylene oxide and propylene glycol are most important. Propylene is obtained by hydration of propylene oxide by heating to 200 ° C, an overpressure of 16 atmospheres and in the presence of alkali. The final product also contains about 20% polypropylene glycol.
Application
Propylene oxide is used for the following purposes:
- synthesis of components for polyester resins, rubber-like polymers and polyurethane, which is widely used in construction, in the manufacture of automotive parts, furniture, sports products, coatings, insulation, in the shoe industry;
- production of propylene glycol ether solvents, lubricants and brake fluids, insecticides;
- sterilization of medical equipment, packaged food products;
- production of detergents, emulsifiers and demulsifiers for technical needs.
Production
On an industrial scale, propylene oxide is produced in several ways:
- Hypochlorination in a solution of hypochlorous acid followed by saponification of propylene chlorohydrin and isolation of the final product (dehydrochlorination). The disadvantage of this method is the expensive raw materials (chlorine and hydrated lime), as well as the formation of a large volume of calcium chloride in dissolved form.
- Epoxidation of propylene with cumene hydroperoxide. This technology is characterized by a high degree of product yield (up to 99%).
- Simultaneous synthesis of styrene and propylene oxide. This technique has been mastered in the petrochemical company Nizhnekamskneftekhim. The feed is ethylbenzene. It is oxidized with oxygen at a temperature of 130 ° C, after which hydroperoxide is obtained, which reacts with propylene. Then methylphenylcarbinol is dehydrated in the presence of titanium dioxide.
- Peroxide way. Propylene is oxidized with organic hydroperoxides (methylpropane and ethylbenzene or peroxidetret-butyl). The process proceeds at a temperature of 100 ° C and a pressure of 20-30 atmospheres, as well as in the presence of a catalyst - molybdenum oxide.
NRRO process
Since the 2000s, a new technology based on hydrogen peroxide (HPPO process) has also begun to be used in the production of propylene oxide. It is based on the direct oxidation of propylene with H 2 O 2 . Many scientists have previously made attempts to obtain this product in this way to simplify the process, reduce production costs and reduce the number of by-products, but the proposed methods were unprofitable and unsafe.
Propylene epoxidation is carried out in a reactor where methanol peroxide with methyl alcohol is used as a solvent. Polymeric or chemical grades of propylene are used as starting material. The reaction takes place in a stationary catalyst at moderate temperature and elevated pressure.
The advantages of the HPPO process are as follows:
- a small amount of by-products;
- lack of chlorine, which is a dangerous and toxic reagent;
- long catalyst life;
- a high degree of conversion (transfer of peroxide to the finished product) and selectivity of the chemical reaction;
- supply of purified solvent to a repeated cycle.
Russian manufacturers
In Russia, propylene oxide is produced at only two enterprises:
- OAO Nizhnekamskneftekhim (located in Tatarstan). Two technologies have been mastered here - the joint synthesis of C 8 H 8 and C 3 H 6 O, as well as the chlorohydrin method (mixing propylene with chlorine, obtaining intermediate propylene chlorohydrin and treating it with milk of lime).
- Khimprom (Kemerovo city).
According to the produced volume, 99% of the substance is obtained at the first enterprise.