Propylene oxide is one of the products of organic synthesis. The volume of consumption of this compound is constantly growing, as it is a raw material for obtaining valuable chemical products. There are several technologies for the 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 for propylene oxide is C3H6O. Synonyms for the name of this compound are methyloxirane; 1, 2 – propylene oxide; 1, 2 - epoxypropane.
Physical properties
The main physical characteristics of this substance are:
- density (under normal conditions) – 859kg/m3;
- boiling point - 34.5 °С;
- heat capacity – 1.97 J/(kg∙K);
- refractive index – 1, 366;
- dynamic viscosity (at 25°С) – 0.28;
- lower concentration flammable limit - 2-21% (by volume).
Toxicity
The substance belongs to the second hazard class, MPC in water is 0.01 mg/l. Contact with propylene oxide may cause the following disorders:
- irritation of skin and mucous membranes;
- impaired coordination of movements;
- circulatory disorders;
- CNS depression;
- corneal burn;
- numbness;
- coma.
This compound is also carcinogenic, mutagenic and cytotoxic.
Chemical properties
The chemical properties of propylene oxide include:
- solubility - good in most organic solvents and in water;
- reacting with water produces propylene glycol;
- in reactions with alcohols and phenols, glycol ethers are obtained;
- reaction 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 of the greatest importance. Propylene is obtained as a result of the hydration of propylene oxide when heated to 200 ° C, excesspressure 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, automotive parts, furniture, sports products, coatings, insulation, footwear industry;
- manufacture 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, obtaining propylene oxide is carried out 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 slaked 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 raw material is ethylbenzene. It is oxidized with oxygentemperature of 130 °C, after which hydroperoxide is obtained, which reacts with propylene. Then dehydration of methylphenylcarbinol is carried out in the presence of titanium dioxide.
- Peroxide way. Propylene is oxidized with organic hydroperoxides (methylpropane and ethylbenzene or tert-butyl peroxide). The process takes place at a temperature of 100 °C and a pressure of 20-30 atmospheres, as well as in the presence of a catalyst - molybdenum oxide.
NRPO process
Since the 2000s, a new technology based on hydrogen peroxide (HPPO process) has also been used in the production of propylene oxide. It is based on the direct oxidation of propylene with H2O2. 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:
- few by-products;
- no chlorine, which is a dangerous and toxic reagent;
- long catalyst life;
- high degree of conversion (transfer of peroxide to the finished product) and selectivity of the chemical reaction;
- feeding the purified solvent to the recycle.
Russian manufacturers
In Russia, propylene oxide is produced only at two enterprises:
- JSC Nizhnekamskneftekhim (located in Tatarstan). 2 technologies have been mastered here - the joint synthesis of С8Н8 and C3H6 O, as well as the chlorohydrin method (mixing propylene with chlorine, obtaining intermediate propylene chlorohydrin and treating it with milk of lime).
- Khimprom (city of Kemerovo).
In terms of the produced volume, 99% of the substances are obtained at the first enterprise.
