Product Name: Propylene Oxide
Cas: 75-56-9
Mf: C3h6o
Einecs Number: 200-879-2

Physical and chemical properties

Propylene oxide is also known as vinyl chloride, 1,2-propylene oxide, propylene oxide, methyl ethylene oxide, referred to as P.O., a colorless, flammable, volatile liquid with an ether-like odor. Relative molecular mass 58.08. Relative density 0.823 (25℃). Melting point -112.13℃. Boiling point 34.23℃. Refractive index 1.3664. Flash point -35℃ (closed). Ignition point 420℃. Vapor pressure (Pa): 1.04×104 (-20℃), 2.80×104 (0℃), 6.53×104 (20℃), 7.59×104 (25℃). Soluble in water (40.5 at 20℃, 60 at 30℃), miscible with most common reagents. It forms a binary azeotrope with water (1%), with a azeotropic point of 39.9℃. It can also form binary azeotropes with dichloromethane, ether, cyclohexane, cyclopentane, pentene, etc. Vapor and air can form explosive mixtures with an explosion limit of 1.9% to 24% (volume fraction). It is optically active, with the specific optical rotation of the d-body being +12.72° (18°C) and the l-body being -8.26° (18°C). There are chemically active epoxy groups in the molecule, which can undergo many chemical reactions. Its chemical activity is slightly lower than that of ethylene oxide. It reacts with substances containing active hydrogen (such as water, alcohol, acid, and amine) to form diols, alcohol ethers, and alcohol amines by ring opening. It undergoes hydrolysis to form propylene glycol. It undergoes etherification to form alcohol ethers. It can produce polyether polyols under the action of a catalyst. It reacts with glycerol to form polyether triols. It reacts with carboxylic acids to form esters. It reacts with ammonia to form alcohol amines. It reacts with hydrogen halides to form halogenated alcohols. It reacts with hydrogen sulfide to form mercaptans. It reacts with thiophenol to generate hydroxypropylphenyl sulfide. Under the action of trimethylamine catalyst, it reacts with carbon disulfide to generate allyl trithiocarbonate. Under the action of catalyst, it can isomerize to generate propionaldehyde. Propylene oxide is toxic and irritating to the skin and eyes, even a 1% dilute solution is irritating. The vapor irritates the respiratory organs and eyes, and has a depressive effect on the central nervous system after inhalation. The oral LD50 of rats is 930mg/kg. The maximum allowable concentration in the workplace is 20×10-6.

Uses of propylene oxide

Propylene oxide is a good low-boiling solvent and organic synthetic raw material. It can be used to prepare propylene glycol, glycerol, propylene glycol, polyester resin, foam plastics and surfactants. It can also be used as a solvent for cellulose acetate, cellulose nitrate and resins. Propylene oxide reacts with ammonia to produce isopropanolamine (monoisopropanolamine, diisopropanolamine, triisopropanolamine). Isopropanolamine is alkaline and can absorb acidic gases. It is widely used in gas purification, such as desulfurization and carbon dioxide removal in the synthetic ammonia industry. The usage of propylene oxide for various purposes: polyether polyols (the main raw material of polyurethane foam plastics) 60%, propylene glycol (raw material of unsaturated polyester resin) 8%~10%, reinforced plastics and non-toxic solvents 20%~25%, surfactants 5%~10%. In 1860, B. Osher of France synthesized propylene oxide in the laboratory for the first time. In 1931, Union Carbide Corporation of the United States built the world's first chlorohydrin process to produce propylene oxide. In the 1960s, Spain and the United States developed the indirect oxidation method. Currently, both methods are in production, accounting for 50% each, but the latter has a tendency to catch up.

Chemical properties

A colorless, low-boiling, flammable liquid with an ether-like odor. The industrial product is a racemic mixture of two optical isomers. It is partially miscible with water [40.5% (weight) solubility in water at 20°C; 12.8% (weight) solubility of water in propylene oxide], miscible with ethanol and ether, and forms binary azeotropes with dichloromethane, pentane, pentene, cyclopentane, cyclopentene, etc.

Propylene oxide Properties

Uses

1. It is an important petrochemical raw material, mainly used in the production of propylene glycol, polyether polyols, polypropylene glycol, propylene glycol ether, synthetic glycerin, surfactants, foaming agents, demulsifiers and mineral processing agents, etc. It is also used to manufacture isopropanolamine, propylene carbonate, etc.
2. Propylene oxide is an intermediate of the herbicide isopropylamine and an important organic synthetic chemical raw material. It can be used to manufacture propylene glycol, acrylamide, propionaldehyde, isopropylamine, synthetic glycerin, organic acids, etc. It can also be used to prepare non-ionic surfactants, wetting agents, emulsifiers, detergents, etc.
3. Propylene oxide is an important organic chemical raw material and the third largest product of the propylene series. Its largest use is to manufacture polyols (polyethers) and then polyurethane. In the distribution of uses in the United States and Western Europe, this use accounts for more than 60% and 70% respectively. Propylene oxide is used to make nonionic surfactants and propylene alcohol, propylene glycol, isopropanolamine, propionaldehyde, synthetic glycerin, organic acids, synthetic resins, foam plastics, plasticizers, emulsifiers, wetting agents, detergents, fungicides, fumigants, etc. Fine chemicals derived from propylene oxide are used in almost all industrial sectors and daily life.

Production method

There are three main methods for preparing propylene oxide: chlorohydrin method, indirect oxidation method and electrochemical chlorohydrin method.
(1) Chlorohydrin method uses propylene as raw material, undergoes hypochlorous acidification, saponification, and then concentration and distillation to obtain the product. The reaction of propylene and hypochlorous acid is carried out in an aqueous solution, in which chlorine, hypochlorous acid and hydrochloric acid are kept in a balanced mixed state. The reaction temperature is 30-50°C. The generated aqueous chloropropanol is saponified with 10% lime milk in a saponification kettle. Water vapor is introduced into the saponification kettle to evaporate the generated propylene oxide, and then condensation and distillation are performed to obtain the finished product. CH3CH=CH2+HOCl→CH3CHOHCH2Cl+CH3CHClCH2OH This method does not require high purity of propylene and has a high yield, but it consumes a large amount of chlorine and lime milk, and the equipment is severely corroded, causing environmental pollution problems. my country mainly uses this method to produce propylene oxide.
(2) Peroxide method The main process is the manufacture of organic hydrogen peroxide, and propylene is oxidized with peroxide. This reaction is a liquid phase reaction whether it is to produce organic hydrogen peroxide or to transfer the oxygen of peroxide to propylene molecules in the presence of a catalyst. In addition to the main product propylene oxide, this method also has a by-product. Currently, the ethylbenzene Hakon process and the isobutane Hakon process have been industrialized. The ethylbenzene Hakon process uses ethylbenzene as a raw material to produce ethylbenzene hydroperoxide through oxidation. Under the action of a catalyst such as copper cyclohexane acid, propylene is epoxidized to obtain propylene oxide and α-phenylethanol, which can be dehydrated to obtain styrene. The reaction temperature of ethylbenzene oxidation is 130-150°C, the pressure is 0.07-0.14MPa, and the selectivity of ethylbenzene hydroperoxide is 90%. The epoxidation temperature is 50-120°C, and the pressure is normal pressure to 0.864MPa. For example, a mixture of 14% ethylbenzene hydroperoxide, 35% propylene, 50% ethylbenzene, and 1% α-phenylethanol (mass fraction) is added with 0.4% cyclopentane manganese-sodium cyclopentane (nMo/nNa=2, molar ratio) as a catalyst, and reacted at 100°C for 1.5h to obtain 99% conversion of ethylbenzene hydroperoxide and 78% selectivity of propylene oxide. The reaction product can be distilled to obtain propylene oxide products, while α-phenylethanol is dehydrated at 250-280°C using TiO3-Al2O3 as a catalyst in a dehydration reactor, and 100% is converted into styrene with a selectivity of 92%. The characteristics of this method are low cost, economic rationality, less three wastes, and co-production of styrene. The isobutane Hakon method uses isobutane as a raw material, and reacts with propylene to obtain propylene oxide and tert-butyl alcohol through the oxidant tert-butyl hydroperoxide. The process is similar to the ethylbenzene Hakon method. The preparation of tert-butyl hydroperoxide is at 100-110°C without a catalyst. Usually, tert-butyl hydroperoxide is used as a secondary initiator. The reaction conditions for propylene epoxidation are a reaction temperature of 121°C and a pressure of 4.1 MPa. The reaction is carried out in the presence of a molybdenum catalyst, and the reaction time is 0.5 h. The yield of propylene oxide is 88% (based on peroxide) and the selectivity is 81%. This method can co-produce tert-butyl alcohol with a yield of about 60%, (CH3)2CHCH3+O2→(CH3)3COOH+(CH3)3COH
(3) Electrochemical chlorohydrin method This method uses the principle that an aqueous solution of sodium chloride (or potassium chloride, sodium bromide, sodium iodide) is electrolyzed to generate chlorine and sodium hydroxide. Propylene is introduced into the anode area to generate chloropropanol, and chloropropanol reacts with sodium hydroxide in the cathode area to generate propylene oxide.

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