Glycol (MPG)

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Propylene glycol

 

Chemical formula: CH2(OH)-CH(OH)-CH3

Density: 1,0363 g/cm3

Reg. number: 57-55-6

 

Propylene glycol — a colorless viscous liquid with a weak characteristic odor, sweet taste, having hygroscopic properties.

Basic properties

1,2-propylene glycol — transparent a viscous fluid. Its density is lower than that of ethylene glycol and glycerol, but higher than ethanol. The viscosity of propylene glycol is higher than that of ethylene glycol and Monohydric alcohols, especially at low temperatures.

 

Solubility

Propylene glycol is a good solvent for different class of compounds. With it fully mixed most low molecular weight organic compounds containing oxygen and nitrogen:

• Monohydric alcohols (methyl, ethyl, propyl, isopropyl, n-butyl, n-amyl, phenylethyl and etc.)

• ethylene and propylene glycol and their esters

• acid (acetic, diethyloxalate, valeric, oleic, etc.)

• aldehyde (anisic, benzoic, mustard, salicylic, furfural, citral) and ketones (acetone, α-ionon, methylisobutyl and methylisobutylketone)

• esters (ethyl, tilhar-, n-butyl-, amyl - and isoamylase, tri-n-butylphosphate, n-butyl lactone, etc.).

 

Chemical properties

Propylene glycol is known in the form two isomers: 1,2-propylene glycol and 1,3 propylene glycol . 1,3-Propylene glycol is more reactive than 1,2-propylene glycol, and prone to polymerization.

Due to the presence of asymmetric the carbon atom has two optical isomers: one, rotating the plane of polarized light to the left (-)-form and the other to the right (+)-form. Propylene glycol produced in industry by the hydration of propylene oxide, is a racemic mixture of both optical isomers (racemate).

Optical isomers of propylene glycol can be obtained from the levo - and dextrorotatory of propylene oxide. In addition, levo isomer obtained when the restoration of the levorotatory ester of lactic acid, a dextrorotatory — when hydrogenation over Nickel left-handed 3-iodine-1,2-propylene glycol.

Chemical properties 1,2-propylene glycol is a typical glycol. With alkali metals and alkalis form glycolate, carboxylic acids and anhydrides — one - and dwuzameshchenny esters; esterification of 1,2-propylene glycol and monoaminov leads to diesters. In the dehydration in the presence of acids or alkalis 1,2-propylene glycol forms a mixture of dimethyl-1,4-dioxane, in the presence of Н3РО4 at 250 °C-propionic aldehyde in the presence of АlРО4 — allyl alcohol (2-propen-1-ol)CH2=CH-CH2-OH and acetone. Catalytic dehydrogenation 1,2-propylene glycol gives acetol CH3-CO-CH2-Oh or propionic aldehyde, propionic acid, methylglyoxal, etc. In the process of oxidation 1,2-propylene glycol reaction products are acetone, propionic aldehyde, lactic acid, formaldehyde, acetaldehyde, etc.

Receiving propylene glycol is carried out by hydration of propylene oxide at a temperature of from 160 to 200 degrees and at a pressure of about 1.6 MPa. However, there is a 85.5% of the of propylene glycol, 13% of dipropyleneglycol and 1.5% of tripropyleneglycol. Allocate glycols in the vacuum distillation column. Warranty period of storage product is one year from the date of manufacture. Food propylene glycol contains about two years. In the process of operation, we should not forget that in case of overheating solutions containing propylene glycol, begins expansion of bases and additives, therefore, possible deterioration of the thermophysical properties of the solution.

Low freezing coolants on aqueous propylene glycol solution is widely used in various industries as coolants (antifreeze), including heating, ventilation, air conditioning of homes and public buildings in cooling systems of food production, and other the heat exchangers in the temperature range from -40 °C to +108 °C.

 

1,2-Propylene glycol are used

• in production of unsaturated polyester resins (for building industry and production of vehicles), elastic polyurethanes, alkyd resins;

• as a solvent in natural and synthetic substances in the preparation of ointments, pastes, creams, shampoos etc the pharmaceutical and cosmetic industry;

• in the food industry as solvent additives and tobacco humidifier. 1,2-Propylene glycol has moderate preservative and antibacterial properties;

• For disinfection of premises to the food industry (sprayed into the air in aerosol form);

• in the manufacture of brake fluids antifreeze, de-icing liquids and coolants;

• as plasticizer in the production of cellophane and polyvinyl chloride films;

• In connection with the replacement of ethylene glycol ethers less toxic compounds increases the use of esters of 1,2-propylene glycol;

In the food the prom