Propylene glycol is a colorless viscous liquid with a weak characteristic odor, sweet taste and hygroscopic properties. Propylene glycol is safe for human health. It is widely used in various branches of the national economy, including the food and cosmetic industries.

          Propylene glycol is soluble in water, diethyl ether, single atomic alcohols of carbonic acids, aldehydes, amines, acetone, ethylene glycol, and is limited in benzene. When mixed with water or amines, the freezing point of solutions sharply decreases; for example, the freezing point of 40% aqueous solution is -23 °С, and 50% -35 °С. This property is used for preparation of antifreeze.

     Propylene glycol (about 40%) is used in the production of unsaturated polyester resins (for the construction industry and car manufacturing), elastic polyurethanes, alkyd resins; in the pharmaceutical and cosmetic industries (approx. 10%) as a solvent of natural and synthetic substances in the preparation of ointments, pastes, creams, shampoos, etc.; in food industry (10-12%) as a solvent of food additives and tobacco moisturizer (due to its hygroscopic properties). 

     Propylene glycol has moderate preserving and bactericidal properties. It is also used in the manufacture of brake fluids, antifreeze and coolants, as a plasticizer in the manufacture of cellophane and polyvinyl chloride films. 

     The toxicity of propylene glycol (LD50 = 20000 mg/kg, rats) is lower than that of ethylene glycol (LD50 = 4700 mg/kg).

Propylene glycol for heating systems

     Propylene glycol has all the properties necessary for an ideal coolant: its crystallization begins at -60⁰C, and boiling at 187⁰C.

     For thermal power engineering the most interesting is the aqueous solution of propylene glycol, the main feature of which is the liquid state in the temperature range from -40⁰C to +108⁰C.

     Another advantage of propylene glycol is its low corrosion activity in comparison with water, which allows to lower the bar of steel quality requirements for heating systems, and, therefore, to reduce their cost.

     Propylene glycol is suitable for all heating systems including steel, cast iron, copper, aluminium, polymeric materials and rubber. Moreover, at its use on an internal surface of heating system precipitation and scale that not only increases its service life, but also provides higher heat emission is not formed.

     By its properties propylene glycol is similar to ethylene glycol, which aqueous solution is also widely used as an antifreeze. The main difference is that ethylene glycol is toxic, and it is not recommended to use it in heating systems, especially if together with the heating of the home the heating of hot water for household needs is made. The fact is that it is difficult to eliminate leaks in heat exchangers, and it is also difficult to determine the presence of ethylene glycol in hot water. Therefore, it is more reasonable to refuse ethylene glycol, preferring more expensive but safe propylene glycol.

Heating system with propylene glycol:

• Not afraid of frost: even with -300C the coolant in it will not freeze, and the pipes will remain intact;
• Resistant to corrosion;
• There is no scale in it;
• For installation of system of heating on propylene glycol it is possible to use less qualitative, and, hence, cheap, steel pipes;
• For water heating in heating system it is possible to use storage boilers (for heating systems with ethylene glycol it is impossible to do it).

Only distilled or unsalted water may be used to dilute propylene glycol. 
Dilution in different proportions is possible. This is convenient when there is no scale

     Preparing the coolant based on the mass, you get similar results, as well as preparing it, based on the volume. Small discrepancies can occur because propylene glycol is slightly heavier than water (1 liter of propylene glycol weighs about 1.1 kg).

• When diluting 1 liter of concentrate with 1 liter of water - freezing point is -34°C
• When diluting 1 liter of concentrate with 2 liters of water - freezing point is-14°C
• When diluting  1 liter of concentrate with  4 liters of water - freezing point is -8°C
• ПWhen diluting  1 liter of concentrate with 9 liters of water - freezing point is -3°C

     In order to prepare heat transfer fluids with a high degree of accuracy, the above diagram can be used. It should be noted that such graphs are most often used to prepare the mixture based on mass fraction or percentage mass. 

     Propylene glycol is a flammable liquid, so it is important to observe explosion and fire safety precautions when handling it. The product should only be handled in a ventilated room with the mandatory use of personal protective equipment that is resistant to chemical influences. It is not advisable to use the solution in systems with galvanized pipes, as the coating may peel off. Mixing with other antifreeze agents without prior inspection is also undesirable as it may affect the anti-corrosion properties of the thermal fluids.

Use of propylene glycol in the production of beer, milk and wine

     Propylene glycol is used to cool beer, wine, milk and other liquids. Cooling is carried out by a method of forced circulation, as a rule, 30 % of a water solution of propylene glycol on coils. The advantage of propylene glycol over water, ethylene glycol and salt solution in water is that due to the non-toxicity of propylene glycol, the product can be used even after small leaks of propylene glycol through the system tightness. The presence of 0.25% propylene glycol does not affect the taste. Concentration of propylene glycol at 30% allows to bring the temperature of the cooler to -12.8°C; water, on the other hand, allows to lower the temperature only to 1.1°C. Propylene glycol automatically lubricates the elements of the cooling system.

Propylene glycol in the paint and coatings industry

     Propylene gicol in the paint and construction industry is used as:

• solvent;
• plasticizer;
• filler;
• humidifier in Wood Mastic;
• in the production of glyphthalic resins. 

     Also propylene glycol is widely used in the production of water emulsion (otherwise known as latex) paints to coat the interiors of architectural buildings, especially for the production of semi-glossy paints. Having properties to dissolve completely in water, propylene glycol improves properties of paints as its low evaporation increases time intervals when brush for paint application can be applied.

     Low-freezing coolants produced on the basis of water solution of propylene glycol are widely used in various industries as coolants - antifreeze, air-conditioning of residential premises, ventilation and other heat-exchange equipment at temperature intervals ranging from minus 40 ° C to plus 108 ° C. In cooling systems of food manufactures antifreeze coolants on a propylene glycol basis are used. In case of emergency spillage of the coolant on the basis of propylene glycol it will be enough to collect it with a wet rag, when at spill of ethylene glycol-containing coolant it is necessary to change a tile or a wooden floor with a heater, absorbed poisonous ethylene glycol.