The properties, production and use of propylene glycol in various industries

Propylene glycol, an organic compound (glycol), is usually a slightly sweet, odorless, colorless, transparent oily liquid that absorbs moisture and is easily mixed with water, acetone, and chloroform.

First, the nature:

1. Flammable liquid. It is hygroscopic and does not corrode to metals. React with dibasic acid to form polyester, react with nitric acid to form nitrate, and react with hydrochloric acid to form chlordyl alcohol. It is converted to propionaldehyde when heated at 170 °C with dilute sulfuric acid. Oxidize with nitric acid or chromic acid to produce hydroxyacetic acid, oxalic acid, acetic acid and the like. Reacts with aldehydes to form acetal. 1,2-Propanediol is dehydrated to form propylene oxide or polyethylene glycol.

2. The toxicity and irritation are very small, and no victim has been found so far. Rat intravenous and intraperitoneal injection LD507000~8000mg/kg, oral LD502800mg/kg. But there have also been reports that when added to foods and beverages in too high a single dose, there is a risk of fatal false sleep and kidney disorders.

3. Present in tobacco leaves and smoke.

Second, the production method:

It can be hydrolyzed by propylene oxide: CH3CHCH2+H2O[H+] →CH3CH(OH)CH2OH.

Direct water legal: propylene oxide and water according to 1:15 molar ratio ingredients, at 150 ~ 200 °C and 1.2 ~ 1.4 MPa reaction for 30min, to obtain aqueous solution containing propylene glycol 16%, after evaporative rectification to obtain the finished product.

Catalytic hydrolysis: The reaction is carried out under the catalysis of sulfuric acid or hydrochloric acid. In 10% to 15% of the aqueous solution of propylene oxide is added 0.5% to 1.0% of dilute sulfuric acid, hydrolyzed at 50 ~ 70 °C; the hydrolysate is neutralized, concentrated under reduced pressure, and refined to obtain a finished product.

Third, the use:

Propylene glycol has good viscosity and hygroscopicity, and is non-toxic, so it is widely used as a moisture absorber, antifreeze agent, lubricant and solvent in the food, medicine and cosmetics industries, and its specific uses in various industries are as follows:

Plastics industry: propylene glycol is an important raw material for unsaturated polyester, epoxy resin, polyurethane resin, plasticizer, surfactant, the amount of this aspect accounts for about 45% of the total consumption of propylene glycol, and this unsaturated polyester is widely used in surface coatings and reinforced plastics.

Food industry: In the food industry, propylene glycol and fatty acids react to generate propylene glycol fatty acid ester, mainly used as a food emulsifier; propylene glycol is an excellent solvent for condiments and pigments, which can dissolve preservatives, pigments, antioxidants and other insoluble food additives in water, and then add food; there is strong moisture absorption, moisturizing and antifreeze effect on food. China stipulates that it can be used for pastries, and the maximum use amount is 3.0g/kg.

Pharmaceutical industry: Propylene glycol is commonly used in the pharmaceutical industry as a solvent, softener and excipient for the manufacture of various types of ointments, ointments, softeners and excipients, etc., and is also used as a solvent for blenders, preservatives, ointments, vitamins, penicillins, etc.

Cosmetics industry: because propylene glycol has good miscibility with various flavors, it is also used as a solvent and softener in cosmetics, etc., and can be used as a wetting agent with glycerol or sorbitol.

Tobacco industry: Propylene glycol is used as a solvent for tobacco humidifiers, mold inhibitors, lubricants for food processing equipment and food marking inks. An aqueous solution of propylene glycol is an effective antifreeze agent. It is also used as tobacco wetting agent, anti-mildew agent, fruit ripening preservative, antifreeze and heat carrier.