Inhibited Glycol: Properties and Manufacturing Process

General Information:

Inhibited glycol or propylene glycol is an organic double alcohol with a chemical formula of C3H8O2 and a CAS number of 57-55-6. Its official IUPAC name is propane-1,2-diol. It is a thick, clear, and nearly odorless substance with a faintly sweet taste. Propylene glycol shares similarities with glycerin - hygroscopic, soluble with water, acetone, and chloroform.

Physical Properties:

Molecular mass:                                76.10 g/mol
Melting point:                                   -59° C
Boiling point:                                    187.6° C
Vapor pressure:                                 0.2 (23° C)
Vapor density:                                   2.62 (air=1)
Viscosity:                                         91.41 cp (10.45° C)
Surface tension:                                40.1 g/s2 (25° C)
Refractive index:                                1.4324 (20° C)
Heat of vaporization:                          66.27 kJ/mol
Heat of combustion:                           -1828 kJ/mol

Manufacturing Process:

Propylene glycol is usually sourced from propylene oxide or glycerol. Manufacturing is done by either catalytic (150°-180°C) or non-catalytic high-temperature process (200°-220°C), with an ion exchange resin or a small amount of sulfuric acid or alkali. Final products include 20% propylene glycol, 1.5% dipropylene glycol, and other polypropylene glycols. Then, resulting glycols are further distilled to be purified prior to storage and distribution. To assure high quality and compliance with the FDA standards, a track-and-trace system is used to monitor the start of the process up to the delivery point.

References:

Wikipedia - http://en.wikipedia.org/wiki/Propylene_glycol

University of Akron Chemical Database - http://ull.chemistry.uakron.edu/erd/Chemicals/8000/
7709.html

Cefic - http://www.propylene-glycol.com/production.html