Module: 3 Lecture: 19 PROPYLENE GLYCOL

Module:3
Lecture:19 Propylene glycol
Dr. N. K. Patel
Module: 3
Lecture: 19
PROPYLENE GLYCOL
INTRODUCTION
Propylene glycol, C3H8O2 or HO-CH2-CHOH-CH3, also called as 1,2propanediol or propane-1,2-diol is colourless, odourless an organic
compound. It is a clear, viscous liquid with a faintly sweet taste, hygroscopic
and miscible with water, acetone, and chloroform. The compound is
sometimes called α-propylene glycol to distinguish it from the isomer
propane-1,3-diol HO-(CH2)3-OH, also called β-propylene glycol. The
propylene glycol family of chemical compound consists of monopropylene
glycol (PG), dipropylene glycol (DPG) and tripropylene glycol (TPG). DPG
and TPG have several structure and stereochemical isomers. This chemicals
finds number of applications. Generally this chemicals are available in high
purity product so well defined manufacturing is possible in chemical
industries.
Propylene glycol was first prepared by Wurtz in 1859. Wurtz carried out
the hydrolysis of propylene glycol diacetate to yield propylene glycol. In
1931, by Carbide and carbon chemicals corporation the same method was
commercialized. In chlorohydrin process, first propylene oxide was produced
and further it was subsequently hydrolyzed to propylene glycol. All the
commercial process required high temperature, high pressure and noncatalytic hydrolysis of propylene oxide. Excess water is used for the
conversion of propylene oxide to propylene glycol.
Propylene glycol is maufactured from propylene oxideeither by noncatalytic high-temperature process at 200 – 2200C, or a catalytic process at
150 – 1800C in the presence of ion exchange resin or a small amount of
sulfuric acid or alkali as catalyst.Final products contain 20% 1,2-propanediol,
1.5% of dipropylene glycol and small amounts of other polypropylene glycols.
Which is further purified to 99.5% or greater. Propylene glycol can also be
bioconverted from waste glycerol produce during biodiesel production.
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Module:3
Lecture:19 Propylene glycol
Dr. N. K. Patel
MANUFACTURE
Raw material
Basis -1000kg Propylene glycol (97% yield)
Propylene oxide
240kg
Water
230kg
Reaction
Manufacture process
Propylene
oxide
Water vapor
Water
mono propylene
glycol
Sulfuric
acid
Steam
out
Steam
in
Steam
out
Steam
in
Steam
out
Reactor
Steam
in
Drying
tower
Multiple effect evaporator
Vacuum
distillation
column
Steam
di- and tripropylene glycol
Figure: Manufacture of propylene glycol by hydrolysis of propylene oxide
Block diagram of manufacturing process
Diagram with process equipment
Animation
For the production propylene glycol, propylene oxide was used as the
basic raw material. Propylene oxide was produced by using chlorohydrine
process or as by-produt in peroxidation process. In previous process chlorine,
water and propylene were reacted together and form a propylene
chlorohydrine. This is then reacted with organic base which produced
propylene oxide. In peroxidation process, ethyl benzene converted into
alkylhydroperoxide which was then reacted with propylene which was
produced propylene oxide.
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Module:3
Lecture:19 Propylene glycol
Dr. N. K. Patel
Mono-, di- and tri-propylene glycol is produced from propylene oxide
(PO) by hydrolysis with excess water under high temperature and high
pressure.
Propylene oxide and water were used as the raw materials for the
production of propylene glycol. Propylene oxide and water were first
introduced into reactor where hydrolysis of propylene oxide was carried out.
The reaction was taken place at 120 – 1900C temperatures and
pressures has to be maintained up to 2170kPa. To increase a temperature in
batch reactor is appreciable because the heat of reaction is 36,400Btu/lbmol
of propylene oxide at 200C.
The reaction can be kept in the liquid phase by controlling the
temperature of the reaction mixture, since propylene oxide is a low-boiling.
As the hydration reaction was completed, reaction mixture containing excess
water was dehydrated in multiple effect evaporator and drying tower where
the excessive water was removed continuously. For purification and
separation of glycols, it was introduced into vacuum distillation tower where
mono-, di- and tri-propylene glycols were separated out.
Engineering aspects
All commercial process employs noncatalytic hydrolysis of propylene
glycol at high temperature and high pressure. Large amount of water in
excess is used in the conversion of propylene oxide to a mixture of mono, di-,
and tri-propylene glycols. Typically by this process 90% propylene glycol and
10% co-products are obtained. Hydration reactor operates at temperature of
120 – 1900C and pressure of 2170kPa. Propylene oxide is manufactured by
chlorohydrin process or peroxidation process.
PROPERTIES





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Molecular formula
Molecular weight
Appearance
Odour
Boiling point
Melting point
Autoignition temperature
: C3H8O2
: 76.09gm/mole
: Colourless liquid
: Odourless
: 186 - 1880C
: -600C
: 4150C
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Module:3
Lecture:19 Propylene glycol
 Density
 Vapour pressure
 Solubility
Dr. N. K. Patel
: 1.036gm/cm3 at 250C
: 0.08mm Hg at 200C
: Fully miscible with water, ethanol,
chloroform, diethyl ether and acetone
USES
Mono-propylene glycol
 Propylene glycol is used as chemical feedstock for the production of
unsaturated polyester resins
 It reacts with propylene oxide to give oligomers and polymers that are
used in polyurethane application
 As an humectant, solvent and preservative in food and for tobacco
products, as well as being the major ingredient in the liquid used in
electronic cigarettes combined with vegetable glycerine
 As solvent in pharmaceutical and personal care productsincluding
oral, injectable and topical formulations, such as for diazepam
andlorazepamthat are insoluble in water, propylene glycol used as a
solvent in their clinical, injectable forms
 It have tendency to lower the melting point of water, so it is used as
aircraft de-icing fluid and also used as automotive antifreeze
 As minor ingredient in the oil dispersant
Di-propylene glycol
 Its higher viscosity and greater solvency for some materials makes
choice compare to other glycol
 Used in hydraulic brake fluid formation along with caster oil
 Used in cutting oils, industrial soap and lubricants due to its affinity in
other oil also
 Used as reactive monomer in producton of polyurethane, plastcizers
and polyester
 Used in perfuminary industry as it having low odour and is standard
base formulating solvent
Tri-propylene glycol
 Has ability to solubilize printing ink so it is used in cream formulation
which removes inks sytains from the hand
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Module:3
Lecture:19 Propylene glycol
Dr. N. K. Patel
 Used in textile soap due to its solubility power for water and organic
compounds and as well low volatility
 Used in cutting oil concentrater and lubricants formulations
 Used to produce acrylate resins
 Used in production of adhesives, inks and radiation cured coatings
 Alkoxylation of TPG results polyether which is used for the
manufacturing of urethane rigid foam insulation
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