propylene glycol is an industrially important chemical

1. Propylene glycol
Commercial production

2. From Naphtha.
• Naphtha is cracked into propene.
• The propene is furthur oxidize to propylene
oxide (mostly by using AgO as catalyst)
• The propylene oxide is converted to 1,2-
propanediol by hydration in presence of acid
or basic catalyst
Ref: Platform Chemical Biorefinery, First Edition, 2016, 77-100 https://doi.org/10.1016/B978-0-12-802980-0.00005-5

3. By Chlorohydrin route
Ref: Platform Chemical Biorefinery, First Edition, 2016, 77-100 https://doi.org/10.1016/B978-0-12-802980-0.00005-5

4. Chlorohydrin Process:
Propylene reacts with an aqueous solution of chlorine (HOCl) to produce chlorohydrin
isomers.
In the second step, propene chlorohydrin is dechlorinated using a base (NaOH or Ca(OH)2),
resulting in propylene oxide and sodium or calcium chloride.
Drawbacks include the formation of 10% dichloropropane and significant amounts of CaCl2
or NaCl, reducing economic viability.
Not commonly used in new plants due to economic and environmental concerns.
Even though the overall propylene oxide selectivity is high (87–
90%) by this route, the serious equipment corrosion and
environment pollution caused by the byproducts necessitate the
search for greener processes.
Ref?: 10.1021/acsomega.8b01121

5. Indirect Oxidation Processes:
Technologies such as Propylene Oxide/Styrene Monomer (PO/SM) or
Propylene Oxide/Methyl Tertiary Butyl Ether (PO/MTBE) involve
oxidation with coproducts.
The Sumitomo process is based on oxidation without intermediates in
a propylene oxide/cumene system.
Hydrocarbons are first oxidized to form hydroperoxide, which reacts
with propylene to yield propylene oxide and alcohol.
The alcohol co-product is dehydrated back to the initial substrate.
Ref: https://doi.org/10.1021/acssuschemeng.3c01018
ACS Sustainable Chem. Eng. 2023, 11, 19, 7274–7287

6. Catalytic Oxidation with Hydrogen Peroxide:
Developed by BASF, Dow, Evonik, and SKC, this process involves the oxidation of
propylene using H2O2 on a TS-1 catalyst under mild conditions.
Main products are propylene oxide and water.
Offers an alternative pathway for propylene oxide production, but the process has
environmental challenges.
Mixed oxide catalyst of CoO, CuO, MoO3, MnO + heteropoly acid to convert glycerol to
1,2-PDO (92% HPLC yield)
US: patent : https://www.freepatentsonline.com/5616817.pdf

7. Hydration of Propylene Oxide:
Propylene oxide reacts with water to form 1,2-propanediol, dipropylene glycol (DPG),
tripropylene glycol (TPG), and higher molecular weight polyglycols.
DPG is used in the production of high-performance resins, polyurethanes, and
plasticizers, while TPG finds applications in brake fluids, machining oils, soaps, and solvents.
The dominant technology involves noncatalytic liquid-phase hydration with excess water,
making it energy-intensive.
Modifications may include the use of acid or base catalysts, but often the technology
relies on increased pressure and temperature.
Worldwide, a continuous process is employed with propylene oxide and water mixed in a
ratio of 1:15 or greater at 1.8 MPa and 190 °C.
Final product purification is carried out by distillation, resulting in 99.5% purity.

8. Alternative One-Step Process:
 US8207360B2 patent describes direct synthesis of 1,2-
propanediol from propylene using a titanium silicalite acid
molecular sieve catalyst and a resin.
 Propylene is oxidized with hydrogen peroxide to form
propylene oxide, which is then hydrated to 1,2-propanediol.
 This one-step process reduces energy consumption compared
to traditional multistep methods but still faces environmental
challenges.

9. All the traditional processes
Ref: https://doi.org/10.1021/acssuschemeng.3c01018
ACS Sustainable Chem. Eng. 2023, 11, 19, 7274–7287

11. From Wikipedia
Manufacturers use either non-catalytic high-temperature process at 200 °C (392 °F) to
220 °C (428 °F), or a catalytic method, which proceeds at 150 °C (302 °F) to 180 °C
(356 °F) in the presence of ion exchange resin or a small amount of sulfuric acid or
alkali.
Final products contain 20% propylene glycol, 1.5% of dipropylene glycol, and small
amounts of other polypropylene glycols.[8] Further purification produces finished
industrial grade or USP/JP/EP/BP grade propylene glycol that is typically 99.5% or
greater.
Similar production data is also given in Ulmann encyclopaedia : Sullivan, Carl J.
(2000). Ullmann's Encyclopedia of Industrial Chemistry || Propanediols. , (), 1–
15. doi:10.1002/14356007.a22_163.pub2
Ref: https://en.wikipedia.org/wiki/Propylene_glycol

12. List of Industrial patents