Chemical Engineering November 2013 - 17

Glycerol
Propylene glycol
HO
OH
Honor AwArd:
PnnL And AdM
Propylene glycol from
renewable resources
Propylene glycol (PG) is used in liquid
detergents, antifreeze, de-icers,
paints, polyesters, cosmetics, personal
care products, pharmaceuticals and
some food additives. Traditionally,
PG has been made from chemicals
derived from petroleum. With the propylene
glycol from renewable sources
(PGRS) process developed by PNNL
and scaled up by ADM, the wide array
of products mentioned above can now
be made cost effectively from renewable
sources: PGRS is said to be the
first bio-based process deployed at industrial
scale that produces PG and
meets all the same specifications as
PG produced from petroleum.
The PGRS process relies on a carbon-supported,
bi-functional metal
catalyst used in combination with a
soluble base co-catalyst. The reaction
OH
Hydrogen
Catalysts
HO
OH
+ Water
Figure 3. PNNL's catalyst enables the dehydration
and hydrogenation of glycerol to occur in a
single reactor
is conducted using an aqueous feed
solution in a trickle-bed reactor under
moderate temperature and hydrogen
pressure. The overall reaction required
to convert glycerol into PG can be
represented by a simple dehydration
reaction (Figure 3), that removes a
primary hydroxyl group and a proton,
with the formation of a carbon-carbon
double bond, followed by hydrogenation
of the C-C double bond.
What is unique about the PGRS
process, compared to other previously
reported processes, is that
PNNL researchers have discovered
catalysts and process conditions that
allow this multiple-step process to
proceed in a single reactor that produces
PG with both high selectivity
and at high conversion. When combined
with the process technology
advancements and separations engineering
at ADM, the process became
economically competitive versus petroleum-based
routes.
When using glycerol as a feedstock,
the PGRS catalysts are well over 90%
selective, converting the majority of the
glycerol into PG. The small amounts
of byproducts formed are useful compounds,
such as bio-based methanol
and ethylene glycol that are separated
and sold; the water product in the reaction
is also recovered and reused.
The catalyst is broadly applicable to
other feeds to produce PG and other
polyols from larger sugar alcohols,
such as sorbitol and xylitol, both of
which can come from various renewable
biomass sources.
The PGRS process made its commercial
debut in early 2011, when licensee
ADM started up its new 100,000 metric
ton per year (m.t./yr) PG manufacturing
facility in Decatur, Ill. Since
November 2011, ADM has been marketing
bio-based PG that meets U.S.
Pharmacopeia (USP) and USDAcertified
(U.S. Dept. of Agriculture)
Biobased Product Label standards.
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Chemical Engineering November 2013

Table of Contents for the Digital Edition of Chemical Engineering November 2013
