15
FUELS & LUBES INTERNATIONAL
Quarter Two 2015
IN THE PAST DECADE, IONIC LIQUIDS
(ILs) or liquid salts have gained more attention as
promising materials with a wide range of possible
applications across many industries—ranging
from pharmaceuticals, lubricants, bio-based/
renewable energy and advanced energy storage
cells to the space industry.
However, enthusiasm must be tempered with
reality.
“Although some ILs are commercially
available, they are still too expensive for high-
volume and low-price applications,” says David
Dodds, president of Dodds and Associates based
in Manlius, N.Y., U.S.A. Dodds has several
decades of experience in organic chemistry and
provides technical consulting and management to
start-up pharma and biotech companies.
Aswath agrees. “In general, ILs are
experimental at this point, and they are not being
used in great quantities. There are still a lot of
challenges that need to be worked out, such as
compatibility challenges and solubility issues,” he
says.
What are ionic liquids?
Put simply, ILs are salts that contain anions
and cations. However, ILs have unique and
interesting properties. They are salts in liquid
state at room temperature with a melting point of
less than 100 degrees centigrade and an ionicity
of greater than 99%. Because they are relatively
polar materials, they do not easily mix with
solvents or non-polar products or molecules.
“Having low vapor pressure and low volatility
gives ILs a big advantage over other materials,”
says Aswath. “Another great advantage is its
tuneability.”
To tune the chemistry of ILs means having the
right functional groups for your purpose. The
functional groups can be tuned so that the core
structure has what you need, but the peripheral
structures can be made hydrophilic or oleophilic.
You have a choice as to what anion or cation to
use at that specific site.
The race to replace ZDDPs
Zinc dialkyl dithiophosphates or ZDDPs are
the workhorse of the additive industry. “It is so
inexpensive and plays a dual role of anti-wear and
antioxidant,” says Aswath. “In the U.S., the ZDDP
market is roughly about USD 250-300 million,
and the global market is probably three times
that,” he says.
Aswath has been collaborating with several
institutions in various countries developing
proprietary ionic liquid chemistries. A U.S.
patent application was recently published
on the “synergistic mixtures of ionic liquids
with other ionic liquids and/or with ashless
thiophosphates for anti-wear and/or friction-
reduction applications,” which ultimately aims
to replace ZDDP as a lubricant additive. Nicole
Doerr, a principal scientist at AC2T, a laboratory
in Wiener-Neusdtadt, Austria which supplies the
ILs, is a co-inventor. More recently, Ali Erdemir,
a distinguished fellow at Argonne National
Laboratory in Lemont, Ill., U.S.A., joined the
collaborative group working on finding the right
combination of ILs to use for their research.
They have been working from the ground
up on a superior anti-wear and friction-
reduction additive as an alternative to ZDDP,
which can poison the catalytic converter. The
proprietary compounds developed by Aswath
and his collaborators are a mixture of at least
one ionic liquid and at least one ashless antiwear
compound. The ashless antiwear compound
can be a second ionic liquid or an ashless
thiophosphate compound. The mixture is diluted
up to 25% by weight in base oil.
A group at Oak Ridge National Laboratory
is conducting research on ILs as an anti-wear
additive for next-generation, low viscosity,
fuel-efficient engine lubricants. The group is
led by Jun Qu, senior R&D staff scientist in the
Materials Science and Technology Division at
the laboratory in Oak Ridge, Tenn., U.S.A. Their
approach differs from that of Aswath in that they
are using existing, fully formulated oils combined
with ILs to enhance their performance. They are
developing oil-soluble ionic liquids as next-
generation, ashless, anti-wear additives to allow
the use of lower-viscosity engine oils.
Aswath acknowledges that while ILs won’t be
a major additive in the near future, they could be
in the long term.
Shell and Oak Ridge National Laboratory are
also collaborating. The key to ILs’ success as a
“The power of ionic liquids is in the infinite
possible combinations you can create so that you
will have the right functional groups to deliver
the chemistry you want,”says Pranesh Aswath,
professor and associate dean at the University of
Texas at Arlington’s College of Engineering.
lubricant additive would depend on their ultimate
price, which needs to be cost competitive.
Aswath predicts that the use of ZDDP may only
be decreased or eliminated due to concerns
regarding emissions that arise from deposits on
catalytic converters. “The regulation does not
come from restricting the amount of ZDDP,
but rather it comes from restricting emissions,”
he said. The emissions are determined by how
effective the catalytic converter is, and that is
controlled by the amount of deposits on it.
“ZDDP is one of the primary culprits for
forming deposits on catalytic converters, as the
decomposition products of ZDDP form glassy
deposits on catalytic converters and make them
less effective. That has been the prime driver for
reducing the amount of phosphorous in engine
oils.”
Whoever wins the race or succeeds in getting
a commercially viable product to market has
one goal: Use ILs as oil additives because of their
advantages over ZDDP, with their anti-wear
properties, enhanced performance and friction
reduction properties, plus their ability to act as
corrosion inhibitors and/or detergents. This may
be the most cost-effective and cost-competitive
use of ILs in the future, and it will be easier to
penetrate the lubricants market as a drop-in
product.
Current industrial
applications of ILs
Although they may not be widely known
or used, ILs exist in the market today.
Eastman Chemical Co. was one of the first to
commercialise ILs. It used phosphonium iodide
ionic liquid as a solvent in the isomerisation of
3,4-epoxy but-1-ene to 2,5 dihydrofuran towards
the production of tetrahydrofuran, which was
then used as a chemical process solvent as well as
an intermediate in the preparation of polymers.
Eastman operated an IL plant producing 1,400
metric tonnes per year in Longview, Texas, U.S.A.
from 1996 to 2004 when it was shut down due to
declining demand in tetrahydrofuran.
Axens, an IFP Energies Nouvelles Group
Company based in Paris, France, is an
international provider of advanced technologies,
catalysts and adsorbents. IFP was the first to
operate an IL plant. Axens’ Dimersol™ process,
which has been around since the 1970s, and
Difasol™ process both use a nickel catalyst
precursor using chloroaluminate ionic liquids
as solvent. The Dimersol-X™ process changes
olefins by dimerisation from butane to octane,
which can be used later to create intermediates.
The Dimersol-G™ process is used to dimerise
light olefins like propene to make high-octane
gasoline. There are about 35 plants worldwide
producing 20,000 to 90,000 tonnes per year of
dimer.
Difasol™ is similar to Dimersol™ and
uses the same nickel catalyst precursor and
chloroaluminate ionic liquids as solvent and
