Earl Christensen, a Senior
Scientist at the National
Renewable Energy Laboratory
(NREL), and his colleagues
have done extensive testing
on biodiesel over the last eight years, and
the findings have impressed him. “As we
did more and more long-term storage
testing, I was a bit surprised at how stable
all these recent samples were.” he said.
“Today’s biodiesel can be very stable and
can be stored for a long time, especially
as a blend, so we have started looking
at even longer storage times and more
storage scenarios.”
The National Biodiesel Board (NBB)
has honored Christensen twice for his
achievements. At the Biodiesel Technical
Workshop in November 2017, Christensen
was named Biodiesel Researcher of
the Year. Then at the 2018 Biodiesel
convention, NBB honored him with the
Eye on Biodiesel Innovation award.
Christensen’s research on relatively
recent market samples of B20 biodiesel
blends indicated B20 meeting today’s
ASTM standards had a minimum simulated
shelf life of over one year, with many of
the samples having a simulated shelf life
of over 3 years.
“The oxidation reserve of a biodiesel
blend is dependent upon both the
petrodiesel and the biodiesel. For the
biodiesel component, the make-up
of the oil or fat used to produce the
biodiesel is one important factor. The
more unsaturated a fuel is the lower the
oxidation reserve in general, so biodiesel
from unsaturated oils/fats like linseed
oil and fish oil won’t have as long of an
unadditized shelf life as biodiesel from
something more saturated like or animal
fats or frying oils. However, some frying
oils are solid at room temperature, so
there is always this balance between cold
flow and unadditized oxidation reserve,”
Christensen explained.
“The secondary factor that really plays
into this is antioxidant additives, and
that’s how you get the really long shelf
life with lower cloud biodiesel (which
tends to be more unsaturated), by adding
antioxidants. You tune that composition
with the different types of feedstocks and
additives you use.”
Producers of high-quality biodiesel
are adept at adjusting fuel properties
for the intended applications, and fuel
buyers can generally specify the oxidation
reserve they need. “As long as the B100
met spec, the ASTM specs were originally
designed to provide a minimum shelf life
of 6 months for B20 or lower blends. All
the B20 samples we collected that met
the 6 hour oxidation reserve spec had a
minimum predicted shelf life of over one
year—that’s some good news. In longer-term
storage scenarios, that is where
you monitor the fuel or use antioxidants
proactively,” Christensen said.
“If you have fuel going into long-term
storage, the ASTM specifications advise
users that successful long term storage
requires attention to fuel selection,
storage conditions, handling and
monitoring of properties during storage.
That goes for either petroleum diesel or a
biodiesel blend,” Christensen said. “One
has to make sure to get good, in-spec fuel
for long term storage and smart users
utilize antioxidants and other fuel storage
enhancing additives up front and monitor
the fuel in storage periodically. Even
petroleum diesel does not have an infinite
shelf life.”
Christensen’s research helped prove
the viability of long term storage options
for biodiesel blends. Users can periodically
test the fuel’s oxidation reserve, which
naturally goes lower over time, and add
more antioxidants to extend the fuel’s
life, which mirrors common practices for
many petroleum products. “Once you
have a fuel that’s in storage for a while
and you see the oxidation reserve start
to drop below target levels, you add a
certain amount of additive and mix or
churn it to disperse it and this extends
the useful life of the fuel,” he said. “In our
readditization study, we achieved over 4
years of simulated storage with B20, which
was impressive.”
Christensen’s work is very important to
fuel distributors and users. “The fuel users
are very interested. I am a lab chemist,
so it’s valuable to me when people share
their experiences about what happens in
the field.”
OEMs also pay close attention. “They
have a huge vested interest in the quality
of the fuels going through their vehicles.
They don’t need to be having any
problems based on fuels.”
“We want to be able to give people
the tools they need” to trust biodiesel, he
said. “It’s unfortunate that a lot of people
have it in their minds that diesel fuel itself
is good forever. That’s not necessarily
the case, and there might even be some
overlooked issues there that might be
worth looking into as well.”
Most of his work has been on blends of
up to B20, but that is changing. “You’re
starting to see a lot of interest in blends up
to B50 and even in applications of B100,
particularly in home heating,” he said. “In
theory, there really shouldn’t be a difficult
transition. There might be considerations
about materials compatibility for seals that
weren’t designed for these fuels, but for
actual combustion, I don’t see too much
difficulty moving up.”
Christensen’s work at NREL has given
him a strong appreciation of biodiesel.
“I’m entirely neutral on how we reduce
the amount of petroleum we use, but
from what I’ve seen of biodiesel, I think it
is a really great path for us to supplement
our diesel usage in a way that reduces
emissions and ultimately gets us all to
where we want to be.”
He believes biodiesel should play
a larger role in the energy mix going
forward. “It doesn’t take a whole lot of
energy to make and we’ve got quite a
bit of oil to make it from,” he said. “It
absolutely deserves to grow as far as it
can go.”
Biodiesel has
been put to
the test and
passed with
flying colors
Biodiesel Success Stories 11