This information, along with yields and
quality of plant material, is all being
entered into a database to help predict
which plants will grow best where.
Bioenergy is not just about growing
crops up, though. It’s even more about
tearing them down. Biomass must be harvested from the field or forest, perhaps
stored, and then shipped to a refinery
for processing. Harvesting equipment,
travel distances and processing methods must all be considered to determine
whether biofuels make economic and
“What is becoming a bigger and bigger issue to people is the logistics of it
all—that’s becoming a barrier to the
whole thing,” says J. Richard Hess,
the technology manager of the Idaho
National Lab program.
An essential part of biofuel logistics
is the preprocessing of plants — cutting,
baling and hauling the bales somewhere
for storage before transporting them to a
refinery. Those preprocessing steps pose
problems with a material that isn’t very
dense or evenly shaped. “It’s like moving
air or feathers,” Hess says.
Ideally, preprocessing would provide an end product that is uniform and
easy to handle, like grain — the biomass
equivalent of crude oil. “We’re not aiming for a certain size, but a certain density that’s easy to ship, is flowable,” says
INL’s Christopher Wright.
Wright and Neal Yancey, also of INL,
are trying to achieve the optimal density
by finding the right balance of shredding
and compacting, ultimately producing
something like the alfalfa pellets fed to
pet rabbits, or perhaps Matchbox car–
sized blocks. This crude can then be
shipped to a refinery to be heated into
an oil-like liquid or broken down by
enzymes into the desired fuel.
Breaking biomass down into fuel is
no small task. The dominant method
is known as biochemical conversion:
processes that use heat, chemicals or
enzymes to turn the biomass into sugars that can be fermented by microbes
such as yeast into ethanol. This ethanol
Running on algae
Pond scum gets a bad rap. but microalgae —tiny, single-celled aquatic organ-
isms — are rising stars in the renewable energy sector. they can provide
oil that can be turned into liquid fuels such as biodiesel and jet fuel.
algal oil is mostly triacylglycerides —long fatty acid chains with glycerol back-
bones —that can be converted to diesel and other fuels in relatively few steps.
algae’s potential lies in their speedy growth rate, efficient photosynthesis and flex-
ible habitat preferences. Many strains can grow in saltwater or wastewater from
treatment plants. in open ponds or closed bioreactors, the microorganisms can
potentially make more than 50 times as much oil as land plants on the same area.
this potential fuel has a long history. in 1978 the Department of energy
launched the aquatic Species Program to develop fuels from algae, but the
program was shut down in 1996. in the intervening years, more than 3,000
strains were investigated, included species from yellowstone national Park’s
hot springs and the Caribbean Sea.
now algae research is surging once again in
both the private and public sectors. Problems still
loom, including how to best extract the oil, scale
up algae farms and control contamination by
unwanted strains or tiny critters like rotifers that
graze on the algal crop. but in June the algae-
to-ethanol company algenol biofuels announced
plans for a pilot plant with Dow Chemical Co.
in freeport, texas. and in January, Continental
airlines conducted a 90-minute test flight of a
boeing 737 fueled in part by a blend derived from
algae and Jatropha plants. Prospects for fuel
from pond scum are starting to look up. — R.E.
is the same whether its origins are corn
or other biomass. But it is currently a lot
easier to get the fermentable sugars out
of a starchy corn kernel than from something like wood chips or a weedy grass.
Plant cell walls are about 75 percent
complex sugars, but getting at these sugars is a bit like trying to get the mortar
and minerals out of a castle’s rampart.
Cell walls, one of the defining features
of plants as a life-form, were made to
resist degradation. Even termites and
cows need special microbes in their guts
to get the job done.
That’s because those sugars are embedded in a complex architectural structure
called lignocellulose — cellulose (long,
unbranched chains of glucose) embedded in a matrix of more sugars (
hemicellulose) embedded in the tough, gluelike lignin. (Biofuels researchers refer to
the “recalcitrance” of the cell wall, as if
it were an obstinate child.) Not only did
cell walls evolve for strength, they also
are a primary defense against microbial
attack, and critters that are up to the task
“Lignin is a highly problematic polymer from the point of view of processing,
but an exemplary evolutionary achievement,” researchers at the University
of York in England commented in May
2008 in New Phytologist.
To prep for the cell wall attack, plant
matter is usually pretreated: the shredded, chopped or pelletized biomass
is typically mixed with dilute acids or
ammonia. At a biofuels symposium held
in May in San Francisco, scientists presented work describing pretreatment
with proton beam irradiation, steam
explosion and microwave reactors. Ionic
liquids — basically liquid salts — are also
“Cellulose doesn’t liquefy in minutes
to hours — it’s hours to days,” says Jim
McMillan of the national lab in Golden.
This step is the main bottleneck in cel-
Pat Corkery, national renewable energy laboratory
28 | SCIENCE NEWS | august 1, 2009