Researchers have long been interested in waste products as sources of
biofuel. In Maine,
those waste items could include treetops and limbs deemed by the forest
products industry as unusable and often left behind in the woods.
A University
of Maine engineer and his
research team have, however, discovered a revolutionary new chemical process
can transform forest residues, along with other materials such as municipal
solid waste, grasses, and construction wastes, into a hydrocarbon fuel oil.
Considering the amount of wood in Maine—including around 6 million green
tons of additional available biomass, according to a 2008 Maine Forest Service
Assessment of Sustainable Biomass Availability—the new fuel has the possibility
of 120 million gallons per year of gasoline, diesel, heating oil, and kerosene
mixtures while providing all the steam and power needs of the processing
plants. In addition, the U.S.
transportation industry, which is dependent on hydrocarbon fuels because of
their high energy density, could benefit from the revolutionary finding.
Based on a mixed-carboxylate platform, the new fuel was developed by M.
Clayton Wheeler, a UMaine associate professor of chemical and biological
engineering, and undergraduate students in his laboratory. The fuel has been
determined to have a number of properties that make it better suited to serve
as a drop-in fuel—which refers to the ease of which it can be used in a number
of fuel tanks and pipelines—than many hydrocarbon fuels being widely researched
and even those currently on the market.
In an early round of analysis, the UMaine oil was found to have boiling
points that encompass those of jet fuel, diesel, and gasoline. Further
refinement to meet emissions standards would be needed in order to use the
UMaine oil in vehicles that drive on public ways, but Wheeler believes the oil
can be refined as simply as any other current oil at a standard refinery.
The process by which the oil is created, known as thermal deoxygenation or
TDO, is relatively simple, Wheeler says, and will work on the cellulose found
in wood or other substances that contain cellulose or carbohydrates.
“The process is unique,” Wheeler says. “No one else in the world is doing
this.”
The TDO process starts with the conversion of cellulose to organic acids.
The acids are combined with calcium hydroxide to form a calcium salt. That salt
is heated to 450 C (900 F) in a reactor, which constantly stirs the salt. This
produces a reaction resulting in a dark amber-colored oil.
The reaction removes nearly all of the oxygen from the oil, which is a key
step that distinguishes TDO from other biofuel processes. Oxygen is removed
from as both carbon dioxide and water, and without the need for any outside
source of hydrogen to remove the oxygen. Therefore, most of the energy in the
original cellulose source is contained in the new oil.
“Biomass has a lot of oxygen in it. All of that oxygen is dead weight and
doesn’t provide any energy when you go to use that as a fuel,” Wheeler says. “If you’re going to make a hydrocarbon fuel, one of the things you have to do
is remove oxygen from biomass. You can do it by using hydrogen, which is
expensive and also decreases the energy efficiency of your process. So if
there’s a way to remove the oxygen from the biomass chemically, then you’ve
densified it significantly. Our oil has less than 1% oxygenates. No one else
has done anything like this.”
Researchers in Wheeler’s laboratory at UMaine recently used unpurified,
mixed carboxylates which were produced from grocery store waste such as banana
peels, cardboard boxes and shelving to successfully make a batch of the fuel.
The use of municipal solid waste illustrates another important point about the
potential of the UMaine fuel—it does not require an uncontaminated cellulose
source, which makes the TDO process and resulting oil even more attractive.
Many other pathways to hydrocarbons require purified feedstocks or
intermediates, which adds more complexity and cost to their processes.
“You don’t need pure wood or pure cellulose,” says Wheeler. “Anytime you can
use something without having to separate it, your costs go down.”
Wheeler and his team already have the ability to produce several liters of
the fuel per month in the laboratory. The process can be scaled up using
equipment and chemicals commonly found in facilities such as some pulp mills.
