One-step cellulose biofuel upgrade?
Oct 31, 2011 - University of Maine researchers have improved upon a centuries old process to convert cellulose directly to heating and transportation fuels. Is this the big break?
October 31, 2011 By Scott Jamieson
The new process was developed by M. Clayton Wheeler, a UMaine
associate professor of chemical and biological engineering, and
undergraduate students in his lab. Based on a mixed-carboxylate
platform, the fuel has been determined to have a number of properties
that make it better suited to serve as a drop-in fuel than many
alternative fuels being widely researched and, bravely suggested, even
those currently on the market.
In an early round of analysis, the UMaine oil product 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 creating the oil is known as thermal deoxygenation (TDO)
is relatively simple, Wheeler says, and will work on the cellulose found
in wood or other substances that contain cellulose or carbohydrates and
the process requires no catalysts or hydrogen, and is “a spin on
chemistry used to make acetone back in the 1800s.”
Wheeler says, “The process is unique. 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 degrees Celsius (900 degrees
Fahrenheit) in a reactor, which constantly stirs the salt. This produces
a reaction resulting in a dark amber-colored oil.
Here it gets very interesting -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.
Wheeler explains, “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. 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 percent oxygenates. No one else has done
anything like this. ”
Wheeler’s lab team 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 feed stocks 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
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.
This has to snap around the minds of very large alternative fuel
users. If it will scale up a major city’s municipal waste could offer a
medium size oil company a very large continuous supply of raw oil for
refining. It should also put an attractive value in the garbage and
trash. Imagine people not pitching out the trash or picking it up for
some extra money.
Watch the University of Maine video on this process here.
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