April 01, 2005
New Method Simplifies Soy Biodiesel Production
Scientists at the USDA’s Agricultural Research Service (ARS) are
exploring a simplified process for soybean biodiesel production that
eliminates the use of an air-polluting chemical and that may eventually
reduce the overall cost of production.
Soybean oil—the feedstock for soy biodiesel—is normally produced by
extracting it from the bean with chemical solvents. Hydraulic presses
are not used much because of the expense and lower yields.
In conventional soybean oil production, the beans are prepped, cut into
flakes, and immersed in a solvent, usually hexane. Hexane is a
colorless, flammable liquid derived from petroleum, and is an air
pollutant the release of which is regulated by the EPA.
The resulting oil then undergoes transesterification using alcohol
(methanol or ethanol) and a catalyst (usually sodium hydroxide).
Transesterification is the process of cracking of the vegetable oil
molecules into fatty acid chains (which ultimately are used for fuel)
The ARS eliminated hexane from the process simply by skipping the
conventional oil-extraction step. Instead, the researchers directly
immersed the soybean flakes in the methanol and sodium hydroxide.
Transesterification occurs directly in the raw soy flakes (“in situ”)
containing the oil.
The initial passes at the process worked, although the researchers noted
that the new method used considerably more methanol than typically
needed, driving up the cost. Without even accounting for the soy flakes
or soy oil, a gallon of biodiesel produced by their new process was
estimated to cost more than $3.00—versus $0.38 per gallon if produced by
the conventional process.
The team reasoned that the moisture naturally present in soybeans, as
much as 10% in soy flakes, could be the reason behind the high methanol
requirement. They discovered that by drying the flakes before starting
the biodiesel synthesis, they could greatly reduce the required methanol
volume. As a result, the estimated cost went down to $1.02 per gallon.
Lead researcher Michael Haas and his colleagues are presently refining
their economic model to account for income from selling the lipid-free,
protein-rich flakes left after the biodiesel reaction for use as animal
feeds and to account for cost differences between refined-oil and
flaked-soybean starting materials.
ARS has filed a patent application on the process. Haas is exploring use
of this new method to produce biodiesel from the lipids in corn
co-products from ethanol plants that use corn as a starting material.
He’s also investigating the suitability of canola seeds and meat and