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) and glycerin.
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 bone meal.