Rice researchers weigh environmental, economic costs of biodiesel production

BY FRANZ BROTZEN
Rice News staff

Biodiesel is seen as a renewable alternative to diesel fuel made from petroleum. As production of biodiesel has risen in recent years, Rice University researchers are looking at ways to make it more cost-effective and environmentally sustainable.

Their report, titled “Sustainable Production and Deployment of Biodiesel in Texas,” explores the implications of alternative approaches to biodiesel production and deployment.

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The authors, Daniel Cohan, assistant professor in civil and environmental engineering; Kyriacos Zygourakis, the A.J. Hartsook Professor in Chemical and Biomolecular Engineering and professor in bioengineering; and Ramon Gonzalez, the William Akers Assistant Professor in Chemical and Biomolecular Engineering, focused on the biodiesel industry in the Houston region, where there are 10 facilities with a combined capacity of 380 million gallons per year.

“Produced by the trans-esterification of vegetable oils and animal fats, biodiesel has similar density, flash point, viscosity and oxidation stability to petroleum diesel,” the authors said. “These similarities enable biodiesel blends to be used in conventional diesel engines without significant modifications.” However, despite its advantages as a fuel, “limitations in the availability of soybeans and other potential feedstocks will likely limit biodiesel to replacing only a modest percentage of diesel fuel use.”

A major part of the report is devoted to an analysis of the effects on air quality — specifically ozone — of substituting biodiesel for petroleum diesel in the Houston region. The authors noted that ozone’s precursor emissions — nitrogen oxides (NOx) and volatile organic compounds (VOCs) — have varying impacts on the atmosphere. “Depending on atmospheric conditions, adding more NOx emission to the atmosphere may increase or decrease ozone concentrations,” they wrote.

The researchers’ goal was to explore how biodiesel could be targeted to optimize its impacts on local air quality. Their examination involved three steps. First, they quantified the change of air-pollutant emission when switching from diesel to biodiesel. Second, they applied an emission model to create air-quality-model input files representing alternative biodiesel scenarios. Third, a regional air-quality model was applied to simulate the air-quality impacts of the hypothetical scenarios of biodiesel use.

Based on the models, the authors concluded that “the air-quality impacts of deploying biodiesel are very complicated.” For instance, while an increase in NOx from deploying biodiesel in Harris County could actually decrease ozone concentrations in the already NOx-rich urban center, deploying biodiesel in the surrounding seven counties could increase ozone concentration over much of the region.

Finally, the authors said that “all of the ozone impacts that have been found in this research are relatively small changes, even for widespread deployment of biodiesel.” But they added that “this research points to the potential for targeting biodiesel in ways that account for its varied air-quality impacts.”

The report was supported by a fellowship from the James A. Baker III Institute for Public Policy’s Energy Forum and by the Shell Center for Sustainability. It is available at http://cohesion.rice.edu/centersandinst/shellcenter/research.cfm?doc_id=11977.