Math model predicts how biofuel molecules degrade in atmosphere

By Erin Voegele | August 03, 2011

A chemist at the University of Copenhagen has developed a mathematical tool that can help predict the environmental impacts of various methods of biofuel production. According to information released by the university, the tool promises to provide a cheaper, faster and safer way to develop new forms of biofuel.

Solvejg Jorgensen, a computational chemist at the University of Copenhagen, actually developed the tool by accident. She was working to improve existing theoretical models for the degradation of large molecules in the atmosphere and needed some physical analysis to compare with her calculations. Since biofuels are chemically comprised of large molecules, the use of them was an attractive choice. Colleagues of Jorgensen had recently completed the analysis of two biodiesel molecules; an ethyl acetate molecule and a methyl propionate molecule. She selected one to use for her modeling, but soon realized she mistakenly modeled the wrong one. According to Jorgensen, she initially based her calculations on the wrong molecule and started over with the correct one. While she expected the resulting models of the two molecules to be similar, they were actually very different.  Essentially, she founds that there is a huge difference in toxicity depending upon how the molecules are assembled during biofuel production.

The calculations demonstrated that biofuel molecules produced by some synthesis paths can decompose into compounds that pose health hazards, such as smog, carcinogenic particles and formaldehyde. While this type of analysis traditionally had to be done with actual fuel, the model developed by Jorgensen provides a virtual method to do so. According to Jorgensen, there is almost an infinite number of ways to synthesize biofuels and the mathematical model can be used to find the least hazardous methods to follow. In addition, she notes the calculations can be completed in a matter of days.

“The model is based on ab initio quantum mechanical calculations where the reaction mechanism is predicted,” Jorgensen said. “From these calculations the rate constant is predicted using a transition state theory. All these methods are already described in the literature. The model predicts how the hydroxyl radical reacts with the given biofuel.” According to Jorgensen, the model could be used to evaluate a wide range of biofuel molecules, including butanol isomers. “The model can screen a number of possible biofuels,” she added. “The model only predicts the atmospheric fate upon reaction with the hydroxyl radical. The atmospheric fate [or] impact can be predicted. From these results one could decide which of the biofuel should be synthesized.”

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