Posts Tagged ‘calculations’

Tuesday, December 18, 2012 @ 11:12 AM gHale

There is now a molecular-level view into how cellulose breaks down in wood to create “bio-oils” which could result in better more efficient ways to create fuels for cars or planes.

Cellulose is the most common organic compound on Earth and the main structural component of plant cell walls.

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Using a supercomputer that can perform functions thousands of times faster than a standard desktop computer, it is possible to calculate what is occurring at the molecular level when wood rapidly heats to high temperatures in the absence of oxygen, a decomposition process known as pyrolysis, said North Carolina State University Chemical and Biomolecular Engineer Dr. Phillip Westmoreland and doctoral student Vikram Seshadri, who also wrote a paper on the subject.

The results of those calculations could help spur more effective and efficient ways of converting farmed and waste wood into useful bio-oils.

Much of the energy that can come from wood exists in the cellulose found in cell walls. Cellulose is a stiff, rodlike substance consisting of chains of a specific type of a simple sugar called glucose. It is the most common organic compound on Earth.

The NC State researchers describe a mechanism for how glucose decomposes when heated. The mechanism is somewhat surprising, Westmoreland said, because it reveals how water molecules and even the glucose itself can trigger this decomposition.

“The calculations in the paper show that although the decomposition products and rates differ in glucose and cellulose, the various elementary steps appear to be the same, but altered in their relative importance to each other,” Westmoreland said.

Knowing the specifics of the decomposition process will allow researchers to make predictions about the ease of extracting energy from different types of wood from various soil types.

The researchers are now conducting experiments to verify their calculations. The U.S. Department of Energy funded their research.

Monday, August 1, 2011 @ 06:08 PM gHale

Using plant-based biofuels instead of gasoline and diesel is crucial to curb climate change. But there are several ways to transform crops to fuel, and some of the methods result in biofuels that are harmful to health as well as nature.

It is possible to predict just how toxic the fuel will become without producing a single drop, according to a new study from the University of Copenhagen. This promises cheaper, faster and above all safer development of alternatives to fossil fuel.

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Among other things the calculations of the computer chemist show that biofuels produced by the wrong synthesis path will decompose to compounds such as health hazardous smog, carcinogenic particles and toxic formaldehyde. But the problem is they had to make the fuel before they could test it. Now there are ways to map out the fuel production via calculations on the computer.

“There is an almost infinite number of different ways to get to these fuels,” said Solvejg Jorgensen, a computational chemist at the Department of Chemistry in Copenhagen. “We can show the least hazardous avenues to follow and we can do that with a series of calculations that take only days.”

Chemically biofuel consists of extremely large molecules. As they degrade during combustion and afterwards in the atmosphere they peel off several different compounds. This was no big surprise. That some compounds are more toxic than others did not come as a revelation either but Jorgensen learned from her calculations there is a huge difference in toxicity depending on how the molecules assemble during production. She also could calculate very precisely the degradation mechanisms for a bio fuel molecule and do it fast.

Solvejg Jorgensen, right, conducted a study that shows using computational chemistry can predict and prevent harmful biofuel production.

Solvejg Jorgensen, right, conducted a study that shows using computational chemistry can predict and prevent harmful biofuel production.


“In order to find the best production method a chemist might have to test thousands of different types of synthesis. They just can’t wait for a method that takes months to predict the degradation mechanisms,” said Jorgensen. “On the other hand: For a chemist who might spend as much as a year trying to get the synthesis right it would be a disaster if their method leads to a toxic result.”

It seems an obvious mission to develop a computational tool that could save thousands of hours in the lab. But Jorgensen wasn’t really all that interested in biofuels. What she really wanted to do was to improve existing theoretical models for the degradation of large molecules in the atmosphere.

To this end she needed some physical analysis to compare to her calculations. Colleagues at the Department of Chemistry had just completed the analysis of two biofuels. One of these would do nicely. But Jorgensen made a mistake. And instead of adding just another piece to a huge puzzle she had laid the foundation for a brand new method.

“I accidentally based my calculations on the wrong molecule, so I had to start over with the right one. This meant I had two different calculations to compare. These should have been almost identical but they were worlds apart. That’s when I knew I was on to something important,” she said.

 
 
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