GRASS TO GASOLINE.
Green Gold -- Derived from plants, bio-oil can be processed into gasoline, diesel or other typical petroleum products such as plastics
Trying to understand the chemistry that turns plant material into the same ener- gy-rich gasoline and diesel we put in our vehicles, researchers have discovered that water in the conversion process helps form an impurity which, in turn, slows down key chemical reac- tions, according to a report by Pacific Northwest National Laboratory (PNNL). The study, which was reported online at the Journal of the American Chemical Society in July, can help improve pro- cesses that produce biofuels from plants. The report further states that the study
examines the conversion of bio-oil, pro- duced from biomass such as wood chips or grasses, into transportation fuels. Researchers used computer simulations to explore what happens to a common bio-oil byproduct. Water, everywhere during biofuels production, turns the byproduct into an impurity that disrupts and blocks the reactions that lead to bio- fuels. The results apply not only to water but to related liquids in bio-oil such as alcohols and certain acids.
The study provides a thorough view of the byproduct phenol reacting with cata- lysts. Catalysts are what chemists useto speed up the reactions that convert plants into fuels, reactions that occurred deep in the Earth over millions of years and gave us the fossil fuels we use to- day. "We are getting to the heart of the fundamentals of biofuels catalysis," said co-author Roger Rousseau, a scientist
at the Department of Energy's Pacific Northwest National Laboratory.
"The work tells us that the impurity is unavoidable and we need to make sure it does not build up enough to interfere. Although this is a very fundamental issue, it points out for us what types of things we can do to help extend the lifetime of the catalysts we are using to make bio-oil."
To make plant matter into products that come from petroleum - gasoline and plastics - biofuels chemists need to understand every step of the process. To make biofuels, researchers rapidly heat up plant matter in a process called pyrolysis.
CATALYST IN THE COMPUTER
While some ideas existed for how this happens, the team used comput- ers to simulate phenol interacting with catalysts and water to see step-by-step what is going on. To explore water's role in the reaction, they also simulated the same reactions in a vacuum, which puts everything but the solid catalyst in vapor carried its electrons, which in turn af- fected how well it catalyzed the reaction between phenol and hydrogen atoms that settle on the catalyst's surface.
"I was surprised at the role liquid plays in the reactivity of the metal catalyst," said PNNL's Yeohoon Yoon, a co-author on the study. "We know a lot about thesehey then use catalysts to convert the pyrolysis oil into transportation fuels. The chemistry that occurs leads to the produc- tion of precursors to fuels and a byprod- uct called phenol. Phenol itself isn't too much of a problem in fuels, but it sits in the vat of chemicals and water that are undergoing a variety of reactions and gets converted into molecules called ketones.
Troublesome ketones will link up with others like them and form long chains that gunk up the catalysts and interfere with important reactions. Researchers at PNNL wanted to know the molecu- lar details on how phenol converts to ketone. Ultimately, they discovered, it's not the catalyst's fault.
form. They performed these simulations using resources in EMSL, DOE's Envi- ronmental Molecular Sciences Labora- tory at PNNL.
In the simulations, the catalyst is essen- tially a piece of metal, either nickel or platinum. The phenol molecules and wa- ter molecules randomly bounce or land on the metal surface where bonds break and reform between atoms within mol- ecules by shifting electrons around. In this way, a phenol might transform into a ketone. The team found that the pres- ence of water dramatically upped the speed with which the final conversion to a ketone happened. In addition, water also affected how the metal catalyst reactions in the gas phase, but almost nothing in the liquid. The principles we've learned can be applied to other catalyst-driven reactions. They will make working in the complex system of real catalysts making real biofuels easier."
And that's the next step. PNNL col- leagues at the Bioproducts, Sciences & Engineering Laboratory, a facility located on the Washington State University Tri- Cities campus where PNNL and WSU researchers collaborate, will use this work to guide development of pyrolysis oil transformation into biofuels. The researchers also presented this work at the American Chemical Society's Annual Meeting in San Francisco on 12 August.
Planting Roots - Bio-oil (right)
is produced from biomass (left) through a process called fast pyrolysis
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