Liquid by-products slow biofuels process – PNNL

Scientists from the Department of Energy’s Pacific Northwest National Laboratory (DOE-PNNL) discovered that water in the biofuel conversion process helps form an impurity which, in turn, slows down key chemical reactions.

The study examines the conversion of bio-oil, produced 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 biofuels. 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 catalysts in a pyrolysis process when plant matters is rapidly heated to produce bio-oil. 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. The team used computers 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 form. They performed these simulations using resources in EMSL, DOE’s Environmental Molecular Sciences Laboratory at PNNL.

In the simulations, the catalyst is essentially a piece of metal, either nickel or platinum. The phenol molecules and water molecules randomly bounce or land on the metal surface where bonds break and reform between atoms within molecules by shifting electrons around. In this way, a phenol might transform into a ketone.

The team found that the presence of water dramatically upped the speed with which the final conversion to a ketone happened. In addition, water also affected how the metal catalyst carried its electrons, which in turn affected how well it catalyzed the reaction between phenol and hydrogen atoms that settle on the catalyst’s surface.

PNNL colleagues 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. This work was supported by the Department of Energy Offices of Science and Energy Efficiency and Renewable Energy.

The researchers presented this work at the American Chemical Society’s Annual Meeting in San Francisco on Aug. 12.