Researchers with Berkeley Lab and the University of California (UC) Berkeley have discovered a mild and relatively inexpensive procedure for removing oxygen from biomass. This procedure, if it can be effectively industrialized, could allow many of today’s petrochemical products, including plastics, to instead be made from biomass.
“We’ve found and optimized a selective, one-pot deoxygenation technique based on a formic acid treatment,” said Robert Bergman, a co-principal investigator on the project who holds a joint appointment with Berkeley Lab’s Chemical Sciences Division and the UC Berkeley Chemistry Department.
The formic acid converts glycerol - a major and unwanted by-product in the manufacturing of biodiesel - into allyl alcohol, which is used as a starting material in the manufacturing of polymers, drugs, organic compounds, herbicides, pesticides and other chemical products. Allyl alcohol is currently produced from the oxidation of petroleum.
“Right now, about five percent of the world’s supply of petroleum is used to make feedstocks that are synthesized into commodity chemicals. If these feedstocks can instead be made from biomass they become renewable and their production will no longer be a detriment to the environment,” said Jonathan Ellman, a UC Berkeley chemistry professor and the project's other principal investigator.
Biomass has become known for its potential to be converted into carbon-neutral biofuels, but there is also huge potential for it to be converted into chemical feedstocks. Unlike petrochemical feedstocks, which are made by adding oxygen to petroleum, biomass feedstocks require the removal of oxygen from the raw material. Feedstocks for products obtained from biomass rather than petroleum would be renewable as well as biodegradable.
Bergman and Ellman used labeling experiments and a unique distillation system to investigate an old chemical reaction in which formic acid, the chemical found in bee venom, was used to remove oxygen from glycerol. In its original conception, the reaction was low-yielding, primarily because of substantial charring - an unselective combustion that leads to an intractable mixture under high heat. The researchers found that simply protecting this reaction from air provided a much improved process for the deoxygenation of glycerol.
“Treating glycerol with formic acid while directing a stream of nitrogen through the reaction mixture completely eliminates charring. Besides protecting the product from atmospheric oxidation, the nitrogen also facilitates distillation of the alcohol. The final product shows substantially improved yield (80 percent) and higher selectivity,” Bergman stated.
In studying the basic chemistry behind the reaction, the researchers uncovered an unexpected reaction pathway that broadens the generality of the reaction and expands its potential applications. With this new reaction pathway, the formic acid-mediated deoxygenation technique developed by Bergman and Ellman could be used to convert the carbohydrates in biomass, as well as other polyhdroxy compounds, into the chemical feedstocks, such as olefins (alkenes) that are now derived from petroleum. The technique could also prove useful in the process by which biomass is converted into liquid transportation fuels.
“Our preliminary results with inexpensive biomass-derived polyols suggest that the reaction of polyhydroxy compounds with formic acid will be a valuable alternative for the manufacture of reduced oxygen content products,” said Bergman. “However, scaling this technique up so that biomass feedstocks are competitive with feedstocks derived from petroleum is going to be an engineering challenge.”