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Synthesis

Formaldehyde protects lignin during biomass processing

Simple treatment keeps natural polymer from turning into sludge

by Bethany Halford
October 31, 2016 | APPEARED IN VOLUME 94, ISSUE 43

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Credit: Alain Herzog/EPFL
When chemists add formaldehyde during lignin extraction (left), they prevent the formation of a dark brown sludge seen without it (right).
Credit: Alain Herzog/EPFL
When chemists add formaldehyde during lignin extraction (left), they prevent the formation of a dark brown sludge seen without it (right).

During biomass processing, tens of millions of metric tons of lignin waste are produced each year. This wasteful sludge could be avoided by simply adding formaldehyde in the early stages of the processing, chemists report. The formaldehyde treatment chemically protects the natural polymer lignin so that it can be transformed into valuable chemical feedstocks.

Lignin accounts for as much as 30% of plants and trees and is made up of valuable aromatic subunits. “Lignin is one of the few natural sources of aromatics, and aromatics are absolutely essential in our chemical industry,” says Jeremy S. Luterbacher, a chemist at the Swiss Federal Institute of Technology, Lausanne (EPFL), who spearheaded the work.

Despite its rich molecular makeup, lignin becomes a waste product because the process that’s used to separate it from a plant’s cellulose and hemicellulose components—which are valuable biofuel feedstocks—causes irreversible C–C bonds to form within the lignin, creating a sludge. Luterbacher’s team found that formaldehyde could chemically prevent those C–C bonds from forming at two key positions (Science 2016, DOI: 10.1126/science.aaf7810).

Formaldehyde adds a hydroxy­methyl group at a nucleophilic position on one of lignin’s aromatic components and creates a 1,3-dioxane at a position that can become an electrophile. These two blocking strategies prevent irreversible C–C bond formation between the nucleophile and electrophile in the lignin.

So far, Luterbacher and colleagues have scaled the reaction up to 1 L. They’ve also patented the process and are currently deciding whether to move forward by starting their own company or by partnering with an existing firm.

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