U Wisc. scientists develop new method to convert lignin to simple chemicals under mild conditions
03 November 2014
Researchers at the University of Wisconsin have disclosed a new method to convert lignin, an important component of biomass waste, into simple chemicals. Lignin, which accounts for nearly 30% of the organic carbon in the biosphere, is a complex material containing chains of six-carbon rings. These aromatics could be the basis for a sustainable supply of useful chemicals, but only if the chains of lignin can be broken down into the individual units. Lignin, however, is highly resistant to breakdown, especially in a cost-effective way.
Prof. Shannon Stahl and his colleagues developed, in work funded by the Great Lakes Bioenergy Research Center at UW-Madison, a method for the depolymerization of oxidized lignin under mild conditions in aqueous formic acid that results in more than 60 wt% yield of low-molecular-mass aromatics. A paper on the method is published in the journal Nature.
The initial oxygen treatment step (producing the oxidized lignin) was reported by Rahimi and Stahl last year. Rahimi explored many different approaches to break down the lignin. Thee team was trying various metals under acidic conditions, when it discovered that acid without metals gave the best result.
The oxidation step weakens the links in the lignin chains. The acid then breaks the links. Under these conditions, the aromatics formed in significantly higher yields than anyone has observed previously.
—Alireza Rahimi, a UW postdoctoral researcher and first author
Any process that competes in industry must be economical, and Stahl says avoiding metals in the process is one of several advantages.
The mild conditions, with relatively low temperatures (110 degrees Celsius/230 degrees Fahrenheit) and low pressures, as well as the lack of need for expensive metal catalysts, makes it different from many other approaches.
—Shannon Stahl
Josh Coon, a professor of chemistry and co-author, and graduate student Arne Ulbrich showed that the resulting product mixture closely matches the distribution of subunits in the natural lignin.
Stahl sees lignin as a key to future biorefineries that would use renewable biomass rather than petroleum as the feedstock to produce fuels or chemicals while reducing environmental impact.
Lignin is the only large volume renewable feedstock that contains aromatics. Aromatics are used to make many things, from plastic soda bottles to Kevlar to pesticides and pharmaceuticals. Today, the aromatics are almost exclusively derived from petroleum. We need to find an economical way to convert lignin to value-added materials. Most of the focus in this field has been on cellulose, but I don’t think there will be sufficient value to compete with petroleum unless we can generate value from lignin, too.
—Shannon Stahl
The Wisconsin Alumni Research Foundation has filed a patent application on the process.
Resources
Alireza Rahimi, Arne Ulbrich, Joshua J. Coon & Shannon S. Stahl (2014) “Formic-acid-induced depolymerization of oxidized lignin to aromatics,” Nature doi: 10.1038/nature13867
I said here many years ago that once you get done with the biomass, gasify the lignin to make synthetic fuels (Roger, the term is "gasify" not pyrolyze, they are two completely different processes). The cellulose ethanol industry can burn the left over lignin for process heat or they can gasify it to make bio synthetic gasoline to go into E85. They have far too much just for process heat, so make gasoline, diesel and jet fuel also.
Posted by: SJC | 03 November 2014 at 10:53 AM
So? No evidence here or in the chem literature of pyrolysis or "gasification". Formic acid is a liquid slightly above the boiling point of water. Coreagents that manufacture formic acid and could add to lignin decomposition are methanol and carbon monoxide. There must be a lot of hydrolysis. Here is a process that could rely almost entirely on liquid phase separation of the products and recycling of gases and liquids, and in situ replenishment of the formic acid.
I'm dying to know the secret innovation. And it has to be an innovative secret.
Posted by: kalendjay | 03 November 2014 at 03:15 PM
110°C is a temperature easily achieved by vented steam from low-pressure stages in power plants, after much of the available energy has already been harvested. Using such steam to convert lignin to simpler molecules (whether for chemical precursors or fuels) looks like an energy multiplier. And the low pressures (less than 0.5 bar gauge pressure) mean the equipment can be cheap and easily manufactured.
Can we hope for phthalates made from cornstalks?
Posted by: Engineer-Poet | 04 November 2014 at 08:53 PM