More Efficient Approach for Turning Plant Biomass into Useful Chemicals

Editor’s note: The following article was originally issued by Georgia Institute of Technology. National Synchrotron Light Source II (NSLS-II) beamline scientist Eli Stavitski collaborated with researchers at Georgia Tech to evaluate their novel method of converting lignin, an organic polymer that gives wood and plants their strength, into valuable chemicals using the force of tiny steel balls instead of solvents. Using  X-ray absorption spectroscopy at the Inner-Shell Spectroscopy (ISS) beamline at NSLS-II, a U.S. Department of Energy (DOE) Office of Science User Facility at DOE’s Brookhaven National Laboratory, the team was able to establish the mechanism of the catalytic process that efficiently breaks the bonds of lignin compounds. For more information on Brookhaven’s role in this research, contact Denise Yazak (dyazak@bnl.gov, 631-344-6371).

Lignin is one of the most plentiful organic polymers on Earth, making up about 20 to 30 percent of the dry mass of wood and other plants. 

Despite this abundance, lignin’s complex structure has challenged researchers in breaking it down into useful components that can be used in the sustainable production of chemicals, plastics, and fuels. Therefore, lignin is often discarded as waste during the production of paper and other plant-based products.

However, researchers at the Georgia Institute of Technology have developed an approach that could transform lignin into valuable chemicals more efficiently than ever before.

The researchers published their findings in the journal ACS Sustainable Chemistry & Engineering on using a method known as mechanocatalysis, which uses physical forces, such as vibration or rotation, in a ball mill to drive chemical reactions without the need for solvents, heat, or high pressure.

Carsten Sievers, a professor in Georgia Tech’s School of Chemical and Biomolecular Engineering, explained that the first step in a lignin biorefinery is depolymerization, which breaks lignin down into small molecules. 

“Unfortunately, many depolymerization processes require the use of solvents, and separating the products from solvents, catalysts, and contaminants can be complicated, energy intensive, and leave behind waste,” Sievers said. 

“One way to reduce the need for these separation steps is to perform lignin depolymerization in a ball mill where collision with steel balls create environments that enable solid-state reactions without the need for solvents or liquid phases.”

Read more on BNL website

Image: Illustration of a mechanical impact that creates a reactive environment for depolymerization of biomass into value-added chemicals.

New studies towards lignin valorisation

A little known, yet ubiquitous polymer

In work recently published in PNAS an international team of researchers characterised an important degradation step, allowing the breakage of lignin that leads to the production of individual components, which can be further harvested. To do so, they utilise several Diamond Light Source instruments:  the I23, I03 and B21 beamlines.

Compared to animals, plants don’t have a bony skeleton. They rely on rigid cell walls that separate each plant cell. These cell walls are composed of cellulose, pectin and lignin, making these molecules among the most abundant on earth. Lignin is a hydrophobic compound and plays a crucial role in vascular tissue, making them impermeable and allowing the transport of water in the plant efficiently. Lignin is a huge and complex molecule composed of different precursors called monolignols. The composition of lignin varies among plants.

From an industrial perspective, lignin is well known in the paper industry because it represents a third of the mass of the paper precursor. Lignin is a coloured component that yellows in the air and needs to be removed to have white paper. Currently there is only limited use for lignin and it is burned as low value fuel in these industries. New research and development have improved the transformation of lignin into value added components (biofuels, chemical compounds…) but research is still needed to improve the degradation process of lignin. A way to harvest these components is through enzymatic degradation. In work recently published in PNAS an international team of researchers characterised an important degradation step, allowing the breakage of lignin that leads to the production of individual components, which can be further harvested. To do so, they utilise several Diamond Light Source instruments:  the I23, I03 and B21 beamlines.

Read more on the Diamond website

Image: Structural architecture of LdpA and substrate interactions. (A) Superposition of SpLdpA (magenta) with NaLdpA (teal). (B) Side view of the SpLdpA trimer. Two protein chains are shown as surfaces (yellow and green) and one protein chain is shown in cartoon mode (red) with bound substrate erythro-DGPD (light blue). (C) Top view of the SpLdpA trimer. (D) Pseudo-stereoscopic view of the interaction of SpLdpA with the erythro-DGPD enantiomers (αS, βR) (Left) and (αR, βS) (Right). When viewed in stereo, alternating eye switching results in an optimal impression of the binding modes of the two diastereomer substrates. (E) Omit electron density map for the (αS, βR)- and (αR, βS)-erythro-DGPD enantiomers bound to SpLdpA at 2.5 σ level. (see Diamond news piece for complete image)