Wood could be the next petroleoum

A societal transition completely away from fossil fuels would be, to put it lightly, a massive endeavor. Take containers and packaging alone, the stuff that holds sodas, keeps eggs in their cartons, and holds late-night snacks in clamshell containers. The Environmental Protection Agency estimates that in 2017, the most recent year for which it has data, that plastic waste amounted to 14.5 million tons of municipal solid waste. Just how could all that packaging be reduced without dramatically upping the price of packaging? An interdisciplinary team at Belgian university KU Leuven has an idea that might sound counterintuitive at first: wood.

Wood, of course, comes from trees. And green energy is very much focused on conserving trees. Deforestation is a major problem around the globe—the Union of Concerned Scientists estimates that an area approximately the size of Switzerland is chopped down each year, and in 2016, the World Bank estimated that the world has lost 1.3 million square kilometers of forests since 1990, an area larger than South Africa.

Forests obviously have to be protected, but it's hard to imagine a future where people don't use trees at all. Despite our digital world, paper is still in widespread use: a Sierra Club estimate from 2014 pointed at a figure of 55 to 110 million trees being used for paper every year. Books, newspapers, looseleaf for school notes — while production is certainly shrinking, these things are not going away for good any time soon.

And since wood is going to be used, the scientists suggest that it should be used holistically. That means using a part of the tree that is often seen as waste: lignin, the organic polymers which bind the cells and fibers of wood together. Their paper, "A sustainable wood biorefinery for low–carbon footprint chemicals production," was published on February 13 in the journal Science.

"In the paper industry, lignin is seen as a residual product and usually burned. That's a pity, since just like petroleum, it can have many high quality uses if it can be properly separated from wood and the right chemical building blocks are extracted," says Professor Bert Sels of the Department of Microbial and Molecular Systems, in a press statement.

Lignin has terrific opportunity, but the challenge for scientists has long been its price point. It's hard to get cheaper than petroleum. That's why the KU Leuven team reached out to the private sector for the study, working with a Belgian-Japanese ink company to see if they could take compounds from lignin to recreate what is currently made with petroleum. As a raw material, they found that wood as a raw material could be profitable "after a few years."

The key here is smart forest management. Sels believes that as the paper industries of Europe and the rest of the world decline, an opportunity for lignin is presenting itself. "There is currently a surplus of wood in Europe,” he says, and beyond that the team is looking for wood that would already be tossed out, contacting waste processors and landscape managers.

Between recycling would-be waste and smart forest management, using lignin as a replacement for petroleum would have a smaller carbon footprint. And beyond what they use, lignin-based products could aslo absorb a small amount of carbon dioxide themselves. "As a result, it would be possible to store carbon from CO₂ in plastics — preferably recyclable ones," Sels says.

With an economic forecast set and the technology down pat, the next step for the team is to scale the technology up. Those 14 millions tons of plastic, which have become so commonplace that their little pieces known as microplastics are becoming ubiquitous worldwide, didn't get into the ecosystem by mistake. They got their because efficient machines could make them at scale for cheap, and lignin would need to follow suit to challenge their dominion.

Right now, the team is further engaging the private sector in hopes of finding more companies to process cellulose pulp and lignin oil. The end goal is a wood biorefinery in Belgium.

“The chemical sector emits a lot of CO₂ globally. A serious change is needed to achieve a carbon neutral chemistry," says Bert Lagrain, Sustainable Chemistry Innovation Manager at KU Leuven. “By scaling up our research project, we hope to get the industry on board.”

Abstract: Profitability and sustainability of future biorefineries are dependent on efficient feedstock utilization. It is essential to valorize lignin when using wood. We have developed an integrated biorefinery that converts 78 wt.% of birch into xylochemicals. Reductive catalytic fractionation of wood gives a carbohydrate pulp amenable to bioethanol production and a lignin oil. After extraction of lignin oil, the crude, unseparated mixture of phenolic monomers is catalytically funneled into 20 wt.% of phenol and 9 wt.% of propylene (on lignin basis) by gas-phase hydroprocessing/dealkylation, whereas the residual phenolic oligomers (30 wt.%) are used in printing ink as replacements for controversial para-nonylphenol. Techno-economic analysis predicts an economically competitive production, and life-cycle assessment estimates a lower CO₂ footprint relative to fossil-based production.