Lignocellulose: how nature's wonder material could help the energy transition

This article was published in collaboration with Neste.

Each year, plants convert some 100 billion tons of carbon dioxide into biomass. That’s 5% of all the carbon dioxide emitted by humans since the Industrial Revolution.

Most of that carbon is converted into lignocellulose, the most abundant organic material on Earth – trunks, stems, leaves and other plant structures.

Lignocellulose has been around forever. Early land plants adapted to dry land by amping up their production of lignocellulose, producing thicker cell walls that supported their vertical growth.

Without lignocellulose, our tulips would flop, and tree trunks would snake along the ground like gigantic, limp noodles. Ultimately, the diversification of plants profoundly altered the atmosphere and drove the evolution of other lifeforms.

One could argue that we wouldn’t even be here were it not for lignocellulose.

This fantastic product of evolutionary engineering has long shown potential as a highly sustainable, renewable source of fuels and materials.

Neste, the world’s leading producer of renewable diesel and sustainable aviation fuel, estimates (based on analysis by McKinsey) that 300 million metric tons of oil equivalent could be produced every year from lignocellulosic biomass in agricultural and forestry residues alone.

“Large amounts of waste and residues from existing forestry and agricultural production remain underutilized and could be transformed into valuable and highly sustainable new raw materials,” says Markus Rarbach, Vice-President, Business Platform, Lignocellulosics at Neste.

Preliminary processes for extracting ethanol fuel from cellulose were developed in the early 1800s, but scalable industrial conversion into fuels and chemicals took time to mature.

While minor levels of industrial fuel production from lignocellulosics emerged during the world wars and the oil shortages of the 1970s, interest waned as these crises faded. Petroleum thus maintained its dominance – until now.

The urgency of the climate crisis has renewed interest in developing new means by which to extract plant-based energy. The European Green Deal has set the goal of carbon neutrality by 2050, and the United States has committed to halving its emissions by 2030.

Advanced biofuels, such as the ones utilizing lignocellulosic biomass wastes and residues, improve upon the technologies used in the development of conventional biofuels, which are distilled from grains like corn and sugarcane.

But the raw materials for lignocellulosic fuels are derived from a huge range of forestry and agricultural manufacturing processes. “That’s what makes lignocellulose an attractive raw material from a sustainability perspective,” Rarbach explains. “We are not using the edible part of the biomass; instead, we can upgrade waste and residues into highly sustainable, new products."

Waste and residue wood products such as sawdust, branches and treetops as well as corn stover, wheat straw and bagasse from sugarcane production all contain lignocellulose that can be reduced to compounds from which value can be extracted.

“We’re seeing technologies enabling us to utilize various lignocellulosic waste and residues becoming mature enough to be scaled up and make the transition from a development environment into a commercial environment,” Rarbach says.

The lignocellulosic fuel technology took so long to develop in part due to the nature of the substance. Lignocellulosic materials are highly resistant to extraction of the energy that they have stored.

This makes perfect evolutionary sense. Plants have developed these complex matrices of cellulose, hemicellulose and lignin in response to brutal environmental pressures. They are not going to give up the goods easily.

Two separate means of extracting value have been developed in response.

Thermochemical methods use heat and pressure to convert plant matter to fuel. They mimic the geologic pressures that result in crude oil and other fossil resources to produce bio-based oil and syngas.

Biochemical methods employ biological catalysts to do the same. They use enzymes to release the sugars contained in lignocellulose, which are then fermented by microorganisms into usable fuels like ethanol.

Sometimes they are deployed in hybrid form: biochemical processes to produce intermediates and thermochemical techniques converting them into finished products.

It is hoped that these plant-based waste and residue materials can make a significant contribution to carbon neutrality in the coming decades.

“We are going to see a huge diversity of technical solutions in the transport sector, where electric vehicles will play a part. It’s also important that other forms of transport energy contribute to achieving sustainability,” says Rarbach.

How lignocellulosic biomass can be sourced sustainably has been a matter of debate. Some have suggested that the move toward lignocellulosic fuels might incentivize timber harvesting and thus damage forest ecosystems. Sustainably managed forests, which grow more wood than is harvested and cultivate biodiversity, are one solution.

Crop, forestry and other waste residues have a further edge. They utilize inevitable byproducts and thus the ecological downsides are minimal.

Rarbach is hopeful that waste will eventually be eliminated entirely. “That would be obviously highly desirable from a market perspective and from a customer perspective,” he enthuses. “Because carbon neutrality is what we are striving for.”