Cellulosic Sugars: The Latest Domtar Innovation

Wood — the building block of all Domtar products — is composed of cellulose, hemicellulose and lignin. Cellulose and hemicellulose can be converted into cellulosic sugars. In our ongoing quest to find innovative ways to use every part of every tree we harvest, our R&D teams are looking for ways to turn those cellulosic sugars into a wide range of biomaterials and biochemicals.

“We are already using wood — and more specifically, cellulose — as a source for paper and other products. Wood is also a reliable source of sugars,” says Dr. Naren Narendranath, Domtar’s director of BioMaterials Research. “This makes it a good feedstock for biofuels, biochemicals and other sugar-based biomaterials.”

Cellulosic Sugars in Our Trees

The idea of converting cellulosic sugars into biofuels and biochemicals isn’t new. Companies have been doing it for years using corn stover (material left after harvesting corn), wheat straw and other lignocellulosic biomass feedstocks. However, they have struggled to find an efficient and cost-effective way of pretreating or breaking down the raw materials and separating the cellulose, hemicellulose and lignin prior to conversion into cellulosic sugars.

“In a pulp and paper mill, we already have that part figured out, and our industry has been doing it for more than 150 years,” says Narendranath. “The digester is where all the pretreatment happens, and we don’t have to purchase or install any expensive new equipment or chemicals to break down the wood chips. The pretreatment is already complete and produces a clean cellulose stream — what we call pulp.”

The next step is to treat the pulp with enzymes that break down the cellulose into glucose and the hemicellulose into xylose (collectively termed cellulosic sugars), which can be used for producing biomaterials. Narendranath says this is where the research really becomes exciting.

“We have been getting 95 to 99 percent conversion of cellulose to glucose with our wood pulp. With corn stover, for example, the best you can get is 75 to 80 percent conversion,” he says. “This has been really encouraging for us. Plus, our sugar is cleaner; easier to ferment into alcohols, such as ethanol, that can be used as a biofuel; and easier to process into end products compared to sugar from other lignocellulosic feedstocks.”

Cellulosic Sugars Are Game Changers

Breaking into highly competitive markets can be extremely difficult, if not next to impossible. “The incumbents are very smart, well-financed and armed with technology and a supply chain that can be more than a century old. Most of all, they do not want to give up market share,” says Mark DeAndrea, vice president and business unit leader of Domtar’s BioMaterials Innovation team.

The good news is that our success in this field is not based on disrupting an incumbent. “Our strategy is to work with incumbents to develop proprietary solutions and to help solve some of their biggest problems,” says Narendranath.

Cellulosic sugars can be made into a wide range of biomaterials that can help our partners reduce their use of fossil fuels and minimize their carbon footprints. Some of the products we’re developing include:

Biochemicals 

From the market side, firms that supply chemicals to the pulp and paper industry are looking for alternatives made from renewable feedstocks, such as trees. These companies make good partners because they are looking for cellulosic sugar-based chemicals, such as acetic acid, methanol and bio-based succinic acid. On the technology side, we are working with partners in the yeast and enzyme production space whose strength lies in converting cellulosic sugars into the necessary chemicals.

“Finding the right partners on the market and technology fronts will ultimately make this a reality,” says Narendranath. “Our strength is in our supply chain of wood and our expertise in converting wood into pulp and pulp into sugar. We don’t need to reinvent the wheel.”

Biofuels

Currently, the focus is on ethanol because the market already exists, and the industry is trying to move away from both fossil fuels and corn-based biofuels in favor of cellulosic carbon-neutral biofuels. We know how to produce cellulosic ethanol, but our wood doesn’t have a qualified pathway to market in the United States or Canada. We have been working with legislators in both countries to clear the path for producing ethanol from tree-based cellulosic sugars.

Food

Our research on cellulosic sugars is leading to potential food additives, such as torula yeast, that can be used as flavorings and nutritional supplements. Torula yeast is currently used to flavor Doritos and other products. We’re also looking into xylitol, which is a sugar alcohol that tastes like sugar but doesn’t have the same glycemic effect. Xylitol is used in diet foods, toothpaste and chewing gum.

“Xylitol, in particular, is exciting because of the growing demand for it,” says Narendranath. “Our Rothschild Mill is a sulfite mill. One of the byproducts from this mill is red liquor, which contains xylose, a sugar. Once separated, xylose can be converted into xylitol. Currently, xylitol sells for more than $3,000 per ton, so it could be a profitable byproduct stream if we can find a cost-effective way to separate it.”

Feed Additives

Cellulosic sugars can feed the algae and yeast used as feed additives for animals. Lignin can also be used as a feed additive for animals. It is a byproduct of both the paper-making process and the production of cellulosic sugars.

Microbial Biomass

We are using cellulosic sugars to feed a certain type of algae that are rich in omega-3 fatty acids. As the benefits of omega-3 fatty acids become better understood, the demand will continue to increase. A significant amount of omega-3 fatty acids are harvested from fish, but this is not sustainable. A non-fish source of omega-3 fatty acid production would be a sustainable solution. The algae we are working with can be used in aquaculture to feed fish, but they are also being used as a source of omega-3 fatty acids for livestock and humans.

Looking Ahead

Some of our research on cellulosic sugars is currently funded by a CA$1.89 million Energy Innovation Program grant awarded by the Canadian government.

“The grant is partially funding our research in how to use cellulosic sugars to produce biofuels or algae for fish feed,” says Narendranath. “These funds also are allowing us to build a pilot-scale, skid-mounted unit to process 0.5 tons of dry pulp a day to produce sugars that we can use to test and create other biobased products. Not all technology is scalable; in fact, sometimes larger scale equates to larger problems. This new pilot unit will help us move out of the lab and start testing on a larger scale.”

Meanwhile, the BioMaterials team, the team at Rothschild Mill and our engineering team have been working to find a way to extract and refine the xylose currently produced as a byproduct. The project team is also conducting market studies to identify opportunities for the xylose and xylitol that can be produced.

“There’s quite a bit of demand and a lot of growth in the markets for cellulosic sugars and their applications,” says Narendranath. “We’re seeing growth rates of 15 percent for algal biomass, 46 percent for biobased succinic acid and 28 percent for polylactic acid, a biodegradable bioplastic.”

All of these opportunities make use of raw materials that are already part of our manufacturing process.

“A pulp and paper mill is a true biorefinery,” says Narendranath. “For example, we can use our cellulosic sugars to make polylactic acid, which can be combined with our lignin and extruded as an alternative to petroleum-based thermoplastics. The resulting plastic is 100 percent biodegradable. Everything could essentially be done in one place using materials we already have. That would be very exciting.”

Learn more about cellulosic sugars.