After Michael Lake got his Ph.D. in chemical engineering and joined the paper company Westvaco, he soon became convinced that lignin—needed by trees but unwanted by the paper industry—was the material of the future.
More than 40 years have passed, and Lake’s enthusiasm for the biopolymer hasn’t dimmed. “Lignin’s time has come, I think,” he says. “But then, I thought the same thing in 1973.”
Lake isn’t the only one to have a romance with lignin. Known as Earth’s most prevalent biopolymer after cellulose, lignin has long intrigued scientists. For the paper industry, lignin is an unwanted by-product that is mostly burned for fuel. Believers see it as a complex polymer full of valuable aromatic rings that otherwise come largely from fossil fuels.
Unlocking those aromatics, they say, will create a new class of renewable chemicals to compete with traditional products derived via petrochemistry. Some of the forecasts are breathtaking. The market research firm Lux Research, for example, sees commercial opportunities for lignin of up to $242 billion.
Acknowledging the potential, paper companies that for decades burned lignin are now starting to recover it with the help of improved separation technology that yields a more consistent product.
Three multi-million-dollar separation plants have been built in the U.S., Canada, and Finland, and marketers are pushing lignin in multiple applications. But lignin sales today are still tiny, and most of the ideas for new applications remain commercially unproven. Not surprisingly, not everyone shares Lake’s conviction that lignin has arrived.
Understanding lignin requires understanding a little about the paper industry. Trees are composed of lignin, cellulose, and hemicellulose in roughly equal proportions. Lignin fills the spaces between the other two, giving a tree strength and rigidity.
Companies such as Westvaco, now called WestRock, that convert trees into pulp and paper are interested mainly in the cellulose. By one estimate, the world’s pulp mills generate about 50 million metric tons of lignin annually, yet they choose to recover only about 2% of it.
The paper industry removes lignin from cellulose in two chief ways. In the older process, called sulfite pulping, lignin is sulfonated to solubilize and separate it. In the newer, more prevalent kraft process, lignin is separated by acid precipitation. The sulfite process yields lignosulfonates as a by-product. The kraft process yields a lignin with a higher phenolic content than native lignin.
A modest lignosulfonate industry has existed since the 1930s, when sulfite-process paper makers began looking for alternatives to dumping their lignosulfonate-containing pulp liquors into lakes and rivers. Today, the sector’s biggest player is the Norwegian firm Borregaard, which both operates its own specialty cellulose plant and markets lignosulfonates produced by other pulp and paper firms.
Morten Harlem, executive vice president of Borregaard LignoTech, explains that lignosulfonates are water-soluble products sold mainly as binders and dispersants. The largest market is concrete, where lignosulfonates improve flow. Other applications include binding animal feed pellets and dispersing water-based crop protection chemicals.
Borregaard sells some 600 different lignosulfonate products to more than 3,000 customers around the world. The firm would sell more, Harlem says, but sulfite pulping has been on the decline and mills have been closing. Global lignosulfonate output has dropped from about 1.6 million metric tons in 2000 to 1.1 million metric tons today, according to Borregaard.
The company is looking for ways to revive lignosulfonate production. Notably, in cooperation with the specialty cellulose maker Rayonier Advanced Materials, it is studying the recovery of lignin from Rayonier’s Fernandina Beach, Fla., pulp mill, where the product is now incinerated. If built, the plant would cost $135 million and turn out up to 150,000 metric tons of lignosulfonates per year.
Compared with lignosulfonates, commercial lignin production is minuscule, since most kraft-process paper companies simply burn lignin to generate steam or electricity. For years, the only company to recover significant amounts of lignin was Westvaco. That business, which is now part of thespecialty chemical company Ingevity, operates a plant in North Charleston, S.C., with a capacity of roughly 40,000 metric tons per year.
Although Ingevity starts with lignin, it turns much of its output into lignosulfonates via a subsequent sulfomethylation step. The firm plays in some of the same markets as Borregaard does, including dye and pesticide dispersion.
But in 2013, a new industry focused on pure lignin started to emerge. With the help of grants from the U.S. Departments of Agriculture and Energy, the paper company Domtar opened a 20,000-metric-ton lignin separation plant in Plymouth, N.C. Last year, Stora Enso started up a 50,000-metric-ton plant at its pulp mill in Finland, and earlier this year, West Fraser opened a 10,000-metric-ton plant in Alberta. Like Domtar, both companies had government assistance.
Lignin from all three companies is now available for customer trials. Andreas Birmoser, senior vice president for strategy and business development in Stora Enso’s biomaterials division, says his firm is targeting lignin as a safer alternative to phenol in phenolic resins used in plywood and similar applications. Stora is already trialing its product on an industrial scale with a customer in the resin industry, Birmoser says.
Other potential applications for lignin include replacing carbon black in rubber reinforcement and substituting for polyacrylonitrile as a precursor to carbon fiber. About a year ago, Birmoser notes, Stora opened a biomaterials innovation center in Stockholm where a team of scientists is dedicated to developing new lignin applications.
By 2022, Birmoser predicts that some 130,000 metric tons of pure lignin will be sold and that the market for all forms of lignin will be worth $6 billion annually. That doesn’t include products that some optimists say will be made by depolymerizing lignin into its monomeric components.
Lake, the former Westvaco researcher, is now chief technology officer at Lignin Enterprises, a small, South Carolina-based company. His firm offers its own lignin recovery technology to the paper industry and is helping West Fraser market lignin from its new Canadian plant. “We’re confident we are going to sell out this 10,000-ton facility,” Lake says.
Like Birmoser, Lake is bullish on replacing phenol in resin applications, although he acknowledges that, for technical reasons, it won’t be a one-for-one switch. “Ten percent replacement is really easy. Forty percent replacement is really hard,” he says.
The Finnish paper company UPM, which distributes Domtar’s lignin in Europe, conducted a study of lignin as a phenol replacement and got its best results with an “alkali-activated” lignin. The company achieved 50% phenol replacement in plywood at industrial scale and 75% replacement in the lab.
Lake also advocates substituting lignin for up to 30% of the polyols used to make stiff polyurethane foams for insulation. Capturing waste or spilled oil in oil-water dispersions is another potential application, he says, as is using lignin as a cost-effective ion-exchange material.
In none of the proposed applications does lignin compete with lignosulfonates, for the simple reason that lignosulfonates are soluble in water and lignin is not. In addition, lignin is rarely a 100% straight replacement for an existing material.
“It’s not a commodity drop-in where you flip a switch,” Lake says. “It’s a one-on-one selling job with each new customer.”
Borregaard’s Harlem, who has spent close to 15 years in the lignosulfonate business, is skeptical about the optimistic predictions being made for lignin. To date, he points out, precious little product has actually been sold. “I haven’t seen anything yet of those processes adding a kilo of sales in the specialty chemicals arena,” he says.
In Harlem’s view, paper companies that are recovering lignin are less interested in new chemical markets than in the 10–15% effective capacity boost that removing lignin provides their recovery boilers, one of the most expensive parts of a pulp mill. Moreover, others point out, once removed, dried lignin can be a source of the high-heat energy needed to convert lime into calcium oxide, which is used to regenerate sodium hydroxide in the mill.
Indeed, Birmoser says that’s exactly what Stora Enso is doing with lignin while it gains experience with its new plant. “But we didn’t do this just for the fuel,” he insists. “There are much more interesting applications.”
Similarly, Lake sees lignin recovery as a win-win for paper makers. They can add capacity to their boilers, and firms like his can help them find new markets for the renewable chemical they take out.
Lake admits he was ahead of his time in the 1970s when he predicted the imminent emergence of a robust lignin industry. But he argues that the stars for the once-unwanted material are really aligning today. “Things are better now for lignin than they have ever been,” he says.