RENEWABLES
Has lignin’s time finally come? After years of burning it, companies are starting to recover the ubiquitous tree biopolymer
nually, yet they choose to recover only about 2% of it. The paper industry removes lignin from cellulose in two chief ways. In the older proMICHAEL MCCOY, C&EN NEW YORK CITY cess, called sulfite pulping, lignin is sulfonated to solubilize and separate it. In the newer, fter Michael Lake got his Ph.D. in chemical engineering and more prevalent kraft process, lignin is separated by acid precipitation. The sulfite joined the paper company Westvaco, he soon became convinced that lignin—needed by trees but unwanted by the paper process yields lignosulfonates as a by-product. The kraft process yields a lignin with a industry—was the material of the future. higher phenolic content than native lignin. A modest lignosulfonate industry has More than 40 years have passed, and Lake’s enthusiasm for the biopolyexisted since the 1930s, when sulfite-promer hasn’t dimmed. “Lignin’s time has come, I think,” he says. “But then, I cess paper makers began looking OH thought the same thing in 1973.” for alternatives to dumping their Lake isn’t the only one to have a romance with lignin. Known lignosulfonate-containing pulp HO OCH3 liquors into lakes and rivers. Toas Earth’s most prevalent biopolymer after cellulose, lignin has O CH3O long intrigued scientists. For the paper industry, lignin day, the sector’s biggest player is O OCH 3 is an unwanted by-product that is mostly burned the Norwegian firm Borregaard, OCH3 HO for fuel. Believers see it as a complex polymer full which both operates its own HO O of valuable aromatic rings that otherwise come specialty cellulose plant and OCH3 largely from fossil fuels. markets lignosulfonates proOH O O HO Unlocking those aromatics, they say, will duced by other pulp and OH create a new class of renewable chemicals paper firms. OH OCH3 HO to compete with traditional products Morten Harlem, exOH ecutive vice president of O derived via petrochemistry. Some of O O the forecasts are breathtaking. Borregaard LignoTech, CH3O The market research firm Lux explains that lignosulfonOCH3 HO Research, for example, sees ates are water-soluble prodOCH3 commercial opportunities for ucts sold mainly as binders O O OCH OH and dispersants. The largest 3 HO O lignin of up to $242 billion. HO Acknowledging the potenmarket is concrete, where OH tial, paper companies that lignosulfonates improve HO HO O OH for decades burned lignin are CH O flow. Other applications include O 3 OH CH3O now starting to recover it with binding animal feed pellets and disOH the help of improved separapersing water-based crop protection tion technology that yields a chemicals. HO more consistent product. Borregaard sells some 600 differO Three multi-milent lignosulfonate products to more OCH 3 HO lion-dollar separation than 3,000 customers around the HO HO plants have been built in OH world. The firm would sell more, Harthe U.S., Canada, and Finlem says, but sulfite pulping has been OH land, and marketers are on the decline and mills have been O CH3O O OH pushing lignin in multiple closing. Global lignosulfonate output OH OH OCH applications. But lignin has dropped from about 1.6 million metric 3 O HO OCH3 sales today are still tiny, and most tons in 2000 to 1.1 million metric tons today, O CH3O of the ideas for new applications reOCH3 according to Borregaard. main commercially unproven. Not surprisingThe company is looking for ways to reHO ly, not everyone shares Lake’s conviction that lignin vive lignosulfonate production. Notably, OCH3 O has arrived. in cooperation with the specialty cellulose O Understanding lignin requires understanding a little maker Rayonier Advanced Materials, it is about the paper industry. Trees are composed of lignin, studying the recovery of lignin from RayOH CH3O cellulose, and hemicellulose in roughly equal proporonier’s Fernandina Beach, Fla., pulp mill, O tions. Lignin fills the spaces between the other two, giving a tree strength and rigidity. Lignin in softwoods is derived mainly from radical coupling reactions of Companies such as Westvaco, now called WestRock, coniferyl alcohol, which form various dimeric building blocks (colored that convert trees into pulp and paper are interested segments) that make up a biopolymer like that shown. Lignins have no mainly in the cellulose. By one estimate, the world’s pulp defined structural sequence, meaning the chance of encountering two mills generate about 50 million metric tons of lignin anidentical lignin molecules is rather small.
CREDIT: DESIGNED BY FENGXIA YUE, FACHUANG LU, AND JOHN RALPH/GLBRC
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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 the specialty 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 Pine forests have include replacing carbon government assistance. the potential black in rubber reinforcement Lignin from all three comto supply vast and substituting for polyacpanies is now available for quantities of lignin. rylonitrile as a precursor to customer trials. Andreas Bircarbon fiber. About a year ago, moser, senior vice president for strategy Birmoser notes, Stora opened a biomateriand business development in Stora Enso’s als innovation center in Stockholm where a biomaterials division, says his firm is tarteam of scientists is dedicated to developgeting lignin as a safer alternative to phenol ing new lignin applications. in phenolic resins used in plywood and simBy 2022, Birmoser predicts that some ilar applications. Stora is already trialing its 130,000 metric tons of pure lignin will be product on an industrial scale with a cussold and that the market for all forms of ligtomer in the resin industry, Birmoser says. nin will be worth $6 billion annually. That Other potential applications for lignin doesn’t include products that some opti-
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mists 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
“Ten percent replacement is really easy. Forty percent replacement is really hard.” —Michael Lake, chief technology officer, Lignin Enterprises
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. ◾
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