Huge strides have been made in the commercial development of lignin, but there is a lot more exciting work on the horizon.
Although the “bio” sector of the forest products industry has been big news recently, many do not realize that this new path was actually trodden upon more than 30 years ago, if not longer.
Michael Paleologou is a research leader in the Innovative Bioproducts Centre of Excellence at Montreal-based FPInnovations, the world’s largest private, not-for-profit forest research institute. He led a team that developed the LignoForce System™ for lignin production from black liquor. Paleologou says the system was invented in 2008, although he says, indirectly, he started the LignoForce work earlier.
He is quick to credit past FPInnovations (formerly Paprican) researchers such as Jim Wearing and Vic Uloth, who did pioneering work in the late 1980s and early 1990s.
“This was followed by work by Jean-Noel Cloutier, who looked at an electrochemical approach to recover lignin from black liquor. I greatly benefitted from their work when I started mine.”
Paleologou has been with FPInnovations for 30 years and has spent the last 10 focusing on the issues surrounding the forest biorefinery concept. With the market in communication papers in steep decline in the early part of the century, the Canadian government was eager to find a way to transform the country’s forest products industry.
Natural Resources Canada (NRCAN) provided a lot of funding for research into “transformative” products. This led to the lignin project. “We focused at first on lignin products rather than the process,” Paleologou explains. “We developed the LignoForce process while trying to destroy the smelly sulphur compounds that come out of black liquor when it is acidified.”
During the initial work at the pilot plant level at FPInnovations, when the team was still thinking about new products, Paleologou says, “The odor was so unbearable, I could not have accepted the idea of people working in that environment. When we discovered the solution, all sorts of other benefits came out.”
And the solution is simple: oxygen (see Fig. 1). Its benefits, compared with air, are many:
• There is no nitrogen deadload in the process.
• With oxygen, temperatures can rise to 140°C because of the exothermic nature of oxidation reactions. This helps with the nucleation process of lignin particles so they can filter and wash well. This is key, Paleologou explains.
• The sulphur compounds are oxidized, but so are the sugars and other organics. This results in a lower pH of the liquor so less carbon dioxide (CO2) is needed to reach the desired lignin precipitation pH of about 10.
Carbon dioxide is the highest operating cost—about 50 percent of the chemical costs in any lignin precipitation process from black liquor, so any reduction is important, Paleologou says.
To evaluate lignin filtration from carbonated black liquor slurries, Paleologou’s team rented a belt filter and a filter press. The former had been used by other companies to produce lignin. Paleologou points out that the belt filter provides a maximum solids content of only 35 percent. The filter press allowed for a solids content of up to 65 percent in cake form.
That cake could be dried further. In fact, the higher the solids content, the lower the operating costs associated with lignin drying. “Also, with the belt filter,” Paleologou says, “we noticed a layer of fiber on top of the lignin, which confirmed the view that lignin might contain a lot of fiber.”
When it came time to scale up to a demonstration plant, the black liquor was filtered to remove the fiber.
FINDING A GOOD PARTNER
The success at the pilot stage convinced the team that it had to “go big.” At this point, FPInnovations teamed up with NORAM Engineering & Constructors Ltd. to build a demonstration plant. This was accomplished with support from the Ontario government through the Centre for Research and Innovation in the Bio-economy (CRIBE).
“We had worked with NORAM before,” Paleologou says. “They already had licenses for several technologies that had been developed here. In particular, we liked the fact that they have extensive expertise in process development and scale-up, with numerous commercial plants operating worldwide in various sectors.”
Also of importance, NORAM has a presence in Latin America, where FPInnovations would like to grow. For example, it has already implemented three Precipitator Dust Purification (PDP) systems in Brazil and Chile.
The LignoForce demonstration plant was located on the site of a swing mill (Resolute Forest Products, Thunder Bay, ON) in order to have access to both softwood and hardwood black liquor (see sidebar.) The plant (see Fig. 2) has also processed some eucalyptus black liquor imported from other parts of the world.
The demonstration plant was built close to the recovery island and has a capacity of 100 kg/day, working about 12 hours daily. The equipment includes:
• Black liquor tanks; liquor at a concentration of 30 to 40 percent is fed to the lignin plant from the mill’s evaporators.
• A black liquor filter.
• A reactor for black liquor oxidation.
• A reactor for black liquor acidification (the team tested different reactor designs).
• A coagulator that allows lignin particles to grow.
• A filter press: this accounts for about 40 percent of the capital cost in industrial-size plants. It dewaters the cake and washes it with sulphuric acid and water.
• Although one was not installed at Thunder Bay or the commercial-scale plant in Hinton, AB, a ring dryer may be used. Paleologou notes a Finnish installation has one.
Speaking about the reactor designs, Paleologou says time was an important factor. “The ones we chose took only a few minutes to complete the oxidation and precipitation steps. We were also looking at efficiencies and always looking at having as continuous a process as possible.”
The black liquor is oxidized up front so there is no odor at subsequent stages of the process. This also means that the lignin at the filter press does not smell, even before being washed with sulphuric acid and water. “So you can take it as is and add it to alkaline processes (e.g., reactor for the manufacture of phenol formaldehyde resins),” Paleologou says. “You do not need to take it to the acid form and add sodium hydroxide to bring the pH level up again.”
The first products came out of the demonstration plant in 2011. “It did not take long to install and debug,” Paleologou adds. “NORAM, as well as our team in Thunder Bay, did a great job.”
Once the product was ready, samples were sent to more than 60 companies, research organizations, and universities. Potential applications being investigated include adhesives/binders, thermoplastics/composites, dispersants/flocculants, carbon fiber, chemicals, activated carbon, and polyurethane foams (to replace polyol). However, the market sector targeted first was wood adhesives, where lignin could replace a significant portion of the phenol formaldehyde (PF) resins in wood products at the mill site or, alternatively, the phenol in the preparation of phenol formaldehyde resins at resin manufacturing sites (see slides).
Why adhesives? Paleologou explains that FPInnovations has a rigorous evaluation process to decide which projects to undertake. It is called NABC: Need, Approach, Benefits, and Competitiveness.
“It needs to make sense,” he stresses. “Back in 2008, we identified this (adhesives) as the lowest hanging fruit. Also, we have a strong adhesives group at FPInnovations so we were able to use their expertise and guidance.”
The first trials were at a plywood mill in British Columbia and the mill was able to reduce the amount of fillers in the glue. Substitution was done at the 50 percent level, but Paleologou says it can go as high as 100 percent.
Commercial scale was just around the corner. As Paleologou notes, many planets must align to achieve a successful result. Shortly after work first started in 2008, British Columbia–based West Fraser Timber became a member company of FPInnovations. With huge production in engineered wood products as well as pulp, the company decided lignin made sense for them as it could become an internal market.
With many Canadian government incentive programs available for innovation development (e.g., IFIT and SDTC), West Fraser applied and was selected. Paleologou says,
“This was something I had dreamed of for years: to have the government initiate programs to help de-risk and implement new technology.”
In spring 2016, a 30 metric tpd commercial-scale LignoForce System facility was started up at the West Fraser pulp mill site in Hinton (see Fig. 3). In operation for more than a year now, the plant has already gone through some modification and upgrading and has a very good design. The plant has attracted attention from around the world.
ONWARD AND UPWARD
Where does the work go from here? Paleologou says high-value lignin products are the focus. “We are still working with adhesives to increase the substitution rate of lignin in PF resins to 40 or even 50 percent.”
As an adhesive in wood pellets, it helps improve their structural integrity. Work is also being done with medium-density fiberboard (MDF) at a pilot plant in Quebec City, replacing isocyanate (p-MDI). The substitution rate is reasonably high, but it is hoped that this can be raised even further.
Looking at other products—for example, polyurethane foam—lignin can replace up to 25 percent of polyol. With depolymerized lignin, the substitution rate can be much higher. Hence, a main focus of FPInnovations’ work is the development of cost-effective lignin depolymerization approaches.
Other added-value possibilities include lignin-based polymers being used as dispersants (textile, wallboard and concrete applications) or as flocculants, for example, in sludge dewatering and suspended solids removal from effluent streams to replace petroleum-based flocculants. “In the next few years, we will try to bring these innovations to an industrial level,” says Paleologou. “We are working to create a lignin culture.”
When asked to compare LignoForce with other technologies, Paleologou says other new processes give good quality lignin in the acid form. “With respect to the equipment needed, we feel that we have an advantage on system footprint. On the operating cost side, we significantly lower carbon dioxide consumption. Another important advantage of our system is the elimination of sulphur compound emissions from both process and product.”
Huge strides have been made recently in what was originally called the forest biorefinery. Maybe it is time to move on from that generalized term as specific products have been successfully brought to market. As Paleologou points out, the developments in nano-technology and lignin are inter-related. “We developed a lot of building blocks at FPInnovations over the last 10 years. We took the tree apart and now we are trying to put it back together in the optimum forms—for example, using cellulose nanocrystals in lignin-based phenolic resins.
“Conventional fibers, cellulose nanocrystals, cellulose filaments, lignin—they are all now available commercially. How can we put them together again in different forms and shapes to address different market needs?”
Hard or Soft
Comparing black liquors from hardwood and softwood pulping processes, Paleologou says hardwood lignin has a more linear and open structure. Softwood lignin works better in phenolic resins, while hardwood lignin is better for polyurethane foams.
Softwood lignin, no matter the wood species, tends to be similar. “We have conducted trials with black liquor from at least 10 different softwood mills and the lignin is all very similar,” Paleologou says. “Hardwood lignin is quite different from softwood lignin, thereby providing the opportunity to tailor the right lignin to the right application.
“Fortunately, we have today, at our disposal, very advanced analytical tools that we did not have 50 years ago. We can use these tools to quite accurately identify important structural and chemical features of lignin that might be of use in particular applications.”
From September 18-20, 2018, the first PAPTAC International Lignin Conference will be held in Edmonton, AB, showcasing all the recent developments in the sector. For more information, visit: http://www.ligninconference.com.
Professor Wolfgang Glasser, a pioneer in the lignin field, will be the keynote speaker. Furthermore, several leading lignin scientists from around the world will be presenting their most recent results on lignin recovery and use. According to Michael Paleologou, conference program chair, it is a great opportunity to further develop the lignin culture at the global level.