Characterization that reveals the characteristics and properties of plants is important
Updated by Tatsuhiko Yamada on July 08, 2025, 4:00 PM JST
Tatsuhiko YAMADA
Forestry and Forest Products Research Institute, National Forestry Research and Development Institute
Senior Researcher, Forestry and Forest Products Research Institute, National Institute of Forestry Research and Development (NIFF) / Scientist who promotes the development of biomass-based materials. D. in 1998 from the Department of Biomaterials Science, Graduate School of Agricultural and Life Sciences, the University of Tokyo, he is also a professor at the University of Tsukuba and a visiting professor at Tokyo University of Technology. In 2023, he will establish Lignin Laboratory, Inc. as a director and CTO, and is also active as a player.
There have been many attempts to utilize biomass as an alternative to fossil resources, and it seems that there have been several booms in this type of effort in the past. There have been numerous attempts to produce liquid fuel from wood since before and after World War II, and in recent years, the production of so-called bioethanol derived from biomass has been actively studied since the early 2000s.
At this time, there was a great deal of domestic and international interest in developing so-called second-generation bioethanol, which is derived not only from starch and other edible sugars, but also from cellulose, i.e., wood itself, bagasse, corn stover (corn stalks and cobs), and other inedible parts of corn.
The author was a researcher at North Carolina State University (NCSU) from 2003 to 2005, first in a program to develop tools for rapid analysis of genetically modified trees, and then, starting in late 2004, in a pretreatment project for second-generation bioethanol production. In the latter half of 2004, he became involved in a pretreatment project for second-generation bioethanol production. This was probably also against the backdrop of the urgent need to establish the technology in the U.S. as well.
The development of bioethanol in the U.S. is largely due to the Department of Energy (DOE), and the National Renewable Energy Laboratory (NREL) is a well-known DOE-appointed laboratory for this type of study, and studies at the level of a large pilot plant were underway from early on.
To tell the truth, there was a time when I was a student that I wanted to join NREL, a cutting-edge research institute in this field, and I had been trying to sell it, but I was frustrated by the 9/11 terrorist attacks and was fortunate to be able to follow up with a chance to join NCSU, which never materialized. After that, I visited NREL several times around 2010, partly because a friend of mine was hired as a researcher at NREL.
As a preliminary note, what is noteworthy about NREL's efforts is that considerable effort was put into establishing a department dedicated to examining the raw materials themselves to better understand them and assigning specialized researchers to this department. Efforts to clarify the characteristics and properties of the raw biomass, or "characterization," were emphasized.
In the common classification of plant biomass, there are conifers, hardwoods, and herbaceous species, but their tissues and compositions are diverse from plant species to plant species. For example, when bioethanol is produced by enzymatic saccharification, the aromatic polymers, collectively called lignin, that cover the cellulose chains in the cell walls must be removed or somewhat beaten to break them down and loosen them enough for the enzymes to act. This is the so-called pretreatment.
At the time, the main pretreatment was dilute acid treatment, perhaps because NREL's biggest target was corn stover, a typical herbaceous biomass; according to NREL, the biomass for which dilute acid treatment was effective included not only herbaceous species but also hardwood chips, and conversion tests were actually conducted. On the other hand, NREL at that time excluded softwoods from the bioethanol target. This was because lignin in softwoods is inherently difficult to decompose by ordinary dilute acid treatment. In other words, they would not go too far in the direction of forcibly converting unsuitable plants.
Therefore, softwood lumber was clearly organized as a target resource for liquefaction by pyrolysis or gasification. This clear organization was made possible because of the functioning of efforts to clarify the characteristics and properties of the biomass, the so-called characterization.
Unfortunately, we feel that there is a common misconception that all plant-based biomass is uniformly interpreted as consisting of cellulose, hemicellulose, and lignin. In reality, however, there is a difference in processing technology and plant species. To use the example of pre-treatment for bioethanol production, broadleaf trees and grasses belong to "angiosperms," while conifers are "gymnosperms," so the dilute acid treatment described above is effective for angiosperms but not gymnosperms.
We tend to organize by whether we are talking about trees or grasses, or forests or farmland, but the difference between gymnosperms (conifers) or angiosperms (broadleaf trees, grasses, crops, etc.) is a much more important matter when it comes to the use of biomass components.
Unfortunately, hemicellulose and lignin are only generic terms, and various types of hemicellulose and lignin actually exist. Fortunately, hemicellulose is composed solely of sugar structures, so that a simple hydrolysis is all that is needed to completely analyze the constituent sugars.
On the other hand, lignin is a macromolecule composed of benzene rings, but it is not uniform and cannot be completely decomposed into its constituent units, so even with the advancement of analytical technology, complete structural analysis has not been achieved. As a side note, there is a view that the complexity of the lignin structure and its unresolved parts make it difficult to use lignin as a material, but this is a typical misunderstanding. Even if there are unexplained parts in the structure, if the same unexplained structure and the same physical properties can be guaranteed every time, the material can be used as an industrial material, and there are many such natural products.
The problem with the use of lignin as a material is the variability due to its diversity and the unregulated transformation of lignin during extraction. It should be noted that the variability in the composition of lignin has a significant impact on the reactivity of the biomass itself.
The technology to utilize biomass as a component is called biorefinery, following the oil refinery. Various biorefineries are being considered, but the raw biomass may be unsuitable or inappropriate due to differences in lignin and other factors. Therefore, it is necessary to know the raw biomass itself, and characterization is the most important consideration. In the next and subsequent articles, the characteristics and composition of the raw biomass will be discussed in more depth. (Tatsuhiko Yamada, Senior Researcher, Forestry and Forest Products Research Institute, National Institute of Forestry Research and Development)
