New forest-based materials can lead to more products, better returns: new technology can add new value to currently low value components in wood processing. The industry must bridge three gap areas to reap these rewards.

Editor's Note: The information in this article was assembled by a team of experts at the Forest, Wood and Paper Industry Technology Summit held in May 2001 in Peachtree City, Georgia, USA. (A more detailed report is available; contact Tom Amidon by email at [e-mail]). The team worked out approaches to the goal of increasing the economic returns for the wood processing industries through the development of new forest based materials (NFBM) using chemical and biochemical methods. A separate NFBM team assembled to pursue materials sciences approaches to current or novel products, and those results are reported separately.

The Technology Summit was sponsored by TAPPI, AF&PA, and the U.S. Department of Energy's Office of Industrial Technology. For more information, go to www.tappi.org/ctosummit.asp.

Economic returns to wood processing have been anemic, and the long-term health of the industry is a risk unless returns that exceed the cost of capital become the norm. The forest products industry is the largest producer of renewable, bio-based products, but the major products--solid wood, reconstituted wood paper, and pulping byproducts--are all under strong competition from non-renewable products, such as steel, plastic, plastic-based composites, and oil-derived chemicals.

Several competitive tactics have proven successful for other industries based on heterogeneous raw materials (mining, oil, corn, and other natural resource based materials). One tactic is to separate the complex resource into more uniform fractions to enhance their value (totaled the separation gap). Another tactic is to change the conversion technology to get more value from the raw material or components (termed the reforming gap). A third tactic is to adapt conversion technologies from other industries to upgrade the lower value fractions (termed the conversion gap).

The forest products industry's goal is to apply these methods to wood processing. The New Forest-Based Materials (NFBM) session at the Technology Summit identified gaps in all three of these tactical approaches and suggested gap-filling work to be done for each. Successfully filling these gaps will enhance the economic sustainability of the biologically sustainable, wood-using industry and provide a very large incremental biobased resource for national economies.

THE GAPS: A CLOSER LOOK

The separation gap focuses on fractionation of the heterogeneous raw material to increase the total value recovered. The chemical fractionation proposed is a continued evolution of the current practice of solid wood merchandising by size and quality. The idea is to extend the separation to recover more value from the portion of the wood flow that has chemical pulping as the highest current value. Some (but not most) of the products envisioned have potential unit values higher than cellulose, though cost effective pathways do not currently exist.

To close this gap, the industry must develop uses for portions of the resource that currently have low value. Hemicelluloses have low value in current processing for bleach grade pulps and have poor fuel value--even for the portion not degraded during pulping. Lignin has good fuel value, but that value is still well below many chemical raw materials.

Filling this gap requires either or both of the following: a clean separation process that can remove hemicelluloses without degrading the cellulose and a pulping process that allows separation of hemicellulose, lignin, cellulose, and pulping byproducts without sulfur reactions. The recovered hemicelluloses could be competitive with other sugar sources in the world and be used in bioconversions to platform chemicals or be converted to some of the basic chemical products currently made from oil. If hemicelluloses can be separated in higher molecular weights, they might be applied in higher value products that use their polymer attributes. Unsulfonated lignin would be a better starting raw material for glues and plastics than the sulfonated lignin currently available. These potential lignin uses are up to 10 times more valuable than the current fuel value of lignin.

The reforming gap emphasizes the development of completely new methods of wood and pulp processing. These methods include plasticizing, swelling, and dissolving wood and wood components to form, reshape, and regenerate them into products that cannot be produced with current processing methods. This gap also potentially includes developing novel glues that could be used in current products.

Continuing evolution in our understanding of the inter- and intra-molecular forces of wood components should lead to future processing methods that use more of this technology. Current examples are work using ionic liquids, the commercialized MMO solvent system, and advances in supercritical fluid knowledge. Past experience with plasticizing whole wood with ammonia is worth revisiting with modern materials sciences tools. The economic gain will be in products that can not currently be made from wood and in novel manufacturing processes that can have higher yield, lower energy costs, or improved environmental attributes The potential products are mostly made from plastics today and permeate modern life.

The conversion gap is focused on adapting processes to make biomass, wood and wood components raw material of choice for chemical, biochemical, and thermal conversion into products that are distinct from those in the tree. Some conversion processes are well developed, based on other substrates. The economic gain is the potential profit from access to large, mostly well-developed chemical markets with cost competitive components of the sustainable resource base that provide little value now.

Past work on converting wood into specific chemicals and polymers distinct from those in the tree have concentrated on either whole wood (designed by nature to be difficult to break down) or on cellulose conversion (difficult to break down, but also the highest-value major component of the wood matrix). A critical need for this work is a customer-based inventory of potentially profitable chemicals that might reasonably be obtained from wood and pulping byproducts. This inventory would ideally include a listing of required properties and the minimum quantities needed to be commercially viable. Future conversion work needs to concentrate on:

* catalysts to facilitate the conversion of biomass into chemicals and polymers;

* cost effective hydrolysis of hemicelluloses and cellulose to sugar and fermentation; and

* technology development to use feedstocks that are high in non-glucose sugars.

A better understanding of pyrolysis (cracking) is also called for since it might provide a useful, and rather direct, path to products from wood, wood components, or pulping byproducts.

CLOSING TWO GAPS: A HEMICELLULOSE EXAMPLE

The following section is an example linking and closing the separation and conversion gaps to produce a basic chemical with a significantly increasing market.

Ethanol from glucose is well developed. Unfortunately, as currently applied in commerce, it uses the currently most valuable cellulose (hydrolyzed to glucose) as the predominant sugar source. Commercial adaptation of the process to wood hemicelluloses is a prerequisite for using this less currently valued component available from biomass and wood. These hemicelluloses are predominately glucurono-xylan in hardwoods and galactoglucomannan in softwoods (with a significant softwood component of an arabino-xylan) and will yield fermentation substrates different from cellulose.

The potentially large supply is demonstrated by an example of a modest size (1000 dry short tons/day of pulp) hardwood pulp mill making bleached grade pulp. The incoming xylan is at least 20% of the hardwood chips. Using a 50% bleached pulp yield, based on wood, the amount of xylan available in the raw material is 400 tons/day (2000 tons of wood processed at 20% xylan content). This equals 140,000 tons/year collected at one spot with the costs of procurement, harvesting, transport, debarking, and chipping covered by the current production system. These 140,000 tons/year would have an annual raw material value of US$16.8 million at US$ 0.06/lb.

The year-round availability of wood chips, without incremental storage costs or losses, aids the development of continuous processing with the attendant capital efficiencies. Adaptation of ethanol fermentation to xylan-derived sugars is also of high interest in agriculture, since inexpensive and seasonably available corn stover has relatively high xylan content. An ethanol production facility based on 140,000 tons/year of raw material would match fuel ethanol facilities currently being built in the United States.

FURTHER DISCUSSION

The effective use of wood in the production of chemicals, fuels, and advanced materials is a key challenge in meeting the U.S. national objective of tripling the use of biobased products by 2010, as established by President Clinton in August 1999 (Executive Order 13134). Current products from wood are part of society's sustainable base; the work suggested here develops pathways for an increase in the amount of products from the currently harvested resource.

The pathways suggested for wood in the gap areas of separation and conversion will develop technologies that are broadly applicable to agricultural residues and woody biomass. This may lead to mixed raw material conversion facilities, though forest grown wood will likely dominate due to continuous availability and higher density. The relatively high value obtained for cellulose combined with the large scale of current processing operations should provide compelling economics at existing pulp mills for incremental production from low value wood components. The existing paper industry has a large advantage over new facilities in applying successful results of the work suggested for the separation and conversion pathways.

The reforming gap is more challenging and fundamental in nature. Current conversion processes emphasize mechanical and chemical disassembly of wood to create other solid materials. Most of these processes fail to convert a considerable amount of the raw material into the intended product and most products retain some undesirable features of the original material, such as dimension change in response to moisture change. Continuing increases in knowledge of materials provides hope that, as we learn more, we will be able to plasticize, swell, and dissolve wood and wood components and mold them into products that can only he made well from plastics today.

The work envisioned largely affects the solid wood and reconstituted wood industry, but may also create new uses for pulp. The manufacturing systems are likely to be very different from those currently used. Advantages to existing facilities will mostly result from location and market knowledge.

The need for more biobased products is urgent. The number of potential products is large enough to impact needs on a national scale. Industry must fill the gaps identified; the outcome of successful research and development in these areas will he increased economic sustainability of the biologically sustainable wood using industry.

New Forest-Based Materials--Chemistry/Biochemistry Session Team Membership:

TOM AMIDON, SUNY ESF 

JOE BOZEL, National Renewable Energy Lab

HOU-MIN CHANG, North Carolina State University 

PAUL GATENHOLM, Chalmers University

TOM JEFFRIES, USDA Forest Products Lab

MIKE LAKE, Westvaco Corp. (now MeadWestvaco)

MARK PASTER, US Department of Energy

About the author: This article was a team project summarized by Thomas E. Amidon, professor and chair of Paper Science and Engineering at the State University of New York College of Environmental Science a Forestry, Syracuse, New York, USA.