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Biochemical conversion technologies involve three basic steps: (1) converting biomass to sugar or other
fermentation feedstock (NREL's process design uses dilute acid pretreatment followed by enzymatic hydrolysis); (2) fermenting
these biomass intermediates using biocatalysts
(microorganisms including yeast and bacteria); and (3) processing the fermentation product to yield
fuel-grade ethanol and other fuels, chemicals, heat and/or electricity.
Researchers are working to improve the efficiency and economics of the biochemical conversion
process technologies by focusing their efforts on the most challenging steps in the process. The
major thrusts of the advanced R&D on biochemical conversion technologies are currently improving pretreatment
technology, for breaking hemicellulose down to component sugars and developing more cost-effective cellulase enzymes, for breaking
cellulose down to its component sugar.
Researchers are also working to demonstrate biochemical conversion processes in real-world applications.
Integration and production activities involve industrial partners and focus on developing valuable products
from sugars and on relatively large
integrated projects that seek to improve the commercial viability of biochemical conversion
technologies.
Researchers are working to improve the efficiency and economics of the biochemical conversion process technologies by
focusing their efforts on the most challenging steps in the process. The major thrust of the advanced R&D on biochemical
conversion technologies is on pretreatment, cellulase enzymes, and catalyst development for products from sugars.
Some form of pretreatment is required in order to hydrolyze hemicellulosic sugars and thereby open up the structure of biomass
sufficiently to allow efficient and effective enzyme hydrolysis of the cellulose, which is protected by a sheath of lignin and
hemicellulose. The barriers to development of a robust pretreatment process include a lack of fundamental understanding related
to: the chemistry at work in pretreatment of biomass and the hydrolysis of hemicellulose, reactor design fundamentals, equipment
reliability, and materials of construction. Advanced R&D pretreatment projects focus on:
- Advanced Pretreatment
- Clean Fractionation
- Hemicellulases and Accessory Enzymes
- Biomass Compositional Analysis
- Maintenance of the Bioethanol Pilot Development Unit
Advanced Pretreatment
The Advanced Pretreatment Project began in partnership with the Biomass Refining Consortium for Applied Fundamentals and Innovation
(CAFI) in late 2000. The overall objective of the project is to expand ongoing efforts to understand the impact of reaction configuration
and reactor design on thermochemical cellulose hydrolysis to include a wider spectrum of biomass pretreatment and fractionation approaches.
Molecular model simulations will help elucidate the energetic rate steps that need to be better understood to define the intrinsic kinetics
of heterogeneous cellulose hydrolysis and release of glucose to the bulk medium. In 2003, the project will identify which existing pretreatments
have the strongest possibilities of achieving broad commercial applicability in an advanced technology sugar/lignin platform, and recommend
how best to direct the on-going fundamental studies to support the development of innovative and economically-viable pretreatment processes for
advanced sugar/lignin platform technologies.
Clean Fractionation
NREL researchers have successfully employed solvent-based pretreatment technology to produce chemical-grade cellulose, hemicellulose sugars,
and lignin. This clean fractionation technology uses a mixture of an organic solvent and water to cleanly separate the three major components
of biomass. It is applicable to a wide variety of biomass feedstocks as an advanced pretreatment option and allows the use of the lignin and
hemicellulose as feedstock for higher value products compared to the conventional technologies, which use the lignin and hemicellulose as fuel
and fermentation feedstock, respectively.
Clean fractionation R&D efforts for 2003 are focused on: developing credible cost estimates for the overall separation process and each
fraction available; determining whether clean fractionation is a cost-effective crosscutting technology for both the advanced pretreatment and
products from sugars task areas; and identifying R&D needs for successful incorporation of these novel pretreatment technologies in the biorefinery.
Product opportunities for each of the clean fractionation fractions derived from a variety of lignocellulosic and agricultural feedstocks will
be defined.
Hemicellulase/Accessory Enzymes
Until recently, NREL's pretreatment processes have focused on thermochemical dilute acid hydrolysis of the non-cellulosic fraction of the
carbohydrates, with the resulting cellulose-rich solids undergoing separate hydrolysis by cellulase enzymes. In comparison to the dilute-acid
pretreatment method, most of the advanced pretreatment methods involve conditions more amenable to enzyme stability and activity, raising the
possibility of incorporating enzymes in several stages of the pretreatment process.
This project is primarily designed to determine if biomass conversion to free sugars can be carried out more efficiently with a greater variety
of enzymes and less severe pretreatment. Realistic economic models of the various alternative pretreatment scenarios incorporating hemicellulase
and accessory enzymes in the process will be developed. Sensitivity analysis will be used to determine economically key areas and these results
will be used to guide additional research in an iterative process between predictive modeling and experimental work.
Biomass Compositional Analysis
The goal of this project is to develop, improve and standardize methods used to analyze and characterize biomass. In 2003, specific activities
include coordinating the external analytical chemistry support activities, which involve sending samples to pre-validated external laboratories to
perform biomass compositional analysis using standard NREL Laboratory Analytical Procedures (LAPs); working with ASTM (Biotechnology Committee E48,
Biomass Conversion Subcommittee 05) to foster the development of consensus standards and test methodologies that facilitate validation and quality
control of biomass conversion processes; and continuing to develop, refine, and validate rapid and inexpensive methods for determining the chemical
composition of biomass samples before and after pretreatment, as well as during subsequent bioconversion processing.
Maintenance of the Bioethanol Pilot Development Unit
NREL's one ton per day process development unit (PDU) was designed to provide a user facility to accelerate the development of processes for the
conversion of a wide variety of lignocellulosic biomass types to ethanol. The objective of this project is to perform routine maintenance and calibration
activities throughout the year to maintain the facility in a state of operational readiness for both internal and external customers. In addition, this
project implements activities that significantly improve the operability of the pilot plant and enhance its capability to supply necessary process
performance data for customers.
A new generation of enzymes and enzymes production technology is needed to cost-effectively hydrolyze cellulose to glucose. Technical barriers for
enzymatic hydrolysis include: low specific activity of current commercial enzymes, high cost of enzyme production, and lack of understanding of enzyme
biochemistry and mechanistic fundamentals. R&D projects in this area include:
- Enzyme Subcontract Liason
- Industrial Enzyme Support and Fundamentals
- Genencor International (GCI) CRADA
Enzyme Subcontract Liason
The goal of this project is to significantly reduce the cost to supply cellulase enzymes to a biomass conversion process. As the technical monitor
for Genencor International's (GCI's) and Novozymes Biotech's (NB's) cellulase cost-reduction subcontract, NREL coordinates the sample benchmarking/testing
and data transfer between NREL researchers and subcontractors, and ensures that appropriate assays and technoeconomic performance metrics are maintained
and utilized to evaluate and quantify cost reduction progress. Potential tests to be performed include numerous kinetic, differential scanning microcalorimetric
(DSC), compositional, and other physico-chemical analyses, in addition to process relevant evaluations of complete enzyme preparations.
At the end of each subcontract's 3-year performance period, NREL will quantitatively measure the improvement that has been achieved in cellulase performance
in terms of the decrease in loading of enzyme protein required to achieve the target extent of conversion of the cellulose in pretreated biomass and evaluate the
impact on the efficiency and economics of the entire process.
Industrial Enzyme Support and Fundamentals
This project focuses on the development of non-competitive, fundamental science necessary to accelerate the commercialization of cellulases in the near-term
(FY2003 to 2006), and to ensure that sound scientific foundations exist for mid- and longer-term technology improvements (i.e., FY2010 and beyond).
In 2003, NREL will support near-term cellulase technology development by (1) conducting highly targeting research to understand the significance of N-linked
glycans and N-terminal amino acid chemistry on the stability and activity of Cel7A enzymes from T. reesei, P. funiculosum, and an Apergillus sp. expressed from
A. awamori, and (2) developing assays for cellobiose produced from cellulase action using cellobiose dehydrogenase (CDH) from P. chrysosporium. To address mid-
and long-term technology needs, NREL will (1) design and conduct experiments elucidating the large differences observed between dialysis saccharification assay
(DSA) and simultaneous saccharification and fermentation (SSF) and (2) determine the extent of product inhibition possible for the case of cellulases acting
on insoluble substrates in optimal mixtures.
Genencor International (GCI) CRADA
NREL isolated the thermophilic organism Acidothermus cellulolyticus from a Yellow Stone hot spring several decades ago. Over the last few years, a gene cluster
from A. cellulolyticus including five glycohydrolase has been characterized. The goal of this project is to characterize glycohydrolases and glycohydrolase mutants
from the NREL collection that may provide functionalities of use in commercial applications. In partnership with Genencor International, NREL will characterize
these glycosylhydolases for thermotolerance, substrate range, and specific activity. A modification is currently being negotiated to extend the work to include
structure-function characterizations of cellobiohydrolase I enzymes.
The development of catalysts for converting biomass sugars into higher value products is only it its infancy, especially when compared to today's petrochemical counterparts.
Key barriers for the development of new catalysts include: the lack of catalyst systems that provide high selectivity to the desired product and the lack of a fundamental
understanding of how reactions take place in the aqueous phase. Advanced R&D in this area is ongoing, under the:
Arabinose Yeast CRADA
Corn fiber is a residue of the corn-to-ethanol process, which is considered a low-value by-product. Since 1997, NREL has been working with the Corn Refiners Association and the
National Corn Growers Association to bring added value to the fiber by-product. Through genetic engineering, NREL researchers are designing unique biocatalysts to ferment the
available sugars in corn fiber. On-going work is being performed which addresses the understanding of the metabolic mechanisms required to efficiently use the residual components
for additional revenues in the process.
Past characterization of S. cerevisiae strains engineered to express bacterial araA, araB, and araD genes has shown that one of the major deficiency
for arabinose fermentation in this yeast species is poor transport of L-arabinose. This CRADA is now focusing on improving L-arabinose transport, one of the major hurdles in developing
yeast capable of fermenting arabinose. By using genetic and molecular biology techniques, the goal for this year is to identify, isolate, characterize and express an L-arabinose
transporter in Saccharomyces cerevisiae.
Researchers are working to demonstrate biochemical conversion processes in real-world applications. Integration and production activities focus on relatively large integrated projects
that, for the most part, involve industrial partners and significant industry cost share. NREL primarily plays a supporting role in the following projects:
- Sugar Platform Integration
- Corn Ethanol Production Improvements
Sugar Platform Integration
The Sugar Platform Integration projects seek to advance development of a lignocellulose-based biorefinery (rather than a corn-based biorefinery) by developing integrated enzymatic
cellulose hydrolysis-based sugar-ethanol platform technologies, and include the:
- Enzyme Sugar Platform
- DuPont CRADA
Enzyme Sugar Platform
The overall objective of this project is to investigate enzymatic cellulose hydrolysis-based biomass-to-ethanol conversion process technology based on a large-scale domestic feedstock
(corn stover is the model feedstock). The goal is to use the improved, lower-cost cellulase enzymes being developed under cost-shared subcontracts by Genencor and Novozymes to reduce
the cost and risk of enzyme-based process technology. Experimentally, the focus is on improving the fundamental understanding about the complex interactions between feedstock characteristics
and thermochemical pretreatment and enzymatic cellulose conversion performance. Analytically, the focus is on developing better analysis tools to facilitate process evaluation and optimization
as well as to learn from studies of similar processes via collaborations.
The Dupont CRADA, established in 2003, is a four-year research project that will provide a technical foundation for DuPont's proposed Integrated Corn-based Bioproducts Refinery. Participants
in this project are DuPont, Diversa, John Deere, Michigan State University, and NREL. The objectives of the NREL work will be to develop a corn stover/fiber pretreatment scheme and microbial
biocatalysts that integrate with enzymatic saccharification. NREL's role includes pretreatment, chemical analysis, and strain development. The pretreatment efforts involve the development
of a mild pretreatment approach and will be developed in concert with Diversa's enzyme discovery and development efforts. The pretreatment effort will involve a bench scale program, including
development of rapid chemical analysis methods specifically for these pretreated feedstocks, followed by scale up in NREL's PDU and eventually, to a dedicated semi works facility built and
operated by DuPont. The strain development efforts involve the collaboration of scientists and engineers at DuPont and NREL to generate a superior ethanologenic Zymomonas mobilis. The work
is scheduled to be performed over a four-year period, between 2003 and 2007.
Corn Ethanol Production Improvement
The objective of this project area is to identify advanced technologies that will improve the profitability of corn based fuel ethanol and chemical production, making it more competitive with
petroleum based technologies. Over the years, ethanol producers have adopted various technologies such as high tolerance yeasts, continuous ethanol fermentation, co-generation of steam and electricity,
and molecular sieve driers to reduce ethanol production costs. In FY03 there are three activities related to improving corn ethanol production:
- Advanced Corn Mills Project
- Broin CRADA
- Abengoa CRADA
Advanced Corn Mills Project
The overall goal of this project is to find new, economically viable processes that generate additional co-products and improved yields from a bushel of corn when applied in conjunction with
current dry milling technology in order to improve dry mill profitability. New technologies for corn utilization are being developed and tested for their economic and technical viability by USDA,
University of Illinois, Michigan Biotechnology Institute (MBI), and NREL. Corn fiber can be separated from the starch component prior to processing utilizing a liquid soaking process or by mechanical
de-germing processes. The fibrous residue can then be converted into various products, including additional ethanol via pretreatment followed by saccharification and fermentation. This process could
improve the economics of a dry mill operation by increasing the amount of ethanol produced from the extracted fiber and lead to the development of new co-products.
The Broin CRADA is a continuation of ongoing efforts to develop new technologies to improve the efficiency of U.S. ethanol production. In the past, Broin & Associates and NREL focused on developing
improvements in process throughput and water management for dry mill ethanol plants, evaluating proprietary yeast strains developed by NREL for improving ethanol yields and, completing an overall process
engineering model of the dry mill technology that identifies new ways to increase efficiencies and improve economics.
In 2003, the Broin CRADA will research and develop a dry mill "biorefinery" for enhancing the economics of existing ethanol dry mills by creating additional co-products and increasing ethanol yields by
fractionation of the bran, germ, and endosperm in the incoming corn feed using proprietary processes and equipment. The objectives of the NREL work within the contract will be to develop a conversion scheme
to increase the total value of second-generation dry mill products.
The goal of this CRADA, a collaboration between NREL, High Plains Corporation (now a subsidiary of Abengoa Corporation), and Novozymes North America, Inc., is to develop process technology that utilizes advanced biorefining techniques to improve dry mill efficiency and profitability. It will also continue to build the bridge between starch and lignocellulose conversion.
This technology will enable a more economical, sustainable industry and will achieve significant additional petroleum displacement by decreasing the process petroleum use per gallon of ethanol produced
and increasing overall ethanol production and availability. In FY03, this project will complete a preliminary investigation of process options, make significant progress towards demonstrating pretreatment
at the bench scale, and begin developing an applicable rapid analysis method. The ultimate goal is to combine novel technologies into one conversion process that will be tested through High Plains' pilot
and demonstration facilities in 2004-2006 accelerating the success of the technologies.
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