Biochemical Conversion Capabilities
NREL researchers are working to improve the efficiency and economics of the biochemical conversion process by focusing on the most challenging steps in the process.
Biochemical conversion of biomass to biofuels involves three basic steps:
- Converting biomass to sugar or other fermentation feedstock through:
- Fermenting these biomass-derived feedstocks using:
- Processing the fermentation product to produce fuel-grade ethanol and other fuels, chemicals, heat, and electricity by:
In plants, cellulose is protected by a sheath of lignin and hemicellulose. NREL researchers are leaders in developing pretreatment technologies to hydrolyze hemicellulosic sugars and open up the structure of biomass to allow further enzyme hydrolysis of the cellulose to glucose. NREL biomass researchers have focused on a process involving dilute acid hydrolysis of hemicellulose to xylose and other sugars.
Conditioning and Enzymatic Hydrolysis
Following dilute acid pretreatment, the material must be made less acidic for enzymes and organisms to function optimally in the hydrolyzate environment. This process of pH adjustment, known as conditioning, aims to minimize sugar losses and promote low hydrolyzate toxicity by removing toxic byproducts that inhibit enzyme and fermentation microorganism activity.
NREL researchers have developed expertise in the basic science underlying enzymatic hydrolysis. They measure the effectiveness of enzymatic hydrolysis under a variety of processing conditions, including different enzyme and solids loadings, mixing and conditioning methods, and pretreatment conditions.
A new generation of enzymes and enzyme production technology is needed to cost-effectively hydrolyze cellulose and hemicellulose to free the sugars needed for fermentation. NREL's research on enzyme development focuses on decreasing the cost of the enzyme unit operation in the biomass saccharification process—a key factor for developing cost-competitive cellulosic ethanol. Researchers have expertise in the basic science underlying enzymatic hydrolysis. They are working closely with major industrial enzyme producers to apply recombinant DNA technology to bacteria and fungi to develop improved cellulase and hemicellulase enzymes and to determine the most efficient method for producing these enzymes.
Microorganisms for Fermentation
NREL researchers are applying sophisticated metabolic engineering techniques to develop microorganisms that can more effectively ferment the variety of sugars derived from biomass. Lignocellulosic biomass contains five-carbon sugars such as xylose (from the hemicellulose) as well as the more common six-carbon sugars such as glucose found in grains. This makes fermentation and other bioprocessing far more challenging.
Researchers are developing microorganisms that can coferment all the sugars in biomass to improve ethanol production economics. They are applying sophisticated metabolic engineering techniques to Zymomonas mobilis that can coferment both xylose and arabinose along with glucose. With industrial partners, researchers are working to develop designer strains for specific feedstocks, feedstreams, and processes and to validate the performance of these strains.
Integrating the Bioprocess
A team of NREL biotechnology researchers focuses on integrating all the unit operations of biomass conversion. With extensive knowledge of the individual unit operations, these researchers focus on linking unit operations together for industrial application and on demonstrating integrated processes at the mini-pilot and pilot scales. They also conduct rigorous bench-scale experimentation to improve specific unit operations within the process.