A Comparison of Batch, Stop- Flow-Stop, and Flowthrough Pretreatments of Corn Stover Chaogang Liu, Charles E. Wyman Thayer School of Engineering Dartmouth College Hanover, New Hampshire AIChE Annual Meeting San Francisco, CA November 20, 2003 Biomass Refining CAFI

USDA IFAFS Project Overview Multi-institutional effort funded by USDA Initiative for Future Agriculture and Food Systems (IFAFS) Program to develop comparative information on cellulosic biomass pretreatment by leading options with common source of cellulosic biomass –Aqueous ammonia recycle pretreatment - YY Lee, Auburn University –Water only and dilute acid hydrolysis by co-current and flowthrough systems - Charles Wyman, Dartmouth College –Ammonia fiber explosion - Bruce Dale, Michigan State University –Controlled pH pretreatment - Mike Ladisch, Purdue University –Lime pretreatment - Mark Holtzapple, Texas A&M University –Logistical support and economic analysis - Rick Elander/Tim Eggeman, NREL Biomass Refining CAFI

Flowthrough (FT) Pretreatment Based on early work by Bobleter, Antal Flows just hot water or very dilute acid solution through stationary biomass Removes large fraction of hemicellulose and lignin Separates sugars from reactor, reducing time for decomposition Achieves high cellulose digestibility Uses less chemicals than co-current process Provides a less corrosive environment However, high amounts of water are needed, increasing energy for pretreatment and recovery Biomass Refining CAFI

How are FT and Batch Different? Batch FT Xylose yield <~90% ~100% Lignin removal 50% Digestion yield <~90% ~100% (by SSF) Digestion time 7 days ~2 days (by SSF) Biomass Refining CAFI

Questions Why is FT so much different from batch? How can FT configuration make this difference? Can we combine the favorable features of FT and batch? Biomass Refining CAFI

Objectives of This Study Evaluate effects of flow rate, temperature, and acid concentration on solubilization of hemicellulose and lignin in a flowthrough reactor Particularly focus on developing detailed time profiles of the fate of major biomass components and closing material balances Seek to understand mechanism responsible for much different behavior of batch and FT to develop advanced systems that can combine the best features of each while overcoming their limitations Evaluate the behavior of a novel approach called stop-flow- stop (SFS) and compare its performance with that for batch and FT Biomass Refining CAFI

Corn Stover Composition NREL supplied corn stover to all project participants (source: BioMass AgriProducts, Harlan IA) Stover washed and dried in small commercial operation, knife milled to pass ¼ inch round screen Glucan36.1 % Xylan21.4 % Arabinan3.5 % Mannan1.8 % Galactan2.5 % Lignin17.2 % Protein4.0 % Acetyl3.2 % Ash7.1 % Uronic Acid3.6 % Non-structural Sugars1.2 % Biomass Refining CAFI

Schematic of FT System Sample Biomass Refining CAFI

Flowthrough Reactors Gasket filters ( Average pore size, 5 μm ) Internal volume : 37.8 mL Biomass loading: ~6.5 g Biomass Refining CAFI Internal volume : 3.8 mL Biomass loading: ~0.5 g Small reactor Big reactor

Effect of Flow Rate and Temperature on Residual Xylose for Compressed Water Biomass Refining CAFI

Effect of Flow Rate and Temperature on Residual Xylose for Compressed Water Biomass Refining CAFI

Effect of Flow Rate and Temperature on Residual Xylose for Compressed Water Biomass Refining CAFI

Total Xylose Yield for 0.05wt% Sulfuric Acid Pretreatment at 180 o C Biomass Refining CAFI

Change in Lignin Removal with Flow Rate for Water Only and Very Dilute Acid at 180 o C after 16 minutes Biomass Refining CAFI

Solubilized Xylan Vs Lignin Removal for Compressed Water Pretreatment Biomass Refining CAFI

Possible Pathway for Hemicellulose Hydrolysis H O L O’ L O S M D H: Hemicellulose O L : Undissolved long-chain oligomers O’ L: Dissolved long-chain oligomers O S : Dissolved short-chain oligomers M : Monomers D : Degradation products Mass transfer control Reaction control Biomass Refining CAFI Reaction control

Mass Balance for FT Pretreatment with Compressed Hot Water at 15 FPU FL reactor Treated Solids Hydrolysis of glucan, 72h Water Corn Stover Residual Solids Hydrolyzate Fermentation 43.4 lb 34.3 lb glucan 0.4 lb xylan 100 lb (dry basis) 36.1 lb glucan 21.4 lb xylan 36.7 lb glucose 0.31 lb xylose 4.45 gal ethanol 7.2 lb Dissolved mass 96.5% glucan to glucose, 68.2% xylan to xylose at 15 FPU/ g of glucan 97% overall glucan and xylan conversion 92% theoretical ethanol yield from glucose + xylose 96.3% overall mass balance closure (total dissolved mass+residual solids + G + X) 52.1 lb 22.2 lb xylose oligomers 1.2 1b xylose monomer 2.1 lb glucose 1.81 gal ethanol 2.64 gal ethanol

Mass Balance For FT Pretreatment with Very Dilute Acid at 15 FPU FL reactor Treated Solids Hydrolysis of glucan, 72h 0.05wt %wt H 2 SO 4 Corn Stover Residual Solids Hydrolyzate Fermentation 46.6 lb 33.2 lb glucan 0.43 lb xylan 100 lb (dry basis) 36.1 lb glucan 21.4 lb xylan 36.1 lb glucose 0.39 lb xylose 13.4 lb Dissolved mass 4.50 gal ethanol 97.8% glucan to glucose, 80% xylan to xylose at 15FPU/g of glucan 97.5% overall glucan and xylan conversion 92% theoretical ethanol yield from glucose + xylose 98.1% overall mass balance closure (total dissolved mass+residual solids + G + X) 48.2 lb 21.5 lb xylose oligomers 1.5 Ib xylose monomer 3.2 lb glucose 1.91 gal ethanol 2.59 gal ethanol

Liquid Fraction Concentrations Over 4 Minute Intervals for FT with Compressed Water at 200 o C Biomass Refining CAFI

Sugar Concentrations in Liquid Fraction Over 4 Minute Intervals for FT Pretreatment with 0.05wt% Acid at 190 o C Biomass Refining CAFI

Stop-Flow-Stop (SFS) Test Modes Biomass Refining CAFI

Total Xylose Fate for Batch, FT, and SFS Runs with Water at 200 o C Biomass Refining CAFI

Residual Xylan for Batch, FT, and SFS Runs with 0.05wt% Acid at 180 o C Biomass Refining CAFI

Concentration of Xylose in Hydrolyzate for Pretreatment with Compressed Hot Water at 200 o C Note: 60, 50, and 40mL of wash water were used for batch, SFS1, and SFS2, respectively.

Hydrolyzate Sugar Concentration for Pretreatment of Corn Stover with Hot Water at 200 o C Modes Hydrolyzate Volume mL Xylose monomer g/L Xylose Oligomers g/L Total Xylose g/L Total xylose Yield % Batch, 20 minutes Batch, 24 minutes FT, 10 mL/min SFS SFS Biomass Refining CAFI Note: 60, 50, and 40mL of wash water were used for batch, SFS1, and SFS2, respectively.

Lignin Removal for Batch, FT, and SFS Runs with Water at 200 o C Biomass Refining CAFI

Lignin Removal for Batch, FT, and SFS Runs with 0.05wt% Acid at 180 o C after 16 minutes Biomass Refining CAFI

Cellulose Digestibility for Batch, FT, and SFS Pretreatment (15 FPU/ gram cellulose, 72 h) Water, 200 o C0.05wt% acid, 190 o C Biomass Refining CAFI

Comparison of Batch, FT, and SFS with Hot Water at 200 o C Total xylose yield, % Total xylose conc, g/ L Lignin removal, % Cellulose digestibility, % Batch~ 46 ~ 11 ~ 10~ 85 FT~ 96 ~ 6 ~ 55~ 95 SFS83~ ~ 90 Biomass Refining CAFI

Summary Flow rate acts somewhat like temperature and acid in effect on solubilization of hemicellulose and lignin Increase in xylan removal with flow rate is inconsistent with traditional first order kinetic models, suggesting that other factors like mass transfer may also play an important role in hemicellulose hydrolysis, especially in the early reaction times Compared with batch, FT can significantly increase the yields of hemicellulose sugars, lignin removal, and cellulose digestibility, but the hydrolyzate is very dilute SFS can significantly reduce the amount of water consumption while realizing good hemicellulose sugar yields and cellulose digestibility In the future, we will optimize the SFS operation and investigate mechanisms responsible for the better performance of FT and SFS so that we can develop a more effective process. Biomass Refining CAFI

Acknowledgments The United States Department of Agriculture Initiative for Future Agricultural and Food Systems Program through Contract for funding our research The United States Department of Energy Office of the Biomass Program and the National Renewable Energy Laboratory Our partners from Auburn, Michigan State, Purdue, and Texas A&M Universities and the National Renewable Energy Laboratory The National Institute of Standards and Technology through award 60NANB1D0064 for funds for some equipment used The Thayer School of Engineering at Dartmouth College Biomass Refining CAFI

Questions? Biomass Refining CAFI