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Pretreatment and Fractionation of Corn Stover with Aqueous Ammonia

Pretreatment and Fractionation of Corn Stover with Aqueous Ammonia. Tae Hyun Kim † , Changshin Sunwoo* and Y.Y. Lee † † Department of Chemical Engineering, Auburn University, AL 36849, U.S.A. * Chemical Engineering, Chonnam National University, Gwangju, Korea. AIChE Annual Meeting

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Pretreatment and Fractionation of Corn Stover with Aqueous Ammonia

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  1. Pretreatment and Fractionation of Corn Stover with Aqueous Ammonia Tae Hyun Kim†, Changshin Sunwoo* and Y.Y. Lee† † Department of Chemical Engineering, Auburn University, AL 36849, U.S.A. * Chemical Engineering, Chonnam National University, Gwangju, Korea AIChE Annual Meeting Indianapolis, Indiana November 4, 2002

  2. Tasks of Auburn Research in IFAFS Project: Pretreatment by Aqueous Ammonia • Optimize the proposed pretreatment technology (reaction & operating conditions) • Characterize resulting fluid and solid streams • Close material and energy balances for each pretreatment process • Determine cellulose digestibility and liquid fraction fermentability • Compare performance of pretreatment technologies on corn stover

  3. Features of the ARP Process • Aqueous ammonia is used as the pretreatment reagent: • Efficient delignification. • Volatile nature of ammonia makes it easy to recover. • Flow-through column reactor is used. (Ammonia Recycled Percolation) • Versatility of the products. • Ethanol • Low-lignin cellulose; “filler-fiber” in paper making • Uncontaminated lignin; value-added chemicals

  4. Processes OptionsBased on Aqueous Ammonia • ARP • Low-liquid ARP • Two-stage processing (Hot Water-ARP) - Fractionation of corn stover

  5. Material and Methods • Corn stover supplied by NREL (1st batch used). • Common feedstock for IFAFS Project • Ground and sieved (10 ~35 mesh). • Flow-through column reactor (SS-316, 9/10 in ID  10 in L, internal volume of 101.9 cm3) is used. Component 1st batch 2nd batch Glucan 37.5 36.1 Xylan 20.8 21.4 Lignin 17.6 17.2 Unit [%]

  6. PG N2 Gas Temp. monitoring system (DAS) C.W. TG PG TG ARP Laboratory Reactor Vent 3-way v/v Aqueous Ammonia Water #1 #2 Pump Oven (Preheating Coil and Reactor) Holding Tank PG : Press. Gauge TG : Temp. Gauge C.W.: Cooling Water #1 : For ARP #2 : For Water or Acid

  7. Reactor System Reactor and System • All reactions are carried out in a Bed-Shrinking Flow-Through (BSFT) Reactor.

  8. Results of ARP Reaction Time Deligni-fication Digestibility Solid Liquid [%] [%] [%] [min] 60FPU 15FPU Xylan Xylan [%] Glucan Glucan 14.3 21.2 0.0 37.5 20.8 0.0 0.0 Untreated 87.9 96.0 80.5 36.0 10.5 1.0 10.5 20 89.2 95.1 82.2 36.0 10.1 1.2 10.7 40 90.2 94.4 9.3 83.9 35.3 1.5 11.2 60 95.0 84.7 34.5 1.6 11.7 99.6 8.9 90 Note. All sugar and lignin content based on the oven-dry untreated biomass. FPU : FPU/g-glucan • Pretreatment conditions: 15wt% of ammonia, 170C, 5mL/min of flow rate, 325psig

  9. Effect of Reaction Time in ARP Pretreatment Digestibility Lignin • Pretreatment conditions: 15wt% of NH3, 170C, 5mL/min flow rate, 325psig

  10. XRD Diagram of ARP Treated Samples • Pretreatment conditions: 15wt% of NH3, 170C, 5mL/min, 325psig -cellulose Untreated

  11. FTIR Spectra of ARP Treated Samples This task was performed at Michigan State University (Courtesy ofProfessor Bruce Dale and his coworkers) • Pretreatment conditions: • 15wt% of NH3, 170C, 5mL/min, 325psig (1) (2) (3) Untreated(Red line) • IR band of C-O in guaiacyl or syringyl ring • IR band of aromatic skeletal vibration + C=O stretching • IR band of aromatic skeletal vibration

  12. SEM and Lignin Staining Untreated (a) Untreated (X50) (b) ARP 90min (X50) ARP 90min (c) Untreated (X300) (d) ARP 90min (X300) By phloroglucinol-HCL

  13. Low-Liquid ARP • Pretreatment conditions • Liquid throughput: 3.33mL of 15wt% NH3 per g of corn stover • Air dried corn stover is used without presoaking. Flow rate; 5ml/min Reaction time; 10 min Aq. NH3 50 ml of 15wt% Aqueous NH3 170 C Reactor (15g of Corn Stover) Reactor Volume:70.9 cm3 Reactor Void Volume: 45.0 cm3

  14. Composition of Treated Low-Liquid ARP Samples • Reaction time of 10 ~ 12.5 minutes. [%] Flow rate Delig.1 Solid Digestibility [%] [%] [ml/min] 60FPU 15FPU Xylan Glucan Lignin S.R.2 14.3 21.2 0.00 37.5 20.8 17.6 100. 0 Untreated 88.5 94.8 73.4 33.7 8.1 4.7 56.3 5.0 87.9 93.7 75.6 34.9 8.6 4.3 57.0 4.0 Note. 1. Delignification 2. Solid remaining after reaction 3. All sugar and lignin content based on the oven-dry untreated biomass.

  15. Economic Factors of ARP(Process Eng. Analysis by NREL) In direct comparison to NREL dilute-acid pretreatment Advantage: No need for neutralization of effluent (reduction of wastewater treatment cost). Disadvantage: Higher steam consumption. Overall Cost: Slightly lower than NREL base case.

  16. Make-up water Steam Steam Steam water ARP Process Diagram Ammonia recycling Ammonia Biomass Reactor Liquid Evaporator Solid Crystallizer Washing Lignin & Other sugar Lignin (Fuel) To Fermentor (SSF) Soluble sugar Washing

  17. Fractionation of Corn Stover Background • ARP is effective in delignification. • Neutral & Acidic pretreatments are effective in hemicellulose hydrolysis. • Selective removal of hemicellulose and lignin is a feasible concept. • ARP can be applied in conjunction with another pretreatment.

  18. Decrease Summary of Water-ARP Treatment Temp Liquid Solid [%] Digestibility [%] YXYL1 [°C] 60FPU 10FPU Xylan Glucan Lignin S.R. 0.00 37.5 20.8 17.6 100. 0 21.2 Untreated 14.3 Water only 60.0 74.0 75.0 35.5 4.3 11.8 58.1 180 67.8 86.8 86.0 35.9 2.6 11.3 Increase 190 55.0 Decrease Increase 73.0 90.9 85.3 35.9 1.4 10.3 53.0 200 87.8 8.8 77.3 35.3 1.1 93.6 51.0 210 92.9 63.3 33.7 0.1 10.1 95.0 50.5 220 Water + ARP 74.4 34.5 3.8 85.0 96.0 47.0 180 2.7 Optimum Increase 83.4 34.6 4.4 82.6 93.6 190 44.9 1.6 Increase 84.0 32.9 5.7 75.9 94.5 44.7 200 1.2 74.2 32.9 5.4 79.7 94.7 43.2 210 0.7 Note 1. Xylan yield in liquid [%] 2. All sugar and lignin content based on the oven-dry untreated biomass.

  19. Net effect of two-stage treatment First Stage (Hot Water Treeatment) 83.4% of Xylan recovery Second Stage (ARP) 75.2% of Delignification Treated Solid contains 82.4% of cellulose

  20. Relationship Between Lignin and Digestibility • Enzymatic digestibilities (at 10FPU/g glucan) are affected by lignin content.

  21. The Fate of Lignin • Residual lignin after water-ARP increase as the temperature of water treatment increases. Explanations • Lignin undergoes condensation and repolymerization, becoming insoluble (Lora, 1978, Genco, 1997, Xu, 1999). • Lignin become bonded to the cellulose at high temperature (Karlsson, 1997).

  22. Conclusions ARP • Pretreatment of corn stover by ARP renders near quantitative enzymatic digestibility with 60 FPU/g-glucan and above 85% digestibilitywith 15 FPU/g-glucan. • It gives a high and adjustable degree of delignification (70-85%). • Lignin content is one of the major factors affecting the enzymatic hydrolysis. • Crystallinity index of corn stover increases by ARP treatment due to removal of amorphous component of corn stover. Crystallinity of the glucan in corn stover is unaffected by treatment by aqueous ammonia.

  23. Conclusions (cont’d) Low-Liquid ARP • Amount of liquid throughput is one of the major cost factors in the ARP. • Low-liquid ARP is as effective asthe conventional ARP: - 73.4% delignification - 88.5% digestibility @ 15FPU/g- glucan

  24. Conclusions (cont’d) Two-stage treatment • Two-stage processing of corn stover (hot water treatment followed by ARP) can effectively fractionate corn stover into three main constituents. • Theend product of two-stage processingcontains82% glucan, a product equivalent to a “filler fiber” used in papermaking.

  25. Conclusions (cont’d) • Hot water treatment aloneat 210-220oCgives unusually high digestibility. • Two-stage processing above 200oC increases the residual “Klason lignin”, an indication that lignin recondensation and/or lignin-carbohydrate complex may occur.

  26. Future Work • Fundamental Study on ARP: Lignin interaction with cellulase Physico-chemical change of ARP samples Lignin recondensation and complex formation with carbohydrate • Develop an effective method of separating lignin from the ARP reactor effluent • Determine the ultimate ethanol yield for the ARP samples by the simultaneous saccharification and fermentation (SSF) experiments • Design and test a proof-of-concept continuous ARP reactor.

  27. Acknowledgement The United States Department of Agriculture Initiative for Future Agricultural and Food Systems Program through Contract 00-52104-9663.

  28. Question?

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