Pretreatment and Fractionation of Corn Stover with Aqueous Ammonia

AAUBURN UBURN UUNIVERSITYNIVERSITY

Pretreatment and Fractionation of Pretreatment and Fractionation of Corn Stover with Aqueous Corn Stover with Aqueous

AmmoniaAmmonia

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, IndianaNovember 4, 2002


Tasks of Auburn Research in IFAFS Project: Tasks of Auburn Research in IFAFS Project: Pretreatment by Aqueous AmmoniaPretreatment by Aqueous Ammonia

1. Optimize the proposed pretreatment technology (reaction & operating conditions)

2. Characterize resulting fluid and solid streams

3. Close material and energy balances for each pretreatment process

4. Determine cellulose digestibility and liquid fraction fermentability

5. Compare performance of pretreatment technologies on corn stover


Features of the ARP ProcessFeatures 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


Processes OptionsProcesses OptionsBased on Aqueous AmmoniaBased on Aqueous Ammonia

1. ARP

2. Low-liquid ARP

3. Two-stage processing (Hot Water-ARP)

- Fractionation of corn stover


Material and MethodsMaterial 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

Xylan

Lignin

37.5

Unit [%]

36.1

20.8

17.6 17.2

21.4


ARP Laboratory ReactorARP Laboratory Reactor

N2 Gas

PG

Vent

Holding TankPumpPG : Press. Gauge

TG : Temp. Gauge

C.W.: Cooling Water

Aq

ueo

us A

mm

on

ia

Wa

ter

3-way v/v

#1 : For ARP

#2 : For Water or Acid

#1 #2

PG

C.W.

Oven

(Preheating Coil and Reactor)

Temp. monitoring

system (DAS)

TG

TG


Reactor and SystemReactor and System• Reactor • System

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


Results of ARPResults of ARP

UntreatedUntreated

80.5 36.0 10.5 1.0 10.5

0.0 37.5 20.8 0.0 0.0

[min] [%] Glucan Xylan

Deligni-fication

SolidReaction Time

20

Digestibility

60FPU 15FPU

40

83.9 35.3 9.3 1.5 11.2

82.2 36.0 10.1 1.2 10.7

60

84.7 34.5 8.9 1.6 11.790

96.0 87.9

21.2 14.3

94.4 90.2

95.1 89.2

99.6 95.0

Glucan Xylan

Liquid

• Pretreatment conditions: 15wt% of ammonia, 170C, 5mL/min of flow rate, 325psig

Note. All sugar and lignin content based on the oven-dry untreated biomass.

[%][%] [%]

FPU : FPU/g-glucan


Effect of Reaction Time in Effect of Reaction Time in ARP PretreatmentARP Pretreatment

0

5

10

15

20

25

0 10 20 40 60 90

Reaction Time [min]

Lig

nin

or

Xyl

an

in S

olid

[%

]

0

20

40

60

80

100

Dig

estib

ility

[%

] or

CrI

Xylan remaining

Lignin remaining

Digestibility-15FPU

• Pretreatment conditions: 15wt% of NH3, 170C, 5mL/min flow rate, 325psig

Digestibility

Lignin


XRD Diagram of ARP Treated SamplesXRD Diagram of ARP Treated Samples

• Pretreatment conditions: 15wt% of NH3, 170C, 5mL/min, 325psig

0

1000

2000

3000

4000

5000

6000

7000

10 15 20 25 30

2

Inte

nsi

ty

Untreated ARP-10 ARP-20 ARP-40

ARP-60 ARP-90 α-Cellulose

-cellulose

Untreated


FTIR Spectra of ARP Treated SamplesFTIR Spectra of ARP Treated Samples

0

5

10

15

20

25

30

400 900 1400 1900 2400 2900 3400 3900

Wavenumber [cm-1]

Inte

nsity

(K

ubel

ka M

unk)

Untreated

ARP 10 min

ARP 20 min

ARP 30 min

(1)(1)

(2(2))

(3)(3)

Untreated (Red line)

1) IR band of C-O in guaiacyl or syringyl ring

2) IR band of aromatic skeletal vibration + C=O stretching

3) IR band of aromatic skeletal vibration

• Pretreatment conditions:

• 15wt% of NH3, 170C, 5mL/min, 325psig

This task was performed at Michigan State University (Courtesy of Professor Bruce Dale and his coworkers)


SEM and Lignin StainingSEM and Lignin Staining

(a) Untreated (X50) (b) ARP 90min (X50)

(d) ARP 90min (X300)

(c) Untreated (X300)

Untreated

By phloroglucinol-HCL

ARP 90min


Low-Liquid ARPLow-Liquid ARP

• Pretreatment conditions Liquid throughput: 3.33mL of 15wt% NH3 per g of

corn stover Air dried corn stover is used without presoaking.Air dried corn stover is used without presoaking.

50 ml of 15wt% Aqueous NH3

170 C

Reactor (15g of Corn Stover)

Reactor Volume:70.9 cm3

Reactor Void Volume: 45.0 cm3

Flow rate; 5ml/min Reaction time; 10 min

Aq. NH3


Composition of Treated Low-Liquid Composition of Treated Low-Liquid ARP SamplesARP Samples

• Reaction time of 10 ~ 12.5 minutes.

5.05.0

75.675.6 34.9 8.6 4.34.3 57.0

73.473.4 33.7 8.1 4.74.7 56.3

[ml/min] [%] Glucan Xylan Lignin S.R.2

Delig.1 SolidFlow rate

4.0

Digestibility

60FPU 15FPU

93.7 87.9

94.894.8 88.588.5

Note. 1. Delignification 2. Solid remaining after reaction3. All sugar and lignin content based on the oven-dry untreated biomass.

[%] [%]

UntreatedUntreated 0.00 37.5 20.8 17.6 100. 0 21.2 14.3


Economic Factors of ARPEconomic Factors of ARP(Process Eng. Analysis by NREL)(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.


ARP Process DiagramARP Process Diagram

Crystallizer

Biomass

Ammonia recycling

To Fermentor (SSF)

Steam

Reactor Liquid

Soluble sugar

Make-up water

Washing

Lignin (Fuel)

Steam

Evaporator

Ammonia

Lignin & Other sugar

Solid

waterWashing

Steam


Fractionation of Corn StoverFractionation of Corn Stover

BackgroundBackground

• ARPARP is effective in delignificationdelignification.

• Neutral & Acidic pretreatments are effective in hemicellulose hydrolysishemicellulose hydrolysis. .

• Selective removal of hemicellulose and lignin is a feasible concept.

• ARP can be applied in conjunction with another pretreatment.


Summary of Water-ARP TreatmentSummary of Water-ARP Treatment

75.0 35.5 4.3 11.8 58.1Water onlyWater only

[°C] YXYL1

Glucan Xylan Lignin S.R.

LiquidSolid [%]

Temp

180

Digestibility [%]60FPU 10FPU

19085.3 35.9 1.4 10.3 53.086.0 35.9 2.6 11.3 55.0

20077.3 35.3 1.1 8.8 51.0210

Water + ARPWater + ARP74.4 34.5 2.7 3.8 47.0180180

19019084.0 32.9 1.2 5.7 44.783.483.4 34.634.6 1.61.6 4.44.4 44.944.9

20074.2 32.9 0.7 5.4 43.2210

96.0 85.0

94.5 75.993.693.6 82.682.6

94.7 79.7

74.0 60.0

90.9 73.086.8 67.8

93.6 87.8Incre

ase

Increa

se

63.3 33.7 0.1 10.110.1 50.5220 95.0 92.9

De

crease

Increa

se

De

crease

Increa

se

OptimumOptimum

Note 1. Xylan yield in liquid [%]2. All sugar and lignin content based on the oven-dry untreated biomass.

UntreatedUntreated 0.00 37.5 20.8 17.6 100. 0 21.2 14.3


Net effect of two-stage treatmentNet effect of two-stage treatment

Treated Solid contains 82.4% of cellulose82.4% of cellulose

Second Stage (ARP)

75.2% of Delignification

First Stage (Hot Water Treeatment)

83.4% of Xylan recovery


Relationship Between Lignin andRelationship Between Lignin and Digestibility Digestibility

Water-ARP

0

2

4

6

8

10

170 180 190 200 210

Temp [C]

Lig

nin

in

So

lid [

%]

0

20

40

60

80

100

En

z.

Dig

estib

ility

[%]

Lignin 10FPU

• Enzymatic digestibilities (at 10FPU/g glucan) are affected by lignin content.


The Fate of LigninThe Fate of Lignin

• Residual lignin after water-ARP increase as the temperature of water treatment increases.

ExplanationsExplanations

1) Lignin undergoes condensationcondensation and repolymerizationrepolymerization, becoming insolublebecoming insoluble (Lora, 1978, Genco, 1997, Xu, 1999).

2)2) Lignin Lignin become bonded to the cellulose bonded to the cellulose at high temperature (Karlsson, 1997).


ConclusionsConclusions

• Pretreatment of corn stover by ARP renders near quantitative enzymatic digestibility with 60 FPU/g-glucan and above 85% digestibilityabove 85% digestibility with 15 FPU/g-with 15 FPU/g-glucanglucan.

• It gives a high and adjustable degree of delignificdelignification (70-85%)ation (70-85%).

• Lignin contentLignin content is one of the major factors affectinaffecting the enzymatic hydrolysisg the enzymatic hydrolysis.

• Crystallinity index of corn stover increasesCrystallinity 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.

ARP


Conclusions (cont’d)Conclusions (cont’d)

• Amount of liquid throughputAmount of liquid throughput is one of the major cost factorsmajor cost factors in the ARP.

• Low-liquid ARP is as effective asas effective as the the conventional ARPconventional ARP:

- 73.4% delignification - 88.5% digestibility @ 15FPU/g-

glucan

Low-Liquid ARP



• Two-stage processing of corn stoverTwo-stage processing of corn stover (hot water treatment followed by ARP) can effectively fractionate corn stovercan effectively fractionate corn stover into three main constituents.

• TheThe end product of two-stage end product of two-stage processingprocessing contains 82% glucan82% glucan, a product equivalent to a “filler fiber” used in papermaking.

Two-stage treatment



• Hot water treatment aloneHot water treatment alone at 210-220at 210-220ooCC gives unusually high digestibilityunusually high digestibility.

• Two-stage processingTwo-stage processing above 200oC increases the residual “Klason lignin”, an indication that lignin recondensationlignin recondensation and/or lignin-carbohydrate complexlignin-carbohydrate complex may occur.


Future WorkFuture Work• Fundamental Study on ARP:

Lignin interaction with cellulasePhysico-chemical change of ARP samplesLignin 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.


AcknowledgementAcknowledgement

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


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Pretreatment and Fractionation of Corn Stover with Aqueous Ammonia