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Soaking in Aqueous Ammonia (SAA) for Pretreatment of Corn Stover

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					Soaking in Aqueous Ammonia (SAA) for Pretreatment of Corn Stover
Tae Hyun Kim and Y. Y. Lee
Department of Chemical Engineering

Auburn University
AIChE 2004 Annual Meeting Austin, TX. Nov, 2004
Biomass Refining CAFI

Auburn University

Research objective
 Overall objective
To develop a economically viable and environmentally benign process for the pretreatment of biomass.

 Factors of interests
Energy and capital costs Enzymatic digestibility Fermentability
Biomass Refining CAFI

Auburn University

Corn stover composition
Uronic acid Protein Acetyl group Ash Galactan
Mannan Arabinan

others

7.1%

Glucan
36.1%

Lignin
17.2%

Xylan 21.4%

Note. NREL supplied corn stover to CAFI members (source: BioMass AgriProducts, Harlan IA). Corn stover was washed and dried in small commercial operation, knife milled to pass ¼ inch round screen Biomass Refining CAFI Auburn University

Ammonia as a pretreatment reagent
• Highly selective and effective in delignifying the biomass • Easy to recover and reuse because of high volatility. • One of the most widely used commodity chemicals (one-fourth the cost of sulfuric acid). • Non-polluting and non-corrosive chemical.
Biomass Refining CAFI

Auburn University

ARP (Ammonia Recycle Percolation)
• A pretreatment method based on aqueous ammonia, which uses a flow-through column reactor (percolation). • Lignin is believed to be a major hindrance to enzymatic hydrolysis. • Efficient delignification; it gives a high and adjustable degree of delignification (70-85%). • It has been proven to be effective for pretreatment of biomass; digestibility is 90% for glucan and 78% for xylan with 15 FPU/g-glucan.
Biomass Refining CAFI

Auburn University

ARP laboratory reactor and reaction conditions
NH3 Feeding

Oven & Reactor
Receiver Tank

Data Acquisition System

N2 Back Pressure

Flow through column reactor

Flow rate; 5 ml/min Aq. NH3 50 ml of 15 wt% Aqueous NH3 (1 reactor void volume) Biomass Refining CAFI

Reaction temp; 170°C
Corn stover Reactor (15 g of Corn Stover) Reactor Volume:70.9 cm3 Reactor Void Volume: 45.0 cm3

Auburn University

Problems in ARP
1. 2. 3. High capital cost (High pressure equipment). High-energy cost (high temperature). Half of xylan is removed (xylan recovery is difficult in the downstream processing)

• SAA (soaking in aqueous ammonia) at room temperature was proposed.
Biomass Refining CAFI

Auburn University

Features of SAA at room temperature
Reaction conditions
• • • • • • • • • Room temperature/ Atmospheric pressure 30 wt.% of aqueous ammonia Solid-to-liquid ratio: 1:8 Treatment time: 10 days
SAA apparatus

Features
Batch Process / no agitation Mild reaction conditions Low equipment cost Lignin is removed/Xylan is retained Simple downstream process

Corn stover

Biomass Refining CAFI

Auburn University

Effect of soaking time on compositional change in SAA at room temperaturetreated corn stover
Composition [% of original corn stover]

40 35 30 25 20 15 10 5 0 0

Glucan

21.4 17.2

18.1 17.8

17.8

Xylan

17.2

7.6 8.8 10 20

5.7

5.6

Lignin 4.6
40 50 60

30

Reaction Time [days]

Note. S:L ratio=1:12, reaction temp.=22–24ºC (R.T.), 29.5 wt.% NH3. All sugar content based on the oven-dry untreated biomass Biomass Refining CAFI Auburn University

Digestibility vs. soaking time
with 15 FPU/g-glucan

100 90 80 70 60 50 40 30 20 10 0 0

Enzymatic Digestibility [%]

10~60 days
4 days 1 days

86% with 10 days-treated corn stover
Untreated 1d 4d 10 d 30 d

Untreated

60 d

24

48

72

96

Time [h]
Note. S:L ratio=1:12, 1-60 days treat.; reaction temp.=R.T., 29.5 wt.% NH3. Biomass Refining CAFI

Auburn University

Problems in SAA at room temperature
1. Longer reaction time (about 10 days). -> Large capital cost (huge reactor) 2. High liquid input (S:L=1:8~1:10). -> Large operating cost

• SAA at moderate temperature was proposed.
Biomass Refining CAFI

Auburn University

Features of SAA at moderate temperature
Reaction conditions
• • • • • Temperature: 60 °C 15 wt.% of Aqueous Ammonia S:L Ratio: 1:6 Treatment Time: 12 hours Atmospheric pressure

Features
• Batch process /no agitation • Lignin is removed/Xylan is retained • Simple downstream process
Biomass Refining CAFI

Auburn University

Effect of temperature, S/L Ratio, and reaction time on Lignin removal
Reaction temperature
80
Delignification [%]
77.2 67.2

Solid-to-liquid ratio And Reaction time
80

24 h
Delignification [%]
70 60 50 40 30 1:2 1:4 1:6 1:8 Solid-to-Liquid ratio [-]

70 60 50 40
50.1

12 h

6h

30 40 50 60 70 80 90 10 0 Temperature [°C]

15 wt.% of NH3; 24 h reaction time; 1:10 of solid-to-liquid ratio. Biomass Refining CAFI

15 wt.% of NH3; 60°C of reaction temperature

Auburn University

Xylan content in SAA-treated corn stover
Reaction temperature
20 18 16 14 12 10 30 40 50 60 70 80 90 100

Xylan [% of original corn stover]

Solid-to-liquid ratio And Reaction time
20 18

Xylan [% of original corn stover]

17.9 17.2 16.5

24 h 6h 12 h

16 14 12 10 1:2

1:4

1:6

1:8

Temperature [°C]

Solid-to-liquid Ratio [-]

15 wt.% of NH3; 24 h reaction time; 1:10 of solid-to-liquid ratio. Biomass Refining CAFI

15 wt.% of NH3; 60°C of reaction temperature

Auburn University

Selectivity of delignification over xylan removal upon various temperature and ammonia concentration
3.1 2.9 2.7 Selectivity [-] 2.5 2.3 40 Temperature [C]
Selectivit y   m lignin  m xylan rate

 where , m  mass reduction

90

15 wt.%

60

30 wt.%

2.1

15 wt.% 30 wt.%

Biomass Refining CAFI

Auburn University

Enzymatic Digestibility of Glucan and Xylan in SAA-treated Corn Stover
(a) Digestibility of glucan
100
Enzymatic digestibility [%] Enzymatic digestibility [%]

(b) Digestibility of
100

xylan

85% at 72 h
80 60 40 20 0 0 24 48 Time [h]
SAA-treated a-Cellulose Untreated

78% at 72 h
80 60 40 20 0

a-Cellulose

Untreated
72 96

Untreated

0

24

48 Time [h]

72

96

SAA-treated

Untreated

Treatment conditions: 60°C, 15 wt.% NH3, 1:6 of S/L, and 12 h
Biomass Refining CAFI

Auburn University

Simultaneous saccharification and fermentation (SSF)
o Microorganism : S. cerevisiae, D5A o Substrate : SAA-treated corn stover o Enzyme loadings: 15 FPU of Spezyme CP + 30 CBU of Novozyme 188 per gram-glucan o YP medium (1% of Yeast extract, 2% of Peptone) o Anaerobic condition
Biomass Refining CAFI

Auburn University

SSF of “SAA-treated” corn stover using D5A yeast
3% w/v glucan loading
100

Ethanol Yield [% of Theoritical] or Glucose Conc. [g/L]

90 80 70 60 50 40 30 20 10 0 0

Ethanol yield, a-Cellulose

Ethanol yield, SAA-treated corn stover 73% of ethanol yield is much lower than 85% of the glucan digestibility.
192

Glucose, SAAtreated C.S.
24 48 72

Glucose, a-cellulose
96 120 144 168

Time [h]

Biomass Refining CAFI

Auburn University

Xylose accumulation in SSF of “SAAtreated” corn stover using D5A
3% w/v of glucan loading 8

Sugar concentration [g/L]

7 6 5 4 3 2 1 0 0 24 48

Xylose

Glucose

72

96

120

144

168

Time [h]

Biomass Refining CAFI

Auburn University

Xylose inhibition on enzyme activity in the cellulose hydrolysis
3 wt.% of glucan loading
100 90 80

E n zym a tic d ig e stib ility [% ]

a -c e llu lo s e o n ly

70 60 50 40 30 20 10 0 0 24 48 72 96

a -c e llu lo s e + 3 % x y lo s e

Lower ethanol yield (73%) than the digestibility (85%) with SAA treated sample is due to inhibition by xylose.

a -c e llu lo s e a -c e llu lo s e + xylo s e

T im e [h ]

Biomass Refining CAFI

Auburn University

SSCF test using “recombinant E.coli ATCC ® 55124 (KO11)”
o LB medium (0.5% of Yeast extract, 1% of Tryptone) o Substrate : 12 h SAA at moderate temp.-treated corn stover (1:6 of S:L ratio). o Enzyme loadings: 15 FPU of Spezyme CP + 30 CBU of Novozyme 188 per gram-glucan o SAA-treated corn stover has about 52% glucan and 26% xylan. o 3% w/v glucan loading: (30g glucan+15g xylan)/L
Biomass Refining CAFI

Auburn University

SSCF of “SAA-Treated” Corn Stover by Recombinant E.coli ATCC® 55124 (KO11)
3% w/v of glucan loading
22

Theoretical max. based on glucan
Concentration [g/L]

20 18 16 14 12 10 8 6 4 2 0

Ethanol yield, SAA-treated corn stover

Ethanol yield, a-cellulose 113% of theoretical maximum based on glucan only
Xylose, SAA-treated C.S. Glucose, SAA-treated C.S.
0 24 48 72 96 120 144

Time [h]

- Utilization of xylose contributes to increase of ethanol yield from 73% to 113%. Biomass Refining CAFI

Auburn University

Sugar concentration in SSCF of “SAA-treated” corn stover by recombinant E.coli ATCC® 55124
3% w/v of glucan loading
3 2.5

Concentration [g/L]

2 1.5 1

Xylose

Glucose
0.5 0 0 24 48 72 Time [h] 96 120 144

*Recombinant E.coli consumed the glucose and xylose simultaneously.
Biomass Refining CAFI

Auburn University

Process options based on aqueous ammonia
2003 ARP (ammonia recycle
percolation)

SAA at room temp.
 Room temp. & Atm. pressure  Retain >85% of xylan in solid  30% ammonia, 1:8~10 of S:L  Pretreatment time : 10 days

 170°C, 2.3 MPa - High capital & energy cost  Remove 50% of xylan

SAA at moderate temp.
 60 °C & Atm. pressure  Retain >85% of xylan in solid  15% ammonia, 1:6 of S:L  Pretreatment time: 12 h
Biomass Refining CAFI

2004
To reduce the pretreatment time to <1 day

Auburn University

Biomass-to-ethanol process using SAASSCF
Conventional SSCF (Biomass-to-Ethanol)
Lignocellulo sic biomass Glucan Pretreatment Enzymatic hydrolysis Pentose sugar Xylooligomer and lignin-rich hydrolysate Conditioning Lignin Separation Lignin + Sugar degradation products SSCF Fermentation

SAA- SSCF (Biomass-to-Ethanol)
Lignocellulo sic biomass Pretreatment Enzymatic hydrolysis SSCF Fermentation

Glucan + >85%Xylan

Lignin &

xylooligomer (1015%)

Biomass Refining CAFI

Auburn University

Toxicity of hydrolysates in SSCF: various treated solids + hydrolysates (soluble sugars)
22 22 20 20 18 18 16 16 14 14 12 12 10 10 8 8 6 6 4 4 2 2 0 0 0 0
Ethanol concentration [g/L] Ethanol concentration [g/L]

ARP-treated solid only

Acid-treated solid only ARP-treated solid +Hydrolysate Acid-treated solid +Hydrolysate
24 24 48 48 72 72
Time [h] Time [h]

96 96

120 120

144 144

Sugar Loadings in SSCF Reactor
Solid Glucan Xylan SAA-treated 3.0 g 1.38 g 3.0 g 0.78 g ARP-treated Acid-treated 3.0 g 0.12 g

Hydrolysate Xylan Glucan -None0g 1.0 g 0.37 g 2.2 g

Total Sugar Loading 4.38 g 4.78 g 5.69 g

Biomass Refining CAFI

Auburn University

Summary
• Soaking in Aqueous Ammonia (SAA) is a simple and technically feasible pretreatment method for corn stover. • SAA retains 85% of xylan in the solid. • SSF of SAA-treated corn stover faces significant inhibition due to xylose accumulation in the reactor. • In SSCF of SAA-treated corn stover using recombinant E.coli (KO11), glucan and xylan are concurrently converted. • Ethanol yield from SSCF is 113% of theoretical maximum on the basis of glucan alone, or 73% on the basis of combined glucan and xylan in untreated corn stover. • Leaving hemicellulose in solids is a desirable pretreatment strategy.
Biomass Refining CAFI

Auburn University

Acknowledgements




 

US Department of Agriculture Initiative for Future Agricultural and Food Systems Program, Contract 00-52104-9663 US Department of Energy Office of the Biomass Program, Contract DE-FG36-04GO14017 Genencor International Our team from Dartmouth College; Michigan State, Purdue, and Texas A&M Universities; the University of British Columbia; and the National Renewable Energy Laboratory

Biomass Refining CAFI

Auburn University

Questions?
Corn stover Rice straw Wood chip

Corn stover

Bagasse

Sawdust

Biomass Refining CAFI

Auburn University


				
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