Biocrude Production from Switchgrass using Subcritical Water

Sandeep Kumar and Ram B. Gupta*

gupta@auburn.edu

Department of Chemical Engineering, Auburn University, Auburn, AL

2

Outline

IntroductionLignocellulosic biomass and possible conversion pathways

Water as reaction medium

ObjectiveLiquefaction of switchgrass to produce biocrude

Experimental studySemi-continuous reactor set up

Results

Conclusion

Cellulose38 - 50%

23 - 32%

Lignin15 - 25%

Other 5 -15%

(Extractives, Ash etc)

Hemicellulose

http://www.nrel.gov

SwitchgrassCorn Stover Bagasse

Wood chips

Lignocellulosic Biomass

3

4

Biochemical Thermochemical

Major pathways for biomass utilization

Pretreatment (< 220 °C)

PhysicalPhysio-chemical

ChemicalHydrothermal

EnzymaticHydrolysis

Fermentation

Pyrolysis(450-600°C)

Pyrolysis Bio-oil

Ethanol

Gasification(600-1000°C)

HydrothermalLiquefaction(250-350°C)

Hydrocarbons Hydrogen Chemicals

F-T Synthesis

Hydrogen

Aqueous-phase

reforming

Supercritical water

reforming

Liquid alkanes Hydrogen

Sugars Chemical

Biocrude and hydrothermal liquefaction

BiocrudeAqueous carbohydrate solution (Oxygenated hydrocarbons)

Transportable through pipelines to central biorefining facility

Easier to gasify

Can be concentrated

AdvantagesNo drying of biomass

Not dependent on the type of biomass

Wet residue from other processes can be used

5

Sub- and supercritical water as a reaction medium

6

(J. W. Tester et. al. In Emerging technologies in hazardous waste management III, volume 518 of ACS Symposium Series, pages 35–76. 1993)

200-350 °C region conducive for acid/base reactions !

25 MPaDecreased Density

Dielectric constant

Viscosity

Increased Ionization constant

Diffusivity

Tunable properties

(ε)

Ioni

zatio

n co

nsta

nt(K

w)

Objectives

Study the liquefaction of switchgrass in subcritical

water

Effect of temperature, and catalyst K2CO3 on

switchgrass liquefaction

Study the rate of solubilization of swithgrass

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Reaction pathway of biomass

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Cellulose

Cleavage of glycosidic linkages and endwise degradation (peeling)

cellulose → glucose → decomposition products

Hemicellulose

Swelling, dissolution, peeling and glycosidic cleavage reactions

Lignin

Cleavage of aryl ether linkages, fragmentation, dissolution and

re-polymerization

Biomass components interact with each other, and leads

to a very complex chemistry

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Experimental set-up

Experimental details

Semi-continuous flow reactor235 - 260 °C, 1.5 ml/min liquid flow

Reactor details

Switchgrass

Size: - 40 to + 60 mesh (0.25 - 0.42 mm)

Composition: Cellulose (37%), Hemicellulose (23%), Lignin (25%)10

0

100

200

300

0 25 50 75Tem

pera

ture

(C)

Time, min

t

Heating cycle

SwitchgrassFrit (0.002mm)

Reactor(9/16” ID tube)

Liquid in Biocrude

Product analysesLiquid product (Biocrude)

Total organic carbon (TOC) in liquid

Sugar and degradation products analysis by HPLC

Solid precipitates collected in the liquid products

X-ray diffraction

Composition analysis

Switchgrass residue

Composition analysis

X-ray diffraction for crystallinity

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Biocrude

Solidprecipitate

Switchgrassresidue

Results: Experiments at 260 °C and 23.5 MPa

No catalyst (K2CO3)82% of switchgrass solubilized in 50 min.

Maximum TOC (31,520 ppm) within 10 min.

Catalyst (K2CO3)

0.25 and 0.50 wt% input resulted in char like solids and

plugged the reactor

High temperature and presence of catalyst promoted

dehydration of biomass materials

Maximum TOC (44,500 ppm) within 10 min.

12Reduce the severity of treatment

Experiments at 235 °C, 13.8 MPa in subcritical water

0

10000

20000

30000

40000

0 10 20 30 40 50 60

TOC

, ppm

Reaction time, min

0 % K2CO3

Liquid flow rate = 1.5 ml/min

Peak TOC within 10 min

Total organic carbon(TOC) profile in the liquid product

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Experiments at 235 °C, 13.8 MPa (K2CO3 Catalyst)

0

10000

20000

30000

40000

0 10 20 30 40 50 60

TOC

, ppm

Reaction time, min

0 % K2CO3

0.15 % K2CO3

Liquid flow rate = 1.5 ml/min

K2CO3 enhanced the rate of liquefaction

Total organic carbon(TOC) profile in the liquid product

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Experiments at 235 °C, 13.8 MPa (catalyst)

0

10000

20000

30000

40000

0 10 20 30 40 50 60

TOC

, ppm

Reaction time, min

0 % K2CO3

0.15 % K2CO3

Total organic carbon(TOC) profile in the liquid product

Cellulose

Maximum TOC from pure cellulose after 10 min

Zhang et. al 2004

Lignin

Hemicellulose

Cellulose

15

16

0

20

40

60

80

100

67.172.2

83.4

Solu

biliz

atio

n(%

)Solubilization of switchgrass (235 C)

5 min 10 min 20 min

80% of switchgrass solubilized after 20 min. of treatment

13.8 MPa, 0.15 wt% K2CO3

Liquid flow rate = 1.5 ml/min

Composition of Switchgrass residue

Char like solids were deposited over the residue biomass

0

25

50

75

Cellulose Lignin

33

5932

66

Com

posi

tion

(%)

5 min 20 min

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XRD Pattern of switchgrass residue

Untreated

5 min

20 min

10 20 30

Inte

nsity

Angle (2θ)

CrystallanityUntreated 51%

5 min 56.6%

20 min 64.3%

Crystallinity of cellulose increased in residual biomass

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XRD pattern of the solid precipitates

Solids collected from the product solution (235 °C, 13.8 MPa, 20 min)

Sugars in solid residue is 22%

0

3000

6000

9000

10 15 20 25 30 35

Inte

nsity

(CPS

)

Angle (2θ)

Solid precipitate

Switchgrass(untreated)

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Biocrude composition (at 235°C, 20 min)

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SugarProducts

15%

HMF4%

Furfural6%

Organic acids17%

Unidentified Compounds

57%

Sugar productsGlucose & oligomers

Xylose & oligomers

Organic acidsLactic acid

Formic acid

Acetic acid

Unidentified compoundsSugar degradation products

Other organic acids

Acid soluble lignin etc

Biocrude

Future work and challenges

Future work

Development of lab scale continuous process set up

for biomass liquefaction

Challenges

Pumping of biomass slurry at high pressure

Presence of solid and liquid in the downstream

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Conclusions

At higher temperature (260°C), biomass tended to dehydrate

and formed char like solid products in the presence of K2CO3

Presence of 0.15 wt% of K2CO3 (235°C) catalyzed the

liquefaction of switchgrass

More than 80% of switchgrass could be solubilized in 20 min

and biocrude having more than 3wt% carbon could be

produced within 10 min. of reaction

Re-polymerization of lignin and deposition of char like solids

over the residual biomass inhibited the complete hydrolysis of

cellulose

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Acknowledgements

National Science Foundation

(grant NSF-CBET-0828269)

Alabama Center for Paper and Bioresource

Engineering

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Thank you !!