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Biocrude Production from Switchgrass using Subcritical Water
Sandeep Kumar and Ram B. Gupta*
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
7
Reaction pathway of biomass
8
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
9
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
11
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
13
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
14
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
17
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
18
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)
19
Biocrude composition (at 235°C, 20 min)
20
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
21
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
22
Acknowledgements
National Science Foundation
(grant NSF-CBET-0828269)
Alabama Center for Paper and Bioresource
Engineering
23
Thank you !!