aich e 2008
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Hydrolysis of Microcrystalline Cellulose in Subcritical and Supercritical Water in a
Continuous Flow Reactor
Sandeep Kumar, Ayhan Demirbas, and Ram B. Gupta*
Department of Chemical Engineering, Auburn University, Auburn, AL
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Outline
Introduction
Cellulosic materials
Subcritical and supercritical water
Objective
Cellulose hydrolysis
Experimental study
Hydrolysis in sub- and supercritical region
Cellulose liquefaction in the presence of K2CO3
Results
Conclusion
SwitchgrassCorn Stover Bagasse
Wood chips
Lignocellulosic Biomass
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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
SupercriticalRegion
Pre
ssu
re
Temperature
Solid
Liquid
Gas
Critical Point
Triple Point
Tc= 374 oCPc= 22.1 MPa c= 0.375 g cm-3
Sub- and supercritical water
(0.01oC, 0.0006 MPa)
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Sub- and supercritical water as a reaction medium
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(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)
Ion
iza
tion
co
nst
an
t (K
w)
Objectives
Study the effect of temperature and residence
time on cellulose hydrolysis
Maximize hydrolysis products yield in
subcritical and supercritical water
Study the effect of K2CO3 on cellulose
liquefaction7
Cellulose reaction pathway
8(Kruse, A.; Gawlik A. Ind. Eng. Chem. Res. 2003, 42, 267-269)
Degradation products
Water-soluble products (n = 2 to 8)
Glucose
Acids/Aldehydes Furfural
PhenolsGases
Heavy molecular weight products
Hydrolysis products
Cellulose
Cellulose, size 20μm
Identified products
Hydrolysis products
Oligomers (Olg) (n = 2 to 8)
Cellobiose (CB) (n = 2)
Glucose (Glu) (n = 1)
Fructose (FR) (n = 1)
Degradation products
5-Hydroxymethyl -2-furaldehyde (HMF)
Furfural (Fur)
Other compounds (OC) such as formic
acid, Lactic acid etc
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Experimental set-up
Water
Alkali Solution
High Pressure Pump, 1
High Pressure Pump, 2
Water CooledHeat Exchanger
TI
TI
PI
Water
High Pressure Pump. 3
Electrical Furnace
Water Pre- heating
Reactor
Gas
Chomatograph
Gas Flowmeter
Liquid Phase,TOC Analysis
PhaseSeparator
Gas Phase
BPRTI
Insulation
Cellulose slurryfeeder
Cellulose slurry input (reactor) = 2.7 wt%
Experimental conditions
At constant pressure (27.6 MPa)
Subcritical region
300 - 366 °C and residence time, 3.3 to 8.1 s
Supercritical region
376 - 405 °C and residence time, 2.5 to 6.2 s
Product analyses
Total organic carbon (TOC)
Liquid products analysis by HPLC
Elemental carbon in solid residues11
Results
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Supercritical
Complete dissolution of cellulose above 330 °C
Yield of hydrolysis products with temperature
Yield of glucose and hydrolysis products
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335 °C 4.7 s
332 °C4.8 s
354 °C 3.5 s
376 °C 3.7 s
Part of hydrolysis products started degrading with temperature
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Yield of degradation products (HMF and furfural)
333 °C 366 °C 376 °C
Optimization of the residence time in subcritical region
Yield of degradation products (OC) with temperature
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Formation of organic acids makes the process autocatalytic
Color of liquid sample is an indication
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302 °C, 5.2 s 376 °C, 3.7 s 345 °C, 6.7 s
Increased acidity (pH < 3), and color shows higher
degradation
pH 3.4 pH 2.7 pH 2.2
Experiments in the presence of K2CO3
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Cellulose liquefaction possible in subcritical water
Study liquefaction in the presence of K2CO3
Catalytic (K2CO3 ) effect
K2CO3 + H2O KHCO3 + KOH
Reaction in alkaline medium
Experiments conducted in subcritical water (302 - 330 °C)
Results
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T
(°C)
t
(s)
K2CO3
(wt% )
% Yield based on carbon
balance
Solid Liquid Gas
302 5.2 0.22 65.5 18.5 16.0
302 5.2 0.44 37.1 27.7 35.2
330 4.8 0.13 35.6 21.0 43.4
Experiments conducted at 27.6 MPa in continuous flow
Gaseous products favored
No hydrolysis products detected in the liquid
Product in the presence of K2CO3
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Increased degradation with K2CO3
0% K2CO3 0.22% K2CO3 0.44% K2CO3
302 °C, 5.2 s
No carbonization of solid
precipitate
Conclusions
Almost complete conversion of cellulose ( >90%) to water-
soluble products above 330 °C in a short residence time
High yield of hydrolysis products (65 - 67%) can be
achieved in subcritical water (335 - 354 °C)
Presence of K2CO3 enhances the formation of gaseous
products
No carbonization of residue solid in short residence time
(4.8 - 5.2 s) in the presence of K2CO3
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Cellulose hydrolysis
Effect of K2CO3 on cellulose liquefaction
Acknowledgements
U.S. Department of Energy
(grant DE-FC26-05424.56)
Alabama Center for Paper and Bioresource
Engineering
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Thank you !!