AICh E 2008

Hydrolysis of Microcrystalline Cellulose in Subcritical and Supercritical Water in a

Continuous Flow Reactor 

Sandeep Kumar, Ayhan Demirbas, and Ram B. Gupta*

gupta@auburn.edu

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 !!