Comparison of Kinetics of Xylose and Lignin Removal During Hot Water and DiluteAcid Pretreatment of Corn Stover using a Continuous Flow-Through Reactor

Yun Ji1, Sridhar Viamajala2, Michael J. Selig3, Todd Vinzant3 and Melvin P. Tucker4

1.Chemical Engineering Department, University of North Dakota, Grand Forks, ND 58202

2. Biological and Irrigation Engineering, Utah State University, 4105 Old Main Hill, Logan, UT 84322

3. Chemical and BioSciences Center 4. National Bioenergy Center, National Renewable Energy Laboratory, 1617 Cole Blvd, Golden, CO, 80401

Effect of Reaction Temperature and Catalyst Concentration

A flow through reactor (FTR) was used to determine 

the kinetics of xylose and lignin removal during hot 

water and dilute-acid pretreatment for bioethanol

Abstract Acid Soluble Lignin

ASL Concentration vs. Time

Monomeric Xylose vs. Time 

at Different H2SO4 Concentrations

25 170oC, 9.9ml/min Flow Rate

Monomeric Xylose vs. Time 

at Different Temperatures

water 25 0.5% H2SO4 and dilute acid pretreatment for bioethanol

production. The removal rates of xylan and lignin 

during hot water (HW) and dilute-acid flow-through 

(DA) experiments with corn stover were studied 

between 170°C and 230°C for HW and 150°C and 210°C 

for DA. During all FTR pretreatments, insoluble dark 

precipitates were observed in the effluent and were 

characterized as lignin-carbohydrate complexes (LCC). 

Oligomeric and monomeric xylan was measured in the 

effluent during all of the FTR experiments. At 

temperatures beyond 200 °C significant xylan 

degradation to unknown products was observed. Total 

xylan removed was proportional to lignin and acetate 

release over the reaction time Increases in

0

2

4

6

8

10

12

14

0 5 10 15 20

Reaction Time (min)

ASL Concentration (g/l)

150oC, 0.5%

170oC, 0.5%

190oC, 0.5%

0

5

10

15

20

25

0 510

Reaction Time (min)

Monomeric Xylose Concentration (g/l)

0%

0.50%

0.80%

0

5

10

15

20

0 510

Reaction Time (min)

Monomeric Xylose Concentration (g/l)

150oC

170oC

190oC

9.9ml/min Flow Rate

Monomeric Glucose vs. Time 

at Different Temperatures

Monomeric Glucose vs. Time 

at Different H2SO4 Concentrations

ASL Concentration vs. Time release over the reaction time. Increases in

pretreatment temperatures from 200°C to 230 °C did 

not significantly enhance the kinetics of xylan, lignin 

or acetate removal. Melting and mobilization of lignin 

also likely contribute to the process of xylan release. 

The results show that a flow through reactor is 

suitable for kinetics studies because the products are 

removed from the reaction zone, therefore less sugar 

degradation and lignin condensation reactions occur 

as compared to a batch reactor system.

M Bl

Experimental Setup

0

1

2

3

4

5

6

7

8

0 5 10

Reaction Time (min)

Monomeric Glucose 

Concentration (g/l)

150oC

170oC

190oC

0.5% H2SO4 

9.9ml/min Flow 

0

1

2

3

4

5

6

7

8

9

0 2 4 6 8 10

Reaction Time (min)

Monomeric Glucose

Concentration (g/l)

0%

0.50%

0.80%

170oC, 9.9ml/min Flow Rate

0

2

4

6

8

10

0 5 10 15 20

Reaction Time (min)

ASL Concentration (g/l)

hot water

170C, 0.5%

170C, 0.8%

Xylose vs Acetic Acid

Experimental Conditions

Temperatures:170oC~230oC for HW, 150oC and 210oC for DA

Acid concentrations: 0, 0.5 and 0.8%, 

Reaction times: 20 minutes

Flow rate: 9.9ml/min

Mass Balance

Experiment 

Sugar

(%)

AIS 

(%)

ASL

(%)

Inhi

(%)

Solid

(%)

Mass Balance

(%)

0% acid, 170oC 37.0 5.5 4.8 1.4 50.0 98.7

0.5% acid, 170oC 41.3 6.1 5.0 3.9 40.0 96.2

0.8% acid, 170oC 35.2 6.1 5.1 4.2 36.4 87.1

150oC, 0.5% acid 43.1 4.9 4.9 2.9 46.0 101.8

170oC, 0.5% acid 41.3 6.1 5.0 3.9 40.0 96.2

190oC, 0.5% acid 56.0 6.1 5.2 5.7 24.5 97.5

Xylose vs. Acetic Acid

0

5

10

15

20

25

02468

Acetic acid concentration (g/l)

Xylose concentration (g/l)

Hot water 

all other pretreatment

In the pretreatment hydrolysate, the xylose 

concentration and acetic acid concentration has a 

linear relationship regardless of the pretreatment 

condition except hot water.

More severe pretreatment condition will be used 

to verify this finding in the future. 

Acknowledgement

This work was supported by the U.S. 

Department of Energy under contract number 

DE-AC36-99GO10337 with the National 

Renewable Energy Laboratory (NREL).

Thanks to Rick Elander, Jim McMillan and 

Inflow - Outflow + Dissolved by Reaction = Accumulated in Reactor

)()(0 tdCVdtmtrdttC )(  xv  c  xr

where r(t) is the rate of xylose release (mg xylose/g biomass/min) 

Фv is the liquid flow rate (ml/min)

Cx(t) is the xylose concentration at time t (mg xylose/ml)

Vr is the reactor volume (ml)

M i th t i ht ( )

c

x

xr r mdt

tdC VtCtr )( 1 )()( 



 





 

Data Reduction Procedure 

The results show that a flow through reactor is suitable for kinetics studies because the products are removed 

from the reaction zone, therefore less sugar degradation and lignin condensation reactions occur as compared to a 

batch reactor system.

Discussion and Conclusion

other staff at the National Bioenergy Center 

(NBC) for their support and help with my 

research work. 

Future Work

Different feedstocks under different 

pretreatment conditions will be evaluated. 

A kinetic model will be calculated to predict 

biomass pretreatment behavior. 

Mc is the corn stover weight (g)

NREL/PO-510-45789

NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable 

Energy, operated by the Alliance for Sustainable Energy, LLC. Presented at the 31st Symposium on 

Biotechnology for Fuels and Chemicals, 3-6 May 2009, San Francisco, California.