Sulfur dioxide (SO2) may be used as catalyst for the hydrolysis of hemicellulose oligomers. Kinetic of xylose production is presented for different SO2 concentrations.

2. Outline
• Background
• Experimental methods
• Results and discussions
• Preliminary conclusions
• Current work

3. Background
Hemicellulose extracts are a mix of sugar oligomers and
monomers.
Fermentation requires monomers to convert sugars into
ethanol.
Hydrolysis breakdown oligomers into monomers.
Problems with traditional dilute sulfuric acid hydrolysis
process.
H2SO4 is not recovered
Gypsum is produced
Sulfur dioxide (SO2) may be used as catalyst for the
hydrolysis of hemicellulose oligomers.
SO2 may be recovered and then recycled

4. Conventional dilute H2SO4 hydrolysis
H2SO4 CaO, H2O
Oligomeric Monomeric To fermentation
extract extract
Gypsum
To disposal
Hydrolysis: 0.5 – 4% H2SO4 Neutralization:
120 – 126º C H2SO4 + CaO + H2O → CaSO4·2H2O

5. Proposed SO2 hydrolysis
SO2 SO2 recycling
Oligomeric Monomeric
extract extract
Fermentation
Inert gas (N2) / air
I. SO2 II. Hydrolysis III. SO2
dissolution (Temperature, time) recovery

6. Experimental methods
Simulated hemicellulose extracts
Composition in weight %
Hot water extract (HWE) Birch xylan 1%
Acetic acid 1%
Water 98%
Near Neutral extract (NNE) Birch xylan 1%
Sodium acetate 2%
Water 97%
COOH
O
OMe OH O
OH
OH
O O O O O
O-Ac
OH
O O-Ac O OH O OH
O O
OH OH O-Ac

7. Near Neutral Extraction Process
Na2CO3 + H2O → CO2 + 2NaOH
COOH
O
OMe OH O
OH
OH
O O O O O
O-Ac
OH
O O-Ac O OH O OH
O O
OH OH O-Ac
CH3COOH + NaOH → CH3COONa + H2O

8. Experimental methods
Sulfur dioxide dissolution
Xylan
extrac
SO t
H2O2
H2SO
2 SO 4
Scal
2
e SO2 + H2O2 → H2SO4
React SO2
or trap
Final SO2 concentration by difference on reactor weight

9. Experimental methods
Hemicellulose hydrolysis
Temperature 130 – 160 C Analysis of monomeric xylan
Time 30 and 60 min by HPAEC-PAD
Xylose hydrolyzate
Xylose yield (%) = X 100
Max. xylose in Birch-xylan
76.8 mg Xylose
100.0 mg Birch-xylan

10. Experimental methods
SO2 recovery
Valve
He/N N2/He
2 H2O
SO Stea 2
m H2S
2
Ice bath O4
React Liquid SO2 trap
or trap 2-
SO2 mass balance by analysis of SO4 using IC

11. Results: Hydrolysis HWE
130 & 140 C
Max. Xylose yield close to 80%

12. Results: Hydrolysis HWE
150 & 160 C
Xylose yield higher in the lower temperature range

13. Modified Severity factor by Lloyd and Wyman1:
⎡ (TH − TR ) ⎤
Mo = t ⋅ nA ⋅ exp ⎢ ⎥
n: assuming a value of 10
⎣ 14.75 ⎦
Proposed modified P-factor based on Tunc and van Heiningen2:
⎛ 15106 ⎞
MP = t ⋅ nA ⋅ exp⎜ 40.48 −
⎜ ⎟ n: assuming a value of 1
⎝ TH ⎟ ⎠
t : time TH : hydrolysis temperature
n : proportionality constant TR : reference temperature
A :acid concentration in weight percent
1. Lloyd, T., Wyman, C.E. (2003). Application of a depolymerization model for predicting
thermomechanical hydrolysis of hemicellulose. Appl. Biochem. Biotechnol. 105/108, 53-67
2. Tunc, M.S., van Heiningen, A.R.P. (2009). Autohydrolysis of mixed southern hardwoods: effect of P-
factor. Nordic Pulp an Paper Journal (accepted for publishing).

14. Results: Using Mo

15. Results: Using MP

16. Results: Hydrolysis NNE
130 & 140 C
Lower xylose yield than in HWE case
Sodium acetate works as a buffer

17. Results: Hydrolysis NNE
150 & 160 C
Lower xylose yield than in HWE case
Sodium acetate works as a buffer

18. Results: Using MP
MP changing with temperature

19. 150 C & 60
min 150 C & 60
Xy Yield = min
70% Xy Yield =
50%
T↑
CH3COO- + H+ ↔ CH3COOH
T ↑
C5H9O5COO- + H+ ↔ C5H9O5COOH

20. Results
SO2 recovery after hydrolysis (140C & 30 min)
Vessel was kept at 90 C.
Original extract
with < 1% SO2
Vessel was kept at 140 C until
steam appeared. Then it was
cooled down
Vessel was cooled down
after hydrolysis
HWE 11.2% SO2 HWE 10.8% SO2 HWE 11.6% SO2

21. Preliminary conclusions
Hemicellulose oligomers can be hydrolyzed using SO2
as catalyst.
NNEs need higher SO2 concentrations than those for
HWE in order to get high xylose yields.
Xylan degradation becomes important for a MP-factor
value higher than 800.
SO2 is a promising catalyst that may be recovered and
recycled in a industrial application.

22. Current work
Effect on pressure and protons concentration will be
studied during the hydrolysis process.
Actual Near Neutral Extracts will be tested for the
hydrolysis of hemicellulose oligomers.

23. Acknowledgments
Funding for this work is provided by The
National Science Foundation under grant
numbers EEC- 06 48793 and EPS-05 54545.