hydrolysis of model hemicellulose extracts catalyzed by sulfur dioxide
DESCRIPTION
Sulfur dioxide (SO2) may be used as catalyst for the hydrolysis of hemicellulose oligomers. Kinetic of xylose production is presented for different SO2 concentrations.TRANSCRIPT
Outline
• Background
• Experimental methods
• Results and discussions
• Preliminary conclusions
• Current work
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
Conventional dilute H2SO4 hydrolysis
H2SO4
Oligomeric extract
Hydrolysis: 0.5 – 4% H2SO4120 – 126º C
To disposal
Monomeric extract
Gypsum
CaO, H2O
To fermentation
Neutralization: H2SO4 + CaO + H2O → CaSO4·2H2O
Proposed SO2 hydrolysis
SO2 SO2 recycling
Fermentation
Oligomeric extract
Monomeric extract
Inert gas (N2) / air
I. SO2dissolution
II. Hydrolysis (Temperature, time)
III. SO2recovery
Experimental methodsSimulated hemicellulose extracts
Hot water extract (HWE) Birch xylan 1%Acetic acid 1%Water 98%
Near Neutral extract (NNE) Birch xylan 1%Sodium acetate 2%Water 97%
Composition in weight %
O
OHOMe
COOH
O
OHO
O-Ac
O
OH
O
OH
O
O
OH
O
OH
O O
OH
O
OH
O-Ac
O-Ac
O
Na2CO3 + H2O → CO2 + 2NaOH
CH3COOH + NaOH → CH3COONa + H2O
Near Neutral Extraction Process
O
OHOMe
COOH
O
OHO
O-Ac
O
OH
O
OH
O
O
OH
O
OH
O O
OH
O
OH
O-Ac
O-Ac
O
Experimental methodsSulfur dioxide dissolution
SO2
SO2
Reactor
SO2trap
H2O2H2SO4
Xylan extract
Scale SO2 + H2O2 → H2SO4
Final SO2 concentration by difference on reactor weight
Experimental methodsHemicellulose hydrolysis
Temperature 130 – 160 C
Time 30 and 60 min
Analysis of monomeric xylan by HPAEC-PAD
Xylose yield (%) =Xylose hydrolyzate
Max. xylose in Birch-xylanX 100
76.8 mg Xylose100.0 mg Birch-xylan
Experimental methodsSO2 recovery
H2O2 H2S
O4
N2/He
Steam
Valve
He/N2
Liquid trap
SO2 trap
SO2
Reactor
Ice bath
SO2 mass balance by analysis of SO42- using IC
Results: Hydrolysis HWE130 & 140 C
Max. Xylose yield close to 80%
Results: Hydrolysis HWE150 & 160 C
Xylose yield higher in the lower temperature range
Modified Severity factor by Lloyd and Wyman1:
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).
( )⎥⎦⎤
⎢⎣⎡ −
⋅⋅=75.14
exp RH TTnAtMo
Proposed modified P-factor based on Tunc and van Heiningen2:
⎟⎟⎠
⎞⎜⎜⎝
⎛−⋅⋅=
HTnAtMP 1510648.40exp
n: assuming a value of 10
n: assuming a value of 1
t : timen : proportionality constantA :acid concentration in weight percent
TH : hydrolysis temperatureTR : reference temperature
Results: Using Mo
Results: Using MP
Results: Hydrolysis NNE130 & 140 C
Lower xylose yield than in HWE caseSodium acetate works as a buffer
Results: Hydrolysis NNE150 & 160 C
Lower xylose yield than in HWE caseSodium acetate works as a buffer
Results: Using MP
MP changing with temperature
C5H9O5COO- + H+ ↔ C5H9O5COOH
CH3COO- + H+ ↔ CH3COOHT ↑
T ↑
150 C & 60 min
Xy Yield = 50%
150 C & 60 min
Xy Yield = 50%
150 C & 60 min
Xy Yield = 70%
ResultsSO2 recovery after hydrolysis (140C & 30 min)
Vessel was cooled down after hydrolysis
Vessel was kept at 140 C until steam appeared. Then it was
cooled down
HWE 11.2% SO2 HWE 10.8% SO2 HWE 11.6% SO2
Vessel was kept at 90 C.Original extract
with < 1% SO2
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.
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.
Acknowledgments
Funding for this work is provided by The National Science Foundation under grant numbers EEC- 06 48793 and EPS-05 54545.