Low Energy Catalytic Electrolysis for Simultaneously ... · PDF fileSimultaneously Hydrogen...
Transcript of Low Energy Catalytic Electrolysis for Simultaneously ... · PDF fileSimultaneously Hydrogen...
Xu DuRenewable Bioproducts Institute
School of Chemical & Biomolecular Engineering
Georgia Institute of Technology
Low Energy Catalytic Electrolysis for
Simultaneously Hydrogen Evolution and
Lignin Depolymerization
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Background
Aromatic ChemicalsPetroleum Sustainable
Biomass
Hydrogen
Steam Reforming
Natural Gas
Catalytic Cracking
Lignin:
Aromatic Rich Structure
Aromatic
ChemicalsGreat Potential
Cellulose Lignin Hemicellulose
Background
1. Weinstock, I.A., et al., Equilibrating metal-oxide cluster ensembles for oxidation reactions using oxygen in water. Nature, 2001. 414(6860): p. 191-195.2. Voitl, T. and P.R. von Rohr, Oxidation of Lignin Using Aqueous Polyoxometalates in the Presence of Alcohols.Chemsuschem, 2008. 1(8-9): p. 763-769.3. Chen, Y.X., et al., Nanotechnology makes biomass electrolysis more energy efficient than water electrolysis. Nature Communications, 2014. 5.
PEM (Proton Exchange Membrane) Electrolysis
Lignin depolymerization by POMs (Polyoxometalates) or Fe3+
Combination?E (Applied potential) >
1.23 V (Standard potential)
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POM
Pt/
1. Lignin depolymerization 2. Electrolysis to hydrogen
E (lignin) < E (POMOx) or E (Fe3+)
0.6-1.2 V0.6-0.8 V
Thermodynamic Conditions
Electrolysis
POMOx(Fe3+)+H2O+lignin → H-POMRed(Fe2+)+Oxidized products (or CO2)
>0.77 V
Oxidation
E (Applied potential) > E (POMRed) or E (Fe2+)
Anode: used for electron transfer; Graphite replaced Pt
Reduction of applied potential (energy)
Lignin depolymerization
Schematic illustration of the lignin depolymerization and electrolysis
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Results-Lignin depolymerization
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POM: H3PMo12O40, noted as PMo12
0 5 10 15 20 25 300.0
0.5
1.0
1.5
2.0
2.5a
PM
o1
2 R
ed
uction
De
gre
e
Reaction Time (hour)
PMo12
-Kraft Lignin
PMo12
-Alkali Lignin
PMo12
-Sulfonated Lignin
0 5 10 15 20 25 300.0
0.1
0.2
0.3
0.4
0.5b
Fe
2+ c
on
ce
ntr
atio
n (
mo
l L
-1)
Reaction Time (hour)
FeCl3-Kraft Lignin
FeCl3-Alkali Lignin
FeCl3-Sulfonated Lignin
Fe3+: FeCl3
Reduced PMo12 / Fe2+
• Reduction Degree: the average number of electrons (mole) that were transferred from
the substrate to one mole of the PMo12 anion
• Fe2+ concentration
100 oC with N2 protection
PMo12: 0.1 mol/L
Lignin: 10 g/L
100 oC with N2 protection
Fe3+: 1 mol/L
Lignin: 10 g/L
6 h/cycle
6 h/cycle
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The reduction of the catalyst (PMo12 or Fe3+) is accompanied by the oxidation of lignin
2D HSQC NMR 31P NMR FTIR XPS
TOC
GC-MS
GC
-functional groups -OH groups -functional groups
-amount of depolymerized products
-products in liquid phase
GPC-dissolved products weight
distribution
-gas products: CO2 and a little
methane (CH4)
-C/O ratio, C-O bonds
Results-Lignin depolymerization
PMo12: 0.1 mol/L100 oC with N2 protection; Lignin: 10 g/L; 6 h/cycle * 3 cycles = 18 h
Fe3+: 1 mol/L
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Results-Lignin depolymerization
Solvent: Ethyl ether
GC-MS
Liquid
The PMo12 or FeCl3 can depolymerize the lignin to small aromatics.
100 oC with N2 protection;
Lignin: 10 g/L;
6 h/cycle * 3 cycles = 18 h
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PMo12+co-catalyst, 150oC, 160 psi O2 80 min Products in liquid (conversion) ~ 90%
Results-Lignin depolymerization
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Results-Lignin depolymerization
Solid Ether bond
2D HSQC
KL-PMo12: most of the ether linkages were broken with only a tiny amount of resinol (β-β) detected.
KL-FeCl3: no ether linkages observed
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Results-Lignin depolymerization
Solid31P NMR
Aliphatic OH
FTIR
-OH
Intensity of 3375 (–OH)
decrease, 1705 (C=O)
carbonyl increase and
wavenumber shift.
All the aliphatic –OH were
consumed and only a small
amount of –OH in guaiacyl
and catechol structures
(138.18-140.20) left after the
reactions.
PMo12 and FeCl3 both can oxidize the –OH group of lignin and cleave most ether linkages.
Results-PEM Electrolysis to Hydrogen
Electrolysis Performance
0.0 0.2 0.4 0.6 0.8 1.0 1.20.0
0.1
0.2
0.3
0.4
0.5b
Curr
ent
density (
A c
m-2)
Potential (V vs RHE)
1M H3PO
4
1M H3PO
4-KL
Fe3+
-KL-6h
Fe3+
-AL-6h
Fe3+
-SL-6h
0.0 0.2 0.4 0.6 0.8 1.0 1.20.0
0.1
0.2
0.3
0.4
0.5c
Cu
rre
nt
de
nsity (
A c
m-2)
Potential (V vs RHE)
Fe3+
-KL 1h
Fe3+
-KL 6h
Fe3+
-KL 10h
Fe3+
-KL 18h
Fe3+
-KL 28h
• the lignin alone cannot be directly used as feedstock
• the source of lignin did not make a significant difference on the electrolysis performance.
• the concentration of Fe2+ is the key factor
• PMo12-electrolysis system: similar conclusion
• Current density (Fe3+>PMo12 system when applied potential > 0.8V): high concentration
Without catalyst
0.0 0.2 0.4 0.6 0.8 1.0 1.20.0
0.1
0.2
0.3
0.4e
Cu
rre
nt
de
nsity (
A c
m-2)
Potential (V vs RHE)
0.1M PMo12
-KL-6h
1M Fe3+
-KL-6h
0.1M Fe3+
-KL-6h
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Energy saved: 40.9%
Energy saved: 46.5%
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Results-PEM Electrolysis to Hydrogen
Faraday (Current) Efficiency & Energy Consumption
Current density:100 mA cm-2 Average Faraday Efficiency
PMo12-KL: 24 ml/26.52ml (Theoretical)= 90.48%
FeCl3-KL: 24 ml/25.89ml (Theoretical)= 92.71%
Energy Consumption
PMo12-KL: 2.54 kW h Nm-3
Alkaline water electrolysis: 4.3 kW h Nm-3
FeCl3-KL: 2.30 kW h Nm-3
Faraday efficiency: efficiency of electrons utilization
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Conclusion
1. Combined lignin depolymerization and hydrogen production by a novel proton
exchange membrane (PEM) electrolysis process
2. Oxidation process: About 14% of Kraft lignin was converted to aromatic chemicals
in three cycles reaction; most of ether linkages were cleaved; most of –OH groups
were reacted
3. Electrolysis process: Noble metal catalyst at anode was replaced by cheap carbon
based material – Graphite; Faraday efficiency was higher than 90%; Saved more
than 40% electric energy in our electrolysis process comparing with the best
alkaline water electrolysis
Thank You14
Acknowledgement
Dr. Yulin Deng @GT, RBI/ChBE
Wei Liu @GT, RBI/ChBE
RBI PSE Fellowship