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Electrochemical Conversion of CO2
Arun S. Agarwal, Edward Rode, Narasi Sridhar, Shan Guan, Davion Hill
Det Norske Veritas, USA
© Det Norske Veritas AS. All rights reserved.
Thursday, 29 September 2011
2
Energy
Storage
Feedstock
Solar Wind
Hydro
Geothermal Tidal
Nuclear
Waste heat
Solvent
Working fluid
Heat transfer
Water hydrogen
Other chemicals Chemical
Electrochemical
Biochemical
Photochemical
Super critical CO2
Enhanced oil recovery (EOR)
Geothermal fluid
Beverages & microcapsules
Formic acid, methanol, DME
Syngas, methane, etc.
Renewable fuels
Carboxylates & lactones
Carbamates
Urea, isocyanates
Inorganic & organic carbonates
Biodegradable polymers
CO2
Non- conversion
use
Conversion/
Recycling
There are many ways to utilize CO2 In
put E
nerg
y &
Chem
icals
© Det Norske Veritas AS. All rights reserved.
Thursday, 29 September 2011
3
Electrochemical Conversion: Input Energy and Selectivity
Electrochemical production of Formic Acid (HCOOH) and CO seem viable!
© Det Norske Veritas AS. All rights reserved.
Thursday, 29 September 2011
4
Advantages
© Det Norske Veritas AS. All rights reserved.
Thursday, 29 September 2011
5
CO2 Flows Across
Porous Cathode
Electrochemical Reduction of Carbon Dioxide to
Formate/Formic Acid (ECFORM)
CO2
gasCatholyte
Anolyte
Ion
ic M
em
bra
ne
O2
evo
l. A
no
de
- +
Po
rou
s T
in C
ath
od
e
Anolyte + O2 gas
Catholyte
+ Product (Formate)
+ by-products (H2 + CO)
+ CO2 (unreacted)
CO2
gasCatholyte
Anolyte
Ion
ic M
em
bra
ne
O2
evo
l. A
no
de
- +
Po
rou
s T
in C
ath
od
e
Anolyte + O2 gas
Catholyte
+ Product (Formate)
+ by-products (H2 + CO)
+ CO2 (unreacted)
Cathode Reactions
CO2(aq) + H+ + 2e- HCOO- (aq)
CO2(aq) + 2H+ + 2e- CO(g) +H2O
2H+ + 2e- H2(g)
Anode Reaction
4OH- 2H2O + O2 + 4e- (alk.)
2H2O 4H+ + O2 + 4e- (acidic)
© Det Norske Veritas AS. All rights reserved.
Thursday, 29 September 2011
6
Breakdown of Technology Development Parameters
CAPEX
Eco
no
mic
Feasib
ility
OPEX
High Current Density
Long Electrode Life
High Catalyst Selectivity
Low Energy Consumption
Low Chemical Consumption
Novel Catalysts
Selectivity & Reactivity
(Cathode, Anode)
Electrode Fab.
True area
lifetime
(Cathode, Anode)
Chemical Routes
In-situ Catalyst
Reactivation
© Det Norske Veritas AS. All rights reserved.
Thursday, 29 September 2011
7
Lab Scale
Novel Cathode & Anode catalysts
Reactivity & Selectivity
Multi-Scale Approach
Semi-Pilot
Reactor Design
Mass Transfer
Bench Scale
Continuous operation
Electrodes, Lifetime
Sn eletrodeposited
carbon fiber
100m20m 100m20m
50~80 mA/cm2, 70% FE,
decrease with time
Macroporous
(>80%) Sn sponge
60~80 mA/cm2, 40% FE,
constant over 1day
© Det Norske Veritas AS. All rights reserved.
Thursday, 29 September 2011
8
Half-cell Setups for Cathode Catalyst Studies
Cathode cell
Anode
compartment
WE
RE (SCE)
CE (Pt wires)
Catholyte Anolyte
Nafion
membrane CO2
Cathode cell
Anode compartment
Nafion film WE
RE
CO2 in
CO2 out
catholyte
Electrolyte
Cathode
Catalyst
Coil electrode
Gas-Liquid-Solid
(GLS) type contact
for CO2-Electrolyte-
Cathode
© Det Norske Veritas AS. All rights reserved.
Thursday, 29 September 2011
9
Bench Scale Reactor System
Salient Features
• Filter press type cell
• 5-10 cm2 superficial electrode area
• Optimal process conditions
PTFE
end frame
(4 input/
output)EFG
(4 I/O)
PTFE
flow frame
(4 I/O)
For CO2
GAS EG
(2 I/O)
Cathode
porous/
GDE/ high
surface
area
(2 I/O)EG
(2 I/O)
PTFE
flow frame
(2 I/O)
catholyte
MG
(no I/O)
MG
(no I/O)
Nafion Anode
porous/
GDE/ high
surface
area
(no I/O)
PTFE
flow frame
(2 I/O)
anolyte
CO2 gas
EFG
(2 I/O)
PTFE
end frame
(2 I/O)EG
(2 I/O)Catholyte
liquid
Anolyte
liquid
© Det Norske Veritas AS. All rights reserved.
Thursday, 29 September 2011
10
Novel Substrates for Cathodes: Multiple-fold Increase in Reactivity
Sn eletrodeposited
carbon fiber
• Need to increase current density > 100
mA/cm2 while maintaining high FE
• Catalysts: Sn electrodeposited samples
(real area 30~300 times superficial
area) and metallic sponges
100m20m 100m20m
50~80 mA/cm2, 70% FE,
decrease with time
Macroporous
(>80%) Sn sponge
60~80 mA/cm2, 40% FE,
constant over 1day
Static operation
in bulk solution
Area < 1 cm2
Commercial
Reactor Cell
Area > 500 cm2
Static operation
in bulk solution
Area < 1 cm2
Commercial
Reactor Cell
Area > 500 cm2
© Det Norske Veritas AS. All rights reserved.
Thursday, 29 September 2011
11
10m
Previous Process Optimized Process
Uniformly coated carbon fibers Non-uniformly coated carbon fibers
Enhancement of Uniformity of Sn Electrodeposition
Substrate: CFP TGP-H-120 Toray paper, Ffiber = 7.5 – 10 m, porosity = 78%
20m
© Det Norske Veritas AS. All rights reserved. 12
0
20
40
60
80
100
2.5 3 3.5 4 4.5
MMO, acid
SS316, acid
Ni, acid
Pt-Nb, acid
MMO, ACID,repeat
Same Current at Lower Vcell Energy Savings with Anode
Vcell (V)
cu
rre
nt
(mA
/cm
2)
0.45 V
saving with
MMO
kWh/ton decreases from 10,150 to
8,935 (12% decrease)
MMO (Ta2O5 + IrO2) shows better
reliability in acidic conditions
SS316 and Ni solid anodes
showed pitting/dissolution
Optimal anode selection (MMO vs. Pt)
decreases ‘Electric Energy’ demand by >12%
© Det Norske Veritas AS. All rights reserved.
Thursday, 29 September 2011
13
Example of OLI in Process Evaluation
Alkaline Anolyte (NaOH/KOH) route
2 M KCl
CO2 satd.
CO2 gas K+
K+
1 M KOH
2 M KCl, +
HCOO-K+
(formate salt)
<1 M KOH
4OH-
2H2O + O2 + 4e-
(OH- consumed)
HCOOK + HCl
HCOOH + KCl
(acidification to
Formic Acid)
HCl
(acid consumed)
Sepn. &
Conc. Formic
Acid
Product
© Det Norske Veritas AS. All rights reserved.
Thursday, 02 June 2011
Alkaline Route: Excessive Bicarbonate Formation
Cathode Reactions:
CO2 + H+ + 2e- HCOO-
2H+ + 2e- H2
3H2O 3H+ + 3OH-
3OH- + 3CO2 3HCO3-
4K+ Anode Reaction:
4OH- 2H2O + O2 + 4e-
From stoichiometry: 1 mole HCOOK forms 1 mole KHCO3
1 mole H2 forms 2 moles of KHCO3
For a known FE where (100-FE%) is current for H2 production (CO assumed
zero), the total KHCO3 species is calculated.
Electrolyte composition based on stoichiometry OLI resultant pH
Calculated (OLI based) pH is good agreement with experimentally
measured values.
© Det Norske Veritas AS. All rights reserved.
Thursday, 02 June 2011
15
Limit for formate concentration upto KHCO3 precipitation.
This maximum limit of formate depends on pH, stoichiometry and FE%
values. CO2 flow rate can also be considered.
75% FE,
70mA/cm2,
2M KCl, CO2
saturated
Varying CO2
flowrates,
10ml/min to
2000ml/min
ECFORM Reactor
Consider only catholyte stream, as anode contribution in terms of K+ ions
Max. HCOOK conc. = 1.7 M
Solubility limiting conc. of
KHCO3 = 2.79 M, pH = 7.8
Wt% of equiv. HCOOH in
solution based on density =
5.97%
Wt% of HCOOK salt = 11.12%
Formate ion concentration in catholyte stream in alkaline route cannot
exceed 1.7M or 5.97 wt% without removal of KHCO3
Limits provided by OLI
Alkaline Route: Excessive Bicarbonate Formation
Experimental Values
© Det Norske Veritas AS. All rights reserved.
Thursday, 02 June 2011
Removing KHCO3 by addition of HCl:
KHCO3 + HCl KCl + H2O + CO2 (gas)
Converting Formate salt to Formic acid
HCOOK + HCl HCOOH + KCl
Disadvantages of Bicarbonate formation:
1. Large HCl (acid) concentrations required, increases chemical consumption
2. CO2 gas, liberated during decomposition, needs to be recycled
3. Excess KCl exceeds solubility needs to be removed before second
stage of concentrating
4. Only 5.97 wt% of formate ion before precipitation
Alkaline Route: Excessive Bicarbonate Formation
© Det Norske Veritas AS. All rights reserved.
Thursday, 02 June 2011
17
Effect of lower starting conc. of KCl (<2M) to increase the wt% of formate salt
in single pass
Starting
KCl
conc
Maximum limit of
HCOOK before
KHCO3 ppt.
Wt% of
HCOOK
%
increment in
wt%
2 M 1.70 M 5.97 --
1 M 1.78 M 6.37 6.7
0.5 M 1.85 M 6.67 11.7
Increase in energy consumption with decrease in KCl conc. due to
increased IR/ Ohmic potential drop
Based on OLI
calculations, the
increment in wt%
is not large
Alkaline Route: Excessive Bicarbonate Formation
© Det Norske Veritas AS. All rights reserved.
Thursday, 02 June 2011
18
Alkaline Route with KHCO3 catholyte
To produce high conc. HCOOK + some KHCO3 mixture that can be directly used as deicing agent
Removes, in theory, need for KCl and its removal and recycling
0.5M
KHCO3,
CO2 satd.
CO2 gas K+
K+
1 M KOH
0.5M
KHCO3, +
formate
<1 M KOH Cathode Reactions:
CO2 + H+ + 2e- HCOO-
2H+ + 2e- H2
3H2O 3H+ + 3OH-
3OH- + 3CO2 3HCO3-
4K+
KHCO3 replaces KCl as supporting
electrolyte in catholyte stream
© Det Norske Veritas AS. All rights reserved.
Thursday, 02 June 2011
19
50% FE,
70mA/cm2,
0.5M KHCO3,
CO2 saturated
Varying CO2
flowrates,
10ml/min to
2000ml/min
ECFORM Reactor
Max. HCOOK conc. = 0.975 M
Solubility limiting conc. Of
KHCO3 = 3.425 M, pH = 7.95
Wt% of HCOOK salt = 6.7%
3M of KHCO3 needs to be removed from process stream before recycling to
stage 2
Only 6.7 wt% of formate salt before decomposition of excess bicarbonate!
Limits provided by OLI Experimental Values
Alkaline Route with KHCO3 catholyte
© Det Norske Veritas AS. All rights reserved.
Thursday, 29 September 2011
20
Acidic Route with KCl as Catholyte
Acidic Anolyte (H2SO4) route
2 M KCl
CO2 satd.
CO2 gas H+
H+
0.5 M H2SO4
2 M KCl, +
HCOO-H+
(formic acid)
0.5 M H2SO4
2H2O
4H+ + O2 + 4e-
(Acid NOT
consumed)
Sepn. & Conc. Formic
Acid
Product
Chemicals Consumption
(ton/tonCO2)
KOH 0
H2SO4 0
Least consumables in acidic route more likelihood of economic feasibility
© Det Norske Veritas AS. All rights reserved. 21
Optimal Value Comparison – Acidic and Alkaline Routes
Acidic
Alkaline
50mA/cm2
at 3.75 V
70mA/cm2
at 3.25 V
Curr
ent
Density,
mA
/cm
2
Vcell, V Vcell, V F
ara
daic
Effic
iency (
%F
E)
pH=14 pH=0
• Cell voltage for acidic route is about 0.75 V higher than alkaline
• Initial selectivity (%FE) of both routes is high and equal (80-90%)
© Det Norske Veritas AS. All rights reserved.
Thursday, 29 September 2011
Significant FE drop in Acidic Route vs. Alkaline Route
22
%F
ara
daic
Effic
iency (
FE
)
No. of Recycled Passes
Acidic: H2SO4
anolyte
Alkaline: KOH anolyte (intrapolated)
• KCl as catholyte
• Initial FE is high
• On recycling same KCl
back into reactor to
increase overall
concentration, the FE
drops for acidic
• Pure acidic route not
the answer!
Currently in the process of evaluating process chemistries and electrode
degradation.
© Det Norske Veritas AS. All rights reserved.
Thursday, 29 September 2011
Trends in Feasibility of Process
Alkaline Route
1. Lower Energy Consumption
2. High Chemical Consumption
3. Relatively Higher Stable FE
Process Feasibility LOW
(High overall OPEX & CAPEX)
Acidic Route
1. Higher Energy Consumption
2. No Chemical Consumption
3. Very Low Stable FE
Process Feasibility LOW
(Very High overall CAPEX)
Process Modifications
(Combine best scenarios with tradeoffs)
1. Lower Chemical Consumption
2. Medium Stable FE
3. Energy Demand within limits
Improve Process Feasibility
(electrolyte chemistry, electrode/catalyst
development)
© Det Norske Veritas AS. All rights reserved.
Thursday, 29 September 2011
24
Semi Pilot Reactor Improved to Small Cell Performance
CO2 in
CO2 out
Catholyte
in
Catholyte
out
Porous
Tin
Plate
Cathode
Metal
Mesh
Anode
Carbon
Paper
Gas
Distributor
Catholyte
Flow
Channel
Anolyte
Flow
Channel
Cation –
Exchange
Membrane
Separator
SS 316
Anode
Holder
SS 316
Cathode Holder
Anolyte in
Anolyte out
CO2 Flow
ChannelSS 316 Back
Plate with
Inlet/Outlet
ports and bolts
SS 316 Back
Plate with
Inlet/Outlet
ports and bolts
Expanded View (not shown: Gaskets in between)
Geometric
Surface Area
= 600 cm2
Assembled
Reactor
Tin electro-deposited on Carbon paper electrodes tested
Hydro-dynamics and contact resistance
issues resolved
Reactor performance equivalent to bench cell
© Det Norske Veritas AS. All rights reserved.
Thursday, 29 September 2011
25
Solar Powered ECFORM Demonstration
Solar Panel
ECFORM Setup
ooc+
© Det Norske Veritas AS. All rights reserved.
Thursday, 29 September 2011
26
Value Chain & Economic Analysis Scale Up Risk Energy
CO2 volume
Gas source
dependent
Revenue CO2 quotas
Cash flow & NPV
En
erg
y
En
erg
y
En
erg
y
Ch
em
icals
Wate
r
CAPEX, OPEX, Disposal cost, Decommissioning cost
En
erg
y
CO2 released
Energy
balance
Products
CO2 capture
CO2 conversion
Economics
CO2 delivery
Gas with CO2
from industry
Gas with CO2
delivery
CO2 converted
En
erg
y
Capacities and operational regularities
Energy
CO2 volume
Gas source
dependent
Gas source
dependent
Revenue CO2 quotas
Cash flow & NPV
En
erg
y
En
erg
y
En
erg
y
Ch
em
icals
Wate
r
CAPEX, OPEX, Disposal cost, Decommissioning cost
En
erg
y
CO2 released
Energy
balance
Products
CO2 capture
CO2 conversion
Economics
CO2 delivery
Gas with CO2
from industry
Gas with CO2
delivery
CO2 converted
En
erg
y
Capacities and operational regularities
Sensitivity analysis:
•Energy costs
•Raw materials cost
•Market/Selling price of
Formic acid product
Process
Modifications
pertinent for
technology
commercialization
© Det Norske Veritas AS. All rights reserved.
Thursday, 29 September 2011
27
Potential New Markets for Formic Acid Usage
Capacity = 0.61 M ton Demand = 0.44 M ton
Current demand is LOW
2005
However, Formic Acid can be used to produce bulk chemicals
World Production Raw Materials for Production
Hydrogen 50 M ton (2004) Natural gas, oil & coal
Methanol 38 M ton (2006) Syn. gas from Natural Gas
Acetic Acid 5 M ton (2005) Methanol and CO
Demand can increase 15 times (9.2 M ton) if 5% of above
chemicals are produced alternatively through formic acid.
Textiles/Leather
Animal Feed
Deicing agent
Drilling Completion Fluids
Pickling/Descaling Steel
© Det Norske Veritas AS. All rights reserved.
Thursday, 29 September 2011
Summary
Electrochemical process development for CO2 Formic acid
Develop high surface area electrodes
Decrease energy requirement by optimal anodes
Decrease consumable chemicals while maintaining high selectivity
Application of OLI in
- setting limits of process / new modifications
- Understanding selectivity vs. process chemistry
- Extrapolate to longer processing times
Evaluate economical feasibility of process as a function of operating parameters
28
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and the environment
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