Electrochemical Conversion of CO2downloads.olisystems.com/OLISimulation...Beverages & microcapsules...

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



3

Electrochemical Conversion: Input Energy and Selectivity

Electrochemical production of Formic Acid (HCOOH) and CO seem viable!



4

Advantages



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)



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



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



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



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



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



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%



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


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.



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


Experimental Values



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




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




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



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



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%)



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.



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)



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



25

Solar Powered ECFORM Demonstration

Solar Panel

ECFORM Setup

ooc+



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



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



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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Electrochemical Conversion of CO2downloads.olisystems.com/OLISimulation...Beverages & microcapsules...

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