ems summer 2000
TRANSCRIPT
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MWElectro-catalytic membrane reactors
EMS Summer School
Cetraro, Italy
9-15 September 2000
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Outline Electro-catalytic membrane reactors
! Chlor-Alkali Electrolysis
The oldest membrane reactor?
! Fuel Cells
The energy supply of the future?
! Bipolar membranes
The new tool to produce acids andbasis?
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Integrated Reaction And Separation
SeparationProblem
ReactionEngineering
Mass
Transport
MaterialScience
MaterialProcessing
Equipment
Design
Process
Technology
IRAS
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Membrane Requirements
! Separate hydrogen and chlorine
! Separate caustic and chlorine! Separate slightly acidic anolyte from strong
caustic
! Transfer sodium from anolyte to catholyte
! Transfer water
! Little electrical resistance
Material
Science
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Membrane materials and morphology
CF CF2 CF2 CF2
O
CF2 CF
CF3
O CF2 CF2 COO-
n m
z
CF CF2 CF2 CF2
O
CF2 CF
CF3
O CF2 CF2 SO3-
n m
z
Nafion
MaterialScience SO3-
SO3-
SO3-
SO3-
SO3-
SO3-
SO3- SO3
-
SO3-
SO3-
SO3-
SO3-
SO3-
SO3-
SO3-
SO3-
SO3- SO3
-
SO3-
SO3-
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Composite membrane concept
MaterialScience
+
--
--
----
-
-
---
--
--
Na+
[Na+] = [OH-]
[OH-]
ShortLongAnode life time
> 2 %< 0.5 %O2 in product chlorine
HighLowElectrical resistance
9675Current effic.at 8 N NaOHLowHighWater content
2-3
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Membrane module requirements
Equipment
design
Prevention of polymerembrittlement
Gas pocket elimination
< 7 mbarReduction of mechanical
stress on membrane
Stable discharge pressure of
mixed G/L flow
0.05%Uniform micro-distribution ofthe current density
Optimum geometry of theelectrodic structures
Limited gradient of caustic
close to the membrane
< 5 g/l NaClLimited gradient of depletedbrine close to membraneHigh mass transfer between
membrane and bulk
32 0.2 %Uniform caustic concentration
210 g/lUniform brine concentration
3 CUniform temperature across
membrane surfaceEfficient mixing in anodic and
cathodic compartments
ValueGoalRequirement
Source: Iacopetti, I. Membrane electrolyser operating at high current density, Modern Chlor Alkali Technology Vol. 6
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Process requirements Process flow diagram
Process
technology
Salt transport, storage, handling
Salt disolver
Primary brine treatment
Secondary brine treatment
Electrolysis
HydrogenTreatment
CausticEvaporator
Chlorine Cooling
And Drying
Chlorine Liquefaction
Power supply
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Outline Electro-catalytic membrane reactors
! Chlor-Alkali Electrolysis
The oldest membrane reactor?
! Fuel Cells
The energy supply of the future?
! Bipolar membranes
The new tool to produce acids andbasis?
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Principle of fuel cells
Anodicoxidation -
cationproduction
Transport ofcation through
membrane
Cathodicreduction
Gas or Liquid (Fuel)
By-product
Mass
Transport
&
React. Eng.
e- e-
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Electrochemical reaction in H2-fuel cell
Anode: 2 H2 4 H+ + 4e-
Hydrogen oxydation reaction
Cathode: O2 + 4H+ + 4e- 2 H20
Oxygen reduction reaction
Reaction
Engineering
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Polymer Electrolyte Fuel Cells Hydrogen based
Graphite plates/Current collector
with gas distributorgrooves
H+
Anode feed H2Cathode feed O2
(Air)
Anode vent Cathode vent
Carbon particles
with platinumcatalyst particles
Gas diffuser
Protonconductingcation-exchangemembrane
Source: S. Gottesfeld, T. Zawodzinski, Polymer Electrolyte Fuel Cells, in: Advances in
Electrochemical Science and Engineering
Equipmentdesign
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Membrane electrode morphologies
MaterialScience
&Processing
Platinum
Ionomer
PTFE Pt/C/PTFECatalyst
Carboncloth
50 mm
Pt/CCatalyst
3 mm
4 mg/cm2 0.5 mg/cm2 0.15 mg/cm2
Ionomer
Ionomer
Source: S. Gottesfeld, T. Zawodzinski, Polymer Electrolyte Fuel Cells, in: Advances in
Electrochemical Science and Engineering
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Cathode catalyst performance
0 5 10 15 20 25
0.2
0
0.4
0.6
0.8
1.0
CellVoltage
(V)
Cathode specific activity (A/mg Pt)
Source: S. Gottesfeld, T. Zawodzinski, Polymer Electrolyte Fuel Cells, in: Advances in
Electrochemical Science and Engineering
Mass
Transport
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Oxygen reduction reaction (ORR)
H+
Air/O2 inletGas diffusion
layerMembrane
Cathodecatalystlayer
P0C= k*P1
Diffusion in porous backing
Oxygen diffusionProtonic conductivityInterfacial losses
OxygenDepletionalong theAir/O2 flowchannel
Mass
Transport
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Limiting current density
0 0.5 1.0 1.5 2.0
0.2
0
0.4
0.6
0.8
1.0
Current density (A/cm2)
CathodePotential
(V)
5 atm O2
5 atm AirN2+O22 atm
(13.5% O2)
N2+O25 atm (5.2% O2)
Mass
Transport
Source: T.E. Springer, M.S. Wilson, S. Gottesfeld, J.
Electrochem. Soc. 140 (1993) 3513
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Outline Electro-catalytic membrane reactors
! Chlor-Alkali Electrolysis
The oldest membrane reactor?
! Fuel Cells
The energy supply of the future?
! Bipolar membranes
The new tool to produce acids andbasis?
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Principle of bipolar membranes
H O2
H+ OH-
Na+ Cl-
cem aem
Na+Cl -
+
+
+
-
-
-cathode anode
H+ OH-
H O2
H O2
bipolar membrane
-
--
+
++
+
+
+
-
-
-
Mass
Transport
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Bipolar Electrodialysis Principle
salt
NaCl
acidHCl
baseNaOH
salt
NaCl
bmaem cem
H O2
OH-H+
Cathode Anode
cem aem
Na
+
Cl-
H O2
Na+
Cl
-
--
----
++
++++
++
++++
++++++
--
----
--
----
Mass
Transport
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Bipolar Electrodialysis Acid + Base production
ED-BPMsalt solution
water
base
acid
diluted salt
Process
technology
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Bipolar ED process
salt solution
water
base
acid
diluted salt
bipolar membrane electrodialysis unit
Membrane Module
123
(ED-BPM)
1
2
3 base
acid
salt
Processtechnology
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Mass transport desired and undesired
acid
H+X-
rinse rinse
OH-
CEM
O
2
H
2
BPM
X-
AEM BPM
H+OH-H+OH-
repeat unit
CEM
M+
CEM
OH-
AEM
salt
M+X-
3 base
base
M+OH-
H2
O
H2O H2O
M+
Membrane Module
2 acid
1 salt
3 base
2 acid
1 salt
H2O
X-OH-
H+
Mass
Transport
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Stacking membranes into module
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Process realization
ACID PRODUCT
organic (lactic-, ascorbic-,salicylic-, amino-) acid
inorganic acid (HF,H2SO4, HCl)
sodium hydroxide
potassium hydroxide
recycling (pickling)
purification
fermentation
PROCESS INTEGRATION
BASE PRODUCT
sodium methoxide
pH-stabilization
Processtechnology
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Installed processes (Eurodia Tokoyama Soda)
Processtechnology
4004001500Installed
membrane area(m2)
Meth. sulf. acid
AAP
OAP
OAP
OAP
AAP
Pickling liquorsrecovery
HF recovery
OAP
OAR
OAP
1986
1994
1995
1996
1997
1998
1999
EuropeJapanUSAYear
Source: Presentation Eurodia, 3rd Bipolar Workshop, Montpellier, June 5th, 2000
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Acid recovery + Precipitation
BaseSalt
Acid
Diluate
Concentrate
Filter
press
Metal hydroxidefilter cake
Waste acid
Pickling bath
ED diluatecake wash
steel sheet
cleansteel sheet
~ 1.5M KOH / 0.5M KF
Acid product HF/HNO3
Aquatech process
Bipolar stack
ED stack
Neutralizationtank
pH=9
Processtechnology
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CDI Continous deionization
+
Anode
----
-----
-
-
++
++
++
+++++
-
---
------
-
++++
+++++
+
+
-
Na+
Cl-Cl-
Na+
Process to prepare low conductivity water: bed of mixed IEX beads increases conductivity
in diluate compartment
Mixed IEX bed
R.W. Baker, Membrane Technology and Applications, 1999, McGraw-Hill
Feed(aqueous salt solution)
ConcentrateConcentrate
Mass
Transport
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Bipolar CDI
+
Anode
----
-------
++
++
+++++
++
---
-
----
--
-
++++
++++++
+
Na+Cl-
catIEX bed
Source Parsi, US Patent 469,983, 1989:
Feed
anIEX bed
Product
-
Cathode
Concentrate
Na+Cl-
OH-H+
Mass
Transport
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Problems-Challenges
! Membrane stability
base stability (loss of capacity, polymerbreakdown)
! Product purity
salt ion leakage membrane selectivity
! Process economics
membrane costs membrane potential
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Systematic study of selectivity performance
support
2dry
CE layer
1cast
CE polymer
5cure
BPM
4press
AE layer
3cast
CE glue
Material
Science
&
Processing
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Membrane structures
Cation permeable layerblend S-PEEK sulphonated poly(ether ether ketone)
PES poly(ether sulfone)
varied substitution, composition, thickness.
Anion permeable layercommercial anion exchange membranes
AMH, AHA, AMX(Tokuyama),
R4030 (Pall), ADP (Solvay)
Attachment
glue with cation layer polymer-blend solution
Bipolar interfacedifferent catalystsintroduce roughness
MaterialScience
&
Processing
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Membrane characterization
Mass
Transport
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Membrane characterization
Mass
Transport
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Membrane characterization
CEM CEM
1 65432
V
H+ OH-
O
2
H2
BPM
H+OH-
X
-
BPMBPM
M+
Na2SO4 NaCl Na2SO4NaClNaClNaCl
Mass
Transport
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Current-Voltage curve
i
[A/m2]
Um [V]
iop
ilim
Uop
1000
3000
10
20
0
JOH-JH+
JM+ + |J X-|
Udiss 1
Mass
Transport
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Concentration profiles - Selectivity
c
z
++++++
base ca acid
OH-
M+X-
H+
cFIX cFIX
BPM
OH-M+ X-H+
X-X- M+ M+
Mass
Transport
2
l im
1
2
M S
M X
f ix
D cJ J i
l c F= = =
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Current-Voltage curve
CE-Layer IEC=1.6
0
5
10
0 1 2
V_mem
0.04 mm
0.09 mm
0.10 mm
2M NaCl
25C26 cm2
current
density[mA/cm2]
Mass
Transport
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Influence of layer thickness
0
50
100
0.0E+00 1.0E-04 2.0E-04
layer thickness [m]
limitingcurrentdensity
[A/m2]
Mass
Transport
2
l im
1
2
M S
f i x
D ci
l c F=
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Variation of ion exchange capacity
0
50
100
0 1 2 3 4membrane potential [V]
currentdensity
[A/m2]
80%90%S-PEEK
20%
40%
70%
60%
Mass
Transport
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Influence of ion exchange capacity
0
50
100
0 1 2
ion exchange capacity [meq/g]
limitingcurrentdensity
[A/m2
]
predicted
measured
Mass
Transport
2
l im
1
2
M S
f i x
D ci
l c F=
Necessary totake swelling into
account (for cand D) !
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Pilot plant
Mass
Transport
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Limiting current density in Pilot Tests
c ca cc b
salt base acidblock
ac
repeat unit
(+) Anode Cathode (-)saltblock block rinserinse
Membrane module with Effective membrane area: 180 cm2
2 repeat units
Membranes commercial heterogeneous types (FuMA-Tech)
Add extra layersto bipolar membrane
Operate 2 mol/L solutions
25 - 30 C
up to 100 mA/cm2
Mass
Transport
I i il d l
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Ilim in pilot module
b
base acid
ac
salt
c
b
base acid
ac
salt
a
b
base acid
ac
salt
b
base acid
ac
salt
ca
ilim = 9 mA/cm2 Current-voltage characterization
Udiss = 0.6 V
ilim = 5 mA/cm2
Udiss = 0.6 V
ilim = 4 mA/cm2
water limitation
ilim = 1.8 mA/cm2water limitation
0
5
10
15
20
0 1 2 3 4 5 6 7 8 9 10
U_module (V)
currentdensity
[mA/cm2]
b ab
abc
bc
Mass
Transport
I it t t
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Impurity transport
b
base acid
ac
salt
a
b
base acid
ac
salt
iLIM total salt flux flux Cl -/ Na+
(measured) (measured)
[mA/cm2] [mol/(m2h)] [-]
standard 9 16.6 20.0
thick (a) layer 5 11.7 29.3
current-voltagecurve
Electrodialysis withacid and baseat 100 mA/cm2
Mass
Transport
C l i
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Conclusions Electro-catalytic membrane reactors
! Chlor-Alkali Electrolysis
The oldest membrane reactor
! Fuel Cells
The energy supply of the future
! Bipolar membranes
The new tool to produce acidsand basis