EMS Summer 2000

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University of Twente

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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! Fuel Cells


! Bipolar membranes


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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



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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)



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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! Fuel Cells


! Bipolar membranes


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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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Mass

Transport

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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


The oldest membrane reactor

! Fuel Cells

The energy supply of the future

! Bipolar membranes

The new tool to produce acidsand basis

Documents

EMS Summer 2000