Ch 9 Gas Separation by Membranes Membrane Flow sheet of a membrane separation Separation of solvent...

Ch 9Gas Separation by Membranes

Membrane

Flow sheet of a membrane separation

Separation of solvent and solute in SFE-processes

Retentate

FeedPermeate

Problems: High pressure ( > 100 bar) Solution of Carbon Dioxide in Polymers Influence on glass transition point

Gas Circuit

CO2

OC

Permeate

Retentate

Membrane Process

GKSS-membrane (organic, active dense layer)

1.86 wt.-%

< 0.06 wt.-%

p = 2.0 MPa

active dense layer

1.5 mole CO2

kg/(m2 h)

P = 18 MPa, T = 323 K

Separation by membranes

Reference Membrane System T, P

Wagner (1986) RO, (Polyamid) Kaffein 473 K, 30 MPa

Semenova et al. (1992, ´93, ´94)

Kapton® (Polyimide)

Ethanol, Petroleum compounds

423 K, 15 MPa

Sarrade et al. (1996, ´97)

Composite with Nafion®

PEG, Triglycerides 333 K, 31 MPa

Nakamura et al. (1994)

Ceramic , NTGS-2100 (Silikon)

PEG 400-600 313 K, 20 MPa

Literature overview

Flat sheet membranes

ROMACO, high pressure RO, (Polyamide, Pall Rochem)

PAN-Fluorinated Polymer (FP), GP, (GKSS)

PEI-FP, GP, (GKSS)

PVDF-FP, GP, (GKSS)

6-FDA-4MPD/DABA 4:1 (Polyimide, crosslinked with ethylene glycol, University of Heidelberg)

Al2O3-TiO2, (Inocermic)

Membranes

N

O

O

N

O

O

COOH

CF3CF3

4 1

CF3CF3

N

O

O

N

O

O CH3

CH3

CH3

CH3

6FDA-4MPD/DABA 4:1

Membranes

Tubular membranes

Carbone membrane, ( 20 nm, Le Carbone-Lorraine)

ZrO2- TiO2, (Schuchmacher)

Al2O3-TiO2 -FP, (US-Filter, GKSS)

Membranes

porous membrane

nonporous membrane

carrier membrane

phase 1 phase 1phase 1phase 2 phase 2 phase 2

Mechanisms of membrane transport

Membranes

Table Fehler! Kein Text mit angegebener Formatvorlage im Dokument..1: Pore

diameter and thickness of inorganic gas separation membranes, after van Veen et al.

(1996).

Membrane systemPore diameter+ (thickness) Membrane system

Pore diameter+ (thickness)

Mesoporous alumina 4 nm(3 m)

Microporous carbon molecularsieve; hollow fibre

appr. 0.5 nm(6 m)

Mesoporous glass 4.5 nm(300 m)

Silicate on ceramic appr. 0.45 nm (5m)

Mesoporous carbon several nm(12–18 m)

Dense SiO2 by CVD modificationof microporous silica on alumina

dense(5 m)

Inorganic Membranes

Membranes

Pore diameter and thickness of inorganic gas separation membranes, after van Veen et al. (1996).

Table Fehler! Kein Text mit angegebener Formatvorlage im Dokument..1:Classification of ceramic membranes (Bonekamp, 1996).

Membrane Process Structure Average pore diameter Separation layerMicrofiltration 1 layer 5 m macroporous

2 layers 0.25 m macroporous3 layers 0.1 m macroporous

Ultrafiltration 4 layers 5 nm mesoporous

Gas separation,Nanofiltration,Pervaporation

5 layers 1 nm microporous

Membranes

Classification of ceramic membranes (Bonekamp, 1996).

Polymeric, Nonporous Membranes

amorphous semicrystalline crystalline

States of polymers

Membranes

v

T

vg

vc

vw

A

B

C

W

TmTg

freevolume

glassystate

rubberystate

Specific volume and free volume as a function of temperature for an amorphous polymer: A: specific volume of a liquid; B: specific volume of a glassy polymer; C: specific volume of a crystal solid; W: van der Waals volume; Tg: glass transition temperature; Tm: melting temperature.

Effect of Temperature on the Polymeric Structure

Effect of Temperature on the Polymeric Structure

Effect of Pressure on the Polymeric Structure

Swelling and Plasticization of Polymers

Aging of Polymers

Membranes

Influences on Membrane Properties

Gas Permeation through Membranes

l

ppP

l

ffP

A

nJ ee 2121

Steady state flux J :

Pe : effective permeability coefficient, (integral value over the whole membrane).

1

2

121

f

fe dfPffP

iii pf pfp

0

limwith

dpp

zp

i

0

1lnFugacity coefficient :

z: compressibility factor.

tApp

lVP

21

cmHgscm

cmSTPcm2

3

The permeability coefficient for ideal–gas conditions

Pressure - normalized flux Q, "membrane permeability":

l

PQ

Separation factor for a binary mixture of component A and B:

BA

BABA xx

yy/


Gaspermeation:

P = D H: Permeationskoeffizient,D = Diffusionskoeffizient, H = Henry-Koeffizient.

Trennfaktor:

jP

zP P ( ).1 2

1Barrer = 10cm (STP) cm

cm s cmHg-10

3

2 .

ABA

B

P

P0 .

Stofftransport

Einheit von P:

Joule-Thomson effect

Definition of the Joule-Thomson coefficient:h

JT p

T

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 300

2

4

6

8

10

343.15 K

333.15 K

323.15 K

313.15 K308.15 K303.15 K J

T [K

MP

a -1]

pFeed [MPa]

Joule-Thomson coefficient of carbon dioxide


E

F

B

A

C

D

A: Hagen-Poiseuille's flow,

B: Knudsen flow,

C: surface flow,

D: multilayer adsorption,

E: capillary condensation,

F: molecular sieving.

Gas Permeation through Porous Membranes

Transport mechanisms through porous membranes

Hagen-Poiseuille Flow

TRl

ppr

TRl

ppppr

TRl

pprJ SSmS

16168

22

21

22121

22

The term p/RT has to be replaced by the mean density rm resulting in the following relation for Hagen-Poiseuille's flow of carbon dioxide through mesoporous membranes:

28

2

COm

mS

Ml

prJ

28

2

COm

mS

Ml

rQ


Surface Diffusion and Capillary Condensation

Surface diffusion is a poorly understood phenomenon The total molar surface flux is calculated by:

dl

dqqDJ ss

with pore length l, porosity e, and density r of the solid. The surface diffusion coefficient Ds is a function of the amount of gas q adsorbed on the surface.

The effective surface coverage qe of gas can be described by adsorption isotherms, for monolayer adsorption: Langnuir isotherm:

pbpbq

q

sate 1

For multilayer adsorption BET isotherm:

re p 1

rrrr pCpp/pC 11

0pppr


1 2

0.0 0.2 0.4 0.6 0.8 1.0

Relative Mean Pressure pm/p0

0.4

0.6

0.8

1.0

Per

mea

bilit

y Q

x10

5(S

td C

.C.-cm

/cm

2–s

ec c

mH

g)

0.1

p/p0 T [K]

0.2

0.054

0.211

273

273

298

298

Permeability of carbon dioxide through vycor glass, after Rhim and Hwang, (1975). Maximum permeability: point where capillary condensation takes place.


The capillary condensation pressure (pt) can be predicted by the Kelvin equation:

2

0

cos2ln

r

tr

p

p

M

TR t

where t represents the thickness of the adsorbed layer. For non-cylindrical capillaries the term 2 cosq (r-t)/r2 has to be replaced by another relation.


Adsorption Isotherms at Sub- and Supercritical Conditions

0 5 10 150,0

0,1

0,2

0,3

0,4

0,5

Mas

s ad

sorb

ed C

O2 [g

g-1

Adsorb

ens]

Pressure [MPa]

Isotherms of the total amount of adsorbed carbon dioxide on two different silica gels. Silica gel with 10 nm mean pore diameter, -- 308.15 K, -- 318,15 K, data replotted from Bamberger (1996) silica gel with 1 nm mean pore diameter, -- 313,15 K, -- 333,15 K, data replotted from Ozawa and Ogino (1972).


The flux Ji of component i is given by Fick’s law:

dl

dcDJ Mi

ii,

2,1, MiMii

i ccl

DJ 2,1,

,ii

Giii pp

l

SDJ

Temperature dependence of the permeability coefficient P = D S:

TREexpPP p 0

Temperature dependence of diffusivity and solubility:

TREDD d exp0

TRHexpSS s 0

TR

EHexpSDP ds00

Gas Permeation Through Nonporous Membranes

TRH435.0SlogTSlog S

0

Sorption of gases in all types of amorphous polymers shows that the solubility of CO2 increases with decreasing temperature (van Krevelen, 1990):

Transport mechanism of penetrants through polymers differs below and above the glass transition of polymers.

The diffusion of penetrants through glassy polymers is a highly non-linear function depending on the state of the polymer.

Gas Permeation Through Nonporous Membranes

cPermeate

cMembrane

cBulkFeed

Boundary Layer

J cPermeate

J c

D dc/dx

x

Membrane

cPermeate

cMembrane= cGel

cBulkFeed

Boundary Layer

x

Membrane

Gel Layer

Concentration polarization at steady state conditions;

left: normal concentration polarization; right: gel-layer formation

Concentration Polarization

400 450 500 550 600 650 700 750 8000

2

4

6

8

10

12

14

16 T = 313 .15 K T = 333 .15 K T = 343 .15 K

Con

cent

ratio

n E

thyl

este

r [w

-%

]

C O

2 [kg m -2 ]

Solubility of fatty acid ethyl esters in carbon dioxide (Riha, 1996).

Concentration Polarization

A liquid layer forms on the retentate surface of the membrane when the solubility ís reached

1 phase

2 phases

Change in concentration when CO2 is removed by a membrane process

Membrane Test Cell

Membrane

Flat Sheet Test Cell

PI

P I

P I

TI

TI

TIC TIC

FI

FI

V1

S2

S1

P1

V2

V1

C 1P2

Experimental Set Up For Testing Flat Sheet Membranes

P l u gF e e d

R e t e n t a t e

M e m b r a n e M o u n t i n g

P e r m e a t e

M e m b r a n eO - R i n g

N u tC o o l i n g -H e a t i n gF l u i d

Tubular membrane test cell.

Experimenatal Membrane Test

TI

TI

P I

P I

P I

F I

TI

F I

d P

P I

P I

CO2

P I

P I

TCA

P C

2 80 b ar

1 20 b ar

1 20 b ar

K üh lwa sser

E V

TS H

LS

TE

TIC

2 50 b ar

2 50 b ar

2 50 b ar

N2

P I

V1

V2

V3

2 50 b ar

Experimental Set-Up

Pure Gas Permeation

0 2 4 6 8 10 12 140

2

4

6

8Q

CO

2 x 1

02 [km

ol m

-2 h

-1 M

Pa-1

]

Upstream Pressure [MPa]

TEOS, pressure-normalized CO2 flux vs. upstream pressure –– 34 °C, –– 49 °C,–– 66 °C –– 0.1 MPa 25 °C manufacturer, p = 0.3–1.9 MPa, 20-mm TC, membrane #2, values taken after 30 minutes.

Membranes

Inorganic Membranes: Titania-Alumina Composite Membranes

TiO2 (0,9 nm)

TiO2 (5 nm)

Al2O3 (macroporous)

approx. 1 mm

Schematic representation of titania-alumina membrane cross-sections

TEOSSubstructure: commercially available -Al2O3 membrane of 18 mm in diameter, mean pore diameter of 5 nm, porosity 50%, surface roughness appr. 0.2 m. Substructure modified by tetraethylorthosilicate (TEOS) treatment.

Polymeric Membranes

PEI-Teflon Membranes

N

O

O

ON

O

O

O

CH3

CH3

n

Chemical structure of polyetherimide (PEI), trademark Ultem by GE.

An intermediate ultrafiltration layer of polyetherimide (PEI) is applied to a polyester support fleece. The PEI-layer is then coated with a selective layer of poly (tetrafluoroethylene) (PTFE).

O O

F F

F3C CF3

n

F

F F

Fm

PDDn TFEm

Repeat unit of poly (2,2-bistrifluoromethyl-4,5-difluoro-1,3-dioxole) [PDD] / PTFE, commercially available under the trademark (AF 2400 Du Pont)

1 Barrer = 10-10 (cm3 cm)/(cm Hg s cm2)

Gas Teflon® PTFE AF2400

CO2 2800 12O2 990 4.2H2 4100 #He 2700 #H2 2200 9.8N2 350 1.4CH4 340 #C2H4 350 #C2H6 180 #

CF2 CF2

CF3 CF3

O O

F F

TFE

PDD

Structure of Monomers of the AF2400-polymer

Gas Permeabilities of PTFE-Polymers

0 5 10 15 20

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

0.18

QC

O2 [k

mol

m-2 h

-1 M

Pa

-1]


TEOS membranes: pressure-normalized CO2 flux vs. upstream pressure, –– #1 increasing pressures, –– #1 decreasing pressures, –– #2 increasing pressures, p = 0.3–1 MPa; T = 50 °C, 20-mm TC.

Pure Gas Permeation

0 2 4 6 8 10 12 14 16 18 200.00.2

0.4

0.6

0.8

1.0

QC

O2 [k

mol

m-2 h

-1 M

Pa-1

]


PEI-TE10x pressure-normalized CO2 flux as a function of upstream and permeate pressure for increasing upstream pressures (solid symbols), and decreasing upstream pressure (open symbols): –– 1 MPa transmembrane pressure difference,–– downstream pressure at atmospheric pressure, T = 50 °C, 47-mm TC.

Pure Gas Permeation: Organic Membranes

0 1 2 3 4 5 60

1

2

3

4

5

J CO

2 [km

ol m

-2 h

-1]

p [MPa]

CO2 flux at different upstream pressures as a function of transmembrane pressure difference for PEI-TE1x, –– 7 MPa, –– 9 MPa, –– 12 MPa, –– 14 MPa, –– 15.9 MPa, –– 18.1 MPa, T = 50 °C, 47-mm TC.

Pure Gas Permeation: Organic Membranes

0 5 10 15 202,5

3,0

3,5

4,0

4,5

5,0

5,5

6,0

6,5

7,0

7,5 Neue Membran 2. Benutzung 3. Benutzung

Q C

O2

[km

ol m

-2h-1

MP

a-1]

Feeddruck [MPa]

Influence of Repeated Use

PAN-AF2400-Membran, 50 °C

0 5 10 15 200

1

2

3

4

5

6R

atio

QP

EI-

TE

1x / Q

PE

I-T

E10x [

-]


CO2-Permeate Flow of PEI-AF2400-1x Related to PEI-AF2400-10x

–– increasing retentate Pressure (Feed side),

–– decreasing retentate pressure (Feed side), T = 50 °C, 47-mm test cell.

0 5 10 15 200

50

100

150

200

PTFE, 50 °C, Muth, (1998)

PMMA, 50 °C, Muth, (1998)

PMMA, 58 °C, Liau, McHugh,(1985)

50°C 45°C

35°C

Teflon AF 2400, 25°CS

olub

ility

[cm

3 CO

2 (S

TP

) cm

-3

poly

mer ]

Pressure [MPa]

Solubility of CO2 in Teflon AF 2400

0 5 10 15 200

1

2

3

4

5

6

De, C

O2 x

105

[m2 h

-1]


Diffusion Coefficient of CO2

7-m Teflon AF 2400 layer on a PEI-AF2400-10x Membran, 50 °C, p = 1 MPa; 50 °C, p2 = atmospheric pressure; 35 °C, p2 = atmospheric pressure (after Merkel et al. (1999).

0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0 2,2 2,4 2,6

3000

4500

600010500

12000

13500

15000

16500

18000

PExt = 23 MPaTExt = 60 °C

40 °C 70 °C 50 °C 80 °C 60 °C 85 °C

Per

mea

tflu

ss v

on C

O2

[mol

m-2 h

-1]

Druckdifferenz P [MPa]

CO2 Permeate Flow

2-HHU-1TEOS - membrane

Sartorelli 2001

0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0 2,20

5

10

15

20

25

30

35

40

40° C 70° C 50° C 80° C 60° C 85° C

Pe

rme

atf

luss

vo

n T

CA

[m

ol m

-2 h

-1]


TEOS-Membrane: Feed: P = 23 MPa; T = 60° C

Sartorelli 2001

0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0 2,2

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1,0 b


40 °C 50 °C 60 °C 70 °C 80 °C 85 °C

Tre

nnfa

ktor

[-]


TEOS-Membrane

Separation Factors

2-HHU-1

Sartorelli 2001

0,2 0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0 2,2 2,4900

1200

1500

1800

2100

2400

2700

3000

3300

3600 P

Ext T

Ext T

m

18 50 50 18 50 60 18 50 70 23 60 50 23 60 60 23 60 70

P

erm

eatflu

ss v

on C

O2 [

mol

m-2 h

-1]

DruckdifferenzP [MPa]

Permeate flows of CO2 at 50 °C, 60 °C and 70 °C,Exp. series: 2-FP-X10 (18 MPa/50 °C) and 3-FP-X10 (23 MPa/60 °C).

Permeate Flow

AF 2400 - Membrane

0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0 2,2

1400

1600

1800

2000

2200

2400

2600

2800

3000

3200

3400

3600

316 K 323 K 333 K 343 K 353 K

PExt = 23 MPaTExt = 333 K

CO

2 P

erm

eate

Flu

x [

mol

m-2 h

-1]

Transmembrane Pressure P [MPa]

CO2 Permeate Flow: AF 2400 membrane

Sartorelli 2001

0,4 0,6 0,8 1,0 1,2 1,4 1,6 1,8 2,0 2,2

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8 316 K 323 K 333 K 343 K 353 K

PExt

= 23 MPaT

Ext = 333 K

Sep

arat

ion

Fac

tor

[-]

Transmembrane Pressure P [MPa]

LVCLVC

LVCLVCx100/x

y100/y

Separation Factor: AF 2400 membrane

Sartorelli 2001

0,00 0,01 0,02 0,03 0,04 0,05 0,06 0,07 0,08 0,090,000

0,005

0,010

0,015

0,020

0,025

0,030


Y -

[J s

c-1]

X - [c Jv c-1]

TM = 43/44 °C TM = 50 °C TM = 60 °C T

M = 70 °C

TM = 80 °C

Determination of Transport Coefficients

Sartorelli 2001

Nanofiltration Membrane, AF 2400 coated

0 1 2 3 4 5 60

1

2

3

4

5

6

7 MPa 9 MPa 12 MPa 14 MPa 16 MPa 18 MPa

J C

O 2 [k

mol3

m-2

h-1]

p [MPa]

Pressure Difference, PEI-FP, 323

0 5 10 15 200

2

4

6

8 PAN-FP PVDF-FP PEI-FP

Q C

O2

[km

ol m

-2h-1

MP

a-1]

Feed Pressure [MPa]

Membrane Comparison, 323 K

0 2 4 6 8 10 12 14 16 18 200

1

2

3

4

5 Increasing Pressure 2.5 Decreasing Pressure 2.5 Increasing Pressure 10 Decreasing Pressure 10

Q C

O 2 [k

mo

l m-2

h-1M

Pa-1

]

Feed Pressure [MPa]

T = 323 K

P = 2 MPa

Hysteresis in the PEI-FP 2,5 and 10 Membranes

Membrane

Type

Q CO2

[kmol m-2 h-1 MPa-1]

? p

[MPa]

cFeed

[%]

LVC

[-]

FDA 1.25 0.85 1.94 0.9

ROMACO 12 0.65 0.83 1.02

PEI-FP 2.5 1.45 2.2 1.2 0.27

PEI-FP 10 0.34 2.2 1.94 > 0.1

Mixture Results Overview

0 1000 2000 3000 40000,00

0,02

0,04

0,06

0,08

0,10

[-

]

Operating Time [min]

T = 323 K

Pf = 18 MPa

P = 2 MPa

PEI-FP 10 Membrane

Scale Up: Plate and Frame Construction

PC

PC

RV1

RV2

WT1 WT2

B2

B1

P1WT3

1

18 MPa323 K

6 MPa323 K

273 K

Supercritical Fluid Extraction

PC

WT2

1

PC

P1

B1

RV3

PC

WT1 K1

RV1

RV2

M1

18 MPa323 K

P = 2 MPa

Coupling With a Membrane Separation Unit

53 kJ/ kgCO2

21 kJ/ kgCO2

7.6 kJ/ kgCO2

1

2

3

Wie in 2Like in 2

Energy For Different Solvent Cycles

Pump-Cycle

Compressor-Cycle

Membrane-Cycle

Sartorelli 2001

Ch 9 Gas Separation by Membranes Membrane Flow sheet of a membrane separation Separation of solvent...

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