Process Safety Aspects in

Water-Gas-Shift (WGS) Catalytic Membrane

Reactors Used for Pure Hydrogen Production

Center for Inorganic Membrane Studies (CIMS)

Worcester Polytechnic Institute

Department of Chemical Engineering

Reyyan Koc, Nikolaos K. Kazantzis and Yi Hua Ma

Mary Kay O’Connor Process Safety Center

International Symposium

October 26-28, 2010 / Texas

Outline

• Introduction

– Pd-Based Membrane Reactor

– H2 Transport Through Pd-Based Membrane

– Pd/Alloy Membrane Reactors in IGCC Plants

• Safety Analysis for Pd/Alloy Membrane Reactors

– Objective

– Modeling Results

[Tfeed, Wcatalyst, H2O:CO Ratio, Driving for H2 permeation (∆PH2)]

– Safety Aspects – HAZOP

[Feed flow rate, Reaction side pressure, Impurities]

• Conclusions

2

Pd-Based Membrane Reactor

3

CO + H2O ↔ CO2 + H2 ΔH298K = - 40.1kJ/mol

½'' OD ×2.5'' Long

4 in2 (25 cm2)

WPI –Pd/Alloy Membranes

Pd supported on porous Inconel

(media grade 0.1 µm)

Prepared by Electroless Plating

Excellent long term H2/He selectivity

GE Syngas

Retentate: Mostly CO2 + H2O

H2r2

r1

1 2 3

4

1 & 3. Inert packing

2. Reaction /Shell side

4. Permeate/Tube side

Pd-based membrane

HT WGS catalyst

Applications of catalytic membrane reactors to refinery products [10] :

• Dehydrogenation & hydrogenation reactions

• Conversion of remote natural gas to syngas and liquid fuels

• Steam reforming

• Water gas shift reaction

H2 Transport Through Pd-Based Membrane

4

Interstitial diffusion of H

atom in Pd lattice[8]

Solution diffusion mechanism

Sieverts’ Law

Pd/Alloy Membrane Reactors in IGCC Plants

GE Gasifier

Highest H2O:CO ratio

Highest XCO and RH2

Lowest H2S +COS concentration

Table 1. Syngas compositions†

†http://sequestration.mit.edu/pdf/LFE_2005-002_WP.pdf

Pshell = 220 & PTube,MR = 15 psia

Ffeed=1.1 scfh , TRxn=450°C

0%

20%

40%

60%

80%

100%

Shell 1Shell 2

GE

20%

42%

98%

44%

60%

91%

XC

O&

RH

2Gasifier Type

CO Conversion H2 Recovery

Safety Analysis for

Pd/Alloy Membrane Reactors - Objective

6

The standard principles of Hazard and Operability (HAZOP) analysis were

followed to identify and prevent potential process risks to personnel,

environment, equipment integrity and/or the efficiency or economics of the

process [5.6].

Pshell = 220 & PTube,MR = 6 psia

FDry feed=1.1 scfh , TRxn=400°C

H2O:CO XCO

[%]

RH2

[%]

FH2Ratio

MR / PBR

MR 2 99 961.2

PBR 9 98 -

Isothermal Case:

Performance target levels: XCO = 98% & RH2 = 95%

Membrane reactor limitations:

1. Reaction side temperature:@ T≤ 300 C for Pure Pd H2 embrittlement &

@ T≥ 550 C intermetallic diffusion and permeance decline

2. Impurities : Poisoning of the Pd membrane due to H2S in the feed

Feed Temperature

7

250 300 350 400

1000

2000

3000

4000

5000

6000

20

30

40

50

60

70

80

RH2

[b]

1

2

TFeed [°C]

250 300 350 400

1000

2000

3000

4000

5000

6000

250

300

350

400

450

500

550

11 1

TMAX

Fe

ed

flo

w r

ate

[sccm

]

TFeed [°C][a]

PShell = 15 atm, PTube = 1 atm, H2O:CO = 2 and 100% ρBulk,max

TRxn,Max = 500 C &TRxn,Min = 300 C for pure Pd membranes

• Tfeed ≤ 300°C to protect the membrane, however XCO = 95% and RH2 = 89%

• The target levels of XCO = 98% and RH2 = 95% were not achieved

Wcatalyst & H2O:CO

8

TFeed = 300°C, PShell = 15 atm, PTube = 1 atm

• 40% ρBulk,max is sufficient enough and the

contact area is increased

• Use excess steam to reduce the TRxn

and also shift the Rxn to the products side

H2O:CO = 2 - Tmax =530 C

XCO = 93% - RH2 = 86%

H2O:CO = 4 - Tmax =470 C

XCO = 98% - RH2 = 82%

20 40 60 80 100

1000

2000

3000

4000

5000

6000

10

20

30

40

50

60

70

80

90

Fe

ed

flo

w r

ate

[sccm

]

Percentage of the ρBulk,max [%]

1

2

[a]

XCO

2 4 6 8

1000

2000

3000

4000

5000

6000

75

80

85

90

95

H2O:CO Mole Ratio

12

[b]

XCO←TRxn>500 C

Process Safety Aspects: FFeed

9

FFeedCauses Consequences Prevention & Repair

More

(Above the

nominal

level)

•Malfunction of

the flow control

instruments

•Inappropriate

adjustment

and/or failure of

the valves and

pressure

regulators

Da>1 •Hot spots

•Membrane damage

•Catalyst sintering

•Regular maintenance and

inspection of the control

instrument, valves and

pressure regulators

•A backup line before the

reactor entrance

• Fast responsive

temperature recorders and

controllers

• Relief valves

• Poisonous gas detectors

on both reaction and

permeate sides

• Regeneration / substitution

of the membrane

Da>>1 •Reduced XCO & RH2

• Decreased TRxn and variations

Less

(Below the

nominal

level)

(same causes

with More and)

•Plugging of the

lines

•Leaks on the

feed line

Da<1 Insignificant changes

Da<<1 •Decreased TRxn due to reduced

∆HRxn

•Reduced H2 production rates

• Pressure increase in the feed

line due to plugging

• Pressure decrease due to leaks

No

(no flow)

Oxidation of the membrane

Process Safety Aspects: H2O:CO

10

H2O:CO Causes Consequences Prevention & Repair

More

(above the

nominal level)

•An error in the

ratio controller

•Failure of the

water pump

Decreased TRxn

Reduced XCO & RH2

•Back up lines

•Relief valves

•Fast responsive pressure

recorders and controller

• Regeneration / substitution of

the membrane and catalystLess

(blow the

nominal level)

•Increased TRxn

•Coke formation (H2O:CO<2)

•Reduced XCO & RH2

•Pressure built up due to , plugging

of the pipelines and/or the membrane

reactor

No

( no steam )

•In addition to the same effects with Ffeed:

70%

75%

80%

85%

90%

95%

100%

0 100 200 300

CO

Co

nve

rsio

n a

nd

H2

Re

co

ve

ry

Run Time (min)

CO Conversion

H2 Recovery

EquilibriumXC

O &

RH

2

Run Time [min]

•Membrane appearance after removal

from the reactor**

**WPI-CIMS from Unpublished data by A. S. Augustine

Increase ΔPH2 : Driving force for H2 permeation

11

0.2 0.4 0.6 0.8 1

2000

3000

4000

5000

6000

85

90

95

PTube [atm] (PShell= 20 atm)

RH2

[b]

1

98

%9

7.6

%9

7 %

10 20 30 40 50 60 70

2000

3000

4000

5000

6000

50

60

70

80

90

PShell [atm] (PTube = 1 atm)

RH2

[a]

2 1

95

.6 %

94

.7 %

92

.7 %

Fe

ed

flo

w r

ate

[sccm

]

TFeed = 300°C, H2O:CO =4 and 40% ρBulk,max

Tmax =470-477 C - XCO ≥ 98% - RH2 ≥ 95%

PShell ≥ 45atm PTube ≤ 0.5 atm

Process Safety Aspects: Pshell

12

P Shell Causes Consequences Prevention & Repair

More •Malfunction of the compressor

and back pressure regulators

•Plugging or closing of the

valves as well as connections

at the zones before/after the

membrane exit

Increased TRxn

Increased XCO & RH2

•Back up lines

•Relief valves

•Fast responsive pressure

recorders and controller

• Excess steam

• Recording the changes in

permeate flow rate

Less

•Decreased TRxn

•Decreased XCO & RH2

H2 Recovery

RH

2[%

]

Run Time [min]

Feed pressure

Re

actio

n s

ide

Pre

ssu

re

[psia

]

•Due to coke formation in

the syngas feed line and

plugging of line**

**WPI-CIMS from Unpublished data

by A. S. Augustine

Process Safety Aspects: Impurities

13

F Impurity Causes Consequences Prevention & Repair

CH2S > 0

Malfunction of the

gas cleaning unit

•Pure Pd membrane: Decreased

selectivity and even demolished [3]

•Pd-Cu and Pd-Au:

Reduced permeance [4]

• Catalyst poisoning

• Corrosion

• Regular maintenance of the gas

cleaning units

•Placement of the gas composition

analyzers

•Regeneration/substitution of the

membrane and catalyst

•Recording the changes in

permeate flow rate

**WPI-CIMS from unpublished data by

Pomerantz & Chen [3-4]

Re

ma

ine

d P

erm

ea

nce

F/F

o[%

]

10 μm 5 μm

20 ppmv H2S/ 320⁰C/ 120 h

Mundschau et al. [9]

Pure Pd foil

10 μm

55 ppmv H2S/ 400⁰C/ 24h

Chen & Ma [3]

Pd/Au alloy coupon 8 wt% Au

H2S Concentration [ppm]**

Conclusions

• A standard Hazard and Operability (HAZOP) analysis was pursued to identify

potential hazards as well as failure modes and hopefully prevent potential risks

• In particular, the effect of variations in the total feed flow rate and temperature,

catalyst loading, H2O:CO ratio, reaction and permeate side pressures and purity

of the feed on the process state in the form of possibly adverse process

excursions/deviations from normal operating conditions were considered.

• The absence of adequate control of the reactor temperature as well as the purity

of the feed which may cause hot spots and decline in the permeance and

selectivity were identified and classified as critical for the operation of the WGS

membrane reactor.

• Utilization of excess steam together with the application of vacuum on the

permeate side was found to be the most effective method of reducing the

temperature rise in the reaction zone without decreasing the overall CO

conversion and H2 recovery.

• If the suggested precautionary measures are taken, the membrane reactor

could be operated safely without compromising the high performance target

levels of 98% CO conversion and 95% extra pure (99.9999%) H2 recovery.

14

15

U.S. Department of Energy Award No. DE-FC26-07NT43058

“Composite Pd and Pd Alloy Porous Stainless Steel

Membranes for Hydrogen Production and Process

Intensification”

DOE Project Manager: Daniel Driscoll

Technology Manager: Daniel C. Cicero

Project Officer: Jason C. Hissam

Disclaimer: This report was prepared as an account of work supported by an agency of the United States Government. Neither

the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or

assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus,

product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any

specific otherwise does not necessarily constitute or imply its endorsement, recommendation, or opinions of authors expressed

herein do not necessarily state or reflect those of the United States Government or any agency thereof.

Acknowledgements

References

1. Khan FI, Abbasi SA, J Loss Prev Process Ind 1997 7;10(4):249-57.

2. Chiappetta G, Clarizia G, Drioli E. , 2006 5/10;193(1-3):267-79.

3. Chen CH, Ma YH. , J Memb. Sci., 2010, In press.

4. Pomerantz N, Ma YH. , Ind Eng Chem Res 2009; 2009 03/23/; 04/15/;48(8):4030-9.

5. Chiappetta G, Clarizia G, Drioli E. , 2006 5/10;193(1-3):267-79.

6. Khan FI, Abbasi SA., J Loss Prev Process Ind 1997 7;10(4):249-57.

7. http://sequestration.mit.edu/pdf/LFEE_2005-002_WP.pdf

8. J. Voelkl, G. Alefeld, Topics in Applied Physics, 28 (1978).

9. Mundschau MV, Xie X, Evenson IV CR, Sammells AF ,Catalysis Today 118 (2006) 12–

23.

10. Armor JN, J Memb. Sci., 147, 1998, 217-233.

Thanks for your attention…

Questions?

16

Backup slide

GE Syngas

Retentate: Mostly CO2 + H2O

H2r2

r1

HT WGS catalyst

1 2 3

4

1 & 3. Inert packing

2. Reaction /Shell side

4. Permeate/Tube side

Pd-based membraneGE Syngas Composition (Dry):

45% CO + 38% H2 + 17% CO2

Properties of Pd/Inconel Membrane:

Qo = 79512 ft3.μm/(ft2.h.psi0.5)

Pd Thickness = 10 μm

Ep = 15.6 kJ/mol

Selectivity (H2/He) = ∞

Mass balance equations at the unsteady state conditions:

Reaction side (1)

Permeate side (2)

(3)

Energy balance equation in the reaction side at the unsteady state conditions