EFFECT OF GAS-PHASE ALKALI ON TAR REFORMING CATALYST Pouya Haghighi Moud1), Klas Engvall1) and Klas J. Andersson2) 1) Dept. of Chemical Engineering and Technology, KTH, Stockholm Sweden

2) Haldor Topsøe A/S, Kongens Lyngby, Denmark

CHALLENGE

Investigations of interactions between tar reforming catalyst and gas phase alkali at realistic conditions

Unknown effects of gas phase alkali on tar reforming catalyst

OBJECTIVE

2

Outline

• Background • Experimental • Results so far

– Gas composition – Tar measurements – Sulfur uptake – Chemical eq calculation – K adsorption

• Summary • On-going work

3

Tar removal

Reforming of the syngas/Catalysis

Gas utilization

Gas clean-up & reforming

Gasification Preprocessing of biomass

Gasifier

Tar removal

Gas clean-up

Downstream cleaning (Tar, particulates,alkali, S, etc)

Gasifying agent

Biomass

Syngas Tar

Application

Background

4

Gasifier Tar reformer Hot gas filter

High temperature hot gas filter

Gasifier Tar reformer

”Clean” tar reforming

Gasifier Tar reformer Hot gas filter

”Dusty” tar reforming

Background

5

Background

Alkali promotion* • Surface carbon gasification • Decrease in intrinsic activity of the nickel in

traditional steam reforming • Type of support influences the alkali interaction

6 *Ref: Concepts in Syngas Manufacture, Jens Rostrup-Nielsen Lars J.Christiansen

Background

Deactivation of the catalyst

• Fouling/coking

• Sintering* – Temperature, pH2O, and pH2 (mobile Ni(OH)2 species)

• Activity suppression by sulfur* – Under reforming conditions all the sulfur compounds are converted

into H2S – H2S+ Me-> Me-S + H2

– Stable saturation uptakes of sulfur 10x10-6 < H2S/H2 < 1000x10-6

– Metal (Ni) surface area/g catalyst => surface saturation by S

7 *Ref: Concepts in Syngas Manufacture, Jens Rostrup-Nielsen Lars J.Christiansen

EXPERIMENTAL

8

Experimental Setup

Dry alkali salt particles

(A) (A) (A)

Gas pre-heater

Product gas

Excess gas

N2

O2 H2

Gas analysis

Atmospheric fluidized bed

Filter vessel

Catalytic reactor

N2

Biomass feeder

(A) Gas analysis - Permanent gases - Tar -others

850 °C 850 °C 850 °C

Ni-based Haldor Topsøe catalyst

9

Experimental Setup

Dry alkali salt particles

(A) (A) (A)

Gas pre-heater

Product gas

Excess gas

N2

O2 H2

Gas analysis

Atmospheric fluidized bed

Filter vessel

Catalytic reactor

N2

Biomass feeder

(A) Gas analysis - Permanent gases - Tar -others

850 °C 850 °C 850 °C

Ni-based Haldor Topsøe catalyst

Alkali and hydrogen sulfide is added after the filter. 10

Experimental Tests

Test campaign 1st test campaign 2nd test campaign

Alkali species KCl, KNO3 KCl

Addition of H2S No addition 50-100 ppm

11

Catalyst characterization

• Surface area of catalyst (BET) • K content (AAS) • Carbon/coke formation (TPR) • Cl content(IC) • S and C content (FTIR, SEM) • Particle size distribution (SMPS)

AAS – Atomic Absorption Spectroscopy FTIR – Fourier Tranform Infrared Spectroscopy TPR – Temperature Programmed Desorption SEM – Scanning Electron Miccroscopy IC – ION Chromatography SMPS – Scanning Mobility Particle Sizer

12

RESULTS

13

Gas composition

0

1

2

3

4

5

6

7

8

9

0 50 100 150 200 250 300 350 400 450 500

Met

han

e co

nte

nt

(%)

Time (minute)

Methane (KCl)

Significant decrease in methane conversion already after one hour 14

KCl 1 ppm H2S ≈10 ppm

Gas composition

0

1

2

3

4

5

6

7

8

9

10

0 50 100 150 200 250 300 350 400 450 500

Met

han

e co

nte

nt

(%)

Time (minute)

Methane (KCl+hydogen sulfide) Methane (KCl)

KCl 1 ppm H2S 50 ppm

At extended exposure time, higher H2S addition results in lower methane conversion

KCl 1 ppm H2S ≈ 10 ppm

15

Gas composition

0

1

2

3

4

5

6

7

8

9

10

0 50 100 150 200 250 300 350 400 450 500

Met

han

e co

nte

nt

(%)

Time (minute)

Methane (KCl+hydogen sulfide) Methane (KCl)

KCl 1 ppm H2S 50 ppm

At extended exposure time, higher H2S addition results in lower methane conversion

KCl 1 ppm H2S ≈ 10 ppm

16

Tar measurement SPA method and online GC

0

10

20

30

40

50

60

70

80

90

2 4 6

Tar

Red

uct

ion

(%

)

Time (hour)

Tar (Excluding Benzene) Naphthalene

KCl 1 ppm H2S 50 ppm

• Decrease in tar reduction for both light and heavy hydrocarbons • A trend is observed: Initial activation drop

17

Sulfur effect

0

0,2

0,4

0,6

0,8

1

1,2

2 4 6

S/

S c

apac

ity

Time on stream(hour)

S content

• Increase in S content of the catalyst: Initial activation drop • Higher H2S addition: S saturation coverage is more rapidly reached

KCl 1 ppm H2S ≈ 10 ppm

KCl 1 ppm H2S 50 ppm

18

K adsorption

0

0,05

0,1

0,15

0,2

0,25

0,3

0

1

2

3

4

5

6

7

8

9

10

0 50 100 150 200 250 300 350 400 450 500

K a

dso

rpti

on

on

cat

alys

t(m

g K

/ g

C

atal

yst)

Met

han

e co

nte

nt

(%)

Time (minute)

Methane (KCl+H2S) Methane (KCl) K adsoption on catalyst

Comparing S and K uptake, initial activity suppression is dominated by S. Therefore important to perform experiments with S coverage equilibrated Ni surface.

KCl 1 ppm H2S 50 ppm

19

Summary so far

There is a trend in gas composition/tar reduction behavior After first hours of run

• Methane conversion is stable (constant catalytic activity) • S content of the catalyst reaches its maximum meaning the surface

is equilibrated

How do we isolate the effect of gas phase alkali on the catalyst in realistic conditions?

• Pre-sulfidation • Ageing (High T and high steam content)

20

Tests

Test campaigns 3rd test campaign

Alkali species KCl (0.1, 0.5, and 1 ppm)

Addition of sulfur H2S/H2 corresponding to surface coverage of 0.9

Pre-treatment Pre-ageing and Pre-sulfidation

Results of pre-treatment indicates: 1. BET surface area is constant from start 2. Sulfur content of the catalyst is constant from start

21

Thermodynamic consideration Chemical eq. calculations* for KCl

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1

reference 0.5 ppm KCl 1 ppm KCl

pp

m (

85

0 °

C) KCL

KOHKK2CO3KCN

KCl

At current conditions of experiment,molecular KCl is the main alkali compound present in the gas phase at different concentrations *NASA computer program

22

Experimental K adsorption data

6 10

0.5 ppm excess KCl

1 ppm excess KCl

K a

dso

rpti

on (

µg

/BET

su

rfac

e ar

ea)

Time on stream (hour)

Experimental value

4 2

2

5

10

20

15

23

Future work

6 10

0.1 ppm KCl

0.5 ppm excess KCl

1 ppm excess KCl

No excess KCl

K a

dso

rpti

on (

µg

/BET

su

rfac

e ar

ea)

Time on stream (hour) Decay time for adsorbed KCl

Experimental value Speculated value

4 2

2

5

10

20

15

• Following the uptake of K at different concentrations, it is possible to observe if the catalyst reaches an equilibrium coverage.

• More data points are needed.

24

Summary

• Pre-ageing and pre-sulfidation : isolate the effect of gas phase alkali on tar reforming catalyst

• Initial uptake of K is different at different gas phase concentrations of KCl

• Following the uptake of K at different concentrations, it is possible to see if the catalyst reaches an equilibrium coverage.

• As the result of the objective of this project, we were able to develop a methodology for investigation of gas phase alkali on tar reforming catalyst

25

On going work

Extended test plan • Longer exposure times • Different KCl concentrations • Decay time of adsorbed K

26

Acknowledgment

SFC

27