effect of gas-phase alkali on tar reforming catalyst
TRANSCRIPT
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
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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
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Acknowledgment
SFC
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