On-Line H2 PPB Impurity
Analysis Using FTIR
Arik Ultsch
MKS Instruments Deutschland
Background
z Volatile fossil fuel prices have created interest in
Hydrogen as a new energy source for the
auto industry
z Impurities in H2 fuel directly affect the longevity of the
combustion or fuel cell engine
z Regulatory agencies have initiated
an H2 quality threshold at the
ppb level
z FTIR spectroscopy is the
most viable method of providing
ppb level H2 impurity detection
on-site at the pump
H2 Impurity Analysis: Content
z Fuel cell principle
z Determining the effect of impurities on fuel cells
– How much can be tolerated?
– Is the effect reversible?
– Effects of impurities
z Sulfur (H2S, COS), ammonia, CO, CO2, H2O
– Impurities from H2 Fuel as well as Air Feed
Î
Cell Analysis by Air Liquide R&D Center USA
z
Robert Benesch, Tracey Jacksier, and Sumaeya Salman
z FTIR Validation for H2 impurity detection
– Method detection limits for:
z
z
Multiple components
Different FTIR detector ranges tested
Fuel Cell Principle
z Fuel cells generate electricity from a simple
electrochemical reaction in which oxygen and
hydrogen combine to form water
z Anode
– Porous carbon coated with tiny particles of platinum (Pt)
– Pt acts as a catalyst to form ions
(2H2 => 4H+ + 4e-)
z Proton Exchange Membrane (PEM)
– Allows positively charged
ions to travel through
z Cathode
– Forms oxygen atoms
– Oxygen and hydrogen
combine to form water
(O2 + 4H+ + 4e- => 2H2O)
Impurity Effects on Cell Voltage
z Decrease in performance
– Affect different physical and chemical processes
z Removal of impurity
– Cell Performance: recoverable or non-recoverable
The Fuel – Hydrogen and Air
z Hydrogen
– Introduced to anode side of fuel cell
z Reducing environment
– Dependant upon production method
z Typical methods
z
- Biological – fermentation, anaerobic digestion
- Electrochemical – electrolysis of H2O
- Thermal – reforming, gasification
Steam Methane Reforming (SMR)
- 95% of US H2 production
- He, N2, CO, H2S, NH3, CH4 …
z Air
– Introduced to cathode side of fuel cell
z Oxidizing environment
Sources of Impurities
z Carbon Monoxide in H2
– Reported Mechanism*
z
z
Physical adsorption onto fuel cell catalyst
CO absorbs onto Pt site blocking H2 adsorption
COg + Pts ⇔Pt⋅COads
Pt⋅COads + H2O→Pts +CO2g +2H+ +2e−
* J. Baschuyuk and X. Li, “Carbon Monoxide Poisoning of Proton Exchange Membrane
Fuel Cells”; Int. J. Energy Res. 2001, 25; 695-713
CO Effect on Fuel Cell
1.0 and 4.5 ppm CO in H2
9.2 ppm CO in H2
Sources of Impurities
z Ammonia in H2
– Reported Mechanism*
z
z
z
Concentration and exposure dependant
Short-term exposure of trace concentrations
(~<10ppm)
- Reversible
- Mainly affects the Electrode
Long-term exposure of trace as well as high
concentrations (~>40ppm)
- Non-Reversible
- Mainly effects the Membrane structure
* F. Uribe, S. Gottesfeld, T. Zawodzinski, “Effect of Ammonia as Potential Fuel Impurity On Proton
Exchange Membrane Fuel Cell Performance” J. Electrochemical Society, 2002, 149 (3) A293-296
NH3 Effects on Fuel Cell
pure H2
0.5, 1.0 ppm NH3 in H2
No Effect
9.0, 44.7 ppm NH3 in H2
9.0 Non - Reversible
44.7 Non - Reversible
Summary of Impurities Tested
Impurity
Electrode
Lowest Test
Conc (ppm)
CO
H2S
NH3
CO
SO2
NO2
anode
anode
anode
cathode
cathode
cathode
0.52
0.10
0.50
0.40
0.07
0.025
Highest Test
Conc (ppm)
9.2
2.0
44.7
68.6
4.8
2.86
% Decrease
at Lowest
Conc
5
not detected
not detected
not detected
3
not detected
% Decrease
at Highest
Conc
>58
>58
14.7
not detected
40
20
Typical Air Sample: (maximum hourly concentration detected at
EPA testing sites in Houston and Chicago area in 2005):
CO [3 ppm], NO [0.65 ppm], SO2 [0.137 ppm]
Current H2 Fuel Cell Specification
SAE J2719
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Property
Ammonia
Carbon Dioxide
Carbon Monoxide
Formaldehyde
Formic Acid
Helium
Hydrogen Fuel Index
Nitrogen and Argon
Oxygen
Particulate Concentration
Particulates Size
Total Gases
Total Halogenated Compounds
Total Hydrocarbons
Total Sulfur Compounds
Water
Value
0.1
2
0.2
0.01
0.2
300
99.97
100
5
1
10
300
0.05
2
0.004
5
Unit
ppm v/v
ppm v/v
ppm v/v
ppm v/v
ppm v/v
ppm v/v
% (a)
ppm v/v
ppm v/v
µg/L@NTP (b)
µm
ppm v/v (c)
ppm v/v
ppm v/v (d)
ppm v/v
ppm v/v
Limit
Maximum
Maximum
Maximum
Maximum
Maximum
Maximum
Maximum
Maximum
Maximum
Maximum
Maximum
Maximum
Maximum
Maximum
Maximum
Maximum
FTIR For H2 Impurity Analysis
z Real-time analysis at ppb levels
z FTIR advantage
– Multiple components analysis with one unit
z Single analyzer for all the impurities except O2, H2, Ar, N2
– High resolution enables speciation between similar molecules
z Butane, Propane, Ethane, Methane, fuel sources, etc.
– Permanent calibration
– Analysis performed at various sites
z H2 production site
z H2 storage site: gas or liquid cylinders
z At - Line analysis at fueling station
Infrared (IR) Spectroscopy
z Based on IR light absorption
– Energy (IR radiation) heats molecule - vibrations and rotations
– The pattern and intensity of the spectrum provides all the information
about gas (type and concentration)
Background and Sample
BACKGROUND (Io)
N2 Purge 1cm-1
SAMPLE (I)
1000 ppm NH3 1cm-1
Absorbance = - Log (I/Io)
Absorbance is Proportional to
Concentration
Absorbance = - Log (I/Io)
Absorbance = ε • C • path
FFT of Sample
1000 ppm NH3 1.0 cm-1
What Can FTIR Do?
Component
Product
Exhaust
40-80
0-10
Oxygen (O2), %
0-1
0-5
Nitrogen (N2), %
0-10
0-80
Hydrogen Sulfide (H2S), ppm
0-300
Low ppm
Carbon Monoxide (CO), %
0-25
0-25
Carbon Dioxide (CO2), %
0-25
0-25
Water (H2O), %
0-25
0-25
Methane (CH4), %
0-10
0-10
Non-methane Hydrocarbons, %
0-10
0-10
Nitric Oxide (NO), ppm
Low ppm
0-100
Nitric Dioxide (NO2), ppm
Low ppm
Low ppm
Sulfur Dioxide (SO2), ppm
Low ppm
0-100
Hydrogen (H2), %
z Analyze all components that:
– Are IR active
– Have Dipole Moments
z Examples
– Ammonia, CO, CO2, H2O,
Hydrocarbons, etc
z Raw Reformed Hydrogen
– Percent level analysis
z Purified Hydrogen
– PPB level analysis
FTIR Components Used For Test
z Gas Cell
– Stainless steel – path length 5.11 meters
– Metal sealed cell: <10-9 Torr / min He leak rate
– BaF2 gas cell windows
z
Infrared cutoff near 850 cm-1
– Gold coated mirrors
z Two Detectors Validated
– 9.2u TE cooled detector
z
Infrared cutoff near 1100 cm-1
– 16u Stirling cooled detector
z
Infrared cutoff @ 850 cm-1 due to BaF2 windows
16u Cutoff
9u Cutoff
Water
Methane
Ethane
Formic Acid
Formaldehyde
CO2
Ammonia
CO
Method Validation
z EPA Method 40 CFR 136 Appendix B
– Build calibrations on FTIR
– Estimate a minimum detection limit
– Determine how low a concentration can be
detected with this method
FTIR Validation Method for H2
z Gases validated on FTIR
– CO, CO2, CH4, C2H6, NH3, H2O, Formaldehyde
and Formic Acid
– All in Balance of H2
z Gas standards creation
– NIST traceable gas cylinders for gases
z 100 ppm of CO, CO2, CH4, C2H6 in H2
– NIST traceable permeation tubes for liquids
z NH3, H2O, Formaldehyde and Formic Acid
– Blended with H2
z Purified H2 (<1ppb H2O, CO CO2)
Method Detection Limits
Contaminant
Ammonia (NH3)
Carbon Monoxide (CO)
Carbon Dioxide (CO2)
Formaldehyde (HCHO)
Formic Acid (HCOOH)
Total Hydrocarbons
(Reported as C1)
Methane
Ethane
Ethylene
Water (H2O)
SAE J2719
Detection
Limits (ppmv)
16u Stirling*
9.2u TE
16u LN2
0.10
0.20
2.00
0.01
0.20
2.00
0.36
0.01
0.01
0.02
0.03
0.81
0.05
0.01
0.02
0.02
0.02
0.01
0.01
0.02
0.02
0.71
0.10
0.10
0.10
5.00
0.02
0.02
0.02
0.05
0.40
0.74
0.03
0.05
0.03
0.12
* Signal to noise ratio (SNR) was 1/3 that of 16u LN2 for this test
* However improved SNR to same level as 16u LN2
Acknowledgments
z Fuel cell work
– Air Liquide Research and Technology Center
z
Robert Benesch, Tracey Jacksier, Sumaeya Salman
z Method validation / calibration work
– Elutions Design Bureau, Inc – Houston, TX
z
Scott Thompson
– MKS Instruments – On Line Product Group
z
Barbara Marshik
– Monetary support for this work
z
z
MKS Instruments
Shell Global Solutions Inc. - Westhollow Technology
Center