Online Analysis of Chlorine Gas Impurities Using Long-Path FTIR
Online Analysis of Chlorine Gas Impurities Using Long-Path FTIR
Online Analysis of Chlorine Gas Impurities Using Long-Path FTIR
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<strong>Online</strong> <strong>Analysis</strong> <strong>of</strong> <strong>Chlorine</strong> <strong>Gas</strong><br />
<strong>Impurities</strong> <strong>Using</strong> <strong>Long</strong>-<strong>Path</strong> <strong>FTIR</strong><br />
Dow Worldwide<br />
Dow is a leader in science and<br />
technology, providing innovative<br />
chemical, plastic and agricultural<br />
products and services to many<br />
essential consumer markets<br />
Wendy C. Flory, Lamar Dewald, Gary Gellise, Todd Beebe, Joe Bonadies<br />
The Dow Chemical Company<br />
Analytical Sciences – Process Analytical
<strong>Chlorine</strong><br />
• Many uses and applications<br />
– Clean drinking water<br />
– Sanitizer<br />
– Many products<br />
• Dow is the world’s largest producer <strong>of</strong> chlorine<br />
• Dow launched initiative to qualify external<br />
suppliers<br />
– Location, location, location!<br />
• Two sites for on-line qualification<br />
– Pittsburg, CA<br />
– Midland, MI<br />
www.chlorinetree.com<br />
WCF Pittcon 2010 2
External <strong>Chlorine</strong> Vendor Qualifications<br />
•Why?<br />
– <strong>Impurities</strong> can interfere with<br />
plants and be costly<br />
•Low yield<br />
• Off-grade<br />
• Selectivity<br />
– Catalyst fouling<br />
– Equipment corrosion<br />
Extreme case = plant shutdown<br />
West Coast<br />
Smokey Mt.<br />
WCF Pittcon 2010 3
Liquid to <strong>Gas</strong> at Dow plants<br />
• Liquid received from railcars, evaporated and<br />
sent to process<br />
• <strong>Gas</strong> phase analysis at point before use<br />
Evaporation<br />
Process<br />
MKS FT -IR<br />
Analyzer<br />
<strong>Chlorine</strong><br />
WCF Pittcon 2010 4
Why Analyze On-Line?<br />
• Sample handling<br />
– Safety<br />
– Adding/changing impurities,<br />
especially low level water<br />
• Real time analysis<br />
• Find the unexpected!<br />
Eye into the process<br />
WCF Pittcon 2010 5
MKS <strong>Chlorine</strong> Purity<br />
FT-IR Analyzer<br />
• 0.5 to 128 high speed <strong>FTIR</strong><br />
• Real-time, on-line purity analysis <strong>of</strong> bulk<br />
process gas<br />
• Ppb level impurity detection<br />
• Specialized zeroing s<strong>of</strong>tware<br />
• Pre-calibrated for a variety <strong>of</strong> gases<br />
• Constructed for corrosive high purity gases<br />
• High resolution analyzer deconvolves<br />
overlapping spectra<br />
• Optics purged with N2<br />
• Sample flow = < 1 l/min<br />
• Sample pressure ~1 atm<br />
• Model analyzes for compounds listed to table<br />
20/20 TM <strong>Long</strong> <strong>Path</strong> (5.11m) <strong>Gas</strong> Cell<br />
Spectral Ranges Used<br />
Spectral range cm -1<br />
H 2 O<br />
3855 - 3795<br />
CO 2 2265 - 2253<br />
CO<br />
2185 - 2093<br />
CH 4 3171 - 3004<br />
HCl<br />
3002 - 2902<br />
HOCl<br />
3509 - 3411<br />
WCF Pittcon 2010 6
Interface to Process Pipe<br />
Electrical<br />
from<br />
plant<br />
from<br />
Cl2 line<br />
V1<br />
H<br />
Flow diagram for <strong>FTIR</strong><br />
analyzer interfaced to<br />
process<br />
V2<br />
C<br />
V4<br />
PG1<br />
R2<br />
PG2<br />
V5<br />
V6<br />
V8<br />
Ethernet<br />
V12<br />
P<br />
V3<br />
power supply<br />
line heater controller<br />
Maintain at Cl2 temp.<br />
V7<br />
MKS<br />
Purity<br />
analyzer<br />
N 2 purge<br />
N 2 vent to area Cl 2 monitor<br />
Area Cl 2<br />
monitor<br />
V9<br />
R1<br />
to<br />
scrubber<br />
V13<br />
box heater - maintain 30C<br />
PG3<br />
V10<br />
V11<br />
N 2<br />
header<br />
WCF Pittcon 2010 7
Interface to Process Pipes<br />
West Coast<br />
Smokey Mt.<br />
WCF Pittcon 2010 8
Normal Absorbance Spectra<br />
1.4<br />
.6<br />
1.2<br />
.4<br />
.2<br />
Absorbance (a.u.)<br />
0.20<br />
0.15<br />
0.10<br />
CO 2<br />
0<br />
0.05<br />
H 2 O<br />
HOCl<br />
HCl<br />
4000 3500 3000 2500 2000 1500<br />
0.00<br />
Arbitrary / Wavenumber (cm-1)<br />
File # 5 = SYMB_163149<br />
Overlay X-Zoom CURSOR<br />
3/27/2007 10:33 AM Res=None<br />
4000 3500 3000 2500 2000<br />
Wavenumber (cm -1 )<br />
West Coast<br />
Smokey Mt.<br />
WCF Pittcon 2010 9
Self-Referencing Spectra<br />
Self referencing is obtaining interferogram at 1 cm -1 resolution and<br />
deresolving the same spectrum to 8 cm -1 and comparing<br />
Advantages<br />
• Removes need for manual<br />
periodic instrument<br />
background, not easily done in<br />
field applications<br />
• Broad instrument and analyte<br />
features are removed, finer<br />
structures or small features are<br />
easier to see against a flat<br />
baseline<br />
• Resulting spectrum looks<br />
derivative-like<br />
Normal Referenced, 1 cm -1 resolution<br />
Normal Referenced, 8 cm -1 resolution<br />
Self-Referenced = Purple – Red<br />
WCF Pittcon 2010 10
Self-Referenced Spectra – a closer look at<br />
water<br />
• H 2 O model with Smokey Mt.<br />
chlorine self referenced<br />
spectrum<br />
• Very good match<br />
• Water is difficult to calibrate<br />
• Usually takes ~2 weeks to<br />
develop calibration in-house<br />
and deliver analyzer to plant<br />
• Out-<strong>of</strong>-box results and quick<br />
turn –around time for<br />
analysis<br />
Absorbance (a.u.)<br />
0.030<br />
0.025<br />
0.020<br />
0.015<br />
0.010<br />
0.005<br />
0.000<br />
-0.005<br />
-0.010<br />
Smokey Mt.<br />
H2O std<br />
3900 3880 3860 3840 3820 3800<br />
Wavenumber (cm-1)<br />
WCF Pittcon 2010 11
Calibrations built in<br />
• Huge advantage!<br />
• Multipoint calibrations<br />
• Reduce error due to<br />
spectral non-linearity<br />
• Generated by MKS in<br />
their lab or using<br />
HITRAN *<br />
• Libraries with 100s <strong>of</strong><br />
compounds supplied<br />
with analyzer<br />
*<br />
HITRAN – High resolution Transmission molecular absorption database<br />
www.harvard.edu/hitran/<br />
WCF Pittcon 2010 12
Calibrations and models give trend charts in<br />
on-line applications<br />
• Preferred by plant<br />
engineers<br />
• Trend charts show the<br />
variance from railcar to<br />
railcar<br />
• Also, shows response<br />
for new supply varies<br />
depending on<br />
component<br />
concentration<br />
nitrogen<br />
<strong>Chlorine</strong><br />
Supply A<br />
HCl (ppmv)<br />
CO2 HI (ppmv)<br />
HOCl (ppmv)<br />
H2O (ppmv)<br />
<strong>Chlorine</strong><br />
Supply B<br />
time<br />
WCF Pittcon 2010 13
Ability to re-evaluate<br />
• Once interferograms are saved,<br />
the model can be re-run to<br />
optimize spectral regions, add<br />
models for concentration<br />
changes, include new<br />
components, etc. 2400<br />
H 2 O<br />
Smokey Mt.<br />
Initial<br />
(ppm)<br />
Smokey Mt.<br />
Reprocessed<br />
(ppm)<br />
CO 2 4x 900x<br />
CO<br />
CH 4<br />
1x<br />
1x<br />
1x<br />
HCl 0.3x<br />
0.30<br />
Initial<br />
0.25<br />
Absorbance (a.u.)<br />
0.20<br />
0.15<br />
0.10<br />
0.05<br />
0.00<br />
-0.05<br />
-0.10<br />
-0.15<br />
-0.20<br />
2350 2300 2250<br />
Wavenumber (cm-1)<br />
0.20<br />
Reprocessed<br />
0.15<br />
Absorbance (a.u.)<br />
0.10<br />
0.05<br />
0.00<br />
-0.05<br />
-0.10<br />
Smokey Mt.<br />
CO2 std<br />
-0.15<br />
2300 2290 2280 2270 2260 2250<br />
Wavenumber (cm-1)<br />
Smokey Mt.<br />
CO2 Std.<br />
WCF Pittcon 2010 14
Ability to re-evaluate<br />
–unidentified features reveal HOCl<br />
0.002<br />
0.004<br />
3463.1<br />
948 spectrum<br />
Intensity (a.u.)<br />
0.001<br />
0.000<br />
948 spectrum<br />
CO2 resize<br />
2624.2<br />
2574.1<br />
2527.3<br />
2483<br />
2440<br />
Intensity (a.u.)<br />
0.002<br />
0.000<br />
3447.2<br />
3442.4<br />
-0.001<br />
3000 2800 2600 2400 2200 2000<br />
Wavenumber (cm -1 )<br />
-0.002<br />
3460 3455 3450 3445 3440 3435 3430<br />
W avenumber (cm -1 )<br />
Niki, J;<br />
Maker, PD;<br />
Savage, CM; Breitenbach, LP; Chem. Phys. Lett.; 66, 2, 1979<br />
Ashby, RA; J. Mol. Spect.; 23, 1967<br />
WCF Pittcon 2010 15
Concentrations <strong>of</strong> impurities vs. Dow <strong>Chlorine</strong><br />
West Coast<br />
2007<br />
Smokey Mt.<br />
2007<br />
Smokey Mt.<br />
2009<br />
(ppm) (ppm) (ppm)<br />
H 2 O 1x 1x 1x<br />
CO 2 200x 900x 600x<br />
CO 1x 1x 1x<br />
CH 4 1x 1x<br />
HCl 1x 0.3x 0.5x – 1x<br />
HOCl 30x 1x – 10x<br />
WCF Pittcon 2010 16
Conclusions<br />
• On-Line <strong>FTIR</strong> indicates impurities are present and have<br />
potential to interfere with process<br />
• Data allows Dow to identify and quantify impurities and<br />
negotiate specifications from potential suppliers<br />
• Having ability to respond quickly was critical for this<br />
project!<br />
Acknowledgements<br />
• MKS for lending equipment and technical support<br />
through this project<br />
• Process Analytical team at Dow Chemical<br />
WCF Pittcon 2010 17
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