Download Removal of Chlorine Removal of Chlorine

Removal of ChlorineChlorine-Containing Chemicals by Zirconium
Hydroxide--based Sorbent Media
Hydroxide
Gregory W. Peterson
Joseph A. Rossin
US Army ECBC
5183 Blackhawk Rd
Bldg. E3549
Aberdeen Proving Ground, MD
21010-5423
(410) 436-5704
Guild Associates, Inc.
5750 Shier-Rings Road
Dublin, Ohio 43016
(614) 760-8007
Background: Identification of Zirconium Hydroxide
o
Zr(OH)4 is commercially available or
readily synthesized via precipitation
o
Structure possesses both bridging and
terminal hydroxyl groups
o
Hydroxyl groups have the potential to
contribute to chemical reactions
Density
Surface Area
Pore Volume
CWS Carbon
0.47 g/cm3
1,100 m2/g
0.648 cm3/g
Zr(OH)4
1.09 g/cm3
365 m2/g
0.235 cm3/g
Density
Surface Area
Pore Volume
CWS Carbon
0.47 g/cm3
517 m2/cm3
0.305 cm3/cm3
Zr(OH)4
1.09 g/cm3
398 m2/cm3
0.256 cm3/cm3
Objectives:
1. Assess the ability of Zr(OH)4 and Zr(OH)4 impregnated with TEDA,
ZnO to remove chlorine gases (Cl2, COCl2 and HCl)
2. Assess the role of TEDA and the hydroxyl groups on the removal of
chlorine gases
Effort represents part of an on-going program aimed at developing highcapacity filtration media for respirator applications
a. Commercially available raw materials
b. Scalable preparation
c. All testing/evaluation in engineered form
Chlorine Gas Removal Chemistry
Hydrogen Chloride
•
Chlorine
Phosgene
Chlorine and phosgene will not react directly with basic surfaces
– Hydrolysis required:
Cl2 + H2O ½O2 + 2HCl
COCl2 + H2O CO2 + 2HCl
•
Hydrogen chloride will react with basic surface, metal oxides
•
Triethylenediamine (TEDA) known to promote hydrolysis reactions
Experimental
•
Materials
– Zr(OH)4 purchased from a commercial vendor (MEL Chemicals)
• Impregnted with zinc
• Impregnated with triethylenediamine (TEDA) via sublimation
– Particles formed via tabletting machine, followed by crushing and
sieving
•
Breakthrough Testing
– Push-pull-vented system
– Chemicals tested @ constant atomic chlorine concentration
– Detection
• Chlorine: Electrochemical cell detector
• Hydrogen chloride: Electrochemical cell detector
• Phosgene: Electron capture detector
•
XPS
– Perkin Elmer Phi 570 ESCA/SAM instrument
– Referenced to carbon 1s peak @ 284.6 eV
Experimental
Parameter
Value
Particle Size
12x30
Bed Depth
2 cm
Bed Volume
26.4 cm3
Airflow Velocity
9.6 cm/s
Airflow Rate
7.6 L/min
Temperature
25°C
Relative Humidity
Challenge Concentration
Breakthrough Concentration
15%
1400 ppm (Cl2, COCl2)
2700 ppm (HCl)
0.5 ppm
Results: Effects of TEDA
HCl effectively removed by
unimpregnated Zr(OH)4
Rapid breakthrough of Cl2 and
COCl2
TEDA promote the removal of Cl2
and COCl2, extending breakthrough
times
Removal of HCl not affected by
TEDA
HCl most effectively removed,
followed by COCl2, the Cl2
Results: Effects of TEDA Loading on Cl2 Removal
Increasing TEDA loading from 3% to 6% does not significantly improve removal
of chlorine.
Results: XPS Analyses of Exposed Media
Zr(OH)4 comprised of
bridging and terminal –OH
groups
Peak at 531.6 eV assigned
to terminal hydroxyl groups
Peak at 529.9 eV assigned
to bridging hydroxyl group
Note decrease in intensity
of terminal –OH following
chemical exposure
In case of HCl exposed
media, virtually no terminal
–OH groups detected
Results: Quantitative XPS Analyses
Sample
Chemical
O/Zr
Cl/Zr
Zr(OH)4
None
3.55
0
Zr(OH)4-6T
Cl2
3.14
0.15
Zr(OH)4
Zr(OH)4-6T
COCl2
COCl2
2.94
2.66
0.28
0.44
Zr(OH)4
Zr(OH)4-6T
HCl
HCl
2.55
2.40
0.88
0.88
Decrease in oxygen is
accompanied by increase
in chlorine
Fraction of terminal –OH
decreases proportional
with increase in chlorine
Bridging –OH not affected
by chlorine gas exposure
Results: Fate of TEDA
Peak at 401.2 eV assigned HCl
nitrogen adduct complex
Reference sample suggests that
HCl adduct is formed first at one
nitrogen atom
Evidence of TEDA adduct formation
for exposed samples
As terminal –OH groups are
consumed, product HCl begins to
interact with TEDA, preventing it’s
contribution to the hydrolysis
reaction
- Breakthrough results
Results: Proposed Reaction Chemistry
TEDA promotes the hydrolysis of Cl2 and COCl2:
Cl2 + H2O TEDA

→ 2HCl + ½ O2
TEDA
COCl2 + H2O 
→ 2HCl + CO2
HCl reacts with terminal –OH leading to the formation of zirconium
oxychloride:
Zr(OH)4 + 2HCl 3H2O + ZrOCl2
HCl filtration performance much greater than either Cl2 or COCl2
- TEDA interacting with HCl, forming an adduct
- Adduct complex no longer contributing to the reaction
Results: Effects of Zinc Loading
Zinc increases the reactive
capacity of the surface,
making more sites available
for the removal of HCl
Results: Summary of Filtration Performance
Material
Cl2*
COCl2**
HCl*
Zr(OH)4-TEDA
28min
87 min
ZnO-Zr(OH)4-TEDA
53 min
48 min
167 min
Reference Carbon
30 min
29 min
60 min
*1,400 ppm Cl2, 2,700 ppm HCl Feed
**2,500 ppm COCl2 Feed
Despite the reduced porosity, the ZnO-Zr(OH)4-TEDA media yields
significantly greater breakthrough times for the chlorine gases than
does the Reference Carbon media.
Summary
Zr(OH)4-based media loaded with TEDA able to effectively remove
chlorine gases from streams of air.
TEDA is necessary to promote hydrolysis reactions involving Cl2 and
COCl2
Terminal hydroxyl groups associated with Zr(OH)4 contribute to the
removal of HCl and product HCl (from hydrolysis of Cl2 or COCl2)
Addition of zinc to the formulation greatly improves the resulting filtration
performance, yielding a media that far exceeds the performance of the
reference impregnated, activated carbon