Removal of ChlorineRemoval of Chlorine--Containing Chemicals by Zirconium Containing Chemicals by Zirconium

HydroxideHydroxide--based Sorbent Mediabased Sorbent Media

Gregory W. Peterson

US Army ECBC

Joseph A. Rossin

Guild Associates, Inc. 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

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

Objectives:

Effort represents part of an on-going program aimed at developing high-

capacity filtration media for respirator applications

a. Commercially available raw materials

b. Scalable preparation

c. All testing/evaluation in engineered form

• Chlorine and phosgene will not react directly with basic surfaces

Chlorine Gas Removal Chemistry

Hydrogen Chloride Chlorine Phosgene

– Hydrolysis required:

• Hydrogen chloride will react with basic surface, metal oxides

• Triethylenediamine (TEDA) known to promote hydrolysis reactions

Cl2 + H2O � ½O2 + 2HCl

COCl2 + H2O � CO2 + 2HCl

• 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

Experimental

– 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 15%

Challenge Concentration1400 ppm (Cl2, COCl2)

2700 ppm (HCl)

Breakthrough Concentration 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 Cl2and 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 groupto 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 AnalysesSample Chemical O/Zr Cl/Zr

Zr(OH)4 None 3.55 0

Zr(OH)4-6T Cl2 3.14 0.15

Zr(OH)4 COCl2 2.94 0.28

Zr(OH)4-6T COCl2 2.66 0.44

Zr(OH)4 HCl 2.55 0.88

Zr(OH)4-6T HCl 2.40 0.88Zr(OH)4-6T HCl 2.40 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 TEDAPeak 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:

HCl reacts with terminal –OH leading to the formation of zirconium

Cl2 + H2O →TEDA

2HCl + ½ O2

COCl2 + H2O →TEDA 2HCl + CO2

HCl reacts with terminal –OH leading to the formation of zirconium

oxychloride:

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

Zr(OH)4 + 2HCl � 3H2O + ZrOCl2

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)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