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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