Laboratory-Scale Investigation of UV Treatment of Ammonia for. Livestock and Poultry Barn Exhaust Applications

Transcription

1 SUPPLEMENTAL INFORMATION for Laboratory-Scale Investigation of UV Treatment of Ammonia for Livestock and Poultry Barn Exhaust Applications Erin M. Rockafellow, Jacek A. Koziel, and William S. Jenks Iowa State University EXPERIMENTAL... 2 CALIBRATIONS AND CONTROL EXPERIMENTS... 5 HIGH RESOLUTION MASS SPECTRAL DATA... 9 ABSORPTION CROSS SECTIONS... 9 REFERENCES S1

2 Experimental Materials. All gas blends were certified commercially as within 2% accuracy. Dry air contained 21.5% O 2, 10 µl L 1 CO, 1000 µl L 1 CO 2, and 24 µl L 1 H 2 O. Hydrogen sulfide and N 2 O stock gases were blended with N 2 at 15 µl L 1 and 5 µl L 1, respectively. Ammonia stock gases were 50 µl L 1 in air, 500 µl L 1 in air, and 500 µl L 1 in N 2. Water was purified to a resistivity above 18 M /cm with a Millipore apparatus. Irradiations. Photolyses were carried out using a Rayonet (Southern New England Ultraviolet) photochemical reactor containing thirteen 185/254 nm low pressure mercury lamps with quartz walls with an output power of approximately 0.02 watts and 8 watts for 185 nm and 254 nm light, respectively, as stated by the manufacturer. The 185 nm light was attenuated by passage through approximately 25 mm of ambient air before hitting the exterior walls of the home built quartz reaction coil. Temperatures inside the reactor were kept very near ambient with a fan built into the reactor floor. All analyses were performed downstream from the reactor at room temperature (ca. 298 K) and atmospheric pressure. Gas flow rates were regulated using mass flow controllers. Scheme S1 illustrates the gas delivery/reaction system made from ~6.5 mm (1/4 inch) O.D. quartz tubing and fittings made of a perfluoroalkoxy (PFA) material. The quartz reaction coil was constructed from a 7.6 m length of quartz tubing with an 8 mm I.D. and 10 mm O.D. The tubing was rated to allow 65% transmission of 185 nm light at the 1 mm wall thickness. The total interior volume of the coil exposed to irradiation was 394 ml. S2

3 Optional dilution line Gas B Water addition Humidity monitor MFC a Gas C Vent MFC a Glass bulb Gas Bubbler c Gas sampling bulb d Detector e Gas A MFC a Quartz reaction coil b Supplemental Scheme 1. Schematic representation of the gas delivery and UV treatment system. The water addition segment and the gas sampling bulb were installed when required. a MFC = mass flow controller. b The reaction coil is placed inside the photochemical reactor. c Contained 200 ml of water when humidification was required. d Used to collect samples for GC MS analysis. e FTIR or NH 3 chemiluminescence analyzer. For H 2 S experiments, Gases B and C were H 2 S in N 2 and N 2, respectively. Analysis. Reactions were analyzed by FTIR, chemiluminescence, or GC MS to identify and quantify reaction products. For IR measurements, 16 scans were taken over roughly 30 s while the gas was continuously passed through a 500 ml FTIR gas cell with a path length equal to 7.2 m (15 cm, 48 reflections) at 1 cm 1 resolution using a DTGS detector. The instrument was constantly purged with N 2 to reduce the background signal from air. S3

4 The following frequencies were used to monitor and determine concentrations: 967 cm 1 for NH 3 (Pouchert, 1989), 1,040 cm 1 for O 3 (NIST Mass Spec Data Center), and 2,236 cm 1 for N 2 O (Pouchert, 1989). The NH 3 (50 µl L 1 ) and N 2 O (5 µl L 1 ) standards were diluted with air or N 2 respectively to obtain calibration curves (Supporting Information). At higher flow rates and low concentrations, a digitalized chemiluminescence ammonia analyzer, which could measure a maximum NH 3 concentration of 100 µl L 1 with a minimum flow rate of 600 ml/min, was used to provide a second check on [NH 3 ]. The lower detection limit was less than 1 µl L 1. Analyses by GC MS were performed using a 25 m CP Volamine column with 0.25 m I.D. and 5 m film thickness and a TOF mass spectrometer. The GC temperature program was 40 C (2 min) ramped at a rate of 20 C/min to 200 C (2 min). Accurate mass was collected using 2,4,6 Tris(trifluoro methyl) 1,3,5 triazine (METRI) as a reference. Quantitative GC MS calibrations for gas concentrations were not obtained since ammonia quantification was unreliable due to adsorption to the sampling flask walls. Control experiments using 5 µl L 1 N 2 O in N 2 showed that photolysis did not lower the observed [N 2 O], presumably due to recapture of the nascent oxygen atoms by N 2 (Warneck, 2000). However, in the "air" samples, photolysis of N 2 O would reduce its steady state concentration due to the reaction of the oxygen atom with other species. S4

5 Calibrations and Control Experiments Abs [NH3], ppm Supplemental Figure S1. FTIR response curve for air dilutions of 50 µl L 1. [NH 3 ] 0 at 100 ml/min (1 HRT unit = 3.94 min) Abs [N 2 O], (ppm) Supplemental Figure S2. FTIR response curve for N 2 dilutions of 5 µl L 1 [N 2 O] 0 at 100 ml/min (1 HRT unit = 3.94 min). S5

6 Abs Time (min) Supplemental Figure S3. Dark adsorption/desorption equilibration of 50 µl L 1 [NH 3 ] 0 at 600 ml/min (1 HRT unit = 0.66 min). Supplemental Figure S4. Spectrum obtained from static residue remaining in the IR gas cell under N 2 after the photolysis of 200 µl L 1 NH 3 in air. S6

7 Supplemental Figure S5. Extended 185/254 nm photolysis of 20 µl L 1 [NH 3 ] 0 in dry air at 100 ml/min (photolysis HRT = 3.9 min). S7

8 Supplemental Figure S6. Comparison of FTIR spectra taken of the 185/254 nm photolysis of 20 µl L 1 [NH 3 ] 0 flowing at 100 ml/min in hypoxic air (8.6% O 2 ) with 9 µl L 1 H 2 S after (a) 15 min and (b) 210 min of irradiation, and (c) extended photolysys, followed by 30 min continued flow in the dark. S8

9 High Resolution Mass Spectral Data Supplemental Table S1. Identification of components by GC MS present after 185/254 nm photolysis of 500 µl L 1 NH 3 after 30 min of flow at 100 ml/min. Entry Retention Time (min) Observed Mass (M +, m/z) , , a a a Peaks overlap in GC trace, but were resolved by single ion chromatograms. Compound Air (N 2, O 2, Ar) CO 2 NH 3 N 2 O H 2 O Absorption Cross Sections Supplemental Table S2. Absorption cross sections ( ) at 300 K used for rate comparisons. Molecule 185 (cm 2 molecule 1 ) 254 (cm 2 molecule 1 ) Ref NH 3 ca. 1 x (Chen et al., 1999) O 2 5 x (Kessler and Kleinermanns, 1992; Yoshino et al.) O 3 6 x x (Mauersberger et al., 1986; Molina and Molina, 1986) H 2 O 7 x (Creasey et al., 2000) S9

10 References Chen F.Z., Judge D.L., Wu C.Y.R., Caldwell J. (1999) Low and room temperature photoabsorption cross sections of NH 3 in the UV region. Planetary and Space Science 47: Creasey D.J., Heard D.E., Lee J.D. (2000) Absorption cross-section measurements of water vapor and oxygen at 185 nm. Implications for the calibration of field instruments to measure OH, HO 2 and RO 2 radicals. Geophysical Research Letters 27: Kessler K., Kleinermanns K. (1992) Atomic hydrogen + molecular oxygen -> hydroxyl + atomic oxygen: excitation function and absolute reaction cross sections. Journal of Chemical Physics 97: Mauersberger K., Barnes J., Hanson D., Morton J. (1986) Measurement of the ozone absorption cross-section at the nm mercury line. Geophysical Research Letters 13: Molina L.T., Molina M.J. (1986) Absolute absorption cross sections of ozone in the 185- to 350- nm wavelength range. Journal of Geophysical Research, [Atmospheres] 91: NIST Mass Spec Data Center S.E.S., director, "Infrared Spectra" in NIST Chemistry WebBook, NIST Standard Reference Database Number 69, Eds. P.J. Linstrom and W.G. Mallard, National Institute of Standards and Technology, Gaithersburg MD, 20899, (retrieved June 9, 2009). Pouchert C.J. (1989) The Aldrich Library of FT-IR Spectra Vapor Phase. 1st ed. Aldrich Chemical Company, Inc., Milwaukee, WI. Warneck P. (2000) Chemistry of the Natural Atmosphere, Second Edition. Yoshino K., Esmond J.R., Cheung A.S.C., Freeman D.E., Parkinson W.H. High resolution absorption cross sections in the transmission window region of the Schumann-Runge bands and Herzberg continuum of O 2. Planetary and Space Science 40: S10