The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Jeongmyeong Ha - One of the best experts on this subject based on the ideXlab platform.
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catalytic dehydrofluorination of 1 1 1 2 3 pentafluoropropane hfc 245eb to 2 3 3 3 tetrafluoropropene hfo 1234yf using in situ fluorinated chromium oxyfluoride catalyst
Catalysis Today, 2016Co-Authors: Jae Wook Choi, Jeongmyeong Ha, Kwang Ho SongAbstract:Abstract As part of an effort to prepare a refrigerant with zero Ozone Depletion Potential (ODP) and with a low global warming Potential (GWP), the catalytic dehydrofluorination of 1,1,1,2,3-tetrafluoropropane (HFC-245eb) is performed to produce 2,3,3,3-tetrafluoropropene (HFO-1234yf). Cr2O3 prepared by the sol-gel method (Cr2O3(SG)) exhibits good catalytic activity attributable to the formation of surface chromium oxyfluoride, which exhibits better catalytic activity with high-valent chromium and a larger fluorine content. The formation of chromium oxyfluoride from chromium oxide is achieved by in-situ fluorination in the early stage of dehydrofluorination, avoiding the conventional fluorination method using toxic HF.
Vladimir L Orkin - One of the best experts on this subject based on the ideXlab platform.
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photochemical properties of trans 1 chloro 3 3 3 trifluoropropene trans chcl chcf3 oh reaction rate constant uv and ir absorption spectra global warming Potential and Ozone Depletion Potential
Journal of Physical Chemistry A, 2014Co-Authors: Vladimir L Orkin, Larissa E Martynova, Michael J KuryloAbstract:Measurements of the rate constant for the gas-phase reactions of OH radicals with trans-1-chloro-3,3,3-trifluoropropene (trans-CHCl═CHCF3) were performed using a flash photolysis resonance–fluorescence technique over the temperature range 220–370 K. The reaction rate constant exhibits a noticeable curvature of the temperature dependence in the Arrhenius plot, which can be represented by the following expression: kt-CFP (220–370 K) = 1.025 × 10–13 × (T/298)2.29 exp(+384/T) cm3 molecule–1 s–1. The room-temperature rate constant was determined to be kt-CFP (298 K) = (3.29 ± 0.10) × 10–13 cm3 molecule–1 s–1, where the uncertainty includes both two standard errors (statistical) and the estimated systematic error. For atmospheric modeling purposes, the rate constant below room temperature can be represented by the following expression: kt-CFP (220–298 K) = (7.20 ± 0.46) × 10–13 exp[−(237 ± 16)/T] cm3 molecule–1 s–1. There was no difference observed between the rate constants determined at 4 kPa (30 Torr) and 40...
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oh reaction rate constant ir absorption spectrum Ozone Depletion Potentials and global warming Potentials of 2 bromo 3 3 3 trifluoropropene
Journal of Geophysical Research, 2011Co-Authors: Victor G Khamaganov, Vladimir L Orkin, Steven L BaughcumAbstract:[1] The rate constant for the gas phase reaction of OH radicals with BTP (2-bromo-3,3,3-trifluoropropene, CH2 = CBrCF3) was measured using a flash photolysis resonance-fluorescence technique over the temperature range 220 K to 370 K. The Arrhenius plot was found to exhibit noticeable curvature. The temperature dependence of the rate constant can be represented askBTP(220 − 370 K) = 4.85 × 10−13 × (T/298)0.92 × exp{+613/T} cm3 molecule−1 s−1. For atmospheric modeling purposes, kBTP(T) can be equally well represented by the standard Arrhenius expression kBTP(220 − 298 K) = 1.05 × 10−12 × exp{+381/T} cm3 molecule−1 s−1. The IR absorption cross-sections of BTP were also measured between 450 cm−1 and 1900 cm−1. BTP atmospheric lifetime, Ozone Depletion Potential (ODP), and Global Warming Potential (GWP) were evaluated in the Whole Atmosphere Community Climate Model for land emissions from 30 to 60°N and from 60°S to 60°N. The global, annual average atmospheric lifetime of BTP in the former scenario was 7.0 days, its ODP was 0.0028, and its GWP (100-yr time horizon) was 0.0050; in the latter scenario, the global, annual average BTP lifetime was 4.3 days, ODP was 0.0052, and 100-yr GWP was 0.0028. The short lifetime, low ODP, and low GWP indicate that BTP should have minimal effects on Ozone and climate. Little BTP reaches the stratosphere in either emission scenario, but 27% of the Ozone loss in the 30 to 60°N scenario and 46% of the Ozone loss in the 60°S to 60°N scenario occurs above the tropopause due to Bry from BTP.
Dimitrios K Papanastasiou - One of the best experts on this subject based on the ideXlab platform.
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the very short lived Ozone depleting substance chbr 3 bromoform revised uv absorption spectrum atmospheric lifetime and Ozone Depletion Potential
Atmospheric Chemistry and Physics, 2014Co-Authors: S A Mckeen, Dimitrios K Papanastasiou, James B. BurkholderAbstract:Abstract. CHBr3 (bromoform) is a short-lived atmospheric trace compound that is primarily of natural origin and is a source of reactive bromine in both the troposphere and stratosphere. Estimating the overall atmospheric impact of CHBr3 and its transport to the stratosphere requires a thorough understanding of its atmospheric loss processes, which are primarily UV photolysis and reaction with the OH radical. In this study, UV absorption cross sections, σ (λ ,T), for CHBr3 were measured at wavelengths between 300 and 345 nm at temperatures between 260 and 330 K using cavity ring-down spectroscopy. The present results are compared with currently recommended values for use in atmospheric models, and the discrepancies are discussed. A parameterization of the CHBr3 UV spectrum for use in atmospheric models is developed, and illustrative photolysis rate calculations are presented to highlight the impact of the revised σ (λ, T) values on its calculated local lifetimes. For example, the photolysis rate in the tropical region obtained with the present spectral data is 10–15% lower (longer lifetime) than obtained using currently recommended cross section values. Seasonally dependent Ozone Depletion Potentials (ODPs) for CHBr3 emitted in the Indian sub-continent were calculated to be 0.10, 0.34, 0.72, and 0.23 (winter, spring, summer, fall) using the semi-empirical relationship of Brioude et al. (2010).
James B. Burkholder - One of the best experts on this subject based on the ideXlab platform.
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cbrf3 halon 1301 uv absorption spectrum between 210 and 320k atmospheric lifetime and Ozone Depletion Potential
Journal of Photochemistry and Photobiology A-chemistry, 2015Co-Authors: Eric L. Fleming, Max R. Mcgillen, Charles H. Jackman, Francois Bernard, James B. BurkholderAbstract:Abstract CBrF3 (Halon-1301) is a man-made Ozone depleting substance that is a major source of bromine in the Earth’s stratosphere. Halon-1301 is predominantly removed from the atmosphere by UV photolysis in the stratosphere at wavelengths between 200 and 225 nm. The existing level of uncertainty in the Halon-1301 UV absorption spectrum temperature-dependence directly impacts the ability to model stratospheric Ozone chemistry and climate change. In this work, the UV absorption spectrum of Halon-1301 between 195 and 235 nm was measured over the temperature range 210–320 K. An empirical parameterization of the spectrum and its temperature dependence is presented. The present results are critically compared with results from previous studies and the current recommendation for use in atmospheric models. A global annually averaged lifetime for Halon-1301 of 74.6 (73.7–75.5) years was calculated using a 2-D atmospheric model and the present results. The range of lifetimes given in parenthesis represents the possible values due solely to the 2σ uncertainty in the Halon-1301 UV spectrum obtained in this work. In addition, the CBrF3 Ozone Depletion Potential was calculated using the 2-D model to be 18.6 (±0.1) using the UV spectrum and 2σ uncertainty from this work.
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the very short lived Ozone depleting substance chbr 3 bromoform revised uv absorption spectrum atmospheric lifetime and Ozone Depletion Potential
Atmospheric Chemistry and Physics, 2014Co-Authors: S A Mckeen, Dimitrios K Papanastasiou, James B. BurkholderAbstract:Abstract. CHBr3 (bromoform) is a short-lived atmospheric trace compound that is primarily of natural origin and is a source of reactive bromine in both the troposphere and stratosphere. Estimating the overall atmospheric impact of CHBr3 and its transport to the stratosphere requires a thorough understanding of its atmospheric loss processes, which are primarily UV photolysis and reaction with the OH radical. In this study, UV absorption cross sections, σ (λ ,T), for CHBr3 were measured at wavelengths between 300 and 345 nm at temperatures between 260 and 330 K using cavity ring-down spectroscopy. The present results are compared with currently recommended values for use in atmospheric models, and the discrepancies are discussed. A parameterization of the CHBr3 UV spectrum for use in atmospheric models is developed, and illustrative photolysis rate calculations are presented to highlight the impact of the revised σ (λ, T) values on its calculated local lifetimes. For example, the photolysis rate in the tropical region obtained with the present spectral data is 10–15% lower (longer lifetime) than obtained using currently recommended cross section values. Seasonally dependent Ozone Depletion Potentials (ODPs) for CHBr3 emitted in the Indian sub-continent were calculated to be 0.10, 0.34, 0.72, and 0.23 (winter, spring, summer, fall) using the semi-empirical relationship of Brioude et al. (2010).
Kwang Ho Song - One of the best experts on this subject based on the ideXlab platform.
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catalytic dehydrofluorination of 1 1 1 2 3 pentafluoropropane hfc 245eb to 2 3 3 3 tetrafluoropropene hfo 1234yf using in situ fluorinated chromium oxyfluoride catalyst
Catalysis Today, 2016Co-Authors: Jae Wook Choi, Jeongmyeong Ha, Kwang Ho SongAbstract:Abstract As part of an effort to prepare a refrigerant with zero Ozone Depletion Potential (ODP) and with a low global warming Potential (GWP), the catalytic dehydrofluorination of 1,1,1,2,3-tetrafluoropropane (HFC-245eb) is performed to produce 2,3,3,3-tetrafluoropropene (HFO-1234yf). Cr2O3 prepared by the sol-gel method (Cr2O3(SG)) exhibits good catalytic activity attributable to the formation of surface chromium oxyfluoride, which exhibits better catalytic activity with high-valent chromium and a larger fluorine content. The formation of chromium oxyfluoride from chromium oxide is achieved by in-situ fluorination in the early stage of dehydrofluorination, avoiding the conventional fluorination method using toxic HF.
