Scientific Assessment of Stratospheric Ozone: 1989, volume 2. Appendix: AFEAS Report

The results are presented of the Alternative Fluorocarbon Environmental Acceptability Study (AFEAS), which was organized to evaluate the potential effects on the environment of alternate compounds targeted to replace fully halogenated chlorofluorocarbons (CFCs). All relevant current scientific information to determine the environmental acceptability of the alternative fluorocarbons. Special emphasis was placed on: the potential of the compounds to affect stratospheric ozone; their potential to affect tropospheric ozone; their potential to contribute to model calculated global warming; the atmospheric degradation mechanisms of the compounds, in order to identify their products; and the potential environmental effects of the decomposition products. The alternative compounds to be studied were hydrofluorocarbons (HFCs) with one or two carbon atoms and one or more each of fluorine and hydrogen

Barometric pumping with a twist: VOC containment and remediation without boreholes. Phase I

The majority of the planned remediation sites within the DOE complex are contaminated with volatile organic compounds (VOCs). In many instances the contamination has not reached the water table, does not pose an immediate threat, and is not considered a high priority problem. These sites will ultimately require remediation of some type, either by active vapor extraction, bioremediation, or excavation and ex-situ soil treatment. The cost of remediating these sites can range from $50 K to more than$150 K, depending on site characteristics, contaminants, and remediation method. Additionally, for many remediated sites, residual contamination exists which could not practically be removed by the applied remediation technology. These circumstances result in modest sites with contamination of limited risk, but by regulation they must still be controlled. A remediation solution being developed by Science and Engineering Associates, Inc. (SEA) for the Department of Energy serves as an in-situ containment and extraction methodology for sites where most or all of the contamination resides in the vadose zone soil. The approach capitalizes on the advective soil gas movement resulting from barometric pressure oscillations

Hydrate Phase Transition-Risk, Energy Potential and CO2 Storage Possibilities

Natural gas hydrate (NGH) can cause crucial flow assurance problems to the oil and gas industry. It is being considered as a potential vast energy resource for the world in the future. It could also potentially provide a long-term offshore storage possibility for carbon dioxide. Therefore, the risk of hydrate formation during processing and pipeline transport of natural gas and CO2, thermodynamics and kinetics of hydrate formation, and simultaneous CH4 production from in-situ hydrate and CO2 long-term offshore storage in form of CO2 hydrate are important research concerns. The main scientific method used in this project is classical thermodynamics based on thermodynamic properties calculated using methods in Quantum Mechanics and Classical Mechanics. Classical thermodynamics was used together with residual thermodynamics description for every phase; this includes the hydrate phase, to analyse different routes to hydrate formation between hydrate formers (or guest molecules) and water. NGHs are formed from water and natural gas at high pressures and low temperatures conditions under the constraints of mass and heat transport. The problem is that natural gas is usually produced together with water and operations are usually at elevated pressures and low temperatures. Current industrial approach for evaluating the risk of hydrate formation is based on liquid water condensing out of the bulk gas at dewpoint and at a specific pressure-temperature (P-T) condition. In this method, the maximum allowable water content will be kept below the projected dew-point mole-fractions during transport, considering the operational P-T conditions. However, a previous study in our research group suggested that solid surface, particularly rust (Hematite) is another precursor to hydrate formation; rust provides another route for liquid water to drop out through the mechanism of adsorption. And pipelines are generally rusty before they are mounted in place for operations. The two approaches have been applied to study the risk of water dropping out from natural gas from different real gas fields. The approach of adsorption of water onto Hematite (rusty surfaces) completely dominates. The dew-point method over-estimates the safe limit (maximum mole-fraction) of water that should be permitted to flow with bulk gas about 18 – 20 times greater than when the effect of hematite is considered, depending on the specific gas composition. That suggests that hydrate may still form when we base our hydrate risk analysis on dew-point technique. The presence of higher hydrocarbon (C2+) hydrate formers causes a decrease in allowable water content with increasing concentration of ethane, propane and isobutane for the temperature range of 273 – 280 K. As their concentrations increase in the bulk gas, these C2+ act to draw down the water tolerance of the gas mixture to a point where they completely dominate or dictate the trends. For the inorganic components, CO2 has little or no significant impact on the allowable upper-limit of water when its concentration increases. While the presence of H2S causes a consideration reduction in water tolerance of the system as its concentration in the mixture increases. The presence of 1 mol% of H2S in the bulk gas may cause about 1 % reduction in water tolerance. The reduction in maximum content of water could be up to about 2 – 3 % and up to about 4 – 5 % if the concentration increases to 5 mol% and 10 mol% respectively. It is not appropriate to interpret hydrate stability entirely based on equilibrium P–T curves as often done in literature. The hydrate stability curve of CO2 hydrate has lower pressures (thus more stable) compared to that of CH4 hydrate but only to a certain temperature. That is the quadruple-point were phase-split occurs causing the pressures of CO2 hydrate going above that of CH4 hydrate due to the increase in density caused by the CO2 liquid phase. A free energy analysis revealed that CO2 hydrate has lower free energy across the entire temperature range, thus more stable at all the temperatures. Therefore, hydrate stability should rather be based on free energy analysis since in real situations hydrate cannot reach equilibrium. Consequently, the most stable hydrate is the hydrate with the minimum free energy. The hydrate with the least or most negative free energy will first form under constraints of mass and heat transport, then followed by the subsequent most stable hydrate. Among the hydrocarbon guest molecules studied, the most stable hydrate is hydrate of isobutane, followed by that of propane, and then by ethane. Induction times are sometimes mistaken as hydrate nucleation times, which is why some works report nucleation times of hours. Hydrate formation is a nano-scale process, and the hydrate nucleation times computed for both heterogeneous and homogeneous hydrate formation in this project are in nano-seconds. The long times experienced before hydrates are detected are caused by mass transport limitations due to the initial thin hydrate film formed at the interface between water and the hydrate former interface. Another misunderstanding about hydrate nucleation is that only one uniform-phase hydrate is formed from either a single guest or a multicomponent mixtures of hydrate formers. Based on the combined first and second laws of thermodynamics, nucleation will commence with the most stable hydrates, under the constraints of heat and mass transport. Nucleation can happen via different routes: hydrate formation will originate at the interface between the guest molecule phase and water. A range of hydrates with different compositions of the original hydrate former(s), different densities and different free energies will form from aqueous solution (dissolve hydrate formers). Theoretically, hydrate can also nucleate from water dissolved in the guest molecules phase. Such hydrate cannot be stable because of the little mass of water that will dissolved in the guest molecule phase as well as limitation of heat transport, especially in the case of hydrocarbon guests like methane which is a poor heat conductor. The thermodynamics of simultaneous natural gas production from in-situ CH4 hydrate and CO2 long-term offshore storage was studied. Two processes where studied: mixing of nitrogen with the CO2 and injecting the mixture into the hydrate reservoir and the implication of the enthalpies of hydrate phase transitions. The study indicated that the proportion of CO2 needed in the CO2/N2 mixture is only about 5 – 12 % without H2S in the gas stream. While it is about 4 – 5 % and 2 – 3 % with the presence of 0.5 % and 1 % of H2S respectively. Virtually, direct solid-state CO2–CH4 swap will be extremely kinetically restricted, and it is not significant. Enthalpy changes of hydrate phase transition in literature obtained from experiment, Clausius-Clapeyron and Clapeyron models are limited and often lack some vital information needed for proper understanding and interpretation. Information on thermodynamic properties such as pressure, temperature (or both), hydrate composition, and hydration number are often missing. The equation of state utilised is also not stated in certain literature. Several experimental data also lack any measured filling fractions, and frequently, they apply a constant value which suggests that the values may be merely guessed. In addition, older data based on Clapeyron equation lack appropriate volume corrections. The calculations of both Clausius-Clapeyron and Clapeyron equations are based on hydrate equilibrium data of pressure and temperature from experiments or calculated data. But hydrate formation is a non-equilibrium process. Information about superheating above the hydrate equilibrium conditions to totally dissociate the gas hydrate to liquid water and gas is normally lacking. The values vary considerably in such a way that some of them decided to base their results on average values over a range of temperatures. For example, Gupta et al. (2008) conducted a study with experiment, Clausius-Clapeyron and Clapeyron equations but all the results varied substantially. We therefore propose a method based on residual thermodynamics which does not have the limitations of the current methods. We do not expect much agreement of our results with a lot of the literature, firstly, because of the limitations of the other methods, especially, the simplicity of both the Clapeyron and Clausius-Clapeyron equations. Secondly, the remarkable disagreement among current data reported in literature. The residual thermodynamics scheme used in this project is based on the unique and straight forward thermodynamic relationship between change in free energy and enthalpy change, with thermodynamic properties evaluated from residual thermodynamics. Such properties are change in free energy as the thermodynamic driving force in kinetic theories, equilibrium curves, and enthalpy changes of hydrate phase transition. With residual thermodynamics, real gas behaviour taking into account thermodynamic deviations from ideal gas behaviour can be evaluated. The results of enthalpy changes of carbon dioxide hydrate phase transitions using residual thermodynamics in this project are around 10 – 11 kJ/mol guest molecule greater than the ones of methane hydrate phase transition for 273 – 280 K range of temperatures. Calculations based on kJ/mol hydrate within the same temperature range gave 0.5 – 0.6 kJ/mol hydrate. Anderson’s results using Clapeyron equation are a little close to the results obtained in this work, precisely 10 kJ/mol and 7 kJ/mol guest molecule at 274 K and at 278 K respectively. While Kang et al. (2001) in their experiment put this difference at 8.4 kJ/mol guest molecule at 273.65 K. However, in replacement of in-situ CH4 hydrate with CO2, it is not the temperature-pressure curve that is most essential, but what is most important is the difference in free energies of both hydrates, CH4 hydrate and CO2 hydrate, and the enthalpies of CO2 hydrate formation relative to the enthalpies of CH4 hydrate dissociation. The free energy of CO2 hydrate is around 1.8 – 2.0 kJ/mol more negative or lower than the free energy of CH4 hydrate within a temperature range of 273.15 – 283.15 K (0 – 10 °C). That confirms that hydrate of CO2 is more stable thermodynamically than hydrate of CH4. It is pertinent to state that this proposition is still under investigation, and it is still under development. In addition, there are constraints that are also under study. Hydrate formation at the interface between CO2 gas and liquid water is very rapid, forming a hydrate film which will quickly block the pore spaces thereby limiting further CO2 supply. Studies also need to be done on finding the most efficient and effective way to reduce the thermodynamic driving force, either by using any thermodynamic inhibitor or other substances.Doktorgradsavhandlin

Critical areas: Satellite power systems concepts

Critical Areas are defined and discussed in the various areas pertinent to satellite power systems. The presentation is grouped into five areas (General, Space Systems, Solar Energy Conversion, Microwave Systems, and Environment/Ecology) with a sixth area (Power Relay) considered separately in an appendix. Areas for Future Consideration as critical areas are discussed in a second appendix

Toxicological profile for chloromethane

supersedes cdc:115334tp106.pd

Matrix isolation study of ozone with some halogen containing alkanes

The main aim of this research is to study, using Fourier-transform infrared spectroscopy, the photochemical reaction of ozone with some halogen-containing alkanes in low temperature matrices. The reactions between halogenated alkanes and ozone, studied in this thesis, can be applied to gas phase atmospheric research with regard to ozone depletion. One example, not expanded on in this thesis, is the search for ozone-friendly species (refrigerants, propellants etc.), especially since one of the provisions of the Montreal protocol is to phase-out such species. Matrix reactions are carried out at low temperatures and, this means that the reactants are often effectively unable to react and, thus many 'reactive' or otherwise 'difficult to study' compounds can be stabilized and studied spectroscopically. In these experiments, the matrices must be photolysed in order to initiate a reaction; and we have used infrared, visible and ultraviolet irradiation to initiate reactions. By careful selection of the photolysis wavelength range used to irradiate the matrix it is possible to form different products and, thus reveal the photochemical reaction path. The matrix environment also enables us to detect reactions that would not occur in the gas phase; in a matrix the species are held in close proximity to one another, allowing a variety of secondary reactions to occur, whilst, in the gas phase the primary products usually separate rapidly. This facet of a matrix reaction - by which the products are held closely together - has enabled us to study a range of nearest-neighbour complexes that were generated in situ by careful selection of the precursors. Using matrix techniques, the reaction of ozone with halogen-containing compounds leads to the observations below. In the cases of the single iodine-containing precursors ozone binds weakly with the iodine atom, and this modifies the photochemistry of ozone, allowing the effective dissociation of ozone. The transfer of an oxygen atom to the precursor leads to the formation of several new species. In addition to detecting these new species, it was possible to determine wavelength-dependent photolysis pathways for these reactions. The reaction of ozone with the halogen-containing precursors, studied in this thesis, leads invariably to the production of carbonyl complexes. The rigid nature of the matrix means that the spectra of these perturbed carbonyl complexes can be recorded, and the wavenumbers of specific bands compared between similar species. Similar comparisons are made between the carbon monoxide...Lewis acid complexes which tend to be produced after further photolysis of the carbonyl complexes. Trends are observed for these complexes in which the bands of the complex are shifted from those of the isolated species; this shift can be related to the Lewis acid strength of the perturber. Finally, the carbonyl (COBrF), formed in the reaction of tribromofluoromethane with ozone, dissociates via an alternative mechanism to produce the radical-atom pair ECO and Br. The study of the subsequent reactions of these two might possibly have important implications with regard to processes occurring in the atmosphere

Toxicological profile for chloromethane : draft for public comment

VERSION HISTORYDate VersionJanuary 2022 Draft for public comment releasedJune 2009 Addenda releasedDecember 1998 Final toxicological profile releasedtp106.pdf20221105

Carbon tetrachloride

prepared by Syracuse Research Corporation under contract no. 205-1999-00024 ; prepared for U.S. Department of Health and Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry."August 2005."Chemical manager(s)/author(s): Obaid Faroon,.Jessilynn Taylor, Nickolette Roney, ATSDR, Division of Toxicology, Atlanta, GA; Margaret E. Fransen,.Suzanne Bogaczyk,.Gary Diamond,.Syracuse Research Corporation, Syracuse, NY --P. ix."A toxicological profile for carbon tetrachloride, draft for public comment was released in September 2003. This edition supersedes any previously released draft or final profile"--P. iii."This toxicological profile is prepared in accordance with guidelines developed by the Agency for Toxic Substances and Disease Registry (ATSDR) and the Environmental Protection Agency (EPA). The original guidelines were published in the Federal Register on April 17, 1987"--P. v.Also available via the World Wide Web.Includes bibliographical references (p. 213-301) and index

Removal mechanisms for volatile organic compounds in the atmosphere and in waste gas streams

Atmospheric lifetimes were calculated from OH radical and Cl atom rate constants measured using a relative rate - smog chamber technique for a series of haloalkanes and aliphatic and cyclic ketones. The reactivities of these organics with respect to OH radicals and Cl atoms were observed to be affected by the presence and position of halogen atoms and the presence of a carbonyl oxygen atom for haloalkanes and ketones respectively; polarity effects and stenc contributions were also observed to influence the magnitude of the rate constant values. The atmospheric lifetimes calculated for the organics under investigation were all sufficiently short to ensure that they would undergo transformation in the troposphere and thus could not be considered a threat to stratospheric ozone. O f the organic compounds investigated in this work dichloromethane is the most commonly used chemical in the industrial work place, therefore methods of monitoring and removing this compound are important. Biofiltration techniques are currently being considered for tlus purpose as they are efficient, cheap and clean. In this work a laboratory-scale biofilter unit containing peat fibre as the filter material was used to remove dichloromethane from an artificially generated gas stream. Inlet and outlet gas concentrations were monitored and the percentage removal and the elimination capacity of the biofilter calculated over a time period of 32 weeks. The percentage removal was calculated to be between 40 - 80% and the elimination capacity was found to be a function of the inlet gas concentration

Scientific assessment of ozone depletion: 1991

Over the past few years, there have been highly significant advances in the understanding of the impact of human activities on the Earth's stratospheric ozone layer and the influence of changes in chemical composition of the radiative balance of the climate system. Specifically, since the last international scientific review (1989), there have been five major advances: (1) global ozone decreases; (2) polar ozone; (3) ozone and industrial halocarbons; (4) ozone and climate relations; and (5) ozone depletion potentials (ODP's) and global warming potentials (GWP's). These topics and others are discussed