Study of Fluoroapatite Reactions: The Effect of Metaphosphate Melts on Fluorine-Containing Substances

Abstract

The interaction of metaphosphate melts with fluorine-containing substances was studied. The major variables were composition and temperature. Sodium metaphosphate in contact with fluorides or fluoroapatite gives rise to reactions above 550°C, which liberate fluorine in the form of volatile compounds, mostly as hydrogen fluoride. At least one gas containing phosphorus and fluorine is released from. the melt. Evidence points to phosporyl trifluoride (POF₃). The relative amcunt of HF to POF₃ depends on the concentration of combined hydrogen in the melt and water vapor in the atmosphere above the melt. The rate of the removal of the gaseous reaction products is markedly affected by the depth of the layer through which they have to diffuse. The interaction of metaphosphate melts with fluorides is a general reaction independent of the type of fluoride, and produces the same major products in the gaseous phase. Calcium ions are more effective in furthering the gas evolution from the melt than sodium ions. The structure of synthetic fluoroapatite is destroyed by sodium metaphosphate above 550°C, and under certain conditions the fluorine content of the sample is reduced by 80% within an hour. The yield in the fluorine-containing gases shows a maximum at about 640°C.     

GC of Catalytic Reactions Products Involved in the Promising Fuel Synthesis

Catalytic reactions involved in the synthesis of the promising kinds of novel fuel and products formed in these reactions were systematized according to the resulting fuel type. Generalization of the retention of the substances comprising these products is presented. Chromatograms exhibiting their separation on chromatographic materials with the surface of different chemical properties are summarized. We propose procedures for gas-chromatographic analysis of the catalytic reactions products formed in the synthesis of hydrogen, methanol, dimethyl ether and hydrocarbons as a new generation of fuel alternative to petroleum and coal. For partial oxidation of methane into synthesis gas, on-line determination of the components obtained in the reaction was carried out by gas chromatography and gas analyzer based on different physicochemical methods (IR spectroscopy and electrochemical methods). Similarity of the results obtained using these methods is demonstrated.

     

Fluorination rates of polyolefins as a function of structure and gas atmosphere

Polyolefins and fluoropolymers were reacted with elemental fluorine under carefully controlled conditions in a thermobalance adapted to be compatible with fluorine gas. The fluorination reactions were monitored by measuring the mass increase as a result of hydrogen substitution by fluorine. The mass increase was directly proportional to the square root of the fluorination time, which indicates that fluorine gas diffusion to the unreacted surface is the rate determining step. The fluorination rate was increased by increasing the fluorine concentration and the fluorination temperature. The fluorination rate is higher when nitrogen rather than helium is used as diluting gas. The fluorination rate for the reaction in which CO₂ is used as diluting gas is the same as during fluorination with nitrogen as diluting gas, while the presence of oxygen dramatically decreased the fluorination rate. Oxygen is incorporated during fluorination with oxygen as diluting gas, while no functionalization was observed when CO₂ was employed as diluting gas. The effect of polymer structure on fluorination was studied. Poly(vinylfluoride) gained mass during fluorination, while no reaction was observed for poly(vinylidenefluoride). The reaction rate for polypropylene was higher than that of polyethylene. In celebration of the 60^th birthday of Dr. Andrew K. Galwey     

Quantum chemical study of the reaction mechanism of ozone and methane with fluorine and chlorine atoms

Ab initio calculations of the potential energy surface for the F + O₃ and Cl + O₃ reactions have been performed using the G3 and G3MP2 methods, which optimize the geometry configuration of reactants, products, intermediates, and transition states. The results show that fluorine atoms react with ozone as violently as chlorine atoms. At the same time, we have studied the reaction mechanisms of F atoms and Cl atoms with methane. It is found that fluorine atoms prefer to react with methane and chlorine atoms with ozone when there is competition between ozone and methane. Therefore, we can reasonably explain why chlorine atoms play the main role of reactants depleting ozone, while the more active fluorine atoms deplete less ozone. © 2002 Wiley Periodicals, Inc.; DOI 10.1002/qua.10119     

Hydrogen Reduction of MoF6 and Molybdenum Carbide Formation in RF Inductively Coupled Low-Pressure Discharge: Experiment and Equilibrium Thermodynamics Consideration

The physical plasma parameters, temperature and electron number density, are studied in the RF-IC (RF inductively coupled) discharge at a reduced pressure of 3 Torr in mixtures of MoF₆ with Ar, H₂ and CH₄. The emission spectra of mixtures are investigated. It is shown that in the presence of argon, the concentration of free electrons in plasma and dissociation rate of MoF₆ increase. A main role of molecular hydrogen is the generation of atomic hydrogen that binds atomic fluorine and leads to the formation of gaseous and solid products. Exhaust gas mixtures exiting the reactor are analyzed by mass spectrometry. It is shown that for all cases, the conversion of MoF₆ into reaction products is close to 100%. A thermodynamic analysis of the equilibrium composition of MoF₆ systems with Ar, H₂ and CH₄ was carried out and the obtained results are in good agreement with experimentally observed composition of the solid and gas phases. Analysis of solid deposits from mixture MoF₆/H₂/Ar revealed the presence of molybdenum powder and large amount of amorphous MoF_x. The deposit obtained from mixtures with methane, MoF₆/H₂/Ar/CH₄, contained crystalline molybdenum carbide, Mo₃C₂.

     

油浆高温快速裂解过程的气固相产物研究

采用高频炉快速热解装置研究油浆的高温快速热解特性,考察了热解温度、氮气流量对气固相产物的组成和产率的影响。温度是影响气相产物产率的关键因素,气相产物主要为甲烷、氢气和乙烯,升高温度可提高甲烷和氢气的产率,而乙烯产率受高温下二次反应的影响在800℃到达最大值后逐渐降低,乙烷、丙烯产率较小且受二次反应的影响在700℃到达最大值后逐渐降低,温度高于800℃时会有少量乙炔生成且升温可提高乙炔产率。增加氮气流量可降低甲烷、氢气分压,缩短乙烯、丙烯等在高温区的停留时间,从而增加气相产物的产率。积炭产率随热解温度升高迅速增加,氮气流量的增加能够削弱二次反应从而降低积炭产率。     

Hydrodechlorination of dichlorodifluoromethane (CFC-12) over Pd/Al2O3 and Pd-Au/Al2O3 catalysts

During an initial stage of the reaction of CCl₂F₂ with hydrogen on alumina-supported Pd and Pd-Au catalysts, an extensive defluorination occurs. However, at steady state, this undesired defluorination is greatly reduced; CH₄ and CH₂F₂ constitute the only major reaction products. A temperature programmed hydrogen treatment study shows retention of fluorine (and carbon) in used catalysts. This revised version was published online in June 2006 with corrections to the Cover Date.     

Photodecomposition of water with methane over titanium oxide photocatalysts modified with metal

Metal-loaded titanium oxide photocatalysts produced hydrogen in the photodecomposition of water vapor with methane in the flow reactor. Ag/TiO₂ has the highest activity in comparison with other metal-loaded catalysts. The experiment in the absence of methane indicated that methane could effectively function as a reducing reagent of water. The significant decrease in the hydrogen formation rate with the time on stream was observed under all reaction conditions. The recalcination and the hydrogen rereduction of the used catalyst led to the restoration of the activity of the hydrogen formation. The adsorption of products and/or reactants on the catalyst surface seemed to cause these deactivations of the hydrogen formation.     

Unravelling the Enigma of Nonoxidative Conversion of Methane on Iron Single-Atom Catalysts

The direct, nonoxidative conversion of methane on a silica-confined single-atom iron catalyst is a landmark discovery in catalysis, but the proposed gas-phase reaction mechanism is still open to discussion. Here, we report a surface reaction mechanism by computational modeling and simulations. The activation of methane occurs at the single iron site, whereas the dissociated methyl disfavors desorption into gas phase under the reactive conditions. In contrast, the dissociated methyl prefers transferring to adjacent carbon sites of the active center (Fe₁©SiC₂), followed by C−C coupling and hydrogen transfer to produce the main product (ethylene) via a key −CH−CH₂ intermediate. We find a quasi Mars–van Krevelen (quasi-MvK) surface reaction mechanism involving extracting and refilling the surface carbon atoms for the nonoxidative conversion of methane on Fe₁©SiO₂ and this surface process is identified to be more plausible than the alternative gas-phase reaction mechanism.     

Katalytischer Wasserstoffaustausch des Äthans am Nickelkatalysator

Zusammenfassung Der Wasserstoffaustausch zwischen Äthan und Deuterium bzw. Tritium wird an Nickelpulver als Katalysator untersucht. Die auf Wasserstoff bezogene Reaktionsordnung nimmt im Temperaturgebeit 147–323°C zu, während die in bezug auf Äthan sich konträr verändert. Auch die Aktivierungsenergie nimmt ein wenig ab. Die Ergebnisse der Untersuchungen mittels Deuterium zeigen, daß die Hauptprodukte des Austausches Äthan-d₂ und Äthan-d₆ sind. Das Verhältnis der Anfangsgeschwindigkeiten der Bildung beider Produkte hängt von der Katalysatoraktivität und der Temperatur ab. Auf Grund des Vergleichs dieser Ergebnisse mit denen des Methanaustausches kann der große Unterschied im Verhalten beider Stoffe durch die Verschiedenheit der Adsorptionsmechanismen erklärt werden.

---

Catalytic hydrogen exchange reaction of ethane over aNi catalyst

The hydrogen exchange between ethane and deuterium as well as tritium has been investigated over nickel powder catalyst. In the temperature range from 147 to 323°C the order of reaction with respect to hydrogen increases whereas for ethane the reverse is observed. The activation energy also decreases slightly. The study with deuterium showed that the main products of exchange were ethane-d₂ and ethane-d₆. The ratio of the initial rater of formation of these products depended on the catalyst activity and the temperature. By comparing these results with those of methane exchange the large difference in behaviour between methane and ethane can be ascribed to the difference in adsorption mechanism.

---

---

Mit 4 Abbildungen

---

Herrn Prof. Dr.E. Broda zum 60. Geburtstag gewidmet.     

Photochlorination of tetramethylsilane and hexamethyldisilane in the gas phase

Preliminary studies of the reaction of chlorine with tetramethylsilane and hexamethyldisilane in the gas phase show that the photochlorination of tetramethylsilane is complex, giving different products from the corresponding reaction in solution and having an explosion boundary. At pressures below the explosion boundary the main products are ethylene, hydrogen chloride, dimethylchlorosilane, and more highly chlorinated methylsilanes. Above the explosion boundary main products after explosion are methane, acetylene, ethylene, hydrogen chloride, and silicon tetrachloride. Hexamethyldisilane reacts rapidly with chlorine in the dark, as it does in solution, forming mainly trimethylchlorosilane along with similar products to those found with tetramethylsilane. Subsequent photochlorination of trimethylchlorosilane follows a similar course to that of tetramethylsilane in the gas phase. Tentative mechanisms involving “hot” molecules are suggested.     

Radiolysis of 2-acetylfuran in 2-propanol in absence of atmospheric oxygen

Gamma radiolysis of 2-acetylfuran (AF) in 2-propanol, in absence of atmospheric oxygen, has been investigated. The radiation yields of hydrogen, methane at different doses as well as radiolytic products in solution were determined. The radiolytic products were determined by gas chromatography coupled with mass spectrometry. The mechanisms for formation of detected radiolytic products and the effect of (AF) concentration on hydrogen and methane yields are discussed.     

Control of the Sorption Properties and Wettability of a Nonwoven Polypropylene Material by Direct Gas Fluorination

The effect of direct gas fluorination on the surface properties of a nonwoven polypropylene material was studied. Direct gas fluorination with mixtures of different compositions allows directional variation of the surface properties of the nonwoven polypropylene material. The surface becomes more hydrophobic when using a mixture of fluorine and nitrogen but less hydrophobic when using a mixture of fluorine, oxygen, and nitrogen. The modification leads to changes in the chemical composition of the surface and in the roughness of the material. The nonwoven polypropylene materials thus obtained exhibit increased sorption capacity for spent oil or water, respectively. Variation of the properties of the nonwoven polypropylene material allows expansion of its applications.

     

Mode correlation of product pairs in the reaction OH+CD4-->HOD+CD3

The hydrogen abstraction reaction from methane by a hydroxyl radical produces two polyatomic molecules. Each product has several vibrational modes that characterize distinct, concerted motions of the constituent atoms of the molecule. This communication describes the first measurement that maps out the coincident information on how the mode of excitation of one product varies with that of the other co-product. Such information on mode correlation of product pairs is particularly appealing in that it provides intuitively a glimpse of the reaction paths by which the chemical transformation occurs.     

On the hydrogenation of CO and CO2 over copper/zirconia and palladium/zirconia catalysts

Summary Zirconia-supported hydrogenation catalysts were obtained by activation of the amorphous precursors Cu₇₀Zr₃₀ and Pd₂₅Zr₇₅ under CO₂ hydrogenation conditions. Catalysts of comparable compositions prepared by co-precipitation and wet impregnation of zirconia with copper- and palladium salts, respectively, served as reference materials. The catalyst surfaces under reaction conditions were investigated by diffuse reflectance FTIR spectroscopy. Carbonates, formate, formaldehyde, methylate and methanol were identified as the pivotal surface species. The appearance and surface concentrations of these species were correlated with the presence of CO₂ and CO as reactant gases, and with the formation of either methane or methanol as reaction products. Two major pathways have been identified from the experimental results. i) The reaction of CO₂/H₂-mixtures on Cu/zirconia and Pd/zirconia primarily yields surface formate, which is hydrogenated to methane without further observable intermediates. ii) The catalytic reaction between CO and hydrogen yields -bonded formaldehyde, which is subsequently reduced to methylate and methanol. Interestingly, there is no observable correlation between absorbed formaldehyde or methylate on the one hand, and gas phase methane on the other hand. The reactants, CO₂ and CO, can be interconverted catalytically by the water gas shift reaction. The influence of the metals on this system of coupled reactions gives rise to different product selectivities in CO₂ hydrogenation reactions. On zirconia-supported palladium catalysts, surface formate is efficiently reduced to methane, which consequently appears to be the principal CO₂ hydrogenation product. In contrast, there is a favorable reaction pathway on copper in which CO is reduced to methanol without C-O bond cleavage; surface formate does not participate significantly in this reaction. In CO₂ hydrogenations on copper/zirconia, methanol can be obtained as the main product, from a sequence of the reverse water gas shift reaction followed by CO reduction.     

Pathways of liquefied petroleum gas pyrolysis in hydrogen plasma: A density functional theory study

A density functional theory (DFT) study has been conducted in this work to investigate the pyrolysis pathways of propane and n-butane, which are the main components of liquefied petroleum gas (LPG), for better understanding the pyrolysis behavior of LPG in hydrogen thermal plasma. Over 60 possible reactions are considered. The reaction enthalpies and activation energies of these reactions are calculated and analyzed with a Gaussian method of B3LYP and basic set of 6-31G (d,p). A most possible reaction pathway is brought up. According to this reaction pathway, the main products of LPG pyrolysis are acetylene, ethylene, methane, ethane and extra hydrogen. Acetylene mainly comes from the pyrolysis of propylene and ethylene, and hydrogen abstraction reactions are the main source of extra hydrogen gas. Active H· radicals are found to play a very important role in many reactions, and they can remarkably lower the energies needed for reactions.     

甲烷在Ni/TiO2催化剂表面的活化

考察了Ni/TiO2催化剂甲烷部分氧化和二氧化碳重整制合成气的反应活性,实验表明,以TiO2为载体的镍系催化剂对于甲烷部分氧化制合成气反应具有较好的活性,尤其对H2的选择性较高,对二氧化碳重整制合成气反应具有较好的低温反应活性.采用脉冲-质谱在线分析等技术,在无气相氧条件下向Ni/TiO2催化剂脉冲CH4,发现甲烷在催化剂表面的活化（转化）及其氧化产物的选择性与金属催化剂表面氧的浓度密切相关.CH4与Ni/TiO2催化剂作用过程中存在明显的氢溢流和氧溢流现象,可能是这种溢流效应使得Ni/TiO2催化剂具有良好的反应活性和抗积碳性能.     

Reaction of hexadecafluorobicyclo[4.4.0]dec-1(6)-ene with diethylamine

The spectral characteristics of products formed in the reaction of an incompletely fluorinated impurity in perfluorodecalin, hexadecafluorobicyclo[4.4.0]dec-1(6)-ene, with amines in various solvents were studied. The reaction rates in various solvents were compared, and the distribution of the reaction products between perfluorodecalin and solvents was examined.     

Hydrogen and syngas production from two-step steam reforming of methane using CeO2 as oxygen carrier

CeO2 oxygen carrier was prepared by precipitation method and tested by two-step steam reforming of methane (SRM). Two-step SRM for hydrogen and syngas generation is investigated in a fixed-bed reactor. Methane is directly converted to syngas at a H2/CO ratio close to 2 : 1 at a high temperature (above 750 °C) by the lattice oxygen of CeO2; methane cracking is found when the reduction degree of CeO2 was above 5.0% at 850 °C in methane isothermal reaction. CeO2?δ obtained from methane isothermal reaction can split water to generate CO-free hydrogen and renew its lattice oxygen at 700 °C; simultaneously, deposited carbon is selectively oxidized to CO2 by steam following the reaction (C+2H2O→CO2+2H2). Slight deactivation in terms of amounts of desired products (syngas and hydrogen) is observed in ten repetitive two-step SRM process due to the carbon deposition on CeO2 surface as well as sintering of CeO2.     

Uncommon oxidative transformations of acetic and propionic acids

The oxidative decarbonylation of acetic and propionic acids with the formation of the corresponding alcohol and alkyl carboxylate is observed in the Rh^III/Cu^I,II/Cl⁻ catalytic system in the presence of O₂ and CO. The decarbonylation of propionic acid in a deuterated solvent results in the substitution of hydrogen atoms by deuterium in the alkyl part of the products to form CH₂DCOOD (CHD₂COOH) and CHD₂COOD (CD₃COOH). The subsequent decarbonylation of deuterated acetic acids affords the corresponding deuteromethanols detected as esters with propionic and deuteroacetic acids. The substitution of the hydrogen atom by deuterium in the alkyl part of molecules of the products of oxidative decarbonylation of propionic acid, when the reaction is carried out in a deuterated solvent, indicates that propionic acid behaves as saturated hydrocarbon and blocks the oxidation of poorly soluble methane. Unlike propionic acid, acetic acid enters only the oxidative decarbonylation reaction and does not block methane oxidation.