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Ethylene/ethane separation is a critical and energy-consuming process in the chemical industry due to the similar properties of the compounds and the great need of ethylene for e.g., polymer production. Many materials have been studied for their implementation as membranes as an energetically favorable alternative to conventional distillation and adsorption processes. Metal-organic frameworks (MOF) have revealed promising properties as highly permeable and selective membranes. Among the most studied and promising MOF candidates is ZIF-8, known for its thermal stability and small pores connected by narrow-sized windows. In this work, we present an analysis of the influence of parameters such as temperature, feed pressure and feed flowrate on the separation of ethylene/ethane through a thin ZIF-8/alumina disc membrane. We observed that the temperature has a significant effect on the separation. The ethylene permeance increased with decreased temperature and reached 8.1 × 10−7 mol/(m2·s·Pa) at −30 °C. At this temperature, the ethylene/ethane selectivity was 2.5. The study concluded with a considerable enhancement of the permeance of ZIF-8 membranes for ethylene/ethane separations, while maintaining a good selectivity compared to the reported values in the literature. The results have important implications for the development of more cost-effective and energy-efficient membrane-based separation technologies for ethylene purification., Validerad;2023;Nivå 2;2023-11-08 (marisr);License fulltext: CC BY-NC-ND

Ethylene/ethane separation is a critical and energy-consuming process in the chemical industry due to the similar properties of the compounds and the great need of ethylene for e.g., polymer production. Many materials have been studied for their implementation as membranes as an energetically favorable alternative to conventional distillation and adsorption processes. Metal-organic frameworks (MOF) have revealed promising properties as highly permeable and selective membranes. Among the most studied and promising MOF candidates is ZIF-8, known for its thermal stability and small pores connected by narrow-sized windows. In this work, we present an analysis of the influence of parameters such as temperature, feed pressure and feed flowrate on the separation of ethylene/ethane through a thin ZIF-8/alumina disc membrane. We observed that the temperature has a significant effect on the separation. The ethylene permeance increased with decreased temperature and reached 8.1 × 10−7 mol/(m2·s·Pa) at −30 °C. At this temperature, the ethylene/ethane selectivity was 2.5. The study concluded with a considerable enhancement of the permeance of ZIF-8 membranes for ethylene/ethane separations, while maintaining a good selectivity compared to the reported values in the literature. The results have important implications for the development of more cost-effective and energy-efficient membrane-based separation technologies for ethylene purification.

We use global airborne observations of propane (C3H8) and ethane (C2H6) from the Atmospheric Tomography (ATom) and HIAPER Pole-to-Pole Observations (HIPPO), as well as U.S.-based aircraft and tower observations by NOAA and from the NCAR FRAPPE campaign as tracers for emissions from oil and gas operations. To simulate global mole fraction fields for these gases, we update the default emissions' configuration of C3H8 used by the global chemical transport model, GEOS-Chem v13.0.0, using a scaled C2H6 spatial proxy. With the updated emissions, simulations of both C3H8 and C2H6 using GEOS-Chem are in reasonable agreement with ATom and HIPPO observations, though the updated emission fields underestimate C3H8 accumulation in the arctic wintertime, pointing to additional sources of this gas in the high latitudes (e.g., Europe). Using a Bayesian hierarchical model, we estimate global emissions of C2H6 and C3H8 from fossil fuel production in 2016-2018 to be 13.3 ± 0.7 (95% CI) and 14.7 ± 0.8 (95% CI) Tg/year, respectively. We calculate bottom-up hydrocarbon emission ratios using basin composition measurements weighted by gas production and find their magnitude is higher than expected and is similar to ratios informed by our revised alkane emissions. This suggests that emissions are dominated by pre-processing activities in oil-producing basins.

The aim is to produce aliphatic liquid hydrocarbons using heterogeneous ethylene oligomerization. Thiscould potentially produce renewable synthetic fuels. Heterogeneous catalysis has some advantages overhomogeneous catalysis regarding some sustainability aspects. To achieve this, a setup was built using a heatedfixed bed reactor with an in-situ has chromatography to study conversion and gaseous products, and ex-situGC as well as NMR for analyzing liquid products. Ethylene was oligomerized on a commercial ZSM-5 zeoliteunder varying temperature conditions and feed gas dilution with hydrogen or helium. The gas and liquidproducts were analyzed and evaluated. Additionally, the ZSM-5 was studied at different silica to alumina ratios. The thesis discusses how conversion, liquid yield and selectivity of gas products using GC together withanalysis of liquid products using H-NMR can be used as a simple and quick evaluation. The liquid product isevaluated by the distribution of olefinic and aromatic hydrocarbon species using the hydrogen signal area inthe characteristic chemical shifts of olefinic and aromatic hydrogen. At 250-400oC, 6 bar of ethylene, with andwithout feed dilution, and WHSV of 204 h-1, conversion was consistently above 95% for the diluted 400oCruns. Though the liquid yield fell to around 6%, compared to the best yield at 18% for the pure 300oC run.Diluting the feed had a positive effect on increasing olefinic hydrogen signal while decreasing aromatichydrogen signal. The difference between diluting with H2 or helium had a surprisingly small effect. Decreasingthe Si/Al ratio had no significant effect on performance, while increasing the Si/Al ratio made the zeolite loseits catalytic ability. With a pure ethylene feed the lowest aromatic hydrogen signal was found at 350oC, whilethe olefinic signal did not vary too much with temperature. With diluted feed the higher temperature did leadto a lower olefinic hydrogen signal and higher aromatic hydrogen signal.

In this research, a binary eutectic composition of KCl and MgCl2 supported over lanthanum exchanged FAU (faujasite) zeolite has been investigated for the oxidative dehydrogenation (ODH) of ethane. The catalyst was prepared by the thermal treatment of La-FAU with a mechanical mixture of alkali chlorides under a flow of helium at 500 degrees C. The eutectic mixture of alkali chlorides formed at this temperature and a molten layer were spread over the support. Synthesized fresh and spent catalysts were characterized to obtain information about changes in crystallinity, textural properties, phase content, chemical composition, and morphology of the catalyst over the reaction time. The initial conversion of ethane was 80% with ethene as the main product (65% yield). The catalyst deactivation has been demonstrated over time on the stream (TOS). The characterization methods confirmed that the chlorine was being removed from the catalyst. The side products detected by mass spectroscopy, including chlorinated hydrocarbons, have been found as a key pathway of chlorine removal from the catalyst. The exchange of chlorine for oxygen in the catalyst led to a significant decrease in the activity and production of higher hydrocarbons and their oxygenates as side products of the ODH reaction., Katalyzátory na bázi binárních eutektických směsí KCl a MgCl2 nanesených na La-FAU zeolitech byly testovány v oxidativní dehydrogenaci etanu. Katalyzátory byly charakterizovány z pohledu krystalinity, texturních vlastností, fázového obsahu a morfologie. Počáteční konverze etanu byla 80 % s etenem jako hlavním produktem (výtěžek 65 %).

The reactions here explored are microscopic analogs of Newton cradle: left thing attack, right thing leaves and central thing remains unaffected. We have studied symmetric S2 reactions, X = N or E, where the attacking and leaving molecules are the same: HN, HB, HC and the central molecules are HB (S2@B), HN (S2) or HC (S2@C). Non-symmetric reactions with different initial and final complexes were also studied and examples where the elements of the lateral molecules differ, P vs N.

Ethane recovery in a conventional turboexpander process is optimized considering different demethanizer pressures and different feeds: a lean gas and a rich one. The design variables are varied, while meeting process constraints, in order to find the optimum conditions achieving the maximum profit. The analysis covers the whole process including the refrigeration part, and the entire typical demethanizer pressure range. The optimum ethane recovery is compared with the maximum possible recovery for each value of the demethanizer pressure. Recommendations are given regarding the selection of the level of ethane recovery, along with the demethanizer pressure, and refrigeration recovery system.

The composition of associated gas differs greatly from each other when studied in the context of fields and depends on the type of fields and development conditions, i-liquefied gases are obtained not only from satellite gases, but also from gas condensate fields.

The ignition delay time (IDT) characteristics of new ternary and quaternary blended C1 – C3 gaseous hydrocarbons, including methane/ethane/ethylene and methane/ethane/ethylene/propane, are studied over a wide range of mixture composition, temperature (∼800 – 2000 K), pressure (∼1 – 135 bar), equivalence ratio (∼0.5 – 2.0), and dilution (∼75 – 90%) using both experimental data and kinetic modeling tools. In this regard, all of the experimental tests were designed using the Taguchi approach (L9) to fulfill the experimental matrix required to generate a comprehensive set necessary to validate a detailed chemical kinetic model. High- and low-temperature IDTs were recorded using low/high-pressure shock tubes (L/HPST) and rapid compression machines (RCM), respectively. The model predictions using NUIGMech1.2 are evaluated versus all of the newly recorded experimental data. Moreover, the individual effects on IDT predictions of the parameters studied, including mixture composition and pressure, are investigated over the temperature range. The results show that NUIGMech1.2 can reasonably reproduce the experimental IDTs over the wide range of the conditions studied. The constant-volume simulations using the chemical kinetic mechanism reveal the synergistic/antagonistic effect of blending on IDTs over the studied temperature range so that IDTs in certain temperature ranges are very sensitive to even small changes in mixture composition.

In aquifers, acetylene (C2H2) is a product of abiotic degradation of trichloroethene (TCE) catalyzed by in situ minerals. C2H2 can, in turn, inhibit multiple microbial processes including TCE dechlorination and metabolisms that commonly support dechlorination, in addition to supporting the growth of acetylenotrophic microorganisms. Previously, C2H2 was shown to support TCE reductive dechlorination in synthetic, laboratory-constructed cocultures containing the acetylenotroph Pelobacter sp. strain SFB93 and Dehalococcoides mccartyi strain 195 or strain BAV1. In this study, we demonstrate TCE and perchloroethene (PCE) reductive dechlorination by a microbial community enriched from contaminated groundwater and amended with C2H2 as the sole electron donor and organic carbon source. The metagenome of the stable, enriched community was analyzed to elucidate putative community functions. A novel anaerobic acetylenotroph in the phylum Actinobacteria was identified using metagenomic analysis. These results demonstrate that the coupling of acetylenotrophy and reductive dechlorination can occur in the environment with native bacteria and broaden our understanding of biotransformation at contaminated sites containing both TCE and C2H2IMPORTANCE Understanding the complex metabolisms of microbial communities in contaminated groundwaters is a challenge. PCE and TCE are among the most common groundwater contaminants in the United States that, when exposed to certain minerals, exhibit a unique abiotic degradation pathway in which C2H2 is a product. C2H2 can act as both an inhibitor of TCE dechlorination and of supporting metabolisms and an energy source for acetylenotrophic bacteria. Here, we combine laboratory microcosm studies with computational approaches to enrich and characterize an environmental microbial community that couples two uncommon metabolisms, demonstrating unique metabolic interactions only yet reported in synthetic, laboratory-constructed settings. Using this compre

We report herein the preparation, characterization, and catalytic performance of a series of heterogeneous catalysts featuring highly dispersed zinc sites on zeolitic SSZ-13 and ZSM-5 frameworks. The materials are evaluated in the CO2-assisted oxidative ethane dehydrogenation, a very important reaction for the synthesis of platform chemicals. In particular, we find that Zn2.92/SSZ-13 exhibits high reactivity in the conversion of C2H6 and CO2 and high ethene selectivity. In line with the experimental results, we show that the selective character of the catalyst is due to the characteristic compositional structure of the support and its topology that can effectively confine CO2 molecules. An in-depth molecular analysis via operando studies and DFT calculations shows that the rate-limiting step of the reaction with CO2 is the second C-H bond dissociation to give C2H4. The addition of CO2 effectively reduces the energy barrier of this step, favoring desorption of C2H4 while limiting byproduct formation. Overall, this work demonstrates the breakthrough potential of catalysts made of highly dispersed zinc species on zeolites in relevant transformations.

In the present work, a simple soft chemistry method was employed to prepare cobalt mixed oxide (Co3O4) materials, which have shown remarkably high activity in the heterogeneously catalyzed total oxidation of low reactive VOCs such as the light alkanes propane, ethane, and methane. The optimal heat-treatment temperature of the catalysts was shown to depend on the reactivity of the alkane studied. The catalytic activity of the Co3O4 catalysts was found to be as high as that of the most effective catalysts based on noble metals. The physicochemical properties, from either the bulk (using XRD, TPR, TPD-O2, and TEM) or the surface (using XPS), of the catalysts were investigated to correlate the properties with the catalytic performance in the total oxidation of VOCs. The presence of S1 low-coordinated oxygen species at the near surface of the Co3O4-based catalysts appeared to be linked with the higher reducibility of the catalysts and, consequently, with the higher catalytic activity, not only per mass of catalyst but also per surface area (enhanced areal rate). The co-presence of propane and methane in the feed at low reaction temperatures did not negatively affect the propane reactivity. However, the co-presence of propane and methane in the feed at higher reaction temperatures negatively affected the methane reactivity.

Here, we report the kinetic energy distributions (KEDs) of the fragment ions produced from multiply ionized ethane (C₂H₆) molecules in single electron capture collisions with 1.2 MeV C²⁺. To systematically investigate the fragmentation dynamics, the KEDs were obtained as functions of the charge state of the intermediate C₂H₆r⁺* ions r transiently generated prior to fragmentation. r was determined from coincidence measurement of the fragment ions and the number of emitted electrons. The KEDs are drastically different depending on the number of broken C–H bonds. The underlying causes are explained by the variation of the relative contributions of the multiply ionized states and preferential fragmentation pathways. For instance, CHn⁺ fragment ions with smaller n exhibit lower KEs because they are likely to be correlated with H⁺ emission, which carries away a large portion of the KE release. In addition, we report the KEDs of H₃⁺ produced from doubly and triply charged states.

[EN] The investigation here presented studies the effect of the synthesis temperature (from 80 to 110 degrees C) and the time (from 1 to 4 days) employed to precipitate catalyst precursors by reflux method, on the physic-chemical and the catalytic properties of the resulting Mo-V-Te-Nb mixed oxide catalysts for both propane partial oxidation into acrylic acid and ethane oxidative dehydrogenation (ODH) to ethylene. The insight obtained has allowed an important optimization of the not commonly used reflux method to prepare Mo-V-Te-Nb oxide materials with competitive catalytic performance. The yields achieved overcome those from optimized catalysts prepared by conventional hydrothermal method, and approach those reached with catalysts prepared using the "slurry method". The optimum rise for the synthesis temperature is found as a key factor for the reflux method. It allows access to an increased vanadium content into the reflux precipitate, which favors the formation of a pseudo-amorphous Mo-V-Te-Nb oxometallate. This precipitate behaves as a precursor for the crystallization, during the solid-state activation step at high-temperature (600 degrees C/N-2), of the structure type (TeO)(2)M20O56 (M = Mo, V, Nb), key for the selective conversion of propane or ethane. On the other hand, for the optimum temperature of synthesis, i.e. 110 degrees C, higher synthesis time of the precursor leads to smaller crystal sizes in the final catalyst (higher specific surface areas) and lowers the average oxidation state of vanadium from V+5 to V+4, which significantly enhances the catalytic behavior.

Nowadays, the issue of global warming and related environmental problems got widespread awareness among scientific society, politics, the industry as well as it has affected our everyday life. The reason for such a negative impact on the atmosphere is attributed mainly to human activities. It is thought that one of the most dangerous greenhouse gases is carbon dioxide (CO2). Nevertheless, the problem of hydrocarbon emissions began to receive particular attention due to the exponential growth of methane emissions in the atmosphere. What is the reason for such behaviour and what about other hydrocarbons, first of all, ethane, propane and butane isomers? In this work, it was proposed that geological emissions, mainly the emission from the dissociation of natural gas hydrates is one of the main reasons for the dramatic rise in hydrocarbon emissions to the atmosphere. Natural gas hydrates are not only composed of methane and water cages but have in their structure a broad range of hydrocarbons, including ethane, propane, butanes and some others. The purpose of this thesis is to investigate the sources of non-methane volatile hydrocarbons in the atmosphere, examine their impact on the environment and explore the correlation of hydrocarbon emissions with CO2 emissions. To reveal the impact of natural gas hydrates to the hydrocarbon budget it was assumed, that hydrocarbons that are contributing to the natural gas hydrate formation have deep mantle origin. To confirm this hypotheses high-pressure high temperature investigation of propane and butanes were conducted. The results of this investigation are presented in this thesis. To model extreme thermobaric conditions the diamond-anvil cell technique with two-sided laser heating was used. The method of Raman spectroscopy was applied for the analysis. The results received show that propane and butane isomers stable in the pressure up to 40 GPa at ambient temperature. Propane remains stable at temperatures up to 900 K. At t, I dagens samhälle har global uppvärmning och relaterade miljöproblem blivit en högst aktuell fråga inom vetenskap, politik, näringsliv samt påverkat vår vardag på individnivå. Den huvudsakliga anledningen till den negativa påverkan på atmo-sfären tillskrivs mänskliga aktiviteter. Man tror att en av de farligaste växthusgaserna är koldioxid (CO2). Ändå har problemet med kolväteutsläpp fått särskild uppmärksamhet på grund av den exponentiella tillväxten av metanutsläpp i atmosfären. Vilka är orsakerna bakom detta fenomen, samt hur står det till med andra kolvätens påverkan: etan, propan och butanisomerer? En huvudhypotes i denna avhandling är att geologiska utsläpp, främst utsläpp som har att göra med dissociation av naturgashydrat, är en av de främsta orsakerna till den dramatiska ökningen av kolväteutsläpp till atmosfären. Naturgashydrater består inte bara av metan- och vattenburar, utan har ett brett spektrum av kolväten (in-klusive etan, propan, butaner och några andra) i sin struktur. Syftet med denna avhandling är att undersöka källor till flyktiga icke-metan kolväten i atmosfären, samt undersöka deras påverkan på miljön och undersöka korrelationen mellan kolväteutsläpp och koldioxidutsläpp. För att avslöja effekterna av naturgashydrater på kolvätebudgeten, antogs det i denna avhandling att kolväten som bidrar till naturgashydratbildningen har sitt ursprung i djupmanteln. För att bekräfta denna hypotes genomfördes en högtrycksundersökning av propan och butaner under hög temperatur. Resultatet av undersökningen presenteras i denna avhandling. För att modellera extrema termobariska förhållanden tillämpas en diamant-städcellteknik med dubbelsidig laseruppvärmning. I analysen till-lämpas metoden för Raman-spektroskopi. Resultaten visar att propan och butaner är stabila i tryckområdet 3-22 GPa vid omgivningstemperatur. Propan förblir stabil vid temperaturer upp till 900 K. Vid temperaturer> 900 K börjar kemiska transformationer av propan att ge en blandning av lät

Biomass burning is an important component of the Earth system in terms of global biogeochemistry, atmospheric composition, climate, terrestrial ecology, and land use. This study examines published ice core trace gas measurements of acetylene, ethane, and methane, which have been used as proxies for paleofire emissions. We investigate the consistency of these records for the past 1,000 years in terms of (1) temporal trends in global fire emissions and (2) quantitative estimates for changes in global burning (dry matter burned per year). Three-dimensional transport and box models were used to construct emissions scenarios for the trace gases consistent with each ice core record. Burning histories were inferred from trace gas emissions by accounting for biome-specific emission factors for each trace gas. The temporal trends in fire inferred from the trace gases are in reasonable agreement, with a large decline in biomass burning emissions from the Medieval Period (MP: 1000–1500 CE) to the Little Ice Age (LIA: 1650–1750 CE). However, the three trace gas ice core records do not yield a consistent fire history, even assuming dramatic (and unrealistic) changes in the spatial distribution of fire and biomes. Substantial changes in other factors such as meteorological transport or atmospheric photochemical lifetimes appear to be required to reconcile the trace gas records.

[EN] A comparative study of the catalytic properties for the oxidation of C2-C3 alkanes and olefins has been carried out over unpromoted and M-promoted NiO catalysts (Me¿=¿K, La, Ce, al, Zr, Sn, Nb). The catalysts have been characterized by several physico-chemical techniques (UV Raman, Visible Raman, FTIR of adsorbed CO and XPS). The characteristics of promoter elements are of paramount importance, since they are able to modify both the nature of the active nickel and the concentration of electrophilic O2¿/O¿ oxygen species. Thus, a relatively high acidity and valence of the promoter oxide (with oxidation state higher than¿+¿3) are necessary to achieve high selectivity to olefins during the oxidative dehydrogenation (ODH) of C2¿C3 alkanes. In addition, an inverse correlation between the selectivity to the corresponding olefin and the concentration of electrophilic oxygen species has been observed, although the selectivity to propene during propane ODH is lower than the selectivity to ethylene achieved during ethane ODH. On the other hand, a very low influence of alkane conversion on the selectivity to the corresponding olefins is observed. This behaviour can be explained by considering that the reaction rate for olefin combustion is lower than the reaction rate for alkane oxidation. However, the comparative study of the oxidation of alkanes and olefins suggest that the differences observed between the ODH of propane and ethane are not related to the reactivity of olefins, but to the different number and reactivity of C¿H bonds in both alkanes. A discussion on the importance of the concentration of active sites and the characteristics of the alkanes fed on the selectivity to olefin during the alkane ODH is also presented.

In this work, the solubility of methane and ethane were studied in aqueous dispersion of silver nanoparticles (1, 5, and 10 ppm) at temperatures of 1, 2.5, 10, and 11.5 degrees C for methane and 2.5, 5, 10, 15.5 degrees C for ethane and at initial pressures 1 to 5.5 and 0.35-2.15 MPa for methane and ethane, respectively. The nanoparticles were synthesized and characterized through UV-vis spectroscopy, dynamic light scattering (DLS), and transmission electron microscopy (TEM) image. The results demonstrated that silver nanoparticles increased the solubility of methane and ethane up to 13 and 16% compared with pure water, respectively. The solubility of methane and ethane were enhanced by increasing the nanoparticles mass loading. The effect of nanoparticles on ethane solubility was more significant than methane solubility.

We provide the first large field investigation of more than 20 gold deposits and sites along the Keraf suture zone, covering an area of ~15,000 km2. The area shows diverse structural settings for gold mineralization in greenschist, amphibolite, and hornfels metamorphosed rocks. The reverse fault and dyke-hosted settings appear to be the most favourable for forming gold deposits. Two major N-S-trending, ~300-km-long corridors of deformation are delineated (West and East) but only the West seems important for gold. From fluid inclusions, 6 types of fluids are distinguished based on specific volatile contents and proportions. Most types can be related to fluid evolution by hydrothermal reactions and phase separations from a primitive fluid of metamorphic origin, containing H2O, CO2, N2, CH4, C2H6, and H2. Regional hydrothermal fields are identified based on the combinations of structural settings and fluid types. The northern field is defined as a single large hydrothermal system accounting for the mineralization of the 3 gold deposits (WG-03, UTM and Central). For sites along the West Corridor, such as Toubi, Anas, NW and Shereik, multiple and overlapping hydrothermal systems are necessary to explain the various fluid types and structural settings, even at the deposit scale (Shereik). Conversely, other sites (SW, Yasmine, Korup, Saijd, Dardora, Negeim, and SE) formed by localized individual hydrothermal systems. The documentation of fluids containing ethane at numerous sites and deposits is the most significant outcome. Such ethane-bearing fluids are generated by the metamorphism of carbonaceous-pyritic sedimentary rocks. These rocks are considered one of the best sources for providing ligands and gold for the formation of orogenic gold deposits. Consequently, the Keraf suture zone, composed mainly of carbonaceous turbidites, is interpreted to have provided such source rocks in the suture zone and below the adjacent cratons during the collision, forming orogenic gold

The direct conversion of ethane to higher-valued petrochemical feedstock such as benzene, toluene and xylenes (BTX) has become more economically attractive because of the recent shale gas revolution. The selectivity towards BTX and catalyst deactivation represent significant technical challenges in this process. In this work, we synthesized a series of bi-functional Pt on acidic ZSM-5 catalysts to investigate the effect of platinum nanoparticle distribution and location on selectivity and deactivation. The best catalyst was Pt encapsulated in desilicated ZSM-5 that remained stable after 15 h of reaction resulting in 60% higher conversion and 75% higher BTX selectivity than Pt supported on conventional acidic ZSM-5 zeolite.

Biomass burning plays a major role in atmospheric chemistry, carbon cycling, and climate. To understand and better predict how biomass burning may change in the future, it is important to investigate how biomass burning has varied in the past. Proxy records of biomass burning over long time periods are necessary to identify the link between biomass burning and climate. This information is needed by Earth system models to make accurate projections about future climate change and biomass burning. In this dissertation, new ice core measurements are used to reconstruct biomass burning variability over the last 2,000 years. The trace gases ethane and acetylene are released to the atmosphere during biomass burning events. New analytical techniques utilizing a wet-extraction method coupled with gas-chromatography and high-resolution mass spectrometry analysis were developed to measure these gases in polar ice cores. The abundance of ethane and acetylene were measured in ice cores from Summit, Greenland, West Antarctic Ice Sheet (WAIS) Divide, Antarctica, and South Pole, Antarctica. The ice core ethane and acetylene records exhibit similar temporal variability over the 2,000-year period. Over Greenland, little variability is observed in the ethane and acetylene levels. Over Antarctica, they both decline substainitally after 1500 CE, ethane by roughly 30% and acetylene by 50%. Using chemistry transport modeling, this decline in Antarctic ethane and acetylene was attributed to a decline in biomass burning emissions in the non-boreal (tropical) biome, rather than the boreal forests, from the warmer Medieval Period to the cooler Little Ice Age. My study presents the first millennial scale record of these trace gases in polar ice cores and demonstrates that long-term paleo-climate records from these reactive, trace-level gases are attainable. The results show spatial and temporal variability in biomass burning emissions which were likely driven by climate. More work is needed to

[ES] La presente tesis doctoral se sitúa en el marco de la actual transición energética, que plantea la sustitución progresiva de materias primas de origen fósil por fuentes renovables, tanto para la obtención de productos químicos como para la producción de combustibles. En este contexto de transición paulatina a las renovables, y teniendo en cuenta los últimos pronósticos, las fuentes fósiles (fundamentalmente gas natural) y derivados de la biomasa, jugarán un papel fundamental durante el cambio. Se ha llevado a cabo un estudio sobre el empleo de óxidos metálicos (basados en bronces de wolframio o en óxido de níquel), como catalizadores para: i) la transformación de derivados de biomasa: de glicerol a acroleína/ácido acrílico; y de compuestos oxigenados de cadena corta presentes en efluentes acuosos (procedentes de tratamientos de extracción de bio-aceites de pirolisis) a combustibles; y ii) la transformación de componentes del gas natural, concretamente la obtención de etileno a partir de etano, mediante deshidrogenación oxidativa (ODH). El trabajo se presenta desde una perspectiva de la química de materiales, haciendo hincapié en las propiedades fisicoquímicas de los distintos sistemas catalíticos, empleando técnicas de caracterización convencionales e in situ, además de reacciones modelo (transformación de metanol y etanol), con el objetivo de entender las funciones catalíticas presentes en cada caso. Tanto para la transformación de glicerol en fase gas, como para la valorización de mezclas acuosas de compuestos oxigenados de cadena corta, se han utilizado catalizadores basados en bronces de wolframio. Se ha tratado de poner de manifiesto la gran versatilidad composicional y estructural (con el consiguiente control de las propiedades funcionales), que presentan este tipo de materiales. En este sentido, las propiedades ácidas y redox de catalizadores W-V-O pueden ser moduladas, para una misma concentración de vanadio, mediante el control de la relación de fases, [CA] Aquesta tesi doctoral es situa dins del marc de l'actual transició energètica, la qual planteja la substitució progressiva de les primeres matèries d'origen fòssil per fonts renovables, tant per a l'obtenció de productes químics com per a la producció de combustibles. En aquest context de transició gradual a les renovables, i tenint en compte els últims pronòstics, les fonts fòssils (principalment el gas natural) i els derivats de la biomassa, exerciran un paper fonamental durant aquest canvi. S'ha dut a terme un estudi sobre la utilització d'òxids metàl·lics (basats en bronzes de wolframi o en òxid de níquel), com a catalitzadors per a: i) la transformació de derivats de la biomassa: de glicerol a acroleïna/àcid acrílic; i de compostos oxigenats de cadena curta presents en efluents aquosos (procedents de tractaments d'extracció de bio-olis de la piròlisi) a combustibles; i ii) la transformació de components del gas natural, concretament l'obtenció d'etilè a partir d'età, mitjançant la deshidrogenació oxidativa. El treball es presenta des del punt de vista de la química de materials, posant l'accent en les propietats fisicoquímiques dels diferents sistemes catalítics, utilitzant tècniques de caracterització convencionals i in situ, a més de reaccions model, amb l'objectiu d'entendre les funcions catalítiques presents en cadascun dels casos. Tant per a la transformació del glicerol en fase gasosa com per a la valorització de les mescles aquoses de compostos oxigenats de cadena curta, s'han utilitzat catalitzadors basats en bronze de wolframi. S'ha intentat posar de manifest la gran versatilitat de composicions i estructures (amb el conseqüent control de les propietats funcionals) que presenten aquest tipus de materials. En aquest sentit, les propietats àcides i redox dels catalitzadors de W - V - O poden ser modulades, per a una mateixa concentració de vanadi, mitjançant el control de la relació de fases cristal·lines (hexagonal i monoclínica) de l'òxid de wolfr, [EN] The present doctoral thesis is set within the scope of the current energy transition, which considers the progressive substitution of non-renewable fossil sources by renewable feedstocks for the production of chemicals and fuels. In this context of gradual transition, and according to recent energy outlooks, fossil sources (especially natural gas) and biomass feedstocks will play a key role during the shift. A study on the use of metal oxides (based on tungsten bronzes or nickel oxides) as catalysts for different reactions has been conducted. Particularly, they have been studied as catalytic materials for: i) the transformation of biomass-derived feedstocks: glycerol transformation into acrolein/acrylic acid, and the transformation of short-chain oxygenates present in aqueous effluents (derived from extraction processes of pyrolysis bio-oils) into fuels; and ii) the valorization of natural gas components, i.e. the transformation of ethane into ethylene by oxidative dehydrogenation. The work is presented from a materials chemistry perspective, emphasizing the physicochemical characteristics of the different catalytic systems by using conventional and in situ characterization techniques and model reactions (gas phase methanol and ethanol transformation); with the aim of understanding the specific catalytic functionalities present in each case. For both gas phase glycerol transformation and the valorization of short-chain oxygenates aqueous mixtures, catalyst based on tungsten oxide bronzes have been used. The compositional and structural versatility of this structural types (with the subsequent control of their functional properties) will be highlighted. In this sense, the acid-redox properties of W-V-O catalysts can be modulated by controlling the crystalline phase composition in the materials (i.e. hexagonal and monoclinic polymorphs of tungsten oxide) at a fixed V concentration. This effect has been studied by using the gas-phase aerobic transformation of meth

Mixtures of gaseous and liquid fuels have the potential to induce flash boiling under in-cylinder conditions close to the top dead center, something that can be expected to be suitable for a premixed diesel combustion that demands a way to enhance lean mixture formation. The present study mixes ethane, which is a natural gas component, into diesel fuel as ethane has a high vapor pressure that facilitates flash boiling and as ethane has a low cetane number that prolongs the ignition delay. This paper investigates spray characteristics of a diesel fuel-Ethane mixture, and the engine performance and exhaust emissions are evaluated in a single cylinder engine. The test results show that the flash boiling enhances the lean mixture formation, and realizes combustion with low soot and low NOx without EGR (exhaust gas recirculation) while also improving thermal efficiency. An additional test was performed to identify the effects of the flash boiling and the ignition delay, and the results show that the long ignition delay plays the most important role in the thermal efficiency and emission changes and that the flash boiling facilitates the formation of leaner mixtures that lower the overall combustion rate and achieves very low NOx emissions.

Emissions of C 2 -C 5 alkanes from the U.S. oil and gas sector have changed rapidly over the last decade. We use a nested GEOS-Chem simulation driven by updated 2011NEI emissions with aircraft, surface, and column observations to (1) examine spatial patterns in the emissions and observed atmospheric abundances of C 2 -C 5 alkanes over the United States and (2) estimate the contribution of emissions from the U.S. oil and gas industry to these patterns. The oil and gas sector in the updated 2011NEI contributes over 80% of the total U.S. emissions of ethane (C 2 H 6 ) and propane (C 3 H 8 ), and emissions of these species are largest in the central United States. Observed mixing ratios of C 2 -C 5 alkanes show enhancements over the central United States below 2 km. A nested GEOS-Chem simulation underpredicts observed C 3 H 8 mixing ratios in the boundary layer over several U.S. regions, and the relative underprediction is not consistent, suggesting C 3 H 8 emissions should receive more attention moving forward. Our decision to consider only C 4 -C 5 alkane emissions as a single lumped species produces a geographic distribution similar to observations. Due to the increasing importance of oil and gas emissions in the United States, we recommend continued support of existing long-term measurements of C 2 -C 5 alkanes. We suggest additional monitoring of C 2 -C 5 alkanes downwind of northeastern Colorado, Wyoming, and western North Dakota to capture changes in these regions. The atmospheric chemistry modeling community should also evaluate whether chemical mechanisms that lump larger alkanes are sufficient to understand air quality issues in regions with large emissions of these species., SCOPUS: ar.j, info:eu-repo/semantics/published

Tato diplomová práce se zabývá studiem difuze v zeolitických materiálech typu MFI a FER pro uhlovodíky C1-C4. Blíže se zaměřuje na metodou ZLC s ohledem na testování její vhodnosti pro měření difuzních koeficientů lehkých uhlovodíků, návrhem metodiky, vyhodnocení dat získaných měřením a jejich porovnáním s dříve publikovanými daty z jiných metod., This Thesis deals with the study of C1-C4 light hydrocarbons diffusion in zeolite materials type MFI and FER. Thesis focuses on the ZLC method from point of view of its suitability for measuring diffusion coefficients, measurement methodology development, evaluation of measured data and their comparison with previously published data from other methods., Fakulta chemicko-technologická, Studentka přednesla prezentaci diplomové práce. doc. Hájek seznámil komisi s posudky. Proběhla diskuse k tématu diplomové práce: 1. V práci jsou uvedeny vzorce převzaté z literatury, které obsahují chyby. Jsou převzaté s chybami? Jaké tvary by byly správné? 2. Na základě jakého předpokladu jsou odvozeny použité vzorce pro výpočet difuzního koeficientu? 3. Jaká je přesnost naměřených výsledků? prof. Čapek: Čím by mohlo být způsobeno, že ZLC metodu nelze využít pro měření difuzních koeficientů C1 - C3 uhlovodíků? Jak by šlo měření, případně modely vylepšit? prof. Bulánek: Co znamenají symboly uvedené v tabulkách v prezentaci diplomové práce? Jaky mají dané symboly význam? doc. Skopal: Ověřovala jste experimentálně zjednodušující předpoklady platnosti modelu pro ZLC? doc. Komersová: Jaké by bylo porovnání hodnot difuzních koeficientů pro biologické systémy?, Dokončená práce s úspěšnou obhajobou

Biomass burning drives changes in greenhouse gases, climate-forcing aerosols, and global atmospheric chemistry. There is controversy about the magnitude and timing of changes in biomass burning emissions on millennial time scales from preindustrial to present and about the relative importance of climate change and human activities as the underlying cause. Biomass burning is one of two notable sources of ethane in the preindustrial atmosphere. Here, we present ice core ethane measurements from Antarctica and Greenland that contain information about changes in biomass burning emissions since 1000 CE (Common Era). The biomass burning emissions of ethane during the Medieval Period (1000-1500 CE) were higher than present day and declined sharply to a minimum during the cooler Little Ice Age (1600-1800 CE). Assuming that preindustrial atmospheric reactivity and transport were the same as in the modern atmosphere, we estimate that biomass burning emissions decreased by 30 to 45% from the Medieval Period to the Little Ice Age. The timing and magnitude of this decline in biomass burning emissions is consistent with that inferred from ice core methane stable carbon isotope ratios but inconsistent with histories based on sedimentary charcoal and ice core carbon monoxide measurements. This study demonstrates that biomass burning emissions have exceeded modern levels in the past and may be highly sensitive to changes in climate.

Miniemulsion polymerization has received significant attention because polymer particles are generated directly from monomer droplets. However, the problem with current methods of synthesizing miniemulsions is the requirement for high energy mixing approaches. The ability to synthesize miniemulsions using low energy methods would be of very significant academic and practical importance. In the present thesis, radical polymerization in heterogeneous systems under compressed gases has been investigated with a view to the development of low energy miniemulsion polymerization.The mechanistic aspects of radical polymerization of styrene in aqueous emulsions pressurized by CO2 have been investigated. It has been demonstrated that CO2 pressurization to the so-called transparency pressure (PT) of an emulsion comprising styrene/hexadecane/Dowfax 8390/water leads to a decrease in droplet size as well as an increase in emulsion stability. However, the radical polymerization under CO2 pressure reveals that these polymerizations do not proceed as true miniemulsion polymerization systems (i.e., via exclusive monomer droplet nucleation) but are also characterized by a significant contribution of particle formation via secondary nucleation as in an ab initio emulsion polymerization.Photopolymerization of miniemulsions under compressed CO2 has been performed under UV and visible-light irradiation. For the UV-light system, the rate of polymerization of a transparent miniemulsion under compressed CO2 was found not to be affected by the transparency. However, the transparency affected the polymerization rate under visible-light irradiation. This is due to the transparency of refractive index matched miniemulsions favours less light scattering than turbid miniemulsions at the at the appropriate wavelength (transparency is associated with high visible light transmission).Pressurization of an emulsion comprising styrene/hexadecane/Dowfax 8390/water to PT has been performed under compresse

This paper investigates the oxidative dehydrogenation of ethane to produce ethylene at low temperatures (500 degrees C) in metallic structured substrates. To check this point, the FeCrAlloy (R) monoliths with different channel sizes (289-2360 cpsi) were prepared. The monoliths were coated with a Ni/Al2O3 catalyst (by washcoating of alumina and the latter nickel impregnation) and characterized by Scanning Electron Microscopy and Energy-Dispersive X-ray analysis (SEM-EDX), Temperature-Programmed Reduction (TPR), X-ray Diffraction (XRD) and X-ray Photoelectron Spectroscopy (XPS). The catalytic results showed that all monoliths coated with similar to 300 mg of catalyst presented similar ethane conversion (15%) at 450 degrees C. However, the lowest selectivity to ethylene was found for the monolith with the lower channel size and the higher geometric surface area, where a heterogeneous catalyst layer with Ni enriched islands was generated. Therefore, it can be said that the selectivity to ethylene is linked to the distribution of Ni species on the support (alumina). Nevertheless, in all cases the selectivity was high (above 70%). On the other hand, the stability in reaction tests of one of the coated monoliths was done. This structured catalyst proved to be more stable under reaction conditions than the powder catalyst, with an initial slight drop in the first 8 h but after that, constant activity for the 152 h left.

Ethane oxidation at intermediate temperatures and high pressures has been investigated in both a laminar flow reactor and a rapid compression machine (RCM). The flow-reactor measurements at 600–900 K and 20–100 bar showed an onset temperature for oxidation of ethane between 700 and 825 K, depending on pressure, stoichiometry, and residence time. Measured ignition delay times in the RCM at pressures of 10–80 bar and temperatures of 900–1025 K decreased with increasing pressure and/or temperature. A detailed chemical kinetic model was developed with particular attention to the peroxide chemistry. Rate constants for reactions on the C2H5O2 potential energy surface were adopted from the recent theoretical work of Klippenstein. In the present work, the internal H-abstraction in CH3CH2OO to form CH2CH2OOH was treated in detail. Modeling predictions were in good agreement with data from the present work as well as results at elevated pressure from literature. The experimental results and the modeling predictions do not support occurrence of NTC behavior in ethane oxidation. Even at the high-pressure conditions of the present work where the C2H5 + O2 reaction yields ethylperoxyl rather than C2H4 + HO2, the chain branching sequence CH3CH2OO⟶CH2CH2OOH⟶+O2OOCH2CH2OOH→branching is not competitive, because the internal H-atom transfer in CH3CH2OO to CH2CH2OOH is too slow compared to thermal dissociation to C2H4 and HO2.

[EN] The discovery of new materials for separating ethylene from ethane by adsorption, instead of using cryogenic distillation, is a key milestone for molecular separations because of the multiple and widely extended uses of these molecules in industry. This technique has the potential to provide tremendous energy savings when compared with the currently used cryogenic distillation process for ethylene produced through steam cracking. Here we describe the synthesis and structural determination of a flexible pure silica zeolite (ITQ-55). This material can kinetically separate ethylene from ethane with an unprecedented selectivity of ~100, owing to its distinctive pore topology with large heart-shaped cages and framework flexibility. Control of such properties extends the boundaries for applicability of zeolites to challenging separations.

In this thesis, we detail an investigation into the photodissociation dynamics and spectroscopy of three atmospherically relevant chemical species: acetone, ethane (C2H6) and nitrous oxide (N2O).A systematic study into the photodissociation mechanisms of acetone has been carried out across its first electronically excited state, covering a wavelength range of 230 - 312nm. The photodissociation of acetone comprises primary and secondary dissociation mechanisms, involving one and two C−C bond ruptures. At wavelengths longer than 306nm, we have discovered a novel dissociation pathway, involving a barrierless dissociation to CH3CO + CH3, reproduced by a statistical prior model. We estimate this mechanism will account for 83% of CH3 formed by absorption of actinic radiation. The remaining 17% is accounted by dissociation in the T1 state, which dominates at wavelengths shorter than 306nm. This reaction channel was readily modelled by a statistically adiabatic-impulsive (SAI) model. At wavelengths shorter than 263 nm, secondary dissociation of acetone can occur. The CH3CO fragment from the primary step undergoes dissociation, yielding CH3 + CO. We refute the roaming mechanism believed to occur in this wavelength region, and the only two pathways observed are the primary and secondary dissociation reactions.High level electronic structure calculations have been undertaken to determine the ionisation energies and dynamics of ethane. Using the HEAT345(Q) procedure, we determine adiabatic ionisation energies for the 2Eg and 2A1g states to be 11.52 and 11.56 eV respectively, with an estimated uncertainty of 0.025 eV. The photoelectron spectrum of C2H6 has also be simulated using a quadratic model vibronic coupling Hamiltonian, comprising the two lowest-lying electronic states of C2H+6 . The linear coupling model reproduces the spectral envelope, and a quadratic model is required for quantitative agreement with the reference spectrum.The O 1D photofragment yield from the photodi

The vanadium (V)-nitrogenase of Azotobacter vinelandii catalyses the in vitro conversion of carbon monoxide (CO) to hydrocarbons. Here we show that an A. vinelandii strain expressing the V-nitrogenase is capable of in vivo reduction of CO to ethylene (C2H4), ethane (C2H6) and propane (C3H8). Moreover, we demonstrate that CO is not used as a carbon source for cell growth, being instead reduced to hydrocarbons in a secondary metabolic pathway. These findings suggest a possible role of the ancient nitrogenase as an evolutionary link between the carbon and nitrogen cycles on Earth and establish a solid foundation for biotechnological adaptation of a whole-cell approach to recycling carbon wastes into hydrocarbon products. Thus, this study has several repercussions for evolution-, environment- and energy-related areas.

On the basis of energy decomposition analysis, the rotational energy profile of ethane is explained by using two models: rigid rotation with instantaneous geometry relaxations of the eclipsed and staggered conformations and relaxed rotation with continuous geometry relaxations. Both models can be applied to the real system. A distinction between the cause of an initial energy rise and energetic consequences of structural changes accompanying the rotation is made. It is concluded that the increased Pauli repulsion is the main cause for the initial energy rise and geometry changes. However, after the structural changes take place, the Pauli repulsion is not responsible for the higher energy of the eclipsed state. It then originates from energetic consequences of geometry changes, which include decrease in electrostatic and orbital stabilization energies, mainly due to the C-C bond lengthening, and an energy rise due tomethyl groups bending.

122 p. : ill. ; 30 cm, La simulation des écoulements des hydrocarbures dans les pipelines apporte de nombreux défis aux pétroliers, particulièrement sur la meilleure façon de créer un profil du pipeline en se basant sur les données disponibles. Très peu de travaux concernant la modélisation des profiles des pipelines ont été présentés dans la littérature [8]. Pour réaliser un modèle simplifié et performant qui conserve d'une part, la géométrie globale de la conduite et d'autre part, les paramètres dynamiques, nous proposons dans ce travail une nouvelle approche pour l'homogénéisation du profil par une technique de l'upscaling. L'objectif de ce travail est d'étudier les éléments essentiels pour la modélisation du profil, la sensibilité de ce modèle sur le design et sur le fonctionnement d'un nouveau pipeline. L'application de notre approche est effectuée sur l'étude de faisabilité du transport de l'éthane. L'objectif est de déterminer une configuration optimale pour le design d'un pipeline transportant l'éthane de la région Hassi Messaoud (HMD) vers la région Arzew sous la forme liquide ou gazeuse. La difficulté de traitement de ce problème réside dans la forte dépendance de l'état du fluide à transporter aux variations de pression, de la température et au changement du relief. Pour cela, un modèle mécanistique permettant de représenter l'écoulement de notre effluent sous forme liquide, gazeuse ou leur présence simultanément

Hlavním cílem diplomové práce bylo srovnání dvou metod příprav V-katalyzátorů, a to metody impregnace a molekulární disperze. Pozornost byla zaměřena na analýzu distribuce VOx částic na alumina a SBA-15 nosičích plynoucí z obou typů příprav V-katalyzátorů a dále pak na aktivitu/selektivitu těchto částic v ODH etanu. Připravené V-Al2O3 a V-SBA-15 katalyzátory byly charakterizovány metodou XRF (chemické složení) a metodami DR UVVIS spektroskopie a H2-TPR (analýza distribuce VOx částic). Oxidativní dehydrogenace etanu byla studována v teplotním rozsahu 400-600 °C, konstantní navážku katalyzátoru 200 mg (W/F 0,12 gkat?s?ml-1) a pro složení reakční směsi 7,5 % etanu, 2,5 % O2 a 90 % He., The diploma thesis was focused on comparison of two V-catalysts preparation methods. Impregnation method and molecular designed dispersion were compared. Firstly, the attention was focused on the analysis of distribution of VOx species on alumina and SBA-15 supports resulting from the differences in catalyst preparation. Secondly, relationship between activity and selectivity of VOx species in C2-ODH was studied. Prepared V-Al2O3 and V-SBA-15 catalysts were characterized by XRF (chemical composition), DR UV-VIS spectroscopy and H2-TPR (VOx particle distribution analysis). Oxidative dehydrogenation of ethane was studied in the temperature range 400 ? 600 °C, constant weight of catalyst 200 mg (W/F 0,12 gkat?s?ml-1) and composition of reaction mixture of 7,5 % ethane, 2,5 % O2 a 90 % He., Katedra fyzikální chemie, 1) Diplomant přednesl prezentaci DP. 2) Doc. Bulánek přečetl posudky. 3) Diplomant odpověděl na dotazy k DP: - Vysvětlení diskutované reakce. (doc. Skopal) - Co obsahuje výstupní směs po reakci? (prof. Šedlbauer) - Vysvětlení energie náběhové hrany. (prof. Málek)

A tunable diode laser absorption spectroscopy system, capable of collecting data at a 10 kHz repetition rate near 4.5 microns. This system was made feasible in recent years due to the development of quantum cascade lasers active in the 4.5 microns region of the spectrum. Reaching into the mid-IR region of the electromagnetic spectrum allowed for an analysis of the fundamental absorption bands for both CO and CO2. The spectral absorption was measured for ethylene, methane, ethane, and propane across a variety of equivalence ratios, at various heights above a Hencken Burner surface. For each fuel, the concentration of CO2 was found to agree with chemical equilibrium analysis (CEA) calculations within approximately 8%. The concentration for CO agreed with CEA but with larger error bounds at approximately 20%. It is believed that such large error can be attributed to taking measurements on a hot band, as well as large amounts of H2O and CO2 absorption in the area. This ultimately resulted the measurement of combustion efficiency, which agreed with expected results with approximately 10% error bounds. With this system's proof of concept, it will be possible to analyze real combustors as well as detonation events., The original document contains color images.

This dissertation involves measurements of ethane and carbon monoxide in the air trapped in polar firn (porous ice) and ice cores from Greenland and Antarctica. Ethane and carbon monoxide are reactive trace gases that are involved in tropospheric ozone formation and impact the atmosphere's oxidative capacity. The major sources of these gases are from anthropogenic fossil fuel use, biofuel use, and biomass burning. Ethane fossil fuel emissions are mainly from evaporative emissions associated with the production, processing and transmission of fossil fuels. Carbon monoxide emissions are primarily due to fossil fuel combustion and atmospheric hydrocarbon oxidation. In this study, past atmospheric levels of ethane and carbon monoxide are reconstructed from polar firn air to examine man's impact on their global budgets. Antarctic and Greenland firn air measurements show that ethane levels rose globally during the twentieth century, reached a peak in the 1980s, followed by a decline to their present-day levels. Ethane emissions reconstructions suggest that the ethane decline since 1980 was likely due to a reduction in fossil fuel emissions. The firn-air based ethane emissions histories suggest the slowdown in the atmospheric methane growth rate during the 1980s and 1990s was also due to reductions in fossil fuel emissions, possibly as a result of capture, recovery, and/or storage of natural gas that was previously vented or flared. In order to develop longer atmospheric histories, ethane was analyzed in air extracted from bubbles in Antarctic ice cores. Both dry extraction and wet extraction procedures were utilized in this study. The results indicate that preindustrial (1000-1900 AD) ethane levels over Antarctica were 40-50% lower than today.Carbon monoxide levels increased by roughly 40% from 1920-1980, with near zero growth after the 1990s, based on the South Pole firn air reconstructions. The rate of CO rise during the mid-twentieth century was faster than the rate of

Metal oxide promoted NiO catalysts with a Ni/(Me + Ni) atomic ratio 0.92 have been investigated for the oxidative dehydrogenation of ethane. These materials have been characterized by several techniques (N-2-adsorption, X-ray diffraction, X-ray photoelectron spectroscopy and Fourier transformed infrared spectroscopy of adsorbed CO and ethylene). The nature of surface sites is strongly influenced by the valence and the acid/base characteristics of the metal oxide promoters, which have a great impact on the selectivity to ethylene. Accordingly, a clear correlation between selectivity to ethylene and the valence of the promoter has been observed in the present work. Additionally, the acidity of the catalyst also enhances the selectivity to ethylene.

MoVTeNb mixed oxide, a highly active and selective catalyst for the oxidative dehydrogenation of ethane to produce ethylene, exhibits the so-called M1 and M2 crystalline phases. The thermal stability of the MoVTeNb catalytic system was assessed under varying reaction conditions; to this end, the catalyst was exposed to several reaction temperatures spanning from 440 to 550 °C. Both the pristine and spent materials were analyzed by several characterization techniques. The catalyst was stable below 500 °C; a reaction temperature of ≥500 °C brings about the removal of tellurium from the intercalated framework channels of the M1 crystalline phase. Rietveld refinement of X-ray diffraction patterns and microscopy results showed that the tellurium loss causes the progressive partial destruction of the M1 phase, thus decreasing the number of active sites and forming a MoO2 crystalline phase, which is inactive for this reaction. Raman spectroscopy confirmed the MoO2 phase development as a function of reaction temperature. From highresolution transmission electron microscopy and energy-dispersive X-ray spectroscopy analyses it was noticed that tellurium departure occurs preferentially from the end sides of the needlelike M1 crystals, across the [001] plane. Detailed analysis of a solid deposited at the reactor outlet showrf that it consisted mainly of metallic tellurium, suggesting that the tellurium detachment occurs via reduction of Te4+ to Te0 due to a combination of reaction temperature and feed composition. Thus, in order to sustain the catalytic performance exhibited by MoVTeNb mixed oxide, hot spots along the reactor bed should be avoided or controlled, maintaining the catalytic bed temperature below 500 °C.

[EN] The robustness of one selected Ni-W-O catalyst has been studied in the oxidative dehydrogenation of ethane. This catalyst initially deactivates for the first 10 h online decreasing 15% of its catalytic activity compared to its initial stable catalytic activity. However from 10 to 60 h online the catalytic activity keeps almost stable. On the other hand, it has been shown that the Ni-W-O catalyst cannot tolerate an oxygen-free atmosphere (C-2 and He) as nickel oxide is transformed into metallic nickel. Methane and hydrogen as well as abundant coke were formed on the surface of the catalyst in these O-free conditions. However a re-calcination in air leads to the removal of coke, the catalytic performance in the oxidative dehydrogenation of ethane being almost completely restored.

Ethylene production by pyrolysis of hydrocarbon gases (ethane, propane, butane) and liquid fractions provides better selectivity to ethylene at higher temperatures, as has been well documented in studies. Temperature increase accelerates chainradical reactions of ethylene formation. Acceleration of chain-radical process can be achieved at a given temperature by the presence of an initiating agent of radical formation in the feedstock. Bimolecular reaction of allene (propadiene) with either alkane or alkene hydrocarbons and is an extremely rapid reaction of radicals formation because the endothermicity of this reaction is small and steric ratio is high. This paper considers the use of allene as the initiator of chainradical reactions of pyrolysis. © 2014 WIT Press.

Two kinetic models based on Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) mechanisms were developed to describe the oxydehydrogenation of ethane to yield ethylene over a Mo-V-Te-Nb catalyst. Obtained in a lab-scale fixed-bed reactor, experimental data at the steady-state were used to estimate the kinetic models parameters via a nonisothermal regression. Experiments were performed using an ethane, oxygen and nitrogen mixture as feedstock, spanning temperatures from 673 to 753 K, inlet partial pressures of oxygen and ethane between 5.0 and 22.0 kPa, and space-time from 10 to 70 g(cat) h(molethane)- (1). Ethylene, CO and CO2 were the only detected products, the selectivity for ethylene ranged from 76% to 96% for an ethane conversion interval 4-85%. A series of tests feeding ethylene instead of ethane were also performed at 713 K, varying inlet partial pressures and space-time in the same ranges as was done for ethane. Ethylene conversion was relatively low, 3-14%, the dominant product being CO with CO/CO2 ratios from 0.73 to 0.79. The LH mechanism was found to represent better the experimental data. The oxydehydrogenation of ethane was the reaction with the lowest activation energy, 108-115 kJ mol (1). Except for the conversion of ethane into CO2, deep oxidations were detected as very energetically demanding steps, 156-193 kJ mol (1). Competitive adsorption between reagents and products occurred in the two mechanisms particularly at relatively high reaction severity, water re-adsorption being weaker in comparison with COx re-adsorption. (C) 2014 Elsevier Ltd. All rights reserved.

6.7-Difluoroquinoxaline (I) reacted with dimedone, indandione, and 3-methyl-1-phenylpyrazol-5-one in DMSO solution in the presence of acid to form mono-substituted products IIa - c. Heating I with resorcinol in EtOH in the presence of acid gave resorcinol derivative IId. 6.7-Difluoroquinoxaline in the presence of base reacted with 3-methyl-1-phenylmethylpyrazol-5-one to form dipyrazolylmethane III and tetrapyrazolylethane derivative IV. Heating products IIa - c with N-methylpiperazine produced 7-methylpiperazine derivatives Va - c of 2-substituted quinoxalines. © 2013 Springer Science+Business Media New York.

Two series of supported nanoscaled NiO catalysts have been prepared using Nb2O5 supports with different surface areas. NiO nanoparticles interacting with Ni–O–Nb mixed phases are active and selective for ethane ammoxidation; both are required in order to have an active and selective catalyst. In this paper we report the dispersion of NiO nanoparticles on two Nb2O5 supports in order to generate an active phase for ethane ammoxidation. The use of a support stabilizes NiO nanoparticles, which otherwise would sinter. This work shows how the activity can be modulated by the size of the NiO nanoparticles and by the NiO/Ni–Nb–O ratio, which depends on the nickel coverage and support surface area. The catalysts obtained are very promising for ethane ammoxidation reaction.