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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Oxidative Dehydrogenation of Ethane: A Chemical Looping Approach

The current study investigates a chemical-looping-based oxidative dehydrogenation (CL-ODH) concept for ethane-to-ethylene conversion. In this cyclic redox scheme, an oxide-based redox catalyst is used to selectively combust hydrogen from ethane dehydrogenation. As the hydrogen product limits ethane conversion, in situ oxidation of hydrogen enhances the ethane conversion and ethylene yield. Moreover, heat required in ODH is compensated by re-oxidation of the oxygen-deprived redox catalyst, enabling auto-thermal operation for the overall process. Compared to steam cracking, CL-ODH can potentially achieve higher efficiency with lower CO 2 and NO x emissions. Silica and magnesia-supported manganese oxides are investigated. It is determined that unpromoted Mn/SiO 2 and Mn/MgO redox catalysts exhibit low selectivity towards ethylene. The addition of promoters such as sodium and tungsten renders effective redox catalysts with satisfactory activity, selectivity, oxygen carrying capacity, and redox stability.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Numerical modeling of chemical looping oxidative dehydrogenation of ethane in parallel packed beds

Chemical looping oxidative dehydrogenation (CL-ODH) of ethane has the potential to be a highly efficient alternative to steam cracking for ethylene production. Accurate reactor modeling is of critical importance to efficiently scale up and optimize this new technology. This study reports a one-dimensional, heterogeneous packed bed model to simulate the CL-ODH of ethane to ethylene with a Na 2 MoO 4 -promoted CaTi 0.1 Mn 0.9 O 3 redox catalyst. Here, the overall reaction kinetics was well-described by coupling the gas-phase steam cracking of ethane with the reduction kinetics of the redox catalyst by H 2 and C 2 H 4 . The impact of H 2 on the formation rate of CO 2 byproduct from C 2 H 4 conversion was also thoroughly investigated to validate the applicability of the kinetic model under operational environments. The temperature variation within the different CL-ODH steps and the temperature distribution along the bed were also carefully considered. The accuracy of the model was validated by experiments conducted in a large lab-scale packed bed reactor (200 g catalyst loading), with an average deviation of 2.8% in terms of ethane conversion and ethylene yield. The model was subsequently used to optimize the operating parameters of the CL-ODH reactor, indicating that up to 63.7% single-pass C 2 +olefin yield can be achieved with the current redox catalyst bed whereas further optimization of the redox catalyst to inhibit C 2 H 4 activation can result in 69.4% single-pass C 2 +yield while maintaining low CO 2 selectivity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Fabrication of a Pillared ZSM-5 Framework for Shape Selectivity of Ethane Dehydroaromatization

Ethane, the second major component of shale gas, is a prospective raw feedstock to valuable chemicals and fuels. Innovative pillared ZSM-5 with various lamellar thicknesses and Si/Al ratios were successfully synthesized with the dual-template method; 0.67 wt % Mo were dispersed over these lamellar ZSM-5, and evaluated for ethane dehydroaromatization. The influence of zeolite morphology and the texture property for the reduction/acidity nature of MoOx species were investigated by X-ray diffraction, scanning electron microscopy, N2-sorption, H2-temperature programmed reduction/oxidation, and NH3-temperature-programmed desorption. The high concentration of acidic sites not only increases ethane conversion and aromatic selectivity, but intensely induces surface coking. Therefore, a moderate Si/Al ratio is utilized to balance catalytic reactivity and stability. Thicker zeolite layers with a long diffusion path exhibited fair ethane conversion, but high aromatization yield. It is of significant importance that the lamellar Mo/MFI catalyst, with Si/Al = 50 and 210 nm layer thickness, demonstrated excellent regenerability during a multicycle reaction/oxidation operation, which could be a promising system for industrial optimization and process deployment.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Local Rearrangement in Adsorption Layers of Nanoconfined Ethane

Fluids under nanoconfinement control many environmental and engineering processes. In particular, nanoconfined ethane commonly occurs in hydrocarbon production and gas separation applications. While previous research has measured the pore critical properties and self-diffusivity of nanoconfined ethane, the relationship between molecular organization and phase behavior in nanoporous media persists as a knowledge gap. Through experimental adsorption measurements and molecular dynamics simulations, we report the impact of pore wall proximity, pore size, and temperature on the structure of nanoconfined ethane. Finally, we offer evidence for an energetically favorable rearrangement of ethane molecules in the adsorption layer that may contribute to more accurate gas-in-place estimates and more efficient design of gas separation membranes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Direct Conversion of Ethane to Oxygenates, Ethylene, and Hydrogen in a Noncatalytic Biphasic Plasma Microreactor

We selectively upgrade ethane (C 2 H 6 ) to ethanol (C 2 H 5 OH), methanol (CH 3 OH), and acetic acid (CH 3 COOH) in a catalyst-free, continuous, argon/water biphasic plasma microreactor. The water (H 2 O) evaporates and electron- dissociates into OH· radicals. OH· recombines with alkyl radicals, produced via electron dissociation of ethane, to generate the oxygenates that absorb into H 2 O. A plasma-assisted path, reminiscent of the low-temperature thermocatalytic ethane steam reforming, leads to significant H 2 coproduction. The gaseous stream also comprises CO 2 and C 2 H 4 . Up to 1.3 and 1 μmol min –1 of liquid C 2 H 5 OH and CH 3 OH are attained, respectively. Compared to CO 2 -assisted ethane plasma conversion, which produces many oxygenates with low selectivity, the carbon selectivity can range from >70% C 2 H 5 OH, CH 3 OH, and CH 3 COOH to 60% C 2 H 4 . Furthermore, the low carbon footprint, electrified, modular, intensified process using a reactive evaporation and separation plasma could pave the way for the valorization of underutilized shale gas resources in remote areas.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Atomically synergistic Zn-Cr catalyst for iso-stoichiometric co-conversion of ethane and CO2 to ethylene and CO

Abstract Developing atomically synergistic bifunctional catalysts relies on the creation of colocalized active atoms to facilitate distinct elementary steps in catalytic cycles. Herein, we show that the atomically-synergistic binuclear-site catalyst (ABC) consisting of $${{{{{\rm{Zn}}}}}}^{\delta+}$$ Zn δ + -O-Cr 6+ on zeolite SSZ-13 displays unique catalytic properties for iso-stoichiometric co-conversion of ethane and CO 2 . Ethylene selectivity and utilization of converted CO 2 can reach 100 % and 99.0% under 500 °C at ethane conversion of 9.6%, respectively. In-situ/ex-situ spectroscopic studies and DFT calculations reveal atomic synergies between acidic Zn and redox Cr sites. $${{{{{\rm{Zn}}}}}}^{\delta+}$$ Zn δ + ( $$0 \, < \, \delta \, < \, 2$$ 0 < δ < 2 ) sites facilitate β-C-H bond cleavage in ethane and the formation of Zn-H δ - hydride, thereby the enhanced basicity promotes CO 2 adsorption/activation and prevents ethane C-C bond scission. The redox Cr site accelerates CO 2 dissociation by replenishing lattice oxygen and facilitates H 2 O formation/desorption. This study presents the advantages of the ABC concept, paving the way for the rational design of novel advanced catalysts.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Ethane and methane at high pressures: Structure and stability

We have performed a combined experimental and theoretical study of ethane and methane at high pressures of up to 120 GPa at 300 K using x-ray diffraction and Raman spectroscopies and the USPEX ab initio evolutionary structural search algorithm, respectively. For ethane, we have determined the crystallization point, for room temperature, at 2.7 GPa and also the low pressure crystal structure (phase A). This crystal structure is orientationally disordered (plastic phase) and deviates from the known crystal structures for ethane at low temperatures. Moreover, a pressure induced phase transition has been identified, for the first time, at 13.6 GPa to a monoclinic phase B, the structure of which is solved based on good agreement with the experimental results and theoretical predictions. For methane, our x-ray diffraction measurements are in agreement with the previously reported high-pressure structures and equation of state (EOS). Finally, we have determined the EOSs of ethane and methane, which provides a solid basis for the discussion of their relative stability at high pressures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2023

Methane, ethane, and propane production in Greenland ice core samples and a first isotopic characterization of excess methane

Air trapped in polar ice provides unique records of the past atmospheric composition ranging from key greenhouse gases such as methane (CH 4 ) to short-lived trace gases like ethane (C 2 H 6 ) and propane (C 3 H 8 ). Recently, the comparison of CH 4 records obtained using different extraction methods revealed disagreements in the CH 4 concentration for the last glacial in Greenland ice. Elevated methane levels were detected in dust-rich ice core sections measured discretely, pointing to a process sensitive to the melt extraction technique. To shed light on the underlying mechanism, we performed targeted experiments and analyzed samples for methane and the short-chain alkanes ethane and propane covering the time interval from 12 to 42 kyr. Here, we report our findings of these elevated alkane concentrations, which scale linearly with the amount of mineral dust within the ice samples. The alkane production happens during the melt extraction step of the classic wet-extraction technique and reaches 14 to 91 ppb of CH 4 excess in dusty ice samples. We document for the first time a co-production of excess methane, ethane, and propane, with the observed concentrations for ethane and propane exceeding their past atmospheric background at least by a factor of 10. Independent of the produced amounts, excess alkanes were produced in a fixed molar ratio of approximately 14 : 2 : 1, indicating a shared origin. The measured carbon isotopic signature of excess methane is (-47.0 ± 2.9) ‰ and its deuterium isotopic signature is (-326 ± 57) ‰. With the co-production ratios of excess alkanes and the isotopic composition of excess methane we established a fingerprint that allows us to constrain potential formation processes. This fingerprint is not in line with a microbial origin. Moreover, an adsorption–desorption process of thermogenic gas on dust particles transported to Greenland does not appear very likely. Instead, the alkane pattern appears to be indicative of abiotic decomposition of organic matter as found in soils and plant leaves.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1976

Ethane and acetylene abundances in the Jovian atmosphere

The paper reports spectra of Jupiter in the spectral region from 755 to 850 kaysers, which covers the nu-9 fundamental of ethane and contains lines from the R branch of the nu-5 fundamental of acetylene. The monochromatic absorption coefficient of the central Q branch of the nu-9 fundamental of ethane, which was determined in the laboratory, is applied in a radiative-transfer calculation to evaluate the ethane mixing ratio in the Jovian atmosphere; the present data are also used to place an upper limit on the acetylene mixing ratio. For the radiative-transfer calculation, emission intensity is computed for the region above the 0.02-atm level assuming both an isothermal inversion layer and a previously reported temperature profile. The resulting maximum mixing ratios consistent with the observations are 0.00003 for ethane and 7.5 by 10 to the -8th power for acetylene.

Tokunaga, A.↗
NASA NTRS1978

Photoabsorption cross sections of methane and ethane, 1380-1600 A, at T equals 295 K and T equals 200 K

Photoabsorption cross sections of methane and ethane have been determined in the wavelength range from 1380 to 1600 A at room (295 K) and dry-ice (200 K) temperatures. It is found that the room-temperature ethane data are in excellent agreement with the older measurements of Okabe and Becker (1963) rather than with more recent determinations and that a small systematic blueshift occurs at the foot of the molecular absorption edges of both gases as the gases are cooled from room temperature to 200 K, a value close to the actual temperature of the Jovian atmosphere. It is concluded that methane photoabsorption will dominate until its cross section is about 0.01 that of ethane, which occurs at about 1440 A, and that ethane should be the dominant photoabsorber in the Jovian atmosphere in the region from above 1440 A to not farther than 1575 A.

Mount, G. H.↗
NASA NTRS1979

Tropospheric and lower stratospheric vertical profiles of ethane and acetylene

The first known vertical distributions of ethane and acetylene which extend into the lower stratosphere are reported. The average upper tropospheric concentrations, between 20,000 ft and 35,000 ft, near 37 deg N-123 deg W were 1.2 micrograms/cu m (1.0 ppb) for ethane and 0.24 micrograms /cu m (0.23 ppb) for acetylene while the values near 9 N-80 W were 0.95 micrograms/cu m (0.77 ppb) and 0.09 micrograms/cu m (0.09 ppb), respectively. Detectable quantities of both ethane and acetylene are present in the lower stratosphere. There is a sharp decrease in the levels of these two compounds as one crosses the tropopause and ascends into the lower stratosphere. The observed levels of ethane and acetylene may allow some impact on the background chemistry of the troposphere and stratosphere.

Cronn, D.↗
NASA NTRS1982

Atmospheric chemistry of ethane and ethylene

It is shown by a study of ethane and ethylene photochemistry that the loss of ethane is controlled by OH in the troposphere and Cl in the stratosphere. Ethane observations indicating free Cl concentrations below 30 km that are only 10% of the value predicted by the present model calculations cannot be explained by heterogeneous aerosol concentration processes, and contradict current stratospheric photochemistry. The chemical destruction of ethane and ethylene leads to the generation of such compounds as carbon monoxide and formaldehyde, and it is found that the tropospheric concentrations of the latter are enhanced by nearly a factor of three for an ethylene mixing ratio of 2 ppb.

Aikin, A. C.↗
NASA NTRS1992

Stratospheric ethane on Neptune - Comparison of groundbased and Voyager IRIS retrievals

Near-simultaneous ground and spacecraft measurements of 12-micron ethane emission spectra during the Voyager encounter with Neptune have furnished bases for the determination of stratospheric ethane abundance and the testing and constraining of Neptune methane-photochemistry models. The ethane retrievals were sensitive to the thermal profile used. Contribution functions for warm thermal profiles peaked at higher altitudes, as expected, with the heterodyne functions covering lower-pressure regions. Both constant- and nonconstant-with-height profiles remain candidate distributions for Neptune's stratospheric ethane.

Kostiuk, Theodor↗
NASA NTRS2009

Ethane's 12C/13C Ratio in Titan: Implications for Methane Replenishment

As the .main destination of carbon in the destruction of methane in the atmosphere of Titan, ethane provides information about the carbon isotopic composition of the reservoir from which methane is replenished. If the amount of methane entering the atmosphere is presently equal to the amount converted to ethane, the 12C/13C ratio in ethane should be close to the ratio in the reservoir. We have measured the 12C/13C ratio in ethane both with Cassini CIRS(exp 1) and from the ground and find that it is very close to the telluric standard and outer planet values (89), consistent with a primordial origin for the methane reservoir. The lower 12C/13C ratio measured for methane by Huygens GCMS (82.3) can be explained if the conversion of CH4 to CH3 (and C2H6) favors 12C over 13C with a carbon kinetic isotope effect of 1.08. The time required for the atmospheric methane to reach equilibrium, i.e., for replenishment to equal destruction, is approximately 5 methane atmospheric lifetimes.

Jennings, Donald E.↗
NASA NTRS2009

Laboratory Studies of Ethane Ice Relevant to Outer Solar System Surfaces

Oort Cloud comets, as well as TNOs Makemake (2045 FYg), Quaoar, and Pluto, are known to contain ethane. However, even though this molecule is found on several outer Solar System objects relatively little information is available about its amorphous and crystalline phases. In new experiments, we have prepared ethane ices at temperatures applicable to the outer Solar System, and have heated and ion-irradiated these ices to study phase changes and ethane's radiation chemistry using mid-IR spectroscopy (2.2 - 16.6 microns). Included in our work is the meta-stable phase that exists at 35 - 55 K. These results, including newly obtained optical constants, are relevant to ground-based observational campaigns, the New Horizons mission, and supporting laboratory work. An improved understanding of solid-phase ethane may contribute to future searches for this and other hydrocarbons in the outer Solar System.

Moore, Marla H.↗
DOE OSTI2024

Investigation of Ethane Dehydrogenation and Hydrogenolysis on Pt(111), Pt(211), and Pt(100): Bayesian Quantification and Correction of DFT-Based Enthalpic and Entropic Uncertainties

Computational investigations of heterogeneously catalyzed reactions using density functional theory (DFT) are often inaccurate, largely due to uncertainties in the choice of DFT functional (enthalpic uncertainty) and approximations for modeling adsorbate movement along the catalyst surface (entropic uncertainty). This work illustrates that both uncertainties are significant in the investigation of ethane dehydrogenation (EDH) and hydrogenolysis on Pt catalysts by considering the complete deconstruction of ethane on Pt(111), Pt(211), and Pt(100) using microkinetic modeling (MKM). Hence, this work uses both noncalibrated and Bayesian-calibrated MKMs to quantify and correct inaccuracies in macroscopic properties due to both uncertainties. A Bayesian approach to the correction of entropic errors was introduced using a “Modified Fermi Function (MFF)” to calibrate between the two bounds of entropy represented by the harmonic oscillator (HO) and free translator (FT) approximations. Regardless of enthalpic and entropic uncertainties, all three surfaces are capable of ethane activation; however, Pt(211) was found to be the most active and is largely responsible for methane production. Next, Pt(111) is largely responsible for acetylene production, and Pt(100) has the highest ethylene selectivity but is most susceptible to coking. By comparison of different calibrated models, the FT entropy approximation was found to better describe EDH under typical experimental conditions. Statistical evidence was found to support Pt(111) as the active site for EDH, assuming that one single site is responsible for the chemistry. On the three surfaces, competing second dehydrogenations to CH 2 CH 2 and CH 3 CH were observed as well as isomerization of CH 3 CH back to CH 2 CH 2 and deeper dehydrogenation of CH 3 CH. In conclusion, C–C cleavage was found to largely proceed via the CH 3 C intermediate on Pt(100) and Pt(111), while on Pt(211), it was via both CHC and CH 3 C.

Bayesian model selection↗
DOE OSTI2021

Achieving high ethylene yield in non-oxidative ethane dehydrogenation

Steam cracking of ethane, a non-catalytic thermochemical process, remains the dominant means of ethylene production. The severe reaction conditions and energy expenditure involved in this process incentivize the search for alternative reaction pathways and reactor designs which maximize ethylene yield while minimizing cost and energy input. Herein, we report a comparison of catalytic and non-catalytic non-oxidative dehydrogenation of ethane. We achieve ethylene yields as high as 67 % with an open tube quartz reactor without the use of a catalyst at residence times ~4 s. The open tube reactor design promotes simplicity, low cost, and negligible coke formation. Pristine quartz tubes were most effective, since coke formation was detected when defects were introduced by scratching the surface of the quartz. Surprisingly, the addition of solids to the quartz tube, such as quartz sand, alumina powder, or even Pt-based intermetallic catalysts, led to lower ethylene yield. Pt alloy catalysts are effective at lower temperatures, such as at 575 °C, but conversion is limited due to thermodynamic constraints. When operated at industrially relevant temperatures, such as 700 °C and above, these catalysts were not stable in our tests, causing ethylene yield to drop below that of the open tube. Furthermore, these results suggest that future research on non-oxidative dehydrogenation should be directed at optimizing reactor designs to improve the conversion of ethane to ethylene, since this approach shows promise for decentralized production of ethylene from natural gas deposits.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2020

Catalytic direct conversion of ethane to value-added chemicals under microwave irradiation

The reaction mechanism of ethane conversion over 4 % Mo-0.5 % Fe/ZSM-5 catalyst was investigated using two different reactors with different heating modes. A microwave fixed-bed reactor (MWFB) was used and its performance was compared to a conventional thermal fixed-bed reactor (CTFB). Over 80 % ethane conversion was achieved under microwave irradiation mode at 375 °C. Here, to achieve the same ethane conversion conventionally, the reaction temperature had to be elevated to 660 °C in the CTFB. The formation rates and selectivity of the products were compared under these two heating methods. The CTFB products had a higher selectivity towards aromatic compounds; whereas, the MWFB products had a higher selectivity towards ethylene; 26.5 % higher than the CTFB. Carbon analysis over spent catalysts of CTFB showed three distinct types of coke, whereas the microwave resulted in a single higher temperature coke type.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗