Thermo-photo catalytic anode process for carbonate-superstructured solid fuel cells

Converting hydrocarbons and greenhouse gases (i.e., carbon dioxide, CO2) directly into electricity through fuel cells at intermediate temperatures (450 to 550 °C) remains a significant challenge, primarily due to the sluggish activation of C-H and C=O bonds. Here, we demonstrated a unique strategy to address this issue, in which light illumination was introduced into the thermal catalytic CO2 reforming of ethane in the anode as a unique thermo-photo anode process for carbonate-superstructured solid fuel cells. The light-enhanced fuel activation led to excellent cell performance with a record-high peak power density of 168 mW cm-2 at an intermediate temperature of 550 °C. Furthermore, no degradation was observed during ~50 h operation. Such a successful integration of photo energy into the fuel cell system provides a new direction for the development of efficient fuel cells.

Nitrate-driven anaerobic oxidation of ethane and butane by bacteria

The short-chain gaseous alkanes (ethane, propane, and butane; SCGAs) are important components of natural gas, yet their fate in environmental systems is poorly understood. Microbially mediated anaerobic oxidation of SCGAs coupled to nitrate reduction has been demonstrated for propane, but is yet to be shown for ethane or butane-despite being energetically feasible. Here we report two independent bacterial enrichments performing anaerobic ethane and butane oxidation, respectively, coupled to nitrate reduction to dinitrogen gas and ammonium. Isotopic 13C- and 15N-labelling experiments, mass and electron balance tests, and metabolite and meta-omics analyses collectively reveal that the recently described propane-oxidizing "Candidatus Alkanivorans nitratireducens" was also responsible for nitrate-dependent anaerobic oxidation of the SCGAs in both these enrichments. The complete genome of this species encodes alkylsuccinate synthase genes for the activation of ethane/butane via fumarate addition. Further substrate range tests confirm that "Ca. A. nitratireducens" is metabolically versatile, being able to degrade ethane, propane, and butane under anoxic conditions. Moreover, our study proves nitrate as an additional electron sink for ethane and butane in anaerobic environments, and for the first time demonstrates the use of the fumarate addition pathway in anaerobic ethane oxidation. These findings contribute to our understanding of microbial metabolism of SCGAs in anaerobic environments.

A Route to Understanding the Ethane Adsorption Selectivity of the Zeolitic Imidazolate Framework-8 in Ethane-Ethylene Mixtures

Ethylene production has a negative environmental impact, with its separation step being one of the major contributors of pollution. This has encouraged the search for energy-efficient alternatives, among which the adsorptive separation of ethane and ethylene stands out. ZIF-8 is a molecular sieve that is potentially useful for this purpose. It is selective to ethane, an exceptional property that remains unexplained. Furthermore, the adsorption of ethane and ethylene above room temperature, such as at steam cracking process outlet temperatures, has not been addressed either. This work aims to fill this knowledge gap by combining experiments at very low volumetric fillings with density-functional theory modelling methods. Adsorption isotherms of ethane and ethylene on ZIF-8 at pressures below 0.3 bar and 311 K, 333 K, and 363 K were measured using zero-length column chromatography. The low-pressure domain of the isotherms contains information on the interactions between the adsorbate molecules and the adsorbent. This favors the understanding of their macroscopic behavior from simulations at the atomic level. The isosteric enthalpy of adsorption of ethane remained constant at approximately -10 kJ/mol. In contrast, the isosteric enthalpy of adsorption of ethylene decreased from -4 kJ/mol to values akin to those of ethane as temperature increased. ZIF-8 selectivity to ethane, estimated from ideal adsorbed solution theory, decreased from 2.8 to 2.0 with increasing pressure up to 0.19 bar. Quantum mechanical modelling suggested that ethylene had minimal interactions with ZIF-8, while ethane formed hydrogen bonds with nitrogen atoms within its structure. The findings of this research are a platform for designing new systems for the adsorptive separation of ethane and ethylene and thus, reducing the environmental impact of ethylene production.

Response of the mechanical and chiral character of ethane to ultra-fast laser pulses

A pair of simulated left and right circularly polarized ultra-fast laser pulses of duration 20 femtoseconds that induce a mixture of excited states are applied to ethane. The response of the electron dynamics is investigated within the next generation quantum theory of atoms in molecules (NG-QTAIM) using third-generation eigenvector-trajectories which are introduced in this work. This enables an analysis of the mechanical and chiral properties of the electron dynamics of ethane without needing to subject the C-C bond to external torsions as was the case for second-generation eigenvector-trajectories. The mechanical properties, in particular, the bond-flexing and bond-torsion were found to increase depending on the plane of the applied laser pulses. The bond-flexing and bond-torsion, depending on the plane of polarization, increases or decreases after the laser pulses are switched off. This is explainable in terms of directionally-dependent effects of the long-lasting superpositions of excited states. The chiral properties correspond to the ethane molecule being classified as formally achiral consistent with previous NG-QTAIM investigations. Future planned investigations using ultra-fast circularly polarized lasers are briefly discussed.

Photocatalytic Oxidative Coupling of Ethane to n-Butane Using CO2 as a Soft Oxidant over NiTi-Layered Double Hydroxide

Selective conversion of ethane (C2 H6 ) to high-value-added chemicals is a very important chemical process, yet it remains challenging owing to the difficulty of ethane activation. Here, a NiTi-layered double hydroxide (NiTi-LDH) photocatalyst is reported for oxidative coupling of ethane to n-butane (n-C4 H10 ) by using CO2 as an oxidant. Remarkably, the as-prepared NiTi-LDH exhibits a high selectivity for n-C4 H10 (92.35%) with a production rate of 62.06 µmol g-1 h-1 when the feed gas (CO2 /C2 H6 ) ratio is 2:8. The X-ray absorption fine structure (XAFS) and photoelectron characterizations demonstrate that NiTi-LDH possesses rich vacancies and high electron-hole separation efficiency, which can promote the coupling of C2 H6 to n-C4 H10 . More importantly, density functional theory (DFT) calculations reveal that ethane is first activated on the oxygen vacancies of the catalyst surface, and the C─C coupling pathway is more favorable than the C─H cleavage to C2 H4 or CH4 , resulting in the high production rate and selectivity for n-C4 H10 .

Photocatalytic Oxidative Coupling of Methane to Ethane Using Water and Oxygen on Ag3PO4-ZnO

Photocatalytic oxidative coupling is an effective way of converting CH4 to high-value-added multi-carbon chemicals under mild conditions, where the breaking of the C-H bond is the main rate-limiting step. In this paper, the Ag3PO4-ZnO heterostructure photocatalyst was synthesized for photocatalytic oxidative coupling of methane (OCM) to C2H6. In addition, an excellent C2H6 yield (16.62 mmol g-1 h-1) and a remarkable apparent quantum yield (15.8% at 350 nm) at 49:1 CH4/Air and 20% RH are obtained, which is more than three times that of the state-of-the-art photocatalytic systems. Ag3PO4 improves the adsorption and dissociation ability of O2 and H2O, benefiting the formation of surface hydroxyl species. As a result, the C-H bond activation energy of CH4 on ZnO was obviously reduced. Meanwhile, the improved separation of photogenerated carriers on the Ag3PO4-ZnO heterostructure also accelerates the OCM process. Moreover, Ag nanoparticles (NPs) derived from Ag3PO4 reduction by photoelectrons promote the coupling of *CH3, which can inhibit the overoxidation of CH4 and increase C2H6 selectivity. This research provides a guide for the design of catalyst and reaction systems in the photocatalytic OCM process.

Novel Carbonaceous Adsorbents Prepared from Glycerin Waste and Dopamine for Gas Separation

Glycerin, a low-valued waste from biodiesel production, and dopamine were used as precursors for adsorbent materials. The study is centered on the preparation and application of microporous activated carbon as adsorbent materials in the separation of ethane/ethylene and of gases that are natural gas or landfill gas components (ethane/methane and carbon dioxide/methane). The activated carbons were produced by the following sequence reactions: facile carbonization of a glycerin/dopamine mixture and chemical activation. Dopamine allowed the introduction of nitrogenated groups that improved the selectivity of the separations. The activating agent was KOH, but its mass ratio was kept lower than one to improve the sustainability of the final materials. The solids were characterized by N₂ adsorption/desorption isotherms, SEM, FTIR spectroscopy, elemental analysis, and point of zero charges (pH_PZC). The order for adsorption of the different adsorbates (in mmolg^-1) on the most well performing material-Gdop0.75-is methane (2.5) < carbon dioxide (5.0) < ethylene (8.6) < ethane (8.9).

Weak Interactions Initiate C-H and C-C Bond Dissociation of Ethane on Nbn + Clusters

The conversion of ethane into value-added chemicals under ambient conditions has attracted much attention but the mechanisms remain not fully understood. Here we report a study on the reaction of ethane with thermalized Nb_n ⁺ clusters based on a multiple-ion laminar flow tube reactor combined with a triple quadrupole mass spectrometer (MIFT-TQMS). It is found that ethane reacts with Nb_n ⁺ clusters to form both products of dehydrogenation and methane-removal (odd-carbon products). Combined with density functional theory (DFT) calculations, we studied the reaction mechanisms of the C-C bond activation and C-H bond cleavage on the Nb_n ⁺ clusters. It is unveiled that hydrogen atom transfer (HAT) initiates the reaction process, giving rise to the formation of Nb-C bonds and an elongated C-C distance in the HNb_n ⁺ CH₂ CH₃ motif. Subsequent reactions allow for C-C bond activation and a competitive HAT process which is associated with CH₄ removal or H₂ release, resulting in the production of the observed carbides.

Preparation, Structure-Performance Relationship, and Reaction Network of ZnZSM-5 for Oxidative Dehydrogenation of Ethane with CO2

Ethylene (C₂ H₄ ) is a major chemical for the modern society, and new technologies for its production are of strategic importance globally. Recently, oxidative dehydrogenation of ethane (C₂ H₆ ) using CO₂ as a milder oxidant (CO₂ -ODH) is proposed as a potential way for C₂ H₄ production, and development of effective catalysts for the process is drawing wide attention. Here, we report on a facilely prepared ZSM-5 supported Zn system, i. e., ZnZSM-5, which showed great promise in CO₂ -ODH. Samples with different Zn loadings were prepared and evaluated, and the highest performance was obtained over 0.05ZnZSM-5 at 700 °C and a CO₂ :C₂ H₆ feeding ratio of 5 : 1. During 340 min TOS, the C₂ H₆ conversion decreased moderately from 36.2 % to 23.1 %, and the C₂ H₄ yield stabilized at 21.9 % to 27.9 %. Based on systematic characterization and investigation of reaction conditions, the structure-performance relationship and reaction network were discussed in detail.

Microwave Heating of the Catalyst Bed as a Way of Energy-Saving Oxidative Dehydrogenation of Ethane on a Mo-V-Te-Nb-Ox Catalyst

In search of a more effective process of ethane oxidative hydrogenation, different operation modes (thermal and microwave heating) are compared. The catalyst Mo₁-V_0.3-Te_0.13-Nb_0.11-O_x was prepared by hydrothermal synthesis and characterized by a set of physicochemical methods (XRD, N₂ adsorption, SEM, EDX). The direct microwave heating of the catalyst layer is proposed as an alternative way of energy-saving ethane-to-ethylene oxidation by a Mo-V-Te-Nb-O_x system. A substantial decrease in the reactor temperature upon the microwave-assisted process is accompanied by extremely high catalyst selectivity, which remains at a very high level of 98+%.

Natural Gas Storage Filled with Peat-Derived Carbon Adsorbent: Influence of Nonisothermal Effects and Ethane Impurities on the Storage Cycle

Adsorbed natural gas (ANG) is a promising solution for improving the safety and storage capacity of low-pressure gas storage systems. The structural-energetic and adsorption properties of active carbon ACPK, synthesized from cheap peat raw materials, are presented. Calculations of the methane-ethane mixture adsorption on ACPK were performed using the experimental adsorption isotherms of pure components. It is shown that the accumulation of ethane can significantly increase the energy capacity of the ANG storage. Numerical molecular modeling of the methane-ethane mixture adsorption in slit-like model micropores has been carried out. The molecular effects associated with the displacement of ethane by methane molecules and the formation of a molecule layered structure are shown. The integral molecular adsorption isotherm of the mixture according to the molecular modeling adequately corresponds to the ideal adsorbed solution theory (IAST). The cyclic processes of gas charging and discharging from the ANG storage based on the ACPK are simulated in three modes: adiabatic, isothermal, and thermocontrolled. The adiabatic mode leads to a loss of 27-33% of energy capacity at 3.5 MPa compared to the isothermal mode, which has a 9.4-19.5% lower energy capacity compared to the thermocontrolled mode, with more efficient desorption of both methane and ethane.

Hydrocarbon Tracers Suggest Methane Emissions from Fossil Sources Occur Predominately Before Gas Processing and That Petroleum Plays Are a Significant Source

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.

Highly Active Co3O4-Based Catalysts for Total Oxidation of Light C1-C3 Alkanes Prepared by a Simple Soft Chemistry Method: Effect of the Heat-Treatment Temperature and Mixture of Alkanes

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.

Electrochemical Oxidative Dehydrogenation of Ethane to Ethylene in a Solid Oxide Electrolyzer

Oxidative dehydrogenation of ethane to ethylene is an important process in light olefin industry; however, the over-oxidation of ethane leads to low ethylene selectivity. Here, we report a novel approach to electrochemical oxidative dehydrogenation of ethane in anode in conjunction with CO₂ reduction at cathode in a solid oxide electrolyser using a porous single-crystalline CeO₂ electrode at 600 °C. We identify and engineer the flux and chemical states of active oxygen species that evolve from the lattice at anode surface to activate and dehydrogenate ethane to ethylene via the reaction of epoxy species. Active oxygen species (O^2- , O₂ ^2- and O₂ ^- ) at the anode surface effectively dehydrogenate ethane to ethylene, but O^- species tend to induce deep oxidation. We demonstrate exceptionally high ethylene selectivity of 95 % and an ethane conversion of 10 % with a durable operation of 300 h.

Chemically Stable Hafnium-Based Metal-Organic Framework for Highly Efficient C2H6/C2H4 Separation under Humid Conditions

Realization of ethane-selective porous materials for efficient ethane/ethylene (C₂H₆/C₂H₄) separation is an important task in the petrochemical industry. Although a number of C₂H₆-selective adsorbents have been realized, their adsorption capacity and selectivity might be mostly dampened under humid conditions due to structure decomposition or co-adsorption of water vapor. A desired material should have simultaneously high C₂H₆ uptake and selectivity, excellent water stability, and ultralow water adsorption uptake for industrial applications, but such a material is elusive. Herein, we report a chemically stable hafnium-based material (Hf)DUT-52a, featuring the suitable pore apertures and less hydrophilicity for highly efficient C₂H₆/C₂H₄ separation under humid conditions. Gas sorption results reveal that (Hf)DUT-52a exhibits both high ethane adsorption capacity (4.02 mmol g^-1) and C₂H₆/C₂H₄ selectivity (1.9) at 296 K and 1 bar, which are comparable to the majority of the top-performing materials. Most importantly, the less pore hydrophilicity enables (Hf)DUT-52a to exhibit a negligible water uptake of 0.036 g g^-1 before 40% relative humidity (RH), effectively minimizing the impact of humidity on separation capacity. This material thus shows excellent separation capacity even under 40% RH with a high polymer-grade ethylene production capacity up to 8.43 L kg^-1 at ambient conditions, as evidenced by the breakthrough experiments.

Effect of Pore Connectivity on the Behavior of Fluids Confined in Sub-Nanometer Pores: Ethane and CO2 Confined in ZSM-22

The behavior of fluids under nano-confinement varies from that in bulk due to an interplay of several factors including pore connectivity. In this work, we use molecular dynamics simulations to study the behavior of two fluids—ethane and CO₂ confined in ZSM-22, a zeolite with channel-like pores of diameter 0.55 nm isolated from each other. By comparing the behavior of the two fluids in ZSM-22 with that reported earlier in ZSM-5, a zeolite with pores of similar shape and size connected to each other via sinusoidal pores running perpendicular to them, we reveal the important role of pore connectivity. Further, by artificially imposing pore connectivity in ZSM-22 via inserting a 2-dimensional slab-like inter-crystalline space of thickness 0.5 nm, we also studied the effect of the dimensionality and geometry of pore connectivity. While the translational motion of both ethane and CO₂ in ZSM-22 is suppressed as a result of connecting the pores by perpendicular quasi-one-dimensional pores of similar dimensions, the effect of connecting the pores by inserting the inter-crystalline space is different on the translational motion of the two fluids. For ethane, pores connected via inter-crystalline space facilitate translational motion but suppress rotational motion, whereas in the case of CO₂, both types of motion are suppressed by pore connection due to the strong interaction of CO₂ with the surface of the substrate.

Reductive degradation of chlorinated organophosphate esters by nanoscale zerovalent iron/cetyltrimethylammonium bromide composites: Reactivity, mechanism and new pathways

Chlorinated organophosphate esters (Cl-OPEs), e.g., tris(2-chloroethyl) phosphate (TCEP), tris(2-chloro-2-propyl) phosphate (TCPP) and tris(1,3-dichloro-2-propyl) phosphate (TDCPP), are widely used as additive flame retardants in commercial and building products. They have potential persistent organic pollutant properties and are frequently detected in various waters, especially in wastewaters. Nanoscale zerovalent iron (nZVI)-based method is an efficient reductive technology for treating waters polluted by halogenated organic pollutants (HOCs). Cetyltrimethylammonium bromide (CTAB) is a ubiquitous surfactant in wastewaters and can favorably affect the interaction between HOCs and nZVI. However, its effect on the Cl-OPEs removal by nZVI-based materials still remains unknown. Herein, the adsorption and degradation efficiencies of Cl-OPEs by nZVI and sulfidated nZVI (S-nZVI) in the presence or absence of CTAB were quantified based on the decreasing concentrations of Cl-OPEs in reaction systems. Our results showed that TDCPP and TCPP were adsorbed onto the nZVI or S-nZVI surface and subsequently degraded. In contrast, TCEP was just adsorbed onto the particle surface without further degradation. The addition of CTAB significantly enhanced the hydrophobic adsorption between Cl-OPEs and nZVI or S-nZVI, leading to increased degradation of Cl-OPEs (especially TCEP). CTAB adsorption isotherms indicated that S-nZVI had a higher adsorption capacity for CTAB than nZVI. The S-nZVI/CTAB composite exhibited a better performance than nZVI/CTAB composite. When S-nZVI was combined with 100.0 mg L^-1 CTAB, 100% of TDCPP, TCPP and TCEP was degraded within 3 hours, 5 and 14 days, respectively. As the concentration of CTAB was increased up to 335.0 mg L^-1, TCEP could be completely degraded within 3 days by S-nZVI. Five degradation products of TCEP were identified, of which O,O-di-(2-chloroethyl) O-ethyl phosphate (DCEEP) and ethane were reported for the first time. We propose that TCEP is dechlorinated by nZVI or S-nZVI through the electron attack at the ethyl-chlorine group to form bis(2-chloroethyl) phosphate, DCEEP, chloride, ethene and ethane, representing previously unknown degradation pathways.

More Than a Methanotroph: A Broader Substrate Spectrum for Methylacidiphilum fumariolicum SolV

Volcanic areas emit a number of gases including methane and other short chain alkanes, that may serve as energy source for the prevailing microorganisms. The verrucomicrobial methanotroph Methylacidiphilum fumariolicum SolV was isolated from a volcanic mud pot, and is able to grow under thermoacidophilic conditions on different gaseous substrates. Its genome contains three operons encoding a particulate methane monooxygenase (pMMO), the enzyme that converts methane to methanol. The expression of two of these pmo operons is subjected to oxygen-dependent regulation, whereas the expression of the third copy (pmoCAB3) has, so far, never been reported. In this study we investigated the ability of strain SolV to utilize short-chain alkanes and monitored the expression of the pmo operons under different conditions. In batch cultures and in carbon-limited continuous cultures, strain SolV was able to oxidize and grow on C₁–C₃ compounds. Oxidation of ethane did occur simultaneously with methane, while propane consumption only started once methane and ethane became limited. Butane oxidation was not observed. Transcriptome data showed that pmoCAB1 and pmoCAB3 were induced in the absence of methane and the expression of pmoCAB3 increased upon propane addition. Together the results of our study unprecedently show that a pMMO-containing methanotroph is able to co-metabolize other gaseous hydrocarbons, beside methane. Moreover, it expands the substrate spectrum of verrucomicrobial methanotrophs, supporting their high metabolic flexibility and adaptation to the harsh and dynamic conditions in volcanic ecosystems.

Fiber-Coupled Quartz-Enhanced Photoacoustic Spectroscopy System for Methane and Ethane Monitoring in the Near-Infrared Spectral Range

We report on a fiber-coupled, quartz-enhanced photoacoustic spectroscopy (QEPAS) near-IR sensor for sequential detection of methane (CH₄ or C1) and ethane (C₂H₆ or C2) in air. With the aim of developing a lightweight, compact, low-power-consumption sensor suitable for unmanned aerial vehicles (UAVs)-empowered environmental monitoring, an all-fiber configuration was designed and realized. Two laser diodes emitting at 1653.7 nm and 1684 nm for CH₄ and C₂H₆ detection, respectively, were fiber-combined and fiber-coupled to the collimator port of the acoustic detection module. No cross talk between methane and ethane QEPAS signal was observed, and the related peak signals were well resolved. The QEPAS sensor was calibrated using gas samples generated from certified concentrations of 1% CH₄ in N₂ and 1% C₂H₆ in N₂. At a lock-in integration time of 100 ms, minimum detection limits of 0.76 ppm and 34 ppm for methane and ethane were achieved, respectively. The relaxation rate of CH₄ in standard air has been investigated considering the effects of H₂O, N₂ and O₂ molecules. No influence on the CH₄ QEPAS signal is expected when the water vapor concentration level present in air varies in the range 0.6–3%.

Multivariate Analysis of Photoacoustic Spectra for the Detection of Short-Chained Hydrocarbon Isotopologues

We report, to our knowledge, the first optical detection scheme for short-chained hydrocarbon isotopologues. The sensor system is based on photoacoustic spectroscopy (PAS). Two continuous wave, thermoelectrically cooled, distributed feedback interband cascade lasers (DFB-ICLs) with emission wavelengths around 3.33 and 3.38 μm, respectively, served as light sources. The investigations comprised the main stable carbon isotopologues of methane (¹²CH₄, ¹³CH₄), ethane (¹²CH₃-¹²CH₃, ¹³CH₃-¹²CH₃, ¹³CH₃-¹³CH₃), and propane (¹²CH₃-¹²CH₂-¹²CH₃, ¹³CH₃-¹²CH₂-¹²CH₃). They were selected because of their importance for numerous applications from climate and planetary research to natural gas exploration. Multiple measurements of single components in nitrogen and synthetic mixtures were conducted at room temperature and atmospheric pressure. Depending on the investigated hydrocarbon isotopologue, detection limits ranging from 0.043 ppmv to 3.4 ppmv were achieved. For a selective concentration determination, multivariate analysis (MVA) was applied. Partial least-squares regression (PLSR) was used to calculate concentrations from the PA spectra. The implementation of MVA has shown that the PA setup in principle works reliably and that the selective concentration determination of short-chained hydrocarbon isotopologues is possible.

Alumina-based Coating for Coke Reduction in Steam Crackers

Alumina-based coatings have been claimed as being an advantageous modification in industrial ethylene furnaces. In this work, on-line experimentally measured coking rates of a commercial coating (CoatAlloy™) have pointed out its superiority compared to an uncoated reference material in an electrobalance set-up. Additionally, the effects of presulfiding with 500 ppmw DMDS per H₂O, continuous addition of 41 ppmw S per HC of DMDS, and a combination thereof were evaluated during ethane steam cracking under industrially relevant conditions (T_gasphase = 1173 K, P_tot = 0.1 MPa, X_C2H6 = 70%, dilution δ = 0.33 kg_H2O/kg_HC). The examined samples were further evaluated using online thermogravimetry, scanning electron microscopy and energy diffractive X-ray for surface and cross-section analysis together with X-ray photoelectron spectroscopy and wavelength-dispersive X-ray spectroscopy for surface analysis. The passivating coating illustrated a better performance than the reference Ni-Cr Fe-base alloy after application of an improved pretreatment, followed by piddling changes on the product distribution. Presulfiding of the coating affected negatively the observed coking rates in comparison with the reference alloy, so alternative presulfiding and sulfur addition strategies are recommended when using this barrier coating.

Oxidative Methane Conversion to Ethane on Highly Oxidized Pd/CeO2 Catalysts Below 400 °C

Methane upgrading into more valuable chemicals has received much attention. Herein, we report oxidative methane conversion to ethane using gaseous O₂ at low temperatures (<400 °C) and atmospheric pressure in a continuous reactor. A highly oxidized Pd deposited on ceria could produce ethane with a productivity as high as 0.84 mmol g_cat ^-1  h^-1 . The Pd-O-Pd sites, not Pd-O-Ce, were the active sites for the selective ethane production at low temperatures. Density functional theory calculations confirmed that the Pd-O-Pd site is energetically more advantageous for C-C coupling, whereas Pd-O-Ce promotes CH₄ dehydrogenation. The ceria helped Pd maintain a highly oxidic state despite reductive CH₄ flow. This work can provide new insight for methane upgrading into C₂ species.

In-Depth Understanding of the Morphology Effect of α-Fe2O3 on Catalytic Ethane Destruction

Shape effects of nanocrystal catalysts in different reactions have attracted remarkable attention. In the present work, three types of α-Fe₂O₃ oxides with different micromorphologies were rationally synthesized via a facile solvothermal method and adopted in deep oxidation of ethane. The physicochemical properties of prepared materials were characterized by XRD, N₂ sorption, FE-SEM, HR-TEM, FTIR, in situ DRIFTS, XPS, Mössbauer spectroscopy, in situ Raman, electron energy loss spectroscopy, and H₂-TPR. Moreover, the formation energy of oxygen vacancy and surface electronic structure on various crystal faces of α-Fe₂O₃ were explored by DFT calculations. It is shown that nanosphere-like α-Fe₂O₃ exhibits much higher ethane destruction activity and reaction stability than nanocube-like α-Fe₂O₃ and nanorod-like α-Fe₂O₃ due to larger amounts of oxygen vacancies and lattice defects, which greatly enhance the concentration of reactive oxygen species, oxygen transfer speed, and material redox property. In addition to this, DFT results reveal that nanosphere-like α-Fe₂O₃ has the lowest formation energy of oxygen vacancy on the (110) facet ( E_vo (110) = 1.97 eV) and the strongest adsorption energy for ethane (-0.26 eV) and O₂ (-1.58 eV), which can accelerate the ethane oxidation process. This study has deepened the understanding of the face-dependent activities of α-Fe₂O₃ in alkane destruction.

Dual-Gas Sensor of CH₄/C₂H₆ Based on Wavelength Modulation Spectroscopy Coupled to a Home-Made Compact Dense-Pattern Multipass Cell

A sensitive dual-gas sensor for the detection of CH₄ and C₂H₆ is demonstrated. Two tunable semiconductor lasers operating at 1.653 μm (for CH₄ monitoring) and 1.684 μm (for C₂H₆) were used as the light source for spectroscopic measurements of CH₄ and C₂H₆. Long-path absorption in a home-made compact dense-pattern multipass cell (Leff = 29.37 m) was employed, combined with wavelength modulation and second harmonic detection. Simultaneous detection of CH₄ and C₂H₆ was achieved by separated wavelength modulations of the two lasers. Modulation frequencies and amplitudes were optimized for sensitivity detection of CH₄ and C₂H₆ simultaneously. The dual-gas sensor exhibits 1σ detection limits of 1.5 ppbv for CH₄ in 140 s averaging time and 100 ppbv for C₂H₆ in 200 s.

Development and Optimization of the Biological Conversion of Ethane to Ethanol Using Whole-Cell Methanotrophs Possessing Methane Monooxygenase

The biological production of ethanol from ethane for the utilization of ethane in natural gas was investigated under ambient conditions using whole-cell methanotrophs possessing methane monooxygenase. Several independent variables including ethane concentration and biocatalyst amounts, among other factors, were optimized for the enhancement of ethane-to-ethanol bioconversion. We obtained 0.4 g/L/h of volumetric productivity and 0.52 g/L of maximum titer in optimum batch reaction conditions. In this study, we demonstrate that the biological gas-to-liquid conversion of ethane to ethanol has potent technical feasibility as a new application of ethane gas.

A Generalized Correlation for Predicting Ethane, Propane, and Isobutane Hydrates Equilibrium Data in Pure Water and Aqueous Salt Solutions

Hydrate formation can cause serious problems in hydrocarbon exploration, production, and transportation, especially in deepwater environments. Hydrate-related problems affects the integrity of the deepwater platforms, leads to equipment blockages, and also increases operational costs. In order to solve these problems, salts are used as thermodynamic inhibitors and also mixed with the drilling fluids in most drilling processes. A comprehensive understanding of hydrate formation in aqueous salt solutions is vital to overcome these problems. Statistical thermodynamic models are commonly used to predict hydrate formation conditions in different aqueous solutions. However, these models involve rigorous computations and are restricted to certain conditions. They give inaccurate predictions of hydrate equilibrium conditions for high-temperature, high-pressure, and high-salinity systems. Therefore, it is paramount to develop a simple-to-use and reliable prediction tool. In this work, an empirical correlation is developed and successfully used to predict the equilibrium conditions of ethane, propane, and isobutane hydrates in pure water and aqueous solutions of sodium chloride, potassium chloride, calcium chloride, and magnesium chloride. Experimental data on hydrate formation conditions for these components are regressed and a generalized correlation is obtained. The predictions in this work show excellent agreement with all the experimental data in the literature.

Sorption, Structure and Dynamics of CO₂ and Ethane in Silicalite at High Pressure: A Combined Monte Carlo and Molecular Dynamics Simulation Study

Silicalite is an important nanoporous material that finds applications in several industries, including gas separation and catalysis. While the sorption, structure, and dynamics of several molecules confined in the pores of silicalite have been reported, most of these studies have been restricted to low pressures. Here we report a comparative study of sorption, structure, and dynamics of CO₂ and ethane in silicalite at high pressures (up to 100 bar) using a combination of Monte Carlo (MC) and molecular dynamics (MD) simulations. The behavior of the two fluids is studied in terms of the simulated sorption isotherms, the positional and orientational distribution of sorbed molecules in silicalite, and their translational diffusion, vibrational spectra, and rotational motion. Both CO₂ and ethane are found to exhibit orientational ordering in silicalite pores; however, at high pressures, while CO₂ prefers to reside in the channel intersections, ethane molecules reside mostly in the sinusoidal channels. While CO₂ exhibits a higher self-diffusion coefficient than ethane at low pressures, at high pressures, it becomes slower than ethane. Both CO₂ and ethane exhibit rotational motion at two time scales. At both time scales, the rotational motion of ethane is faster. The differences observed here in the behavior of CO₂ and ethane in silicalite pores can be seen as a consequence of an interplay of the kinetic diameter of the two molecules and the quadrupole moment of CO₂.

Large changes in biomass burning over the last millennium inferred from paleoatmospheric ethane in polar ice cores

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.

Molecular Sieving of Ethane from Ethylene through the Molecular Cross-Section Size Differentiation in Gallate-based Metal-Organic Frameworks

Purification of C₂ H₄ from an C₂ H₄ /C₂ H₆ mixture, one of the most important while challenging industrial separation processes, is mainly through energy-intensive cryogenic distillation. Now a family of gallate-based metal-organic framework (MOF) materials is presented, M-gallate (M=Ni, Mg, Co), featuring 3D interconnected zigzag channels, the aperture sizes of which (3.47-3.69 Å) are ideally suitable for molecular sieving of ethylene (3.28×4.18×4.84 ų ) and ethane (3.81×4.08×4.82 ų ) through molecular cross-section size differentiation. Co-gallate shows an unprecedented IAST selectivity of 52 for C₂ H₄ over C₂ H₆ with a C₂ H₄ uptake of 3.37 mmol g^-1 at 298 K and 1 bar, outperforming the state-of-the-art MOF material NOTT-300. Direct breakthrough experiments with equimolar C₂ H₄ /C₂ H₆ mixtures confirmed that M-gallate is highly selective for ethylene. The adsorption structure and mechanism of ethylene in the M-gallate was further studied through neutron diffraction experiments.

Effect of Long-Term High Temperature Oxidation on the Coking Behavior of Ni-Cr Superalloys

The service time of an industrial cracker is strongly dependent on the long-term coking behavior and microstructure stability of the reactor coil alloy. Super alloys are known to withstand temperatures up to even 1400 K. In this work, several commercially available alloys have been first exposed to a long term oxidation at 1423 K for 500 h, so-called metallurgic aging. Subsequently, their coking behavior was evaluated in situ in a thermogravimetric setup under ethane steam cracking conditions (T_gasphase = 1173 K, P_tot = 0.1 MPa, X_C2H6 = 70%, continuous addition of 41 ppmw S/HC of DMDS, dilution δ = 0.33 kg_H2O/kg_HC) and compared with their unaged coking behavior. The tested samples were also examined using scanning electron microscopy and energy diffractive X-ray for surface and cross-section analysis. The alloys characterized by increased Cr-Ni content or the addition of Al showed improved stability against bulk oxidation and anti-coking behavior after application of metallurgic aging due to the formation of more stable oxides on the top surface.

CNT Foam-Embedded Micro Gas Preconcentrator for Low-Concentration Ethane Measurements

Breath analysis has become increasingly important as a noninvasive process for the clinical diagnosis of patients suffering from various diseases. Many commercial gas preconcentration instruments are already being used to overcome the detection limits of commercial gas sensors for gas concentrations which are as low as ~100 ppb in exhaled breath. However, commercial instruments are large and expensive, and they require high power consumption and intensive maintenance. In the proposed study, a micro gas preconcentrator (μ-PC) filled with a carbon nanotube (CNT) foam as an adsorbing material was designed and fabricated for the detection of low-concentration ethane, which is known to be one of the most important biomarkers related to chronic obstructive pulmonary disease (COPD) and asthma. A comparison of the performance of two gas-adsorbing materials, i.e., the proposed CNT foam and commercial adsorbing material, was performed using the developed μ-PC. The experimental results showed that the synthesized CNT foam performs better than a commercial adsorbing material owing to its lower pressure drop and greater preconcentration efficiency in the μ-PC. The present results show that the application of CNT foam-embedded μ-PC in portable breath analysis systems holds great promise.

Measuring the respiratory gas exchange by grazing cattle using an automated, open-circuit gas quantification system

Ruminants are a source of enteric CH₄, which has been identified as an anthropogenic greenhouse gas that contributes to climate change. With interest in developing technologies to decrease enteric CH₄ emissions, systems are currently being developed to measure CH₄ emissions by cattle. An issue with grazing cattle is the ability to measure CH₄ emissions in open-air environments. A scientific instrument for this task is an automated, open-circuit gas quantification system (GQS; C-Lock, Inc., Rapid City, SD). The GQS is a head chamber that grazing cattle occasionally visit (3 to 8 min/visit; 3 to 6 visits/d), and while the animal consumes a small portion of bait (0.5 to 1.0 kg/visit), the GQS captures the animal's breath cloud by exhausting air through the GQS. The breath cloud is then analyzed for CH₄, CO₂, and O₂ concentrations. Data are hourly uploaded to a server where it is processed using algorithms to determine total daily fluxes. Several factors affect emission estimates generated by the GQS including the animal's visitation rate, length of sampling period, and airflow through the system. The location of the GQS is an important factor in determining the cattle's willingness to visit. Further, cattle need to be trained to use the GQS, which normally requires 4 to 8 wk. Several researchers have shown that 30 or more visits are required to obtain high-quality estimates of gas fluxes. Once cattle are trained to use the GQS, the bait delivery rate has little effect on the animal's willingness to use the system. Airflow through the GQS is an important factor, but as long as airflow is maintained above 26 L/s the breath-cloud capture seems nearly complete. There is great concern regarding circadian variation in the instantaneous production rates of CH₄ because the GQS normally only spot-samples 2 to 4 times/d. Preliminary analysis has shown that variation in the instantaneous production rates of CH₄ do not vary as greatly with grazing cattle compared with meal-fed cattle. It seems that increasing the visitation length decreases variation in estimated emissions, but there is a diminishing return to increasing visitation length. The GQS is a useful tool for researching the nutrition and emissions of grazing cattle, but great care must be taken to obtain the best quality data possible for use in this high-impact research.

Low-Temperature and Rapid Growth of Large Single-Crystalline Graphene with Ethane

Future applications of graphene rely highly on the production of large-area high-quality graphene, especially large single-crystalline graphene, due to the reduction of defects caused by grain boundaries. However, current large single-crystalline graphene growing methodologies are suffering from low growth rate and as a result, industrial graphene production is always confronted by high energy consumption, which is primarily caused by high growth temperature and long growth time. Herein, a new growth condition achieved via ethane being the carbon feedstock to achieve low-temperature yet rapid growth of large single-crystalline graphene is reported. Ethane condition gives a growth rate about four times faster than methane, achieving about 420 µm min^-1 for the growth of sub-centimeter graphene single crystals at temperature about 1000 °C. In addition, the temperature threshold to obtain graphene using ethane can be reduced to 750 °C, lower than the general growth temperature threshold (about 1000 °C) with methane on copper foil. Meanwhile ethane always keeps higher graphene growth rate than methane under the same growth temperature. This study demonstrates that ethane is indeed a potential carbon source for efficient growth of large single-crystalline graphene, thus paves the way for graphene in high-end electronical and optoelectronical applications.

Optimizing Open Iron Sites in Metal-Organic Frameworks for Ethane Oxidation: A First-Principles Study

Activation of the C-H bonds in ethane to form ethanol is a highly desirable, yet challenging, reaction. Metal-organic frameworks (MOFs) with open Fe sites are promising candidates for catalyzing this reaction. One advantage of MOFs is their modular construction from inorganic nodes and organic linkers, allowing for flexible design and detailed control of properties. In this work, we studied a series of single-metal atom Fe model systems with ligands that are commonly used as MOF linkers and tried to understand how one can design an optimal Fe catalyst. We found linear relationships between the binding enthalpy of oxygen to the Fe sites and common descriptors for catalytic reactions, such as the Fe 3d energy levels in different reaction intermediates. We further analyzed the three highest-barrier steps in the ethane oxidation cycle (including desorption of the product) with the Fe 3d energy levels. Volcano relationships are revealed with peaks toward higher Fe 3d energy and stronger electron-donating group functionalization of linkers. Furthermore, we found that the Fe 3d energy levels positively correlate with the electron-donating strength of functional groups on the linkers. Finally, we validated our hypotheses on larger models of MOF-74 iron sites. Compared with MOF-74, functionalizing the MOF-74 linkers with NH₂ groups lowers the enthalpic barrier for the most endothermic step in the reaction cycle. Our findings provide insight for catalyst optimization and point out directions for future experimental efforts.

Accurate adsorption energies for small molecules on oxide surfaces: CH4 /MgO(001) and C2 H6 /MgO(001)

A hybrid method is applied that combines second order Møller-Plesset perturbation theory (MP2) for cluster models with density functional theory for periodic (slab) models to obtain structures and energies for methane and ethane molecules adsorbed on the MgO(001) surface. Single point calculations are performed to estimate the effect of increasing the cluster size on the MP2 energies and to evaluate the difference between coupled cluster (CCSD(T)) and MP2 energies. The final estimates of the adsorption energies are 12.9 ± 1.3 and 18.9 ± 1.8 kJ/mol for CH4 and C2 H6 , respectively. © 2016 Wiley Periodicals, Inc.

Application of Cavity Enhanced Absorption Spectroscopy to the Detection of Nitric Oxide, Carbonyl Sulphide, and Ethane--Breath Biomarkers of Serious Diseases

The paper presents one of the laser absorption spectroscopy techniques as an effective tool for sensitive analysis of trace gas species in human breath. Characterization of nitric oxide, carbonyl sulphide and ethane, and the selection of their absorption lines are described. Experiments with some biomarkers showed that detection of pathogenic changes at the molecular level is possible using this technique. Thanks to cavity enhanced spectroscopy application, detection limits at the ppb-level and short measurements time (<3 s) were achieved. Absorption lines of reference samples of the selected volatile biomarkers were probed using a distributed feedback quantum cascade laser and a tunable laser system consisting of an optical parametric oscillator and difference frequency generator. Setup using the first source provided a detection limit of 30 ppb for nitric oxide and 250 ppb for carbonyl sulphide. During experiments employing a second laser, detection limits of 0.9 ppb and 0.3 ppb were obtained for carbonyl sulphide and ethane, respectively. The conducted experiments show that this type of diagnosis would significantly increase chances for effective therapy of some diseases. Additionally, it offers non-invasive and real time measurements, high sensitivity and selectivity as well as minimizing discomfort for patients. For that reason, such sensors can be used in screening for early detection of serious diseases.

Conversion of CO2 and C2H6 to propanoic acid over a Au-exchanged MCM-22 zeolite

Finding novel catalysts for the direct conversion of CO2 to fuels and chemicals is a primary goal in energy and environmental research. In this work, density functional theory (DFT) is used to study possible reaction mechanisms for the conversion of CO2 and C2H6 to propanoic acid over a gold-exchanged MCM-22 zeolite catalyst. The reaction begins with the activation of ethane to produce a gold ethyl hydride intermediate. Hydrogen transfers to the framework oxygen leads then to gold ethyl adsorbed on the Brønsted-acid site. The energy barriers for these steps of ethane activation are 9.3 and 16.3 kcal mol(-1), respectively. Two mechanisms of propanoic acid formation are investigated. In the first one, the insertion of CO2 into the Au-H bond of the first intermediate yields gold carboxyl ethyl as subsequent intermediate. This is then converted to propanoic acid by forming the relevant C-C bond. The activation energy of the rate-determining step of this pathway is 48.2 kcal mol(-1). In the second mechanism, CO2 interacts with gold ethyl adsorbed on the Brønsted-acid site. Propanoic acid is formed via protonation of CO2 by the Brønsted acid and the simultaneous formation of a bond between CO2 and the ethyl group. The activation energy there is 44.2 kcal mol(-1), favoring this second pathway at least at low temperatures. Gold-exchanged MCM-22 zeolite can therefore, at least in principle, be used as the catalyst for producing propanoic acid from CO2 and ethane.

Geomicrobiological linkages between short-chain alkane consumption and sulfate reduction rates in seep sediments

Marine hydrocarbon seeps are ecosystems that are rich in methane, and, in some cases, short-chain (C₂–C₅) and longer alkanes. C₂–C₄ alkanes such as ethane, propane, and butane can be significant components of seeping fluids. Some sulfate-reducing microbes oxidize short-chain alkanes anaerobically, and may play an important role in both the competition for sulfate and the local carbon budget. To better understand the anaerobic oxidation of short-chain n-alkanes coupled with sulfate-reduction, hydrocarbon-rich sediments from the Gulf of Mexico (GoM) were amended with artificial, sulfate-replete seawater and one of four n-alkanes (C₁–C₄) then incubated under strict anaerobic conditions. Measured rates of alkane oxidation and sulfate reduction closely follow stoichiometric predictions that assume the complete oxidation of alkanes to CO₂ (though other sinks for alkane carbon likely exist). Changes in the δ¹³C of all the alkanes in the reactors show enrichment over the course of the incubation, with the C₃ and C₄ incubations showing the greatest enrichment (4.4 and 4.5‰, respectively). The concurrent depletion in the δ¹³C of dissolved inorganic carbon (DIC) implies a transfer of carbon from the alkane to the DIC pool (−3.5 and −6.7‰ for C₃ and C₄ incubations, respectively). Microbial community analyses reveal that certain members of the class Deltaproteobacteria are selectively enriched as the incubations degrade C₁–C₄ alkanes. Phylogenetic analyses indicate that distinct phylotypes are enriched in the ethane reactors, while phylotypes in the propane and butane reactors align with previously identified C₃–C₄ alkane-oxidizing sulfate-reducers. These data further constrain the potential influence of alkane oxidation on sulfate reduction rates (SRRs) in cold hydrocarbon-rich sediments, provide insight into their contribution to local carbon cycling, and illustrate the extent to which short-chain alkanes can serve as electron donors and govern microbial community composition and density.

First-principles elucidation of the surface chemistry of the C(2)H(x) (x = 0-6) adsorbate series on Fe(100)

Ab initio total-energy calculations of the elementary reaction steps leading to acetylene, ethylene and ethane formation and their decomposition on Fe(100) are described. Alongside the endothermicity of all the formation reactions, the crucial role played by adsorbed ethyl as main precursor towards both ethylene and ethane formation, characterises Fe(100) surface reactivity towards C(2)H(x) (x = 0-6) hydrocarbon formation in the low coverage limit. A comprehensive scheme based on three viable mechanisms towards ethyl formation on Fe(100), including methyl/methylene coupling, methyl/methylidyne coupling followed by one hydrogenation and methyl/carbon coupling followed by two hydrogenations, is the main result of this article.

Ammonia clathrate hydrates as new solid phases for Titan, Enceladus, and other planetary systems

There is interest in the role of ammonia on Saturn's moons Titan and Enceladus as the presence of water, methane, and ammonia under temperature and pressure conditions of the surface and interior make these moons rich environments for the study of phases formed by these materials. Ammonia is known to form solid hemi-, mono-, and dihydrate crystal phases under conditions consistent with the surface of Titan and Enceladus, but has also been assigned a role as water-ice antifreeze and methane hydrate inhibitor which is thought to contribute to the outgassing of methane clathrate hydrates into these moons' atmospheres. Here we show, through direct synthesis from solution and vapor deposition experiments under conditions consistent with extraterrestrial planetary atmospheres, that ammonia forms clathrate hydrates and participates synergistically in clathrate hydrate formation in the presence of methane gas at low temperatures. The binary structure II tetrahydrofuran + ammonia, structure I ammonia, and binary structure I ammonia + methane clathrate hydrate phases synthesized have been characterized by X-ray diffraction, molecular dynamics simulation, and Raman spectroscopy methods.

The rotational barrier in ethane: a molecular orbital study

The energy change on each Occupied Molecular Orbital as a function of rotation about the C-C bond in ethane was studied using the B3LYP, mPWB95 functional and MP2 methods with different basis sets. Also, the effect of the ZPE on rotational barrier was analyzed. We have found that σ and π energies contribution stabilize a staggered conformation. The σ(s) molecular orbital stabilizes the staggered conformation while the stabilizes the eclipsed conformation and destabilize the staggered conformation. The π(z) and molecular orbitals stabilize both the eclipsed and staggered conformations, which are destabilized by the π(v) and molecular orbitals. The results show that the method of calculation has the effect of changing the behavior of the energy change in each Occupied Molecular Orbital energy as a function of the angle of rotation about the C-C bond in ethane. Finally, we found that if the molecular orbital energy contribution is deleted from the rotational energy, an inversion in conformational preference occurs.

Torsional Splittings and Assignments of the Doppler-Limited Spectrum of Ethane in the C-H Stretching Region

The Doppler-limited absorption spectrum of the C-H stretching region of ethane has been recorded at T≃ 119 K with a tunable difference-frequency laser spectrometer. The strong torsional hot band structure at room temperature is eliminated at 119 K, and the enhanced resolution from the Doppler width reduction allows us to observe small torsional splittings. The two fundamentals in the region, v ₇, a perpendicular band and, v ₅, a parallel band have been essentially completely assigned as have a large number of transitions in the parallel component of the v ₈ + v ₁₁ combination band. A number of perturbations of both global and local nature have been observed. The complete spectrum and a listing of transition wavenumbers, intensities and assignments are presented here to facilitate identification and quantitative analysis of ethane in a variety of monitoring applications. Precise ground state rotational constants have been determined from combination differences.

Measurements of the Specific Heats, Cσ , and Cv of Dense Gaseous and Liquid Ethane. J Res Natl Bur Stand A Phys Chem 1976;80A:739-759. [PMID: 32196297 PMCID: PMC5312758 DOI: 10.6028/jres.080a.069]

The specific heats of saturated liquid ethane, Cσ , have been measured at 106 temperatures in the temperature range 93 to 301 K. The specific heats at constant volume, Cv have been measured at 19 densities ranging from 0.2 to 3.1 times the critical density, at temperatures between 91 and 330 K, with pressures to 33 MPa, at 200 PVT states in all. The uncertainty of most of the measurements is estimated to be less than 2.0 percent. As the critical point is approached the uncertainty rises to about 5.0 percent. The measurements were performed to provide input data for accurate calculations of the thermodynamic properties for ethane. They are believed to be the most comprehensive specific heat measurements available for the liquid and vapor states of ethane.

PVT and Vapor Pressure Measurements on Ethane

New measurements of the vapor pressures and PVT properties of ethane are reported. PVT determinations have been made from near the triple point to 320 K at pressures to 33 MPa. The density range investigated extends to more than three times the critical density. The new measurements of the vapor pressures of ethane extend from 160 K to near the critical point.

Equation of State for Thermodynamic Properties of Fluids

This equation of state was developed from PVT compressibility data on methane and ethane. The highly-constrained form originates on a given liquid-vapor coexistence boundary (described by equations for the vapor pressures and the orthobaric densities). It then requires only five least-squares coefficients, and ensures a qualitatively correct behavior of the P(ρ, T) surface and of its derivatives, especially about the critical point. This nonanalytic equation yields a maximum in the specific heats C υ (ρ, T) a t the critical point.