Pure CH4 Research Articles

Highly efficient gas sensor based on quasi-periodic phononic crystals

Highly sensitive gas sensors have been introduced for the sensing of air, NH3, O2, CO2, or CH4 gases. The quasi-periodic structures of simple and generalized Fibonacci, simple and generalized Thue-Morse, Rudin-Shapiro, and symmetry structures have been regarded composed of diverse materials of PDMS, Epoxy, Al, and Steel and the detection gas. The proposed quasi-periodic structures have been investigated for maximum 10 alternating layers of solid-fluid arrangement with thickness ratio of (dsoild:dfluid)=(9:1). The study has been carried out by the transfer matrix method for the longitudinal wave propagation and the FC(5,1) and RS(4) structures composed of Al and Steel as solid material presented single peak shift for different gas infiltration. The sensitivities of 0.5988 MHz.m3. kg−1, 0.7777 MHz.m3. kg−1, 0.8738 MHz.m3. kg−1, and 0.9346 MHz.m3. kg-1 have been obtained in the frequency range of MHz for pure CO2, O2, NH3, and CH4 gases, respectively. Also, the best layer sequence for highly efficient gas sensor in 1D phononic quasi-crystals has been obtained, discussed, and optimized to get high quality factor.

Experimental, Modeling and AspenPlus Simulation of Different Configurations of Membrane Separation Systems for Highly Loaded CO2 Selective Pebax 1657-ZIF-8 Membrane

ZIF-8 powder was synthesized and added with concentrations from 10 to 60 wt.% to the Pebax 1657 matrix modified with Di-butyl-methylimidazolium fluoride (DBMF) ionic liquid. SEM, XRD and 13C-NMR analysis were applied for the characterization of particles and mixed matrix membranes (MMMs). The results of 13C-NMR analysis suggested that there are possible new carbon-carbon bonds at particle-polymer interface. The CO2/CH4 mixed gas test results showed that the utilization of high concentrations of ZIF-8 in Pebax 1657 matrix was effective. MMMs containing 60 wt.% and 30 wt.% of ZIF-8 showed the highest (24.4) and lowest (12) CO2/CH4 selectivity among the all synthesized MMM and pure polymeric samples, respectively. The results of the Microsoft Excel/Aspen Plus modeling and simulation showed that the increase in membrane area, number of membrane modules and the pressure difference across membranes led to performance advantages for the single-step with permeate recycling (SiSRP) and double step with retentate recycling (DoSRR) configurations of separation systems. The highest CH4 recovery was observed for the double-step with permeate recycling (DoSPR) configurations when the feed was nearly pure CH4. The temperature rise showed a notable increasing effect on permeates flow rates of both gases leading to the deterioration of the separation effectiveness for all configurations. The analysis of membrane thickness on gas permeation showed that the synthesis of thinner membranes leads to better separation performance utilizing permeant or/and retentate recycle lead to more purified products.

Production Method under Surveillance: Laboratory Pilot-Scale Simulation of CH4–CO2 Exchange in a Natural Gas Hydrate Reservoir

The “guest exchange” of methane (CH4) by carbon dioxide (CO2) in naturally occurring gas hydrates is seen as a possibility to concurrently produce CH4 and sequester CO2. Presently, process evaluation is based on CH4–CO2 exchange yields of small- or medium-scale laboratory experiments, mostly neglecting mass and heat transfer processes. This work investigates process efficiencies in two large-scale experiments (210 L sample volume) using fully water-saturated, natural reservoir conditions and a gas hydrate saturation of 50%. After injecting 50 kg of heated CO2 discontinuously (E1) and continuously (E2) and a subsequent soaking period, the reservoir was depressurized discontinuously. It was monitored using electrical resistivity, temperature and pressure sensors, and fluid flow and gas composition measurements. Phase and component inventories were analyzed based on mass and volume balances. The total CH4 production during CO2 injection was only 5% of the initial CH4 inventory. Prior to CO2 breakthrough, the produced CH4 roughly equaled dissolved CH4 in the produced pore water, which balanced the volume of the injected CO2. After CO2 breakthrough, CH4 ratios in the released CO2 quickly dropped to 2.0–0.5 vol %. The total CO2 retention was the highest just before the CO2 breakthrough and higher in E1 where discontinuous injection improved the distribution of injected CO2 and subsequent mixed hydrate formation. The processes were improved by the succession of CO2 injection by controlled degassing at stability limits below that of the pure CH4 hydrate, particularly in experiment E2. Here, a more heterogeneous distribution of liquid CO2 and larger availability of free water led to smaller initial degassing of liquid CO2. This allowed for quick re-formation of mixed gas hydrates and CH4 ratios of 50% in the produced gases. The experiments demonstrate the importance of fluid migration patterns, heat transport, sample inhomogeneity, and secondary gas hydrate formation in water-saturated sediments.

Pilot-Scale Evaluation of Natural-Gas-Based Foam at High Pressures, Temperatures

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 201611, “A Pilot-Scale Evaluation of Natural-Gas-Based Foam at Elevated Pressure and Temperature Conditions,” by Griffin Beck, Swanand Bhagwat, and Carolyn Day, Southwest Research Institute, et al., prepared for the 2020 SPE Annual Technical Conference and Exhibition, originally scheduled to be held in Denver, 5–7 October. The paper has not been peer reviewed. The complete paper presents recent results from a rigorous pilot-scale demonstration of natural-gas (NG) foam over a range of operating scenarios relevant to surface and bottomhole conditions with a variety of base-fluid mixtures. The NG foams explored in these investigations exhibited typical shear-thinning behavior observed in rheological studies of nitrogen- (N2) and carbon-dioxide- (CO2) based foams. The measured viscosity and observed stability indicate that NG foams are well-suited for fracturing applications. Test Facilities Two test facilities were used to explore properties of NG foams at a variety of relevant operating conditions to determine whether NG foam is a suitable alternative to typical water-based fracturing fluids. Pilot-Scale Foam-Test Facility. The pilot-scale foam-test facility (PFTF) is a single-pass pilot plant used to generate and characterize foams at conditions relevant to surface and reservoir conditions. The facility is capable of generating aqueous and oil-based foams using a variety of gases for the internal phase [e.g., methane (CH4), N2, and CO2]. Foams can be characterized at pressures up to 7,500 psi and temperatures up to 300°F. A key benefit of the PFTF is that it can be used to demonstrate new or challenging foaming processes before large-scale or field demonstrations. Further, these processes can be evaluated at conditions relevant to the final application. The test facility consists of three subsystems: a base-fluid system to pressurize and heat the liquid/viscosifier/surfactant mixture, a gas system to pressurize and heat the liquefied gas stream, and the foam test sections to measure various fluid properties of the NG foam. Laboratory Foam-Test Facility. Tests performed on the PFTF were limited to foams generated with pure CH4 and tap water. Additional laboratory tests were conducted to investigate the effects of multiconstituent natural gas mixtures and produced water on foam stability. For these tests, the aqueous base fluid for the foam half-life and foam rheology experiments was prepared from either de-ionized water, tap water, or a synthetic produced water based on a water sample from the Permian Basin. Foam fracturing fluids also typically contain a gelling agent and a foaming agent. The gel was prepared by slow addition of guar to a stirred water sample followed by 30 minutes of mixing to ensure complete hydration. The foaming agent was added and stirred in gently. Three foaming agents were used in this study: anionic Foamer A, nonionic Foamer B, and zwitterionic Foamer C.

Mechanical and Optical Properties of Amorphous SiN-Based Films Prepared By ECR PECVD and CCP PECVD

Hydrogenated amorphous silicon nitride (a-SiN:H) and silicon carbonitride (a-SiCN:H) films grown by plasma enhanced chemical vapor deposition (PECVD) are widely investigated for their interesting optical and electrical properties [1]. In this work, we discuss the effect of the deposition power on SiN-based films during plasma deposition. The influence on the optical and mechanical properties of the films was investigated. In order to study this issue on a broader basis, two types of plasmas were applied to deposit 0.5 to 1.5 μm a-SiN:H and a-SiCN:H films. First, a-SiN:H and a-SiCN:H films were deposited by electron cyclotron resonance (ECR) PECVD using the same deposition parameters for all films. During the deposition process, the carbon content in the a-SiCN:H thin films was introduced into the chamber through a pure CH4 gas source to avoid any perturbation on the deposition pressure. Second, a-SiN:H films were deposited by a capacitively coupled plasma reactor CCP PECVD using a SiH4/NH3/N2/Ar precursor mixture. In both deposition processes, the ion bombardment energy was tuned only by the deposition power. The mechanical properties of the films were determined ex-situ by profilometry to evaluate the residual stress using the wafer curvature method and by nanoindentation to determine Young’s modulus and hardness of the films. The thickness and the refractive index were measured by variable angle spectroscopic ellipsometry (VASE). It was observed that the evolution of the residual stress according to the deposition power in the ECR PECVD was different from the CCP PECVD. Besides, we notice a slight increase in the refractive index when the residual stress becomes more compressive as illustrated in figure 1 for a-SiN:H and a-SiCN:H films. Through this discussion, we try to have a better understanding of the different interactions taking place when the deposition power increases in terms of ion bombardment energy. Then, we will study the effect of ion bombardment on the film structure based on the composition and structure of the films and the hydrogen bond concentration measured by Fourier transmission infrared spectroscopy (FTIR). In addition, we have also investigated the influence of carbon incorporation on a-SiN:H thin film properties. We notice a decrease in the refractive index and an increase in the compressive residual stress caused by the carbon incorporation.[1] A. Abdelal, Z. Khatami, and P. Mascher, “Optical and Electrical Properties of ECR-PECVD Grown SiCN Thin Films,” ECS Meet. Abstr., vol. MA2018-01, no. 17, p. 1189, Apr. 2018, doi: 10.1149/ma2018-01/17/1189. Figure 1

Molecular insights into carbon dioxide enhanced multi-component shale gas recovery and its sequestration in realistic kerogen

Understanding the governing processes of CO2 huff-n-puff in shales is essential for enhancing shale gas recovery and CO2 sequestration. However, existing studies have not fully accounted for the chemical composition and geometry of kerogen nanopores and the reality that natural gas is a multi-component mixture. We used grand canonical Monte Carlo (GCMC) simulations to study the competitive adsorption between CO2 and typical hydrocarbon components (CH4, C2H6, and C3H8). We further studied the recovery mechanisms of CO2 huff-n-puff within kerogenic circular nanopores at reservoir conditions. We probed the effects of pressure, pore geometry, and size on gas recovery and CO2 sequestration efficiency. Although pressure drop readily exploits CH4 in the adsorption layer, the recovery due to CO2 injection primarily occurs within the kerogen matrix for pure CH4. Injecting CO2 facilitates the recovery of heavier hydrocarbons, whereas pressure drawdown exhibits better performance for lighter components. CO2 huff-n-puff may serve as a promising method for gas exploitation in circular pores, whereas pressure drop favors the production in kerogen slit. The tremendously different gas adsorption and recovery behavior in distinct pore geometries and compositions necessitate the study using realistic shale kerogen models. Moreover, enlarging the pore size improves the recovery of each component during pressure drawdown but restrains the performance of CO2 injection; meanwhile, the total gas recovery and CO2 sequestration efficiency increase. This study provides a more in-depth understanding of multi-component gas recovery mechanisms within realistic shale kerogen nanopores and sheds light on the CO2 sequestration in shale reservoirs.

Sorption and Diffusion of Methane, Carbon Dioxide, and Their Mixture in Amorphous Polyethylene at High Pressures and Temperatures

Molecular dynamics (MD) simulations are performed to study the sorption and transport properties of CH4 and CO2 in amorphous polyethylene at temperatures from 350 to 600 K and pressures up to 500 bar. The uptake of CH4 and CO2 by polyethylene generally increased with increasing pressure and decreasing temperature. However, at high pressures, for example, the uptake of methane by polyethylene increases with temperature. The self-diffusion coefficients of methane and carbon dioxide generally increase with pressure. These results are, in general, consistent with the swelling behavior of the polymer. Interestingly, for the penetrants, the activation barrier of diffusion decreases with pressure. MD simulations are also carried out for the CH4/CO2 mixture in amorphous polyethylene. Here, the overall sorption and transport properties were similar to those reported for pure CH4 and pure CO2 in polyethylene. The sorption selectivity of CO2/CH4 decreases with increasing pressure and temperature and was mostly independent of the bulk mole fraction of methane. Importantly, at high pressures, the mobility of methane found here is higher than that of the corresponding pure methane in polyethylene and the opposite trend is observed in the case of carbon dioxide. These results might be due to the fact that the swelling of the polymer in the presence of carbon dioxide is significantly higher than that in the presence of methane, especially at high pressures. The diffusion and membrane selectivities of carbon dioxide/methane show a similar trend to the sorption selectivity data. Furthermore, the simulation data were in good agreement with the theoretical calculations based on the PC-SAFT equation of state.

Local structure analysis of low-temperature neutron pair distribution function coupled with molecular dynamics simulations of CH4 and CO2 hydrates from 2 to 210 K

CH4 hydrates occur naturally and are an abundant potential fuel source with a corresponding risk of potent greenhouse gas release, due to their stability conditions at low temperature and high pressure. Byproduct CO2 can be exchanged with CH4 in these natural deposits and can potentially stabilize the hydrates at higher temperatures. CH4, CO2, and mixed CH4-CO2 hydrates are studied with in situ neutron pair distribution function experiments from 2 to 210 K to investigate the impact of varying the CH4-CO2 guest composition in the gas hydrate structure. These experiments combined with Reverse Monte Carlo analysis allow for the characterization of intermolecular CH4 and CO2 interactions with the water molecules which form the hydrate lattice and how they impact the local structure of the lattice itself. Results indicate that when CH4 and CO2 co-occupy the hydrate, the host is more strongly distorted than in the pure CH4 and CO2 hydrates, but this becomes less defined with increasing temperature. The presence of CO2 in mixed hydrate increases the stability range and creates a barrier for CH4 to completely leave the structure.

Investigation of CO2 and CH4 competitive adsorption during enhanced shale gas production

CO2–CH4 competitive adsorption during shale gas production is investigated through a replacement dynamics method at an isotherm temperature of 30 °C from 14.12 to 7.46 MP CH4 production experiments from pure CH4 (with no other gas injection), a mixture of CO2–CH4, and a mixture of N2–CH4 tests were conducted on a Silurian age Lower Jurassic whole shale sample. Gas production performances, pore size distribution, pressure, CO2/CH4 concentration ratio, and gas flow, are discussed to assess their impacts on CO2–CH4 competitive adsorption. Experimental results are validated by the Langmuir model of adsorption and model for multicomponent gas flow dynamics. At the initial stage of production when pressure is high, gas recovery is largely dependent on depressurization, while in the later stage as pressure decreases, competitive adsorption becomes significant. Observed dominances of bulk flow in larger pores (>10 nm) and surface diffusion in smaller pores (<10 nm), show gas recovering mechanism transforms from being largely dependent on reservoir depressurization to competitive adsorption as pressure decreases. Results from this study suggest that CO2–CH4 competitive adsorption is a dynamic process that changes with production conditions.

Reducing direct drive preheat with dopants

Preheat in laser-driven experiments can have negative impacts on inertial confinement fusion (ICF) and hydrodynamic experiments. While many groups employ the use of dopants to reduce or block preheat, direct quantification has not previously been explored. We developed a planar platform and a series of ablator targets to measure the electron and x-ray spectra generated by laser-plasma interactions with a direct drive using OMEGA-60. By comparing both thin ablators (75m) and thick ablators (270 m) that were either pure CH, 3% Si doped or 3% I doped, we were able to measure differences in electron and x-ray spectra. In addition, we observed the preheat growth of tracer layers and observed reductions in the growth with different materials. We find that iodine or a thin gold layer is the best at tamping the direct-drive preheat at OMEGA, but that the growth is still significant.

Numerical simulation of the feasibility of supercritical CO2 storage and enhanced shale gas recovery considering complex fracture networks

In recent years, the greenhouse gas control has been a hot issue. A solution of injecting supercritical CO 2 (scCO 2 ) in Longmaxi shale gas formation (in Southwest China) is proposed in this study. To evaluate the feasibility of this method that storing CO 2 and enhanced gas recovery (EGR) simultaneously, we first carried out isothermal adsorption experiments on samples from Longmaxi formation to describe the adsorption behavior of CH 4 and CO 2 , and a generalized Ono-Kondo Lattice (OK) model was applied to predict adsorption amount of pure CH 4 /CO 2 and their binary mixtures under supercritical, high-pressure conditions. In addition, discrete fracture network (DFN) model was adopted to characterize the complex hydraulic fracture networks constructed from micro-seismic monitoring (MSM) data and engineering analysis. The porous flow in shale matrix was modeled with the multiple interacting continua (MINC) and fractal theories. A multiscale compositional numerical model based on unstructured tri-prism grids was finally developed and solved by control volume finite element (CVFE) method. The simulation results of base and CO 2 injection cases presented that scCO 2 huff ‘n’ puff in Longmaxi formation might be an effective method for CO 2 storage and EGR, and the orthogonal experiments were designed to optimize scenarios in the field application and obtain a maximum balanced result of EUR and CO 2 storage capacity (CSC) for multistage fractured horizontal well (MFHW) with complex fracture networks in shale. • The OK model was applied to predict pure CH 4 /CO 2 and their mixtures adsorption amount under supercritical conditions. • The hybrid DFN and MINC model was established to describe the flow in fractal porous media and complex fracture system. • The CVFE simulator was successfully conducted for comprehensive analysis of mechanisms of scCO 2 storage and EGR in shale.

Quantitative evaluation of geological fluid evolution and accumulated mechanism: in case of tight sandstone gas field in central Sichuan Basin

Tight gas exploration plays an important part in China’s unconventional energy strategy. The tight gas reservoirs in the Jurassic Shaximiao Formation in the Qiulin and Jinhua Gas Fields of central Sichuan Basin are characterized by shallow burial depths and large reserves. The evolution of the fluid phases is a key element in understanding the accumulation of hydrocarbons in tight gas reservoirs. This study investigates the fluid accumulation mechanisms and the indicators of reservoir properties preservation and degradation in a tight gas reservoir. Based on petrographic observations and micro-Raman spectroscopy, pure CH4 inclusions, pure CO2 inclusions, hybrid CH4–CO2 gas inclusions, and N2-rich gas inclusions were studied in quartz grains. The pressure–volume–temperature–composition properties (PVT-x) of the CH4 and CO2 bearing inclusions were determined using quantitative Raman analysis and thermodynamic models, while the density of pure CO2 inclusions was calculated based on the separation of Fermi diad. Two stages of CO2 fluid accumulation were observed: primary CO2 inclusions, characterized by higher densities (0.874–1.020 g/cm3) and higher homogenization temperatures (> 210 °C) and secondary CO2 inclusions, characterized by lower densities (0.514–0.715 g/cm3) and lower homogenization temperatures: ~ 180–200 °C). CO2 inclusions with abnormally high homogenization temperatures are thought to be the result of deep hydrothermal fluid activity. The pore fluid pressure (44.0–58.5 MPa) calculated from the Raman shift of C–H symmetric stretching (v1) band of methane inclusions is key to understanding the development of overpressure. PT entrapment conditions and simulation of burial history can be used to constrain the timing of paleo-fluid emplacement. Methane accumulated in the late Cretaceous (~ 75–65 Ma), close to the maximum burial depth during the early stages of the Himalayan tectonic event while maximum overpressure occurred at ~ 70 Ma, just before uplift. Later, hydrocarbon gas migrated through the faults and gradually displaced the early emplaced CO2 in the reservoirs accompanied by a continuous decrease in overpressure during and after the Himalayan event, which has led to a decrease in the reservoir sealing capabilities. The continuous release of overpressure to present-day conditions indicates that the tectonic movement after the Himalayan period has led to a decline in reservoir conditions and sealing properties.

Highly Durable C2 Hydrocarbon Production via the Oxidative Coupling of Methane Using a BaFe0.9Zr0.1O3−δ Mixed Ionic and Electronic Conducting Membrane and La2O3 Catalyst

The oxidative coupling of methane (OCM) is an attractive technology for the production of ethane (C2H6) and ethylene (C2H4); and significant performance and efficiency gains as well as reduced carbon dioxide (CO2) emissions are expected when OCM takes place within mixed ionic and electronic conducting (MIEC) ceramic membrane reactors (CMRs). So far, research on OCM in CMRs has been limited to unstable and incompatible materials investigated under short-term measurements that hinder upscaling and commercial application. To this end, this work demonstrates long-term stable OCM performance enabled by a BaFe0.9Zr0.1O3−δ (BFZ91) perovskite utilized as the oxygen-ion MIEC membrane and lanthanum oxide (La2O3) used as the OCM catalyst. Experimental measurements conducted in the temperature (T) range of 750–900 °C and at inlet methane (CH4) mole fractions (XCH4in) of 0–30% revealed a highly stable performance during 23 days of continuous operation, which was further confirmed by material characterization. Under the aforementioned operating conditions, BFZ91 offers a high oxygen (O2) permeation flux (JO2) between 0.5−1.5 (μmol/cm2/s); CH4 conversion (CCH4) reached ∼35% while the selectivities to C2H6 (SC2H6) and C2H4 (SC2H4) were as high as ∼50% and ∼40%, respectively, showing a strong dependency on the operating conditions. Yields of C2H6 (YC2H6) and C2H4 (YC2H4) in the range of 1–5% and 1–7%, respectively, were measured, with more C2H4 being produced at higher T. In the absence of La2O3, CCH4 and C2 (C2H6 and C2H4) yields are lower confirming that BFZ91 does not promote CH4 oxidation, reforming, or coupling on its surface at high rates. The OCM performance of BFZ91 with La2O3 was also found to be stable under partial O2 consumption and pure CH4 conditions. Furthermore, a detailed analysis of the mixture composition allowed the identification of the primary reactions in the OCM chemistry. Our results reveal that within our reactor, CH4 full oxidation to CO2 and steam (H2O) happens simultaneously with CH4 oxidation to C2H6 and H2O (both on the La2O3 catalyst), but the production of the valuable C2H4 is primarily taking place through the C2H6 non-oxidative dehydrogenation in the gas phase; this reaction was not found to proceed on the La2O3 catalyst. Besides the promise of the investigated materials toward commercialization, the methods to study the OCM chemistry and the membrane catalyst coupling presented here are expected to promote further advances in the field of OCM.

Gas hydrate potential of the Sea of Marmara

In this study, the gas hydrate potential of the Sea of Marmara was analyzed in detail in terms of energy resource potential and environmental geohazards. Initially, GHSZ thickness maps for different gas compositions in the Sea of Marmara were drawn according to the estimations made by using HEP simulator and an algorithm developed in this study. Pure/nearly pure CH4 hydrate is not stable in the conditions of the Sea of Marmara, but thermogenic gas hydrates were recovered in the Sea of Marmara. It was shown that when C3H8, CO2, and H2S concentration in gas compositions increases, the thickness of GHSZ also increases. For the best scenario, GHSZ thickness is nearly 287.2 m below the seafloor. Technically recoverable natural gas hydrate potential in the Sea of Marmara is up to 125.8 bcm (billion cubic meters). In this study, it was proposed that the importance of gas hydrates in the Sea of Marmara is higher in terms of environmental perspectives rather than its energy resource potential. Up to 1820.2 bcm of natural gas might be stored in sII gas hydrates of the Sea of Marmara. In terms of environmental perspectives, free gas sections in the bottom of gas hydrates at the bottom boundary of GHSZ are risky because the possible connection of the free gas section with the seafloor due to tectonic activities might cause catastrophic results for the environment. Overall, gas seeps through the atmosphere are possible in the Sea of Marmara, where is crossed lengthwise by the Northern branch of the North Anatolian Fault (NAF).

Control methods for variations in natural gas composition in air–fuel controlled natural gas engines

In the present study, the countermeasures are proposed to minimize the problem on torque and power output performance and exhaust gas emissions of natural gas engine with use of lower calorific gas. An experiment was conducted to identify thermal efficiency and harmful exhaust gas emission characteristics under partial load conditions in order to improve efficient fuel use in engines affected by the introduction of low calorific gases. A countermeasure for coping with emission gas regulations and preventing thermal efficiency deterioration under rated power operating conditions was then presented. An 11 L six-cylinder turbo-charged engine for city buses compliant with the EURO 6 regulation was used in the experiment, and the results obtained using the reference natural gas fuel were compared with those obtained using simulated low calorific gases. Pure methane (CH 4) was also used to investigate the effects of gas composition changes on thermal efficiency and exhaust gas emissions.When N2 is added or pure CH 4 is used under partial load operating conditions, the combustion rate decreases; consequently, the optimum ignition timing is additionally advanced relative to that obtained when the reference natural gas fuel is used. If the N2 mixing ratio is increased to a minimum of 4.7% under rated power operating conditions, combustion becomes unstable. Stable operation can be secured by increasing the set base fuel amount, 2.35% and 9.41% for pure CH 4 and 8% N2, respectively; however, torque decreases in proportion to the combustion speed of the gas fuel. The strategy of boost pressure control for the torque compensation can minimize the decrease in thermal efficiency.

A MOF‐based Ultra‐Strong Acetylene Nano‐trap for Highly Efficient C2H2/CO2 Separation

AbstractPorous materials with open metal sites have been investigated to separate various gas mixtures. However, open metal sites show the limitation in the separation of some challenging gas mixtures, such as C2H2/CO2. Herein, we propose a new type of ultra‐strong C2H2 nano‐trap based on multiple binding interactions to efficiently capture C2H2 molecules and separate C2H2/CO2 mixture. The ultra‐strong acetylene nano‐trap shows a benchmark Qst of 79.1 kJ mol−1 for C2H2, a record high pure C2H2 uptake of 2.54 mmol g−1 at 1×10−2 bar, and the highest C2H2/CO2 selectivity (53.6), making it as a new benchmark material for the capture of C2H2 and the separation of C2H2/CO2. The locations of C2H2 molecules within the MOF‐based nanotrap have been visualized by the in situ single‐crystal X‐ray diffraction studies, which also identify the multiple binding sites accountable for the strong interactions with C2H2.

Pressure–temperature–time–composition (P–T–t–x) of paleo–fluid in Permian organic–rich shale of Lower Yangtze Platform, China: Insights from fluid inclusions in fracture cements

Recently, much attention has been paid to Permian shale from the Yangtze Platform because of the high–quality hydrocarbon source rock. This research investigates fracture veins derived from conventional cores of the Permian Leping Formation in the Pingle Depression, Lower Yangtze Platform. Based on petrographic observations, micro–Raman spectroscopy, and fluorescent spectrometry, hybrid CH4–C2H6 gas inclusions, pure CH4 inclusions, dissolved CH4 aqueous inclusions, and different abundant blue-green fluorescence petroleum inclusions were discovered in quartz and calcite. The pressure–temperature–time–composition properties of the CH4–bearing inclusions were obtained by quantitative Raman analysis and thermodynamic models. The pore fluid pressure (59.05–87.78 MPa) calculated from Raman shift of C–H symmetric stretching (v1) band of methane indicates inclusions trapped at close to lithostatic pressures, which can provide a key evidence for understanding the formation and evolution of overpressure. PT entrapment conditions, reconstruction of hydrocarbon generation and simulation of burial history permit to constrain accumulation time sequence of paleo-fluid in shale veins. Blue-green fluorescence with high-mature petroleum fluid trapped in late Cretaceous (~81–71 Ma); hybrid CH4–C2H6 fluid trapped in early Paleogene (~68–61 Ma); and CH4 fluid trapped in Paleogene (~62–51 Ma). Dry gas generation period close to the age of maximum burial depth at early Himalayan uplift period.

Pluto's Sputnik Planitia: Composition of geological units from infrared spectroscopy

We have compared spectroscopic data of Sputnik Planitia on Pluto, as acquired by New Horizons' Linear Etalon Imaging Spectral Array (LEISA) instrument, to the geomorphology as mapped by White et al. (2017) using visible and panchromatic imaging acquired by the LOng-Range Reconnaissance Imager (LORRI) and the Multi-spectral Visible Imaging Camera (MVIC). We have focused on 13 of the geologic units identified by White et al. (2017), which include the plains and mountain units contained within the Sputnik basin. We divided the map of Sputnik Planitia into 15 provinces, each containing one or more geologic units, and we use LEISA to calculate the average spectra of the units inside the 15 provinces. Hapke-based modeling was then applied to the average spectra of the units to infer their surface composition, and to determine if the composition resulting from the modeling of LEISA spectra reflects the geomorphologic analyses of LORRI data, and if areas classified as being the same geologically, but which are geographically separated, share a similar composition. We investigated the spatial distribution of the most abundant ices on Pluto's surface - CH4, N2, CO, H2O, and a non-ice component presumed to be a macromolecular carbon-rich material, termed a tholin, that imparts a positive spectral slope in the visible spectral region and a negative spectral slope longward of ~1.1 μm. Because the exact nature of the non-ice component is still debated and because the negative spectral slope of the available tholins in the near infrared does not perfectly match the Pluto data, for spectral modeling purposes we reference it generically as the negative spectral slope endmember (NSS endmember). We created maps of variations in the integrated band depth (from LEISA data) and areal mass fraction (from the modeling) of the components. The analysis of correlations between the occurrences of the endmembers in the geologic units led to the observation of an anomalous suppression of the strong CH4 absorption bands in units with compositions that are dominated by H2O ice and the NSS endmember. Exploring the mutual variation of the CH4 and N2 integrated band depths with the abundance of crystalline H2O and NSS endmember revealed that the NSS endmember is primarily responsible for the suppression of CH4 absorptions in mountainous units located along the western edge of Sputnik Planitia. Our spectroscopic analyses have provided additional insight into the geological processes that have shaped Sputnik Planitia. A general increase in volatile abundance from the north to the south of Sputnik Planitia is observed. Such an increase first observed and interpreted by Protopapa et al., 2017 and later confirmed by climate modeling (Bertrand et al., 2018) is expressed geomorphologically in the form of preferential deposition of N2 ice in the upland and mountainous regions bordering the plains of southern Sputnik Planitia. Relatively high amounts of pure CH4 are seen at the southern Tenzing Montes, which are a natural site for CH4 deposition owing to their great elevation and the lower insolation they are presently receiving. The NSS endmember correlates the existence of tholins within certain units, mostly those coating the low-latitude mountain ranges that are co-latitudinal with the tholin-covered Cthulhu Macula. The spectral analysis has also revealed compositional differences between the handful of occurrences of northern non-cellular plains and the surrounding cellular plains, all of which are located within the portion of Sputnik Planitia that is presently experiencing net sublimation of volatiles, and which do not therefore exhibit a surface layer of bright, freshly-deposited N2 ice. The compositional differences between the cellular and non-cellular plains here hint at the effectiveness of convection in entraining and trapping tholins within the body of the cellular plains, while preventing the spread of such tholins to abutting non-cellular plains.

NO Reburning by CH4-H2 Mixture under High CO2 Concentration in a Jet-Stirred Reactor

New experimental and numerical results for NO reduction of CH4-H2 mixture were obtained in a 0-dimensional jet stirred reactor (JSR), the effects of the following four factors are considered: temperature(T): 800-1300 K; equivalence ratio(φ): 0.5-2.5; proportions of H2:CH4 in fuel: 0:6, 1:5, 3:3 and 5:1 (expressed in terms of FUEL-CH4, FUEL-1:5, FUEL-3:3 and FUEL-5:1, respectively); CO2 concentration in dilution gas: 0, 30% and 60% (expressed by terms D-N2, D-30%CO2 and D-60%CO2, respectively). Compared with pure CH4, mixing with H2 weaken the NO reduction in high temperature region, The NO reburning reduction rate of FUEL-3:3 increases first and then decreases with the increase of φ. The strongest reduction effect is obtained at T=1300 K and φ=1.2, and the reduction efficiency is about 70%. The NO reburning reaction was obviously inhibited by increasing CO2 concentration, but the effect was limited when the CO2 concentration reached a certain level. The reburning effect of FUEL-CH4, FUEL-1:5, FUEL-3:3 is approximative, but the reburning effect of FUEL-5:1 is significantly inhibited by high proportions of H2:CH4.

Effect of Cu-MOFs incorporation on gas separation of Pebax thin film nanocomposite (TFN) membrane

MOF-based membranes, which have appropriate MOF dispersion and suitable interaction, have shown high CO2 permeability and significant CO2/CH4 and CO2/N2 selectivity. In this study, a layer of Pebax was coated on polysulfone (PSF), which this layer incorporated by various content of Cu-MOFs to improve the performance (permeability and CO2/CH4 and CO2/N2 selectivity) of all membranes. Characterization techniques such as SEM, TGA, BET, and gas adsorption verified that Cu-BTC was successfully dispersed into the Pebax matrix. Pure CO2 and CH4 gases permeation experiments were performed to investigate the impact of Cu-MOFs on the gas permeability of prepared MOF-based membranes. The “Pebax” embedded by 15 wt% CuBTC and 15 wt% of NH2-CuBTC over PSF support exhibited higher gas separation performance compared to the pristine one. They demonstrated a CO2 permeability of 228.6 and 258.3 Barrer, respectively, while the blank membrane had a CO2 permeability of 110.6 Barrer. Embedding the NH2-Cu-BTC intensified the interaction between incorporated MOF particles and the polymer phase that led to increase the CO2/CH4 and CO2/N2 selectivity. In addition, the performance of prepared membranes was evaluated at various feed pressures with the range of 2–10 bar. The CO2/CH4 and CO2/N2 separation was enhanced as the feed pressure surged.