CH4 Gas Mixture Research Articles

Morphology-Dependent Chemiresistive-Potentiometric Gas Sensing Properties of ZnO Nanorods for CH4 and CO

In this study, one-dimensional ZnO nanorods sensing electrodes were grown in situ on the surface of the Ce0.8Gd0.2O1.9 electrolyte to fabricate chemiresistive-potentiometric (C-P) bivariate sensors for the detection and identification of CH4 and CO. Four C-P sensors were developed by adjusting the hydrothermal growth time of the nanorods. The effect of hydrothermal duration on the morphology of nanorods was examined. The C-P response to CH4 and CO initially increased and then decreased with increasing hydrothermal duration. Similar variations in the response to the gas mixtures of CH4 and CO with the hydrothermal duration were observed. The highest C and P response values for CH4, CO, and their mixtures were obtained at a hydrothermal duration of 1.5 h. The enhanced C-P sensing performance was discussed in terms of the defect density, the number of contact junctions, and the length of ZnO nanorods. Accurate differentiation of five different gases (CH4, CO, and three gas mixtures) with an identification accuracy of 100% was achieved by the array assembled with the ZnO-1.0 and the ZnO-1.5 sensors. Our findings demonstrate the morphology-dependent C-P sensing behaviors of ZnO nanorods and provide a facile and cost-effective method for the detection and identification of CH4 and CO.

Determination of hydrate phase equilibrium (H-L-V) data for the binary CO2–CH4 gas mixture in the presence of 1,3 dioxolane

Present work details the determination of three phase hydrate equilibrium data (H-L-V) using temperature search method for the binary CO2/CH4 gas mixture (50:50 molar ratio) in presence of 1,3 dioxolane (DIOX). DIOX concentration used for phase equilibrium determination were 1,3 and 5.56 mol% respectively. In the presence of DIOX, it was observed that phase equilibrium curve was shifted right with respect to the curve using same gas mixture with no additive (pure water). This indicates that the presence of DIOX moderates the hydrate formation equilibrium conditions. Also, as DIOX concentration increases from 1 mol% to 5.56 mol%, a decrement in phase equilibrium pressure at same temperatures was observed, confirming the potential of DIOX as an effective thermodynamic promoter. Enthalpy of hydrate dissociation was calculated for CO2/CH4 gas mixture in presence of DIOX using Clausius- Clapeyron plot and it was found to be 90.81±6.55 KJ/mol which confirms the sII structure of CO2-CH4-DIOX mixed hydrate. Besides providing the phase equilibrium data of formed hydrates with CO2/CH4 gas mixture using different concentration of DIOX, the present study will aid in determining suitable experimental conditions for examining kinetics and performing separation studies of CO2/CH4 gas mixture through hydrate formation.

Experimental study and thermodynamic modeling of CO2+CH4 gas mixture hydrate phase equilibria for gas separation efficiency

Gas separation is a critical application of gas hydrates, and accurately predicting separation performance is crucial. In this study, we used thermodynamic calculations to predict the equilibrium phase of gas hydrates for various mole fractions of CO2 + CH4 gas mixtures. We also determined the mole fraction of each gas component trapped within the hydrate clathrate. To predict the equilibrium points, we used the Soave–Redlich–Kwong（(SRK) equation of state for the gas phase, the nonrandom two-liquid (NRTL)model for the liquid phase, and the Chen–Guo model for the hydrate phase. We modified the hydrate fugacity formula and introduced a new function to improve the accuracy of the Chen–Guo model. By incorporating experimental equilibrium results from our study and another study, we developed a correlation based on gas mixture composition and temperature, resulting in highly accurate predictions. The use of this new correlation for hydrate fugacity calculation significantly improved precision, as evidenced by an average absolute deviation percent of calculated pressures (AADP) of 1.34% for pure CO2 and 1.25% for CH4. When considering the 27 data points of different CO2 + CH4 mixtures, the AADP% was 1.98%.To implement the model to predict equilibrium phases, we used the Chen–Guo framework to determine the mole fraction of each gas component in the hydrate mixture. Interestingly, we discovered a linear correlation between the CO2 mole fraction in the hydrate and equilibrium pressure, with a slope of approximately 0.001 and a y-intercept of less than one, for all gas compositions. Therefore, we can conclude that low thermodynamic conditions (temperature and pressure) result in a high CO2 mole fraction in the hydrate phase and great separation efficiency.

A PLC-Embedded Implementation of a Modified Takagi–Sugeno–Kang-Based MPC to Control a Pressure Swing Adsorption Process

The paper presents a case study that applies a model predictive control (MPC) approach in a Micro850 programmable logic controller (PLC) to a laboratory pressure swing adsorption (PSA) process used for separating gas mixtures of CO2 and CH4. PLC is an industrial hardware characterized by its robustness to hazardous environments and limited computational capacities, which poses computational challenges for MPC implementation. This paper’s main contribution is the application of the modified Takagi–Sugeno–Kang-based MPC (MTSK-MPC) algorithm to this PSA unit, which provides features to investigate and implement feasible MPC designs in PLCs. The investigation consists of a sensitivity analysis of how some design parameters influence the PLC memory and the MPC implementation and a comparative evaluation of the computational processing from different MPC algorithms and simulations. The comparison comprises software-in-the-loop simulations with three algorithms in the PC: an implicit MPC, an explicit MPC, and the MTSK-MPC. Additionally, it includes a hardware-in-the-loop simulation with the implemented MTSK-MPC in Micro850. The results show that the MPC algorithms achieve close performance, tracking setpoint changes and rejecting output disturbances, with the MTSK-MPC presenting the lower processing time among the MPCs in the PC. The study concludes that the implementation of MTSK-MPC in the Micro850 is feasible.

Optimizing methane plasma pyrolysis for instant hydrogen and high-quality carbon production

The European Green Deal has set a target for Europe to achieve net-zero greenhouse gas emissions by 2050, necessitating a transition to more sustainable energy sources. Hydrogen gas (H2) has emerged as a promising solution, with methane pyrolysis presenting a viable method for its production. This study explores the optimization of methane plasma pyrolysis for hydrogen and high-quality carbon production. Employing a statistical approach by a design of experiment software, critical process parameters are systematically analyzed to predict their impact within a defined range. Additionally, the paper conducts comprehensive characterization of the solid carbon produced during pyrolysis using imaging, spectroscopic and elemental analysis, and gas sorption analysis methods. The experimental investigation was conducted using a thermal plasma reactor with several settings of influential parameters including methane gas (CH4) content in the plasma gas, electric current, and arc length. The DC-transferred plasma arc is formed using a variable gas mixture of argon gas (Ar) and CH4, with a constant flow rate of 5 Nl/min. Thirteen tests were designed, evaluating responses such as power input, process stability, and H2 yield. The H2 yield indicates the hydrogen produced from CH4, with 100% representing total conversion. While the process exhibited inconstancy, attributed to reactor design constraints, a high H2 yield of 67%–100% was achieved. The results indicate that a higher CH4 content in the plasma gas and extended arc lengths disturb the plasma arc, hence reducing the H2 yield. Increased power input, achieved through higher amperage levels, and a wider reaction zone eased by extending the arc length both led to an improved H2 yield. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) revealed microstructural differences, with carbon samples from the filter exhibiting finer textures and carbon samples from the reactor larger sizes and dendritic particles. Raman spectroscopy confirmed crystalline graphitic-like structures with low defect concentrations, a finding supported by X-ray diffraction (XRD) analysis. Inductively coupled plasma mass spectroscopy (ICP-MS) analysis confirmed high-purity carbon with slight impurities from initial filter contamination. Brunauer-Emmett-Teller (BET) specific surface area calculations based on gas sorption analysis showed significant variations, with filter-collected samples exhibiting 40–170 m2/g and reactor-collected ones showing 7–30 m2/g.

The roles of different migration mechanisms in the transport of H2O–CH4 gas mixture in shales

Studying the roles of different migration mechanisms in shale matrix gas transport is beneficial for shale gas extraction and CO2 sequestration. The roles of different transport mechanisms in shale H2O–CH4 gas mixture transport were investigated considering their contributions to fluid flux. A permeability model coupling multiple gas migration mechanisms was developed by combining the pore network-related effective medium approximation, which was validated using process data from simultaneous H2O–CH4 transport in shales. The results showed that the gas transport mechanisms dominating methane and water vapor migration in shale differed. Slip flow and Knudsen diffusion contributed approximately 99% to methane migration. Water vapor surface diffusion as well as slip flow and Knudsen diffusion primarily contributed to the water vapor permeability before and after a time point, respectively. Water vapor and methane permeability generally decreased with time. The equilibrium water vapor and methane permeabilities ranged from 2.7699×10−22–12.312×10−22 m2 and 0.2640×10−21–4.9036×10−21 m2, respectively. The methane surface diffusion permeability increased slowly with time before approaching methane monolayer adsorption (before ∼100 s). An increase in relative humidity (approximately 300–3600 s) can promote the transport of water vapor. Water vapor and methane adsorption, especially the condensation of adsorbed water, could largely explain the decrease in shale gas permeability.

Enhanced CH4/N2 Separation Efficiency of UiO-66-Br2 through Hybridization with Mesoporous Silica.

Efficient separation of CH4 from N2 is essential for the purification of methane from nitrogen. In order to address this problem, composite materials consisting of rod-shaped SBA-15-based UiO-66-Br2 were synthesized for the purpose of separating a CH4/N2 mixture. The materials were characterized via PXRD, N2 adsorption-desorption, SEM, TEM, FT-IR, and TGA. The adsorption isotherms of CH4 and N2 under standard pressure conditions for the composites were determined and subsequently compared. The study revealed that the composites were formed through the growth of MOF nanocrystals on the surfaces of the SBA-15 matrix. The enhancements in surface area and adsorption capacity of hybrid materials were attributed to the structural modifications resulting from the interactions between surface silanol groups and metal centers. The selectivity of the composites towards a gas mixture of CH4 and N2 was assessed utilizing the Langmuir adsorption equation. The results of the analysis revealed that the U6B2S5/SBA-15 sample exhibited the greatest selectivity for CH4/N2 adsorption compared to the other samples, with an adsorption selectivity parameter (S) of 20.06. Additional research is necessary to enhance the enrichment of methane from CH4/N2 mixtures using SBA-15-based metal-organic framework materials.

Experiment design as a tool for hydrate phase equilibria prediction of CO2 + CH4 gas mixture in the presence of tera-butylammonium bromide in LW–H–V systems

In this study, we introduce experimental design as a novel approach to derive an equation that predicts the hydrate phase equilibrium temperature in a LW–H–V (liquid water, hydrate, vapor) system, based on pressure, gas composition, and the concentration of tetra-n-butylammonium bromide (TBAB). Our phase equilibria model is informed by experiments under nine different conditions, varying in gas compositions (CH4, CO2, and a 50/50 mole % CH4/CO2 mixture) and TBAB concentrations (15 and 30 wt.%). From these, we calculated temperature responses for 13 experiments, leading to the formulation of two models: a model without pressure transformation, which lacked predictive accuracy, and a more accurate model incorporating a natural logarithm pressure transformation (NLPT). The NLPT model demonstrated exceptional predictive power, with R2, adjusted R2, and predicted R2 values of 0.9975, 0.9958, and 0.9914, respectively. Additionally, it achieved an F-value of 565.90 in the analysis of variance (ANOVA). Validation diagrams, comparing predicted results to experimental data, confirmed the ability of the NLPT model to accurately predict hydrate phase equilibria, underscoring the efficacy of our experimental design approach.

Exploring the separation properties of high-Si CHA membranes for the CO2 capturing technology: Impact of the selective layer thickness and growth mechanism

This study investigates the influence of the CHA selective layer's thickness, coated on a mono-channel alumina support using the secondary growth method, on the performance of CO2 separation from CH4. The membrane layer's thickness was explored by adjusting the concentration and duration of the seeding process, as well as the distribution of crystal size in the suspension. Single gas analysis results revealed that utilizing smaller crystal seeds, with an average crystallite size of approximately 600 nm, exhibited the highest performance. Furthermore, a membrane thickness of 2.1 μm demonstrated an ideal CO2/CH4 permselectivity of 205 with a CO2 permeance of 2.39 x 10-6 [mol/(m2sPa)]. For the equimolar CO2 - CH4 gas mixture, the high-Si membrane displayed a CO2/CH4 selectivity of 210 with a CO2 permeance of 8.06 x 10-7 [mol/(m2sPa)]. In both gas permeation measurement, CO2 permeance exhibited a slight linear decrease with increasing thickness, while CH4 permeance initially decreased and then increased non-linearly.

Deposition of vertical carbon nanostructures by microwave plasma source on nickel and alumina

Vertical carbon nanostructures on metal and ceramic substrates are deposited successfully using planar microwave plasma source at frequency of 2.45 GHz. The PECVD (Plasma Enhanced Chemical Vapor Deposition) with microwave surface wave discharge is applied because it produces a dense plasma providing efficient decomposition of the methane and creation of a large number of reactive particles which results in lower substrate temperature for graphene deposition compared to CVD method. Optimization of the gas mixture of H2, Ar and CH4, and the gas pressure in the chamber results in a homogeneous graphene structures deposition on the substrates of Ni-foil, Ni-foam and alumina ceramics at substrate temperatures ∼600 °C. The plasma parameters of surface wave discharge such as gas temperature, electron temperature and density are obtained by measuring OH-band and Ar-lines using optical emission spectroscopy. The morphology of the vertical carbon structures is obtained using SEM analysis and the characteristics of the graphene layers were determined by Raman spectroscopy.

Tailoring gas hydrate lattice dimensions for enhanced methane selectivity in biogas upgrading

Gas hydrates, specifically clathrate hydrates, have emerged as a potential separation medium for biogas containing methane (CH4) and carbon dioxide (CO2). However, the efficient separation of CH4 and CO2 remains challenging due to their similar cage occupation behavior within the hydrate structure. This study aimed to enhance CH4 selectivity by modifying the hydrate lattice to exclude CO2 from large cages and reduce the size of small cages through lattice engineering. To achieve this, tert-butyl alcohol (TBA) and trimethylene oxide (TMO) were employed as thermodynamic promoters, inducing strong and weak cage expansion, respectively. The results revealed that TMO hydrates, with their weak cage expansion, exhibited improved CH4 selectivity compared to TBA hydrates, which displayed strong cage expansion due to the larger size of TBA. Multi-stage separation experiments demonstrated that TMO hydrates required four unit stages, while TBA hydrates necessitated more than five unit stages to obtain purified CH4 (> 85%) from an initial gas mixture of CH4 (50%) and CO2 (50%). Additionally, TMO hydrates consistently exhibited higher separation factors than TBA hydrates in all unit stages. The findings emphasize the influence of the thermodynamic promoter's size on the separation performance of gas hydrates in separating CH4 from CH4 + CO2 mixtures. The study provides valuable insights into enhancing CH4 selectivity through lattice engineering and offers guidance in selecting suitable thermodynamic promoters for gas hydrate-based biogas upgrading applications.

Impurity Analysis of 5.5 N Nitrogen Gas and Its Impact on the Preparation of Class I Type Calibration Gas Mixtures

AbstractKnowledge of impurities in matrix gas is one of the critical requirements for the preparation of class I type calibration gas mixtures (primary reference gas mixtures, PRGMs) as per ISO 6142‐1. PRGMs are prepared gravimetrically using high‐purity component gas and high‐grade nitrogen, here 99.9995 % (5.5 N) as matrix gas. In this study, quantification of gaseous impurities such as moisture (H2O), methane (CH4), and carbon monoxide (CO) in 5.5 N nitrogen is performed using CRDS (cavity ring down spectroscopy). Carbon dioxide (CO2) and total hydrocarbons (THC) are analyzed using gas chromatography flame ionization detector (GC‐FID), while the determination of nitrogen dioxide (NO2) impurity is conducted colorimetrically using a UV‐Vis spectrophotometer. Total impurities in 5.5 N nitrogen are found to be (2945±21.5) ppb. The impact of utilizing this nitrogen is examined through the stability study of ambient range binary component gas mixtures of CH4 and CO in nitrogen and found that 5.5 N nitrogen can be used as matrix gas for preparing PRGMs of CH4 and CO. However, the component gas impurity present in nitrogen potentially affect the accuracy of gravimetrically prepared gas mixture.

Structure and Property of Diamond-like Carbon Coating with Si and O Co-Doping Deposited by Reactive Magnetron Sputtering

In this paper, diamond-like carbon (DLC) coatings with Si and O co-doping (Si/O-DLC) were deposited by reactive magnetron sputtering using a gas mixture of C2H2, O2 and Ar to sputter a silicon/graphite splicing target. The O content in the Si/O-DLC coatings was controlled by tuning the O2 flux in the gas mixture. The composition, chemical bond structure, mechanical properties and tribological behavior of the coatings were investigated by X-ray photoelectron spectroscopy, Fourier infrared spectrometer, Raman spectroscopy, nanoindentation, a scratch tester and a ball-on-disk tribometer. The electrical resistivity of the Si/O-DLC coatings was also studied using the four-point probe method. The results show that the doping O tends to bond with Si to form a silicon–oxygen compound, causing a decrease in the sp3 content as well as the hardness of the coatings. The tribological performance of the coatings can be improved due to the formation of the silicon–oxygen compound, which can effectively reduce the friction coefficient. In addition, the insulating silicon–oxygen compound is doped into the C-C network structure, significantly improving the surface resistivity of the DLC coating with a low sp3 content. The Si/O-DLC coatings with good mechanical properties, tribological performance and electrical insulation properties might be used as protection and insulation layers for microelectronics.

Calculating Coefficients of the Gas Hydrate Distribution of CO2 and H2S when Removing Them from a Methane-Containing Gas Mixture

A study is performed of the effect process temperature and pressure have on the distribution of CO2 and H2S gas hydrate in a model methane-containing gas mixture of CH4 (89.00 mol %)–CO2 (5.00 mol %)–n-C4H10 (3.00 mol %)–N2 (2.00 mol %)–H2S (1.00 mol %) containing components of natural gas. Modeling is done at low (4.00 MPa) and high (8.00 MPa) pressures in the 272.15–278.15 K range of temperatures. The temperature dependences of the coefficients of the gas hydrate distribution of natural gas components are shown to differ. The maximum coefficients of the gas hydrate distribution of CO2 and H2S are 1.24 and 31.83, respectively, at a process temperature of 272.15 K and a pressure of 8.00 MPa. It is found that n-C4H10 in natural gas lowers the coefficient of the gas hydrate distribution of CO2. It is concluded that natural gas deposits with low contents of n-C4H10 must be used to effectively concentrate CO2 in the gas hydrate phase.

Effects of Gas Dissolution on Gas Migration during Gas Invasion in Drilling.

Sour gas reservoirs (including CO2 and H2S) are vulnerable to gas invasion when drilling into reservoir sections. The high solubility of the invaded gas in drilling fluid makes the gas invasion monitoring "hidden" and "sudden" for later expansion, and the blowout risk increases. Accurate prediction of gas dissolution is highly significant for monitoring gas invasion. In this study, the gas-liquid flow control equations considering gas dissolution were established. Focusing on the gas dissolution effect, a solubility experiment for CO2 and CH4 in an aqueous solution was performed using a phase equilibrium device. The experimental and simulation results revealed that the addition of CO2 can significantly increase gas dissolution, and the presence of salts decreases it. For solubility prediction of pure CH4 and CO2, the fugacity-activity solubility model, calculated using the Peng-Robinson equation of state, was more accurate than the Soave-Redlich-Kwong equation of state. The Soave-Redlich-Kwong equation of state has higher accuracy for the CO2 and CH4 gas mixture. If the gas dissolution effect is considered for wellbore gas-liquid flow, the time required for the mud pit gain to reach the early warning value increases. When the contents of CO2 and H2S in intrusive gases are higher, the time for mud pit gain change monitored on the ground increases, the concealment increases, and the risk of blowout increases.

Microstructure and tribological properties of multilayered ZrCrW(C)N coatings fabricated by cathodic vacuum-arc deposition

In this study, a series of ZrCrW(C)N multilayer coatings with various transition layers were deposited on AISI304 stainless steel using cathodic vacuum-arc deposition in N2–C2H2 gas mixture. The tribological behaviors of sliding against Al2O3 balls under dry friction and lubricant conditions were investigated using a reciprocating tribometer. The results demonstrated that the ZrCrW(C)N coatings comprised (Zr, Cr, W) (C, N) crystallites and an amorphous carbon phase. It possessed a nano-hardness of 35.4 GPa and an elastic modulus of 417.7 GPa. The friction coefficient of the coating was reduced by 14% compared to that of the 304 matrices, and the wear mechanism changed from adhesive wear to slight abrasive wear under the lubrication steady state. Under dry friction conditions, the ZrCrW(C)N coatings with the entire CrWN transition layer exhibited wear rates of 1.27 ± 0.04 × 10−8 mm3 (N m)−1, which were one order of magnitude lower than that of the 304 steel. Compared with the untreated AISI304 stainless steel, the ZrCrW(C)N coating exhibits excellent mechanical and tribological properties under lubricated and dry friction conditions, which are crucial for engineering applications.

Dissolved CO2 profile in bio-succinic acid production from sugars-rich industrial waste

The inorganic carbon source (CO2) availability to the microorganisms has a key role in the succinic acid (SA) fermentation process. This study aims to investigate the behavior of the inorganic carbon source for SA production and underline the importance of CO2 in the fermentation process. The effect of pressure was investigated for CO2 availability and its overall impact on the fermentation process. Results obtained demonstrated a significant effect of pressure on yield, productivity and CO2 fixation rate. Industrial waste, rich in maltose, glucose, and sucrose, was used as feedstock combined with a gas mixture of CH4 and CO2, which simulated biogas composition. A final titer for succinic acid of 25.5 ± 2.4 g/L was detected at a headspace gas pressure of 1.4 atm. The yield raised from 0.48 g/g sugars to 0.64 and 0.65 g/g sugars when 1.4 and 1.6 atm pressure was applied, respectively. Overall, this study represents one of the first attempts to explore CO2 availability during succinic acid production, using biogas as a CO2 source and sugars-rich industrial waste as feedstock.

Crosslinked thermally rearranged polybenzoxazole derived from phenolphthalein-based polyimide for gas separation

We have developed a novel ortho-hydroxyl diamine 3,3-diaminophenolphthalein and formed a polyimide (Ac-6FDA-DAP) via chemical imidization between this compound and 4,4′-(hexafluoroisopropylidene) diphthalic anhydride. The acetate groups and lactone ring of the diamino moiety degraded and subsequently formed a biphenyl crosslinked polyimide, enabling subsequent conversion of the thermally crosslinked polyimide into a polybenzoxazole (PBO) with superior CO2 separation performances. Compared to the polyimide precursor, the CO2 permeability of the TR PBO, thermally rearranged at 400 °C, increased by at least 21 folds (30.1 to 613 Barrer), with 10% decrement in the CO2/CH4 selectivity (36.7 to 33.5). The CO2/CH4 separation performances of the TR PBO surpassed the “2008 Robeson Upper Bound”, and no plasticization was observed at a CO2 pressure up to 30 atm for pure CO2 and 40 atm for 50:50 CO2 and CH4 gas mixtures. The TR-PBO polymer derived from Ac- 6FDA-DAP showed a strong potential for carbon capture and natural gas treatment.

Multi-component gas measurement aliasing spectral demodulation method for interference separation in laser absorption spectroscopy

The interference between overlapping gas absorption lines often occurs in the measurement of multi-component gas mixture with using laser absorption spectroscopy. It has become a “bottleneck” problem in many application areas. Therefore, in this paper, we take the measurement of CH4 and CO gas mixture as an example to develop a dual-gas sensor using tunable diode laser absorption spectroscopy with a novel multi-component gas measurement aliasing spectral demodulation method for interference separation. With the assistance of the above methods, the concentrations of CO and CH4 are inverted by analyzing the severely aliased second harmonic signal (2f) in the coexistence of trace CO and CH4 with high concentration. Experiments have verified that precise measurement results can be obtained, whether it is to measure individual CO or CH4, or to measure the gas mixture. Even in the presence of 1.6 × 104 ppm CH4, the measurement error of 10 ppm CO is no more than 0.9 ppm. And, the response time of this sensor for CO and CH4 detection are both ~17 s. Finally, the repeatability of this sensor is validated by continuous detection analysis, which indicates that measurement precision is 0.10 ppm for 20 ppm CO and 1.02 ppm for 200 ppm CH4, respectively. Therefore, this novel processing method avoids the shortage of low-pressure control without adding any hardware, which is more universal and convenient.

Experimental Study of Desorption and Seepage Characteristics of Single Gas and CO2–CH4 Gas Mixture in Coal

Experimental Study of Desorption and Seepage Characteristics of Single Gas and CO2–CH4 Gas Mixture in Coal