CO2 Diffusion Research Articles

A comprehensive investigation on the structural transformation and dissolution loss reaction of coke during gasification in CO2 atmosphere

The in-situ investigation of the structural transformation of coke during gasification can provide useful insights into its dissolution loss reaction in blast furnaces. In this study, the structural properties of coke are evaluated by analyzing its carbon matrix, pore distribution, and ash composition using scanning electron microscopy (SEM), wide-angle X-ray scattering (WAXS), small-angle X-ray scattering (SAXS), Raman spectroscopy, mercury intrusion porosimetry (MIP), and X-ray fluorescence (XRF) spectrometry. The pore evolution and carbon structural transformation during gasification in CO2 atmosphere are analyzed in-situ using synchrotron radiation SAXS-WAXS techniques for three coke samples prepared from coals with varying ranks. The strength and reactivity of coke are assessed based on its structure and dissolution-loss reaction mechanism during gasification. The results indicate that the high breakage resistance index (M13) of coke is attributed to the interlocking of bent aromatic carbon layers with AD/AG less than 1.837. The amorphous structures characterized by A(VL+VR+SL+S)/AD higher than 0.935 in coke serve as the initiation site of reaction with CO2, leading to a decrease in the fractal dimension (DS) and interlayer spacing (d002) as well as an increase in the stacking width (La). Subsequently, the etching of the carbon microcrystals and the dissolution loss of defective carbon structures alternately occur during gasification. The rough pore surface with DS more than 2.91 hinders the CO2 diffusion, while the carbon matrix with AD/AG more than 2.269 effectively decreases the coke reactivity index (CRI) of coke. Overall, the findings of this study can offer a theoretical foundation for coke quality evaluation and effective optimization of iron-making processes.

Tunable gas selectivity of cellulose nanocrystals – Polyethylene glycol composite membranes

The kinetics of the CO2, D2 and CH4 transport through self-supporting cellulose nanocrystals (CNCs) films containing low-molecular weight poly(ethylene glycol) (PEG) additive as plasticizer agent was studied in single gas condition at 293 K and sub-atmospheric feed pressure. Neat CNC and PEG-CNC with 7 wt % PEG films act as impermeable barrier for CO2 and CH4 and exhibit D2 permeability values not larger than 0.05 barrer with penetrant diffusivity in the 10−10 cm2/s range. PEG addition at larger contents improves the permeability and diffusivity of all penetrant gases and gives to the PEG-CNC membrane a CO2 selective character. The CO2 permeability and ideal CO2/D2 selectivity of the PEG-CNC films are 0.42 ± 0.04 barrer and ∼3, respectively, at 14 wt % PEG content, 2.5 ± 0.2 barrer and ∼5 at 21 wt % PEG. The preferred CO2 transport exhibits a solution-selective character being the D2 diffusivity a factor ∼10 larger than the CO2 diffusivity. PEG addition, on the contrary, does not change the D2 selective character for the D2/CH4 gas couple. PEG well mixed with the gas-impermeable CNCs increases the PEG-CNC free volume and preferentially improves the CO2 solubility given the specific interactions between the quadrupolar CO2 penetrant and the dipolar ether groups of the PEG additive.

The quandary of sources and sinks of CO2 efflux in tree stems-new insights and future directions.

Stem respiration (RS) substantially contributes to the return of photo assimilated carbon to the atmosphere and, thus, to the tree and ecosystem carbon balance. Stem CO2 efflux (ECO2) is often used as a proxy for RS. However, this metric has often been challenged because of the uncertain origin of CO2 emitted from the stem due to post-respiratory processes. In this Insight, we (i) describe processes affecting the quantification of RS, (ii) review common methodological approaches to quantify and model RS and (iii) develop a research agenda to fill the most relevant knowledge gaps that we identified. Dissolution, transport and accumulation of respired CO2 away from its production site, reassimilation of respired CO2 via stem photosynthesis and the enzyme phosphoenolpyruvate carboxylase, axial CO2 diffusion in the gas phase, shifts in the respiratory substrate and non-respiratory oxygen (O2) consumption are the most relevant processes causing divergence between RS and measured stem gas exchange (ECO2 or O2 influx, IO2). Two common methodological approaches to estimate RS, namely the CO2 mass balance approach and the O2 consumption technique, circumvent some of these processes but have yielded inconsistent results regarding the fate of respired CO2. Stem respiration modelling has recently progressed at the organ and tree levels. However, its implementation in large-scale models, commonly operated from a source-driven perspective, is unlikely to reflect adequate mechanisms. Finally, we propose hypotheses and approaches to advance the knowledge of the stem carbon balance, the role of sap pH on RS, the reassimilation of respired CO2, RS upscaling procedures, large-scale RS modelling and shifts in respiratory metabolism during environmental stress.

Self-templating approach to Co9S8 hexagonal sheets via Kirkendall effect with efficient photocatalytic performance

The Co9S8 Hexagonal Sheets (HSs) with an average side length of approximately 1 μm have been successfully prepared by a one-step hydrothermal route. XRD, FESEM, XPS, BET and UV–Vis spectra were used to analyze the crystal structure, morphology, surface element states, specific surface area and optical properties of the products. An SRS (Hexagonal Sheets-Hexagonal Rings-Hexagonal Sheets) growth mechanism of Co9S8 HSs was proposed based on the Kirkendall effect. The formation of Co9S8 HSs attributed to the gradual diffusion of Co2+ outward from the inner and S2- from outside into the core. The Co9S8 HSs exhibited excellent photocatalytic activity to degrade Rhodamine B (RhB) due to the larger specific surface area (13.74 m2/g) and lower band-gap (1.28 eV). The degradation rate of RhB (25 mg/L) reached 95 % in 60 min for Co9S8 HSs. After four cycles of degradation, the degradation rate can reach up to 90 %, indicating that Co9S8 HSs have good reusability. Furthermore, given radical quenching experiments and photocatalytic reactions, the degradation mechanism of Co9S8 HSs was also analyzed in detail. This work may enlighten the design and fabrication of nanomaterials for various applications.

Transformation of Diffusion and Local Structure of CH4 , CO2 , SO2 and H2 O Mixtures in Graphene Under Wide Temperature and Pressure Range: A Molecular Dynamics Simulation Study.

As a material with high specific surface area and excellent chemical stability, graphene exhibited remarkable adsorption and separation performance as well as a wide range of potential applications. The graphene layer played a significant role in influencing gas transmission. In this study, we employed molecular dynamics simulation to investigate the diffusion characteristics and local structures of a mixed system consisting of CH4 , CO2 , SO2 and H2 O. Additionally, we further examined the transformation of the behavior of these mixtures within graphene layers. The order of diffusion coefficients of the four molecules without graphene was H2 O>SO2 >CO2 ≫CH4 . However, in the double-layer graphene, the order changed to CH4 >CO2 ≫H2 O>SO2 . Higher temperatures and lower pressures were found to facilitate gas diffusion. Temperature and pressure had great effects on the local structures of CH4 , CO2 and SO2 , while their impact on H2 O was limited due to the extensive network of hydrogen bonds formed by H2 O molecules. The statistical results of average coordination number revealed that CH4 tended to aggregate with itself, whereas CO2 and SO2 exhibited a tendency to aggregate with H2 O. The graphene structure enhanced the separation and transportation of CH4 from mixed systems.

Turning Normal to Abnormal: Reversing CO2/C2‐Hydrocarbon Selectivity in HKUST‐1

AbstractMetal–organic frameworks (MOFs) can efficiently purify hydrocarbons from CO2, but their rapid saturation, driven by preferential hydrocarbon adsorption, requires energy‐intensive adsorption–desorption processes. To address these challenges, an innovative approach is developed, enabling control over MOF flexibility through densification and defect engineering, resulting in an intriguing inverse CO2/C2 hydrocarbon selectivity. In this study, the densification process induces the shearing of the crystal lattice and contraction of pores in a defective CuBTC MOF. These changes have led to a remarkable transformation in selectivity, where the originally hydrocarbon‐selective CuBTC MOF becomes CO2‐selective. The selectivity values for densified CuBTC are significantly reversed when compared to its powder form, with notable improvements observed in CO2/C2H6 (4416 vs 0.61), CO2/C2H4 (15 vs 0.28), and CO2/C2H2 (4 vs 0.2). The densified material shows impressive separation, regeneration, and recyclability during dynamic breakthrough experiments with complex quinary gas mixtures. Simulation studies indicate faster CO2 passage through the tetragonal structure of densified CuBTC compared to C2H2. Experimental kinetic diffusion studies confirm accelerated CO2 diffusion over hydrocarbons in the densified MOF, attributed to its small pore window and minimal interparticle voids. This research introduces a promising strategy for refining existing and future MOF materials, enhancing their separation performance.

Novel Ni–Co-based superalloys with high thermal stability and specific yield stress discovered by directed energy deposition

We report on the rapid alloy screening of Ni–Co–Ti–Al–Mo superalloys with high thermal stability and specific yield stress by means of directed energy deposition. A laser directed energy deposition, a specific type of additive manufacturing, was employed using multiple powder feeders and elemental powders. Fifty superalloys of different compositions were deposited and the heat-treated microstructure and γ' solvus temperature were examined. The 43Ni–38Co–9Ti–6Al–4Mo superalloy (atomic percent composition) exhibited a uniform γ/γ' microstructure and a γ' solvus temperature of 1202°C. The beneficial properties of the superalloy were also found in the cast superalloy of identical composition. The cast superalloy exhibited a thermally stable γ/γ' microstructure with cuboidal γ' precipitates even after long-term aging heat treatments at 800°C, 900°C, and 1000°C up to 500 h. The γ'-coarsening mechanism was evaluated based on the Lifshitz–Slyozov–Wagner model and the trans-interface diffusion-controlled model. A transition between these two mechanisms was observed with an increase in aging temperature. Atom probe tomography analyses revealed that the sluggish interface diffusion of Co and corresponding reduction of the interfacial energy induced the transition of the γ'-coarsening mechanism. Moreover, the cast superalloy showed an enhanced specific yield stress attributed to its exceptionally low alloy density of 7.61 g/cm3.

CO2-Enhanced Radial Borehole Development of Shale Oil: Production Simulation and Parameter Analysis

Shale oil resources, noted for their broad distribution and significant reserves, are increasingly recognized as vital supplements to traditional oil resources. In response to the high fracturing costs and swift decline in productivity associated with shale oil horizontal wells, this research introduces a novel approach utilizing CO2 for enhanced shale oil recovery in radial boreholes. A compositional numerical simulation method is built accounted for component diffusion, adsorption, and non-Darcy flow, to explore the viability of this technique. The study examines how different factors—such as initial reservoir pressure, permeability, numbers of radial boreholes, and their branching patterns—influence oil production and CO2 storage. Our principal conclusions indicate that with a constant CO2 injection rate, lower initial reservoir pressures predominantly lead to immiscible oil displacement, hastening the occurrence of CO2 gas channeling. Therefore, maintaining higher initial or injection pressures is critical for effective miscible displacement in CO2-enhanced recovery using radial boreholes. Notably, the adsorption of CO2 in shale oil results in the displacement of lighter hydrocarbons, an effect amplified by competitive adsorption. While CO2 diffusion tends to prompt earlier gas channeling, its migration towards areas of lower concentration within the reservoir reduces the extent of channeling CO2. Nonetheless, when reservoir permeability falls below 0.01 mD, the yield from CO2-enhanced recovery using radial boreholes is markedly low. Hence, selecting high-permeability “sweet spot” regions within shale oil reservoirs for the deployment of this method is advisable. To boost oil production, utilizing longer and broader radial boreholes, increasing the number of boreholes, or setting the phase angle to 0° are effective strategies. Finally, by comparing the production of shale oil enhanced by CO2 with that of a dual horizontal well fracturing system enhanced by CO2, it was found that although the former’s oil production is only 50.6% of the latter, its cost is merely 11.1%, thereby proving its economic viability. These findings present a new perspective for the economically efficient extraction of shale oil, offering potential guidance for industrial practices.

Greenhouse gas emission flux (CO2, CH4, N2O) from marine shrimp (Litopenaeus vannamei) monoculture cultures in the Brazilian semi-arid region

Greenhouse gases (GHG) and their rising atmospheric concentrations have been one of the most important international subjects due to their huge impact on climate change (IPCC, 2022). Aquaculture is of crucial importance to the human food supply and nutrition since it is one of the major sectors providing animal protein, besides reducing the pressure on the fishery stocks from natural resources worldwide (Cai, Zhou, 2019; FAO, 2022). On the other hand, it represents a threat to the environment by generating waste. Thus, this research aims to evaluate the GHG flux dynamics in marine shrimp (Litopenaeus vannamei) monoculture cultures. The study was carried out in two aquaculture farms, both located in the Brazilian semi-arid region. In order to measure the production of greenhouse gases, three cultures of marine shrimp were monitored. The dynamics of the diffusive and ebullitive emission of CO2, CH4, and N2O were monitored in the three units during the daytime (6:00 AM) and nighttime (6:00 PM). The results showed the stocking density as the main regulator for ebullitive CO2 emissions. A decreasing trend in diffusive CO2 emissions was observed. Aeration played a crucial role in controlling the diffusive and ebullitive emissions of CH4 and N2O, effectively reducing their release. The diffusive CH4 emissions exceeded ebullitive emissions and the oxygen content suppressed the anoxic pathway for N2O, and the ponds acted as a sink for this gas. This research aims to evaluate the dynamics of greenhouse gas flow in marine shrimp (Litopenaeus vannamei) monoculture cultures in the Brazilian semi-arid region and to verify whether lower stocking densities emit less greenhouse gases when compared to higher densities.

The decisive role of Au in CO diffusion on Pt surfaces: a DFT study.

The modification of metallic surfaces with adsorbed atoms of a second metal is presented as an ideal method for producing electrocatalysts. In this work, we examined the role of Au...

Molecular dynamics simulation on the displacement behaviour of crude oil by CO2/CH4 mixtures on a silica surface.

Produced gas re-injection is an effective and eco-friendly approach for enhancing oil recovery from shale oil reservoirs. However, the interactions between different gas phase components, and the oil phase and rocks are still unclear during the re-injection process. This study aims to investigate the potential of produced gas re-injection, particularly focusing on the effects of methane (CH4) content in the produced gas on shale oil displacement. Molecular dynamics simulations were employed to analyze the interactions between gas, oil, and matrix phases with different CH4 proportions (0%, 25%, 50%, and 100%), alkanes and under various burial depth. Results show that a 25% CH4 content in the produced gas achieves almost the same displacement effect as pure carbon dioxide (CO2) injection. However, when the CH4 content increases to 50% and 100%, the interaction between gas and quartz becomes insufficient to effectively isolate oil from quartz, causing only expansion and slight dispersion. Interestingly, the presence of CH4 has a synergistic effect on CO2, facilitating the diffusion of CO2 into the oil film. During the gas stripping process, CO2 is the main factor separating oil from quartz, while CH4 mainly contributes to oil expansion. In addition, for crude oil containing a large amount of light alkanes, extracting light components through mixed gas may be more effective than pure CO2. This study offers valuable insights for applications of produced gas re-injection to promote shale oil recovery.

Improved electrochemical reduction of CO2 to syngas with a highly exfoliated Ti3C2Tx MXene-gold composite.

Transforming carbon dioxide (CO2) into valuable chemicals via electroreduction presents a sustainable and viable approach to mitigating excess CO2 in the atmosphere. This report provides fresh insights into the design of a new titanium-based MXene composite as a catalyst for the efficient conversion of CO2 in a safe aqueous medium. Despite its excellent electrocatalytic activity towards CO2 reduction and high selectivity for CO production, the high cost of Au and the decline in catalytic activity on a larger scale hinder its large-scale CO2 conversion applications. In this research, we have successfully prepared an Au/Ti3C2Tx composite and tested its catalytic activity in the electrochemical CO2 reduction reaction (ECRR). The as-prepared composite features strong interactions between gold atoms and the MXene support, achieved through the formation of metal-oxygen/carbon bonds. The Au/Ti3C2Tx electrode demonstrated a significant current density of 17.3 mA cm-2 at a potential of -0.42 V vs. RHE, in a CO2 saturated atmosphere (faradaic efficiency: CO = 48.3% and H2 = 25.6%). Nyquist plots further indicated a reduction in the charge-transfer resistance of the Au/Ti3C2Tx layer, signifying rapid charge transfer between the Au and Ti3C2Tx. Furthermore, it is known that liquid crossover through the Gas Diffusion Electrode (GDE) significantly improves CO2 diffusion to catalyst active sites, thereby enhancing CO2 conversion efficiency. The goal of this work is to design an interface between metal and MXene so that CO2 can be electroreduced to fuels and other useful chemical compounds with great selectivity.

A microfluidic system for the cultivation of cyanobacteria with precise light intensity and CO2 control: enabling growth data acquisition at single-cell resolution.

Quantification of cell growth is central to any study of photoautotrophic microorganisms. However, cellular self-shading and limited CO2 control in conventional photobioreactors lead to heterogeneous conditions that obscure distinct correlations between the environment and cellular physiology. Here we present a microfluidic cultivation platform that enables precise analysis of cyanobacterial growth with spatio-temporal resolution. Since cyanobacteria are cultivated in monolayers, cellular self-shading does not occur, allowing homogeneous illumination and precise knowledge of the photon-flux density at single-cell resolution. A single chip contains multiple channels, each connected to several hundred growth chambers. In combination with an externally applied light gradient, this setup enables high-throughput multi-parameter analysis in short time. In addition, the multilayered microfluidic design allows continuous perfusion of defined gas mixtures. Transversal CO2 diffusion across the intermediate polydimethylsiloxane membrane results in homogeneous CO2 supply, with a unique exchange-surface to cultivation-volume ratio. Three cyanobacterial model strains were examined under various, static and dynamic environmental conditions. Phase-contrast and chlorophyll fluorescence images were recorded by automated time-lapse microscopy. Deep-learning trained cell segmentation was used to efficiently analyse large image stacks, thereby generating statistically reliable data. Cell division was highly synchronized, and growth was robust under continuous illumination but stopped rapidly upon initiating dark phases. CO2-Limitation, often a limiting factor in photobioreactors, was only observed when the device was operated under reduced CO2 between 50 and 0 ppm. Here we provide comprehensive and precise data on cyanobacterial growth at single-cell resolution, accessible for further growth studies and modeling.

Plastron effect enhanced electrochemical CO2 reduction activity over hydrophobic three-dimensional nanoporous silver.

The electrochemical reduction of CO2 on catalyst surfaces is hindered by the inefficient mass transfer of CO2 in aqueous solutions. In this study, we employed an electrochemical reduction approach to fabricate a hydrophobic three-dimensional nanoporous silver catalyst with a plastron effect, aiming to enhance the CO2 diffusion. The resulting catalyst exhibited an exceptional performance with the FECO peaking at 95% at -0.65 V (vs. RHE) and demonstrated remarkable stability during continuous electrolysis for 48 hours. Control experiments, together with Tafel analysis, EIS measurements, and contact angle results, confirmed that the notable enhancement of performance was attributed to the hydrophobic porous structure that facilitated efficient storage and rapid mass transfer of low-solubility CO2 gas reactants.

Mg2-xCaxAl layered double hydroxide-derived mixed metal oxide porous hexagonal nanoplatelets for CO2 sorption.

Porous hexagonal nanoplatelets of mixed metal oxide (MMO) derived from the calcination of MgAl layered double hydroxide exhibits a CO2 sorption capacity of 1.99 mmol g-1 at 30 °C, with a retention of 87% sorption capacity over 10 carbonation-decarbonation cycles and a CO2 sorption capacity of 1 mmol g-1 at 200 °C with a 40% increase in capacity over 10 cycles. The high sorption capacity is attributed to the porous nanoplatelet structure of the MMO with a BET surface area of 115 m2 g-1, which enables increased CO2 diffusion. Upon partially replacing magnesium with calcium (33, 50 and 66 mol%), the CO2 sorption capacity of the MMO increases with an increase in temperature. MMO derived from LDH, in which 66% of magnesium is replaced by calcium (MgCaAl-66), delivers CO2 sorption capacities of 1.38, 1.31, 2.50, 4.85 and 7.75 mmol g-1 at 200, 300, 350, 400 and 600 °C, respectively, which is significant for application in the sorption-enhanced water gas shift (SEWGS) process. MgCaAl-66 MMO exhibits a sorption capacity of 1 mmol g-1, which is stable over 10 cycles at 200 °C, and a sorption capacity of 3.68 mmol g-1 at 400 °C with 85% capture efficiency retention over 10 cycles. While the incorporation of Ca2+ serves multiple purposes such as increasing basic defect sorption sites and improving stability to repress the sintering-induced limitation of MMO over sorption cycles, the porous nanoplatelets act as individual sorbent units resisting volume changes through carbonation-decarbonation cycles.

Statistical modeling of diffusive CO2 emissions before the creation of the SINOP hydroelectric reservoir, Brazil.

Several discussions have arisen about energy from hydroelectric plants being considered clean energy and its reservoirs have been investigated due to the large emission of greenhouse gases (GHG), such as carbon dioxide, methane, and nitrous oxide. The present work shows a statistical study of the diffusive CO2 emissions before the formation of the reservoir of the hydroelectric power plant (HPP) of SINOP, Brazil. The association between emissions collected at the surface (water-air) and at the bottom of the reservoir (sediment-water) was investigated during four data collection campaigns, carried out from November 2017 to September 2018. This study aims to compare the effect of reservoir depth on the diffusive flow of CO2 at 34 collection points. The variable depth analyzed was defined from points collected on the surface and bottom of the reservoir. The objective is to detect whether different periods of time and whether the depth of the reservoir have a direct impact on the behavior of diffusive CO2 emissions. As the measurements of the observational unit are repeatedly observed, there is a multilevel structure, individuals are independent of each other, but there is an intra-individual correlation. Considering this data configuration, an estimation of generalized equations (GEE) was performed, which is a technique that estimates the intra-individual correlation matrix and thus produces estimates for the parameters of the generalized regression models (Generalized Regression Models - GLM) that are not biased. The study showed that the average diffusive CO2 emissions are higher on the reservoir surface. The study also found that, on average, there are more emissions during the rainy season in the region than during the dry season.

Effects of bonding temperature on mechanical properties and interfacial morphology of YG8/40Cr joints fabricated using SPS diffusion bonding

The diffusion bonding of YG8 cemented carbide and 40Cr steel was performed using spark plasma sintering with Ni powder as the interlayer. The influence of bonding temperatures ranging from 700 to 1100 °C on the bonding interface morphology, mechanical properties, and failure mechanism of the joints was studied. By calculating the diffusion coefficients of Ni and Fe and observing the changes in the interface morphology, the pores at the Ni/40Cr interfaces were identified as Kirkendall voids formed because of the unbalanced diffusion of Ni and Fe. The diffusion activation energy of Ni in Fe was 87.37 kJ/mol, and that of Fe in Ni was 58.08 kJ/mol. The use of a pulsed current significantly reduced the diffusion activation energy, making diffusion easier. The bending strength of the joints increased sharply in the range from 700 to 900 °C, subsequently increased slowly, and tended to stabilise in the range from 900 to 1100 °C. The highest bending strength of 1080 MPa was achieved for the joint bonded at 1100 °C, which was attributed to the improved bonding of the YG8/Ni and Ni/40Cr interfaces and the resulting effects of the interlayer plastic constraint. The thickness of the CoNi diffusion zone at the YG8/Ni interface appeared to form a decisive factor in determining the failure locations of the joints. As the bonding temperature increased, the improved diffusion of Co and Ni enhanced the metallurgical bonding of the YG8/Ni interface, and the fracture position shifted from the polished surface of the YG8 base material (700 °C) to the Ni interlayer (1100 °C).

Influence of natural fibers on hydration and carbonation of reactive magnesium oxide cement (RMC)

This study offers insights into the influence of cellulose fibers at 0, 0.25, and 0.5 vol% on the hydration and carbonation of reactive magnesium oxide cement (RMC). The cumulative heat increased with the fiber content, attributed to the nucleation and possibly internal curing effects of the fibers. The reinforcing action provided by the fibers also improved the mechanical performance of the air-cured samples, yet the compressive strength under 20% CO2 and 80% RH was maximized at 0.25 vol%. At 0.5 vol%, the contents of brucite and carbonates were reduced due to confinement and crack control, which restricted the growth of brucite and CO2 diffusion. The carbonation phase was mainly poorly crystalline or amorphous, marked by a fused structure and with a thermal decomposition peak at approximately 405 °C. The cellulose fibers with a porous cell wall and cavity provided a pathway for enhanced CO2 diffusion, resulting in concentrated carbonates at the fiber-matrix interface.

Poly ether block Amide/Polyvinyl Alcohol/ MgO nanocomposite membranes: Selectivity for CO2 and CH4 gases

One of the methods of improving mixed matrix membranes is the use of nanoparticles and compounds containing hydroxyl and carboxyl groups, which can be a suitable choice to help more permeability of gases. In this study, a mixed matrix membrane comprising polyether block amide/polyvinyl alcohol (Pebax/PVA) and magnesium oxide (MgO) nanoparticles was fabricated via solution casting. The Pebax/PVA membrane with MgO loadings of 10–15 % at varying PVA weight ratios (0, 20, 50, 80 %) was evaluated for CH4 and CO2 gas separation performance. Characterization via Fourier transform infrared (FTIR), X-ray diffraction (XRD) and field emission scanning electron microscopy (FESEM) revealed the nanoparticles well-dispersed within the polymer matrix, with surface roughness increasing with MgO addition. XRD analysis indicated stronger interaction between MgO and PVA chains versus Pebax. Peaks at ∼ 42, 62° suggest nanoparticles lodged between polymer strands. Variables assessed as independents impacting CH4 and CO2 permeability included PVA content, MgO loading, pressure and temperature. ANOVA showed the quadratic model best fitted correlations between variables and responses. Experimental data yielded the formulation with optimum selectivity. Molecular dynamics simulation (MDS) via Materials Studio estimated CH4 and CO2 diffusion through selected membranes. Simulated results matched experimental data well. Relative to prior separation data and outcomes herein, the synthesized nanocomposite membrane proved highly effective, promising potential for diverse gas mixtures. Membrane permeabilities were also evaluated.

A Case Study on the CO2 Sequestration in Shenhua Block Reservoir: The Impacts of Injection Rates and Modes

Carbon capture and storage (CCS) is the most promising method of curbing atmospheric carbon dioxide levels from 2020 to 2050. Accurate predictions of geology and sealing capabilities play a key role in the safe execution of CCS projects. However, popular forecasting methods often oversimplify the process and fail to guide actual CCS projects in the right direction. This study takes a specific block in Shenhua, China as an example. The relative permeability of CO2 and brine is measured experimentally, and a multi-field coupling CO2 storage prediction model is constructed, focusing on analyzing the sealing ability of the block from the perspective of injection modes. The results show that when injected at a constant speed, the average formation pressure and wellbore pressure are positively correlated with the CO2 injection rate and time; when the injection rate is 0.5 kg/s for 50 years, the average formation pressure increases by 38% and the wellbore pressure increases by 68%. For different injection modes, the average formation pressures of various injection methods are similar during injection. Among them, the pressure increases around the well in the decreasing injection mode is the smallest. The CO2 concentration around the wellbore is the largest, and the CO2 diffusion range continues to expand with injection time. In summary, formation pressure increases with the increase in injection rate and injection time, and the decreasing injection mode has the least impact on the increase in formation pressure. The CO2 concentration is the largest around the well, and the CO2 concentration gradually decreases. The conclusion helps determine the geological carrying capacity of injection volumes and provides insights into the selection of more appropriate injection modes. Accurate predictions of CO2 storage capacity are critical to ensuring project safety and monitoring potentially hazardous sites based on reservoir characteristics.