Diffusion Coefficients Of CO2 Research Articles

Controlling Microstructure-Transport Interplay in Poly(ether-block-amide) Multiblock Copolymer Gas Separation Membranes.

In this study, we investigated the effect of morphology on the gas-transport properties of a poly(ether-block-amide) (PEBA) multiblock copolymer. We annealed the copolymer samples and varied the annealing temperature to evaluate the influence of changes in the microstructure on the gas transport properties of PEBA. In addition, we used time-resolved attenuated total reflection Fourier transform infrared spectroscopy to evaluate the diffusion coefficient of CO2 in PEBA based on the Fickian model. The effect of the annealing temperature on the microphase-separated structure of the multiblock copolymer is discussed in detail. Furthermore, the gas diffusivity was significantly affected by the purity of the soft domains. The annealed sample demonstrated a 38% increase in CO2 permeability while maintaining a high CO2/N2 permselectivity of approximately 53. The findings of this study provide valuable insight into the design and optimization of PEBA membranes for gas separation applications.

Carbonation of a Synthetic CAF Compound by CO2 Absorption and Its Effect on Cement Matrix

In the field of construction materials, the development of fundamental technologies to reduce energy consumption and CO2 emissions, such as manufacturing process improvement and the expanded use of alternative materials, is required. Technologies for effectively reducing energy consumption and improving CO2 absorption and reduction that can meet domestic greenhouse gas reduction targets are also required. In this study, calcium–aluminate–ferrite (CAF), a ternary system of CaO·Al2O3·Fe2O3, was sintered at a low temperature (1100 °C) to examine the possibility of CO2 adsorption, and excellent CO2 absorption performance was confirmed, as the calcite content was found to be 11.01% after 3 h of the reaction between synthetic CAF (SCAF) and CO2. In addition, the physical and carbonation characteristics were investigated with respect to the SCAF substitution rate for cement (10%, 30%, 50%, 70%, and 100%). It was found that SCAF 10% developed a compressive strength similar to that of ordinary Portland cement (OPC 100%), but the compressive strength tended to decrease as the SCAF substitution rate increased. An increase in the SCAF substitution rate led to the rapid penetration of CO2, and carbonation was observed in all the specimens after 7 days. As carbonation time increased, the CO2 diffusion coefficient tended to decrease. This is because the diffusion of CO2 in the cement matrix follows the semi-infinite model of Fick’s second law. SCAF can contribute to reduced energy consumption and CO2 emissions because of the low-temperature sintering and can absorb and fix CO2 when a certain amount is substituted.

Engineering design of direct‐air‐capture contactors composed of sorbent particles using numerical simulations

AbstractWe study the transport of CO2 molecules inside direct‐air‐capture (DAC) contactors made of packed beds of solid‐sorbent‐particles separated by airgaps using numerical solution of the convection‐diffusion and first‐order adsorption kinetics equations. We quantify an apparent slowdown in the CO2 uptake in such contactors relative to the CO2 uptake of a high‐capacity sorbent particle making the bed. We derive two naturally occurring length‐scales associated with the adsorption process: (1) thickness of the sorbent related to the sorbent chemistry (capacity and adsorption rate constants), packing density, and diffusion coefficient of CO2 inside bed; and (2) extent of the bed in the air‐flow direction related to convective air‐flow velocity, sorbent chemistry, packed bed thickness, and packing density. DAC designs that have a bed thickness of O() and streamwise extent O() are shown to have faster CO2 uptake and more economical capture costs ($/ton‐CO2) compared with designs further away from this design set‐point. Our work should provide guidance to engineering design of DAC contactors with packed bed sorbents and related porous materials.

CO2 diffusion in shale oil based on molecular simulation and pore network model

Field practices show that CO2 huff and puff can effectively promote the exploitation of shale resources, and CO2 diffusion is noteworthy as a crucial mechanism of enhanced oil recovery (EOR). Understanding the confinement effect on CO2 diffusion is imperative to accurately characterize the fluid transport in shale nanopores and further upscaling. We integrate molecular simulation and pore network model (PNM) to study CO2 diffusion behavior at the nanoscale and pore scale. We first explored CO2 diffusion into heptane in kerogen and calcite pores using molecular dynamics, and analyzed the impacts of pore size, molar fraction, temperature, and pore pressure on the confined Fick diffusion. Based on the molecular simulation results, a model characterizing the ratio of the confined diffusion coefficient to that of the bulk phase is constructed for further upscaling. Based on the PNM containing organic and inorganic pores, we established a model to simulate the CO2 diffusion at the pore scale by introducing the characterization model at the nanoscale into the convective diffusion equation. Considering the microscale effects and the influence of CO2 concentration on diffusion is beneficial to improve the simulation accuracy at the pore scale. The estimated CO2 diffusion coefficients are in good agreement with the experimental results. This work provides better insight into CO2 diffusion behavior in shale oil, which can afford effective support for industrial exploitation and the breakthrough of the technical bottleneck of shale oil production.

Effect of Graphene Oxide-Modified CaAl-Layered Double Hydroxides on the Carbon Dioxide Permeation Properties of Fluoroelastomers.

This work aimed to investigate the CO2 gas barrier and mechanical properties of fluorine rubber nanocomposites filled with Ca/Al layered hydroxide (graphene oxide [GO]/LDH-Ca2Al) modified by GO. GO/LDH-Ca2Al nanocomposite fillers were prepared by depositing Ca/Al layered hydroxide (LDH-Ca2Al) into the surface of alkalized GO (Al-GO). The prepared GO/LDH-Ca2Al nanocomposite fillers and complexes were characterized by Fourier infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) for structural and micromorphological characterization. The results showed that GO/LDH-Ca2Al was successfully prepared with strong interactions between Al-GO and LDH, and the compatibility of GO/LDH-Ca2Al nanocomposite fillers with the polymer was significantly improved compared with that of LDH-Ca2Al. Consequently, both the fracture strength (σb) and strain (εb) of GO/LDH-Ca2Al nanocomplexes remarkably increased, and they exhibited excellent mechanical properties. Differential scanning calorimetry and thermogravimetric analysis were used to characterize the thermal stability of GO/LDH-Ca2Al nanocomposite fillers, and GO/LDH-Ca2Al nanocomposite fillers have better thermal stability than LDH-Ca2Al. The reaction products (S-LDH-Ca2Al and S-GO-Ca2Al) of LDH-Ca2Al and GO/LDH-Ca2Al with CO2 were characterized using XRD and TGA, respectively, and the results show that LDH-Ca2Al reacts readily and chemically with CO2, resulting in a lower diffusion coefficient of CO2 in the LDH-Ca2Al nanocomplexes than that of the GO/LDH-Ca2Al nanocomplexes and leading to the destruction of the laminar structure of LDH-Ca2Al, while GO/LDH-Ca2Al has better CO2 resistance stability. GO/LDH-Ca2Al nanocomplexes exhibited a reduced content of hydroxyl groups with pro-CO2 nature exposed on the surface of LDH-Ca2Al, improving the interfacial interaction between the nanofillers and the rubber matrix and enhancing the dispersion of GO/LDH-Ca2Al in the polymers. Moreover, CO2 in the soluble GO/LDH-Ca2Al nanocomposites was significantly reduced, while the diffusion properties demonstrated weak temperature dependence on solubility. The mechanism of the CO2 gas barrier of polymers filled with GO/LDH-Ca2Al was proposed on the basis of the Arrhenius equation.

Copolyimide Brushes as a Component of a Hybrid Poly(phenylene Oxide) Membrane for Controlling Gas Separation: Effect of Water, Methanol, and Hexane Vapors.

The effect of water, methanol, and hexane vapors on gas permeability was studied in a hybrid membrane containing 5 wt% copolyimide brushes with poly(methyl methacrylate) side chains (PI-g-PMMA) in a poly(phenylene oxide) (PPO) matrix, and in a pristine PPO membrane. These membranes in the form of dense nonporous films were further examined by atomic force microscopy (AFM) and scanning electron microscopy (SEM), as well as by measuring their mechanical and gas transport properties. A gas separation study of the membranes in a dry state and the membranes saturated with water, methanol, and hexane vapors was performed to estimate the effect of each vapor on the H2, CO2, N2 permeability and selectivity in the separation of H2/N2 and CO2/N2 pairs. In general, saturation with water, methanol, and hexane vapors caused a decrease in the gas permeability of both membranes. The hybrid membrane containing copolyimide brushes demonstrated enhanced selectivity in the separation of H2/N2 and CO2/N2 pairs. It was found that a special effect of the vapors used for membrane saturation is associated with their molar volume. The solubility and diffusion coefficients of N2 and CO2 were obtained by Grand Canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations.

PEI@MOFs thin film nanocomposite (TFN) membrane for efficient CO2 separation

Polyetherimide (PEI) membrane exhibits high CO2 selectivity while suffer from low permeance thus limiting the further application in CO2 separation. Thin film nanocomposite (TFN) membrane which contains a thin selective functional layer with nanomaterials porous fillers is a new class of high-performance membranes. In this work, a series of novel PEI@MOFs TFN membranes were prepared for efficient CO2 separation. The sub-micro scale PEI layers (about 400 nm) with four kinds of MOFs fillers including 3-dimensional MOFs nanoparticles (UiO-66 and MIL-101 (Cr)) and MOFs nanosheets (2-D CuBDC and Zn2(bim)4) were prepared by a simple spin-coating strategy. The properties and CO2 separation performance of the TFN membranes were further studied. The MOFs in PEI increased the diffusion coefficient and selectivity for CO2, at the same time, the ultra-thin functional layer maximized reducing the CO2 transport resistance. As a result, the PEI@MOFs TFN membranes exhibited high CO2 permeance as well as enhanced CO2 separation performance which close to the Robeson upper bound. The PEI@CuBDC TFN membrane exhibited CO2 permeance of 15.6 GPU (3.3 times higher than the neat PEI membrane), and the selectivity of CO2/CH4 reached 39.8 (2.2 times higher than the neat PEI membrane). In addition, the PEI@MOFs TFN membranes showed good thermal and operation stability.

Diffusion model of gas hydrate formation from ice considering the gas pressure drop

A kinetic model of the process of gas hydrate formation from ice that considers the gas pressure drop caused by this process is presented. This model is based on the diffusion equation. The issues during the formation of gas hydrate from ice powder and that from a flat ice layer are considered separately. For each of these problems, a solution in the framework of a quasi-stationary approximation is obtained, allowing for the calculation of the gas pressure drop in the gas phase. The calculated data are compared with available experimental data on the kinetics of CO2 hydrate formation from pure ice powder and ice powder with the addition of sodium dodecyl sulfate (SDS) at a mass concentration of 240 ppm: the calculated and experimental curves of CO2 pressure drop are compared with each other. From this comparison, the values of the diffusion coefficient of CO2 through a layer of CO2 hydrate formed from pure ice and ice with the addition of SDS at a mass concentration of 240 ppm were determined. Based on these values, it was found that SDS molecules present in the gas hydrate affect the rate of gas diffusion through the gas hydrate layer.

Molecular dynamics simulation of CO2 dissolution-diffusion in multi-component crude oil

In order to study the dissolution-diffusion process and mechanism of CO2 in multi-component crude oil, a model of multi-component crude oil system with octane as the main component and 16 other alkanes as a compound was constructed by using molecular dynamics simulation method. We estimated the CO2 density distribution in crude oil model and the shift in crude oil model volume change. We then investigated the microscopic influence mechanism of CO2 dissolution-diffusion on the volume expansion of crude oil by simulating the action of CO2 dissolution-diffusion in the multi-component crude oil model. Based on the variation law of mean square displacement between crude oil molecules, the dissolution and diffusion coefficients of CO2 were predicted, and the influence of CO2 dissolution-diffusion on crude oil mobility was analyzed. It is found that temperature intensifies the molecular thermal motion and increases the voids between alkane molecules, which promotes the dissolution of CO2 and encourages CO2 molecules to transmit, making the crude oil expand and viscosity decrease, and improving the flow ability of crude oil; with the enhancement of given pressure, the potential energy difference between the inside and outside of the crude oil model becomes larger, and the voids between alkane molecules become larger, which is favorable to the dissolution of CO2. Nevertheless, the action of CO2 molecules’ diffusing in the crude oil sample is significantly limited or even tends to zero, besides, the mobility of crude oil is affected due to the advance of external pressure. The mechanism of CO2 dissolution and diffusion in multi-component crude oil is revealed at the microscopic level, and provides theoretical guidance for the development of CO2 flooding.

CO2 diffusive characteristics and influencing factors in the porous medium with saturated polyacrylamide solutions

Polyacrylamide has been widely utilized to store CO2 in reservoirs in order to alleviate the greenhouse impact. However, no studies have been conducted on the motion of CO2 in a polyacrylamide solution within porous media. This study illustrates the effect of polyacrylamide molecular weight, concentration, pressure, temperature, and pore size on the dynamic diffusion of CO2 in the core with saturated polyacrylamide solutions. The diffusion motion characteristics of CO2 were obtained by diffusion experiments. The microscopic analysis of core slices following testing showed the presence of polyacrylamide on rock particles. The pressure and CO2 mass fraction distribution inside the core were calculated by constructing a mathematical model. The results show that the increase in molecular weight and concentration of polyacrylamide decreased the diffusion ability of CO2, while temperature and pressure accelerated the diffusion of CO2. The polyacrylamide moved into the core to form an effective inhibiting effect, which was affected by CO2 and pressure. While the increase in pore size accelerates the flow rate of the polyacrylamide, it also enhances the sealing capacity of the polyacrylamide solution. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) showed that the core had a high content of polyacrylamide solution inside it, and these molecules were attached to the surface of the core particles in an irregular lamellar pattern. The calculation model was consistent with the diffusion experimental results, where the CO2 diffusion coefficient in the polyacrylamide solution was in the order of 10-12 m2/s under the conditions of 5–30 MPa, 323–343 K, and a core permeability of 60 × 10-3 μm2. The results of this paper provide a new calculation for evaluating the performance of polymer plugging.

Modeling competitive adsorption and diffusion of CH4/CO2 mixtures confined in mature type-II kerogen: Insights from molecular dynamics simulations

In this study, the adsorption and competitive diffusion of methane (CH4) and carbon dioxide (CO2) mixtures through a molecular model of mature type-2 kerogen was investigated using molecular dynamics simulations. The Dual Control Volume-Grand Canonical Molecular Dynamics method was used to analyze the system and the results were focused on the selectivity of kerogen towards mixtures under a wide range of thermodynamic conditions. The results showed that the adsorption selectivity of CO2/CH4 was around 2–4 and decreased with temperature in the range 350–450 K. The Extended Langmuir (EL) model was found to underestimate the selectivity, and a correction was proposed in the form of the Corrected Extended Langmuir (CEL) model, which improved the estimations of the adsorption of CH4/CO2 mixtures in kerogen with only one adjustable parameter independent of thermodynamic conditions. Interestingly, we noticed that, out of equilibrium, the adsorption selectivity was not affected by the flow conditions when a pressure gradient was imposed, and the CEL model can thus be used to describe the contribution of adsorption to the selectivity under flow conditions. The results showed that the ratio of the collective diffusion coefficients of CH4 and CO2 was around 0.3−0.4, which was about two times lower than other simulations found in the literature. To describe the global selectivity, a simple approach combining the CEL model and the average ratio of diffusion coefficients was proposed, resulting in a selectivity of around 1.

Effect of Steam on Carbonation of CaO in Ca-Looping.

Ca-looping is an effective way to capture CO2 from coal-fired power plants. However, there are still issues that require further study. One of these issues is the effect of steam on the Ca-looping process. In this paper, a self-madethermogravimetric analyzer that can achieve rapid heating and cooling is used to measure the change of sample weight under constant temperature conditions. The parameters of the Ca-looping are studied in detail, including the addition of water vapor alone in the calcination or carbonation stage and the calcination/carbonation reaction temperatures for both calcination and carbonation stages with water vapor. Steam has a positive overall effect on CO2 capture in the Ca-looping process. When steam is present in both calcination and carbonation processes, it increases the decomposition rate of CaCO3 and enhances the subsequent carbonation conversion of CaO. However, when steam was present only in the calcination process, there was lower CaO carbonation conversion in the following carbonation process. In contrast, when steam was present in the carbonation stage, CO2 capture was improved. Sample characterizations after the reaction showed that although water vapor had a negative effect on the pore structure, adding water vapor increased the diffusion coefficient of CO2 and the carbonation conversion rate of CaO.

Solubility and diffusivity of CO2 and C2H4 in the ionic liquids 1-alkyl-2,3-dimethylimidazolium bis(trifluoromethanesulfonyl)imide by tube-in-tube reactor method

In this paper, the solubility and diffusivity of CO2/C2H4 in ionic liquids 1-Ethyl-2,3-dimethylimidazolium Bis(trifluoromethanesulfonyl)imide([Emmim][Tf2N]), 1-Propyl-2,3-dimethylimidazolium Bis(trifluoromethanesulfonyl)imide([Pmmim][Tf2N]), 1-Butyl-2,3-dimethylimidazolium Bis(trifluoromethanesulfonyl)imide([Bmmim][Tf2N]) and 1-Hexyl-2,3-dimethylimidazolium Bis(trifluoromethanesulfonyl)imide([Hmmim][Tf2N])) are measured at the temperature range of 303–333 K with a tube-in-tube reactor. The new device can greatly decrease the measurement time to several minutes in the tube-in-tube reactor. The solubility data is determined by the steady-state method with less than 10% deviation compared with previous reports. The diffusivity data is measured by an unsteady-state method within 3 min. The diffusion coefficient of CO2 in ionic liquids can be predicted with Morgan’s diffusivity correlation equation. For the diffusivity of C2H4 in ionic liquids, an empirical formula is developed and the predicted values using this correlation agree well with measured values with less than 17% deviation. The measured solubility and diffusivity data of CO2/C2H4 in ionic liquids and corresponding correlations can help to develop a more efficient process involving CO2/C2H4/ionic liquids system.

Patterns of effect of spark plasma sintering temperature on microstructure of thermoelectric composites based on Bi<sub>2</sub>Te<sub>2.1</sub>Se<sub>0.9</sub>Bi<sub>2 </sub>matrix with cobalt inclusions

Effect of spark plasma sintering temperature on the formation of Co filler particles in the Bi2Te2.1Se0.9 matrix has been examined. Owing to high-temperature diffusion redistribution of atoms in the matrix and filler materials and chemical interaction between these materials, in the Bi2Te2.1Se0.9 + 0.33 wt % Co, core–shell filler particles (Co@CoTe2) are formed. With increasing the sintering temperature, fraction of the “CoTe2 shell” in the particles increases, while fraction of the “Co core” decreases. This behavior is due to an increasing in the diffusion coefficient of Co in the Bi2Te2.1Se0.9 matrix with increasing in the sintering temperature. The concentration profiles of the Co distribution of in the Bi2Te2.1Se0.9 matrix, governed by diffusion, are well described using Fick’s second law for diffusion from a limited source of a diffusing substance. The diffusion coefficient of Co increases with increasing un the sintering temperature in accordance with the Arrhenius law and with an activation energy of ~0.61 eV.

Coupling covariance matrix adaptation with continuum modeling for determination of kinetic parameters associated with electrochemical CO2 reduction

Coupling covariance matrix adaptation with continuum modeling for determination of kinetic parameters associated with electrochemical CO2 reduction

Viscosity, activation energy, and CO2 diffusion coefficient of non-aqueous solutions of 3-methylamino propylamine (MAPA)/3-dimethylamino-1-propylamine (DMAPA) with polyethylene glycol (PEG200)

In this paper, viscosity (η) of 3-Methylaminopropylamine (MAPA)/3-dimethylamino-1-propylamine (DMAPA) with polyethylene glycol (PEG200) was detected over the range of (from 303.2 K to 323.2 K) temperature with amine mass fractions in the range of (from 0.30 to 0.60) at atmospheric pressure. The dependence of η on temperature and mass fractions was clarified. On the experimental basis, the activation energy (Ea) and CO2 diffusion coefficient (D CO2) in MAPA/DMAPA-PEG200 non-aqueous solutions were deduced.

Al-26 and O-18 tracer diffusion in a titania-coated sodium aluminosilicate glass

Although TiO2 is a common nucleating agent in the production of aluminosilicate glass-ceramics, its role as a catalyst for the nucleation of the functional crystal remains unclear. Therefore, the Ti, Al and O mobility was studied in situ using 26Al and 18O tracer diffusion and Ti chemical diffusion experiments in an aluminosilicate melt of albite composition. The albite glass serves as a surrogate for lithium and magnesium aluminosilicate glass-ceramic compositions, as it allows to study atomic mobilities free of crystallisation artefacts. The depth profiles showed that Al mobility increased significantly and became comparable to that of oxygen when Ti simultaneously diffused into the glass. In the absence of Ti, the diffusivity of Al was two orders of magnitude lower than that of oxygen. The co-diffusion coefficients of Ti and Al seem to confirm a proposed preferential structural linkage between Al and Ti species in the network structure of aluminosilicate melts.

Diffusion coefficient and the volume swelling of CO2/light oil systems: Insights from dynamic volume analysis and molecular dynamics simulation

The oil volume expansion and CO2 diffusion are one of the main mechanism of CO2-enhanced oil recovery (CO2-EOR). This paper established a series of experiments, numerical simulations, and molecular dynamics (MD) simulations to describe mass transfer behaviors between oil–gas phases. Expressly, the CO2 diffusion coefficient and light oil swelling factor are signification parameters to quantify and analyze these behaviors. In detail, the CO2 diffusion coefficient and the oil swelling factor were obtained from the traditional pressure decay method and the advanced MD simulation. Synthetically, the pressure decay method and MD simulation results were mutually verified. The results showed that the equilibrium pressure was proportional to the mole fraction of CO2 and inversely proportional to the mole fraction of light oil. The equilibrium time was proportional to the mole fraction of CO2 and light oil. At the temperature of 333.15 K and the initial pressure of 7.5 MPa, the CO2 diffusion coefficient in light oil was positively correlated with the relative molar proportion of CO2, while the light oil swelling factor was vice versa. In addition, the closer to the CO2-light oil interface, the greater the light oil's potential energy and self-diffusion coefficient, and the stronger the transport ability.

Molecular interactions of CO2 and CH4 and their adsorption behaviour in kerogens with different grades of maturity

ABSTRACT CO2 sequestration (CS) into the shale formations can reduce not only carbon emissions but also enhance gas recovery (EGR). The adsorption and diffusion behaviour of CO2 and CH4 on kerogens with different maturity play a crucial role in CS-EGR as they determine the efficiency of CO2 storage and energy recovery. In this work, GCMC and MD simulations were performed to investigate the adsorption and diffusion behaviour of CO2 and CH4 on kerogen models at different grades of maturity. It indicated that, in the same maturity, the CO2 adsorption capacity was more significant than that of CH4. With increasing maturity, the adsorption capacity and diffusion rate increased. With the increase of water contents, the swelling ratio of kerogens increased, and the adsorption capacity and the diffusion coefficients of CH4 and CO2 decreased. However, the adsorption selectivity of CO2 over CH4 significantly increased. H2O and CO2 molecules both preferred to adsorb on functional groups of oxygen, nitrogen and sulfur. This study consolidated our hypothesis that an injected CO2 to shale gas and oil formations contributed positively to enhanced energy recovery owing to the difference in adsorption and diffusion behaviour of CH4 and CO2 in kerogens with different maturity in gas and oil reservoirs.

The effect of water-soluble polymers on the dynamics of carbon dioxide sorption by lime sorbents

The effect of water-soluble polymers with different structure on the sorption properties of nonregenerable lime sorbents of carbon dioxide was studied. It was found that the introduction of water-soluble polymers into the sorbents could either decrease or increase the protective power time of the sorbents. To explain the revealed regularities, pore structure of the sorbents was investigated, molecular-dynamic modeling of the carbon dioxide transport was performed, and CO2 diffusion coefficients in water-polymer solutions were calculated. The results of the modeling correlate with the sorption experiment data: a high dynamic sorption capacity of the sorbent is reached after adding a water-polymer medium with a high CO2 diffusion coefficient. The results obtained can be used both to optimize the systems for the recovery of carbon dioxide from gas mixtures and to intensify mass transfer in the systems intended for photo- and electrocatalytic conversion of CO2 to useful products.