Diffusion Coefficients Of CO2 Research Articles

Slowing down CO2 effective diffusion speeds in recycled aggregate concrete by using carbon capture technology and high-quality recycled aggregate

The diffusion of atmospheric CO2 in concrete structures is mainly responsible for their internal steel corrosion; but the effective diffusion speed of CO2 in recycled aggregate concrete is far from being fully understood. Hereby, the pore structure characteristics of new and old mortars in recycled aggregate concretes prepared with different types of recycled aggregates were examined. The CO2 effective diffusion coefficients in new and old mortars were then modelled using a validated model based on Fick's second law and mass conservation law. The effects of aggregate type and carbon capture condition on the pore structures and diffusion coefficients were further explored. The findings of the study revealed that the CO2 effective diffusion coefficients in the new and old mortars of hardened concrete can be effectively reduced by the carbon capture of recycled aggregate and selecting a high-quality recycled aggregate. Additionally, the latter presented preferable deliverables compared with the former. Besides, the effect of carbon capture under high-concentration CO2 on the reduction of CO2 diffusion coefficient in hardened concrete was more obvious than that under low-concentration CO2.

Improvement of the calculation and experimental method of evaluation of carbonization of reinforced concrete structures of sewerage underground systems

Carbonization of concrete leads to a decrease in the alkalinity of concrete, an increase in the number of hydrogen ions in the pores, is one of the main factors that lead to corrosion of reinforcement, the formation of cracks and the subsequent reduction of load-bearing capacity of structures. The study of the depth of carbonization of concrete is to determine the pH of the pore liquid at different depths. There are devices with automatic maintenance of a given concentration of carbon dioxide, to determine the diffusion permeability of concrete to carbon dioxide, based on data on the rate of neutralization (carbonization) of concrete with carbon dioxide. Basically, this method is intended for use in the development of technology and design of concrete composition, providing long-term maintenance of structures in non-aggressive and aggressive gaseous environments, as chips are not prepared immediately before the test and after reaching the design age are placed in the installation with reagents for 7 days. But to determine the carbonization directly on the construction site or object often use the pH method, i.e. the indicator method of pH determination. To assess the concentration of hydrogen ions used acid-base indicators - organic substances – dyes, the color of which depends on the pH from the obtained results the algorithm of definition of depth of carbonization consists in the following actions. The improved formula of definition of depth of carbonization of concrete taking into account degree of aging and corrosion damages for what in the final formula the corresponding coefficients kst and kkor are entered: hcarb = {(2D˖C˖τ) / (mo˖kst ˖kkor)} 1/2, where the effective diffusion coefficient of CO2 in the concrete of the existing reinforced concrete structure, which is determined by the condition D = (mo˖δ2) / (2C˖t ). The thickness of the neutralized layer δ is determined experimentally on an existing structure using a physicochemical method (phenolphthalein solution or using depth gauges. .Concentration of CO2 in air C should be determined by chemical analysis of air samples taken directly from the structure or take ≈ 0.03%. Re. the ability of concrete mo is determined by the formula mo = 0.4 (C˖p˖f), taking the amount of cement, kg per 1m3, respectively, the strength of concrete. neutralization of concrete is equal to f = 0.5.

Insights from molecular dynamics on CO2 diffusion coefficient in saline water over a wide range of temperatures, pressures, and salinity: CO2 geological storage implications

Successful design and execution of CO2 sequestration in saline aquifers requires a comprehensive understanding of CO2 transport properties. CO2 diffusion coefficient affects CO2 dissolution behavior in water/brine and controls phenomena such as shape of viscous fingers and onset of instabilities. Experimental determination of CO2 diffusion coefficient is a technically and economically challenging task. In this research work, we used Molecular Dynamics (MD) simulation to compute CO2 diffusion coefficient in various NaCl saline water concentrations (1–6 mol NaCl/kg water) under a broad range of temperatures (294–423 K) and pressures (10–30 MPa) to acquire a data set for CO2 diffusion coefficient in different conditions. According to the results, NaCl concentration increase gives rise to a decrease in CO2 diffusion coefficient by 15%, 29%, 49%, and 64% at 1 M, 2 M, 4 M, and 6 M solutions, respectively, compared to pure water. Presence of more cations due to salinity increase forms further hydration shells act as a barrier for CO2 diffusion. In addition, the rise in CO2 diffusion at elevated temperatures can be explained by the cation's hydration shell size reduction with temperature increment due to intensifying repulsive forces among water molecules. We proposed a new precise correlation for estimation of CO2 diffusion coefficients over temperatures and salinity ranges of this study. Regarding the pressure variation effects, no tangible changes were observed with pressure increase, validating a negligible influence on diffusion coefficient. Furthermore, the CO2 diffusion coefficient variability in presence of other salts, namely MgCl2, CaCl2, KCl, and Na2SO4, were computed separately. Comparing the influence of various salts, CaCl2 and KCl have the highest and lowest effect on the CO2 diffusion coefficient, respectively. Finally, a set of direct numerical simulations were conducted to study the impact of CO2 diffusion coefficient on CO2 dissolution process. The results obtained from this research work shed light on the importance of CO2 diffusion coefficient changes in saline water for prediction of dissolution process behavior.

A new prediction model of CO2 diffusion coefficient in crude oil under reservoir conditions based on BP neural network

Diffusion is the key mechanism of enhanced oil recovery (EOR) by CO2 injection in unconventional oil reservoirs. The accurate measurement of the diffusion coefficient in porous media is essential for forecasting and optimizing CO2 injection. The pressure decay technique is the most commonly used method for measuring the diffusion coefficient, which is well acknowledged. However, it has a long experimental period with higher requirements on the equipment and operation. This paper firstly proposed a quick and simple prediction methods of diffusion coefficient for both CO2-oil systems within/without porous media based on back propagation (BP) neural network. The average errors are 18.73% and 18.80%, respectively. With the continuous supplement of the data, models can be continuously updated to provide more accurate estimates of the supercritical CO2-oil system without/with porous media conditions. Temperature, pressure, permeability, porosity and surface area positively correlate with the diffusion coefficient. Oil viscosity, oil density, and volume of porous media have a negative correlation with the diffusion coefficient. It is worth noting that for rocks with certain volume, the increase of surface area can significantly increase the diffusion coefficient, which implies that direct upscale of the measured CO2 diffusion coefficient in the lab is totally unreasonable.

Carbon dioxide diffusions in Methane-Dissolved pore Fluids: Implications for geological carbon storage and utilization in tight formations

Fluid immobilizations in tight formations augment the importance of CO2 molecular diffusions in the processes of geological carbon utilization and storage. This study, for the first time, investigates the CO2 diffusions in unconventional tight formations which are saturated with in-situ gas-dissolved pore fluids, both experimentally and theoretically. A novel high-pressure high-temperature diffusion cell was designed to reproduce the actual CO2 diffusions in extremely low-permeability on-site geological cores saturated with methane-dissolved crude oils at the reservoir conditions and various scenarios (e.g., different gas–liquid ratios). On the other hand, a comprehensive mathematical model, which consists composition and diffusion models, was developed for quick predictions and in-depth evaluations. The CO2 diffusion coefficients at the pressure of 18.5 MPa and temperature of 80 °C with varying gas–liquid ratios were obtained from a genetic algorithm-fitting of the measured and calculated data. With the gas–liquid ratios increasing from 0 to 40 sm3/m3, the CO2 diffusion coefficient was found to decrease from 7.90 × 10−9 to 3.09 × 10−9 m2/s and the average velocity of diffusion front reduced from 0.0121 to 0.0050 m/d. This finding indicates methane dissolutions into the crude oil at the reservoir conditions would be detrimental for the CO2 diffusions. Hence, the methane amount is suggested to be well controlled in the processes of geological carbon storage and utilization for oil production. This study will support the foundation of more general application pertaining to geological CO2 utilization and storage, especially in the unconventional tight or shale oil reservoirs.

Nanopore Confinement Effect on the Phase Behavior of CO2/Hydrocarbons in Tight Oil Reservoirs considering Capillary Pressure, Fluid-Wall Interaction, and Molecule Adsorption

The pore sizes in tight reservoirs are nanopores, where the phase behavior deviates significantly from that of bulk fluids in conventional reservoirs. The phase behavior for fluids in tight reservoirs is essential for a better understanding of the mechanics of fluid flow. A novel methodology is proposed to investigate the phase behavior of carbon dioxide (CO2)/hydrocarbons systems considering nanopore confinement. The phase equilibrium calculation is modified by coupling the Peng-Robinson equation of state (PR-EOS) with capillary pressure, fluid-wall interaction, and molecule adsorption. The proposed model has been validated with CMG-Winprop and experimental results with bulk and confined fluids. Subsequently, one case study for the Bakken tight oil reservoir was performed, and the results show that the reduction in the nanopore size causes noticeable difference in the phase envelope and the bubble point pressure is depressed due to nanopore confinement, which is conductive to enhance oil recovery with a higher possibility of achieving miscibility in miscible gas injection. As the pore size decreases, the interfacial tension (IFT) decreases whereas the capillary pressure increases obviously. Finally, the recovery mechanisms for CO2 injection are investigated in terms of minimum miscibility pressure (MMP), solution gas-oil ratio, oil volume expansion, viscosity reduction, extraction of lighter hydrocarbons, and molecular diffusion. Results indicate that nanopore confinement effect contributes to decrease MMP, which suppresses to 650 psi (65.9% smaller) as the pore size decreases to 2 nm, resulting in the suppression of the resistance of fluid transport. With the nanopore confinement effect, the CO2 solution gas-oil ratio and the oil formation volume factor of the oil increase with the decrease of pore size. In turn, the oil viscosity reduces as the pore size decreases. It indicates that considering the nanopore confinement effect, the amount of gas dissolved into crude oil increases, which will lead to the increase of the oil volume expansion and the decrease of the viscosity of crude oil. Besides, considering nanopore confinement effect seems to have a slightly reduced effect on extraction of lighter hydrocarbons. On the contrary, it causes an increase in the CO2 diffusion coefficient for liquid phase. Generally, the nanopore confinement appears to have a positive effect on the recovery mechanisms for CO2 injection in tight oil reservoirs. The developed novel model could provide a better understanding of confinement effect on the phase behavior of nanoscale porous media in tight reservoirs. The findings of this study can also help for better understanding of a flow mechanism of tight oil reservoirs especially in the case of CO2 injection for enhancing oil recovery.

Effects of water and carbon dioxide pressure on the adhesion of Na2SiO3 and K2SiO3 binders on silica sand surface: Comparison of experimental data and molecular dynamics simulation

In this study, the effects of different water amounts, CO2 blowing pressures, Na2O:SiO2 and K2O:SiO2 ratios were studied on the bonding strength of Na2SiO3 and K2SiO3 binders. It was concluded that the increase in water content had an adverse effect on the bonding strength of CO2-hardened Na2SiO3 sand. The blowing pressure did not have a linear relationship with the bonding strength, but it was closely related to the diffusion coefficient of CO2. Based on scanning electron microscopic results, it was inferred that the low strength was caused by the formation of lamellar crystals after the adhesive was hardened. It was found that the low strength was caused by the formation of lamellar crystals after the adhesive was hardened. Based on molecular dynamics simulations, different pressures and water contents had a great influence on the diffusion coefficient of CO2 in the silicate binder system. This research provides an important theoretical background to improve the technology of CO2-hardened Na2SiO3- and K2SiO3-bonded sands during the casting process.

CO2 absorption into a polymer within a multilayer structure: The case of poly(ethylene-co-vinyl acetate) in photovoltaic modules

The delamination of photovoltaic modules with supercritical CO2 is an interesting approach to integrate photovoltaics into a circular economy. This article describes the first phase of this process: the absorption of CO2 into poly(ethylene-co-vinyl acetate) (EVA-28), one of the layers in a photovoltaic module. The swelling of the polymer, determined by an on-line coupling between high pressure cell and an optical method using digital camera, under 60–200 bar at 60, 75 and 90 °C, was well reproduced by a modified Sanchez-Lacombe equation of state. The diffusion coefficient of CO2 into EVA-28 was determined using the same approach and was found to range, at 130 bar, from 1.1 × 10−9 m2·s−1 at 60 °C to 1.8 × 10−9 m2·s−1 at 90 °C. A preferential CO2 diffusion at the rear side of the cell, due to a high porosity, and at the “backsheet” interface was highlighted.

A dynamic model of CO2 diffusion coefficient in shale based on the whole process fitting

CO2 diffusion is of great importance for enhanced oil recovery (EOR), production prediction, and performance forecast of carbon capture and storage (CCS) in shale reservoirs. This work aims to determine the diffusion coefficient of the shale reservoir during CO2 huff and puff development. Firstly, combining pressure decay experiments and mathematical modeling studies, this paper developed a dynamic method to determine the diffusion coefficients of CO2 in cores under shale reservoir conditions. Based on Fick's law, MATLAB software was used to build the fitting chart under different diffusion coefficients. The diffusion coefficient was determined by matching experimental data. During the experiment, the reservoir's pore pressure and confining pressure were simulated, and a saturation-depletion-diffusion experiment method was established to simulate the natural reservoir conditions. The effects of different initial pressures on diffusion were compared in pressure decay experiments. The mathematical model of the diffusion coefficient of CO2 was established, and the fitting chart of diffusion coefficient considering time step was derived. The diffusion distance of different diffusion coefficients and different times was compared. The results show that the diffusion coefficient of CO2 in shale is between 5*10-8 ~ 5*10-7 cm2/s, and the diffusion rate is 0.28 cm/d under the condition of 20 MPa and 319.55 K. In addition, when the diffusion coefficient increases by one order of magnitude, the diffusion distance increases by 200%.

Solubility and effective diffusion coefficient of CO2 in fresh cheese (type Minas Frescal)

AbstractCarbon dioxide (CO2) is the most important gas used in modified atmosphere packaging of nonrespiring foods. In this technique, the gas solubilizes into the aqueous and lipid phases of food and exerts an antimicrobial effect. In the present study, the solubility and effective diffusion coefficient of CO2 in fresh cheese (type Minas Frescal) were determined at 4, 7, and 10°C by a manometric method. The value was obtained using the mathematical modeling (transient mass transfer and Fick's law) and a numerical procedure (exhaustive search method) to minimize the error between experimental and predicted values. The highest solubility value was obtained at 4°C, resulting from combined effects of temperature and complex phase transitions in fat content, shown by differential scanning calorimetry curves. Higher values corresponded to lower . Solubility and effective diffusion coefficient are important parameters for designing and developing new food products and food processes.Practical ApplicationsThis study presented a procedure to quantify the mass transfer of CO2 gas in fresh cheese. The knowledge of the CO2 transfer properties in food can help the industry concerning about the choice of the amount and composition of the gas used in modified atmosphere packaging. In which, a gaseous mixture (CO2/N2) is introduced into packaging resulting in the extension of the cheese shelf life. Additionally, the procedure used in cheese can be easily extended to estimate the transfer properties of CO2 in other nonrespiring food.

Diffusion of CO2 in Magnesite under High Pressure and High Temperature from Molecular Dynamics Simulations

CO2 transports in the Earth’s interior play a crucial role in understanding the deep carbon cycle and the global climate changes. Currently, CO2 transports inside of the Earth under extreme condition of pressure and temperature have not been understood well. In this study, the molecular dynamics (MD) calculations were performed to study CO2 transports under different CO2 pressures in slit-like magnesite pores with different pore sizes at 350~2500 K and 3~50 GPa are presented. Diffusion of CO2 in magnesite was improved as the temperature increases but showed the different features as a function of pressure. The diffusion coefficients of CO2 in magnesite were found in the range of 9 × 10 − 12 m 2 s − 1 ~ 28000 × 10 − 12 m 2 s − 1 . Magnesite with the pore size of 20~25 Å corresponds to the highest transports. Anisotropic diffusion of CO2 in magnesite may help to understand the inhomogeneous distribution of carbon in the upper mantle. The time of CO2 diffusion from the mantle to Earth surface was estimated to be around several tens of Ma and has an important effect on deep carbon cycle. The simulation of CO2 transports based on the Earth condition provides new insights to revealing the deep carbon cycle in the Earth’s interiors.

Are choline chloride-based deep eutectic solvents better than methyl diethanolamine solvents for natural gas Sweetening? theoretical insights from molecular dynamics simulations

Molecular dynamics simulations were performed to investigate the performance of three deep eutectic solvents (DESs) in the separation of acid gases from natural gas. To evaluate the efficiency of these DESs, their performance was compared with that of the conventional methyl diethanolamine (MDEA) system. For this purpose, the acidic DES (phenyl propionic acid and choline chloride; with 67 mol % Phpr), same acidic DES accompanied by boron-nitride nanotube (Nano-DES), and acidic DES with methyl diethanolamine (DES-MDEA) were considered. The solubility selectivity and diffusion selectivity were evaluated and compared to those of MDEA system. The Nano-DES system showed the best performance in terms of solubility selectivity of H2S over CH4, while the high solubility selectivity of CO2 over CH4 was obtained for pure DES systems. Likewise, the aqueous MDEA and the DES-MDEA systems exhibited the largest diffusivity selectivity of H2S over CH4 and CO2 over CH4, respectively. These results were rationalized and explained by analyzing the density profile and interaction energies. Besides, the radial and spatial distribution function, Gaussian normalized distribution of measured dipole moment of species, and the orientation of dipole moment species were investigated to explain the obtained results. Furthermore, dynamical properties such as mean square displacement and corrected diffusion coefficient of species indicated that CO2 molecules diffuse faster than H2S for studied systems except for aqueous MDEA. Likewise, the diffusion coefficient of H2S and CO2 in the considered systems follow the trends Nano-DES < DES-MDEA < DES < MDEA < aqueous MDEA, and DES < DES-MDEA < MDEA < Nano-DES < aqueous MDEA in the liquid phase, respectively.

Electrochemical tools to disclose the electrochemical reduction mechanism of CO2 in aprotic solvents and ionic liquids

Carbon dioxide (CO 2 ) plays a key role in controlling the temperature of the Earth. But the increase in the concentration of CO 2 in the atmosphere brings with it a series of consequences, originating several environmental problems. The use of electrochemical, spectroscopic and molecular dynamics techniques are useful toolkits to valorize carbon dioxide, and to know the reduction mechanism as a function of CO 2 concentration, the cathode nature, and the electrolyte. This manuscript will be mainly centered in the use of ionic liquids (IL) for efficient CO 2 capture and valorization into different valuable products thanks to the CO 2 electrochemical reduction. In this sense, spectroelectrochemistry based on cyclic voltammetry coupled with Polarization Modulation-Infrared Reflection-Absorption Spectroscopy (PM-IRRAS) and Infrared Reflection-Absorption Spectroscopy (IRRAS) appear to be an efficient instrument to follow the CO 2 reactivity in imidazolium ionic liquids. Finally, we present molecular dynamics paired with cyclic voltammetry in order to calculate the diffusion coefficient of CO 2 and the number of electrons involved in its reduction process, respectively. Therefore, the current research opens the door to the use of theoretical-experimental approaches altogether to determine how is the CO 2 reduction mechanism. The CO 2 reduction products in function of the solvent and nature of the cathode is suggested, proving that the product obtained from the electrochemical reduction of CO 2 depends on the electrode material and the solvent.

Diffusion coefficients of CO2–SO2–water and CO2–N2–water systems and their impact on the CO2 sequestration process: Molecular dynamics and dissolution process simulations

AbstractThe high cost of the CO2 sequestration in saline aquifers is a barrier to the implementation of them. However, a large portion of the cost is invested to purify and transport the CO2 from the flue gas stream of the emission sources. Therefore, the possibility of injecting impure CO2 will reduce the costs strongly. The diffusion coefficient is an important factor that plays a significant role in different aspects of the process. In spite of its importance, it is got less attention due to complex experimental procedures and low range of temperature and pressure applicability in the experimental conditions. To shed light on the effects of the impurity on the diffusion coefficient of CO2‐water systems, two types of impurities (SO2 and N2) in two levels are considered in this study through the molecular dynamics simulation approach. Simulations are done on a wide range of pressure and temperature conditions to cover a wide range of operational conditions for CO2 sequestration projects. The outcomes of these simulations were used in the direct numerical simulations to analyze the effect of the diffusion coefficient matrix changes on the CO2 dissolution process such as dissolution flux, the motion and shape of convective fingers, and their patterns. Results indicate that impurity has a great impact on the diffusion coefficient, and consequently on the CO2 dissolution behavior. We hope that reported results will pave the way for future studies regarding impure CO2 sequestration in saline aquifers. © 2021 Society of Chemical Industry and John Wiley &amp; Sons, Ltd.

Hydrodynamic and mass transfer parameters for CO2 absorption into amine solutions and its blend with nano heavy metal oxides using a bubble column

ABSTRACT In this work, hydrodynamic and mass transfer of CO2 absorption into metal oxide nanofluid includes TiO2, ZnO, and ZrO2 nanoparticles at Piperazine (Pz) solution in the bubble column was studied. The novel rigorous correlations were extended based on the variable parameters for the calculation of gas holdup, enhancement factor, and mass transfer coefficients in the reactive absorption processes using the π-Buckingham method. The correlations were constructed based on dimensionless numbers, including nanoparticle loading, film parameter, CO2 partial pressure ratio to the total pressure, the film thickness of phases, CO2 loading, and ratio of diffusion coefficients of CO2 in the gas and liquid phases. Experimental data were used to calculate the correlations, consisting of Pz concentration, CO2 partial pressure, nanoparticle loading, and stirrer speed in the range of 0.1–0.5 mol/l, 16.0–35.2 kPa, 0.0–0.1 wt%, and 0–300 rpm, respectively. The film parameter was applied to exert the influence of chemical reactions on the performance of absorption. The mean squared error (RMSEP), the average absolute error (%AARD), and the coefficient of correlation of the results (R2 ) for the correlations were in the range 0.021–2.604, 3.78–18.14, and 0.861–0.980, respectively, which represents the excellent accuracy of the proposed correlation.

Mass-transfer kinetics of CO2 in a hybrid choline-2-pyrrolidine-carboxylic acid/polyethylene glycol/water absorbent

Understanding the mass-transfer kinetics of CO2 in novel hybrid absorbents with physical and chemical contributions is essential for process design and evaluation. In this study, the liquid-side mass-transfer coefficients (kL) and second-order reaction rate constants (k2) of CO2 in hybrid absorbents (namely, choline-2-pyrrolidine-carboxylic acid salt/polyethylene glycol/water ([Cho][Pro]/PEG200/H2O)) were determined. The kL values for the hybrid absorbents were obtained from the CO2 diffusion coefficients (DCO2) and the kL values in PEG200/H2O. The DCO2 value was calculated from the density and viscosity of the hybrid absorbents, whereas the kL values in PEG200/H2O were measured experimentally. The k2 values of CO2 in the hybrid absorbents were estimated according to the reaction mechanism, the enhancement factor, and the kL values, and compared with those of other commercialized absorbents. The results showed that 30 wt% [Cho][Pro] + 70 wt% H2O had the highest kL and k2 values at atmospheric pressure, whereas the values of kL and k2 of CO2 in 30 wt% [Cho][Pro]/H2O + PEG200 were comparable to those in diethanolamine aqueous and amino-functionalized ILs. The hybrid absorbent of [Cho][Pro]/PEG200/H2O could be promising for CO2 separation considering its thermodynamic and kinetic properties.

Toward In Silico Prediction of CO2 Diffusion in Champagne Wines.

Carbon dioxide diffusion is the main physical process behind the formation and growth of bubbles in sparkling wines, especially champagne wines. By approximating brut-labeled champagnes as carbonated hydroalcoholic solutions, molecular dynamics (MD) simulations are carried out with six rigid water models and three CO2 models to evaluate CO2 diffusion coefficients. MD simulations are little sensitive to the CO2 model but proper water modeling is essential to reproduce experimental measurements. A satisfactory agreement with nuclear magnetic resonance (NMR) data is only reached at all temperatures for simulations based on the OPC and TIP4P/2005 water models; the similar efficiency of these two models is attributed to their common properties such as low mixture enthalpy, same number of hydrogen bonds, alike water tetrahedrality, and multipole values. Correcting CO2 diffusion coefficients to take into account their system-size dependence does not significantly alter the quality of the results. Estimates of viscosities deduced from the Stokes–Einstein formula are found in excellent agreement with viscometry on brut-labeled champagnes, while theoretical densities tend to underestimate experimental values. OPC and TIP4P/2005 water models appear to be choice water models to investigate CO2 solvation and transport properties in carbonated hydroalcoholic mixtures and should be the best candidates for any MD simulations concerning wines, spirits, or multicomponent mixtures with alike chemical composition.

Mechanistic Understanding of CO2 Adsorption and Diffusion in the Imidazole Ionic Liquid–Hexafluoroisopropylidene Polyimide Composite Membrane

The integration of molecular design and imidazole ionic liquids produces a synergistic effect to enhance and fine-tune the molecular sieve capability of polyimide (PI) membranes. The most difficult problem was to choose the right ionic liquids and moderate polymer combination. In this work, a series of systems of CO₂ in [EMIM][Tf₂N], [EMIM][BF₄], and [EMIM][PF₆] composited with 6FDA-based PI with different IL concentrations were discussed by all-atom molecular dynamics simulations. The results indicated that the CO₂ diffusion coefficient decreases with the compatibility of the PI structure with CO₂ molecules and increases with an increased IL concentration of up to 75 wt %. Therefore, this study may provide guidance for the design of PI membranes.

Diffusion Law and Calculating Method of Diffusion Coefficient of CO2 in Porous Liquid

Porous liquid combines the two unrelated things of solid porosity and liquid fluidity, and has showed a great potential gas separation.CO2 diffusion plays an important role in CO2 absorption capacity and rate of porous liquids. In this study, the 2-Methylimidazole zinc salt(ZIF-8) with porous structure was chosen and dispersed into 1-ethyl-3-methy limidazolium bis[(trifluoromethyl)sulfonyl]imide ([EMIm][NTf2]) for synthesizing porous liquids. And then the density and viscosity of porous liquid were measured in different temperature, pressure and ZIF-8 mass concentration. In addition, based on the CO2 absorption experiment of porous liquid taken in a static CO2 absorption system and theoretical calculation, the pressure decay of the system was recorded and CO2diffusion coefficient was calculated to study the CO2 diffusion characteristics of porous liquid under different experimental parameters including ZIF-8 mass fraction, pressure and temperature.

Unveiling Carbon Dioxide and Ethanol Diffusion in Carbonated Water-Ethanol Mixtures by Molecular Dynamics Simulations.

The diffusion of carbon dioxide (CO) and ethanol (EtOH) is a fundamental transport process behind the formation and growth of CO bubbles in sparkling beverages and the release of organoleptic compounds at the liquid free surface. In the present study, CO and EtOH diffusion coefficients are computed from molecular dynamics (MD) simulations and compared with experimental values derived from the Stokes-Einstein (SE) relation on the basis of viscometry experiments and hydrodynamic radii deduced from former nuclear magnetic resonance (NMR) measurements. These diffusion coefficients steadily increase with temperature and decrease as the concentration of ethanol rises. The agreement between theory and experiment is suitable for CO. Theoretical EtOH diffusion coefficients tend to overestimate slightly experimental values, although the agreement can be improved by changing the hydrodynamic radius used to evaluate experimental diffusion coefficients. This apparent disagreement should not rely on limitations of the MD simulations nor on the approximations made to evaluate theoretical diffusion coefficients. Improvement of the molecular models, as well as additional NMR measurements on sparkling beverages at several temperatures and ethanol concentrations, would help solve this issue.