Diffusion Coefficients Of CO2 Research Articles

Control of pore-size distribution on CO2 adsorption volume and kinetics in Gondwana coals: Implications for shallow-depth CO2 sequestration potential

We report experimental CO2 adsorption isotherms and diffusion-related parameters of fresh coal samples from Jharia (350–360 m) and South Karanpura (50–60 m) coalfields, India at three different temperatures (28, 35 and 45 °C) and up to 4 MPa CO2 pressures. The results confirm that temperature possesses an inverse relationship with the excess adsorption volume. Data modelling with the Langmuir and Dubinin-Radushkevich (D-R) equations show the D-R equation better predicts the experimental excess adsorption data. A conversion of the excess adsorbed volume to absolute adsorption further reveals that the modified D-R equation is even a better model to estimate absolute adsorption than the conventional D-R equation. Adsorption kinetics data indicate that temperature has a positive influence on the adsorption rate. We determined the diffusion coefficients of CO2 in these coals using the unipore model, which suggest that it increases with pressure and temperature. Effective diffusivity and diffusion-time maintain a direct and inverse relationship, respectively, with the elevation of temperature. The experimental adsorbed volume and kinetics data are correlated with the corresponding pore-size distribution of the samples. Shallow depth South Karanpura samples have lower average pore diameter, higher volumetric proportion of micropores and surface area compared to those of higher depth Jharia coal samples. Lower adsorption volume and sluggish adsorption kinetics in Jharia coals result from a small surface area and relatively sparse distribution of semi open-ended micropores with poor interconnection. Based on our experimental observations, we discuss and suggest the potential and possible conditions for CO2 sequestration in the Permian Gondwana coalfields, India.

Experimental Study on the Viscosity of 1-(2-HE)PP Aqueous Solutions

In this paper, we measured the viscosities (η) data of aqueous solutions of 1-(2-Hydroxyethyl)-piperidine (1-(2-HE)PP) by using NDJ-5S digital rotary viscometer. The mass fractions of 1-(2-HE)PP ranged from 0.1 to 1, and the experimental temperatures were 303.2 K, 313.2 K and 323.2 K respectively. The effects of temperature and W1_(2-HE)pp on viscosity were demonstrated. Based on the experimental data of viscosity, we deduced the activation energy (Ea) and CO2 diffusion coefficient (Dco2) of 1-(2-HE)PP aqueous solutions.

Fluid-Fluid Interfacial Effects in Multiphase Flow during Carbonated Waterflooding in Sandstone: Application of X-ray Microcomputed Tomography and Molecular Dynamics.

Fluid-fluid interfacial reactions in porous materials are pertinent to many engineering applications such as fuel cells, catalyst design, subsurface energy recovery (enhanced oil recovery), and CO2 storage. They have been identified to control physicochemical properties such as interfacial rheology, multiphase flow, and reaction kinetics. In recent years, engineered waterflooding has been identified as an effective way to increase hydrocarbon recovery and solid-fluid interaction has been assessed as the key mechanism. However, in this study, we demonstrated that in the absence of solid-fluid interactions (in strong hydrophilic porous media), fluid-fluid interfacial reactions can significantly affect multiphase flow and thus lead to an increased hydrocarbon recovery during engineered carbonated waterflooding. We designed a microwaterflooding system to evaluate the interfacial reactions during two phase flow with engineered carbonated waters. Given that salinity controls the amount of dissolved CO2, we injected carbonated high salinity water and carbonated low salinity water to achieve different fluid-fluid reactions. We injected the carbonated water in a sandstone with 99.5% quartz under X-ray microcomputed tomography (μCT) scanning at a resolution of 3.43 μm per pixel. Image processing shows that carbonated low salinity waterflooding can recover 8% more oil than carbonated high salinity waterflooding, while the quartz-rich sandstone remains strongly hydrophilic in both samples. A gradual CT intensity distribution indicates an interfacial phase generation between carbonated brine and crude oil during carbonated waterflooding. Therefore, we attributed the additional hydrocarbon recoveries to the fluid-fluid interfacial reactions. To understand the effects of fluid-fluid reactions on interfacial properties, we performed molecular dynamics simulations to investigate the chemical species distribution at the interface, interfacial tension (IFT) changes, and CO2 diffusion. The MD simulation results revealed a layered structure of the interface, a lower CO2 diffusion coefficient in carbonated high salinity water, a lower IFT in carbonated low salinity water, a swelling hydrocarbon phase in carbonated low salinity water, and more CO2 accumulated at the interface between the hydrocarbon phase and carbonated low salinity water. This work provides a general and fundamental understanding of the influence of fluid-fluid interactions on the interfacial properties between carbonated water and the hydrocarbon interface.

Experimental Determination of CO2 Diffusion Coefficient in a Brine-Saturated Core Simulating Reservoir Condition

CO2 diffusion coefficient plays a crucial part in saline aquifers for the CO2 storage and the safety of long-term sequestration. Therefore, it is particularly important to measure the diffusion coefficient accurately. As far as we know, there are currently no CO2 brine diffusion data in real cores under reservoir temperature and pressure conditions. In this paper, a study on the CO2 diffusion coefficient diffused in a brine-saturated Berea core along the radial direction was conducted at temperatures of 313.15 K to 373.15 K and pressures of 8 MPa to 30 MPa. On account of the experimental results, the effect of permeability, NaCl concentration, temperature and pressure on the CO2 diffusivity is analyzed. The results in this study indicate that the diffusion coefficient increases with increasing permeability, pressure and temperature and decreases with increasing NaCl concentration. However, the relationship between pressure and the diffusion coefficient is not linear. As the pressure gradually increases, the effect of pressure will become weak. In addition, an empirical correlation of the relationship between temperature–pressure and the CO2 diffusion coefficient could be obtained based on the experimental data. The data in this paper fill the blank on the study of the CO2 diffusivity in brine under reservoir conditions, which has positive significance for the study of supercritical CO2 diffusion in a brine-saturated core.

Molecular level understanding of CO2 capture in ionic liquid/polyimide composite membrane

Ionic liquid (IL)/polyimide (PI) composite membranes demonstrate promise for use in CO2 separation applications. However, few studies have focused on the microscopic mechanism of CO2 in these composite systems, which is important information for designing new membranes. In this work, a series of systems of CO2 in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide composited with 4,4-(hexafluoroisopropylidene) diphthalic anhydride (6FDA)-based PI, 6FDA-2,3,5,6-tetramethyl-1,4-phenylene-diamine, at different IL concentrations were investigated by all-atom molecular dynamics simulation. The formation of IL regions in PI was found, and the IL regions gradually became continuous channels with increasing IL concentrations. The analysis of the radial distribution functions and hydrogen bond numbers demonstrated that PI had a stronger interaction with cations than anions. However, the hydrogen bonds among PI chains were destroyed by the addition of IL, which was favorable for transporting CO2. Furthermore, the self-diffusion coefficient and free energy barrier suggested that the diffusion coefficient of CO2 decreased with increasing IL concentrations up to 35 wt-% due to the decrease of the fractional free volume of the composite membrane. However, the CO2 self-diffusion coefficients increased when the IL contents were higher than 35 wt-%, which was attributed to the formation of continuous IL domain that benefitted the transportation of CO2.

Measurement of CO2 diffusion coefficients in both bulk liquids and carven filling porous media of fractured-vuggy carbonate reservoirs at 50 MPa and 393 K.

Diffusion coefficients are necessary to describe the mass transfer and adsorption rate of CO2 in formation fluids. However, data is scarcely reported for actual reservoir conditions of high pressure and temperature, which are normal in most scenarios of the CO2-enhanced oil recovery process in China's fractured-vuggy reservoirs and carbon storage process. Accordingly, this work employed the pressure decay method (PD) and relevant mathematical models to determine the CO2 diffusion coefficient in both liquids and cavern filling porous media at 50 MPa and 393 K. The effects of the type of reservoir fluids, the properties of carven filling porous media, and water saturation on CO2 diffusion coefficients were investigated. Results in bulk reservoir liquids showed that the CO2 diffusion coefficient in the oil sample was 4.1243 × 10−8 m2 s−1, much higher than those in the pure alkane phase, pure water and brine sample from reservoirs. Results of CO2 diffusion in carven filling porous media saturated with oil demonstrated a significant dependence on properties such as porosity and permeability, and a correlation in the CO2 diffusion coefficients between the bulk oil phase and cavern filling porous media in the form of touristy was documented. CO2 diffusion in the fractured cavern porous media was much higher than that without fracture. An increase in water saturation reduced CO2 diffusion coefficients in the carven filling porous medium studied, herein. Thus, the CO2 diffusion coefficient is essentially related to the type of liquid and properties of the filling media.

Study on CO<SUB align="right">2 diffusion process in heavy oil saturated porous media using experiment and simulation

To explore the CO2 diffusion in heavy oil saturated porous media, a mathematical model was developed to simulate the diffusion process by coupling the gas state equation. Then the experiment of CO2 diffusion in heavy oil saturated porous media was carried out and CO2 diffusion coefficient was determined by fitting the experimental data with the established model. Using the measured diffusion coefficient as an input parameter, the CO2 diffusion process in porous media was simulated and the factors that affected the diffusion process were analysed in this paper. The simulation results show that diffusion direction on the rock surface is in the tangential direction of the rock and points to where the CO2 concentration potential decreases. Furthermore, the contact area of the heavy oil and CO2 has a vital impact on the CO2 diffusion amount and CO2 concentration distribution. [Received: November 24, 2019; Accepted: August 7, 2020]

Liquid fuel synthesis via CO2 hydrogenation by coupling homogeneous and heterogeneous catalysis

Summary Synthesis of liquid fuel (C5+ hydrocarbons) via CO2 hydrogenation generally involves cascade catalysis of reverse water gas shift (RWGS) and Fischer-Tropsch synthesis (FTS) reactions over heterogeneous catalysts. Because of thermodynamic limitations of the cascade reactions, the reported heterogeneous catalysts usually suffer from high temperature (above 300°C) and low selectivity. Here, we report the liquid fuel production from CO2 hydrogenation by coupling homogeneous RuCl3 and heterogeneous Ru0 catalysts, which proceeded at the lowest temperature reported so far (180°C) and reached the highest C5+ selectivity to date (71.1%). The TOF of the CO2 hydrogenation reached 9.5 h−1, which is comparable with that of the reported Ru0 catalyzed FTS reaction using syngas. Detailed study indicates that synergy of homogeneous and heterogeneous catalysis is the key for the outstanding performance.

Molecular simulation of N2 and CO2 injection into a coal model containing adsorbed methane at different temperatures

To research the dynamic mechanism of nitrogen and carbon dioxide displacement of methane, we used the grand canonical Monte Carlo (GCMC) simulation method to determine the lowest energy coal model containing adsorbed methane. The desorption behavior of CH4 after the injection of N2 and CO2 at different temperatures was studied. Results show that CO2 and N2 were mainly used to drive off methane gas by occupying adsorption sites. The total energy of the CH4-CO2 model was lower than that of the CH4-N2 model. With the increased of temperature, the average relative concentration and motion velocity of CH4 in the vacuum layer increased. The relationship of the average relative concentration and average velocity distribution of the three gases in the vacuum layer was CH4>CO2>N2. Under the same time conditions, the relationship between the mean square displacement and diffusion coefficient of CH4, CO2, and N2 in different models was CH4>CO2>N2, and they all increased with temperature. The diffusion activation energy of CH4 in the model injected with CO2 was reduced by 20.53%, and the effect of injecting CO2 to promote the desorption of methane was better than that of N2.

Experimental and numerical study of the polyurethane foaming process using high-pressure CO2

A simulation of simultaneous bubble nucleation and growth was performed for polyurethane/CO2 physical foaming process. The single-factor and comprehensive effects of viscoelastic properties, Henry’s constant, CO2 diffusion coefficient and surface tension on the cell morphology were numerically analyzed. The results show that the cell density of PU foam ( N0) increases and its average cell diameter ( Dv) reduces with increased Henry’s constant and slower gas diffusion. Both N0 and Dv reduces with the curing degree ( α). In addition, the effects of α and foaming conditions on the cell structure were experimentally investigated. With an increase of α at foamable range, Dv decreases continuously and N0 increases first and then declines. With increasing saturation pressure and depressurization rate or decreasing temperature, N0 increases and Dv reduces. There is an intrinsic correlation between the simulated and experimental variables, and the results of the simulation and experiment are generally consistent.

Transport mechanisms and emission of landfill gas through various cover soil configurations in an MSW landfill using a static flux chamber technique

This study evaluated the transport mechanisms and emission rates of landfill gas (LFG) from 200- (vegetated with short grass), 300- (vegetated with short grass), and 450-mm-thick (non-vegetated) interim cover soils within a municipal solid waste landfill. LFG emission and diffusion mechanisms were evaluated using static flux chambers and laboratory-scale diffusion columns. Overall, the greatest CH4 and CO2 emissions were consistently observed from the 200-mm-thick cover soil with an average flux rate of 39.2 mg m−2 h−1 and 3.07 × 103 mg m−2 h−1, respectively. In addition to CH4 and CO2, H2S migration through a 450-mm interim cover soil was also evaluated. The H2S emission rate was relatively more uniform at an average of 2.47 × 10−5 mg m−2 h−1. Long-term LFG emission was predicted using an emission model based on a first-order decomposition rate equation and compared with the static flux chamber method. The field-measured CO2, CH4 and H2S emissions were less than the estimated emissions from the emission model, by 22%, 85%, and 91%, respectively. Further, the diffusion coefficients of CH4, CO2, and H2S for the interim cover soils were determined using a laboratory-scale diffusion column test and compared with a three-parameter diffusion model. The measured and estimated diffusion coefficients for the three landfill gases were within the 10% variation limits. Based on these findings, the LFG emission rate varied depending on the physical-chemical properties of the cover soil (e.g., cover thickness, moisture content, compaction ratio, uneven distribution of soil), organic material content and age of buried refuse, and seasonal environmental conditions (such as temperature). Test results showed that fugitive CH4 emissions can be reduced one fourth by utilizing an appropriate cover soil (300-mm to 450-mm, CL) compared to cases with a thinner cover soil.

Experimental Determination of H2 and CO Diffusion Coefficients in a Wax Mixture Confined in a Porous Titania Catalyst Support.

The ability to measure and predict molecular diffusion coefficients in multicomponent mixtures is not only of fundamental scientific interest but also of significant relevance in understanding how catalytic processes proceed. In the present work, the direct measurement of the molecular diffusion of H2 and CO gas-phase species diffusing in n-alkane mixtures using pulsed-field gradient (PFG) nuclear magnetic resonance (NMR) methods is reported. The work is of direct relevance to Fischer-Tropsch (FT) catalysis, with the measurements being made of the gas-wax system with the wax in both the bulk liquid state and when confined within a titania catalyst support, at temperatures and pressures typical of low-temperature FT synthesis. Molecular diffusion coefficients of H2 and CO within wax-saturated porous titania in the range (1.00-2.43) × 10-8 and (6.44-8.50) × 10-9 m2 s-1, respectively, were measured in the temperature range of 140-240 and 200-240 °C for H2 and CO, respectively, at a pressure of 40 bar. The wax mixture was typical of a wax produced during FT catalysis and had a molar average carbon number of 36. It is shown that the hydrogen diffusion coefficient within this wax mixture is consistent, to within experimental error, with the hydrogen diffusion coefficient measured in pure single-component n-hexatriacontane (n-C36) wax; this result held with the waxes in the bulk liquid state and when confined within the porous titania. The tortuosity of the porous titania was also measured using PFG NMR and found to be 1.77; this value is independent of temperature. The ability of existing correlations to predict these experimentally determined data was then critically evaluated. Although the Wilke-Chang correlation was found to underestimate the molecular diffusion coefficients of both H2 and CO diffusing in the wax in both the bulk state and when confined within the porous titania, parameterized correlations based on the rough hard sphere model, having accounted for the experimentally determined tortuosity factor, predicted the H2 and CO diffusion within bulk and confined wax to within 3%.

Solubility and diffusion coefficient of supercritical CO2 in polystyrene dynamic melt

Abstract The solubility and diffusion coefficient of supercritical CO2 in polystyrene (PS) dynamic melt were studied by using a new constant pressure experimental device. By comparing the experimental results with those of other researchers, the validity of the experimental device and the reliability of the calculated results are verified. The solubility and diffusion coefficient of supercritical CO2 in polystyrene dynamic melts at different temperatures and pressures were obtained. The numerical calculation method, dissolution process, and experimental results are analyzed and compared with that of the static melt. Finally, the effects of stirring speed, pressure, and temperature fluctuation on the solubility and diffusion coefficient are also analyzed.

Screening of Ionic Liquids and Deep Eutectic Solvents for Physical CO2 Absorption by Soft-SAFT Using Key Performance Indicators

The efficient screening of solvents for CO2 capture requires a reliable and robust equation of state to characterize and compare their thermophysical behavior for the desired application. In this work, the potentiality of 14 ionic liquids (ILs) and 7 deep eutectic solvents (DESs) for CO2 capture was examined using soft-SAFT as a modeling tool for the screening of these solvents based on key process indicators, namely, cyclic working capacity, enthalpy of desorption, and CO2 diffusion coefficient. Once the models were assessed versus experimental data, soft-SAFT was used as a predictive tool to calculate the thermophysical properties needed for evaluating their performance. Results demonstrate that under the same operating conditions, ILs have a far superior performance than DESs primarily in terms of amount of CO2 captured, being at least two-folds more than that captured using DESs. The screening tool revealed that among all the examined solvents and conditions, [C4 py][NTf2] is the most promising solvent for physical CO2 capture. The collection of the acquired results confirms the reliability of the soft-SAFT EoS as an attractive and valuable screening tool for CO2 capture and process modeling.

Kinetics model adaptability analysis of CO2 sequestration process utilizing steelmaking slag and cold-rolling wastewater

Better adaptive kinetics model for CO2 sequestration utilizing wastes in steelmaking plant has a big significance for establishing green out-circulating network system. This work investigated the effect of temperature, L/S ratio and cold-rolling wastewater concentration on carbonation degree in basic oxygen furnace slag and CRW carbonation process, then their kinetics was discussed by surface coverage model and shrinking core model, respectively, in order to evaluate their adaptability and accuracy. Furthermore, CO2 sequestration intensifying factor was originally proposed for considering the carbonation depth, through comparing diffusion coefficient of CO2 between water carbonation and wastewater carbonation. The results showed that carbonation conversion increased as temperature and CRW concentration increased except for L/S ratio, and the maximum carbonation could reach 41.499 ± 1.240%. Because higher prediction error existed in surface coverage model, the shrinking core model had a better adaptability and accuracy for analyzing carbonation process in autoclave. Meanwhile, the CO2 sequestration intensifying factor was 1.6 times as big as carbonation process in distilled water as a result of DCO2 value. CO2 sequestration reaction in our work was controlled by calcium diffused because of DCO2 (0.700–0.976 × 10−4 cm2 s−1) and DCa (0.935–1.149 × 10−5 cm2 s−1). The results above will be helpful for us to better comprehend the reaction kinetics at micro-scale, when the idea of triple wastes self-circulation system network will be established to industrial application.

An experimental approach for measuring carbon dioxide diffusion coefficient in water and oil under supercritical conditions

Several direct or indirect approaches have been proposed to measure diffusion coefficient of gases into liquids. The main complexity of indirect techniques such as pressure decay method is interpreting early pressure–time data which strongly affected by incubation period effect or convective instability. In the current approach, accurate apparatus and precise experimental setup including a high pressure and temperature PVT cell, a high precision Sanchez pump, heating and recording sub-system are implemented and a novel data analysis procedure is applied to modify pressure decay method. The effect of incubation period is reduced remarkably and diffusion coefficient of carbon dioxide in water in wide range of pressures and temperatures is determined and the effects of temperature, pressure and carbon dioxide phase alteration from gas to supercritical are investigated and the value of uncertainty is estimated. Furthermore, diffusion coefficient of CO 2 and methane in an oil sample from one of the Iranian southwest oil formations is determined precisely using the experimental approach while no incubation period is detected. The results showed that incubation period duration decreases with increasing diffusion coefficient. Additionally, when CO 2 state is gas, rate of increasing diffusion coefficient with pressure is decreased with temperature and when CO 2 state is supercritical, the rate of increasing diffusion coefficient with pressure is decreased significantly.

Effect of the CO2-philic ionic liquid [BMIM][Tf2N] on the single and mixed gas transport in PolyActive™ membranes

This study reports on the gas transport properties of four different grades of PolyActive™ polyether-co-polyester multi-block copolymer membranes containing different concentrations (4.8, 9.1, 16.7, 23.1 and 28.6 wt%) of the low-viscous CO2-philic ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][Tf2N]). Single gas permeability, solubility and diffusion coefficients of He, H2, N2, O2, CH4 and CO2 were determined at 1 bar and 25 °C in a constant-volume time lag setup. Mixed gas permeability measurements of CO2/CH4 and CO2/N2 mixtures containing 35 and 15 vol% CO2, respectively, were carried out at 25 °C in the pressure range from 1 to 6 bar(a). The transport properties were correlated with the ionic liquid content of the samples, the specific PolyActive™ grade (i.e. chain length, copolymer composition), and previously determined microstructure, crystallinity, thermal and mechanical properties. For all PolyActive™ grades, the single gas permeability decreased in the order CO2 ≫ H2 > He > O2 ≈ CH4 > N2 and it typically increased with increasing IL content, whereas the ideal selectivity decreased with IL content for most gas pairs. None of the membranes revealed significant dependence on the feed pressure in both single and mixed gas permeation tests. Such behavior is typical for predominantly rubber-like materials. Samples based on PolyActive™ 4000PEOT77PBT23 had the strongest dependence on the IL concentration due to its higher weight fraction and higher crystallinity of the polyether phase.The specific behavior of the four polymers was illustrated via their different trends with increasing IL concentration in the Robeson diagrams. The study demonstrates how blending with ionic liquid can be used to tailor the permeability and selectivity of the membranes. It provides insight into the influence of ionic liquid and the weight percentages of the PEO blocks and the PBT blocks in the copolymers on the individual contributions of the solubility and diffusion coefficients on the permeability.

Service life of GGBFS concrete under carbonation through probabilistic method considering cold joint and tensile stress

Carbonation is a typical deterioration phenomenon which accelerates steel corrosion through pH drop in pore water by intrusion of external carbon dioxide (CO2). Many researches have been performed on carbonation process considering carbonic reaction, mixture conditions, and exterior conditions. Recently probabilistic approaches have been adopted for considering engineering uncertainties such as complicated material behavior, simple evaluation system, and limited sample numbers. In the study, the service life variation was evaluated considering several effects of induced tensile stress level, cold joint, and GGBFS (Ground Granulated Blast Furnace Slag) through probabilistic approach. Utilizing the previous test results, the effect of loading conditions on carbonation depth was investigated. Four design parameters like cover depth, exterior CO2 concentration, carbonatable material, and CO2 diffusion coefficient were assumed as random variables for probability analysis. Through MCS (Monte Carlo Simulation) with normal distributions and intended PDF (Probability of Durability Failure) of 10%, variations of service life were simulated for the RC structure under loading conditions. The effects of COVs (Coefficient of Variation) for design parameters were also simulated. The comparisons of the predicted service life from the probabilistic and deterministic methods were quantitatively discussed, and the safety index with service life was also investigated. The results of this study can provide useful information on maintenance priority and service life evaluation for RC structures containing cold joint subjected to tensile stress.

Microscopic and macroscopic investigation on the gas diffusion in poly(ether-block-amide) membranes doped with polysorbate nonionic surfactants

Gas transport properties through nanocomposite membranes incorporating nonionic surfactants (polysorbates) in a poly (ether-block-amide), Pebax®1657, were investigated by two complementary techniques: the time-lag method in a manometric apparatus to analyze the permeation process of CO2 and CH4, and the 1H and 13C NMR spectroscopy to study the molecular dynamics by the direct measurements of the self-diffusion coefficients (Pulsed Field Gradient-PFG technique) and spectral analysis.The diffusion coefficients of CO2 and CH4 gas molecules measured by microscopic and macroscopic techniques are in agreement, provided that the gas pressure is opportunely set. NMR allows a deeper study of the molecular dynamics and confinement effects, revealing dual pathways within the nanocomposite membranes that result in different self-diffusion for the bulkier CH4 molecules. Morphological and thermal analyses proved the effect of the polysorbate incorporation on the microstructure of the nanocomposite films: lowered glass transition temperature of the polymer polyether block and reduced crystallinity of the Pebax blocks, additional endothermic peak and presence of ‘micellar-like’ domains.

Comments on the paper “experimental study and modelling on diffusion coefficient of CO2 in water” by H. Ahmadi et al. (2020)

This comment addresses several points regarding data interpretation in a recent paper in the Journal, which results in an inaccurate interpretation of experimental data on CO2 diffusion in water. The experimental data were interpreted by Fick’s law of diffusion, while the existence of convection was disregarded.