CO2 Density Research Articles

Density and viscosity measurements at phase transition in supercritical carbon dioxide + 1-dodecanol + 2-dodecanol mixtures

The density and viscosity of binary CO2 + 1-dodecanol and CO2 + 2-dodecanol mixtures, and the ternary CO2 + (50 % 1-dodecanol+50 % 2-dodecanol) mixture were measured at phase transition. Phase transition was detected in a visual synthetic variable-volume view cell that had a torsional quartz crystal to measure viscosity. Density was calculated from the calibrated cell volume. Measurements are reported for 308 – 348 K and up to 28 MPa, and were modelled in Aspen Plus. Mutual solubility for the three mixtures decreases in the order CO2 + 2-dodecanol > > CO2 + (50 % 1-dodecanol+50 % 2-dodecanol) > > CO2 + 1-dodecanol. Phase transition pressures display temperature inversion in all three mixtures. At corresponding temperatures and pressures: 1) all mixtures have densities within 20 kg/m3 of each other; and 2) CO2 + 1-dodecanol mixture viscosities are the highest (maximum of ∼2 mPa.s), while ternary mixture viscosities (maximum of ∼1.2 mPa.s) are within 0.10 mPa.s of CO2 + 2-dodecanol mixture viscosities.

Dayside Temperature Maps of the Upper Mesosphere and Lower Thermosphere of Mars Retrieved From MAVEN IUVS Observations of O I 297.2 nm Emission

AbstractWe present temperature maps derived from number density retrievals of carbon dioxide (CO2) for the upper mesosphere and lower thermosphere of Mars using limb observations from the Imaging Ultraviolet Spectrograph (IUVS) aboard NASA's Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft. We retrieve CO2 densities using O(1S) metastable atoms that radiatively relax by emitting photons at 297.2 nm, producing a double‐peaked emission profile detectable by IUVS. Retrieved CO2 densities are used to derive altitude profiles of temperature as a function of latitude, longitude, local time, season, dust activity, and solar activity. CO2 density and temperature profiles retrieved using the O I 297.2 nm emission feature presented herein extend previous IUVS retrievals from 130–170 km down to 80 km. We validate retrieved CO2 densities and derived temperatures using coincident measurements and corresponding data products produced by MAVEN IUVS, as available. Analysis of this comprehensive data set, which spans Mars years 32–36, shows (a) a consistently well‐defined mesopause at approximately 120 km, (b) warming at high pressures (typically below ∼100 km) for a variety of geophysical conditions, (c) asymmetry in temperatures at dawn and dusk with respect to latitude during different seasons (warmer temperatures at dawn during northern hemisphere autumn/winter and cooler temperatures at dusk during spring/summer), and (d) longitudinal waves with a dominant wave‐3 component in both the upper mesosphere and lower thermosphere, with lower (80–90 km) and upper (135–145 km) atmospheric waves about 65° out of phase.

Martian Atmospheric Temperature and Density Profiles During the First Year of NOMAD/TGO Solar Occultation Measurements

AbstractWe present vertical profiles of temperature and density from solar occultation (SO) observations by the “Nadir and Occultation for Mars Discovery” (NOMAD) spectrometer on board the Trace Gas Orbiter during its first operational year, which covered the second half of Mars Year 34. We used calibrated transmittance spectra in 380 scans, and apply an in‐house pre‐processing to clean data systematics. Temperature and CO2 profiles up to about 90 km, with consistent hydrostatic adjustment, are obtained, after adapting an Earth‐tested retrieval scheme to Mars conditions. Both pre‐processing and retrieval are discussed to illustrate their performance and robustness. Our results reveal the large impact of the MY34 Global Dust Storm (GDS), which warmed the atmosphere at all altitudes. The large GDS aerosols opacity limited the sounding of tropospheric layers. The retrieved temperatures agree well with global climate models (GCM) at tropospheric altitudes, but NOMAD mesospheric temperatures are wavier and globally colder by 10 K in the perihelion season, particularly during the GDS and its decay phase. We observe a warm layer around 80 km during the Southern Spring, especially in the Northern Hemisphere morning terminator, associated to large thermal tides, significantly stronger than in the GCM. Cold mesospheric pockets, close to CO2 condensation temperatures, are more frequently observed than in the GCM. NOMAD CO2 densities show oscillations upon a seasonal trend that track well the latitudinal variations expected. Results uncertainties and suggestions to improve future data re‐analysis are briefly discussed.

X-Ray Morphology Due to Charge-exchange Emissions Used to Study the Global Structure around Mars

Soft X-ray emissions induced by solar wind ions that collide with neutral material in the solar system have been detected around planets, and were proposed as a remote probe for solar wind interaction with the Martian exosphere. A multi-fluid three-dimensional magnetohydrodynamic model is adopted to derive the global distributions of solar wind particles. Spherically symmetric exospheric H, H2, He, O, and CO2 density profiles and a sophisticated hybrid model that includes charge-exchange and proton–neutral excitation processes are used to study the low triplet line ratio (0.77 ± 0.58) of O vii and the total X-ray luminosity around Mars. We further calculate the emission factor α-value with different neutrals over wide ion-abundance and velocity ranges. Our results are in good agreement with those of previous reports. The evolution of the charge stage of solar wind ions shows that sequential recombination due to charge-exchange can be negligible in the interaction region. This only appears below an altitude of 400 km. The anonymous low disk G-ratio can be easily explained by the collisional quenching effect at neutral densities higher than 1011 cm−3. However, the quenching contribution is small in Mars’ exosphere and only appears below 400 km. Charge-exchange with H2 and N2 is still the most likely reason for this low G-ratio. X-ray emissivity maps in collisions with different neutrals differ from each other. A clear bow shock arising from the collision with all the neutrals is in accordance with previous reports. The resulting total X-ray luminosity of 6.55 MW shows better agreement with the XMM-Newton observation of 12.8 ± 1.4 MW than that of previous predictions.

Surface modification of Co3O4 nanostructures using wide range of natural compounds from rotten apple juice for the efficient oxygen evolution reaction

In this study, a new strategy has been produced to use a rotten apple juice as a source for the surface modification of Co3O4 nanostructures, giving rise to efficient electro-catalysts for driving oxygen evolution reaction (OER) at relatively low over potential. We have studied the morphology, chemical composition, and crystalline aspects of Co3O4 nanostructures using different analytical techniques. The Co3O4 nanostructures grown with rotten apple juice were observed with low impurity of Fe and P, surface modification, reduced particle size, high concentration of oxygen vacancies, defects and cubic phase of Co3O4. Furthermore, we have used the surface modified Co3O4 nanostructures for water electrolysis and noticed the significant performance towards OER in alkaline conditions. The electrochemical characterization revealed that the Co3O4 nanostructure prepared with 20 mL of rotten apple juice exhibits an overpotential value of 269 mV at 20 mA/cm2 current density. The charge transport resistance (Rct) at the interface was estimated around 118.9 Ω, confirming an excellent reaction kinetics on the Co3O4 nanostructures and highly supported efficient performance towards OER. The Co3O4 nanostructures prepared with 20 mL of rotten apple juice has shown an acceptable durability for 40 h, verifying the long-term use. The performance of Co3O4 nanostructures with apple juice could be attributed to high oxygen vacancies due to high density of Co2+ ions on the surface, impurities of Fe and P, reduced nanoparticle size, defects in the structures, and favorable chemical composition. At the end, surface modified Co3O4 nanostructures was observed as an outperformed electrocatalyst when prepared with rotten apple juice. Therefore, this can be used in diverse purposes including energy conversion and storage applications.

Supercritical fluid coating of flavonoids on excipients enhances drug release and antioxidant activity

Supercritical anti-solvent fluidized bed (SAS-FB) technology can be applied to reduce particle size, prevent particle aggregation, and improve the dissolution and bioavailability of poorly soluble drugs. In this work, drug-loaded microparticles of three similar structures, the flavonoids luteolin (LUT), naringenin (NGR), and dihydromyricetin (DMY) were prepared using SAS-FB technology, to explore its effect on the coating of flavonoid particles. Operating temperature, pressure, carrier, solvent, and concentration of drug solution were investigated for their effects on the yield and dissolution of flavonoid particles. The results showed that temperature, pressure, carrier, and drug solution concentration have a large effect on yield. Within the study range, low supercritical CO2 density at higher temperature and lower pressure, a larger surface area carrier, and moderate drug solution concentration led to a higher yield. The effect of the solvent on the yield of flavonoids is a result of multiple factors. Scanning electron microscopy (SEM) images showed that the drug-loaded particles prepared from different carriers and solvents have different precipitations pattern on the carrier surface, and their particle sizes were smaller than unprocessed particles and those prepared by the SAS process. Fluorescence microscopy (FM) results showed that the flavonoids were uniformly coated on the carrier. X-ray powder diffraction (XRPD) results showed that the crystalline morphology of SAS-FB particles remained unchanged after the SAS-FB process, although the diffraction peak intensity decreased. The cumulative dissolution of SAS-FB particles was more than four times faster in the first 5 min than that of the unprocessed flavonoids. The antioxidant activity of SAS-FB processed LUT, NGR and DMY was 1.89-3.78 times, 4.92-10.68 times and 0.99-2.57 times higher than that of the untreated flavonoids, respectively. The approach provides a reference for the application of SAS-FB technology in flavonoids.

Experimental study of the effect of CO2 on temperature and soot volume fraction in C2H4/air co-flow laminar diffusion flame.

The threat of global warming caused by greenhouse gases such as CO2 to the environment is one of the most intractable challenges. The capture and utilization of CO2 are essential to reduce its emission and achieve the goal of being carbon neutral, in which CO2-diluted combustion is an efficient carbon capture technology. In this research, the effects of CO2 addition in the fuel side (CO2-F), oxidizer side (CO2-O) and both sides (CO2-F/O) on temperature and soot formation in C2H4/air laminar co-flow diffusion flames were researched. The flame images were measured by a complementary metal-oxide-semiconductor (CMOS) imaging equipment. The two-dimensional distributions of temperature and soot volume fraction in C2H4/air laminar co-flow diffusion flames were measured employing the inverse Abel transform. The results demonstrated that the effect of amount variation of CO2-F on the decrease of flame temperature was enhanced by the CO2-O. The reduction in peak flame temperature was 4 K in the CO2-F cases, while the reduction in peak flame temperature was 83 K in the CO2-F/O cases. The soot formation was suppressed significantly by the effects of CO2-F/O. Compared with the CO2-F cases, the reductions in peak soot volume fraction were 22.5% and 23.5% in the CO2-F/O cases. The suppression effect of amount variation of the CO2-F on soot formation became more significant with the increase of flame height. The reductions in peak soot volume fractions were 0.3%, 3.07% and 6.38% at the flame heights of 20 mm, 30 mm and 40 mm in the CO2-F cases, and the corresponding reductions were 4.92%, 5.2% and 16% in the CO2-F/O cases, respectively.

Experimental study of adsorption CO2 storage device for compressed CO2 energy storage system

Compressed CO2 energy storage is a reliable physical energy storage solution. The main challenge of compressed CO2 energy storage system is how to solve the high-density storage of low-pressure CO2. In this study, we proposed a new type of adsorption transcritical compressed CO2 energy storage system. We used adsorbents to adsorb CO2 for achieving low-pressure, high-density storage of low-pressure CO2. We investigated the gas storage capacity of the adsorption storage system and the heat and mass transfer process. Results demonstrate that the storage density (57.6 °C–25 °C) of adsorption gas storage is 43.46 kg/m3, which is 24.8 times of the CO2 density (1.75 kg/m3, 30 °C, 1 bar). If the adsorbents are heated above 160 °C, then the storage density will increase 3–4 times. The whole process is controlled by heat exchange efficiency. The heat exchange efficiency greatly affects the response time of the system during the application.

Numerical Simulation of the Proppant Settlement in SC-CO2 Sand-Carrying Fluid in Fracturing Fractures

Supercritical CO2 fracturing has unique advantages for improving unconventional reservoir recovery. Supercritical CO2 can penetrate deep into the reservoir and increase reservoir reform volume, and it is less damaging to reservoir and easy to flow back. However, when the supercritical CO2 flows as the sand-carrying fluid in the fracture, the settlement of the proppant is still worth studying. Based on the study of supercritical CO2 density and viscosity properties, assuming that the reservoir has been pressed out of the vertical crack by injecting prepad fluid, the proppant characteristics in sand-carrying fluid under different conditions were studied by numerical simulation. After the analysis, the proppant accumulation and backflow will occur at the end of the crack. Large sand diameters, high fluid flow rates, high sand concentrations, high reservoir temperatures, and low reservoir pressures can help to shorten deposition time, and the small particle size, high fluid flow rate, low sand concentration, low reservoir temperature, and high reservoir pressure can help increase the uniformity of sand deposition. Shortening the sand deposition time can help to complete the fracturing efficiently, and increasing the deposition uniformity can improve the fracture conductivity. This article has studied the proppant settling and crack formation characteristics. It is hoped that this study can provide theoretical support for field fracturing and provide theoretical assistance to relevant researchers.

High-precision analysis of carbon isotopic composition for individual CO2 inclusions via Raman spectroscopy to reveal the multiple-stages evolution of CO2- bearing fluids and melts

The carbon isotopic composition of CO2 inclusions trapped in minerals reflects the origin and evolution of CO2-bearing fluids and melts, and records the multiple-stages carbon geodynamic cycle, as CO2 took part in various geological processes widely. However, the practical method for determination isotope composition of individual CO2 inclusion is still lacking. Developing a microanalytical technique with spatial resolution in micrometers to precisely determinate the δ13C value of individual CO2 inclusion, will make it possible to analyze a tiny portion of a zoning mineral crystal, distinguish the differences in micro-scale, and possible to find many useful information that could not be obtained with the bulk extraction and analysis techniques. In this study, we systematically collected Raman spectra of CO2 standards with different δ13C values (−34.9 ‰ to 3.58 ‰) at 32.0 °C and from ∼7.0 MPa to 120.0 MPa, and developed a new procedure to precisely determinate the δ13C value of individual CO2 inclusion. We investigated the relationship among the Raman peak intensity ratio, δ13C value, and CO2 density, and established a calibration model with high accuracy (0.5 ‰−1.5 ‰), sufficient for geological application to distinguish different source of CO2 with varying δ13CO2. As a demonstration, we measured the δ13C values and the density of CO2 inclusions in the growth zones of alkali basalt-hosted corundum megacrysts from Changle, Shandong Province. We found the significant differences of density and δ13C between the CO2 inclusions in the core of corundum and those inclusions in the outer growth zones, the δ13C value decreases from core to rim with decreasing density: δ13C values are from −7.5 ‰ to −9.2 ‰ for the inclusions in the core, indicating the corundum core was crystallized from mantle-derived magmas; from −13.5 ‰ to −18.5 ‰ for CO2 inclusions in zone 1 and from −16.5 ‰ to –22.0 ‰ for inclusions in zone 2, indicating the outer zones of corundum grew in a low δ13C value environment, resulted from an infilling of low δ13C value fluid and/or degassing of the ascending basaltic magma.

Pore- and Core-Scale Mechanisms Controlling Supercritical Cyclic Gas Utilization for Enhanced Recovery under Immiscible and Miscible Conditions in the Three Forks Formation

Tight formations such as the Three Forks Formation in the Williston Basin have very low primary recovery factors (typically 10% or less), which potentially leave billions of barrels stranded in the reservoir. According to the results of gas enhanced oil recovery (EOR) pilot tests that have been conducted in the Bakken Formation, cyclic gas injection appears to be a promising strategy for increasing oil recovery in unconventional reservoirs. Despite the pilot tests and the reported results in Bakken shale, Middle Bakken, and Three Forks Formations, little is known about the mechanisms of cyclic gas injection and the behavior between the injected gases and Three Forks reservoir fluids. In this paper, a series of experiments are applied under different constraints. The parameters that are examined include the effect of soaking time under immiscible and miscible conditions, the effect of fluid state (vapor, supercritical), injection pressure, selected gases (CO2, ethane, and propane), target formations (Upper Three Forks (UTF) and Middle Three Forks (MTF)), and the effect of pore size distribution on the recovery factor. During the Huff-n-Puff process, the nuclear magnetic resonance (NMR) technique was used to analyze the microscopic oil production and the micro residual oil distribution before and after CO2 injection. The results showed that the soaking time enhanced the recovery factor dramatically in both formations under and near the minimum miscibility pressure (MMP) of CO2, while the soaking time was less efficient in cases with injection pressures above the MMP. Propane proved to be the most effective gas at low injection pressure, followed by ethane, with CO2 being the least effective. On increasing the pressure, the performance of ethane and CO2 increased due to the sufficient change in the ethane and CO2 densities. Additionally, according to the NMR tests in UTF, micropores, mesopores, and small pores were predominant in oil extraction during the first cycle. After a few Huff-n-Puff cycles, oil in micropores becomes the primary source of oil extraction. However, in MTF, the dominant pore distributions were mesopores, small pores, and fewer micropores than in UTF. The findings in this study provide new insight to better understand the mechanisms of gas HnP enhanced recovery in the Three Forks Formation, which is of great significance for the efficient hydrocarbon exploitation and greenhouse gas utilization in shale reservoirs.

Improved Catalytic Activity and Stability of Co9S8 by Se Incorporation for Efficient Oxygen Evolution Reaction.

Combining an excellent electrocatalytic activity with the good structural stability of Co9S8 remains challenging for the oxygen evolution reaction (OER). In this study, density functional theory was used to demonstrate the importance of moderate adsorption strength with *O and *OOH intermediate species on Co9S8 for achieving excellent electrocatalytic performances. A novel strategy was proposed to effectively optimize the *O oxidation to *OOH by introducing Se heteroatoms to adjust adsorption of the two intermediates. This process also allowed prediction of the simultaneous enhancement of the structural stability of Co9S8 due to the weak electronegativity of a Se dopant. The experimental results demonstrated that Se doping can regulate the charge density of Co2+ and Co3+ in Co9S8-xSex, leading to a substantially improved OER performance of Co9S8-xSex. As a result, our Co9S6.91Se1.09 electrode exhibited an overpotential of 271 mV at 10 mA cm-2 in a 1.0 M KOH solution. In particular, it also demonstrated an excellent stability (∼120 h) under a current density of 10 mA cm-2, indicating the potential for practical applications. Overall, the proposed strategy looks promising for regulating the electronic structures and improving the electrochemical performances of sulfide materials.

Effect of Magnetic Field on Corrosion Performance of Ni–Co Alloy Coatings

The corrosion protection efficacy of Ni–Co alloy coatings was tried to improve by magnetoelectrodeposition (MED) approach. The magnetic field of varying strength (B) was applied in perpendicular and parallel to the direction of diffusion of metal ions, simultaneously to the process of deposition. The corrosion behaviour of the deposited coatings was studied through electrochemical DC method and results revealed that Magneto-electrodeposited (MED) Ni–Co alloys coatings were found to be more corrosion resistant than their conventionally electrodeposited (ED) counterparts. Moreover, the effect of magnetic field is more pronounced in perpendicular field direction and was explained by Lorentz force. Under optimal condition, MED Ni–Co alloy coating obtained at a magnetic field intensity of B = 0.3 T (Perpendicular) was found to be less prone to corrosion than its ED alloy (B = 0 T) counterpart. The increased limiting current density (iL) of Co2+ ions in turn increases the corrosion resistant properties of MED Ni–Co alloy coatings. The effect of magnetic field on improved corrosion resistance of the deposited coatings have been investigated in terms of their changed surface morphology, composition, phase structure and surface roughness using Scanning electron microscopy (SEM), Energy dispersion spectroscopy (EDS), X-Ray diffraction (XRD) technique and Atomic Force Microscopy (AFM) respectively.

Tidal Structures in the Mesosphere and Lower Thermosphere and Their Solar Cycle Variations

We studied the correlations between the migrating and non-migrating tides and solar cycle in the mesosphere and lower thermosphere (MLT) regions between 60° S and 60° N, which are in LAT-LON Earth coordinates, by analyzing the simulation datasets from the thermosphere and ionosphere extension of the Whole Atmosphere Community Climate Model (WACCM-X). A least squares fitting method was utilized to obtain the daily mean migrating tides and non-migrating tides. The Pearson linear correlation coefficient was used to analyze the correlations between tides and solar activity. Our analysis shows that the negative correlations between tides and solar activity are mostly impacted by the first symmetrical structure of the tidal modes for both migrating and non-migrating components. The coefficient of molecular thermal conductivity for the first symmetrical structure is small at low solar flux, so the tides dissipate more slowly when the F10.7 cm radio flux level is low. Thus, the amplitudes of tidal variations under a solar minimum condition are larger than those under a solar maximum condition. The correlation between tides and solar activity could also be influenced by some other factors, such as geomagnetic activity and the density of carbon dioxide CO2 on Earth. The tidal variations can be influenced by westward background wind, which grows stronger as geomagnetic activity rises. Further, dissipation of the tides decreases because the heat conduction and molecular viscosity are weakened in the cooling thermosphere caused by increasing CO2, which results in larger tidal amplitudes under the solar maximum condition. It is found that the correlations between tides and solar cycle vary at different altitudes and latitudes. The negative correlations are most possibly influenced by the first symmetrical structure of tidal variations and may also be impacted by geomagnetic activity. The positive correlations are impacted by the density of CO2.

Thermodynamic property measurements and modelling of CO2 + difluoromethane (R32): Density, heat capacity, and vapour-liquid equilibrium

Accurate thermodynamic property data and models are demanded to reduce the design margins of industrial processes based on these fluids. In this work, measurements of density (ρ), heat capacity (cp), and vapour-liquid equilibrium (VLE) for CO2 + difluoromethane (R32) have been performed by the vibrating tube densimeter and the magnetic suspension balance densimeter, the visual cell and gas chromatograph, and the differential scanning calorimeter, respectively. Experiments were conducted over the temperatures ranging from (208.3 to 334.3) K and pressures reaching 10.04 MPa at CO2 concentrations of 0.7, 0.8 and 0.9. The measured data, together with the results reported in literature where applicable, were subsequently applied to regress the binary interaction parameters utilised in the mixture functions of Helmholtz energy model from REFPROP 10 software package. Noticeable improvements have been achieved for the model's ability to represent thermodynamic property data. The most significant achievement exists in density description: compared with the default parameters, the root-mean-square (RMS) deviation has been decreased by half.

Composition of Mars's Dayside Ionosphere Under Changing Solar Irradiance Conditions

AbstractThe response of the Mars ionosphere to changes in solar irradiance is an important aspect of how conditions on Mars are shaped by our dynamic Sun. Changes in the composition of ionospheric plasma with changes in solar irradiance will affect how the ionosphere mediates the interaction of the neutral atmosphere with the surrounding space environment. Here we use MAVEN ion and neutral density measurements acquired at low (Deep Dip 8) and high (Deep Dip 2) solar irradiance conditions to determine how ion and neutral densities change when the ionizing solar irradiance doubles. We find that the neutral composition does not change significantly when examined at fixed total neutral number density. Furthermore, we find that and O+ densities increase by a factor of 2, but densities increase by a factor of 1.5. The relative abundance of decreases as solar irradiance increases. These results are explained by straightforward theoretical considerations of changes in ion production and loss rates. However, a photochemical model fails to reproduce these results with its default set of inputs. Consistent with previous modeling efforts, densities are over‐predicted. Acceptable model–data agreement requires significant adjustments to important model inputs, such as reduction in irradiance by 15%, reduction in CO2 density by a factor of 2, and increase in O density by a factor of 2. These large adjustments are suggestive of the need for improvements to the state of Mars ionosphere models based on MAVEN inputs rather than issues with the underlying data.

The CO2 profile and analytical model for the Pioneer Venus Large Probe neutral mass spectrometer

We present a significantly updated CO2 altitude profile for Venus (64.2–0.9 km) and provide support for a potential deep lower atmospheric haze of particles (≤17 km). We extracted this information by developing a new analytical model for mass spectra obtained by the Pioneer Venus Large Probe (PVLP) Neutral Mass Spectrometer (LNMS). Our model accounts for changes in LNMS configuration and output during descent and enables the disentanglement of isobaric species via a data fitting routine that adjusts for mass-dependent changes in peak shape. The model yields CO2 in units of density (kg m−3), isotope ratios for 13C/12C and 18O/16O, and 14 measures of CO2 density across 55.4–0.9 km, which represents the most complete altitude profile for CO2 at ≤60 km to date. The CO2 density profile is also consistent with the pressure, temperature, and volumetric gas measurements from the PVLP and VeNeRa spacecraft. Nominal and low-noise operations for the LNMS mass analyzer are supported by the behaviors (e.g., ionization yields, fragmentation yields, and peak shapes) of several internal standards (e.g., CH3+, CH4+, 40Ar+, 136Xe2+, and 136Xe+), which were tracked across the descent. Lastly, our review of the CO2 profile and LNMS spectra reveals hitherto unreported partial and rapidly clearing clogs of the inlet in the lower atmosphere, along with several ensuing data spikes at multiple masses. Together, these observations suggest that atmospheric intake was impacted by particles at ≤17 km and that rapid particle degradation at the inlet yielded a temporary influx of mass signals into the LNMS.

Universal intelligent models for liquid density of CO2 + hydrocarbon mixtures

Developing precise predictive methods for liquid density of CO2 + hydrocarbon mixtures is vital to model, optimize, and design of the enhanced oil recovery (EOR) and the CO2 storage processes. The CO2 injection into the oil reservoir can noticeably change the density of solution. In addition, forecasting this parameter over a wide range of conditions is extremely challenging due to the complicated behaviors of hydrocarbons. The earlier empirical models are only valid for specific hydrocarbons under very restricted conditions. Therefore, in this study, three robust machine learning based approaches were implemented to build robust and universal models based on an immense databank, comprising 17,168 experimental data extracted from 52 independent studies. The databank covered 46 varied mixtures at a broad range of conditions, including temperature, pressure and CO2 mole fraction. The statistical and the cumulative frequency analyzes showed that the radial basis function (RBF) model provides the best results among the all approaches, with an average absolute relative error of 1.61 % and a relative root mean squared error (RRMSE) of 4.29 %, respectively for the test data samples. It also provided favorable predictions for physical attitudes of the mixture density under different operating conditions, and properly described the “density crossover” phenomenon at high CO2 concentrations. The RBF-based model outperformed earlier empirical correlations in terms of precision, applicability, and generality. Overall, the machine learning-based models developed in this study are efficient and reliable methods to assist the designers and engineers involved with in CO2-EOR process.

In situ Raman spectroscopic measurement of the 13C/12C ratio in CO2: Experimental calibrations on the effects of fluid pressure, temperature and composition

The carbon isotope (δ13C) signature of CO2 within fluid inclusions is of significance to investigate because it can be used to decipher the carbon source of geological fluids. Raman spectroscopy has been applied to determine the δ13C of pure CO2. However, whether this approach can be applied to natural inclusions with complex compositions remains unknown. Here we present Raman spectra of CO2 ± N2 ± CH4 systems with known 13C/12C ratio (0.01–1.12) at temperatures (T) of 21 °C and 40 °C and at pressures (P) ranging from 0.5 to 50 MPa. Peak areas and peak heights of the 13CO2 (∼1370 cm−1) and 12CO2 (∼1285 cm−1) bands were determined to calculate the Raman spectroscopic quantification factors (F- and G-factor ratio). The results show that the quantification factors vary significantly with rising pressure in the low pressure range (e.g., <10 MPa), especially for pure CO2 system. Different fluid systems are characterized by pressure dependences. Specifically, both F- and G-factor ratios for CO2 fluid with a low 13C/12C ratio (e.g., 0.01) are different from that with a high 13C/12C ratio (e.g., 0.13) under the same T-P conditions. Fluid temperature does not result in significant variation in F- or G-factor ratios at the investigated temperatures. Based on these calibrations, we suggest that fluid pressure and composition (x) are prerequisites for Raman spectroscopic measurements of the 13C/12C ratio of CO2. However, the 13CO2 (∼1370 cm−1) band for CO2 from natural fluid inclusions is characterized by low Raman intensity, resulting in large errors in calculated peak area and peak height. Thus, accurate determination of the 13C/12C ratio of fluid inclusion CO2 is not feasible for inclusions with low CO2 density. Nevertheless, this method can be applied to investigate the carbon isotope fractionation in 13C labelled hydrothermal experiments, where CO2 with high a 13C/12C ratio is produced.

A novel methodology for measurement of the diffusion coefficient between CO2 and oil based on quantification of the oil droplet swelling behavior

Accurate and fast determination of the diffusion coefficient of the CO2/oil system is essential in CO2 enhanced oil recovery (CO2-EOR) and CO2 geological sequestration practices. In this work, a novel methodology is proposed and demonstrated on measuring the diffusion coefficient of the immiscible CO2/oil binary systems based on quantification of the oil droplet swelling behavior. Five oil samples, including n-decane, n-dodecane, n-tetradecane, n-hexadecane and liquid paraffin, are employed as the oil phase and the diffusion coefficient for each CO2/oil system were determined. After validation of the methodology based on good agreements between the measurement and the reported results for both the pure component oil and the synthetic oil, the diffusion characteristics of the CO2/oil systems are scrutinized in the pressure range 2–10 MPa and the temperature range 26.9–82.1 ℃. The measurement results clearly show the elevated system pressure could lead to stronger diffusion processes between the CO2 and the oil phase, while the temperature impacts on the diffusion process are more complex due to the synergistic effects of CO2 density and the oil viscosity. Performed in the state-of-the-art drop shape analyzer within a short measurement period, it is expected the proposed methodology could provide an efficient supplementary for diffusion coefficient measurements of the CO2/oil binary systems.