Dioxide Mixtures Research Articles

Thermodynamics of supercritical carbon dioxide mixtures across the Widom line.

Supercritical carbon dioxide (scCO2) mixtures are essential for many industrial applications. However, the knowledge of their thermophysical properties in the extended critical region is insufficient. Here, supercritical liquid- and gas-like regions dominated by distinct dynamics and thermodynamics exist and are demarcated by the so-called Widom line. The nature of the anomalies observed for several thermophysical properties at the crossover between these two regions is the subject of a lively debate. Hence, the extended critical region of scCO2 and seven of its binary mixtures with hydrogen, methane, ethane, isobutane, benzene, toluene or naphthalene is studied with respect to thermodynamic, transport and structural properties on the basis of molecular dynamics simulations and equation of state calculations. The Widom line is evaluated employing five criteria and a new empirical equation is proposed for its prediction. Further, the crossover anomalies are investigated in the light of pseudo-boiling theory, diffusion and viscosity as well as structural characteristics given by the radial distribution function.

Optimization of channel structure in micro networked gas separator utilizing the Soret effect

In recent years, hydrogen energy, which does not emit carbon dioxide when used, has been attracting attention as a candidate solution to environmental issues. Hydrogen is produced as a mixture of hydrogen and carbon dioxide or other gases, mainly using fossil fuel reforming. Therefore, in order to use hydrogen as an energy source, the gas mixture must be separated and purified to a high-purity hydrogen. The methods currently used require advanced technology, leading to increased costs. This research has developed a gas separation system utilizing the Soret effect, a thermal diffusion phenomenon caused by a temperature gradient, as a simple and low-cost method to extract hydrogen from a hydrogen and carbon dioxide mixture. Since the separation caused by the Soret effect is very small at one time, previous studies have employed network separation structures to achieve high efficiency. This time, we succeeded in improving the separation performance by optimizing the size of the partition structure inserted at the gas branching area.

Thermal Stability of Calcium Oxalates from CO2 Sequestration for Storage Purposes: An In-Situ HT-XRPD and TGA Combined Study

Calcium oxalates are naturally occurring biominerals and can be found as a byproduct of some industrial processes. Recently, a new and green method for carbon capture and sequestration in stable calcium oxalate from oxalic acid produced by carbon dioxide reduction was proposed. The reaction resulted in high-quality weddellite crystals. Assessing the stability of these weddellite crystals is crucial to forecast their reuse as solid-state reservoir of pure CO2 and CaO in a circular economy perspective or, eventually, their disposal. The thermal decomposition of weddellite obtained from the new method of carbon capture and storage was studied by coupling in-situ high-temperature X-ray powder diffraction and thermogravimetric analysis, in order to evaluate the dehydration, decarbonation, and the possible production of unwanted volatile species during heating. At low temperature (119–255 °C), structural water release was superimposed to an early CO2 feeble evolution, resulting in a water-carbon dioxide mixture that should be separated for reuse. Furthermore, the storage temperature limit must be considered bearing in mind this CO2 release low-temperature event. In the range 390–550 °C, a two-component mixture of carbon monoxide and dioxide is evolved, requiring oxidation of the former or gas separation to reuse pure gases. Finally, the last decarbonation reaction produced pure CO2 starting from 550 °C.

Effect of competitive adsorption on the deformation behavior of nanoslit-confined carbon dioxide and methane mixtures

Understanding the behaviors of nanoslit-confined carbon dioxide and methane mixtures is of great importance in geological storage of carbon dioxide (CO2) and extraction of methane (CH4) from shale/coalbeds. Herein, the effects of pore width, bulk mixture composition, and geographic depth on the mixture adsorption and pore deformation tendency are studied by using the classical density functional theory. The solvation pressure against pore width shows an oscillating distribution, indicating a deformation transition from expansion to contraction in nanopores. A high recovery ratio of CH4 can be found in small pores at low temperatures and under high bulk pressure. For the 0.68 nm pore, a remarkably high optimal recovery ratio is identified at the geographic depth of about 0.2 km, while for the pores with pore width of 0.9–1.2 nm a modest optimal recovery ratio locates at the depth of about 0.5–1.0 km. This work provides a thorough understanding of the adsorption and deformation behavior of slit-confined mixtures.

RETRACTED ARTICLE: A brief comparative examination of tangent hyperbolic hybrid nanofluid through a extending surface: numerical Keller–Box scheme

A novel hybrid nanofluid was explored in order to find an efficient heat-transmitting fluid to replace standard fluids and revolutionary nanofluids. By using tangent hyperbolic hybrid combination nanoliquid with non-Newtonian ethylene glycol (EG) as a basis fluid and a copper (Cu) and titanium dioxide (TiO2) mixture, this work aims to investigate the viscoelastic elements of the thermal transferring process. Flow and thermal facts, such as a slippery extended surface with magnetohydrodynamic (MHD), suction/injection, form factor, Joule heating, and thermal radiation effects, including changing thermal conductivity, were also integrated. The Keller–Box method was used to perform collective numerical computations of parametric analysis using governing equivalences. In the form of graphs and tables, the results of TiO2–Cu/EG hybrid nanofluid were compared to those of standard Cu/EG nanofluid in important critical physical circumstances. The entropy generation study was used to examine energy balance and usefulness for important physically impacting parameters. Detailed scrutiny on entropy development get assisted with Weissenberg number, magnetic parameter, fractional volumes, injection parameter, thermal radiation, variable thermal conductivity, Biot number, shape variation parameter, Reynolds and Brinkman number. Whereas the entropy gets resisted for slip and suction parameter. In this case, spotted entropy buildup with important parametric ranges could aid future optimization.

Thermodynamics of carbon dioxide mixtures at cryogenic conditions

Carbon capture and sequestration / utilization using cryogenic conditions have found attention due to lower energy penalty compared to other separation methods. In cryogenic processes, carbon dioxide is likely to desublimate from a vapor phase or freezes out from a liquid phase. This study deals with phase equilibrium calculations where solid carbon dioxide forms in the presence of vapor phase (SLV), liquid phase (SLE), or both (SLVE). Two of the successful solid fugacity models are used with predictive cubic equations of state (EOSs) in calculating the phase equilibrium of carbon dioxide mixtures. The advantages and limitations of the models are discussed. In addition, a new fugacity model which describes solid carbon dioxide along solid–liquid coexistence curve is developed. This model remedies the previous models and is used from low to very high pressure. This model reduces to an analytical expression for describing carbon dioxide melting curve. When coupled with the predictive cubic EOSs, this model satisfactorily describes the SVE, SLE, and SVLE of carbon dioxide mixtures.

Efficient Separation of Acetylene-Containing Mixtures Using ZIF-8 Membranes.

Metal–organic framework (MOF) membranes show great potential in the separation of acetylene mixtures. In this work, we have prepared ZIF-8 membranes on polyamide (PA) substrates for the highly selective separation of acetylene/methane and acetylene/carbon dioxide mixtures. The C2H2/CH4 and C2H2/CO2 mixtures can be successfully separated using the ZIF-8 membranes, with separation factors of 12.1 and 1.8, respectively. Based on the results of the cross-permeation tests of C2H2/CH4, CO2/CH4, and C2H2/CO2, the separation mechanism of C2H2/CH4 in our ZIF-8 membrane can be attributed to a higher affinity for acetylene and molecular sieving effect, while C2H2/CO2 separation is related to thermodynamic factors. It is worth noting that this is the first example of MOF membranes to successfully separate C2H2 from CH4 and CO2.

Construction of 5H‐Dibenzo[c,e]azepine Framework from Dibenzothiophene Dioxides andN‐Benzylimines through SNAr Reactions

AbstractTreatment of a mixture of dibenzothiophene dioxides and benzaldehydeN‐benzylimines with potassium hexamethyldisilazide induces sequential intermolecular and intramolecular SNAr reactions to eventually form the corresponding 5H‐dibenzo[c,e]azepines without any formation of the conceivable five‐membered fluorene derivatives.

RETROFIT OF OUTDOOR MEDIUM VOLTAGE CIRCUIT BREAKER WITH ECO-FRIENDLY GAS TO REPLACE SF 6

In this paper, some stages of the assessment for the replacement of sulphur hexafluoride (SF6) with the fluoronitrile (C4F7N) and carbon dioxide (CO2) mixture in a medium-voltage vacuum interrupting circuit breaker, HORIZON 38kV Outdoor Circuit Breaker manufactured by BRUSH Switchgear, is presented. The circuit breaker volume is filled with the fluorinated gaseous mixture and tested for both basic lightning impulse and short duration power frequency withstand following the recommendations of the relevant standards. It should be noted that some crucial modifications were made to the design to suit the new gas mixture under test. Prior to the test campaign, a series of electric field computations were performed, using a commercial finite element method (FEM) software package, to ensure that a safety margin from the critical electric field values is maintained and identify areas of excessive electric field stress that can be potentially improved. Data on the properties of the fluoronitrile compound and its mixture with CO2 is presented. Initial test results demonstrate that the more environmentally friendly gaseous mixture of 20% fluoronitrile content offers satisfactory insulation withstand performance, indicating its suitability from an insulation performance perspective.

Experimental investigation of the effect of nitrogen on the phase equilibrium behavior of the CH4–CO2 mixture at low temperature for natural and biogas purification

New fluid-fluid and solid-fluid(-fluid) equilibrium measurements at 4 MPa for the N 2 + CH 4 + CO 2 system have been carried out using a static-analytic method in order to investigate the effect of nitrogen on the phase equilibrium behavior of the methane + carbon dioxide mixture at temperatures between 170 K and 210 K. With respect to equilibria involving solid carbon dioxide, the addition of nitrogen to the mixture reduces the solubility of carbon dioxide in the fluid phase, widens the temperature region of existence of the solid-vapor equilibrium, and spreads the temperature range of existence of the solid-liquid-vapor equilibrium. The comparison between measured values and values calculated by means of the Peng-Robinson Equation of State as implemented in Aspen HYSYS® shows that tabulated binary interaction parameters (regressed with respect to fluid-fluid equilibria) are not always suitable when applied to the calculation of low temperature equilibria.

Variation characteristics of active groups and macroscopic gas products during low-temperature oxidation of coal under the action of inert gases N2 and CO2

This research is aimed at studying the different effects and mechanisms of CO2 and N2 on inhibiting coal spontaneous combustion (CSC) and providing theoretical guidance for the prevention and control of CSC in the goaf. The variations of free radicals and functional groups and the generation of indicator gas CO during low-temperature oxidation of coal under the conditions of dry air (DA), dry air-nitrogen mixture (DA + N2) and dry air-carbon dioxide mixture (DA + CO2) were investigated based on electron spin resonance spectrometer, Fourier transform infrared spectroscopy and gas chromatograph. The experimental results reveal that the reaction of free radicals and the transformation of functional groups occur in the low-temperature oxidation process. In the whole oxidation heating process (30–230 °C), the concentrations of free radicals (Ng) increase by 4.04 × 1017 spin/g, 2.24 × 1017 spin/g and 1.90 × 1017 spin/g under the conditions of DA, DA + N2 and DA + CO2, respectively. The variation ranges of peak areas of active functional groups (–C-O–, –CO, –CH2–, –CH3 and –OH) under the action of inert gases (CO2 and N2) are notably smaller than those in the DA environment. The time and amount of CO generation both exhibit an obvious “hysteresis effect”, indicating that the presence of N2 and CO2 inhibits coal oxidation and conduces to CSC prevention. A comparison between the values of inhibition effect parameters R (RCO, RNg, R-C-O- and R-CO) and P (P-CH2-, –CH3, P-OH) discloses that CO2 boasts a superior ability to inhibit CSC than N2. This study presents a comparison between N2 and CO2 in CSC prevention and control based on the variation characteristics of indicator gas and active groups. It provides an experimental and theoretical basis for developing and improving the technology of fire prevention and extinguishing by inert gases.

A novel liquid energy storage system based on a carbon dioxide mixture

A novel liquid energy storage system based on a carbon dioxide mixture

Improvement of the efficiency of the superposition method applied to the WSGG model to compute radiative transfer in gaseous mixtures

A new method for the treatment of radiative heat transfer in mixtures of participating species in the framework of the weighted-sum-of-gray-gases (WSGG) model is proposed, based on a modification of the existing superposition method. This new approach allows for a reduction in the number of times that the WSGG radiative transfer equation must be solved by decreasing the total number of gray gases that needs to be considered for modeling the mixture. Although it may be extended to mixtures of any number of species, in this paper the new method is only applied to water vapor-carbon dioxide mixtures. The reference for the comparisons is provided by line-by-line (LBL) integration of absorption spectra generated from a high-resolution spectral database. Results show that the method does not yield a loss in accuracy relative to the standard superposition method, and performs better than an existing WSGG model developed for H2O−CO2 mixtures with varying mole fraction ratio. There is also a reduction of about 50% in the computational time required for the solution compared to the original superposition method, thus making the new method more efficient and more competitive in relation to other methodologies for modeling radiative transfer in non-homogeneous mixtures.

Numerical analysis of SiO2-SDS surfactant effect on oil recovery in sandstone reservoirs

Currently, the demand for using nanoparticles (NPs) in Enhanced Oil Recovery (EOR) is very high. The use of NPs can drastically benefit EOR by changing the rock wettability, improving the mobility of oil phase and decreasing the interfacial tension (IFT) between oil/water. Most of the previous studies were experimentally conducted and limited to specific operating conditions. This study contributes to the understanding of nanoparticle behaviour at altered operating conditions. In this investigation, a 3-D numerical model of silica nanofluid proposed for EOR is presented. A numerical model of core-scale sandstone was developed using Computer Modelling Group (CMG)-STARS simulator. The developed model was well validated against an experimental data. Then Silicon Dioxide (SiO2) and Sodium Dodecyl Sulphate (SDS) nano-surfactant mixture were injected with different concentrations. The optimum concentration of SiO2–SDS solution was obtained at 0.15 wt% with the highest recovery factor of 71.86% achieved. Moreover, SiO2–SDS solution injection rate and temperature were investigated and it was found that the optimum operating conditions of injection rate and temperature were 2 cc/min and 60 °C with the highest recovery achieved. In addition, a heavy crude oil showed a significant increment of oil recovery compared with a light crude with 3.13% and 0.6%, respectively. The intermediate viscosity of used crude oil had the highest oil recovery increment.

Study on stretch extinction characteristics of methane/carbon dioxide versus oxygen/carbon dioxide counterflow non-premixed combustion under elevated pressures

As a clean gaseous fuel, methane (the main constituent of natural gas) has been widely used in the lives of residents and industrial processes. The oxy-fuel combustion technology for methane/carbon dioxide is an effective way to reduce the pollutant emissions of NOx, which is also beneficial to the capture of carbon dioxide. Herein, the stretch extinction characteristics of non-premixed flames induced by methane/carbon dioxide mixtures versus oxygen/carbon dioxide mixtures counterflow combustion with various fuel concentrations were studied in high-pressure environments. The computed flame extinction strain rates of oxygen-enriched and air combustions in low fuel concentration range at pressures of 0.1, 0.5 and 0.7 MPa have a good consistency with the experiment results obtained from previous literature. The results show that the increase of flame extinction limit represented by the stretch rate for the oxygen-enriched combustion with increasing pressure is more significant than that for the air combustion. The analyses of reaction pathways, integral of reaction rates and sensitivity coefficients suggest that the OH formation rates of near extinction flames limits can be used to estimate the ratio of the flame extinction strain rate for oxygen-enriched combustion to that for air combustion under high pressures. The reasons for the enhancement of the OH formation rate aroused by increasing pressures were clarified.

Homogeneous water nucleation in carbon dioxide–nitrogen mixtures: Experimental study on pressure and carrier gas effects

New homogeneous nucleation experiments are presented at 240 K for water in carrier gas mixtures of nitrogen with carbon dioxide molar fractions of 5%, 15%, and 25%. The pulse expansion wave tube is used to test three different pressure conditions, namely, 0.1, 1, and 2 MPa. In addition, a restricted series of nucleation experiments is presented for 25% carbon dioxide mixtures at temperatures of 234 and 236 K at 0.1 MPa. As pressure and carbon dioxide content are increased, the nucleation rate increases accordingly. This behavior is attributed to the reduction in the water surface tension by the adsorption of carrier gas molecules. The new data are compared with theoretical predictions based on the classical nucleation theory and on extrapolations of empirical surface tension data to the supercooled conditions at 240 K. The extrapolation is carried out on the basis of a theoretical adsorption/surface tension model, extended to multi-component mixtures. The theoretical model appears to strongly overestimate the pressure and composition dependence. At relatively low pressures of 0.1 MPa, a reduction in the nucleation rates is found due to an incomplete thermalization of colliding clusters and carrier gas molecules. The observed decrease in the nucleation rate is supported by the theoretical model of Barrett, generalized here for water in multi-component carrier gas mixtures. The temperature dependence of the nucleation rate at 0.1 MPa follows the scaling model proposed by Hale [J. Chem. Phys. 122, 204509 (2005)].

Two component phase equilibria for the 3-methoxy-3-methyl-1-butanol and 1-methoxy-2-methyl-2-propanol in supercritical carbon dioxide

Two component mixtures, 3-methoxy-3-methyl-1-butanol (MMB)+carbon dioxide and 1-methoxy-2-methyl-2-propanol (MMP)+carbon dioxide, were investigated at 313.2, 333.2, 353.2, 373.2 and 393.2 K and at 4.29 to 20.95 MPa to get phase equilibrium data. The phase separation of vapor+liquid behavior for the MMB and MMP plays a momentous function as the organic solvent in a diversity of industrial processes. The two MMB+carbon dioxide and MMP+carbon dioxide components have mixture critical curves that have maxima in the p-T plot between the Tc (critical temperatures) of MMB and carbon dioxide or MMP and carbon dioxide. The two component systems of MMB+ carbon dioxide and MMP+carbon dioxide mixture display type-I in simplest behavior. The measured results for the two component mixtures, MMB+carbon dioxide and MMP+carbon dioxide, are modelled with a general cubic equation of state, the Peng-Robinson, containing the kij, ηij adjustable factor.

Experiments and modeling of atmospheric pressure microwave plasma reforming of a methane-carbon dioxide mixture

Atmospheric pressure microwave plasma reforming was conducted on a methane (CH4) and carbon dioxide (CO2) mixture, and characterized by measuring the temperature of the plasma and gas composition of the reforming product via optical emission spectroscopy (OES) and gas chromatographic measurement. The temperature at the plasma reached as high as 5900 K regardless of the specific energy input, while at microwave power of 2 kW and flow rate of 10 slm, nearly all CH4 and CO2 were converted into hydrogen (H2) and carbon monoxide (CO). The plasma temperature higher than the level achievable from uniform gas heating implied that only a part of the flow will enter the plasma region, and the rest will bypass and mix with the plasma stream downstream. Thus, a reactor network-type simulation was performed by modeling the plasma and surrounding streams, each as a series of perfectly-stirred reactors; the reactors at the same downstream locations interacted for the gas diffusion and heat conduction. The simulation reproduced the measured gas compositions well, revealing that the reforming proceeded as the surrounding gas enters and diffuses out of the plasma stream due to the flow mixing, as well as through the heating of the surrounding stream by the plasma stream.

Extraction of Antioxidants from Strawberry Leaves with Supercritical Carbon Dioxide and Water Mixtures

Extraction of Antioxidants from Strawberry Leaves with Supercritical Carbon Dioxide and Water Mixtures

High-purity hydrogen production via a water-gas-shift reaction in a palladium-copper catalytic membrane reactor integrated with pressure swing adsorption

A Pd-Cu catalytic membrane reactor (CMR) integrated with pressure swing adsorption (PSA) was developed to produce fuel cell grade hydrogen from syngas. The enhanced water-gas-shift reaction in the Pd-Cu CMR packed with a high-temperature shift catalyst was experimentally conducted by using a carbon monoxide (CO)/hydrogen (H2)/carbon dioxide (CO2) mixture (65:30:5 vol%) at 360–380 °C, 6–10 bar, and a steam/carbon (s/c) ratio of 1–5. Since H2 was used as the sweeping gas, pure H2 could be directly obtained from the permeate side. The temperature inside the packed catalysts was well distributed in the developed CMR module without any specific hotspots during the reaction and separation. The CO conversion in the CMR increased from 85.4% to 94.8% with the recovery of 53.4% to 56.1% when the s/c ratio increased from 1 to 5. The conversion rate was enhanced by 10.0–16.7% compared with the fixed catalytic bed reactor. When four-bed PSA using activated carbon and zeolite was integrated to recover more H2 from the retentate flow, the recovery of H2 was additionally improved by 31.2–35.7%. The integrated Pd-Cu CMR with four-bed PSA could produce H2 of over 99.9991% with a recovery of 91.37% and 8.67 ppm CO. For H2 produced with less than 0.2 ppm CO, the recovery was reduced to 85.99% with 0.15 ppm CO. The feasibility of CMR with PSA to enhance CO conversion and H2 recovery is suggested for the production of fuel cell grade H2 for a proton-exchange membrane fuel cell (ISO 14687).